CODE DIVISION MULTIPLE ACCESS
May-june 2011
CODE DIVISION MULTIPLE ACCESS
CDMA TECHNOLOGY
THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
Bachelor of Engineering in Electr ical
BY
Ravi Shekhar Sengar
Roll No:-377
SUPERVISOR
PROF. I K Pattharwala
DEPARTMENT OF ELECTRICAL ENGINEERING
GOVERNMENT ENGINEERING COLLEGE
MODASA
CERTIFICATE
This is to certify that
Ravi Shekhar Sengar (377)
Of VIIIth Electrical have has satisfactorily completed his
Project Report
In
CODE DIVISION MULTIPLE ACCESS
And submitted this report
as a part of his project work for the term ending
IN
MAY-JUNE 2011
INTERNAL GUIDE:- Head of department:-
Prof I.K.Pattharwala Prof. H.R.Dave
Date:-
ACKNOWLEDGMENT
I place on record and warmly acknowledge the continuous
encouragement, invaluable supervision, timely suggestions and
inspired guidance offered by my guide Prof. I K pattharwala
,Department of Electrical Engineering ,Government Engineering
College , Modasa in bringing this report to a successful
completion.
I am grateful to Prof. H R Dave , Head of the Department of
Electrical Engineering for permitting me to make use of the
facilities available in the department to carry out the project
successfully. Last but not the least I express my sincere thanks to
all my friends who have patiently extended all sorts of help for
accomplishing this undertaking.
Finally I extend my gratefulness to one and all who are directly
or indirectly involved in the successful completion of this project
work.
Ravi Shekhar Sengar (377)
CONTENT: PAGE-NO:
1. INTRODUCTION.07
2. MAIN TYPES OF CDMA.10
3. BIRTH OF CDMA. 12
4. EVOLUTION OF CDMA. 13
5. CDMA PRINCIPLE.14
6. WORKING OF CDMA.15
7. CDMA IMPLEMENTATION.20
7.1 CDMA CHANNELS
7.2 CDMA FORWARD CHANNELS
7.3 CDMA REVERSE CHANNELS
7.4 CDMA MODULATION
7.5 CDMA FOR CELLULAR
8. DS-CDMA IN CELLULAR SYSTEMS. 23
8.1 THE OBJECTIVES OF IMT-2000
8.2 DS-CDMA TECHNIQUE
8.3 TRANSMITTER STRUCTURE
8.4 RECEIVER STRUCTURE
8.5 PROPERTIES OF DS-CDMA
9. FEATURES OF CDMA. 28
10. GSM 29
11. CDMA VS GSM. 30
12. ADVANTAGES OF CDMA. 35
13. DISADVANTAGES OF CDMA. 36 14. APPLICATION OF CDMA
TECHNOLOGY. 38
15. FUTURE OF WCDMA 38
16. CONCLUSION. 40
17. BIBLIOGRAPHY. 41
Generally a fixed amount of frequency spectrum is allocated to a
cellular system by the national regulator (e.g. in the United
states,the Federal communication commission). Multiple-access
techniques are then deployed so that many users can share the
available spectrum in an efficient manner. Multiple access systems
specify how signals from different sources can be combined
efficiently for transmission over a given radio frequency band and
then separated at the destination without mutual interference.The
three basic multiple access methods currently in use in cellular
systems are:
Frequency division multiple access (FDMA)
Time division multiple access (TDMA)
Code division multiple access (CDMA)
In case of FDMA ,users share the available spectrum in the
frequency domain,and user is allocated a part of the frequency band
called the traffic channel.
In TDMA techniques that are utilized in many digital cellular
systems,the available spectrum is partitioned into narrow frequency
bands or frequency channels (as in FDMA),which in turn are divided
into a number of time slots.An individual user is assigned a time
slot that permits access to the frequency channel for the duration
of the time slot.
The CDMA systems utilizes the spread spectrum technique,whereby
a spreading code(called a pseudo-random noise or PN code) is used
to allow multiple users to share a block of frequency spectrum.In
CDMA cellular systems (e.g. IS-95 in the United States) that use
direct sequence spread (DSS) spectrum techniques,the(digital)
information from an individual user is modulated by means of the
unique PN code (spreading sequence) assigned to each user.All the
PN code-modulated signals from different users are then transmitted
over the entire CDMA frequency channel (e.g.,1.23 MHZ in case of
IS-95).Since the signal in the case of CDMA utilize the entire
allocated block of spectrum,no guard bands of any kind are
necessary within the allocated block.
CDMA permits a more uniform distribution of energy in the
emitted bandwidth Short for Code Division Multiple Access, a
digital cellular technology that uses spread-spectrum techniques.
Unlike competing systems, such as GSM that use TDMA, CDMA does not
assign a specific frequency to each user. Instead, every channel
uses the full available spectrum. Individual conversations are
encoded with a pseudo-random digital sequence. The older version of
the CDMA technology and now it is now known as cdmaOne as well as
IS-95. The other types of CDMA technology has CDMA2000,WCDMA
(Wideband CDMA). The spread spectrum may be viewed as a kind of
modulation scheme in which the modulated(spread spectrum) signal
bandwidth is much greater than the message(baseband) signal
bandwidth. Thus, spread spectrum is a wideband scheme.
The final assessment on the potential superiority of CDMA
systems over TDMA systems,in terms of capacity,cost, and speech
quality,will emerge only after both systems have been in operation
in dense,urban areas with full complements of subscribers and
services.
A CDMA system is clearly not a collision avoidance system like
FDMA and TDMA. The opposite is true and explains the differences in
the behavior of CDMA systems compared to FDMA and TDMA. In general,
the collisions at the channel is a disadvantage of CDMA system and
can be mitigated by careful selection of the sequence and power
control that is close to perfect. CDMA is restricted to a short
distance charging area(SDCA). Currently, there are 2600 SDCAs
within the country. A CDMA-based phone can thus roam only within
its SDCA. This is NOT a technological restriction. In India,
Reliance Infocom and Tata Indicom use CDMA technology to provide
WILL services. In remote rural areas, where installing cables is
difficult as well as expensive, CDMA-based WILL networks can be
deployed quickly. A CDMA doesnt have a SIM card, which makes
m-commerce difficult.
Daily application possible with CDMA is daily downloading, text
communication such as chat,e-mail,sms,member search etc.sending
photo on the air,entertainment and games.
1. INTRODUCTION
This paper is intended to provide an introduction to CDMA use in
wireless telephone systems. The focus is on explaining, in
generally non-technical language, both the key aspects of CDMA
technology, and the primary benefits the technology offers to
wireless communication system operators and their subscribers.
There is a tremendous amount of detailed technical information
which is intentionally not covered in this forum.
It has been necessary, though, to assume at least a rudimentary
familiarity with cellular telephone systems, including the basic
characteristics of radio and the RF spectrum, as well as
fundamental system design concepts such as frequency re-use.
What is CDMA?
One of the most important concepts to any cellular telephone
system is that of "multiple access", meaning that multiple,
simultaneous users can be supported. In other words, a large number
of users share a common pool of radio channels and any user can
gain access to any channel (each user is not always assigned to the
same channel). A channel can be thought of as merely a portion of
the limited radio resource which is temporary allocated for a
specific purpose, such as someone's phone call. A multiple access
method is a definition of how the radio spectrum is divided into
channels and how channels are allocated to the many users of the
system.
The CDMA Cellular Standard
With CDMA, unique digital codes, rather than separate RF
frequencies or channels, are used to differentiate subscribers. The
codes are shared by both the mobile station (cellular phone) and
the base station, and are called "pseudo-Random Code Sequences."
All users share the same range of radio spectrum.
For cellular telephony, CDMA is a digital multiple access
technique specified by the Telecommunications Industry Association
(TIA) as "IS-95".
In March 1992, the TIA established the TR-45.5 subcommittee with
the charter of developing a spread-spectrum digital cellular
standard. In July of 1993, the TIA gave its approval of the CDMA
IS-95 standard.
IS-95 systems divide the radio spectrum into carriers which are
1,250KHz (1.25MHz) wide. One of the unique aspects of CDMA is that
while there are certainly limits to the number of phone calls that
can be handled by a carrier, this is not a fixed number. Rather,
the capacity of the system will be dependent on a number of
different factors. This will be discussed in later sections.
CDMA - Code Division Multiple Access
IS-95 uses a multiple access spectrum spreading technique called
Direct Sequence (DS) CDMA.
Each user is assigned a binary, Direct Sequence code during a
call. The DS code is a signal generated by linear modulation with
wideband Pseudorandom Noise (PN) sequences. As a result, DS CDMA
uses much wider signals than those used in other technologies.
Wideband signals reduce interference and allow one-cell frequency
reuse.
There is no time division, and all users use the entire carrier,
all of the time.
CDMA Technology
Though CDMA application in cellular telephony is relatively new,
it is not a new technology. CDMA has been used in many military
applications, such as anti-jamming (because of the spread signal,
it is difficult to jam or interfere with a CDMA signal), ranging
(measuring the distance of the transmission to know when it will be
received), and secure communications (the spread spectrum signal is
very hard to detect).
Spread Spectrum
CDMA is a "spread spectrum" technology, which means that it
spreads the information contained in a particular signal of
interest over a much greater bandwidth than the original
signal.
The standard data rate of a CDMA call is 9600 bits per second
(9.6 kilobits per second). This initial data is "spread," including
the application of digital codes to the data bits, up to the
transmitted rate of about 1.23 megabits per second. The data bits
of each call are then transmitted in combination with the data bits
of all of the calls in the cell. At the receiving end, the digital
codes are separated out, leaving only the original information
which was to be communicated. At that point, each call is once
again a unique data stream with a rate of 9600 bits per second.
Traditional uses of spread spectrum are in military operations.
Because of the wide bandwidth of a spread spectrum signal, it is
very difficult to jam, difficult to interfere with, and difficult
to identify. This is in contrast to technologies using a narrower
bandwidth of frequencies. Since a wideband spread spectrum signal
is very hard to detect, it appears as nothing more than a slight
rise in the "noise floor" or interference level. With other
technologies, the power of the signal is concentrated in a narrower
band, which makes it easier to detect.
Increased privacy is inherent in CDMA technology. CDMA phone
calls will be secure from the casual eavesdropper since, unlike an
analog conversation, a simple radio receiver will not be able to
pick individual digital conversations out of the overall RF
radiation in a frequency band.
Synchronization
In the final stages of the encoding of the radio link from the
base station to the mobile, CDMA adds a special "pseudo-random
code" to the signal that repeats itself after a finite amount of
time. Base stations in the system distinguish themselves from each
other by transmitting different portions of the code at a given
time. In other words, the base stations transmit time offset
versions of the same pseudo-random code. In order to assure that
the time offsets used remain unique from each other, CDMA stations
must remain synchronized to a common time reference.
The primary source of the very precise synchronization signals
required by CDMA systems is the Global Positioning System (GPS).
GPS is a radio navigation system based on a constellation of
orbiting satellites. Since the GPS system covers the entire surface
of the earth, it provides a readily available method for
determining position and time to as many receivers as are
required.
The Balancing Act
CDMA cell coverage is dependent upon the way the system is
designed. In fact, three primary system characteristics - Coverage,
Quality and Capacity - must be balanced off of each other to arrive
at the desired level of system performance.
In a CDMA system these three characteristics are tightly
inter-related. Even higher capacity might be achieved through some
degree of degradation in coverage and/or quality. Since these
parameters are all intertwined, operators can not have the best of
all worlds: three times wider coverage, 40 time capacity, and "CD"
quality sound. For example, the 13kbps vocoder provides better
sound quality, but reduces system capacity as compared to an 8kbps
vocoder.
Motorola is using system simulation and real world testing to
identify and implement the correct balances in CDMA system
application. Operators will have the opportunity to balance these
parameters to best serve a particular area. The best balance point
may change from cell site to cell site. Sites in dense downtown
areas may trade off coverage for increased capacity. Conversely, at
the outer edges of a system, capacity could be sacrificed for
coverage area.
Motorola's system expertise, as demonstrated by its winning of
the 1995 NCSA Industrial Grand Challenge Award for system
simulation and testing achievements, is especially beneficial to
operators in their efforts to balance system parameters.
2. MAIN TYPES OF CDMA
CDMAONE:
This is the older version of the CDMA technology and now it is
now known as cdmaone as well as IS-95.
CDMA 2000:
We now have cdma2000 and its variants like 1X EV, 1XEV-DO, and
MC 3X. The reffer to variants of usage of a 1.25MHz channel. 3X
uses a 5 MHz channel.
This first phase of cdma2000 - variously called 1XRTT, 3G1X, or
just plain 1X - is designed to double current voice capacity and
support always-on data transmission speeds 10 times faster than
typically available today, some 153.6 kbps on both the forward and
reverse links.
CDMA2000 Technical Detail:
Frequency band: Any existing band. Minimum frequency band
required: 1x: 2x1.25MHz, 3x: 2x3.75 Chip rate: 1x: 1.2288, 3x:
3.6864 Mcps Maximum user data rate: 1x: 144 kbps now, 307 kbps in
the future 1xEV-DO: max 384 kbps - 2.4 Mbps, 1xEV-DV: 4.8 Mbps.
WCDMA:
Wideband CDMA that forms the basis of 3G networks, Developed
originally by Qualcomm, CDMA is characterized by high capacity and
small cell radius, employing spread-spectrum technology and a
special coding scheme. WCDMA uses 5 MHz bandwidth.
CDMA Phones at Glance:
Samsung SCH-N191
LG RD2030
LG-Elect-TM910
LG Electronics TM510
THE Tata Indicom CDMA Mobile Cost Table
Activation Cost
Rs.1050
Monthly Rental
Rs.450
Deposit
Rs.3,000
Handset
Hyundai HGC-310E Rs.9,800Samsung SCH-620 Rs.10,800
3.BIRTH OF CDMA
At World War II
CDMA is a military technology first used during World War II by
the English allies to foil German attempts at jamming
transmissions. The allies decided to transmit over several
frequencies, instead of one, making it difficult for the Germans to
pick up the complete signal.
History Of CDMA
Somewhere close to the Second World War, Hollywood
actress-turned-inventor, Hedy Lamarr and co-inventor George
Antheil, co-patented a way for controlling torpedoes by sending
signals over multiple radio frequencies using random patterns. They
called this frequency hopping.
After some hue and cry, the US Navy discarded their work as
architecturally unfeasible. In 1957, Sylvania Electronic System
Division, in Buffalo, New York , took up the same idea. After the
expiry of the inventors patent, they used the same technology to
secure communications for the US military.
In the mid-80s, the US military declassified what is now called
CDMA technology, a technique based on spread-spectrum technology,
for use in wireless communication. The spread-spectrum technology
works by digitizing multiple conversations, attaching a code(known
only to the sender and receiver), and then breaking the signals
into bits and reassembling them.
Qualcomm, which patented CDMA, and other telecommunication
companies, were attrached to the technology because it enabled many
simultaneous conversations, rather than the limited stop-and-go
transmissions of analogue technology and the previous digital
option.
4.EVOLUTION OF CDMA
1940s and 1950s Spread Spectrum technique for military anti-jam
applications.
1949 Claude Shannon and Robert Pierce develop basic ideas of
CDMA
1970s Several CDMA developments for military systems (e. g.
GPS)
In March 1992, the TIA (Telecommunications Industry Association)
established the TR-45.5 subcommittee with the charter of developing
a spread spectrum digital cellular standard. In July of 1993, the
TIA gave its approval for the CDMA Technology standard.
1993 IS-95 CDMA standard finalized
1995 Commercial operation of N-CDMA system (IS-95) in Hong
Kong/Korea
October 1, 2000 SK Telecom of Korea launches the first
commercial cdma2000 network
April 17, 2001 Ericsson and Vodafone UK claim to have made the
world's first WCDMA voice call over commercial network.
October 1, 2001 NTT DoCoMo launched the first commercial WCDMA
3G mobile network.
January 28, 2002 SK Telecom in Korea launched the world's first
commercial CDMA2000 1xEV-DO.October 1, 2002 Qualcomm announces
world's first Bluetooth WCDMA (UMTS) and GSM Voice Calls.
5.CDMA PRINCIPLE
If we change our communication topology from point-to-point to
point-to-multipoint, we have hanged the communication environment
from single-link to a multiple-access link. The multiple-access
scheme in a spread-spectrum system is termed code-division
multiple-access (CDMA).
Each access to a common channel needs some form of
orthogonality. For frequency-division multiple-access (FDMA), we
achieve orthogonality in the frequency domain by selecting
nonoverlapping unique frequency bands to each user. We achieve
orthogonality in the time domain by selection nonoverlapping unique
time segments to each user; this process is referred to as
time-division multiple-access (TDMA). The spread-spectrum form of
multiple access exploits the orthogonality in the code domain and
is termed code-division multiple-access (CDMA).
The multiuser environment in the spread-spectrum case is set up
for each user in assigning each user a unique spreading sequence
out of a family of orthogonal sequences. Each user in a CDMA
network occupies the same channel bandwidth.
A CDMA system is clearly not a collision avoidance system like
FDMA and TDMA. The opposite is true and explains the differences in
the behavior of CDMA systems compared to FDMA and TDMA. In general,
the collisions at the channel is a disadvantage of CDMA system and
can be mitigated by careful selection of the sequence and power
control that is close to perfect.
6.WORKING OF CDMA
The CDMA uses the spread spectrum technology. The spread
spectrum refers to any system that satisfies the following
conditions :1. The spread spectrum may be viewed as a kind of
modulation scheme in which the modulated(spread spectrum) signal
bandwidth is much greater than the message(baseband) signal
bandwidth. Thus, spread spectrum is a wideband scheme.
2.The spectral spreading is performed by a code that is
independent of the message signal. This same ode is also used at
the receiver to despread the received signal in order to recover
the message signal (from spread spectrum signal). In secure
communication, this code is known only to the person(s) for whom
the message is intended.
The spread spectrum increases the bandwidth of the message
signal by a factor N, called the processing gain. If the message
signal bandwidth is B Hz and the corresponding spread spectrum
signal bandwidth is Bss Hz, then Processing gain N = Bss / B
Thus, the key to CDMA is to be able to extract the desired
signal while rejecting everything else as random noise. A somewhat
simplified description of CDMA follows:
In CDMA each bit time is subdivided into m short intervals
called chips. Typically, there are 64 or 128 chips per bit, but in
the example given below we will use 8 chips/bit for simplicity.
Each station is assigned a unique m-bit code or chip sequence.
To transmit a 1 bit, a station sends its chip sequence. To transmit
a 0 bit, it sends the ones complement of its chip sequence. No
other patterns are permitted. Thus for m = 8, if a station A is
assigned the chip sequence 00011011, it sends a 1 bit by sending
00011011 and 0 bit by sending 11100100.
If we have 1-MHz band available for 100 stations, with FDM each
one would have 10 kHz and could send at 10 kbps (assuming 1 bit per
Hz). With CDMA, each station uses the full 1 MHz, so the chip rate
is 1 Megachip per second. With fewer than 100 chips per bit, the
effective bandwidth per station is higher for CDMA than FDMA, and
the channel allocation problem is also solved.
It is more convenient to use a bipolar notation, with binary 0
being 1 and binary 1 being +1. We will show chip sequences in
parentheses, so a 1 bit for station A now becomes
(-1-1-1+1+1-1+1+1). In Fig. (1), we show the binary chip sequence
assigned to four example stations. In Fig. (2), we show them in our
bipolar notation.
A: 0 0 0 1 1 0 1 1 A: (-1-1-1+1+1-1+1+1)
B: 0 0 1 0 1 1 1 0 B: (-1-1+1-1+1+1+1-1)
C: 0 1 0 1 1 1 0 0 C: (-1+1-1+1+1+1-1-1)
D: 0 1 0 0 0 0 1 0 D: (-1+1-1-1-1-1+1-1)
Fig. (1)Binary chip Fig. (2)Bipolar chip sequence
Sequence for 4 stations
Six Examples:
_ _1_ C S1= ( -1 +1 1 +1 +1 +1 1 -1)
_ 11_ B+C S2= ( -2 0 0 0 +2 +2 0 -2)
1 0_ _ A+B S3= ( 0 0 2 +2 0 -2 0 +2)
1 0 1 _ A+B+C S4= ( -1 +1 3 +3 1 1 1 +1)
1 1 1 1 A+B+C+D S5= ( -4 0 -2 0 +2 0 +2 -2)
1 1 0 1 A+B+C+D S6= ( -2 2 0 2 0 2 +4 0 )
Fig. (3) Six example of Transmission
S1(C = (1+1+1+1+1+1+1+1)/8 = 1
S2(C = (2+0+0+0+2+2+0+2)/8 = 1
S3(C = (0+0+2+2+0-2+0-2)/8 = 0
S4(C = (1+1+3+3+1-1+1-1)/8 = 1
S5(C = (4+0+2+0+2+0-2+2)/8 = 1
S6(C = (2-2+0-2+0-2-4+0)/8 = -1
Fig. (4) Recovery of station Cs signal
Each station has its own unique chip sequence. Lets use symbol S
to indicate the m-chip vector for station S , and S for its
negation. All chip sequences are pairwise orthogonal, by which we
mean that the normalized inner product of any two distinct chip
sequences, S and T (S(T) is 0. In mathematical terms,
m
S(T = 1/m ( Si * Ti = 0
i=1
in plain, English, as many pairs are same as are different. This
orthogonality property will prove crucial. Note that if S(T = 0
then S(T= 0. The normalized inner product of any chip sequence with
itself is 1:
m m
S(S = 1/m ( Si * Si = 1/m ((+1)=1
i=1 i=1
This follows because each of the m terms in the inner product is
1, so the sum is m. Also note that S(S = -1.
During each bit time, a station can transmit a 1 by sending its
chip sequence, it can transmit a 0 by sending negative of its chip
sequence, or it can be silent and transmit nothing. For the moment,
we assume that all stations are synchronized in time, so all chip
sequence begin at the same instant.
When two or more station transmit simultaneously, their bipolar
signals add linearly. For example, if in one chip period three
stations output +1 and one station outputs 1, the result is +2. One
can think of this as adding voltages: three stations outputting +1
volts and 1 station outputting 1 volts gives 2 volts.
In Fig.(3), we see six examples of one or more stations
transmitting at the same time. In the first example, C transmits a
1 bit, so we just get Cs chip sequence. In the second example, both
B and C transmit 1 bits, so we get the sum of their bipolar chip
sequences.
In the third example, station A sends 1 and station B sends a 0.
The others are silent. In the fifth example, all four stations
sends 1 bit. Finally, in the last example A, B, and D sends a 1
bit, while C sends a 0 bit. Note that each of the six sequences S1
through S6 given in Fig. (3) represents only one bit time.
To recover the bit stream of an individual station, the receiver
must know that stations chip sequence in advance. It does the
recovery by computing the normalized inner product of the received
chip sequence (the linear sum of all the stations that transmitted)
and the chip sequence of the station whose bit stream it is trying
to recover. If the received chip sequence is S and the receiver is
trying to listen to a station whose chip sequence is C, it just
computes the normalized inner product, S(C.
To see why this works, imagine the two stations, A and C, both
transmit a 1 bit at the same time that B transmit a 0 bit. The
receiver sees the sum: S = A+B+C and computes
S(C = A(C+ B(C+ C(C =0+0+1 = 1
The first two terms vanish because all pairs of chip sequence
have been carefully chosen to be orthogonal. Now it should be clear
why this property must be imposed on the chip sequence.
To make the decoding process more concrete, let us consider the
six examples of fig.(4) again. Suppose that the receiver is
interested in extracting the bit sent by station C from each of the
six sums S1 through S6. It calculates the bit by summing the
pairwise products of the received S and C vector of Fig.(2), and
then taking 1/8 of the result (since m=8 here). As shown, each time
the correct bit is decoded.
Assumptions in the above Example:
First, we assumed that all the chips are synchronized in time.
In reality, doing so is impossible. What can be done is that the
sender and receiver synchronize by having the sender transmit a
long enough known chip sequence that the receiver can lock onto.
All other (unsynchronized) transmissions are then seen as random
noise.
An implicit assumption in the above example is that the power
levels of all stations are the same as perceived by the receiver.
CDMA is typically used for wireless systems with a fixed base
station and many mobile stations at varying distances from it. The
power levels received at the base station depends on how far away
the transmitters are. A good heuristic here is for each mobile
station to transmit to the base station at the inverse of the power
level it receives from the base station, so a mobile station
receiving a weak signal from the base will use more power than one
getting a strong signal. The base station can also give explicit
commands to the mobile stations to increase or decrease their
transmission power.
We have also assumed that the receiver knows who the sender is.
In principle, given enough computing capacity, the receiver can
listen to all the senders at once by running the decoding algorithm
for each of them in parallel. In real life, suffice it to say that
this is easier than done.
7.CDMA IMPLEMENTATION7.1 CDMA Channels
Just when one grasps an understanding of the CDMA carrier which
is 1.25 MHz wide, someone talks about "traffic channels" and
confuses the issue. The fact is that with CDMA, the path by which
voice or data passes is the entire carrier, as described
previously.
CDMA traffic channels are different: they are dependent on the
equipment platform, such as Motorola's SC products, on which the
CDMA is implemented. Motorola designates channels in three ways:
effective traffic channels, actual traffic channels and physical
traffic channels.
The number of "Effective" traffic channels includes the traffic
carrying channels less the soft handoff channels. The capacity of
an effective traffic channel is equivalent to the traffic carrying
capacity of an analog traffic channel.
The number of "Actual" traffic channels includes the effective
traffic channels, plus channels allocated for soft handoff.
The number of "Physical" traffic channels includes the Pilot
channels, the Sync channels, the Paging channels, the Soft Handoff
Overhead channels and the Effective (voice and data) traffic
channels.
CDMA uses the terms "forward" and "reverse" channels just like
they are used in analog systems. Base transmit equates to the
forward direction, and base receive is the reverse direction.
("Forward" is what the subscriber hears and "reverse" is what the
subscriber speaks.)
7.2 CDMA Forward ChannelsPilot Channel
The pilot channel is used by the mobile unit to obtain initial
system synchronization and to provide time, frequency, and phase
tracking of signals from the cell site.
Sync Channel
This channel provides cell site identification, pilot transmit
power, and the cell site pilot pseudo-random (PN) phase offset
information. With this information the mobile units can establish
the System Time as well as the proper transmit power level to use
to initiate a call.
Paging Channel
The mobile unit will begin monitoring the paging channel after
it has set its timing to the System Time provided by the sync
channel. Once a mobile unit has been paged and acknowledges that
page, call setup and traffic channel assignment information is then
passed on this channel to the mobile unit.
Forward Traffic Channel
This channel carries the actual phone call and carries the voice
and mobile power control information from the base station to the
mobile unit.
7.3 CDMA Reverse ChannelsAccess Channel
When the mobile unit is not active on a traffic channel, it will
communicate to the base station over the access channel. This
communication includes registration requests, responses to pages,
and call originations. The access channels are paired with a
corresponding paging channel.
Reverse Traffic Channel
This channel carries the other half of the actual phone call and
carries the voice and mobile power control information from the
mobile unit to the base station.
7.4 CDMA Modulation
Both the Forward and Reverse Traffic Channels use a similar
control structure consisting of 20 millisecond frames. For the
system, frames can be sent at either 14400, 9600, 7200, 4800, 3600,
2400, 1800, or 1200 bps.
For example, with a Traffic Channel operating at 9600 bps, the
rate can vary from frame to frame, and can be 9600, 4800, 2400, or
1200 bps. The receiver detects the rate of the frame and processes
it at the correct rate. This technique allows the channel rate to
dynamically adapt to the speech or data activity. For speech, when
a talker pauses, the transmission rate is reduced to a low rate.
When the talker speaks, the system instantaneously shifts to using
a higher transmission rate. This technique decreases the
interference to other CDMA signals and thus allows an increase in
system capacity.
CDMA starts with a basic data rate of 9600 bits per second. This
is then spread to a transmitted bit rate, or chip rate (the
transmitted bits are called chips), of 1.2288 MHz. The spreading
process applies digital codes to the data bits, which increases the
data rate while adding redundancy to the system.
The chips are transmitted using a form of QPSK (Quadrature Phase
Shift Keying) modulation which has been filtered to limit the
bandwidth of the signal. This is added to the signal of all the
other users in that cell. When the signal is received, the coding
is removed from the desired signal, returning it to a rate of 9600
bps. When the decoding is applied to the other users' codes, there
is no despreading; the signals maintain the 1.2288MHz bandwidth.
The ratio of transmitted bits or chips to data bits is the coding
gain. The coding gain for the IS-95 CDMA system is 128, or 21
dB.
7.5 CDMA for Cellular
When implemented in a cellular telephone system, CDMA technology
offers numerous benefits to the cellular operator and their
subscribers. These can be summarized as follows:
Capacity increases: 8 to 10 times that of an AMPS analog system,
and 4 to 5 times that of a GSM system.
Improved call quality: CDMA will provide better and more
consistent sound as compared to AMPS. Cellular telephone systems
using CDMA should be able to provide higher quality sound and phone
calls than systems based on other technologies.
Simplified system planning: Engineers will no longer have to
perform the detailed frequency planning which is necessary in
analog and TDMA systems.
Enhanced privacy: Increased privacy over other cellular systems,
both analog and digital, is inherent in CDMA technology.
Increased talk time and standby time for portables: Because of
precise power control and other system characteristics, CDMA
subscriber units normally transmit at only a fraction of the power
of analog and TDMA phones
Advanced Features: These include Multiple/High Quality Vocoders,
Short Messaging Services, Over-the-Air-Activation, Sleep Mode, and
Data/Fax.
8. DS-CDMA IN CELLULAR SYSTEMS
Originally, CDMA technique was employed in military
applications. The purpose was to counteract intentional jamming. At
1980s, Qualcomm investigated the applicability of DS-CDMA on
cellular communications. Finally, they introduced the narrowband
CDMA IS-95 standard in 1993 in which year also the commercial
operation started. Since 1990, wideband CDMA techniques have been
studied and CDMA based cellular systems are now in use in USA and
Korea and will hopefully start in Turkey by 2005. These third
generation cellular systems known as IMT-2000 (International Mobile
Telecommunications System 2000) in USA and UMTS (Universal Mobile
Telecommunications System) in Europe will bring many superior
services as compared to narrowband systems such as GSM.
Wideband cellular systems have many objectives to achieve which
will be summarized next.
8.1 The objectives of IMT-2000
1. Obtaining higher bit rates as:
Full coverage and mobility for 144kbps (ISDN Basic Rate),
preferably 384kbps (ISDN Primary Rate)
Limited coverage and mobility for 2Mbps
Hovewer market demand will determine the actual data rates.
Figure 5 shows the data rates, different cellular systems offer at
different mobility levels.
More flexibility to introduce new services
2. Simultaneous multiple services for one user
3. Services with different Qos.
4. High spectrum efficiency
8.2 DS-CDMA TechniqueSystem Model
We will start with explaining how the CDMA system serves
multiple users.
Suppose there are N transmission sources which share the common
air interface. Any of these sources ,say source i, intends to send
narrowband information Sni. Sni in Figure 6 represents the
narrowband signal. A spreading operation (i() turns the narrowband
signal at point a into a wideband signal at point b which is the
antenna output of the transmitter. In the channel, the wideband
signal Swi is mixed with the other N-1 wideband signals and also
with noise. A despreading operation (i() at the receiver turns the
wideband information Swi into narrowband signal Sni and keeps the
other wideband signals still wideband. The portion of these
wideband signals spectrum and noise spectrum in the information
bandwidth adds up as interference to Sni.
In the channel, all the wideband signals make the total wideband
signal Swk
k
Swk = (k(Snk), k : kth user in the same frequency band
k k(k :spreading operation of user k.
In the receiver, the despreading operation is done :
(i-1( Swk) = Sni + Swik
k k,ki
Bandpass filtering F turns this equation into
F((i-1( Swk)) = Sni + Srik
k k,ki
As a result the original signal Sni is reproduced.There is also
an additional low-level interference component Srik.
k,ki
8.3 Transmitter Structure
The transmitter is made up of a spreading module (multiplier)
and a modulator. A transmitter block diagram is shown in Figure 7.
The source data Sn(t) is a bipolar signal having a value 1 during
one bit period Tb. It is multiplied with a higher frequency
spreading signal C(t) which is also a bipolar signal with a value
1. C(t) has a period Tc which is called chip period.Tc is typically
much smaller than Tb.
An example spreading operation is shown in Figure 8. The output
signal is Sc(t). Tb is a multiple of Tc. The multiplication factor
is in fact the code length. In this example the code length is
12.
Sc(t) is a wideband signal whereas the original signal Sn(t) is
a narrowband signal. From Figure 8 we understand that the bandwidth
of Sc(t) is determined by C(t) but not Sn(t). Therefore, the more
the multiplication factor Tb/Tc, the more the bandwidth Sc(t) has
Sc(t) is fed to a modulator. The modulator can be any type such as
BPSK, QPSK, MSK modulator. This modulator moves the baseband signal
to a high frequency band.
8.4 Receiver Structure
The receiver does the reverse of what the transmitter does. It
despreads and demodulates the received signal.It should also have a
synchronization block. A receiver block diagram is shown in Figure
9.
At the output of the receiver the sum of original source signal
Sn(t),low-correlation interference signal and noise is
obtained.
8.5 Properties of DS-CDMAMultiple Access Capability
If there are multiple users in the channel, then there will be
many DS signals overlapping in both time and frequency. Provided
that crosscorrelations between the code of the desired user and
others are small, the interfering power at the receiver output will
be much smaller than the desired information power.
An example of multiple access capability under the light of the
previously described DS-CDMA technique is shown in Figure 10.
9. FEATURES OF CDMA
CDMA and WiLL
For many years now, India has been a GSM subscriber. In 1999,
when MTNL decided to provide the CDMA-based WiLL(Wireless in Local
Loop) service in India, quite a few eyebrows were raised. The
biggest reason why mobile operators opposed the entry of WiLL is
that it is uncertain to allow mobility in the local loop.
CDMA is restricted to a short distance charging area(SDCA).
Currently, there are 2600 SDCAs within the country. A CDMA-based
phone can thus roam only within its SDCA. This is NOT a
technological restriction.
In India, Reliance Infocom and Tata Indicom use CDMA technology
to provide WiLL services. In remote rural areas, where installing
cables is difficult as well as expensive, CDMA-based WiLL networks
can be deployed quickly.
3G (3rd Generation)
3G, as it is popularly called, refers to the 3rd generation of
wireless networks. The 3rd generation provides higher frequency
bands (of 2Ghz and more) and a bandwidth of around 5 MHz. The
Bandwidth and frequency is matched by speeds of 384 Kbps in a
mobile environment.
Will CDMA be the path towards 3G The world seems to be divided
on this. While the standard choosen by Reliance-CDMA2000 1x-is the
3G avatar of CDMA, the restrictions imposed by the TRAI(Telecom
Regulatory Authority of India) doesnt let it explore the 3G realms.
Plus, some Wide CDMA supporters(W-CDMA) arent helping the situation
by claiming CDMA 1x is not 3G. Third-generation applications
includes WCDMA, 1x and High Data Rate (HDR).
10. GSM
GSM(Global System for Mobile Communications: originally
fromGroupe Spcial Mobile) is the most popularstandardformobile
telephonysystems in the world. TheGSM Association, its promoting
industry trade organization of mobile phone carriers and
manufacturers, estimates that 80% of the global mobile market uses
the standardGSM is used by over 1.5billionpeopleacross more than
212 countries and territories.Its ubiquity enables
internationalroamingarrangements betweenmobile network operators,
providing subscribers the use of their phones in many parts of the
world. GSM differs from its predecessor technologies in that both
signaling and speech channels aredigital, and thus GSM is
considered asecond generation(2G) mobile phone system. This also
facilitates the wide-spread implementation of data communication
applications into the system.
The ubiquity of implementation of the GSM (Global System Market)
standard has been an advantage to both consumers, who may benefit
from the ability to roam and switch carriers without replacing
phones, and also to network operators, who can choose equipment
from many GSM equipment vendors.GSM also pioneered low-cost
implementation of theshort message service(SMS), also called text
messaging, which has since been supported on other mobile phone
standards as well. The standard includes a worldwideemergency
telephone numberfeature (112).
Newer versions of the standard were backward-compatible with the
original GSM system. For example,Release '97of the standard added
packet data capabilities by means ofGeneral Packet Radio
Service(GPRS). Release '99 introduced higher speed data
transmission usingEnhanced Data Rates for GSM Evolution(EDGE).
11. CDMA Vs GSM (The Old Horse)
In India, clutching a cell phone is still sometimes a status
symbol. And if the phone uses technology that is said to be far
superior to the one used in America, well, that calls for a
celebration. That is how it was with GSM technology. But just as
the drinks were being served, Reliance entered the party, bringing
with it outclassed technology. Suddenly, the phones stopped
ringing. Because the outclassed technology had become the
technology. The same people who had said CDMA had no takers were
suddenly fascinated with it. What happened? Why did GSM lose its
appeal? Or, did it?
The Basics
Lets begin by learning what these two acronyms stand for. TDMA
stands for "Time Division Multiple Access", while CDMA stands for
"Code Division Multiple Access". Three of the four words in each
acronym are identical, since each technology essentially achieves
the same goal, but by using different methods. Each strives to
better utilize the radio spectrum by allowing multiple users to
share the same physical channel. You heard that right. More than
one person can carry on a conversation on the same frequency
without causing interference. This is the magic of digital
technology.
Where the two competing technologies differ is in the manner in
which users share the common resource. TDMA does it by chopping up
the channel into sequential time slices. Each user of the channel
takes turns transmitting and receiving in a round-robin fashion. In
reality, only one person is actually using the channel at any given
moment, but he only uses it for short bursts. He then gives up the
channel momentarily to allow the other users to have their turn.
This is very similar to how a computer with just one processor can
seem to run multiple applications simultaneously.
CDMA on he hand really does let everyone transmit at the same
time. Conventional wisdom would lead you to believe that this is
simply not possible. Using conventional modulation techniques, it
most certainly is impossible. What makes CDMA work is a special
type of digital modulation called "Spread Spectrum". This form of
modulation takes the user's stream of bits and splatters them
across a very wide channel in a pseudo-random fashion. The "pseudo"
part is very important here, since the receiver must be able to
undo the randomization in order to collect the bits together in a
coherent order. If you are still having trouble understanding the
differences though, perhaps this analogy will help you. This my own
version of an excellent analogy provided by Qualcomm:
Imagine a room full of people, all trying to carry on one-on-one
conversations. In VDMA each couple takes turns talking. They keep
their turns short by saying only one sentence at a time. As there
is never more than one person speaking in the room at any given
moment, no one has to worry about being heard over the background
din. In CDMA, each couple talk at the same time, but they all use a
different language. Because none of the listeners understand any
language other than that of the individual to whom they are
listening, the background din doesn't cause any real problems.
Voice Encoding
At this point many people confuse two distinctly different
issues involved in the transmission of digital audio. The first is
the WAY in which the stream of bits is delivered from one end to
the other. This part of the "air interface" is what makes one
technology different from another. The second is the compression
algorithm used to squeeze the audio into as small a stream of bits
as possible.
This latter component is known at the "Voice Coder", or Vocoder
for short. Another term commonly used is CODEC, which is a similar
word to modem. It combines the terms "COder" and "DECoder".
Although each technology has chosen their own unique CODECs, there
is no rule saying that one transmission method needs to use a
specific CODEC. People often lump a technology's transmission
method with its CODEC as though they were single entities. We will
discuss CODECs in greater detail later on in this article.
Voice encoding schemes differ slightly in their approach to the
problem. Because of this, certain types of human voice work better
with some CODECs than they do with others. The point to remember is
that all PCS CODECs are compromises of some sort. Since human
voices have such a fantastic range of pitch and tonal depth, one
cannot expect any single compromise to handle each one equally
well. This inability to cope with all types of voice at the same
level does lead some people to choose one technology over
another.
All of the PCS technologies try to minimize battery consumption
during calls by keeping the transmission of unnecessary data to a
minimum. The phone decides whether or not you are presently
speaking, or if the sound it hears is just background noise. If the
phone determines that there is no intelligent data to transmit, it
blanks the audio and reduces the transmitter duty cycle (in the
case of TDMA) or the number of transmitted bits (in the case of
CDMA). When the audio is blanked, your caller would suddenly find
themselves listening to "dead air", and this may cause them to
think the call has dropped.
To avoid this psychological problem, many service providers
insert what is known as "Comfort Noise" during the blanked periods.
Comfort Noise is synthesized white noise that tries to mimic the
volume and structure of the real background noise. This fake
background noise assures the caller that the connection is alive
and well.
However, in newer CODECs such as EVRC (used exclusively on CDMA
systems), background noise is generally suppressed even while the
user is talking. This piece of magic makes it sound as though the
cell phone user is not in a noisy environment at all. Under these
conditions, Comfort Noise is neither necessary, nor desirable. You
can read my article on EVRC by clicking here.
Spectral Efficiency
Channel capacity in a TDMA system is fixed and indisputable.
Each channel carries a finite number of "slots", and you can never
accommodate a new caller once each of those slots is filled.
Spectral efficiency varies from one technology to another, but
computing a precise number is still a contentious issue. For
example, GSM provides 8 slots in a channel 200 kHz wide, while
IS-136 provides 3 slots in a channel only 30 kHz wide. GSM
therefore consumes 25 kHz per user, while IS-136 consumes only 10
kHz per user.
One would be sorely tempted to proclaim that IS-136 has 2.5
times the capacity of GSM. In a one-cell system this is certainly
true, but once we start deploying multiple cells and channel reuse,
the situation becomes more complex. Due to GSM's better error
management and frequency hopping, the interference of a co-channel
site is greatly reduced. This allows frequencies to be reused at
closer range without a degradation in the overall quality of the
service.
Capacity is measured in "calls per cell per MHz". An IS-136
system using N=7 reuse (this means you have 7 different sets of
frequencies to spread out around town) the figure is 7.0. In GSM we
get figures of 5.0 for N=4 and 6.6 for N=3. It was hoped that
IS-136 could use tighter reuse than N=7, but its inability to cope
with interference made this impossible.
Computing this figure for CDMA requires that certain assumptions
are made. Formulas have been devised, and using very optimistic
assumptions, CDMA can provide a whopping 45 users per cell per MHz.
However, when using more pessimistic (and perhaps more realistic)
assumptions, the value is 12. That still gives CDMA an almost 2:1
advantage over the TDMA competition.
In-building Coverage
Now let's deal with another issue involving CDMA and TDMA.
In-building coverage is something that many people talk about, but
few people properly understand. Although CDMA has a slight edge in
this department, due to a marginally greater tolerance for weak
signals, all the technologies fair about the same. This is because
the few dB advantage CDMA has is often "used up" when the provider
detunes the sites to take advantage of this process gain.
Buildings come in many configurations, but the most important
aspect to their construction is the materials used. Steel frame
buildings, or those with metal siding, shield their interiors more
thoroughly than building made of wood. Large window openings allow
signals to penetrate more deeply into buildings, so malls with
glass roofs will generally provide better service than fully
enclosed ones. More important than the type of building however, is
the proximity of the nearest site. When a site is located just
outside a building, it can penetrate just about any building
material. When a site is much further away however, the signals
have a much harder time of getting past the walls of a structure
when it comes to distance, remember that signals are subject to the
"distance squared law". This means that signals decrease by the
square of the distance. A site at 0.25 kilometers away will have 4
times the signal strength of a site at 0.50 kilometers away, and 16
times that of a site 1.0 kilometers away. Distance squared however,
is the rate of signal reduction in free space.
Recent studies have shown that terrestrial communications are
usually subject to rates as high as "Distance cubed", or even
"Distance to the 4th". If the latter is true, then a site 1.0
kilometers away will actually be 256 times weaker than a site 0.25
kilometers away.
In-building penetration is therefore less a technology issue
than it is an implementation issue. Service providers who have
sites close to the buildings you commonly visit will inevitably
look better those who don't. Never use someone else's in-building
experiences unless you expect to go in the same buildings as they
do. You cannot make useful generalizations about in-building
coverage based upon one person's experience.
CDMA does however have one peculiarity concerning in-building
penetration that does not affect TDMA. When the number of users on
a channel goes up, the general level of signal pollution goes up in
tandem. To compensate for this the CDMA system directs each phone
to transmit with slightly more power. However, if a phone is
already at its limit (such as might be the case inside a building)
it cannot do anything to "keep up with the pack". This condition is
known as "the shrinking coverage phenomenon" or "site breathing".
During slow periods of the day you might find coverage inside a
specific building quite good. During rush hour however, you might
find it exceedingly poor (or non-existent).
Some Final Observations
CDMA really comes into its element when you are out in the
countryside with few sites covering large expanses of land. Under
these conditions CDMA provides extremely stable audio with few
frame errors to mess things up. This is because Channel Pollution
is almost unknown in these situations. Under similar conditions
TDMA suffers too readily from interference and it will often blank
the audio. Many people who use CDMA systems in sparsely populated
areas have given this technology extremely high marks.
TDMA systems also have great difficulties in open regions just
outside densely populated areas. In this situation your phone is
exposed to signals coming from countless sites in the densely
populated areas, but there are no dominant signals from a close-by
site. CDMA can suffer under these conditions too (due to channel
pollution), but not quite so badly. Valleys don't present a big
problem for TDMA, but high ground is a killer. You can experience
choppiness in the audio even when your signal indicator is reading
2 or 3 bars.
So in the end, can we really proclaim a winner in the CDMA Vs
TDMA war? For the time being I think not. Perhaps in the future
when newer technologies built around the W-CDMA standard (wideband
CDMA) come into existence, the issue will warrant another look. By
that time, even GSM will have moved to CDMA as its air interface of
choice, but don't let that fool you into believing that they think
the current TDMA air interface is inadequate for its purpose.
Future standards are being built around high speed data.
TECHNOLOGYWISE MARKET SHARE IN INDIA
TECHNOLOGYWISE MARKET SHARE IN WORLD
12. ADVANTAGES OF CDMA
(No SIM card is required.
(Improved call quality: CDMA provides better and more consistent
sound quality than systems based on other technologies.
(Enhanced privacy when compared to systems using other
technologies.
(Increased talk time and standby time for mobiles.
(They are difficult to intercept for an unauthorized person.
(They are easily hidden. For an unauthorized person, it is
difficult to ever detect their presence in many cases.
(They are resistant to jamming.
(Capacity increases of 8 to 10 times that of an AMPS Analog
system, and 4 to 5 times GSM , because of CDMAs unique spread
spectrum technology.
(Many users can share the same carrier frequency, and without
time-sharing. This means that mobile phone service providers can
handle more customers on a CDMA network than on a GSM network.
(Improved call quality, with better and more consistent sound ,
CDMA systems use precise power controlthat is, the base station
sends commands to every mobile phone currently involved in a call,
turning down the power on the nearby ones, and increasing the power
of those further away. The result is a nice, even noise level
across the carrier, with lower overall power levels and no spiky
interference.
(In this civilized atmosphere, each station can easily pick out
its own coded data frames, decode them and deliver a clean end
result. Dropped calls are minimized by CDMA's unique ability to
keep every sector of every cell on the same frequency, so handoffs
are "soft" as the mobile phone moves from one area to the next.
(There is no hole in the signal as one cell is dropped and another
is acquired.)
(CDMA decoders interpret constant sounds, such as road noise, as
having no useful content, and ignore them as much as possible.
(Simplified system planning through the use of the same
frequency in every sector of every cell. Other types of systems
(analog, GSM, etc.) need to break up their frequency spectrum
allotments so that each cell uses a different frequency. And since
no two adjoining cells can use the same frequency, a given cell has
to be surrounded by a circle of six other cells, all of which have
to be on different frequencies. This translates to frequency re-use
of only 1 in 7, and if you change one (by adding a cell for
example), the effects ripple through the system.
(To an eavesdropper, the call looks like unintelligible noise.
CDMA was originally developed by the military for this very
reason.
(CDMA providers have no such planning earaches, since every
sector of every cell uses the same frequency. Enhanced Privacy is
inherent in the way CDMA works. Each call is spread over the entire
1.25 MHz carriermuch wider bandwidth than is needed for a single
call.
(The data bits used to convey real information are mixed with
digital coding that is known only to the base station and the
individual mobile phone.
(Improved coverage characteristics, allowing for the possibility
of fewer cell sites This comes from the accurate power control of
all mobile phones using the site, and the fact that individual
sites don't interfere with each other, since they are all on the
same frequency.
13. DISADVANTAGES OF CDMA
Collision :
In general, the collisions at the channel is a disadvantage of
CDMA system and can be mitigated by careful selection of the
sequence and power control that is close to perfect.
Roaming :
Since most countries have chosen the GSM standard, roaming on
CDMA is limited.
M-commerce :
A CDMA doesnt have a SIM card, which makes m-commerce
difficult.
15. 3G Squeeze: GSM & the Future of Wideband CDMA
The much-longer-than-anticipated cycle of operator investment in
2G GSM and Enhanced Data rates for GSM Evolution (EDGE) networks
combined with moves by Verizon Wireless, NTT DoCoMo, and others to
bring forward the commercial timescale for 4G UMTS Terrestrial
Radio Access Network (UTRAN) Long Term Evolution (LTE) is creating
something of a "3G squeeze" on Wideband CDMA (W-CDMA) and its High
Speed Packet Access (HSPA) releases. Continued high global
investment in GSM/EDGE, combined with industry-wide disappointment
in the performance of W-CDMA up until very recently, have served to
contain investment in W-CDMA for either voice or data services. As
a result, more than three out of four Europeans still uses a plain
old 2G GSM phone today, rather than a 3G W-CDMA phone.Over the last
18 months, HSPA has finally started to deliver on the mobile
broadband marketing promise of 3G that has been bandied about since
the late 1990s. There is genuine excitement on the part of users at
being able to get out their laptops across extensive urban and
suburban areas and consistently get at least 1 Mbit/s throughput
over the air. Yet just as W-CDMA is finally starting to
differentiate itself from 2G and establish itself as the preferred
global platform for mobile broadband services, it faces the
prospect of being made redundant by an acceleration in the time to
market of the 4G mobile WiMax and LTE standards. These technologies
have been designed to be deployed in much larger spectrum channel
widths and offer better spectral efficiency, higher throughput, and
lower latency than anything W-CDMA/HSPA can support.
14. APPLICATION OF CDMA TECHNOLOGY
Daily applications possible with CDMA
Daily Downloads :
ringers
characters
images
horoscopes
Real time stock quotes :
of different stock exchanges
Text Communication :
Chat
instant messaging
SMS
e-mail
message board
member search
Sending photos over the air :
MMS messages
Position Location Services :
navigation assistance
friend finder
Games and Entertainment :
magazine
comic book store
All these services are already being offered in South Korea and
Japan.
List of Telephone Operating Companies In IndiaFixed line
operators
Bharat Sanchar Nigam Limited (BSNL)
Mahanagar Telephone Nigam Limited (MTNL)
Airtel
Reliance
Tata Teleservices
Ping Mobile - only in Punjab region
MTS India - in Rajasthan circle only
Idea Cellular
Vodafone
Tata Docomo(joint venutre of tata and docomo
Uninor
Aircel
virgin
videocon
Mobile operators
Bharat Sanchar Nigam Limited (BSNL)
Mahanagar Telephone Nigam Limited (MTNL) - Dolphin (GSM) and
Garuda (CDMA)
Airtel
Vodafone Essar
Reliance
Tata Indicom
Aircel
Idea
Loop Mobile -
Ping Mobile - CDMA Mobile service from HFCL, operates only in
Punjab
Virgin Mobile India (MVNO) -
MTS India - (previously Shyam Telelink) offers CDMA service
under Sistema-Shyam joint venture.
Tata DoCoMo - GSM services from Tata Teleservices Ltd. with
partnership with Japan's NTT DoCoMo.
Uninor - Telenor and Unitech Group's Joint Venture.
S Tel - Batelco has stakes in it.
T24 or Talk24 - a Future Group -Tata DoCoMo joint venture.
MVNO
Videocon Mobile Service - a joint venture between Videocon and
HFCL
Cheers Mobile Service - Etisalat DB Private Ltd.
In India, only Reliance and Tata Teleservices (thus, Virgin
Mobile too) offers dual mode operations, i.e. CDMA & GSM
services. Now HFCL & Videocon as per brand sharing agreement
they have dual mode operation in Punjab.
Future-dated Mobile Operators
CDMA Mobile service from state-owned BSNL
3G Operators
MTNL
BSNL
India completed 3G airwave(GSM) auction and planned to allocate
3G airwaves soon(September, 2010) to the winners. Aircel, Airtel,
Idea Cellular, Reliance (GSM), S Tel, Tata Teleservices (Tata
Docomo), Vodafone won licenses for 3G services. No operator won pan
India 3G license.
16. CONCLUSION
After these wonderful particulars of CDMA technology I arrive at
the conclusion as follows:
Where CDMA scores
Where CDMA needs to scores
Where CDMA scores :
Voice Quality :
CDMA reduces background noise and cross talk, ensuring better
voice quality, which is further enhanced by the microprocessors
inside the phones.
Call Security :
By design, CDMA is more secure against evasdropping.
Talk Time :
A CDMA phone consumes very little power, and has a longer talk
time.
Bandwidth :
CDMA 2000 1x offers 144kbps, which makes it capable for
multimedia tasks.
Weight :
CDMA phones due to their low-power requirements can do with
smaller-sized batteries, which decrease the overall weight of a
CDMA phone.
Where CDMA needs to score :
Roaming :
Since most countries have chosen the GSM standard, roaming on
CDMA is limited.
M-commerce :
A CDMA doesnt have a SIM card, which makes m-commerce
difficult.
17. BIBLIOGRAPHY
Websites :
www.cdg.org
www.umts.org
www.palowireless.com
www.ieee.org
www.yahoo.com
www.google.com
Figure 5 Data rates of different cellular systems
Sni
(i( )
Sw
channel
inv{(i ( )} =(i( )
Sni
n(t) i(t)
Figure 6: System model of spread spectrum CDMA communication
a
b
c
d
Sw(t)
C(t) = +-1
Data Modulator
(BPSK,QPSK,MSK,...)
Carrier Generator
Bipolar Data
Sn(t)
Figure 3 : Spread Spectrum Transmitter Block Diagram
Spreading
Sc(t)
Code Synch/Tracking
C(t) = +-1
Figure 9: Spread Spectrum Receiver Block Diagram
Code Generator
Data
DeModulator
Carrier Generator
r(t)
Sn(t) + I(t)+n(t)
Despreading
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GOVERNMENT ENGINEERING COLLEGE, MODASA