TELECOMMUNICATION SYSTEM

Telecommunication System



Telecommunication System

Task 1

Elements of Analogue & Digital Communication System

Electrical communication systems are designed to send messages or information from a source that generates the messages to one or more destinations (O'Hara, 2007). In general, a communication system can be represented by the functional block diagram shown in Figure 1.1. The information generated by the source may be of the form of voice (speech source), a picture (image source), or plain text in some particular language, such as English, Japanese, German, French, etc (Schubert, 2007). An essential feature of any source that generates information is that its output is described in probabilistic terms; i.e., the output of a source is not deterministic. Otherwise, there would be no need to transmit the message.

Figure 1.1—Functional block diagram of a communication system.

Analog communication systems, amplitude modulation (AM) radio being a typifying example, can inexpensively communicate a band limited analog signal from one location to another (point-to-point communication) or from one point to many (broadcast) (Schiffer, 2001). Although it is not shown here, the coherent receiver provides the largest possible signal-to-noise ratio for the demodulated message. An analysis of this receiver thus indicates that some residual error will always be present in an analog system's output.

Characteristics of Electromagnetic Waves & their Application to Communication System

There has been much recent interest in the application of electromagnetic wave techniques to the solution of a variety of problems such as civil aviation security, crash sensors, automatic braking devices, vehicular location systems and others. Many of these applications, such as, for example, crash sensors for use in automobiles, involve a high density of users in relatively close proximity (Rappaport, 2002). In such cases, it becomes readily apparent that means must be provided to minimize crosstalk in order to avoid spurious indications of a crash situation when, in fact, none exists. The obvious solution to this problem is to provide a separate channel for each user. However, with millions of vehicles on the road, this approach would consume an undue amount of frequency spectrum and, as such, is not an attractive solution to the problem. Nor would it be economically feasible to incorporate sophisticated circuitry into such devices as a means of avoiding the problem of spurious indications if, indeed, it could be done at all. Obviously, if these problems are to be resolved it must be done in an economic manner, economic in both cost and in the use of the available frequency spectrum (Pierce, 2000).

In accordance with the present invention, the above referred to economies are realized by operating solely at a transmission frequency that is highly attenuated by the atmosphere. For purposes of the present invention, highly attenuated shall be understood to mean that the absorption loss through the atmosphere is about 10 db per kilometer or greater. This would include, for example, the band of frequencies between 55 to 63 gigahertz (Phillips, 2001). In particular, by transmitting at a carrier frequency of 60 gigahertz, maximum attenuation by the oxygen in the atmosphere is ...