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UBC Theses and Dissertations

Multimedia services in DS/CDMA cellular networks : Erlang capacity and scheduling schemes Fattah, Hossam

Abstract

Broadband wireless networks are being envisioned to provide ubiquitous multimedia services to mobile users. Supporting multimedia services along with the legacy wireless applications such as voice in an integrated networking framework requires a new network infrastructure and the provision of Quality of Service (QoS) guarantees. This thesis addresses QoS issues in CDMA networks, specifically, Erlang capacity and blocking probability of a CDMA system with multimedia traffic and the design of several radio link-layer scheduling schemes employing service differentiation, and providing QoS guarantees. A new method is proposed for calculating the Erlang capacity of a DS/CDMA system that can accommodate different traffic sources with variable transmission bit rates. In this approach, each source is modeled using a continuous-time Markov process. The evaluation is illustrated for networks with both homogeneous (one class) and heterogeneous (multiple classes) traffic sources. Imperfection in power control due to channel impairments is also considered. Such a model can capture traffic burstiness and yield more realistic results. A transmission rate scheduling scheme is proposed that can provide either absolute or relative QoS guarantees for different service classes. The proportional differentiated services model is introduced which enables the network operator to tune QoS ratios among these classes independent of the class loads. An optimization problem is also proposed that maximizes the transmission rate allocations among Mobile Stations (MSs) while ensuring the stability of packet queues and meeting the transmit power level constraint. Analysis and simulation results are used to illustrate the viability of the scheduling scheme which could be applied in the emerging Differentiated Services (DS) Internet. A load-based transmission rate (LTR) assignment scheme is introduced for non-real time data services in an integrated voice/data network. The LTR scheme takes into account session arrival processes and optimally determines the required transmission rate for each session so as to minimize the overall average packet transfer delay. It is shown that the average packet transfer delay of LTR is significantly lower than that of the conventional traffic-based grouping transmission (TGT) scheme. A reservation policy combined with a number of centralized dynamic priority based packet-level schedulers is proposed for providing soft QoS guarantees for multimedia traffic while achieving a high channel utilization. In the reservation scheme, the number of packets selected for transmission from a session is changed dynamically depending on the traffic type, traffic load, Time of Expiry (TOE)/Time of Arrival (TOA) values of packets and/or packet queue length. The proposed scheme is shown to provide high channel utilization while achieving per-class QoS guarantees in a multimedia traffic environment. The scheme can be used in the DS networks. A fair queueing architecture is proposed which allows many of the proposed wireline fair queueing algorithms to be used in wireless CDMA systems. The architecture addresses the issue of time scheduling using a new Generalized Processor Sharing (GPS) approach that utilizes the available power resource efficiently by assigning variable power indices to the mobile stations. This approach supports multirate transmission techniques such as variable spreading gain or multicode. Finally, a new scheduling algorithm "Wireless Deficit Round Robin (WDRR)" is proposed. WDRR is a round robin scheduler that has low implementation complexity and provides a low delay bound, tight fairness index, and almost perfect isolation property. The algorithm provides short-term fairness among sessions that perceive a clean channel, long-term fairness among all sessions, ability to meet specified throughput objectives for all sessions, and graceful service degradation among sessions that received excess service. Both analysis and simulation are used to verify the WDRR properties.

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