검색 상세

Interference Mitigation Strategies Using Coordinated Multipoint Transmission for Cellular Communication Systems

협력적 다점 전송의 활용을 통한 셀룰러 통신 시스템의 간섭 완화 방안

초록/요약

For cellular mobile wireless systems, co-channel interference (CCI) is one of the major obstacles in performance enhancement. Besides the conventional type of CCI generated from adjacent base-stations (BSs), different types of CCI are appearing due to new transmission techniques in next-generation cellular mobile systems. In this dissertation, we first consider the problem of inter-user CCI generated by multi-user multiple-input multiple-output (MUMIMO) transmission for a given transmission point. Using the capacityachieving optimal transmission beamforming, the maximum weighted sumrate (WSR) for given arbitrary weights is investigated for Gaussian broadcast channels (GBCs). Although it involves an iterative algorithm in general, we focus on the important special case of the two-user channel to provide a closed-form expression for the maximum WSR based on the uplink-downlink duality. When multiple BSs are available as serving nodes for a user equipment (UE) of interest, the UE can select the most desired BS as the serving node among multiple candidates. To mitigate the inter-cell CCI, the selection is conducted to maximize the performance metric of signal-to-interference ratio (SIR). In this case, an exact analytic expression for the maximum SIR is presented for an arbitrary channel environment. As an illustrative example, the maximum SIR distribution is determined in a closed-form formula for Rayleigh fading channels when a UE is surrounded by three BSs. For heterogeneous network (HetNet) systems employing different types of multiple transmission nodes within a cell, the intra-cell CCI also plays a significant role in degrading the system performance. Various efforts to mitigate inter- and intra-cell CCI problems are being made for the Long Term Evolution (LTE) systems, including coordinated multipoint transmission (CoMP) and enhanced inter-cell interference coordination (eICIC). In this regard, we present several operational strategies utilizing CoMP and eICIC, and their performance is evaluated by Monte-Carlo system-level simulations. For the presented CCI mitigation methods, perfect channel state information (CSI) is required at the transmitter side to achieve the theoretical performance limit. However, obtaining the CSI at the transmitter side is closely related to practical issues including the feedback overhead. We propose a resourceefficient feedback method which reports the differential CSI between two adjacent time instances to the transmitter through the rate-limited feedback link. Adopting MU-MIMO transmission, it is shown by numerical results that the proposed scheme nearly achieves the performance of the perfect CSI at the transmitter case even with much smaller feedback resources than the conventional CSI feedback scheme.

more