W-CDMA: Air Interface for 3G Systems
Download
Report
Transcript W-CDMA: Air Interface for 3G Systems
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
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…