Performance analysis of Cooperative Communication System based on Decode and Forward Relay System an

IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613

Performance Analysis of Cooperative Communication System based on Decode and Forward Relay System and Adaptive Modulation Dr. Amita Soni1 Krishnananda Basumatary2 1 Assistant Professor 2M.E. Student 1,2 Department of Electronics & Communication Engineering 1,2 PEC University of Technology, Chandigarh, UT, India Abstract— Signal fading is one of the major concerns in wireless communication. Many different ways had been opted till now to mitigate signal fading. There is still a lot of research left to be done on signal fading. Diversity is one of the many techniques that can be used to mitigate fading. It is a burning topic nowadays. Space diversity is one of them.

Based on this space diversity, many types of relay network systems, MIMO systems etc. have been developed. In these mentioned systems, the data signal is conveyed to the receiver over multiple independently fading signal paths. and then, combining these signals at the receiver appropriately, helps in removing noise. In this paper, cooperative wireless system based on decode and forward(DAF) one-way relay technique and adaptive modulation(AM) has been proposed, where BRS(best relay selection) method has been implemented. EM (Exception Maximum) algorithm is used for BRS. The proposed system has been named as EM cooperative system. Performance evaluation has been done for the proposed system over independent Nakagami-m and Rayleigh channels in terms of bit error rate (BER). System performance has been compared with direct transmission, where no algorithm has been used and BRS-DAF cooperative system [7]. Simulation has been done using MATLAB. According to the results, the proposed EM cooperative system proves to be the superior one. EM cooperative system achieves higher spectral density and the desired BER at lower SNR values as compared to the direct transmission and BRS-DAF cooperative.

Key words: Decode And Forward (DAF), Adaptive Modulation, Best Relay Selection, Exception Maximum (EM) Algorithm SNR, BER I. INTRODUCTION Communication had been in need since the very existence of life on earth. Since the ancient ages, people had been using different ways to communicate. As the civililisations were advancing, people started expanding their horizons and exploring different lands throughout the world, even across seas. Thus, need to communicate across the world rose eventually. But there wasn’t any significant development in the means of communication until the modern days. In the late 18th century, the invention of wireless communication proved to be one of the greatest inventions in the history of mankind. Wireless communication evolved remarkably since then. In modern days, it has become one of the largest topics of research. However, the wireless medium introduces difficulties due its very inherent nature. The atmosphere reflects, absorbs, scatters the radio waves. The transmission gets affected by interference, noise, blockage, attenuation and sometimes even complete distortion.[12].

The fading phenomenon basically occurrs due to existence of multiple paths.

Cooperative communication has gained much interest among many researchers and it is playing a key role in enabling technology for efficient spectrum use in future.

It ensures that, the communication resources is being utilised in most efficient way. It is done by allowing nodes or terminals in a communication network to collaborate with each other in information transmission. The basic idea in cooperative communication is that some extra transmission paths are added in addition to the direct transmission between the source and the destination. As a result, the diversity is enhanced. Through cooperative communication, the network connectivity can be improved, power can be saved and spectrum efficiency can be enhanced, and also the communication reliability is improved. Mainly two methods are there to implement cooperative communication system: Amplify-and-forward (AAF) (non-regenerative relays) and Decode-and-forward (DAF) (regenerative relays) method. In the AAF method, the relay node receives the signal from the source, amplifies it and retransmits it to the destination [10].

In the DAF method, the relay decodes the signal received from the source, re-encodes it and re-transmits it to the destination [11].

II. SYSTEM MODEL A co-operative wireless communication system has been considered as shown below in Fig.1, which consists of a source node (S), a destination node(D) and N number of relay nodes R1, R2, R3,........ RN randomly distributed in between the source and the destination. The symbols, g s,Ri , g Ri ,D and g S,D , i=1,2......N denote channel coeffients between SR(source to relay), Ri-D(relay to destination) and SD(source to destination) respectively. These channel coefficients g s,Ri , g Ri,D have δ2S,Ri and δ2Ri,D as their variance, respectively.

Fig. 1: Cooperative wireless communication system model with Rb as best selected relay for transmission.

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Performance Analysis of Cooperative Communication System based on Decode and Forward Relay System and Adaptive Modulation (IJSRD/Vol. 4/Issue 05/2016/065)

A. Assumptions 

All the channel coefficients are mutually independent zero- mean, complex Gaussian random variables (flat Rayleigh fading).  Source and relay transmit signals with same amount of power.  Distance between source and destination does not vary at any point of time.  AWGN (additive white Gaussian noise) for all the individual links are taken as zero-mean complex Gaussian random variables with variance N0.  CSI (channel state information) are available at the source node, destination node and all the relay nodes.

Now, signal is broadcasted to the N number of relays as well as to the destination directly by the source.

Then the signals are received both at the destination and the relays which can be represented respectively as đ?‘Ś S,Ri = √đ?‘? gs,Ri x + nS,Ri .....................................1 đ?‘Ś S,D = √đ?‘? gs,D x + nS,D .....................................2 Where, p is the transmitted power, x is the transmitted information symbol and nS,D and nS,Ri are the additive noise at the receiving ends. In this system, a certain threshold value for SNR has been set for channel beween source and the relays. The relay will decode the signal and retransmit it to the destination only if the SNR value of the received signal from the source exceeds the threshold.

However, if the received signal at any particular relay has the SNR value less than threshold, the relay becomes inactive. All the relays which are now eligible to decode the signal according to the SNR threshold, set previously, collectively forms a decoding set represented by symbol É„.

Among the relays from the decoding set É„, a best relay (Rb) where the received signal has the maximum SNR value is selected using an algorithm called EM(exception maximum). Then Rb decodes the signal and forward it to the destination. The received signal at the destination sent by the best relay selected Rb can be represented as đ?‘Śđ?‘…đ?‘? ,đ??ˇ = Q (đ?‘Śđ?‘†,đ?‘…đ?‘? ) đ?‘”đ?‘…đ?‘? ,đ??ˇ + đ?‘›đ?‘…đ?‘? ,đ??ˇ (3) Where, the function Q(.) denotes the EM DAF cooperative protocol implemented at the selected best relay node Rb. B. Decoding set É„ The decoding set itself is a part of the EM algorithm. It is a set of all the relay nodes whose received signal has SNR value greater than or equal to the threshold.

Let the instantaneous SNR between source and the relay Ri be as đ??¸ ÂĽgs,R = |g s,Ri |2 đ?‘ (4)

The decoding set É&#x201E; is defined by taking into account the spectral efficiency Ρ and is given by É&#x201E; = {k â&#x201A;Ź N, â&#x201D;&#x201A;gS,Rkâ&#x201D;&#x201A;2 â&#x2030;Ľ áż&#x2020; , k < N } (8) Where is given by áż&#x2020;=

22đ?&#x153;&#x201A; â&#x2C6;&#x2019;1

(9)

đ??¸đ?&#x2018; /đ?&#x2018; đ?&#x2018;&#x153;

Then, the best relay Rb from the decoding set É&#x201E; is selected such that [5] b = đ?&#x2018;&#x17D;đ?&#x2018;&#x;đ?&#x2018;&#x201D;đ?&#x2018;&#x161;đ?&#x2018;&#x17D;đ?&#x2018;Ľđ?&#x2018;&#x2013;=1,2,â&#x20AC;Śâ&#x20AC;Śđ?&#x2018; đ?&#x2018;&#x161;đ?&#x2018;&#x17D;đ?&#x2018;Ľđ?&#x2018;&#x2122;đ?&#x2018;&#x153;đ?&#x2018;&#x201D;(ÂĽgs,R â&#x201D;&#x201A;ÂĽg R ,S ) (10) i

đ?&#x2018;

= đ?&#x2018;&#x2122;đ?&#x2018;&#x153;đ?&#x2018;&#x201D; â&#x2C6;&#x2018; đ?&#x2018;&#x2013;=0

i

p(ÂĽg s,R , ÂĽg R ,S ) i

i

(11)

Now, the mutual information of EM cooperative system is given by [6]

III. RESULT AND DISCUSSION In this section simulation model is presented and the results are being discussed. In table 4.1 the simulation and their values which has been used during the simulation are given.

Parametes Values System bandwidth 5 MHz Sampling rate 5 Mega Samples Per Second PSK, BPSK,QPSK, QAM, Digital Modulation 16-QAM 32-QAM and 64QAM IFFT size 1024 Cyclic Prefix Length 10 samples and 20 samples Subcarrier Spacing 10 KHz Distance between Source 1, 2, 3, 4 KM and Destination (D) Number of Relay Nodes 10 Considered Channels Nakagami-m and Rayleigh Channel Equalization MSE Table 1: Simulation parameters and their values

đ?&#x2018; đ?&#x2018;&#x153;

i

And the instantaneous SNR between relay Ri and the destination be as đ??¸ ÂĽâ&#x201E;&#x17D;đ?&#x2018;&#x2026; ,đ??ˇ = |g Ri ,D |2 đ?&#x2018; (5) đ?&#x2018; đ?&#x2018;&#x153;

đ?&#x2018;&#x2013;

These instantaneous SNR are exponentially distributed with parameters 1/ÂĽâ&#x20AC;˛â&#x201E;&#x17D;đ?&#x2018;&#x2020;,đ?&#x2018;&#x2026; and 1/ÂĽâ&#x201E;&#x17D;đ?&#x2018;&#x2020;,đ?&#x2018;&#x2026; , đ?&#x2018;&#x2013; đ?&#x2018;&#x2013; respectively, where đ??¸ ÂĽâ&#x20AC;˛â&#x201E;&#x17D;đ?&#x2018;&#x2020;,đ?&#x2018;&#x2026; = E[ÂĽgs,R ] = δ2S,Ri đ?&#x2018; (6) đ?&#x2018;&#x2013;

i

ÂĽâ&#x20AC;˛â&#x201E;&#x17D;đ?&#x2018;&#x2026; ,đ??ˇ = E[ÂĽâ&#x201E;&#x17D;đ?&#x2018;&#x2026; ,đ??ˇ ] = δ2Ri,D đ?&#x2018;&#x2013;

đ?&#x2018;&#x2013;

đ?&#x2018; đ?&#x2018;&#x153; đ??¸đ?&#x2018;

đ?&#x2018; đ?&#x2018;&#x153;

And E[.] denotes expectation [1].

(7)

Fig. 2: BER vs SNR plot for different numbers of nodes â&#x20AC;&#x2DC;Nâ&#x20AC;&#x2122; between transmitter and receiver using QPSK modulated signal

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Performance Analysis of Cooperative Communication System based on Decode and Forward Relay System and Adaptive Modulation (IJSRD/Vol. 4/Issue 05/2016/065)

Fig. 2 shows the BER performance comparision between EM cooperative DAF system and BRS- DAF cooperative system for different number of relay nodes ‘N’ between source and the destination, considering the transmission is over Nakagami-m distributed fading channels using QPSK modulated signal. Here it is clearly visible that, for both the systems, the BER level is decreasing as the number of relay nodes increases. It is also seen that the BER level for the EM cooperative DAF system is lower as compared to that of the BRS-DAF cooperative system.

Fig. 3: BER vs SNR plot for different values of distance ‘D’ between transmitter and receiver using QPSK modulated signal.

Fig.3 shows the BER performance comparison between EM cooperative DAF system and BRS-DAF cooperative system for different values of distance ‘D’ between source and the destination, considering the transmission is over Nakagami-m distributed fading channels using QPSK modulated signal. Here it is clearly visible that, for both the systems, the BER level is decreasing as the distance betewwn source and destination decreases. It is also seen that the BER level for the EM cooperative DAF system is lower as compared to that of the BRS- DAF cooperative system. By observing both Fig.2 and Fig.3, it is clear that, the BER value for every SNR value for EM cooperative system is always lower than that for the based BRS-DAF cooperative system [7]. Hence, the EM (exception maximum) algorithm which is used in the proposed system proves to be more efficient than the one which is used in BRS-DAF cooperative system.

modulated signal and 16-QAM modulated signal through Nakagami-m channel in the proposed EM cooperative system. It is seen that the BER value for 16-QAM modulated signal doesn’t change too much. In case of QPSK the BER level decreases in a very steady rate. While in BPSK, the change in value of BER is not steady. At first it remains almost constant for certain increase in SNR value then the decreasing slope becomes steep for certain values of SNR and then it again it becomes constant. Thus observing the graph, it can be concluded that QPSK modulated signal works smoothly in the proposed system.

Fig. 5: BER performance analysis between BPSK, QPSK and 16-QAM modulation through the Rayleigh distribution channel.

In Fig.5, the same thing has been done except for the transmission channel, which is Rayleigh fading channel instead of Nakagami-m fading channel. Observing the figure it can be seen that, in case of Rayleigh fading also, QPSK works better for the proposed EM cooperative system.

Fig. 6: BER performance comparision between EM cooperative system DAF, BRS cooperative DAF system and original fixed cooperative channel.

Fig. 4: BER performance analysis between BPSK, QPSK and 16-QAM modulation through the Nakagami-m distribution channel In Fig.4, BER vs SNR has been plotted to compare the behaviour between the BPSK modulated, PSK

Fig. 7: Average spectral efficiency vs. SNR comparison between EM cooperative system and the Based cooperative system at BER= 10-3 at constant.

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Performance Analysis of Cooperative Communication System based on Decode and Forward Relay System and Adaptive Modulation (IJSRD/Vol. 4/Issue 05/2016/065)

In Fig. 6, BER performance comparison has been done EM cooperative, BRS-DAF cooperative and the original fixed cooperative DAF system without using any algorithm through Rayleigh distribution. The figure shows that the BER level for the EM cooperative DAF system is lower as compared to both the other system. Hence it is proved that, the EM cooperative system attains the required BER value for lower values of SNR.

Fig. 8: BER vs SNR comparision between EM cooperative and based BRS-DAF cooperative In Fig.7, average spectal efficiency vs SNR has been plotted both for EM cooperative and BRS-DAF cooperative system. By observing the figure, it is seen that, the proposed EM cooperative system attains higher average spectral efficiency than the BRS-DAF cooperative system.

In Fig.8, it is seen that, for both the system , for required BER level the SNR they have lower value of SNR through Nakagami fadig channel than through the Rayleigh fading channel. It is also seen that the EM cooperative system outperforms the BRS-DAF cooperative system [7].

IV. CONCLUSION In this thesis, EM cooperative system has been proposed.

The proposed system is based on decode and forward (DAF) one-way relay technique and adaptive modulation (AM), where BRS (best relay selection) method has been implemented. EM (Exception Maximum) algorithm is used for to implement BRS. In the proposed system, different types of adaptive modulation schemes have been used. So, to provide multiple transmission mode, an adaptive modulator has been installed at the source modes, where each mode is specified by one of the different modulation schemes. The source node selects one of the modulation schemes and the modulated signal is broadcasted to N number of relays and also to the destination directly. To analyse the performance of the proposed cooperative communication system its performance is compared with direct transmission where no algorithm has been used and BRS- DAF cooperative system [7]. Simulation has been done using MATLAB. According to the results, the proposed EM cooperative system proves to be the superior one. EM cooperative system achieves higher spectal density and the desired BER at lower SNR values as compared to the direct transmission and BRS-DAF cooperative.

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