ZXG10 EDGE Solution

EDGE (Enhanced Data Rate for GSM Evolution) is a kind of modulation and codec technology. It enhances the transmission speed of air interface. Traditional GSM networks adopt Gaussian Minimum Shift Keying (GMSK) modulation technology. EDGE system introduces 8PSK modulation to support higher speed data transmission. EDGE supports both circuit switching and packet switching, and both symmetrical and non-symmetrical data transmission.
  The structure of an EDGE system is the same as a GPRS network and there is no new node or interface introduced into the existing GPRS network. Operators only need to upgrade the existing BTS and PCU to make broadband data service available.

1 GSM Data services
Voice is the main service in a traditional mobile communication system. Subscribers require data services as the market and technology develop. As shown in Figure 1, in GSM Phase II+, HSCSD (High Speed Circuit Switched Data) and GPRS (General Packet Radio Service) technology are introduced in the GSM system to support data services in the 2G system. Both HSCSD and GPRS adopt multi-channel transmission technology. HSCSD is based on circuit switching and the data transmission speed can reach up to 57.6 kb/s (4×14.4 b/s/6×9.6 b/s) while GPRS is based on packet swictching and the data transmission speed can reach up to 171.2 kb/s (CS4).

  Owing to the different features of circuit switching and packet switching, HSCSD and GPRS have different characteristics. HSCSD is suitable for real-time service while GPRS is suitable for non-real-time service.
Since packet transmission ensures fuller utilization of the network resources, GPRS is widely used by GSM operators to support data services.

  EDGE is the abbreviation of Enhanced Data Rate for GSM Evolution. EDGE technology enables GSM systems to support 384 kb/s data transmission for mobile subscribers and the date rate can even reach up to 2 Mb/s in motionless conditions. It has achieved the data transmission speeds of 3G system and it can meet almost all the requirements of wireless applications.

  Both the Enhanced Circuit Switched Data (ECSD) mode and the Enhanced GPRS (EGPRS) mode can be adopted to support EDGE. EGPRS is more popolar. The data transmission speed of EGPRS is nearly three times the speed of normal GPRS. It conforms to the same service concept as that of GPRS and new QoS parameters is defined to reflect the higher speed. Thus, EDGE is based on the GPRS system. It enables the existing GSM operators to provide broadband data services, the quality of which is as good as 3G. Therefore, EDGE is the most sensible choice for existing GSM operators.

2 Features of EDGE  Technology
EDGE is based on packet transmission. Its network structure is the same as the existing GPRS network. There is no new hardware required and no existing equipment needs to be discarded. It will not impact the existing GSM core network.

  EDGE brings the following new characteristics to BSS (Base Station Subsystem):

  (1) 8PSK Modulation
  EDGE is a kind of modulation and codec technology. It changes the transmission speed of air interface. Traditional GSM networks adopt Gaussian Minimum Shift Keying (GMSK) modulation technology. EDGE system introduces 8PSK modulation to support higher speed data transmission.

  8PSK is a kind of linear modulation. It can map three continuous bits to one symbol in I/Q coordinate that enables higher data transmission speed and increases the frequency use ratio.  The header segment of 8PSK burst pulse is the same as GMSK, but the effective load of 8PSK is 303% more than that of GMSK. The system can automatically switch between 8PSK time-slot and GMSK time-slot according to link quality, which is the so-called link adaption.
To support EDGE, both BTS and mobile phone should support 8PSK.

  (2) New Channel Codec Scheme
  The characteristic of EGPRS is that it adopts link quality control techinique, which includes LA (Link Adaption) and IR (Incremental Redundancy). LA is the selection of a suitable modulation and coding scheme for the subsequent data bits according to the predicted channel quality. This selection of a better coding scheme in the same coding group makes the data transmission more effective. IR is the carrying out of receiver-assisted decoding by selecting different schemes for data transmission, and data cannot be segmented in this case. For data transmission, EGPRS supports both LA mode and LA-IR combination mode. LA mode supports data transmission by segments. In LA-IR mode, LA is automatically selected when IR is not available. The above two modes can be supported through modification of the RLC/MAC protocol of GPRS.

  EDGE system supports both circuit switching and packet switching. It supports both symmetrical and
non-symmetrical data transmission, which is important for mobile Internet applications.

3 Upgrade of ZXG10 to Support EDGE
The structure of EDGE network is shown in Figure 2. It has the same structure as the existing GPRS network.
If the existing GSM network does not support GPRS, then PCU (Packet Control Unit), SGSN (Serving GPRS Support Node) and GGSN (Gateway GPRS Support Node) should be added. Meanwhile, BTS (Base Transceiver Station) should be upgraded.

  If the existing GSM network supports GPRS, then only BTS should be upgraded to support EDGE modulation and codec.

4 Conclusion
In an EDGE system, the channel assignment for air interface and the structure of TDMA (Time Division Multiple Access) frame are the same as a GSM system. The structure of EDGE system is the same as the GPRS network and there is no new node or interface introduced into the existing GPRS network. Operators only need to upgrade the existing BTS and PCU to make broadband data service available. EDGE can protect the benefits for operators and subscribers to the maximum extent and it is being widely adopted by operators globally.

Manuscript received: 2004-11-30