Explain EDGE for 2.5 G GSM & IS-136.

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written 5.8 years ago by

teamques10 ★ 67k

• modified 5.8 years ago

EDGE which stands for Enhanced Data rates for GSM for Global Evolution is more advanced upgrade to the GSM standard and requires additional hardware and software at existing base stations. It introduces a new digital modulation format, 8-PSK (Octal Phase Shift Keying) which is used in addition to GSM and GMSK modulation.
EDGE allows nine air interface formats, known as Multiple Modulation and Coding Schemes with varying degree of error control protection. Because of the higher data rates and relaxed error control covering in many of the selectable air interface formats, the coverage range is smaller in EDGE than in GPRS. Edge is sometimes referred to as Enhanced GPRS.
It uses higher order 8-PSK modulation and family of MCSs for each GSM radio channel time slots so that each user connection may adaptively determine the best MCS setting for the particular radio propagation conditions and data access requirements of the user.
This adaptive capability to select the best air interface is called incremental redundancy whereby packets are transmitted first with maximum error protection and maximum data rate throughput and then subsequent packets are transmitted until the link has an unacceptable delay.
Rapid feedback between the base station and subscriber unit then restores the provision acceptable air interface state, which is presumably at an acceptable level but with required coding and minimum bandwidth and power drain.
Incremental redundancy ensures that the radio link for each user will quickly reach a condition that uses the minimum amount of overhead thereby providing acceptable link quality for each user while maximizing user capacity on the network.
When EDGE uses 8 PSK modulations without any error protection and all 8 timeslots of a GSM radio channel dedicated to single user, a raw peak throughput data rate of 547.2 kbps can be provided.
In practice the slotting schemes use in EDGE when combined with practical network connection issues and error control coding requirement, limits practical data rates to about 384 kbps for a single dedicated user on single GSM channel.

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