Spatial Reuse Precoding for Scalable Downlink Networks

In this paper, we develop linear precoding schemes for MIMO downlink networks with quasi-static channels that are scalable, in the sense that they can be implemented with moderate complexity in networks with increasing numbers of cells and users. The principle that underlies the proposed precoding scheme is to exploit the decomposable structure of the equivalent channel matrix by designing the precoders at the base stations to be decomposable as well. Thus, the channel matrices and the designed precoders can be expressed as the Kronecker product of constituent matrices. For networks with a finite number of cells, the proposed structured precoding schemes enable inter-cell interference cancellation without the need for inter-cell feedback and provide more degrees of freedom than conventional interference avoidance schemes, while incurring a latency that grows only linearly in the number of cells. The proposed structured precoding schemes also enable a scaling approach for unbounded networks that we have called “spatial reuse precoding” (SRP). SRP is based on the observation that at each receiver, the signals from interfering sources that employ the same precoder arrive in the same subspace, regardless of the particular channel matrices between the interfering sources and the receiver. In some typical cellular architectures we show how an SRP scheme based on the proposed structured precoders can be designed to eliminate the dominant sources of interference without requiring cooperation between cells. In addition, we show that SRP can provide substantial performance gains in certain heterogeneous networks.