A Power-Enhanced Femto Cooperative Scheme in OFDM Heterogeneous Networks

Femtocells constitute a promising solution to increase the data rates of next generation wireless demands, not only by extending the coverage, but also by acting as relays to achieve diversity gains. However, when deployed in areas already covered by macrocells, the interference levels are also expected to increase. Time multiplexing is a standard way to avoid interference, but it also reduces the transmission time of each user. By serving as relays like in a FeCOPE system, femtocells can forward the received signals in a different time slot and the receiver can then combine them to cancel out interference. However, most cooperative approaches for femtocells do not consider the frequency selectivity of the channel of each receiver and simply transmit with constant power in all subcarriers. Therefore, we propose cooperative waterfilling (Coop-WF), an algorithm that varies the power allocation in a FeCOPE system by exploiting users diversity to achieve diversity gains in OFDM heterogeneous networks.