On the use of implicit pilots for channel estimation with OFDM modulations

A coherent detection of OFDM signals (Orthogonal Frequency Division Multiplexing) allows good performances in severely time-dispersive channels. However, coherent receivers require good channel estimates, a difficult task when the channel impulse response is long and/or when space diversity techniques are employed. Usually, the channel estimates are obtained with the help of pilot symbols multiplexed with data symbols, which reduces the useful bit rate, decreasing the spectral efficiency of the systems. To avoid this, we consider the use of implicit pilots instead of multiplexed pilots. Since the interference levels between data and pilots might be very high, we propose an iterative receiver with joint detection and channel estimation. Our performance results show that our technique allows the use of low-power pilots, with performances close to the ones with perfect channel estimation, even when space diversity techniques are employed(1).