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[attachment=3431]
EDGE Compact and EDGE Classic Packet Data Performance
Abstract
Even though cellular radio services have been extremely successful in providing untethered voice communications, wireless data services have captured only a limited market share so far. One obstacle for wireless data services is their limited peak bit rates. Existing wireless data rates, up to several tens of kb/s, may be over one order of magnitude short of what is required to make popular applications user-friendly. To accomplish these necessities we go for EDGE(Enhanced Data Rates for GSM Evolution) employs adaptation between a number of modulation and coding schemes (link adaptation) as a means for providing several hundred kb/s peak rates in a macro-cellular environment while supporting adequate robustness for impaired channels. In this paper we discuss the two phases of EDGE, classic and compact. We start our discussion with the page link adaptation and incremental tendency techniques. Secondly we go for discussing EDGE classic and compact systems and their deployment scenarios, followed by downlink performance comparison and some MAC layer enhancement techniques which improve the performance.
Key words
EDGE, GPRS, GSM, GMSK, MCS, SINR.
Presented By:
K. Naveen Krishna (Y1EC054): K.K.S. Anil Kumar (Y1ECO27):
V.R.Siddhartha Engineering College,
Vijayawada.
1. INTRODUCTION
The GSM system is the most popular second-generation wireless system today. It employs TDMA technology to support mobile users in different environments. This system, initially standardized and deployed in Europe, is currently deployed worldwide. The TDMA community adopted EDGE for high-speed data services in the third-generation, radio transmission technology proposal to ITU for IMT-2000 (UWC-136). Typically, current GSM service provider s employ 3/9 or 4/12 reuse plans and they may not impose a different frequency reuse plan for EDGE, which is thus termed EDGE Classic. However, in North America, initial deployment using 1MHz in each direction is being considered due to limited spectrum and the potential need to re-deploy spectrum currently used for ANSI 136 systems. This implies very aggressive frequency reuse having a minimum of only three 200-kHz frequency carriers. This means allocating one frequency to each of the three sectors per base station and reusing the frequency set everywhere (1/3 reuse) and providing control signaling with extra reuse protection in the time domain, which is named EDGE Compact due to its compact spectrum requirement.
2. MODULATION AND CODING ADAPTATION
The basic concept of EDGE is to provide higher data rates per radio time slot than is possible with GMSK modulation. This allows the support of existing services with a lower number of time slots. In addition it allows the introduction of new services with up to 59.2 kb/s per timeslot or almost 480 kb/s per carrier in multi-slot operation, hence offering an evolution path for GSM to support multimedia applications.
2.1 Radio page link formats
Discussions in the ETSI workshops resulted in selection of 8PSK/GMSK to provide higher rates than the GMSK modulation with small envelope fluctuations and to provide backward compatibility to GSM and GPRS. The EDGE concept can be seen as an extension of GPRS for packet service, which is called EGPRS. ETSI has also combined EDGE with circuit switched data modes, and these modes are called ECSD. Efficient page link adaptation is a key feature for EDGE and has been jointly developed with EDGE enhanced modulation. With a high degree of compatibility in the bandwidth and symbol rates with GSM, EDGE provides higher rates for users with good signal to interference plus noise ratios (SINR). This is achieved by employing lower channel-coding redundancy and/or 8PSK, which carries 3 bits per symbol (as opposed to 1 bit per symbol achieved by GMSK). Table 1 shows the bit rate provided by different MCS (Modulation and Coding Scheme) modes. An EGPRS capable terminal will have 9 modulations and coding schemes available compared to 4 for GPRS.
Table 1: An overview of packet data services for EDGE
2.2 Radio page link control
Fig 1. Throughput as a function of SIR for different transmission modes
Radio page link control selects among the MCS options, in response to SINR or equivalent quality measures. Link adaptation explicitly changes MCS modes based on page link quality estimates, and is also called mode selection. Hybrid ARQ transmits additional redundancy bits after errors are observed. It is made possible by sending the packets with different puncturing patterns from the same mother code during retransmission. This allows data transmission to begin with low redundancy and increases redundancy only when errors occur, thus adaptively changing the effective date rates.
The criterion for selecting a particular data-rate as proposed is defined by
S=Rc(1-BLERc)
where Rc and BLERc are the data-rate and BLER (Block Error Rate, where a block is the RLC (radio page link control) block.) for the transmission mode chosen. Figure 1 shows the throughput as a function of SIR for different modes. It is found that this threshold criterion is generally effective in achieving a high aggregate system throughput, but the QoS (Quality of Service) for individual users can be degraded as system load increases. Furthermore, page link adaptation requires the receiver to continuously perform quality measurements and provide timely feedback to the transmitter, so typical operation may be with somewhat higher thresholds.
3. EDGE Compact and EDGE Classic
3.1 Classic
GSM systems are usually planned on the basis of 4/12 (4 base stations, 3 sectors each, per cluster) or 3/9 frequency arrangements. The carriers that contain broadcast control channels (BCCH carriers) are required to transmit continuously and without hopping on control time slots to facilitate handoff measurements, control channel acquisition, and so on. These carriers usually are arranged in a 4/12 reuse pattern. Traffic channels can frequency-hop and, on non-BCCH carriers, they can use discontinuous transmission (based on voice-activity detection), and if so, typically are arranged in a 3/9 reuse pattern. These arrangements provide the strong SIR protection typically required for delay-intolerant voice services and non-acknowledged control channels. EDGE Classic is defined to be a system using continuous BCCH carriers that are typically in a 4/12 or 3/9 reuse pattern and which requires at least 2.4 MHz bandwidth in each direction. Additional traffic carriers, if available with higher total bandwidth, can be deployed under a lower reuse factor. Some system operators, particularly those in North American where 3G spectrum has been partially allocated for PCS, have to re-allocate in-service spectrum to deploy EDGE.
3.2 Compact
In that case, EDGE Compact may be used for initial deployment using as little as 1 MHz in each direction allowing only three 200-KHz frequency carriers. This means allocating one frequency to each of the three sectors per base station, and the frequency set is reused at every base station (1/3 reuse for EDGE Compact mode). While good spectrum efficiency is achieved, the provisioning of common control functionality, such as system broadcast information, paging, packet access and packet grant, cannot be deployed with 1/3 reuse. 4/12 or 3/9 reuse is required for reliable control channels. In order to achieve adequate co-channel reuse protection for the control channels, reuse in the time domain is exploited, which requires frame synchronization of base stations. Figure 2 shows an example with 4 timing groups in addition to 1/3 frequency reuse to obtain 4/12 reuse for the control channels.
Fig 2. Example cell pattern for a 4/12 time and frequency reuse
EDGE Compact uses discontinuous transmission based on a 52 -multiframe2 (a multi-frame consisting of 52 frames) and designates different time slots and frames for sending control information. In blocks (blocks are non-overlapping and are each comprised of timeslots from the same timeslot number of 4 successive frames) when a sector belonging to one of the time-groups transmits or receives common control signaling (serving time-group), the sectors belonging to other (non-serving time-groups) are idle. This creates an effective reuse of 3/9 or 4/12, which is necessary for control signaling, while allowing 1/3 reuse for the traffic channels. Specifically, slots 1, 3, 5 and 7 are used for timing groups 0, 1, 2 and 3, respectively, to send common control information on frames 0-3, 21-24, 34-37 and 47-50. Frames 12, 25, 38 and 51 are also not allowed for traffic as they are reserved as idle frames or to send timing advance, frequency correction or synchronization information. More frames can be allocated for control signaling as needed. Therefore, up to 32 frames or 8 blocks per 52 multi-frame can be allocated for traffic channels on the designated control slots. This is 2/3 that of a regular slot capacity in which 48 frames in a 52 multi-frame are used for traffic in a given non-BCCH slot. When using 3 time-groups (i.e., effectively 3/9 reuse), one of the 4 time-groups is unused and it is instead used as a traffic channel. Figure 3 shows the control channel BLER distribution for both 3/9- and 4/12-reuse based systems. For about 90% of the cases, the BLER is better than 4% and 15% for 4/12 and 3/9 reuse, respectively, corresponding to the overall average BLER of about 2.4% and 5.2 % (not shown in the figure), respectively. The performance of the 3/9-reuse system may not be reliable enough at the tail end of the distribution. However, since the traffic channel performance is highly correlated with that of the control channel, i.e., a mobile station with poor control channel BLER most likely cannot support reliable traffic performance, the tail end performance may not be very crucial. The control channel performance for EDGE Classic is expected to be similar because the same reuse factor is employed for the control channel.
Fig 3. Distribution of BLER for control channels
4. DEPLOYMENT SCENARIOS
The minimum spectrum required for Compact deployment is 600 kHz and that for Classic is 2.4 MHz (neglecting guard bands in both cases). Therefore, at 2.4 MHz and above, there exists the option of either Compact or Classic deployment. The choice of system is partly dependent on the performance of the systems. The performance in turn is dependent on the reuse configuration employed in the deployment. For the purposes of this study and to eligible valid comparisons, the reuse configurations are such that control channels are always at 4/12 reuse while traffic channels are at 1/3 reuse whenever possible. The exceptions are the traffic channels of a Classic control (BCCH) carrier, which are at 4/12 reuse. We also consider the same control-channel capacity (one active slot of a carrier) for both cases under all scenarios. Table 2 and the text following describe the scenarios considered:
Table 2: Deployment Scenarios
a) 600 kHz deployment
i. Compact (Scenario 1)
There are three 200 kHz carriers, one per sector of a tri-sectored base station. A carrier in a given sector can use the even-numbered slots and the unused portion of the odd-numbered control slots for traffic in a 1/3 reuse. Here, we do not consider the unused portion of the odd numbered control slots.
b) 2.4 MHz deployment
i. Compact (Scenario 2)
There are twelve 200 kHz carriers. Three of the carriers are deployed in a configuration identical to that of the 600 kHz deployment. The remaining nine carriers are dedicated to traffic and deployed in a 1/3 reuse configuration. Therefore, any given sector of a tri-sectored base station has four carriers, three of which have eight traffic slots each and the fourth has four traffic slots, all in a 1/3 reuse pattern.
ii. Classic (Scenario 3)
There are twelve 200 kHz carriers, all continuous control carriers with one allocated per sector of a tri-sectored base station. Therefore, a given sector has one carrier of which one slot is dedicated for control and seven slots are dedicated for traffic. All control and traffic slots are in a 4/12 reuse configuration.
c) 4.2 MHz deployment
i. Compact (Scenario 4)
There are twenty-one 200 kHz carriers. Three of the carriers are deployed in a configuration identical to that of the 600 kHz deployment. The remaining eighteen carriers are dedicated to traffic and deployed in a 1/3 reuse configuration. Therefore any given sector of a tri-sectored base station has seven carriers, six of which have eight traffic slots each and the seventh has four traffic slots, all in a 1/3 reuse pattern.
ii. Classic (Scenario 5)
There are twenty-one 200 kHz carriers, twelve of which are in a 4/12 reuse pattern and the remaining nine in a 1/3 reuse pattern. Therefore, a given sector of a tri-sectored base station has four carriers. One of these is the continuous control carrier and it has seven slots dedicated for traffic in a 4/12 reuse pattern. The other three carriers have a total of twenty-four slots in a 1/3 reuse pattern.
5. PERFORMANCE COMPARISONS
Figures 4 and 5 show the average user-packet delay as the throughput per base station (in three sectors) increases for the 2.4 MHz and 4.2 MHz scenarios, respectively. Here we can clearly see the trade-off between QoS, as determined by the delay experienced by the web-browsing users, and the system capacity, as indicated by the total throughput that a typical base station can deliver to all users who are sharing the radio resources.
Note that with aggressive frequency reuse, EDGE Compact achieves higher efficiency due to additional traffic capacity that can be provided for the same bandwidth compared to EDGE Classic. It is therefore a viable option not only for an initial deployment but also for a system with higher available bandwidth. However, the requirement of synchronized base stations and other related issues must be carefully addressed in practical deployment.
Fig 4: Comparison of classic and compact performance for 2.4 MHz Scenario
Fig 5: Comparison of classic and compact performance for 4.2 MHz Scenario
6. PERFORMANCE ENHANCEMENTS
In this section we outline several enhancement techniques. All of these techniques can be implemented in the physical and MAC layers with little or no impact on standards. All the performance results shown below assume EDGE with one carrier per sector. Control channels are not explicitly simulated, so we assume 8 traffic slots are available per carrier. In addition, we consider 600 kHz total
bandwidth in Figures 7-8 and 2.4 MHz in Figure 9. Furthermore, the radio page link performance was based on an earlier proposal with rate adaptation among QPSK/16QAM modes, which were 15%-20% higher in the bit rates. However, the general performance trends for GMSM/8PSK mode adaptation are similar.
6.1 Simple diversity or interference suppression at terminals and smart antennas at base stations
These are techniques that can be implemented in the physical layer. Simple diversity selects the better one between two diversity branches available at a mobile terminal. Interference suppression uses the MMSE (Minimum Mean Square Error) algorithm to further suppress co-channel interference at a two-branch diversity receiver. Smart antennas are implemented by forming four fixed beams on the downlink, with the beam that provides the strongest signal to serve a given terminal. In Figure 6, the left curves show the improvement experienced by a user, in terms of the throughput at a moderate load, by using these methods, while the right curves indicate system capacity enhancement as traffic load increases. Clearly, all these methods are effective in improving user experience as well as system capacity.
Fig 6: Performance improvement by diversity, interference suppression, smart antennas
6.2 Improved resource assignment
All the results shown so far are obtained based on random slot assignment as demand arrives. Several possible enhancements in the MAC layer can be introduced, ranging from simple, autonomous processes performed at individual base stations to those involving more sophisticated coordination among base stations. The key enabler of intelligent resource assignment is signal quality measurements, which are inherently required to perform page link adaptation.
Fig7: Performance improvement by LI-DPA and its combination with mode-0
Here we show an example of LI-DPA. Mode-0 is an additional MCS mode for which no transmission is allowed if the signal quality is below a threshold. Using mode-0, transmissions that are likely to fail are eliminated; this reduces interference without causing reduction of total system throughput. In fact, since the radio resources are made available to users who are likely to succeed, system throughput is increased. LI-DPA, least interference dynamic packet assignment, selects the time slot with the lowest interference to deliver the packets. Figure 7, showing the message delay which is greater than what 90% of the users experience as the throughput per slot increases, clearly indicates that there is significant improvement that can be achieved by this method; a combination of LI-DPA with mode-0 can further enhance performance.
7. CONCLUSION
The TDMA and GSM systems have chosen the same EDGE radio-access and GPRS packet-switched core network technologies to provide third-generation services in existing spectrum. Accordingly, a common access for data services can be offered to more than 370 million mobile subscribers. EDGE can be deployed in two modes in TDMA systems: Classic and COMPACT. The Classic system requires only minimum extension to GSM EDGE and uses standard GSM/GPRS control channels, which facilitates global roaming.
The COMPACT system introduces a novel control channel configuration, synchronized base stations, and discontinuous transmission on the first carriers, which facilitates the deployment of EDGE control channels in a 1/3 frequency-reuse pattern. Thus, the initial deployment of COMPACT requires only a very limited amount of spectrum 600 kHz plus guard bands. With fractional loading, excellent spectral efficiency can be attained with data rates of up to 384 kbit/s. COMPACT thus supports UWCC requirements for third-generation services with high spectral efficiency and initial deployment within less than 1 MHz of spectrum.
8. REFERENCES
[1] J. Cai and D. J. Goodman, General Packet Radio Service in GSM, IEE Communications Magazine, October 1997, pp.122-131.
[2] ETSI Tdoc SMG2 1015/97, EDGE Feasibility Study, Work Item 184; Improved Data Rates through Optimised Modulation, version 1.0, December 1997.
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[attachment=3684]
TECHNICAL PAPER PRESENTATION ON
ENHANCED DATA FOR GSM EVOLUTION
(EDGE)
A Mobile communication technology
PRESENTED BY
N.V.RAVI RAJ KIRAN,
04811A0475,
II/IV B.Tech,
Department of Electronics & Communications
Engineering,
Avanthi Institute of Engineering and Technology,
Visakhapatnam
ABSTRACT
Today s 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.
INTRODUCTION
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 page link method to increase the data rates on adaptation mechanisms, make these the radio page 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 page 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.
CODING SCHEMES
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.
PACKET HANDLING
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 page link adaptation (LA) must work ADDRESSING WINDOW Before a sequence of coded radio page 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 (Figure 6).
INTERLEAVING
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.
CONCLUSION
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 operator 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.
REFERENCES
ericsson.com
EDGEtechnology.com
bsnl.co.in
siemens.com
alcatel.com
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[attachment=1470]
EDGE Compact and EDGE Classic Packet Data Performance
Abstract
Even though cellular radio services have been extremely successful in providing untethered voice communications, wireless data services have captured only a limited market share so far. One obstacle for wireless data services is their limited peak bit rates. Existing wireless data rates, up to several tens of kb/s, may be over one order of magnitude short of what is required to make popular applications user-friendly. To accomplish these necessities we go for EDGE(Enhanced Data Rates for GSM Evolution) employs adaptation between a number of modulation and coding schemes (link adaptation) as a means for providing several hundred kb/s peak rates in a macro-cellular environment while supporting adequate robustness for impaired channels. In this paper we discuss the two phases of EDGE, classic and compact. We start our discussion with the page link adaptation and incremental tendency techniques. Secondly we go for discussing EDGE classic and compact systems and their deployment scenarios, followed by downlink performance comparison and some MAC layer enhancement techniques which improve the performance.
INTRODUCTION
The GSM system is the most popular second-generation wireless system today. It employs TDMA technology to support mobile users in different environments. This system, initially standardized and deployed in Europe, is currently deployed worldwide. The TDMA community adopted EDGE for high-speed data services in the third- generation, radio transmission technology proposal to ITU for IMT-2000 (UWC-136). Typically, current GSM service provider s employ 3/9 or 4/12 reuse plans and they may not impose a different frequency reuse plan for EDGE, which is thus termed EDGE Classic. However, in North America, initial deployment using 1MHz in each direction is being considered due to limited spectrum and the potential need to re-deploy spectrum currently used for ANSI 136 systems. This implies very aggressive frequency reuse having a minimum of only three 200-kHz frequency carriers. This means allocating one frequency to each of the three sectors per base station and reusing the frequency set everywhere (1/3 reuse) and providing control signaling with extra reuse protection in the time domain, which is named EDGE Compact due to its compact spectrum requirement.
MODULATION AND CODING ADAPTATION
The basic concept of EDGE is to provide higher data rates per radio time slot than is possible with GMSK modulation. This allows the support of existing services with a lower number of time slots. In addition it allows the introduction of new services with up to 59.2 kb/s per timeslot or almost 480 kb/s per carrier in multi- slot operation, hence offering an evolution path for GSM to support multimedia applications.
Radio page link formats
Discussions in the ETSI workshops resulted in selection of 8PSK/GMSK to provide higher rates than the GMSK modulation with small envelope fluctuations and to provide backward compatibility to GSM and GPRS. The EDGE concept can be seen as an extension of GPRS for packet service, which is called EGPRS. ETSI has also combined EDGE with circuit switched data modes, and these modes are called ECSD. Efficient page link adaptation is a key feature for EDGE and has been jointly developed with EDGE enhanced modulation. With a high degree of compatibility in the bandwidth and symbol rates with GSM, EDGE provides higher rates for users with good signal to interference plus noise ratios (SINR). This is achieved by employing lower channel-coding redundancy and/or 8PSK, which carries 3 bits per symbol (as opposed to 1 bit per symbol achieved by GMSK). Table 1 shows the bit rate provided by different MCS (Modulation and Coding Scheme) modes. An EGPRS capable terminal will have 9 modulations and coding schemes available compared to 4 for GPRS.
Radio page link control
Radio page link control selects among the MCS options, in response to SINR or equivalent quality measures. Link adaptation explicitly changes MCS modes based on page link quality estimates, and is also called mode selection. Hybrid ARQ transmits additional redundancy bits after errors are observed. It is made possible by sending the packets with different puncturing patterns from the same mother code during retransmission. This allows data transmission to begin with low redundancy and increases redundancy only when errors occur, thus adaptively changing the effective date rates. The criterion for selecting a particular data-rate as proposed is defined by S=Rc(1-BLERc) where Rc and BLERc are the data-rate and BLER (Block Error Rate, where a block is the RLC (radio page link control) block.) for the transmission mode chosen. Figure 1 shows the throughput as a function of SIR for different modes. It is found that this threshold criterion is generally effective in achieving a high aggregate system throughput, but the QoS (Quality of Service) for individual users can be degraded as system load increases. Furthermore, page link adaptation requires the receiver to continuously perform quality measurements and provide timely feedback to the transmitter, so typical operation may be with somewhat higher thresholds.
EDGE Compact and EDGE Classic
Classic
GSM systems are usually planned on the basis of 4/12 (4 base stations, 3 sectors each, per cluster) or 3/9 frequency arrangements. The carriers that contain broadcast control channels (BCCH carriers) are required to transmit continuously and without hopping on control time slots to facilitate handoff measurements, control channel acquisition, and so on. These carriers usually are arranged in a 4/12 reuse pattern. Traffic channels can frequency-hop and, on non-BCCH carriers, they can use discontinuous transmission (based on voice-activity detection), and if so, typically are arranged in a 3/9 reuse pattern. These arrangements provide the strong SIR protection typically required for delay-intolerant voice services and non-acknowledged control channels. EDGE Classic is defined to be a system using continuous BCCH carriers that are typically in a 4/12 or 3/9 reuse pattern and which requires at least 2.4 MHz bandwidth in each direction. Additional traffic carriers, if available with higher total bandwidth, can be deployed under a lower reuse factor. Some system operators, particularly those in North American where 3G spectrum has been partially allocated for PCS, have to re-allocate in-service spectrum to deploy EDGE.
Compact
In that case, EDGE Compact may be used for initial deployment using as little as 1 MHz in each direction allowing only three 200-KHz frequency carriers. This means allocating one frequency to each of the three sectors per base station, and the frequency set is reused at every base station (1/3 reuse for EDGE Compact mode). While good spectrum efficiency is achieved, the provisioning of common control functionality, such as system broadcast information, paging, packet access and packet grant, cannot be deployed with 1/3 reuse. 4/12 or 3/9 reuse is required for reliable control channels. In order to achieve adequate co-channel reuse protection for the control channels, reuse in the time domain is exploited, which requires frame synchronization of base stations. Figure 2 shows an example with 4 timing groups in addition to 1/3 frequency reuse to obtain 4/12 reuse for the control channels.
EDGE Compact uses discontinuous transmission based on a 52 -multiframe2 (a multi-frame consisting of 52 frames) and designates different time slots and frames for sending control information. In blocks (blocks are non-overlapping and are each comprised of timeslots from the same timeslot number of 4 successive frames) when a sector belonging to one of the time-groups transmits or receives common control signaling (serving time-group), the sectors belonging to other (non-serving time-groups) are idle. This creates an effective reuse of 3/9 or 4/12, which is necessary for control signaling, while allowing 1/3 reuse for the traffic channels. Specifically, slots 1, 3, 5 and 7 are used for timing groups 0, 1, 2 and 3, respectively, to send common control information on frames 0-3, 21-24, 34-37 and 47-50. Frames 12, 25, 38 and 51 are also not allowed for traffic as they are reserved as idle frames or to send timing advance, frequency correction or synchronization information. More frames can be allocated for control signaling as needed. Therefore, up to 32 frames or 8 blocks per 52 multi-frame can be allocated for traffic channels on the designated control slots. This is 2/3 that of a regular slot capacity in which 48 frames in a 52 multi-frame are used for traffic in a given non-BCCH slot. When using 3 time-groups (i.e., effectively 3/9 reuse), one of the 4 time-groups is unused and it is instead used as a traffic channel. Figure 3 shows the control channel BLER distribution for both 3/9- and 4/12-reuse based systems. For about 90% of the cases, the BLER is better than 4% and 15% for 4/12 and 3/9 reuse, respectively, corresponding to the overall average BLER of about 2.4% and 5.2 % (not shown in the figure), respectively. The performance of the 3/9-reuse system may not be reliable enough at the tail end of the distribution. However, since the traffic channel performance is highly correlated with that of the control channel, i.e., a mobile station with poor control channel BLER most likely cannot support reliable traffic performance, the tail end performance may not be very crucial. The control channel performance for EDGE Classic is expected to be similar because the same reuse factor is employed for the control channel.
DEPLOYMENT SCENARIOS
The minimum spectrum required for Compact deployment is 600 kHz and that for Classic is 2.4 MHz (neglecting guard bands in both cases). Therefore, at 2.4 MHz and above, there exists the option of either Compact or Classic deployment. The choice of system is partly dependent on the performance of the systems. The performance in turn is dependent on the reuse configuration employed in the deployment. For the purposes of this study and to eligible valid comparisons, the reuse configurations are such that control channels are always at 4/12 reuse while traffic channels are at 1/3 reuse whenever possible. The exceptions are the traffic channels of a Classic control (BCCH) carrier, which are at 4/12 reuse. We also consider the same control-channel capacity (one active slot of a carrier) for both cases under all scenarios. Table 2 and the text following describe the scenarios considered:
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This is the main thing about it. 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. It is the most important in the GSM.
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