M.Sc Thesis

M.Sc StudentKatz Gil
SubjectOn Layered Transmission in Clustered Cooperative Cellular
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Shlomo Shamai )Shitz(


In today's cellular systems, each base station is in charge of serving only the mobile stations that belong to the same cell. This strategy causes high levels of interference throughout the network, which becomes interference limited. As demand to high data rates grows, dividing costly resources between cells becomes less appealing as an option for coping with the problem. One way of contending with the issue is by proposing base-station cooperation. While global cooperation was already shown to achieve significant improvement in system performance, its implementation becomes prohibitively complex as the size of the network grows. Thus, local base-station cooperation may offer a fine balance between system performance and complexity.

In this work, an approach to local cooperation between neighboring cells is explored. "Layered" rate-splitting based transmission strategies are investigated for the uplink of cellular communication systems employing clustered cooperative processing. Accordingly, partial decoding of some received out-of-cluster ``layers" is employed, while undecoded "layers" are treated as noise. A two-dimensional Wyner-type system model is considered, by which only adjacent cell interference is present and characterized by a single parameter alpha.

Focusing on the average throughput per cell, the setting is shown to be equivalent to a certain multiple-input multiple-output (MIMO) multiple access channel (MAC). An achievable average throughput is then obtained by efficiently solving an appropriately formalized Complementary Geometric Programming (CGP) problem.  Significant performance enhancement is demonstrated compared to non-cooperative single-cell processing, as well as to "naive" cooperation, where out-of-cluster interference is treated as noise.

Both non-fading and flat fading channels are considered. It is demonstrated that the optimal power-allocation strategy, under the proposed layering scheme, is significantly different for each of the considered environments. While results show significant improvement in performance for both cases, it is especially in the Rayleigh-fading environment that results encouragingly approach upper bounds in extreme SNR regimes.