1. 2G/Digital Wireless Technologies EECS4215 – Mobile Communications York University 1

2. Outline Overview of Cellular Network Generations Development and History of Digital Cellular Technology Digital Wireless Advantages over Analog Cellular Systems Global System for Mobile Communication Technology 2

3. Cellular Generations Overview (8.1) 1G 2G, 2.5G, 2.75G 3G, 3.5G (HSPA), 3.75G (HSPA+) 4G 3

4. Evolution of Cellular Networks 4

5. Cellular Generations Matrix Cellular Generation TechnologiesKey DifferentiatorsPractical Timeframe Official Sunset Date 1G AMPS (USA) TACS (Europe) J-TACS (Japan) Frequency reuse; analog systems 1983-1996February, 2008 2G (Voice) TDMA (IS-54; IS-136); GSM; CDMA (IS-95) First all-digital systems; used sectorization 1992-presentProjected: 2016 2.5G GPRSGSM-based; 171 Kbps transmission speed 2000-2011Beginning in 2012 2.75G (or 2.9G) EDGEGSM-based; 384 Kbps transmission speed 2003-presentTBD 3G UMTS; CDMA2000 (1xEV-DO); WiMAX Multimedia transmissions2002-presentTBD 3.5G HSPA14.4 Mbps downlink speed2006-presentTBD 3.75G HSPA+42 Mbps downlink speed2010-presentTBD 4G LTEDownload speed in tons of megabits 2010-presentTBD 5

6. 1G Networks Launched in early 1980s. Transmitting only voice. Used “frequency reuse” concept. Prominent 1G networks were: – AMPS (Advanced Mobile phone System) – Nordic NMT (Nordic Mobile Telephone) – European TACS (Total Access Communication System) – J-TACS 6

7. 2G Networks First all-digital cellular systems. Launched in early-to-mid 1990s. Mobile-assisted handoff capabilities. Prominent 2G networks: – GSM – cdmaOne (IS-95A/B) – D-AMPS (IS-136) 7

8. 2.5G and 2.75G Networks 2.5G: – Included GPRS and CDMA2000 1x technologies – Data rates up to about 144 Kbps 2.75G: – GSM-based EDGE wireless data technology – Sometimes also labeled as “2.9G” 8

9. 3G Networks Third generation networks. Having data rates of 384 Kbps and higher. Prominent 3G networks: – UMTS (Universal Mobile Telecommunication Service) In United States: – UMTS and CDMA2000 1xEV-DO have been deployed FDD means different frequencies are used. TDD means one frequency is used in both up and down links. 9

10. 3.5G and 3.75G Networks 3.5G (HSPA – High-speed packet access): – Evolved from UMTS 3.75G (HSPA+) 10

11. 4G Networks Consists of WiMAX and Long-term evolution (LTE). WiMAX never really “caught on” in the industry. True 4G technology is LTE Advanced (LTE-A). 11

12. Development and History of Digital Cellular Technology GSM and CDMA are still operational within carrier networks: – Not the first-choice technology to carry traffic – Hanging around for multiple regulatory and operational reasons By around 2016, most wireless carriers will officially “sunset” 2G technologies. 12

13. Performance of Cellular Systems Performance of cellular systems is restricted primarily by co-channel interference. Until around 1992, cellular carriers had always used analog technology and 850-MHz spectrum in their networks. 13

14. Early Problems to Cellular Carriers By the mid-1990s, the critical problem for 850- MHz cellular carriers became system capacity. Frequency division multiple access (FDMA), an earliest multiple-access methods used to derive more capacity. 14

15. Cell Splits From 1983 until the early 1990s, the only option to increase the system capacity was to do cell splits. This method still didn’t produce enough additional capacity, wireless carriers turned to digital wireless technologies to augment network capacity. 15

16. Illustrating Cell Splits Notice that the coverage area stays the same; yet there are three base stations in place after the cell split instead of two. So there is a 33 percent increase in coverage and capacity in the same geographic area after the cell split occurs. 16

17. Digital Wireless Technology In 1992, the first digital wireless technology in the US, known as IS-54 or “D-AMPS” (digital AMPS): – used time division multiple access (TDMA) technology in order to increase system capacity 17

18. Digital-Radio Technology In the early-to-mid-1990s, three types of digital- radio technology were used around the world: – IS-136 (TDMA), which evolved from IS-54 D-AMPS, global system for mobile (GSM) communication, and code division multiple access (CDMA). IS-136 is now a dead technology – GSM has evolved over the years into more advanced digital wireless technologies such as UMTS and HSPA – CDMA technology, like GSM, has evolved into more advanced digital wireless technologies as well 18

19. Digital Wireless Advantages over Analog Cellular Systems Support substantially larger amounts of capacity than the legacy analog (AMPS) system. Digital base stations cost far less than analog base stations. Produce cleaner and quieter signals. Provide greater security: – Nearly impossible to hack, especially CDMA systems. 19

20. Digital Wireless Advantages over Analog Cellular Systems (2) No cloning fraud. Fraudsters could access AMPS control channel transmissions. Smaller and more lightweight handsets. Mobile handset has a role in determining when a call-handoff is required, and to what cell or cells the handoff occurs: – Decreases the potential for dropped calls during the handoff process Use bit error rate (BER) and frame error rate (FER) measurements instead of dB to assess interference. 20

21. Global System for Mobile Communication Technology GSM technology is a TDMA technology: – TDMA systems assign both different frequencies (FDMA) and different time slots (TDMA) to each transmission. Separate channels exist for uplink and downlink transmissions. 21

22. GSM and Incompatible Cellular Systems At the time GSM was developed: – Six incompatible cellular systems were in operation throughout Europe – A mobile phone designed for one system could not be used with another system Groupe Special Mobile (GSM) to develop a digital cellular standard for the European market. Later, GSM = Global System for Mobile communications 22

23. Initial Era of GSM The first systems were activated in 1991. Commercial service began in 1992 and, by 1996, there were over 35 million GSM customers being served by over 200 GSM networks. GSM has been deployed in the 900-, 1800-, and 1900-MHz frequency bands. 23

24. Initial Era of GSM (2) Many of the American PCS carriers chose GSM as their digital radio wireless standard in late 1995. A full-rate vocoder allows for eight users (conversations) over a 200-kHz channel (carrier): – Each channel occupies 25 kHz – Each GSM channel transports eight calls simultaneously 24

25. GSM 200-kHz Channel/Frame GSM 200-kHz channel/frame and (eight) time slots. MS = mobile station. 25

26. GSM Architecture Multiple 200-kHz channels will be assigned to each base station. One time slot must be allocated for control channel purposes: – Up to seven subscribers can use a 200-kHz channel simultaneously 26

27. GSM Subsystems GSM networks are divided into four subsystems: 1.The base station subsystem (BSS) 2.The network subsystem (NSS) 3.The operations and support subsystem (OSS) 4.The mobile station subsystem 27

28. 1 - The Base Station Subsystem The base station subsystem is comprised of: – Base station controller (BSC) – Base transceiver station (BTS) – The air interface The BTS consists of the antenna and the radio transceiver at the base station. 28

29. GSM Network Architecture The GSM network architecture. Note the various subsystems. MSCs can always connect to other MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations and support subsystem. 29

30. Base Station Controller (BSC) The BSC is the control computer that manages many BTSs: – Usually housed at the MTSO location – Manages which radio channels are being used by which BTSs – Also manages the call-handoff process between BTSs – Regulates the transmit power levels of the base stations and mobile handsets 30

31. Base station controller (2) – As a handset gets closer (farther from) to the tower, the BSC signals the mobile to lower (increase) its transmitter power levels. – Handle overheads associated with frequency management, call setup, and call-handoff 31

32. 2 - The Network Subsystem The MTSO-based switch is the central component of the network. Authentication center: – Equipment Identity Register (EIR) 32

33. MTSO-based Switch Provides connection to the landline PSTN. Provides subscriber management functions: – Mobile registration – Location updating – Authentication – Call routing to a roaming subscriber Houses the home location register (HLR): – HLR is a database that registers users in a cellular network – VLR: database that registers visitors 33

34. GSM Network Architecture The GSM network architecture. Note the various subsystems. MSCs can always connect to other MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations and support subsystem. 34

35. Authentication Center (AuC) Part of the network subsystem Provides the parameters needed for authentication and encryption functions. The Equipment Identity Register (EIR) is a database used for security and holds records for three types of mobile phones: – Black: barred (e.g., stolen) – Grey: to be tracked; may be used in network – White: valid phones 35

36. IMEI (International Mobile Equipment Identity) When a mobile phone requests service from the network, its IMEI is checked against the EIR to assess which category the mobile phone is placed in. Every GSM handset manufactured has a unique identification number known as IMEI. The IMEI number is a unique 15-character number for every valid phone that a GSM network uses to identify a mobile phone. 36

37. IMEI (2) It is assigned to the phone in the factory. If a subscriber’s phone gets stolen, the IMEI number can be blocked, rendering it useless. It is unique and no two cell phones will have the same original number. – The word “original” is used here because the IMEI can be changed with special software and a unique cable. New IMEIs can be programmed into stolen handsets – 10% of IMEIs are not unique, per BT-Cellnet. 37

38. IMEI (3) You can see the IMEI number of your phone by dialing *#06# from the keypad. The IMEI number of each handset is stored in the EIR: – If the handset has been lost or stolen, the IMEI is placed on the black list of the EIR and will not work on the network. 38

39. 3 - The Operations and Support Subsystem (OSS) It is the command center that is used to monitor and control the GSM network. If a major outage occurs at a base station, the OSS can determine where that BTS is located, what type of failure occurred, and what equipment the site engineer will need to repair the failure. 39

40. GSM Network Architecture The GSM network architecture. Note the various subsystems. MSCs can always connect to other MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations and support subsystem. 40

41. 4 - The Mobile Station Subsystem Consists of two components: – The mobile handset – The subscriber identity module (SIM) 41

42. The Mobile Handset The handset in a GSM network is different from analog phones. The identification information of the subscriber is programmed into the SIM module and not the handset itself. 42

43. The SIM The SIM is a microcontroller embedded into a small piece of plastic, which holds the GSM operating program and customer and carrier-specific data. Identification information of the subscriber is programmed into the SIM. The SIM card provides: – Authentication – Information storage – Subscriber account information – Data encryption 43

44. GSM Authentication The GSM system used authentication technology to thwart wireless fraud. To date, there has been no cloning fraud on GSM systems, mainly due to the fact that authentication technology was incorporated into the original standard. 44

45. Mobile-Assisted Handoff (MAHO) The mobile phone plays an active part in the handoff process: – The mobile phone, not the switch at the MTSO, continuously monitors adjacent (neighboring) base stations, measuring signal strength of adjacent cell’s control channels. Identities of the 6 best BSs are sent to the switch. The network decides when to initiate a call handover. 45

46. GSM Network Architecture The GSM network architecture. Note the various subsystems. MSCs can always connect to other MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations and support subsystem. 46

47. GSM Adjunct Systems The gateway MSC (GMSC): – Query the HLR (home location register) to determine the location of subscribers – Calls from other networks (i.e., the PSTN) will first terminate into the GMSC before being routed to other network elements for processing (i.e., the switch, or the voice mail system) Short message service center (SMS-SC): processes text messages (160 characters max) Equipment identity register (EIR): identifies what handsets are acceptable in a GSM network 47

48. GSM Adjunct Systems (2) Gateway GPRS support node (GGSN): gateway providing access to external hosts wishing to communicate with mobile subscribers – GPRS will be discussed next. Service GPRS support node (SGSN): – mediate access to network resources – implements packet scheduling policy between different QoS classes 48

49. GSM Data Communication Technologies: GPRS and EDGE General packet radio service (GPRS) is not really in use anymore in GSM networks today. GPRS has been replaced by its successor technology EDGE (Enhance Data rates for Global Evolution). 49

50. General Packet Radio Service (GPRS) It’s been known over the years as “2.5G”. It implemented a packet-switched domain in addition to the circuit-switched domain that existed in GSM networks. Theoretical maximum speeds of up to 171.2 kilobits per second (Kbps) were achievable with GPRS using all eight GSM timeslots at the same time. 50

51. GPRS Architecture Before GPRS, existing MTSOs were designed to support circuit-switched traffic and could not process packetized traffic. The two GPRS support nodes, required in a GPRS-enabled wireless network: – The serving GPRS support node (SGSN) – The gateway GPRS support node (GGSN) 51

52. GPRS Network Architecture The GSM/GPRS network architecture. Note how circuit-switched and packet-switched (data) traffic domains are separated for processing. Note that this architecture is very similar when EDGE technology is deployed. 52

53. The serving GPRS support node (SGSN) SGSN performs mobility management functions such as mobile subscriber attach/detach and location management. The SGSN is connected to the base station subsystem (BSS) via a connection to the packet control unit (PCU) in the BSC. Handles all packet-switched data within the GSM network. The SGSN performs the same functions as the MTSO- based switch for voice traffic. The SGSN is connected to the BSC, and is the service access point to the GPRS network for mobile users. 53

54. GPRS network architecture 54

55. The gateway GPRS support node (GGSN) The GGSN is used as an interface to external IP networks. Connect to other GPRS networks to facilitate GPRS roaming operations. GGSNs maintain routing information that’s necessary to tunnel the protocol data units (PDUs) to the SGSNs. 55

56. Other Network Nodes for Implementation of GPRS Service PCU (packet control unit): – a separate hardware element associated with the BSC – decides whether data to be routed to the circuit switched or packet-switched network Mobility management to locate the GPRS mobile station. A new air interface for packet traffic. New security features such as ciphering. New GPRS-specific signaling systems. 56

57. GPRS Base Station Subsystem When either voice or data traffic is originated by a wireless GPRS/GSM subscriber: – It is transported over the air interface to the BTS – From the BTS to the BSC in the same way as a standard GSM call However, at the output ports of the BSC, the traffic was separated: – Voice traffic is sent to the mobile switch (at the MTSO) per standard GSM voice call processing – Data is sent to the SGSN via the PCU over a frame relay interface 57

58. EDGE: Enhanced Data GSM Environment EDGE is occasionally called E-GPRS (enhanced GPRS). Also known as “2.75G” technology. It’s mainly used as a fallback option in areas where 3G UMTS capacity or technology is unavailable – A bridge between legacy GSM systems and W-CDMA EDGE is introduced within existing specifications and descriptions rather than by creating new ones. 58

59. Data: GPRS vs EDGE Each GPRS time slot can handle: – A maximum of 20 Kbps of user data for a theoretical peak rate of 172 Kbps when all eight time slots are used simultaneously EDGE squeezes more data into each time slot: – A single EDGE time slot can handle up to 59.2 Kbps, for a total of 473.6 Kbps with all eight time slots in use 59

60. GPRS and EDGE: Technical Differences GPRS introduced packet-switched data into GSM networks. EDGE introduces a new modulation technique and new channel coding: – EDGE is an add-on to GPRS and GSM-based wireless carrier cannot deploy EDGE unless they have first deployed GPRS 60

61. GPRS and EDGE: Modulation Techniques GPRS uses GMSK (Gaussian Minimum Shift Keying) EDGE uses 8-phase shift keying (8-PSK) 61

62. GPRS and EDGE: Technical Differences (2) GPRS and EDGE have different protocols and different behavior on the base station system side. GPRS and EDGE share the same packet- handling protocols on the core network side. EDGE increased capacity: – The same GSM time slot can support more users with EDGE 62

63. Table Showing Functional Differences between GPRS and EDGE Technologies Feature/FunctionGPRSEDGE ModulationGMSK8-PSK/GMSK Modulation bit rate270 Kbps810 Kbps Radio data rate, per time slot22.8 Kbps69.2 Kbps User data rate per time slot (radio data rate – packet headers) 20 Kbps59.2 Kbps User data rate (all 8 time slots) 160 Kbps473.6 Kbps 63

64. EDGE Impact on GSM/GPRS Networks The base station was affected by the new transceiver unit capable of handling EDGE modulation. The core GSM network does not require any modifications. EDGE technology could be deployed with limited investments and within a short-time frame. 64