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EEE464
Wireless Communications
Shahzad A. Malik,
Ph.D.
[email protected]
CDMA Cellular Networks
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 links
Shahzad Malik
Wireless Communications
Lecture 8
3
CDMA Evolution
 IS-95A (2G)
First CDMA protocol, published in May’99
14.4/9.6 kbps circuit/packet data
 IS-95B (2.5G)
Some technical corrections
New Capabilities, such as higher data rate
64 kbps packet data
 CDMA2000 1X/3X
High speed data (144 kbps packet data with Mobile IP)
Coding (Turbo) and Modulation (Hybrid QPSK)
New dedicated and common channels
Enhanced Power Control
Shahzad Malik
Wireless Communications
Lecture 8
4
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
Shahzad Malik
Wireless Communications
Lecture 8
5
IS-95
(CdmaOne)
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
45 MHz
847.74 MHz
Shahzad Malik
Wireless Communications
892.74 MHz
Lecture 8
7
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
Wireless Communications
Lecture 8
8
IS-95 Channel Structure
Shahzad Malik
Wireless Communications
Lecture 8
9
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
Wireless Communications
Lecture 8
10
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
Wireless Communications
Lecture 8
11
Forward Link Transmission
Shahzad Malik
Wireless Communications
Lecture 8
12
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
Wt
cos wot
Baseband
Filter
Baseband
Filter
Q-PN
Shahzad Malik
Wireless Communications
sin wot
Lecture 8
13
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
Wireless Communications
Lecture 8
14
Reverse Link Transmission
Shahzad Malik
Wireless Communications
Lecture 8
15
Power Control
Near-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
Wireless Communications
Lecture 8
16
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 receiver
RAKE 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
Wireless Communications
Lecture 8
17
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
Wireless Communications
Lecture 8
18
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
Wireless Communications
Lecture 8
19
Soft Handoff
A unique feature of CDMA Mobile
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
Shahzad Malik
Wireless Communications
Lecture 8
20
Soft Handoff Architecture
MSC
R
BSC
BSC
old link
R
BTS
BTS
R
R- handoff request
sent to the old cell
Shahzad Malik
Wireless Communications
BTS
BTS
energy measurements
are made at the mobile
Lecture 8
21
Soft Handoff Gain
Power
(dBm)
Cell A
Cell B
Total at MS
Distance
Shahzad Malik
Wireless Communications
Lecture 8
22
cdma2000
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
Wireless Communications
Lecture 8
24
cdma2000
cdma2000 allocates resources dynamically
Admission 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
Shahzad Malik
Wireless Communications
Lecture 8
25
Third Generation (3G)
Mobile Cellular Systems
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 PSTN
 144 kbps available to users in vehicles over large areas
 384 kbps available to pedestrians over small areas
 Support for 2.048 Mbps for office use
 Symmetrical and asymmetrical data rates
 Support for packet-switched and circuit-switched services
 Adaptive interface to Internet
 More efficient use of available spectrum
 Support for variety of mobile equipment
 Flexibility to allow introduction of new services and
technologies
Shahzad Malik
Wireless Communications
Lecture 8
27
UMTS and IMT-2000
 Proposals for IMT-2000 (International Mobile Telecommunications)
 UWC-136, cdma2000, W-CDMA
 UMTS (Universal Mobile Telecommunications System) from ETSI
 UMTS
 UTRA (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
Wireless Communications
Lecture 8
28
Frequencies for IMT-2000
1850
1900
ITU allocation
(WRC 1992)
Europe
China
IMT-2000
GSM DE
1800 CT
GSM
1800
Japan
T
D
D
2000
1900
T
D
D
IMT-2000
Wireless Communications
MHz
MSS

MSS

cdma2000 MSS
W-CDMA 
MSS

2000
2200
UTRA MSS
FDD  
cdma2000 MSS
W-CDMA 
1950
2100 2150
IMT-2000
MSS

PCS
1850
2050
MSS

UTRA MSS
FDD  
IMT-2000
PHS
North
America
Shahzad Malik
1950
rsv.
2050
2100 2150
MSS

2200
Lecture 8
MHz
29
IMT-2000 family
Interface
for Internetworking
IMT-2000
Core Network
ITU-T
GSM
(MAP)
Shahzad Malik
IP-Network
Flexible assignment of
Core Network and Radio Access
Initial UMTS
(R99 w/ FDD)
IMT-2000
Radio Access
ITU-R
ANSI-41
(IS-634)
IMT-DS
IMT-TC
IMT-MC
IMT-SC
IMT-FT
(Direct Spread)
(Time Code)
(Multi Carrier)
(Single Carrier)
(Freq. Time)
UTRA FDD
(W-CDMA)
3GPP
UTRA TDD
(TD-CDMA);
TD-SCDMA
3GPP
cdma2000
UWC-136
(EDGE)
UWCC/3GPP
DECT
Wireless Communications
3GPP2
Lecture 8
ETSI
30
UMTS services
Data transmission service profiles
Service Profile
High Interactive MM
High MM
Bandwidth
Transport mode
128 kbit/s Circuit switched
2 Mbit/s Packet switched
Medium MM
384 kbit/s Circuit switched
Switched Data
14.4 kbit/s Circuit switched
Simple Messaging
14.4 kbit/s Packet switched
Voice
Bidirectional, video telephone
Low coverage, max. 6 km/h
asymmetrical, MM, downloads
SMS successor, E-Mail
16 kbit/s Circuit switched
Virtual Home Environment (VHE)
 Enables access to personalized data independent of location,
access network, and device
 Network operators may offer new services without changing the
network
 Service providers may offer services based on components
which allow the automatic adaptation to new networks and
devices
 Integration of existing IN services
Shahzad Malik
Wireless Communications
Lecture 8
31
UMTS Architecture (Release 99)
 UTRAN (UTRA Network)
Cell level mobility
Radio Network Subsystem (RNS)
Encapsulation of all radio specific tasks
 UE (User Equipment)
 CN (Core Network)
Inter system handover
Location management if there is no dedicated connection
between UE and UTRAN
Uu
UE
Shahzad Malik
Iu
UTRAN
Wireless Communications
CN
Lecture 8
32
UMTS domains and interfaces
Home
Network
Domain
Zu
Cu
USIM
Domain
Mobile
Equipment
Domain
Uu
Access
Network
Domain
Iu
Yu
Serving
Network
Domain
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
Shahzad Malik
Wireless Communications
Lecture 8
33
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
Wireless Communications
Lecture 8
34
UTRAN architecture
RNS
RNC: Radio Network Controller
RNS: Radio Network Subsystem
UE1
Node B
Iub
Iu
RNC
CN
UE2
Node B
UE3
Iur
Node B
Iub
Node B
RNC
Node B
 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
RNS
Shahzad Malik
Wireless Communications
Lecture 8
35
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
Wireless Communications
Lecture 8
36
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
Not as flexible as newer releases (5, 6)
Shahzad Malik
Wireless Communications
Lecture 8
37
Core network: architecture
VLR
BTS
Abis
BSS
Iu
BSC
MSC
GMSC
PSTN
Node
BTSB
IuCS
AuC
EIR
HLR
GR
Node B
Iub
Node B
RNC
SGSN
GGSN
Gn
Node B
RNS
Shahzad Malik
Gi
IuPS
Wireless Communications
CN
Lecture 8
38
Core network: protocols
VLR
MSC
GSM-CS
backbone
RNS
GMSC
PSTN/
ISDN
GGSN
PDN (X.25),
Internet (IP)
HLR
RNS
SGSN
Layer 3: IP
Layer 2: ATM
Layer 1: PDH,
SDH, SONET
UTRAN
Shahzad Malik
GPRS backbone (IP)
SS 7
CN
Wireless Communications
Lecture 8
39
UMTS protocol stacks (user plane)
UE
Uu
UTRAN
IuCS
3G
MSC
apps. &
protocols
Circuit
switched
RLC
MAC
RLC
MAC
radio
radio
UE
Packet
switched
Shahzad Malik
apps. &
protocols
IP, PPP,
…
PDCP
Uu
SAR
SAR
AAL2
AAL2
ATM
ATM
UTRAN
IuPS
3G
SGSN
Gn
IP tunnel
3G
GGSN
IP, PPP,
…
GTP
RLC
RLC
GTP
UDP/IP
MAC
MAC
AAL5
AAL5
L2
L2
radio
radio
ATM
ATM
L1
L1
PDCP
Wireless Communications
GTP
UDP/IP UDP/IP
GTP
UDP/IP
Lecture 8
40
Support of mobility: macro diversity
UE
Node B
Shahzad Malik
Node B
RNC
CN
Wireless Communications
 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
Lecture 8
41
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
SRNS
 Change of SRNS requires change of Iu
 Initiated by the SRNS
 Controlled by the RNC and CN
Node B
Iub
UE
CN
SRNC
Node B
Iur
Iu
DRNC
Iub
Shahzad Malik
Wireless Communications
Lecture 8
42
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-orthogonal
data1
data2
data3
data4
data5
spr.
code1
spr.
code2
spr.
code3
spr.
code1
spr.
code4
scrambling
code1
sender1
Shahzad Malik
Wireless Communications
scrambling
code2
sender2
Lecture 8
43
OSVF Coding
OVSF - Orthogonal Variable Spreading Factor
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
X,X
1,1,-1,-1,-1,-1,1,1
1
X
...
1,1,-1,-1
1,-1,1,-1,1,-1,1,-1
X,-X
...
1,-1,1,-1
1,-1,1,-1,-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
SF=1 SF=2
Shahzad Malik
Wireless Communications
SF=4
SF=8
Lecture 8
44
UMTS FDD frame structure
W-CDMA
Radio frame
10 ms
0
1
2
...
12
13
14
Time slot
666.7 µs
Pilot
TFCI
FBI
TPC
uplink DPCCH
2560 chips, 10 bits
666.7 µs
uplink DPDCH
Data
2560 chips, 10*2k bits (k = 0...6)
666.7 µs
Data1 TPC TFCI Data2
Pilot
DPDCH DPCCH DPDCH DPCCH
2560 chips, 10*2k bits (k = 0...7)
Slot structure NOT for user
separation but synchronisation
for periodic functions!
Shahzad Malik
downlink DPCH
 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
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
Wireless Communications
Lecture 8
45
Typical UTRA-FDD uplink data rates
User data rate [kbit/s]
12.2
(voice)
64
144
384
DPDCH [kbit/s]
60
240
480
960
DPCCH [kbit/s]
15
15
15
15
Spreading
64
16
8
4
Shahzad Malik
Wireless Communications
Lecture 8
46
UMTS TDD frame structure
Radio frame
10 ms
666.7 µs
0
1
2
Time slot
Data
Midample
1104 chips 256 chips
2560 chips
...
Data
GP
1104 chips
12
13
14
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 (100-800 power control cycles/s)
Shahzad Malik
Wireless Communications
Lecture 8
47