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

OVERVIEW

To design a communication system according to user requirements is a challenging task because the requirements differ from user to user and there are many design trade-offs to be considered. The design of a communication system has to be carried out keeping in view the following factors:

• What are the information sources? Data, voice, fax, video, or all of them? Depending on the requirements, the bandwidth requirements will be different.

• What is the coverage area? The coverage area decides which transmission medium has to be chosen, and sometimes a combination of media may be required (for instance, a combination of twisted pair and satellite).

• Is a secure network required? For defense and corporate networks, a highly secure system is required to ensure that the information is kept confidential. Special security features have to be incorporated in such cases.

• What are the performance criteria? For data applications, particularly such as in banking and other financial transactions, performance requirements are very stringent. For instance, even a one-bit error in a million bits transmitted is not acceptable. Such criteria call for efficient modulation techniques and error detection/correction mechanisms. On the other hand, for voice and video applications, delay should be minimum.

• What are the signaling requirements? Is a separate signaling channel/network required?

• Which national/international standards have to be followed? The days of providing proprietary solutions are gone; every communication system has to be designed according to the available international standards. Before designing a communication system, the relevant standards need to be studied, and the design has to be carried out.

• Given an unlimited budget, we can design a world-class communication system for every user segment. But the user is always constrained by budget. For a given budget, to design the optimal system that meets the requirements of the user is of course the biggest challenge, and as usual, we need to consider the various trade-offs.

In this chapter, we discuss the issues involved in designing communication systems. We also study the important aspects in designing radio communication systems. The special attraction of the radio systems is that they provide mobility to users, but every attraction comes with a premium—radio systems pose special design challenges.

When designing a communication system, the following requirements need to be considered: coverage area, information sources, security issues, performance issues, signaling requirements, international/national standards to be followed, and the cost.