Bounds on the Capacity of the Gaussian Soft-Handover Channel

In this paper, we introduce the model for a Gaussian soft-handover channel (SHC), which adds a new dimension of flexibility to the well-known interference channel (IC). We provide a unified framework for computing achievable rate regions for the SHC in both the uplink and downlink cases. This achievable rate region for SHC is given by the convex hull of the union of certain multiple-access, interference, broadcast, and Z-channels. Some properties of the achievable region are studied. Specifically, we show the following key results: 1) in an uplink SHC, there are channel conditions under which decoding at a single receiver based, for example, on a maximum SNR condition does not achieve the entire boundary of the achievable region; 2) in a downlink SHC, multiple base stations should transmit independent information to all users to achieve the boundary points of the achievable region; and 3) when a mobile communicates with multiple base stations, the ratio of the uplink rates with different base stations could be different from the ratio of the downlink rates with those base stations. A simple outer bound on SHC capacity based on the capacity of multiple-input-multiple-output (MIMO) systems is also given.