Briefing Technical Briefing Technical Briefing Technical www.wraycastle.com February 2009 © Wray Castle Limited The Need for More Performance GSM/GPRS must surely be one of the most successful communicati ons technologies the world has ever known. After all, more than half the world’s population has a mobile phone based on GSM technology, far more people even than have had access to fixed-line telephones. Nevertheless, GSM has been around for almost two decades and interest now seems focused on 3.5G and 4G technologies. So perhaps the time has come for GSM to step politely aside, content in the knowledge of a job well done. Not so. Work is continuing apace to enable GSM operators t o offer significantly enhanced data services through their existing GSM/GPRS infrastructure without the need to migrate directly to next-generation technologies such as UMTS or WiMAX. It may seem inevitable that a GSM operator would wish to upgrade as soon as possible to UMTS and HSPA, but this upgrade path can be very problematic and expensive. Not all operators have new spectrum in which to operate UMTS, whic h requires at least one clear 5 MHz block. Even for those that have the option for new spectrum, there is the consideration of the very large investment required in licence fee and new network build. In addition, operators that have not at this stage already begun investment in UMTS should certainly be considering the implications of the potential availability of LTE in only two years’ time. An upgrade once to UMTS and then again to LTE within a very short timeframe is certainly not desirable. Thus if GSM/GPRS could be given a significant performance boost then it may be able to bridge the gap to 4G. This should be a very attractive option for many operators and this is exactly what EDGE Evolution is about. The Status Quo Almost all existing GSM networks are using GPRS and more than 400 of these have added EDGE capability. However , while GPRS has seen the germination of more advanced services such as the Multimedia Messaging Service (MMS) and limited web browsing, the theoretical bit rate of 171.2 kbit/s has proved stubbornly elusive. Limitations in mobile station multi-slot capability and error protection coding schemes have restricted bit rates for most operators to below 50 kbit/s in the downlink and below 20 kbit/s in the uplink. Cost per bit also remains very high with consequently low revenue generated from data services. The situation has somewhat improved with the introduction of Enhanced Data rates for Global Evolution (EDGE), but because of similar multi-slot and error protection limitations it rarely exceeds half of its potential of more than 470 kbit/s. Additionally, for both technologies, latency remains relatively high, further degrading the data experience for subscribers. The Aims for EDGE Evolution The changes for EDGE Evolution arrive in releases 7 and 8 of the standards and the most obvious improvement is to the data rates achievable in a GSM-based channel. Potentially, the first phase of EDGE Evolution provides bit rates in excess of 1 Mbit/s in the downlink and in exc ess of 400 kbit/s in the upli nk. However, to appreciate fully the advancement t hat comes with EDGE Evolution it is necessary to understand that it is an integral part of the wider changes that bring an all-IP, and UMTS-like, Evolved GSM EDGE Radio Access Network (GERAN), known as GERAN Evolution (GEV). Coupled with this is the progression through soft switching toward an all-IP based core network with real-time services controlled by an IP Multimedia Subsystem (IMS). This last point is important because, with the IMS in place, EDGE Evolution is intended as an upgrade for voice as well as data services. EDGE Evolution – Sweating the Assets GSM/GPRS GSM/EGPRS UMTS UMTS/HSPA LTE EDGE Evolution