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What is EDGE | What is EGPRS

This page describes what is EDGE and mention features of EDGE(Enhanced Data rates for GSM Evolution) or EGPRS(Enhanced GPRS).

This technology is introduced to extend the capabilities of existing GSM/GPRS technologies. EDGE stands for Enhanced Data rates for GSM Evolution or Enhanced GPRS. EDGE technology increases the data rate supported by GPRS system drastically.
EDGE introduced modulation schemes which carry more bits per symbol to increase the data rate such as 8-PSK, 16QAM etc. For the case of 8-PSK three bits are carried over one symbol.
GPRS allows data rates up to 115kbps, EDGE or EGPRS is capable of providing data rates of 384 kbps approx.
EDGE supports various modulation-coding schemes MC1 to MC9. MCS1 to MCS4 use GMSK modulation and MCS5 to MCS9 use 8PSK modulation. These schemes are divided among four families.

Family A - MCS 3, 6, 9
Family A' - MCS 3, 6, 8
Family B - MCS 2, 5, 7
Family C - MCS 1, 4

Following figure describes various MCS families with their respective payload units. From this it is imperative that fall back from one MCS to the other MCS is easy within the same family based on channel conditions due to same size of payloads.

EDGE families

EDGE can retransmit a packet with more robust coding scheme hence re-segmentation is possible here, while in GPRS re-segmentation is not possible. This improves throughput.
In EDGE packets are addressed up to 2048 and window size to 1024. In GPRS packets were numbered from 1 to 128 and addressing window size was 64.
In EDGE interleaving is changed to increase performance. Here higher coding schemes such as MCS7 to MCS9 actually transmit 2 radio blocks over 4 bursts. Interleaving occurs over 2 bursts instead of 4 bursts. This reduces the number of bursts that need to be re-transmitted when errors occur.
Further to achieve the maximum possible throughput over wireless link, EGDE/EGPRS uses a combination of link adaptation and incremental redundancy functionalities.

Evolved EDGE

In EDGE it takes about 20 ms to transmit one radio block in 4 consecutive TDMA frames. This TTI is reduced to half i.e. 10 ms in Evolved EDGE, also called RTTI (Reduced Transmission Time Interval).

Fast Ack/Nack reporting is done by inserting fixed-size piggy-backed Ack/Nack field in the RLC radio block.

Higher order of modulations such as 16-QAM and 32-QAM is introduced to achieve further higher data rates.

DLDC (downlink dual carrier) i.e. different frequencies at same time concept is introduced in Evolved EDGE. DLDC means 2 different carrier frequencies are transmitted/received by the same mobile terminal.

REFERENCES

3GPP TS 44.060

GPRS useful Links

GPRS protocol stack
GPRS Modem vendors
GSM versus GPRS
EDGE/EGPRS Basics
What is GPRS
GPRS/EGPRS Modulation-Coding Schemes

What is?

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RF and Wireless Terminologies


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