W-CDMA
AIR INTERFACE FOR 3G SYSTEMS
By
Medapati, Sai Raghavendra Reddy
Gadige, Raghunath
INTRODUCTION
 What is W-CDMA?
 Stands for Wideband Code Division Multiple



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Access
It is a type of 3G cellular network. It acts as
an air interface for 3G systems.
It is an ITU’s IMT-2000 standard.
Uses CDMA technology
Uses 5MHz wide frequency band.
Evolution from 2G to 3G
 From 2G to 2.5G
 GPRS (General Packet Radio Service)
 data rates 56 kbps to 114 kbps
 From 2.5G to 2.75G
 GPRS to EDGE (Enhanced Data rates for
GSM Evolution)
 From 2.75G to 3G
 EDGE to UMTS (Universal Mobile
Telecommunications Service)
 Data rates 144kbps, 384kbps, 2 Mbps.
Compare…
Development
 GSM Successful, Plans 3G systems
 CoDiT (Code Division Testbed) started,
first W-CDMA
 FRAMES ( Future Radio wideband
Multiple Access Systems) started, to
support European 3G standards
 5 groups formed by ETSI (European
Telecommunications Standard
Institute)
Contd…
 W-CDMA developed by NTT DoCoMo
as air interface for 3G FOMA
(Freedom of Mobile Multimedia
Access)
 ITU accepted W-CDMA as IMT-2000
standard.
 W-CDMA adopted in 55 countries
Technical Features
 Data rates 384 kbps (wide coverage),
2 Mbps (local coverage)
 Operates in 2 modes FDD and TDD
 High service flexibility
 Efficient packet access
Contd…
 Supports inter frequency handover,
handover to other systems
 Uses 5 MHz wide frequency band.
High speed.
 Built in support for future
technologies and coverage enhancing
technologies.
Technologies Used
 Asynchronous Network Operation
 Cell Search
 As Asynchronous, no need to search for base
stations
 Uses common base station code with unique
base station time shifts
 Soft Handover
 Communicates same information through 2
or more base stations
 Per call synchronization
Contd…
 Compressed mode
 Mobile devices dual mode
 Handover from WCDMA to GSM crucial
 Compressed mode, SF is changed and
compress the transmitting and receiving
information for a short time span.
 Remaining time for measuring other
frequencies. Measures sent to network
Contd…
 Uplink Power Control
 Due to near-far problem
 Power control for uplink needed
 Open loop and Closed loop
 Closed loop is used with update rate of 1500
Mhz. 2G systems use update rate of 800 Mhz
Contd…
 Random access
 RACH( Random Access Channel), initial
access.
 RACH codes transmitted through downlink
 Scrambling codes and a signature are
randomly selected and sent with increasing
power
 Sufficient power, acquisition indicator.
Contd…
 Coherent Uplink Detection
 Used for data reception.“Pilot symbols” used in
Uplink and Downlink.
 CDMA2000 adopted these Pilot symbols
 OVSF Codes
 higher flexible bearer system to send all kinds of
data
 OVSF (Orthogonal Variable Spreading Factor)
codes, formed form code tree principle.
 Reduces interference, minimizes crosstalk
 Data Rate Indication
 TFCI (Transport Format Combination Indicator)
 Blind-rate detection
Contd…
 Speech Codec
 Speech signal transmitted efficiently with
high capacity, speech codec required
 12. 2 kbps AMR codec used
 High-speed Packet Data
 HSPA (High-Speed Packet Access) an
extension of W-CDMA
 Enhanced data rates up to 100 Mbps
 These are the 4 schemes used in HSPA
shared channel with channel dependent
scheduling, fast link adaption, hybrid
ARQ with sort combining, a short TTI are
used.
Contd…
 Broadcast and Multi cast Services
 MBMS (Multimedia Broadcast and Multicast
Service)
 The user residing at the cell edge, signal from
adjacent base station is used. Downlink soft
handover used.
 Increase in data rates and coverage
 W-CDMA uses same carrier for MBMS where
CDMA2000 uses separate carrier and
separate receiver
Analysis
 Commercial WCDMA network
Development
 WCDMA Subscribers base evolution
WCDMA in Practice
 Uplink Capacity of satellite based WCDMA Systems
Contd…
 The commercial and military
operations now a days using satellite
based WCDMA systems.
 The main factors to be considered are
Uplink and Downlink Capacity.
 There are 2 types of WCDMA used in
this system. Terrestrial WCDMA and
GEOS( Geosynchronous) WCDMA.
Contd…
 Equation to calculate pole capacity.
Where, LF = Load Factor < 1
ful = Adjacent beam to within- beam MAI
b = reduction in adjacent beam MAI due to beam forming
G (lambda/μ) = 1+ (2.32/ sqrt( lambda μ) ) : Effect of dynamic
traffic
W = 3.84 MChips/sec
Preq = Eb/(No+I0) required to meet QOS
M = Channel fade margin needed to guarantee 99% availability ≥ 1
PC Gain = Reduction in fade margin due to power control ≥ 1
L = Losses (implementation losses) ≤ 1
Contd…
 Equation to calculate the capacity of
the mixture of users
Where, k = user type and channel combination
Rcap( i) = Capacity of all users belonging to ith channel
 The above two equations are used to
calculate the uplink capacity of
satellite based WCDMA systems.
Advantages
 W-CDMA provides faster data
connection ( 384kbps and in future
10Mbps
 Can do all the activities that a normal
phone does (SMS, MMS, INTERNET
etc.) and supports fast video
streaming.
 Simultaneous usage of all the
activities even on call.
 We will only be billed for the data
transferred but not for the time
connected.
Contd…..
 In W-CDMA , cells use single
frequency with differentiated codes.
 Cell planning is easier.
 Uses asynchronous operation.
 Longer battery life.
Limitations
 Uses wide frequency band.
Mechanism for maximum usage.
 Cell planning is easier but it should
be done carefully.
Conclusion
 Drastic change in cellular technology
 HSPDA ( High Speed Downlink Packet
Access). Extension of UMTS.
 W-CDMA used in almost every 3G
mobile.
 Research on 4G started.
Literature Cited

http://scholar.lib.vt.edu/theses/available/etd-122199-153028/unrestricted/fakhrul_thesis.pdf

http://www.comlab.hut.fi/opetus/238/lecture4_Intro_to_WCDMA.pdf( intro to wcdma)

http://www.tech-faq.com/wcdma.shtml

http://0el70beril.blogspot.com/2007/06/technical-features.html

http://www.ericsson.com/technology/whitepapers/innovations_in_wcdma.pdf

http://en.wikipedia.org/wiki/2G

http://en.wikipedia.org/wiki/3G

http://en.wikipedia.org/wiki/W-CDMA

http://www.umtsworld.com/technology/wcdma.htm

http://www.researchinchina.com/report/Telecommunications/470.html

http://delivery.acm.org/10.1145/1300000/1292336/a4shanmugan.pdf?key1=1292336&key2=1523038221&coll=GUIDE&dl=GUIDE&CFID=13694613&CFTO
KEN=23668837
Thank You…