Instituto Superior Técnico. Key aspects of the Access in 3 rd Generation Communications Networks

Transcription

1 Universidade Técnica de Lisboa! Instituto Superior Técnico Key aspects of the Access in 3 rd Generation Communications Networks 1

2 The 3 rd Generation Networks The society is in the middle of the change towards what is being called the information society. An important communication dimension is added by mobility, allowing access to the Internet, with all its current and future services and applications, anywhere, anytime. This new dimension is promoting the concept of Unified Networks where mobility, the Internet and Broadband access form the framework for the next generations of network architectures. The International Telecommunications Union (ITU) has in this context defined the so-called 3 rd Generation network (3G Network) in its mobile communications standard, the International Mobile Telecommunication 2000 (IMT-2000). 3G Networks were designed for Multimedia communications 2

3 The Unified Network Services & Management Layer Wireless & Wireline, Voice & Data, Business & Residential Application Servers IN Voice Mail Messaging E-Commerce Info Services Management Servers Calls Mobility GSN Billing OAM&P Transport & Networking Infrastructure Layer Gateways Internet/Extranet Intranet PSTN PDNs PLMNs Access Layer Packet Centric networking solution integrating both voice and data on a single "switch-less" infrastructure 3

4 The 3G Standardization 1st gen (1980 s) : analogue RTT voice service AMPS, NMT, TACS etc 2nd gen (1990 s): digital RTT, capacity voice service GSM, DAMPS, PDC, IS-95 (cdmaone) 3rd gen (2000 s): adds non-voice, higher bit rates, capacity TIA ANSI 3GPP2 (TIA, ARIB, TTC, TTA) cdma2000-based 2G: GSM G: RTT W-CDMA 2G: cdmaone & DAMPS 3G: cdma2000 RTT: (one mode) Multi Carrier CDMA Core Network: ANSI NSS ITU: OHG T1 ETSI 2G: GSM 3G: UMTS RTT: Mode 1 W-CDMA (FDD) Mode 2 TD-CDMA (TDD) Core Network: GPRS ITU: (FPLMTS) IMT-2000 IMT-2000 Vision anywhere, anytime (global roaming) multimedia bandwidth on demand TTA 2G: cdmaone 3G: RTT W-CDMA 3GPP UMTS-based Harmonised RTT W-CDMA and TD-CDMA proposal - First phase of standards freeze 31 dec service launch 2004? IMT-2000 Concept Land based & Satellite access End-user services bit rates up to 2 Mbits/s VBR, PS, QoS CWTS ARIB & TTC 2G: PDC & cdmaone 3G: RTT W-CDMA (NTTDoCoMo) 2G: GSM & cdmaone 3G: RTT TD-CDMA Harmonise 3G CDMA Radio Transmission Technologies of 3GPP and 3GPP2 4

5 The Mobile generations First Generation mobile systems appeared massively in the 80 s of the XX century, characterized as being Analog and National: NMT, TACS, AMPS.... Second Generation mobile systems were digital and appeared commercially in the 90 s, but compatibility between them was not reached: cdmaone (IS-95), D-AMPS, GSM GSM however, as a world standard, was the first to have intrinsic compatibility between networks of the same system, and the first to have a new mobility feature: Roaming. Third Generation mobile systems, first called FPLMTS (Future Public Land Mobile Telecommunication Systems) and then simplified to IMT-2000, began in the early 90 s as an idea for truly universal mobile systems. Its birth can be situated in 1992 when the WARC (World Association Radio Conference) allocated the bandwidth in the 2 GHz spectrum for a third generation system. 5

6 The Mobile Goals The idea was to federate all the different digital systems, like private, public, cordless, satellite, pagers and cope with the explosive growth of data exchanges due to the expansion of the Internet. Satellite interfaces cover LEO, MEO and GEO orbits as well as those specifically aimed at maximizing the commonality between terrestrial and satellite interfaces. Broadband multimedia services, accessed from fixed and mobile terminals, were defined in IMT-2000 standards, where cdma2000 and UMTS would form the basis of target networks enabling operators to offer such multimedia services. Recognizing the importance of the Internet Protocol (IP) in today's networks, this technology has been included in the evolution strategies of IMT

7 The Need for Speed Technology 3 G EDGE GPRS HSCSD 2G Transmission Capacity Data Rate (Kbps) Services/Applications Voice, SMS Internet Web DB Access Synchronization Document Transfer Location Services Still Image transfer Low Quality Video High Quality Video Service Level = Excelent = Medium = Weak 7

8 The Need for Quality Voice vs Redes Redes de de Acesso Acesso Multi Multi Serviço Serviço 8

9 Main Features of UMTS The key features : A high degree of commonality of design worldwide; Compatibility of services within IMT-2000 and with fixed networks; High quality and integrity; Accommodation of a variety of types of terminals, including pocket-sized; Worldwide roaming capability; Capability for multimedia applications and wide range of services: video-teleconferencing, high speed Internet, speech, high data-rate (2 Mbit/s); 9

10 Deployment scenarios of UMTS 10

11 Architecture of UMTS 11

12 Architecture of UMTS UTRAN : UE User Equipment ME Mobile Equipment USIM UMTS Subscriber Identity Module Node B Radio base station RNC Radio Network Controller Uu Iub Iu Gn CORE Network : Node B HLR Home Location Register database that stores the user s service Profile Wireless Gateway (SGSN) MSC/VLR Mobile Switching Center/Visitor Location Register is the switch (MSC) and database (VLR) that serves the User Equipment in its current location for Circuit Switched (CS) services. VLR stores the visiting user s service profile. GMSC Gateway MSC is the switch at the point where UMTS is connected to external Circuit Switched networks SGSN Serving GPRS Support Node is the switch for Packet Switched (PS) services GGSN Gateway GPRS Support Node is the Gateway point where UMTS is connected to Packet Switched networks RNC Core Gateway (GGSN) 12

13 Domains of UMTS PSTN MSC VLR GMSC USIM Cu ME Uu Node B Iu bis RNC Iu _cs camel SCP E SMS-GMSC SMS-IWMSC D F C Gs AuC H HLR C Home Network Domain Iu _ps camel Gd Gr Gf EIR Gc SGSN Ga CGF Ga Gn /p GGSN Serving Network Domain Transit Network Domain USIM Domain Mobile Equipment Domain Access Network Domain Core Network Domain User Equipment Domain Infrastructure Domain 13

14 Planes (Stratum) of UMTS Application Plane MSC/ VLR EIR SCP HLR AUC GMSC Home Plane SGSN GGSN Services Plane RNC Transport Network (SDH, ATM, IP) ISDN/PSTN Media Gateway Media Gateway Access Plane Internet Intranets Transport Plane Customer Information Control and Signalling 14

15 User Plane in the Access Non-Access Stratum Radio protocols Radio protocols Iu proto cols Iu proto cols UE Radio (Uu) Access Stratum UTRAN Iu CN 15

16 UTRA FDD Radio Interface (Uu) protocol architecture Non Access Stratum Access Stratum Control Plane Gc Nt Dc User Plane L3 Logical Channels SAP (Service Access Point) RRC (Radio Resource Control) AM UM TR AM UM TR RLC (Radio Link Control) RLC L2 Logical Channels Common Channel pch Dedicated Control Channel Dedicated Traffic Channel MAC (Medium Access Control) Transport Channels Common CH Shared CH Dedicated CH ODMA CH L1 Physical Data Channels Channel coding Common Shared Dedicated ODMA pch pch pch pch Physical Control Spreading Channel & Modulation 16

17 UTRAN Interface (Iu-CS) protocol architecture Radio Network Layer Control Plane RANAP User Plane Iu UP Protocol Layer RANAP-RAN Application Part BroadBand SS#7 protocols over IP or ATM: SCCP-Signalling Connection Control Part MTP3b-Message Transfer Part Transport Network Layer TransportNetwork User Plane Transport Network Control Plane Q FFS TransportNetwork User Plane M3UA-MTP3 User Adaptation Layer SSCF-NNI- Service Specific Coordination Function M3UA SCTP IP SCCP MTP3b SSCF- NNI SSCOP AAL5 Q MTP3b SSCF- NNI SSCOP AAL5 FFS**) IP AAL2 RTP/ RTCP*) UDP/IP SSCOP-Service Specific Connection-Oriented Function SCTP-Stream Control Transmission Protocol Q , Q Signaling Protocol for setting AAL2 connection and Adaptation on BB SS#7 Data Transport protocols over IP or ATM: Data Link ATM ATM Data Link ATM Data Link RTCP-Real Time Control Protocol Physical Layer *) RTCP is optional **) For Further Study-Depend on Transport Signaling alternatives 17

18 UTRAN Interface (Iu-PS) protocol architecture Radio Network Layer Control Plane RANAP User Plane Iu UP Protocol Layer RANAP-RAN Application Part BroadBand SS#7 protocols over IP, IPoATM or ATM: SCCP-Signalling Connection Control Part Transport Network Layer TransportNetwork User Plane SCCP MTP3-B M3UA M3UA SCTP SCTP SSCF-NNI SSCOP AAL5 IP IP Transport Network Control Plane TransportNetwork User Plane GTP-U GTP-U UDP UDP IP AAL5 IP MTP3b-Message Transfer Part M3UA-MTP3 User Adaptation Layer SSCF-NNI- Service Specific Coordination Function SSCOP-Service Specific Connection-Oriented Function SCTP-Stream Control Transmission Protocol Data Transport protocols over IP or IPoATM: GTP-U-GPRS Tunnelling Protocol ATM Data Link ATM Data Link Physical Layer Physical Layer 18

19 UTRAN Interface (Iu-BC) protocol architecture Radio Network Layer SA Broadcast Plane SABP Protocol Layer SABP-Service Area Broadcast Protocol Data Transport protocols may be over IP or IPoATM Transport Network Layer Transport Network User Plane TCP TCP IP AAL5 IP ATM Data Link Physical Layer 19

20 Evolution steps of UMTS UMTS (Release 99): The first Release of the third generation specifications was essentially a consolidation of the underlying GSM specifications and also the development of the new radio access network. The foundations were laid for future high-speed traffic transfer in both circuit switched and packet switched modes. UMTS Release 4 & 5 (previous Release 2000): These releases address essentially the need for more functionality on UMTS Radio Access Network (like 2 Mbit/s rates) and the evolution of the Core Network to the provisioning of IP-based multimedia services. The commercial launch was planned for 2002 but delayed to 2004?. UMTS Release 6: This release is scheduled for 2003 and will be the one where 3G UMTS will be All-IP. 20

21 The 2G GSM Network BTS VLR HLR SIM Card BTS PSTN BTS BSC MSC WAP Gateway Firewall IP Network BTS EIR AuC MSC: Mobile switching Center BSC: Base Station Controller BTS: Base Transceiver Station HLR: Home Location Register EIR: Equipment Identity Register AuC: Authentication Center SIM: Subscriber Identity Module WEB Server 21

22 First Release (R 99) of UMTS 3G Radio Access Network (RAN) is connected to an upgraded GSM core through a 3G MSC (Mobile Switching Center) and an SGSN (Serving GPRS Support Node). The 3G MSC is a Call Server for Circuit Switched services The SGSN is for Packet Switched data services; The GGSN is a gateway for Packet Switched data services 22

23 Next Releases (R 4 to 6) of UMTS Data traffic (including voice) will be handled by the GPRS nodes (GGSN and SGSN) The All-IP mobile network will not include circuit switching; The same Core Network serves all access networks; 23

24 IP Mobility Provided within and between access types Builds on IETF MIP+ seamless user/device handover and roaming between different access types Roaming between (visited/foreign) networks 24

25 IP Mobility 25

26 The 3 rd Generation UMTS Mobile Network IP Mobility Each mobile node is assigned a pair of addresses. The home IP address is used for identification, the care-of-address (CoA), is used to determine the current position of the node and is defined in the address space of the visited/foreign access subnetwork. Continuous tracking of CoA allows the Internet to provide subscribers with roaming services the different types of architecture in the multi-access system of 3G networks (UTRAN, GSM/GPRS, etc) have to cope with location management. There are three procedures: Internet network location management: Identifies the point of access to the Internet network Intrasegment location management: Executed by segment-specific procedures when the terminal moves within the same access network Intersegment location management: Executed by systemspecific entities when the terminal moves from one access network to another. 26

27 The Radio Access Modes for 3G Direct-Sequence Spread WCDMA or FDD (IMT-DS) Multi Carrier or cdma2000 (IMT-MC) Time Code WCDMA or TDD (IMT-TC) Single Carrier or TD-SCDMA (IMT-SC) Frequency Time or DECT (IMT-FT). WCDMA within 3GPP is called UTRA-UMTS Terrestrial Radio Access and covers both FDD (Frequency Division Duplex) and TDD (Time Division Duplex) operations. UTRA is the Access Network that characterizes the UMTS-Universal Mobile Telecommunication System 27

28 The 3 rd Generation UMTS Mobile Network UMTS Air Interface WCDMA is a wideband Direct-Sequence Code Division Multiple Access, i.e, user information bits are spread over a wide bandwidth. WCDMA supports high user data rates and increased multipath diversity. WCDMA supports highly variable user data rates. Each user is allocated frames of 10 ms duration, but data capacity among users can change from frame to frame. WCDMA employs coherent detection on uplink and downlink based on the use of pilot symbols or common pilot. WCDMA air interface supports CDMA receiver concepts such as MUD-Multi-user Detection and Smart Adaptive Antennas. WCDMA supports Service Multiplexing in single connections. WCDMA supports the operation of asynchronous base stations, not requiring global time reference, such as GPS. 28

29 Spectrum Allocation ITU IMT-2000 Sat. IMT IMT-2000 Sat. IMT PHS Japan IMT-2000 MSS S-PCN (UL) T D D IMT-2000 MSS S-PCN (DL) DECT Europe GSM 1800 (DL) T D D UMTS FDD UMTS MSS (UL) T D D UMTS FDD UMTS MSS (DL) USA PCS (UL) PCS Un. Lic. PCS (DL) MSS S-PCN (DL) MSS S-PCN (UL) MHz 29

30 Air Interface grouping 30

31 Band allocation per operator Up Link Down Link GSM Up Link Down Link Mhz each operator x 3 = 24Mhz 6 Mhz each operator Each GSM channel 200 Khz w/ 8 time slots UMTS Up Link Down Link Mhz each operator TDD unpaired Each UMTS channel - 5 Mhz 15 Mhz each operator FDD - Paired 31

32 FDMA GSM Radio Access Modes Power 200Khz Time User 1 User 2 User 3 User 4 Freq. FTDMA - GSM Power 200Khz Time Freq. 8 x Time Slots User User 9-16 User 1-8 User

33 WCDMA Radio Access Modes Code Multiplex Power Time C ch 76 UMTS USER 2 DS-CDMA FDD C ch 31 UMTS USER 1 C ch 15 C ch 15 5 MHz 5 MHz Uplink Spectrum Downlink Spectrum 1920 MHz 1980 MHz 2110 MHz 2170 MHz Duplex Spacing : 190MHz Frequency TD-CDMA TDD Power C ch 61 C ch 38 5 MHz C ch 91 Time DL UL DL DL UL 625 µs C ch 25 UMTS USER 2 UMTS USER 1 Code Multiplex & Time Division Frequency 1900 MHz or 2010 MHz 1920 MHz or 2025 MHz 33

34 Spreading and Despreading In WCDMA Spread Spectrum technology the information contents are spread by unique, digital codes (spreading sequences). The basic unit of a code sequence is one chip. The rate of the spreading code is denominated as chip rate Rc (chip/s or cp/s). The ratio between the chip rate Rc (cp/s) and the information rate Rb (symb/s) is denominated as Spreading Factor SF: SF = Rc/Rb. The bandwidth after spreading, B (modulation bandwidth), is in rough terms SF times the bandwidth before spreading W: B SF W. Typically, the narrow-band signal is spread up for a factor of some 100, creating a wide-band signal. The bandwidth increases with spreading but the spectral power density necessary for transmission decreases. For WCDMA only very small power densities, often below the level of natural background noise, are needed. 34

35 Spreading and Despreading Data Code (pseudo noise) Data x Code Chip Symbol Symbol Chip Spreading Spectrum Despreading Code +1-1 Data +1-1 Power TDMA Power Spread Spectrum noice Frequency noice Frequency 200kHz band per GSM carrier 5MHz band per WCDMA carrier 35

36 Spreading and Despreading 36

37 The 3 rd Generation UMTS Mobile Network Coding In WCDMA, two operations are applied to the physical channels: -the channelization, which transforms every bit into a SF number of chips -thescrambling, where a scrambling code is applied to the spread signal. In the channelisation operation, Orthogonal Variable Spreading Factor (OVSF) codes are used to preserve the orthogonality between the physical channels of connections operating at different rates. Options are Convolutional or Turbo coding. The SF depends on the bit rate (type of service). High bit rates requires low SF (low # of users) and Low bit rates requires high SF (high # of users). In the uplink, each user has his own scrambling code and can utilise all the codes in the OVSF code-tree. 37

38 Coding The scrambling code is related to the user The spreading code to the type of service at a given bit rate. Downlink scrambling code planning The maximum number of scrambling codes (Gold sequence of chips) are (not all used) divided into 512 sets of primary scrambling codes with 15 secondary scrambling codes (a total of 8192). Each cell is allocated one and only one primary scrambling code. Downlink spreading codes planning The maximum number of OVSF downlink spreading codes is 512. All users in a cell share the available channelisation codes in the OVSF code tree. The use of a single scrambling code per user implies theoretical orthogonality of different services provided by the cell, but the multipath environment disrupts the orthogonality, hence the system is interference limited. 38

39 Channel Coding In CDMA the spreading (& scrambling) process is closely associated with modulation (QPSK): For separating channels from same source: channelisation For separating different cells: FDD mode: Gold codes with 10 ms period (38400 chips at 3.84 Mcps) TDD mode: Scrambling codes with the length 16 For separating different UEs: FDD mode: Gold codes with 10 ms period, or alternatively S(2) codes 256 chip period TDD mode: codes with period of 16 chips and sequences of different length depending on the environment 39

40 Channel Coding Orthogonal Variable Spreading Factor tree (OVSF) 3.84 Mbps 1.92 Mbps 960 kbps 480 kbps 15 kbps CC 1,0 = (0) CC 4,0 = (0,0,0,0) CC 2,0 = (0,0) CC 4, 1 = (0,0,1,1) CC 4, 2 = (0,1,0,1) CC 2,1 = (0,1) CC 4, 3 = (0,1,1,0) CC 8,0 CC 8,1 CC 8,2 CC 8,3 CC 8,4 CC 8,5 CC 8,6 CC 8,7 SF = 1 SF = 2 SF = 4 SF = 8 SF = 16 SF = 256 Variable bitrate User data 15 kbps Mbps Chip stream (3.84 Mchip/s) Channelisation Code (CC) - defines bit rate and channel short code (4-256 chips) always one bit long Scrambling Code (SC) - defines who is transmitting long code ( chips) 40

41 Radio Channels Physical channels are defined by: In FDD, a specific carrier frequency, scrambling code, channelization code, time start & stop (giving a duration) and, on the uplink, relative phase (0 or π/2). In TDD by code, frequency, and time-slot. A logical channel is a radio bearer, or part of it, dedicated for exclusive use of a specific communication process. Different types of logical channel are defined according to the type of information transferred on the radio interface. The channels that are offered by the physical layer for data transport between peer Layer 1 entities are denoted as Transport Channels Radio frames are 10 ms and divided into 15 slots (2560 chip/slot at the chip rate 3.84 Mcps). 41

42 Radio Channels one WCDMA carrier can support 1000 data users with the following assumptions: -100 simultaneous sessions, average data rate per session, 3 kbps. Session length less than 10 minutes in idle mode -90 to 95 calls are inactive, thus not using radio resources -5 to 10 calls are in active session with radio resource allocated, data rate between kbps and the active session lasts a few seconds. Simultaneously 1000 voice users can be supported with assumption of 25 merl. per user load. (Typical capacity of WCDMA carrier, 50 % uplink load. One WCDMA carrier corresponds approximately to 7 GSM carriers (TRX) ) Soft Capacity 50 Erlang 800kbps L1 rate Data Traffic Voice traffic 100% Voice 100% Data 42

43 Multipath Radio Channels and RAKE reception WCDMA is less prone to deep multipath fading. The RAKE-receiver, takes advantage of multipath, as the signals of several correlation receivers belonging to the strongest multipath components are combined to provide an enhanced signal with better quality. 43

44 Multipath Radio Channels and RAKE reception The Rake receiver consists of a bank of Correlators ( fingers ) connected in parallel, with one input of a delayed version of the received signal, and the other input with replica of the Pseudo-Noise sequence used as the spreading code for the generation of the Spread Spectrum signal at the transmitter. Code generators and the Correlators perform the despreading and integration to user data symbols. A matched filter is used to determine and update the multipath delay profile of the channel, used to assign the Rake fingers to the largest peaks. τ 3 Impulse response τ2 Macro diversity τ 1 τ 2 τ 3 time 44 τ 1 Micro diversity fingers PN generator adaptive channel delay τ 1 τ 2 τ 3 Linear combiner Σ data

45 Radio Channels Power Control Power Control is the most important aspect in WCDMA (Near-Far problem) Node B performs estimates of received SIR and commands the Mobile station on a rate of 1500 Hz (faster than path losses) to lower or raise power in UL Downlink Power Control used to update SIR setpoint at Node B - Access slot -P out Node B - UL interference order Open loop power control Up Down System info. (BCCH) P out to use next time Inner loop power control Outer loop Node B will measure BER and FER and set a SIR reference value. This value is sent to UE. If UE measures a lower value on the dl, then it asks Node B to power up, else it asks Node B to power down. Similarly Node B can ask UE to power up or down based on the SIR ref. value TPC request Up Down (DCCH) TPC is sent 1500 times per second (one each timeslot) in L1 info. TPC is either up or down! 45 TPC

46 Radio Channels Handovers Soft handover is an operating mode where more than one Base Station has a communications link established with an UE CORE NETWORK Iu CORE NETWORK Iu RNC Iur DRNC Iub Iub Iub Iub Node B Node B Node B Node B Soft Handover Intra RNC Soft Handover Inter RNC 46

47 Radio Channels Handovers Softer handover is the special case of a soft handover between sectors/cells belonging to the same base station site RNC Node B Softer Handover 47

48 Smart Antennas consist of antenna arrays capable of providing enhanced coverage and range extension, robustness to system perturbations, improved link quality through multipath management, improved system capacity and also spatial separation of signals. Smart Antennas use Adaptive techniques of Signal Processing for Position Location, Optimum Array Processing, Spatial Filtering, and Software Radio Smart Antennas Beamforming MUSIC BEAMPATTERN Direction of Arrival

49 Cell Planning Differences GSM-UMTS CDMA: No frequency planning Joint prediction of coverage and capacity and quality Must consider mix of services and bit rates 1 mobile 2 mobiles n mobiles higher bitrates have lover SF => lower range or higher E b EDGE 384 kbps UMTS 384 kbps GSM 1800 UMTS 144 kbps GSM 900 UMTS 64 kbps UMTS Speech Potential problem in a dense network -adding new cells may decrease capacity -pilot pollution Careful power planning required 49

50 Coverage - Differences GSM-UMTS 47 sites 2G 3G 176 sites 2G Coverage vs. 3G Coverage a 50% decrease in cell radius and a 4.2x increase in number of sites! (voice vs. 384 kbps) 50

51 Terminal Equipment Faster Processors, More Memory 51

52 Software Radio A direct-conversion software-defined cellular handset can handle a wider range of frequencies and bandwidths because it goes directly from RF to baseband (or vice versa) without an I-F section and its inflexible components. The unit saves bandwidth by using quadrature RF converters that split signals into inphase and quadrature (I and Q) components, which can be transmitted over the same channel without interfering with one another. ADC=analog-to-digital converter DAC = digital-to-analog converter DSP = digital signal processor I-F = intermediate frequency RF = radio frequency 52

53 Software Radio 53