Service disciplines performance for GPRS with link adaptation and heterogeneous traffic

摘要

The general packet radio service (GPRS) system provides a packet switched data service with quality of service (QoS) over a GSM infrastructure. In order to cope with the QoS requirements, packet scheduling strategies are used. On the other hand, GPRS introduces four coding schemes with different degrees of data protection according to the radio channel conditions. The selection of an appropriate coding scheme according to the time variant channel conditions can lead to a substantial increment of the QoS. Two scheduling policies, namely MED (modified earliest deadline) and MLT (minimum laxity threshold) are evaluated, assuming both link adaptation (LA) strategy, based on BLER (block erasure rate) estimation, and heterogeneous traffic. Web browsing, fleet management, SMS (short message service) and e-mail services are assumed. The performance of the proposed scheduling policies is evaluated in terms of throughput and delay. For urban environments with high load conditions, the obtained results show that a simple LA enhances QoS system performances, even though there is a trade-off with respect to the network packet loss.