Written by: Ros-Marie Furtenback, Torsten Hunte, Dalibor Turina and Ulrik Wahlberg

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Many of today’s GSM operators view WCDMA as a technology enhancement that enables them to offer new data services and as a cost-effective extension in capacity for voice service.

Operators who are rolling out WCDMA and EDGE are advised to pay extra attention to the end-user experience, because end-users expect the quality of the new bearers to exceed that of GSM. Operators who introduce WCDMA coverage are thus advised to build a WCDMA layer that provides continuous coverage and offers sufficient capacity. They should also build out WCDMA indoor coverage.

Initially, those GSM operators who deploy WCDMA will experience significant gains in capacity. But eventually they will want to use all available radio spectrum as a common resource. Doing so, however, will require traffic-steering mechanisms. Ericsson has already begun introducing mechanisms for steering traffic between WCDMA and GSM. Parameters that trigger redirection are load, coverage, a specific service, or QoS requirement.

Giving ample consideration for end-user perception and the optimization of network resources, Ericsson has identified and addressed an enhanced approach to idle-mode distribution. This, in turn, has resulted in four main assertions:
(a) the mobile station should camp in the network that can most efficiently provide the requested subscriber service;
(b) lack of coverage is the prime justification for employing mechanisms that steer traffic between different radio access technologies;
(c) traffic-steering mechanisms for balancing load should be designed for the dominant application; and
(d) end-users need not be aware of which underlying radio access technology is currently serving them. To steer the traffic of ongoing sessions, the performance of the underlying service-continuity mechanism must match the QoS class, and relevant services must be available both in WCDMA and GSM.

[First published in Ericsson Review no. 01, 2004]