CDMA

Telecom Tutorials
Monday, June 03, 2013www.tempustelcosys.com
CDMA SYSTEM

1: Direct sequence and frequency hopped spread spectrum, spreading
sequence and their correlation functions, Acquisition and tracking of
spread spectrum signals.
2: Error probability for DS-CDMA, on AWGN channels, DS-CDMA on
frequency selective fading, channels, Performance analysis of cellular
CDMA.
3: Capacity estimation, Power control, effect of imperfect power
control on DS CDMA performance, Soft Handoffs.
4: Spreading /coding tradeoffs, multi-carrier CDMA, IS-95 CDMA
system, third generation CDMA systems, multi-user detection.

• 1G Analog Cellular
• 2G TDMA - GSM
• 2G CDMA - IS-95
• 2.5G
• 3G
• 4G and Beyond

First Generation (1G) mobile systems were designed to
offer a single service, i.e., speech.
Second Generation (2G) mobile systems were also
designed primarily to offer speech with a limited capability to
offer data at low rates.
Third Generation (3G) mobile systems are expected to
offer high-quality multi-media services and operate in
different environments.
3G systems are referred to as Universal Mobile
Telecommunications System (UMTS) in Europe and
International Mobile Telecommunications 2000 (IMT2000)
worldwide.

1G: First generation wireless cellular: Early 1980s
Analog transmission, primarily speech: AMPS (Advanced Mobile
Phone Systems) and others
2G: Second generation wireless cellular: Late 1980s
Digital transmission
Primarily speech and low bit-rate data (9.6 Kbps)
High-tier: GSM, IS-95 (CDMA), etc
Low-tier (PCS): Low-cost, low-power, low-mobility e.g. PACS
2.5G: 2G evolved to medium rate (< 100kbps) data
3G: future Broadband multimedia
144 kbps - 384 kbps for high-mobility, high coverage
2 Mbps for low-mobility and low coverage
Beyond 3G: research in 4G

AAMPSPS
IS-95
GSM
CDMA-2000
1XRTT
GPRS
CDMA2000
3XRTT
(UMTS)
EDGE
W-CDMA
(UMTS)1G-2G Migration
TDMA Migration
CDMA Migration
1980 1999 2000 2001 2002 2003
1 Kbps
10 Kbps
50 Kbps
100 Kbps
150 Kbps
500 kbps
2 Mbps

Mobile radio telephones were used for military communications in early
20th century
Car-based telephones first introduced in mid 1940s
Single large transmitter on top of a tall building
Single channel used for sending and receiving
To talk, user pushed a button, enabled transmission and disabled
reception
Became known as “push-to-talk” in 1950s
CB-radio, taxis, police cars use this technology
IMTS (Improved Mobile Telephone System) introduced in 1960s
Used two channels (one for sending, one for receiving)
No need for push-to-talk
Used 23 channels from 150 MHz to 450 MHz

1G uses analog signals and has 9.6 KHz maximum
transmission speed
Based on Advanced Mobile Phone Service (AMPS),
1G uses 800-900 MHz frequency
Each channel is 30 KHz wide with 45 KHz passband
832 frequencies are available, with 790 used for voice
traffic and 42 for control channel
Two frequencies are required for conversation,
so there are actually only 395 voice channels and
21 control channels
Analog cellular phones are insecure

The need for efficient frequency utilization of the
radio frequency spectrum and the desire to use
digital encoding of voice and digital modulation
of the radio carrier led to the development of this
generation of systems.
This second generation is considered to be a
digital one as opposed to the analogue first
generation.

Voice, data and fax can be integrated into a single
system.
Better compression can lead to better channel
utilization.
Error correction codes can be used for better quality.
Sophisticated encryption can be used.

Digital traffic channels – first-generation systems are almost
purely analog; second-generation systems are digital
Encryption – all second generation systems provide encryption
to prevent eavesdropping
Error detection and correction – second-generation digital traffic
allows for detection and correction, giving clear voice reception
Channel access – second-generation systems allow channels to
be dynamically shared by a number of users

Completely designed from scratch (no backward
compatability)
Uses 124 channels per cell, each channel can support 8
users through TDM (992 users max)
Some channels used for control signals, etc
Several flavors based on frequency:
GSM (900 MHz)
GSM 1800 (called DCS 1800)
GSM 1900 (called DCS 1900) - used in North America

Public
Switched
Telephone
Network
(PSTN)HLR
Gateway
MTSC
Terminating
MSC
VLR
1
10
3
2
10
5
4
10
6
9
10
1. Call made to mobile unit (cellular
phone)
2. Telephone network recognizes number
and gives to gateway MSC
3. MSC can‟t route further, interrogates
user‟s HLR
4. Interrogates VLR currently serving user
(roaming number request)
5. Routing number returned to HLR and
then to gateway MSC
6. Call routed to terminating MSC
7. MSC asks VLR to correlate call to
the subscriber
8. VLR complies
9. Mobile unit is paged
10. Mobile unit responds, MSCs convey
information back to telephone
Legend: MTSC= Mobile Telephone Service Center, BTS = Base Transceiver Station
HLR=Home Location Register, VLR=Visiting Location Register

 Code Division Multiple Access (CDMA) is a digital wireless
technology that was pioneered and commercially developed by
QUALCOMM.
CDMA works by converting speech into digital information, which is
then transmitted as a radio signal over a wireless network. Using a
unique code to distinguish each different call, CDMA enables many
more people to share the airwaves at the same time - without
static, cross-talk or interference.
Commercially introduced in 1995, CDMA quickly became one of the
world's fastest-growing wireless technologies. In 1999, the
International Telecommunications Union selected CDMA as the
industry standard for new "third-generation" (3G) wireless systems.
 Today, over 100 million consumers worldwide rely on CDMA for
clear, reliable voice communications and leading-edge dataMonday, June 03, 2013www.tempustelcosys.com

IS-95 is the best known example of 2G with CDMA
Advantages of CDMA for Cellular
 Frequency diversity – frequency-dependent transmission
impairments have less effect on signal
 Multipath resistance – chipping codes used for CDMA
exhibit low cross correlation and low autocorrelation
 Privacy – privacy is inherent since spread spectrum is
obtained by use of noise-like signals
 Graceful degradation – system only gradually degrades
as more users access the system

 Self-jamming – arriving transmissions from
multiple users not aligned on chip boundaries
unless users are perfectly synchronized
 Near-far problem – signals closer to the receiver
are received with less attenuation than signals
farther away
 Soft handoff – requires that the mobile acquires
the new cell before it relinquishes the old; this
is more complex than hard handoff used in
FDMA and TDMA schemes

 Pilot (channel 0) - allows the mobile unit to acquire
timing information, provides phase reference and
provides means for signal strength comparison
 Synchronization (channel 32) - used by mobile station
to obtain identification information about cellular system
 Paging (channels 1 to 7) - contain messages for one or
more mobile stations
 Traffic (channels 8 to 31 and 33 to 63) – the forward
channel supports 55 traffic channels

 UMTS™ (Universal Mobile Telephone Service) is a
Third Generation (3G) Mobile System being
developed by ETSI™ within the ITU‟s IMT-2000
framework. It will provide data speeds of up to 2
Mbps, making portable videophones a reality.

Fourth generation mobile communications
systems that are characterised by high-
speed data rates at 20 to 100 Mbps, suitable
for high-resolution movies and television.

 Also known as „Mobile Broadband everywhere‟
 „MAGIC‟
› Mobile Multimedia Communication
› Anywhere, Anytime with Anyone
› Global Mobility Support
› Integrated Wireless Solution
› Customized Personal Service.

Higher data rates ~2-20 Mbps.
New air interface needs to be developed
Potential candidate OFDM.
Smart antennas can form directed beams to increase strength of the
desired signal.
A new spectrum needs to be assigned.
All-IP vision: base stations become an access router

Transmission at 20 Mbps
2000 times faster than mobile data rates
10 times faster than top transmission rates planned in final
build out of 3G broadband mobile
10-20 times faster than standard ADSL services.
Companies developing 4G technology
Cellular phone companies: Alcatel, Nortel, Motorola,
IT Companies: Hughes,HP,LG Electronics

Unlike the 3G networks which are a combination of circuit
switched and packet switched networks ,4G will be
based on packet switching only .This will allow low
latency data transmission .

Thank You

CDMA

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