A hidden pilot assisted demodulation technique for channel estimation in m‐qam transmissions
Franco Mazzenga · European Transactions on Telecommunications · 2002
Abstract Multipath effects represent the limiting factor for reliable wireless communications with high efficiency modulation schemes such as M‐QAM or M‐PSK. Pilot assisted modulation techniques have been proposed to overcome multipath fading effects and an equalizer operating on the basis of a received pilot is commonly deployed. The pilot sequence used to train the equalizer is usually time division multiplexed with the information sequence. This solution reduces the bandwidth efficiency and may become unusable when too frequent updating of the communications parameters is needed in the receiver. In this letter it is shown that bandwidth efficiency can be preserved at the expense of an increase in transmit power. The additional transmitted power is used to send a known pilot sequence hidden into the information sequence. The pilot is superimposed onto the information symbols to be transmitted before waveform modulation. Therefore each pilot symbol has the same period of the information symbol so that bandwidth spreading is avoided. The M‐QAM modulation format is considered but the technique can be extended to any digital communication system. The channel estimation problem is analyzed since the equalizer impulse response can be easily derived from the estimated channel impulse response. To prove the effectiveness of the proposed technique simulation results are provided.