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CMPE 477
Evolution of GSM in to 2.5G and 3G
New Data Services for GSM
HSCSD
GPRS
3G – UMTS
IMT2000
UMTS Architecture
UTRAN Architecture
CMPE 477 – Wireless and Mobile Networks
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 transmissionAIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F14.4
4.8 1
9.6 2 1
14.4 3 1
19.2 4 2
28.8 3 2
38.4 4
43.2 3
57.6 4
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 rate 171.2kbps but …
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
advantage: one step towards UMTS, more flexibledisadvantage: more investment needed (new hardware)
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
GPRS architecture and interfaces
MS BSS GGSNSGSN
MSC
Um
EIR
HLR/GR
VLR
PDN
Gb Gn Gi
SGSN
Gn
Towards 3G: UMTS and IMT-2000
Proposals for IMT-2000 (International Mobile Telecommunications)
UWC-136, cdma2000, WP-CDMA
UMTS (Universal Mobile Telecommunications System) from ETSI (European Proposal)
UMTS
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
IMT-2000 family
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
GSM(MAP)
ANSI-41(IS-634)
IP-NetworkIMT-2000Core NetworkITU-T
IMT-2000 (3G)Radio AccessITU-R
Interface for Internetworking
Flexible assignment of Core Network and Radio Access
Initial UMTS(R99 w/ FDD)
As a single standard could not be found, the ITU standardized five groups of 3G Radio Access Technologies
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 …
UMTS architecture (Release 99)
UTRANUE CNIuUu
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
UMTS domains and interfaces I
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
USIMDomain
MobileEquipment
Domain
AccessNetworkDomain
ServingNetworkDomain
TransitNetworkDomain
HomeNetworkDomain
Cu Uu Iu
User Equipment Domain
Zu
Yu
Core Network Domain
Infrastructure Domain
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-to-end connections
Access Network Domain
Access network dependent functions
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
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
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
OVSF coding
1
1,1
1,-1
1,1,1,1
1,1,-1,-1
X
X,X
X,-X 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,-1,-1,-1
SF=1 SF=2 SF=4 SF=8
SF=n SF=2n
...
...
...
...
Spreading and Scrambling of user Data
data1 data2 data3
scramblingcode1
spr.code3
spr.code2
spr.code1
data4 data5
scramblingcode2
spr.code4
spr.code1
sender1 sender2
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.
UMTS FDD frame structure
W-CDMA• 1920-1980 MHz uplink• 2110-2170 MHz downlink• chipping rate:
3.840 Mchip/s• spreading: UL: 4-256;
DL:4-512
0 1 2 12 13 14...
Radio frame
Pilot FBI TPC
Time slot
666.7 µs
10 ms
Data
Data1
uplink DPDCH
uplink DPCCH
downlink DPCHTPC TFCI Pilot
666.7 µs
666.7 µs
DPCCH DPDCH
2560 chips, 10 bits
2560 chips, 10*2k bits (k = 0...6)
TFCI
2560 chips, 10*2k bits (k = 0...7)
Data2
DPDCH DPCCH
FBI: Feedback InformationTPC: Transmit Power ControlTFCI: Transport Format Combination IndicatorDPCCH: Dedicated Physical Control ChannelDPDCH: Dedicated Physical Data ChannelDPCH: Dedicated Physical Channel
Slot structure NOT for user separation but synchronisation for periodic functions!
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
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
UMTS TDD frame structure (burst type 2)
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 (100-800 power control cycles/s)
0 1 2 12 13 14...
Radio frame
Data1104 chips
Midample256 chips
Data1104 chips
Time slot
666.7 µs
10 ms
Traffic burstGP
GP: guard period96 chips2560 chips
UTRAN architecture
UTRAN comprises several RNSs
Node B can support FDD or TDD or both
RNC is responsible for handover decisions requiring signalingto the UE
Cell offers FDD or TDD
RNC: Radio Network Controller
RNS: Radio Network SubsystemNode B
Node B
RNC
Iub
Node B
UE1
RNS
CN
Node B
Node B
RNC
Iub
Node B
RNS
Iur
Node B
UE2
UE3
Iu
RNC functions
Admission control
Congestion control
Encryption/Decryption
ATM Switching and Multiplexing
Radio resource control
Code allocation
Handover control
Management
B-node and User Equipment
B-Node
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
Core network: architecture
BTS
Node B
BSC
Abis
BTS
BSS
MSC
Node B
Node B
RNC
Iub
Node BRNS
Node BSGSN GGSN
GMSC
HLR
VLR
IuPS
IuCS
Iu
CN
EIR
GnGi
PSTN
AuC
GR
Core network
The Core Network (CN) and thus the Interface Iu, 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), IuCS
Packet Switched Domain (PSD) GPRS components (SGSN, GGSN)
IuPS
Release 99 uses the GSM/GPRS network and adds a new radio access! Helps to save a lot of money …
Much faster deployment
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
Soft handover
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
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
CNNode B RNC
Node BUE
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
SRNC
UE
DRNC
Iur
CN
Iu
Node BIub
Node BIub
Example handover types in UMTS/GSM
RNC1
UE1
RNC2
Iur
3G MSC1
Iu
Node B1
IubNode B2
Node B3 3G MSC2
BSCBTS 2G MSC3
AAbis
UE2
UE3
UE4
Intra Node-B, intra RNC (Softer Handover): Between the antennas of a B-nodeInter Node-B, intra RNC: RNC1 supports soft handover by combining and splitting dataInter RNC: Internal or external inter-RNCInter MSC: Hard handover MSC2 takes overInter system: Hard handover from 3G UMTS network to 2G GSM.
Review Terms
HSCSDGPRSIMT-2000UMTSEDGECAMELUTRAUTRANOVSF codeDS-CDMAUTRA-FDDUTRA-TDDGateway GSNServing GSN
GPRS RegisterB-nodeRNCHard HandoverSoft HandoverSofter Handover
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