Performance evaluation of fixed and variable zero padding length in ultra-wideband receiver design using MB-OFDM based on ECMA-368 standard
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Traditional OFDM systems use Cyclic Prefix (CP) in front of an OFDM symbol to maintain orthogonality. Ultra Wide Band (UWB) systems use Multiband OFDM approach in implementing applications of Wireless Personal Area Network (WPAN). Federal Communications Commission (FCC) put some regulations on UWB to co-exist with other narrowband and spread spectrum users. MB-OFDM follows OFDM modulation scheme where CP is used but CP introduces a structure into the transmitter due to which the ripples are produced in Power Spectral Density (PSD). Because of this ripples, power back-off is required at the receiver which is as large as 1.5 dB. As an alternative to CP, Zero Padding (ZP) is used where a flat PSD is obtained which requires zero power back-off. Circular convolution in CP is a natural phenomenon but for ZP, Overlap and add method (OLA) is used to ensure circular convolution. The ZP length used for OLA method is fixed and equal to 32 samples according to ECMA-368. If timing synchronization estimation errors occur, fixed ZP length may cause Inter Symbol Interference (ISI). So, a variable ZP length is required to avoid ISI depending upon the current band. Hence, a Multi Band Timing Synchronization algorithm is proposed to achieve variable ZP length based on current band for OLA method. This method benefits large delay spread channels. Improvement in SNR is achieved at particular Bit Error Rate (BER) for large delay spread channels.