On Preamble-based FBMC/OQAM Highly Frequency Selective Channel Estimation Without Guard Symbols

Intrinsic interference is known to present a challenge for signal processing tasks in systems employing offset quadrature amplitude modulation-based filter bank multicarrier (FBMC/OQAM) transmission. In preamble-based channel estimation, in particular, this otherwise called self interference will corrupt the pilot symbols, thus preventing accurate estimation, unless special means, such as inserting sufficiently many null guard FBMC symbols between the training and the information part, are employed, with a consequent loss in spectral efficiency. Iterative procedures that alternatingly estimate the channel and the interfering data symbols have been proposed to tackle this problem, and they are almost exclusively intended for channels of relatively (to the FBMC symbol duration) low delay spread. In this paper, the problem of preamble-based channel estimation without guard symbols is re-visited, with no simplifying assumption on the relative frequency selectivity of the channel. An optimal (in the mean squared error (MSE) sense) preamble in the presence of data interference is designed, assuming the availability of the second-order statistics of the channel and the signal-to-noise ratio. The effect of adopting this interference-aware preamble in an iterative estimation/detection procedure is assessed via simulations with realistic channels. A significant gain in the detection performance is demonstrated compared to the use of the preamble that is only optimal in the absence of interference.