Resource allocation and opportunistic scheduling for UMTS-TDD

In UMTS-TDD (Universal Mobile Telecommunications System - Time Division Duplex) the data rates and the service quality (bit error rate, delays) are provided by the Radio Resource Management (RRM). The RRM manages the transmission power, the spreading factor and the orthogonal code assignment. The specifications leave open the choice of the RRM strategy. This work proposes a scheme suitable for mixed traffic consisting of Real Time (RT) services and Non Real Time (NRT) services in downlink. The access to the RT services is controlled by the Call Admission Control (CAC) using a Power-based algorithm. This algorithm determines the OVSF (Orthogonal Variable Spreading Factor) codes of a user in order to optimize the sharing of the transmitted power in the downlink in the most uniform manner over the assigned slots in the frame. The OVSF codes given by this algorithm are attributed to a Dedicated Channel. For NRT services, in presence of RT services, a channel allocation power-based strategy is combined at the physical layer with an opportunistic scheduling at the Medium Access Control (MAC) layer to minimize Node-B transmitting power and schedule mixed traffic that benefits of a good radio channel and respects Quality of Service (QoS) constraints and fairness rules. The overall RRM strategy minimizes the number of RT rejected calls and the Block Error Rate (BLER) of NRT services. The NRT services are mapped to Downlink Shared Channel.