Part 6. 3G Mobile Communication Systems WCDMA and cdma2000

Transcription

1 Part 6. 3G Mobile Communication Systems WCDMA and cdma2000 p. 1

2 Introduction Objectives to develop 3G Achieving significantly higher transmission speed capability, encompassing circuit- and packet-switched networks as well as support of multimedia services. Data Networks 2G: low rate 2G: low rate 3G: high rate 3G: high rate 2G: voice 3G: voice, image, video Higher spectral efficiency and overall cost improvement by utilizing advanced technologies. Maximizing the commonality by radio interfaces for multiple operating environments. Compatibility of services within IMT-2000 and fixed networks. p. 2

3 Introduction Key Properties Emphasized in 3G Improved performance over 2G, including: Improved capacity; Improved coverage, enabling migration from a 2G deployment. A high degree of service flexibility, including: Support of a wide range of services with maximum bit rates above 2 Mb/s and the possibility for multiple parallel services on one connection; A fast and efficient packet-access scheme. A high degree of operator flexibility, including: Support of asynchronous inter-base-station operation; Efficient support of different deployment scenarios, including hierarchical cell structure and hot-spot scenarios; Support of evolutionary technologies such as adaptive antenna arrays and multi-user detection. p. 3

4 Introduction Differences Between 2G and 3G Systems Flexible offer of mobile multimedia services Voice/fax/data Wideband data services (high speed Internet/high quality images) Slow bit pipe provided by 2G Voice Low rate data <64kbps (25-64kHz) Faster bit pipe by 3G Multi-media Images Internet 2Mbps (5MHz) Voice p. 4

5 Introduction Spectrum allocation of 3G (1) 1992, ITU, World Administrative Radio Conference the frequencies around 2GHz were available for use by 3G mobile systems called International Mobile Telephony 2000 (IMT-2000) defined several different air interfaces based on CDMA or TDMA target: a single common global IMT-2000 air interface for 3G Target: a single common global IMT-2000 air interface for 3G Europe and Asia: same air interface WCDMA, frequencies around 2GHz North America: spectrum around 2GHz has been auctioned for 2G and no new spectrum is available for IMT-2000, 3G must be implemented within the existing bands by replacing part of the spectrum with 2G p. 5

6 Introduction Spectrum allocation of 3G (2) WRC-2000 IMT-2000 Frequencies source: technology/frequencies.htm p. 6

7 Introduction 3G Standards The nature of communications has been changing People to People People to Things Things to Things Family of ITU standards consisting of two main systems Direct Spread Option (Wideband CDMA) with chip rate of 3.84 Mcps and BW of 5 MHz. Multi-Carrier Option (Cdma2000). Key 3G Requirements: High Speed Packet Data: 144 kbps -- Vehicular; 384 kbps -- Pedestrian, 2 Mbps -- Indoor Global Roaming p. 7

8 Introduction Standardization Efforts (1) Japan Universal Wireless Consortium (UWC) China North America Korea Japan Europe Standard Development Organization Partnership Project Radio Interfaces source: Willie W. Lu, "Broadband wireless mobile" p. 8 SDO working for radio interfaces standardization

9 Introduction Standardization Efforts (2) 3GPP (3G Partnership Project) Spearheaded by ETSI (European Telecommunication Standards Institute) Memberships as in December 1998: ARIB (Japan), ETSI (Europe), T1 (USA), TTA (Korea) and TTC (Japan); May 1999: CWTS (China) Aim: to prepare, approve, and maintain globally applicable technical specifications and technical reports for a 3G mobile system (called Universal Mobile Telecommunication System UMTS) based on the evolved GSM core network and Universal Terrestrial Radio Access (UTRA) (UTRA TDD+FDD=> WCDMA) 3GPP2 Spearheaded by ANSI (American National Standards Institute) Memberships as in January 1999: ARIB, TIA (USA), TTA and TTC. Aim: to cooperate in the preparation of globally applicable technical specifications for a 3G mobile system based on the evolved ANSI/TIA/EIA-41 core networks and cdma2000. OHG (Operators Harmonization Group) To prevent a multiple standard problem. p. 9

10 Introduction Standardization Efforts (3) IMT-Direct Spread IMT-Multi Carrier IMT-Time Code IMT-Single Carrier IMT-Frequency Time IMT Radio Technologies Access Technologies Radio interfaces defined for IMT-2000 p. 10 source: Willie W. Lu, "Broadband wireless mobile"

11 Introduction IMT2000 Capability (1) Planned to deploy in May 2001 Frequency band:2ghz band Information rates: up to 2Mbps IMT2000 Network p. 11 Indoor 2Mbps Pedestrian 384kbps Vehicular 144kbps 11

12 Introduction IMT2000 Capacity (2) Variable bit rates to offer bandwidth on demand Multiplexing of services with different quality requirements on a single connection, e.g., speech video and packet data Delay requirements from delay-sensitive real-time traffic to flexible best-effort packet data Quality requirements from 10% frame error rate to 10-6 bit error rate Coexistence of second and third generation systems and inter-system handovers for coverage enhancements and load balancing Support of asymmetric uplink and downlink traffic, e.g., web browsing causes more loading to downlink than to uplink High spectrum efficiency Coexistence of FDD and TDD modes source: H. Holma and A. Toskala, "WCDMA for UMTS" p. 12

13 Introduction Commercial 3G Services (1) Start with crazy spectrum auctions in Europe Huge success of 2G Telecommunication companies in Europe spent more than 120 billion$ on 3G licenses Great Britain: 34 billion$ Germany: 46 billion$ Vodafone: 9.4 billion$ for one license in Great Britain We spent 10 billion too much Sir Peter Bonfield, CEO, BT Sunday Times, London, 18th February 2001 p. 13

14 Introduction Commercial 3G Services (2) A successful example of 3G The world first 3G network was launched by NTT DoCoMo, Japan, in 2001 Big success of its 3G services i-mode : internet services are added to voice communications Creation of mobile multimedia era ing Web browsing Transactions Banking Reservations for flights and accommodations Stock trading, etc Data base Restaurant guide Town page Dictionary Train transfer info. Cooking recipes, etc. Daily information Weather News Stock prices, etc. Entertainment Karaoke Network game Movie listings Fortune-telling etc. Voice p. 14

15 Introduction Commercial 3G Services (3) 3G in Hong Kong Mainland China: no 3G services Hong Kong: only WCDMA is employed all mobile subscribers: 10.98million four 3G licenses; valid for 15 years; each with a spectrum of 2x14.8MHz +1x5MHz 3G subscribers: 1million 3G subscribers: 2.38million Oct Spectrum Auction Jan Hutchison Dec Smartone H.K. CSL Jun Sunday Jul Jun p. 15

16 Introduction Commercial 3G Services (4) p. 16

17 Introduction Commercial 3G Services (5) CDMA20001x WCDMA CDMA2000 1xEV-DO p. 17

18 Summary: What Is 3G? Why necessary? Explosive expansion of markets Mobile multimedia communications Global standard terminals Big business chances Lower cost due to mass markets Which services? Unknown, but services indicated by the success of i-mode Point-to-point, point-multi points, broadcasting services p. 18

19 WCDMA p. 19

20 Introduction (1) Wideband CDMA a predominant wireless access technology for the 3G systems designed to offer wideband services wireless internet services: download information from the Web, video transmission,... data rate: indoor: 2Mbps, pedestrian: 384kbps, vehicular: 144kbps wide bandwidth (5MHz) is needed for high data rate physical limitations and impairments on radio uplink channels presents a fundamental technical challenge to reliable high data rate communications downlink BS Two Modes: FDD and TDD Frequency division duplex: optimized for widearea coverage, i.e., public macro and micro cells Time division duplex: optimized for public micro and pico cells and unlicensed cordless applications BS MS MS p. 20

21 Introduction (2) FDD: paired spectrum; ideal for symmetric services (voice); inefficient for asymmetric services (e.g. mp3 downloading) 5MHz Uplink 190MHz Downlink Uplink 5MHz Downlink Freq. Time 5MHz TDD: no need for paired spectrum; flexible, efficient for asymmetric services Downlink Uplink Freq. Uplink Downlink Downlink Downlink Time p. 21

22 Introduction (3) Main features of WCDMA Asynchronous inter-base-station operation no requirement on any external system such as GPS new challenges like cell acquisition and soft handoff p. 22

23 Main features of WCDMA Variable rate transmission Introduction (4) to provide multimedia services multi-code transmission is employed in downlink to achieve higher bit rates Adaptive antenna array null out interference and maximize the signal to interference ratio particularly useful for multimedia communications a small number of high rate users give Desired significant interference to low rate users. user with Without adaptive antenna array, the link low rate capacity would be significantly reduced. services dedicated pilot symbols in both up- and down-link facilitate user-unique antenna patterns Turbo coding large coding gain with high rate services like online game p. 23

24 New protocols for WCDMA System Architecture (1) p. 24 UMTS R99 Architecture source: bile_technology_globe.html

25 UTRA Terminologies UE: User Equipment System Architecture (2) interfaces the user and the radio interface consists of Mobile Equipment (ME) and UMTS Subscriber Identity Module (USIM) UTRAN: UMTS Terrestrial Radio Access Network handles all radio related functionality consists of Node B (Base Station) and Radio Network Controller (RNC) Core Network evolved GSM core network switching and touting calls and data connection to external networks consists of Home Location Register (HLR), Mobile Services Switching Center (MSC), Visitor Location Register (VLR), Gateway MSC, Service GPRS Support Node (SGSN), Gateway GPRS Support Node (GGSN) External Network consists of Circuit Switching (CS) network and Packet Switching (PS) network p. 25

26 System Architecture (3) Compare GSM and UMTS Terminologies Note: the functionality of each pair is not necessary the same p. 26

27 Radio Interface - Channel Concepts Three separate channel concepts in UTRA: logical channel, transport channel and physical channel Logical channels define what type of data is transferred Transport channels define how and with which type of characteristics the data is transferred by the physical layer Physical channels define the exact physical characteristics of the radio channel p. 27

28 Radio Interface - Transport Channels (1) Transport Channels: Data generated at higher layers is carried over the air with transport channels, which are mapped in the physical layer to different physical channels Higher Layers Physical Layer p. 28

29 Radio Interface - Transport Channels (2) CCTrCh (Coded Composite Transport Channel): a technology in the UMTS physical layer, is the connection between Transport Channel and Physical Channel which results a data stream from encoding and multiplexing of one or several transport channels One physical control channel + one or more physical data channel => one CCTrCh Two types of Transport Channels dedicated channel (DCH): identified by a certain code on a certain frequency, reserved for a single user only; carries all the information intended for the given user from layers above the physical layer, including data for the actual services and higher layer control information Features: fast power control, fast data rate change on a frame-by-frame basis, support adaptive antenna, support soft handover (illustrated in later sections) common channel: a resource divided between all or a group of users in a cell p. 29

30 Radio Interface - Transport Channels (3) Six types of Common Transport Channels Broadcast Channel (BCH): downlink, transmit network information, e.g., available random access codes and access slots, important for register Forward Access Channel (FACH): downlink, carry control information or packet data Paging Channel (PCH): downlink, carry data relevant to the paging process when the network wants to initiate communication with the terminal Random Access Channel (RACH): uplink, carry control information from the terminal, e.g., requests to set up a connection, or packet data Uplink Common Packet Channel (CPCH): uplink, carry packet-based user data Downlink Shared Channel (DSCH): downlink, carry dedicated user data and/or control information, shared by several users, associated with a downlink DCH Basic network operation needs BCH, RACH, FACH and PCH; DSCH and CPCH is optional p. 30

31 Radio Interface - Transport Channels (4) Mapping of Transport Channels onto the physical channels Transport Channels DCH BCH FACH PCH RACH DSCH CPCH Not directly visible to higher layers, carry only information relevant to physical layer procedures Physical Channels Dedicated Physical Data Channel (DPDCH) Dedicated Physical Control Channel (DPCCH) Primary Common Control Physical Channel (PCCPCH) Secondary Common Control Physical Channel (SCCPCH) Physical Random Access Channel (PRACH) Physical Downlink Shared Channel (PDSCH) Physical Common Packet Channel (PCPCH) Synchronization Channel (SCH) Common Pilot Channel (CPICH) Acquisition Indication Channel (AICH) Paging Indication Channel (PICH) CPCH Status Indication Channel (CSICH) Collision Detection/ Channel Assignment Indicator Channel (CD/CA-ICH) p. 31

32 Physical Layer (FDD) Multiple access method: DS-CDMA System bandwidth 5M allocated spectrum: MHz and MHz chip rate: 3.84Mcps Radio frame structure 10ms/frame, 15slots, 2560chips/slot T slot =2560 chips Slot #0 Slot #1 Slot #i Slot #14 One radio frame: T f =10ms p. 32

33 Uplink - Introduction Spreading factors: modulation scheme: BPSK Two type of uplink dedicated physical channels uplink dedicated physical data channel (uplink DPDCH) carry the DCH transport channel can be zero, one, or several DPDCH on each radio link uplink dedicated physical control (or pilot) channel (uplink DPCCH) carry control information: known pilot bits to support channel estimation for coherent detection, transmit power control (TPC) commands, feedback information (FBI), and an optional transport-format combination indicator (TFCI) one and only one uplink DPCCH on each radio link DPDCH and DPCCH are I/Q code multiplexed within each radio frame Variable data rate: change the spreading factor on DPDCH on a frame-by-frame basis p. 33

34 Uplink - Frame Structure Frame structure for uplink DPDCH/DPCCH p. 34 Source: Jiangzhou Wang, Broadband Wireless Communications, 3G, 4G and Wireless LAN

35 Uplink - Spreading Complex Scrambling Spreading for uplink DPCCH and DPDCHs Source: Jiangzhou Wang, Broadband Wireless Communications, 3G, 4G and Wireless LAN p. 35

36 Uplink - Design Criteria (1) Two terminal oriented design criteria maximize the terminal amplifier efficiency minimize the audible interference from the terminal transmission Uplink DPDCH and DPCCH: Why I/Q code multiplexed (Dual channel QPSK modulation)? Time multiplexed: audible interference due to discontinuous transmission p. 36

37 Uplink - Design Criteria (2) uplink DPDCH and DPCCH: Why I/Q code multiplexed? (Con't) Pure code multiplexed: multicode transmission, increases transmitted signal envelope variations => Higher PAPR (Peak-to-Average Power Ratio) I/Q code multiplexed: DPCCH is maintained on a separate continuous channel, no pulse transmission, minimize audible interference p. 37

38 Uplink - Design Criteria (3) uplink DPDCH and DPCCH: Why complex scrambled? power levels of the DPDCH and DPCCH are typically different; lead to extreme cases to BPSK-type transmission if transmitting the branches independently the I and Q branches are mixed using complex scrambling p. 38

39 Uplink Multiplexing CRC attachment Transport block concatenation/code block segmentation Channel coding Radio frame equalization First Interleaving (20, 40, or 80ms) Source: Harri Homa and Antti Toskala, WCDMA for UMTS Other Transport Channels DPDCH #1 DPDCH #2 DPDCH #N Physical channel mapping Second interleaving (10ms) Physical channel segmentation Radio frame segmentation Rate Matching Transport Channel Multiplexing p. 39

40 Downlink (1) Spreading factors: modulation scheme: QPSK One type of downlink dedicated physical channel downlink dedicated physical channel (downlink DPCH) dedicated data (downlink DPDCH) and control information (downlink DPCCH) (pilot bits, TPC, TFCI) are transmitted on DPCH in time multiplex mode p. 40

41 Downlink (2) Common downlink pilot channels (CPICH) fixed rate, SF=256, 30kbps carry predefined symbol/bit sequence Primary Common Pilot Channel (P-CPICH): a phase reference for the downlink channels Secondly Common Pilot Channel (S-CPICH): a phase reference for a secondary CCPCH carrying downlink access channels only and /or a downlink DPCH p. 41

42 Downlink (3) downlink DPDCH and DPCCH: Why time-multiplexed? Time multiplexed: the common channels have continuous transmission, no audible interference I/Q code multiplexed: downlink multicode transmission: no need for optimization of PAPR as with single code (pair) transmission Code multiplexed: reserving a code for DPCCH results in worse code resource utilization p. 42

43 Downlink (4) downlink spreading: one scrambling code (one code tree) per sector in the base station Variable data rate: rate matching operation or discontinuous transmission Why cannot the spreading factor on DPDCH vary on a frame-by-frame basis? scramble code #4 scramble code #3 scramble code #5 scramble code #1 scramble code #0 scramble code #2 scramble code #6 scramble code #7 scramble code #8 scramble code #0 scramble code #1 downlink scrambling: long codes number of scrambling codes: limited to 512 codes, otherwise the cell search procedure would become too excessive p. 43

44 Downlink Multiplexing CRC attachment DPDCH #1 DPDCH #2 DPDCH #N Transport block concatenation/code block segmentation Channel coding Rate matching Source: Harri Homa and Antti Toskala, WCDMA for UMTS Physical channel mapping Second interleaving (10ms) Physical channel segmentation Insertion of DTX indication (with fixed bit positions only) Other Transport Channels Insertion of DTX indication (with flexible positions only) First Interleaving (20,40 or 80ms) Radio frame segmentation Transport Channel Multiplexing p. 44

45 Scrambling Codes (1) Scrambling in WCDMA is used on top of spreading does not change the signal bandwidth and symbol rate to separate terminals or base stations from each other; use pseudo-noise (PN) codes Spreading in WCDMA increase signal bandwidth to separate channels from each other (channelisation); use orthogonal codes (channelisation codes) p. 45

46 Scrambling Codes (2) Two types of scrambling codes: long and short scrambling codes p. 46

47 Scrambling Codes (3) Uplink physical channels: complex-valued scrambling code, either long or short Long scrambling codes: used if the base station uses a Rake receiver Short scrambling codes: used if the base station uses advanced multiuser detectors or interference cancellation receivers long scrambling code #1 long scrambling code #0 long scrambling code, shift #1 GPS long scrambling code, shift #0 WCDMA long: BS has a Rake receiver short: BS uses multiuser detection IS-95 or CDMA2000 p. 47

48 Signal detection at BS Scrambling Codes (4) Terminal #0 (Scrambling code #0) Terminal #1 (Scrambling code #1) Terminal #2 (Scrambling code #2) long scrambling code: one frame: 10ms, chips Slot #0 Slot #1 Slot #0 Slot #1 Slot #15 Slot #15 Time Time Slot #0 Slot #1 Slot #15 Time Received signal at BS p. 48

49 Scrambling Codes (5) Multiuser detectors or interference cancellation receivers Descrambling using scrambling code #0 Signal detection for user #0 Recovered data symbols for user #0 Received signal at BS Descrambling using scrambling code #1 Signal detection for user #1 Recovered data symbols for user #1 Descrambling using scrambling code #2 Signal detection for user #2 Recovered data symbols for user #2 Delay Interference Regenerator for user #0 Descrambling using scrambling code #0 Signal detection for user #0 Recovered data symbols for user #0 Advantage of short scrambling codes: reduce of processing delay p. 49

50 Channelisation Codes (1) Transmissions from a single source are separated by channelisation codes downlink connection within one sector dedicated channels in the uplink from one terminal WCDMA uses Orthogonal Variable Spreading Factor (OVSF) codes c (c,c) (c,-c) c 2,1 =(1,1) c 4,1 =(1,1,1,1) c 1,1 =(1) c 4,2 =(1,1,-1,-1) c 4,3 =(1,-1,1,-1) c 2,2 =(1,-1) c 4,4 =(1,-1,-1,1) OVSF allows the spreading factor to be changed and orthogonality between different spreading codes of different lengths to be maintained p. 50