USER COOPERATIVE COMMUNICATIONS

1. USER COOPERATIVE COMMUNICATIONS INSTRUCTOR: Dr. GEORGE COLLINS PRESENTED BY: SRUTHI REDDY MANDADI

2. CONTENTS • Introduction • Diversity • Relay Channels • A General Three Node Relay Channel • Wireless Relay Channels • User Cooperation In Wireless Networks • Multi-hop Relay Channel • Summary • References

3. INTRODUCTION • User cooperative communication is a form of communication in which users work together to deliver their data. • Cooperative diversity – node act as a relay to forward the received information from the source. • Signal received directly from the source is combined at the destination with that forwarded by the rely to retrieve the transmitted message. • Diversity reduces the risk of being in a deep fade by offering a number of independent copies of reception.

4. DIVERSITY Diversity can be obtained by time, frequency, space The four types of diversity are 1.Temporal Diversity- retransmitting data packets in time intervals greater than channel coherence time. 2.Spatial Diversity-transmitting data streams over multiple independent paths. 3.Macro Diversity-combining signals received at different base stations. 4.Cooperative Diversity-diversity obtained by relaying

5. RELAY CHANNELS • It is the basic building block for user cooperative systems. • It consists of a single source node, a single destination node and a relay node . • Relays can be applied to multiple-access channels and broadcast channels. • Relays were mainly proposed to tackle problems like earth curvature, path loss and irregular terrains. • Relays can increase the transmission rate and save energy.

6. R S D Multiple Access Broadcast S1 D1 Single Point to Point Chanel R R S D S2 D2 Broadcast Channel Multi Access Channel S R D dsr dsr dsd A linear network with a source, a relay, and a destination node

7. A General Three-Node Relay Channel: Model 1/2 • A three-node relay channel consists of • A source nodeS. • A Destination node, D. • A relay node, R. • Two approaches to process the received signal at the relay • Amplify-and-forward (AF): sends a scaled copy of the received noisy signal. • Decode-and-forward (DF): First try to encode the received signal. If successful, re-encode and transmit.

8. General Relay Channel The proposed relaying strategies , derived the achievable rate regions, and provided an upper bound to the capacity for the general relay channel. Model

9. Coding Time Slot 1 Time Slot 2 Time Slot 3 Time Slot 4 Source X(w1) X(w2) X(w3) X(1) Xr(1) Xr(w1) Xr(w2) Xr(w3) Relay • Regular encoding/sliding window decoding. • Encoding (the source and the relay nodes) • Message w is divided into B blocks w1,w2 . . .wBtransmitted in B + 1 time slots. • In time slot i, the source sends x(wi ) and the relay sends x(wi−1). • A constant sequence is sent by the relay n time slot 1 and by the source in time slot B + 1. A regular encoding/sliding window decoding scheme

10. Advantages: • Simple. • Limited delay. • Achieves maximum rate. • Can be extended to multi-hop relaying.

11. WIRELESS RELAY CHANNELS • Wireless systems have there unique attributes this is due to the nature of propagation in the wireless environment and hard ware limitations. • Key features that differentiate wireless channels and networks • 1.Wireless broadcast property (WBP) • Fully Connected -A signal transmitted by a node is received by all the nodes located with in the coverage area of that node. • To avoid interference, Orthogonality between signals can be achieved by TDMA, FDMA or FDMA.

12. 2. Half – Duplex Constraint In half duplex transmission time or bandwidth is shared between the source and the relay. Relay Relay Destination Destination Source Source SNR SNR Time Time The source node broadcasts the message to both the relay and destination nodes The relay node forwards the transmission in the second stage

13. 3. Channel Behavior • In addition to path loss, communication over the wireless medium suffers from large- scale and small-scale fading caused by shadowing . • The probability of experiencing a fade on the channel is a limiting factor in the link’s performance. • The effects of fading can be combated by using diversity techniques. • When mounting multiple antennas is unfeasible, spatial diversity can be obtained through relaying.

14. USER COOPERATION IN WIRELESS NETWORKS • User cooperative diversity helps resource utilization in the wireless network. • Spectrum efficiency can be improved. • Cooperative transmission can be fixed or adaptive. • Fixed Relaying- the relay continuously forwards the signal received from the source. • Adaptive Relaying-the relay remains in listening mode ad relays only when necessary

15. Two-User Cooperative Network • System Constraints • The way user A and user B cooperate depends on the resources available, constraints that govern the use of these resources and any other constraints of the system. • Regarding the transmission power, cooperating users may operate under one of the following constraints • Fixed uniform peak transmit power • P1i = P2i = Ṗi, for iЄ {A,B} • 2. Average transmit power per user • P1A (1 – ƮA) + P2AƮB = ṖA • 3. Total power • P1A (1 – ƮA) + P2AƮB + P1B (1 – ƮB) + P2BƮA = Ṗ

16. Optimizing Performance

17. MULTIHOP RELAY CHANNEL • Multiple relays cab be arranged into different groups where nodes at the same level decode the message at the same time and cooperatively retransmit it during the same time period. • In this a source- destination pair assisted by a number of other users. • Cooperating users are arranged to help in a multi-hop fashion. • Multi-hopping to Exploit Gray Holes • In the paradigm of cognitive radio, the spectrum of licensed channels can be categorized as • White holes • Gray holes • Black holes

18. Multi-hop Relay Channel • Model • Non-cooperative Relaying: information is sent in a consecutive fashion first from the source to the first relay and then to second relay • Transmission from node0(source) to node5 (destination) over five hops. Nodes 0-4 transmit the signal using τ0,….,τ4 of the available time in each hop 3 3 1 4 1 4 5 5 0 0 2 2 0 0 1 τ0τ1τ2τ3τ4 τ0τ1τ2τ3τ4

19. 3 3 1 1 4 4 5 5 0 0 2 2 0 1 2 0 1 2 3 τ0τ1τ2τ3τ4 τ0τ1τ2τ3τ4 3 3 Χ0(4) 1 1 4 4 5 5 0 0 2 2 0 1 2 3 4 0 1 2 3 τ0τ1τ2τ3τ4 τ0τ1τ2τ3τ4 The accumulated rate at node 4 after four hops, Χ0(4

20. Multi-hop Relay Channel: Achievable Rate

21. Multi-hop Relay Channel: Outage Probability

22. SUMMARY • In this paper, cooperative diversity obtained via relaying is introduced and relay channel • Is the basic element. • The wireless case is considered as a special case of the general relay channel. • Space diversity is obtained by employing multiple receiver antennas for independent reception.

23. REFERENCES • End-to-End Antenna Selection Strategies for Multi-Hop Relay Channels • http://wncg.org/itmanet/publications/VazeHeath_Asilomar.pdf • Relay-Coded Multi-User Cooperative Communications • http://www.techrepublic.com/whitepapers/relay-coded-multi-user-cooperative-communications-for-uplink-lte-advanced-4g-systems/2374113 • The Multi-way Relay Channel • http://wsl.stanford.edu/ITMANET/ITMANET_Publications/gunduz_isit09_yener.pdf

24. Thank you