| Ultra Wideband (UWB) has emerged as a new technology providing high data rates, large channel capacity, low power, low implementation cost, the spectrum reuse, accurate position localization exceptional multipath immunity, low interference and low probability of intercept. Because of the benefits, UWB has recently received significant attention in both academia and industry especially for indoor wireless communications in recent years. It has been proved that UWB can support data rates higher than 100Mbits/s, even 1Gbits/s, within a 10 meters distance and coexist well with existing narrowband wireless systems. UWB impulse radio makes up of ultra-short duration pulses and the transmission of series of sub nanosecond pulses, the energy of which spreads from near DC to a few GHz. The pulse train is transmitted without using a sinusoidal carrier, which can he realized with simple equipments. It should be noted that the transmitted pulse average interval is much longer than the pulse duration. Thus, this significantly reduces fading effects in indoor multipath environments.In a communication system, its fundamental purpose is to delivery the information to the destination without errors. In real wireless communication system, due to the reflection and scattering of surrounding buildings and objects, there are multipath interference and fading, which may cause serious decline of the transmission performance. It is necessary to adopt measures against fading. Diversity is an important anti-fading technology, which can greatly enhance the transmission reliability of the multipath fading channel. Studying on UWB wireless communication system channel, we found that multipath interference was quite serious. Therefore, Rake receiver which is easy to realize and good at anti-fading is used in UWB system.The traditional, single ultra-wide bandwidth communication system has the undesired feature of reliability, combining the principle of pulse amplitude modulation and pulse position modulation, the communication system of hybrid modulated UWB signals is proposed, the simulation and performance of the best receiver in Gaussian Channel and RAKE receiver in multipath Channel adopted joint detection algorithm are analyzed in detail, which have the desired feature of reliability and reduce the bit error rate (BER) of the whole system effectively .It is shown by the simulation results that the system performance of hybrid modulated UWB signals is better than PAM-DS-UWB adopted the best receiver.With short-distance wireless communications using in the military affairs,industry,science,medical treatment and our daily-life, various portable individual communications equipment's and appliance wiring equipment's increasing, the source of finity spectrum is more scarcity. Power spectral density (PSD) refers to the average power of the signal in each unit band width, which has supplied the important information in the power distribution spectrum. Sharing and highest efficiency using spectrum source is a pressing technical problem. A basic requirement by the FCC is that UWB systems do not generate interference to other narrowband communication systems operating in the same spectrum;the FCC has assigned conservative emission masks between 3.1 GHz and 10.6 GHz for commercial UWB devices in 2002. The maximum allowed power spectral density for these devices is -41.3dBm/MHz. UWB signals in the military, the main objective is to signal the probability of being caught minimum, which requests transmission signal's frequency spectrum must be very low. In addition, in order to achieve normal communications, UWB signal must have certain average power. Therefore, for ultra-wideband wireless communications systems, the frequency distribution of modulation signal is very important.When studying the spectrum coexisting and compatible problems between UWB systems and other radio systems, the important factors which need to be considered are the power spectrum mask. In this paper, the Direct Sequence- Ultra wideband (DS-UWB) communication system using different chaotic spread sequence are proposed, the power spectral density (PSD) of DS-UWB is carried out, the maps for PSD of PAM-DS-UWB using different sequences are established by MATLAB, the effect of PSD mask using different chaotic sequences is analyzed. Compares with the conventional Gold sequence, the simulation results show that the power of PAM-DS-UWB using Logistic chaotic sequence is broadest in the spectrum; the peak value in PSD of PAM-DS-UWB using Logistic sequence, Chebyshev sequence is approximately the half and two-thirds of the peak value in PSD of PAM-DS-UWB using the Gold sequence.In a word, Main Content of this thesis:Chapter one has clarified the developments, history and background of UWB. At the end of this chapter main content and chapter arrangement are introduced.Chapter two gave an introduction to the basic UWB theory from definition, advantages, method utilizing UWB, emission mask and key technology.Chapter three described multiple access of UWB system, Time-Hopping UWB and Direct–Sequence UWB are introduced in detail. The transmitted system, the expressions and the simulation maps of PPM-TH-UWB,PAM-TH-UWB and PAM-DS-UWB are given. Take this as foundation, the hybrid modulated UWB signals are constructed.Chapter four studied the Power Spectral Estimation of Direct Sequence- Ultra Wideband based on chaotic sequences. The methods of generating several familiar chaotic sequences and their performance are analyzed , the power spectral density (PSD) of DS-UWB is carried out, the Direct Sequence- Ultra wideband (DS-UWB) communication system using different chaotic spread sequence are proposed, the effect of PSD mask using different chaotic spread sequences is analyzed.Chapter five compared the performance of typical UWB signals in Gaussian Channel. Main content contained Gaussian Channel, the structure of the best receiver for PPM-TH-UWB and PAM-DS-UWB. On this basis, the structure of the receiver for the hybrid modulated UWB signals is constructed and the simulation results are given by MATLAB. It is shown by the simulation results that the system performance of hybrid modulated UWB signals is better than PAM-DS-UWB adopted the best receiver.Chapter six analyzed the performance of typical UWB signals in multipath channel. Main content contained channel model of UWB recommended by IEEE 802.15.3a and RAKE receiver, the structure of the RAKE receiver for the hybrid modulated UWB signals is introduced in detail and the simulation results are given by MATLAB. It is shown by the simulation results that the performance of A-RAKE is better than that of S -RAKE and the performance of S-RAKE is better than that of P- RAKE; the RAKE receiver for the hybrid modulated UWB signals can reduce the bit error rate(BER) and boost the ability of anti-jamming in the whole system.Chapter seven summarized the work content of this dissertation, and made further prospects according to the status of the research work. |
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