| Wireless systems in the future will have to provide multimedia services where different users have different physical-layer and network-layer QoS requirements. We investigate the use of power control and scheduling in CDMA systems to accommodate these diverse service requirements.; We first derive the explicit formula of the instantaneous capacity region for any channel state which is given in terms of the set of user bit rates that can be supported simultaneously subject to the power constraint set being bounded, closed, convex and coordinate convex and bit energy per interference power density constraints in multi-cell systems. We define the time-sharing capacity region as the convex hull of the instantaneous capacity region and we show that, for a single-cell system and for peak power constraint, it may be obtained by time sharing between operating points where each user either uses full power or is silent.; By choosing any bit rate vector in the time-sharing capacity region, we automatically satisfy the physical-layer QoS. Thus, it is the control knob used by the scheduler to satisfy the network layer QoS. We consider the problem of scheduling on both static and dynamic channels. In the static channel case, the channel state changes slowly relatively to the time-scale of the data traffic, and hence is assumed known and fixed. The system is required to meet pre-specified delay bounds or minimum service curve requirements for traffic streams, which are specified in terms of a traffic profile such as a sigma-rho constraint, and to guarantee stability. In the dynamic channel case, where the channel state changes more rapidly, we design a class of scheduling policies that guarantees system stability. We use simulation to compare the performance of various policies in this class. Specially, we show that the “Minimum Draining Time” policy has certain desirable qualities vis-a-vis the “Cone” policy and “Modified Cone” policy. All three turn out to be special cases of the policy class for which we show stability. |
