On Performance of Limited Feedback Coordinated Multipoint Transmission for Mobile Systems

Mobile networks are expected provide consistent quality of experience across the service area. Yet, intercell interference is one of the main causes for the inconsistent user experience in contemporary mobile systems especially when the universal reuse of spectrum is applied. To mitigate and/or even exploit the intercell interference, coordinated multipoint (CoMP) transmission/reception has been considered as a promising technique and it is incorporated in the fourth generation mobile standard. Various CoMP techniques have been investigated in literature and practice, each offering differing trade-offs between performance and implementation requirements. Thus, effective use of various CoMP realizations requires thorough understanding of the mentioned trade-offs associated with each CoMP technique. The contribution of this thesis includes practical approaches for development of effective CoMP transmission methods. Dissertation investigates the methods from three perspectives, namely: by proposing a flexible and practical hierarchical feedback structure to effectively combine different beamforming techniques in CoMP transmission; by studying the performance degradation of CoMP systems due to channel power imbalance in practical CoMP methods with limited feedback; and by evaluating CoMP performance gains in realistic urban deployment scenarios using deterministic 3D propagation models. Performance results reveal that in addition to implementation flexibility, notable performance gain can be achieved by simple limited feedback CoMP methods. Our results also demonstrate that the use of amplitude feedback – fast or slow – is important to effectively compensate the impact of channel power imbalance. Furthermore, our results show that CoMP may significantly relax the capacity gap between backhaul and access links of self-backhauled low power nodes.