Enhancement Of MB-OFDM UWB Systems Based On Adaptive Technology

With the development of information technology and emergence of various mobile terminals and consumer electronics, the demand for reliable, instantaneous and convenient connections among devices is growing. To support multimedia applications, e.g. HDTV, the connectivity among devices needs extremely high short-range (around 10 meters) data rate, usually above several hundred mega bits per second, even beyond gigabits per second. For the users' convenience, wireless connection is much preferred. However, wireless technologies currently in use (Wi-Fi, Bluetooth) cannot satisfy the throughput requirement. The emerging Ultra-wideband(UWB) technology which can offer very high data rate with enormous bandwidth and low power consumption is accepted as a promising solution and attracts intensive attentions.Traditional UWB technology mainly refers to time-domain short-duration impulse radio communication, whereas several UWB transmission schemes have been proposed since FCC regulated UWB spectrum without specifying UWB transmission method. With the spectrum flexibility to adapt to various spectral regulations in different areas, MB-OFDM scenario proposed by WiMedia Alliance has gained a lot of supports. The current MB-OFDM scheme whose objective is to replace USB can achieve a maximum data rate of 480Mb/s. It is much higher than other wireless technologies but still far from the target to support high-quality media applications such as HDTV. This thesis mainly focuses on utilizing adaptive transmission and multiple-antenna schemes to improve the MB-OFDM system performance. The contributions of this thesis can be summarized as follows:1. An MB-OFDM simulation model conforming to WiMeida Alliance's standard has been presented. An adaptive MB-OFDM simulation platform has also been established by adding adaptive transceiver blocks to the basic model.2. Taking the UWB circumstance and stringent limit on transmission power specified by FCC into consideration, a bit allocation algorithm which minimizes BER has been proposed. Simulation results show that the adaptive system which adopts the algorithm obtains at least 2dB SNR gain when target BER is 10^-4 and the performance improvement increases when the data rate is higher. Base on the analysis of the bit allocation problem and the previous algorithm, a simplified algorithm has also been proposed. The simulation results suggest that the simplified algorithm exhibits insignificant loss compared to the previous algorithm.3. Two kinds of multiple-antenna adaptive MB-OFDM systems, named Alamouti transmit diversity MB-OFDM system and MIMO spatial-multiplexing MB-OFDM system, which employ the bit allocation algorithm proposed in this thesis are investigated. Simulation results show that when BER is 10^-4 the adaptive transmit diversity system with a data rate of 480Mb/s can attain 2dB SNR gain. The performance improvement in spatial-multiplexing system is more significant, SNR gain over 10dB can be observed when data rate is 480Mb/s.