Edge In Gsm

INTRODUCTION

GPRS networks are able to handle higher bit rates than GSM networks, but the data rates still fall short of what is required to make existing GSM networks deliver services at a speed comparable to that promised by third-generation networks. The delay in the deployment of third-generation systems led to the emergence of a technology known as EDGE. This was capable of delivering services similar to those of third-generation networks, yet with implementation on the existing second-generation networks (e.g. GSM).

EDGE stands for 'enhanced data rates for GSM evolution'. The enhancement from GSM was to GPRS (i.e. voice and packet), while further enhancement of GPRS led to EDGE networks, as shown in Figure 1. The fundamental concept remains the same, i.e. voice, CS data and PS data being carried, and the network architecture is the same as in a GPRS network. Enhancement of HSCSD is known as ECSD (enhanced circuit-switched data), while enhancement of GPRS is known as EGPRS.

EGPRS implementation has a major effect on protocol structure (e.g. on layer 1 or layer 2). The modulation and coding schemes are quite different in EGPRS (this is explained later in the chapter).

In ECSD, though user data rates do not go beyond 64 kbps, fewer time slots are required to achieve this compared HSCSD. The architecture of ECSD is based on HSCSD transmission and signalling, thus having minimal impact on existing specifications

THE EDGE SYSTEM

As shown in Figure 2, the EDGE system is quite similar to the GPRS system (compare with Figure 1), but with the capability for higher data rates. The most important change the new modulation scheme. In GSM and GPRS, the GMSK modulation scheme was Used

In GMSK modulation, only one bit per symbol is used. In an EDGE network, octagonal phase-shift keying (8-PSK) modulation is used which enables a threefold higher gross data rate of 59.2 kbps per radio time slot by transmitting three bits per symbol. GMSK is a constant-amplitude modulation while 8-PSK has variations in the amplitude. This amplitude variation changes the radio performance characteristics, so hardware changes in the base stations are mandatory.

EDGE NETWORK PLANNING

The radio network planning process is similar to that for GSM and GPRS networks. How¬ever, because of minor hardware and software changes in the existing network, that lead major changes in network performance, the network planning parameters change quite a bit. Owing to increased bit rates, transmission planning undergoes a major change with introduction of the concept of a dynamic A-bis interface. In contrast, core network planning virtually the same as