Efficient pre-coding schemes for FMT broadband wireless systems

The filtered multitone (FMT) modulation requires both equalization of the transmission channel and of the transmit subchannel filters. Since decision feedback equalization is affected by error propagation and yields a greater complexity when combined with coding, in this paper we consider the use of pre-coding for FMT. However, by observing that precoding disrupts partially the subchannel orthogonality, we propose a new fractionally spaced pre-coding scheme, and consequently a novel subchannel filter design method based on a MSE criterion. The resulting scheme restores the subchannel orthogonality and it is also simpler than previous architectures. By simulations performed on an indoor broadband wireless transmission scenario we show that in general precoding schemes outperform equalization schemes. Furthermore, the fractionally spaced pre-coding scheme outperforms classical pre-coding schemes by about 2 dB.