The development of mobile communication technology to walk very fast. In a relatively short time, since diperkenlakannya using AMPS as mobile communication technology in the first generation tahung 1978, up to now (in 2006), its development of technology has reached the 4th generation, although still under research and testing. GSM itself as one of the technology a second-generation mobile communications, is a technology that is currently the most widely used in various countries. In the process, GSM is able to deliver voice communications and low speed data (9.6 - 14.4 kbps), then developed into a capable GPRS voice and also distribute the data with better speed, 115 kbps. In the next phase, the need for a mobile communication system capable of distributing data with higher speeds, and to respond to this need and introduced EDGE (Enhanced Data rates for GSM Evolution) is able to deliver data at speeds up to 3 times the speed of GPRS, which is 384 kbps.
In further development, third-generation technology was introduced, one of which UMTS (Universal Mobile Telecommunication Service), which can deliver data at speeds up to 2 Mbps. With speeds up to 2 Mbps, UMTS networks can serve multimedia applications (video streaming, Internet access or video conferencing) via mobile devices quite well. Perkembangandi world of mobile telecommunications is believed will continue to grow, until eventually introduced new technologies better than the current yangada. Lately, scientists trying to develop a mobile telecommunication technology with a very wide bandwidth, high mobility rates, integrated services, and berbasikan IP (Mobile IP). This technology was introduced with the name "Beyond 3G" or 4G.
As the name suggests, EDGE (Enhanced Data rates for GSM Evolution), is a technology developed with the basic GSM and GPRS technologies. The EDGE system is developed by using equipment that remain are on the GSM / GPRS network. So can not EDGE alone. A GPRS system consists of the SGSN (Serving GPRS Support Node) and GGSN (Gateway GPRS Support Node), which is corenya network, which added to a previous GSM network. While on the radio, GPRS network requires the addition of PCU in GSM network radio devices before. The figure below shows the GPRS network diagrams in general.
Implementation of existing EDGE GPRS network requires only the addition of the radio access side only. While on the side of its core network, EDGE uses the device and protocol similar to that used in previous GPRS network. Differences GPRS and EDGE networks only in akssnya radio side only, while on the corenya networks, EDGE and GPRS equipment and using the same protocol. A GPRS network can be upgraded into a network with EDGE system by simply adding a Transceivier EDGE Unit (TRU) on the side of the radio access. The figure below shows the block diagram of a GPRS network is upgraded to EDGE in general.
EDGE is a way to increase data speeds on GSM radio link. Using modulation techniques and coding schemes are different from the previous GPRS system, and by setting the protocol radio link, EDGE offers a thoughput capacity and significantly greater than that owned by the GPRS system. So in general there are three aspects of new techniques to EDGE if we compare with the GPRS, namely:
* Modulation Technique
* Coding Techniques
* Radio Access Network (RAN)
3.1. EDGE modulation
To get a transfer speed higher than GPRS using GMSK modulation (Gausian Minimum Shift Keying), EDGE uses a different modulation technique with GPRS is 8PSK (8-Phase Shif Keying). Figure below shows the visualization of the GMSK modulation on the GPRS and EDGE 8PSSK pasa depicted a diagram of I / Q, where I is the real axis and Q is the imaginary axis.
If we look at the image visualization GMSK and 8PSK modulation above, the distance between the 8PSK symbol is shorter than the distance between the GMSK symbols, because the ad 8PSK symbol sedengkan at 8 GMSK there are only 2 symbols. Shorter distances between the symbols of signal level caused between one symbol with another symbol is more difficult to distinguish. So the possibility of greater error. But the condition of the radio signal is good enough, the difference between the symbol distance is not too much effect on the quality of data sent. At the time of the radio signal conditions are bad, it would require the addition of extra bits that will be used as the error correction, so that any data received can be improved. So the quality of data on EDGE is not inferior to the quality of data on GPRS using MPSK. After all, EDGE is also used in MPSK modulation is used in CS1 to CS4 - his, and also in a process EDGE "packet adjustment" that can change the type of CS used in case of errors in data sent. Mechanism "packet adjustment" will be explained later in the chapter su Coding Scheme.
3.2. EDGE Coding Techniques
9 EDGE known coding techniques, the MCS (Modulation Coding Scheme) 1 to MCS9. While in GPRS only used 4 pieces coding techniques, ie CS (Coding Scheme) 1 to SC4. The first four coding techniques on EDGE, MCS1 to MCS4, using GMSK modulation, the same as that used in GPRS. Whereas 5 other coding techniques, MCS5 to MCS9, using 8PSK modulation. The figure below shows the type of modulation used in GPRS and EDGE with the maximum speed can be achieved.
Although MCS1 to MCS4 the same EGDE uses GMSK modulation as CS1 to CS4 on GPRS, but both have different speeds. This is because of the use of different headers. In EDGE, the data packet contains a header which allows for the re-segmentation of data packets. That is, if a data packet sent with a level higher coding schemes (higher speed, error correction is less) and the data was not well received at the receiver side. So after the re-transmission request (re-transmition) the wrong data packet is received, the next delivery, coding scheme used can be changed and adjusted to the condition of the radio interface. That is, the next delivery, the data packet will be sent by using coding schemes lower, which has error correction mechanism better. Which is expected in this second delivery data can be well received at the receiver side. While in GPRS, the re-segmentation of this data packet can not be done. Therefore, when a data packet has been sent by using a specific coding scheme. So although the data titerima wrong on the receiver side, at the time of the next delivery, the data will still be sent by using the same coding scheme. Making it more likely that any data packet received at the receiver side is still as great as when the first shipment. Thus a balance is achieved between the transfer speed and quality of data being transferred.
Reference :
* Http://www.ericsson.com, white paper: EDGE - Introduction of Haigh-speed data in GSM / GPRS network
* Lappeenranta University of Technology, Seminar materials: GSM / EDGE Radio Access Network
* Siemens Indonesia, Training material: GPRS Overview
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