In order to further increase the data transmission speeds a new modulation and coding scheme,which uses 8PSK, has been introduced into the standards. The new coding scheme forms thebasis of the ‘enhanced data rates for GSM evolution’ package, which is also called EDGE.
The packet-switched part of EDGE is also referred to in the standard as enhanced GPRS or EGPRS. In the GPRS context, EGPRS and EDGE are often used interchangeably. By using 8PSK, EDGE puts three bits into a single transmission step. This way, data transmission speeds can be up to three times faster compared to GSM and GPRS which both use GMSK modulation which only transmits a single bit per transmission step. While with GMSK the two possibilities 0 and 1 are coded as two positions in the I/Q space, 8PSK codes the three bits in eight different positions in the I/Q space.
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