Bounds and protocols for a two-way multiple node channel

Abstract

Often in multiuser wireless systems like cellular networks, data is present in both directions (uplink and downlink). One way to formulate protocols for such networks, is to design the uplink and downlink independently. But such a design ignores the two-way nature of data. We show that by jointly designing the uplink and downlink, we get rate gains as long as there is data in both the directions. We make a distinction between data being two-way and the channel being two-way and show that for the case where only the channel is two-way, a disjoint design is optimal. The rate gains can be attributed to the inherent feedback in two-way schemes which enables cooperation in all topologies (including hidden node topologies). Furthermore, in near-far situations, the weak user gains appreciably from such cooperation. Finally we demonstrate that several well known inner bounds can be derived as special cases of our rate region.