Enhanced Data Rates for GSM Evolution
Enhanced Data rates for GSM Evolution (EDGE) (also known as Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC), or Enhanced Data rates for Global Evolution) is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM. EDGE is considered a pre-3G radio technology and is part of ITU's 3G definition. EDGE was deployed on GSM networks beginning in 2003 – initially by Cingular (now AT&T) in the United States.
Through the introduction of sophisticated methods of coding and transmitting data, EDGE delivers higher bit-rates per radio channel, resulting in a threefold increase in capacity and performance compared with an ordinary GSM/GPRS connection.
Evolved EDGE continues in Release 7 of the 3GPP standard providing reduced latency and more than doubled performance e.g. to complement High-Speed Packet Access (HSPA). Peak bit-rates of up to 1Mbit/s and typical bit-rates of 400kbit/s can be expected.
EDGE/EGPRS is implemented as a bolt-on enhancement for 2.5G GSM/GPRS networks, making it easier for existing GSM carriers to upgrade to it. EDGE is a superset to GPRS and can function on any network with GPRS deployed on it, provided the carrier implements the necessary upgrade. EDGE requires no hardware or software changes to be made in GSM core networks. EDGE-compatible transceiver units must be installed and the base station subsystem needs to be upgraded to support EDGE. If the operator already has this in place, which is often the case today, the network can be upgraded to EDGE by activating an optional software feature. Today EDGE is supported by all major chip vendors for both GSM and WCDMA/HSPA.
In addition to Gaussian minimum-shift keying (GMSK), EDGE uses higher-order PSK/8 phase shift keying (8PSK) for the upper five of its nine modulation and coding schemes. EDGE produces a 3-bit word for every change in carrier phase. This effectively triples the gross data rate offered by GSM. EDGE, like GPRS, uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission. It introduces a new technology not found in GPRS, Incremental Redundancy, which, instead of retransmitting disturbed packets, sends more redundancy information to be combined in the receiver. This increases the probability of correct decoding.
EDGE can carry a bandwidth up to 236 kbit/s (with end-to-end latency of less than 150 ms) for 4 timeslots (theoretical maximum is 473.6 kbit/s for 8 timeslots) in packet mode. This means it can handle four times as much traffic as standard GPRS. EDGE meets the International Telecommunications Union's requirement for a 3G network, and has been accepted by the ITU as part of the IMT-2000 family of 3G standards. It also enhances the circuit data mode called HSCSD, increasing the data rate of this service.
EDGE modulation and coding scheme (MCS)
The channel encoding process in GPRS as well as EGPRS/EDGE consists of two steps: first, a cyclic code is used to add parity bits, which are also referred to as the Block Check Sequence, followed by coding with a possibly punctured convolutional code. In GPRS, the Coding Schemes CS-1 to CS-4 specify the number of parity bits generated by the cyclic code and the puncturing rate of the convolutional code. In GPRS Coding Schemes CS-1 through CS-3, the convolutional code is of rate 1/2, i.e. each input bit is converted into two coded bits. In Coding Schemes CS-2 and CS-3, the output of the convolutional code is punctured to achieve the desired code rate. In GPRS Coding Scheme CS-4, no convolutional coding is applied.
In EGPRS/EDGE, the Modulation and Coding Schemes MCS-1 to MCS-9 take the place of the Coding Schemes of GPRS, and additionally specify which modulation scheme is used, GMSK or 8PSK. MCS-1 through MCS-4 use GMSK and have performance similar (but not equal) to GPRS, while MCS-5 through MCS-9 use 8PSK. In all EGPRS Modulation and Coding Schemes, a convolutional code of rate 1/3 is used, and puncturing is used to achieve the desired code rate. In contrast to GRPS, the Radio Link Control (RLC) and Media Access Control (MAC) headers and the payload data are coded separately in EGPRS. The headers are coded more robustly than the data. The coding schemes are summarized in the tables below. Note that the bit rates do not include the overhead incurred by channel coding and the RLC and MAC headers.
| Bit Rate
| EDGE Modulation and Coding
| Bit Rate
Evolved EDGE improves on EDGE in a number of ways. Latencies are reduced by lowering the Transmission Time Interval by half (from 20 ms to 10 ms). Bit rates are increased up to 1 Mbit/s peak bandwidth and latencies down to 80 ms using dual carrier, higher symbol rate and higher-order modulation (32QAM and 16QAM instead of 8PSK), and turbo codes to improve error correction. And finally signal quality is improved using dual antennas improving average bit-rates and spectrum efficiency. EDGE Evolution can be gradually introduced as software upgrades, taking advantage of the installed base. With EDGE Evolution, end-users will be able to experience mobile internet connections corresponding to a 500 kbit/s ADSL service.
The Global mobile Suppliers Association (GSA) states that, as of May 2013, there were 604 GSM/EDGE networks in 213 countries, from a total of 606 mobile network operator commitments in 213 countries.
- http://www.itu.int/ITU-D/imt-2000/MiscDocuments/IMT-Deployments-Rev3.pdf[dead link]
- ETSI SMG2 99/872
- 3rd Generation Partnership Project (2012-09). "3GGP TS45.001: Technical Specification Group GSM/EDGE Radio Access Network; Physical layer on the radio path; General description". Retrieved 2013-07-20.
- "EDGE, HSPA and LTE: The Mobile Broadband Advantage". Rysavy Research and 3G Americas. 2007-09-01. pp. 58–65. Retrieved 2010-09-27.
- "GSA – The Global mobile Suppliers Association EDGE Databank". Gsacom.com. Retrieved 2013-03-05.