Information Rates and Capacity for Multi-Antenna Cellular Systems with Fading

The demand for high throughput cellular communications has motivated the need for new approaches aimed at maximizing achievable rates over the wireless channel. The idea of using multiple antennas both at the base station and the mobile user side to increase achievable rates over the fading channel has been considered in previous literature. However, most literature on Multi-antenna systems does not make a clear distinction between the uplink and the downlink. While it is reasonable to assume that the downlink is coherent under certain conditions, it is not realistic to assume the same for the uplink. This dissertation presents results on the achievable information rates as well as the capacity of both the uplink and downlink of a cellular system with multiple antennas.

For the uplink, the dissertation considers a system having a large number of competing users trying to maximize their rate under a peak power constraint. The dissertation proves that the optimal strategy in this non cooperative scenario is for the users to transmit i.i.d PSK inputs at full power. The dissertation then presents an analytic expression for the information rate of the Multi-antenna fading system in the wideband regime. This result is useful for a designer to judge the performance of new coding schemes for the cellular uplink (just like BPSK capacity is useful to evaluate the performance of binary codes on the point-to-point AWGN channel).

For the downlink, this dissertation presents a new paradigm for studying and designing full diversity and high rate codes. In existing literature, space-time coding is presented as a solution to the problem of coding for the downlink when the base station has multiple antennas. The new paradigm operates on a symbol by symbol basis (as opposed to space-time codes which operate on a block of transmitted symbols). The dissertation applies this principle to design spatial modulators schemes for the downlink. The results show that spatial modulators offer a simple elegant design for Multi-antenna systems which performs better than conventional space-time codes in terms of achievable information rates.