User cooperation scheme with decoded-interference forwarding in a two-cell system

Abstract

In a conventional cellular system, the achievable rates of the cell edge users are severely degraded by interferences from neighboring base stations since each base station simultaneously transmits information to its user. To mitigate the interference at the cell edge users, we propose a user cooperation scheme that improves achievable rates of a cell edge users in a two-cell system. In the proposed user cooperation, one user helps the other user`s decoding by either desired signal forwarding or interference forwarding. In desired signal forwarding, one user retransmits the other`s data if it has the data by decoding the interference from SIC. Then, the relayed user decodes its data from the received signal based on the enhanced signal-to-interference plus noise. In interference forwarding, one user relays its own data to the other user. If the received interference from the relayed user is sufficiently large, it can rather decode the interference first and subtract it from the received signal from base station. Consequently, the relayed user decodes the desired data without any interference.

We derive achievable rate region of the proposed user cooperation and compare it with that of a conventional interference channel. It is shown that the proposed user cooperation exploiting either SF or IF is beneficial in terms of achievable rate region compared to the conventional interference channel. We also consider the cases that chase combining and incremental redundancy techniques are applied to our proposed user cooperation to achieve more gains. Finally, we proposed the hybrid forwarding scheme which combines desired signal forwarding and interference forwarding.