Multiple access and interference management in wideband downlink cellular systems

Abstract

The key feature of wideband cellular systems is universal frequency reuse. Since simultaneous transmissions interfere with each other in the systems, a careful design of multiple access and interference management can improve capacity and quality of service (QoS). In this thesis, we deal with several issues of multiple access and interference management in wideband downlink cellular systems: soft handoff in code division multiple access (CDMA) systems and multiple access schemes in orthogonal frequency division multiplexing (OFDM) systems. First, an analysis on CDMA downlink capacity and QoS is provided comparing hard and soft handoffs. For soft handoff, three different power allocation schemes among cells are investigated: equal power, equal signal to interference ratio and selection diversity. In capacity part, a handoff decision based on filtered pilot signal strengths, which is ignored in most of previous research, is considered. Contrary to previous results that soft handoff provides a capacity decrease in the CDMA downlink, it is concluded that soft handoff mitigates capacity loss due to filtering through diversity gain, and may in fact provide higher capacity. In QoS part, effects of soft handoff on QoS under imperfect power control are investigated. It is shown that the power allocation schemes of soft handoff except the selection diversity scheme greatly improve signal quality, especially under power control errors with small standard deviations. Collectively, we reveal that soft handoff can still enhance capacity and QoS efficiently managing interference in downlink as well as in uplink. Secondly, downlink performance of orthogonal frequency division multiple access (OFDMA) cellular systems is provided for both intercell synchronous and asynchronous cases. A downlink interference model and bit error rate (BER) performance for M-ary quadrature amplitude modulation (M-QAM) are analyzed under imperfect channel estimation. It is shown that the interfe...