Decentralized Transmit Beamforming scheme for interference coordination in small cell networks

To cope with the growing demand of mobile data in hot spot areas of wireless networks, the use of massive small cell deployments with universal frequency reuse is essential. Such an aggressive reuse of spectral resources increases the level of co-channel interference, and calls for advanced multi-cell interference coordination techniques to capitalize cell densification gains. One option to address this problem is to use multiple antennas at the Base Stations (BSs), and implement Transmit Beamforming (TBF) to coordinate the interference generated to neighboring cells. A small cell BS should be low-cost by definition, and should be designed to serve typically a small number of Mobile Stations (MSs). Accordingly, we consider that each BS uses the same TBF vector to communicate with its associated MSs in the whole frequency band, and that the optimal TBF vector is determined utilizing a cooperative decentralized scheme. The proposed scheme seeks the maximization of a global utility function of the whole Small Cell Network (SCN), and relies solely on the exchange of low-rate signaling information among neighboring cells. As expected, the gain of the proposed cooperative TBF scheme increases as the number of MSs per cell decreases. A similar behavior is observed when the number of cooperative BSs per cell cluster grows. Thus, the proposed scheme seems to be applicable to SCNs with notable performance gains.