secured CDMA
Transcript of secured CDMA
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)
2
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
3
(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.
4
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.
5
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.
6
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
7
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
8
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.
9
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
10