o some extent random, varia- rate control tions in the experienced quality of each radio link in a cell, variations that must be taken into account and Historically, dynamic transmit-power control has been preferably exploited. used in CDMA-based mobile-communication systems In this chapter, some of the techniques for handling such as WCDMA and cdma2000 to compensate for variations in the instantaneous radio-link quality will be variations in the instantaneous channel conditions. As the discussed. Channel-dependent scheduling in a mobile- name suggests, dynamic power control dynamically communication system deals with the question of how to adjusts the radio-link transmit power to compensate for share, between different users (different mobile termi- variations and differences in the instantaneous channel nals), the radio resource(s) available in the system to conditions. The aim of these adjustments is to maintain achieve as efficient resource utilization as possible. Typ- a (near) constant Eb/No at the receiver to successfully ically, this implies to minimize the amount of resources transmit data without a too high error probability. In needed per user and thus allow for as many users as principle, transmit-power control increases the power at possible in the system, while still satisfying whatever the transmitter when the radio link experiences poor quality-of-service requirements that may exist. Closely radio conditions (and vice versa). Thus, the transmit related to scheduling is link adaptation, which deals with power is in essence inversely proportional to the channel how to set the transmission parameters of a radio link to quality as illustrated in Figure 4.5-1a. This results in handle variations of the radio-link quality. a basically constant data rate, regardless of the channel Both channel-dependent scheduling and link adapta- variations. For services such as circuit-switched voice, tion tries to exploit the channel variations through this is a desirable property. Transmit-power control can appropriat