FEQ for Standard OFDM Systems with Insufficient CP

摘要

In Orthogonai frequency division multiplexing (OFDM) systems, when the length of the Cyclic prefix (CP) is shorter than the channel length, there exist Intersymbol interference (ISI) and Interchannel interference (ICI) and the one-tap frequency domain equalizer is not applicable any more. A Time-domain equalizer (TEQ) is usually used in the receiver to reduce the duration of the overall response of the transmission system, and therefore minimize the ISI and ICI. However, the optimum design of TEQ turns out to be a difficult task. In this paper, we propose a Frequency domain equalizer (FEQ) for standard OFDM systems with insufficient CP by employing the null side sub-carriers and CP redundancy. The equalizer has a sparse matrix structure and thus a low computational complexity. Theoretical anaiysis and simulation results indicate that it can efficiently remove ISI and ICI caused by insufficient CP and recover the transmitted data. Moreover, we derive the condition for the existence and uniqueness of FEQ, i.e., the combined length of CP and null subcarriers is not shorter than the channel order, which means that the insufficiency of CP in time domain can be compensated by the redundancy in frequency domain.