SECURED VOICE COMMUNICATION

AND SUPERIOR VOICE CLARITY IN

CODE DIVISION MULTIPLE ACCESS (CDMA)

ABSTRACT

As the fastest growing communications technology, Code

Division Multiple Access (CDMA) is the world's premiere wireless

communications technology. 3G CDMA networks provide more

capacity for voice traffic, along with high-speed data capabilities.

CDMA has greater voice quality and call clarity than other

technologies because it filters out background noise, cross-talk and

interference. The Radio Carrier Station (RCS) and Fixed Subscriber

Unit (FSU) are used to communicate the source and destination

such as two mobiles. In 1999, the International Telecommunications

Union (ITU) selected CDMA as the basis for 3G wireless systems.

With fewer dropped calls because of increased voice and

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. In Simple 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. Generally

voice will be converted to digital signals in transmitting end and in

receiving end the digital signals are converted into audio signals.

Here we have encoded the converted digital signals and transmit

them and then decode the signals again back to digital signals in

receiving end. This provides secured voice communication and

superior voice clarity without interference and cross – talk.

INTRODUCTION

Code Division Multiple Access (CDMA) technology, pioneered

by QUALCOMM, provides excellent voice capacity and data

capability for mobile and fixed wireless networks. Because of its

advantages, CDMA serves as the foundation for 3G services

worldwide. This technology was invented by the QUALCOMM CDMA

Technologies. Commercially introduced in 1995, CDMA quickly

became one of the world's fastest-growing wireless technologies.

This technology supports current voice and data needs while

providing a cost-efficient evolutionary path to tomorrow's systems.

History

CDMA is a military technology first used during World War II

by 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.

Key Words

APC (Automatic Power Control)

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FSU (Fixed Subscriber Unit)

RCS (Radio Carrier Station)

Process

A wireless transmission method in which signals are encoded

using a random sequence, or code, to define a channel. CDMA offers

improved spectral efficiency over analog transmission.

CDMA works by converting speech into digital information,

which is then transmitted as a radio signal over a wireless network.

Using a unique code to distinguish each different call, CDMA enables

many more people to share the airwaves at the same time - without

static, cross-talk or interference.

Encoding and Decoding Signals:

Now, associate with one sender a vector from this set [(0,0),

(0,1), (1,0), (1,1), (0,-1), (-1,0), (-1,-1). (1,-1), (-1,1)] say v, which is

called the chip code. Associate a zero digit with the vector -v, and a

one digit with the vector v. For example, if v=(1,-1), then the binary

vector (1, 0, 1, 1) would correspond to (1,-1,-1,1,1,-1,1,-1). Each

vector is given a unique number and then the number is

transmitted. This constructed vector the transmitted vector.

Each sender has a different, unique vector chosen from that set, but

the construction of the transmitted vector is identical.

Now, the physical properties of interference say that if two signals

at a point are in phase, add up the signals to give twice the

amplitude of each signal. Digitally, this behaviour can be modelled

simply by the addition of the transmission vectors, component by

component. So, if we have two senders, both sending

simultaneously, one with the chip code (1, -1) and data vector (1, 0,

1, 1), and another with the chip code (1, 1), and data vector

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(0,0,1,1), the raw signal received would be the sum of the two

transmission vectors as given (1,-1,-1,1,1,-1,1,-1) + (-1,-1,-1,-

1,1,1,1,1) = (0,-2,-2,0,2,0,2,0).

Suppose a receiver gets such a signal, and wants to detect what the

transmitter with chip code (1, -1) is sending. The receiver will make

use of the property described in the above foundation section, and

take the dot product to the received vector in parts. Take the first

two components of the received vector, that is, (0, -2). Now, (0, -2).

(1, -1) = (0)(1)+(-2)(-1) = 2. Since this is positive, we can deduce

that a one digit was sent. Taking the next two components, (-2, 0),

(-2, 0).(1,-1)=(-2)(1)+(0)(-1)=-2. Since this is negative, we can

deduce that a zero digit was sent. Continuing in this fashion, we can

successfully decode what the transmitter with chip code (1, -1) was

sending: (1, 0, 1, 1).

Likewise, applying the same process with chip code (1, 1): (1, 1).(0,-

2) = -2 gives digit 0, (1, 1).(-2,0)=(1)(-2)+(1)(0)=-2 gives digit 0,

and so on, to give us the data vector sent by the transmitter with

chip code (1, 1): (0, 0, 1, 1).

Two events can initiate a call

The FSU (Fixed Subscriber Unit) receives a page from the RCS (Radio Carrier Station). This is called a terminating call.

The FSU generates an off-hook signal in response to subscriber equipment. The FSU locks on to the Global Pilot. This is called an originating call.

Once either of these events occur, call setup proceeds as follows:

1. FSU requests access

FSU transmits Short Access Pilot Code.

RCS detects transmission and acknowledges. Flags Call Setup Channel as busy.

FSU transmits Long Access Pilot Code.

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RCS synchronizes to the FSU and confirms sync over Control Channel.

RCS measures received power and starts transmitting APC (Automatic Power Control) signal on APC Control Channel.

RCS and FSU exchange messages on Access and Control Channels. Type of service and types of traffic channels are specified.

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STEP 1

Short Access Pilot

Fast Broadcast

Global PilotRCS

FSU Long Access Pilot

Control

Global PilotRCS

FSU

STEP 2

APC Control

Global PilotRCS

FSU

STEP 3

APC Control

Access

Control

Global Pilot

RCS

FSU

STEP 4

2. RCS assigns channel group to FSU

RCS designates assigned code on Control Channel

FSU generates complex PN codes for all channels in its assigned group.

The call is connected.

The RCS flags the Call Setup Channel as available, and assigns it to the next available modem.

Note that the RCS now tracks the Assigned Pilot; the FSU continues to track the Global Pilot.

CDMA Technology in Current Trend

Many leading wireless operators have commercially launched

or are now upgrading to 3G CDMA networks in order to provide

more capacity for voice traffic, along with high-speed data

capabilities.

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Call Setup Process

Some o f the CDMA releases by QUALCOMM Technology.

cdmaOne®

A brand name, trademarked and reserved for the exclusive

use of CDG member companies. cdmaOne which made use

of 1.25 MHz channels to deliver voice and data.

CDMA2000®

A direct evolution from cdmaOne technology. CDMA2000

offer enhanced voice and data capacity. CDMA2000 is

recognized by the ITU as a global standard for 3G wireless

systems. The CDMA2000 family includes:

CDMA2000 1X

CDMA2000 1X is a 3G technology that is commercially

available today. 1X is 21 times more efficient than analog

cellular and 4 times more efficient than TDMA networks.

Typical 1X networks provide peak rates of 144 Kbps for

acket data and provide an average throughput range of 60-

90 Kbps on a loaded network.

CDMA2000 1XEV-DO

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1xEV-DO is short for First Evolution, Data Optimized. 1xEV-

DO provides peak data rates of up to 2.4 Mbps in a

standard 1.25 MHz channel used exclusively for data.

1xEV-DO provides average throughput speeds of over 700

Kbps—equivalent to cable modem speeds—and fast

enough to support applications such as streaming video

and large file downloads.

CDMA2000 1xEV-DV

1xEV-DV is short for 1X Evolution, Data and Voice. This

standard is under development and is expected to be

commercially deployed in 2007. CDMA200 1xEV-DV will

support voice as well as data. Release C supports a forward

link of 3.08 Mbps and a reverse link of 153 Kbps. Release D

supports a forward link of 3.08 Mbps and a reverse link of

approximately 1.0 Mbps.

FEATURES

CDMA has greater voice quality and call clarity than other

technologies because it filters out background noise, cross-talk and

interference. With fewer dropped calls because of increased voice

and 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 and

you have it all with CDMA.

Key Attributes of CDMA

Direct sequence spread spectrum

Universal frequency reuse

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Multipath propagation for diversity

Variable-rate transmission

Unique forward and reverse links

CONCLUSION

When comparing to GSM’s TDMA Technology and other

technologies CDMA Technology gives a big support to the

communications for the current trend. In Simple 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.

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REFERENCES

Journals

1. Viterbi, A. CDMA: Principles of Spread Spectrum

Communication Addison-Wesley Wireless Communications

Series, 1995

2. Pickholtz, R. L., Schilling, D. L., and Milstein, L. B. “Theory of

Spread-Spectrum Communications—A Tutorial” IEEE Trans.

Commun., vol. COM30, no. 5, May 1982, pp 855-884.

3. Pickholtz, R. L., Schilling, D. L., and Milstein, L. B. Revisions to

“Theory of Spread-Spectrum Communications—A Tutorial”

IEEE Trans. Commun., vol. COM32, no. 2, Feb 1984, pp 211-

212.

Links to Gather:

4. http://www.cdmatech.com/resources/index.jsp

5. http://wi-fiplanet.webopedia.com/TERM/C/CDMA.html

6. http://www.cisco.com/warp/public/cc/so/neso/gprs/

gprs_wp.htm

7. http://www.wirelessdevnet.com/newswire-less/

feb012002.html

8. http://cas.et.tudelft.nl/~glas/thesis/node7.html

9. http://www.umtsworld.com/technology/cdmabasics.htm

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