Wang, Di

We developed a cross layer design which combines retransmission diversity and
multi-user diversity for wireless communication. To this end, a joint design of
adaptive modulation and coding with retransmission-based automatic repeat request
protocol is outlined. This design is applied to devise multi-user scheduling schemes,
which can optimally capture the available multi-user and retransmission diversities. In
addition, the proposed on-line scheduling algorithms can operate even when the
underl ying fading channel distribution is unknown, while asymptotically converging
to the offline benchmark with guarantees on prescribed fairness and rate requirements.
Numerical results are provided to verify the merits of our novel schemes for
multi-user transmissions over Nakagami block fading channels.

Wireless devices in wireless networks are powered typically by small batteries that are not replaceable nor recharged in a convenient way. To prolong the operating lifetime of networks, energy efficiency is indicated as a critical issue and energy-efficient resource allocation designs have been extensively developed. We investigated energy-efficient schemes that prolong network operating lifetime in wireless sensor networks and in wireless relay networks. In Chapter 2, the energy-efficient resource allocation that minimizes a general cost function of average user powers for small- or medium-scale wireless sensor networks, where the simple time-division multiple-access (TDMA) is adopted as the multiple access scheme. A class of Ç-fair cost-functions is derived to balance the tradeoff between efficiency and fairness in energy-efficient designs. Based on such cost functions, optimal channel-adaptive resource allocation schemes are developed for both single-hop and multi-hop TDMA sensor networks. In Chapter 3, optimal power control methods to balance the tradeoff between energy efficiency and fairness for wireless cooperative networks are developed. It is important to maximize power efficiency by minimizing power consumption for a given quality of service, such as the data rate; it is also equally important to evenly or fairly distribute power consumption to all nodes to maximize the network life. The optimal power control policy proposed is derived in a quasi-closed form by solving a convex optimization problem with a properly chosen cost-function. To further optimize a wireless relay network performance, an orthogonal frequency division multiplexing (OFDM) based multi-user wireless relay network is considered in Chapter 4.