Study of Wimax for Future Mobile Communication-part two

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Chapter One

Overview of WiMAX Introduction to WiMAX for Broadband Wireless Access

Now a day, there are basically three different options to access the internet:

Broadband Access -- access by using a Digital Subscriber Line (DSL) or Cable

Modem or T1 / T3 line.

Wi-Fi Access – either by using Wi-Fi router or by Wi-Fi hot spots in restaurants,

hotels, coffee shops and libraries.

Dial-up Access – access to the broadband internet can be done by dial-up access

when broadband access is not available or too expensive.

But the main problems with broadband access are that, it is pretty expensive and does not

reach all areas particularly in rural and distant areas. The main problem with Wi-Fi access is

that, Wi-Fi hot spots are very small, so that the coverage area is insignificant.

But, if there were a new technology that solved all of these problems and provides:

High speed broadband service at reduced cost.

Wireless access instead of wired access. So that, it would be less expensive than

cable or DSL and easy to extend to suburban and especially rural areas.

Broad coverage like the cell phone network instead of small Wi-Fi hotspots.

Such a promising technology is in reality right now and this is the Worldwide

Interoperability for Microwave Access abbreviated as WiMAX.

1.1 What is WiMAX?

WiMAX stands for “Worldwide Interoperability for Microwave Access” and is a wireless

communications technology intended at providing wireless data over long distances in a

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variety of ways such as from point-to-point links to full mobile cellular type

access. It is based on the standard IEEE 802.16, which is also entitled as

Wireless MAN.

The name WiMAX was created by the WiMAX Forum and is defined as; "WiMAX is a

standards-based technology enabling the delivery of last mile wireless broadband access as

an alternative to wired broadband like cable and DSL. WiMAX provides fixed, nomadic and

portable and soon, mobile wireless broadband connectivity without the need of directs line-

of-sight with the base station.”

1.2 IEEE 802.16 Specifications

Range - 30-mile (50-km) from base station.

Speed - 70 megabits per second.

Line-of-sight not needed between user and base station.

Frequency bands - 2 to 11 GHz and 10 to 66 GHz (Both licensed and unlicensed

bands)

Defines both the MAC and PHY layers and allows multiple PHY-layer

specifications.

1.3 What Can WiMAX Do?

WiMAX could potentially wipe out the suburban and rural blackout areas that

currently have no Broadband Internet Access.

It sends data from one computer to another via radio signals. A computer outfitted

with WiMAX would receive data from the WiMAX transmitting station and probably

using encrypted data keys to prevent unauthorized access.

WiMAX has the potential to access to the broadband internet, In the same way, cell

phones have the access to the wireless cellular network

WiMAX could replace cable and DSL services, providing universal internet access

just about anywhere you go.

The fastest Wi-Fi connection can transmit up to 54Mbps under best possible

conditions. WiMAX should be able to handle up to 70Mbps that can be split up

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between several dozen businesses or a few hundred home users, which can provide at

least the equivalent of cable-modem transfer rates to each user.

WiMAX will cover a radius of 30 miles (50 km) with wireless access. The increased

range is due to the frequencies used and the power of the transmitter.

1.4 Features Which Makes the WiMAX System Outstanding

WiMAX is a wireless broadband solution that offers a rich set of features with a lot of

flexibility in terms of deployment options and potential service offer. Some of the salient

features that deserve highlighting are as follows:

1.4.1 Orthogonal Frequency Division Multiplexing (OFDM)

OFDM mitigates interference by breaking the original signal into some orthogonal

subcarriers. Which results that, during transmission loss of data on a small fraction of

subdivided signals do not degrade the reception of the received signal quality, security

and mobility.

Figure#1.1: Illustration of Breaking into Multiple Subcarriers Transmission.

1.4.2 Orthogonal Frequency Division Multiple Access (OFDMA)

Mobile WiMAX uses OFDM as a multiple-access technique, whereby different users can

be allocated different subsets of the OFDM tones. OFDMA facilitates the utilization of

frequency diversity and multiuser diversity to extensively improve the system capacity.

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1.4.3 Scalable Bandwidth and Data Rate Support

WiMAX has a scalable physical-layer architecture that allows the data rate to scale easily

with available channel bandwidth. This scalability is supported in the OFDMA mode,

where the Fast Fourier Transform (FFT) size may be scaled based on the available

channel bandwidth. This scaling may be done dynamically to support user roaming

across different networks that may have different bandwidth allocations. For example;

512-bit or 1048-bit FFTs based on whether the channel bandwidth is 5MHz or 10MHz,

respectively.

1.4.4 Adaptive Antenna System (AAS)

AAS uses beam-forming technologies to focus the wireless beam for communication

between the base station and the subscriber station.

Figure#1.2: Illustration of Adaptive Antenna System and Beam Forming Technology.

This diminishes the possibility of interference with other transmitting station as the beam

goes straight between the two communicating points.

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1.4.5 Dynamic Frequency Selection (DFS) and Multiple In Multiple Out

Dynamic Frequency Selection enables the mobile devices to switch between different

radio frequencies channel on the basis of certain channel measurement criterion. Such as,

signal to interference ratio. A DFS radio sniffs the airwaves to determine where

interference does not occur and selects the open frequency to avoid the frequencies where

interference occurs.

Figure#1.3: Illustration of DFS in Case of Interference

Multiple in and Multiple out (MIMO) antenna systems are worked on the same principle.

With multiple transmitters and receivers built into the antenna, the transmitter and

receiver can coordinate to move to open frequency when interference occurs.

1.4.6 Dynamic Bandwidth Allocation (DBA) and Modulation Scheme

Firstly, the coding and modulation schemes e.g. 64-QAM/16-QAM/QPSK ensure the

steady signal strength over increasing traveling distance between the communicating

devices.

Secondly, Dynamic Bandwidth Allocation (DBA) is taking place. Which is a mechanism

that continuously monitor the network and when interference or other detractions to

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signal strength occur, the base station allocates more bandwidth and power for the

troubled signal stream to overcome the trouble.

Figure#1.4: Illustration of DBA and Modulation Scheme

1.4.7 Very High Peak Data Rates as high as 70Mbps when operating using a 20MHz

wide spectrum.

1.4.8 Supports Time Division Duplex and Frequency Division Duplex as well as a Half-

Duplex FDD, which allows a low-cost system implementation.

1.5 Family Standards of 802.16

WiMAX has four main standards. Among them, fixed wireless services covered by IEEE

802.16d standard and mobile wireless services covered by IEEE 802.16e standard are the two

main variants. In addition with these two standards, the other two standards are discussed

briefly in the following section.

1.5.1 IEEE 802.16

The IEEE 802.16 standard which is also known as the air interface for fixed wireless

broadband access (FWBA), is the first version of 802.16 families published in April,

2002. It operates in licensed spectrum from 10–66 GHz band. Which is expensive, but by

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means of more bandwidth and less interference. IEEE 802.16 defines two network

topologies; (a) point-to-point (PTP) and (b) point-to-multipoint (PMP) and only used for

line of site (LOS) condition.

In IEEE 802.16 standard modulation scheme used is a single-carrier modulation scheme,

in which all packets are sequentially transmitted through a single carrier frequency and is

supported by three modulation schemes, QPSK (Quadrature phase shift keying), 16QAM

(Quadrature amplitude modulation) and 64QAM (Quadrature amplitude modulation) and

also supports duplexing technique both TDD and FDD.

1.5.2 IEEE 802.16a

IEEE 802.16a is an improved version of 802.16 which extends the 802.16 spectrum down

to a lower frequency range from 2 to 11GHz. So that, it can utilize both the unlicensed

and licensed bands and enables Non Line of Site (NLOS) transmission. NLOS

transmissions are more desirable in urban areas because radio waves at 2–11GHz

frequency bands can penetrate, reflect and bend around the obstacles but such a situation

causes attenuation.

With introduction of unlicensed band in 802.16a, results increase of the rate of

interference. So, a Dynamic Frequency Selection (DFS) mechanism is specified in

802.16a to reduce the interference.

802.16a uses flexible bandwidth choices, including channel bandwidth between 1.25MHz

and 28MHz, which provides the flexibility to operate in different frequency band with

varying channel requirements over long distance communication. Because sometimes it

is very difficult for some power-sensitive devices such as, laptop and other handheld

equipments, to transmit signal to the Base Station over long distance if the channel

bandwidth is too wide.

In addition to PTP and PMP, 802.16a introduces the Mesh topology, which is more

flexible, effective, reliable, and portable network architecture based on the multi hop

concept.

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Another new feature of 802.16a standard is Adaptive Modulation scheme, which allows

the provision of more flexible services to customers by enabling the BS dynamically

assign modulation schemes to the clients. This supports different modulation technique as

its previous standard, including QPSK, 16QAM, and 64QAM. The higher the order of

modulation, the higher is the bit rate achieved.

1.5.3 Fixed WiMAX / 802.16-2004 / 802.16d

It is combined and improved version of IEEE 802.16 and 802.16a in which both 10–

66GHz and 2–11GHz frequency bands are specified and its bandwidth can be as narrow

as 1.25MHz and as wide as 28MHz. This is designed for fixed BWA systems to support

multiple services.

Fixed WiMAX deployments do not provide handoff between the Base Stations; therefore

the service provider cannot offer mobility.

1.5.4 Mobile WiMAX /802.16-2005/ 802.16e

IEEE 802.16e standard published in December 2005 aims to provide portability and

mobility to wireless devices and supports for higher layer handover, which are lacking in

the previous standard. 802.16e also enhances the network performance in fixed

environment by using “Orthogonal Frequency Division Multiple Access (OFDMA)”.

However, the frequency bands suitable for mobility must be below 6GHz. Compared

with 802.16d, 802.16e has lower throughput (up to 15Mbps), but it supports both hard

and soft handoffs.

Using OFDMA, fixed user devices can be supported with the same data rate as OFDM,

while mobile users trade off mobility against bandwidth. Compared to OFDM, OFDMA

supports larger FFT size of 1024 so that it enables more flexible subcarrier bandwidth

allocation.

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1.6 WiMAX Standard Difference

There are four main variants of WiMAX standards. All this standards cab be distinguished by

their outstanding features and application.

In the following table, the four main standards are summarized;

Table#1.1 Comparison among the four main standards of WiMAX

Issue 802.16 802.16a 802.16d 802.16e

Frequency

Range

10-66GHz 2-11 GHz 2-11 GHz &

10-66 GHz

2-6 GHz

Channel

Conditions

LOS only NLOS NLOS NLOS

Channel

Bandwidth

20, 25 and 28

MHz

1.25-28 MHz 1.25-28 MHz 1.25-20 MHz

Modulation

Scheme

QPSK, 16 QAM

and 64QAM

OFDM, QPSK,

16QAM and

64QAM

OFDM, QPSK,

16QAM and

64QAM

OFDM, QPSK,

16QAM and

64QAM

Network

architecture

PTP, PMP PTP, PMP, Mesh PTP, PMP, Mesh PTP, PMP,

Mesh

Bit Rate 32 – 134Mps Up to 70 Mbps Up to 75 Mbps Up to 15 Mbps

Mobility Fixed Fixed Fixed Regional

roaming, max

mobility

support: 125

km/h

Typical cell

Radius

1-3 miles Maximum range

is 30 miles on the

basis of antenna

height & gain &

Maximum range

is 30 miles on the

basis of antenna

height & gain &

1-3 miles

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transmit power transmit power

Application Replacement of

E1/T1 line,

backhaul for hot

spots, residential

broadband

access, SOHO

Alternative to

E1/T1, DSL,

cable backhaul

for cellular and

Wi-Fi, VoIP,

Internet

connections

801.16 plus

802.16a

applications

802.16-2004

applications plus

fixed VoIP, QoS

based

applications and

enterprise

networking

1.7 How it is Better than DSL and Cable Modems?

The two main problems with DSL and Cable Modem suffered are of low speed and a lot of

wire. They need to boost up the speed every few kilometers and so that fill up the cities with

wires everywhere. With WiMAX these disadvantages can be removed as:

As being wireless there is no disorder around in space.

Each station can provide a boost of 70Mbps download speed which can cover the

entire city easily.

This also gets rid of the problem of maintaining the wires as well as their connection

which has definite weakness when it gets damaged somewhere.

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Figure#1.5: Illustration of WiMAX for Wire Free World. (Courtesy of Intel Corporation)

1.8 WiMAX Applications

WiMAX attribute opens the technology to a wide variety of applications because of its high

transmission rate; high bandwidth and large coverage distance and makes it suitable for the

following potential applications:

1.8.1 Fixed Applications of WiMAX

Wireless Backhaul

A backhaul refers to both the connection from the access point (AP) back to the

service provider and the connection from the service provider to the core network.

WiMAX can be used as a wireless backhaul which is a cost-effective backhaul

solution and typically use PTP and LOS connections to maximize the effectiveness

and reliability of the network.

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WiMAX VoIP Application

The WiMAX VoIP allows people to make local, long-distance and even international

calls through the broadband internet connection, bypassing the phone companies

entirely at reduced cost. Almost anyone with a WiMAX-compatible computer or

PDA could make VoIP calls.

Internet Protocol TV Offered by WiMAX

IPTV enables a WiMAX service provider to offer the same program as cable or

satellite TV service provider offers. Depending on compression algorithms, IPTV

requires at least 1MHz of channel bandwidth between the WiMAX base station and

the subscriber. IPTV over WiMAX also enables the service provider to offer local

programming as well as revenue generating through local advertising.

Figure#1.6: WiMAX VoIP Architecture (Source: WiMAX Application)

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Figure#1.7: WiMAX IPTV and Video on Demand Service (WiMAX in 50pages)

In addition to IPTV program, the service provider can also offer a variety of video on

demand (VoD) services. The program can be selected by the subscriber for their

television and this may be more desirable to the subscriber as they pay only for what

they want to watch as opposed to having to pay for dozens of channels they don’t

want to watch.

The high capacity of WiMAX enables it to provide multimedia services, such as

video conferencing in more flexible and convenient way to access anytime, anywhere.

WiMAX can be used to provide faster online gaming in both the rural and urban

areas.

Connecting Wi-Fi hotspots with each other and to other parts of the Internet.

Fixed Wireless Applications (FWA)

Bulk of United States businesses and residences receive their telephone service and

internet access through the telephone company’s copper wires (T1/E1). Telephone

Company’s T1 line may be sold at $800/month in many US cities. About 50% of that

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expense is “local loop” charges or paying to use the telephone company’s copper wire

to access to the wide network.

Figure#1.8: WiMAX FWA for Substitution of Telephone Company’s T1/E1/DS3.

A WiMAX service provider could purchase the bandwidth equivalent of a T1 (1.54

Mbps) at $45 (say) and resell to an enterprise customer for $400/month. Through this

oversubscription a WiMAX service provider could make the profit multiple.

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Figure#1.9: Illustration of WiMAX Fixed, Portable, Nomadic And Mobile Application.

1.8.2 Mobile Applications of WiMAX

WiMAX as Cellular Alternative

Among the entire sub industries in telecommunications, possibly the one best

positioned to take advantage of WiMAX is the cellular service provider as they have

a millions of “early adaptor” customers and serving cellular network infrastructure.

On the other hand, the transition from legacy circuit switching and a dependency on

the present telephone service provider’s network will not be easy or inexpensive.

As the diagram below, a large percentage of a cell phone operator’s monthly

operating expense (OPEX) is T1 backhaul to support their base stations. In addition,

they use paging circuit switches (Mobile Switching Centers) to switch phone calls.

These come with expensive annual service contracts. A WiMAX substitute for the

cell phone infrastructure could be operated at as little as 10% of the OPEX of a

cellular operator using legacy infrastru

Figure#1.10

Replacing a cell phone infrastructure with WiMAX will need to integrate a large

mobile data and mobile TV element with cell phone infrastructure. This is because;

data bandwidth claim is

Figure#1.11: Mobile

When one mentions “mobile” the first thing to come to mind is cell phone service,

which is a giant industry in itself. However,

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cellular operator using legacy infrastructure.

10: The Cellular Mesh Network (Source: Trensmedia)



data bandwidth claim is far greater than the voice-centric cell phone network.

obile Wireless Application for Mobile Voice and D


industry in itself. However, the mobile phone company


(Source: Trensmedia)



centric cell phone network.

Voice and Data.


phone company now offers a

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wide range of services beyond voice to include mobile data and TV as well as

emergency services such as police, fire-brigade and ambulance.

A wireless operator will want to pay close attention to their ARPU while minimizing

their OPEX. WiMAX allows an operator to do both simultaneously. Failure to update

a legacy network could put an operator at risk of losing business to new market

participant equipped with WiMAX.

1.9 Advantages and Disadvantages of WiMAX

1.9.1 Advantages of WiMAX

Easy Installation as being wireless.

802.16e version allows Mobility. Maximum mobility support: 125 km/h.

Line of sight not required in urban area.

High Throughput.

Longer Range.

Low cost customer premises equipment (CPE) and subscriber station (SS).

Improved user connectivity.

Higher Quality of Service (QoS).

Ensures Interoperability.

1.9.2 Disadvantages of WiMAX

Line-of-sight (LOS) is required over long distance (5-30 mile) communication.

Certain conditions like ground, weather, large and high rise buildings can act to

reduce the maximum range.

Other wireless electronics can interfere with the WiMAX connection and cause a

reduction in data throughput

Licensed frequency spectrums are limited.

Unlicensed frequency spectrums are free. But RF design needs serious attention

and it is very difficult to control service quality if other users use the same band.

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1.10 Quality of Service

In broad term QoS refers to “collective effect of service” as perceived by the user. More

narrowly QoS refers to meeting certain requirements typically, throughput, packet error rate,

delay and jitter associated with a given application. Broadband wireless network should

support a variety of applications, such as voice, video, data and multimedia application and

each of these has different traffic patterns and QoS requirements based on their specific

application.

In addition to the application-specific QoS requirements, networks frequently need to also

enforce policy-based QoS, such as giving differentiated services to users based on their

subscribed service plans. The unpredictability in the QoS requirements across applications,

services and users make it a challenge to accommodate all these on a single-access network,

particularly in wireless networks, where bandwidth is a premium issue.

The problem of providing QoS in broadband wireless systems is of managing the radio

resources effectively. Effective scheduling algorithms that balance the QoS requirements of

each application and user with the available radio resources need to be developed. In other

words, capacity needs to be allocated in the right proportions among users and applications at

the right time. This is the challenge the MAC-layer protocol must meet with simultaneously

handling multiple types of traffic flows like bursty and continuous, varying throughputs and

latency requirements.

Again, delivering QoS is more challenging for mobile broadband than for fixed broadband.

The time variability and unpredictability of the channel become more sensitive and

complication arise from the need to hand over sessions from one cell to another as the user

moves across their coverage boundaries. Handovers cause packets to be lost and introduce

additional latency. Reducing handover latency and packet loss is also an important aspect of

delivering QoS. Handover also necessitates coordination of radio resources across multiple

cells. So far, QoS has been limited to delivering it across the wireless link.

From a user standpoint, the perceived quality is based on the end-to-end performance of the

network to be effective. Therefore, QoS has to be delivered end-to-end across the network,

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which may include, a variety of aggregation, switching and routing elements between the

communication end points.

The following table summarizes some application specific QoS supported in WiMAX;

Table#1.2 : Quality of Services Supported in WiMAX

Parameter Interactive

Gaming

Voice Streaming

Media

Data Video

Data rate 50–85Kbps 4-64Kbps 5-384Kbps 0.01-00Mbps > 1Mbps

Applications Interactive

gaming

Vo IP Music,

speech, video

clips

Web browsing,

e-mail, instant

messaging(IM)

file downloads

IPTV, movie

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% for

audio; < 2%

for video

Zero < 10–8

Delay

variation

Not

applicable

< 20 ms < 2 sec Not applicable < 2 sec

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

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Chapter Two

WiMAX and other Wireless Technologies

2.1 WiMAX and Other Wireless Technologies

WiMAX is not the only solution for delivering broadband wireless services. Several

solutions, particularly for fixed applications, are already in the market. A few solutions, such

as i-Burst technology and Flash-OFDM support mobile applications also. In addition to these

solutions, there are standards-based alternative solutions that at least partially overlap with

WiMAX, particularly for the portable and mobile applications. In the near term, the most

significant of these alternatives are third-generation cellular systems and IEEE 802.11-based

Wi-Fi systems.

2.2 Third Generation Cellular Network

Mobile operators over the world are upgrading their networks to 3G technology for

delivering broadband access service. GSM operators are deploying Universal Mobile

Telecommunication System (UMTS) and High Speed Downlink Packet Access (HSDPA)

technologies as part of their 3G evolution. On the other hand, CDMA operators are deploying

1x Evolution Data Optimized (1x EV-DO) as their 3G solution for broadband data. All of

these 3G solutions provide data throughput capability on the order of a few hundred Kbps to

a few Mbps.

HSDPA is capable of providing a peak user data rate of 14.4Mbps, when operating on a

5MHz channel. Typical average rates that users obtain are in the range of 250Kbps to

750Kbps. It should be noted that, HSDPA is a downlink-only interface; hence until an uplink

complement is implemented, the peak data rates achievable on the uplink will be less than

384Kbps, in most cases averaging 40Kbps to 100Kbps.

1x EV-DO is a high-speed data standard defined as an evolution to second-generation IS-95

CDMA systems by the 3GPP2 standards organization. The standard supports a peak

downlink data rate of 2.4Mbps over 1.25MHz channel. Typical user-experienced data rates

are in the order of 100Kbps to 300Kbps.

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In addition to providing high-speed data services, 3G systems are evolving to support multi-

media services. For example, 1x EV-DO Rev A enables voice and video telephony over IP.

To make these services possible, 1x EV-DO Rev A reduces air-link latency to almost 30ms,

introduces inter user QoS and fast inter sector handoffs. Multicast and broadcast services are

also supported in 1x EV-DO. Similarly, development efforts are under way to support IP

voice, video and gaming, as well as multicast and broadcast services over UMTS/HSDPA

networks.

2.3 Wi-Fi System

Wi-Fi stands for Wireless Fidelity. This is based on the IEEE 802.11 family of standards

which is mainly a wireless local area network (WLAN) designed to provide in-building

broadband coverage typically for few hundreds of meters. Current Wi-Fi systems based on

IEEE 802.11a/g support a peak physical-layer data rate of 54Mbps under best possible

condition. Wi-Fi uses unlicensed spectrum to provide access to a network; typically covering

only the network operator's own property and which may or may not be connected to the

Internet.

2.4 Comparison of WiMAX with 3G Cellular Network

The throughput capability of WiMAX depends on the channel bandwidth. WiMAX defines a

scalable channel bandwidth from 1.25MHz to 20MHz, which allows for a very flexible

deployment. When deployed using the more likely 10MHz TDD channel, assuming a 3:1

downlink-to-uplink split and 2×2 MIMO, WiMAX offers 46Mbps peak downlink throughput

and 7Mbps uplink. The dependence of WiMAX on OFDM allows them to support very high

peak data rates. However 3G systems have a fixed channel bandwidth and do not use OFDM.

Again WiMAX can achieve spectral efficiencies higher than what is typically achieved in 3G

cellular systems. This is because WiMAX accommodate multiple antenna technique, which

gives WiMAX a boost in spectral efficiency.

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Figure#2.1: Spectral Efficiency Comparison of WiMAX and 3G

On the other hand, in 3G systems, multiple antenna support is being added in the form of

revisions. Further, the OFDM physical layer used by WiMAX is more amenable to MIMO

implementations than are CDMA systems. OFDM also makes it easier to utilize frequency

diversity and multiuser diversity to improve the system capacity. Therefore, when compared

to 3G cellular system, WiMAX offers higher peak data rates, greater flexibility, and higher

average throughput and system capacity.

Another advantage of WiMAX is its ability to efficiently support more symmetric links

useful for fixed applications, such as T1 replacement and support for flexible and dynamic

adjustment of the downlink-to-uplink data rate ratios. Typically, 3G systems have a fixed

asymmetric data rate ratio between downlink and uplink.

WiMAX may be the potential for lower cost due to its lightweight IP architecture. IP

architecture simplifies the core network and reduces the capital expenses as well as the

operating expenses (OPEX). On the contrary, 3G cellular system has a complex and separate

core network for voice and data services and the number of base stations required are greater

than that of WiMAX.

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Figure#2.2: Number of Required Base Stations for WiMAX and 3G

Table#2.1 summarize the comparison among the WiMAX and the somewhat 3G technology

Table#2.1: Comparison of WiMAX and 3G Technologies

Issue CDMA2k 1xEVDO WCDMA HSDPA WiMAX 802.16e

Duplexing FDD FDD FDD/TDD

Multiplexing

DL/UL

CDMA

DS-CDMA

SOFDMA

Freq. Band 2 GHz 2.1 GHz 2.3, 2.5, 3.5 GHz

Bandwidth 2X1.25MHz 2X5MHz 1.25/5/8.75/10/20MHz

Frame Size

DL/UL

1.67/6.67 ms

2/2,10 ms

5 ms

DL Modulation QPSK/8PSK/QAM16 QPSK/QAM16 QPSK/QAM16/QAM64

UL Modulation BPSK/QPSK/8PSK BPSK/QPSK QPSK/QAM16/QAM64

FFT Size NA NA 128/512/1024/2048

Transmission

BR (DL/UL)

3.1/1.8 Mbps

14/5.8 Mbps

31.68/23.52 Mbps

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Sub channel NO NO YES

Scheduling

Fast scheduling in

DL

Fast scheduling in DL Fast scheduling in

DL and UL

Handoff Virtual soft handoff Network initiated

hard handoff

Network optimized hard

handoff

Beam forming NO YES YES

AAS NO NO YES (Source : WiMAX system architecture, analysis and simulation)

2.5 Comparison of WiMAX with Wi-Fi

Both WiMAX and Wi-Fi have a connection to wireless connectivity and Internet service. But

the two standards are aimed at different applications.

WiMAX is a long-range system, covering many kilometers that typically uses licensed

spectrum to deliver a point-to-point connection to the Internet from an ISP to an end user.

Different 802.16 standards provide different types of access, from mobile broadband access

to fixed wireless access. If WiMAX provides services analogous to a cell phone, Wi-Fi is

more analogous to a cordless phone. The following table summarizes the comparison

between the WiMAX and the Wi-Fi technology

Table#2.2: Comparison of WiMAX and Wi-Fi Technologies

Issue WiMAX (802.16a) Wi-Fi (802.11b) Wi-Fi (802.11a/g)

Primary Application Broadband Wireless

Access

Wireless LAN Wireless LAN

Frequency Band Licensed/Unlicensed

2G to 11GHz

2.4GHz ISM 2.4GHz ISM (g),

5GHz U-NII (a)

Channel Bandwidth Adjustable 1.25M

to 20MHz

25MHz 20MHz

Duplex Full Half Half

Radio Technology OFDM Direct Sequence OFDM

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(256-channels) Spread Spectrum (64-channels)

Bandwidth efficiency ≤ 5 bps/Hz ≤ 0.44 bps/Hz ≤ 2.7 bps/Hz

Modulation BPSK, QPSK,

16/64/256-QAM

QPSK BPSK, QPSK,

16-QAM, 64-QAM

Encryption Mandatory- 3DES

Optional- AES

Optional- RC4

(AES in 802.11i)

Optional- RC4

(AES in 802.11i)

Access Protocol

-Best Effort

-Data Priority

-Consistent Delay

Request/Grant CSMA/CA CSMA/CA

Yes Yes Yes

Yes 802.11e WME 802.11e WME

Yes 802.11e WSM 802.11e WSM

Mobility Mobile WiMAX

(802.16e)

In development In development

Mesh Yes Vendor

Proprietary

Vendor Proprietary

Source: A comparison of technologies, Markets and business plan, Michael Finneran, dBrn Associates, Inc

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Chapter Three

WiMAX Architecture 3.1 Network Toplogy

Topology refers the way in which the radio nodes are organized. Topolgy shows the

relationship between the communication links and the radio nodes. For WiMAX basically

there are three different topology for interconnection of the radio nodes.

3.1.1 Point To Point (PTP)

Under PTP topology a dedicated link connects only the Base Station and the Subscriber

Station. It utilizes resources in an inefficient way and substantially causes high operating

charges. It is usually used to serve high-value customers who need extremely high

bandwidth, such as business high-rises, video postproduction houses or scientific research

organizations. This architecture calls for a highly focused beam between the points so

that throughput of a point-to point nodes will be higher than that of point-to-multipoint

link.

Firgure#3.1: Illustration of PTP Topology

Page# 27

3.1.2 Point To Multi Point (PMP)

In point to multipoint topology, a group of dissimilar subscriber are connected to single

base station separately in terms of bandwidth and services offered. In this case, the

available bandwidth is shared among a group of users. So that, bandwidth charges for

each user is also reduced. For PMP topology, sectoral antennas with highly directional

parabolic dishes are used for frequency reuse.

Firgure#3.2 : Illustration of PMP Topology

3.1.3 Mesh Topology

Mesh topology is the more flexible, effective and reliable network architecture as there

are at least two pathways of communication to each radio node. Mesh networks give the

subscriber stations (SS) more intelligence than traditional wireless transmitters and

receivers. With mesh topology, every SS can act as an access point and is able to route

packets to its neighbors by itself. But the drawback is that, it is highly expencive.

Mesh topology can be divided into two basic categories;

Switched Mesh Network

In a switched mesh network, a fixed route between two radio nodes is predetermined

and all packets follow the same path during the transmission. If the connection is

down or the QoS of the link is degraded, a new route have to be established to replace

the old one.

Routed Mesh Network

In routed mesh architecture, there is

All packets may follow different paths and be forwarded by intelligent network nodes

on the basis of the assessment of link conditions measured

parameters, like throughput, traf

Firgure 3.3:

3.2 Modes of Operation

In reality WiMAX can provid

3.2.1 The Line-of-Sight (

Line of site is a condition where a signal travels over the air directly from a wireless

transmitter to receiver without passing any obstacle. This is an ideal condition used for

wireless communication for the reason that, the propagation ch

weather/atmospheric parameters and the characteristic of its operating frequency.

Page# 28

ork

architecture, there is no fixed path from the source to the destination.


on the basis of the assessment of link conditions measured upon

meters, like throughput, traffic density, packet loss, delay, jitter, SIR

Firgure 3.3: Illustration of Mesh Topology

In reality WiMAX can provide two forms of wireless service;

Sight (LOS) Service

a condition where a signal travels over the air directly from a wireless


wireless communication for the reason that, the propagation challenge only comes from

atmospheric parameters and the characteristic of its operating frequency.

fixed path from the source to the destination.


upon a number of

, SIR.

a condition where a signal travels over the air directly from a wireless


allenge only comes from

atmospheric parameters and the characteristic of its operating frequency.

Under LOS type service, a fixed outdoor WiMAX subscriber antenna points directly to

the WiMAX tower. This type of connection is stronger and more stable; also it is able to

send a lot of data at longer distance with fewer errors to WiMAX

routers set up within the transmitter's 30

Figure 3.4:

3.2.2 The Non-Line-of-Sight (

Non line of site is a cond

obstacles before arriving at a receiver. The signal may be reflected, refracted, diffracted,

absorbed or scattered. All of

a receiver at different times, from different paths

only that, those problems made

capable systems simplify

installation expenses by making indoor CPE installation. This also reduces the need for

pre installation site surveys and improves the accuracy of NLOS planning tools.

In this approach, WiMAX uses a

access are limited to a 4

easily interrupted by physical obstructions

around obstacles.

Page# 29

LOS type service, a fixed outdoor WiMAX subscriber antenna points directly to


lot of data at longer distance with fewer errors to WiMAX-enabled computers or

set up within the transmitter's 30-mile radius.

Figure 3.4: LOS vs. NLOS Propagation

Sight (NLOS), Wi-Fi Type Service

is a condition where a signal from a wireless transmitter passes several


All of those phenomenons create multiple signals that will arrive at

ent times, from different paths and with different signal strength.

that, those problems made the system more complex than those for LOS. But NLOS

capable systems simplify the network planning and site acquisition and as well as reduc



In this approach, WiMAX uses a lower frequency range; 2-to-11 GHz and

limited to a 4-to-6 mile radius. Lower wavelength transmissions are not as

by physical obstructions as they are better able to diffract, or bend,

LOS type service, a fixed outdoor WiMAX subscriber antenna points directly to


enabled computers or

ition where a signal from a wireless transmitter passes several


create multiple signals that will arrive at

and with different signal strength. Not

the system more complex than those for LOS. But NLOS

as well as reduce



11 GHz and this class of

6 mile radius. Lower wavelength transmissions are not as

they are better able to diffract, or bend,

Page# 30

3.3 WiMAX Network Reference Model (NRM)

The NRM identifies the functional unit in the architecture as well as the reference points

linked the functional unit over which interoperability is achieved. The NRM divides the end-

to-end system into three logical parts:

Mobile stations (MS) which is owned by the subscriber to access the network.

The Access Service Network (ASN) which is owned by a Network Access Provider

(NAP) and comprises one or more Base Stations as well as one or more ASN gateways

that form the Radio Access Network (RAN).

The Connectivity Service Network (CSN), which is owned by an Network Service

Provider (NSP) and provides IP connectivity to users and performs all the IP core

network functions. The subscriber is served from the CSN belonging to the visited NSP;

the home NSP is one, from where the subscriber belongs. For nonroaming case, the

visited NSP and home NSP imply the same.

Figure 3.5: Block Diagram of WiMAX Reference Network Architecture

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Figure#3.6: Graphical Illustration of Reference Network Architecture

3.4 WiMAX Network Nodes

3.4.1 Access Service Network (ASN)

ASN is defined as the complete set of network functions needed to provide radio access

to a WiMAX subscriber. As such, it comprises of one or more base station as well as one

or more ASN Gateway.

The roles of ASN are the following;

Network discovery and selection of the subscriber’s preferred CSN/NSP.

Relay functionality for establishing IP connectivity between the MS and the CSN.

Radio Resource Management (RRM) and allocation based on the QoS policy and/or

request from the NSP or the ASP.

Performs Mobility-related functions, like handover, location management and paging

within the ASN, including support for mobile IP with foreign-agent functionality.

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3.4.2 Base Station (BS)

The BS is defined as a wireless hub for the whole of the network infrastructure and

implementing the IEEE 802.16e interface to the MS. MS are linked to the BS through air-

interface technology. A BS may be connected to more than one ASN-GW for load

balancing or redundancy purposes.

It is responsible for all the radio related functions in the system like;

Radio communication with the Subscriber Station.

Handover of calls in progress between cells or within sectors of the cell.

Management of all radio network resources and cell configuration data.

Additional functions that may be handled by the base station include;

Scheduling for the uplink and the downlink, traffic classification, and service flow

management (SFM) by acting as the QoS policy enforcement point (PEP) for traffic

through the air interface.

Provides terminal activity (either active or idle) status, support tunneling protocol

toward the ASN-GW, providing dynamic host control protocol (DHCP) proxy

functionality, transmits authentication messages between the MS and the ASN-GW.

Reception and delivery of the traffic encryption key (TEK) and the key encryption

key (KEK) to the MS.

Serve as resource reservation protocol (RSVP) proxy for session management, and

managing multicast group association via Internet Group Management Protocol

(IGMP) proxy.

3.4.3 Mobile Station (MS)/ Subscriber station (SS)

The technical term for customer premise equipment (CPE) is subscriber station. It. is the

wimax enabled mobile equipment set and may be both outdoor and indoor verson.

Mobile station provides connectivity between subscriber equipment (PDA, laptop, hybrid

cell phone, small indoor/outdoor antenna) and the base station.

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3.4.4 Access Service Network Gateway (ASN-GW)

A very significant component of Mobile WiMAX network is the ASN Gateway, which

combines subscriber and control traffic from base station within an access network. ASN

Gateway is situated at the heart of the access network and plays an important role in

subscriber management, network optimization, and forwarding of traffic. The ASN- GW

function enables service providers to deploy highly scalable mobile broadband network

and provides an opportunity for delivering advanced features to enable differentiated

service offer. It performs the following functions;

ASN location management and paging.

Acts as a server for network session and mobility management.

Performs admission control and temporary caching of subscriber profiles and

encryption key.

Acts as an authenticator as well as Authentication, Authorization, and Accounting

AAA.

Client/proxy, provides mobility tunnel establishment and management with BSs

Performs service flow authorization (SFA), based on the user profile and QoS policy.

Provides foreign agent functionality and performs routing to select CSNs.

ASN gateway may optionally be decomposed into two groups of functions: (a) Decision

point (DP) functions and (b) Enforcement point (EP) functions. The EP functions include

the bearer plane functions and the DP functions may include non–bearer plane control

functions. When decomposed in such a way, the DP functions may be shared across

multiple ASN Gateways. Examples of DP functions include intra-ASN location

management and paging, regional radio resource control and admission control, network

session/mobility management (server), radio load balancing for handover decisions,

temporary caching of subscriber profile and encryption keys and AAA client/proxy.

Examples of EP functions include mobility tunneling establishment and management

with BS, session/mobility management (client), QoS and policy enforcement, foreign

agent and routing to select CSN.

Page# 34

3.4.5 Connectivity Service Network (CSN)

CSN is a concept in the mobile WiMAX network and is the core of the WiMAX network

architecture providing control and management for the ASN and subscribers with

services such as DHCP server, AAA, FTP, inter-operator and inter-technology roaming,

services and other applications. The CSN also provides subscriber with IP connectivity,

and other public and corporate networks connectivity.

Role of Connectivity Service Network (CSN) are as follows;

IP address allocation to the MS for user meeting.

AAA proxy or server for user, device and services authentication, authorization and

accounting (AAA).

Policy and QoS management based on the contract with the user. The CSN of the

home NSP distributes the subscriber profile to the NAP directly or via the visited

NSP.

Subscriber billing and inter-operator settlement.

Inter-CSN tunneling to support roaming between NSPs.

Inter-ASN mobility management and mobile IP home agent functionality.

3.4.6 Reference Points (RP)

The WiMAX Network Working Group (NWG) defines RP as a conceptual link that

connects two groups of functions that is located in different functional unit in the system.

Reference points are not necessarily a physical interface, except when the functional unit

on either side of it are implemented on different physical devices. The WiMAX Forum

will verify interoperability of all exposed RPs based only on specified normative

protocols and procedures for a supported capability across an exposed RP.

Table#3.1: WiMAX Reference Points

RP End Points Description

R1 MS and ASN Implements the air-interface (IEEE 802.16e) specifications.

Page# 35

R2 MS and CSN Only a logical interface and not a direct protocol interface for

authentication, authorization, IP host configuration management

and mobility management.

R3 ASN and CSN Supports AAA, policy enforcement, and mobility-management

capabilities. R3 also cover the carrier plane methods to transfer IP

data between the ASN and CSN.

R4 ASN and ASN A set of control protocols originating/terminating in various units

within the ASN that coordinate MS mobility between ASNs. R4 is

the only interoperable interface between heterogeneous or

dissimilar ASNs.

R5 CSN and CSN A set of control protocols for interworking between home and

visited network.

R6 BS & ASN-

GW

A set of control or carrier plane protocols for communication

between the BS and the ASN-GW. The carrier plane consists of

intra-ASN data paths or intra-ASN tunnels between the BS and the

ASN-GW. The control plane includes protocol for mobility tunnel

management based on MS mobility events. R6 may also serve as a

conduit for exchange of MAC states information between

neighboring BSs.

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 and BS A set of control plane message flows and, possibly, bearer plane

data flows between BSs to ensure fast and seamless handover. The

bearer plane consists of protocols that allow the data transfer

between BSs involved in handover of a certain MS. The control

plane consists of the inter-BS communication protocol defined in

IEEE 802.16e and additional protocols that allow controlling the

data transfer between the BS involved in handover of a certain MS.

Page# 36

3.5 Alcatel WiMAX Full IP Architecture

The mobile WiMAX end-to-end network architecture is based an All-IP platform. It offers

the advantage of reduced cost of ownership during the lifecycle of a WiMAX network

deployment. The use of All-IP means that a common network core can be used, without the

need to maintain both packet and circuit core networks. A further benefit of All-IP is that, it

places the network on the performance growth curve of general purpose processors and

computing devices. Progress in computer marketplace is much faster than

progress in telecommunications equipment because general purpose hardware is not

limited to telecommunications equipment. This end results in lower cost, high scalability and

rapid deployment since the networking functionality is all primarily software-based services.

3.5.1 WiMAX All-Purpose Access Network System

A WiMAX-based access network permits operators to benefit from:

Broadband mobile wireless access to complement existing fixed or mobile

infrastructures.

Seamless services offer across different infrastructures.

The Alcatel WiMAX architecture is adaptable to the needs of diverse operator profiles,

including current, challenger or greenfield licensees. For operators with fixed-network

access, it complements the DSL or cable infrastructure in terms of geographic coverage

or by extending existing broadband services beyond a fixed location to nomadic or

mobile usage. For operators with wireless/mobile networks, WiMAX raises the

possibility of multimode access to services and applications either via WiMAX wideband

or the existing 2G/3G or Wi-Fi infrastructure. Whatever the variant, this solution lets the

operators provide services and applications like;

Everywhere and always on to enable DSL like end user experience anywhere and

anytime.

Reliable to deliver manageable, carrier-grade QoS mechanisms.

Secure to provide authentication and control mechanisms to protect the network,

while encryption is employed to safeguard user-data privacy and integrity.

Page# 37

Seamless to assure multiple access networks share a common authentication,

authorization and accounting (AAA) platform, while a common NGN/IMS core

makes the networks both user and application-aware. The net result is greater

convenience and value for end-users, as well as higher subscriber retention and cost

optimization for operators.

3.5.2 The Alcatel WiMAX End-To-End Reference Architecture

The WiMAX-based end-to-end architecture is divided into two key parts; (a) The

WiMAX radio access network (RAN), as well as the core network (CN) and (b)

Application part. Both parts are linked by clear and standardized interfaces in order to

ensure

Compatibility with the existing infrastructure and investment protection and

The flexibility to progress the network to meet future user needs.

Due to the many elementary building blocks that are part of the Alcatel portfolio, a key

feature of the Alcatel WiMAX end-to-end solution is its capability of integrating

seamlessly with an existing infrastructure and its adaptability to varying operator

requirements. In this respect, the portfolio can provide either stand-alone radio access to

broadband services or complement existing fixed or mobile network infrastructures.

3.6 Core Network Architecture Options

Alcatel has designed several architectures based on WiMAX in order to meet the specific

requirements of different network operators. Figure#3.7 identifies three main variants in the

core network, corresponding to the following requirements:

Full next generation network (NGN)/ IP multimedia subsystem (IMS) integration, with

total multimedia support (I+II+III).

NGN capabilities supporting QoS for VoIP, in either complementary or stand-alone

networks (I+II).

Data-access fundamentals, suitable for wholesale or simple “wireless DSL” type

deployments (I only).

Figure #3.7: Alcatel

Page# 38

Alcatel –Lucent WiMAX End-To-End Reference Architecture

End Reference Architecture

Page# 39

3.6.1 Full WiMAX Integration with IMS and NGN

It allows for a complete integration of the WiMAX access network into a fixed [DSL or

Gigabit Passive Optical Network (GPON)] or mobile (UMTS or CDMA) architecture. In

the case of integration with a mobile network, the proposed solution allows the end user

to access services due to the common authentication and authorization mechanisms

implemented in the fixed or mobile network part. Specifically, the 1430 Home Subscriber

Service (HSS) provides AAA functions in addition to IMS HSS. The Alcatel IP

Multimedia Subsystem solution’s value proposition can be summarized as follows:

A. Open - Any third party can develop on top of the Alcatel 5350 IMS Application Server

be grateful to the open Application Programming Interfaces (API), which are standards

based [Session Initiation Protocol (SIP) Servlet].

B. Ready to launch - This solution provides an end-to-end, consistent and future proof

platform for introducing user-centric services. Moreover, Alcatel provides the core, the

applications and the terminal software. This translates into reduced time-to-market and

opportunities to achieve a competitive advantage. The service set, which has been

developed on top of the Alcatel 5350 IMS Application Server, includes:

Instant Messaging

Push-to-Talk, Push-to-Show, Push-to-Share

Presence Server

Group List Management

Video over IP Calling

Video Conferencing

C. Ready for Massive VoIP Deployment - The Alcatel IMS solution is designed with

carrier-class operational and performance constraints. Due to the openness of the Alcatel

NGN/IMS portfolio, the system is not only adaptable to different existing or planned

network technologies but also sufficiently scalable to cope with operational deployment

and subscriber growth.

D. Extensible to Stay Ahead - The IMS solution is open, modular and extensible to easily

integrate new external services.

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E. Linked with the Operator Environment - The IMS solution integrates with the existing

environment, thus providing operators with access bearer diversity while ensuring non-

IMS and IMS service interoperability.

3.6.2 Next Generation Network Capabilities Supporting QoS for VoIP

One of the key strengths of this architecture is the ability to provide end users with

always-on mobile broadband IP services. This enables anywhere, anytime continuous

Internet service, with sufficient QoS to support real-time applications such as VoIP,

regardless of terrestrial displacement. Moreover, where regulatory rules impose, reduced

mobility or fixed service can be provided using the same architecture, too. The WiMAX

access network can also be stand-alone or can be deployed to complement an existing

access infrastructure be it fixed, mobile, wired or radio based.

In the stand-alone case, mobility under the WiMAX coverage provides continuous

service access to end users be grateful to WiMAX mobile IP features.

In the case of being associated with other access networks, WiMAX permits the

operator to provide access to end users irrespective of access technologies due to the

common authentication, authorization and accounting (AAA) platform.

3.6.3 Data-Access Fundamentals

Another advantage of the Alcatel WiMAX architecture is that it is flexible enough to

provide for operators with less stringent requirements. These include:

Operators who wish, as a first step, to offer WiMAX as a fixed high-speed Internet

solution with no forecast need to bring operator-charged services, such as VoIP or

other multimedia applications.

Wholesalers that intend to split the radio access network among customer ISPs. In

this case, the radio and network infrastructure are shared and managed by the

wholesaler, but subscriber administration/management and service/application

management remain the ISP’s responsibility.

Page# 41

3.7 Nortel WiMAX 802.16e Network Architecture Model

Nortel offers a comprehensive end-to-end solution for WiMAX 802.16e that includes Base

Stations, Access Service Network Gateways, Connectivity Service Network and

Applications, Devices, Network Management, WiMAX Backhaul and Global Services.

Figure#3.8: Nortel WiMAX End to End Architecture

Page# 42

3.8 WiMAX Cell Structure

Each base station antenna provides wireless coverage over an area called a cell. WiMAX cell

structure is similar in concept to cell structure of the cellular mobile networks. As with

conventional cellular mobile networks, the BS antennas can be omnidirectional, giving a

circular cell shape but this limits its range and ultimately signals strength or directional for

point to point use or for increasing the network capacity by effectively dividing a large cell

into several smaller sectoral areas and served by using sectoral antenna.

3.9 WiMAX Base Station (BS)

WiMAX base station is similar in concept to a cell phone tower. A single WiMAX BS can

transmit voice, video, and data signals across distances of up to 50 kilometer from a central

tower with unobstructed line of site condition at a rate as high as 70Mbps and has the ability

to cover up to 3000 square miles. This allows WiMAX service provider to provide coverage

to remote and rural areas at reduced installation cost.

Figure#3.9: WiMAX Base Station (Courtesy of Unwired WiMAX Technology)

Page# 43

3.10 Customer Premise Equipment (CPE)

The technical term for customer premise equipment (CPE) is subscriber station. The first

generation CPE is an outdoor installable subscriber station (SS) similar to a small satellite

dish. The second generation CPE is indoor self-installable modems similar to a cable or DSL

modem. The third generation CPE is a small box or a PCMCIA card or they could be built

into a laptop like Wi-Fi access.

Outdoor CPE, very simply put, offers somewhat better performance over indoor CPE given

that WiMAX reception is not obstructed by walls of concrete or brick, RF blocking glass or

steel in the building’s walls. Outdoor CPE will cost more than indoor CPE due to a number

of factors including extra measures necessary to make outdoor CPE weather resistant.

Mobile Devices Outdoor subscriber station Mobile Broadband

Figure#3.10: Customer Premise Equipment

WiMAX Protocol Architecture4.1 IEEE 802.16 Protocol Architecture

IEEE 802.16 Protocol Architecture composed of four layers;

a) Convergence layer

b) Media Access Control layer

c) Transmission Layer and

d) Physical Layer

This can be mapped into two lowest layers of OSI model; P

Figure#4.1:

4.1.1 Physical (PHY) Layer

The IEEE-802.16 PHY layer provides high

as subscriber stations may be located at various distances from the b

experience different signal

bandwidth, modulation and coding schemes to overcome the varying SNR and provides

Page# 44

Chapter Four

WiMAX Protocol Architecture IEEE 802.16 Protocol Architecture

tocol Architecture composed of four layers;

Media Access Control layer

Transmission Layer and

wo lowest layers of OSI model; Physical Layer and

Figure#4.1: IEEE 802.16 Protocol Architecture

Physical (PHY) Layer

802.16 PHY layer provides high flexibility in terms of modulation and coding

s may be located at various distances from the base

experience different signal-to-noise ratio (SNR). The BS dynamically ad

and coding schemes to overcome the varying SNR and provides

hysical Layer and Data Link layer

flexibility in terms of modulation and coding

ase station so that

. The BS dynamically adjusts the

and coding schemes to overcome the varying SNR and provides

Page# 45

improved system performance. Orthogonal Frequency Division Multiplexing

(OFDM) coupled with forward error correction (FEC) techniques are used when

implementing the OFDM PHY.

Physical Layer Functions

Encoding/Decoding of signals.

Preamble generation/removal.

Bit transmission/reception.

4.1.2 Media Access Control (MAC) Layer

Though the MAC layer of WiMAX has been standardized, there are certain features that

can be tuned and made application and channel specific. For example, the MAC layer

allows variable-sized frames to be constructed and transmitted. The MAC layer of

WiMAX comprises three sub-layers that interact with each other through the service

access points (SAPs). These three sub-layers are-

The Service Specific Convergence Sub-Layer which provides the transformation

or mapping of external network data, with the help of the SAP.

The MAC Common Part Sub-Layer which receives this information in the form

of MAC service data units (MSDUs), which are packed into the payload fields to

form MAC protocol data units (MPDUs). This common part sub-layer is the core

functional layer that provides bandwidth and establishes and maintains connection.

The Privacy sub-layer which provides authentication, secure key exchange and

encryption on the MPDUs and passes them over to the PHY layer.

Media Access Control Layer Functions

On transmission, assemble data into a frame with address and error detection fields.

On reception, disassemble frame & perform address recognition & error detection.

Govern access to the wireless transmission medium.

Page# 46

Figure#4.2: WiMAX MAC Layer with SAPs.

4.1.3 Convergence Layer Functions

Encapsulate PDU framing of upper layers into native 802.16 MAC/PHY frames.

Map upper layer’s addresses into 802.16 addresses.

Translate upper layer QoS parameters into native 802.16 MAC format.

Adapt time dependencies of upper layer traffic into equivalent MAC service.

4.2 WiMAX Slot and Frame Structure

The WiMAX PHY layer is responsible for slot allocation and framing over the air. The

minimum time-frequency resource that can be allocated by a WiMAX system to a given link

is called a slot. Each slot consists of one sub-channel over one, two or three OFDM symbols,

Depending on the particular sub-channelization scheme used.

The frame is divided into two sub-frames: a downlink frame followed by an uplink frame

after a small guard Interval. The downlink-to-uplink sub-frame ratio may be varied from 3:1

to 1:1 to support different traffic profiles. WiMAX also supports FDD, in which case the

frame Structure is the same except that both downlink and uplink are transmitted

simultaneously over different carriers.

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The downlink sub-frame begins with a downlink preamble that is used for physical-layer

procedures, such as time and frequency synchronization and initial channel estimation. The

downlink preamble is followed by a frame control header (FCH), which provides frame

configuration information, such as the map message length, the modulation and Coding

scheme, and the usable subcarriers. Multiple users are allocated data regions within the

Frame and these allocations are specified in the uplink and downlink map messages that are

broadcast following the FCH in the downlink sub-frame. Map messages include the burst

profile for each user, which defines the modulation and coding scheme used in that link.

Figure#4.3: OFDMA and OFDM Frame when Operating in TDD Mode

A single downlink frame may contain multiple bursts of varying size and type carrying data

for several users. The frame size is also variable on a frame-by-frame basis from 2ms -20 ms

and each burst can contain multiple concatenated fixed-size or variable-size packets or

fragments of packets received from the higher layers. At least initially all WiMAX

equipment will support only 5ms frames.

Page# 48

The uplink sub-frame is made up of several uplink bursts from different users. A portion of

the uplink sub-frame is set aside for contention-based access that is used for a variety of

purposes. This sub-frame is used mainly as a ranging channel to perform closed-loop

frequency, time and power adjustments during network entry as well as periodically

afterward. The ranging channel may also be used by SS/MS to make uplink bandwidth

requests. Besides the ranging channel and traffic bursts, the uplink sub-frame has a channel-

quality indicator channel (CQICH) for the SS to feed back channel-quality information that

can be used by the base station (BS) scheduler and an acknowledgment (ACK) channel for

the subscriber station to feed back downlink acknowledgements.

Figure#4.4: Frame Structure

4.3 MAC Frame Format

A generic MAC header consists of a generic MAC frame header (GMH), optional Sub-

headers, payload, and optional forward error correction codes (FEC). The 6 byte GMH

Page# 49

contains details of the entire MPDU. The header type (HT) bit at the beginning, when set to

0, indicates that the header is a GMH.

Figure#4.5: A Generic MAC Frame with Header Format

The Encryption Control (EC) Bit indicates whether or not the payload is encrypted and if so,

the Encryption Key Sequence (EKS) Bits indicate which key was used to encrypt the frame

payload. Type field reflects the content of payload in terms of whether aggregation,

fragmentation, automatic repeat request (ARQ) or mesh feature of the MAC is used. CRC

Indicator (CI) Bit, when set, reveals the presence of error-correction codes at the end. The

LEN field indicates the number of bytes in the MPDU including the header and the cyclic

redundancy check (CRC). The CID defines the connection that the packet is servicing. HCS

is appended at the end of GMH, which works as the cyclic redundancy code for the GMH.

The optional sub-headers are used to define the bits necessary for aggregation, fragmentation,

ARQ, and mesh features of the MAC.

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4.4 Network Entry Process

During the network entry process as well as during RF verification with signaling, complex

data communications taking place in the Physical Layer and in the MAC Layer of a WiMAX

Mobile Station. Errors may occur, for example, during the ranging process or a connection

may drop completely.

Figure#4.6: Network Entry Process.

Page# 51

4.5 Modulation and Coding Supported In WiMAX

WiMAX supports a variety of modulation and coding schemes and allows for 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 and downlink and assign a modulation and coding

scheme that maximizes the throughput for the available signal-to-noise ratio.

Adaptive modulation and coding significantly increases the overall system capacity, as it

allows real-time trade-off between throughput and robustness on each link. The table given

below summarizes the modulation and coding scheme supported in WiMAX.

Table#4.1: Modulation and Coding Supported in WiMAX

Downlink Uplink

Modulation

BPSK, QPSK, 16 QAM, 64

QAM; BPSK optional for

OFDMA-PHY

BPSK, QPSK, 16 QAM; 64

QAM optional

Coding

Mandatory:

convolution codes at rate

1/2, 2/3, 3/4, 5/6

Optional:

convolution 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:

convolution codes at rate

1/2, 2/3, 3/4, 5/6

Optional:

convolution turbo codes at

rate 1/2, 2/3, 3/4, 5/6;

repetition codes at rate

1/2, 1/3, 1/6, LDPC

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4.6 PHY-Layer Data Rate at Various Channel Bandwidths and Modulation Scheme

As the physical layer of WiMAX is quite flexible, so that data rate varies based on the

operating parameters such as channel bandwidth, the modulation and coding scheme used.

Other parameters, such as number of sub-channels, OFDM guard time, and oversampling

rate, also have an impact.

Table#4.2: PHY-Layer Data Rate at Various Channel Bandwidths

Channel

bandwidth

3.5MHz 1.25MHz 5MHz 10MHz 8.75MHz

PHY mode 256 OFDM 128 OFDMA 512 OFDMA 1,024 OFDMA 1,024 OFDMA

Oversampling 8/7 28/25 28/25 28/25 28/25

Modulation &

Code Rate

PHY-Layer Data Rate in Kbps

DL UL DL UL DL UL DL UL DL UL

BPSK, 1/2 946 326 Not applicable

QPSK, 1/2 1,882 653 504 154 2,520 653 5,040 1,344 4,464 1,120

QPSK, 3/4 2,822 979 756 230 3,780 979 7,560 2,016 6,696 1,680

16 QAM, 1/2 3,763 1,306 1,008 307 5,040 1,306 10,080 2,688 8,928 2,240

16 QAM, 3/4 5,645 1,958 1,512 461 7,560 1,958 15,120 4,032 13,392 3,360

64 QAM, 1/2 5,645 1,958 1,512 461 7,560 1,958 15,120 4,032 13,392 3,360

64 QAM, 2/3 7,526 2,611 2,016 614 10,080 2,611 20,160 5,376 17,856 4,480

64 QAM, 3/4 8,467 2,938 2,268 691 11,340 2,938 22,680 6,048 20,088 5,040

64 QAM, 5/6 9,408 3,264 2,520 768 12,600 3,264 25,200 6,720 22,320 5,600

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Chapter Five

WiMAX Frequency

Utilization, Regulation & Availability 5.1 WiMAX Forum Frequency Allocations

The availability of frequency spectrum is the key to providing BWA. Several frequency

bands can be used for deploying WiMAX including both licensed bands and license-exempt

bands. Each band has unique characteristics that have a significant impact on system

performance. The operating frequency band often says fundamental bounds on achievable

data rates and coverage range.

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. Brief descriptions of these bands are given below;

Licensed 2.5GHz Band: The bands between 2.5GHz and 2.7GHz have been allocated in the

United States, Canada, Mexico, Brazil, and some Southeast Asian countries and is called

Broadband Radio Services (BRS) band. Among all the available bands, this one offers the

most promise for broadband wireless, particularly within the United States. The BRS band

now has 195MHz, including guard bands. Regulations allow a variety of services, including

fixed, portable and mobile services but in many countries, this band is restricted to fixed

applications. But both FDD and TDD operations are allowed. Licenses were issued for eight

22.5MHz slices of this band. A majority of this spectrum in the United States is controlled by

Sprint Nextel, and Clearwire.

Licensed 2.3GHz Band: This band, called the wireless communications services (WCS)

band in the United States and is also available in many other countries such as Australia,

South Korea, and New Zealand. In fact, the WiBro services being deployed in South Korea

uses this band. A major constraint in this spectrum is the tight out-of-band emission

requirements enforced by the FCC to protect the adjacent DARS (digital audio radio

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services) band (2.320GHz to 2.345GHz). This makes broadband services, particularly mobile

services, difficult in the sections of this band closest to the DARS band.

Figure#5.1: Allocated Frequency Band over the World (Source: WiMAX Forum)

Licensed 3.5GHz Band: This is the primary band allocated for FWBA in several countries

over the world. Internationally, the allocated band is in the general vicinity of 3.4GHz to

3.6GHz, with some newer allocation in 3.3GHz to 3.4GHz and 3.6GHz to 3.8GHz. The

available band is usually split into many individual licenses, varying from 2×5MHz to

2×56MHz. The available bandwidth varies from country to country, but it is generally around

200MHz as well as the spectrum aggregation rules. In most countries, the current rules in this

band do not allow for nomadic and mobile broadband applications.

A major constraint in this spectrum is the heavier radio propagation losses at 3.5GHz,

however, is likely to make it more difficult to provide nomadic and mobile services in this

band.

License-exempt 5GHz Band: The license-exempt frequency band 5.25GHz to 5.85GHz is

of interest to WiMAX. This band is generally available worldwide. Being free for anyone to

use, this band could enable grassroots deployments of WiMAX, particularly in underserved,

rural and remote areas at reduced cost. The large bandwidth available may enable operators

to coordinate frequencies and mitigate the interference concerns surrounding the use of

license-exempt bands, particularly in underserved markets. A major constraint in this

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spectrum is the relatively high frequency, coupled with the amount of transmitted power

restrictions in this band imposed by the Governmental regulatory commission, will, however,

make it extremely difficult to provide nomadic or mobile services. Even fixed applications

will, in most cases, require installing external antennas at the subscriber premise. Within the

5GHz band, it is the upper 5.725GHz to 5.850GHz band that is most attractive to WiMAX.

It should be noted that there is another 80MHz of license-exempt spectrum, in the 2.4GHz

band, which could also be used for WiMAX.

5.2 Regulatory Issues

The most important regulatory aspect of WiMAX is the availability and subsequent use of

spectrum. Unlicensed spectrum allows any one to broadcast within certain power limit.

Licensed spectrum protects the broadcaster by giving them special right to broadcast on that

spectrum and can be obtained directly through a national government (Federal

Communications Commission in the US, for example) or via a sub lease from someone who

has obtained spectrum from the national government. The regulation agency is planning a

procedure that allows a simplified and fast assignment of licenses, which can be limited to

regional areas or to other technical parameters. WiMAX efforts are currently focused on test

equipments supporting 256-OFDM physically operating in 2.5GHz, 3.5GHz and 5.8GHz

frequency bands.

5.3 Spectrum Availability

Spectrum congestion is another issue for WiMAX, which is going forward. Spectrum needs

to be available for WiMAX to be successful. Wi-Fi uses spectrum in bands that are

unlicensed in most regions of the world. The situation for WiMAX is much more complex

because of the higher transmit-power levels and the fragmented radio spectrum in both

licensed and unlicensed bands, which differ from country to country.

5.4 Spectrum Interference

WiMAX uses 5MHz channels that sometimes splat all over Wi-Fi and interfere with WLAN

and 3G bands. This issue is a challenge. Moreover in security and emergency services, there

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is no room for signal interference, which calls into question the viability of unlicensed

spectrum, such as 2.4GHz and 5.8GHz. However, vendors are working on technological

solutions (such as smart antennas and multiple-input, multiple-output [MIMO]) and the

Federal Communications Commission (FCC) appears to be readying itself to expand

available spectrum.

5.5 Frequency Reuse

Mobile WiMAX supports frequency reuse of one, i.e. all cells/sectors operate on the same

frequency channel to maximize spectral efficiency. However, due to heavy co-channel

interference (CCI) in frequency reuse one deployment, users at the cell edge may suffer

degradation in connection quality. With Mobile WiMAX, users operate on sub-channels,

which only occupy a small fraction of the whole channel bandwidth; the cell edge

interference problem can be easily addressed by appropriately configuring sub-channel usage

without resorting to traditional frequency planning. In Mobile WiMAX, the flexible sub-

channel reuse is facilitated by sub-channel segmentation and permutation zone. A segment is

a subdivision of the available OFDMA sub-channels (one segment may include all sub-

channels). One segment is used for deploying a single instance of MAC. Permutation Zone is

a number of contiguous OFDMA symbols in DL or UL that use the same permutation. The

DL or UL sub-frame may contain more than one permutation zone as shown in the following

figure.

Figure#5.2: Fractional Frequency Reuse

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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 or

sector operates on the zone with a fraction of all sub-channels available. In Figure 5.2, F1, F2

and F3 represent different sets of sub-channels in the same frequency channel. With this

configuration, the full load frequency reuse one is maintained for center users to maximize

spectral efficiency and fractional frequency reuse is implemented for edge users to assure

edge-user connection quality and throughput. The sub-channel reuse planning can be

dynamically optimized across sectors or cells based on network load and interference

conditions on a frame by frame basis. All the cells and sectors therefore, can operate on the

same frequency channel without the need for frequency planning.

5.6 WiMAX Radio Channel

WiMAX radio channels can be composed of single carrier or multiple carriers. The

bandwidth of WiMAX radio channels can vary from 1.25MHz to 28MHz in steps of

1.75MHz since WiMAX supports scalable bandwidth. A WiMAX system that is using

multicarrier OFDMA, some orthogonal subcarriers have been assigned to a specific user.

Figure#5.3: Illustration of Single and Multi-Carrier

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5.7 Link Budget

A link Budget is the totaling of all the gains and losses acquired in operating a

communication link. In particular balance sheet constituting the link budget provides a

detailed accounting of three broadly defined terms;

Distribution of the resources available to the transmitter and the receiver.

Sources responsible for the destruction of signal strength.

Sources of noise.

Considering all these items together into the link budget, we can evaluate the performance of

a wireless link, which may be an uplink or downlink.

Figure#5.4: Illustration of Link Budget

Calculation of link budget: Ptx + Gtx – Apl + Grx – Am = Prx

Here;

Prx = Received Signal Power in dBm

Ptx = Transmitted Signal Power in dBm

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Gtx = Transmitter antenna gain in dBi

Apl = Path loss in dB

Grx =Receiver antenna gain in dBi

Am = Attenuation (Link Margin, Diffraction Losses, Tree, Wall, Rain, etc)

The figure above illustrates a link budget. It is the equation of the power of a signal

transmitted minus detractions between the transmitter and receiver (Rain, interference from

other broadcasters, vegetation, gain at the antennas of either end) and what signal is received

at the receiver.

Page# 60

Chapter SIX

Backward Compatibility

of WiMAX with Second Generation Network 6.1 Data Access Survey

3rd Generation cellular network is already present in many countries and currently offers a

maximum downlink speed of 384Kbps and a maximum uplink speed of 64Kbps. 2nd

generation service provider (such as GSM service provider) who are willing to provide 3G

like services, can upgrade their 2G network to 3G. But such a type upgrading requires huge

capital investment by the operators and the resulting high monthly subscription fees. So this

is not cost effective solution to implement such a service especially in rural areas where

GSM traffic per cell is already very low. As per as, the surveys conducted by Vodafone in

the United Kingdom showed that voice contributes 80% of the overall revenue structure of

this service, with SMS second at 16%, and data at only 4%. To solve this problem WLAN

over GSM is under consideration.

Wireless data networks on the basis of IEEE 802.16 standards are currently perhaps the most

promising wireless technology. Given their popularity in developed countries, it is practical

to consider the use of wireless access in developing countries as well. Such wireless

technologies can easily be adopted as possible solution for rural and under-served areas by

virtue of ease of set-up, use and maintenance, relatively high bandwidth and relatively low

cost for both users and operators.

The radio part of this system is cost-effective, but an operator has nevertheless to link it to

the rest of a network, which is not only expensive but also problematic. Since the main

problem with WLAN is finding a way to connect the wireless access point to an existing

backbone network. A solution of this problem is to integrate WiMAX with GSM. This

solution would not only boost the usage of GSM access networks in rural areas, but also

enable potential subscribers to gain access to IP services at reduced rates. Moreover, the

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implementation requires a relatively small investment and it could potentially allow a GSM

operator to migrate directly from 2G to 4G in rural areas, thus avoiding the expenses

associated with 3G rollout.

6.2 Different Ways of Integrating a Wireless Network with a Cellular Network

There are essentially two different methods for integration of WLAN and cellular networks,

namely, loose coupling and tight coupling.

6.2.1 Loose Coupling

Loose coupling means integration is performed at the core network level. The cellular

and WLAN access are independent and the IP backbone is simply linked to the cellular

core network. Therefore, the relations between the networks are minimal. Such a type of

network has been successfully implemented by Nokia*. It allows sharing (a) part of the

core network and (b) functionalities like authentication, locating or charging. It also

permits roaming and the use of most of the services offered by the GSM operator. Dual-

purpose WLAN and GSM enabled seamless use of mobile phones on both networks.

Figure#6.1: Loose Coupling

* J. Ala-Laurila, J. Mikkonen, and J. Rinnemaa, Wireless LAN, access network architecture for mobile

operators, IEEE Communications Magazine, vol. 39, no. 11, pp. 82–89, November 2001.

Page# 62

6.2.2 Tight Coupling

Tight coupling means integration of the networks is performed at the access level. In this

case, a unique core network is shared. The WLAN access point can be connected to the

BSC in the case of GSM network. Nevertheless, tight coupling requires a new access

network. For rural areas such transmission links used for access are expensive to install

and will not be optimally utilized. Despite these difficulties, the GSM Abis interface can

be used for this purpose.

Figure#6.2: Tight Coupling.

6.3 WLAN over GSM

The minimum bandwidth of the Abis interface is 2Mbps. In many cases, operators use

cascaded BTS configuration in semirural and rural areas to provide several times the capacity

of an E1 link. This capacity is dedicated to GSM traffic, which can be quite low in many

rural areas. The integration of IP traffic on the Abis interface, providing capacity to a WLAN

network, is a way to improve the utilization of the GSM network in the rural and semirural

areas.

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Two possibilities have been investigated,

sharing the Abis interface and

Overlapping WLAN (based on WiMAX or Wi-Fi) and GSM traffic.

6.3.1 Sharing the Abis Interface

To interface a WLAN with the GSM network, several medications have been

implemented. It seems possible to interface WLAN with GSM without acting on the BSC

or MSC, but in such a case, the interface has to comply strictly with GSM standards,

which complicates implementation.

With only a few medications to the GSM network, a much simpler solution can be

designed. The WLAN can be interfaced with the discontinuous cross connector (DXX),

and the BTS configuration does not need to be modified. As shown in Figure 6.3, a semi-

permanent connection is established through the BSC and MSC. This connection through

the BSC means that a time slot is reserved before and after the BSC and the only task of

the BSC is to copy the time slot received to the time slot transmitted.

Figure#6.3: Modifying GSM Network.

A direct connection can be established between the WLAN interface and the

Interworking Unit (IWU) in the MSC. The IWU can be connected to the Internet through

the fixed network. Its function is to convert cellular traffic to Internet traffic. If such a

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system is used, the WLAN interface is directly connected to the IWU by means of

reserved time slots and then the WLAN interface can establish a connection to the

Internet. Instead of having to respect GSM standard to communicate with the BTS, the

WLAN interface simply has to communicate with IWU, which is much easier.

6.3.2 Overlapping WLAN and GSM Traffic

Multiplexing of GSM/GPRS and Ethernet Traffic on the Abis Interface

To combine GSM traffic with Ethernet traffic (to be used for WiMAX), an E1/Ethernet

multiplexer and a new procedure were developed. The way this work is set out below.

For the E1 input:

If a time slot is used for synchronization (TS0) or signaling, no multiplexing.

If a time slot is used for traffic, multiplexing on the time slot is allowed.

For the Ethernet Input

The Ethernet packets are sent to the transmission buffer. When an Ethernet packet has to

be transmitted, it is divided in four-byte blocks, which should be forwarded on the same

E1 output time slot. If there is an error in the transmission of the Ethernet packet, the

Ethernet packet is sent to the retransmission buffer. A counter is used to verify that the

transmission of each Ethernet packet is complete. For each four-byte block, an identity

byte can be added to maintain the correct order of transmission and to rebuild the

Ethernet packet at the receiving side. For multiplexing, each traffic time slot of the E1

input is monitored. Multiplexing is therefore performed on a time slot by time slot basis.

Since the E1 time slot of the Abis interface is divided into four traffic channels, the

multiplexing process has to check four times whether the Abis time slot to be used is

empty. For these reasons, the Ethernet frame is also transmitted 4 bytes at a time and if an

error occurs during transmission, the full Ethernet packet is sent to the retransmission

buffer to be transmitted again. Note that the acknowledgement of the transmission is not

done at this level, but only at the Ethernet protocol level.

The complete proposed architecture with the protocol stack of the Ethernet transmission

is shown in Figures 6.4 and 6.5.

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Figure#6.4: Description of the complete proposed architecture

Page# 66

Figure#6.5: Protocol Stack of the Ethernet Transmission over the GSM Network.

6.3.3 Simulations, Implementation, and Tests of the Overlapping WLAN and GSM

. Traffic Solution

In The French South African Technical Institute in Electronics (F’SATIE)

Telecommunication laboratory an OMNET C++ simulation of the complete architecture

was done before implementation and testing. The simulations and the tests of the new

architecture have been performed by using Matlab®, Simulink®, (shown in figure#6.6)

OMNET C++®, Cisco® routers, and the developed multiplexer.

Page# 67

Figure#6.6: Simulink Model of the E1/Ethernet Multiplexer.

Page# 68

To implement the algorithm in a real network and to verify the accuracy of the proposed

algorithm, two test multiplexers/demultiplexers were implemented using field

programmable gate array (FPGA) technology with four E1 ports and the Ethernet port on

the input and four E1 ports as outputs. The complete state diagram for multiplexing is

given in Figure 6.7.

Figure#6.7: Multiplexing State Diagram

Page# 69

In the state diagram the abbreviations used are noted below.

Sync: Synchronization of the E1 line with the time slot 0

Send: Check if Ethernet packets are received on the Ethernet port

TxD: Transmission data to the E1 output port

RxD: Reception data on the E1 input port

ZD: Zero detector

Addr: Address

Txcnt: Transmission counter (2 bit counter)

Rxcnt: Reception counter (2 bit counter)

PZD: Previous zero detector

L: Counter of byte for the Ethernet transmission

Len: Length of the Ethernet packet

Ercnt: Error counters

Start: Check if data are received on the demultiplexer.

Explanations of the state diagram at different states are as the following;

1. IDLE: It synchronizes with the E1 line. If nothing is received on the Ethernet port,

the data coming from the E1 input port are transmitted to the E1 output port. As an

exception, if the value (1111 1111), corresponding to the hexadecimal value (FF) is

received, the value (1111 1110) corresponding to the hexadecimal value (FE) is

transmitted.

2. SEND: It is used when Ethernet packets have to be transmitted (send=1). The zero

detector checks if the E1 time slot is empty during four consecutive frames. As there

are four traffic channels per time slot on the GSM Abis interface, the zero detector

checks whether each of the traffic channels are empty. If there is traffic on the E1

input port, this traffic is sent to the E1 output port. If there is no traffic on the E1 input

port, the value (FF) is transmitted on the E1 output port and the transmission counter

txcnt is set to zero.

3. TX4Z, WRITE, and READ: These three states allow the transmission of 4 bytes of

an Ethernet packet on the E1 output port. The counter txcnt is incremented for each

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transmission of a byte. When it reaches the value (11), corresponding to txcnt(2)=‘1’,

the next state diagram is entered.

4. INCRL: It checks if there is still nothing received on the E1 input port with the

previous zero detector. PZD periodically checks the content of each of the four traffic

channels allocated to one E1 time slot in the Abis interface. If there is no transmission

on the E1, L is incremented and the transmission of the Ethernet packet continues on.

Moreover, L is set to zero, the Ethernet packet has to be retransmitted and Ercount

counter is incremented. If the value of Ercount reaches a preset value, the Ethernet

packet is forwarded to another E1 time slot. If the value of Ercount stays more than 0

for a set period of time (30 ms for example), the Ethernet packet is also sent to

another E1 time slot.

5. FINAL: This state is reached when an Ethernet packet has been completely

transmitted (L & “11’’= Len). It allows the transmission of Ethernet packets with a

fixed length by using an Ethernet bridge at the Ethernet input and by setting Len to a

specific value or for transmitting Ethernet packets with variable length. The Ethernet

bridge preserves the processing capacity of the FPGA. It can facilitate the hardware

implementation and decreases the retransmission rate, which occurs when large

Ethernet packets are transmitted. In fact, the size of an Ethernet packet is variable and

always a multiple of 4 bytes. When the packet is completely transmitted, the byte (00)

is sent to indicate the end of an Ethernet packet to the receiver.

The complete architecture has also been simulated with OMNET++. (Shown in Fig #6.8)

The GSM and Ethernet data coming from the WiMAX are collected on the BTS and

forwarded through the multiplexer. Data are delivered via E1 links to the demultiplexer

of the BSC. The Ethernet data exit the BSC via a semi-permanent connection, acting as a

transparent link to connect a Cisco router. Frame relay over E1 connectivity is established

between the two routers as on the Gb interface of the GPRS network. The subsequent

tasks are divided into three steps.

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Figure#6.8: OMNET++® Model of the Complete Proposed Architecture.

First, Frame relay connectivity between the two routers is established.

Next, The multiplexers are linked to the routers with E1 and provide priority to GSM or

GPRS traffic.

Finally, GSM and Ethernet traffic is supplied to the routers.

The integration of the GPRS interworking function (GIF) at the BSC level, as well as the

WLAN adaptation function (WAF) (shown in Figure#6.9) could allow a customer to use

WLAN network when it is available and the GSM/GPRS otherwise.

Traditionally, the integration of cellular and WLAN networks takes place in the switching

system part. This study proposed integration at a lower level, utilizing unused capacity on the

Abis links of the GSM network to provide basic services at an affordable cost.

Naturally, the blockage created by the Abis interface is a limitation. This interface only

provides several Mbps of capacity, whereas a WiMAX or Wi-Fi system can deliver more

than 10Mbps per user. However, this work demonstrated that by introducing a new

procedure, it was possible to transmit WLAN traffic on the Abis interface by adding a

multiplexer developed and patented for this purpose and that up to 70% of the Abis capacity

could be reallocated for Ethernet traffic (carrying services like Internet). For a typical Abis

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interface, with four E1s correctly configured, up to 5.6Mbps could be shared between

different users. It is not enough to provide broadband services, but compared to <22Kbps

commonly available for a fixed line dial-up, it could allow for the simultaneous connection of

250 users. 20Kbps are enough for checking emails, to connect to Internet and even to run a

VoIP service.

Figure#6.9: Protocol Stack for Combined Cellular, WLAN Application.

The mobile station (MS) then supports two radio subsystems for transporting GPRS signaling

and user data. The first interface is implemented with the GPRS-specific RLC/MAC and

physical layers, whereas the second is implemented with the 802.11/802.16-specific MAC

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and physical layers. These two interfaces provide two alternative means for transporting LLC

packet data units (PDUs). Typically, when the MS is outside a WLAN area, LLC PDUs are

transmitted over the GPRS interface (Um). However, when the mobile enters a WLAN area,

LLC PDUs are transmitted over the WLAN interface. This switching is performed with the

aid of WAF and could be completely transparent to the user and to upper GPRS layers. This

kind of architecture could allow basic 4G services.

Page# 74

Chapter Seven WiMAX Status over the World

7.1 Current WiMAX Status over the World

From the time it first introduced, WiMAX demand is constantly raising. More than 360

companies are working for WiMAX to take this technology ahead. Many operators have

taken WiMAX to serve wireless broad band services as a solution. In this chapter, current

WiMAX status over the world is briefly discussed.

Table# 7.1: Some Current WiMAX Operators & Service Deployments

Operator Location WiMAX activities Always On Network Bangladesh

Bangladesh WiMAX network plans to deliver free Internet access to Bangladesh primary schools and colleges, as well as broadband services to underserved rural and urban areas

Bharat Sanchar Nigam Ltd. (BSNL)

India Spend up to $750 million on mobile WiMAX network in India, covering both urban and rural areas. Initial services in late 2008 or early 2009 for broadband and voice. the other applications will follow.

Clear wire / Sprint Nextel

USA Plans to cover 120–140 million people by the end of 2010. First services in some city areas from existing nonmerged companies due late 2008.

Digital Bridge Communications

USA Deploying WiMAX broadband services to small and medium-sized communities of up to 150,000 people nationwide. First service in Rexburg, Idaho, in 2007; 12 cities covered by April 2008. Mobile services introduced in Jackson, Wyoming, in June 2008.

Enforta Russia Small office, home office, or business communications services offered by a mix of technologies, including WiMAX and pre-WiMAX, in a network rollout that reached 32 cities by the end of 2007.

Ertach Argentina Argentina 8002.16e WiMAX trial in the city of Rosario,

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targeting SME and corporate users with primary fixed and nomadic broadband services, high-speed internet and advanced voice services.

lliad France Trials in 2007. Mipps Canada Trials of fixed broadband wireless access in

2007 Personal Paraguay Network completed in Asuncion and Great

Asuncion in 2007, with continuing national rollout, offering business and residential services.

Primus Canada Trials of 802.16e broadband wireless access in 2007

Summa Telecom Russia Plans to build a nationwide WiMAX network that will cover some 330 cities by 2010 with fixed and later mobile broadband services.

Telekom Slovenije Slovenia WiMAX trials began in 2007. Unwired Group Australia Pre-WiMAX ISP to deploy 802.16e mobile

WiMAX. Warid Uganda Deploying IMS/WiMAX network to support

advanced services. WiMAX Telecom Austria,

Germany, Switzerland, Slovakia, Croatia

Deploying 802.16d and 802.16e WiMAX networks mainly for residential broadband Internet and VoIP since 2005. Currently expanding in Croatia (initially the areas of Split and Osijek followed by other regions) and Switzerland. Plans advanced multimedia services.

Most of these deployments were announced or became operational during 2007 and 2008. Many of the recent ones use the so called 802.16e standard. Even if only fixed or nomadic services are currently offered. Source: Light Reading, 2008.

7.2 Current WiMAX News

7.2.1 O3b Links with Google for Fast Satellite Internet Capacity

Tuesday, September 09, 2008

Satellite Company O3b Networks has linked up with Google and other investors to bring

cheaper, high-speed wireless Internet access to areas unlikely to see investments in fiber

infrastructure. O3b stands for "other 3 billion," a reference to the world's population that

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still can't access the Internet. O3b, which is based in the U.K.'s Channel Islands, said

construction is under way on 16 satellites that will drop the cost for ISPs and operators to

provide Internet access over 3G and WiMAX networks.

7.2.2 Intel Invests In WiMAX Provider Aicent

Friday, September 05, 2008

Intel's investment arm Intel capital has invested in data network services provider Aicent

to accelerate its 3G and 4G global data roaming initiatives and WiMAX deployment.

Aicent provides data network, messaging and roaming applications to 100 GSM and

CDMA mobile operators, serving approximately 1 billion mobile subscribers. The

company, which operates one of the largest multimedia messaging exchanges, competes

with Syniverse and VeriSign. Aicent said it will use the investment to drive WiMAX

ecosystem development and service deployment worldwide.

7.2.3 Samsung Builds Russian WiMAX Network. Martyn Williams, IDG News

Tuesday, September 02, 2008 8:00 PM PDT

Samsung Electronics has built a WiMAX network in the Russian cities of Moscow and

St. Petersburg for local operator Startel, it said Tuesday.

The network operates in the 2.5GHz to 2.7GHz frequency range and will cover about 20

million people by the end of the year, said Samsung. Startel plans to expand it to other

cities across Russia using Samsung equipment, the South Korean electronics maker said.

Samsung has provided 1,600 base stations to Startel for the network, it said.

Samsung has previously won WiMAX network equipment contracts in several countries

including Brazil, Croatia, the U.S. and Venezuela.

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7.2.4 Intel set to introduce sub-$400 WiMAX laptop

By Michael Schwartz, 03 Sep 2008 00:00 GMT+1

News, WiMAX, Computers, Education, Digital Divide, India, Asia-Pacific:

India's Business Standard and Economic Times have both recently investigated claims by

Intel that it can help provide India with WiMAX-enabled laptops for under US$400, if

not for as little as US$300. Source of the claim is Intel India's newly appointed Managing

Director for its WiMAX Division, C S Rao. Mr Rao stated: "Intel believes a WiMAX-

ready laptop could be available in the Indian market at around US$300 - US$400 dollars

in a few months."

In turn Intel is confident that around 8% of these new subscribers will be attracted to

WiMAX. Intel itself is leading into specifically WiMAX-oriented products, eg, Mobile

Internet Devices (MIDs), USB variants, and other types of WiMAX notebook.

7.2.5 Megafon Launches WiMAX Network

Russia's third largest mobile operator, MegaFon, started commercial service over a large

scale WiMAX network in the Samara region. The WiMAX network covers a total

population of over 32 million as well as businesses in a 2,500 sqkm region. It operates in

a wide frequency range -5.150GHz to 6.080GHz and in different channel sizes: 5MHz,

10MHz, and 20MHz. MegaFon began testing WiMAX in 2006 and now with its large-

scale launch in the Samara region the mobile operator is contributing to a burgeoning

WiMAX market in the country’s regions outside Moscow and St. Petersburg. The two

most ambitious WiMAX players in Russia are Enforta and Synterra. Enforta has already

announced plans to have WiMAX operational in 65 cities by the end of the year,

primarily in the 5.2GHz frequency band. Synterra plans to build "mini" 802.16e mobile

WiMAX networks in 1,000 towns and cities where it has 2.5 - 2.7GHz spectrum rights.

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7.3 WiMAX in Bangladesh

7.3.1 ISPs urge govt. to open WiMAX to Bangladesh Firms

Tue, Jul 8th, 2008 7:21 pm BDST

Dhaka, July 8 (bdnews24.com) -Internet service providers Tuesday asked the government

to open up WiMAX licensing to the Bangladeshi organizations which will qualify on

merit.

Bangladesh Telecommunication Regulatory Commission will provide three licenses for

WiMAX through bidding, with floor prices for each at Tk25 crore in acquisition fees

which will increase thanks to the bidding.

“So, local ISPs will probably lag behind in the bidding. We ask BTRC to issue licenses to

local companies on the basis of qualifications,” ISP Association of Bangladesh said in a

statement.

In a press conference at Dhaka Sheraton Hotel, ISPAB general secretary Russell T

Ahmed spoke of “contradictory telecoms policies”.

The government’s ILDTS (International Long Distance Telecommunication Services)

policy bars any foreign investment, but the draft WiMAX policy leaves scope for foreign

investors with up to 60 percent stakes in entities to bid for WiMAX licenses, Ahmed said,

“This is a contradictory policy.”

Ahmed suggested an arrangement where the government can evaluate ISPs’ business

plans on WiMAX technology to issue licenses on merit.

A higher licenses acquisition fee will create pressure on consumers, Ahmed said; “Which

means it will not be possible to lower internet charge for end users.” added the ISP

association leader.

On “unlicensed or illegal” ISPs mainly catering to home-users, Ahmed said there are

more than 500 such providers operating across the country.

Page# 79

“We are not against them. But since they are liable to none, they do not maintain the

quality of services. The government is not getting revenues from their businesses either.”

Recognizing contributions by unlicensed ISPs, Ahmed said such operators should be

brought under a regulatory framework.

On call-centre operations, the ISPAB leader said the government has barred call centers

from operating through regular internet connections and made IPLC (International

Private Leased Circuit) connections mandatory for them.

“An IPLC connection is very expensive and requires being a client of foreign gateway

service providers. For instance, if someone runs a call centre of a British company then

he would have to buy services from companies like Telstra,” Ahmed explained.

ISPAB president MA Salam told the reporters that, “through the government opened up

VoIP business through licensing, the process of granting licenses for IP telephony was

delayed for some unknown reason”

7.3.2 Huawei in talks with Warid; Banglalink rejects WiMAX (Bangladesh)

June 6th, 2008

Fresh from securing a network expansion contract with Grameen Phone Ltd, Huawei has

announced that it is negotiating with Warid, Bangladesh’s four largest mobile operators

by subscribers, reports local newspaper The Daily Star. ‘We are in talks to sign a deal

with Warid. But some time is required to complete the deal,’ said an official of Huawei.

Meanwhile, in separate but related news, during his visit to Dhaka last month, Naguib

Sawiris, chairman of Orascom Telecom Holding (OTH), said Banglalink is committed to

3G W-CDMA rather than WiMAX. “We will stick to 3G. Because, we believe, it is the

continuation of GSM. It’s much easier for us to upgrade our technology by adopting 3G

rather than WiMAX” he said.

Page# 80

7.3.3 WiMAX to Reduce Digital Gap between Rural and Urban Bangladesh

Introduction of WiMAX would have a synergetic effect on rural Bangladesh, an

emerging market for the technology, Bangladesh Telecommunications Regulatory

Commission (BTRC) experts and leading international vendors said at a meeting here last

week.

BTRC, the telecom watchdog, announced in the two day meet that it would issue

WiMAX license this year.

Experts from Alcatel-Lucent, Cisco, Huawei, Intel, Motorola, Nokia and Siemens in the

city to explore the business prospects of WiMAX, attended the meet.

WiMAX or the Worldwide Interoperability for Microwave Access is a

telecommunications technology for providing wireless data across long distances through

point-to-point links, with full access to mobile phones.

The WiMAX service, reaching Bangladesh rather late, will draw about 10,000 users by

the end of 2008 and over 200,000 by the end of 2010.

WiMAX is replacing traditional phone technologies across the world the experts said at

the meet.

BTRC Chief Major General (Retd) Manzurul Alam said WiMAX will definitely unleash

the Internet, creating a new optimism for Bangladesh. Being a densely populated country

the technology is expected to prove better results to Bangladesh than many western

countries, he added.

Dr. M. Zafar iqbal of Shahjajal University of Science and Technology in his presentation

explained WiMAX as a dynamic provider of communication to link distant places, how it

works, and the position of Bangladesh in the global information distant places, how it

works, and the position of Bangladesh in the global information super highway network.

WiMAX, he expects, would be able to bridge the gap of existing digital divide and

requested the regulators to ensure that it does not become a monopoly business.

Page# 81

WiMAX 30 times faster than 3G mobile technology and 100 times faster than wireless

data rates, can solve the problems of rural connectivity. WiMAX can replace GSM and

CDMA cellular phone technologies, or increase capacity, used as a layover. It has been

used as a wireless backhaul technology for 2G, 3G, and 4G networks in both developed

and developing countries.

As Bangladesh’s Telecom Industry is booming with a growing middle-class, experts

expect a big demand for broadband wireless services and WiMAX. Bangladesh will have

around 12 million WiMAX subscribers by 2012, they expect.

7.4 Companies Involved In WIMAX Implementation

Intel is a leader in promoting WiMAX and has developed its own chipset. However, it is

notable that most of the major semiconductor companies have to date been more cautious of

involvement and most of the solutions come from specialist smaller or start-up suppliers. For

the client-side these include GCT, Altair, Beceem, GCI, Runcom, Motorola with TI,

NextWave, Sequans, Redpine signals, Wavesatand a number of others. Both Sequans and

Wavesat manufacture solutions for both clients and network while TI, DesignArt and

PicoChip are focused on WiMAX chipsets for base stations. In addition to Cisco Systems,

ClearWire (Partnering with Sprint in the U.S), Juniper, Time Warner Cable, Ericsson, Nortel

are working also for WiMAX.

7.5 Available WiMAX Devices and Components

The market applications of WiMAX can be classified into two types. The first type is the

indoor fixed terminal based on 802.16e that can be installed by users themselves, like

customer premise equipment (CPE), PCMCIA and the USB modem. This type of access

service can be provided for both enterprise and household users.

The second type is the laptop computer with built-in chips based on 802.16e, like the MID,

UMPC, PDA, and multi-mode cell phones. This type of mobile broadband data service is

aimed at individual users.

(a) PDA N800 (Source:

NOKIA)

Figure

Samsung's mobile WiMAX phone

wireless broadband converged services delivered from a single IP

Samsung can handle broadcasting, home networking, videoconferenc

more.

7.6 Cost Estimation of WiMAX

WiMAX costs less to deploy than any other broadband technology. For service providers

using an expensive landline technology

an investment in many billions of dollars t

WiMAX operator could enter the market and far less capital expenditure (CAPEX)

wireless.

Table#7.2 summarizes the cost comparison of the popular broadband services.

Table#7.2 Cost Comparison of the Popular Broadband Ser

Broadband Technology

Digital Subscriber Line

Cable

Page# 82

(b) Notebook & PC Integration (Source: Intel)

(c) Samsung's WiMAX phone handset Samsung)

Figure#7.1: WiMAX Enabled Devices

Samsung's mobile WiMAX phone (As shown in the figure#7.1c), the M8000, provides

wireless broadband converged services delivered from a single IP-based network. The

Samsung can handle broadcasting, home networking, videoconferencing, video on demand &

7.6 Cost Estimation of WiMAX


using an expensive landline technology like Fiber to The Home (FTTH) or cable is that after

y billions of dollars the will be able to serve one small region.

WiMAX operator could enter the market and far less capital expenditure (CAPEX)

summarizes the cost comparison of the popular broadband services.

st Comparison of the Popular Broadband Services

Installed BS/CAPEX Cost/Home Passed

$270 Bn $30-$50 1

$65 Bn $1,200 1

Samsung's WiMAX phone handset (Source:

Samsung)

, the M8000, provides

based network. The

ing, video on demand &


Fiber to The Home (FTTH) or cable is that after

he will be able to serve one small region. A

WiMAX operator could enter the market and far less capital expenditure (CAPEX) as being

summarizes the cost comparison of the popular broadband services.

Cost/Home Passed

Page# 83

2/2.5/3G $405 Bn $502

Fiber to the home (FTTH) $93 Bn (estimated) $1,250

WiMAX $3 Bn (estimated) $8 3

Sources: (1) Hal Varian University of California and Robert Litan, Brookings Institute (2004)

(2) Morgan Stanley 2004

(3) Business Week 04/06/05 + Cahners + Kevin Suitor, Redline Communications

Figure#7.2: Cost Estimation of WiMAX (Source: Forrester Research Inc)

Figure#7.2 indicates that cost of CPE is reduced over time and by the end of 2012, a

WiMAX enabled CPE will get at 10-15 US dollar only.

Page# 84

Chapter Eight

Conclusion

WiMAX is a very interesting new development in the area of wireless broadband access. It is

expected to be deployed by different kinds of network operators using different business

models; wireless Internet service providers, cellular service provider, DSL (Digital

Subscriber Line) operators, cable television company.

WiMAX is going to have a far bigger impact than we have seen from the cellular phone

services in the past 15 years. Most of the hot applications like streaming video, video over

Internet, voice over Internet, online gaming, IPTV and other multimedia services require

high-speed access and WiMAX is the promising technology that can fulfill all of those

demands. So it may be expected that, in the next decade those who control the WiMAX

highways will become the next giants of our wireless industry.

Technologically, WiMAX shows a lot of promise. In matters of throughput, it opens the door

to numerous services and in time, the use of single terminal will centralize all of our

communication tools. Its capacity in covering "the last kilometer" is particularly attractive to

France Telecom's R&D, which is actively working on providing broadband coverage to 90%

of the metropolitan population.

WiMAX offers fast deployment and a cost-effective solution to the last-mile wireless

connection problem in metropolitan areas and underserved rural areas. This is an ideal

complement to cable networks and on a planetary scale, developing countries are the ones

that could take the advantage of this efficient and initially less costly technology to infuse

new growth in their economies.

Recently, significant effort has been dedicated within the IEEE standard body to develop new

802.16j and 802.16m amendments in order to support multiple hop relay operation and to

meet the requirements of 4G IMT-Advanced Mobile Networks. The multiple hop nature of

the IEEE 802.16j entails numerous design challenges, ranging from OFDMA frame structure

design to traffic forwarding and path management. Moreover, in order to support 1 Gbps

Page# 85

data rate in low mobility applications and 100Mbps in high-speed mobility applications

aimed at by 4G, a wide spectrum of physical layer and Medium Access Control (MAC) layer

innovations need to be introduced. Other issues such as regulation, spectrum management,

application innovation and economic model for WiMAX deployment for 4G all deserve

thorough discussion and investigation.

Finally, we have seen that, WiMAX has a large number of mechanisms and is expected to be

used for many applications. The near future will tell us which of these mechanisms will be

implemented, and how they will be implemented.

Page# 86

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Documents

Study of Wimax for Future Mobile Communication-part two