Feasibility Conditions of SIR-based Power Control in TDMA Wireless Systems

In this paper, the problem of SIR-based power control in narrowband wireless systems is revisited. Results on feasibility conditions of SIR-based power control are given. We stated and proved the relations between the achievable SIR and the link gain matrix in a narrowband system. Taking into account the orders of the realistic values for the problem quantities and assuming the desired SIR is chosen properly, then there exist infinite many solutions of the SIR-based power control problem. Otherwise, there is hardly a solution since the existence conditions are very restrictive. It is noticeable that these feasibility conditions have important implications on systems capacity and can be applied to call admission control(CAC). Based on the feasibility conditions, an improved stepwise removal algorithm (ISRA) is proposed for TDMA systems to achieve a better performance. I. Review of SIR based Power Control in Narrowband Wireless Networks In a cellular wireless network, certain quality-of-service (QoS) should be maintained for all active users in the network. A quantity that measures the user’s provided QoS is the signalto-interference ratio (SIR). In narrowband systems, it is also called carrier-to-interference ratio (CIR). A general idea to achieve the desired SIR for all the active users is to allocate the network resources in the most efficient way. Resource allocation in a cellular wireless network include channel allocation, power control, etc. The transmitter power is the most valuable resource in the network. By proper control of each transmitter power, the interference can be minimized. At the same time, power control extends the battery life in the handset. In this paper, only narrowband wireless networks are considered. Time and frequency slots are partitioned in a narrowband wireless network in order to avoid mutual interference between users. Nevertheless, users can share the same time or frequency slot provided they are sufficiently far apart, and such users are termed as cochannel users. The issue of power control in narrowband wireless networks arises because the cochannel users interfere with each other. The optimum open loop power allocation problem is formulated as