Relay-Aided Communication Schemes for Wilreless Multiple Access and Multicast Channels

Abstract

User cooperation through relaying is a powerful tool to combat fading and to increase robustness of wireless networks. This thesis explores cooperative schemes for wireless multiple access and multicast channels in the presence of a single dedicated relay. Novel cooperative schemes presented here are based upon relay performing decode-and-forward (DF), noisy network coding (NNC) or a combination of both DF and NNC. The first half of this thesis presents cooperative schemes for a multiple access channel. It considers an uplink non-orthogonal multiple access relay channel (NOMARC) in which multiple users wish to communicate to a single base-station (BS) with the help of a single dedicated relay. Firstly for a two- user setup, we derive the improved achievable rate region by employing NNC-only relaying as opposed to conventional compress-and-forward (CF) relaying. Next, for the multiple user setup, we propose a novel Joint NNC-DF (J-NNC-DF) scheme that utilizes DF cooperation when messages from all user are successfully decoded at the relay and NNC when the relay is unable to decode message of any one of the users. In the scenario when the relay is capable of successfully decoding messages from only a subset of users, J-NNC-DF performs joint DF and NNC encoding with DF applied to the set of messages that were decoded successfully, and NNC for the set of messages that were not decoded successfully. After presenting the achievable rate regions, we derive closed form expression for probability of outage for the proposed schemes. These outage expressions permit selection of optimal quantizer noise variance selection to minimize probability of outage. Both analysis and simulations confirm that the proposed J-NNC-DF scheme outperforms other existing benchmarks such as DF-only, NNC-only and NNC-or-DF. In the second part of this dissertation, we propose a cooperative scheme for a downlink multicast network in which a BS wishes to communicate the same message to multiple users with the help of a single dedicated relay. For this setup, we propose a layered multiplexed-coded decode-and-forward (LMDF) relaying scheme. This scheme comprises of two major components: layering at the BS and mulitplexed DF encoding at the relay. BS message is split into two layers, independentlyencoded and mapped to a quadrature amplitude modulated (QAM) constellation, thus achieving superposition. The benefit of superposition coding of the two layers is that it allows partial message recovery at the relay and the users. On the other hand, multiplexed coding at the relay enables each user to divert all channel resources towards decoding the layer(s) that remains unrecoverable from the BS’s transmission. After deriving achievable rate regions, performance comparison is carried out for the proposed schemes against superposition coded and unlayered BS transmissions. In short, the dissertation proposes, analyzes and simulates J-NNC-DF and LMDF as viable candidates for future generation wireless communication networks.