||Packet Buffering and Delay in Cooperative Networks
||Institute of Computer & Communication
In this thesis, we study the relay selection problem for a finite buffer-aided decode-and-forward (DF) cooperative wireless network. In , the author proposed the max-max relay selection (MMRS), which selects the strongest source-relay (S-R) and the strongest relay-destination (R-D) channels for reception and transmission, respectively. Since MMRS may incur data loss when the relay buffer is full, infinite buffer must be assumed. A more practical scheme, called hybrid relay selection (HRS), which combines opportunistic relay (OR) and MMRS has also been proposed for relays with finite buffers. Although HRS achieves the same outage probability as MMRS with infinite buffer size, it incurs severe delay because of the prolonged initialization phase. To mitigate undesired delay for performing cooperative relaying, we propose composite relay selection (CRS), which combines OR and shortest-in longest-out (SILO), to utilize the channel and buffer status simultaneously. The proposed CRS is evaluated theoretically considering a toy example with two relays. Simulations are conducted to validate the analysis accuracy. Extensive comparisons of CRS and other related schemes are also presented. It is shown that the proposed CRS scheme significantly reduces the delay under the same outage probability compared with HRS. In terms of delay, the difference between CRS and HRS is 96% for K=3 relays and SNR=15 dB, and the improvement is more pronounced when the number of relays increases.
1 Introduction 1
2 Background and Literature Review 3
2.1 Opportunistic Relay 3
2.2 Max-Max Relay Selection 4
2.3 Hybrid Relay Selection 4
3 Shortest-In Longest-Out Relaying and Composite Relay Selection 6
3.1 System Model 6
3.2 Proposed Schemes 8
3.2.1 Shortest-In Longest-Out Relaying 8
3.2.2 Composite Relay Selection 8
3.3 Performance analysis 9
3.3.1 Opportunistic Relay 9
3.3.2 Shortest-In Longest-Out Relaying 10
3.3.3 Composite Relay Selection 10
3.4 Example 12
3.4.1 Steady-state probability 12
3.4.2 Probability vectors 25
4 Numerical Results and Discussions 27
4.1 Outage Performance 27
4.2 The Impact of Initial Buffer Length 29
4.3 Theoretical and Simulation Results 33
4.4 The Impact of CRS Switching to OR 35
5 Conclusions 37
5.1 Future Works 38
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