Impulse response shortening through limited Time reversed channel in MB OFDM UWB systems

Multiband orthogonal frequency division multiplexing ultra wideband (MB OFDM UWB) systems severely suffer from long channel delay spreads. In the worst case channel scenarios, the rms delay spread is expected to be more than 25 ns. This exceeds the typical length of cyclic prefix (CP) and causes inter-carrier interference (ICI). Time domain equalizers (TEQ) are traditionally used to mitigate this problem. Beside some other existing channel shortening schemes, equalization through time reversed (TR) channel also serves the same purpose. Since UWB channels are highly rich in multipaths, an equalizer using complete TR channel is too complex to implement. In this paper, we investigate a TEQ design based on limited time reversal of the channel impulse response (CIR) in MB OFDM UWB environment. We show that the proposed scheme performs almost same as the full TR scheme but with significantly reduced complexity. The proposed TEQ design exhibits comparatively low noise enhancement and can achieve better signal to noise ratio (SNR). It also simplifies the Rake receiver structure by reducing the number of effective channel taps.