Multi-Hop Capacity of MIMO-Multiplexing Relaying in WiMAX Mesh Networks

Abstract

One of the main challenges for metro-scale WiMAX mesh network deployments is related to capacity scaling. In a full mesh mode, a WiMAX node acts as a mesh router as well as a client access node. To improve latency and speed performance, typical dual- and multi-radio mesh solutions use different radio channels to create separate links for access and mesh relaying services. The available spectrum is therefore split between mesh and client access services. Network operators operating the WiMAX system over the licensed spectrum are not keen to provide separate radio channels for access and mesh relay services, as this reduces the total number of users serviced per spectrum allocation. MIMO-multiplexing relaying approach however provides separate links for access and mesh relaying services on the same radio channel. In this paper, we discuss the multi-hop capacity of OFDM-based MIMO-multiplexing relaying in WiMAX networks. For an NxN MIMO-multiplexing relaying with amplification factor alpha at relay nodes, R-hops relaying degrade the capacity by at most -Nlog <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (alpha <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2R</sup> /(1 +Sigma <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r-1</sub> alpha <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2r</sup> N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sup> )) + <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RN</i> /log <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (N) bits/sec/Hz. Therefore, greater capacity loss is experienced in networks employing high-order MIMO- multiplexing relaying. We also show that the capacity loss is independent of the OFDM configurations employed; thus network operators could employ higher OFDM configurations to compensate data rate loss in access services when some of the MIMO-multiplexing links are dedicated to mesh relay. This analysis provides useful guidelines for operators planning MIMO-multiplexing option for mesh support in WiMAX network.