shahzad a. malik, ph.d. eee464 wireless communications
DESCRIPTION
Shahzad MalikLecture 83Wireless Communications CDMA IS-95 CDMA – Code Division Multiple Access A digital wireless technology that allow multiple users to share radio frequencies at the same time without interfering with each other IS-95 Second generation CDMA scheme Primarily deployed in North America Transmission structures different on forward and reverse linksTRANSCRIPT
CDMA Cellular Networks
Shahzad Malik Lecture 8 3Wireless Communications
CDMA IS-95CDMA – Code Division Multiple Access A digital wireless technology that allow multiple
users to share radio frequencies at the same time without interfering with each other
IS-95 Second generation CDMA scheme Primarily deployed in North America Transmission structures different on forward and
reverse links
Shahzad Malik Lecture 8 4Wireless Communications
CDMA Evolution IS-95A (2G)
First CDMA protocol, published in May’9914.4/9.6 kbps circuit/packet data
IS-95B (2.5G)Some technical correctionsNew Capabilities, such as higher data rate64 kbps packet data
CDMA2000 1X/3XHigh speed data (144 kbps packet data with Mobile IP)Coding (Turbo) and Modulation (Hybrid QPSK)New dedicated and common channelsEnhanced Power Control
Shahzad Malik Lecture 8 5Wireless Communications
CDMA Evolution 1X EV-DO
(1xRTT Evolution for high-speed integrated Data Only)
The objective is to provide the largest practical number of users to run high-speed packet data applications
2.4 Mbps packet data 1X EV-DV
(1xRTT Evolution for high-speed integrated Data and Voice)
Voice and High Speed Data mixed on one carrier Backward-compatible with CDMA2000 1X 3.1 Mbps packet data
IS-95 (CdmaOne)
Shahzad Malik Lecture 8 7Wireless Communications
IS-95 CDMA Direct Sequence Spread Spectrum Signaling on Reverse
and Forward Links Each channel occupies 1.25 MHz Fixed chip rate 1.2288 Mcps
Reverse CH Forward CH
847.74 MHz 892.74 MHz45 MHz
Shahzad Malik Lecture 8 8Wireless Communications
Spreading Codes in IS-95 Orthogonal Walsh Codes
To separate channels from one another on forward link Used for 64-ary orthogonal modulation on reverse link.
PN Codes Decimated version of long PN codes for scrambling on
forward link Long PN codes to identify users on reverse link Short PN codes have different code phases for different
base stations
Shahzad Malik Lecture 8 9Wireless Communications
IS-95 Channel Structure
Shahzad Malik Lecture 8 10Wireless Communications
IS-95 Forward Link Up to 64 logical CDMA channels each occupying the same 1.25 MHz bandwidth (Chip rate = 1.2288 Mcps) Four types of channels:
Pilot (channel 0) Continuous signal on a single channel Allows mobile unit to acquire timing information Provides phase reference for demodulation process Provides signal strength comparison for handoff
determination Consists of all zeros
Synchronization (channel 32) 1200-bps channel used by mobile station to obtain
identification information about the cellular system System time, long code state, protocol revision, etc.
Shahzad Malik Lecture 8 11Wireless Communications
IS-95 Forward Link Paging (channels 1 to 7)
Contain messages for one or more mobile stations Traffic (channels 8 to 31 and 33 to 63)
55 traffic channels Original specification supported data rates of up to
9600 bps Revision added rates up to 14,400 bps
All channels use same bandwidth Chipping code distinguishes among channels Chipping codes are the orthogonal 64-bit Walsh codes
derived from 64 64 Hadamard matrix
Shahzad Malik Lecture 8 12Wireless Communications
Forward Link Transmission
Shahzad Malik Lecture 8 13Wireless Communications
Cell Separation Walsh code spreading is followed by quadrature
spreading using PN chips with time offsets Adjacent cells have different PN offsets. This prevents interference since time shifted PN
sequences are orthogonal to each other
I-PN
Q-PN
Wt BasebandFilter
BasebandFilter
sin wot
cos wot
Shahzad Malik Lecture 8 14Wireless Communications
IS-95 Reverse Link Up to 94 logical CDMA channels
Each occupying same 1.25 MHz bandwidth (1.2288 Mcps)
Supports up to 32 access channels and 62 traffic channels
Traffic channels mobile unique Each station has unique long code mask based on
serial number 42-bit number, 242 – 1 different masks Access channel used by mobile to initiate call, respond
to paging channel message, and for location update One of the logical channel is permanently and uniquely
associated with each MS. The channel does not change upon handoff.
Shahzad Malik Lecture 8 15Wireless Communications
Reverse Link Transmission
Shahzad Malik Lecture 8 16Wireless Communications
Power ControlNear-Far Problem: a user near the base station would
jam the user far from the base station Power Control - Motivation
Overcomes near-far problem CDMA wouldn’t work without it Copes with path loss and fading Capacity is maximized
By having each user transmitting just sufficient SNR to maintain a target FER
Power Control - Algorithm Open Loop Estimate
Initial transmit power level for the mobile is determined by the received pilot strength
Closed Loop Power Control Base station controls the power level on the mobile by the
received quality information.
Shahzad Malik Lecture 8 17Wireless Communications
Use of Multipath in CDMA Systems FDMA/TDMA (narrow-band)
multipath hurts equalizers are used to cancel multipath
CDMA (wide-band) can discriminate between the multipath arrivals Rake receivers are used to combine multipath signals to reduce
error rate at the receiverRAKE Receiver Concept Multi-path diversity channels (micro-diversity) Problem is how to isolate various multi-path signals?
If the maximal delay spread (due to multi-path) is Tm seconds and if the chip rate 1/Tc = W >> 1/Tm, then individual multi-path signal components can be isolated
Amplitudes and phases of the multipath components are found by correlating the received waveform with delayed versions of the signal
Multi-path with delays less than Tc can’t be resolved
Shahzad Malik Lecture 8 18Wireless Communications
Rake Receiver in IS-95 Rake Receiver is used in Mobile receiver for
combining Multi-path components Signal from different base stations (resolve multi-path
signals and different base station signals) 3 Parallel Demodulator (RAKE Fingers)
For tracking and isolating particular multi-path components (up to 3 different multi-path signals on FL)
1 Searcher Searches and estimates signal strength of
multi-path pilot signals from same cell site pilot signals from other cell sites
Shahzad Malik Lecture 8 19Wireless Communications
Handoff in CDMA System CDMA is specifically designed not only to reduce handoff
failures but also to provide seamless service Handoffs between cells are supported while the mobile is in
traffic or idle MS continuously keeps searching for new cells as it moves
across the network MS maintains active set, neighbor set, and remaining set as
well as candidate set Soft Handoff (macro-diversity)
Mobile commences Communication with a new BS without interrupting communication with old BS
same frequency assignment between old and new BS provides different site selection diversity
Softer Handoff Handoff between sectors in a cell
CDMA to CDMA hard handoff Mobile transmits between two base stations with different
frequency assignment
Shahzad Malik Lecture 8 20Wireless Communications
Soft Handoff
Advantages Contact with new base station is made before the call is
switched Diversity combining is used between multiple cell sites
additional resistance to fading If the new cell is loaded to capacity, handoff can still be
performed for a small increase in BER Neither the mobile nor the base station is required to change
frequency Reduces number of call drops Increases the overall capacity Mobile transmit power is reduced Voice quality near the cell boundaries are improved MS reports the SNR of the candidate sets
A unique feature of CDMA Mobile
Shahzad Malik Lecture 8 21Wireless Communications
Soft Handoff Architecture
MSC
BSC
BTS BTS
BSC
BTSBTS R new lin
k old linkR
R- handoff request sent to the old cell
energy measurements are made at the mobile
R
Shahzad Malik Lecture 8 22Wireless Communications
Soft Handoff Gain
Power(dBm)
Distance
Cell ACell BTotal at MS
cdma2000
Shahzad Malik Lecture 8 24Wireless Communications
cdma2000 cdma2000 supports both voice and data services in
the same carrier provides enhanced voice capacity
Forward link Fast power control in forward/reverse links Lower code rates New code channels
Reverse Link Coherent detection
Higher data rates: 1x up to 153.6 kbps and 1x EV-DV up to 3.09 Mbps
Battery life is improved – efficient power control Introduction of Turbo codes provides better link
quality for supplemental channels
Shahzad Malik Lecture 8 25Wireless Communications
cdma2000cdma2000 allocates resources dynamicallyAdmission control is important to ensure quality of
service for the existing users when new resources are requested
A new request can be call setup, supplemental channel set-up, handoff, data rate change
Available Walsh codes, residual power in the forward and reverse links are considered before granting a request
Third Generation (3G) Mobile Cellular Systems
Shahzad Malik Lecture 8 27Wireless Communications
Third Generation Systems Objective to provide fairly high-speed wireless communications
to support multimedia, data, and video in addition to voice ITU’s International Mobile Telecommunications for the year
2000 (IMT-2000) initiative defined ITU’s view of third-generation capabilities as:
Voice quality comparable to PSTN144 kbps available to users in vehicles over large areas384 kbps available to pedestrians over small areasSupport for 2.048 Mbps for office useSymmetrical and asymmetrical data ratesSupport for packet-switched and circuit-switched servicesAdaptive interface to InternetMore efficient use of available spectrumSupport for variety of mobile equipmentFlexibility to allow introduction of new services and
technologies
Shahzad Malik Lecture 8 28Wireless Communications
UMTS and IMT-2000 Proposals for IMT-2000 (International Mobile Telecommunications)
UWC-136, cdma2000, W-CDMA UMTS (Universal Mobile Telecommunications System) from ETSI
UMTSUTRA (was: UMTS, now: Universal Terrestrial Radio Access)enhancements of GSM
EDGE (Enhanced Data rates for GSM Evolution): GSM up to 384 kbit/s
CAMEL (Customized Application for Mobile Enhanced Logic) VHE (virtual Home Environment)
fits into GMM (Global Multimedia Mobility) initiative from ETSI 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
Shahzad Malik Lecture 8 29Wireless Communications
Frequencies for IMT-2000
IMT-2000
1850 1900 1950 2000 2050 2100 2150 2200 MHz
MSS
ITU allocation(WRC 1992) IMT-2000 MSS
Europe
China
Japan
NorthAmerica
UTRAFDD
UTRAFDD
TDD
TDD
MSS
MSS
DECT
GSM1800
1850 1900 1950 2000 2050 2100 2150 2200 MHz
IMT-2000 MSS IMT-2000 MSS
GSM1800
cdma2000W-CDMA
MSS
MSS
MSS
MSS
cdma2000W-CDMAPHS
PCS rsv.
Shahzad Malik Lecture 8 30Wireless Communications
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-Network
IMT-2000Core NetworkITU-T
IMT-2000Radio AccessITU-R
Interface for Internetworking
Flexible assignment of Core Network and Radio Access
Initial UMTS(R99 w/ FDD)
Shahzad Malik Lecture 8 31Wireless Communications
UMTS servicesData transmission service profiles
Virtual Home Environment (VHE)Enables access to personalized data independent of
location, access network, and deviceNetwork operators may offer new services without
changing the networkService providers may offer services based on components
which allow the automatic adaptation to new networks and devices
Integration of existing IN services
Circuit switched16 kbit/sVoiceSMS successor, E-MailPacket switched14.4 kbit/sSimple Messaging
Circuit switched14.4 kbit/sSwitched Dataasymmetrical, MM, downloadsCircuit switched384 kbit/sMedium MMLow coverage, max. 6 km/hPacket switched2 Mbit/sHigh MMBidirectional, video telephoneCircuit switched128 kbit/sHigh Interactive MM
Transport modeBandwidthService Profile
Shahzad Malik Lecture 8 32Wireless Communications
UMTS Architecture (Release 99)
UTRANUE CN
IuUu
UTRAN (UTRA Network)Cell level mobilityRadio Network Subsystem (RNS)Encapsulation of all radio specific tasks
UE (User Equipment) CN (Core Network)
Inter system handoverLocation management if there is no dedicated
connection between UE and UTRAN
Shahzad Malik Lecture 8 33Wireless Communications
UMTS domains and interfaces
User Equipment DomainAssigned to a single user in order to access UMTS
services Infrastructure Domain
Shared among all usersOffers 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
Shahzad Malik Lecture 8 34Wireless Communications
UMTS domains and interfaces Universal Subscriber Identity Module (USIM)
Functions for encryption and authentication of users Located on a SIM inserted into a mobile device
Mobile Equipment Domain Functions for radio transmission User interface for establishing/maintaining end-to-
end connections Access Network Domain
Access network dependent functions Core Network Domain
Access network independent functions Serving Network Domain
Network currently responsible for communication Home Network Domain
Location and access network independent functions
Shahzad Malik Lecture 8 35Wireless Communications
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 ControllerRNS: Radio Network Subsystem
Node 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
Shahzad Malik Lecture 8 36Wireless Communications
UTRAN functions Admission control Congestion control System information broadcasting Radio channel encryption Handover SRNS moving Radio network configuration Channel quality measurements Macro diversity Radio carrier control Radio resource control Data transmission over the radio interface Outer loop power control (FDD and TDD) Channel coding Access control
Shahzad Malik Lecture 8 37Wireless Communications
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. signalingResource reservation at connection setupGSM 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 deploymentNot as flexible as newer releases (5, 6)
Shahzad Malik Lecture 8 38Wireless Communications
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
Shahzad Malik Lecture 8 39Wireless Communications
Core network: protocols
MSC
RNS
SGSN GGSN
GMSC
HLR
VLR
RNS
Layer 1: PDH, SDH, SONET
Layer 2: ATM
Layer 3: IPGPRS backbone (IP)
SS 7
GSM-CSbackbone
PSTN/ISDN
PDN (X.25),Internet (IP)
UTRAN CN
Shahzad Malik Lecture 8 40Wireless Communications
UMTS protocol stacks (user plane)
apps. &protocols
MAC
radio
MAC
radio
RLC SAR
Uu IuCSUE UTRAN 3GMSC
RLC
AAL2
ATM
AAL2
ATM
SAR
apps. &protocols
MAC
radio
MAC
radio
PDCP GTP
Uu IuPSUE UTRAN 3GSGSN
RLC
AAL5
ATM
AAL5
ATM
UDP/IP
PDCP
RLC UDP/IP UDP/IP
Gn
GTP GTP
L2
L1
UDP/IP
L2
L1
GTP
3GGGSN
IP, PPP,…
IP, PPP,…
IP tunnel
Circuitswitched
Packetswitched
Shahzad Malik Lecture 8 41Wireless Communications
Support of mobility: macro diversity Multicasting of data via
several physical channels Enables soft handover FDD mode only
Uplink simultaneous reception of
UE data at several Node Bs Reconstruction of data at
Node B, SRNC or DRNC Downlink
Simultaneous transmission of data via different cells
Different spreading codes in different cells
CNNode B RNC
Node BUE
Shahzad Malik Lecture 8 42Wireless Communications
Support of mobility: handoff From and to other systems (e.g., UMTS to GSM)
This is a must as UMTS coverage will be poor in the beginning RNS controlling the connection is called SRNS (Serving RNS) RNS offering additional resources (e.g., for soft handover) is
called Drift RNS (DRNS) End-to-end connections between UE and CN only via Iu at the
SRNSChange of SRNS requires change of Iu Initiated by the SRNSControlled by the RNC and CN
SRNC
UE
DRNC
Iur
CN
Iu
Node BIub
Node BIub
Shahzad Malik Lecture 8 43Wireless Communications
Spreading and scrambling of user data 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, quasi 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 precise synchronisation not necessary as the scrambling codes
stay quasi-orthogonaldata1 data2 data3
scramblingcode1
spr.code3
spr.code2
spr.code1
data4 data5
scramblingcode2
spr.code4
spr.code1
sender1 sender2
Shahzad Malik Lecture 8 44Wireless Communications
OSVF 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,-1,11,-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
...
...
...
...
OVSF - Orthogonal Variable Spreading Factor
Shahzad Malik Lecture 8 45Wireless Communications
UMTS FDD frame structureW-CDMA 1920-1980 MHz uplink 2110-2170 MHz downlink chipping rate: 3.840 Mchip/s soft handover QPSK complex power control (1500 power control cycles/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 DPCCHFBI: 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!
Shahzad Malik Lecture 8 46Wireless Communications
Typical UTRA-FDD uplink data rates
User data rate [kbit/s]12.2 (voice)
64 144 384
DPDCH [kbit/s] 60 240 480 960DPCCH [kbit/s] 15 15 15 15Spreading 64 16 8 4
Shahzad Malik Lecture 8 47Wireless Communications
UMTS TDD frame structure
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 period 96 chips2560 chips