Iterative timing-induced interference suppression in a two-tier OFDMA uplink network

Abstract

Consider a scenario in a two-tier cellular network wherein all subscribers adjust their transmission-times to be synchronously received at the macro base-station (MBS). This transmission timing arrangement causes asynchronous reception of signals and inter-carrier interference (ICI) at the femto base-station (FBS). In this paper, an iterative interference suppression scheme for reducing the ICI at the FBS is presented. By assuming a number of macro-users (MUs) and a single femto-user (FU), the mean square error (MSE) cost-function is first defined, based on which, the closed-forms for 3 underlying parameters, i.e., precoder, equalizer and the automatic gain controller are then derived by proposing a partial derivative-based sub-optimization scheme. To counteract the interrelation of the aforementioned parameters, an iterative algorithm is further proposed which results in finding a local-optimum point of the cost-function. To demonstrate the successful interference suppression performance of the proposed scheme, a per-subcarrier interference power analysis is also derived. The simulation results demonstrate a reasonable convergence after 6 iterations. Moreover, for the proposed scheme, a close bit error rate (BER) performance to that of a system without any timing-induced interference at low and medium SNRs (i.e., <20 dB) and a comparable performance at higher SNRs (i.e., 20 dB & <30 dB) are observed.