Research On Channel Estimation Technologies For UWB Impulse Radio

As a promising candidate for future short-range high-speed wireless communication, impulse radio ultra-wide bandwidth (IR-UWB) technology has attracted growing interests for the last decade. In its rule-making proposal of April 2002, the Federal Communications Commission (FCC) defined ultra-wideband (UWB) technology as any wireless transmission scheme that occupies a relative bandwidth not less than 20%. Specialized in transmitting ultra-short pulse in time domain, IR-UWB has become the most popular technique used in UWB systems. The advantage of IR-UWB include extremely high data transfer rate and user capacity; lower cost, less power consumption, simple circuit; high-resolution, anti-MAI and dissemination of multi-path; difficult to monitor and strong robustness. The application of IR-UWB covers personal computers, mobile terminals, consumer electronics, WPAN, sensor network, image forming systems, on-board radar systems. The techniques can be realized in the coming future mainly include wireless USB, precise positioning and ultra high-speed data transmission. provided an overview on this signaling format and in depth discussions on its potential to countering multiple-access interference and multipath propagation. Among the existing receiver structures for UWB systems, adaptive equalization and diversity combining (RAKE) techniques have been extensively applied in improving the receiver performance , and the knowledge of fading coefficients and delays for different channel paths are required to realize these techniques, in other words, accurate channel estimation is indispensable.In this paper, after a brief introduction of IR-UWB systems, we summarize the classic literature in channel estimation field for IR-UWB systems. Then, in light of previous works, two improved algorithm are proposed.The first algorithm proposed a frequency-domain pre-filter algorithm against the problem of UWB channel estimation under dense multipath environments. This algorithm can be used for estimating and tracking the channel impulse response (CIR), which includes two steps: frequency-domain pre-filter and kalman filter. The main method is by introducing frequency-domain pre-filter before traditional kalman filter to simplify kalman measurement equation. Thus the kalman measurement update equations, which include the solutions of measurement update, kalman gain and error covariance matrix, can become more concise. This algorithm can simplify the kalman iterative process so that reduces the computational complexity. The promising performance of this improved algorithm has been proved by simulations and comparisons.Based on prior statistical characteristics and system-specific receiver structures, the second algorithm is proposed for estimating and tracking the channel impulse response (CIR) of time-varying channels. By fitting zero-tap detection algorithm and UTE (unstructured CR estimate with threshold) algorithm into kalman filtering process, the improved algorithm presents different strategies for different receiver structures. Simulations and comparisons are implemented to illustrate the promising improvement of the proposed algorithm.