Enhanced Data rates for GSM Evolution (EDGE) is a radio based high-speed mobile data standard which acts as an enhancement for General Packet Radio Service (GPRS) networks. It is a technology that gives GSM Network the capacity to handle services for 3G.It was developed to provide a maximum speed of up to 472 Kbps but in real users experience the average speed of 80 kbps to 130 kbps. It can boost network capacity and data rates of both circuit switching (HSCSD) and packet switching (GPRS), to meet the demands of wireless multimedia applications.
EDGE provides three times of data capacity of GPRS and it can handle thrice more subscriber than GPRS. And since it uses the same TDMA frame structure, logic channel and 200 kHz carrier bandwidth as GSM networks, which allows existing cell plans to remain intact, only EDGE-compatible transceiver units must be installed and the base station subsystem needs to be upgraded to support EDGE. In GSM physical channel in the cell can be viewed as being one of at least four channel types:
1. GSM speech and GSM circuit-switched data (CSD);
2. GPRS packet data;
3. Circuit-switched data, Enhanced circuit switched data (ECSD), and GSM speech;
4. Edge packet data (EGPRS), which allows a mix of GPRS and EGPRS users simultaneously.
While standard GSM transceivers only support channel types 1 and 2, Edge transceivers
Support all four channel types.
HSCDA and GPRS provide high bit rates through multi slot operation. But since these techniques are based on original Gaussian minimum-shift keying (GMSK) modulation, they yield only a moderate increase in bit rates per time slot .Whereas in EDGE, the combination of multislot operation and the new modulation scheme, 8-PSK (based on the 30 kHz carrier bandwidth), increase data rate.The symbol rate of 8-PSK remains at 271 kbit/s, yielding a grossbit rate of 69.2 kbit/s per time slot (compared with the current 22.8 kbit/s), while still fulfilling the GSM spectrum mask and leaving the burst duration unchanged.
Many EDGE physical layer parameters are identical those of GSM. The 8-PSK burst format is similar: a burst includes a training sequence of 26 symbols in the middle, three tail symbols at either end, and 8.25 guard symbols at one end. Each burst carries 2 x 58 data symbols, each comprising 3 bits Channel coding and interleaving are intimately related to the layer 2 protocols.
Improvement in Existing Radio Interface Network using EDGE-
In existing cellular system different users tend to have different channel qualities in terms of signal-to-interference ratio (SIR), due to differences in distance to the base station and interference. Since there is a minimum limit specified for SIR below which quality is unacceptable. Therefore, the radio network planning must make sure that only a small fraction of users are below the SIR target. But it will provide a large part of user population unnecessarily high SIR. So EDGE is designed to improve the situation by employing link quality control.
Link quality control dynamically selects the modulation and coding scheme for transmission of data over the air interface. The protection of the data is adapted to the channel quality to ensure optimal bit rate. Standard GPRS saturates at rather low SIR, whereas EDGE user quality increases with increased channel quality.
