An enhanced zero-forcing equalizer for combinerless LINC-OFDM systems

The energy efficiency of OFDM systems is known to be low due to the high peak-to-average power ratio problem. The linear-amplification-with-nonlinear-component (LINC) technique can solve the problem by decomposing the input signal into two constant-envelop component signals and applying high-efficient nonlinear amplifiers. However, the power combiner, a key component used to combine the amplified signals, is difficult to implement. Combinerless LINC systems employ two transmit antennas such that two component signals can be naturally combined at the receiver. Unfortunately, the performance of combinerless LINC-OFDM systems is seriously degraded if difference exists, even small, between the two channels that the two component signals propagate. In this paper, we propose an enhanced zero-forcing equalizer to solve this problem. The main idea is to reduce a self-interference induced by the channel difference. A closed-form expression for the optimum parameter of the proposed equalizer is also derived. Simulations show that the proposed equalizer can effectively enhance the performance of combinerless LINC-OFDM systems.