Rake Receiver Technology And Performance Analysis Based On Ultra-wideband Systems

Ultra-wideband (UWB), a wireless communication technology for short-range high rate links, has the merits of wide bandwidth, low power consumption, low cost and so on. Therefore, it is viewed as a competitive solution for wireless personal area networks (WPANs). Compared with traditional wireless communication systems, UWB systems suffer more serious frequency selective fading which leads to serious energy dispersion and waveform distortion. So, the design of UWB receiver is an important issue. Rake receiver is a key technique for UWB communication systems. Rake receivers capture and collect multi-path components effectively, and thus improve the performance of UWB systems.Traditionally, Rake receivers employ a single template matched with transmitted signal to collect multi-path components. Due to serious waveform distortion and energy dispersion in received signals, Rake receivers with a single template can not collect the energy of the received signal effectively. Consequently, the system performance is degraded. The traditional Rake receivers are investigated in combination with typical impulse radio UWB (IR-UWB) systems in this work. A new Rake receiver, which employs a couple of orthogonal templates, is proposed to boost the performance of UWB systems. Based on the proposed Rake structure, two path selection methods are presented. Simulations have been done to verify the performance of the proposed the Rake receiver in typical UWB channel scenarios, where different strategies on path selection and multi-path combination are taken into consideration. The contributions of this thesis include:1) A new Rake receiver structure employing a couple of orthogonal templates is studied. A channel estimation algorithm for the improved Rake receiver is introduced. By using a couple of orthogonal templates, one is the Hilbert transform of the other, much more energy can be collected by the improved Rake receiver with a fixed number of fingers, and the system performance can be improved considerably.2) Two path selection schemes, named path selection based on orthogonal multi-path and path selection based on time arrival, are proposed for use in the proposed Rake receiver. The proposed path selection schemes can be combined with MRC (maximal ratio combining) and EGC (equal gain combining) flexibly. Thereby, it is easy to make balance between system performance and complexity.3) The performance of the improved Rake receiver in typical UWB channels is analyzed and compared with that of transitional Rake receiver by simulations. The simulation results suggest that:1) In comparison with the traditional Rake receiver, a SNR gain of 3dB can be achieved by the improved Rake receiver when the bit error rate is 10-3.2) Regarding the performance of the improved Rake receiver, MRC outperforms EGC in terms of SNR, e.g., a 2dB gain in SNR is achieved by MRC in the case of BER=10-3.3) The performance of the improved Rake receiver is not sensitive to channel estimation accuracy.4) Regarding the performance of the proposed path selection schemes, the scheme based on time arrival performs better than the scheme based on orthogonal multi-path, e.g., the scheme based on time arrival has 1dB gain in SNR in the case of BER=10-4.