Improving the Spectral Efficiency of Amplify-and-Forward Cooperative Relay Network with Adaptive M-QAM Modulation

Abstract

This paper investigates the performance of cooperative amplify-and-forward (CAF) relay networks with adaptive M-ary quadrature amplitude modulation (M-QAM) technique in Nakagami-m and Rice wireless fading environments. We derived closed form upper bound expression for the marginal MGF of end-to-end SNR of CAF relay system in Nakagami-m fading to compute average bit error rate (ABER), mean achievable spectral efficiency, and outage probability performance metrics. Additionally, along with the above bounding techniques, we have adopted an accurate approximate MGF of end-to-end SNR of CAF relay system to compute above mentioned performance metrics. Employing the above novel approach based on "approximate MGF" allows us to simplify the computation complexity of achievable spectral efficiency as well as ABER of CAF relay system in generalized fading environments by simply replacing appropriate single channel MGF as readily available. The accuracies of our analytical results have been validated via Monte Carlo simulations.Index Terms -----cooperative communications, wireless link adaptation, adaptive M-QAM modulation. I. MOTIVATIONThe demand for wireless communication system in recent years has necessitated a need to improve the performance, reliability and data rate of wireless channels. To address these needs, several attempts have been made on each of these improvement areas. The broadcast nature of wireless transmissions has enabled a new communication paradigm known as "cooperative communication" where the source node communicates with a destination node with the help of one or more relay nodes to harness the new form of spatial diversity and combat multipath fading. This introduced additional reliability improvements. Adaptive transmission is yet another powerful wireless communication technique for improving the spectral efficiency wherein the signal constellation size, power level and/or coding rate are "matched" to the prevailing channel conditions based on the acquired channel-side-information (CSI) on the feedback channel. Although there have been extensive prior work on performance analyses of non-adaptive (i.e., fixed-rate or fixed-power) cooperative diversity systems and also on adaptive transmission techniques for traditional (noncooperative) wireless networks, the art of adaptive link layer in cooperative wireless networks is still in its infancy [1]- [3]. But theoretical studies of such systems would be of interest to several emerging IEEE 802 standards such as 802.11s and 802.16j that are considering the use of cooperative techniques in their multi-hop relay architecture for enhancing coverage, throughput, and network capacity.In this paragraph a brief review of prior research on cooperative diversity with adaptive transmission is discussed. The problem of optimal power allocation in wireless relay networks was investigated in [4]-[5], but source rateadaptation was not considered. In [6], the author investigated the adaptive transmission for a two-hop (regenerative and nonregenerative) relay network (...

Joint-Design of Link-Adaptive Modulation and Coding with Adaptive ARQ for Cooperative Amplify and Forward Relaying System

“…Authors in ref. [5]- [9] have considered Adaptive Modulation and/or optimal power allocation amongst collaborating nodes in cooperative relay systems. Whereas authors in ref.…”

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“…By exploiting a "desirable" exponential integral representation for ln (.) function [12], it is straight-forward to show that the normalized ergodic capacity (with respect to bandwidth B) of CAF relay networks is given by Following the development similar to (22), it is also possible to evaluate (24) in closed-form for Rayleigh and Nakagami-m channels (positive integer m). For instance, it is not difficult to show that normalized ergodic capacity with a single cooperative relay over an i.n.d Nakagami-m channel is given by v B (18)) is recommended for its simplicity and applicability to a wide range of fading environments.…”

“…In fact, (18) could dramatically speed-up the evaluation of performance metrics of interest such as the achievable average spectral efficiency and the average bit error rate (ABER) for CAF multi-relay networks that employ adaptive modulation via the analytical framework employed in [22]- [25]. The average normalized spectral efficiency AM C and ABER with adaptive modulation AM BER with T modulation switching modes are given by (26) and (27), respectively: …”

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“…Following the development similar to (22), it is also possible to evaluate (24) in closed-form for Rayleigh and Nakagami-m channels (positive integer m). For instance, it is not difficult to show that normalized ergodic capacity with a single cooperative relay over an i.n.d Nakagami-m channel is given by v B (18)) is recommended for its simplicity and applicability to a wide range of fading environments.…”

“…Another important application of our MGF formula (18) is the joint-design of cooperative diversity with discrete-rate adaptive modulation. In fact, (18) could dramatically speed-up the evaluation of performance metrics of interest such as the achievable average spectral efficiency and the average bit error rate (ABER) for CAF multi-relay networks that employ adaptive modulation via the analytical framework employed in [22]- [25]. The average normalized spectral efficiency AM C and ABER with adaptive modulation AM BER with T modulation switching modes are given by (26) and (27), respectively:…”