Impact of RF Imperfections on 60 GHz Wireless Communication Systems

Over the last couple of decades, wireless communication has proved to be a phenomenal success and has generated a booming industry with over 5 billion mobile handsets in use worldwide. This has on one end eased the life of its users while on the other end has introduced new challenges for wireless system designers. The varying nature of the wireless communication channel results in large differences in the instantaneous received signal strength. Since most mobile terminals are battery powered and operate in a network, simply increasing the transmission power is not an attractive solution, as it reduces the battery life and increases interference. Thus a major challenge in wireless communication is to increase the communication rate and link reliability by utilizing low power, low cost and spectrally efficient systems. Even with the advent of efficient signal processing techniques and miniaturized low power signal processing hardware, the physical bottleneck still remains the available system bandwidth. This has led to the introduction of the 60 GHz band as an attractive alternative. Among other benefits, the 60 GHz band is unlicensed and can provide system bandwidths up to 7 GHz, which is ideally suited for short range indoor wireless services such as wireless local area networks. There are, however, certain challenges that need to be overcome before full potential of 60 GHz band can be harnessed. These challenges include the design of hardware components such as antennas, amplifier and mixers, identification and utilization of suitable base band processing algorithms and efficient communication protocols for wireless networks operating in the 60 GHz domain. This dissertation deals with the design and development of baseband processing techniques for communication devices operating at a carrier frequency around 60 GHz. Firstly, two practical candidates for baseband implementation are identified. The performance of these two alternatives namely single-carrier and multi-carrier is analyzed under various radio frequency circuit imperfections such as phase noise and amplifier non-linearity because low cost radio frequency circuits operating in the 60 GHz band are expected to have less than ideal performance. For both schemes, the performance degradation in terms of operating parameters such as the required number of bits in digital-to-analog converter/analog-to-digital converter and input back-off requirements for the power amplifier as a function of bit error probability, is determined. It is shown that the single-carrier schemes suffer a lower degradation in system performance for a given set of circuit parameters. The single-carrier scheme is therefore, identified as a suitable candidate for 60 GHz baseband implementation. Secondly, we investigate the possibility of using low cost and complexity RF level diversity combining schemes to boost the system performance. Three low complexity diversity combining schemes namely equal gain combining, selection combining and switched combining are considered. An analytical framework for system performance evaluation of different diversity combining schemes by using low complexity RF level quantized phase combining is developed. Analytical expressions for the bit and symbol error rate of multi-level phase shift keying modulated symbols over Rayleigh fading channels are derived. The derived expressions are then utilized to compare the performance with non-coherent schemes under diversity reception. It is shown that the number of quantization levels required to achieve near ideal performance are dependent on the number of the receive antennas and the modulation level. The analysis is also utilized to investigate the impact of phase quantization on the switching threshold for switched combining schemes. It is shown that the switching threshold is not severely affected by phase quantization. The ability to perform various system level trade-offs is also demonstrated. Lastly, a low cost audio demonstrator is proposed. The acoustic channels investigated in this thesis are seen to provide a multi-path rich environment typical of 60 GHz channels. This offers a practical way of verifying the performance of various baseband processing algorithms in a cost effective manner.TelecommunicatieElectrical Engineering, Mathematics and Computer Scienc