Abstract
Channel fading and co-channel interference are two major sources of system performance degradation in wireless cellular networks. In recent years, multiple-input-multiple-output (MIMO) systems with adaptive array processing techniques, also referred to as smart antennas, have received extensive attention in wireless communications due to their ability to combat the above mentioned problems. Beam-forming is one of most promising techniques employed by smart antennas in order to increase signal to interference and noise ratio (SINR) by mitigating co-channel interference thanks to increased received signal power. Another most widely used technique is called antenna diversity which is used by smart antennas to combat fading effects. This work focuses on transmit beam-forming techniques for uplink direction of WCDMA cellular systems where user terminals are equipped with antenna arrays and utilizing both antenna diversity and beam-forming techniques. Effect of limited information and imperfect feedback channel was investigated and based on availability of channel state information, practical and optimum transmission diversity schemes were mathematically analysed and verified by link and system level simulations. Antenna diversity impacts at both receiver and transmitter side was investigated. Impact of flat fading channel, frequency selective channel, correlation between transmit or receive branches and feedback delay for single and cellular multi user scenarios were studied. Two novel transmit beam-forming techniques were proposed. It was shown that capacity and coverage of uplink of WCDMA system can be improved by 92% in flat fading channel and up to 46% in frequency selective channel, and at the same time, system coverage can be increased by 41% and 19% respectively.