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The Applications Of CDMA Computer Science Essay

Q1. Explain the working of CDMA technology in details. Implement in the mathematical way (example) to show how mobile tower generate unique code to send the signal. Also demonstrate that if a noise data added to the Sent signal then result varies. Assume to take Key/code size of 7

A1. Code division multiple access (CDMA) is a channel access method used by various radio communication technologies

1. CDMA(CODE DIVISION MULTIPLE ACCESS) technology is a wireless technology used in transmission os signal from one place to another with high secury and noise reduction.

2. CDMA works on the principle of Spresd spectrum.Herewith the help of a CODE, data signal is spread like a noise like signal which is unable to detect by provides security.Since the spreaded signal is below the noise level noise has no effect on the signal.its provides noise reduction

3. CDMA was developed during second world war inorder to transmit signals in military.high security provides a wide application in military

Applications of CDMA:

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One of the early applications for code division multiplexing is in GPS. This predates and is distinct from its use in mobile phones.

The Qualcomm standard IS-95, marketed as cdmaOne.

The Qualcomm standard IS-2000, known as CDMA2000. This standard is used by several mobile phone companies, including the Globalstar satellite phone network.

The UMTS 3G mobile phone standard, which uses W-CDMA.

CDMA has been used in the OmniTRACS satellite system for transportation logistics.

Working of CDMA:


CDMA takes an entirely different approach from TDMA. CDMA, after digitizing data, spreads it out over the entire available bandwidth. Multiple calls are overlaid on each other on the channel, with each assigned a unique sequence code. CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range.

In CDMA, each phone's data has a unique code.

All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is spread over the entire bandwidth by a unique spreading code. At the receiver, that same unique code is used to recover the signal. Because CDMA systems need to put an accurate time-stamp on each piece of a signal, it references the GPS system for this information. Between eight and 10 separate calls can be carried in the same channel space as one analog AMPS call.

Each user is associated with a different code, say v. A 1 bit is represented by transmitting a positive code, v, and a 0 bit is represented by a negative code, -v. For example, if v = (1, -1) and the data that the user wishes to transmit is (1, 0, 1, 1), then the transmitted symbols would be (v, -v, v, v) = (v0, v1, -v0, -v1, v0, v1, v0, v1) = (1, -1, -1, 1, 1, -1, 1, -1). For the purposes of this article, we call this constructed vector the transmitted vector.

Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical.

Now, due to physical properties of interference, if two signals at a point are in phase, they add to give twice the amplitude of each signal, but if they are out of phase, they subtract and give a signal that is the difference of the amplitudes. Digitally, this behaviour can be modelled by the addition of the transmission vectors, component by component.

If sender0 has code (1, -1) and data (1, 0, 1, 1), and sender1 has code (1, 1) and data (0, 0, 1, 1), and both senders transmit simultaneously, then this table describes the coding steps:


Encode sender0

Encode sender1


code0 = (1, -1), data0 = (1, 0, 1, 1)

code1 = (1, 1), data1 = (0, 0, 1, 1)


encode0 = 2(1, 0, 1, 1) - (1, 1, 1, 1)

= (1, -1, 1, 1)

encode1 = 2(0, 0, 1, 1) - (1, 1, 1, 1)

= (-1, -1, 1, 1)


signal0 = encode0 âŠ- code0

= (1, -1, 1, 1) âŠ- (1, -1)

= (1, -1, -1, 1, 1, -1, 1, -1)

signal1 = encode1 âŠ- code1

= (-1, -1, 1, 1) âŠ- (1, 1)

= (-1, -1, -1, -1, 1, 1, 1, 1)

Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw signal:

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

This raw signal is called an interference pattern. The receiver then extracts an intelligible signal for any known sender by combining the sender's code with the interference pattern, the receiver combines it with the codes of the senders. The following table explains how this works and shows that the signals do not interfere with one another:


Decode sender0

Decode sender1


code0 = (1, -1), signal = (0, -2, -2, 0, 2, 0, 2, 0)

code1 = (1, 1), signal = (0, -2, -2, 0, 2, 0, 2, 0)


decode0 = pattern.vector0

decode1 = pattern.vector1


decode0 = ((0, -2), (-2, 0), (2, 0), (2, 0)).(1, -1)

decode1 = ((0, -2), (-2, 0), (2, 0), (2, 0)).(1, 1)


decode0 = ((0 + 2), (-2 + 0), (2 + 0), (2 + 0))

decode1 = ((0 - 2), (-2 + 0), (2 + 0), (2 + 0))


data0=(2, -2, 2, 2), meaning (1, 0, 1, 1)

data1=(-2, -2, 2, 2), meaning (0, 0, 1, 1)

Further, after decoding, all values greater than 0 are interpreted as 1 while all values less than zero are interpreted as 0. For example, after decoding, data0 is (2, -2, 2, 2), but the receiver interprets this as (1, 0, 1, 1). Values of exactly 0 means that the sender did not transmit any data, as in the following example:

Assume signal0 = (1, -1, -1, 1, 1, -1, 1, -1) is transmitted alone. The following table shows the decode at the receiver:

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Decode sender0

Decode sender1


code0 = (1, -1), signal = (1, -1, -1, 1, 1, -1, 1, -1)

code1 = (1, 1), signal = (1, -1, -1, 1, 1, -1, 1, -1)


decode0 = pattern.vector0

decode1 = pattern.vector1


decode0 = ((1, -1), (-1, 1), (1, -1), (1, -1)).(1, -1)

decode1 = ((1, -1), (-1, 1), (1, -1), (1, -1)).(1, 1)


decode0 = ((1 + 1), (-1 - 1),(1 + 1), (1 + 1))

decode1 = ((1 - 1), (-1 + 1),(1 - 1), (1 - 1))


data0 = (2, -2, 2, 2), meaning (1, 0, 1, 1)

data1 = (0, 0, 0, 0), meaning no data

When the receiver attempts to decode the signal using sender1's code, the data is all zeros, therefore the cross correlation is equal to zero and it is clear that sender1 did not transmit any data.

When a measurement is digitised, the number of bits used to represent the measurement determines the maximum possible signal-to-noise ratio. This is because the minimum possible noise level is the error caused by the quantization of the signal, sometimes called Quantization noise. This noise level is non-linear and signal-dependent; different calculations exist for different signal models. Quantization noise is modeled as an analog error signal summed with the signal before quantization ("additive noise").

This theoretical maximum SNR assumes a perfect input signal. If the input signal is already noisy (as is usually the case), the signal's noise may be larger than the quantization noise. Real analog-to-digital converters also have other sources of noise that further decrease the SNR compared to the theoretical maximum from the idealized quantization noise, including the intentional addition of dither.

Although noise levels in a digital system can be expressed using SNR, it is more common to use Eb/No, the energy per bit per noise power spectral density.

Q2. Discuss the strategies of different network operators while migrating towards third generation systems. List the issue involved in migration and discuss the procedure to solve these issues.

A2. In the 3G wireless market, two dominant technologies emerged: WCDMA, as the default evolution of GSM operators and the cdma2000 evolution for CDMA operators. 3G technologies adhere requirements of ITU to be labeled as 3G mobile technologies. Under ideal circumstances, GSM operators would migrate to WCDMA and CDMA operators would migrate to cdma2000 systems NTT DoCoMo, Japan and Vodafone, Japan were the first to deploy WCDMA systems in 2001. 38 operators were offering UMTS/WCDMA services in a total of 23 countries in Asia, Europe, and the Arab states as of April 2004. As of June 2005, 126 operators have launched 123 cdma2000 1X and 22 1xEV-DO commercial networks across Asia, Europe and the Americas [14] (see figure 2). 20 1X and 20 1xEV-DO networks are scheduled to be deployed in 2005 [14]. In North America, Verizon Wireless offers Wireless Internet Broadband access based on cdma2000 1xEV-DO in more than 30 markets nationwide at a monthly rate of $79.99 for unlimited access. An operator that migrates from 2.5G to 3G faces several critical

issues e.g., new spectrum requirements, capital investment, backward compatibility of handhelds, new handhelds, and applications to be offered, etc. For example, a GSM operator migrating to WCDMA would require new spectrum allocation and new cell phones that makes the migration a capital intensive project. A CDMA operator on the other hand, can build on the existing spectrum "spectrum re-farmingTo address the problem operators are migrating from existing separate, legacy ATM and TDM backhauling networks to a more cost-effective, converged, MPLS-enabled, and multi-purpose infrastructure. In addition to reducing operational costs, MPLS-based networks will also lay the foundations for the delivery of next generation mobile services, such as location-based services, mobile gaming and mobile TV, and for the use of future technologies such as Long Term Evolution (LTE) and mobile WiMAX. Ultimately, this fully consolidated network will be able to handle many different types of traffic on a single cell site, enabling the operator to offer many different services to many different types of customer.

Third-generation mobile networks have become a reality. By November 2007 there were 190 3G networks in commercial service across 83 countries worldwide with over 800 different types of 3G devices launched into the market available from around 90 suppliers . This trend allows mobile operators to generate revenues from a range of new "next generation" data services that are designed to generate revenues in addition to those from legacy voice services.

The rapid, widespread deployment of WCDMA and an increasing uptake of third-generation mobile systems (3G) services are bringing network performance into sharp focus. Besides efficiently supporting an increasing number of subscribers, network systems should also give end-users a high-speed experience. To solve this equation, with its seemingly conflicting components, we need to understand performance and how it is measured. Likewise, present-day and evolving 3G systems should include features for increasing system performance. New high-speed services and greater end-user demand for performance are driving the evolution. WCDMA Evolved supports an enhanced broadband experience of WCMDA systems. WCDMA Release 99 (Rel-99) services have evolved into WCDMA Releases 5 and 6 (Rel-5, Rel-6), which will reach commercial deployment by year-end 2005. Systems based on CDMA2000 are going through a similar evolution.

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High Speed Packet Access (HSPA)[1] is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA protocols. A further improved 3GPP standard, Evolved HSPA (also known as HSPA+), was released late in 2008 with subsequent worldwide adoption beginning in 2010. The newer standard allows bit-rates to reach as high as 168 Mbit/s in the downlink and 22 Mbit/s in the uplink.

The Cisco architecture enables mobile network operators to cost-effectively address many of the challenges facing them in today's market and enables more lucrative services in the future via an all-IP network. It does while protecting investments that have already been made and supports the need, in many cases, for multivendor solutions. In addition to providing the technical elements of the architecture, Cisco has the partnering expertise, market knowledge, and financial resources necessary to assist mobile network operators with the challenges that lie ahead.

Q3. Suppose two people talking on phone. If both of them stop speaking or become silent then the channel will be useless for that time period. Propose a solution for this problem so that we can utilize this unused bandwidth. Consider it as multiple access channels.


Characteristics of Frequency Division Multiplexing

There are some multiplexing concept, here we will explain the Frequency Division Multiplexing .FDM-Frequency Division Multiplexing is possible when the useful bandwidth of the transmission medium exceeds the required bandwidth of signals to be transmitted. A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency and the carrier frequencies are sufficiently separated that the bandwidths of the signals do not overlap.  Figure below describe a FDM-Frequency Division Multiplexing:

others definition of  Frequency-division multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel of the transmission.

Frequency Division multiplexing or FDM is an analog technique which is used to multiplex signals. Frequency Division multiplexing or FDM can be applied when the bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be transmitted. In FDM, the signals generated by each sending device modulate different carrier frequencies. After that, these modulated signals are combined into a single composite signal that can be transported by the link. Carrier frequencies are separated by sufficient band width to accommodate the modulated signal. These bandwidth ranges are the channels through which the various signals travel.

From FDM-Frequency Division Multiplexing figure above there are Six signal sources are fed into a multiplexer, which modulates each signal onto a different frequency (fi, . . . , f6). Each modulated signal requires a certain bandwidth centered around its carrier frequency, referred to as a channel. To prevent interference, the channels are separated by guard bands, which are unused portions of the spectrum.

The composite signal transmitted across the medium is analog. Note, however, that the input signals may be either digital or analog. In the case of digital input, the input signals must be passed through modems to be converted to analog. In either case, each input analog signal must then be modulated to move it to the appropriate frequency band.

When FDM is used in a communications network, each input signal is sent and received at maximum speed at all times. This is its chief asset. However, if many signals must be sent along a single long-distance line, the necessary bandwidth is large, and careful engineering is required to ensure that the system will perform properly. In some systems, a different scheme, known as time-division multiplexing, is used instead.

there are some advantages and disadvantages in Frequency Division Multiplexing/FDM :


In Frequency division multiplexing there is a need to filter bandpass, the price is relatively expensive and complex to be built (the use of these filters are usually used in the transmitter and receiver).

In Frequency division multiplexing Power amplifier (power amplifier) in the transmitter that is used has the characteristics of the nonlinear (linear amplifier is more complex to be made), and nonlinear amplification lead to the making of the spectral components out-of-band that can interfere with other FDM channels.


FDM - Frequency Division Multiplexing is not sensitive to the propagation / development delays. Technics equation channel (channel equalization) needed for FDM systems are not as complex as used in the TDM Time-Division Multiplexing system.

To utilize unused bandwidth

The Physical and MAC layers have been specified in IEEE 802.16 networks. The quality of service is ensured by the bandwidth reservation. The subscriber station should reserve the bandwidth more than its demand. But the bandwidth is fully utilized by SS, but not all the time. So the bandwidth has recycled by the process of recycling the unused bandwidth. The main objective of the proposed scheme is to utilize the unused bandwidth by recycling and maintain the QOS service. By recycling the throughput can be improved which maintains the QOS in the proposed scheme. During this recycling process to maintain the QOS services, the amount of reserved bandwidth is not changed. The proposed scheme can utilize the unused bandwidth up to 70% on average.

Q4. "Very low frequency waves transmit through the earth's surface" Justify the statement and discuss why are they not used for data transmission in computer networks?

A4. Low frequency radio signals can be used for data transmission, but only at a very low baud rate. That makes them "too slow" to be really effective. For instance, at 30 MHz, the fastest baud rate that can be used is about 300 baud. If a higher baud rate is used, some of the pulses of the RF signal can be seen by the receiver as data bits (and they are not). That will cause a CRC error. In the second place, low frequency transmitters are more complicated to design than VHF or UHF transmitters. A 433.92 MHz transmitter can handle baud rates of up to 9600 baud and can be manufactured on a very small PCB.

Because lower Frequencies are for long range whereas higher frequencies such as microwave go much shorter distances such as line of sight but can carry more information due to the complexity of the waveform. Do a search for spectrum management and you can find what you are looking for. I just think of a radio wave as the least complex because it is a low frequency and has lots of power behind it to broadcast to a big audience by blanketing a large surface whereas a satellite is a small complex antenna that discharges a high frequency burst from point to point but can carry a lot more information.

Q5. In India the call rate for mobile phone have slashed drastically. Analyze the technological innovations which made this possible.

A5. India's telecommunication network is the third largest in the world on the basis of its customer base and it has one of the lowest tariffs in the world enabled by the hyper-competition in its market. Major sectors of the Indian telecommunication industry are telephony, internet and broadcasting.

Telephonic network in the country, which is in an ongoing process of converging to next generation network, employs an extensive system of network elements such as digital telephone exchanges, mobile switching centers, media gateways and signalling gateways at the core, interconnected by a wide variety of transmission systems using media, such as optical fiber or Microwave radio relay. The access network, which connects the subscriber to the core, is highly diversified with different copper-pair, optic-fibre and wireless technologies. DTH, a relatively new broadcasting technology has attained significant popularity in the Television segment. The introduction of private FM has given a fillip to the radio broadcasting in India . Telecommunication in India has greatly been supported by the INSAT system of the country, one of the largest domestic satellite systems in the world. India possesses a diversified communications system, which links all parts of the country by telephone, Internet, radio, television and satellite.[3]


Given the technological sophistication of our media, its importance in communications, and its widespread utilization by broad segments of the population, we should not be surprised that discussions of media technology often emphasize the awesome power of the newest media to affect society. But it is easy to overstate the influence of media technologies by

claiming that they dictate processes of social change; this is referred to as technological determinism. As we will see below, the arguments of technological determinists can raise important questions about the social impact of new technologies, but they fail to recognize that technology is only one element of the media process in the social world.

Technological Determinism

We can think of technological determinism as an approach that identifies technology, or technological developments, as the central causal element in processes of social change. In other words, technological determinists emphasize the "overwhelming and inevitable" effects of technologies on users, organizations, and societies (Lievrouw and Livingstone 2006: 21). Sociologist Claude Fischer (1992) characterizes the most prominent forms of techno­logical determinism as "billiard ball" approaches, in which technology is seen as an exter­nal force introduced into a social situation, producing a series of ricochet effects. From this perspective, technology causes things to happen, albeit often through a series of intermedi­ary steps. For example, the invention of the automobile might be said to cause a reduction in food prices because the automobile "reduced the demand for horses, which reduced the demand for feed grain, which increased the land available for planting edible grains," mak­ing food less expensive (Fischer 1992: 8). The problem, however, is that there is no human agency in this type of analysis. The technological determinist's view is all structural con­straint and no human action. It argues that technological properties demand certain results and that actual people do not use technologies so much as people are used by them. In this view, society is transformed according to a technical, rather than a human, agenda.

Q6. Write the procedure to create an AD-HOC network in wireless. Connect two laptops together and write the procedure for configuring IP address, SSID, security aspects and firewall exception. Take screen shots to show your demonstration by sharing a file giving specific permission to a file as read only.

A6. Create an Ad Hoc Wireless Network

If you want to share information stored on your computer with other people nearby and everyone’s computer has a wireless network adapter, a simple method of sharing is to set up an ad hoc wireless network. In spite of the fact that members must be within 30 feet of each other, this type of network presents a lot of possibilities. For example, you might consider establishing an ad hoc network at a meeting of mobile computer users so that you can share information with other attendees on their own screens rather than an overhead projector. (After establishing the network, you can do this by using Windows Meeting, for instance.)

Ad hoc networks are by definition temporary; they cease to exist when members disconnect from them, or when the computer from which the network was established moves beyond the 30-foot effective range of the others. You can share an Internet connection through an ad hoc network, but keep in mind that the Internet connection is then available to anyone logging on to a computer that is connected to the network, and thus is likely not very secure.

To disconnect from an ad hoc network, display the Connect To A Network window, click the ad hoc network, and then click Disconnect.

Click on Start (Windows icon) and type wireless. Click on Manage wireless networks.

Click on Add to add on a network

3. Click on Create an ad hoc network.

3. Click on Next

4. Enter a name for your network and configure the security options. Click on Next when you are done

Setting up the IP-address

1. From my previous tip: Open the Network Connections

type and launch the command: ncpa.cpl

or Control ncpa.cpl

2. Right-Click the Wireless Network Connection > Properties > Internet Protocol Version 4 (TCP/IPv4) > Properties Button > Select "Use the following IP address:"

Examples: Class C - Most Common Home Configuration

Computer A

Computer B

Device C

Range: -

To Connect: Right-Click the Wireless Icon > Connect to a Network > Find the name of the ad hoc Network > Click the Connect Button > Input the Passphrase or Security Key and finally Click the Connect Button again.

Windows XP

Right-Click the Wireless Network Icon > Choose View Network Wireless Networks

In the Left Pane > Click "Change advanced settings" link

Make sure that you are using Windows to configure your wireless network settings and click the Add Button

Enter the Network Name (SSID), Set the Network Authentication, Data Encryption, Network key and Choose the option "This is a computer-to-computer (ad hoc) network; wireless access points are not used.


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