Capacity And Power Control Of Multiuser Systems

No mater how fast the evolution speed of the wireless network is, the rate of the wireless network can not transcend the theoretical limits-system capacity of the network under the perspect of information. Study the network theorical capacity can help us to know the developing goal of possible techniques and to explore the potential of the current networks. Besides, study the mathematic characters of system capacity can inspire us to find the neccesary condition and sufficient condition to reach the capacity, which indicates the directors for the design of the practical techniques.The information capacity for point to point communications was originally arised by Shannon. When extend the Shannon formula to multiuser systems, many problems have to be considered, e.g. multiuser schedule, power control, interferences among users and channel side information feedback designs. At the same time, the measurement of capacity is changed from a single scalar to many new concepts such as capacity region and sum capacity. This paper is focus on sum capacity and power control of multiuser systems. Both downlink and uplink are considered:(1) For the downlink of single cell multiuser systems, sum capacity with quantized channel side information is studied. The system capacity with quantized channel side information under Max C/I scheduler is studied. The optimal solutions for the scenarios with/without power control, with/without fixed quantization boundaries are derived, and the optimal joint design of power, rate and quantization boundaries are provided.(2) For the uplink of single cell multiuser systems, the optimal power control for sum rate maximization is studied. It is proved that under the users’ peak power constrains, binary power control is optimal, i.e. all scheduled users should transmit with peak power. Based on this property, the structure of the optimal power control is derived, the sufficient condition for time divison scheduler to be optimal scheduler is provided. With these conclusions, the optimal power control algorithm and a low complexity suboptimal algorithm are proposed.(3) For the uplink of single cell multiuser systems, sum capacity and its optimal power allocation for users with Quality of Service(QoS) requirement and users with experience differentiations are studied respecitively. Mathemetic properties of the optimal power allocation are derived. Based on these properties, the power control for users with QoS constraints and users with different experience are provided respectively.(4) For multicell multiuser systems, sun capacity and its optimal power control are studied. The optimal power control for uplink systems are analysised fisrtly, based on the properties of the optimal power control, some suboptimal algorithms are provided. Then we discuss the sum capacity of the downlink systems. The system model of uplink includes the cases of base stations with/without successive interference cancelation(SIC) technique. For the scenarios that binary power control can achieve similar performance as the optimal power control, many suboptimal algorithms as well as a fairness algorithm are proposed.