Co-pilots in channel estimation

A new pilot-aided subspace channel estimation algorithm for orthogonal frequency division multiplexing (OFDM) systems is proposed. The channel model is a sparse L-multipath channel with gains subject to Rayleigh fading. The new algorithm constructs M² virtual pilot tones from M physical pilot tones, and employs the subspace method, MUSIC, to estimate the multipath time delays. With the delay information, a minimum mean square error (MMSE) estimator is derived to estimate the frequency response of OFDM systems. The proposed algorithm can identify up to O(M²) multipath delays by using M physical pilot tones. It is also demonstrated that the proposed channel estimation algorithm can help the OFDM system to keep relatively good bit error rate (BER) performance, compared to conventional subspace channel estimation method with uniform pilots, even when the number of multipaths is greater than the number of pilots.