s it to be overlaid directly onto an existing GSM network. For many existing GSM/GPRS networks, EDGE is a simple software upgrade. EDGE allows the delivery of advanced mobile services such as the downloading of video and music clips, full multimedia messag- ing, high-speed color Internet access, and e-mail on the move. Due to the very small incremental cost of including EDGE capability in GSM network deployment, virtu- ally all new GSM infrastructure deployments are also EDGE capable, and nearly all new mid- to high-level GSM devices also include EDGE radio technology. EDGE basically enables a greater data transmission speed to be achieved in good conditions, especially near the base stations. It does so by implementing an 8-PSK modulation scheme instead of Gaussian Minimum-Shift Keying (GMSK). 8-PSK enables each pulse to carry 3 bits of information versus GMSK's 1 bit per pulse rate. Thus, EDGE has the potential to increase the data rate of existing GSM systems by a factor of three. For EDGE to be effective, it should be installed along with the Chapter 14 Wireless WANs packet-switching upgrades used for GPRS. Again, this entails the addition of the GGSN and the SGSN. In addition, an EDGE transceiver unit must be added to each cell, and the base stations must receive remote software upgrades. EDGE can coexist with GSM traffic, switching to EDGE mode automatically. EDGE ultimately allows the combination of digital TDMA and GSM and pro- vides an enhanced version of GPRS. It supports 48Kbps to 69.2Kbps per time slot, and by aggregating time slots, it can support up to 384Kbps. GSM's 200KHz chan- nel spacing is also maintained in EDGE, allowing the use of existing spectrum bands. EDGE is also sometimes referred to as a 2.75G system. At the end of 2005, there were 121 commercial EDGE networks in 70 coun- tries, and there were 174 GSM/EDGE terminal devices available. There were also 57 mobile operators deploying combined EDGE/W-CDMA networks and 26 com- bined EDGE/W-CDMA networks already in service. EDGE has become a 