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From ARQ to Relay assisted Hybrid ARQ
Retransmission mechanisms in wireless communications existed since the invention of ARQ by Van Duuren [Van Duuren, 1943] in the 1940s. The reliability of these mechanisms is improved thanks to Forward Error Correction (FEC) techniques which combined with retransmission mechanisms gave birth to HARQ. In parallel, relay networks were developed regardless of the presence of an HARQ mechanism. Few recent works, including our contribution, combine HARQ with relay-assisted communication to improve the performance metrics of the system. In this Section, we give the necessary fundamentals of the study of relay assisted HARQ to understand the work that will be presented throughout this Chapter.
Numerical results and comparison of the protocols
We verify the analytical expressions of the performance metrics and illustrate numerically the interest of the investigated protocol. For this purpose, we describe in Section 1.6.1 the path loss model for numerical evaluation of the protocols. In Section 1.6.2, we validate numerically the correctness of the Markov chain model that describes the investigated protocol and its derived metrics. Then we compare, in Section 1.6.3, this protocol to other protocols presented throughout this Chapter. These numerical results provide insights on the usefulness of the investigated protocol in comparison to other relay assisted HARQ protocols. In addition, we study the performance of the investigated protocol with different relay positions in Section 1.6.4. Furthermore, numerical optimization of power allocation when using the investigated protocol is provided in Section 1.6.5. Afterwards in Section 1.6.6, we show simulation results of the protocols using practical codes.
Validation of the Markov chain model of the investigated protocol
We provide numerical results to validate the Markov chain model, depicted in Section 1.5, of the investigated protocol. For this purpose, the throughput andMERof the protocol are numerically evaluated via three different methods, as follows. In all cases, we consider the investigated protocol with IR-HARQ using capacity-achieving codes where C = 2 and R = 0.8. The relay is located halfway between the source and the destination as explained in the previous Section 1.6.1 (relay in the middle). 48 1. Relay assisted Hybrid ARQ Protocol simulation designates the simulation of the investigated protocol as described in Section 1.4.4. Since we use capacity-achieving codes, successful (or failed) decoding is determined by comparing the accumulated mutual information at the receiver to the coding rate. We use counters (of the number of ACKs, time-slots, generated messages and dropped messages) to evaluate the performance metrics (throughput and MER). Monte Carlo evaluation of T designates the evaluation of each transition probability, given by Eq. (1.20), based on the randomly generated channels. Then, the steady state probabilities are evaluated as in Section 1.5.3, and the performance metrics are obtained using Eq. (1.39) and Eq. (1.40). Analytical form of T designates the evaluation of the closed-form expression of each transition probability except for t1,8, whose expression cannot be written in closed-form. These expressions were derived in Section 1.5.2. The corresponding plots of the throughput and MER are provided in Fig. 1.14 and Fig. 1.15, respectively. For validation purposes, these performance metrics are evaluated in function of the energy per symbol to noise ratio (in dB), which is denoted by Es/N0. Actually the source as well as the relay transmit their symbols with energy Es.
Table of contents :
List of Acronyms
List of Symbols
General Introduction
1 Relay assisted Hybrid ARQ
1.1 Introduction
1.2 From ARQ to Relay assisted Hybrid ARQ
1.3 Performance evaluation framework for HARQ protocols
1.4 Relay assisted HARQ protocols
1.5 Markov chain model of the investigated protocol
1.6 Numerical results and comparison of the protocols
1.7 Conclusion
2 Multi-Packet Hybrid ARQ with Delayed Feedback
2.1 Introduction
2.2 From Stop-and-Wait HARQ to Multi-packet HARQ
2.3 Proposed Protocol
2.4 Numerical results
2.5 Conclusion
Conclusions and Perspectives
Bibliography
