In third generation cellular systems, new services will be offered. Some of these suggested services require a guaranteed Quality of Service (QoS). An example of these services is streaming, which for example requires a certain guaranteed bit rate and delay. Since the system resources are limited, it may sometimes be necessary to deny access for new users in order to preserve the QoS for users already active in the system.
In this thesis it is indicated that admission control is necessary for streaming in order to maintain the quality demands in overload situations. A theoretical model of a cellular streaming scenario is developed, and based on this model a simulator is implemented in Matlab. Different load combinations of speech and streaming users have been simulated. It is shown that a system without admission control may become overloaded (jammed) at higher loads and the number of satisfied users decreases rapidly.
In order to investigate methods of how to avoid overloaded systems and unsatisfied users, a number of different admission control algorithms have been developed and evaluated. These algorithms can be combined for a specific scenario depending on system parameters and known variables. The finally proposed algorithm is based on a prediction of the total throughput available for streaming users, with information from the admitting and neighboring cells. Based on this, it is possible to allow a certain number of users in the admitting cell, with a certain probability of keeping all users satisfied. A load dependent threshold is applied to decrease the blocking rates at low loads. Speech users have strict priority over streaming users. This means that timeslots used by streaming users may be “stolen”, or pre-empted, and the streaming user’s session may be terminated
With the proposed algorithm it is shown that admission control is beneficial, and necessary to keep a system stable. The algorithm gives, in terms of the number of satisfied users, nearly the same performance as without admission control for low loads, and outstanding performance at high loads.
Author: Johansson, Per
Source: Luleå University of Technology
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