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  • 1. HELSINKI UNIVERSITY OF TECHNOLOGY DEPARTMENT OF COMPUTER SCIENCE TIK-109.551 Research Seminar on Telecommunications Business II POSITIONING EDGE IN THE MOBILE NETWORK EVOLUTION 12.3.2003 Vesala Sami 47278H Koivu Katja 44217E
  • 2. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 1 Table of Contents TABLE OF CONTENTS..................................................................................................................1 ABBREVIATIONS............................................................................................................................1 1. INTRODUCTION...........................................................................................................................4 2. EVOLUTION FROM GSM TO GPRS NETWORK ARCHITECTURE...............................5 2.1 CELLULAR PLATFORM EVOLUTION ................................................................................................5 2.2 GSM.....................................................................................................................................6 2.2.1 Functioning of the GSM system...........................................................................................7 2.2.2 Architecture of the GSM network.........................................................................................7 2.2.3 GSM mobile stations and SIM cards..................................................................................12 2.3 HIGH SPEED CIRCUIT SWITCHED DATA........................................................................................13 2.4 GENERAL PACKET RADIO SERVICE..............................................................................................14 2.4.1 GPRS in general.................................................................................................................14 2.4.2 GPRS Architecture.............................................................................................................16 2.4.3 Logical Channels of GPRS.................................................................................................17 2.4.4 GPRS coding schemes........................................................................................................18 2.4.5 GPRS terminals..................................................................................................................19 2.5 EVOLUTION OF GSM DATA SERVICES TOWARDS EDGE.................................................................19 2.5.1 Short Message Service........................................................................................................20 2.5.2 Wireless Access Protocol...................................................................................................21 2.5.3 Multimedia Message Service..............................................................................................21 2.5.4 HSCSD and GPRS enabled services and data rates in practice.......................................22 3. EDGE TECHNICAL FUNDAMENTALS.................................................................................24 3.1 8-PSK MODULATION IN GSM/EDGE STANDARD..........................................................................25 3.2 ENHANCED GENERAL PACKET RADIO SERVICE (EGPRS)..................................................................25 3.2.1 Link adaptation...................................................................................................................26 3.2.2 Incremental redundancy.....................................................................................................27 3.3 ENHANCED CIRCUIT SWITCHED DATA (ECSD)...............................................................................27 3.4 EDGE EVOLUTION TOWARDS GERAN REL´5..............................................................................28 3.4.1 GERAN Rel´5 features........................................................................................................29 3.4.2 GERAN Rel´5 system architecture.....................................................................................29 3.5 MODIFICATIONS TO THE GSM NETWORK IMPOSED BY EDGE...........................................................30 3.5.1 EDGE radio network planning compared with GSM/GPRS planning..............................31 4. VENDORS EDGE STRATEGIES..............................................................................................33
  • 3. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 2 5. SERVICES ENABLED BY EDGE.............................................................................................35 6. TERMINAL AVAILABILITY....................................................................................................38 7. INVESTMENT COSTS AND REVENUES CAUSED BY EDGE..........................................40 8. EDGE INVESTMENT STRATEGIES......................................................................................43 8.1 GSM OPERATORS WITHOUT 3G LICENSES .....................................................................................43 8.2 GSM OPERATORS WITH 3G LICENSE............................................................................................44 9. FUTURE ROLE OF EDGE........................................................................................................46 10. CONCLUSIONS.........................................................................................................................49 REFERENCES.................................................................................................................................51
  • 4. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 1 Abbreviations 3GPP 3rd Generation Partnership Project 8-PSK Octagonal Phase Shift Keying AMR Adaptive Multi Rate ARPU Average Revenue Per User ARQ Automatic Retransmission Request ATM Asynchronous Transfer Mode AuC Authentication Center BER Bit Error Rate BLER Block Error Rate BSC Base Station Controller BSS Base Station Subsystem BTS Base Transceiver Station CCS Common Channel Signaling CDMA Code Division Multiple Access CI Cell Identity CN Core Network CS Circuit Switched D-AMPS Digital Advanced Mobile Phone System DCS Digital Cellular System DS Direct Sequence ECSD Enhanced Circuit Switched Data EDGE Enhanced Data rates for Global Evolution EGPRS Enhanced General Packet Radio System EIR Equipment Identity Register ETSI European Telecommunications Standard Institute FDMA Frequency Division Multiple Access GCR Group Call Register GERAN GSM EDGE Radio Access Network GGSN Gateway GPRS Support Node GMSK Gaussian Minimum Shift Keying GoS Grade of Service
  • 5. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 2 GPRS General Packet Radio Service GSM Global System for Mobile Communications HLR Home Location Register HSCSD High Speed Circuit Switched Data IMS Internet Multimedia Subsystem IMS-2000 International Mobile Telecommunications 2000 IMSI International Mobile Subscriber Identity IP Internet Protocol IR Incremental Redundancy ISP Internet Service Provider ITU International Telecommunications Union LA Link Adaptation LA Location Area LAN Local Area Network MCS Modulation and Coding Scheme MMI Man-machine interface MMS Multimedia Message Service MSC Mobile Switching Centre MS Mobile Station MSRN Mobile station roaming number NACC Network assisted cell change NSS Network Sub-system OMC Operations and Maintenance Center OSS Operations Sub-system PSTN Public Switched Telephone Network QoS Quality of Service RAN Radio Access Network RF Radio Frequency RNC Radio Network Controller RTP Real-time Protocol SGSN Serving GPRS Support Node SIR Signal-to-Interference Ratio SMS Short Message Service SS Spread Spectrum
  • 6. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 3 TDD Time Division Duplex TDMA Time Division Multiple Access TRAU Transcoder / Rate Adapter Unit TRX Transceiver UDP User Datagram Protocol UE User Equipment UMTS Universal Mobile Telecommunications System UTRAN UMTS Terrestrial Radio Access Network VLR Visitor Location Register WAP Wireless Application Protocol WCDMA Wideband Code Division Multiple Access
  • 7. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 4 1.Introduction EDGE technology gives GSM the capacity to handle services for the third generation of mobile networks. EDGE was developed to enable the wireless transmission of large amounts of data at a higher speed than before. EDGE will allow GSM operators to use existing GSM radio bands to offer IP-based multimedia services and applications at theoretical maximum speeds of 384 kbps with a bit-rate of 48 kbps per timeslot and up to 69.2 kbps per timeslot in good radio conditions. Implementing EDGE will be relatively easy and will require relatively small changes to network hardware and software as it uses the same TDMA (Time Division Multiple Access) frame structure, logic channel and 200 kHz carrier bandwidth as today's GSM networks, which allows existing cell plans to remain intact.
  • 8. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 5 2.Evolution from GSM to GPRS network architecture 2.1 Cellular Platform Evolution Cellular radio networks are generally divided into three generations. Analogue cellular systems, such as Nordic Mobile Telephone (NMT), are considered to be the first generation of cellular technologies. The second generation is the present digital network generation which includes systems like Global System for Mobile communications (GSM), Digital Cellular System (DCS), Digital Advanced Mobile Phone System (D-AMPS), and Interim Standard –95 (IS-95). The second generation includes also enhancements to GSM: High Speed Circuit Switched Data (HSCSD), General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE). These enhancements are called the generation 2G+ or 2,5. According to International Telecommunications Union (ITU) specifications, the third generation cellular networks will offer data transmission speeds up to 2Mbps. Universal Mobile Telecommunications System (UMTS) is one of the mobile communications systems being developed within the ITU framework known as International Mobile Telecommunications IMT-2000.
  • 9. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 6 GSM 9.6kbps UMTS 2Mbps HSCSD 57.6kbps GPRS 115kbps EDGE 384kbps 1999 2000 2001 2002 2003 Figure 2.1. Evolution paths of GSM towards third generation networks The different GSM evolution paths are shown in Figure 2.1. The data rates are the maximum data rates theoretically provided by different systems. In reality, maximum data rates are achieved only in very limited circumstances, if at all. 2.2 GSM GSM, which was first introduced in 1991, is one of the leading digital cellular systems. Originally a European standard for digital mobile telephony, GSM has become the world's most widely used mobile system and it is in use in over 170 countries. Over 578 million subscribers use GSM in 400 different networks. GSM networks operate on the 900 MHz and 1800 MHz waveband in Europe, Asia and Australia, and on the MHz 1900 waveband in North America and in parts of Latin America and Africa. GSM is an open, standardized, non-proprietary system that is constantly evolving. The growth of GSM continues unabated with more than 160 million new customers in the last 12 months. Since 1997, the number of GSM subscribers has increased by 10 fold.
  • 10. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 7 In addition to voice services, GSM simplifies data transmission to allow laptop and palmtop computers to be connected to GSM phones. It provides integrated voice mail, high-speed data, fax, paging and short message services capabilities, as well as secure communications. GSM offers the best voice quality of any current digital wireless standard. Furthermore, one of GSM strengths is the international roaming capability. Roaming gives subscribers seamless connection to mobile networks. In addition, GSM satellite roaming has extended service access to areas where terrestrial coverage is not available. [Ericsson 2003][Gsmworld 2003] 2.2.1Functioning of the GSM system GSM uses narrowband TDMA as a multiple access method where eight simultaneous calls can occupy the same radio frequency while using a full rate speech codec (eight timeslots/200kHz). Using a halfrate speech codec, where two users can share the same timeslot, can double the capacity. However, using the halfrate codec has a deteriorating effect on speech quality. Operators have multiple frequencies and thus GSM is in fact a combination of TDMA and FDMA (frequency division multiple access) technologies. Each timeslot is called a physical channel and can be used as a traffic channel and/or a control (signaling) channel. Traffic and control channels are called logical channels. In GSM, there are different frequency ranges for uplink (from the mobile station’s transmitter to the base station’s receiver) and downlink (from the base station to the mobile station) traffic. [Penttinen 2002] 2.2.2Architecture of the GSM network GSM network consists of network and switching sub-system (NSS), the base station sub-system (BSS) and the operations sub-system (OSS), which controls the functioning of the NSS and BSS (see Figure 2.2.). In addition to these three elements, GSM network contains also other elements for for example billing and voice mailbox services. [Penttinen 2002]
  • 11. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 8 Figure 2.2. GSM network architecture Base Station Sub-system The main task of the base station sub-system is to connect the mobile stations to the network and to switch the sub-system in briefly. The base station sub-system consists of base transceiver stations (BTS) and base station controllers (BSC) and a transcoder / rate adapter unit (TRAU). One BTS consists of equipment space, a Transmitter/Receiver (TRX) with power supply, a combiner, a power splitter, antenna cables, a mast, a scrambler, antennas and an antenna pre-amplifier. One TRX transmits traffic on a single frequency if there is no synthetic frequency hopping. As mentioned earlier, each frequency is divided into eight time slots, and if full rate codec is used, each frequency can carry eight users at maximum. Not all the available time slots can be used for speech or data transmission because some of
  • 12. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 9 them are used in signaling (SDCCH channels). Usually one cell consists of from one to six TRX, which means that it is possible that there is up to forty-five users per cell depending on the number of SDCCH channels. The geometry of the cell could be circular or conical. Circular cells are usually used in the countryside and in areas where it is sensible to use omnidirectional antennas. On the other hand, conical cells are used in areas where directivity is needed, for example freeway areas and cities. Different cells are separated from each other with individual cell identities (CI). Another essential element in the BSS system is the earlier mentioned BSC, the main function of which is to control and manage the BSS and the radio channels. It transfers signaling information to and from the mobile stations (MS) and manages the handovers between the cells. In the GSM system this kind of assignments are defined apart from the mobile switching center so that the MSC would have more time to switch calls through. MSC connects the calls via the right BSC to the MS, and BSC handles the events of the radio interface during connection. One BSC controls several BTSs, and grouping them enables constituting location areas (LA). It is also possible that base transceiver stations constituting the LA are in the area of two different BSC’s. Figure 2.3. The structure of the location areas If the MS moves in a standby state from the location area to another it has to update the location in the BSC. When the network knows the location area of each MS, it enables that in case of incoming call the network has to call MS via the cells in the certain location area only (paging). BSC controls the channel al-location and knows all the time, which channels are in use and which are free in each cell in its area. On the basis of the measurement reports sent by mobile stations the BSC also knows the interference level of each channel. Normally BSC only reports for the MSC about
  • 13. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 10 the performed channel changes but in the case of handover between two BSC’s the MSC takes part of the channel change. The handover may occur e.g. because of the field strength or the quality level. In the GSM system the decision of the handover is made by BSC on the basis of the measurement reports of the MS and BTS. In addition to all assignment mentioned above, the BSC also controls the parameters of the radio interface. There are typically a lot of parameters in the radio interface containing e.g. frequency hopping sequences of the TCHs and location updates. Usually one MSC administers several BSCs, and several base transceiver stations are typically connected at one BSC. The amounts depend on the capacity of the devices, which changes between different manufacturers. The capacity also depends on the capacity of the registers in the central system. [Mouly 1992] [Penttinen 1999] [Nokia 2000] Network and Switching Sub-system Network and Switching Sub-system (NSS) is composed of MSC’s and registers related to it. Related registers are home location register (HLR), visitor location register (VLR), equipment identity register (EIR), authentication center (AuC) and group call register (GCR). NSS handles the connections between external network and MS. NSS also handles internal connections in the GSM network. These connections are links between two MSC’s and internal connections of MSC. Specified interfaces are defined to the MSC because of the external connections for both speech and data services. In these connections, fixed network numbering and common channel signaling (CCS) are normally used. Because of data services, matching functions against the external networks are defined. MSC is the most important part of the NSS, and its main tasks are to connect, maintain, and discharge connections in the area. The structure of the MSC is almost identical to the structure of switching centers in the fixed networks. The structures of these two different centers are so similar that the switching centers in the fixed network sees the MSC as any digital transit exchange. Compared to the centers in the fixed network, the MSC has special functions related to the e.g. mobility management and connection protect.
  • 14. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 11 One or more BSCs are connected to each MSC on the A-interface. There can also be one or more connections to the centers of the external phone or ISDN networks. It is specified that the MSC must be able to process a great amount of service requests because the processor load of the MSC is multiple compared to the centers in the fixed network. This is a consequence of the great amount of signaling concerning the mobility management, handovers and other signaling functions characteristic of GSM networks. As mentioned above, there can be five registers connected to the MSC, but only two of these five registers are necessary. Necessary registers are HLR and VLR and the remaining three are only possible but not necessary. In the HLR, there are a captured subscriber and billing information and the supplementary services of the number. This information can be permanent or changing. Permanent information includes mobile subscriber ISDN number (MSISDN), international mobile subscriber identity (IMSI), encryption parameters of the subscriber, and the type of the subscriber connection. Changing information, on the other hand, includes elusiveness and routing information, and information of the call transfer. Each subscriber is registered in only one HLR and the operator of the home network makes this. In practice, the HLR is a computer equipped with a large hard disk and this computer is connected to the MSC via the C-interface. VLR contains the subscriber information of each MS outside the home network. When the MS updates at the new MSC area, the VLR of that area requests the subscriber information from the HLR and at the same time updates the location information to the HLR. The subscriber information of the MS will be stored in the VLR as long as the MS stays on the area of that VLR. In addition to HLR, the subscriber information will always be found in one VLR. When the subscriber moves in the network to the area of new VLR the subscriber information of the MS will be deleted from the old VLR and removed to the new VLR. In practice the VLR contains e.g. MSISDN and IMSI numbers, temporary mobile subscriber identity (IMSI), mobile station roaming number (MSRN), and the in-formation about the location area (LA). In addition, the VLR also contains the service specifications and encryption parameter (encryption triplets). One VLR is always integrated on each MSC, and for this reason the mobile switching center is often indicated with acronym MSC/VLR. The VLR is connected to the MSC via the B interface. Because
  • 15. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 12 of the MSC and VLR are always integrated, the B-interface is not specified. VLR is connected to the HLR via the D-interface and the signaling to the other VLR elements is carried out via the G-interface. [Mouly 1992][Penttinen 1999][Nokia 2000][ETSI 2000] Operations Sub-system Operations sub-system (OSS) is not specified very exactly. Consequently, a high degree of freedom of choice is left for the network manufacturers. On the other hand, the interfaces between OSS and other network elements are specified. The OSS has several tasks, which demands connection with BSS or NSS. Most important tasks of the operations sub-system are operation and maintenance of the network and the management of the subscriber information and mobile stations. There are one or more operations and maintenance center (OMC) in the OSS, in which it is possible to install software of the network elements, enter parameters and supervise the statuses of the network elements. OMC is in direct connection to the MSC and the BSC, and to the BTSs via the Abis-interface of the BSC. OMC is usable from the workstations via the man-machine interface (MMI). OMC is connected to the other network elements with strictly specified Q3-interface to enable compatibility between devices of different manufacturers. In practice, this compatibility did never exist so there must be as many OMCs as there are devices from different manufacturers in the network. [Mouly 1992] [Penttinen 1999] [Nokia 2000] 2.2.3GSM mobile stations and SIM cards Each GSM mobile station consists of the actual mobile equipment and the subscriber identity module (SIM) card. The SIM card provides GSM system with the safety functions and flexible adding and removing of services. A mobile station can function on one or more frequencies (multiband) and in several systems (multimode). [Penttinen 2002]
  • 16. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 13 2.3High Speed Circuit Switched Data High Speed Circuit Switched Data (HSCSD) adds many improvements to the basic GSM. The most substantial change is that multiple time slots can be allocated for one connection (1-8). That is called a multislot technique. In addition, the new channel coding increases the bit rate in one time slot from 9,6kbps to 14,4kbps. Because of the circuit-switched nature of HSCSD, the access times to packet data networks, e.g., the Internet and intranets are relatively high. HSCSD is one major competitor to the GPRS competing the title of the fastest mobile data service at the moment. HSCSD has been in use commercially since 1999. RTSLs 9.6 kbps 14.4 kbps 1 9.6kbps 14.4 kbps 2 19.2 kbps 28.8 kbps 3 28.8 kbps 43.2 kbps 4 38.4 kbps 57.6 kbps Table 2.1. Data rates achieved by HSCSD HSCSD terminals are already on the market, but they do not support more than three timeslots downlink and one uplink. They allow GSM high-speed data services for faster web browsing or file transfers. High-speed functionality can be used when a phone or a phone card with HSCSD capabilities is connected to a compatible computer via an infrared (IR) connection, cable, PCMCIA or Bluetooth. As mentioned earlier, the main idea of the HSCSD multislot technique is to use several channels in data transmission. GSM specifications state that the maximum amount of the channels used concurrently is eight but in the HSCSD Phase 1 use of four channels only is supported at once. It is unlikely that networks and terminals would support the functionality of using all eight timeslots for one connection in the near future because of the complexity of the technique. In addition, a network can rarely guarantee the simultaneous use of eight time slots for data for extended time periods. [Penttinen 1999] [Nokia 2000] [Penttinen 2002]
  • 17. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 14 2.4General Packet Radio Service General Packet Radio Service (GPRS) is a packet-switched enhancement of existing GSM networks. It is developed to allow large amounts of data to be sent over cellular networks at speeds three to four times greater than conventional GSM systems. Because GSM is the most widely used mobile system in the world, for most operators GPRS is the easiest and most logical way of offering customers fast simultaneous data services, such as multimedia messaging, gaming, entertainment, and news. GPRS has been implemented in many GSM networks since 2000. Currently 188 telecommunications operators have invested in GPRS technology, 78 networks are already in commercial service. [Ericsson 2003][Penttinen 2002] 2.4.1GPRS in general GPRS is designed for the transmission of bursty data based on the Internet protocol (IP). GPRS uses radio resources only when there is data to be sent or received, and is thus well adapted to the very bursty nature of data applications. One main idea of the GPRS system is that it will not necessarily consume any capacity of the circuit switched functions in the radio path. This is possible because the GPRS system can be parametered to use only the capacity that is left over from the circuit switched calls and data transmission. GPRS takes the advantage of the over-capacity, which would remain unused otherwise (see Figure 2.4.).
  • 18. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 15 Figure 2.4. The usage of the on-demand GPRS channels With GPRS data is handled as a series of packets that can be routed over several paths through the network, rather than as a continuous bit-stream over a dedicated dial-up connection. GPRS splits information into packets, which are transmitted over any available circuit. When there are no packets being sent by one phone, the circuits are made available for data packets from other phones. This makes highly efficient use of available network resources and enables the introduction of always-on mobile communication. In second-generation mobile networks, calls are handled using traditional circuit-switching technology. A dedicated circuit (timeslot) is allocated between two points for the duration of a call. No other phone can use this circuit during the call, regardless of whether any data is being transmitted. GPRS has no dial-up time so it is always connected to the Internet. GPRS offers session establishment times below one second. GPRS users have continuous access to Mobile Internet services for as long as the phone is switched on. In today’s GSM radio networks, individual time slots offer a data rate of 9.6 Kbps (or 14.4 Kbps in some upgraded networks). GPRS uses the same time slots, but can use several at the same time (multislot technique) enabling much higher data rates without having to establish a dedicated connection. The packet-switching capability provided by GPRS is fundamental to the introduction of 3G mobile communications, which builds on IP-based
  • 19. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 16 communications to deliver broadband mobile multimedia services. [Ericsson 2003] [Penttinen 2002] 2.4.2GPRS Architecture The implementation of the packet switched data service causes several changes to the existing GSM network. New network elements will be needed when updating the GSM network for the GPRS use. The BTSs and BSCs of the GSM network will need at least software and possibly hardware updates depending on the device implementation and the version. HLR can be updated in the software level. In addition to all this, an extension to the GSM network is needed, in the form of whole new IP-based GPRS backbone network. The backbone network can be built with the existing infrastructure using for example ATM technique. Due to these changes several new interfaces will be formed compared to the GSM network. [Penttinen 2002] Two new network elements are required to handle GPRS applications: the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN), see Figure 2.5. These new nodes are scalable so operators can plan the network expansion that is most affordable and best fits subscriber’s needs. Operators can start by offering high- speed packet data services using small nodes in selected areas cost-effectively, and then add extra capacity, as it is needed. [Ericsson 2003] The SGSN concentrates on serving and tracking the mobile. It provides packet routing to and from a SGSN service area. The SGSN functions are authentication, session management, Short Message Services (SMS), mobility management and routing. Also, charging and security functions are performed.
  • 20. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 17 Figure 2.5. Structure of GSM/GPRS network (Rantanen 2001) The mobility management (MM) in the GPRS differs from the traditional GSM system. In the GPRS there are three mobility management states named Idle, Standby and Ready. Mobility management of the GPRS includes GPRS-attach and GPRS-detach functions, security functions, routing and location updates, and the activation and deactivation of the PDP context. GPRS differs significantly from the GSM in the case of handovers because there are no handovers in the GPRS. The GPRS system has only cell reselection, which is made autonomously by the mobile. [Penttinen 2002] The GGSN functions as an interface to and from external packet-switched networks. The GGSN is connected with SGSNs via an IP-based GPRS backbone network. The GGSN performs almost the same set of functions as the SGSN excluding SMS. 2.4.3Logical Channels of GPRS In addition to GSM channels, special packet channels to the GPRS are determined. These channels are divided into physical and logical channels. The logical channels
  • 21. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 18 are divided into signaling and traffic channels. Physical channels meant for packet data are called packet data channels (PDCH). A PDCH is a timeslot on a GSM RF- carrier and logical packet data channels are mapped on the physical channels dedicated to packet data traffic. Packet data logical channels can be divided into four groups. [Penttinen 2002] 2.4.4GPRS coding schemes Channel coding is a technique used to protect the transmitted data packets against errors. Four channel coding schemes are defined on GPRS standards for packet data traffic channels. These coding schemes are marked as CS-1…CS-4. CS-1 has highest error correction and lowest data throughput and the channel coding technique it uses is the same as in the SDCCH of the GSM (ETSI Specification GSM 05.04). Coding schemes 2 and 3 are punctured versions from CS-1. In CS-4 channel coding is not used at all. The more efficient channel coding used, the smaller is the proportion of the payload in the emission. Thus, higher data rates are achieved by reducing or removing the error correction bits. Table 2.2. presents the most important parameters for different coding schemes. Class Code rate Payload Data rate (kbps) CS-1 1/2 181 9,05 CS-2 ~2/3 268 13,4 CS-3 ~3/4 312 15,6 CS-4 1 428 21,4 Table 2.2. Most important parameters for GPRS coding schemes. Channel coding schemes have a straight correlation to the C/I ratio in the way that the lower the channel coding scheme used, the better the C/I ratio must be. On account of this, all channel coding schemes have their own dissentient coverage areas. The coverage area achieved with CS-1 is the same class as the coverage areas in the traditional GSM systems with same coding scheme. The weaker the coding scheme used, the smaller the achieved coverage area is. In practice, this means highest data rates near by the base station and lowest near the borders of the coverage areas (see Figure 2.6.). [Penttinen 2002]
  • 22. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 19 Figure 2.6. Principle of the coverage areas achieved with different coding schemes 2.4.5GPRS terminals GPRS terminals (GPRS MS) are divided into three classes according to their functionality: Class A is the most demanding class of GPRS terminals. A terminal of this class is able to establish simultaneous connections both with circuit switched (CS) and packet switched (PS) side of the network. Class A terminals are not available on the market. Class B is able to select automatically either circuit switched or packet switched connection but only one can be active at the time. So if the MS has both CS and PS connection formed another service is in wait condition. Class C terminals cannot be attached to both services at the same time and the selection of the operation mode must be done manually. This class includes a special case, terminals supporting only packet switched services. [Penttinen 2002] 2.5Evolution of GSM Data Services towards EDGE Voice services are still the most important services provided by mobile communications networks. However, the earlier presented enhancements to ordinary
  • 23. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 20 GSM technology bring new possibilities for various data services. At the same time, the importance of other than voice services grows rapidly. The development of mobile data services follows the evolution path of cellular technologies. The first generation analogue cellular systems offered extremely slow and unreliable data connections and identification methods were not well developed. The second-generation digital cellular systems made an improvement to the data services and data rates. In addition, Subscriber Identification Module (SIM) cards in GSM phones improved security and enabled, for example, safe bank connections and using of cellular phones for money transactions. The Short Message Service (SMS) provides guaranteed delivery of small data packets even if the phone is switched off when the message is first sent. Now, second-generation services offer higher bit rates and packet-switched connections. The development path advances towards UMTS and third generation services that offer the ground for many high-speed services. In addition, wearable computers and totally computerized homes can be a part of everyday life after a few years. Wireless Local Area Network (WLAN) products and other possible wireless network applications can have a remarkable role in parallel with advanced cellular network services. 2.5.1Short Message Service Short Message Service (SMS) is included in GSM design to fulfill the customer need for speaking and paging from one single terminal [Mouly 92]. Short Message Service (SMS) can be seen as the first packet-oriented data transmission service implemented in cellular radio networks. According to ETSI standard, the actual SMS message can be up to 160 characters long. However, with some mobile terminals also longer messages can be written, but the text is divided in to several single messages before it is sent to the receiver. SMS messages have been the fastest growing area of mobile telecommunications during the last few years. The current SMS in GSM systems offers people the opportunity to send and receive simple pictures and messages and it also provides a possibility to access different information and entertainment sources such as weather
  • 24. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 21 reports, bus timetables and jokes. Also paying with SMS messages is possible, e.g. tram tickets. SMS transfer will be implemented also in GPRS, EDGE and UMTS. 2.5.2Wireless Access Protocol The Wireless Application Protocol (WAP) is an advanced intelligent messaging service for mobile terminals. The WAP specification is published by WAP Forum, which creates license-free standards for the entire industry to use or develop products. WAP was introduced on markets in 1999 and in 2001 there were over 18 million WAP users and over 50 million WAP-enabled handsets shipped worldwide. In addition to information, messaging and entertainment services, WAP is used for transactions demanding security: banking, finance, and M-commerce. However, WAP has not been as successful as it was meant to be. Currently WAP functions over GSM and GPRS, in the future it can be utilized with EDGE and UMTS terminals. WAP is based on The Wireless Markup Language (WML), which complies with XML standards. It is used in order to provide, for example, Web pages to the mobile devices. The language is designed to enable effective applications within the constraints of handheld devices. WML provides a smaller, telephony aware, set of markup tags. This capability makes it more appropriate to implement within handheld devices than Hypertext Markup Language (HTML). This means that HTML coded pages have to be converted into WML code before they can be used in the WAP mode. [WAPForum 2003] 2.5.3Multimedia Message Service The multimedia message service (MMS) has become a significant issue for mobile operators future growth strategies. MMS is expected to be the most important service for operators, content providers and service providers since MMS will provide them with a new source of revenue now and in the 3G markets. The key to MMS is to maintain the fundamental features that have made SMS a success story, while offering consumers a more versatile and personal experience. MMS will enable consumers to send and receive multimedia messages between mobile terminals as well as between terminals and content servers. MMS messages
  • 25. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 22 combine image, sound and text, and even animation and video. The camera phones, which are currently available, do not produce pictures, which are bigger than 100Kbytes. Now, mobile operators have started to push MMS services seriously. At the start of 2002, only a single operator, Norway’s Telenor, had launched MMS-based picture messaging. By November 2002, over 60 operators worldwide were offering picture messaging. One of the key factors that will determine the answer to whether or not large numbers of consumers will take picture messaging part of their lifestyle is service pricing. MMS-compatible phones are expensive and users will only be persuaded to buy these camera phones if they can afford to use them. The widespread usage of SMS text messaging has been enabled by service pricing which is both easy to understand and fairly cheap. [Nokia 2003][Ovum 2003] 2.5.4HSCSD and GPRS enabled services and data rates in practice Today, HSCSD and GPRS connections are mainly used for accessing email, getting information from the Internet, web surfing in general, entertainment (e.g. downloading video clips, music, etc.), banking and shopping. The data rates achieved by using HSCSD and GPRS with terminals available on the market are quite similar. The current terminals and networks do not support much over 40 kbps data rates in practice – this means slower and more unstable connections than ordinary fixed-line modems can offer. HSCSD connections are more stable compared with GPRS connections because of the circuit-switched nature of HSCSD. Even though, it is not assured, that a HSCSD user gets all the three timeslots his terminal can carry for the downlink traffic. In many cases, circuit-switched speech is prioritized over HSCSD and GPRS traffic and thus timeslots first allocated for data are allocated for speech on the go. In the current GPRS networks only CS-1 and CS-2 coding schemes are used. The average C/I from tested networks leads to 11,5 kbps/timeslot. Therefore in practice, the networks offer “best effort” service quality and slow connections.
  • 26. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 23 Giving data users enough capacity is also a pricing issue. Adding capacity to the network is always an extra investment. Operators in Finland have different pricing strategies and thus also their network parameters for GPRS traffic differ from each other.
  • 27. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 24 3.EDGE technical fundamentals Enhanced Data rates for GSM Evolution (EDGE) is a major enhancement to GSM/GPRS data rates and it improves the GSM air-interface performance significantly. EDGE offers improved data rate through optimized modulation (8- PSK) and it introduces a large number of channel coding schemes along with Incremental Redundancy (IR), Link Adaptation (LA) enhancements and in the near future adaptive multirate AMR. The new modulation and the possibility to adapt the transmission rate to channel quality are the core of the EDGE concept. Introducing EDGE in a GSM network does not imply changes in the basic architecture. In any case, modifications of the Mobile Station (MS), Base Station (BTS) and Base Station Controller (BSC) are needed, which means, among other things, software and hardware upgrades in circuit- and packet-switched parts of the network. EDGE offers both circuit- and packet-switched connections depending on the platform it is implemented in. The scope of the EDGE phase 1 standard is to increase GPRS bit rate, improve GPRS link quality control (EGPRS) and to offer high circuit-switched data rate with fewer timeslots and fast power control (ESCD). The scope of the EDGE phase 2 includes supporting real-time services over EGPRS. GSM networks have already offered advanced data services from single SMS and circuit-switched 9,6 kbps data services to 64kbps HSCSD and 160 kbps (theoretical speed) GPRS. With EDGE, the data rate offered by the original HSCSD or GPRS networks can triple. [Halonen et al 2002]
  • 28. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 25 3.18-PSK modulation in GSM/EDGE standard EDGE is specified to reuse the channel structure, channel width, channel coding and the existing mechanisms and functionality of GSM, HSCSD and GPRS. The enhancement behind tripling the data rates is the introduction of the new modulation type. The modulation type that is used in GSM is the Gaussian minimum shift keying (GMSK), which is a kind of phase modulation. EDGE introduces the octagonal phase shift keying (8-PSK) modulation in addition to the existing GMSK, see Figure 3.1. (d(3k),d(3k+1),d(3k+2))= (0,0,0) (0,1,0) (0,1,1) (0,0,1) (1,1,1) (1,0,1) (1,1,0) (1,0,0) Figure 3.1. 8-PSK signal constellation principle The number of symbols sent within a certain period of time, the symbol rate, remains the same as for GMSK but an 8-PSK signal is able to carry three bits instead of one. The total data rate is therefore increased threefold. An 8-PSK modulated signal is more sensitive to errors and thus the highest data rates can only be achieved with limited coverage. GMSK modulation is more efficient under very poor radio conditions and therefore EDGE coding schemes are a mixture of both GMSK and 8-PSK. [Ericsson 2002][Halonen et al 2002] 3.2Enhanced general packet radio service (EGPRS) Enhanced general packet radio service (EGPRS) is build on top of GPRS. Four different coding schemes are defined for GPRS (CS-1 to CS-4). Each has different amounts of error-correcting coding that is optimized for different radio
  • 29. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 26 environments. For EGPRS nine modulation and coding schemes (MCS) are introduced. Classes MCS-1 – MCS-4 use the basic GSM 0.3 GMSK modulation, whereas classes MCS-5 – MCS-9 use the new 8-PSK modulation. Table 3.1. shows EGPRS modulation and coding schemes along with their maximum throughputs. Table 3.1. EGPRS modulation and coding schemes Another improvement that has been made to EGPRS standard is the ability to retransmit a packet that has not been decoded properly with a more robust coding scheme, whereas for GPRS re-segmentation is not possible. In GPRS once packets have been sent, they must be retransmitted using the original coding scheme even if the radio environment has changed. 3.2.1Link adaptation EGPRS uses automatic link adaptation (LA). LA is used to select the best MCS for the radio link conditions. LA uses the radio link quality measured either by the mobile station or by the base station to select the most appropriate modulation and coding scheme for transmission of packets. Each modulation and channel coding class is optimized for a certain range of C/I (interference) values, outside of which the data rate no longer increases together with the C/I value, but saturates. LA algorithms compare the estimated channel quality to threshold values and that leads to optimized throughput. In reality, the link adaptation may not be close to the ideal situation where the maximum data rate is (as a function of the C/I curve) achieved by switching channel coding class “on the go”. [Ericsson 2002][Halonen et al 2002]
  • 30. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 27 3.2.2Incremental redundancy Another way to choose the optimal channel coding class is to use the incremental redundancy technique (IR). Incremental redundancy initially uses a coding scheme with very little error protection (such as MCS-9) and without consideration for the actual radio link quality. When information is received incorrectly, additional coding is transmitted and the resent information is soft combined in the receiver with the previously received information. IR adjusts the code rate of the transmission to true channel conditions with incremental transmissions of the redundant information until the decoding is successful. For the mobile stations, incremental redundancy support is mandatory in the standard. The information about the radio link is not necessarily to support incremental redundancy. IR gives additional 2-3dB to the radio link. [Ericsson 2002][Halonen et al 2002] 3.3Enhanced circuit switched data (ECSD) Enhanced circuit switched data (ECSD) is based on the current HSCSD is GSM networks. The ECSD architecture is mainly based on HSCSD transmission and signaling. ECSD does not increase the maximum 64 kbps data rate of HSCSD but it makes the network more efficient: the same data rates can be achieved with allocation of fewer timeslots and simpler MS implementation. Circuit-switched data connections up to 64kbps are sufficient for providing various transparent and non-transparent services, e.g. interworking with audio modems and ISDN at various data rates and various video based services ranging from still image transfer to videoconferencing services. In the future, Enhanced Adaptive Multi Rate codec (EAMR) enables the transfer of high-quality speech and music. The same restrictions apply to EAMR connections as apply to ECSD, as EAMR is also circuit-switched. [Halonen et al 2002][Penttinen 2002]
  • 31. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 28 3.4EDGE evolution towards GERAN Rel´5 GSM/EDGE radio access network (GERAN) Rel´5 includes a definition of enhancements to the GPRS radio link interface and will provide support for conversational and streaming service classes as defined for WCDMA. With the adoption of the UMTS Iu interface and the UMTS quality of service (QoS) architecture in Rel´5, GERAN and UTRAN can be efficiently integrated under a single UMTS multi-radio network. In addition, GERAN will include performance enhancements for existing services. GPRS/EDGE Radio Network EDGE BS Network Subsystem BTS BSC MSC/VLR PSTN HLR UTRAN BTS RNC GPRS-backbone BTS RNC SGSN GGSN IP Network UMTS Radio Network Core Network Figure 3.2. A simplified model of the combined GSM GPRS/EDGE and UMTS network (Rantanen 2001) In general, the goals and impacts of GERAN Rel’5 specification are to enable GERAN to the same 3G CN (core network) as UTRAN creating first steps towards efficient resource optimizations in multi-radio networks, and to enable GERAN to provide the same set of services as UTRAN, making the radio technology invisible to the end-user, while allowing operators to efficiently manage the available spectrum. The existing GERAN radio protocols need to undergo significant modifications, and this will increase the complexity of radio interface protocols. In addition, standardization of the GERAN Rel´5 should support a true multi-vendor environment and GSM/EDGE radio access should be backwards compatible, i.e.
  • 32. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 29 support of services for pre-Rel’5 terminals must be ensured. [Ericsson 2002] [Halonen et al 2002] 3.4.1GERAN Rel´5 features In the 3rd Generation Partnership Project (3GPP) Rel´5 overall, the most significant new functionality is the Internet multimedia subsystem (IMS). From the GERAN perspective, the support for the IMS services implies introduction of the Iu interface, and definition of the header adaptation mechanism for the real-time protocol (RTP), user datagram protocol (UDP), and Internet protocol (IP) traffic. Rel´5 includes also major enhancements for speech: wideband AMR speech for enhanced speech quality, half-rate 8-PSK speech for improved speech capacity, and fast power control for speech. In addition to the abovementioned enhancements, Rel’5 implies location service enhancements for Gb and Iu interfaces and inter-BSC and BSC/RNC network assisted cell change (NACC). [Halonen et al 2002] 3.4.2GERAN Rel´5 system architecture To connect to the WCDMA/GPRS core networks, GERAN will use the Iu interface, as shown in Figure 3.3. The Iu interface connects to the circuit-switched domain (Iu- cs) and to the packet-switched domain of the core network (Iu-ps). GERAN also connects to the second-generation core network nodes by using the A and Gb interfaces. These interfaces remain intact in Rel’5 to support Rel’99 terminals. Iu-ps interface is not used for Rel´99 terminals because the functional split between the radio access network and the core network differ substantially between Iu and A/Gb.
  • 33. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 30 GERAN BSS Iur-g MS A BTS Gb Um BSC MS BTS Iu Iur-g UTRAN RNC GSM/WCDMA Core Network Figure 3.3. GERAN architecture in Rel’5 The radio interface Um between GERAN and the mobile station is based on the Rel ´99 radio interface link specifications. However, several modifications are needed on radio link protocol layers in order to provide adequate radio bearers for real-time services. These modifications imply to support for cell reselection for packet- switched domain, separation of user and control planes, and transparent modes in the radio link protocol layers. [Ericsson 2002][Halonen et al 2002] 3.5Modifications to the GSM network imposed by EDGE The implementation of GSM EDGE requires basically only TRX change to EDGE TRXs in the GSM base stations and software updates to GSM BSC and GPRS IP- backbone. A bigger investment would most probably be the upgrade of Abis interface from 16 kbit/timeslot connection to EDGE capable 64 kbit/timeslot connection. [Rantanen 2001] The impact of EGPRS on the existing GSM/GPRS network is limited to the base station system due to the minor differences between GPRS and EGPRS. A new transceiver unit capable of handling EDGE modulation as well as new software that
  • 34. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 31 enables the new protocol for packets over the radio interface in both the base station and base station controller. The core network remains intact. [Ericsson 2002] OS S 2 G S GS N GGS N BTS G n BS C Iu A-bis A MS C BTS GS M/EDGE Figure 3.4. EDGE implementation [Auramo 2002] In Ericsson case, EDGE is compatible with recent equipment. If an operator has an Ericsson RBS 2000 macro base station from 1995 or later, it is easy to take on EDGE. Some additional hardware using plug-in transceivers, and new software that can be installed remotely is all that is needed for operators to start offering high- quality Mobile Internet services over their existing infrastructure. [Ericsson 2003] In Figure 3.4, the elements for EDGE implementation are shown. 3.5.1EDGE radio network planning compared with GSM/GPRS planning If we think the implementation of EDGE of the radio network planning perspective, the same principles as in the GSM/GPRS network planning apply. As in GPRS, EDGE performance is dependent on the achievable C/I (and RXlev) in the network. The most effective means to gain high performance in good radio conditions is to come up with a optimized frequency plan. Frequency plan optimization can make a significant difference for the achievable throughput.
  • 35. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 32 TRX requirements Interference matrix Propagation Coverage Frequency • co-channel estimations Analysis plan • adjacent channel Separation constraints Figure 3.5. EDGE network planning EDGE deployment doesn’t bring dramatic changes to radio network planning with GPRS. Main concerns are the allocation of capacity and steering of traffic to wanted layer/cell/TRX. EDGE network planning process is shown in Figure 3.5. Changes to transmission capacity will be needed, if larger scale EDGE deployment per cell/area is done. The easiest way to implement EDGE from the network planning point of view is the TRX replacing strategy, where new frequency plan is not mandatory. The replacing can be done for every 1-3rd site to achieve coverage and EDGE services e.g. hotspots or rural area can be selected for EDGE, but with limited amount of data throughput. Higher data amounts with EDGE can be offered if it is implemented by bringing an additional EDGE TRX dedicated to data usage to (some of) the cells in the network and/or by reserving more timeslots for the use of EDGE data users from the TRXs. However, that leads to decrease in the GoS experienced by the speech users. In real life these actions are not always possible to perform and they will require significantly more implementation and planning work. In order to utilise EDGE performance in full, a totally new frequency plan and possibly new GSM cell structure are required.
  • 36. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 33 4.Vendors EDGE strategies Due to the delays in UMTS implementation compared to the early predictions, most vendors have taken EDGE back to the table. EDGE as a technology was firstly developed to support the GSM evolution towards 3G in especially US markets. As UMTS hype began in 1999/2000 EDGE was put to less priority among most of the vendors, because UMTS implementation seemed to happen so fast and with large scale that it was natural to shift all focus to support this. After the enormous UMTS license fees most of the operators’ capabilities to invest in to the networks were decreased significantly. At the same time making the UMTS technology work needed more work from the vendors than anticipated, which together with the operators decreased investment capabilities caused the delays in UMTS implementation. EDGE was again an issue, because the needed investments on it are a fraction of those needed for UMTS and the end user performance is quite close to UMTS in the beginning. Of course the capacity offered by UMTS is enormous compared to EDGE, but as there is no pressure on the capacity side for the operators (because the data traffic haven’t proved to increase still) UMTS capacity is not really needed yet. When the US operators, for example AT&T, started to implement EDGE capable HW as they decided to go for the GSM evolution towards 3G rather than IS-95 based, there was suddenly a need for the operators to start making EDGE terminals as well. As the biggest reason for the US operators to choose GSM based system is the roaming traffic gained globally, there is a clear need to have EDGE happening in
  • 37. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 34 the Europe and Asia as well. This was the reason why EDGE marketing started again with full steam for European operators as well by the biggest vendors. The biggest two vendors, Nokia and Ericsson, are the most active with EDGE marketing. Nokia has been clearly the market maker in Europe and Asia Pacific for EDGE. It’s of course in interests of all the vendors to make EDGE a success, but due to its strong position in terminal market, Nokia is in better position to drive the market than it’s competitors. Ericsson has clearly taken a follower role in EDGE market, focusing clearly on driving the UMTS market. This is also partly due to the difficult financial situation of Ericsson currently, where the ability to take risks in new market areas is limited. When the two vendors are compared from the point of view of needed increments to the legacy network infrastructure (to make EDGE possible), Ericsson is in stronger position than Nokia with better applicability of the older infrastructure in the field. All the other noticeable GSM network vendors (Siemens, Alcatel, Motorola, Nortel) have taken a reactive role with EDGE, waiting for the market to start up. Outside USA there has been little marketing done for EDGE by these vendors and they are clearly waiting and seeing whether the big vendors (mainly Nokia) can have the market created for EDGE and then jumping on board. Of course they all have EDGE infrastructure and terminals as well in their road-maps, but they are not put into number one priority and committed on. The problem with EDGE is for a network vendor that it has been earlier positioned as 3G technology thus competing with the UMTS market. So, as the potential UMTS market is clearly bigger than EDGE, it has been decided by most vendors not to drive EDGE strongly towards their customers. This could have an negative effect on the UMTS sales. The answer is to position EDGE more as a enhancement to existing GPRS networks and to co-exist with UMTS. Currently as first Nokia and then Sony-Ericsson have committed to bring EDGE terminals to Europe-Asia GSM bands as well, it seems that the market is clearly starting. The availability of terminals and thus necessary penetration is in vital role in possible EDGE success.
  • 38. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 35 5.Services enabled by EDGE The Release 99 EDGE implementation does not offer significant new possibilities for services compared with the current HSCSD and GPRS networks. As mentioned before, circuit-switched data connections up to 64kbps are sufficient for providing various transparent and non-transparent services, e.g. interworking with audio modems and ISDN at various data rates and various video based services ranging from still image transfer to videoconferencing services. Packet-switched connections are optimal for bursty data traffic, e.g. web browsing and email. In Rel’5 UMTS 3GPP traffic classes are enabled in EDGE and thus 3G services delivery across all frequency bands and bearers becomes possible. Handovers across GSM/EDGE/WCDMA are enabled from the start. However, there are still uncertainties in standardization of Rel´5 and the Iu interface. When compared to GPRS phase 1 QoS classification, the QoS grouping of UMTS release 99 takes into account the applications that will become available through the increased data rates of UMTS and EDGE. The main distinguishing factor between the traffic classes is the sensitiveness of applications, as presented in Table 5.1. [Rantanen 2001]
  • 39. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 36 Traffic class Example of application Fundamental characteristics Conversational Voice and video Preserve time relation between class telephony information elements, low delay Streaming Real time Preserve time relation between, class streaming video low level retransmission Interactive Web browsing and real Preservation of content, class time control channels retransmission, "request response" Background Downloading of files Delay insensitive, preservation of class and email content, retransmission Table 5.1. QoS classes for UMTS and EDGE Conversational and streaming classes are mainly intended to be used to carry real- time traffic flows. The main difference between them is the delay sensitiveness of the classes. Interactive class and background class are mainly meant to be used by the Internet type applications e.g. web browsing and e-mail. Due to looser delay requirements compared to conversational and streaming classes, both provide better error recovery by means of retransmission. Voice Conversational Voice Info tainment Video telephony Communication FAX Transaction WCDMA Collaborative working services Conversational Video s treaming Advertis ing Streaming Corporate solutions Audio s treaming Gaming Conversational Corporate Data Access Interactive E-mail EGPRS WEB Browsing WAP Applications GPRS Conversational Multimedia Messaging Background Audio clip downl. Short Messaging Video clip downl. Data rate 0 8 16 48 128 473 24 08 Figure 5.1.Service QoS Requirements for Bearers, Data rates and services 2003 [Auramo 2002] The main difference between interactive and background class is that interactive class traffic will have higher priority in scheduling than the background class traffic.
  • 40. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 37 This means that background applications may use transmission resources only when other applications do not need them. [Halonen et al 2002] Although the conversational class is specified in the QoS classes of UMTS release 99, the most delay-critical applications such as speech and video telephony will be carried on circuit-switched bearers in the first phase of the third generation mobile networks. Later it will be possible to support delay-critical services as packet data with QoS functions. Different QoS requirements of services are shown in Figure 5.1.
  • 41. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 38 6.Terminal availability The first terminals for EDGE will be on the market by 2H2003 by Nokia and Motorola. These are aimed for the US market, but will have also European GSM frequencies available. For example the Nokia 6200 will have GSM 1900/1800/800 frequencies and support for MCS1-9. With the same timetable Nokia will also introduce an EDGE terminal with GSM 900 frequency available. The Motorola t725 will have also both European frequencies imbedded and supports MCS1-9. The t725 will be available by 2H2003. Sony-Ericsson has also said that it will bring EDGE capable terminals for both European and US markets in the second half of 2003. An interesting product will be also the PC-card with GPRS/EDGE from Sony-Ericsson, which will be available also in the second half of 2003.
  • 42. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 39 Nokia 6200 Motorola t725 The most important fact when EDGE terminals are considered is the information given by Nokia, that it will include EDGE to all of its GPRS terminals that are introduced after 6/2003. Nokia has also said that it will have EDGE included in all of its terminal categories from the beginning of 2004. This is extremely good news for EDGE, since it almost positively ensures that the terminal penetration will start to develop and that other vendors will join in manufacturing EDGE terminals. It also gives operators a positive signal to include EDGE in their network evolution strategy as a realistic option.
  • 43. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 40 7.Investment costs and revenues caused by EDGE EDGE is a further development of the GSM/GPRS networks and thus it can be integrated in the already established GSM/GPRS networks with relatively low investment. Beside from the hardware and software upgrades, it only affects the network by increasing capacity and data rates. The cost of operation will not increase. Operators can deploy EDGE using the existing GSM spectrum. EDGE has higher spectral efficiency than GSM/GPRS and thus there is free capacity for carrying more data and voice traffic and for serving more subscribers. The size of the investments on EDGE depends on the operator. The worst case is that large part of the network infrastructure is old enough to not support easy EDGE implementation. The capability of the infrastructure depends of the network vendor. In some cases the base stations must be fully replaced by newer ones before EDGE can be implemented. In typical cases only EDGE capable TRXs and BSS software must be implemented along with changes to Abis interface capacity. If the network infrastructure is new enough, the base stations can be already equipped with EDGE capable TRXs. Then only software and enhanced transmission capacity must be implemented and thus costs can be kept quite minimal. In typical cases of operators’ network evolution the changes are made concurrently as much as possible. This means that for example if the network infrastructure is old enough to require new base stations if EDGE is considered, can the changes planned
  • 44. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 41 so that UMTS/EDGE capable base stations are introduced at the same time. This lowers the needed investments (and the operational expenses) for EDGE, which would separately be quite enormous. Similarly EDGE capable infrastructure can be moved to replace older infrastructure in the needed areas if available. This also makes the investments lower. Depending on the situation of the operator, the following costs are related to EDGE implementation: • EDGE capable GSM/GPRS base stations • EDGE capable TRXs • EDGE capable BSS software • Enhancements to Abis capacity • NMS/OMC changes • Possible upgrades to GPRS core network • Network planning costs (site configuration planning, frequency planning etc.) • Operational costs of implementation Since the investments needed for EDGE are highly dependant on operators network, strategy and cost structure and network vendor’s capability and pricing towards a specific operator, it’s quite impossible to give generic cases of the needed total investments. It can however be said that they are a fraction of that needed for UMTS. EDGE can be implemented to every third site for example, so it enables lots of different capacity/coverage strategies, which can be used to optimize the costs involved. Some practical cases have shown that the pricing for EDGE TRXs and BSS software is quite similar or only a bit higher to that of GPRS equipment. This can also be due to the fact that the vendors need the reference networks up and running, which usually means that the margins for the sales are kept lower than usual. As the EDGE capable terminals reach a feasible penetration percentage, the data traffic is more economical to be served with EDGE rather than GPRS, this is
  • 45. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 42 because the capacity provided by EDGE is almost 3-fold compared to GPRS, with relatively small investments needed. This fact also allows more capacity for speech service, taken that the network is parameterized accordingly. This enables greater revenues for an operator. Also the higher throughput offered by EDGE for the users can be priced higher than the conventional GPRS. Later if the GERAN offers same QoS functions as UTMS it will create even more possibilities to generate revenue from the users.
  • 46. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 43 8.EDGE investment strategies Different second-generation systems have different evolution paths towards third generation IMT-2000 services. Network operators that are not granted UMTS licenses can implement EDGE to offer IMT-2000 alike services. However, an operator with UMTS license may still deploy EDGE to create a wireless data market before third generation CDMA systems are launched or use EDGE in areas where there is no UMTS service. 8.1GSM operators without 3G licenses For those operators without 3G license, EDGE offers a pretty straightforward business case as a stepping stone before UMTS. Of course an operator can choose not to go for UMTS at all and offer high data rate services with GPRS/EDGE network. This type of stepping stone approach is currently used by some of the US operators (such as AT&T), which have not decided the UMTS bandwidth and are implementing GSM-EDGE networks as this is written. In Europe most of the countries have already granted their licenses so there are very few left to implement this strategy. In Asia, there is a technology standard war going on between CDMA2000, WCDMA and TD-SCDMA. In this area EDGE is clearly seen as a less attractive option. EDGE as a stepping stone to UMTS can be seen only feasible in markets with no strong UMTS commitment: No licenses yet awarded or they are very inexpensive or
  • 47. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 44 no present market push for 3G or if the GSM business is still developing. Besides US, this kind of situation exists e.g. in East-Europe. Although if the first UMTS launches (e.g. Hutchison UK, Italy) are successes and UMTS terminals come faster to market and are more strongly subsided than the EDGE terminals, then the window for EDGE feasible will become smaller rapidly for this type of strategy. The only clear situation is in the US, because they will not have UMTS licenses awarded for some time. If this type of strategy is chosen by the operator, all the services can/will have to be planned on top of GSM-EDGE. This means that if for example streaming services are to be offered must EDGE standardization support this. In the first releases of EDGE the QoS will be similar to GPRS, which doesn’t enable similar services as can be offered by the UMTS. EDGE as a stepping stone can require EDGE to be implemented over the network, which of course will make the investments bigger as well. If the network is built directly to support EDGE then the investments can be made smaller. Of course EDGE can be implemented only to e.g. cities and GPRS elsewhere, which lowers the incremental costs. 8.2GSM operators with 3G license EDGE and WCDMA can also be complementary 3G technologies that together will sustain the operator’s need for nation-wide mobile data and speech capacity during the expected traffic boom. They are both IMT-2000 capable radio access technologies in different frequency bands. They can both provide 3G services for the end-user, accessing a common core network, given that the Iu-interface is standardized to be supported by the GERAN as well. Possible business cases for the operator with a UMTS license are for example the following: EDGE used as a complementary solution, to different coverage areas. In this case EDGE is implemented e.g. to more rural areas and UMTS to the cities and sub- urbans and main roads. This case makes it possible to offer high-data rate services also in the areas where UMTS coverage is not available. The investments of EDGE
  • 48. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 45 implementation can be made lower by guaranteeing that the infrastructure in the “EDGE areas” is the most EDGE capable one, if possible by swapping. This case requires though that there will be multi-mode terminals available quite rapidly (i.e. UMTS/EDGE/GPRS), because otherwise the experienced throughput can be higher in the rural areas than in the cities, which is not very feasible. EDGE and UMTS co-exist, for different user segments. In this case EDGE and UMTS are implemented to same coverage areas, but used to serve different user segments. For example EDGE could be used to offer robust data for corporate access and UMTS to offer fancy 3G services, such as video streaming etc. This case will require quite large investments, because EDGE is to be implemented over the network or at least to most locations. This case would also require that there would not be multi-mode terminals widely available very rapidly, so the segmentation could be made more easily through terminals.
  • 49. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 46 9.Future role of EDGE In Figure 9.1, the current situation of EDGE globally is depicted. Global EDGE Status China: Europe: Political WCDMA US+Canada: commitments technology EDGE roll-outs to every commitment. on the way and technology. EDGE will be Strong need No rush to deployed for delaying 3G. No public during 2003 UMTS roll-outs EDGE commitments Growing yet APAC: interest Latin America: Market follows global towards EDGE, Will eventually trends. “Ongoing but no public follow US. technology standard commitments war”. Also public yet. commitments to EDGE Figure 9.1. Global situation of EDGE As can be seen from Figure 9.1, the only market areas in which public commitments to EDGE have been made is the US and Asia Pacific. In Europe, which is the key market area for a larger scale EDGE success, has not yet seen any public EDGE commitments from the operators. Although the biggest vendors claim to have multiple contracts for EDGE deliveries, no of them are public yet in Europe.
  • 50. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 47 The future role of EDGE depends very highly on the following: • The success of EDGE in USA • The availability of EDGE terminals • The early success of UMTS • Subsidisation of UMTS terminals • The completeness of EDGE standardization The biggest guarantee that EDGE will become one of the steps of GSM network evolution, which be implemented as well, is the availability of EDGE capable terminals. This has already happened as Nokia & Motorola will bring the terminals by the 2H of 2003. Basically this was obvious after the big US vendors started to implement GSM-EDGE networks. The only question mark is whether EDGE will be widely deployed or will it become a niche technology. This depends much on the early success of UMTS in Europe. If the first implementations in 1H2003 succeed, which will bring in more network launches in 2H2003 and 1H2004, then EDGE will more probably stay as a niche technology deployed only to part of the networks. This is because when UMTS succeeds, the focus of the industry is again shifted to UMTS and the investments on GSM networks will be minimized. Then EDGE will probably experience similar situation as HSCSD did. Most probably there will be also operators, which will not go for UMTS in the near future and for those EDGE offers a feasible solution. Altogether early UMTS success would make EDGE a niche technology. If UMTS success won’t happen in short term, due to for example technical difficulties, then EDGE has a better chance to become a widely deployed technology. In this case there will be wider range of EDGE terminals available before UMTS is deployed in larger scale. This will also bring in more EDGE operators as the investments on network technology are considerably smaller. The long-term success of EDGE is also dependant on the operators strategy on driving UMTS with terminal subsidization. This is easily the case in countries where the license terms are tight and demand a quite rapid and wide UMTS deployment.
  • 51. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 48 The most probable case is that EDGE will live alongside UMTS and will in most cases be used as a geographical complement to UMTS. The UMTS early success is not very likely, so it will give operators a chance to consider EDGE as well (which is already ready as a technology) and invest still to their GSM networks. Also as the technology develops in the future, it will be more likely that EDGE will be included in the terminals very cheaply in the long run. This makes the multi-mode terminal manufacturing more feasible to the vendors. So it seems that EDGE will have a relatively good future ahead, especially in those countries, which don’t have too tight UMTS license terms for the operators or have granted licenses cheap. In the long run the standardization must succeed to include the Iu-interface support to GERAN, otherwise EDGE can easily be positioned as the “poor man’s UMTS” in the market as similar QoS and services cannot be offered.
  • 52. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 49 10.Conclusions EDGE is relatively easy and cheap to bring to the operators network. It demands for significantly minor changes to the operational side as well. This means that it can be quite attractive for an operator, which have not made strong commitments to UMTS. EDGE uses 8-PSK modulation, which enables approximately 2,5 times the performance or capacity of GPRS. This new modulation scheme requires new radio parts for the terminals as well, which means that new terminals must be introduced from the vendors and the penetration of the EDGE capable terminals grow enough before this capacity gain compared to GPRS can be fully utilized by the operators. At the moment there are commitments made from the biggest vendors to introduce EDGE terminals by 2H2003. The size of the investments on EDGE depends on the operator. The worst case is that large part of the network infrastructure is old enough to not support easy EDGE implementation. The capability of the infrastructure depends of the network vendor. In some cases the base stations must be fully replaced by newer ones before EDGE can be implemented. In typical cases only EDGE capable TRXs and BSS software must be implemented along with changes to Abis interface capacity. If the network infrastructure is new enough, the base stations can be already equipped with EDGE capable TRXs. Then only software and enhanced transmission capacity must be implemented and thus costs can be kept quite minimal. The strategy for an operator to choose on EDGE depends on many things. Most of it can be even personal (preferences of decision making people) or contractual
  • 53. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 50 (towards vendors) reasons, which drive the network evolution. But in principle one deciding factor is the commitment towards UMTS and the license terms of the UMTS license. For those operators without 3G license, EDGE offers a pretty straightforward business case as a stepping stone before UMTS. For operators with UMTS license a strategy of EDGE and UMTS co-exist, but for different user segments, can be useful if EDGE is decided to be deployed as widely as (or wider than) UMTS. Another strategy can be seen to deploy EDGE as a complementary solution, to different coverage areas. This is the most feasible strategy if there are multi-mode terminals available widely. The future role of EDGE depends very highly on the success of EDGE in USA, the availability of EDGE terminals, the early success of UMTS, subsidization of UMTS terminals and the completeness of EDGE standardization. The most probable case is that EDGE will live alongside UMTS and will in most cases be used as a geographical complement to UMTS. The UMTS early success is not very likely, so it will give operators a chance to consider EDGE as well (which is already ready as a technology) and invest still to their GSM networks. Also as the technology develops in the future, it will be more likely that EDGE will be included in the terminals very cheaply in the long run. This makes the multi-mode terminal manufacturing more feasible to the vendors. So it seems that EDGE will have a relatively good future ahead, especially in those countries, which don’t have too tight UMTS license terms for the operators or have granted licenses cheap. In the long run the standardization must succeed to include the Iu-interface support to GERAN.
  • 54. Tik-109.551 Positioning EDGE in the mobile network evolution Spring 2003 References Auramo 2002 Auramo J. 2002. Enhance Your GSM Networks to 3G with EDGE. Presentation. Nokia. Ericsson 2002 http://www.ericsson.com/products/white_papers_pdf/ edge_wp_technical.pdf Ericsson 2003 www.ericsson.com, accessed 2003 ETSI 2000 ETSI. 2000. ETSI GSM 03.08, V7.4.0, Organization of Subscriber Data. ETSI. GSMWorld 2003 www.gsmworld.com, accessed 2003 Halonen et al 2002 Halonen T., Romero J., Melero J. 2002. GSM, GPRS and EDGE performance - Evolution towards 3G/UMTS. Wiley. Mouly 1992 Mouly, M. & Pautet. 1992. The GSM System for Mobile Communications. Published by the authors. Nokia 2000 Nokia Networks Oy. 2000. NED (Nokia electronic documents) viewer version 3.11. Nokia Networks Oy. Nokia 2003 http://www.nokia.com/, accessed 2003 Ovum 2003 http://www.ovum.com/go/ovumcomments/016489.htm, accessed 2003 Penttinen 1999 Penttinen, Jyrki. 1999. GSM-tekniikka; Järjestelmän toiminta, palvelut ja suunnittelu. (GSM Technique; Function, Services and Planning of the System, in Finnish). Porvoo: WSOY. Penttinen 2002 Penttinen Jyrki. 2002.GPRS in Wireless Data. WSOY Rantanen 2001 Rantanen J. 2001. The Third Generation Cellular Network Solutions from Operator’s Perspective. Master’s thesis. TKK. WAPForum 2003 http://www.wapforum.org/, accessed 2003

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