Network capacity and quality of service management in F/TDMA cellular systems

Abstract

As a consequence of rapidly increasing mobile communications, efficient utilization of the scarce radio resources becomes one of the most important issues in the system evolution. Increase of the system capacity has been investigated in two ways. The first way is to replace the fixed channel allocation (FCA), with the more efficient dynamic channel allocation (DCA). The second way is to utilize those traffic channels not being used by voice services to provide a packet data service, like general packet radio service (GPRS) and cellular digital packet data (CDPD). In this thesis, the author have proposed two DCA schemes and developed an analysis method to investigate the GPRS impact on the GSM voice services. In addition, the GPRS downlink performance is investigated and some guidelines or principles for GPRS network planning have been presented.

In the proposed DCA algorithms, the effect of the channel allocation on existing calls is considered by the evaluation of the call outage rate or a cost function. In the first proposed algorithm, in order to evaluate the call outage caused by those candidate channels, a method of estimating the average signal to interference ratio (SIR) variation of on-going calls due to the assignment of a coming call has been developed. This algorithm improves the capacity or QoS performance compared with the first available and maximum SIR schemes. In the second proposed algorithm, a cost function has been introduced to estimate the cost of the assignment of a candidate channel. The performance evaluation shows that by using the cost-function for channel pre-selection the problem of high intracell handover rate for the first available based scheme can be decreased to an adequate level and the time of the call set-up can be shortened.

An analysis method to calculate the outage probability of the GSM-GPRS network for both the non-frequency hopping and frequency hopping systems has been presented to investigate the GPRS impact on GSM voice services. It is found that: GPRS affects more on the QoS of voice services of the network with small reuse factor; GPRS will reduce the cell service area, but the reduction percentage of the cell service area for the system with small reuse factor is higher than that for the system with large reuse factor; those channels unused by voice services might not all be used for carrying GPRS traffic; the number of unused voice channels which can be allocated to GPRS depends on the difference between the outage level of the existing GSM network and the maximum acceptable level.

From final part of this work, it is found that: GPRS capacity performance in downlink is quite different from that in uplink because of the difference in the transmission protocols; multiple-slot allocation does not show a gain of the mean throughput neither a decrease on the mean delay compared to single slot allocation. This result is different from the result of the uplink performance. In multi-rate services, the multi-slot services significantly increase the delay of the single-slot service, consequently, a control of the multi-slot services is needed.