Research On Key Technologies Of Impulse Broadband Wireless Communications

Impulse radio (IR) broadband wireless communication can be traced back to more than one hundred years ago, in which wireless communication was invented. The earliest inventor of radio, Popov Marconi made use of spark discharge generating the radio pulse signals to send the telegraph. From 40s to 60s in the last century, Louisde Rosa, Conrad H. Hoeppner, Gerald Ross, and Henning Harmuth had done a lot of contributions to IR communication, and the name of IR was widely used by scientists and researchers. With the promotion of American military, IR communications have been researched and developed greatly, since last 90s. Federal Communications Commission (FCC) issued the first civilian standard specification about ultra wide band (UWB) in April 2002. IR mechanism is one method to realize UWB, and IR-UWB becomes a key technology in high speed transmission systems, imagining systems, radar systems, etc.Different from traditional broadband communications, IR signal is transmitted without carrier, and information is modulated on the pulse waveform. This scheme has significant advantages and characteristics:low spectral density, low probability of interception, anti-multipath fading, high penetrating ability, and the simple transceiver. IR communication includes but not limited to IR-UWB, and it has a wide range of research and applications.The key technologies of IR broadband communications include:a. Modeling of IR channel; b. Generating of narrow impulse and modulation; c. Realizing of radio frequency (RF) front end at receiver; d. Acquisition and sychronization techniques. In the above key techonlogies, the first two have be researched widely, and are more mature. Therefore, this thesis mainly introduces the existing results about these two aspects. Because channel model is relavent to the following research algorithm, chapter 2 analyzes the property of IR broadband channel. In the following chapters, we put our emphsis on the realization and receive algorithms at the receiver.The main contributions of this thesis lie in:1. Research on the RF front end at receiver in IR broadband communication systems. Based on the research on perheterodyne receivers, image rejection receiver, Zero-IF Receiver (ZIR), direct amplifications sampling receivers, and other receiving structure, this thesis proposes a front-end implementation scheme of time division (TD) duplex transceiver based on the architecture of direct amplification and sampling. In the specific circuit implementation, for which low noise, high gain, and wide band are required, this thesis designs a first stage low noise amplifier based on double feedback with cascode architecture, automatic gain control circuit based on broadband mirror symmetry attenuator, and last stage gain driver based on resistance of parallel negative feedback. The integrated transceiver module decomposes the high demand into multiple sub-functions. Therefore, the overall difficulty is reduced. Finally, test reults show that the real production module is outstanding and can provide the front-end for baseband verification. Besides, the proposed scheme is also suitable for system-on-chip design.2. Research on differential and auto-correlated receive algorithm for IR broadband communications. Based on the traditional coherent receiver, noncoherent and energy detection receiver, and differential receiver, this thesis points out that differential receiver is the best choice with lowest complexity for moderate speed transmission. For the property of quasi-static with short period, this thesis proposes adaptive differential and auto-correlation receive algorithm based on template averaging. Signal to noise ratio (SNR) is derived based on the proposed scheme. The polar blind restoration mechanism of the proposed scheme is adaptively controlled according to bit error rate (BER). The adverse effect on template is reduced, and error-delivery problem in traditional differential receiver is also improved. Simulation results show that the BER performance is improved significantly, and the proposed scheme is utility and of worthiness.3. Research on the acquisition technology for IR broadband communications. In the coherent receiver, acquisition is the key point to achieve the maximum data rate. For the property of narrow impulse and large duty cycle, this thesis proposes a novel receive algorithm, which carries out auto-correlation only during the chip interval of received impulses. Compared with traditional algorithm, which carries out auto-correlation during the whole symbol period, the short time correlation reduces the noise integration significantly. Therefore, the noise figure is improved, and the computation complexity becomes low. Besides, the auto-correlated value of consecutive short pulses is cumulated, and the cumulative gain can be achieved to improve the performance of acquisition. According to the proposed scheme, this thesis does research on acquisition algorithm based on generalized auto-correlation, and designs the optimal auto-correlation sequence for IR high speed transmission. The research results show that the acquisition threshold is not sensitive to the channel environment. Therefore, the threshold can be kept the same for different channel environment. Finally, simulation results show that the proposed algorithm can achieve better acquisition performance.