Accurate and spectral efficient channel estimation using inter-block precoding and superimposed pilots in optical OFDM systems

A new inter-block precoding-based channel estimation (CE) scheme is proposed and experimentally demonstrated in an optical OFDM system with a superimposed pilot (SP). The proposed inter-block precoding scheme targets on eliminating the statistical mean of the unknown data symbols, and thereby improves the performance of SP-aided CE. We investigate the impact that both the precoding matrix and SP have on the system performance, from which we obtain the optimum value of signal-to-pilot power ratio (SPR) as well as the block length. We show through simulations and experiments that the proposed CE scheme, in comparison with the conventional preamble based scheme, has the advantage of entailing a much smaller overhead size, while offering similar performance in terms of CE accuracy and bit-error ratio (BER) performances. Furthermore, the proposed precoding scheme has no limit to the design of SP, and thus is applicable for any periodic pilots.