An Efficient Cooperation Strategy and Cooperation Region Analysis in Cognitive Femtocell Networks

We consider a two-phase cooperative transmission strategy in cognitive femtocell networks, where a femto-base station (BS) employs cooperative relaying to increase throughput of a macro-mobile station (MS) at cell edge in reward for the access of the spectrum allocated to the macro-MS. Under this strategy, we formulate optimization problem to maximize the femto-MS rate while satisfying the rate requirement of macro-MS and illustrate the optimal policy: optimal time duration and power allocation. In addition, we analytically derive the critical cooperation region where a femto-BS can always achieve the rate requirement of the macro-MS, which is expressed in terms of distances between femto-BS and macro-MS and between macro-BS and femto-BS. The simulation results show the derived cooperation regions for different β and confirm rate gain of the cooperation strategy.