A Practical Layered Multiplexed-Coded Relaying Scheme for Wireless Multicast

Abstract

We design and implement a practical layered multiplexed-coded decode-forward (LMDF) relaying strategy for a wide-band wireless multicast network. The proposed LMDF scheme relies on layering at the source, with the individual layers provided unequal power allocation through a simple bit-mapping operation to quadrature amplitude modulation constellations. At the relay, LMDF utilizes a multiplexed-coded approach that, with a single transmission, caters for the disparity in the number of layers decoded at different destinations. Under a practical setup of hard-decision decoding and coding across the subcarriers of orthogonal frequency division multiplexing (OFDM) modulated transmissions, we derive the information theoretic achievable rates of LMDF and use the IEEE 802.11 TGn channel model for performance evaluations. LMDF is then implemented using convolutional codes, with the relay's code optimized specifically keeping its multiplexed nature in mind. In addition to simulations, we also evaluate the performance of LMDF through a system-level implementation by using the National Instruments USRPs 2921. We conduct over-the-air experiments in an indoor office environment using an OFDM-based physical layer, and illustrate the considerable performance benefits of LMDF over benchmarks such as conventional two-hop decode-forward.