Study Of Signal PSD And Pulse Shape Design In Ultra-wideband Wireless Communication

The growth of need for wireless multimedia services makes short-range and high-speed become trends of the wireless communication technologies. The market needs technology that can resolve the conflict of high-speed access demand and crowded spectrum resource allocation. Ultra-wideband (UWB) is considered a solution for its characteristics of high speed, large capacity, low cost and low power consumption. At present, its unified commercial standard isn't yet addressed. To get a reasonable one, a lot of technical issues must be considered, such as modulation, channel coding technology, etc. Federal Communications Commission authorizes to apply UWB technology for communication purposes in the band from 3.1 to 10.6 GHz. For impulse radio ultra-wideband, inappropriate pulse shape will make it difficult to receive signals in the complex wireless communication environment of high data rate, and can't guarantee the performance. More importantly, the normal work of other wireless systems will be interfered with. To solve this problem, the modulating technique, transmission power, pulse shape, etc. must be designed comprehensively.In this paper, modulation method, spectrum distribution and pulse shape design of ultra-wideband system are studied. The specific dedication is as follows:(1) Research of ultra-wideband modulation technique. First of all, give a brief description of the basic pulse waveform that commonly used in impulse radio ultra-wideband, that is, Gaussian pulse and its derivative. After giving their time-domain and the frequency-domain simulation waveforms, as well as the general expression of the pulse sequence, subsequently data modulation methods are discussed, the main two are PPM and PAM; and also the multiple access modulation techniques, such as time-hopping and direct sequence spread spectrum. Next, TH-PPM, TH-PAM and DS-UWB modulation are modeled and simulated separately, and the simulation results of transmitters are giving. Finally, introduce modulation technique of the multiband-OFDM ultra-wideband, and make the corresponding transmitter simulation.(2) Formula derivation of power spectral density in impulse radio ultra-wideband communication, spectrum analysis and simulation. At first, the power spectral density of stochastic process is discussed, the random features of digital base-band signal are analyzed, and its power spectral density is derived equivalent to a Markov chain. Next, derives the power spectral density of two kinds of popular ultra-wideband pulse signal . Both of them belong to non-stationary process, have cyclostationary random process characteristics, the analysis is done based on it. For the former, because of the complexity of time-hopping, the probability density function is used to describe the random characteristics, and relative derivation followed by the corresponding formula of the power spectral density. For DS-UWB signal, because of the need to analyze the effect factors of power spectral density, analysis is simplified and retains integrity of the corresponding formula. Subsequently, the various factors that distribute to the impact of the power spectral density are analyzed, and the conclusion is that distribution of power spectral density can be controlled by adjust the sequence characteristics, pulse repetition frequency and pulse energy spectral density. Also the theoretical analysis is verified through a series of simulation. Finally, through the study of interference that ultra-wideband communication system to do with narrow-band system, and the analysis of impact factor of narrow-band wireless systems power, the conclusion is that design of ultra-wideband signal power spectral density can limit the interference, which will solve the problem of coexistence.(3) Optimal design of the ultra-wideband pulse waveform. The relevant provisions of UWB transmitter power mask are presented after discussion of UWB system coexistence. On the basis of numerical approximation theory, two novel methods to design the pulse waveform are given, which according with the mask requirements of power, can reduce the interfere of ultra-wideband systems and existing wireless systems and increase the spectrum utilization. The method based on the frequency sampling is taken from the interpolation theory. The method based on the Chebyshev best uniform approximation theory can control the precision of approximation by limiting parameters. And based on the theoretical analysis, several simulations are made with different parameters. Simulation results show the effectiveness of the two methods. Finally, the design methods of UWB pulse are summarized and compared.