GPRS (i.e. voice and packet0, as covered in Chapter 5, while further enhancement of GPRS led to EDGE networks, as shown in Figure 6.1. 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. In this chapter we will focus on EDGE network planning aspects from the EGPRS perspective. Fundamentals of Cellular Network Planning & Optimisation A.R. Mishra. © 2004 John Wiley & Sons, Ltd. ISBN: 0-470-86267-X EDGE: NETWORK PLANNING AND OPTIMISATION Packet Switch Circuit Switch Voice EGPRS HSCSD Voice HSCSD Voice HSCSD Figure 6.1 EDGE evolution 6.2 THE EDGE SYSTEM As shown in Figure 6.2, the EDGE system is quite similar to the GPRS system (compare with Figure 5.1), but with the capability for higher data rates. The most important change is 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 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 Functionality SMSGMSC Network More Capacity in the interfaces HLR/AuC GPRS IP Backbone Network Figure 6.2