ENHANCED DATA FOR GSM EVOLUTION full report
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TECHNICAL PAPER PRESENTATION ON ENHANCED DATA FOR GSM EVOLUTION (EDGE)A Mobile communication technology
Today fast growing world needs fast communication either it may be voice or data. This calls for a new technology which is faster than all existing technologies in mobile communication and hence can replace technologies like GPRS. Enhanced Data for GSM Evolution (EDGE) is such a technology .EDGE is a member of global system for mobile communications (GSM).In short EDGE is a technology which enhances data rate for mobile communications.
EDGE not only enhances data rates but also intended for efficient spectrum utilization which it has passed successfully. This paper is intended for explaining how theoretical data rates of 384 kbps are possible with EDGE technique. And how enhanced data for global evolution (EDGE) can play an important role in the evolution toward wideband code division multiple access (WCDMA).And this paper also includes brief details on EDGE and modulation scheme used for EDGE. EDGE can be introduced in two ways: (1) as a packet-switched enhancement for general packet radio service (GPRS), known as enhanced GPRS or EGPRS, and (2) as a circuit-switched data enhancement called enhanced circuit-switched data (ECSD). My paper, however, will only discuss the packet-switched enhancement, EGPRS. Due to the minor differences between GPRS and EGPRS, the impact of EGPRS on the existing GSM/GPRS network is limited to the base station system. The base station is affected by the new transceiver unit capable of handling EDGE modulation as well as new software that enable the new protocol for packets over the radio interface in both the base station and base station controller.The core network does not require any adaptations. Due to this simple upgrade, a network capable of EDGE can be deployed with limited investments and within a short time frame. The goal of EDGE is to boost system capacity, both for real-time and best effort services, and to compete effectively with other third- generation radio access networks such as WCDMA and cdma2000.
N.V.RAVI RAJ KIRAN,
Department of Electronics & Communications Engineering,
Avanthi Institute of Engineering and Technology, Visakhapatnam
EDGE is the next step in the evolution of GSM and IS-136. The objective of the new technology is to increase data transmission rates and file transfers. GPRS/EGPRS will be one of the pacesetters in the overall wireless technology evolution in conjunction with WCDMA. Higher transmission rates for specific radio spectrum efficiency and to facilitate resources enhance cap a c i t y b y new applications and increased enabling more traffic for both circuit- capacity for mobile use .With the introduction of EDGE in GSM phase 2+, existing services such as GPRS and high-speed circuit switched data (HSCSD) are enhanced by offering a and packet-switched services. The goal of EDGE is to boost system capacity, both for real-time and best effort services, and to compete effectively with other third- generation new physical layer. The services radio access networks such as themselves are not modified. EDGE WCDMA and cdma2000. introduced within existing TECHNICAL DIFFERENCES specifications and descriptions rather than by creating new ones. EGPRS is capable of offering data rates of 384 kbps and, theoretically, of up to 473.6 kbps. A new BETWEEN GPRS AND EGPRS Regarded as a subsystem within the GSM standard, GPRS has introduced packet-switched data into GSM networks. Many new protocols modulation technique and error- and new nodes have been introduced tolerant transmission methods, to make this possible. EDGE is a combined with improved link method to increase the data rates on adaptation mechanisms, make these the radio link for GSM. Basically, EGPRS rates possible. This is the key EDGE only introduces new to increased spectrum efficiency and modulation technique and new enhanced applications, such as channel coding that can be used to wireless Internet access, e-mail and transmit both packet-switched and circuit-switched voice and data system and is therefore much easier to services. EDGE is therefore an add- on to GPRS and cannot work alone. GPRS has a greater impact on the GSM system than EDGE has. By adding the new modulation and coding to GPRS and by making introduce than GPRS (Figure.1) In addition to enhancing the throughput for each data user, EDGE also increases capacity. With EDGE, the same time slot can support more users. This decreases the number of adjustments to the radio link radio resources required to support protocols, EGPRS offers significantly the same traffic, thus freeing up h i g h e r t hroughput and capacity.
capacity for more data or voice GPRS and EGPRS have different protocols and different behavior on services. EDGE makes it easier for circuit-switched and packet-switched the base station system side. traffic to coexist while making more efficient use of the same radio resources. Thus in tightly planned networks with limited spectrum, EDGE may also be seen as a capacity booster for the data traffic. However, on the core network side; GPRS and EGPRS share the same packet-handling protocols therefore, behave in the same way. Reuse of the existing GPRS core infrastructure (serving GRPS support node/gateway GPRS support node) emphasizes the fact that EGPRS is only an add-on to the base station EDGE technology EDGE leverages the knowledge gained through use of the existing GPRS standard to deliver significant technical improvements. Figure 2 compares the basic technical data of GPRS and EDGE. Although GPRS and EDGE share the same symbol rate, the modulation bit rate differs. EDGE can transmit three times as many bits as GPRS during the same period of time. This is the main reason for the higher EDGE bit rates. The differences between the radio and user data rates are the result This 384 kbps data rate corresponds to 48 kbps per time slot, assuming an eight-time slot terminal. EDGE modulation technique The modulation type that is used in GSM is the Gaussian of whether or not the packet headers minimum shift keying (GMSK), are taken into consideration. These which is a kind of phase modulation. This can be visualized in an I/Q diagram that shows the real (I) and different ways of calculating imaginary (Q) components of the throughput often cause misunder- transmitted signal (Figure-3). standing within the industry about actual throughput figures for GPRS and EGPRS. The data rate of 384 kbps is often used in relation to Transmitting a zero bit or one bit is then represented by changing the phase by increments of + or - p. Every symbol that is transmitted represents EDGE.
The International Tele- one bit; that is, each shift in the phase communications Union (ITU) has defined 384 kbps as the data rate limit represents one bit. To achieve higher bit rates per time slot than those required for a service to fulfill the available in GSM/GPRS, the International Mobile Tele- modulation method requires change. communications-2 0 0 0 ( I M T -2000) standard in a pedestrian environment. EDGE is specified to reuse the channel structure, channel width, channel coding and the existing mechanisms and functionality of GPRS and HSCSD. The modulation standard selected for EDGE, 8-phase shift keying (8PSK), fulfills all of those requirements. 8PSK modulation has the same qualities in terms of from interpretation of the symbols because it is more difficult for the radio receiver to detect which symbol it not matter. Under poor radio conditions, however, it does. The extra bits will be used to add more error correcting coding, and the correct information can be recovered. generating interference on adjacent Only under very poor radio channels as GMSK. This makes it environments GMSK more possible to integrate EDGE channels into an existing frequency plan and assign new EDGE channels in the same way as standard GSM channels. The 8PSK modulation method is a efficient. Therefore the EDGE coding schemes are a mixture of both GMSK and 8PSK.
For GPRS, four linear method where three different coding schemes, designated consecutive bits are mapped onto one symbol in I/Q plane. The symbol rate, or the number of symbols sent within a certain period of time, remains the same as for GMSK, but each symbol now represents three bits instead of one. The total data rate is therefore increased by a factor of three. The CS1 through CS4, are defined. Each has different amounts of error- correcting coding that is optimized for different radio environments. For EGPRS, nine modulation coding schemes, designated MCS1through MCS9, are introduced. These fulfill the same task as the GPRS coding distances between the different schemes. The lower four EGPRS symbols is shorter using 8PSK modulation than when using GMSK. coding schemes (MSC1 to MSC4) use GMSK, whereas the upper five Shorter distances increase the risk (MSC5 to MSC9) use 8PSKmodulation. Figure 4 shows performance for the GMSK both GPRS and EGPRS coding modulated coding schemes.
Re- schemes, along with their maximum throughputs .GPRS user throughput reaches saturation at a maximum of 20 kbps with CS4, whereas the EGPRS bit rate continues to increase as the radio quality increases, until throughput reaches saturation at 59.2 kbps .Both GPRS CS1 to CS4 and EGPRS MCS1 to MCS4use GMSK modulation with slightly different throughput performances. This is due to differences in the header size (and payload size) of the EGPRS packets. This makes it possible to re-segment EGPRS packets. A packet sent with a segmentation is not possible with GPRS.
Another improvement that has been made to the EGPRS standard is the ability to retransmit a packet that has not been decoded properly with a higher coding scheme(less error correction) that is not properly received, can be retransmitted with a lower coding scheme (more error correction) if the new radio environment requires it. This re- more robust coding scheme. For segmenting (retransmitting with G P R S , r e -segmentation not another coding scheme) requires changes in the payload sizes of the radio blocks; this is why EGPRS and possible. Once packets have been sent, they must be retransmitted using the original coding scheme even if the GPRS do not have the same radio environment has changed. This has a significant impact on the throughput, as the algorithm decides the level of confidence with which the link adaptation (LA) must work.
Before a sequence of coded radio link control packets or radio blocks can be transmitted over the Um (radio) interface, the transmitter must address the packets with an packets. If an erroneously decoded packet must be retransmitted, it may have the same number as a new packet in t h e q ueue. If so, the protocol identification number. This between the terminal and the information is then included in the header of every packet. The packets network stalls, and all the packets belonging to the same low- layer in GPRS are numbered from 1 to 128.After transmission of a sequence capability retransmitted. frame In must EGPRS, be the of packets (e.g., 10packets), the addressing numbers have been transmitter asks the receiver to verify increased to 2048 and the window the correctness of the packets has been increased to 1024 in order received in the form of an to minimize the risk for stalling. acknowledged/unacknowledged This, in turn, minimizes the risk for report. This report informs the retransmitting low- layer capability transmitters which packet or packets frames and prevents decreased were not successfully decoded and must be retransmitted. Sin c e t h e number of packets is limited to 128 and the addressing window is 64, the packet sending process can run out of throughput.
To increase the performance of the higher coding schemes in EGPRS (MCS7 to MCS9) even at low C/I, the addresses after 64 interleaving procedure has been likelihood of receiving two consecutive error free bursts is higher than receiving four consecutive error free bursts. This means that the higher coding schemes for EDGE have a better robustness with regard to frequency hopping. changed with in changing on a per- burst level. Because a radio block is interleaved and transmitted over four bursts for GPRS, each burst may experience a completely different interference environment. If just one of the four bursts is not properly received, the entire radio block will not be properly decoded and will have to be retransmitted. In the case of CS4 for GPRS, hardly any error protection is used at all. With EGPRS, the standard handles the higher coding scheme differently than GPRS to combat this problem. MCS7, MCS8 and MCS9 actually transmit two radio blocks over the four bursts, and the interleaving occurs over two bursts instead of four. This reduces the number of bursts that must be retransmitted should errors occur. The EGPRS BENEFITS: CAPACITY & PERFORMANCE EGPRS introduces a new modulation technique, along with improvements to the radio protocol, that allows operators to use existing frequency spectrums (800, 900, 1800 and 1900 MHz) more effectively. The simple improvements of the existing GSM / GPRS protocols make EDGE a cost-effective, easy-to implement add- on. Software upgrades in the base station system enable use of the new protocol; new transceiver units in the base station e nable use of the new modulation technique. EDGE triples the capacity of GPRS. This capacity boost improves the performance of existing applications and enables new services such as multimedia services. It also enables each transceiver to carry more voice and/or data traffic. EDGE enables new applications at higher data rates.
The above emphasized technology is now going to emerge as a full pledged technology due to its This will attract new subscribers and inherent advantages. The increase an operatorâ„¢s customer base. implementation of EDGE can over Providing the best and most attractive s h a d o w t he existing mobile services will also increase customer loyalty.
HARMONIZATION WITH WCDMA
EDGE can be seen as a foundation toward one seamless GSM technologies in near future. Edge is a straightforward upgrade to GSM and is also compatible with other TDMA systems. In tightly planned networks with limited spectrum, EDGE may also be seen as a capacity booster for and WCDMA network with the data traffic. Thus we can aspire combined core network and different access methods that are transparent to major strides in mobile technologies with EDGE which leverages existing the end user. This part of the GSM / GSM systems and complements EDGE evolution focuses on support for the conversational and streaming service classes, because adequate support for interactive and background services already exists. Additionally, WCDMA for further growth.
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