EDGE 9 types of encoding techniques, the MCS (Modulation Coding Scheme) 1 up to MCS9. While GPRS uses four pieces of encoding technique, ie CS (Coding Scheme) 1 up to SC4. The first four encoding techniques on EDGE, MCS1 until MCS4, using GMSK modulation, the same as that used in GPRS. While five other coding techniques, MCS5 until MCS9, using 8PSK modulation.
Both the GPRS or EDGE, levels higher coding schemes offering higher data speeds too but besides that, the higher the level of encoding scheme, then the lower the resistance to errors. It means that the higher speed packet data, the easier the data packets that have errors in delivery. This is because, the higher level encoding scheme, then the level of mechanisms "error correction" used the lower.
Although MCS1 until MCS4 on EGDE both use GMSK modulation, such as CS1 to CS4 on GPRS, but both have different speeds. This is because the use of the headers are different. In EDGE, the data packet contains a header that allows data packets resegmentasi. That is, if a data packet is sent by using a high-level coding scheme (higher speed, less error correction) and data were not well received at the receiver side.
After a retransmission request (retransmission) packet of data received, at the next delivery, the encoding scheme used can be changed and adapted to conditions of the radio interface. That is, on the next delivery, the data packet will be sent by using a lower coding scheme, which had an error correction mechanism better. Hopefully, in this second delivery data can be well received in the receiver side.
In contrast to the GPRS, resegmentasi packet data can not be done. Therefore, when a data packet has been sent using a particular encoding scheme. So although the data is received either on the receiver side, when the next delivery, the data will still be sent by using the same encoding scheme. Consequently, the possibility that the data packet is received at the receiver side is still as large as when the first shipment. Therefore, it can achieve a balance between speed and quality transfer of data transferred.
Source : http://id.wikipedia.org/wiki/Enhanced_Data_Rates_for_GSM_Evolution#Teknik_Pengkodean_Pada_EDGE