Base Station Assignment and Power Control Algorithms for Data Users in a Wireless Multi-Access Framework

In this report, we consider the problem of assigning data users to base stations and modulating their transmit power in a multi- access wireless framework. The goal is to perform the assignment and power control in order to maximize the total throughput of the users in the up link channel. Base stations transmit over different frequency bands, thus eliminating any inter- cell interference. We also assume that base stations employ interference cancellation in order to achieve the maximum total throughput. Two separate scenarios are investigated. In the first case, called the static case, we assume that the channels between the mobiles and the base stations are stationary. The mobiles then transmit with constant power and the problem reduces to simply assigning each mobile to a base station. Prior research [2], [7] has considered integrated base station assignment and power control for voice users. However, for data users, the problem is fundamentally different from the context of voice users. Data users operate in the high SNR regime where the linear approximation of rate as a function of transmit power may no longer be valid. This non-linearity increases the complexity of the base station assignment problem. We show that the problem is NP complete and propose sub-optimal polynomial time algorithms and bound their performance. In the second case, called the dynamic case, we assume that the channels between the mobiles and the base stations are independent random processes with known distributions. The instantaneous channel state is known at both the receivers and the transmitters. The objective is to select, for each mobile a base station and a transmit power as a function of the channel state in order to maximize the expected total up link throughput. We derive the optimal power control and base station assignment in the case of a single data user and multiple base stations. This algorithm is then extended to a joint base station assignment and power control algorithm, for the multiple base stations and multiple users wireless system. We show that the algorithm reduces to the optimal solution in the single base station and multiple users case [5].