Analysis of the Channel Capacity under OFDM System with Insufficient CP

Abstract

The standard OFDM signal requires a cyclic prefix (CP) of length larger than the channel impulse response. This paper investigates the effect of CP length to the capacity of OFDM system. We have found that full CP or none CP may not be optimal in the sense of capacity. Specifically, the capacity is a monotonic function of CP length in the low and high SNR regime and is approximately concave down when SNR is about 3dB.