Adaptive Overlap-and-Add Techniques for MB-OFDM Systems

Traditional OFDM systems use a cyclic prefix (CP) to simplify the processing at the receiver. In power-limited systems, such as those which use the ultra-wideband (UWB) spectrum, using a CP has a big disadvantage. The CP introduces structure into the transmitted signal and as a result, ripples in the power spectral density. These ripples necessitate a power back-off at the transmitter in order to comply with FCC requirements and reduces the overall range. The multi-band OFDM (MB-OFDM) system eliminates these ripples by employing a zero-padded suffix (ZPS) instead of a CP. To retain the circular convolution property, the receiver for a MB-OFDM system needs to use an overlap-and-add (OLA) technique to combine the original samples (those intended for the FFT) and additional samples that are equal to the length of the suffix. When the memory of the channel is shorter than that of the suffix, the OLA technique with samples equal to the suffix can result in SNR loss due to adding samples that contain only noise. In this paper, we present an algorithm that adaptively selects the appropriate number of samples to use in the OLA technique. This algorithm generates an estimate of the channel length based on the time-domain preamble sequence.