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									Prepared By:
Sapan M. Raval (6th I.T.)
Rishin S. Kumar (6th I.T.)
C.U.SHAH COLLEGE OF ENGG. & TECH.
WADHWAN CITY.
                       Code Division Multiple Access




                      WADHWAN CITY
                   DIST: SURENDRANAGAR



                         CERTIFICATE



This is to certify that Mr. / Ms.            SAPAN M. RAVAL

Mr. / Ms.          RISHIN S. KUMAR                     is / are studying in
Sem – VI of B.E. Information Technology having Roll No. 40 & 41

has / have completed his / her / their seminar on the following topic

successfully.

Topic Name:              CDMA TECHNOLOGY




Staff – Incharge                                           Head of Dept.


                                                       (Miss Saroj Bodar)
Date : ___________




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                         Code Division Multiple Access

               ACKNOWLEDGEMENT


       We take this opportunity to thank our respected H.O.D. Saroj

Bodar and Mr. H. D Kothari without whose support and

encouragement, this paper could not have been completed. We also

take this opportunity to thankfull to our other faculty members and

friends who have helped us in gathering and organizing the required

information.




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                       Code Division Multiple Access
ABSTRACT




The world is demanding more from wireless communication
technologies than ever before. More people around the world are
subscribing to wireless services and consumers are using their
phones more frequently. Add in exciting Third-Generation (3G)
wireless data services and applications - such as wireless email,
web, digital picture taking/sending and assisted-GPS position
location applications - and wireless networks are asked to do much
more than just a few years ago. And these networks will be asked
to do more tomorrow.

This is where CDMA technology fits in. CDMA consistently provides
better capacity for voice and data communications than other
commercial mobile technologies, allowing more subscribers to
connect at any given time, and it is the common platform on which
3G technologies are built.

      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.

      CDMA is a "spread spectrum" technology, allowing many
users to occupy the same time and frequency allocations in a given
band/space. As its name implies, CDMA assigns unique codes to
each communication to differentiate it from others in the same
spectrum. In a world of finite spectrum resources, CDMA enables



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many more people to share the airwaves at the same time than do
alternative technologies.

       CDMA has greater voice quality and call clarity than other technologies
because it filters out background noise, cross-talk and interference. CDMA has
fewer dropped calls because it increases voice and date transmission
reliability. CDMA has greater spectral efficiency because it packs more
transmissions into the same space, resulting in fewer cell sites, which
lowers operators' costs. Add to this increased capacity, enhanced privacy,
and improved coverage… why would you use any other wireless
technology?

      The CDMA air interface is used in both 2G and 3G networks. 2G
CDMA standards are branded cdmaOne and include IS-95A and IS-95B.
CDMA is the foundation for 3G services: the two dominant IMT-2000
standards, CDMA2000 and WCDMA, are based on CDMA.


CDMAONE: THE FAMILY OF IS-95 CDMA TECHNOLOGIES



cdmaOne describes a complete wireless system based on the
TIA/EIA IS-95 CDMA standard, including IS-95A and IS-95B
revisions. It represents the end-to-end wireless system and all the
necessary specifications that govern its operation. cdmaOne
provides a family of related services including cellular, PCS and
fixed wireless (wireless local loop).

CDMA 2000: Leads To 3G revolution
CDMA2000 represents a family of ITU-approved, IMT-2000 (3G)
standards and includes CDMA2000 1X and CDMA2000 1xEV
technologies. They deliver increased network capacity to meet
growing demand for wireless services and high-speed data services.
CDMA2000 1X was the world's first 3G technology commercially
deployed (October 2000).

CDMA Deployments
CDMA is the fastest growing wireless technology and it will continue


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                        Code Division Multiple Access
to grow at a faster pace than any other technology. It is the
platform on which 2G and 3G advanced services are built.




                          INDEX

1.    INTRODUCTION                                              2

       1.1  Definition.
       1.2  Overview.
2.    TYPES OF CDMA TECHNOLOGY.                                 3
       2.1  CDMA one.
       2.2  CDMA 2000.
       2.3  Technical details.
       2.4  Wide band CDMA.
3.    BIRTH OF CDMA                                             4
       3.1  CDMA at world war-2.
       3.2  History of CDMA.
4.    EVOLUTION OF CDMA                                         5
5.    SPREAD-SPECTRUM AND CDMA PRINCIPLE                        6
6.    WORKING OF CDMA                                           7
7.    FEATURES OF CDMA                                          11
       7.1  CDMA and WLL.
       7.2   3G Technology.
8.    APPLICATIONS OF CDMA                                      16
9.    COMPARISON OF CDMA AND GSM                                17
        9.1  Introduction.
        9.2   The Basics.
        9.3   Voice Encoding.
        9.4   Spectral efficiency.
        9.5   In building coverage.
        9.6   Final Observations.
10.   ADVANTAGES OF CDMA TECHNOLOGY                             22

11.   DISADVANTAGES OF CDMA TECHNOLOGY                          24

12.   CONCLUSION                                                25
13.   BIBLIOGRAPHY                                              26




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                          1.INTRODUCTION
       1.1 DEFINITION :

       A coding scheme, used as a modulation technique, in which multiple channels
are independently coded for transmission over a single wideband channel.

       1.2 SOME IMPORANT NOTES:

        Note 1: In some communication systems, CDMA is used as an access method
that permits carriers from different stations to use the same transmission equipment
by using a wider bandwidth than the individual carriers. On reception, each carrier
can be distinguished from the others by means of a specific modulation code, thereby
allowing for the reception of signals that were originally overlapping in frequency
and time. Thus, several transmissions can occur simultaneously within the same
bandwidth, with the mutual interference reduced by the degree of orthogonality of the
unique codes used in each transmission .

        Note 2: 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.
       Because Qualcomm Inc. created communications chips for CDMA
technology, it was privy to the classified information. Once the information became
public, Qualcomm claimed patents on the technology and became the first to
commercialize it.
        Code Division Multiple Access (CDMA) is the ultimate in inside
communications technology. The fastest growing wireless technology, CDMA
already has tens of millions of users throughout the world. The reasons for this are
simple. CDMA supports current voice and data needs while providing a quick, cost-
efficient evolutionary path to tomorrow’s systems.
        CDMA has greater voice quality and call clarity than other technologies
because it filters out background noise, cross-talk and interference. CDMA has fewer
dropped calls because it increases voice and date transmission reliability. CDMA has
greater spectral efficiency because it packs more transmissions into the same space,
resulting in fewer cell sites, which lowers operators' costs. Add to this increased
capacity, enhanced privacy, and improved coverage… why would you usee for any
other wireless technology?




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                          Code Division Multiple Access



       2.Main types of CDMA technology:


       2.1 cdmaOne
      This is the older version of the CDMA technology and now it is now known
as cdmaOne as well as IS-95.
       2.2 cdma2000
        We now have cdma2000 and its variants like 1X EV, 1XEV-DO, and 3X. The
refer to variants of usage of a 1.25Mhz channel. 3X uses a 5 Mhz channel.MC
        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.

       2.3 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: 14.4 kbps now, 115 kbps in the future 1xEV-DO:
max 307 kbps - 2.4 Mbps, 1xEV-DV: 4.8 Mbps.

       2.4 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.

       2.5 CDMA Phones at Glance
             Samsung SCH-N191
             LG RD2030
             LG-Elect-TM910
             LG Electronics TM510




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       3. BIRTH OF CDMA

       3.1 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.

        3.2 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 inventor’s 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.




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                 Code Division Multiple Access



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.




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       5. SPREAD SPECTRUM AND CDMA PRICIPLE

       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.
      CDMA2000 systems are currently being deployed in the 450 MHz, 800 MHz,
1700 MHz, 1900 MHz and 2100 MHz bands.




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       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 preson(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 one’s
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. (a), we show the binary chip sequence
assigned to four example stations. In Fig. (b), 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)




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                            Code Division Multiple Access
       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. (a)Binary chip               Fig. (b)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)
       101_      A+B+C            S4= ( -1 +1 –3 +3 –1 –1 –1 +1)
       1111      A+B+C+D          S5= ( -4 0 -2 0 +2 0 +2 -2)
       1101      A+B+C+D          S6= ( -2 –2 0 –2 0 –2 +4 0 )

                       Fig. (c) 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              Fig. (d) Recovery of station
       S4C = (1+1+3+3+1-1+1-1)/8 = 1                       C’s signal
       S5C = (4+0+2+0+2+0-2+2)/8 = 1
       S6C = (2-2+0-2+0-2-4+0)/8 = -1

        Each station has its own unique chip sequence. Let’s 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)²=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.

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        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.(c), 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 C’s 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. (c) represents only one bit time.




        To recover the bit stream of an individual station, the receiver must know that
station’s 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



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                           Code Division Multiple Access
        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.(d) 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.(b), 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.




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       7.FEATURES OF CDMA

       7.1 CDMA AND WLL

        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 diffucult as
well as expensive, CDMA-based WiLL networks can be deployed quickly.


       7.2 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


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        CDMA, the restrictions imposed by the TRAI(Telecom Regulatory Authoriy
of India) doesn’t let it explore the 3G realms. Plus, some Wide CDMA supporters(W-
CDMA) aren’t helping the situation by claiming CDMA 1x is not 3G.

      Third-generation applications includes WCDMA, 1x and High Data Rate
(HDR).

       7.2.1 3G-MIGRATION

         CDMA2000 3G offers a viable solution for any existing cellular and PCS as
well as new 3G licensed operator. CDMA2000 was designed so that any wireless
carrier, regardless of existing air interface, frequency or core network standards can
benefit from its spectrum efficiencies and data capabilities




       7.2.1.1 CCDMA ONE TO CDMA2000 MIGRATION

         CDMA2000 is the natural 3G evolution for cdmaOne operators, requiring
only minor upgrades to the network and small capital investment. CDMA2000
handsets are backward compatible with the legacy cdmaOne infrastructure. Because
of this, the transition from cdmaOne to CDMA2000 1X is relatively easy for
operators and transparent for consumers
       This inherent advantage of cdmaOne gives operators significant market
advantage.
      cdmaOne operators lead deployment of 3G across markets in Asia, the
Americas and Europe.

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       The transition from cdmaOne to CDMA2000 requires channel card and
software upgrades to cdmaOne base stations (older base stations may require some
hardware upgrades) and introduction of new handsets.

       7.2.1.2 TDMA to CDMA2000 Migration

        Lacking a technological migration path to enable higher voice capacity and
bandwidth-intense mobile data services, TDMA has reached its limit. Thus, TDMA
operators are faced with a difficult decision to choose a technology that will assure
their future in the wireless market. CDMA2000 is an extremely attractive solution for
TDMA operators. It offers them a direct path to3G, preserves their investment in the
existing core network, and allows them flexibility to migrate to 3G over time, as the
market for advanced service evolves.

Advantages of CDMA2000 as a migration path for TDMA:
             Offers a direct path to 3G via a single evolutionary step rather than
              two or three upgrades required for an alternative path
             Reuses IS-41 elements of the existing core network, providing for
              substantial cost savings and enabling service transparency for end
              users
             Increases capacity of the existing TDMA air interface by 4 to 8 times
              to meet future demand for voice services
             Requires only a small amount of spectrum (1.25 MHz) for advanced
              services while preserving capacity to service existing customers
             Does not require new spectrum. CDMA2000 is designed to operate in
              all existing cellular and PCS bands, including 800 MHz and 1900
              MHz where TDMA currently is deployed.
             A wide range of competitively priced devices are commercially
              available
             A number of infrastructure manufacturers offer solutions today

        For TDMA operators in Latin America, CDMA2000 also opens significant
roaming markets in the Americas. Because CDMA2000 is backward compatible with
cdmaOne, the subscribers would be able to roam in 15 countries in South America, as
well as with the U.S. and Canada.

       Already a number of TDMA operators have selected CDMA2000 as a
migration path either through cdmaOne or directly to CDMA2000.


       7.2.1.3 GSM1X : GSM TO CDMA 2000 MIGRATION
       The CDMA2000 family of standards, including CDMA2000 1x and
CDMA2000 1x EV-DO, can also be a 3G solution for GSM operators. GSM1x, is an
overlay solution which enables the coexistence of CDMA2000 1X radio access

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                           Code Division Multiple Access
networks with GSM-MAP core service networks in existing or new spectrum. With
GSM1x, GSM operators can seamlessly leverage their existing GSM core network
and services while enhancing the data capabilities and spectral efficiencies of their
radio access with CDMA2000 infrastructure.

       GSM1x Components
       A GSM1x network has four primary components:
       1.      The service core network is a standard GSM core network. This
               enables existing network equipment to be utilized. And further offers
               GSM service transparency for both basic and supplementary service.
       2.      The radio access network is standard CDMA2000 radio infrastructure
               which is IOS4 compliant. This enables CDMA2000 capacity of 35
               calls per sector per 1.25 MHz channel, and peak data rates up to 153
               kbps with CDMA2000 1x and 2.4 Mbps with CDMA2000 1x EVDO
       3.      The handsets are standard SIM-enabled CDMA2000 handsets, the
               same SIM as GSM handsets.
       4.      The mobile switching node (MSN) interfaces with both the
               unmodified core network and the radio access network concurrently,
               integrating both voice and data traffic.




        GSM1x Overview
        GSM1x takes the concept of network convergence to a new level. It combines
the feature-rich services of GSM with the spectral efficiency of the CDMA2000
family of air interfaces.
        GSM1x is a unique solution that takes full advantage of an operator's
investment in its existing GSM core network. It has also been designed to overlay an
existing GSM network with no impact to current services and features. GSM1x


       C.U.Shah College of Engg. & Tech.                                            - 19 -
                          Code Division Multiple Access
provides a seamless integration to the GSM core network and services, by
maintaining all existing infrastructure. The GSM1x MSN (Mobile Switching Node)
interfaces with both the unmodified GSM core network and the CDMA20001x and/or
1x EVDO radio access networks concurrently, integrating both voice and data traffic.

       By utilizing CDMA2000 radio access to improve efficiency of existing
spectrum (800, 900, 1800, 1900 and 2100 MHz), GSM1x will increase an operator's
voice and data capacity. And service transparency between the GSM and the GSM1x
network is maintained.
        As with CDMA20001x, GSM1x provides peak rates of 307 kbps per sector
and peak data rates up to 2.4 Mbps with 1xEV-DO in a 1.25 MHz channel. This
allows GSM operators to offer advanced capabilities, in a cost effective manner,
while maintaining the inherent strength of the core network. Furthermore, an operator
can provide simultaneous voice and data through the enhanced capacity of this
solution.

       GSM1x uses a standard CDMA2000 handset with a CDMA SIM interface and
a software upgrade to accept GSM SIM cards. Dual-mode, single-mode, and dual-
band handsets will be available, to meet the diverse needs of subscribers.
        In conclusion, GSM1x provides a unique combination of both technical and
economic advantages to the carrier using existing GSM technology (please see
below). GSM1x further enables new profitable service models such as landline
replacement, high-speed VPN, and dispatch services. By utilizing this dynamic and
revolutionary technology, carriers will be able to grow their business with minimal
outlay of additional capital.




       `




       C.U.Shah College of Engg. & Tech.                                          - 20 -
                          Code Division Multiple Access


       8. APPLICATIONS OF CDMA TECHNOLOGY.
       8.1 DAILY APPLICATIONS POSSIBLE WITH CDMA
       8.1.1 Daily Downloads :
             ringers
             characters
             images
             horoscopes

       8.1.2 Real time stock quotes :

             of different stock exchanges

       8.1.3 Text Communication :
             Chat
             instant messaging
             SMS
             e-mail
             message board
             member search

       8.1.4 Sending photos over the air :
             MMS messages

       8.1.5 Position Location Services :
             navigation assistance
              friend finder

       8.1.6 Games and Entertainment :
             magazine
             comic book store

All these services are already being offered in South Korea and Japan.




       C.U.Shah College of Engg. & Tech.                                 - 21 -
                           Code Division Multiple Access

       9. CDMA Vs GSM (The Old Horse)


       9.1 INTRODUCTION
        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?

       9.2 BASICS
         Let’s 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 TDMA 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



       C.U.Shah College of Engg. & Tech.                                           - 22 -
                            Code Division Multiple Access
       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.

       9.3 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.




       C.U.Shah College of Engg. & Tech.                                               - 23 -
                           Code Division Multiple Access


       9.4 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.

       9.5 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

       C.U.Shah College of Engg. & Tech.                                             - 24 -
                            Code Division Multiple Access


        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).

       9.6 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

       C.U.Shah College of Engg. & Tech.                                               - 25 -
                           Code Division Multiple Access


       they think the current TDMA air interface is inadequate for its purpose. Future
standards are being built around high speed data.

       If you are presently in the market for a new phone, my advise to you is to
ignore the hype surrounding the technologies and look at service provider instead.
Judge each with an eye to price, phone choice, coverage, and reputation. Technology
should play a very small roll in your choice. If you follow this advice, you'll probably
be much happier with the phone and service you inevitably wind up with.




       C.U.Shah College of Engg. & Tech.                                             - 26 -
                   Code Division Multiple Access

 10.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 CDMA’s 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 control—that 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.

C.U.Shah College of Engg. & Tech.                                           - 27 -
                   Code Division Multiple Access


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 carrier—much
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.




C.U.Shah College of Engg. & Tech.                                         - 28 -
                         Code Division Multiple Access




      11. DISADVANTAGE

      11.1 COLLISIONS
       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.

       11.2 ROAMING
        Since most countries have chosen the GSM standard, “roaming” on CDMA is
limited.

    11.3 M-COMMERCE
      A CDMA doesn’t have a SIM card, which makes m-commerce difficult.




      C.U.Shah College of Engg. & Tech.                                        - 29 -
                        Code Division Multiple Access


12. CONCLUSION
                         Where CDMA scores
                         Where CDMA needs to scores

12.1 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.

     12.2 WHERE CDMA NEEDS TO SCORE

   Roaming
         Since most countries have chosen the GSM standard, “roaming” on
    CDMA is limited.

   M-commerce
            A CDMA doesn’t have a SIM card, which makes m-commerce
    difficult.




     C.U.Shah College of Engg. & Tech.                                       - 30 -
                        Code Division Multiple Access

      BIBLIOGRAPHY

      REFERENCE BOOKS
       1.          CRESPO, P.M., HONIG, M.L., and SALEHI, J.A. : “Spread-
Time Code-Division Multiple Access” IEEE Trans. On Commun., vol 43, pp. 2139-
2148, June 1995.

      2.            COMPUTER NETWORKS, 3rd Ed. - By Andrew S.
Tanenbaum

     3.            VITERBI, A.J.: CDMA Principle of Spread Spectrum
Communications, Reading ,MA: Addison-Wesley, 1995.



      Websites
      www.cdg.org
      www.umts.org
      www.palowireless.com
      www.ieee.org
      www.yahoo.com
      www.google.com




      C.U.Shah College of Engg. & Tech.                                    - 31 -

								
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