What is EDGE
EDGE stands for ‘Enhanced Data Rates for GSM Evolution’. As the name suggests this technology is in fact an upgrade over the second generation GSM cellular systems in order to provide enhanced data rates to the users. The need of this technology arose from the advent of modern internet applications like internet radio, video streaming etc. that required such high data rates.
EDGE technology is a 2.5G technology and its networks require addition of extra hardware and software at only the Base Station Controllers of a GSM Network. The following are the main features of this technology:-
Just like in GSM, EDGE uses a combination of Frequency Division multiplexing and Time Division multiple Access (FDM/TDMA). Each frequency channel is divided in to eight time slots similar to a GSM Network. It uses a total of nine multiple modulation and coding schemes (MCS) on an adaptive basis depending upon the data rate requirements of the user along with the radio environment encountered in the transmission. In GSM systems, only a single modulation scheme of Gaussian Minimum Shift Keying (GMSK) is used that supports low data rates. In EDGE technology, two modulation schemes namely Gaussian Minimum Shift Keying (GMSK) and octal phase shift keying (8-PSK) are used depending on the data rate requirement. For schemes supporting lower data rates GMSK is used while for the ones supporting higher data rates 8-PSK is used. It uses a varying degree of error control according to the radio environment encountered in the transmission in order to provide data packets with minimum overhead. This is achieved by a process known as incremental redundancy. In this process, the first time data is transmitted to the user; it is transmitted with maximum error control and bandwidth. In subsequent transmissions both the error control and bandwidth are incrementally reduced until the link gets degraded below the threshold level. Then a quick communication between the mobile station and the base station restores the transmission to conditions just above the threshold level. Thus data transmission takes place with minimum overhead and maximum spectral efficiency.
The maximum theoretical data rate that can be provided by a single TDMA EDGE channel is 547.2 Kbps but practically this value reduces to 384 Kbps. Although the users can be provided with data rates up to a couple of Mbps by using multiple time slots in a frame for a single user.