On the use of pilot tones for impulse noise cancellation in Hiperlan2

Abstract

This paper presents an elegant solution to impulse noise cancellation in OFDM systems. A parallel between Reed Solomon codes in the complex field and multicarrier transmission using OFDM is first presented. This shows that when the signal is sent over some channel composed of Gaussian plus impulse noise, the impulse noise can be removed by a procedure similar to channel decoding, using information carried by the "syndrome". These results are first derived in a simple situation (oversampled DMT, additive channel), which is merely of theoretical interest. In any case consecutive zeroes, in the output of the OFDM modulator, do not correspond to real subcarriers. However in many cases, pilot tones are emitted for synchronization or channel estimation purposes. These pilot tones are generally scattered among the information ones. Our approach is to use these pilot tones as "syndromes", in order to correct impulse noise. We show that the correction capacity is conditioned by the position of these pilot tones in the emitted sequence. Efficiency of this technique is corroborated with simulation in the practical context of the Hiperlan2.