An analytical framework for calculation of Erlang capacity per cell of UMTS with perceptual-based power control is derived. A comparison of the capacity of the system using the proposed power control algorithm with its conventional counterpart is performed. This is supported by numerical results on Erlang capacity over a variety of system parameters for both considered power control approaches. It is shown that the use of perceptual speech quality metrics in power control results in a capacity gain of at least 10% over that of conventional UMTS. I. INTRODUCTION A major proportion of traffic in mobile radio systems such as UMTS is still comprised of speech. It is, therefore, important for speech service providers to monitor the QoS that is delivered to customers. This will allow them to control speech quality by making necessary adjustments on their side so as to compensate for any potential loss of quality at the customer side. The need for QoS control can be addressed by employing accurate speech quality measurement methods together with link adaptation techniques such as power control which are based on such methods. Speech quality in mobile radio systems is traditionally extracted at the receiver (1), (2) relating to some channel quality measure such as Frame Error Rate (FER) and Signal- to-Interference Ratio (SIR). It has been shown that these measures do not necessarily provide accurate and reliable estimates of quality (3). Thus, more appropriate speech quality measurement methods that take human perception into account would be desirable. The available perceptual speech quality measurement methods such as the ITU-T standard P.862, also known as Perceptual Evaluation of Speech Quality (PESQ) (4), provide a solution. These methods may be used to predict Mean Opinion Scores (MOS) as a measure of human perception in a technical system. Given the potential for performance improvements of power control using perceptual-based algorithms over conventional power control as revealed by simulation in our previous work reported in (5) and (6) for GSM and UMTS, respectively, a generic analytical framework for perceptual-based power control shall be derived in this paper. A truncated Markov chain model of the power control algorithms is used as basis of the derivation. On this foundation, an analytical framework for the calculation of Erlang capacity per cell of UMTS with perceptual-based power control is derived. In particular, the transition probabilities for the truncated Markov chain model of the power control algorithm are developed. A comparison of the capacity of the system using the proposed power control al- gorithm, which is based on perceptual speech quality metrics, with respect to its conventional counterpart is performed. This is supported by numerical results on Erlang capacity over a variety of system parameters for both considered power control approaches. It is shown that the use of perceptual speech quality metrics in power control of UMTS results in a capacity gain of at least 10% over that of the conventional UMTS. As analytical expressions are given, an overview of the impact of system parameters on performance can be easily obtained without depending on time consuming simulations. This paper is organized as follows. In Section II, an analyti- cal approach for calculation of Erlang capacity of UMTS with its power control based on conventional speech quality metrics is laid out. In Section III, by modifying the framework for con- ventional power control to incorporate the effect of perceptual speech quality metrics, an analytical approach for perceptual- based power control in UMTS is presented. Numerical results that show the benefits of perceptual-based power control over conventional power control in UMTS are given in Section IV. Finally, Section V concludes the paper.
['B. Rohani', 'Hans-Jurgen Zepernick']
Erlang Capacity of UMTS Using Perceptual-Based Power Control: An Analytical Framework