Study Of Receiving Technology In UWB System

IntroductionUltra-wideband (UWB) communication is a novel short-distance wireless communication technique, in which data are transferred using non-sinusoidal pulses with very short duration. It has many advantages, such as high transmission rate, low power consumption, good security, robustness to multipath and low cost. Especially, it does not need extra frequency spectrum, and can coexist with the existing wireless communication systems at the same frequency band, which makes it attract much attention nowadays when the frequency spectrum resource has become more and more precious. One of the most expected applications of UWB technologies is wireless personal area network (WPAN).1. Rake CombiningIn 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 is quite serious. Therefore, Rake receiver which is easy to realize and good at anti-fading is used in UWB system.In this paper, we choose the maximal ratio combining scheme to compare the performance of All-Rake, Selective-Rake and Partial-Rake.2. Pre-Rake CombiningRake receiver can achieve better performance with more fingers, which may increase the receiver complexity and defeats the purpose of making personal portable device low-power and low-cost. In practice, the number of multipath components that can be utilized in Rake combiner is limited by the power consumption issues, the design complexity, and the channel estimation. The impact of the number of Rake fingers is then a critical design issue.In this paper, we propose to use Pre-Rake scheme in UWB wireless system. The advantage of Pre-Rake scheme is that the portable unit without complex Rake receiver. When the Pre-Rake transmission is applied instead of Rake receiving, it can be maintained simply and cost-efficientlyThe purpose of the Pre-Rake combination is to facilitate the arrival of a signal that is already a Rake-like combination of the multipath signals. For the Pre-Rake combiner parameters need to be set in advance of signal transmission. This means that the future path strength, path delay and path phase must be estimated. Because both forward and reverse links have similar channel parameters, the present channel parameters can be directly estimated from the received signal by using a suitable algorithm in the UWB system. In this paper, we assume the channel information is known.3. MISO UWB SystemIn this paper, we propose a MISO (multiple-input single-output) UWB system which also has a simplified receiver. In this system, improved performance is demonstrated when compared to a conventional system with a RAKE receiver at the MS and a Pre-Rake system with only one transmit antenna. In MISO UWB system, the power of every transmit antenna is allocated by use the maximum-ratio combining (MRC) method, and the transmit signal of every antenna is treated with Pre-Rake combining. Only one antenna and one-finger matched filter is used at the receiver.This system combines the advantages of pre-RAKE diversity, which can provide multipath diversity, and transmit antenna diversity, which can provide space diversityEarly work on transmit antenna diversity for DS/CDMA systems has revealed that it can mitigate the multipath fading effect and suppress cochannel interference. Thereby, it can improve the transmission quality and enhance the system performance.4. Simulation ResultSimulation results indicate that in each of the four channel circumstances (CM1, CM2, CM3, CM4), when the bit rate is low, the Pre-Rake combiner with one transmit antenna and the Rake combiner have similar performance; however,Pre-Rake combiner performs better than the Rake combiner under higher transmitting bit rate.In MISO UWB wireless communication system, numerical simulation results are provided, which demonstrate significant performance improvement when compared to the conventional Rake receiver and Pre-Rake system with one transmit antenna. It is also demonstrated that the system performance improvement increases when the MISO system has more transmit antennas.