EDGE technology: what is it and why is it necessary?
The past 3GSM World Congress Congress, and after him and the CeBIT 2006 exhibition in Hanover brought with them a lot of announcements of new cell phones With the support of EDGE technology (Enhanced Data for Global Evolution or, as else, you can sometimes hear, Enhanced Data Rates for GSM Evolution). This is not by chance - although mobile phone vendors are paying more and more attention to the support of third-generation standards (3G), such as CDMA2000 1x, W-CDMA and UMTS, the development of 3G networks is extremely slow, and interest in second-generation networks (2G) and second A half (2.5G) does not weaken, but, on the contrary, it grows, both in the markets of developing countries and in the markets of developed countries.
Evolution of cellular standards
In the name of "propaedeutics without bloodshed" I will return a little in history and tell about what generation standards cellular communication Now known science. The same of you who are already familiar with this question may immediately go to the next section dedicated directly to the EDGE technology.
it's standards first generation cellular communication (1G), (developed in 1978, was put into operation in 1981) and (introduced in 1983), were analog: the low-frequency voice of a person was transmitted to a high-frequency carrier (~ 450 MHz in the case of NMT and 820-890 MHz in case AMPS) using the amplitude-frequency modulation scheme. In order to provide a link at the same time a few people, in the AMPS standard, for example, the frequency ranges were divided into channels of 30 kHz width - this approach was named FDMA (Frequency Division Multiple Access). The first generation standards were created for and provided an exceptionally voice connection.
Standards second generation (2G), such as (Global System for Mobile Communications) and (Code Division Mutiple Access) brought with them several innovations. In addition to the frequency separation of FDMA communication channels, the voice of a person has now passed a digitization (coding), that is, the modulated carrier frequency was transmitted via the communication channel, as in the 1G standard, but no longer analog signal, and digital code. This is the overall trait of all second generation standards. They differ in the methods of "seals" or channel separation: A TDMA temporary seal approach is used in GSM, and in CDMA - code separation of communication channels (Code Division Mutiple Access), which is why this standard is called. The second generation standards were also created to provide voice communication, but due to their "digital nature" and in connection with the need arising during the dissemination of the global web to provide Internet access on mobile phones, provided the possibility of transmitting digital data on a mobile phone, as an ordinary wired modem. Initially, the second generation standards did not provide high bandwidth: GSM could provide only 9600 bps (exactly so much required to provide voice in one "compacted" using the TDMA channel), CDMA is a few dozen kbps.
In standards third generation (3G), the main requirement to which, according to the Specifications of the International Telecommunications Union (ITU) IMT-2000, began to provide video communication at least in the QVGA resolution (320x240), it was necessary to achieve a bandwidth of digital data transmission of at least 384 kbps. To solve this task, the frequency bands of the increased width (W-CDMA, Wideband CDMA) are used or a greater number of frequency channels involved simultaneously (CDMA2000). By the way, initially the CDMA2000 standard could not provide the required bandwidth (providing only 153 kbps), but with the introduction of new modulation schemes and multiplexing technologies using orthogonal carriers in the "add-in" 1x RTT and EV-DO, 384 Kbps threshold C was successfully overcome. And such a data transmission technology, as CDMA2000 1X EV-DV, should provide a bandwidth up to 2 Mbps, while being developed and promoted in W-CDMA networks HSDPA technology (High-Speed \u200b\u200bDownlink Packet Access) - up to 14.4 Mbps.
In addition, in Japan, South Korea and China are currently underway on the standards of the next, fourth generation, which will be able to provide the speed of transmission and reception of digital data over 20 Mbps, thus becoming an alternative to wired broadband networks.
However, despite all the prospects that the third generation network are promised, not many rush to them. There is a lot of reasons: it is the high cost of telephone sets caused by the need to return to the funds invested in research and development; and high cost of airtime, associated with a high cost licensed licenses and the need to transition to an incompatible infrastructure equipment; And small battery life due to excessively high (compared to second-generation devices) load when transferring large amounts of data. At the same time, the standard of the second generation GSM is due to the initially laid global roaming capability and lower cost of apparatus and airtal time (here the licensing policy of the main supplier CDMA-technologies, Qualcomm played a cruel joke with her), received truly global distribution, and Already last year, the number of GSM subscribers exceeded 1 billion people. Not to take advantage of the situation would be wrong both from the point of view of operators who would like to increase the average revenue from one subscriber (ARPU), and ensure the provision of services that are competitive with 3G network services and from users who would like to have mobile access to the Internet. The same thing that happened to this standard in the future, it is quite possible to call a small miracle: was invented evolutionary approachThe ultimate goal of which was to turn the GSM to the third generation standard compatible with UMTS (Universal Mobile Telecommunications System).
Strictly speaking, mobile Internet access was available for a long time: CSD technology (Circuit-Switched Data) allowed a modem connection at a speed of 9600 bits / s, but first, it was inconvenient due to low speed, and secondly - Because of the coming billing. Therefore, the GENERAL PACKET RADIO SERVICE (General Packet Radio Service) was first invented, and then marked the start of the transition to the packet approach, and then the EDGE technology. By the way, there is also an alternative GPRS technology HSCSD (High-Speed \u200b\u200bCircuit Switched Data), but it is less common, as it also implies compensated billing, while in GPRS traffic is taken into account - shipping packages. This is the main difference between GPRS and various technologies based on the CSD approach: In the first case, the subscriber terminal sends packets to the air, which goes arbitrary channels to the addressee, in the second - between the terminal and the base station (working as a router) is set to the point type -To items using a standard or extended communication channel. The GSM standard with GPRS technology occupies an intermediate position between the second and third communication generations, therefore is often called the second and a half generation (2.5G). It is also called that GPRS marks half the GSM / GPRS networks to compatibility with UMTS.
EDGE technology, as it is easy to guess from its name (which can be translated as "improved data transfer rates for the GSM standard evolution") plays two roles at once: first, it provides a higher bandwidth for transmitting and receiving data, and secondly , It serves another step towards GSM to UMTS. The first step is the introduction of GPRS, has already been made. Not far from the corner and the second step - the introduction of EDGE has already begun in the world and in our country.
Card covering the EDGE network of the MegaFon operator in Moscow (at the end of February 2006)
Edge - What is it and what is it eating with?
EDGE technology can embed two different ways: as a GPRS extension, in this case it should be called EGPRS (Enhanced GPRS) or as an extension CSD (ECSD). Considering that GPRS is widespread much wider than HSCSD, we will discover EGPRS.
1. EDGE is not a new cellular standard.
However, EDGE implies an additional physical level that can be used to increase the bandwidth of GPRS or HSCSD services. At the same time, the services themselves are provided in the same way as before. Theoretically, the GPRS service is able to provide bandwidth to 160 kbps (at the physical level, in practice, supporting GPRS Class 10 or 4 + 1/3 + 2 devices provide only to 38-42 kbps And then, if you can load a cellular network), and EGPRS is up to 384-473.6 kbps. This requires the use of a new modulation scheme, new channel encoding methods and error correction.
2. EDGE, in fact, is a "superstructure" (or rather, adjustment, if we assume that the physical layer is below the rest) to GPRS and cannot exist separately from GPRS. EDGE, as mentioned above, implies the use of other modulation and codecures, while maintaining compatibility with the CSD voice service.
Figure 1. Changed nodes are shown in yellow.
Thus, from the point of view of the client terminal, nothing should change with the introduction of EDGE. However, the infrastructure of the base station will undergo some changes (see Fig. 1), although not so serious. In addition to increasing the bandwidth for data transmission, the introduction of EDGE increases the capacity of the cellular network: in the same time slot, you can now "pack" a larger number of users, respectively, you can hope not to receive the message "Network is busy" in the most inappropriate moments.
| Table 1. Comparative characteristics EDGE and GPRS. | ||
| GPRS. | Edge. | |
| Modulation scheme | GMSK. | 8-PSK / GMSK |
| Character transfer rate | 270 thousand per second | 270 thousand per second |
| Bandwidth | 270 kbps | 810 kbps |
| Time slot bandwidth | 22.8 kbps | 69.2 kbps |
| Data transfer rate on a time slot | 20 kbps (CS4) | 59.2 Kbps (MCS9) |
| Data transfer rate using 8 time slots | 160 (182.4) Kbps / s | 473.6 (553.6) Kbps / s |
Table 1 illustrates different EDGE and GPRS specifications. Although EDGE, and in GPRS per unit of time, the same number of characters is sent, thanks to the use of a different modulation circuit, the number of data bits in EDGE is tripled. Immediately alleged here that the bandwidth values \u200b\u200band data transfer rates given in the table differ from each other due to the fact that the headlines of the packets are also taken into account, the user is unnecessary. Well, and the maximum data transfer rate of 384 kbps (required for compliance with IMT-2000 specification) is obtained if eight time slots are used, that is, each time slot accounts for 48 kbps.
Modulation diagram EDGE.
The GMSK modulation scheme is used in the GMSM standard (GAUSSIAN Minimum Shift Keying, a gaussian minimum shift encoding), which is a type of phase modulation of the signal. To explain the principle of the GMSK scheme, consider the phase diagram of Fig. 2, on which the real (I) and imaginary (q) part of the complex signal is depicted. The phase of the transmitted logical "0" and "1" differ from each other Phase P. Each time transmitted per unit corresponds to one bit.
Figure 2. Different modulation schemes in GPRS and EDGE.
The EDGE technology uses the 8PSK modulation scheme (8-phase shift keying, phase shift, as seen from the figure, is P / 4) using all the same specification of the structure of frequency channels, encoding and bandwidths, as in GSM / GPRS. Accordingly, neighboring frequency Channels Create exactly the same mutual interference, as in GSM / GPRS. A smaller phase shift between the characters in which not one bit is now encoded, and three (characters correspond to combinations 000, 001, 010, 011, 100, 101, 110 and 111), makes the detection task more complicated, especially if the signal level is low. However, in a good level of signal and stable reception, each symbol is not difficult to discriminate.
Coding
In GPRS it is possible to use four different coding schemes: CS1, CS2, CS3 and CS4, each of which uses its error correction algorithm. For EGPRS, nine coding schemes have been developed, MCS1..mcs9, respectively, the purpose of which is also in ensuring error correction. Moreover, the "Junior" MSC1..msc4 uses the GMSK modulation scheme, in the "senior" MSC5..msc9 is the 8PSK modulation scheme. Figure 3 shows the dependence of the data transfer rate from the use of different modulation schemes to associate with different encoding schemes (the data transfer rate varies depending on how many redundant information correction algorithms needed to work into each coded package). It is easy to guess that the worse the reception conditions (signal-to-noise ratio), the more you have to lay out redundant information into each package, which means that the data rate. A small difference in the data transfer rate observed between CS1 and MCS1, CS2 and MCS2, etc., is associated with a difference in the magnitude of the packet headers.
Figure 3. Different code circuits in GPRS and EDGE.
However, if the Signal / Noise ratio is not entirely lost: in the senior modulating and code diagrams of EGPRS MCS7, MCS8, MCS9, the "overlay" procedure is provided: since the standard is able to send groups of packets on different carriers (inside the frequency range) for each of which conditions (and above all - "noise") can be different, in this case again the transmission of the entire block can be avoided, if you know, in which group there is a failure and re-broadcast this group. Unlike the high-end code circuit GPRS CS4, where a similar error correction algorithm is not used, in EGPRS MCS7, MCS8, MCS9 different blocks of data "are superimposed" to each other, so when it is broken in one of the groups (as shown in the figure), re-shipping only half of the packages (see Fig. 4).
Figure 4. Using the application of package groups in EDGE.
Package processing
If for some reason the package sent using the "senior" coding schemes was not correctly accepted, EGPRS allows it to be retransable again using a "low" encoding scheme. In GPRS, such an opportunity called "Resegmentation" (Resegmentation) was not provided: the incorrectly received packet is sent again along the same modulation and encoding scheme as the previous time.
Addressing Window (Addressing Window)
Before the sequence of coded (that is, the "words", consisting of several bits) of packets (frame), can be transferred by a radio frequency interface, the transmitter assigns the identification number included in the header of each packet to packets. Package numbers in GPRS are from 1 to 128. After the sequence of packets (for example, 10 pieces) is sent to the addressee, the transmitter is waiting for the confirmation receiver that they were adopted. The report that receiver sends back the transmitter, contains the number of packages that were successfully decoded, and which the recipient could not decode. Important nuance: Package numbers take values \u200b\u200bfrom 1 to 128, and the width of the address window is only 64, as a result of which the newly transmitted package can get the same number as in the previous frame. In this case, the protocol is forced to re-send the entire current frame, which adversely affects the data transfer rates as a whole. To reduce the risk of the occurrence of such a situation in the EGPRS, the package number may receive values \u200b\u200bfrom 1 to 2048, and the address window is increased to 1024.
Measurement accuracy
To ensure correct operation of the GPRS technology in the GSM environment, you have to constantly measure the radio: the signal / noise level in the channel, the frequency of errors, etc. These measurements do not affect the quality of voice communication, where it is enough to constantly use the same encoding scheme. When data transfer to GPRS, the measurement of radio conditions is possible only in "pauses" - twice for a period of 240 ms. In order not to wait every 120 ms, EGPRS defines such a parameter as the likelihood of bits error (BEP, BIT ERROR PROBABILITY), in each frame. The BEP value affects both the signal-to-noise ratio and the time dispersion and the speed of the terminal movement. The change in the frame from the frame to the frame allows you to evaluate the speed of the terminal and the "trembling" of the frequency, but for a more accurate estimate, the average probability value of the error on the bit for every four frame and its selective standard deviation is used. Due to this, EGPRS responds faster to changes: increases the data transfer rate when the BEP is reduced and vice versa.
Connection speed control in EGPRS
EGPRS uses a combination of two approaches: adjustment of the speed of the compound and incremental redundancy. Connection rate adjustment measured either by a mobile terminal by the number of data taken per unit or a base station by quantity, respectively, transmitted data allows you to select the optimal modulation code diagram for subsequent data volumes. Usually, the use of a new modulation code pattern can be assigned when transferring a new block (four groups) of data.
Incremental redundancy is initially used for the highest modulating code pattern, MCS9, with minor attention to error correction and excluding radio conditions. If the information is decoded by the addressee incorrectly, the data itself is transmitted over the communication channel, but a certain control code that is "added" (used for conversion) to the data already loaded until the data is decoded successfully. Each such "incremental piece" of an additional code increases the likelihood of successful decoding transmitted data - this is redundancy. The main advantage of this approach is that there is no need to follow the quality of radio communications, so incremental redundancy is mandatory in the EGPRS standard for mobile terminals.
EGPRS integration into existing GSM / GPRS networks - UMTS not far off!
As mentioned above, the main difference between GPRS and EGPRS is used in the use of a different modulation scheme at the physical level. Therefore, to support EGPRS, it is enough to install on the base station supporting new modulation transceiver modulation schemes and software For processing packages. To ensure compatibility with not supporting EDGE mobile phones, the following is written in the standard:
- Supporting and non-supporting EDGE mobile terminals must be able to use the same time slot
- Supporting and non-supporting EDGE transceivers must use the same frequency range
- POSSIBLE EDGE support is possible.
- Supporting modulation scheme 8PSK only in the receiving data stream (DOWNLINK) and
- Supports 8PSK both in the receiving and in the transmitting (Uplink) data stream
The introduction of EGPRS, as mentioned above, allows you to achieve bandwidth, approximately three times more than in GPRS technology. It uses exactly the same QoS profiles (Quality of Service, the quality of service), as in GPRS, but taking into account the increased bandwidth. In addition to the need to install a transceiver at the base station, the software support is required to support the EGPRS, which must process the changed packet transmission protocol.
The next evolutionary step on the path of the GSM / EDGE cellular systems to the "full-fledged" networks of the third generation will be further improved package shipping services (data) to ensure their compatibility with UMTS / UTRAN (UMTS Terrestrial Radio Access Network). These improvements are currently undergoing consideration, most likely will be included in the future version of 3GPP specifications (3G Partnership Project). The main difference between Geran from implemented in currently EDGE technology will support QoS for interactive, background, streaming and negotiating classes. Support for these QoS classes already exists in UMTS, so that in UMTS networks (let's say, W-CDMA 2100 or 1900 MHz) is an opportunity, for example, video link. In addition, in the future, the EDGE generation is planned to provide simultaneous parallel processing of data streams with different QoS priority.
Let's start with GPRS as the slowest standard. GPRS (General Packet Radio Service - Package Radio Communication) is an add-in over GSM, which is used for batch data transfer. The GPRS standard allows the user to make data sharing with other devices in the GSM network and with devices that are in external networks, including on the Internet.
GPRS collects information in packets (packet principle) and transmits it through voice channels that this moment not used. Voice priority or data (which is more important - voice or data?) Selected by the operator. Usually the voice is more important than the data.
If GPRS uses multiple free channels, then the data transfer rate is low, but quite sufficient to work on the Internet. The maximum speed with all busy channels (or time slots) is 171 kbps. It is clear, in practice, you can only dream of such a speed.
There are various classes GPRS. All of them are distinguished by the data rate and the possibility of combining voice call and data transmission.
- Class A - Allows you to make or receive a call and simultaneously transmit data. The class is outdated, since the 2005th year of the class and no longer produce.
- Class B - Provides automatic switching between sessions, i.e. In the interruptions between reception sessions and data transmission, you can make calls.
- Class C - Used in GPRS modems (and not in mobile phones) and implies only one type of service - only data transmission or only voice calls.
In general, GPRS classes consist of two parts: the first part of the class we have already considered (A, B and C) it determines the possibility of simultaneous data and voice transmission. And the second part of the class sets the number of time slots and, consequently, the data transfer rate.
GPRS classes (transfer rate)
| Class | Reception | Broadcast | Total |
| 1 | 1 | 1 | 2 |
| 2 | 2 | 1 | 3 |
| 3 | 2 | 2 | 4 |
| 4 | 3 | 1 | 4 |
| 5 | 2 | 2 | 4 |
| 6 | 3 | 2 | 4 |
| 7 | 3 | 3 | 4 |
| 8 | 4 | 1 | 5 |
| 9 | 3 | 2 | 5 |
| 10 | 4 | 2 | 5 |
| 11 | 4 | 3 | 5 |
| 12 | 4 | 4 | 5 |
| 13 | 3 | 3 | - |
| 14 | 4 | 4 | - |
| 15 | 5 | 5 | - |
| 16 | 6 | 6 | - |
| 17 | 7 | 7 | - |
| 18 | 8 | 8 | - |
| 19 | 6 | 2 | - |
| 20 | 6 | 3 | - |
| 21 | 6 | 4 | - |
| 22 | 6 | 5 | - |
| 23 | 6 | 6 | - |
| 24 | 8 | 2 | - |
| 25 | 8 | 3 | - |
| 26 | 8 | 4 | - |
| 27 | 8 | 5 | - |
| 28 | 8 | 6 | - |
| 29 | 8 | 8 | - |
| 32 | 5 | 3 | 6 |
Reception is the number of time slots for data reception, and the transfer is the number of time slots for data transmission.
As in any other data network, data can be transmitted from the network (download) and to the network (UPLOAD). Modern phones can simultaneously use four time slots to download data from the network (download) and up to two time slots to download data to the network (UPLOAD) is class 10 - circuit 4 + 2 (see table). The simultaneous use of four time slots to load data from the network allows you to reach 85 kbps data transfer rate. That is, one time slot provides data transmission at a speed of 21.4 kbps. It is clear that the maximum speed (85 kbit / s) can not be achieved, since there are no four free channels.
When connected to the GPRS, the subscriber is allocated virtual channel. Channel dynamic, i.e. Now it is used by one user, and when he is no longer needed, it can be used by another user. The same channel can be used by different users. This leads to a queue for packet transmission and communication delay. In modern networks, one time slot can be used by sixteen subscribers at different times and up to 5 time slots at a frequency, as a result, 80 subscribers are obtained, which use GPRS on one communication channel (average maximum speed (21.4 x 5) / 80 \u003d 1.3 kbps per subscriber).
But there is another case when time slots are packaged into one continuous stream with the displacement of voice subscribers to other frequencies. In this case, the speed will reach the maximum possible for class 10 - 4 + 2 time slot or 85 kbps for data reception and 42.8 kbps to send.
EDGE (Enhanced Data Rates for GSM Evolution) - Digital technology for mobile communications, which is an add-in over GPRS.
- To provide EDGE support in the GSM network, the following modifications are used:
- ECSD (Enhanced Circuit-Switched Data) Accelerated Internet access via CSD channel;
- EHSCSD (Enhanced High Speed \u200b\u200bCircuit Switched Data) - high-speed Internet access via HSCSD channel;
- EGPRS (Enhanced GPRS) - access via GPRS.
EDGE technology uses 8PSK modulation for five of eight code circuits (MCS). Compared to GPRS, this modulation increases the data transfer rate by 3 times.
The maximum theoretical data transfer rate is 474 kbps (8 time-slots of 59.2 kbps each), such a speed is achieved with the MCS-9 encoding scheme (see table).
EDGE data transfer rate
| Coding scheme | Speed \u200b\u200bof one slot, kbps / s | Maximum speed, kbps (when using 8 channels) | Modulation |
| MCS-1. | 8.8 | 70,4 | GMSK. |
| MCS-2 | 11.2 | 89,6 | GMSK. |
| MCS-3. | 14.8 | 118,4 | GMSK. |
| MCS-4. | 17.6 | 140,8 | GMSK. |
| MCS-5. | 22.4 | 179,2 | 8-PSK. |
| MCS-6. | 29.6 | 236,8 | 8-PSK. |
| MCS-7. | 44.8 | 358,4 | 8-PSK. |
| MCS-8. | 54.4 | 435,2 | 8-PSK. |
| MCS-9. | 59.2 | 473,6 | 8-PSK. |
Now we approached our days closely - to 3G technology. More precisely, 3G is not a technology, but the third generation of mobile communications, combining not only data transfer, but high-speed data transmission - the Internet access speed is up to 2 Gbit / s. Two standards 3G are common in the world: UMTS (mainly in Europe) and CDMA2000 (in the USA).
UMTS (Universal Mobile Telecommunications System - Universal Mobile Communication System) in practice provides access speeds up to 2 Mbps (this is a practical limit, and not theoretical), i.e. Theoretical Maximum EDGE in 474 Kbps for UMTS is generally not the limit.
What standard to choose? It all depends on your needs and opportunities. If you need high-speed Internet access, then only UMTS (3G), but here you must remember: Such access is more expensive, and the terminals (i.e. Mobile phones) with UMTS support are more expensive, while EDGE support is in any modern phone (even in budget variant). The GPRS is generally better forgotten because GPRS does not provide the data rate required by the current user. Compared to DSL access, EDGE is also quite expensive, but over time the situation will change, and broadband wireless access to the Internet will become not only high-speed, but also cheap. If there is money, then you can buy a phone with support for UMTS - behind this standard future.
Your question:
How to turn off in the phone edge?
Master's answer:
In some cases, it becomes extremely necessary to disable GPRS / EDGE data in the mobile phone. For example, this function is absolutely not needed in roaming conditions. Another example of the need to disable this feature is to excess traffic.
For models samsung phone Disable the function occurs through the request * # 4777 * 8665 #. In the "Attach Mode Settings" menu, select the "GPRS Detach" item and remove the mark from it. After that, the phone is turned off and loaded repeatedly, as a result of which the function is deactivated.
To disable the EDGE service, you need to change the APN access settings - through it this service comes to your phone. For example, at the end of the address you can put a point, and the function will not work. If you want to query the data, the message "Service is not connected" will receive in response, so the information cannot be transmitted. Return the setting is simply - it is enough to remove the point and the address will become the right one.
You can use the SBSetting utility. This program can be taken on the Internet, where it is available and free. After installing the program to a mobile phone, you need to go to the menu and find the Enable-Disable EDGE option.
It is not difficult to disable the function and owners of iPhone iOS 4.0. In the phone menu, select the "Settings" section, then the "Main" item is "Network". The option "Cell data" needs to be disconnected. After its inclusion through GPRS traffic, no program will not be included in the Internet.
The subscriber needs to go to mobile Internet – browser Safari.. According to the link "iPhone No Data.com" go to the specified resource. Having found the "Turn Off EDGE / 3G" button (it means shutdown), you need to click on it. A dialog box opens with the "Install" button, after clicking on which a dialog box is displayed with the "Install NOW" button. If you press the button, the EDGE service will turn off on the iPhone. If the subscriber uses WiFi connection, this function can not be turned off.
The subscribers of the Network Beeline can contact the customer service of their cellular operator. The operator must disable the Any APN service, which is automatically connected. This service is responsible for providing the EDGE service. When the "APN" service becomes zero, the phone will be out of the network. You can also ask the operator to deactivate GPRS. The fact is that EDGE is a simple expansion, thanks to which GPRS operates at a higher speed.
EDGE technology is another step in the development of GSM networks. Purpose of implementation new technology - Increased data transfer rates and more efficient use of the radio frequency spectrum. With the advent of EDGE in the GSM networks of the phase 2+, the existing GPRS and HSCSD parameters are significantly improved due to changes in the signal transmission at the physical level (modulation and coding) and new radio algorithms during data transmission. The GPRS and HSCS D technologies themselves do not change and can work in parallel with EDG E. Along with the EDGE abbreviation, you can find the EGPRS term (enhanced GPRS - "Superior GPRS), indicating the use of GPRS service with new physical level EDGE. Next, we will consider EDGE only applied to GPRS, since HSCSD technology has not been distributed in Russia.
The theoretical limit of the data rate in the radio channel when using EGPRS is 473.6 cbv, while with GPRS - only 160 cbv. High speed values \u200b\u200bare achieved thanks to a new modulation method and applying a modified radio signal transmission method that is resistant to errors. In addition, the changes touched the algorithms for adaptation to the quality of the channel.
Based on the foregoing, it can be concluded that EDGE is an addition to GPRS and cannot exist separately. From the consumer's point of view, GPRS expands the GSM network capabilities, while EDGE improves GPRS technical parameters.
With reference to the GSM network infrastructure, EGPR S requires changes to base stations. In this case, the existing GSM infrastructure kernel is used, and the introduction of EDGE means only the installation of additional equipment (Fig. 1).
Fig. one.
EDGE Parameters
The table shows the main technical characteristics of GPRS and EDGE technologies.
Table 1.
As can be seen from the table, the EDGE can transmit three times more data than GPRS in the same period of time. The difference between the speed in the radio channel (RADI O Data Rate) and the actual data transfer rate (User Data Rate) is explained by the fact that the user data is added to the user data block in the form of a packet header. This often leads to confusion when determining GPRS and EGPRS bandwidth, as there are different speed indicators in publications. In connection with the EDGE technology, a figure of 384 Kbps is more common: International Telecommunications Union - ITU) determines the International Telecommunications this speed In accordance with the requirements of the IMT-2000 standard (International Mobile Telecommunications), which involves the use of eight time-slots at a speed of 48 kbps each.
New modulation type
When transmitting data in GPRS mode, Gaussian manipulation with a minimum frequency shift GMSK - Gaussian Minimum Shift Keying (Fig. 2) is used, which is a type of phase modulation. When transmitting the bit "0" or "1" phase of the signal receives a positive or negative increment. Each transmitted symbol contains one bit of information, that is, each phase shift represents one batch. To achieve a greater data transfer rate on one time interval (in one time slot), you need to change the modulation method.
Fig. 2.
EDGE was developed to use the same frequency mesh, channel widths, channel coding methods and existing mechanisms and functions used by GPRS and HSCSD. For EDG E, an eight-step phase modulation 8PSK (8-Phase Shift Keying) was selected, which satisfies all these conditions. If we talk about interference between adjacent channels, 8PSK has the same quality parameters as GMSK. This allows you to integrate EDGE channels into an existing frequency plan and assign new EDGE channels in the same order as conventional GSM channels.
8PSK is a linear modulation method in which 3 bits of information correspond to one transmitted symbol. The rate of symbol transmission (or the number of characters transmitted per unit time) remains the same as in GMSK, but each character carries information in 3 instead of 1 bt. Consequently, the data transfer rate increases 3 times. The phase distance between characters in 8PSK is less than in GMSK, which increases the risk of a symbol recognition error. With a good signal / noise, this is not a problem. For successful work in poor radio channels, use error correction codes. Only with a very weak radio signal GMSK modulation has an advantage over 8PSK. In order to be able to efficiently work with any signal / noise ratio, both types of modulation are used in the EDGE encoding schemes.
Coding schemes and package formation
For GPRS, four encoding schemes are defined: CS1-CS4. Each contains a different amount of corrective bit by optimizing each encoding scheme for a certain quality of the radio. EGPRS uses nine coding schemes that are indicated by MCS1-MSC9. Younger four schemes use GMSK modulation and are designed to work at worst signal / noise ratio. The MSC5-MSC9 schemes use the 8PSK modulation. In fig. 3 presents the maximum data rates, achievable when using different coding schemes. The GPRS user can obtain a maximum data transfer rate of 20 cbv, while the EGPRS speed increases up to 59.2 cbv as radioline quality improves (approximation to the base station).
Fig. 3.
Despite the fact that the CS1-CS4 and MSC 1-MSC4 schemes use the same type of GMSK modulation, the EGPRS radio packets have a different length of the headers and the amount of useful data. This allows you to change the encoding scheme "on the fly" to retransmit the package. If the package with an older encoding scheme (with less noise immunity) is obtained with an error, it can be sent again using a smaller coding scheme (with greater noise immunity) to compensate for the deteriorating radioline parameters. Transmission with another encoding scheme (resegmentation) requires a change in the number of useful bits in the radio burst. In GPRS, this possibility is not provided, therefore the GPRS and EGPRS encoding schemes have different efficiency.
In GPRS, the packet repetition is possible only with the original coding scheme, even if this coding scheme ceased to be optimal due to deterioration of the quality of the radio. Consider on the example of a packet transmission scheme (Fig. 4).
A. The GPRS terminal receives data from the base station. Based on the previous report on the quality of the radio domain, the base station controller decides to send the following data block (number 1-4) with the CS3 encoding scheme. During transmission, the radioline condition deteriorated (the signal / noise ratio decreased), as a result, the packets 2 and 3 were obtained with an error. After transferring the packet group, the base station requests a new report - an assessment of the quality of the radio.
B. The GPRS terminal transmits the base station information about incorrectly delivered packets along with information on the quality of the radio system (in reportpit).
FROM. Given the deterioration in the quality of communication, the adaptation algorithm selects a new, more obstacle CS1 encoding scheme for transmitting packets 5 and 6. However, due to the impossibility of relaxation in GPRS, the retransmission of packets 2 and 3 will occur with the same CS3 encoding scheme, which significantly increases the risk of incorrect reception. These packages GPRS terminal.
The GPRS adaptation algorithm requires a very careful selection of encoding scheme to prevent, as far as possible, retransmission packets. Due to the EGPRS relaxation can use a more efficient method of selecting a coding scheme, since the likelihood of package delivery during retransmission here is significantly higher.
Table 2. A group of coding schemes
Packet addressing
When the package block is transmitted through the radio channels inside the block number, from 1 to 128. This identification number is turned on in the title of each packet. In this case, the number of packets in the block transmitted to a specific GPRS terminal should not exceed 64. A situation may occur when the number of the re-transmitted packet coincides with the number of the new package in the queue. In this case, it is necessary to re-pass the entire unit entirely. In EGPRS, packet address space is increased to 2048, and the sliding window size is 1024 (the maximum number of packets in one block), which significantly reduces the likelihood of such collisions. Reducing repeated gears at the RLC level (Radio Link Control) in the end leads to an increase in bandwidth (Fig. 5).
Measuring the quality of radio channel
Radioline's quality assurance in GPRS is made by measuring the level of the received signal, estimate the BER parameter (Bit Error Rate - the relative number of incorrectly accepted bits), etc. The execution of this assessment takes away from the GPRS terminal for some time that, in principle, not Plays a large role with a constant use of one encoding scheme. When packet switching data, it is necessary to quickly monitor the quality of the radio system to quickly change the coding scheme depending on the state of the radio. The procedure for assessing the quality of the channel in GPRS can be performed only twice within 240 ms period. This makes it difficult to operate the correct encoding scheme. In EGPRS, measurements are made at each reception by assessing the probability of erroneous bits (BEP - BIT ERROR PROBABILITY). Based on each transmission data, the BEP parameter reflects the current signal / noise ratio and the time dispersion of the signal. As a result of this approach, the assessment of the quality parameters of the transmission channel turns out to be sufficiently accurate even on the short measured period. This determines the higher efficiency of the adaptation scheme compared to GPRS.
Radio control functions and increased redundancy
To ensure the maximum transfer rates in the conditions of the existing quality of the radio channel in EGPRS, the following mechanisms are used:
- Adaptation to the quality of the channel. Based on measurements of the quality of the line during data transmission (both in the direction of the mobile terminal and from it), the adaptation algorithm selects a new coding scheme for the next packet sequence. Coding schemes are grouped into three families - A, B and C. The new coding scheme is selected from the same family, which the same belongs to (Fig. 5).
- Increased code redundancy. Incremental Redundancy is used for senior coding schemes in cases where, instead of analyzing the parameters of the radio and coding schema, send is applied for more information For subsequent transmissions. If errors occurred when receiving a package, excess information may be sent in the next package, which will help you correct the previously accepted bits. The procedure may be repeated until a complete recovery of information in the previously adopted package.
In Russia, the "Big Troika" operators are already provided by the EDGE service in several parts of Moscow and in a number of regions of the country. The introduction of the EDGE occurs gradually, as the equipment is updated the basic stations. MegaFon plans until the end of 2005 to cover EDGE technology about 500 base stations. VimpelCom is going to fragmentary to introduce an edge in Moscow within the Moscow Ring Road (at sections with increased GPRS traffic), and in Russia - in all regions by the end of 2006 - the beginning of 2007. MTS declares that "work is carried out very intensively: the EDGE coverage in the Moscow region is expanding almost daily."
Literature
- EDGE. INTRODUCTION OF HIGH-SPEED DATA IN GSM / GPRS NETWORKS (www.ericsson.com/products/white_papers_pdf/edge_wp_technical.pdf). / Link is lost /
- Materials of the "Mobile Forum" site (http://mforum.ru/news/article/01-5533.htm). / Link is lost /
It is still used in many banking systems and is very resistant to hacking and leakage of data. Unfortunately, in Russia, it is very expensive, but it does not cancel his degree of demand for a certain circle of persons.
GPRS technology is a package technology, it collects all the information into conditional units (packets) and transmits them at the rate of 56 before 114 Kbit / s. This provides Internet access, loading melodies, pictures, games, transmitting short multimedia messages (MMS), communication on ICQ or mail.
EDGE transmits data about three times faster than GPRS - theoretically EDGE is able to maintain file sharing speed 474 kbit / s, while peak value at gprs - 171,2 Kbit / s. The numbers speak for themselves, although in practice the speed indicators are much more modest.
(from the English. Third Generation - Third Generation) - Mobile GSM-Communication Technologies of the Third Generation, which combines both voice-related possibilities and high-speed mobile access to the Internet. The third generation of radio communications differs from previous versions increased speed by transferring data at speeds to 3,6 Mbit / s. This makes it possible to enjoy mobile device All advantages of high-speed Internet: Watch On-line movies and television programs, organize mobile video telephone communication, download large amounts of data, etc.
Step 1. Connect the GPRS / EDGE / 3G service
In all operators, the GPRS / EDGE / Internet service is initially connected. But in some cases, the service needs to be connected independently. The Internet access speed depends on the device that the user uses at a certain point and from the coating zone in which it is located. The coating is greatly inferior to GPRS / EDGE, but it gives a colossal gain in the speed of connecting to the network.
