Study On Reception Techniques For Ultra Wideband Systems

As a short range communications formula, Ultra-wide band (UWB) uses pulse todeliver information. The pulse is usually short in duration (nano-second), so it issubstantially a system with of extremely large bandwidth (Giga Hertz). Besides, UWBis profiled in high data rate, high positioning accuracy, low cost and low powerconsumption, all the feature enable UWB a promising technology for wireless sensornetwork (WSN) and wireless personal area network (WPAN).In indoor environment, however, the UWB wireless channel is natured with densemulti-path, the inter symbol interference (ISI) raised from which degrades systemperformance significantly. Besides, with the increase of users, the multi-userinterference (MUI) becomes a vital factor in influence on the system performance. It is,therefore, a critical issue on how to figure out a UWB receiver that is high performanceand low complexity.A conventional Rake receiver is simple in structure and is advanced in multi-pathcombination. But, since the number of the multi-path may be up to tens or evenhundreds in a typical UWB channel, the Rake receiver will become too complicated tobe implemented with the increase of the multi-path. Moreover, it is unable to suppressMUI. For mitigating MUI, the multi-user detection (MUD) techniques have been usingin UWB system, in which the blind adaptive algorithms are paid special attention inconcerning the computational complexity and the channel’s time-varying feature. Thisdissertation deals with the problem of signal detection for UWB systems under theenvironment of multi-user and multi-path, its main contributions are as follows.1. Both multi-user interference (MUI) and inter symbol interference (ISI) are themajor factors of influencing the bit error ratio (BER) performance in ultra-wideband(UWB) system. A novel blind Rake scheme is proposed in this paper, which firstlyexploits the properties of the desired user time-hopping sequence to figure out a filterfor eliminating partial MUI and ISI, and then uses projection approximation subspacetracking with deflation (PASTd) algorithm to estimate channel, do maximal ratiocombining (MRC) to further improve signal to interference plus noise ratio (SINR).Simulation results show that the proposed blind Rake receiver achieves a significantperformance gain in comparison with the conventional receiver and Rake receiver, andcan converge at the steady state rapidly. Furthermore, it requires less priori knowledgeand has lower complexity. 2. A blind multi-user detection algorithm based on linear prediction is proposed forthe direct sequence ultra-wideband (DS-UWB) system to provide resistance to MUI andISI. The algorithm first applies linear transformation and linear prediction on thereceived data in order to suppress MUI, and then estimate the channel by subspacetracking algorithm. According to the simulation results with the IEEE802.15.3a UWBchannel model, the proposed algorithm exhibits reasonably good performance andnear-far resistance in multiuser environment compared with the conventional receiver.3. A novel receiver is proposed in this paper that uses the blind adaptive MUDtechnique to deal with the presence of MUI and ISI in terms of high speed time-hoppingultra-wideband (TH-UWB) system. The receiver firstly adopts constrained recursiveleast squares constant modulus algorithm (RLS-CMA) to conduct adaptivedecorrelation for eliminating MUI and ISI, and then improve the performance of systemby channel estimation and MRC. The simulation results show that the proposed receivercan go to convergence rapidly under all four IEEE’s UWB channel models, the BERperformance is better than that of the traditional receiver and Rake receiver.4. A blind adaptive reduced-rank detection is developed for ultra-wideband (UWB)systems in dense multipath channels, which is composed of two stages: in the first stage,a reduced-rank algorithm based on the multi-stage Wiener filter (MSWF) is consideredto reduce the MUI and extract multi-path components; channel estimation using thePASTd algorithm and multi-path combining are then performed to further enhance theSINR of the desired user in the second stage. Several representative simulationexamples confirm that the proposed scheme has excellent performance in suppressingthe ISI and MUI with a low complexity.