Principles Digital Communication System & Computer Networks (Charles River Media Computer Engineering)

2017-07-07 02:10:07

< Day Day Up >

10.8 COST

The cost is the most important of the design parameters. To design a communication system that meets all the performance criteria at minimum cost is the major challenge to communication engineers. The choice of the transmission medium (twisted pair, coaxial cable, radio or fiber, etc.) needs to keep in view the cost. In communication system design, engineers do not develop each and every subsystem. The various subsystems are procured from different vendors and integrated. In such a case, the engineer has to choose the subsystem that meets all the performance requirements and is cost effective. Experience is the best teacher for choosing the right subsystems.

Cost is the most important design parameter while designing communication systems. To design a system that meets all the performance requirements at the lowest cost is the callenge for all communcation engineers.

Summary

In designing a communication system, a number of issues need to be taken into consideration. These include services to be supported such as data, voice, video, etc., which decide the data rate requirements; error detection and correction mechanisms; type of modulation; performance criteria such as bit error rates; security aspects; standards to be followed for the implementation; and the cost. These issues are discussed in detail in this chapter.

References

K. Krechmer. "Standards Make the GIH Possible." IEEE Communications Magazine, Vol. 34, No. 8, August 1996. This paper gives information about the history of standardization and the various standards authorities.

IEEE Communications Magazine, Vol. 34, No. 8, August 1996. This is a special issue on "Emerging Data Communications Standards."

http://www.ansi.org The Web site of American National Standards Institute.

http://www.iso.org The Web site of International Organization for Standardization.

http://www.itu.int The Web site of International Telecommunications Union.

http://www.etsi.org The Web site of European Telecommunications Standards Institute.

http://www.amdah.com The Web site of Fiber Channel Association.

http://www.ietf.org The Web site of Internet Engineering Task Force.

Questions

List the various issues involved in telecommunication systems design.

What are the special issues to be considered for radio system design?

List some important international standardization bodies.

What criteria are used to compare different modulation techniques?

What are the common security threats? Explain the concept of encryption.

Exercises

1.	Conduct a survey of the various international and national standardization bodies and prepare a report.
2.	Conduct a survey of commercial products available for planning and designing a cellular mobile communication system.
3.	Study the performance of different digital modulation schemes using Bit Error Rate (BER) and bandwidth requirement as the performance criteria.
4.	Design a local area network for your college campus. Design it based on the available international standards. List the various options available.

Answers

1.	The various standardization bodies are American National Standards Institute (ANSI) Advanced Television Systems Committee (ATSC) Alliance for Telecommunications Industry Solutions (ATIS) Cable Television Laboratories, Inc. (CableLabs) European Committee for Standardization (CEN) European Committee for Electrotechnical Standards (CENELEC) European Computer Manufacturers Association (ECMA) Electronic Industries Alliance (EIA) European Telecommunications Standards Institute (ETSI) Federal Communications Commission (FCC) International Electrotechnical Commission (IEC) Institute of Electrical and Electronics Engineers (IEEE) International Organization for Standardization (ISO) Internet Society (ISOC) International Telecommunications Union (ITU) Telecommunications Industry Association (TIA) World Wide Web Consortium (W3C) A number of industry consortia and special interest groups (SIGs) formulate the telecommunications specifications. Some such consortia and groups are 10 Gigabit Ethernet Alliance ATM Forum Bluetooth SIG CDMA Development Group DSL Forum Enterprise Computer Technology Forum Frame Relay Forum HomeRF Working Group International Multimedia Telecommunications Consortium Infrared Data Association Object Management Group Personal Communications Industry Association Personal Computer Memory Card International Association Satellite Broadcasting and Communications Association SONET Interoperability Forum Society for Motion Picture & Television Engineers WAP Forum Wireless Ethernet Compatibility Alliance Wireless LAN Association
2.	To plan and design a cellular mobile communication system, a radio survey needs to be carried out. A radio survey involves study of the terrain and deciding where to install the base stations. The radio propagation characteristics need to be studied for which computer models are available. Leading mobile communication equipment suppliers such as Motorola, Ericsson, and Nokia provide these tools.
3.	BER is a design parameter. You need to find out the BER required for the communication system being designed. For this BER, the modulation technique, which requires the least energy per bit, is the best. However, other considerations such as the implementation complexity or cost of the modulator/demodulator also play an important role while choosing a modulation technique.
4.	The standards for various types of LANs have been formulated by the professional body IEEE. IEEE 802.3 LAN is based on the Ethernet, FDDI is for optical fiber–based LANs, and IEEE 802.11 is for wireless LAN. You can design a backbone network based on fiber and then interconnect 802.3 LANs and wireless LANs to obtain a campus-wide network.

Projects

Prepare the paper design of a communication system to provide Internet access to 50 communities that are located within a radius of about 30 km from the district headquarters. Consider the various design options: data rate support, transmission medium, multiple access technique, performance, delay, and of course the cost of the system.

Simulate a digital communication system. The software has to (a) generate a continuous stream of bits, (b) introduce errors by converting 1 to 0 or 0 to 1 at random places in the bit stream, and (c) modulate the bit stream using different modulations.

Prepare a paper design of a communication system interconnecting all the colleges providing technical education in your state. The system is to be used for providing distance education. From a central location (state capital), lectures have to be broadcast with a video data rate of 384kbps, audio and data at 64kbps. At each college, there should be a provision to send data or voice to interact with the professor at the central location.

Design a communication system that links two branch offices of an organization. The two branches are separated by a distance of 10km. The employees of the two branches should be able to talk to each other, exchange computer files, and also do video-conferencing using 64kbps desktop video conferencing systems. Make appropriate assumptions while preparing the design.