BD-ZCS: Multi-cell interference coordination via Zadoff-Chu sequence-based block diagonalization

Multi-cell interference coordination via Block Diagonalization (BD), which is widely used in LTE-Advanced interference management, has three main drawbacks: (1) limitation on the number of supported co-channel users; (2) performance degradation in Doppler channels with feedback delay and quantization; and (3) high signaling overhead to exchange Channel State Information (CSI) and to generate precoding matrix. In this paper, a new approach is proposed to overcome these drawbacks and to improve the multi-cell interference coordination. The core idea is to create a null space only to the users within one cell; to achieve this goal, Zadoff-Chu Sequence (ZCS) spreading is used to eliminate the multi-cell interference by leveraging the zero-correlation property of cyclic shifts of the ZCS. This way, the capacity of the cellular network is improved in Doppler channels with delayed and quantized feedback; moreover, signaling overhead and computational complexity are both reduced. The auxiliary sampling capability of the hardware is utilized to realize the higher sampling rate required by the proposed approach. The new interference-management solution is compared against the existing one via computer simulations and is shown to lead to significant capacity gains even in high-mobility scenarios.