Evolution of GSM in to 2.5G and 3G

Transcription

1 CMPE 477 Wireless and Mobile Networks Evolution of GSM in to 2.5G and 3G New Data Services for GSM CMPE 477 HSCSD GPRS 3G UMTS IMT2000 UMTS Architecture UTRAN Architecture

2 Data services in GSM I Data transmission standardized with only 9.6 kbit/s advanced coding allows 14,4 kbit/s not enough for Internet and multimedia applications HSCSD (High-Speed Circuit Switched Data) mainly software update bundling of several time-slots to get higher AIUR (Air Interface User Rate) (e.g., 57.6 kbit/s using 4 slots, 14.4 each) advantage: ready to use, constant quality, simple disadvantage: channels blocked for voice transmission AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F

3 Data services in GSM II GPRS (General Packet Radio Service) Avoids the problems of HSCSD by packet switching Network providers charge on volume rather than duration One to 8 slots can be allocated per frame, no fixed assignment but on demand Maximum advantage: rate one 171.2kbps step towards but UMTS, more flexible disadvantage: more investment needed (new hardware) Available data rate depends on the current cell load: using free (idle) slots only if data packets ready to send Transfer rate depends on the capabilities of the MS, also the maximum number of slots per frame is limited Typical Class 10 device achieves a receiving rate of 53.6kbps and a sending rate of 26.8kbps All GPRS services can be used in parallel to conventional GSM services

4 GPRS network elements GSN (GPRS Support Nodes): GGSN and SGSN (Routers) GGSN (Gateway GSN) interworking unit between GPRS and PDN (Packet Data Networks; IP, X25) Performs address conversion, tunnels data Connected to IP networks SGSN (Serving GSN) supports the MS (location, billing, security-ciphering) the delivery of data packets from and to the mobile stations within its geographical service area GR (GPRS Register also called Gateway Location Register) user addresses, part of HLR, current SGSN, current VLR

5 GPRS architecture and interfaces SGSN G n MS BSS SGSN GGSN PDN U m G b G n G i MSC HLR/ GR VLR EIR

6 Towards 3G: UMTS and IMT-2000 Proposals for IMT-2000 (International Mobile Telecommunications) UMTS UWC-136, cdma2000, WP-CDMA UMTS (Universal Mobile Telecommunications System) from ETSI (European Proposal) UTRA (was: UMTS, now: Universal Terrestrial Radio Access): the radio interface requirements min. 144 kbit/s rural (goal: 384 kbit/s) min. 384 kbit/s suburban (goal: 512 kbit/s) up to 2 Mbit/s urban Should be compatible with GSM, IP and ISDN-based networks

7 IMT-2000 family As a single standard could not be found, the ITU standardized five groups of 3G Radio Access Technologies Interface for Internetworking IMT-2000 Core Network ITU-T GSM (MAP) ANSI-41 (IS-634) IP-Network Initial UMTS (R99 w/ FDD) Flexible assignment of Core Network and Radio Access IMT-2000 (3G) Radio Access ITU-R IMT-DS (Direct Spread) UTRA FDD (W-CDMA) 3GPP IMT-TC (Time Code) UTRA TDD (TD-CDMA); TD-SCDMA 3GPP IMT-MC (Multi Carrier) cdma2000 3GPP2 IMT-SC (Single Carrier) UWC-136 (EDGE) UWCC/3GPP IMT-FT (Freq. Time) DECT ETSI

8 Enhancements of GSM EDGE (Enhanced Data rates for GSM Evolution) 2.75G: GSM up to 384 kbit/s, using the same 200kHz wide carrier and the same frequencies Uses enhanced modulation techniques, 8PSK instead of GMSK CAMEL (Customized Application for Mobile Enhanced Logic) VHE (virtual Home Environment) for visiting subscribers services to be offered when a subscriber is roaming, like, for instance, no-prefix dialing QoS Aspects, several migration aspects

9 UMTS architecture (Release 99) UTRAN (UTRA Network) Cell level mobility Radio Network Subsystem (RNS) Encapsulation of all radio specific tasks (handover, resource management, etc.) UE (User Equipment) CN (Core Network) Inter system handover Gateways to other networks UE U u UTRAN I u CN

10 UMTS domains and interfaces I Home Network Domain Z u USIM Domain C u Mobile U u Access I u Equipment Network Domain Domain Serving Network Domain Y u Transit Network Domain Core Network Domain User Equipment Domain Infrastructure Domain User Equipment Domain Assigned to a single user in order to access UMTS services Infrastructure Domain Shared among all users Offers UMTS services to all accepted users

11 UMTS domains and interfaces II Universal Subscriber Identity Module (USIM) Functions for encryption and authentication of users Located on a SIM inserted into a mobile device, stores all user related data Mobile Equipment Domain Functions for radio transmission User interface for establishing/maintaining end-toend connections Access Network Domain Access network dependent functions

12 UMTS domains and interfaces III Core Network Domain Access network independent functions Serving Network Domain Network currently responsible for communication Home Network Domain Location and access network independent functions Transit Network Domain Necessary if the serving network cannot directly contact the home network domain

13 Spreading and scrambling of user data UMTS uses DS-CDMA Constant chipping rate of 3.84 Mchip/s Different user data rates supported via different spreading factors higher data rate: less chips per bit and vice versa User separation via unique, orthogonal scrambling codes users are not separated via orthogonal spreading codes much simpler management of codes: each station can use the same orthogonal spreading codes

14 Spreading Data The first step in a sender is spreading user data using orthogonal spreading codes. This separates the different data streams of a sender. These codes are called orthogonal variable spreading factor (OVSF) codes. Doubles a chipping sequence X with and without flipping the sign of the chips: X and X The spreading factor sf=n become sf=2n

15 OVSF coding 1,1,1,1 1,1 1,1,-1,-1 X,X X 1 X,-X 1,-1,1,-1 SF=n SF=2n 1,-1 1,-1,-1,1 1,1,1,1,1,1,1,1 1,1,1,1,-1,-1,-1,-1 1,1,-1,-1,1,1,-1,-1 1,1,-1,-1,-1,-1,1,1 1,-1,1,-1,1,-1,1,-1 1,-1,1,-1,-1,1,-1,1 1,-1,-1,1,1,-1,-1,1 1,-1,-1,1,-1,1,1, SF=1 SF=2 SF=4 SF=8

16 Spreading and Scrambling of user Data OVSF spreads the data streams but the spreading codes chosen in the senders can be the same After spreading all chip streams are added and scrambled. Scrambling does not further spread the chip sequence but XORs chips based on a code In the FDD mode, this code is unique for each sender and separates all senders In the TDD mode, the scrambling code is cell specific. data 1 data 2 data 3 data 4 data 5 spr. code 1 spr. code 2 spr. code 3 spr. code 1 spr. code 4 scrambling code 1 scrambling code 2 sender 1 sender 2

17 10 ms µs UMTS FDD frame structure Radio frame Time slot Pilot TFCI FBI TPC 2560 chips, 10 bits uplink DPCCH W-CDMA MHz uplink MHz downlink chipping rate: Mchip/s spreading: UL: 4-256; DL: µs µs Data uplink DPDCH 2560 chips, 10*2 k bits (k = 0...6) Data 1 TPC TFCI Data 2 Pilot downlink DPCH DPDCH DPCCH DPDCH DPCCH 2560 chips, 10*2 k bits (k = 0...7) FBI: Feedback Information TPC: Transmit Power Control TFCI: Transport Format Combination Indicator DPCCH: Dedicated Physical Control Channel DPDCH: Dedicated Physical Data Channel DPCH: Dedicated Physical Channel Slot structure NOT for user separation but synchronisation for periodic functions!

18 UTRA-FDD Channels Dedicated Physical Data Channel (DPDCH): Conveys user or signaling data. Spreading factor varies between 4 and 256 Data rates: 960 kbps(spreading factor 4), 480, 240, 120, 60, 30, 15kbps (spreading factor 256) Dedicated Physical Control Channel (DPCCH): Conveys control data for the physical channel Constant spreading factor, 256. Dedicated Physical Channel (DPCH): Multiplexes user and control data Spreading factors between 4 and 512 Data rates 6, 24, 51, 90, 210, 432, 912, and 1872kbps

19 UTRA-FDD Medium Access No collisions on the downlink: Only the Basestation sends Uplink: Nodes use slotted Aloha (15 random access slots) Access a slot by sending a preamble with the lowest transmission power If no acknowledgement is received, try another slot with the next transmission power level

20 UMTS TDD frame structure (burst type 2) 10 ms Radio frame µs Data 1104 chips Time slot Midample 256 chips 2560 chips Data 1104 chips GP Traffic burst GP: guard period 96 chips TD-CDMA 2560 chips per slot spreading: 1-16 symmetric or asymmetric slot assignment to UL/DL (min. 1 per direction) tight synchronisation needed simpler power control ( power control cycles/s)

21 UTRAN architecture RNS RNC: Radio Network Controller RNS: Radio Network Subsystem UE 1 Node B I ub I u RNC CN UE 2 Node B UTRAN comprises several RNSs UE 3 Node B can support FDD or TDD or both Node B I ub I ur RNC is responsible for handover decisions requiring signalingto the UE Node B RNC Cell offers FDD or TDD Node B RNS

22 RNC functions Admission control Congestion control Encryption/Decryption ATM Switching and Multiplexing Radio resource control Code allocation Handover control Management

23 B-Node B-node and User Equipment Power control to mitigate near-far effects Measuring connection qualities and signal strength Supports softer handover User equipment Power control, signal quality measurements, spreading, modulation, encryption and decryption, requesting services from the network Cooperates with RNC for handover

24 Core network: architecture BTS A bis BSS I u VLR Node BTS B BSC I u CS MSC GMSC AuC PSTN EIR HLR Node B GR I ub Node B Node B RNC RNS I u PS SGSN G n GGSN G i CN

25 Core network The Core Network (CN) and thus the Interface I u, too, are separated into two logical domains: Circuit Switched Domain (CSD) Circuit switched service incl. signaling Resource reservation at connection setup GSM components (MSC, GMSC, VLR), I u CS Packet Switched Domain (PSD) GPRS components (SGSN, GGSN) I u PS Release 99 uses the GSM/GPRS network and adds a new radio access! Helps to save a lot of money Much faster deployment

26 Handover Hard Handover: Similar to GSM, switching between different antennas or systems. Inter-frequency handover: Changing the carrier frequency Inter-system handover: Handover to and from GSM or to other IMT-2000 systems Soft handover: New mechanism in UMTS: With hard handoff, a definite decision is made on whether to handoff or not With soft handoff, a conditional decision is made on whether to hand off Available in the FDD mode

27 Soft handover UE Node B Node B RNC Multicasting of data via several physical channels UE can receive signals from up to three antennas which may belong to different node B s Uplink CN simultaneous reception of UE data at several Node Bs by splitting data Reconstruction of data at RNC Downlink Simultaneous transmission of data via different cells Different spreading codes in different cells

28 Soft Handover, Intra RNC RNS controlling the connection is called SRNS (Serving RNS) RNS offering additional resources (e.g., for soft handover) is called Drift RNS (DRNS) SRNC forwards data to its not B and to the DRNC SRNC combines both data streams and forwards to CN Node B SRNC CN UE I ub I ur I u Node B DRNC I ub

29 Example handover types in UMTS/GSM UE 1 Node B 1 RNC 1 3G MSC 1 UE 2 Node B 2 I ub I ur I u UE 3 Node B 3 RNC 2 3G MSC 2 UE 4 BTS BSC 2G MSC 3 A bis A Intra Node-B, intra RNC (Softer Handover): Between the antennas of a B-node Inter Node-B, intra RNC: RNC1 supports soft handover by combining and splitting data Inter RNC: Internal or external inter-rnc Inter MSC: Hard handover MSC2 takes over Inter system: Hard handover from 3G UMTS network to 2G GSM.

30 Review Terms HSCSD GPRS IMT-2000 UMTS EDGE CAMEL UTRA UTRAN OVSF code DS-CDMA UTRA-FDD UTRA-TDD Gateway GSN Serving GSN GPRS Register B-node RNC Hard Handover Soft Handover Softer Handover