Reverse link power control for packetized DS-CDMA in a slowly Rayleigh fading environment

Abstract

This paper proposes a packetized direct sequence code division multiple access (DS-CDMA) multimedia wireless communication system that allows for seamless interfacing to asynchronous transfer mode (ATM) broadband networks. The issue of reverse link power control is examined in the context of an indoor environment characterized by a slowly Rayleigh fading channel. Three algorithms are discussed: open loop, channel estimation, and closed loop power control. It is shown that closed loop power control with channel estimation achieves the best performance. The system capacity with perfect power control is calculated. The effect of power control imperfection on the capacity and received signal statistics is studied based on computer simulation. It is shown that actual cell capacity using a two-bit power control command is approximately 40% greater than that using a one-bit power control command at the expense of twice the feedback overhead. IntroductionThere is an urgent need for wireless networks to co-exist with new fiber based broadband communication networks. One challenge is to design a seamless interface between an error-prone wireless channel and a very high fidelity fiber channel. Since asynchronous transfer mode (ATM) is the leading protocol for broadband services, one important issue is the choice of a suitable radio multiple access technique capable of providing multimedia service in a protocol compatible with ATM. Direct sequence code division multiple access (DS-CDMA) and ATM have common characteristics which can offer significant advantages [l]. DS-CDMA can support variable rate traffic by modifying the processing gain or assigning multiple spreading codes to one user. The availability of many spreading codes allows for near perfect statistical multiplexing of the DS-CDMA channel [2]. As a result, this paper proposes a packetized DS-CDMA multimedia wireless communication system that allows for seamless interfacing to ATM broadband networks.Power control is a key issue in achieving high capacity for a DS-CDMA wireless system. Conventional power control uses an open loop algorithm, a closed loop algorithm, or some combination of the two [3]- [4]. For the packetized DS-CDMA system model presented in this paper, power control must be re-examined in consideration of packetization and a slowly Rayleigh fading channel. Closed loop power control can be designed to have a sampling rate that is faster than the rate of multipath fading without the need for excessive feedback overhead. A closed loop algorithm on its own is not sufficient for accurate power control in a packetized network since there may be a large interval between the transmission of consecutive packets. The utility of the feedback information diminishes as the interval between packets increases. On

Forward link partial-balance power control algorithm for W-CDMA communication

“…Power control is well known a key approach for both improving transmission quality and achieving high capacity [ 2,3]. In a multimedia wireless communication system, there exist different traffics with different transmission rates and different Quality of Service(QoS) requirements.…”

“…These result in power control schemes for multimedia system will different from that in the system which has only one type traffic. Recent years, for studying power control of multimedia CDMA systems, more attentions are focused on reverse link [3][4][5][6], whereas there are little about forward link. Forward link power control is identified by Lee IT].…”