Know the EDGE (Enhanced Data rates for GSM Evolution) 1. Development of Mobile Communications Technology The development of mobile communication technologies is running very rapidly. In a relatively short time, since the introduction of the use of AMPS as a first-generation mobile communications technology in 1978, up to now (in 2006), its development has reached the 4th generation technology, although still in the stage of research and trials. GSM itself as one of the second-generation mobile communications technology, a technology that is currently the most widely used in various countries. During its development, GSM is capable of delivering voice and low speed data (9.6 - 14.4 kbps), then evolved into a GPRS capable of delivering voice and data with better speed, 115 kbps. In the next phase, the increasing need for a mobile communication system capable of delivering data at speeds higher, and to respond to these needs and then introduced EDGE (Enhanced Data rates for GSM Evolution) is capable of delivering data at speeds up to 3 times the speed of GPRS, which is 384 kbps. In subsequent development, introduced the third generation technology, one of the UMTS (Universal Mobile Telecommunication Service), capable of delivering data at speeds up to 2 Mbps. With speeds of up to 2 Mbps, UMTS network can serve multimedia applications (video streaming, Internet access or video conferencing) via mobile devices quite well. Developments in mobile telecommunications world is believed will continue to grow, until eventually introduced new technologies better than currently available. Lately, scientists are trying to develop a mobile telecommunication technology with a very wide bandwidth, high levels of mobility, integrated services, and IP-based (mobile IP). This technology is introduced with the name "Beyond 3G" or 4G. 2. Implementing EDGE As the name suggests, EDGE (Enhanced Data rates for GSM Evolution), is a technology that was developed with the basic GSM technology and GPRS. A system was developed with EDGE still using equipment found on the GSM / GPRS network. So it can not EDGE alone. A GPRS system consists of the SGSN (Serving GPRS Support Node) and GGSN (Gateway GPRS Support Node), which is its core network, which added to a previous GSM network. While on the radio, GPRS requires the addition of the PCU in GSM radio networks. The figure below shows the general diagram of the GPRS network. Implementing EDGE on existing GPRS network requires only the addition of the radio access side only. While on his side of the core network, EDGE uses the same device and protocol to that used in previous GPRS network. Differences GPRS and EDGE networks only in the radio access only, while on the side of its core network, EDGE and GPRS using the same equipment and protocol. A GPRS network can be upgraded to a network with EDGE system by simply adding an EDGE Transceiver 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. 3. How Can Achieve EDGE Speed That? EDGE is a way to increase data speeds on GSM radio link. By using the technique of modulation and coding scheme that is different from the previous GPRS system, as well as by adjusting the radio link protocol, EDGE offers the capacity and though the put is significantly much larger than that of the GPRS system. So in general there are three aspects of new techniques on EDGE if we compare with the GPRS, namely: • Modulation Technique • Coding Techniques • Radio Access Network (RAN) 3.1. In the EDGE modulation To obtain higher transfer speeds than GPRS uses GMSK modulation (Gaussian Minimum Shift Keying), EDGE uses a different modulation technique with GPRS is 8PSK (8-Phase shift Keying). Figure below shows the visualization of the GMSK modulation on GPRS and EDGE 8PSSK depicted on a diagram of a phase I / Q, where I is the real axis and Q is the imaginary axis. By using 8PSK modulation, a symbol is encoded using 3 bits, while in GMSK a symbol is encoded with 1 bit. Because GMSK and 8PSK symbols have the same rate, amounting to 270 k symbols / s, then the overall rate in the 8PSK modulation will be 3 times larger than GMSK, amounting to 810 kb / s. 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 symbols on the GMSK, because in ad 8 8PSK symbol while in GMSK there are only two symbols. The shorter the distance between the symbols of the resulting signal level between one symbol with another symbol is more difficult to distinguish. So the greater the likelihood of error. But the conditions are pretty good radio signal, the difference in distance between symbols is not particularly affect the quality of data being sent. At the time of the radio signal a bad condition, it would require the addition of extra bits that will be used as error correction, so that incorrect data is received could be improved. So the quality of data on EDGE is not inferior to the quality of data on GPRS using MPSK. Moreover, the EDGE is also used MPSK modulation is used in CS1 to CS4 - its, and also in a process EDGE "packet adjustment" that can change the type of CS used when errors occur in data being sent. Mechanism "packet adjustment" will be explained later in the chapter us Coding Scheme. 3.2. Coding Techniques On EDGE On EDGE known nine kinds of coding techniques, namely the MCS (Modulation Coding Scheme) 1 to MCS9. While in GPRS only used 4 pieces of 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. While five other coding techniques, MCS5 to MCS9, using 8PSK modulation. The figure below shows the type of modulation technique used on GPRS and EDGE and the maximum speed that can be achieved. Either on GPRS or EDGE, Coding Scheme levels higher offer higher data speeds as well, but in addition, the higher the level of its coding scheme, then the lower the resistance to error. That means higher-speed packet data, then the easier the data packet that has errors in its delivery. This is because, the higher the level of its coding scheme, then the level of the mechanism of "error correction" used the lower. Although MCS1 to MCS4 EGDE alike use 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 re-segmentation of the data packet. That is, if a data packet sent using a high-level coding scheme (higher speed, error correction is less) and the data are not well received at the receiving end. So after requests retransmission (re-transition) packet data received was incorrect, the next delivery, the coding scheme used can be changed and adapted to the conditions of the radio interface. That is, on the next delivery, the data packet will be sent using a lower coding scheme, which has a mechanism that better error correction. So expect the second delivery of this data can be well received at the receiver side. While in GPRS, the re- segmentation of the data packet can not be done. Therefore, when a data packet has been sent using a particular coding scheme. So although the data is received either on the receiving side, when the next shipment, the data remains will be sent using the same coding scheme. So it is likely that any data packet received at the receiver side is still as great as when the first shipment. Thus it can achieve a balance between speed and quality of data being transferred.
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