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  • 1. 3G Basic Understanding Vishal Sharma
  • 2. Aims of Course • To attain a general understanding of UMTS systems – GSM Evolution Towards UMTS – 3g Standards – Code Division Multiple Access Technology – UMTS Network Elements and Architecture – UMTS Air Interface Introductory Session
  • 3. Locator Slide • 1st and 2nd Generation Cellular Systems Overview • 3rd Generation Drivers and Standards • CDMA Mobile Technology Overview • UMTS Architecture Overview • UMTS Air Interface Locator Slide
  • 4. Cellular Generations • People talk about mobile technology in terms of generations: – 1st Generation or 1G – 2nd Generation or 2G – 2.5G – 3rd Generation or 3G • But what do these mean? time Data rate Progress of data rates with time and generation 1978 1992 2000 2001 1st and 2nd Generation Cellular Systems Overview
  • 5. 1st Generation • 1976+, though really the technology of the 1980’s • Analogue modulation • Frequency Division Multiple Access • Voice traffic only • No inter-network roaming possible • Insecure air interface 1st and 2nd Generation Cellular Systems Overview
  • 6. 1st Generation Standards • AMPS (Analogue Advanced Mobile Phone System) – North American Standard in cellular band (800MHz) • TACS (Total Access Communications System) – UK originated Standard based on AMPS in 900MHz band • NMT (Nordic Mobile Telephony System) – Scandinavian Standard in 450MHz and 900MHz bands • C-450 – German Standard in 450MHz band • JTACS (Japanese Total Access Communications System) – Japanese Standard in 900MHz band 1st and 2nd Generation Cellular Systems Overview
  • 7. 1st Generation Planning • Macrocellular – High sites for coverage driven planning – Antennas above roof height • Frequency planning required – For networks with more cells than frequencies these must be planned • Large cell size – Order 30km • Handover – Mobile only ever connected to a single cell 1st and 2nd Generation Cellular Systems Overview
  • 8. 2nd Generation • 1990’s • 1st system to use Digital modulation • Voice and low rate circuit switched data • Same technology allows international roaming • Secure air interface 1st and 2nd Generation Cellular Systems Overview
  • 9. GSM • First networks in 1992 • European developed standard, but with worldwide subscriber base • Different frequency bands – GSM450, GSM900, GSM1800, GSM1900 • Largest 2nd Generation subscriber base • Frequency/Time Division Multiple Access GSM phones from 1999/2000 1st and 2nd Generation Cellular Systems Overview
  • 10. GSM Planning• Macrocells and microcells – Capacity driven planning • Frequency planning required • Optional parameters requiring planning – Hierarchical Cell Structures – Frequency Hopping – Discontinuous Transmission – Power Control • Simple subscriber/traffic analysis – Capacity limited by number of TRX’s • Handover - yes 1st and 2nd Generation Cellular Systems Overview
  • 11. D-AMPS/PDC • TDMA (D-AMPS) – North American TDMA/FDMA based standard based upon AMPS – Predominantly used in North and South America – ANSI-41 Core Network – Planning Similar to GSM • PDC – Japanese TDMA/FDMA based standard – Predominantly used in Asia – Planning Similar to GSM TDMA and PDC phones from 1999/2000 1st and 2nd Generation Cellular Systems Overview
  • 12. cdmaOne • First networks in 1996 • Derived from Qualcomm IS-95 air interface • Largely American subscriber base with some Asian networks • Code Division Multiple Access – The closest 2nd generation standard to many of the 3rd generation standards • ANSI-41 core network • Chip rate of 1.2288Mcps 1st and 2nd Generation Cellular Systems Overview
  • 13. cdmaOne Planning • Macrocells and microcells • Single Frequency – multiple frequencies for hotspots • Soft Handover (multiple connections between mobile and network) • Code Planning • Capacity Interference Limited 1 Connection 2 Connections 3 Connections 1st and 2nd Generation Cellular Systems Overview
  • 14. Worldwide Mobile Communications 0 100 200 300 400 500 600 700 1991 1993 1995 1997 1999 2001 Second Generation - D-AMPS Second Generation - PDC Second Generation - GSM Second Generation - cdmaOne First Generation - Analogue MillionSubscribers Year Source:Wideband CDMA for 3rd Generation Mobile Communications, Artech House, 1998 1st and 2nd Generation Cellular Systems Overview
  • 15. Worldwide Mobile Subscribers 0 500 1000 1500 2000 1995 2000 2005 2010 European Union Countries North America Asia Pacific Rest of World MillionSubscribers Year Source:Third Generation Mobile Communications, Artech House, 2000 1st and 2nd Generation Cellular Systems Overview
  • 16. 2.5G • Digital modulation • Voice and intermediate rate circuit/packet switched data • Same technology roaming • Secure air interface • Based upon existing dominant standards such as GSM and cdmaOne 1st and 2nd Generation Cellular Systems Overview
  • 17. GPRS • General Packet Radio Service • Enhancement to the GSM standard • Utlilises – Multiple Timeslots – Packet Switching • Packet Switched Data typically to rates of 56kbps 1st and 2nd Generation Cellular Systems Overview
  • 18. IS-95B • Enhancement to cdmaOne standard • Utilises – High rate coding scheme – Combined code channels – Packet switching • Packet Switched Data to rates of 114kbps Qualcomm PDQ Smartphone 1st and 2nd Generation Cellular Systems Overview
  • 19. Locator Slide • 1st and 2nd Generation Cellular Systems Overview • 3rd Generation Drivers and Standards • CDMA Mobile Technology Overview • UMTS Architecture Overview • UMTS Air Interface Locator Slide
  • 20. IMT-2000 • International Mobile Telecommunications 2000 is a program focussed on providing a single global standard for mobile communications • Development started in 1985 as FPLMTS – Future Public Land Mobile Telecommunications System • Proposed by the ITU (International Telecommunications Union) 3rd Generation Drivers and Standards
  • 21. Who does IMT-2000 serve? • Integrating all the following users – fixed – cellular – cordless – professional mobile radio – paging – satellite – specialised (aeroplane, etc) 3rd Generation Drivers and Standards
  • 22. Aspects of IMT-2000 Networks 3rd Generation Drivers and Standards
  • 23. The Road to 3G HSCSD 3rd Generation Drivers and Standards •HDR – High Data Rate ftp.tiaonline.org/uwc136 www.cdg.orgwww.3gpp.org
  • 24. What are the IMT-2000 goals? • Data Rates – Local area - 2 Mbps • In office, stationary – Limited mobility - 384 kbps • Urban pedestrian – Full mobility - 144 kbps • Rural in car • High spectrum efficiency compared to existing systems • High flexibility to introduce new services 3rd Generation Drivers and Standards
  • 25. IMT-2000 Spectrum 1800 20501900 1950 20001850 2100 2150 2200 ITU Allocation Europe Japan Korea USA 1885 1980 20102025 2110 2170 2200 1920 1980 20102025 2110 2170 2200 1920 1980 2110 2170 2110 21701920 1980 1850 1910 1930 1990 2110 2200 MSS MSS IMT-2000 Land Mobile IMT-2000 Land Mobile UL IMT-2000 Land Mobile UL IMT-2000 Land Mobile IMT-2000 Land Mobile DL IMT-2000 Land Mobile DL UMTS Paired UL UMTS Paired DL MSS MSS UMTS Unpaired UMTS Unpaired IMT-2000 Land Mobile PCS UL PCS DL Reserved 1900 DECT GSM 1800 1880 3rd Generation Drivers and Standards
  • 26. IMT-2000 Spectrum 1800 20501900 1950 20001850 2100 2150 2200 ITU (WARC-92) Europe Japan Korea USA 1885 1980 20102025 2110 2170 2200 1920 1980 20102025 2110 2170 2200 1920 1980 2110 2170 2110 21701920 1980 1850 1910 1930 1990 2110 2200 MSS MSS IMT-2000 Land Mobile IMT-2000 Land Mobile UL IMT-2000 Land Mobile UL IMT-2000 Land Mobile IMT-2000 Land Mobile DL IMT-2000 Land Mobile DL UMTS Paired UL UMTS Paired DL UMTS SAT UMTS SAT UMTS Unpaired UMTS Unpaired IMT-2000 Land Mobile PCS UL PCS DL Reserved 1900 DECT GSM 1800 1880 3rd Generation Drivers and Standards
  • 27. 3rd Generation Cellular 2002+ •Digital modulation •Voice and high rate data •Multi technology roaming •Secure air interface •Standards • UMTS FDD (CDMA based) • UMTS TDD (CDMA based) • cdma2000 (CDMA based) • EDGE (TDMA based) 3rd Generation Drivers and Standards
  • 28. UMTS FDD • UMTS Frequency Division Duplexing Mode • Built onto enhanced GSM core network • Utilises: – QPSK modulation (Quadrature phase shift keying) – Multiple channel coding and bearer rates – Variable spreading factors and multi-code transmission – CDMA – FDD • Data up to rates of 2Mbps 3rd Generation Drivers and Standards
  • 29. UMTS TDD• UMTS Time Division Duplexing Mode • Built onto enhanced GSM core network • Utilises: – QPSK modulation – Multiple channel coding and bearer rates – CDMA – TDD • Data up to rates of 2Mbps • Will happen after UMTS FDD 3rd Generation Drivers and Standards
  • 30. cdma2000 • Built onto ANSI - 41 core network • Utilises: – QPSK modulation – Multiple channel coding and bearer rates – CDMA – FDD – Multiple carriers on the downlink • allows compatibility with cdmaOne – Synchronous operation • Data up to rates of 2Mbps (typically less) 3rd Generation Drivers and Standards
  • 31. EDGE• Enhanced Data for GSM Evolution – Sometimes called E-GPRS (Enhanced GPRS) • Enhancement to the GSM and TDMA standards • Utlilises: – 8PSK Modulation – Possible 1.6 MHz carrier under IS-136 – 8 Channel Coding Schemes – Multiple Timeslots (similar frame structure to GSM) – TDMA • Data rates up to 384kbps (typically less) 3rd Generation Drivers and Standards
  • 32. 4th Generation... 3rd Generation Drivers and Standards
  • 33. Locator Slide • 1st and 2nd Generation Cellular Systems Overview • 3rd Generation Drivers and Standards • CDMA Mobile Technology Overview • UMTS Architecture Overview • UMTS Air Interface Locator Slide
  • 34. Multiple Access Explained• Imagine you are in a cocktail party… • Now imagine you are trying to talk to somebody • If you are trying to listen to somebody you need to be able to pick out their speech from everybody else’s speech. • Everybody is using the same medium to talk - the air in the room CDMA Mobile Technology Overview
  • 35. Terminology Explanation • This is Multiple Access – Many conversations/channels share the same medium • There are a number of different Multiple Access (MA) strategies you can try: – Time Division Multiple Access (TDMA) – Frequency Division Multiple Access (FDMA) – Code Division Multiple Access (CDMA) CDMA Mobile Technology Overview
  • 36. TDMA at the Party• We divide time into a number of timeslots • Everybody takes turns to speak within a timeslot • Once everybody has spoken we go back to the start of the list and begin again - this is a frame • This ensures that two conversations/channels don’t get confused. • Conversation/Channel separation is provided in time. • Bit of a problem if people speak too late or too early… – We may need guard periods between timeslots when nobody speaks • People need to know when to speak… – We need signalling to tell people their timeslot CDMA Mobile Technology Overview
  • 37. TDMAfrequency time User 1 User 1 Timeslot Period Frame Period Idealised TDMA (with no guard periods) Available Frequency Band CDMA Mobile Technology Overview
  • 38. FDMA at the cocktail party • We divide the available frequency band into a number of frequency channels of the same channel bandwidth • People speak continuously at different frequencies/pitches, and use earpieces to filter out frequencies they’re not interested in. • Again this ensures that two conversations don’t get confused. • Conversation/Channel separation provided in frequency. • Bit of a problem as the filters aren’t perfect… – We may need guard bands between channels where nobody speaks • People need to know the frequency of the conversation… – We need signalling to tell people their frequency channel CDMA Mobile Technology Overview
  • 39. FDMA at the cocktail party • FDMA is difficult to illustrate in terms of speech as everyone’s voice is at a similar frequency. • FDMA is the oldest form of multiple access technique. • You have used FDM when you tune into a radio channel. • Radio channels advertise their frequency. E.g. 95.1 MHz Capital. CDMA Mobile Technology Overview
  • 40. FDMA frequency time User 1 Frame Period (we may still need frames/timeslots for signalling) Channel Bandwidth Idealised FDMA (with no guard bands) CDMA Mobile Technology Overview
  • 41. FDMA and TDMA compared • FDMA can be used for digital or analogue systems • TDMA is realistically a digital technology • TDMA reduces distortion interference effects (inter-modulation) by allowing only one user access to the system at a time. • Digital signals are easier to buffer and re-process and therefore cope better with a hostile radio channel. CDMA Mobile Technology Overview
  • 42. FDMA/TDMA • Of course we could also be clever and use a combination of TDMA and FDMA…like in GSM • This is commonly referred to as simply TDMA CDMA Mobile Technology Overview
  • 43. CDMA Spreading•Essentially Spreading involves changing the symbol rate on the air interface Identica l codes Tx Bit Stream P f Code Chip Stream Spreading P f Channel Air Interface Chip Stream P f Code Chip Stream Despreading P f Rx Bit Stream P f CDMA Mobile Technology Overview
  • 44. Spreading and Despreading Rx Bit Stream Air Interface Chip Stream Tx Bit Stream 1 -1 Code Chip Stream XSpreading Code Chip Stream XDespreading CDMA Mobile Technology Overview
  • 45. Spreading and Dispreading with code Y Air Interface Chip Stream Tx Bit Stream 1 -1 Code Chip Stream XSpreading XDespreading Code Chip Stream Y Rx Bit Stream CDMA Mobile Technology Overview
  • 46. Spreading in noise • The gain due to Despreading of the signal over wideband noise is the Processing Gain Signal P f Spreading Code Tx Signal P f Rx Signal (= Tx Signal + Noise) f P Channel Wideband Noise/Interference P f Spreading Code Signal P f CDMA Mobile Technology Overview
  • 47. Spreading in noise (time domain) • Here, the message is recovered with a SNR of -6 dB. The spreading code is at a rate 8 times greater than the data. CDMA Mobile Technology Overview Run exe
  • 48. CDMA in Cellular • Cellular systems have multipath propagation with variable delay • Channels from the same transmitter are no longer perfectly orthogonal • i.e Channelisation codes are no longer perfectly synchronised • Downlink Channels on the same cell will interfere with each other • An ‘orthogonality factor’ (0.6 in urban macrocells typically) – The orthogonality factor gives the percentage of interference that is rejected CDMA Mobile Technology Overview
  • 49. A Channelised Transmitter Channel 1 Bit Stream Channel 2 Bit Stream Channel 3 Bit Stream Pulse Shaping and Modulation c1 c2 c3 s1 In a Base Station, channels are first spread and channelised using the channelisation codes, then combined and finally scrambled together. Each base station will be allocated one of 512 primary scrambling codes. CDMA Mobile Technology Overview
  • 50. Types of Code• Summarising: – Channelisation Codes •Are used to separate channels from a single cell or terminal – Scrambling Codes •Are used to separate cells and terminals from each other rather than purely channels • Different base stations will use the same spreading codes with separation being provided by the use of different scrambling codes. S1 S2 S3 C1 C2 C3 C1 C2 C3 C1 C2 C3 CDMA Mobile Technology Overview
  • 51. Pilot Channels • Pilot channels are used in the cell selection process (i.e. “best server” means “strongest pilot”) • Pilots contain no baseband information - no ‘bits’. • The pilot is spread by the all 1’s channelisation code. – Effectively the pilot is the scrambling code • The required pilot channel SNR is referred to as Ec/Io (EcIo) • Pilots allow channel estimation to be carried out. • The result of channel estimation is used to programme the Rake receiver. CDMA Mobile Technology Overview
  • 52. Soft Handover • Soft Handover is where more then one cell is in communication with a terminal • The cells in communication with the terminal are known as an active set • The best serving cell is known as the primary cell - and maintains the primary channel • Other channels are known as handover channels • The gain associated with soft handover is known as the macrodiversity gain – This occurs due to the uncorrelated nature of fast fading between cells and the variation in slow fading between cells – Note that slow fading is not entirely uncorrelated for different cells CDMA Mobile Technology Overview
  • 53. Hard Handover (e.g.GSM) Handover Hysteresis Margin RX_Level Direction of Travel Cell A Cell B Distance In hard handover the mobile is only ever instantaneously connected to a single cell CDMA Mobile Technology Overview
  • 54. Soft Handover • During soft handover more than one cell is in communication with the mobile. MS CDMA Mobile Technology Overview
  • 55. Soft Handover (e.g. in cdmaOne) Active set = 1 = 2 = 1 Pilot Ec/Io T_ADD T_DROP Cell A Cell A and Cell B Cell B Direction of Travel Add Time Delay Drop Time Delay In soft handover the mobile may be instantaneously connected to more than one cell Distance CDMA Mobile Technology Overview
  • 56. More CDMA at the Cocktail Party - Cell Breathing • The higher the noise at a party the louder you have to speak • You get to a point where you can’t shout louder and can’t have a conversation where you are standing • The further away you are to the listener the louder you have to speak • If it is noisy only people standing close together can have a conversation • As it gets noisy the area that can be covered by a conversation decreases • Conversely the quieter it is then the area covered by a conversation can be larger • This is called Cell Breathing and occurs in mobile CDMA networks CDMA Mobile Technology Overview
  • 57. Cell Breathing• An increase in traffic results in an increase in interference • Mobiles at the extremities of cells may be pushed out of the cells effective coverage area due to decreased Eb/No • This effect may occur over the course of 24 hours due to changes in traffic demand over peak hours 6am Noon 9pm CDMA Mobile Technology Overview
  • 58. Cell Breathing :- “good” or “bad” ? . • Cell Breathing is integral to WCDMA cellular radio systems. • Its disadvantage is that it leads to the creation of gaps in the network coverage. • Its advantage is that it maximises capacity when it is demanded. • The amount of cell breathing can be controlled by limiting the Noise Rise in the admission algorithm. • It cannot, however be eliminated. CDMA Mobile Technology Overview
  • 59. Cell Breathing . Very rough rule of thumb. Area shrinkage (%) = Coverage with 3 dB Noise Rise Coverage with 10 dB Noise Rise Unloaded Coverage ( )      −× − 5.17 101100 NR CDMA Mobile Technology Overview
  • 60. More CDMA at the Cocktail Party - Power Control • If somebody is shouting louder than they need, it increases the overall noise • This is inefficient, as it reduces the number of people who can have conversations • We need to speak as quietly as possible to maximise the number of simultaneous conversations. • This is called Power Control in mobile networks • In CDMA networks it is very important that this power control is efficient – We use fast power control with a much quicker feedback loop than in TDMA networks CDMA Mobile Technology Overview
  • 61. Locator Slide • 1st and 2nd Generation Cellular Systems Overview • 3rd Generation Drivers and Standards • CDMA Mobile Technology Overview • UMTS Architecture Overview • UMTS Air Interface Locator Slide
  • 62. User Equipment UMTS Terrestrial Radio Access Network Core Network UU IU UE UTRAN CN UMTS Architecture Overview UMTS High Level Architecture New
  • 63. Major Network Elements in UMTS UU IU UE UTRAN CN CU IUb IUr USIM ME Node B Node B Node B Node B RNC RNC MSC/VLR SGSN GGSN GMSC HLR PLMN, PSTN, ISDN Internet, X25 Packet Network Mobile Equipment UMTS SIM Radio Network Controller Radio Network Controller Serving GSN Gateway GSN Gateway MSC Mobile Switching Centre Home Location Register Iu-ps Iu-cs IUb UMTS Architecture Overview
  • 64. General UE Architecture UU UE CU USIM ME Mobile Equipment UMTS SIM UTRAN Terminal Equipment UMTS Architecture Overview
  • 65. Elements of the UE • Mobile Equipment – The radio terminal used for radio communication over the Uu interface • UMTS Subscriber Identity Module – The smartcard that holds the subscriber identity, authentication and encryption keys etc • Additionally one can define a Terminal Equipment item that connects to the UE – This carries the application specific user interface UMTS Architecture Overview
  • 66. General Core Network Architecture IU CN MSC/VLR SGSN GGSN GMSC HLR Serving GSN Gateway GSN Gateway MSC Mobile Switching Centre Home Location Register Other SGSN Other MSC UTRAN UTRAN External Circuit Switched Networks External Packet Switched Networks Iu-cs Iu-ps Gs Gn Gn Gr Gc D D Gi F F UMTS Architecture Overview
  • 67. Functions of the CN • Switching • Service Provision • Transmission of user traffic between UTRAN(s) and/or fixed network • Mobility Management • Operations, Administration and UMTS Architecture Overview
  • 68. General UTRAN Architecture UU IU UE UTRAN IUb IUr Node B Node B Node B Node B RNC RNC Radio Network Controller Radio Network Controller Iu-ps Iu-cs IUb CN (MSC) CN (SGSN) UMTS Architecture Overview
  • 69. UTRAN • UTRAN is the UMTS Terrestrial Radio Access Network • The functions of UTRAN are: – Provision of Radio Coverage – Security and privacy – Handover – Radio resource management and control UMTS Architecture Overview
  • 70. Elements of UTRAN • Radio Network Controller – Owns and controls radio resources in its domain (BSC in GSM) – Service Access point for all services that UTRAN provides for the CN • Node B – Acts as the radio basestation (BTS in GSM) – Converts the data flow between the Iub and Uu interfaces UMTS Architecture Overview
  • 71. Radio Network Subsystem (RNS) • A Radio Network Subsystem consists of: – A single RNC – One or more Node B’s – Cells belonging to Node B’s RNC Node B Cell Cell Cell Node B Cell Cell Cell Iur Iu Uu UMTS Architecture Overview
  • 72. Radio Network Controller (RNC) • Responsible for the use and integrity of the radio resources • Responsible for the handover decisions that require signalling to the UE • Provides a combining/splitting function to support macrodiversity between different Node Bs RNC Node B Cell Cell Cell Node B Cell Cell Cell Iur Iu Uu UMTS Architecture Overview
  • 73. Node B • Logical node responsible for radio transmission / reception in one or more cells to/from the UE • Dual mode Node B can support FDD and TDD mode RNC Node B Cell Cell Cell Node B Cell Cell Cell Iur Iu Uu UMTS Architecture Overview
  • 74. Cell • A cell is an area of radio coverage serviced by one or more carriers RNC Node B Cell Cell Cell Node B Cell Cell Cell Iur Iu Uu UMTS Architecture Overview
  • 75. Major Interfaces in UMTS • There are four major new interfaces defined in UMTS – Iu •The interface between UTRAN and the CN – Iur •The Interface between different RNCs – Iub •The interface between the Node B and the RNC – Uu •The air interface RNC Node- B RNC UE CN Uu Iu Iub Iur UMTS Architecture Overview
  • 76. Iub • The Iub is the interface between the RNC and the Node-B • The Node B effectively performs a relay function between the Iub and the Uu • Thus the Iub needs to carry: – Layer 2+ signalling between the UE and the UTRAN – Signalling directly to the Node B • To control radio resource allocation • General control of the Node-B • O&M Functionality UMTS Architecture Overview
  • 77. Iur • The Iur is the interface between two RNCs • Thus the Iur needs to support: – Basic Inter RNC Mobility – Dedicated Channel Traffic – Common Channel Traffic – Global Resource Management UMTS Architecture Overview
  • 78. Iu • The Iu is the interface between the Core Network and the UTRAN • There are two instances of the Iu: – The Iu-ps connecting UTRAN to the Packet Switched Network – The Iu-cs connecting UTRAN to the Circuit Switched Network UMTS Architecture Overview
  • 79. Handover in UMTS • There are three basic types of handover – Intra frequency handovers • Handovers between 2 UMTS codes at the same frequency • These can be soft handovers – Inter frequency handovers • Handovers between 2 UMTS carriers at different frequencies • These are hard handovers – Inter system handovers • Handovers between UMTS and GSM carriers • These are hard handovers UMTS Architecture Overview
  • 80. Handover Sets in UMTS • Active Set – Cells forming a soft handover connection to the mobile • Candidate Set • Neighbour Set – Those cells which are continuously monitored but do not yet qualify for the Active Set UMTS Architecture Overview
  • 81. Macrodiversity between Node B’s • If an active set consists of two connections to cells parented to different Node Bs then the combining of the two channels occurs at the RNC • This is known as a soft handover • This doubles the transmission ‘cost’ of the call RNC Node B Cell Cell Cell Node B Cell Cell Cell Iur Iu Uu UMTS Architecture Overview
  • 82. Macrodiversity between Cells on the Same Node B • If an active set consists of two connections to cells parented to the same Node B – combining of the two channels occurs at the Node B • This is known as a softer handover • This has no transmission implication • But does have capacity implications, if cells are collocated. RNC Node B Cell Cell Cell Node B Cell Cell Cell Iur Iu Uu UMTS Architecture Overview
  • 83. = 2 Cell A and Cell C = 2 Cell A and Cell B Handover Decisions in UMTS Pilot Ec/Io Direction of Travel Window_DROP Drop Time Delay Window_ADD Add Time Delay Replace Time Delay Window_REPLACE Active set = 1 Cell A A Active B Active C Active UMTS Architecture Overview
  • 84. Locator Slide • 1st and 2nd Generation Cellular Systems Overview • 3rd Generation Drivers and Standards • CDMA Mobile Technology Overview • UMTS Architecture Overview • UMTS Air Interface Locator Slide
  • 85. Contents and Session Aims • This session aims to explain the protocols and operation of the air interface – To give an overview of the UMTS specific operation of the air interface UMTS Air Interface •Overview of the Air Interface
  • 86. Role of the Air Interface • To provide a number of bearer or physical channels – supports data transfer over the radio path. • To provide control channels – to manage the cell • To provide a number of traffic channels – at an acceptable error performance and at various rates • To provide signalling channels – for call set up, etc. UMTS Air Interface
  • 87. Role of the Air Interface • In providing all of this we must also: • Ensure an efficient use of the available spectrum • Minimise interference to other cells and services • Minimise the use of power, particularly from the mobile • Provide synchronisation UMTS Air Interface
  • 88. UMTS FDD Air Interface Overview Parameter Value Multiple Access Scheme Direct Sequence CDMA Duplexing Method FDD Chip Rate 3.84 Mcps Carrier Spacing 5 MHz Carrier Spacing Raster 200 kHz Frame Length 10 ms Slots per Frame 15 Inter-cell Synchronisation None Spreading factor Variable (4-512) User Data Rate 8->384 kbps UMTS Air Interface
  • 89. Multiple Access Scheme • UMTS FDD mode makes use of CDMA • In the case of UMTS this is commonly referred to as Wideband CDMA - WCDMA • However there are elements of FDMA and TDMA in UMTS – Common channels for paging (TDMA) – Packet access share codes between UEs (TDMA) – Multiple carriers are used per operator (FDMA) UMTS Air Interface
  • 90. Duplexing Method • UMTS FDD mode makes use of Frequency Division Duplexing – The UL and DL Channels are carried on separate carriers • In the case of UMTS in Europe: – The Uplink band is between 1.92 and 1.98GHz – The Downlink band is between 2.11 and 2.17GHz – The Uplink/Downlink Separation is 190MHz 1.8G H z 2.05G H z 1.9G H z1.95G H z2G H z 1.85G H z 2.1G H z2.15G H z2.2G H z 190MHz 2.17G H z 2.11G H z 1.98G H z 1.92G H z UL DL UMTS Air Interface
  • 91. Chip Rate • The chiprate used in UMTS FDD mode is 3.84Mcps • This leads to a carrier bandwidth of approximately 5MHz • This chip rate was chosen because it: – Could be generated simply from existing GSM clock rates – Provided a similar bandwidth to cdma2000 to allow shared use of filters etc in UEs UMTS Air Interface
  • 92. Carrier Spacing and Carrier Spacing Raster • The nominal carrier spacing for UMTS is 5MHz • This was chosen to comply with the American market, where spectrum has been awarded in 5MHz blocks • It is possible to move the centre frequency of the carrier on a 200kHz raster 5MHz 200kHz UMTS Air Interface
  • 93. Adjacent Channel Interference • Adjacent channel interference may have a significant impact on UMTS capacity • Required attenuation (by standards) – adjacent carrier 33dB – 2nd adjacent carrier 43dB UMTS Air Interface
  • 94. Inter Cell Synchronisation • Cells in a UMTS network are not synchronised in time with each other. • This is a significant difference from cdmaOne which is synchronised. • This removes the need for tight synchronisation between the base stations • There is no need for GPS receivers at sites – This makes implementation of picocells and their integration with the network simpler as satellite Line of Sight is not required UMTS Air Interface
  • 95. Spreading Factor and User Data Rates • UMTS has been designed to provide flexibility to allow the user to use multiple services, some of which we cannot foresee at the moment • Rather than having a fixed bit rate and spreading factor, each of the channels on the user interface has a range of bit rates that can be used • This makes the channels more complicated than for GSM…but certainly more flexible UMTS Air Interface
  • 96. Power Control • Power control commands are either Power Up or Power Down. • Step size is usually 1 dB. • It is intended to compensate for fast and slow fading. • Fast fading results from multi-path propagation resulting in signal strength gradients of up to approximately 1 dB per centimetre in space. • Mobile speeds faster than approximately 15 m/s may cause problems with power control. UMTS Air Interface
  • 97. Power Control – Power Rise • If the mobile reacts to Power Control commands, it is usual for the average power to increase. • This increases the level of interference experienced by neighbouring cells • The difference between the average power level on a fading and non-fading channel is known as the Power Rise. -5 0 5 10 15 20 25 Mobile Tx Pwr Average Non-fading •Power Rise
  • 98. Power Control – Soft Handover • A mobile near the edge of a cell will be causing almost as much Noise Rise on the neighbouring cell as it is on the serving cell. •Serving Cell •Neighbouring Cell
  • 99. Power Control – Soft Handover • Establishing a second connection from the neighbouring cell provides advantages on the uplink. • Tx power on the uplink is reduced by: • Macro-diversity: Eb/N0 estimate is passed to RNC that selects best connection. • Lower incidence of power up commands results in lower Power Rise. RNC
  • 100. Power Control – Soft(er) Handover • If both active cells are on the same site, the handover is called “softer” handover. • In this case, the benefits are greater as the two signals are combined using a maximal combiner. • A maximal combiner is also used in the mobile.
  • 101. Thank You