Optimisation of Downlink Resource Allocation Algorithms for UMTS Networks
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ptimisation of Downlink Resource Allocation Algorithms for UMTS Networks Michel Terre´ Conservatoire National des Arts et M´etiers (CNAM), 292 rue Saint Martin, 75003 Paris, France Email: [email protected]
Emmanuelle Vivier Institut Sup´erieur d’Electronique de Paris (ISEP), 28 rue Notre Dame des Champs, 75006 Paris, France Email: [email protected]
Bernard Fino Conservatoire National des Arts et M´etiers (CNAM), 292 rue Saint Martin, 75003 Paris, France Email: [email protected] Received 22 October 2004; Revised 3 June 2005; Recommended for Publication by Sayandev Mukherjee Recent interest in resource allocation algorithms for multiservice CDMA networks has focused on algorithms optimising the aggregate uplink or downlink throughput, sum of all individual throughputs. For a given set of real-time (RT) and non-real-time (NRT) communications services, an upper bound of the uplink throughput has recently been obtained. In this paper, we give the upper bound for the downlink throughput and we introduce two downlink algorithms maximising either downlink throughput, or maximising the number of users connected to the system, when orthogonal variable spreading factors (OVSFs) are limited to the wideband code division multiple access (WCDMA) set. Keywords and phrases: resource management, capacity optimisation, code division multiple access, OVSF, multiservices.
1.
INTRODUCTION
Third generation (3G) wireless mobile systems like UMTS provide a wide variety of packet data services and will probably encounter an even greater success than already successful existing 2G systems like GSM [1]. With the growing number of services, the optimisation of resource allocation mechanisms involved in the medium access control (MAC) layer is a difficult aspect of new radio mobile communications systems. The resource allocation algorithm allocates the available resources to the active users of the network. These resources could be radio resources: they are time-slots in the case of a 2.5G network like (E)GPRS, but in a 3G network like UMTS, using WCDMA technology, they are spreading codes and power. Each user of data services can request, depending on his negotiated transmission rate, a spreading code of variable length with a corresponding transmission power at each moment. In a cell, we have real-time (RT) communications services that are served with the highest priority This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
and non-real-time (NRT) communications services that are served with the lowest priority. Having allocated resources to the RT services, the base station then has to allocate resources to NRT services. In this paper we consider two possible criteria: the greatest number of allocated NRT services and the maximisation of the downlink throughput [2]. Most of notations used in this paper are close to those of [3, 4, 5, 6] where the downlink case was analysed, and of
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