Combine-and-forward: A linear cooperative multi-level communication strategy for distributed MIMO relays

Abstract This work analyzes cooperative networks in which a single source message is retransmitted by multiple levels of relays that are equipped with multiple antennas. In the considered scheme, each relay linearly combines its receptions from multiple antennas and multiple levels before adjusting its power and forwarding it. The proposed scheme outperforms the previously proposed methods that are based on decoding and forwarding in the low SNR regime. The contributions of this paper are two-fold: (i) it provides an analytical framework for the statistics of the accumulated signal and the accumulated noise as functions of network parameters such as noise level, power level, number of antennas, and multi-hop diversity for dense networks; (ii) it shows that the performance of multi-level networks can be improved simply by combining the receptions from the previous levels and multiple antennas in a linear fashion.