An Essay On Computer Systems Architecture Communications Essay

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CDMA is a form ofmultiplexing, which allows numerous signals to occupy a single transmissionchannel, optimizing the use of available bandwidth. It is a cellular technology that uses spread-spectrum techniques. Both data and voice are separated from signals using codes and then transmited using a wide frequency range. Because of this, there are more space left fordatatransfer (this was one of the reasons why CDMA is theprefered technology for the 3G generation, which is broadband access and the use of big multimediamessages). The CDMA system works directly on 64 kbit/sec digital signals. These signals can be digitized voice, ISDN channels, modem data, etc

Basically CDMA is a type of multiple access sceheme( which means allotting the given bandwidth to multiple users) and makes use of spread spectrum technique which is essentially increasing the size of spectrum.In CDMA each user is provided a unique code and all the conversation between 2 users are coded.

The importance of the technology for human beings at work and social life:

The best example to show the importance of this technology is that CDMA was developed during Second World War in order to transmit signals in military. High security provides a wide application in military. The military loved CDMA because coded signals with trillions of possible combinations resulted in extremely secure transmissions.

CDMA is nowadays the becoming most the most important wireless technology in cellular networks.In India CDMA mobile services were introduced in December 2002. Today, more than 100 million satisfied CDMA subscribers, on networks across India that boast the best voice quality and excellent data throughput, vindicate CDMA services in India.Making it the world's second-largest CDMA market. Reliance Communications and Tata Teleservices are placed among the top five CDMA operators globally, ranking second and fourth, respectively.

As it is more secured and faster than the other present wireless technologies therefore its demand is higher than the other technologies such as GSM, TDMA etc. CDMA mobile broadband is already satisfying the demand for affordable high-speed wireless data services, especially as 3G arrives and we are able to unleash the full potential of applications and servicesin India.

CDMA triggered the wireless revolution in India by making mobile communication affordable, and has played a key role in bridging the digital divide.

The modulation technique used and basic requirement for successful implementation of the technology:

SPECTRUM OF CDMA

CDMA is a Direct Sequence Spread Spectrum system. In CDMA technology every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. CDMA which incorporates spread-spectrum technology works by digitizing multiple conversations. It attaches a code known only to the sender and receiver, and then dicing the signals into bits and reassembling them.

There are many devices which use the same spread spectrum (hence multiple access). There is one physical channel, and a special code for every device in the coverage network. Using this code, the signal of the device is multiplexed, and the same physical channel is used to send the signal (the codes may or may not change). CDMA scheme has two concepts, spread spectrum techniques with single user detection and multi user concepts with joint detection of user signals. CDMA gives the user entire spectrum all of the time. CDMA spread spectrum technology in which it uses unique spreading codes to spread the baseband data before transmission. The receiver then dispreads the wanted signal, which is passed through a narrow band pass filter. The unwanted signals are not dispread and will not be passed through the filter. The codes are a sequence of zeros and ones produced at a much higher rate of that of the baseband data. The rate of spreading code is referred to as chip rate.

Modulation Technique:

CDMAuses a special type ofdigital modulationcalledspread spectrumwhich spreads the voice data over a very wide channel inpseudorandomfashion. The receiver undoes the randomization to collect the bits together and produce the sound.

CDMA supports variable bandwidth connections, with enhanced standards at 13Kbps and 64Kbps for superior quality speech and faster data connections. This 'bandwidth-on-demand' limits the number of simultaneous connections to a particular base station.

CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized (ADC) into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes; this enhances privacy and makes cloning difficult. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

Since during the calls most conversations are consists mostly of silence, thus CDMA phones have to transmit less data as they don't have to send silence, like GSM or TDMA phones do. Hence more CDMA calls can be fit into a given amount of frequency spectrum which is more efficient for the network. . CDMA uses newer vocoder called EVRC, which suppress the background noise even when the user is talking.

The Concept of signal spreading and its uses in communications

Let's take a stright forward binary signal of symbol rate 2. To modulate this signal, we would multiply this sequence with a sinusoid and its spectrum would look like as In figure 2. The main lobe of its spectrum is 2 Hz wide. The larger the symbol rate the larger the bandwidth of the signal. Now we take an another binary sequence of data rate 8 times larger than of sequence shown in sequence

Instead of modulating with a sinusoid, we will modulate the sequence 1 with this new binary sequence which we will call the code sequence for sequence 1. The resulting signal looks like Fig. 4. Since the bit rate is larger now, we can guess that the spectrum of this sequence will have a larger main lobe.

The spectrum of this signal has now spread over a larger bandwidth. The main lobe bandwidth is 16 Hz instead of 2 Hz it was before spreading. The process of multiplying the information sequence with the code sequence has caused the information sequence to inherit the spectrum of the code sequence (also called the spreading sequence).

CDMA Tutorial

The spectrum of the spread signal is as wide as the code sequence The spectrum has spread from 2 Hz to 16 Hz, by a factor of 8. This number is called the the spreading factor or the processing gain (in dBs) of the system. This process can also be called a form of binary modulation. Both the Data signal and the modulating sequence in this case are binary signals.

In CDMA we do modulation twice. First time with a binary sequence and second time by a carrier. The binary sequence modulation ahead of the carrier modulation accomplishes two functions

  1. It spread the signal
  2. It introduces a form of encryption because the same sequence is needed at the receiver to demodulate the signal.

SOFT HANDOFF AND HARD HANDOFF:

In a traditional hard handoff process the connection to the new cell site is made after breaking a connection to the present cell site. While in the soft handoff process, the connection to the new cell site can be made without breaking the connection of the present cell site. Since CDMA uses the same frequency CDMA uses the soft hand off. Soft handoff requires less power, which reduces interference and increases capacity. The CDMA network chooses one or more alternative sites that it feels are handoff candidates while a call is in progress. It simultaneously broadcasts a copy of the call in each of these sites. It can then choose one of the sites and can move between them whenever it feels like it. This puts the phone in complete control of the handoff process.

A CDMA network consists of the following components:

 Mobile station.

The CDMA mobile station (or mobile phone) communicates with other parts of the system through the base-station system.

 Base station (BS).

The base station (BS) handles the radio interface to the mobile station. The base station is the radio equipment (transceivers and antennas).

 Base station controller (BSC).

The BSC provides the control functions and physical links between the MSC and BTS. It provides functions such as handover, cell configuration data and control of RF power levels in base transceiver stations. A number of BSCs are served by a MSC.

 Mobile switching center (MSC).

The MSC performs the telephony switching functions of the system. It also performs such functions as toll ticketing, network interfacing, common channel signalling, and others.

 Home location register (HLR).

The HLR database is used for storage and management of subscriptions. The home location register stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status.

 Visitor location register (VLR).

The VLR database contains temporary information about subscribers that is needed by the mobile services switching center (MSC) in order to service visiting subscribers. When a mobile station roams into a new mobile services switching center (MSC) area, the visitor location register (VLR) connected to that MSC will request data about the mobile station from the HLR, reducing the need for interrogation of the home location register (HLR).

Authentication center (AC).

The AC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The authentication center (AUC) also protects network operators from fraud.

 Operation and administration (OAM).

The OAM is the functional entity from which the network operator monitors and controls the system. The purpose of operation and support system is to offer support for centralized, regional, and local operational and maintenance activities that are required for a CDMA network.

Due to higher bandwidth available in CDMA the number of channels(users) that can be allocated in a given bandwidth is comparatively higher for CDMA than for GSM. CDMA networks are built with standard IP packet data protocols. Other networks require costly upgrades to add new data equipment in the network and will require new data phones. Standard CDMA phones already have TCP/IP and PPP protocols built into them The cost of setting up a CDMA network is also comparatively less than the GSM network.

Security issues of the CDMA technology:

The CDMA technology is generally known as powerful security during communication. CDMA uses a drastically different approach to what GSM does. It assigns a unique code to put multiple users on the same bandwidth channel at the same time. These unique codes used are called "pseudo-random code sequence" is used by both the mobile station (handset) and the base station to differentiate between conversations. This gives a greater level of privacy and security to the communication.

CDMA which incorporates spread-spectrum technology works by digitizing multiple conversations. It attaches a code known only to the sender and receiver, and then dicing the signals into bits and reassembling them.

Increased privacy is inherent in CDMA technology. CDMA phone calls will be secure from the casual eavesdropper since, unlike an analog conversation, a simple radio receiver will not be able to pick individual digital conversations out of the overall RF radiation in a frequency band.

CDMA air interface is inherently secure and is clearly superior to first-generation analog and

(TDMA) systems. The inherent security of CDMA air interface comes from spread spectrum technology. Spreading techniques are used to form unique code channels for individual users in both directions of the communication channel. Because the signals of all calls in a coverage area are spread over the entire bandwidth, it creates a noise-like appearance to other mobiles or detectors in the network as a form of disguise, making the signal of any one call difficult to distinguish and decode.

In CDMA data signal is spread like a noise like signal which is unable to detect by others which provides security. Since the spread signal is below the noise level noise has no effect on the signal which results in noise reduction.

CDMA air interface technology is inherently secure for protection of signalling and bearer traffic with excellent security in service provisioning for handset and parameter distribution.

CDMA employs a fast power control, 800 times per second, to maintain its radio link. It is

difficult for a third party to have a stable link for interception of a CDMA voice channel, even with a full knowledge of a Walsh code.

Advantagesand Strengths of CDMA technology:

Ø Outstanding Voice and Call Quality

CDMA filters out background noise, cross-talk, and interference so you can enjoy crystal-clear voice quality, greater privacy, and enhanced call quality. It uses a vocoder EVRC for noise reduction where the background noise is reduced. This is exclusively available in CDMA technology only CDMA combines multiple signals and improves signal strength. This leads to the near elimination of interference and fading. Both computer noise and background conversations are filtered out by using narrow bandwidth which corresponds to the frequency of the human voice. This reduces the background noise and interference out of your conversations.

Ø Greatest Coverage for Lower Cost

CDMA's spread spectrum signal provides the greatest coverage in the wireless industry.Because CDMA system require fewer cell sites, CDMA networks can be deployed and expanded faster and more cost effectively than most wireless networks. Fewer cell sites translate to reduced operating expenses, which results in savings to both operators and consumers.

Ø Extended reach:

One of the main advantages of CDMA is that network failure occurs only when the phone is at least twice as far from the base station. Thus it is used in the rural areas where GSM cannot cover. which is beneficial to rural users situated far from cells.

Ø Low power requirements and Smaller Phones

CDMA handsets typically transmit at the lowest power levels allowing for longer battery life which results in longer talk time and standby time. battery power is conserved since the handset only transmits when it actually has something to send. CDMA handsets can also incorporate smaller batteries, resulting in smaller, lighter-weight phones. Easier to carry and use.

Ø Increased cellular communications security:

CDMA is digitally encoded, Because of spread spectrum technology it uses transmissions resist eaves dropping. Designed with about 4.4 trillion codes, CDMA virtually eliminates cloning and other types of fraud.

Ø Greater Capacity

CDMA as a very high spectral capacity that it uses spread spectrum technology which can provide up to 10-20 times the capacity of analog equipment and more than three times the capacity of other digital platforms that allows the largest number of subscribers per MHz of bandwidth. With dual-mode phones, CDMA is compatible with other technologies for seamless widespread roaming coverage.

Ø Continuing Advances

CDMA technology enables users to access a wide range of new services, including caller identification, short messaging services and Internet connections. Simultaneous voice and data calls are also possible using CDMA technology.

Ø higher data and voice transmission quality

Because of the spread spectrum technology it uses, which has increased resistance to multipath distortion. Various factors such as echoes, call dropping, or voice distortion are almost non-existent in CDMA, whereas in GSM, there is a high probability of errors.

Ø Mostharmless among other technologies:

CDMA is harmless among other existing technologies. CDMA technology checks 800 times per second its transmission level. Therefore, radiation level is 10 times less than GSM. Another point is that less radiation is being created from the phone towards the user. In CDMA system user gets the radiation only when the user starts conversation.

ØHighest data transmission capacity

Following table indicates the data transmission of different technologies.:

Cellular technology

Generation

Data transmission capacity

GSM

2G

56 Kps

CDMA (IS-95B)

2.5G

64 Kps - 140 Kps

CDMA 2000

3G

2 MBps

Disadvantages of CDMA:

Ø CDMA is relatively new technology, and its network is also not as mature as GSM. Therefore all of CDMA's defects are not known to the engineering community. Also limited variety of the handset in CDMA, because at present the major mobile companies use GSM technology since it is not old and simpler as GSM.

Ø One major disadvantage in this technology CDMA cannot offer international roaming. when compared to GSM . The ability to upgrade or change to another handset is not easy with this technology because the network service information for the phone is put in the actual phone unlike GSM which uses SIM card for this.

Ø One major problem in CDMA technology is channel pollution, where signals from too many cell sites are present in the subscriber's phone but none of them is dominant. When this situation arises the quality of the audio degrades

Ø Another problem for CDMA users is of carriers. The law requires CDMA carriers to provide handsets to users, for which the users cannot change their carriers. Whereas, GSM users can change their carriers whenever they want.

Ø Another problem in CDMA mobile phones is that there is a special number 112 that every GSM compatible device in the world can call in case of an emergency. But in CDMA, this cannot be implemented because of certain technological limitations.

Ø CDMA mobiles also transmit microwaves while on standby mode, like other technologies do.

Intake:PT0881/2/3

Module Code:

AICT001-3-2

Lecturer:Vidhu Bhasin (vidhu@apiit.edu.in)

In course Assignment Percentage: 50%

Objectives:

Computer architecture is a vibrant and ever changing field; This assignment will attempt to convey that to students. The primary objective of this group assignment is to provide an understanding of the principles underlying the structure of computer hardware by illustrating and developing an understanding of the various engineering, scientific and economic tradeoffs necessary in the design and implementation of computer systems. Additionally, this assignment emphasizes the ability to work within a team and to respond to the challenging requirements through cooperative activity.

Instructions:

  1. The assignment consists of FOUR (4) questions.
  2. Working in groups of three (3), you will select only one (1) of these questions.
  3. Each question is in multiple parts and must be divided equally among the team members.
  4. No marks will be awarded for the entire assignment if any part of it is found to be copied directly from printed materials or from another student.
  5. All submissions should be made on or before the due date.
  6. Any late submissions after the deadline will not be entertained.
  7. Zero(0) mark will be awarded for late submission, unless extenuating circumstances are upheld.

Questions:

In groups of three/Four, select one (1) question from the list below.

Question 1: General Architecture

The microprocessor is the heart of any normal computer, whether it is a desktop machine, a server or a laptop. A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is fabricated on a single chip. Each member of your group will select and investigate one of the following:

A. Discuss the major trends affecting microprocessor performance and design in recent years.

B. What are the major differences between microprocessor design goals for desktop, server, and embedded systems?

C. The frequency of the microprocessor is often used to compare the performances of different personal computers. E.g. a Pentium 133MHz PC is supposed to be faster than a Pentium 75MHz one. This method however does not always hold, especially among computers from different manufacturers. Instead, a method called benchmarking is widely used. You are to research the various types and uses of benchmarking programs available.

D. As a group, you will use the knowledge acquired from your lectures and additional readings, to select a computer in the two scenarios below. List any assumptions you made when justifying your selection e.g. computer use.

  1. A has a 5GHz. Processor and 512 KB cache, whereas B has a 3GHz processor with a 5 MB cache. Both have the same kind of RAM clocked with 600 MHz. Which of the two computers would you prefer and why?
  2. You have the choice of buying two different computers X and Y. X has an ALU that is twice as fast as normal while Y has two ALUs at the normal speed. Which of the two computers would you prefer and why? If any part of your answer depend on aspects of the software being run (e.g., Instruction level parallelism), explain how.

Question 2: Advanced Architecture

The performance of modern CPUs is intrinsically tied to its architecture. Over the past half century, there have been many major advances in CPU design that have dramatically improved performance.

A. Each member of your group will select and investigate one of the following architectures:

− VLIW (Very Long Instruction Word),

− Superscalar,

− Superpipeling,

− Multithreaded,

− Explicitly Parallel Instruction Computing(EPIC)

− Multicore,

− Multiprocessing

Your research may include the following:

  1. Brief description of the design
  2. Reasons for its development
  3. How it works
  4. How it differs from the Von Neumann architecture taught in class
  5. Which CPU vendor uses it
  6. Success (or failure) of the design

B. As a group, you will summarize the results of your research by producing a table comparing

  1. Similarities and Differences.
  2. Advantages and Disadvantages

of the three approaches

Question 3 : Memory Architecture

A computer usually consists of different types and performance levels of memory. Your group will select a computer system (e.g. x86, AMD K*, Mac etc) and investigate the three major types of memory found in the system i.e. registers, cache and RAM. Each member of your team will select and investigate one of the following:

A. Use of registers in a modern computer. Your research may include the following :

  1. Reasons for registers
  2. Types of registers
  3. Register size
  4. Register organization

B. Use of cache in a modern computer. Your research may include the following:

  1. Reasons for cache
  2. How cache works
  3. Levels of cache
  4. Cache memory organization
  5. Write strategies for cache memories

C. Use of RAM in a modern computer. Your research may include the following:

  1. Reasons for RAM
  2. How RAM works
  3. Types of RAM

D. As a group, you will summarize the results of your research by describing the principle and the benefits of a memory hierarchy formed by these memory types. Your summary will include:

  1. Why a memory hierarchy is required
  2. <
  3. How a memory hierarchy works

Question 4 : Buses

If you've ever opened up a computer and looked inside or read the specifications for a system, you've probably heard terms like PCI, ISA, EISA, or even NuBus mentioned when discussing the computer's bus. Your group will select a computer system (e.g. x86, AMD K*, Mac etc) and investigate the major types of buses found in the system. Each member of your team will select and investigate one of the following

A. Bus Characteristics:

  1. Bus width, Bus speed,
  2. Different types of buses and bus lines
  3. Advantages/disadvantages of a “bus” to a “network”.

B. Bus Arbitration:

  1. Purpose of arbitration.
  2. How does the arbitration protocol work
  3. Multiplexing

C. Bus Topology:

  1. Point-to-Point
  2. Multipoint

D. As a group, you will summarize the results of your research by describing the principle

and the benefits of a bus hierarchy formed by these bus types. Your summary will include:

  1. Why a bus hierarchy is required
  2. How a bus hierarchy works
  3. Additional hardware circuitry required

Guidelines for the Report:

Your completed documentation should include the following:

  1. Table of Contents
  2. Gantt Chart
  3. Work Breakdown Structure (breakdown of tasks among the members)
  4. Abstract
  5. Introduction
  6. Chapters/sections
  7. Conclusion.
  8. Frequently Ask Question (FAQ).
  9. Minutes of Mandatory Meetings
  10. Bibliography or References.

Document the results of your group's work in a professional and systematic manner, in the form of a computerized report.

The total word count of the report should range from 2500 to 3000words. You must include a word count at the end of the report. The report should be in 1.5 spacing, with an appropriate cover sheet. It shall be comb-bound, with a clear plastic sheet on the front page. Students are required to include the student marking matrix as the first page of their document.

Computer Systems Architecture (CSA)

Group and Individual Marks

Student's Particulars

Intake:

Question

Total Number of Pages:

Group No:

Student

Particulars

Name

Student ID

TM

1

Member / Group Leader

2

Member

3

Member

Lecturer's Use only

Marks Allocated (%)

Marks

Obtained (%)

Total / Grading

Group (30%)

Documentation

15

Summary

15

Individual (70%)

Student 1 Name :

1

Presentation

10

Research

20

Analysis

20

Overall Achievement

10

References

10

Student 2 Name :

2

Presentation

10

Research

20

Analysis

20

Overall Achievement

20

References

10

Student 3 Name :

3

Presentation

10

Research

20

Analysis

20

Overall Achievement

10

References

10

Computer Systems Architecture (CSA)

Group and Individual Marks

Student's Particulars

Intake:

Question

Total Number of Pages:

Group No:

Student

Particulars

Name

Student ID

TM

1

Member/Group Leader

2

Member

3

Member

4

Member

Lecturer's Use only

Marks Allocated (%)

Marks

Obtained (%)

Total / Grading

Group (20%)

Documentation

10

Summary

10

Individual (80%)

Student 1 Name :

1

Presentation

10

Research

20

Analysis

20

Overall Achievement

20

References

10

Student 2 Name :

2

Presentation

10

Research

20

Analysis

20

Overall Achievement

20

References

10

Student 3 Name :

3

Presentation

10

Research

20

Analysis

20

Overall Achievement

20

References

10

Student 4 Name :

4

Presentation

10

Research

20

Analysis

20

Level 1 Asia Pacific Institute of Information Technology 2010

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