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What you spend years building, someone may try to destroy overnight. Build anyway because you had to give the world the best you have, even if it may never be enough; Give the world the best you have anyway. When clocks reverse, time never runs back. So, hard work had to be your way to face the world. Wi Team July, 2008

Presented by:

Abd Al-Rahman Mostafa Fekry Ali Mohammad Alauldin Ali Salem Ayman Abdo Solayman Ali Ehab Kamal Al-din Ahmad Al-Sayed Hossam Al-din Hasan Mahmod Islam Mohammad Saad Hussin Sherif Mohammad Saad Hussin

▬▬▬▬▬▬▬▬ Acknowledgments

Thanks to Allah, first & foremost. For nothing is worth working for if it isn’t for the sake of Allah. It is only due to Allah’s blessing that we reached this far.

We thank Allah for everything, especially for providing us with hope when we were close to losing it, guidance he blessed us with to complete our work, & people that Allah leads us to & made reasons for our success…

Prof. Ahmad, our supervisor, the light – hearted teacher & the kind father image

who guided us through all of our work and was very patient in hearing our problems. He always provided us with easy, yet creative solutions for any road blocks we ran into.

We also would like to thank the other groups for support throughout our work

and everyone has been participated in this project.

 

▬▬▬▬▬▬▬▬ Content Part (1): WiMAX Overview

1. Chapter (1): IEEE 802.16e Overview…………………………………….1 1.1. Introduction:……...…………………………………………………….1 1.2. Evolution of Broadband Wireless:…………………………….……….3 1.3. WiMAX Applications:………………………………………………....5 1.4. WiMAX versus other systems:…………………………………………5 1.5. WiMAX bands & broadband bands:…………………………..……….8 1.6. WiMAX challenges:……………………………………………………9 1.7. Quality of Service:…………………………………………………….10 1.8. Fractional Frequency Reuse…………………………………..……….11 1.9. Remarks………………………………………………………………..11 1.10. Bibliography……………………………………………………...……12 2. Chapter (2): Orthogonal Frequency Division Multiplexing…...……...…14 2.1. Multicarrier Modulation:……………………………...……………….14 2.2. Orthogonality:…...……………………………………………………..15 2.3. IFFT & FFT:…………………………...………………………………15 2.4. Cyclic Prefix:……………………..……………………………………16 2.5. OFDM Symbol:……………………..…………………………………17 2.6. Peak – to – Average Ratio:…………………………………………….18 2.7. OFDMA:………………………………………………………………19 2.8. Resource – Allocation Techniques for OFDMA:…………….……….20 2.9. OFDMA Frame Structure:……………...……………………………..21 2.10. Sub–Channel & Sub–Carrier Permutations:…………………………..21 2.11. SOFDMA:………….………………………………………………….22 2.12. Bibliography:………………………………………………………….23 3. Chapter(3)Physical Layer:……………....……………………………….24 3.1. Transmitter:……………………...…………………………………….25 3.1.1. Randomizer:……………………..…………………………………….25 3.1.2. Frame Error Correction (FEC):……………………..…………………26 3.1.2.1. Concatenated Reed–Solomon–Convolutional Code:…………..….26 3.1.3. Interleaver:………………...…………………………………………..28 3.1.4. Symbol Mapping:……………………………………………………..29 3.1.5. Pilot Symbol:…………….………………………………………...….30 3.1.6. Training Sequences:……………..…………………………………....30

3.1.7. Inverse Fast Fourier Transform (IFFT):……………………………....31 3.1.8. Cyclic Prefix (CP):………………………...……………………….....32 3.1.9. RF stage:………………...…………………………………………….32 3.2. Channel:……………………………………………………………….32 3.3. Receiver:…………….………………………………………………...32 3.4. Bibliography:……………..…………………………………………...33 4. Chapter (4): MAC Layer:……..…………………………………………35 4.1. Convergence Sub–layer (CS):………………………………………...36 4.2. Common Part Sub–layer:…………...………………………………...36 4.2.1. MAC PDU Construction & Transmission:…………………………...36 4.2.2. Network Entry & Initialization:……………………………………....37 4.2.3. Power–Saving Operations:…………………………………………...38 4.2.4. Mobility Management:……………………………………………….38 4.2.4.1. Handoff Process & Cell Reselection:……...……………………...39 4.2.4.2. Macro Diversity Handover & Fast BS Switching:………….…….39 4.3. Security Sub–layer:…………………………………………………...40 4.3.1. Security Sub–layer Architecture:……………….…………………….40 4.3.2. Authentication architecture:………………...………………………...41 4.4. Bibliography:……………….………………………………………...42 5. Chapter(5): Advanced Techniques in WiMAX:………………………...44 5.1. Adaptive Modulation & Coding (AMC):…………………………….44 5.1.1. Modulation:………………….……………………………………….45 5.1.2. Coding:………….……………………………………………………46 5.2. AMC in Uplink & Downlink:…………….………………………….46 5.3. Performance of the AMC scheme:…………………………………...47 5.4. Channels:…………….……………………………………………….48 5.4.1. Propagation Characteristics of Mobile Radio Channels:……….........48 5.4.1.1. Attenuation:………..……………………………………………...48 5.4.1.2. Multipath effect (Rayleigh & Ricean Fading):………..………….48 5.4.1.3. Doppler Shift:………….………………………………………….50 5.5. Modeling of Channels:………….……………………………………50 5.6. Channel estimation:…………..………………………………………51 5.6.1. Preamble & Pilot:…………….………………………………………51 5.6.2. Pilot Signal Estimation:……………………………………………....51 5.6.2.1. Least Square Estimation:…………….…………………………....52 5.6.2.2. Linear Minimum Mean Square Error Estimation:………….……..52 5.6.3. Channel Interpolation:…………...…………………………………...52

5.6.3.1. Linear Interpolation:…………...………………………………….53 5.6.3.2. Spline & Cubic Interpolation:………….………………………….53 5.6.3.3. Low Pass Interpolation:…………………………………………...53 5.7. Adaptive Antenna Systems (AAS):………….……………………….53 5.7.1. Spatial Diversity:………….………………………………………….54 5.7.2. Beam forming:…………...…………………………………………...56 5.7.3. Multiple–Antenna Techniques:……………...……………………….57 5.7.3.1. Channel Estimation for MIMO–OFDM:………………………….58 5.8. Bibliography:…………….…………………………………………...59 6. Chapter (6): WiMAX Network Architecture…...………………………61 6.1. Network reference model (NRM):……………...……………………61 6.2. The Access service network (ASN):…………..……………………..62 6.3. Connectivity service network (CSN):………….…………………….63 6.4. Reference points (RP):………….……………………………………64 6.5. Bibliography:…………………….…………………………………..65

Part (2): Simulation & Implementation

7. Chapter(7): System Simulation Using Matlab:...…….………………...69 7.1. Simulink:………………………………………………….…………69 7.1.1. Simple System:…………….………………………………………...69 7.1.2. MIMO System:……………...……………………………………….75 7.1.3. Special Blocks Configurations:……………………………………...76 7.1.4. IIR Filter:……………..……………………………………………...78 7.1.4.1. Testing the filter:……………….………………………………...79 7.1.5. Audio Reverberation:………………………………………………..81 7.2. Remarks:…………………....………………………………………..81 7.3. M–File:……………….……………………………………………...81 7.4. Additional Reading:………………...……………………………….81 8. Chapter(8): System Implementation:…………………………………..83 8.1. Introduction:…………………………………………………………83 8.2. Starting Code Composer Studio:…………………………………….85 8.3. System Model Implementation:……………………………………..86 8.4. VCP Progress:……………………………………………………….88 8.5. Troubleshooting errors:……………………………………………...88 8.6. Bibliography (Very Important Documents):………………………...89

System Parameters…………………………………………………...A

▬▬▬▬▬▬▬▬ Figure

Figure 1.1 Evolution of 3G versus WiMAX. Figure 1.2 Worldwide subscriber growth 1990–2006 for mobile telephony,Internet usage, &

broadband access. Figure 1.3 Metropolitan Area Figure 1.4 Possible scenarios for WiMAX deployment. Figure 1.5 WiMAX fills gap between WLAN & 3G (Rate–Mobility tradeoff). Figure 1.6 Net Throughput per Channel/ Sector. Figure 1.7 Spectral Efficiency. Figure 1.8 Fractional Frequency Reuse. F1, F2, & F3 are different sets of sub–channels in

the same frequency channel. Figure 2.1 Multicarrier Modulation. Figure 2.2 Subdivision of bandwidth, in MC transmission, into Nc sub–bands. Figure 2.3 Spectrum of OFDM signal. Figure 2.4 Cyclic Prefix. Figure 2.5 Relation between cyclic prefix & delay spread. Figure 2.6 Frequency domain representation of OFDM symbol. Figure 2.7 A typical power amplifier response. Figure 2.8 A peak cancellation as a model of soft limiter when γ =5dB. Figure 2.9 OFDMA & OFDM. Figure 2.10 OFDMA Frame Structure. Figure 3.1 Basic system structure. Figure 3.2 Functional Stages of WiMAX PHY Layer (Transmitter). Figure 3.3 Transmitter of WiMAX System. Figure 3.4 Randomizer. Figure 3.5 Convolutional Encoder & tailbiting in IEEE 802.16e. Figure 3.6 Turbo Encoder (Constituent Encoder) in IEEE 802.16e. Figure 3.7 BPSK, QPSK, 16–QAM, & 64–QAM Constellations. Figure 3.8 PRBS Generator for Pilots. Figure 3.9 DL Preamble structure (PSHORT than PEVEN). Figure 3.10 Receiver of WiMAX System. Figure 4.1 WiMAX MAC Layer. Figure 4.2 Segmentation and concatenation of SDUs in MAC PDUs. Figure 4.3 WiMAX PDU headers: generic (on the top) & bandwidth request (on the button). Figure 4.4 Network Entry & Initialization. Figure 4.5 DL MOHO: combining. Figure 4.6 UL MDHO: Selection. Figure 4.7 Security Sub–layer. Figure 4.8 Authentication architecture Figure 4.9 PKMv2 key hierarchy. Figure 5.1 Adaptive Modulation & Coding. Figure 5.2 Adaptive modulation & coding block diagram. Figure 5.3 Shannon capacity & modulation constrained Shannon capacity. Figure 5.4 Throughput versus SINR, assuming that the best available constellation & coding

configuration are chosen for each SINR.

Figure 5.5 Multipath fading. Figure 5.6 Rayleigh & Rice Distribution. Figure 5.7 LOS vs. N–LOS Figure 5.8 Channel Modeling Representation. Figure 5.9 Receiver Diversity (on the top) & Transmitter Diversity Figure 5.10 Average bit error probability for selection combining (on the left) & maximal

ratio combining (on the right) using coherent BPSK. Owing to its array gain, MRC typically achieves a few dB better SNR than does SC.

Figure 5.11 Open–Loop 4–2 stacked STBC transmitter. Figure 5.12 Closed–Loop Transmit Diversity. Figure 5.13 Beam pattern using this weight vector (Null–steering beam pattern) with unity

gain for desired user & nulls at directions of interferers. Figure 5.14 MIMO transmission. Figure 5.15 MIMO & OFDM. Figure 5.16 Training symbol structure of preamble–based & pilot–based

channel estimation methods. Figure 6.1 Overview of WiMAX, UMTS & GSM combined network structure. Figure 6.2 WiMAX Network Reference Model. Figure 6.3 ASN security architecture & deployment models: integrated deployment model

(on the left) & stand–alone deployment model (on the right). Figure 6.4 Functions Performed Across Reference Points. Figure 7.1 Basic system structure. Figure 7.2 Simple system structure. Figure 7.3 Adaptive Modulation & Coding. Figure 7.4 Sub–system. Figure 7.5 S/ P, inserting pilots & DC null to the data. Figure 7.6 OFDM symbol creation process. Figure 7.7 rateID sub–block. Figure 7.8 OFDM symbol creation process. Figure 7.9 The Sub–block components. Figure 7.10 Adaptive Demodulation & Decoding. Figure 7.11 Sub–System. Figure 7.12 BER Calculator System. Figure 7.13 Input Data Calculations which is used for applying correct frame length for each

modulation scheme. Figure 7.14 MIMO System structure. Figure 7.15 IIR Filter structure. Figure 7.16 Filter Design. Figure 7.17 The testing model (multi–frequency sine wave bank). Figure 7.18 Spectrum Output (The cutoff freq. is at 500 Hz), [On top,before filtering & after

filtering on the button]. Figure 7.19 Audio Reverberation Applied to an Audio Input Signal. Figure 8.1 Functional block and CPU (DSP core) diagram. Figure 8.2 L2 Architecture Memory. Figure 8.3 Basic system structure. Figure 8.4 VCP programming process.

▬▬▬▬▬▬▬▬ Tables

Table 1.1 Hypothetical Metropolitan Area. Table 1.2 Comparison of WiMAX with other standards. Table 1.3 Summary of WiMAX bands. Table 1.4 Technical design challenges summery to wireless broadband. Table 1.5 Sample traffic parameters for wireless broadband applications Table 2.1 OFDM parameters. Table 2.2 OFDMA Rate–Adaptive Resource–Allocation Schemes. Table 2.3 Sub–Carrier Permutations. Table 2.4 Scalable OFDMA Parameters. Table 3.1 Inner Convolutional Code with Puncturing Configuration. Table 3.2 Mandatory Channel Coding per Modulation. Table 3.3 Block Size of the Interleaver. Table 4.1 Convergence Sub–layer of WiMAX. Table 5.1 SNR required for each modulation, & bits/ Symbol. Table 5.2 Modulation & Coding Supported in WiMAX (UL & DL). Table 5.3 AMC Modulation & Coding Schemes. Table 6.1 Functional Decomposition of ASN. Table 6.2 WiMAX Reference Points. Table 7.1 Sub–system component function. Table 7.2 Sub–block component function. Table 7.3 Sub–block component function. Table 7.4 Sub–block component function. Table 7.5 Sub–block component function. Table 7.6 Sub–block component function. Table 7.7 Puncturing array. Table 7.8 Soft Decoding. Table 8.1 Word width with Ti DSP’s. Table 1 Different WiMAX Standard Table 2 Fixed & Mobile WiMAX Certified Profiles. Table 3 PHY–Layer Data Rate at Various Channel Bandwidths.

▬▬▬▬▬▬▬▬ Preface

Broadband wireless sits at the confluence of two of the most remarkable growth stories of the telecommunications industry in recent years. Both wireless & broadband have on their own enjoyed rapid mass–market adoption. Internet grew from being a curious academic tool to having about a billion users. This staggering growth of the Internet is driving demand for higher–speed Internet–access services, leading to a parallel growth in broadband adoption. Due to the rapid changes in communication environment many technologies have been developed to facilitate communication, like wireless broadband systems. Now, we may say thanks to Broadband wireless communication, the world has become a small village. All of the new advanced applications need powerful tools to carry the up to life, which also required being economically to have their wide use. So, digital signal processors, such as the TMS320 family of processors was introduced by texas Instruments, are used in a wide range of applications, such as in communications, controls, speech processing, & so on. They are used in cellular phones, digital cameras, high–definition television (HDTV), radio, fax transmission, modems, and other devices. These devices have also found their way into the university classroom, where they provide an economical way to introduce real – time digital signal processing (DSP) to the student. The TM320C6x processor, based on the very–long instruction–word (VLIW) architecture. This new architecture supports features that facilitate the development of efficient high–level language compilers. This book has 8 chapters sorted into two parts. Part I has six chapters which are concern on the WiMAX system. Part II consists of two chapters, which have the Matlab simulations & describes the architecture of the Digital signal processor TI TMS320C6416 & how to program it in short. The project codes & implementation are included on the CD provided with the book.

 

 

 

  Part. 1 

WiMAX Overview

Chapter. 1 

  

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1.1 Introduction:

Broadband access today is delivered via Digital Subscriber line (DSL) family “using telephone twisted pairs” or cable modem technology “coaxial cables of TV” which offers high – speed Internet – access services. Growth of the broadband subscribers & wide varieties of applications requires more reliable & flexible solutions, which can be carried out via wireless systems. We may consider that the first generation of those systems is the Wi–Fi technology (802.11 family), but that family suffers from the small range of coverage & limited number of users. So, the need for the better system in coverage & number of served users was required. The second generation appears under the name WiMAX (802.16 family). So, WiMAX take wireless internet access to the next level.

Figure 1.1: Evolution of 3G versus WiMAX. Now, what is wireless broadband? Wireless broadband is about bringing the broadband experience to a wireless context, which offers users certain unique benefits and

Chapter

1 IEEE 802.16e Overview

Chapter. 1

  

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convenience. There are two fundamentally different types of broadband wireless services. The first type attempts to provide a set of services similar to that of the traditional fixed – line broadband but using wireless as the medium of transmission. This type, called fixed wireless broadband, can be thought of as a competitive alternative to DSL or cable modem. The second type of broadband wireless, called mobile broadband, offers the additional functionality of portability, nomadicity, & mobility. 1 Mobile broadband attempts to bring broadband applications to new user experience scenarios and hence can offer the end user a very different value proposition. What is WiMAX? WiMAX is the abbreviation for Worldwide Interoperability for Microwave Access. It is based on Wireless Metropolitan Area Networking (WMAN) standards developed by the IEEE 802.16 group & adopted by both IEEE & the ETSI HIPERMAN group. The aim is to provide a supplement respectively a substitution to fixed line broadband access technologies as ADSL. Furthermore, later evolutional steps of WiMAX cover full mobile technology features as provided by 3G. Important of this system can be illustrated via following curve:

Figure 1.2: Worldwide subscriber growth 1990–2006 for mobile telephony, Internet usage, & broadband access. The metropolitan area composed of different densely populated regions (highest densely populated area is the city center & decreasing outwards).

1 Nomadicity implies the ability to connect to the network from different locations via different base stations. Mobility implies the ability to keep ongoing connections active while moving at vehicular speeds.

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Figure 1.3: Metropolitan Area

Region Area Year 1 Population Population density

Dense Urban 100 km2 800,000 8,000 /km2 Urban 200 km2 500,000 2,500 /km2 Suburban 500 km2 400,000 800 /km2 Rural & Open Space 700 km2 50,000 71 /km2 Metro Area 1500 km2 1.750,000 1,166 /km2

Table 1.1: Hypothetical Metropolitan Area. What is WiMAX FORUM? It’s an industry – led, non – profit corporation formed to promote & certify compatibility & interoperability of broadband wireless products. It was formed by equipment & component suppliers to support the IEEE 802.16 system by helping to ensure the compatibility & interoperability of equipments which will lead to lower cost through chip – level implementation. What is WiSOA? WiMAX Spectrum Owners Alliance is the first global organization composed exclusively of owners of WiMAX spectrum without plans to deploy WiMAX technology in those bands. WiSOA focused on regulation, commercialization & deployment of WiMAX spectrum in the 2.3 – 2.5 GHz & the 3.4 – 3.5 GHz ranges. WiSOA are dedicated to educating & informing its members, industry representatives & government regulators of the importance of WiMAX spectrum, its use & potential for WiMAX to revolutionize broadband.

1.2 Evolution of Broadband Wireless: WiMAX technology has evolved through four stages:

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(1) Narrowband wireless local-loop systems (WLL): They were quite successful in developing countries whose high demand for basic telephone services could not be served using existing infrastructure. (2) First – generation line – of – sight (LOS) broadband systems: As local multipoint distribution systems (LMDS) band at 2.5GHz, 3.5GHz & in millimeter wave frequency bands (24GHz & 39GHz). Later, multichannel multipoint distribution services (MMDS) band at 2.5GHz. Using high transmitted power LOS coverage to distances up to 35 miles & required that subscribers install at their premises outdoor antennas high enough and pointed toward the tower for a clear LOS transmission path. (3) Second – generation non – line – of – sight (NLOS) broadband systems: Overcome LOS issue & provides more capacity using cellular architecture & implementation of advanced – signal processing techniques to improve the link and system performance under multipath conditions. (4) Standards – based broadband wireless systems: Institute of Electrical and Electronics Engineers (IEEE) formed a group called 802.16 to develop WMAN. Originally, this group focused on developing solutions in the 10GHz to 66GHz band. The IEEE 802.16 group produced a standard that was approved in December 2001. This standard, Wireless MAN – SC, specified a physical layer that used single – carrier modulation techniques & a media access control (MAC) layer with TDM structure that supported both FDD and TDD. After completing this standard, the group started work on extending and modifying it to work in both licensed and license – exempt frequencies in the 2 – 11 GHz range, which would enable NLOS deployments. This amendment, IEEE 802.16a, was completed in 2003, with OFDM schemes added as part of the physical layer for supporting deployment in multipath environments. 802.16a also specified additional MAC-layer options, including support for OFDMA. Further revisions to 802.16a were made and completed in 2004. This revised standard, IEEE 802.16-2004, replaces 802.16, 802.16a, & 802.16c with a single standard, which has also been adopted as the basis for high – performance metropolitan area network (HIPERMAN) by ETSI. In 2003, the 802.16 group began work on enhancements to the specifications to allow vehicular mobility applications. That revision, 802.16e, was completed in December 2005 and was published formally as IEEE 802.16e-2005. It specifies scalable OFDM for the physical layer and makes further modifications to the MAC layer to accommodate high – speed mobility. The 802.16f/ g are future management plane for previous standards.

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Note that IEEE developed the specifications but left to the industry the task of converting them into an interoperable standard that can be certified. The WiMAX Forum was formed to solve this problem and to promote solutions based on the IEEE 802.16 standards.  

1.3 WiMAX Applications: Applications using a wireless solution can be classified as:

1. Point – to – Point. 2. Point – to – Multipoint.

And there are a lot of business models for WiMAX like: BWA technology for rural areas where no fixed lines are available. Coverage of cities with BWA in competition to fixed lines, as an

equivalent to WLAN with larger coverage. Hot Spots / Hot Zones. Backhauling of WLAN/ WiMAX Hot Spots. Broadband 4G mobile technology with mobility up to 120km/h.

 Figure 1.4: Possible scenarios for WiMAX deployment.

1.4 WiMAX versus other systems: WiMAX system can be compared with respect to 3G family, IEEE 802.11 [Wi–Fi], & others as IEEE 802.20 [Mobile Broadband Wireless Access (MBWA)] and IEEE 802.22 [Wireless Regional Area Network (WRAN)]. Here is a brief comparison between some systems:  

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Parameters Fixed WiMAX Mobile WiMAX HSPA 1x EV – DO

Rev A Wi – Fi

Standards IEEE 802.16d – 2004

IEEE 802.16e – 2005 3GPP Release 6 3GPP2 IEEE 802.11

(a/b/g/e/n)

Peak DL data rate

9.4 Mbps (in 3.5 MHz with 3:1 DL/ UL ratio [FDD]). 6.1 Mbps (in 3.5 MHz with 1:1 [TDD]).

46 Mbps (in 10 MHz with 3:1 DL/ UL ratio [FDD]). 32 Mbps (in 10 MHz with 1:1 [TDD]). Using 2 × 2 MIMO.

14.4 Mbps (using all 14 codes). 7.2 Mbps (using 10 codes).

3.1 Mbps. Rev. B will support 4.9 Mbps.

54 Mbps. More than 100 Mbps peak layer 2 throughput using (n). Both are shared between Dl & UL. Peak UL data

rate

3.3 Mbps (in 3.5 MHz with 3:1 DL – to – UL ratio [FDD]). 6.5 Mbps (in 3.5 MHz with 1:1 [TDD]).

7 Mbps (in 10 MHz with 3:1 DL – to – UL ratio [FDD]). 4 Mbps (in 10 MHz with 1:1 [TDD]).

1.4 Mbps. Later, 5.8 Mbps.

1.8 Mbps.

Bandwidth

3.5 & 7 MHz in 3.5 GHz band. 10 MHz in 5.7 GHz band.

3.5, 5, 7, 8.75, 10 MHz initially.

5 MHz. 1.25 MHz. 20 MHz. 20/ 40 MHz (n).

Modulation QPSK, 16 – QAM, & 64 – QAM.

QPSK, 16 – QAM, & 64 – QAM.

QPSK, & 16 – QAM.

QPSK, 8 – PSK, & 16 – QAM.

BPSK, QPSK, 16 – QAM, & 64 – QAM.

Multiplexing TDM. TDM/ OFDMA. TDM/ CDMA. TDM/ CDMA. CSMA.

Duplexing TDD, FDD & Half – duplex FDD.

TDD, FDD & Half – duplex FDD.

FDD. FDD. TDD.

Frequency 3.5, & 5.7 GHz. 2.3, 2.5, & 3.5 GHz.

800, 900, 1800, 1900, & 2100 MHz.

800, 900, 1800, & 1900 MHz. 2.4, 5 GHz.

Coverage 3 – 5 Miles. < 2 Miles. 1 – 3 Miles. 1 – 3 Miles.

< 100 ft (indoor). < 1000 ft (outdoors).

Mobility Not applicable. Medium. High. High. Low.

Advantages Throughput & coverage area. Mobility & coverage area. Throughput & cost.

Disadvantages Interference (& not mobile). Interference. Expensive & low rates. Small coverage.

Table 1.2: Comparison of WiMAX with other standards.

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Figure 1.5: WiMAX fills gap between WLAN & 3G (Rate–Mobility tradeoff).

Figure 1.6: Net Throughput per Channel/ Sector.

Figure 1.7: Spectral Efficiency.

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1.5 WiMAX bands & broadband bands: From a global perspective, the 2.3GHz, 2.5GHz, 3.5GHz, and 5.7GHz bands are most likely to see WiMAX deployments. The WiMAX Forum has identified these bands for initial interoperability certifications. A brief description of these bands follows:

Designation Frequency Allocation Spectrum Notes

UHF band 700 MHz

698 MHz – 746 MHz (lower band). 747 MHz – 792 MHz (upper band).

3o MHz upper band & 48 MHz lower band. Unlicensed.

Advanced wireless services (AWS)

1.710 GHz – 1.755 GHz. 2.110 GHz – 2.155 GHz. (Bands are paired)

2 × 45 MHz (paired). In USA, other countries used in 3G services.

Wireless Communications Services (WCS) 2.3 GHz

2.305 GHz – 2.320 GHz. 2.345 GHz – 2.360 GHz.

Paired (2 × 5 MHz) & unpaired 5 MHz.

Need licenses. WiBro (South Korea) uses this band. Major constraint, tight out – of – band emission requirements enforced by the FCC to protect adjacent DARS (digital audio radio services) band (2.320GHz to 2.345GHz) mobile services difficult in the sections of this band.

License exempt 2.4 GHz 2.405 GHz – 2.4835 GHz. One block 80 MHz.

Unlicensed. Mainly used by Wi–Fi.

Broadband radio services (BRS) 2.5 GHz

2.495 GHz – 2.690 GHz. separation between two blocks 10 MHz – 55 MHz.

Total 194 MHz which consist of 8 slices 22.5 Mhz [16.5 MHz (DL) paired with 6 MHz (UL)].

Need licenses. Allow TDD, FDD. many countries make this band available & attractive for mobile WiMAX.

Fixed wireless access (FWA) 3.5GHz

3.4 GHz – 3.6 GHz. 3.3 GHz – 3.4 GHz. 3.6 GHz – 3.8 GHz.

Total 200 MHz mostly varies from 2 × 5 MHz to 2 × 56 MHz (paired).

Need licenses. Allow TDD, FDD. (3.65 GHz – 3.70 GHz allocated for unlicensed operation in USA). Heavier radio propagation losses, difficult to provide nomadic & mobile services.

License exempt 5 GHz 5.25 GHz – 5.35 GHz. 5.725 GHz – 5.825 GHz.

200 MHz available & additional 255 MHz is allocated.

Unlicensed. Called unlicensed national information infrastructure (U – NII) is

Chapter. 1 

  

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USA. Note that lower band have severe power restrictions, extremely difficult to provide nomadic or mobile services.

Table 1.3: Summary of WiMAX bands.

1.6 WiMAX challenges: For WiMAX to be successful, it must deliver significantly better performance than current alternatives, such as 3G & Wi-Fi. There are some technical designs challenges like:

Developing reliable transmission & reception schemes to push broadband data through a hostile wireless channel.

Achieving high spectral efficiency & coverage in order to deliver broadband services to a large number of users, using limited available spectrum.

Supporting & efficiently multiplexing services with a variety of QoS requirements.

Supporting mobility through seamless handover & roaming. Achieving low power consumption to support handheld battery –

operated devices. Providing robust security. Adapting IP – based protocols & architecture for the wireless

environment to achieve lower cost & convergence with wired networks.

Service Requirements Technical Challenges Potential Solution

NLOS Mitigation of multipath fading & interference. Diversity, channel coding, etc.

High data rate & Capacity

Achieving high spectral efficiency Cellular architecture, adaptive modulation & coding, spatial multiplexing, etc.

Overcoming intersymbol interference (ISI). OFDM, equalization, etc.

Interference mitigation Adaptive antennas, sectorization, dynamic channel allocation, CDMA, etc.

Quality of service (QoS)

Supporting voice, data, video, etc, on a single access network. Complex MAC layer.

Radio resource management. Efficient scheduling algorithms.

End – to – end QoS. IP QoS (as DiffServ, IntServ, MPLS, etc).

Mobility Ability to be reached regardless of location.

Roaming database, location update, & paging.

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Session continuity while moving from the coverage area of one base station to another.

Seamless handover.

Session continuity across diverse networks (as between WiMAX & Wi–Fi).

IP – based mobility (Mobile IP).

Portability Reduce battery power consumption on portable subscriber terminals.

Power efficient modulation, sleep/ idle modes, low power circuits, & efficient signal processing algorithms.

Security Protect privacy of user data. Encryption. Prevent unauthorized access to network. Authentication & access control.

Low cost Provide efficient & reliable communication using IP architecture & protocols.

Adaptation of IP – based protocols for wireless & adapt layer 2 protocols for IP.

Table 1.4: Technical design challenges summery to wireless broadband. As is often the case in engineering, solutions that effectively overcome one challenge may aggravate another. Design trade – offs have to be made to find the right balance among competing requirements. 1.7 Quality of Service:

QoS is a broad and loose term that refers to the “collective effect of service,” as perceived by the user. In addition to the application–specific QoS requirements, networks often need to also enforce policy–based QoS, such as giving differentiated services to users based on their subscribed service plans. The variability in the QoS requirements across applications, services, and users makes it a challenge to accommodate all these on a single–access network, particularly wireless networks, where bandwidth is at a premium.

Parameter Interactive gaming Voice Streaming

media Data Video

Data rate 50 – 85 Kbps. 4 – 64 Kbps. 5 – 384 Kbps. 0.01 – 100 Mbps. > 1 Mbps.

Example Interactive gaming. VoIP. Music, video

clips.

E – mail, web browsing, instant messaging (IM), telnet, file download.

IPTV, movies download, peer – to – peer video sharing.

Traffic flow Real time. Real time (continuous).

Continuous, bursty.

Non – real time, bursty. Continuous.

Packet loss Zero < 1% < 1% (audio). < 2% (video).

Zero < 10 -8

Delay variation Not applicable. < 20 ms. 2 seconds. Not applicable. < 2 seconds.

Chapter. 1 

  

Page11 

Delay < 50 – 150 ms. < 100 ms. < 250 ms. Flexible. < 100 ms.

Table 1.5: Sample traffic parameters for wireless broadband applications

1.8 Fractional Frequency Reuse:

Mobile WiMAX support frequency reuse one, i.e. all cells/sectors operate on one frequency channel to maximize spectrum utilization. However, due to heavy interference in frequency reuse one deployment, users at the cell edge may suffer low connection quality. Since in WiMAX, users operate on sub–channels, which only occupy a small fraction of channel bandwidth, the cell edge interference problem can be easily addressed by reconfiguration of the sub–channel usage without resorting to traditional frequency planning. The sub–channel reuse pattern can be configured so that users close to the base station operate on the zone with all sub–channels available. While for the edge users, each cell/sector operates on the zone with a fraction of all sub–channels available.

Figure 1.8: Fractional Frequency Reuse. F1, F2, & F3 are different sets of sub–channels in the same frequency channel.

1.9 Remarks:

• For mobile WiMAX, the most significant challenge comes from 3G technologies that are being deployed worldwide by mobile operators. Mobile operators are more likely to seek performance improvements through 3G evolution than to adopt WiMAX.

Chapter. 1

  

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• CPE’s should kept simple by low transmitted power & simple efficient digital signal processing) in order to keep small size, to have long life battery (because it’s a limited source), & minimizing the cost.

• WiMAX allow Multimedia Broadcast/ Multicast Service (MBMS) –as like TV services & so on–; because OFDM allows for high–efficient Multicast/ Broadcast Single–Frequency Networking (MBSFN) operation. So we have identical transmissions from set of tightly synchronized cells which increased received power & reduced interference.

1.10 Bibliography:

[1] Fundamentals of WiMAX for Jeffrey G. Andrews, Ph.D., Arunabha Ghosh, Ph.D., Rias Muhamed. [2] The Business of WiMAX for Deepak Pareek – Resource4Business, India. [3] Implementation of a WiMAX simulator in Simulink for Amalia Roca. [4] Mobile WiMAX: The Best Personal Broadband Experience! June 2006 – WiMAX Forum. [5] Fixed, nomadic, portable & mobile applications for 802.16 – 2004 & 802.16e WiMAX networks, November 2005, Prepared by Senza Fili Consulting on behalf of the WiMAX Forum. [6] Mobile WiMAX – Part II: A Comparative Analysis, WiMAX Forum. [7] A Comparative Analysis of Mobile WiMAX Deployment Alternatives in the Access Network, WiMAX Forum. [8] Introduction into WiMAX, CHRISTIAN BAUER (Alcatel).

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Chapter. 2

  

Page14 

Orthogonal Frequency Division Multiplexing is a digital multicarrier (MC) modulation scheme. Its basic idea is to divide the transmitted bit–stream (high data rate) into many sub–streams (narrowband subcarriers – low data rate), & then each of these on a different carrier frequency.

Figure 2.1: Multicarrier Modulation.  

2.1 Multicarrier Modulation: To overcome the ISI & distortion while achieving high data rates, Multicarrier modulation is the solution. Basic idea of the multicarrier modulation is to divide the available bandwidth (W) into a number (Nc) of sub–bands, commonly called subcarriers. Each one of these subcarriers has a width of ∆f=W/Nc. The symbol duration for a multicarrier scheme is then Tsym=Nc/R.

Figure 2.2: Subdivision of bandwidth, in MC transmission, into Nc sub–bands.

Chapter

2 Orthogonal Frequency

Division Multiplexing

Chapter. 2 

    

Page15 

2.2 Orthogonality: In order to assure a high spectral efficiency, sub–channels waveforms must have overlapping transmit spectra. Nevertheless, to enable simple separation of these overlapping sub–channels at receiver, they need to be orthogonal. Orthogonality is a property that allows the signals to be perfectly transmitted over a common channel & detected without interference. Set of functions are orthogonal to each other if they match following condition:

⎩⎨⎧

≠=

=⋅∫ jijiC

tStST

ji 0)()(

0

Figure 2.3: Spectrum of OFDM signal.

2.3 IFFT & FFT: After the OFDM symbols are stacked up into the frame, it is then converted to time domain using the Inverse Discrete Fourier Transform (IDFT). An efficient way of implementing IDFT is IFFT (Inverse Fast Fourier Transform). IFFT is useful for OFDM because it generates samples of a waveform with frequency components satisfying orthogonality conditions, i.e., the IFFT modulates each Sub–channel onto a precise orthogonal carrier. The IFFT of subcarrier X(k) is given as below:

1,...,1,0,)(1)(21

0

−=⋅=⋅⋅−

=∑ NnforekX

NnX N

kjN

k

nπ

And using FFT in the receiver to recover the subcarriers X(k):

1,...,1,0,)(1)(21

0

−=⋅=⋅⋅

−−

=∑ NnforenX

NkX N

kjN

k

nπ

Chapter. 2

  

Page16 

2.4 Cyclic Prefix: If successive OFDM symbols were sent one directly after another, in order to keep each OFDM symbol independent of others after going through a wireless channel, it is necessary to introduce a guard time between OFDM symbols. This guard period, which is called the cyclic prefix (CP), is a copy of the last part of the OFDM symbol.

Figure 2.4: Cyclic Prefix. Where total length of symbol can be written as: Ts=Tg+Tb. Ts: total length of the symbol in samples. Tg: length of the guard period in samples. Tb: size of the IFFT used to generate the OFDM signal, representing the useful symbol time. To completely avoid the effects of ISI & thus, to maintain the orthogonality between the signals on the subcarriers, i.e., to also avoid ICI, a guard interval inserted must be Tg≥  τmax, Where τmax is the maximum impulse response of the channel. However, the length of the cyclic prefix has to be chosen carefully. On one hand, it should be, at least, as long as the significant part of the impulse response experienced by the transmitted signal, it should be as small as possible because the transmitted energy increases with its length, causing a loss in the SNR:

⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

s

gloss T

TSNR 1log10 10

Moreover, the number of symbols per second that are transmitted per Hz of bandwidth also decreases with the CP. 802.16 standards offer the following set of guard interval sizes (Tg/Ts): 1/4, 1/8, 1/16, & 1/32.

Chapter. 2 

    

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Figure 2.5: Relation between cyclic prefix & delay spread.

2.5 OFDM Symbol: The OFDM symbol structure consists of three types of subcarriers:

1. Data subcarriers for data transmission. 2. Pilot subcarriers for estimation & synchronization purposes (for

IFFT size=256, −88, −63, −38, −13/ +13, +38, +63, +88). 3. Null subcarriers for no transmission; used for guard bands (for

IFFT size=256, −128, −127... −101/ +101, +102... +127) & DC carriers.

The number of these subcarriers will determine the required size for the FFT (or IFFT) algorithm.

Figure 2.6: Frequency domain representation of OFDM symbol. The transmitted baseband signal which is an ensemble of the signals in all the sub–carriers can be represented as:

TteistxL

i

tiBfj c ≤≤⋅= ∑−

=

⋅+Δ⋅⋅− 0][)(1

0

)(2π

s[i]: Symbol carried on the ith subcarrier. Bc: Frequency separation between two adjacent subcarriers (subcarrier B.W.). Δf: Frequency of the first subcarrier. T: Total useful symbol duration (without the CP).

Chapter. 2

  

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Symbol Description Relation WiMAX B Nominal bandwidth B= 1/Ts 10 MHz L Number of subcarriers Size of IFFT/FFT 1024 G Guard fraction % of L for CP 1/8 Ld Data subcarriers L – pilot/ null subcarriers 768 Ts Sample time Ts=1/B 1 µsec Ng Guard symbols Ng=GL 128 Tg Guard time Tg=TsNg 12.8 µsec T OFDM symbol time T=Ts(L+Ng) 115.2 µsec Bsc Subcarrier bandwidth Bsc=B/L 9.76 KHz

Table 2.1: OFDM parameters.

2.6 Peak – to – Average Ratio: OFDM signals have a higher peak – to – average ratio (PAR) than single – carrier signals. The reason is that multicarrier signal is the sum of many narrowband signals in time domain. At some time instances, this sum is large & at other times is small, which means that the peak value of the signal is substantially larger than the average value. This high PAR is one of the most important implementation challenges that face OFDM, because it reduces the efficiency & hence increases the cost of the RF power amplifier.

Figure 2.7: A typical power amplifier response. To avoid such undesirable nonlinear effects, a waveform with high peak power must be transmitted in the linear region of the HPA by decreasing the average power of the input signal. This is called input backoff (IBO) & results in a proportional output backoff (OBO). The input backoff is defined as:

in

insat

PPIBO 10log10=

Chapter. 2 

    

Page19 

Where Pinsat is the saturation power, above which is the nonlinear region, & inP is the average input power. The amount of backoff is usually greater

than or equal to the PAR of the signal. In order to avoid operating the Power Amplifier (PA) in the nonlinear region, the input power can be reduced by an amount about equal to the PAR. Clipping, sometimes called soft limiting, truncates the amplitude of signals that exceed the clipping level as:

⎩⎨⎧

≤⋅

=∠

AnxIfnxAnxIfeA

nXnxj

L ][][][

][~ ][ >

Where x[n] is the original signal, & ][~ nX L is the output after clipping. The soft limiter output can be written in terms of the original signal & a canceling, or clipping, signal as:

1,...,0],[][][~ −=+= LnforncnxnX L Where C[n] is the clipping signal defined by:

⎪⎩

⎪⎨⎧

≤⋅−

=AnxIfAnxIfenxA

nCnj

][0][][

][>θ

Where θ[n]=arg(–x[n]); that is, the phase of C[n] is out of phase with x[n] by 180°, & A is the clipping level, which is defined as:

x

A

nxE

Aε

γ ==})({ 2

Figure 2.8: A peak cancellation as a model of soft limiter when dB5=γ .

2.7 OFDMA:

Orthogonal Frequency Division Multiple Access is the way that users share subcarriers & time slots (resources) “this technique can be compared relative to TDMA, FDMA, & CDMA – Multiple access techniques –”. OFDMA is the classical extension of the OFDM & essentially a hybrid of FDMA &

Chapter. 2

  

Page20 

TDMA; users are dynamically assigned subcarriers (FDMA) in different time slots (TDMA). One significant advantage of OFDMA relative to OFDM is its potential to reduce the transmit power & to relax the peak – to – average – power ratio (PAPR) problem.

Figure 2.9: OFDMA & OFDM.

2.8 Resource – Allocation Techniques for OFDMA:

Resource allocation algorithms aren’t specified by the WiMAX standard, & all WiMAX developer is free to develop their own innovative procedures. The idea is to develop algorithms for determining which users to schedule, how to allocate subcarriers to them, & appropriate power levels for each user on each subcarrier. Some of these algorithms are mentioned below: 

Algorithm Sum Capacity Fairness Complexity Maximum sum rate (MSR) Best Poor & inflexible Low

Maximum fairness (MF) Poor Best but inflexible Medium Proportional rate constraints (PRC) Good Most flexible High

Proportional fairness (PF) Good Flexible Low

Table 2.2: OFDMA Rate–Adaptive Resource–Allocation Schemes.

Chapter. 2 

    

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2.9 OFDMA Frame Structure:

Figure 2.10: OFDMA Frame Structure.

2.10 Sub–Channel & Sub–Carrier Permutations:

Different ways of grouping subcarriers (tons) into channels called permutations. Permutations are summarized in the following table:

Name Basic Unit Sub–Carrier Group Sub–Channel FUSC Not applicable  Not applicable. 48 distributed subcarrier.

DL PUSC Cluster: 14 adjacent sub – Carrier over 2 symbols with 4 embedded pilot sub–Carriers.

Cluster divided into 6 groups. 2 clusters.

UL PUSC Tile: 4 adjacent sub–Carriers over 3 symbols with 4 embedded pilot sub–Carriers.

Tile divided into 6 groups. 6 tiles.

Optional UL PUSC

Tile: 3 adjacent sub–Carriers over 3 symbols with 1 embedded pilot sub–Carriers.

Tile divided into 6 groups. 6 tiles. 

TUSC 1 Tile: 4 adjacent sub–Carriers over 3 symbols with 4 embedded pilot sub–Carriers.

Tile divided into 6 groups. 6 tiles. 

TUSC 2 Tile: 3 adjacent sub–Carriers over 3 symbols with 1 embedded pilot sub–Carriers.

Tile divided into 6 groups. 6 tiles. 

AMC Bin: 9 adjacent sub–Carriers over 1 symbol with 1 embedded pilot sub–Carriers.

Not applicable.

6 adjacent bins over 6 consecutive OFDM symbol or 2 bins over 3 OFDM symbols or 3 bins over 2 OFDM symbols.

Table 2.3: Sub–Carrier Permutations.

Chapter. 2

  

Page22 

2.11 SOFDMA:

Scalable Orthogonal Frequency Division Multiple Access allows adjusting the number of sub carriers (FFT size) to the transmission channel bandwidth. SOFDMA guarantees a higher spectral efficiency due to a constant sub carrier spacing in different channel bandwidths. That is only achievable if a different number of sub carriers are used for different channel bandwidths. The number of carriers should be a multiple of 128. So far there are 4 sets of sub carrier sets: 128, 512, 1024, & 2048.

Parameters Value System Channel Bandwidth (MHz) 1.25 5 10 20 Sampling Frequency (Fp in MHz) 1.4 5.6 11.2 22.4 FFT Size (NFFT) 128 512 1024 2048 Number of Sub–Channels 2 8 16 32 Sub–Carrier Frequency Spacing 10.94 KHz Useful Symbol Time (Tb=1/f) 91.4 µsec. Guard Time (Tg=Tb/8) 11.4 µsec. OFDMA Symbol Duration (Ts=Tb+Tg) 102.9 µsec. Number of OFDMA Symbols (5 msec frame) 48

Table 2.4: Scalable OFDMA Parameters.

2.12 Bibliography:

[1] Fundamentals of WiMAX for Jeffrey G. Andrews, Ph.D., Arunabha Ghosh, Ph.D., Rias Muhamed. [2] Implementation of a WiMAX simulator in Simulink for Amalia Roca. [3] 802.16 IEEE Standards for Local and metropolitan area networks. [4] Introduction into WiMAX, CHRISTIAN BAUER (Alcatel).

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Chapter. 3

  

Page24 

Physical layer (PHY) of mobile WiMAX is based on the IEEE 802.16e–2005 standard & was designed with much influence from Wi–Fi, especially IEEE 802.11a. Although many aspects of the two technologies are different due to the inherent difference in their purpose & applications, some of their basic constructs are very similar. WiMAX is based on the principles of orthogonal frequency division multiplexing (OFDM) like Wi–Fi which is a suitable modulation/ access technique for non–line–of–sight (N–LOS) conditions with high data rates. The IEEE 802.16 suite of standards (IEEE 802.16–2004/ IEEE 802–16e-2005) defines within its scope four PHY layers, any of which can be used with the media access control (MAC) layer to develop a broadband wireless system. The PHY layers are: 1. WirelessMAN SC: a single–carrier PHY layer intended for frequencies

beyond 11GHz requiring a LOS condition. 2. WirelessMAN SCa: a single–carrier PHY for frequencies between 2GHz

& 11GHz for point–to–multipoint operations. 3. WirelessMAN OFDM: a 256–point FFT–based OFDM PHY layer for

point–to–multipoint operations in N–LOS conditions at frequencies between 2GHz & 11GHz.

4. WirelessMAN OFDMA: a 2,048-point FFT–based OFDMA PHY for point–to–multipoint operations in N–LOS conditions at frequencies between 2GHz & 11GHz. In the IEEE 802.16e–2005, this layer has been modified to Scalable OFDMA (SOFDMA), where the FFT size is variable and can take any one of the following values: 128, 512, 1,024, and 2,048.

As any communication system, physical layer may be cut to three different parts in order to group the functions done by each side. Simply the three different parts are: 1. Transmitter. 2. Channel. 3. Receiver.

Chapter

3 Physical Layer

Chapter. 3 

    

Page25 

 Figure 3.1: Basic system structure.

Figure 3.2: Functional Stages of WiMAX PHY Layer (Transmitter).

3.1 Transmitter:

Figure 3.3: Transmitter of WiMAX System.

3.1.1 Randomizer: As described in the standard, the information bits must be randomized before the transmission. Randomization process is used to minimize the possibility of transmissions of non–modulated subcarriers. The process of randomization is performed on each burst of data on the downlink & uplink, & on each allocation of a data block (sub–channels on the frequency domain and OFDM symbols on the time domain).

Chapter. 3

  

Page26 

 Figure 3.4: Randomizer.

3.1.2 Frame Error Correction (FEC): WiMAX define many types of encoders as: 1. Concatenated Reed–Solomon–Convolutional Code (RS–CC)

[Mandatory]. 2. Block Turbo Coding (BTC) [Optional]. 3. Convolutional Turbo Coding (CTC) [Optional]. 4. Low Density Parity Check (LDPC) [Optional].

3.1.2.1 Concatenated Reed–Solomon–Convolutional Code:

Concatenated Reed–Solomon–convolutional code (RS–CC) as a mandatory channel encoder for the system. The Reed–Solomon encoding shall be derived from a systematic RS (N = 255, K = 239, T = 8) code using GF(28), where: N: number of overall bytes after encoding. K: number of data bytes before encoding. T: number of data bytes which can be corrected. The following polynomials are used for the systematic code:

HEXTxxxxxg 02),)...()()(()( 12210 =++++= − λλλλλ

Field Generator Polynomial: 1)( 2348 ++++= xxxxxp

For the binary convolutional encoder, which shall have native rate of 1/2, constraint length equal to 7, & shall use the generator polynomials: G1 = 171OCT FOR X G2 = 173OCT FOR Y Puncturing process is done in order to change the code rate of the encoder.

Chapter. 3 

    

Page27 

Figure 3.5: Convolutional Encoder & tailbiting in IEEE 802.16e.

Code Rate Rate 1/2 2/3 3/4 5/6 dfree 10 6 5 4 X 1 10 101 10101 Y 1 11 110 11010

XY X1Y1 X1Y1Y2 X1Y1Y2X3 X1Y1Y2X3X4X5

Table 3.1: Inner Convolutional Code with Puncturing Configuration.

Modulation Uncoded block size (bytes)

Coded block size (bytes)

Overall coding rate RS code CC code

rate BPSK 12 24 1/2 (12, 12, 0) 1/2 QPSK 24 48 1/2 (32, 24, 4) 2/3 QPSK 36 48 3/4 (40, 36, 2) 5/6 16–QAM 48 96 1/2 (64, 48, 8) 2/3 16–QAM  72 96 3/4 (80, 72, 4) 5/6 64–QAM  96 144 2/3 (108, 96, 6) 3/4 64–QAM  108 144 3/4 (120, 108, 6) 5/6

Table 3.2: Mandatory Channel Coding per Modulation.

Chapter. 3

  

Page28 

Figure 3.6: Turbo Encoder (Constituent Encoder) in IEEE 802.16e. Note that it contains interleaver, so when using it, there are no need for the interleaver.

3.1.3 Interleaver: Data interleaving is generally used to scatter error bursts & thus, reduce error concentration to be corrected with the purpose of increasing efficiency of FEC by spreading burst errors introduced by the transmission channel over a longer time. Interleaving result is that burst of errors in the channel after interleaving becomes in few scarcely spaced single symbol errors, which are more easily correctable. All encoded data bits shall be interleaved by a block interleaver with a block size corresponding to the number of coded bits per the allocated subchannels per OFDM symbol, Ncbps. The interleaver is defined by a two step permutation. First ensures that adjacent coded bits are mapped onto nonadjacent subcarriers. The second permutation insures that adjacent coded bits are mapped alternately onto less or more significant bits of the constellation, thus avoiding long runs of lowly reliable bits. The first permutation is defined by Equation:

1,...,1,01212 )12mod( −=⎟

⎠⎞

⎜⎝⎛+⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛= cbps

cbpsk Nkkfloork

Nm

The second permutation is defined by Equation:

[ ] 1,...,1,0)/12()mod(

−=⋅−++⎟⎠⎞

⎜⎝⎛⋅= cbpsscbpskcbpsk

kk NkNmfloorNm

smfloorsj

Chapter. 3 

    

Page29 

Ncbpc: number of coded bits per subcarrier, i.e., 1, 2, 4 or 6 for BPSK, QPSK, 16–QAM, or 64–QAM, respectively. K: index of the coded bit before the first permutation. mk: index of that coded bit after the first & before the second permutation. jk: index after the second permutation, just prior to modulation mapping.

( )2/cbpcNCeils =

(Default) 16 sub–channels 8 sub–channels 4 sub–channels 2 sub–channels 1 sub–channels

Ncbps BPSK 192 96 48 24 12 QPSK 384 192 96 48 24 16–QAM 768 384 192 96 48 64–QAM 1152 576 288 144 72

Table 3.3: Block Size of the Interleaver.

3.1.4 Symbol Mapping: After bit interleaving, the data bits are entered serially to the constellation mapper. BPSK, Gray–mapped QPSK, 16–QAM, & 64–QAM.

Figure 3.7: BPSK, QPSK, 16–QAM, & 64–QAM Constellations.

Chapter. 3

  

Page30 

3.1.5 Pilot Symbol: Pilot symbols can be used to perform frequency offset compensation at the receiver. Additionally, they can be used for channel estimation in fast time–varying channels. Pilot symbols allocate specific subcarriers in all OFDM data symbols. These pilots are obtained by a pseudo–random binary sequence (PRBS) generator that is based on the polynomial 1911 ++ XX .

Figure 3.8: PRBS Generator for Pilots.

3.1.6 Training Sequences: In WiMAX systems, preambles, both in DL & UL, are composed using training sequences. Although three types of training sequences are specified. All preambles are structured as either one of two OFDM symbols. For DL transmissions, the first preamble as well as the initial ranging preamble consists of two consecutive OFDM symbols. The first symbol is a short training sequence, PSHORT, used for synchronization. The frequency domain sequence for this first DL preamble is defined in following equation:

( )⎪⎩

⎪⎨⎧

≠=⋅⋅

=000)(22

)()4mod(

)4mod(

kkkPconj

Kp ALLSHORT

The second OFDM symbol uses a long training sequence, necessary in the receiver for channel estimation. It is called PEVEN. The following equation defines the frequency domain sequence for this long training:

( )⎪⎩

⎪⎨⎧

≠=⋅

==000)(2

)()2mod(

)2mod(

kkkP

kP ALLEVEN

In both equations, a factor of 2 representing a boost of 3dB appears. Furthermore, there is an additional factor of 2 in PSHORT which has the

Chapter. 3 

    

Page31 

aim of equating the root–mean–square (RMS) power with the power of the data symbols. Another training sequence shall be used when transmitting space–time Coded (STC) downlink bursts. Because the STC scheme achieves diversity by transmitting with two antennas, a preamble has to be transmitted from both transmit antennas simultaneously. Thus, the first antenna transmits a preamble using PEVEN & preamble transmitted from the second antenna is set according to the sequence PODD.

( )⎩⎨⎧

≠⋅=

==0)(200

)()2mod(

)2mod(

kkPk

kPALL

ODD

Figure 3.9: DL Preamble structure (PSHORT than PEVEN).

3.1.7 Inverse Fast Fourier Transform (IFFT): IFFT is used to produce a time domain signal, as the symbols obtained after modulation can be considered the amplitudes of a certain range of sinusoids. This means that each of the discrete samples before applying the IFFT algorithm corresponds to an individual subcarrier. Besides ensuring the orthogonality of the OFDM subcarriers, the IFFT represents also a rapid way for modulating these subcarriers in parallel, and thus, the use of multiple modulators & demodulators (multi crystal oscillators) spend a lot of time & resources to perform this operation, is avoided. Furthermore, the FFT (or IFFT) should be of length 2r (where r is an integer number) to facilitate the realization of the algorithm. For this reason, the FFT length is given by:

[ ]( )dataHceilFFTN 2log2=

& OFDM symbol can be written as: ( ) Tteistx

L

i

tBifj C ≤≤⋅= ∑−

=

⋅⋅+Δ⋅− 0][)(1

0

2π

s[i]: symbol carried on the ith subcarrier. Bc: frequency separation between two adjacent subcarriers (subcarrier bandwidth). Δf: frequency of the first subcarrier. T: total useful symbol duration (without the cyclic prefix).  

Chapter. 3

  

Page32 

3.1.8 Cyclic Prefix (CP): As mentioned before [Ch. 2], robustness of any OFDM transmission against multipath delay spread is achieved by having a long symbol period with the purpose of minimizing the inter–symbol interference (ISI). Sometimes it’s called guard time or guard interval & usually its 1/4.

3.1.9 RF stage: The Previous stages were the baseband processing of the system. After that, the radio frequency stage (RF) completes the job. It consists of D/A & oscillator having the system frequency. Resultant signal is at the operating frequency.

3.2 Channel: When communicating over a wireless radio channel, received signal can’t be simply modeled as a copy of transmitted signal corrupted by additive Gaussian noise (AWGN). Instead, signal fading & other channel effects [Ch. 5], caused by the time–varying characteristics of propagation environment, appears which lead to a phenomenon known as multipath propagation. The time dispersion in a multipath environment causes the signal to undergo either flat (easy to compensate) or frequency–selective fading (OFDM solve its problem). Furthermore, time dispersion is manifested by the spreading in time of the modulated symbols leading to inter–symbol interference (ISI), & cyclic prefix compensate it. In addition, root–raised cosine (RRC) filters, usually used for band–limiting the transmitted signal distort the signal.

3.3 Receiver:

Figure 3.10: Receiver of WiMAX System.

Chapter. 3 

    

Page33 

Receiver carries out the reverse operations of the transmitter. It starts by a filter to limit the noise, than down conversion of the frequency by RF stage to the intermediate frequency (IF) to be ready for the baseband processing. The first step of the baseband processing is to remove the cyclic prefix, than FFT, removing null sub–carriers & taking pilot symbols to be used later in channel estimation, than signal enters the symbol de–mapper, after words it goes to the de–interleaver & channel decoder, after words data goes to the higher layers. The WiMAX de–interleaver performed in two steps too. The first permutation is defined by Equation:

1,...,1,0))/12(()/( )mod( −=⋅++⋅= cbpsscbpsj NjNjfloorjsjfloorsm The second permutation is defined by Equation:

1,...,1,0)/12()1(12 −=⋅⋅−−⋅= cbpscbpsjcbpsjj NjNmfloorNmk Noting that the convolutional encoder decoder is the viterbi decoder which may operate in different modes like: 1. Unquantized operation. 2. Hard decoding (decision) which takes samples of the received signal,

determines whether each sample is over or under a given threshold and thus decides whether the incoming signal represents a ‘1’ or a ‘0’.

3. Soft decoding (decision) which keeps distance of a sample value from the decision threshold is measured, and then used to enhance the decoding process & overcome the losses of data done by hard decoding –soft decoding shows better performance by 3dB [shows the same BER & lower 3dB SNR] by dividing the incoming signal into many levels within its incoming range & represent level using multi–bit–.

3.4 Bibliography:

[1] Fundamentals of WiMAX for Jeffrey G. Andrews, Ph.D., Arunabha Ghosh, Ph.D., Rias Muhamed. [2] 802.16 IEEE Standards for Local and metropolitan area networks. [3] Implementation of a WiMAX simulator in Simulink for Amalia Roca. [4] Essentials of Error–Control Coding, for Jorge Castiñeira Moreira.

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Chapter. 4 

    

Page35 

Media Access Control (MAC) layer, which resides above the PHY layer, is responsible for controlling & multiplexing various such links over the same physical medium.

Figure 4.1: WiMAX MAC Layer.

Some of the important functions of the MAC layer: • Segment or concatenate the service data units (SDUs) received from

higher layers into MAC PDU (protocol data units), the basic building block of MAC–layer payload.

• Select the appropriate burst profile & power level to be used for the transmission of MAC PDUs.

• Retransmission of MAC PDUs that were received erroneously by the receiver when automated repeat request (ARQ) is used.

• Provide QoS control & priority handling of MAC PDUs belonging to different data & signaling bearers.

• Schedule MAC PDUs over the PHY resources. • Provide support to the higher layers for mobility management. • Provide security & key management.

Chapter

4 MAC Layer

Chapter. 4

  

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• Provide power–saving mode & idle–mode operation.

4.1 Convergence Sub–layer (CS): The various higher–layer protocol convergence sub–layers –or combinations– that are supported in WiMAX are:

Value Convergence Sub–layer 0 ATM CS 1 Packet CS IPv4 2 Packet CS IPv6 3 Packet CS 802.3 (Ethernet) 4 Packet CS 802.1/ Q VLAN 5 Packet CS IPv4 over 802.3 6 Packet CS IPv6 over 802.3 7 Packet CS IPv4 over 802.1/ Q VLAN 8 Packet CS IPv6 over 802.1/ Q VLAN 9 Packet CS 802.3 with optional VLAN tags & ROHC header compression

10 Packet CS 802.3 with optional VLAN tags & ERTCP header compression 11 Packet IPv4 with ROHC header compression 12 Packet IPv6 with ROHC header compression

13–31 Reserved

Table 4.1: Convergence Sub–layer of WiMAX.

4.2 Common Part Sub–layer:

4.2.1 MAC PDU Construction & Transmission: SDUs arriving at the MAC common part sub–layer from the higher layer are assembled to create the MAC PDU the basic payload unit handled by the MAC & PHY layers. Based on the size of the payload, multiple SDUs can be carried on a single MAC PDU, or a single SDU can be fragmented to be carried over multiple MAC PDUs.

Figure 4.2: Segmentation and concatenation of SDUs in MAC PDUs.

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Each MAC PDU consists of a header followed by a payload & a cyclic redundancy check (CRC). The CRC is based on IEEE 802.3 & is calculated on the entire MAC PDU (header & the payload). WiMAX has two types of PDUs, each with a very different header structure: 1. Generic MAC PDU: carries data & MAC–layer signaling messages. 2. Bandwidth request PDU: used by the MS to indicate to the BS that more

bandwidth is required in the UL, due to pending data transmission. A bandwidth request PDU consists only of a bandwidth–request header, with no payload or CRC. Note that BS indicates this allocation to the MS, using the DL–MAP message.

Figure 4.3: WiMAX PDU headers: generic (on the top) & bandwidth request (on the button).

WiMAX also defines five sub–headers that can be used in a generic MAC PDU: 1. Mesh sub–header. 2. Fragmentation sub–header. 3. Packing sub–header. 4. Fast-feedback allocation sub–header. 5. Grant-management sub–header.

4.2.2 Network Entry & Initialization:

Network entry & initialization process done by the CPE’s is illustrated using following flowchart:

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Figure 4.4: Network Entry & Initialization.

4.2.3 Power–Saving Operations:

The IEEE 802.16e standard introduces several new concepts related to mobility management & power management. Power management enables MS to conserve its battery resources, a critical feature required for handheld devices. The power–management features of a WiMAX network: 1. Sleep Mode. 2. Idle Mode.

4.2.4 Mobility Management:

Mobility management enables MS to retain its connectivity to the network while moving from the coverage area of one BS to the next. In order to be aware of its dynamic radio frequency environment, the BS allocates time for each MS to monitor & measure the radio condition of the neighboring BS’s. This process is called “scanning”, & the time allocated to each MS is called “scanning interval”. During a scanning interval, MS measures the received signal strength indicator (RSSI) & the SINR of the neighboring BS & can optionally associate with some or all the BSs in the neighbor list, which requires the MS to perform some level of initial ranging with the neighboring BS. Three levels of association are possible during the scanning process: 1. During association level 0 (scan/ association without coordination).

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2. During association level 1 (scan/ association with coordination). 3. Association level 2 (network assisted association reporting).

4.2.4.1 Handoff Process & Cell Reselection:

Handoff process is defined (in WiMAX) as the set of procedures & decisions that enable an MS to migrate from the air interface of one BS to the air interface of another & consists of the following stages: 1. Cell reselection. 2. Handoff decision and initiation. 3. Synchronization to the target BS. 4. Ranging with target BS. 5. Termination of context with previous BS.

4.2.4.2 Macro Diversity Handover & Fast BS Switching:

WiMAX also defines two optional handoff procedures: 1. Macro diversity handover (MDHO). 2. Fast base station switching (FBSS).

In order for FBSS or MDHO to be feasible, BSs in the diversity set of an MS must satisfy the following conditions: • BS’s involved in FBSS are synchronized, based on a common timing

source. • DL frames sent from BS’s arrive at the MS within cyclic prefix interval. • BS’s involved in FBSS must be on the same carrier frequency. • BS’s involved in FBSS must have synchronized frames in DL & UL. • BS’s involved in FBSS are required to share all information that MS &

BS normally exchange during network entry. • BS’s involved in FBSS must share all information, such as SFID, CID,

encryption, & authentication keys.

Figure 4.5: DL MOHO: combining.

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Figure 4.6: UL MDHO: Selection.

4.3 Security Sub–layer:

Security sub–layer provides subscribers with privacy, authentication, or confidentiality across mobile broadband wireless network. It does this by applying cryptographic transforms to MPDUs carried across between connections between SS & BS. In addition, security sub–layer provides operators with strong protection from theft of service. The BS protects against unauthorized access to these data transport services by securing associated service flows across network. Security sub–layer employs an authenticated client/ server key management protocol in which BS, server, & controls distribution of keying material to SS. Additionally, basic security mechanisms are strengthened by adding digital–Certificate–based SS device–authentication to the key management protocol.

4.3.1 Security Sub–layer Architecture:

Privacy has two component protocols as follows: a) An encapsulation protocol for encrypting packet data across the BWA network. This protocol defines: 1. Set of supported cryptographic suites, i.e., pairings of data encryption

& authentication algorithms. 2. Rules for applying those algorithms to a MAC PDU payload.

b) A key management protocol (PKM) providing secure distribution of keying data from BS to SS. Through this key management protocol, SS & BS synchronize keying data; in addition, the BS uses the protocol to enforce conditional access to network services.

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Figure 4.7: Security Sub–layer.

4.3.2 Authentication architecture:

EAP methods run between the terminal & the home AAA (EAP for device authentication may eventually terminate in the visited network). Underlying protocols are: • RADIUS or DIAMETERS (Both will be supported by the solution)

between the WAC & the home AAA. • PKMv2 protocol on the air interface. • A signaling protocol between BS & the authenticator located in the

WAC. EAP exchanges include messages between the WAC & MS (e.g. authentication triggering) & messages between AAA & MS (typically those conveying authentication exchanges). The supplicant, the authenticator & authentication server of the EAP model are respectively the terminal, the WAC and the AAA server.

Figure 4.8: Authentication architecture

AAA

Home networkTerminal

PKMv2-EAP

EAP method (e.g. TTLS/ CHAP, TLS, SIM etc.)

EAP

BS-WAC signaling protocol RADIUS or DIAMETER

EAP

BS WAC

SIM/ MAP

HLR

CHAP AAACHAP/ RADIUS

AAA

Home networkTerminal

PKMv2-EAP

EAP method (e.g. TTLS/ CHAP, TLS, SIM etc.)

EAP

BS-WAC signaling protocol RADIUS or DIAMETER

EAP

BS WAC

SIM/ MAP

HLR

CHAP AAACHAP/ RADIUS

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Figure 4.9: PKMv2 key hierarchy.

4.4 Bibliography:

[1] Fundamentals of WiMAX for Jeffrey G. Andrews, Ph.D., Arunabha Ghosh, Ph.D., Rias Muhamed. [2] 802.16 IEEE Standards for Local and metropolitan area networks. [3] Security in WiMAX, Alcatel solution.

MSKu (512)

PMKu (160)PMKd (160)

Dot16KDF(PMKd, PMKu, MSID, BSID , # )

AK (160)

Dot16KDF (AK, MS MAC @, BSID, # )

Trunk

CMAC-Key-UL (128) CMAC-Key-DL (128) KEK (128)

MSK: Master Session Key

PMK: Pair wise Master Key

EIK: EAP integrity key

AK: Authentication Key

SSID: SS Identity

MSID: MS Identity

MAC: Message Authentication Code

CMAC: Cipher MAC

HMAC: Hash MAC

UL/ LD: Uplink / Downlink

KEK: Key Encryption Key

GKEK: Group wise KEK

TEK: Traffic Encryption Key

GTEK: Group wise TEK

GD: Group wise Downlink

# : Dot16KDM operation identifier

{GKEK, TEK}

protected by KEK

{GTEK}

protected by GKEK

Dot16KDF(GKEK, # )

TEK (128)GKEK (128)

GTEK

CMAC-Key-GD (128)

MSKd (512)

Trunk

MSKu (512)

PMKu (160)PMKd (160)

Dot16KDF(PMKd, PMKu, MSID, BSID , # )

AK (160)

Dot16KDF (AK, MS MAC @, BSID, # )

Trunk

CMAC-Key-UL (128) CMAC-Key-DL (128) KEK (128)

MSK: Master Session Key

PMK: Pair wise Master Key

EIK: EAP integrity key

AK: Authentication Key

SSID: SS Identity

MSID: MS Identity

MAC: Message Authentication Code

CMAC: Cipher MAC

HMAC: Hash MAC

UL/ LD: Uplink / Downlink

KEK: Key Encryption Key

GKEK: Group wise KEK

TEK: Traffic Encryption Key

GTEK: Group wise TEK

GD: Group wise Downlink

# : Dot16KDM operation identifier

{GKEK, TEK}

protected by KEK

{GTEK}

protected by GKEK

Dot16KDF(GKEK, # )

TEK (128)GKEK (128)

GTEK

CMAC-Key-GD (128)

MSKd (512)

Trunk

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WiMAX support many advanced techniques in order to improve the overall system performance as AMC in order to increase the spectrum efficiency, & use advanced antenna solutions like Multi–layer transmission (MIMO), Diversity & Beam–forming to improve Capacity, Coverage & provide very high data rates.

5.1 Adaptive Modulation & Coding (AMC): WiMAX supports a variety of modulation & coding schemes and allows the scheme to change on a burst–by–burst basis per link, depending on channel conditions. Using the channel quality feedback indicator, the mobile can provide the base station with feedback on the downlink channel quality. For the uplink, the base station can estimate the channel quality, based on the received signal quality. The base station scheduler can take into account the channel quality of each user’s uplink & downlink and assign a modulation & coding scheme that maximizes the throughput for the available SNR. AMC significantly increases the overall system capacity, as it allows real–time trade–off between throughput & robustness on each link.

Figure 5.1: Adaptive Modulation & Coding.

Chapter

5 Advanced Techniques

in WiMAX

Chapter. 5 

    

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Figure 5.2: Adaptive modulation & coding block diagram.

5.1.1 Modulation: For each transmission step, several bits are coded on each subcarrier. For example when clear line of sight exists between sender & receiver over short distances, 64–QAM is used, which codes six bits on a single subcarrier (Symbol), Under harsher conditions, less demanding modulation schemes like 16–QAM, QPSK & BPSK are used, which code fewer bits on a subcarrier per transmission step.

Figure 5.3: Shannon capacity & modulation constrained Shannon capacity.

Modulation Scheme Required SNR Description

64–QAM 22 dB 6 bit’s/ Symbol. (LOS & very short distance).

16–QAM 16 dB 4 bit’s/ Symbol. QPSK 9 dB 2 bit’s/ Symbol.

BPSK 6 dB 1 bit/ Symbol. (Very robust, used with harsh environments).

Table 5.1: SNR required for each modulation, & bits/ Symbol.

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5.1.2 Coding: The coding rate is the ratio between the number of user data bits & the number of error correction & detection bits sent over the air interface. The lowest coding rate is 3/4. Where three user data bits are encoded in four bits, which are then sent over the air interface. This coding rate can only be used for exceptionally good signal conditions. For less favorable conditions coding rates of 2/3 or 1/2 are used. 1/2 coding basically cuts the data rate in half.

Figure 5.4: Throughput versus SINR, assuming that the best available constellation & coding configuration are chosen for each SINR.

5.2 AMC in Uplink & Downlink: In uplink, base station can change modulation & coding used by a subscriber station at any time by assigning a different burst of an uplink sub–frame. The decision is based on the reception quality of previous MAC packets at the subscriber station. For the downlink, base station has no direct information about the change in reception quality over time for a subscriber station using a certain modulation & coding scheme. Thus, it is the client’s device responsibility to request a change in the modulation or coding scheme if required. This can be done by the subscriber station.

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Downlink Uplink

Modulation BPSK (optional for OFDMA–PHY), QPSK, 16–QAM, & 64–QAM.

BPSK, QPSK, 16–QAM, & 64–QAM (optional).

Coding

Mandatory: Convolutional codes at rates 1/2, 2/3, 3/4, & 5/6. Optional: Convolutional turbo codes at rate 1/2, 2/3, 3/4, & 5/6 & repetition codes at rate 1/2, 1/3, & 1/6 LDPC, RS–Codes for OFDM–PHY.

Mandatory: Convolutional codes at rates 1/2, 2/3, 3/4, & 5/6. Optional: Convolutional turbo codes at rate 1/2, 2/3, 3/4, & 5/6 & repetition codes at rate 1/2, 1/3, & 1/6 LDPC.

Table 5.2: Modulation & Coding Supported in WiMAX (UL & DL). A bank of seven encoders & mappers, each one with a fixed AMC scheme, is set up so that transmitter can switch from one AMC scheme to another based on the feedback information.

AMC Modulation RS code CC code rate Overall code rate 1 BPSK (12, 12, 0) 1/2 1/22 QPSK (32, 24, 4) 2/3 1/23 QPSK (40, 36, 2) 5/6 3/4 4 16–QAM (64, 48, 4) 2/3 1/2 5 16–QAM  (80, 72, 4) 5/6 3/4 6 64–QAM  (108, 96, 6) 3/4 2/3 7 64–QAM  (120, 108, 6) 5/6 3/4

Table 5.3: AMC Modulation & Coding Schemes.

5.3 Performance of the AMC scheme: A good performance of AMC schemes requires accurate channel estimation at receiver & a reliable feedback path between that estimator & the transmitter on which the receiver reports channel state information (CSI) to the transmitter. To perform a good implementation we needs following: 1. Channel estimation of the expected channel conditions for the next

transmission interval. 2. The choice of the appropriate modulation & coding mode to be used in

the next transmission. 3. Feed back the selected mode to the transmitter. And there are some challenges that face AMC as following: 1. Knowledge can only be gained by prediction from past channel

estimations (delay between quality estimation & actual transmission). 2. Mobile channel is time – varying, & thus, the feedback of the channel

information becomes a limiting factor. Therefore, the adaptive system can only operate efficiently in an environment with relatively slowly–varying channel conditions. Where in

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this way, there will be no delay or transmission error that can occur in the feedback channel.

5.4 Channels: When communicating over a wireless radio channel the received signal cannot be simply modeled as a copy of the transmitted signal corrupted by additive Gaussian noise. Instead, signal fading, while caused by the time–varying characteristics of the propagation environment, appears. In this way, short term fluctuations caused by signal scattering of objects in the propagation environment lead to a phenomenon known as multipath propagation.

5.4.1 Propagation Characteristics of Mobile Radio Channels:

5.4.1.1 Attenuation: Attenuation is the drop in the signal power when transmitting from one point to another. It can be caused by the transmission path length, obstructions in the signal path, and multipath effects.

5.4.1.2 Multipath effect (Rayleigh & Ricean Fading): Wireless channels can be characterized with tap coefficients that are complex valued gaussian random variables. A channel model where there are only non line–of–sight (N–LOS) communications is characterized by a rayleigh distribution. On the contrary, if dominating paths are present, the channel coefficients are modeled by a ricean distribution.

Figure 5.5: Multipath fading.

Chapter. 5 

    

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As already mentioned, rayleigh distribution is normally used to model N–LOS communications. It is statistically characterized by a fading amplitude α(t), modeled with a rayleigh probability distribution, which has zero–mean gaussian components. Furthermore, the phase Ф(t) is uniformly distributed over the interval (0, 2π). The fading amplitude is described by the probability density function (pdf):

⎪⎩

⎪⎨⎧

≥⎟⎟⎠

⎞⎜⎜⎝

⎛ −⋅=

00

0exp)( 2

2

2

<α

ασα

σαa

fRayleigh

On the other hand, when the components of α(t) are Gaussian with non–zero mean values & the phase is also non–zero mean, the amplitude is characterized statistically by the rice probability distribution. In this case, the channel presents multipath propagation with some dominating paths i.e. representing a major part of the channel energy. The (pdf) of the ricean fading amplitude is given by:

( )⎪⎩

⎪⎨⎧

≥⎟⎠⎞

⎜⎝⎛ ⋅

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛ +−⋅=

00

0exp)( 22

22

2

<α

ασρα

σρα

σα oRice

Iaf

Where ρ2 represents the power of the received non–fading signal component, & Io is the modified Bessel function of first kind & order zero.

2

2

2 σα⋅

=k

Figure 5.6: Rayleigh & Rice Distribution.

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Figure 5.7: LOS vs. N–LOS.

5.4.1.3 Doppler Shift: When a signal source &/or receiver are moving relative to one another, received signal frequency will change. When they are moving away, frequency of received signal decreases & vice versa for approaching.

( )αcos⋅⋅±=Δcvff od

Δf: is the change in frequency of the source seen at the receiver. fo: the frequency of the source. v: the speed difference between the source & transmitter. c: speed of light α: angle between transmitter–receiver & direction of travel of mobile.

5.5 Modeling of Channels:

Received signal r(t) over a fading multipath channel can be represented by:

∫∞

∞−

−⋅= τττ dtsthtr )(),()(

s(t): transmitted signal. h(τ, t): channel impulse response at delay τ & time instant t. In discrete form:

∑∞

−∞=

⋅−⋅⋅=i

ss TinsnTihnr )(),()(

Ts: symbol duration. N: represents the sampling index. Compact notation for time varying channel coefficients in the form:

),()( nTihnh si ⋅= Form of received signal suggests impulse response of fading multipath channel which can be modeled as a tapped delay line filter (finite impulse response filter) with tap spacing Ts & time varying coefficients hi(n) characterized as random processes.

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Figure 5.8: Channel Modeling Representation.

5.6 Channel estimation: Received signal is additionally affected by the multiple reflections due to multipath transmission. Thus, receiver must determine from received signal which of all possible messages was the transmitted one. On the other hand, detection algorithms at the receiver require knowledge of the channel impulse response (CIR) which can be provided by performing channel estimation. Usually, channel estimation is based on known sequences of bits, which are unique at the transmitter & repeated in every transmission burst. This way, the channel estimator is able to estimate CIR for each burst separately by exploiting the known transmitted bits & the corresponding received samples.

5.6.1 Preamble & Pilot: There are two ways to transmit training symbols: preamble or pilot tones. Preambles entail sending a certain number of training symbols prior to the user data symbols. In the case of OFDM, one or two preamble OFDM symbols are typical. Pilot tones involve inserting a few known pilot symbols among the subcarriers. Channel estimation in MIMO–OFDM systems can be performed in a variety of ways, but it is typical to use the preamble for synchronization & initial channel estimation and the pilot tones for tracking the time–varying channel in order to maintain accurate channel estimates.

5.6.2 Pilot Signal Estimation: Channel can be estimated at pilot frequencies by two ways:

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1. (LS) Estimation. 2. (LMMSE) Estimation.

5.6.2.1 Least Square Estimation: Idea behind least square (LS) is to fit a model to measurements in such a way that weighted errors between measurements & model are minimized.

2ˆˆ

minHXY

HH ls ⋅−=

The LS estimate of the attenuations h, given the received data Y & the transmitted symbols X is:

)()(1

kXkYYXHls =⋅= −

5.6.2.2 Linear Minimum Mean Square Error Estimation: Linear minimum mean square error (LMMSE) estimate has been shown to be better than the LS estimate for channel estimation in OFDM systems based on block type pilot arrangement. Idea of LMMSE estimation is to min square of different between real value & estimated value.

YWkHHHEH

H Hls ⋅=−⋅= )(ˆ,ˆ

ˆmin 2

Then the channel estimated will be:

( ) ⎥⎦⎤

⎢⎣⎡ ⋅⋅⋅⋅+⋅=

−−

YXXXRRHH

HHHHLMMSE11

2ˆ σ

Superscript (.)H denotes hermitian transpose function & RHH=Σ(H HH).

5.6.3 Channel Interpolation: After the estimation of the channel transfer function of pilot tones, the channel transpose of data tones can be interpolated according to adjacent pilot tones. We consider the following interpolation schemes:

1. Linear Interpolation. 2. Spline Interpolation. 3. Cubic Interpolation. 4. Low Pass Interpolation.

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5.6.3.1 Linear Interpolation: In linear interpolation algorithm, two successive pilot subcarriers are used to determine the channel response for data subcarriers that are located in between the pilots. The linear channel interpolation can be implemented by using digital filtering such as Farrow–structure. For data subcarrier k, mGI < k < (m+1)GI, the estimated channel response using linear interpolation method is given by:

)1(ˆ)(ˆ1)(ˆ)(ˆ +⋅+⋅⎟⎠⎞

⎜⎝⎛ −=+⋅⋅= mH

GIlmH

GIllGImkHkH

5.6.3.2 Spline & Cubic Interpolation: Spline & Cubic interpolations are done by using (interp1) function of matlab. Spline & Cubic interpolations produce a smooth & continuous polynomial fitted to given data points. Spline interpolations works better than linear interpolation for comb pilot arrangement.

5.6.3.3 Low Pass Interpolation: The low pass interpolation is performed by inserting zeros into the original sequence & then applying a low pass FIR filter that allows the original data to pass through unchanged & interpolates between such that the mean–square error between the interpolated points & the ideal values is minimized.

5.7 Adaptive Antenna Systems (AAS): The 802.16(e) standard includes sophisticated antenna technologies to enhance broadband service distribution. WiMAX needs Adaptive Antenna System (AAS) to increase the throughput of a mobile network system or to increase the coverage range respectively decrease interference derives from the high frequency reuse & the high path loss in NLoS environments (improved link budget). Moreover, broadband systems use sophisticated modulation schemes, which require a high CINR (Carrier to Interference + Noise Ratio). To achieve this, smart antennas are used in three different applications: 1. RX / TX Diversity. 2. Beam Forming. 3. MIMO (Multiple Input Multiple Output).

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5.7.1 Spatial Diversity: Spatial diversity employs multiple antennas, usually with the same characteristics, that are physically separated from one another. Depending upon the expected incidence of incoming signal, sometimes a space on the order of a wavelength is sufficient (correlated). Other times much larger distance is needed (to be uncorrelated). The advantages of diversity are: 1. Increase signal to noise ratio (extend coverage & increase capacity). 2. Decreased Error Rate. 3. Increased Data Rate.

Diversity could be applied at receiver which increases the SNR, or it could be applied at the transmitter as it has particularly attractive for the downlink but processing will be required at both transmitter & receiver.

   

    Figure 5.9: Receiver Diversity (on the top) & Transmitter Diversity (on the button), where h1, h2 … & hNr represent the different channels response. We can do this by one of the following: 1. Selection combination (SC):

∑=

⎟⎟⎠

⎞⎜⎜⎝

⎛++++⋅=⋅=

rN

i rSC Ni1

1...31

2111 γγγ

2. Equal gain combination (EGC):

2

2

1

σ

εγ

⋅

⋅=

∑=

r

N

iix

EGC N

hr

3. Maximum gain combination (MGC):

∑∑

=

= =⋅

=r

r

N

ii

N

iix

MRC

h

12

2

1 γσ

εγ

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Figure 5.10: Average bit error probability for selection combining (on the left) & maximal ratio combining (on the right) using coherent BPSK. Owing to its array gain, MRC typically achieves a few dB better SNR than does SC. Diversity may be classified into two main categories: 1. Open–Loop Transmit Diversity:

Code is known to the receiver is applied at the transmitter. Alamouti code or orthogonal space/ time block code (OSTBC) is used as they are easy implementation & defined for in WiMAX standard.

Figure 5.11: Open–Loop 4–2 stacked STBC transmitter. 2. Closed–Loop Transmit Diversity:

Feedback is added to the system, the transmitter may be able to have knowledge of the channel between it & the receiver. It is used at high mobility as the channel changes quickly. Transmit selection diversity (TSD) is the simplest form of closed–loop transmit diversity, only a subset of the available antennas are used at a given time. The selected subset typically corresponds to the best channels between the transmitter & the receiver.

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Figure 5.12: Closed–Loop Transmit Diversity. The closed–loop diversity shows better performance than open–loop diversity but it needs larger spectrum allocation (additional band for feedback channel).

5.7.2 Beam forming: In contrast to the transmit diversity techniques, available antenna elements can instead be used to adjust the strength of the transmitted & received signals. This focusing of energy is achieved by choosing appropriate weights for each antenna element with a certain criterion. The advantages of beam forming: 1. Extended coverage. 2. Increase capacity (better link quality & higher modulation scheme). 3. Reduce interference by null steering of side lobes towards strong

interferer’s → less interference applied to other users. There are two principal classes of beam forming: 1. Direction of arrival (DOA) which is viable only in LOS environments

or in environments with limited local scattering around the transmitter. 2. Based beam forming & Eigen beam forming.

Figure 5.13: Beam pattern using this weight vector (Null–steering beam pattern) with unity gain for desired user & nulls at directions of interferers.

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5.7.3 Multiple–Antenna Techniques: Multiple antenna systems –sometimes called multi–layer transmission or MIMO– are the systems which have several transmit & receive antennas, or several transmitting antennas, for a single receiving antenna –MISO, for single transmitting antenna –SIMO–, & for single transmitting & receiving antenna –SISO–. When increasing the number of the transmitting & receiving antennas, it improves the performance but practically, there are some limit that after it increasing the number of antennas doesn’t improve the performance. The advantages of Multiple–Antenna Technique: 1. Theoretically n–times capacity with n TX antennas. 2. RX does not necessarily need more antennas (but it is better for the

SNR).

Figure 5.14: MIMO transmission.

Figure 5.15: MIMO & OFDM. MIMO could be performed as an open–loop MIMO & closed–loop MIMO, each of them have several techniques for detection. For optimum decoding there are two techniques which are: 1. Maximum–Likelihood Detection. 2. Linear Detectors.

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5.7.3.1 Channel Estimation for MIMO–OFDM: When OFDM is used with a MIMO transceiver, channel information is essential at the receiver in order to coherently detect the received signal & for diversity combining or spatial interference suppression. Accurate channel information is also important at the transmitter for closed–loop MIMO. Channel estimation can be performed in two ways: 1. Training–based channel estimation where known symbols are

transmitted specifically to aid the receiver’s channel estimation–algorithms it has better convergence speed & estimation accuracy.

2. Blind channel estimation where receiver must determine the channel without the aid of known symbols; higher–bandwidth efficiency can be obtained in expanse of system complexity.

Training–based channel–estimation techniques are supported by WiMAX standard. The estimated channel coefficients are calculated for each receive antenna by using two long training sequences, PEVEN & PODD when applying MIMO transmissions. There are two ways to transmit training symbols: preamble or pilot tones. Preamble are used for synchronization & initial channel estimation while the pilot tones are used for tracking the time–varying channel in order to maintain accurate channel estimates.

Figure 5.16: Training symbol structure of preamble–based & pilot–based channel estimation methods.

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5.8 Bibliography: [1] Fundamentals of WiMAX for Jeffrey G. Andrews, Ph.D., Arunabha Ghosh, Ph.D., Rias Muhamed. [2] Communication Systems for the Mobile Information Society for Martin Sauter. [3] Implementation of a WiMAX simulator in Simulink for Amalia Roca. [4] Essentials of Error Control Coding for Jorge Castiñeira Moreira & Patrick Guy Farrell. [5] Multi Carrier and Spread Spectrum System for K.Fazel & S. Kaiser. [6] 802.16 IEEE Standards for Local and metropolitan area networks. [7] Channel estimation in OFDM systems for kamran arshad. [8] Space–Time Processing for MIMO Communications for A. B. Gresham & N. D. Sidiropoulos. [9] Adaptive space–frequency coding for MIMO–OFDM systems for Antonius D. Valkanas. [10] Introduction into WiMAX, CHRISTIAN BAUER (Alcatel). [11] WiMAX’s technology for LOS and NLOS environments, WIMAX Forum. [12] Wireless Communications for Andrea Goldsmith. [13] Multicarrier Techniques for 4G Mobile Communications for Shinsuke Hara, & Ramjee Prasad.

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Network architecture deals with interoperable network architecture framework that deals with the end–to–end service aspects such as IP, session management, security, QoS & so on. WiMAX Forum’s Network Working Group (NWG) has developed & standardized these end–to–end networking aspects that are beyond the scope of the IEEE 802.16e–2005 standard which had to support loosely coupled interworking with all existing wireless networks (3GPP, 3GPP2) & wire networks.

Figure 6.1: Overview of WiMAX, UMTS & GSM combined network structure.

4.1 Network reference model (NRM): NRM divide the system into three logical parts: 1. Mobile stations (MS) 2. Access service network (ASN). 3. Connectivity service network (CSN).

Chapter

6 WiMAX Network

Architecture

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Figure 6.2: WiMAX Network Reference Model.

4.2 The Access service network (ASN): The ASN functions are:

• IEEE 802.16e–based layer 2 connectivity with the MS. • Network discovery & selection of the subscriber’s preferred

CSN/NSP. • AAA proxy: transfer of device, user, & service credentials to

selected NSP AAA. • Relay functionality for establishing IP connectivity between MS &

CSN. • Radio resource management (RRM) & allocation based on the QoS

policy. • Mobility–related functions, such as handover, location management,

& paging. Within the ASN, the security architecture consists of four functional entities: 1. Authenticator. 2. Authentication relay. 3. Key distributor. 4. Key receiver.

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Figure 6.3: ASN security architecture & deployment models: integrated deployment model (on the left) & stand–alone deployment model (on the right). The NRM defined three profiles for the ASN Shown below:

Functional Category Function ASN Entity Name

Profile A Profile B Profile C

Security

Authenticator ASN–GW ASN ASN–GW Authentication relay BS ASN BS Key distributor ASN–GW ASN ASN–GW Key receiver BS ASN BS

Mobility

Data path function ASN–GW & BS ASN ASN–GW & BS Handover control ASN–GW ASN BS Context server & client ASN–GW & BS ASN ASN–GW & BS MIP foreign agent ASN–GW ASN ASN–GW

Radio resource management

Radio resource controller ASN–GW ASN BS Radio resource agent BS ASN BS 

Paging Paging agent BS ASN BS Paging controller ASN–GW ASN ASN–GW

QoS Service flow authorization ASN–GW ASN ASN–GW Service flow manager BS ASN BS

Table 6.1: Functional Decomposition of ASN.

4.3 Connectivity service network (CSN): CSN functions are: • IP address allocation to the MS for user sessions. • AAA proxy or server for user, device & services authentication,

authorization, & accounting (AAA). • Policy & QoS management based on the SLA/ contract with the user. • Subscriber billing & interoperator settlement. • Inter–CSN tunneling to support roaming between NSPs. • Inter–ASN mobility management & mobile IP home agent

functionality. • Connectivity infrastructure & policy control for such services as

Internet access, access to other IP networks, ASPs, location–based

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services, peer–to–peer, VPN, IP multimedia services, law enforcement, & messaging.

4.4 Reference points (RP): The WiMAX NWG defines a reference point (RP) as a conceptual link that connects two groups of functions that reside in different functional entities of the ASN, CSN, or MS. A brief illustration of reference points are illustrated below:

Reference Points End Points Description

R1 MS & ASN Implements air–interface (IEEE 802.16e) specifications. R1 may additionally include protocols related to the management plane.

R2 MS & CSN

For authentication, authorization, IP host configuration management, & mobility management. Only a logical interface & not a direct protocol interface between MS & CSN.

R3 MS & CSN

Support AAA, policy enforcement, & mobility – management capabilities. Also encompasses the bearer plane methods (e.g. tunneling) to transfer IP data between ASN & CSN.

R4 MS & ASN

A set of control & bearer plane protocols originating/ terminating in various entities within the ASN that coordinate MS mobility between ASN’s. In release 1. R4 is the only interoperable interface between heterogeneous or dissimilar ASN’s.

R5 MS & CSN A set of control & bearer plane protocols for internetworking between the home & visited network.

R6 BS & ASN–GW

A set of control & bearer plane protocols for communication between the BS & the ASN–GW. The Bearer plane consists of intra–ASN data path or inter–ASN tunnels between the BS & the ASN–GW. The control plane includes protocols for mobility tunnel management (establish, modify & release) based on MS mobility events. Also R6 may serve as a conduit for exchange of MAC states information between neighboring BS’s.

R7 ASN–GW–DP & ASN–GW–EP

An optional set of control plane protocols for coordination between the two groups of functions identified in R6.

R8 BS & BS

A set of control plane message flows & possibly bearer plane data flows between BS’s to ensure fast & seamless handover. The bearer plane consists of protocols that allow the data transfer between BS’s involved in handover of a certain MS. The control plane consists of the inter–BS communication protocol defined in IEEE 802.16e additional protocols that allow controlling the data transfer between the BS involved in handover of a certain MS.

Table 6.2: WiMAX Reference Points.

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Figure 6.4: Functions Performed Across Reference Points.

4.5 Bibliography: [1] Fundamentals of WiMAX for Jeffrey G. Andrews, Ph.D., Arunabha Ghosh, Ph.D., Rias Muhamed. [2] Recommendations & requirements for networks based on WiMAX Forum certified TM products. Release 1.5, April 27, 2006. [3] WiMAX end–to–end network systems architecture. Stage 2: Architecture tenets, reference model & reference points. Release 1.0, V&V Draft, August 8, 2006. [4] WiMAX end–to–end network systems architecture. Stage 3: Detailed protocols & procedures. Release 1.0, V&V Draft, August 8, 2006. [5] Introduction into WiMAX, CHRISTIAN BAUER (Alcatel).

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  Part. 2 

Simulation & Implementation

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Matlab is a very powerful tool that supports researchers & engineers in their fields. Matlab can be used for simulations, simple programming. In our project, the main tool box was used is the communication tool box which consists of simulink blocks & MATLAB functions to simulate the physical layer of the Mobile WiMAX. The used copy to carry out this simulations is Matlab R2007b (7.5). The simulation was based on the simple system structure as following:

 Figure 7.1: Basic system structure.

1. Simulink:

As mentioned before [Ch. 3], the system parameters are used to configure the system blocks.

7.1.1 Simple System:

Figure 7.2: Simple system structure.

Chapter

7 System Simulation

Using Matlab

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1. Binary generator: used to generate a sequence of random bits with number of samples per frame equal 864 & output type (Boolean) to be able to operate the soft viterbi decoding.

2. Coding & Modulation: this sub–block consist of FEC, interleaving & modulation techniques which contain different coding rates & modulation schemes [adaptive modulation & coding]. The sub–block structure:

Figure 7.3: Adaptive Modulation & Coding. And one sub–system (for example, QPSK 3/4) structure:

Figure 7.4: Sub–system.

Select bits Divide the bit stream to smaller frames of bits Zero pad tail byte Insert 8 zero bits for each frame Convolutional encoder Insert a redundancy bits for FEC Interleaver Interleave the data streams with known order Modulator Modulates the data with a known modulation technique

Table 7.1: Sub–system component function.

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For enabling sub–systems, rateID is used which will be illustrated later. 3. IFFT input & backing: sub–block is used for sub–channelization & Pilot

and zero insertion. And the sub–block structure:

Figure 7.5: S/ P, inserting pilots & DC null to the data. 4. IFFT: this sub–block performs IFFT process, adding guard band,

preamble & cyclic prefix. The sub–block structure:

Figure 7.6: OFDM symbol creation process. Insert Preamble Insert the preamble sequence used for channel estimation process Add Guard Band Add 28 zeros upper guard band and 27 zeros for the lower guard band IFFT Execute the IFFT algorithm for the OFDM technique. Add cyclic prefix Repeat the last sequence of bits in the sequence beginning. P/S Parallel to serial.

Table 7.2: Sub–block component function. 5. AWGN & rateID: AWGN sub–block simulate the real communications

channel (noisy environment), & the rateID sub–block calculate the related rateID for the SNR which have following structure:

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Figure 7.7: rateID sub–block.

Constant Define the SNR in dB RateID calculator Calculate the rateID for the applied SNR 1/invdB Transfer the SNR from dB to AWGN variance rateID (Goto) Send the output rateID to the AMC blocks

Table 7.3: Sub–block component function. RateID is a m–File as following:

function y = fcn(u) % This block supports the Embedded MATLAB subset. if u <= 4; y = 1; %BPSK 1/2 elseif u <= 10; y = 2; %QPSK 1/2 elseif u <= 12; y = 3; %QPSK 3/4 elseif u <= 19; y = 4; %16QAM 1/2 elseif u <= 22; y = 5; %16QAM 3/4 elseif u <= 28; y = 6; %64QAM 2/3 else u > 28; y = 7; %64QAM 3/4 end

6. FFT: this sub–block performs FFT process, & removing cyclic prefix.

The sub–block structure:

Figure 7.8: OFDM symbol creation process.

S/P Serial to parallel Remove cyclic prefix Remove the cyclic prefix inserted in the IFFT block FFT Apply the FFT algorithm

Table 7.4: Sub–block component function. 7. Extract data carriers: this sub–block perform channel estimation process

using the preamble bits, & remove pilot & zero sub–carriers. The sub–block structure:

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Figure 7.9: The Sub–block components.

Separate data & guard bands Remove the lower and upper guard bands from the data Select training/data Separate the data and preamble Channel estimation Estimate the communications channel using LS algorithm Separate data & pilots Remove the pilots and zero sub-carriers from the data P/S Parallel to serial

Table 7.5: Sub–block component function. The channel estimation block is an M–File estimate the communications channel using the LS estimation algorithm as following:

function estimated = fcn(pilots, data) % This block supports the Embedded MATLAB subset. x=complex(ones(201,1)); h_est=pilots./x; estimated = data./h_est;

8. Demodulation & Decoding: this sub–block reverse the coding &

modulation operation & the sub–block structure is:

Figure 7.10: Adaptive Demodulation & Decoding.

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As mentioned in FEC, one sub–system (for example, QPSK 3/4) structure:

Figure 7.11: Sub–System.

Demodulator Demodulates the modulated data streams with the convention modulation techniques Deinterleaver Rearrange the interleaved data with the WiMAX parameters Quantizer Used to quantize the bit streams to apply the soft decoding Viterbi decoding Decodes the data and detect and correct error

Table 7.6: Sub–block component function. 9. Error rate calculation: because of the adaptive modulation & coding, we

need special system to calculate the BER. The system structure is:

Figure 7.12: BER Calculator System.

Figure 7.13: Input Data Calculations which is used for applying correct frame length for each modulation scheme.

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And the error rate calculations calculate the bit error rate between input–output data streams & display number of errors & BER. 10. Constellation: used to obtain the constellation diagram of the

modulation & showing the AMC.

7.1.2 MIMO System:

Figure 7.14: MIMO System structure. System is similar to the old one, but the communication channel take into consideration the Rayleigh fading effect in this system. To modify simple system to support MIMO, We use (2-1) Alamouti code. Transmitter M–File:

function [ant1, ant2] = stbcenc(u) % STBCENC Space-Time Block Encoder % Outputs the Space-Time block encoded signal per antenna. ant1 = complex(zeros(size(u))); ant2 = ant1; % Alamouti Space-Time Block Encoder, G2, full rate % G2 = [s0 s1; -s1* s0*] for i = 1:size(u,2)/2 s0 = u(:, 2*i-1); s1 = u(:, 2*i); ant1(:, [2*i-1 2*i]) = [s0 s1 ]; ant2(:, [2*i-1 2*i]) = [-conj(s1) conj(s0)]; end

In receiver we use the reverse operation where the preambles are divided into Podd & Peven [Ch. 3]. Receiver M–File:

function z = stbcdec(preamble, data) % STBCDEC Space-Time Block Combiner chEst1_bef=complex(zeros(200,1)); chEst2_bef=complex(zeros(200,1)); chEst1_before=[preamble(1:2:99) preamble(103:2:201)]; chEst2_before=preamble(2:2:201);

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for i=1:100 chEst1_bef(2*i-1)=chEst1_before(i); chEst1_bef(2*i)=chEst1_before(i); chEst2_bef(2*i-1)=chEst2_before(i); chEst2_bef(2*i)=chEst2_before(i); end chEst_last1=[chEst1_bef chEst1_bef]; chEst_last2=[chEst2_bef chEst2_bef]; chEst1=chEst_last1./complex(ones(200,2)); chEst2=chEst_last1./complex(ones(200,2)); dat=[data(1:100,:);data(102:201,:)]; N = 2; M = 1; z = complex(zeros(size(dat))); z0 = complex(zeros(size(dat,1), M)); z1 = z0; % Space Time Combiner for i = 1:size(dat,2)/2 z0(:, M) = dat(:, 2*i-1).* conj(chEst1(:, 2*i-1))+conj(dat(:, 2*i)).* chEst2(:, 2*i); z1(:, M) = dat(:, 2*i-1).* conj(chEst2(:, 2*i-1))-conj(dat(:, 2*i)).* chEst1(:, 2*i); z(:, [2*i-1 2*i]) = [z0 z1]; end

7.1.3 Special Blocks Configurations:

1. Convolutional encoder: • Trellis structure: poly2trellis(7,[171 173]) • Operation mode: Truncated (reset every frame). • Puncture vector:

Code rate Puncture code 1 / 2 [1] 2 / 3 [1 1 1 0] 3 / 4 [1 1 0 1 1 0]

Table 7.7: Puncturing array.

Note that the frame size must be divisible by the code rate. 2. General block interleaver & deinterleaver:

• Elements: int_PBSK_1_2’ (M–File name). The M–File:

Ncbps=1152; %the number of input bits to the Interleaver. Ncpc=6; %the power of 2 for each modulation ex: %for (BPSK=1),(QPSK=2),(16QAM=4),(64QAM=6). k = 0:Ncbps-1; mk = (Ncbps/12)*mod(k,12)+floor(k/12); s = ceil(Ncpc/2); jk = s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x, intTable] = sort(jk); % per symbol

3. Modulators (BPSK, QPSK, 16–QAM, 64–QAM), from baseband

modulators. For QAM, use rectangular QAM. • Input type: bits.

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• Constellation ordering: Gray. • Output data type: double. • For BPSK, Phase offset (rad): 0. • For QPSK, Phase offset (rad): pi/4. • For 16–QAM, M–ary number: 16. • For 64–QAM, M–ary number: 64. • Normalization method: Min. distance between symbols • Min. Distance: 2.

Note that Hint you must choose the input frame size to be divisable by Power of two of modulation number.

4. Subchannel Selector: used to add pilots & DC null, preamble & guard bands added by the same way.

• Select: Rows. • Indices to output:

{[1:12],[13:36],[37:60],[61:84],[85:96],[97:108],[109:132],[133:156],[157:180],[181:192]}.

• Invalid Index: Generate Error. Hint: we can use the switch or merge block to do the same operation.

5. IFFT & FFT: • IFFT [of size 256] needs to add a gain after it with the value of

sqrt(256)×sqrt(256/200) to work correctly. • The gain unit is added before FFT block [of size 256] with value

of 1/(sqrt(256)*sqrt(256/200)) to reverse the gain effect in IFFT sub–system.

6. Demodulation: as modulation, so we will talk about the modifications to the blocks to apply the soft decoding on the Viterbi decoder.

• Decision type: Log–likelihood ratio. 7. Decoding: applied by viterbi decoder. For soft decisions decoding, we

need quantizer as following: Quantizer: to quantize the data bits into integers various from 0 to 2b–1 where (b: the number of soft decisions bits).

Viterbi decoder: • Trellis structure: same convolutional encoder. • Puncture vector: same convolutional encoder. • Decision type: Soft decision. • Number of soft decision bits: 3. • Traceback depth: 50. • Operation mode: same convolutional encoder. • Data type tab: Boolean –for correct operation by

Viterbi in the soft decision mode–.

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Number of soft decision is 3 bits, so input varying from (0 to 7) with different probability of certainty, see next:

Input value Interpretation 0 Most confident zero 1 Second most confident zero 2 Third most confident zero 3 Least confident zero 4 Least confident one 5 Third most confident one 6 Second most confident one 7 Most confident one

Table 7.8: Soft Decoding. Note that from decision type, it can be changed to unquantized or hard decision.

7.1.4 IIR Filter:

Figure 7.15: IIR Filter structure. This model transfer the analog voice to digital samples & then filter samples digitally by IIR filter then transfer it back to analog speaker to hear the filtered voice. 1. From wave device & uniform encoder: these blocks receives the analog

voice & convert it to digital samples. Uniform Encoder: • Peak: 1. • Bits: 8.

2. Uniform decoder & to wave device: reverse the operation of from wave device & uniform encoder convert, so the digital samples converted into analog sound & speakers output the sound. Blocks use same parameters as from wave device & uniform encoder convert.

3. Digital Filter:

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Figure 7.16: Filter Design.

7.1.4.1 Testing the filter: To see the performance of the IIR filter we use the model shown below:

Figure 7.17: The testing model (multi–frequency sine wave bank).

Steps of performance testing:

1. We enter 5 different sine waves with known frequencies to the filter (only two are active, 300 & 1000 Hz).

2. Get the frequency domain spectrum before & after the filter.

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Figure 7.18: Spectrum Output (The cutoff freq. is at 500 Hz), [On top, before filtering & after filtering on the button].

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7.1.5 Audio Reverberation:

Figure 7.19: Audio Reverberation Applied to an Audio Input Signal. This model encodes the audio signal & then adds this signal with delayed version of itself with gain less than one then decode these signal so that the output audio signal is reverberated.

7.2 Remarks: Important Notes: 1. Using buffers & unbuffers blocks causes error rate so it’s better to use

pad & submatrix blocks. 2. We face problems in channel estimation with puncturing codes. Goals to be achieved: 1. Apply more sophisticated channel estimations algorithms like

“LMMSE”. 2. Solving the problems appears in the channel estimation with the

puncture code in the simulation process. 3. Applying the MIMO concept to improve the bit error rate of the system.

Applying OFDMA, SOFDMA.

7.3 M–File: System may also be implemented using Matlab functions, so the final program looks like a written text not a block diagram as Simulink. The transmitter & receiver M – Files are included in the CD.

7.4 Additional Reading: [1] Simulink Communications Toolbox [Modeling, Simulation, Implementation] User’s Guide Version 2 for Weizheng Wang. [2] Communications Toolbox 4 User’s Guide, Matlab.

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8.1 Introduction:

TMS320C6416 is a fixed point digital signal processor that have a great properties & it’s a power full kit. This kit is mapped to the famous family C6400. The kit model is provided below:

Figure 8.1: functional block and CPU (DSP core) diagram.

Chapter

8 System

Implementation

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The kit contains TCP (Turbo Co–processor), & VCP (Viterbi Co–processor) which carries out the the turbo & viterbi decoder algorithms. Also, the kit contains RTDX (Real Time Data Exchange) which helps to exchange the data between the computer (Matlab) & the kit via USB port. Kit contains A/ D & D/ A to exchange data between analog speaker & microphone. Simply the memory architecture are:

Figure 8.2: L2 Architecture Memory. The different between the fixed point & floating point are that floating point have greater accuracy in the expanse of the processing speed, the fixed point DSP’s own high processing speed (TMS320C6416 reach 1 GHz) on the expanse of the received value accuracy.

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Table 8.1: Word width with Ti DSP’s. The programs have to be installed within a certain order as following: 1. Code composer studio 3.1. 2. Flash burn. 3. Drivers for C6416. 4. Matlab (R2006b “7.3”). Note that the Matlab R2006b is only the compatible version with the code composer studio 3.1. The implementation as the simulation was based on the simple system structure as following:

 Figure 8.3: Basic system structure. Note that the project files are included in the CD.

8.2 Starting Code Composer Studio:

At first we wanted to use Simulink to build the whole system , it all went well until we got to the Viterbi decoder, it just didn’t work .Also the FFT from C6000 library in Simulink didn’t work too, so we had to write the code ourselves. To start writing code using CCS: 1. Create a new project. 2. Save the code files in the folder of your project, and add them to the project (right click on project→Add files to project...). 3. Click “Build All” to build the project. 4. If no errors occurred, load the output file to the DSP memory (File→Load file…).

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5. Click “Run” to start the program.

8.3 System Model Implementation: This part concerning about the construction & implementation steps on the DSP starter kit. In our implementation we concentrated on the encoding/ decoding, interleaver/ de–interleaver, symbol mapping/ de–mapping, & IFFT/ FFT stages. We will discuss each part in implementation separately. 1. Encoder/ Decoder: We used a simple code to encode data with generating polynomials of our choice. To decode the data we use the VCP (Viterbi co–processor) as this algorithm is very complex and needs a lot of processing so the VCP saves processing time & resources. To run the VCP in our implementation, we used the VCP testing code provided by Texas Instruments (TI) & modified it to our needs. 2. Interleaver: We used the WiMAX block interleaver equations. In this code, the element with index “intlv2” will be saved at its new index (i). The de–interleaver makes the reverse operation to restore the original data. 3. Mapper: The mapper is a simple BPSK mapper, with (0→1) & (1→–1). We didn’t need a Demapper as the Branch Metrics are calculated from the mapped data. • Transmitter: System operates as follows: Data (32 bits) is first encoded with code rate = 1/2 (64 bits output), & then interleaved with a frame size of (96 bits), then its input to a 128–point IFFT stage. Cyclic prefix is then added to the output of the IFFT. • Receiver Cyclic prefix is removed, than signal is input to the FFT stage & then is de–interleaved. Now we are ready to calculate the Branch metrics. There will be 2 branch metrics for every 2 samples(code rate=½).Then each 4 branch metrics are concatenated to form a 32–bit word then it is fed to the VCP, with the right parameters, the output of the VCP will be the reversed version of the input data. The flow chart of operating the Viterbi Co–processor are shown below:

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Figure 8.4: VCP programming process.

Convolutional Encoder

Rate ½

Block Interleaving

Mapping BPSK

IFFT @ 128 Points

+ Cyclic Prefix

AWGN

Deinterleaver

Remove Cyclic Prefix

FFT @ 128 Points

Branch Metrics calculation

Viterbi Decoding (VCP)

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8.4 VCP Progress: This is what we’ve done with the code provided by TI:

• Removed all users’ data and VCP parameters and only kept one user. • Branch metrics was input to the VCP from an .asm file, we changed it so

we can input the Branch metrics from an array from the previous stage in system.

• EDMA channels initialization and starting was used as is from the TI code.

8.5 Troubleshooting errors:

• “Undefined symbol- symbol referencing…” errors:- Check the files included, make sure all .h files and all used libraries needed are included.

Most needed libraries:

rts6400.lib “../CCStudio_v3.1/C6000/cgtools/lib/”

rtxd.lib, rtdx64xx.lib “../CCStudio_v3.1/C6000/rtdx/lib”

• “#error NO CHIP DEFINED” errors:-

Add “-dCHIP_6416” to (Project→Build options→Compiler).

• If there is too many errors “>100”, check the first error, it’s most likely to

be a syntax error.

To Do: • Use Turbo coding and TCP (Turbo co-processor). • Add more modulation schemes, Adaptive modulation & code rates. • Add scalability to the FFT size, pilot and zero insertion. • Interface two kits as transceivers. • Optimize code to meet the WiMAX frame processing time constraints

(TDD).

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8.6 Bibliography (Very Important Documents): [1] TMS320C6414, TMS320C6415, TMS320C6416 fixed point digital signal processors. [2] Using TMS320C6416 Coprocessors: Viterbi Coprocessor (VCP), TI. [3] TMS320C6416 Coprocessors and Bit Error Rates, TI. [4] Comparing Fixed & Floating Point DSPs. Does your design need a fixed- or floating-point DSP? The application data set can tell you, TI. [5] TMS320C6416 Coprocessors and Bit Error Rates, TI. [6] Digital Signal Processing Selection Guide, TI. [7] TMS320C64x DSP Viterbi-Decoder Coprocessor (VCP) Reference Guide, TI. [8] TMS320C6416T DSK Technical Reference, TI. [9] TMS320C6000 Instruction Set Simulator Technical Reference Manual, TI. [10] Help documents in Code composer studio.

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A  

▬▬▬▬▬▬▬▬ System Parameters

Table 1: Different WiMAX Standard

B  

Table 2: Fixed & Mobile WiMAX Certified Profiles.

C  

Table 3: PHY – Layer Data Rate at Various Channel Bandwidths.

▬▬▬▬▬▬▬▬ Acronyms

3GPP 3G Partnership Project 3GPP2 3G Partnership Project 2 AAA Authentication, Authorization, & Accounting AAS Adaptive Antenna System Also Advanced Antenna System AMC Adaptive Modulation & Coding ARQ Automated Repeat Request ASN Access Service Network ASP Application Service Provider AWGN Additive White Gaussian Noise AWS Advanced Wireless Services BER Bit Error Rate BLAST Bell Labs Layered Spaced Time BLER Block Error Rate BPSK Binary Phase Shift Keying BS Base Station BTC Block Turbo Code BW Band Width CC Convolutional Codes CDMA Code Division Multiple Access CID Advanced Wireless Services CINR Carrier To Interference + Noise Ratio CIR Channel Impulse Response CP Cyclic Prefix CPE Customer Premises Equipment CRC Cyclic Redundancy Check CSI Channel State Information CSN Connectivity Service Network CTC Convolutional Turbo Code DL Down Link DoA Direction Of Arrival DSL Digital Subscriber Line DSP Digital Signal Processor EAP Extensible Authentication Protocol EGC Equal Gain Combining ETSI Advanced Wireless Services EVDO Evolution Data Optimized Or Evolution Data Only FBSS Fast Base Station Switching FCH Frame Control Header FDD Frequency Division Duplexing FDMA Frequency Division Multiple Access FEC Frame Error Correction FEC Forward Error Correction FEQ Frequency Equalizer

FFT Fast Fourier Transform FIR Finite Impulse Response FWA Fixed Wireless Access HDTV High–Definition Television H–FDD Half-Frequency Division Duplex HIPERMAN High-Performance Metropolitan Area Network HPA High Power Amplifier HSDPA High-Speed Downlink Packet Access HSPA High-Speed Packet Access IBO Input Backoff ICI Inter Carrier Interference IDFT Inverse Discrete Fourier Transform IEEE Institute Of Electrical And Electronics Engineers IF Intermediate Frequency IFFT Inverse Fast Fourier Transform IM Instant Messaging IP Internet Protocol ISI Inter Symbol Interference ISP Internet Service Provider LDPC Low Density Parity Check LMMSE Linear Minimum Mean Square Error LOS Line Of Sight LS Least Square MAC Media Access Control Layer MAN Metropolitan Area Network MBMS Multimedia Broadcast/ Multicast Service MBSFN Multicast/ Broadcast Single–Frequency Networking MBWA Mobile broadband wireless access MC Multicarrier MDHO Macro Diversity Handover MIMO Multiple Input Multiple Output MISO Multi Input Single Output MMDS Multichannel Multipoint Distribution Services MPDU MAC Protocol Data Unit MRC Maximal Ratio Combining MRT Maximum Ratio Transmission MS Mobile Station MSE Mean Square Error MSR Maximum Sum Rate NAP Network Access Provider NLOS Non–Line-Of-Sight NRM Network Reference Model NSP Network Services Provider NWG Network Working Group OBO Output Backoff OFDM Orthogonal Frequency Division Multiplexing OFDMA Orthogonal Frequency Division Multiple Access OSTBC Orthogonal Space/Time Block Code PAPR Peak-To-Average-Power Ratio PAR Peak-To-Average Ratio

PDF Probability Density Function PDU Protocol Data Units PHY Physical Layer PKM Key Management Protocol PKMv2 Privacy And Key Management Version 2 PRBS Pseudo–Random Binary Sequence PUSC Partial Usage Of Subcarriers QAM Quadrature Amplitude Modulation QPSK Quadrature Phase Shift Keying RF Radio Frequency RMS Root–Mean–Square RP Reference Points RRC Root–Raised Cosine Filters RRM Radio Resource Management RS–CC Concatenated Reed–Solomon–Convolutional Code RSSI Received Signal Strength Indicator SC Selection Combining SDUs Service Data Units SFID Service Flow Identifier SIMO Single Input Multi Output SINR Signal-To-Interference-Plus-Noise Ratio SISO Single Input Single Output SNR Signal-To-Noise Ratio S–OFDMA Scalable OFDMA SS Subscriber Station STBC Space/Time Block Code STC Space/Time Code SVD Singular-Value Decomposition TDD Time Division Duplexing TDM Time Division Multiplexing TDMA Time Division Multiple Access TSD Transmit Selection Diversity TUSC Tile Usage Of Subcarriers UHF Ultrahigh Frequency UL Uplink UMTS Universal Mobile Telephone System U–NII Unlicensed National Information Infrastructure VLIW Very–Long Instruction–Word VPN Virtual Private Network WAC Washington Administrative Code WCS Wireless Communications Services WiBro Wireless Broadband Wi–Fi Wireless Fidelity WiMAX Worldwide Interoperability For Microwave Access WiSOA WiMAX Spectrum Owner Alliance WLL Wireless Local Loop WMAN Wireless Metropolitan Area Network WRAN Wireless Regional Area Network