Research On The RF Transceiver Front-end In Wideband Wireless Communications

As wireless communication products become an everyday part of people's lives, the need for higher performance at lower costs becomes even more important. Overcoming the challenges involved in the design of radio frequency(RF) transceivers can help meet this need. This dissertation presented the prototype wideband RF transceivers for Ad.Hoc communication systems developed by the author and design issues for achieving both high performance and low cost. The main contributions of the dissertation are as following:1. In a wireless communication system using QPSK modulation, it is well known the intermodula caused by the nolinearity of PA (power amplifier) will generate adjacent channel and co-channel interference thereby increasing the BER (bit rate error). This fact motivate us to conduct a statistic spectral analysis of the PA. A relation of the third order intermodulation (IM3), playing a key role for the nonlinear distortion generated by PA, vs the BER is derived and justified by computer simulations. The result will be helpful in designing a high perfomance PA in QPSK communications systems.2. In a CDMA IS-95 base station, the power amplifier usually employs feed-forward linearization technique, such as carrier cancellation and intermodulation cancellation, to improve its linearity. Design formulas for the feed-forward linearized power amplifier (FFLPA) are derived and justified by computer simulations. The influence of the imperfect amplitude/phase carrier and intermodulation cancellation upon the IM3 is evaluated quantitatively in these formulas, A prototype FFLPA hardware was designed based on these formulas, then integrated into the base station. The specifications of the station as well as the performance of the FFLPA were tested and measured respectively. Measurement results are proved to be satisfactory.3. For a digital microwave QPSK communication system, the phase noise existing in a PLL based local signal source could be one of the major factors responsible for the degradation of system performance. Design criteria for such signal source are derived, upon which one can choose the PLL loop bandwidth by trade-off considerations, to get a relatively low BER, simultaneously obtain low spurious output and fast frequency hopping as well.4. An chaotic FH wireless communication system is studied with the emphasis on a DDS-PLL hybrid frequency synthesizer design as well as a new spread spectrum sequence based on a second order discrete chaotic mapping.5. A brief survey on tranceiver design for wireless communications is addressed, also given are prototype tranceivers for Ad. Hoc communication systems developed by the author, including those used in CDMA base station, wideband wireless access system, chaotic FH system and DSRC/ITS.