Study On The Channel Code Of Ultra Wideband Communications Systems

In recent years, as a new spread spectrum system, Ultra Wideband (UWB)communications has attracted much attention and been considered as one of the keytechnologies in wireless communications. In this thesis, the design and the BERperformance of coded UWB communications systems are analyzed on base of the UWBtheory research. Based on all these efforts, some positive results are obtained andsummarized as follow:1. The principle, features and received signal processing are systematicallysummarized in the UWB communications. The BER performance expressionsare derived for a THMA-BPPM-UWB system.2. The characteristics of UWB indoor channel model are described, and the pulseimpulse responses are simulated in four channel environments. The simulationparameters were proposed by the IEEE802.15task group. The analyses of theRMS delay spread and the path amplitudes fading distribution are representedrespectively.3. The rake technology of UWB receiver is studied in the multipath environment.The impacts on received energy are analyzed in different multipath combinemanners including ideal rake, selective rake and partial rake.4. We propose a Turbo coded Ultra wideband (UWB) system with parallelmodulation. The proposed system employs Turbo codes as forward errorcorrecting codes, and a set of orthogonal Hermite pulses modulated parallel datarespectively. Under required performance of system, the maximal datatransmissions rate could be achieved by adjusting the parameters including therate of Turbo codes, the number of path and the number of pulse repetitions.Our simulation results and analysis on an AWGN channel show that for thesame data transmissions rate, we had better make the number of repetitionpulses smaller and the rate of Turbo code lower to achieve the better BERperformance.5. We propose a multilevel coded Ultra wideband system with combined iterativepulses demapping and decoding algorithm. The simulation result of three levelcoded system show that the bit error performance improves prominently touncoded situation. Iterative multistage algorithm and iterative parallel algorithmrequire three iterations and four iterations respectively in AWGN channel inorder to achieve optimal performance, and in indoor multipath channels twoiterations and three iterations are needed respectively. Iterative parallelalgorithm achieves equivalent performance under optimal iteration to iterativemultistage algorithm, and require only1/3time delay than latter.