An outage-based transmission strategy for MIMO femtocells

This paper studies transmit optimization for a multiple-input multiple-output (MIMO) femtocell that coexists with a macrocell by concurrently accessing the same frequency bands in an uncoordinated manner. Due to the lack of active cooperation between macrocell and femtocell, a stochastic strategy that exploits channel distribution is considered, in an attempt to optimize the femtocell performance as well as guarantee the macrocell service quality in the form of outage-probability. By investigating the upperbound/lowerbound of the macrocell outage-probability, a suboptimal femtocell transmission strategy is proposed, whose solution leads to the single eigenmode transmission and thus aggressively simplifies the original problem. Moreover, it is shown that when single antenna is equipped for the macro-link, the upper and lower bounds become tight to each other. Numerical results are provided to validate the efficiency of the proposed strategy.