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1 Gormus, S., Kaleshi, D., McGeehan, J. P., & Munro, A. T. D. (2006). Performance comparison of cooperative and non-cooperative relaying mechanisms in wireless networks. In IEEE Wireless Communications and Networking Conference. (Vol. 2, pp ). Institute of Electrical and Electronics Engineers (IEEE) /WCNC Link to published version (if available): /WCNC Link to publication record in Explore Bristol Research PDF-document University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: Take down policy Explore Bristol Research is a digital archive and the intention is that deposited content should not be removed. However, if you believe that this version of the work breaches copyright law please contact open-access@bristol.ac.uk and include the following information in your message: Your contact details Bibliographic details for the item, including a URL An outline of the nature of the complaint On receipt of your message the Open Access Team will immediately investigate your claim, make an initial judgement of the validity of the claim and, where appropriate, withdraw the item in question from public view.

2 Performance Evaluation of Relaying Mechanisms in Wireless Networks Sedat Gormus,, Dritan Kaleshi, Joe McGeehan, Alistair Munro Department of Electrical and Electronic Engineering, University of Bristol, UK

3 Outline Overview and motivation Relaying in wireless networks Simulation setup Simulation scenarios Link performance of the selected relaying algorithms for LOS and NLOS environments Conclusions

4 Application: WLAN and Cellular Poor WWAN Link Good WWAN Link Distributed relaying can be used to improve coverage but also link quality and capacity.

5 Distributed / Cooperative Relaying Idea Nodes on the source-destination path can cooperate to create a better link.

6 Main research question and Motivation How does relaying affect throughput of a communications system? In terms of capacity Coverage (already covered extensively) Link quality Interference and power consumption Latency

7 Simulation Environment Qualnet Simulator Channel Model Position information Network Layer Mac Layer SISO, STBC 2x1 PHY Simulator BER Tables PHY Propagation Channel Model

8 PHY Layer simulator Node positions can be easily manipulated for different relaying scenarios Response of the channel Modes BER for particular scenario PHY layer simulator can produce BER information for both D&F, S- D&F, and STBC using AWGN and Channel Model A channel models, it also uses standard compliant constraint length seven Viterbi decoder with convolutional encoder. Auto BER calculation

9 Relaying Scenarios for Link Throughput * s 1 s 0 h 0 r = h s + hs + n * * * s s h 1 0 r = h s + hs + n 0 D-STBC S-D&F For D-STBC S-D&F Relaying relaying takes the the packet is is decoded stored advantage at and the of destination forwarded space time at block in MAC the layer. first codes transmission to There improve no the cooperation. period. error In the second performance transmission of the period the stored communicating packet is nodes. used to improve the error performance of the link Direction S-R (m) Direction S-R (m) Source Relay Destination Source Relay Destination S-D (m) Start position of the relays S-D (m) End position of the relays 1 st transmission 2 nd transmission

10 Simulation Parameters The nodes are placed in pre-determined locations and for each location a simulation is run for 60 seconds. In all simulation scenarios a constant bit rate (CBR) traffic with 1800 bytes packet length is used in order to investigate the maximum achievable throughput. The packet transmission interval at the application layer is chosen to be 800 microseconds. The node queues are assumed to be large enough that there is no packet drop. The CBR traffic generated by the application is chosen to be always greater than link throughput so there is no idle time in the wireless medium.

11 AWGN Results MAC-D&F MAC-Direct MAC-STBC MAC-S-D&F S-D Dis tance (m ) E E E E E E E+06 Notes from simulation results: Deploying relays (cooperative or noncooperative) does not improve the capacity of the link considerably for LOS scenarios. Only coverage increase is significant since the signal is regenerated and transmitted by the relay. Path loss model for AWGN is: Throughput (bit/s) L p = 10log λ 2 10 (4πd / )

12 CHNLA Results MAC-STBC MAC-D&F MAC - Direct MAC-S-D&F 2.5E E E E E+06 All the evaluated relaying algorithms perform better with a Channel A model as compared to the AWGN channel with free space propagation. The main reason is the NLOS (non-line-ofsight) propagation environment in which the signal degrades very rapidly compared to LOS (lineof-sight) environments. Significant coverage increases can also be attained using relaying in NLOS environments. 3.0E+05 Path loss model for Channel Model A; S-D Distance (m) L p = 10log 10 (4πd / λ) 2 + αd α = 0.5

13 Direction Source Multi-Stage D-STBCD Relays Relays Direction Destination Start position of the nodes h 0 h 1 h 2 h 3 1 st Tier VAA 2 nd Tier VAA 3 rd Tier VAA 4 th Tier VAA Source Relays h 0 Relays Destination End position of the nodes h 3 h 1 h 2 1 st Tier VAA 2 nd Tier VAA 3 rd Tier VAA 4 th Tier VAA 2 2x1 MIMO channels If the packet travels over more than one relaying VAA, it is possible to form multistage relaying links. It is clear that the link between 2 nd tier and 3 rd tier VAA is a MIMO-like link and can support higher throughput compared to the source-2 nd VAA and 3 rd VAAdestination link. In our simulation the relays are fixed and the source and destination distance is decreased by a constant value for each run of the simulation.

14 Results for Multi-Stage D-STBCD 6.0E E+06 MA C-D&F MA C-STBC 7.0E E+06 MAC-STBC MA C-D&F Throughput (bit/s) 4.0E E E+06 Throughput (bit/s) 5.0E E E E E E E S-VAA and VAA-D distance (m ) 0.0E S-VAA and VAA-D distance (m) a) Channel A b) AWGN For Multi Stage relaying deploying cooperative relays improves link throughput compared to non-cooperative relaying. The trend in the figure shows that Multi Stage relaying performs better in NLOS propagation environments.

15 Uplink and Downlink Source Relays Destination If we ignore the transmission from the source, the achievable rate can be shown to be; R maxmin{( I X1; Y2 X2), I( X2; Y3 )} DF p( x1, x2) 1 st Tier VAA 2 nd Tier VAA 3 rd Tier VAA Uplink Downlink First term in the formula represents the rate at which the relay node(s) can decode the source message reliably, the second term represents the rate at which destination node can decode the retransmitted message from the relay. The maximum mutual information is always limited by the individual channel throughput between nodes. The main limiting factor for D-STBC cooperative systems is the difficulty of implementing coding on both uplink and downlink channels (non-reciprocal behaviour), since in Downlink channel space time coding can be used but not in uplink channel, if inter-relay communication is not allowed.

16 Multi Stage D-STBCD Source Relays h 3 h 0 h 1 Relays Destination For multi stage D-STBC systems; the requirement of retransmission of the packet along the source-destination link, which will create delay in the link and drop the efficiency, is one of the limiting factors. The efficiency of the system in terms of transmission time can be given as; 1 st Tier VAA 2 nd Tier VAA h 2 3 rd Tier VAA 4 th Tier VAA Ε i, j = i, j ( Td i, j i, j Td + Tack i, j i, j + Tifs i, j ) 2 2x1 MISO channels This is a draw back for multi-stage D-STBC systems since the source node needs to be close to the first stage VAA, and destination to the last stage VAA.

17 Conclusions For free space communication environment (no multi-path propagation), the proposed relaying methods provided almost no advantage over direct communication in terms of throughput increase. In multi-path fading environments all relaying schemas performed considerably well; D-STBC cooperative relaying was found to be the best candidate for these environments. Even though single stage D-STBC provided the best performance for two hop scenarios, the observed increase was quite significant compared to non-cooperative D&F method. But this difference is less impressive if one takes into account the complexity of the cooperative relaying methods (such as D-STBC and S-D&F). The multi-stage results show that D-STBC relaying provides better throughput than D&F relaying for scenarios where the transmitted packet travels thorough the same route for both relaying methods. The throughput increase is limited when the channel conditions between the source and the first stage VAA or the last stage VAA and destination is poor

18 Thank You and Questions?