Downlink Interference Alignment

TLDR

Uplink interference alignment requires inter‑cell CSI exchange, whereas the proposed downlink IA only needs intra‑cell feedback. The study develops a downlink interference alignment technique for cellular systems. The scheme is implemented with minimal changes to existing cellular systems, leveraging existing intra‑cell feedback for multi‑user MIMO. The scheme yields a four‑fold throughput gain in a two‑cell layout and about 20% gain in a realistic 19‑cell wrap‑around layout, demonstrating substantial performance improvement.

Abstract

We develop an interference alignment (IA) technique for a downlink cellular system. In the uplink, IA schemes need channel-state-information exchange across base-stations of different cells, but our downlink IA technique requires feedback only within a cell. As a result, the proposed scheme can be implemented with minimal changes to an existing cellular system where the feedback mechanism (within a cell) is already being considered for supporting multi-user MIMO. Not only is our proposed scheme implementable with little effort, it can in fact provide substantial gain especially when interference from a dominant interferer is significantly stronger than the remaining interference: it is shown that in the two-isolated cell layout, our scheme provides four-fold gain in throughput performance over a standard multi-user MIMO technique. We show through simulations that our technique provides respectable gain under a more realistic scenario: it gives approximately 20% gain for a 19 hexagonal wrap-around-cell layout.