Written by: Håkan Axelsson, Peter Björkén, Peter de Bruin, Stefan Eriksson and Håkan Persson
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GSM/EDGE has evolved into the most widely deployed cellular telephony standard in the world, offering high-performance voice and data services. To keep GSM/EDGE competitive, even in years to come, Ericsson has proposed steps to further evolve the standard.
The authors describe the proposed technology enhancements, which improve average and peak bit rates, latency, service coverage, and spectrum efficiency. Specific solutions include dual-antenna terminals, multicarrier EDGE, mobility enhancements, reduced transmission time intervals, higher-order modulation, and new coding schemes. The combination of these solutions fulfills the requirements set by 3GPP.
Background
When introduced to the market in 1992, the Global system for mobile communication (GSM, defined by ETSI as the internationally accepted digital cellular telephony standard) was primarily a voice-only system with SMS and some low-bit-rate circuit-switched data services. Since then, however, GSM has continued to evolve unabated.
General packet radio service (GPRS), for example, introduced packet-data capabilities. And the subsequent introduction of Enhanced data rates for GSM evolution (EDGE) or Enhanced GPRS has greatly extended the capabilities of packet-data services. EDGE technology, which is backward compatible with GPRS, offers up to a 200% increase in data bit rates.
At present, GSM/EDGE is undeniably the most widely spread cellular technology in the world (Figure 1). Only two countries, Japan and South Korea, rely exclusively on other standards. There are currently more than 1.7 billion GSM/EDGE users world-wide, and subscriber growth continues to be high. In November 2005, the Global mobile Suppliers Association (GSA) reported that 121 GSM operators were offering commercial EDGE-based services in 70 countries, and 172 operators in 92 countries had committed to providing EDGE.
Improving service performance
To keep GSM/EDGE competitive, even in years to come, Ericsson has proposed a num-
ber of enhancements that facilitate truly conversational multimedia services and improve service performance and service continuity. All major vendors and many operators have pledged their support for a continued evolution, which is being standardized in 3GPP. The general objectives are to improve service performance and provide more efficient bearers. Seamless operation or service continuity between GSM/EDGE and WCDMA networks is also being addressed.
Objectives
The proposed technology enhancements are meant to improve average and peak bit rates, latency, service coverage, and spectrum efficiency. Box B (Item I) shows the targets used in the standardization.
The first objective, increased spectrum efficiency, mainly benefits operators. In many urban areas, the existing frequency spectrum is being used to the maximum extent. However, by enhancing spectrum efficiency (that is, improved ability to withstand greater levels of interference) operators can increase traffic volumes without compromising quality.
Best-effort services, such as web browsing and file downloads, typically benefit from increased peak and mean bit rates. Depending on the degree of user interactivity, these services might also considerably benefit from reduced latency.
Conversational services, such as voice over IP (VoIP) and enhanced Push to talk over
Cellular (PoC), as well as online gaming services typically benefit from (or might even require) reduced latency and faster access.
All services (voice as well as packet-data) stand to benefit from improved coverage and from having terminals that are always connected to the most appropriate base station.
Most services can benefit from faster initial response from the network. This is especially true for conversational services and applications with limited system interactivity prior to uploading or downloading application data (for example, WAP, MMS and FTP). Although not presently pursued in 3GPP, solutions have been proposed that would decrease access time (when the mobile terminal is known in the packet control unit, PCU) to less than 500ms.
Given that the installed base of GSM/EDGE equipment is very large, Ericsson has tried to minimize the effects of the proposed technology enhancements on base station hardware. As a consequence, the proposed solutions have no impact on transceiver units and other base station hardware. What is more, they assume the same (current) network architecture (Figure 2). In general, only radio network software and terminals will need to be updated.
