Improved initial ranging methods for OFDMA systems

Uplink multiuser timing synchronization and power control in orthogonal frequency division multiple access (OFDMA) systems are crucial for avoiding/suppressing interferences and hence maintaining reliable multiuser wireless links. The existing/emerging OFDMA systems such as the IEEE wireless metropolitan area networks (MAN) standards 802.16a/e necessitate a ranging process to address these uplink synchronization and power control issues.;In this dissertation, we first develop an initial ranging method that takes advantage of multiuser diversity in single input single output (SISO) OFDMA system. We present new ranging signal designs which provide multiuser diversity gain and facilitate efficient low-complexity algorithms for multiuser ranging signal detection, timing offset estimation and power estimation. In the proposed approach, each ranging user obtains channel knowledge from the downlink channel in a time-division duplexing (TDD) system, chooses the best ranging subchannel, and applies initial power control to yield multiuser diversity gain and power saving. By exploiting the multiuser diversity and initial power control, we also develop efficient low-complexity signal processing algorithms for OFDMA ranging. The proposed OFDMA ranging method achieves significant gains in ranging performance, power saving, and complexity reduction over the existing ranging methods while using the same amount of time and frequency resources.;Next, we extend our proposed ranging method and ranging signal designs to multiple input multiple output (MIMO) OFDMA systems by developing three ranging transmission schemes. By exploiting multiuser and multi-antenna diversity gains, we develop low-complexity algorithms for multiuser ranging signal detection, timing offset estimation and power estimation. We also extend several existing initial ranging methods from SISO to MIMO setup. The advantages of the proposed approach over existing methods in terms of ranging performance, energy saving, and complexity saving are illustrated by analytical and simulation results.;We also study the impact of multipath, multi-antenna, and multiuser diversities on OFDMA initial ranging process. The ranging transmission schemes with different combinations of diversities are discussed and compared by simulations in terms of energy efficiency, network entry latency, detection and estimation performance.