Smart antenna: adaptive beamforming algorithms and slot allocation schemes
Garret T. Okamoto, Chih‐Wei Chen · 2005
Beamforming algorithms and slot allocation schemes are two major smart antenna research areas for the next generation of wireless communication systems. The thesis proposes new approaches for both areas and compares their performance to current methods. Smart antenna systems use multiple antenna elements at either the receiver or transmitter to improve system performance. These systems provide a promising way to solve critical considerations like deep fading and capacity in wireless communications. Compared to a conventional system installed with a single antenna, a smart antenna system can achieve significant improvement by reducing multipath fading, extending the terminal battery life, increasing system capacity, extending coverage area, and increasing the transmission data rate. Beamforming algorithms attempt to extract a desired signal-of-interest from the background noise and interfering signals. The performance of the beamforming algorithm is judged by SINR improvement, convergence rate, misadjustment, robustness, computational complexity, and tracking ability. Typically, the convergence rate of most beamforming algorithms is slow, and the computational load is high compared to the simplest algorithm, LMS. This thesis presents two novel adaptive beamforming algorithms for which the transition time to converge to the optimum solution of the beamforming weight is not required. Thus, the convergence rate of both proposed algorithms is high, and resulting in an excellent tracking ability when a user is moving. One of the proposed algorithms provides computational load close to LMS. Both proposed algorithms are derived analytically and compared to some well-known adaptive beamforming algorithms in this thesis. Slot allocation schemes are critical for enabling Space Division Multiple Access (SDMA) systems. Since mobile terminals rarely occupy the same spatial coordinates, SDMA-enabled systems can simultaneously transmit signals to and receive signals from multiple mobile terminals by scheduling transmissions based on slot allocation schemes. This can increase the capacity of a wireless communication system by allowing more users. SDMA-enabled systems are still a rarely explored area. In this thesis, slot allocation schemes are evaluated to understand the impact of scheduling for SDMA. To combat the excessive computational load in scheduling, a novel slot allocation algorithm with comparable performance to other algorithms is presented. Issues such as sorting process and multipath scenario are also discussed in this thesis. Finally, the concept of a smart antenna-enabled wireless LAN is discussed, including communication scenarios and overhead comparison.