Research On Synchronization And Demodulation Algorithms For Noncoherent UWB Impulse Radio

Ultra-wideband impulse radio (UWB-IR) is a kind of underlay communication technique which has tremendous bandwidth and is able to coexist with current narrow/broad band systems. It has been considered as a promising candidate for short range indoor communication on account of several attractive features, such as low power consumption, low implementation complexity, capabilities to support high data-rate connectivity as well as the high definition ranging. Although the UWB systems enjoy so many merits, there are plenty of challenges for implementation and synchronization remains the biggest one ahead. In this paper, we focus on the noncoherent UWB systems and propose three synchronization and demodulation schemes in presence of inter-symbol interference (ISI) and inter-frame interference (IFI).Firstly, this paper proposes a data-aided synchronization algorithm in the differential transmitted reference (DTR) UWB systems. The aided data and the m-sequence are introduced into the differential coding. It results in that pulse polarities of the training sequence are still the cyclic m-sequence. Thus the synchronization information is involved in the shift phase of the m-sequence. The proposed algorithm aims at estimating the shift phase to acquire synchronization. Taking the advantage of the m-sequence autocorrelation function, the maximum is significantly different from other values. Consequently, the noise and IFI can be mitigated effectively.Secondly, a blind synchronization and demodulation algorithm is proposed for noncoherent receiver that is robust to ISI and IFI. The proposal aggregates the observed signals into one frame-long segment by a series of code matching and signal aggregation (CMSA) and averaging operations. Exploiting judiciously designed direct sequence (DS) spreading code, the aggregated segment suppresses interference effectively and accumulates the maximum energy at the synchronization time. Because the proposed scheme utilizes the observed signals efficiently and eliminates randomness of the source data, synchronization can be acquired rapidly. Then the aggregated segment is reused as the demodulation template which significantly improves the BER performance.Finally, the paper proposes an improved algorithm based on the previous blind synchronization and demodulation scheme. As the severest interferences come from the closest frame ahead, for the given symbol the most interferences of this kind come from itself. As soon as the codeword is chosen, the interference pattern is set. Furthermore, this pattern will not vanish as the times of averaging operations increase. To settle this problem, the paper proposes a particular block signaling. Block is the basic transmission unit that contains two symbols. Within the block, the frames of two symbols are sent alternately. The severest interference terms close to the given signals change to independent random variables due to particular signaling and these interferences can be further brought down by the subsequent average operations. Consequently, the proposed scheme can improve the BER performance at high SNR, in the mean time, the performance of synchronization will not degrade.