SUMMARYFemto cell technology is a promising solution for indoor coverage of cellular systems. The interference between macro and femto cells can be mitigated via cooperation between the macro base station (BS) and the inside femto sites (FSs). In this paper, the idea of multi-cell multi-input and multi-output is introduced, whereby the macro BS shares the same frequency band with the inside FSs in support of the femto users. Both single-user and multi-user precoding at the macro BS are proposed to support the cooperative transmission between the macro BSs and FSs. In single-user precoding and multi-user precoding without power allocation, only the angle information of the FS-user channels is required to be sent from the users to the macro BS. If the magnitude information is also sent by each user, multi-user precoding with power allocation can be employed to support cooperation between macro BSs and FSs, which is an extension of the classical water-filling optimization problem. Theoretical derivations and an iterative algorithm are both presented to solve this optimization problem. Analytical and simulation results with respect to the signal received with interferences validate the effectiveness of cooperation between the macros BSs and FSs.
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