Channel Estimation Assisted by Postfixed Pseudo-Noise Sequences Padded with Null Samples for Mobile OFDM Communications

A channel estimation (CE) technique that uses a postfixed pseudo-random sequence padded with zeros is investigated in this paper to extend pseudo-random-postfix orthogonal-frequency-division-multiplexing (PRP-OFDM) communications onto mobile applications. The proposed technique takes advantage of pseudonoise (PN) sequences periodically inserted after each OFDM block within the original guard interval (GI) in conventional zero-padded OFDM (ZP-OFDM) or within the original cyclic prefix (CP) in conventional CP-OFDM. This allows accurate estimation of the channel impulse response (CIR). In addition, the proposed technique takes advantage of the null samples padded after the PN sequences for reducing inter-symbol interference (ISI) occurring with the CEs and the information detection in the conventional PRP-OFDM. The proposed technique successfully applies either (1) a least-squares (LS) CE with assistance from decision-directed (DD) data or (2) approximate LS (ALS) CE method onto PRP-OFDM-like communications for the purpose of improving CE performance on rapid time-varying channels. Computer simulations show that the proposed technique can achieve lower error probabilities in mobile environments.