Diamond Structures based Relaying techniques for ...

Diamond Structures based Relaying techniques for enhanced Cooperative Communication Ali Aitizaz [email protected]

Ghulam Ishaq Khan Institute of Engineering Sciences and Technology Faculty of computer science and Engineering, Topi Kpk

Abstract—In

recent times, cooperative communication has gained major importance due to the fact that it exploits spatial diversity and produces capacity/performance gain over usual single-input single-output (SISO) systems. A moveable station having only one antenna can cooperate with a close mobile station having only one antenna in multi-user network to produce the effect of virtual multiple antenna system, reduce the complication caused by the system having more than one antenna .Apart from the miniature size and power limitations a movable station can be beneficiated. In this thesis we have chosen two cooperative communication protocols namely Amplify and forward (AF) ; and Decode and Forward for Diamond structure. All the previous work was general and was carried out on collinear geometry. Keywords— AF, DF, DtF, Relay, Diamond structure, SISO.

1. Introduction Cooperative communication can be defined as the communication system which allows users to send each others data to the projected destination. Cooperative communication is an emerging field of wireless communication [8]. The idea of cooperative communication was first attributed by the Thomas M.cover and Abbas A.EI Gamal back in 1979[5]. They modelled a relay channel to include a source node, a relay node and a destination node. Figure 1 shows cooperative communication system. The source sends packets of data to the destination, relay intercepts this transmission. The relay can be a user node or base station. Relay operates on relaying techniques. The relaying

techniques can be either amplify and forward, decode and forward or detect and forward. Relay, according to the relaying scheme amplifies the signal and then forwards it to the destination.

2. Background and Motivation Cooperative communication has just received tremendous importance in certain communication organizations. A lot of the work in cooperative communication presents enormous perfection in the performance of wireless and sensor network. Research has analysed that station with a single installed antenna when provide with channel coding and cooperation could attain the same range to those of multiple antenna systems in terms of diversity gains. Through analysis and it is well established that single mobile station with a single antenna can cooperate with similar mobile station in multiuser communicating environment to produce the result of virtual multiple antenna systems [2]. If there are more than one antenna systems then it can achieve enough diversity gain but its installation is not feasible due to some limitations in the wireless systems. To get the challenging requirement it is demanded that a rapid, efficient, and consistent communication system could be established.

The proposed communications model consists of: 1) Source: it sends packets of symbols which are in the form of binary. 2) Encoder: it encodes the data and then forwards it. 3) Modulator: it modulates the coded symbols. Fig. 1.Cooperative Communication

3. System Model In this type of arrangement there are two relays between source and destination. It can be Symmetric or asymmetric. We have considered diamond topology in this research. It consists on a Source, two relays and destination. If the distance between source and destination and the two relays are equal then it is called as symmetric diamond structure. If the path distance is not the same then it is called as asymmetric diamond structure. In this thesis we have compared the performance of amplify and forward, decode and forward relaying protocols over diamond structure as well as collinear structure. Through simulation the results are compared that the performance of the diamond structure is better than that of the collinear arrangement. Figure 2 illustrates Diamond arrangement which is proposed in this

4) Demodulator: it demodulates the packets and then transmits it. 5) Relays: Relays are nodes which amplify and forward data, it can be a user node or base station. 6) Channel: it represents media among relays, source and destination. 7) In the Figure 3 is shown the proposed communication model and all of its processing sections.

research.

Fig.3.Communication Model

3.2 Assumptions

Fig.2Diamond Structure The source and destination are the other two ends. When the source sends data then as the nature of the wireless network is broadcast so relay intercepts the communication then using either relay protocols to transmit the data to the destination quickly [7].

3.1 Communication Model

A. While designing the proposed system the following assumptions are taken in the mind. B. The transmission channel is assumed to be frequency non selective flat fading. In this case the frequency components are affected by the similar fading coefficients. C. The transmitted symbols are binary in this system. D. Techniques for coding are used in order to reduce the errors rate. E. The signals which are transmitted are first encoded by an encoder. F. Modulation uses binary phase shift keying. G. The noise is assumed to be Additive White Gaussian Noise whose variance is N0/2.

FIG.6 RELAY MODEL

3.3Path Model The path model that is designed is frequency non selective and Rayleigh faded with the presence of the AWGN (Additive White Gaussian Noise).The transmission path model is independent and it is identically distributed random Gaussian process. The variance is equal to zero and the it is unity. Fig 4 illustrates Path model for the system model.

3.6. Destination Model In the proposed system the traffic that the destination receive are of two types, i.e. the first data which the destination receives from the source directly to the destination. The second data which the destination receives is either from the relay 1 or relay 2. These signals are then combined by using maximum ratio combining technique. Fig 7 illustrates the destination model.

Fig.4 path model

3.4Transmission Model The transmission model is supposed to transmit a random number of bits or signals which is received by random generator. Through this generator when the data is received and is then encoded through a mechanism called half rate convolution encoder and when the data is encoded it is modulated by binary phase shift keying (BPSK).Fig 5 shows transmission model.

Fig.5 Transmission Model

3.5Relay Model The relay is used in cooperative communication plays a vital role in the cooperation. The transmission power is kept equal to unity. The relay uses BPSK when it modulates the signal. When relay modulate the incoming signal it is in form of bits that is transmitted by source. It is important that the relay is fully aware of the inter user channel. The relay when receive the signal process it according to the cooperative protocols that are used in the cooperation and forwards to the destination. In the Figure 6 is shown the relay model. In Diamond structure as there are two relays so each relay when intercept the information will process the signal according to the cooperative Communication strategies and then forwards it to the destination. Conclusions

Fig.7 Destination Model

4. Relaying Techniques There are two different classes of the relaying schemes in the Cooperative Communication. The first one is called selective scheme wherein the relay cooperate with some condition. The second one is called fixed relaying scheme in which the relay can cooperate in all condition [5], there are two fixed and two selective schemes are compared using symbol error rate. It is compared for both collinear and Diamond Structures.

4.1 Amplify and Forward Scheme for Diamond arrangement In this type of relaying scheme, first the source node transmit data to the relay and relay then after receiving or intercepting the data ,Amplify it up to some multiplication factor. The relation between power received and that of the multiplication factor is inverse [14].

√

(1)

The equation (1) can be expended for Diamond structure as below:

(

is the channel between source and relay, is the noise between source and relay. The power is normalized i.e.

)

(14)

=1, which yields

(15) ]

(√

(√

]

[

)

(2) (3) (4)

In the equation (3.16) it is termed as average of noise power. The signal amplified can be written as,

√

|

4.2 Decode and Forward scheme for Diamond arrangement

In this strategy the signal is first Decoded and then it is further encoded and is sent to the destination. The

(5)

|

(16)

equation derived for the relaying signal at the destination node is given by equation [14].

Substituting

√|

the equation (6) yields:

| |

|

(17) In the equation (17) represents the signal encoded by the relay. The combined signal at the receiver side is given by;

(6)

The amplification factor is derived for Diamond Structures

(7) The signal received by the receiver is given by the equation (3.21)

(8) (9) The equation (11) is used for the collinear arrangement for Diamond Structures the equation can be derived For the relay R1 the equation cane be write as;

(10) For the relay R2 the equation can be written as;

(11) The composite signal at the destination is given as,

(12) (13)

(18) The equation is for single relay, for two relay the equation (19) is further expanded as.

5. Results The proposed arrangement is diamond which consists on two relays. For simulation we have used MATLAB. The Montecarlo code is simulated for Diamond arrangement.The results are compared and the performance is evaluated.The AF,DF and DtF protoclos are completely analysed and two references are taken i.e. SER and SNR .For different channel conditions.the diversity gain is high as illustrted in the Fig 8 and 9.

Fig.8 simulation Reults of Diamond structure

Fig.10.Bad source uplink

4.2. Bad Source uplink(LESS 10 DB) The source uplink is considered bad or worse when it is less than the relay upper link 10 DB [14]. Source upper link is the link directly connected with the destination. If the source uplink is worse than the diversity gain can be achieved by applying better uplink channels conditions. Figure 10 illustrates the worse source uplink. There are errors in the direct communication in case of bad source uplink. In the simulation results DF outperforms to the other two protocols. The simulation results in the Figure 4.7 also show that all of the schemes i.e.AF,DF,StDF gaining full diversity gain but at middle level of SNR. Figure 9 shows simulation results for bad source uplink for Diamond structure.

Fig.9 Results for best case

4.1Worse Relay Upper link condition This conditions occurs when the relay upper channel is 10 DB lesser than that of the relays and that of the source [14]. As in case of Diamond Structures there are two relay then this situation occurs very rear. When one relay has uplink less than 10 db this condition strongly effects the cooperation. In this scenario the relay with worse channel condition is not allowed for cooperation. In this scenario the Diamond Structures show better performance as compared to collinear and triangular geometry. The cooperation in this scenario is high as compared to other geometries. Figure 8 represents the comparison of the different curves of the selected relaying protocols when the relay has 10 DB weaker uplink as compared to other two channels as shown in Fig. 10.

Fig.11 simulation of Bad source uplink

4.3. Best Source Upper Link Comparison The best source upper link is that when the source is 10 DB best than that of the Relays R1 and R2 as well as inter user path [14]. The simulation in the Figure

DF DtF AF 2*1MISO

-1

10

-2

10

SER

4.8 shows the comparison and the diversity gain of the different scheme using best source upper link. In this case the base station is very near to the source considering both relay in case of Diamond arrangement. From the Figure 10 it is clear that the both selected protocols after best performance at the lowest SNR. In this scenario AF is performing better than that of the DF but it is similar approximately to 2*1 MISO.

-3

10

-4

10

-5

10

0

5

10

15

20 SNR(dB)

25

30

35

40

Fig.14 simulation results for Best inter user channel

5. Conclusion and future work

Fig.12 simulation of Best Relay uplink AF DF DtF 2*1MISO

-1

10

-2

SER

10

-3

10

-4

10

-5

10

0

5

10

15

20 SNR(dB)

25

30

35

40

Fig. 13 comparison of selected protocol for In figure 12 is shown the comparison of the collinear as well as Diamond structure. From the figure 12 it is clear that the cooperative relaying protocols are getting more diversity gain as compared to collinear arrangement because AF and DF in case of Diamond structure are getting more diversity gain as compared to collinear which is represented by AFL and DF-L. In this simulation a new protocol is also analyzed which is S-DTF. A protocol that is used to select the required signal and then forwards it to the destination.

The main focus of this thesis is on the performance analysis of the selected cooperative relaying techniques and protocols, which are applied on the Diamond geometry. Improvement in the wireless network can be seen by applying advanced cooperative techniques. Data received by the destination from three different paths i.e. the path which is directed to the destination from source, and relaying paths from the two relays. At the destination maximum combining techniques are used at the destination. The proposed system is applied to the selected relaying protocols namely Amplify and Forward, Decode and Forward and Detect and Forward. In Diamond Structures AF and DF shows better performance as compared to DtF. In case of AF and DF best diversity gain is shown by AF as compared to DF. At high error rate DF show promising performance as channel conditions changes. As compared to other two protocols DtF does not provide high performance gain. At high Signal to Noise Ratio DtF provides coding gain in Diamond Structures. Overall performance was better than that of the collinear arrangement. In Diamond Structures DF gain diversity very faster as compared to the AF. The main advantage of the Diamond Structures is that each relay can be used for AF and at the same time for DF simultaneously. The delay factor can be reduced up to certain limits in Diamond Structures. DF depends upon better inter user channel. If the inter user channel is better then it achieves high performance without any error. The error propagation in Diamond Structures is very minimal because there are two relays and we have used high path loss. When the path loss is high then the error rate is very minimal so diversity gain will be

high. Similarly Fig 13 and 14 illustrates comparison of selected relaying protocols for Diamond structure. 6. References [1]S. Haykin and M. Moher, Modern Wireless Communication Systems, Upper Saddle River, NJ: Pearson Prentice-Hall Education, 2007.

[8] R. Deepa, Dr. K. Baskaran, P. Unnikrishnan, A. Kumar, “Study of Spatial Diversity Schemes in Multiple Antenna Systems”, Journal of Theoretical and Applied Information Technology, pp. 619-624.

[9]. A. Shokrollahi, “Raptor codes,” Transaction on Information Theory,

IEEE

vol. 52, no. 6, pp. 2551–2567, June 2011. [2]H. Mheidat and M. Uysal, “Non-coherent and mismatched-coherent receivers For distributed STBCs with amplify-and-forward relaying,” IEEE Trans. Wireless Commun. vol. 6, no. 11, pp. 4060–4070, November 2010.

[3] H. Hourani, “An Overview of Diversity Techniques in Wireless Communication Systems”, Helsinki University of Technology, Communications Lab, pp. 1-5, 2005.

[10] B. Q. V. Ngyuen, H. Y. Kong, C. H. Dinh, and T. L. Tien, “BER Performance of Decode-and Forward Relaying Using Selection Combining over Rayleigh Fading Channels”, ATC, pp. 301-304, October 2011.

[11] Y. Li and S. Kishore, “Asymptotic analysis of amplify-and-forward relaying in Nakagami-fading environments,” IEEE Trans. Wireless Commun.,vol. 6, no. 12, pp. 4256–4262, Dec. 2007.

[4] W. Stallings, Wireless Communications and Networks, 2nd ed. Pearson Prentice-Hall, 2005.

[5] P. S. Ahmed, “Turbo Multi-Hop Relaying for Cooperative Communications”, Master Thesis, University of Southampton, September 25, 2009.

[6] J. N. Laneman, and G. W. Wornell, “EnergyEfficient Antenna Sharing and Relaying for Wireless Networks”, IEEE, pp. 7-12, 2010.

[7] B. Hohmann, M. Debbah and A. Kröpfl, “Reliable Multimedia Transmission in Wireless Ad Hoc Networks for Telehealth Systems”, Second Int. Conference on Pervasive Computing Technologies for Healthcare, Finland, 2008.

[12] Boyer J., D. Falconer, and H. Yanikomeroglu. 2001. A theoretical characterization of the multi-hop wireless communications channel with diversity, In Proceedings of IEEE Global Telecommunications Conference.

[13] Y. Ding, J. K. Zhang and K. M. Wong, “The Amplify and Forward Half Duplex Cooperative System: Pair wise Error Probability And Precoder Design”, IEEE Transaction on Signal Processing, Vol. 55, No. 2, pp. 605-617, February 2007. [14]Afaq and Sahibzada,”Perfromance Analysis of selected Relaying techniques for Cooperative Communication’s thesis,BTH,Sweden,2010

[15] F. A. Onat, A. Adinoyi, Y. Fan, H. Yanikomeroglu, J. S. Thompson, and I. D. Marsland, “Threshold selection for SNR-based selective digital relaying in cooperative wireless networks,” IEEE Trans. Wireless Commun., vol. 7, no. 11, pp. 4226– 4237,2011