Ever since Marconi demonstrated the possibility of continuous communication over wireless links in 1897, newer methods to push more information over the medium have been rigorously developed and adopted. But like every good thing, the medium of transmission of this information is limited. Bandwidth has always been a bottleneck in wireless communications. When the need to transmit digital media apart from voice data was felt in Europe with the GSM technology after 1990, a mere 9.4kbps per slot offered by GPRS services was found insufficient. As a primary step towards greater speeds, Enhanced Data-rate for GSM Evolution or more popularly EDGE was developed.
GSM technology rolled out for the first time in Europe in 1990 and had good market by 1992. However it was a voice-only service primarily with a few additional features like SMS and low-bit circuit switched data services. Improving upon this, High Speed Circuit Switched Data (HSCSD) service was introduced in 1998. Circuit switched services had their disadvantages and hence General Packet Radio Service (GPRS) was introduced in 1999 which allowed data transmission and reception in packet transfer mode within a PLMN without a permanent dedicated route between mobile and the external network. This was done keeping in view that the terminal equipment on the user end should remain unaffected and optimizing radio resources at the same time. It worked within GSM networks by taking more than one user slots in the TDMA frames.
However, it was capable of only 171.2 Kbps theoretically even when all time slots were allocated to data services. For multimedia services, a minimum throughput of at least 384 Kbps is required. As a result, Enhanced Data-rate for GSM Evolution was proposed to European Telecommunications Standards Institute in 1997. It was approved by Universal Wireless Communications Consortium (UWCC) and ETSI after feasibility studies conducted in ETSI and then standardized in the ETSI/3GPP Release 99 and later the EDGE Evolution by 3GPP in its Release 7. Most countries now use this standard with an exception of a few like South Korea and Japan which rely exclusively on other standards. EDGE is often called Enhanced GPRS (EGPRS) and concurrent work by ETSI and UWCC ensures that the framework developed works fine with both GSM and TDMA/136 systems. The roadmap was laid in two phases, the first emphasized on developing EGPRS and ECSD and the second focused on improving multimedia and real time support.
EDGE is a high speed mobile data standard which can work with GSM/GPRS and IS-136 networks over a radio interface and hence also known as Enhanced Data Rate for Global Evolution. This is achieved over the same GSM network bands of 800, 90, 1800 and 1900 MHz. EDGE manages to increase data speeds using the same 200 kHz GSM radio carriers by means of a different type of modulation. Along with the old Gaussian Mean Shift Keying, EDGE also uses the Eight State Phase Shift Keying (8-PSK). This is a linear, higher level modulation scheme which provides higher spectral efficiency, higher data rates and moderate implementation complexity. In both GMSK and 8 PSK Modulation Schemes, the symbol rate stays the same at 271 kb/s. However in 8-PSK, one symbol has 3 bits and hence bit rate per time slot amounts to 69.2 kbps which almost three times as that of 22.8 kbps in GMSK. Following is a brief overview of EDGE technology:
Outer block coding, inner Convolutional Coding
TDMA and FDMA
Uplink: 890- 915 MHz Downlink: 935-960 MHz
RF Carrier Bandwidth
8 (each of .577 ms)
Channel Coding Schemes
CS-1 to CS-4 and MCS1 to MCS-9
Though proposed as an evolution to GSM initially, it is now more of a generic air interface for providing high data rates efficiently facilitating a migration path from the second generation to the third as described in the Release 99, hence often termed as a 2.5G Technology, and also to complement UTRAN as fully capable Radio Access Network (RAN) integrable in the UMTS core and maintain backward compatibility at the same time. This means that no new licenses are required explicitly for EDGE services. It is not only aimed at the Packet Switched GPRS networks, but also at the global evolution of Circuit Switched GSM and the D-AMPS (IS136) networks.