Paper Title (use style: paper title) - ER Publications · Web viewThe paper also highlights detail insight about OFDM technology and our modem design using MATLAB.. Keywords: SDR;

International Journal of Enhanced Research Publications, ISSN: XXXX-XXXXVol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com

A Commincation Modem Designing based on Software Defined Radio for Satellite Cross link

Farrukh Shah1, Tariq Jameel2, Syed Naveed Jaffri3

1 Lecturer , Department of Electrical Engineering Comsats Lahore Pakistan 2Associate Professor, Department of Computer Science, Muet Jamshoro, Pakistan 3Associate Professor, Department of Computer Science, Muet Jamshoro, Pakistan

Abstract: There is a rapid growth in recent methods of information sharing in modern systems which include voice, data, broadcast, video, command and control, emergency responses, indoors and out-door communications. The robust modification of existing radio devices and cost effectiveness has become critical from business perception. Software Defined Radio (SDR) introduces flexibility, power and cost efficiency at an open platform to integrate multiple standards. SDRs are reconfigurable radios. Current developments and enhancements in SDR domain have opened new doors in the field of satellite communication. Current efforts include development of SDR controlled ground stations, network ground station operation for increased efficiency. This paper presents state of art technology for design of the reconfigurable radio in the form of SDR for satellite communication links. For communication aspect Orthogonal Frequency Division Multiplexing (OFDM) modem is designed and embedded on TITMS320C6713 DSK board to realize true hardware radio designing aspect for the satellite link. The paper also highlights detail insight about OFDM technology and our modem design using MATLAB.

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Keywords: SDR; OFDM Matlab, TITMS320C6713 DSP kit, Real Time Work Shop, Code composer studio (CCS), General Purpose Display (GPD)

1. Introduction

In today’s technological development era, Radio technology is continuing to shift towards programmable radios which can be upgraded and reconfigured via software to adopt environmental changes having new protocols and frequency bands. These adoptive radios are called as Software Defined Radio (SDR). The term SDR was coined by Joseph Mitola in 1991 [1]. The ways in which people need to communicate via voice communication, broadcasting, control communication need the modification of radio devices cost affectivity and easily. One can bring flexibility, cost efficiency and power efficiency by the use of SDR. SDR can be trivially defined as following; “The Radio in which some or all of the physical layer functions are software defined [2].”The purpose of SDR is to provide single radio unit which can operate on various wireless and mobile standards only by modifying software [2,3].The aim of next generation wireless communication system is to integrate existing technologies such as Wireless Local Area Network (WLAN), Global System for mobile communication (GSM), Blue tooth and others. The next generation systems are aiming to have single radio system that will be capable to accommodate different standards of wireless and can operate on various bands of frequencies [3]. In terms of system architecture, SDR system eliminated the need of intermediate frequency section and put base band unit close enough to Radio Frequency unit. This type of system will be compact in size and more powerful to handle multiple standards [6].The simplest form of SDR architecture is shown in figure 1

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Fig. 1 SDR system architecture [2]

The rest of the paper consist the followings; Section II discusses SDR for Satellite communication OFDM model is presented in section III. Section IV presents satellite cross link aspects of OFDM, section V testing the communication system for binary and text data, VI present BER computation of communication system and finally VII concludes the paper.

2. SDR for Satellite Communication

SDR platform has been the subject of development and research in satellite communication. SDR systems have requirements for operating in an adversarial spectrum environment. There can be significant constraints on size weight and power available to the RF subsystem to provide needed capabilities for satellite communication. A numbers of authors have proposed the use of SDR system technology for dealing jamming and adversarial conditions in the recent year [8]. To reduce power, size and weight there are two ways , either direct reduction keeping performance of subsystem constant or by providing enhance performance (e-g multi mission capability with in a constant size, weight and power target [9].There are number of challenges faced by space environment which are not present in air and or terrestrial applications. Space based research and development have been initiated by National Aeronautics and Space Administration (NASA) [9] and by the US Naval Research Laboratory [10]. Air Force Research Laboratory. (AFRL) space vehicles directorate has started a research, development and application of SDR to the problems of satellite communication including satellite commanding satellite cross-links and traditional space-based relay [10]. With the help of SDR one can design reconfigurable radio system for satellite communication. The radio system can be used to implement new technologies while replacing existing technology to meet current standard demand. This will be cost effective and flexible.

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3. OFDM FOR NEXT GENERATION COMMUNICATION

OFDM for next generation Communication The rapid pervasion of mobile telephony and equally growth of voice, data and video communication over the Internet, justify the great expectation for next generation communication. Wireless Broadband Multimedia Communication Systems (WBMCS) are now under consideration [11]. The next generation WBMCS system may be able to integrate variety of functions and able to support many applications. WBMCS is required to provide its users high data rates. To support high such high data rates choosing of suitable modulation technique is required [12]. OFDM seems to be a suitable modulation technique for WBMCS systems. OFDM is being used as a powerful modulation technique in wireless air interface standards such as Institute of Electrical and Electronics Engineers IEEE 801.11/Wireless fidelity (WIFI), IEEE 802.16/ World Wide Interoperability for Microwave Access (WiMax) and Digital Video Broadcast-Terrestrial DVB-T [12]. OFDM is also applied in satellite and military applications [13]. OFDM has been exploited in Joint Terminal Engineering office research JTEO‘s research effort for identifying the optimal air-interface MILSATCOM networks via Wideband Global Satcom (WGS) system [14].OFDM is a kind of multi-carrier transmission scheme which splits single stream of data into number of low data rate subcarriers. OFDM is a modulation as well as multiplexing technique. OFDM effectively removes the problem of Intersymbol interference ISI which occurs due to the frequency selective fading FSF. There is a bank of orthogonal subcarriers in OFDM that are modulated by using Quadrature Amplitude modulation (QAM) or phase shift keying (PSK). If ai+Ns/2 are the complex QAM symbols, Ns is the number of the sub carrier , T the symbol duration and Fc is carrier frequency at t = ts can be written as ,

m ( t )=ℜ{ ∑i=N s

N ss −1

aᵢ exp¿¿¿ ts ≤ t ≤ t + T (1)

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m(t) = o ts < t ts and t > ts +T

Figure shows the operation of OFDM modulator in a block diagram

Fig. 2 OFDM modulatorFigure shows OFDM signal subcarrier. The subcarriers have the same phase and amplitude for all subcarriers the result of integration would become zero because the frequency difference (i-j)/T produces an integer number of cycle with in the integration interval T.

∫ts

ts+T

∑i=N s

N ss −1

aᵢexp¿¿¿¿dt (2)

The eq (01) of OFDM signal is the Inverse Fast Fourier Transform (IFFT) of Ns QAM input symbols. OFDM makes use ot FFT/IFFT algorithm for computations.. The FFT/IFFT drastically reduces amount of calculation [13]. As with large number of subcarrier the IDFT complexity grows quadratically with N while with IFFT complexity only grows slightly faster than linear.

m (t )=∑i=0

N−1

aᵢexp ( jπ ¿N

) (3)

Fig . 03 OFDM subcarriers

4. Communication Modem Designing for Satellite Cross Link

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The satellite downlink transceiver is designed in this work which uses OFDM as a modulation technique for communication. The work has been divided in the following phases

1) Designing of Satellite communication system which incorporated OFDM. 2) Testing the communication system for binary and text data. 3) BER f computation of Communication system.4) Embedding the Communication system onto C6713DSK board to realize real time simulation.

A. Designing of Satellite communication system which incorporated OFDM

The following figure shows Satellite downlink transmitter and receiver respectively

While running the simulation , double -click on the blocks to open or close scopes

Tx DishAntenna Gain

-K-Rectangular16 -QAM

RandomInteger

Raised CosineTransmit Filter

Normal

OFDMTransmitter

High PowerAmplifier

CubicPolynomial

DownlinkPath

Free SpacePath Loss196 dB

Doppler andPhase Error

Phase/Frequency

Offset

Fig. 4 Satellite downlink system transmitter

Select AGC

MagnitudeAGC

Satellite ReceiverSystem Temp

NoiseTemperature

20 KRx Dish

Antenna Gain

-K-Rectangular16 -QAM

Raised CosineReceive Filter

Normal

PhaseNoise

PhaseNoise OFDM

ReceiverpilotsDoppler and Phase

Compensation

Phase /Frequency

Offset

Fig. 5 Satellite downlink system Receiver

Transmitted Signal

Rectangular QAMModulatorBaseband

Rectangular256 -QAM

OFDMTransmitter

Multipath RayleighFading Channel

RayleighFading

ConvolutionalEncoder

ConvolutionalEncoder

Bernoulli RandomBinary Generator

BernoulliBinary

Fig. 6 OFDM transmitter

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Out1

Zero pad for OFDM

Zero padfor OFDM

Unipolar toBipolar

Converter

PN SequenceGenerator

PN SequenceGenerator

MultiportSelector

SelectRows

MatrixConcatenation

1

IFFT

IFFT

-1

0+0i

Add CyclicPrefix

U YIn1

Fig. 7 OFDM carrier generation

Viterbi Decoder

Viterbi Decoder

Unipolar to Bipolar

Unipolarto Bipolar

Rectangular QAMDemodulator

Baseband

Rectangular256 -QAM OFDM

Receiverpilots

Denormalize

Fig. 8 OFDM receiver

Remove CyclicPrefix

U Y

Remove zero -padding

andreorder

U Y

Frame Conversion

ToFrame

FFT

FFT Received signal

1

Fig. 9 OFDM receiver operation

The figure shows power spectrum of Satellite downlink system

Fig. 10 Power spectrum of the Satellite modem

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The figure shows spectrum of OFDM modem

Fig. 11. Frequency response of OFDM modem

5. Testing the communication system for binary and text data

The following bits are transmitted and received via Communication modem successfully

1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 0 1 0 1 0 1 1 0 1 1 1 1 0

The received bits on receiver side are

0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 0 1 0 1 0 1 1 0 1 1 1 1 0

In case of Rayleigh channel the transmitted and received bits are

0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 0 1 0 1 0 1 1 0 1 1 1 1 0

The received bits on receiver side are

0 1 0 1 1 1 1 1 0 1 0 1 1 1 1 1 0 1 1 0 1 0 1 0 1 1 0 1 1 1 1 0

In order to send text first it needs to be converted into binary numbers 01100011011011110110110101101101011101010110111001101001011000110110000101110100011010010110111101101110

After setting the configuration the same “Communication” was received at the receiver side

01100011011011110110110101101101011101010110111001101001011000110110000101110100011010010110111101101110

nam =Communication “Received”

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6. BER computation of Communication system

The following graph shows BER of the Satellite commuincation system and OFDM modem

Fig. 12 BER of 16 QAM for satellite Down link modem

Fig. 13 BER of 256 QAM OFDM modem for satellite Down link modem

Next target was to Embedding the Communication system onto C6713DSK board to realize real time simulation In order to embed the whole OFDM modem onto DSK board Matlab Real Time workshop is used and to configure the channel between PC and DSK board General Purpose Display(GPD) is used. The Matlab Real-Time Workshop generated the C codes of the whole OFDM modem and downloaded onto the targeted DSP kit. The next step is to retrieve those bits from the DSP kit into the Matlab. For this purpose RTDX is to be established between PC and DSP kit.

After configuring the output channel following bits are received in MATLAB

0 1 0 1 0 0 1 1 1 0 0 0 1 0 0 1

These are same as at the OFDM modem processing onto the DSP kit.

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After successfully processing bits the OFDM modem is tested to send and process text. The same procedure is applied to retrieve text from DSP kit as it is in the case of binary data. After configuring the output channel the text “Communication” is received in the MATLAB. Fig no 09 shows BER of OFDM modem before and after implementation on DSK board. It shows that BER increases when OFDM modem is implemented onto DSK board.

Fig. 14 BER of 256 QAM OFDM modem before and after embedding onto DSK board

Fig. 15. Received power of non SDR and SDR system for Satellite system based on OFDM modem

Figure no 15 shows power level for OFDM modem based on SDR system and non SDR system for satellite system for co and cross polarization. It is evident that SDR system has greater received power level compared to the non SDR

system for satellite cross link. It is because SDRs system can adjust their system parameters according to

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7. Conclusion

This paper presents designing of OFDM modem and its embedding on TITMS320C6713 DSK board to realize a SDR base communication system for satellite cross link. Our work presents designing of reconfigure radio link for satellite cross link communication using Matlab and CCS. The Matlab window provides easy and interactive way of designing communication modem which facilitates the improved OFDM modem. It is also shown that 256 QAM has better performance in terms of BER when OFDM modem is embedded on DSK board to realize true SDR system. Furthermore received power level is also measured for SDR and Non SDR system which shows that Satellite system based on SDR has greater amount of received power.

References

[1]. Luiz Garcia Reis, A.; Barros, A.F.; Gusso Lenzi, K.; Pedroso Meloni, L.G.; Barbin, S.E., Introduction to the Software-defined Radio Approach, Latin America Transactions, IEEE (Revista IEEE America Latina) , vol.10, no.1, pp.1156,1161, Jan. 2012

[2]. Alam, M.Z.; Sobhan, M.A., Spectrum sensing approach of CI/OFDM based software defined radio transceiver in Cognitive Radio (CR), Informatics, Electronics & Vision (ICIEV), 2012 International Conference on , vol., no., pp.258,262, 18-19 May 2012

[3]. Ruolin Zhou; Xue Li; Chakarvarthy, V.; Zhiqiang Wu, Software Defined Radio Implementation of SMSE Based Overlay Cognitive Radio in High Mobility Environment, Global Telecommunications Conference (GLOBECOM 2011), 2011 IEEE , vol., no., pp.1,5, 5-9 Dec. 2011

[4]. Ruolin Zhou; Xue Li; Chakarvarthy, V.; Zhiqiang Wu, Software Defined Radio Implementation of SMSE Based Overlay Cognitive Radio in High Mobility Environment, Global Telecommunications Conference (GLOBECOM 2011), 2011 IEEE , vol., no., pp.1,5, 5-9 Dec. 2011

[5]. Chunxiao Li; Raghunathan, A.; Jha, N.K., An architecture for secure software defined radio, Design, Automation & Test in Europe Conference & Exhibition, 2009. DATE '09. , vol., no., pp.448,453, 20-24 April 2009

[6]. Chunxiao Li; Raghunathan, A.; Jha, N.K., An architecture for secure software defined radio, Design, Automation & Test in Europe Conference & Exhibition, 2009. DATE '09. , vol., no., pp.448,453, 20-24 April 2009

[7]. Dissanayake, S.D.; Armstrong, J., Comparison of ACO-OFDM, DCO-OFDM and ADO-OFDM in IM/DD Systems, Lightwave Technology, Journal of , vol.31, no.7, pp.1063,1072, April1, 2013

[8]. Xue Li; Hong, S.; Chakravarthy, V.D.; Temple, M.; Zhiqiang Wu, Intercarrier Interference Immune Single Carrier OFDM via Magnitude-Keyed Modulation for High Speed Aerial Vehicle Communication, Communications, IEEE Transactions on , vol.61, no.2, pp.658,668, February 2013

[9]. Borkar, N.J.; Bormane, D.S., BER performance of OFDM system with adaptive modulation, Complex Systems (ICCS), 2012 International Conference on , vol., no., pp.1,8, 5-6 Nov. 2012



[12]. Nieto, J.W., An investigation of coded OFDM and CEOFDM waveforms utilizing different modulation schemes on HF channels, Communication Systems, Networks and Digital Signal Processing, 2008. CNSDSP 2008. 6th International Symposium on , vol., no., pp.358,362, 25-25 July 2008

[13]. Abu-alhiga, R.; Haas, H., Subcarrier-index modulation OFDM, Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on , vol., no., pp.177,181, 13-16 Sept. 2009

[14]. Kelley, Brian, Software defined radio for broadband OFDM protocols, Systems, Man and Cybernetics, 2009. SMC 2009. IEEE International Conference on , vol., no., pp.2309,2314, 11-14 Oct. 2009

[15]. Tsugi, T.; Itami, M., A study on adaptive modulation of OFDM under impulsive power line channel, Power Line Communications and Its Applications, 2008. ISPLC 2008. IEEE International Symposium on , vol., no., pp.304,309, 2-4 April 2008

[16]. Maji, P.; Patra, S.K.; Mahapatra, K.K., Design of Fuzzy Logic Controller based on TMS320C6713 DSP, Intelligent Systems Design and Applications (ISDA), 2012 12th International Conference on , vol., no., pp.635,639, 27-29 Nov. 2012.

[17]. Mohammed, M.; Bijoy, K.E., Analysis of digital audio effects using Simulink and C6713 DSK, Innovations in Emerging Technology (NCOIET), 2011 National Conference on , vol., no., 1pp.55,60, 17-18 Feb. 2011

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Paper Title (use style: paper title) - ER Publications · Web viewThe paper also highlights detail insight about OFDM technology and our modem design using MATLAB.. Keywords: SDR;