Pilot Aided Synchronization Estimation Algorithms For MB-OFDM Based UWB Systems

Synchronization is one of key technologies, particully with base-band singals, forMB-OFDM based UWB systems. Varieties of applications based on MB-OFDM UWBtechnology, such as wireless home environment systems, are power sensitive systems,which have demanding requirement, like low power and low complexity. Synchronizationissue goes through receiving process, which has much more duration than other basebandtechniques. As a result, synchronization is of high power consumption, generally. Inaddition, synchronization effectiveness directly affects performance of the system. Anyerrors in synchronization processes, such as timing shift in the capture and carrier estimationerror would rapidly degrade system performance. Overall, the system synchronizationcovers physical layer and network layer synchronization. The physical layer basedsynchronization technologies are with time domain and frequency domain synchronization.Only if time domain synchronization is completed, does the system could implement FFTprocessing, further correction of frequency domain channel estimation and quantification, aswell as frequency offset and tracking. With effective synchronization, time frequencyconversion could be worked out, as long as receiving information and appropriate treatment.Therefore physical layer synchronization is the foundation of receiver performance forMB-OFDM based UWB systems.Current researches have solved synchronization key issues for MB-OFDM based UWBsystems from different aspects. However, there are still many imperfections, such asineffective pilot identification schemes, threshold restriction and timing uncertain outcomein symbol timing synchronization, high computational complexity in frequency offsetestimation, and so on. In this paper, a preamble identification method based on derivative ofenergy peak detection, a symbol timing synchronization method based on preamblepolarities comparison, a simplifying timing synchronization approach guaranteeing theuniqueness of synchronization sample, and a synchronization solution of non-full-cycle phase rotation frequency offset estimation method are proposed based on deep study ofsystem requirements. The research provides a solution to get a compromise between energyconsumption and synchronization performance. The main innovations of this article are asfollows.1. A pattern recognition method was first proposed based on derivative of energy peakdetection. Receiver calculates energy of the first received pilot symbol.70%of the energy istaken as the threshold. Then energy of a symbol period of several symbol periods distanceaway from the first pilot symbols is computed and compared with the threshold. Matchingthe output of pilot symbols energy with different patterns, preamble modes could beestimated. The proposed method avoids weak noise resistance of peak detection, whichcould effectively distinguish preamble modes of pilots, no matter with TFC1, TFC3, orTFC5.2. A new approach for timing synchronization estimation with polarity comparison forMB-OFDM based UWB systems is proposed. We attempt to locate the start sample of framesequences (FS) by calculating difference of the two cross correlation functions amongreceived symbols, the successive received symbols and predefined preamble sequence. Itmakes sense to propose polarity comparison and identification ideas to the scenario, thecross correlation difference exceeding predefined threshold is not unique. If polarities ofselected symbols are not all the same, the estimator is put forward to find out a peak ofcorrelation summation to figure out the unique timing point and promote synchronizationaccuracy. Uniqueness and accuracy of timing synchronization, therefore, could beguaranteed. The performance of the proposed estimator is evaluated by MSE andsynchronization probability. The proposed estimator could carry out timing synchronizationfor MB-OFDM based UWB systems and make the uniqueness of timing index for sure. TheMSEs of the proposed estimator are evidently lower than the reference method for a greatdeal. Total synchronization probability could reach as much as99%.3. A simplified polarity comparing and uniqueness guarantee (PCUG) timingsynchronization estimation approach for MB-OFDM based UWB systems is proposed. Pilotpolarities comparison is carried out for the first exceeding threshold sample instead of allsamples exceeding threshold. If the polarity of the first exceeding threshold sample is thesame with PS polarity, a further step is needed; otherwise, it is a FS sequence, the currentsample is the estimated timing point. The proposed algorithm could make the uniqueness oftiming index for sure. Simulations indicate that this proposal could get a performanceapproximating with polarity comparing method. Meanwhile, a computation complexity ofM-1XOR and adding operation are reduced.4. In view of the complexity and high accuracy requirement of frequency offset estimatealgorithm for MB-OFDM based UWB system,1/2and1/4times of pilot symbol cycleCAZAC sequences are defined as pilot frequency sequence. Estimation within one symbol cycle is carried out through averaging samples of two neighboring symbol cycles, afterwhich the operation expands to all the symbol cycles in one band group. Taking multipatheffect into account, the concept of phase rotation is proposed for a further step. Adjustingthe phase difference of estimated symbols by phase rotation, cross estimation could be done.Theoretical and simulation analysis indicate that CRLB does not only relate to estimationsymbol length, but also be influenced by phase difference of estimation symbols seriously.In the condition that the length of estimation is fixed, the bigger the phase rotation angle is,the smaller the CRLB is. The algorithm performs well. The complexity of proposedalgorithm is less than full cycle average estimation method for almost50%.