Network Performance under Different Scheduling Strategies for NRT Traffic in HSDPA

WCDMA evolution (HSDPA) appears as an umbrella of features to improve both user and system performance. The concept includes a reduction of the Transmission Time Interval (TTI) to 2 ms, an Adaptive Modulation and Coding (AMC) scheme, and a fast physical layer Hybrid ARQ mechanism. One of the key functions in the system is the packet scheduler. The scheduler is in charge of distributing the network resources among the users within the coverage area. The scheduler targets at optimising the cell capacity while delivering minimum acceptable quality of service for the users. In HSDPA, the Packet Scheduler functionality is located in the Node B, which enables to track instantaneous variations of the user?s channel quality. The present investigation analyses the network capacity of different scheduling strategies for delay-tolerable (NRT) traffic with minimum data rates guarantees. The investigation has specially concentrated on assessing different Packet Scheduling methods with different degrees of fairness for non delay-sensitive services because it determines the QoS perceived by the users. The results have shown that under minimum throughput guarantees the Proportional Fair algorithm provides the highest cell capacity of all tested algorithms. This scheduler serves the user with highest ratio C/I/UE Throughput. If the random component of the C/I (non distance dependent) follows the same distribution for all users, and these are independent among users, then this algorithm allocates the same asymptotic fraction of time to all users. The maximum capacity provided by this algorithm yields around 150% gain over WCDMA technology with similar degree of fairness (in macrocell environments). The provision of data rates guarantees of 64, 128 and 384 kbps (at 5% outage) incurs on a cell capacity reduction respectively of around 10, 30 and 80% relative to the maximum cell capacity (under heavy load conditions). (Pablo Ameigeiras, Preben E. Mogensen; Jeroen Wigard, Nokia)