Facilities of Wireless Communication | Data Communication | Computer Science

Wireless communications may require the use of different facilities at different times. These are: Radio transmission and Microwave transmission. We shall look at each of them separately.

1. Radio Transmission:

Radio transmission is one of the ways that wireless transmission can take place; the other widely used method of wireless transmission usually is microwave transmission. All these methods of transmission depend upon the frequency utilised for transmission. Some basic facts that may help in understanding the transmission of signals may be recapped here to help our understanding of radio and microwave transmissions.

No signal or object can travel faster than light. This speed is traditionally referred to as c which is a constant equal to 3 x 10⁸ metres per second.

Another important fact to be noted is that in vacuum, all electromagnetic waves always travel precisely at the speed of light. Since all transmission takes place in the form of waves, the frequency of transmission f and the wavelength (traditionally referred to by the Greek letter ʎ) thus are linked with the speed of light by

ʎ f = c

and since c is constant, the frequency f and the wavelength ʎ are inversely proportional. The frequency is usually measured in hertz (after the famous German physicist Heinrich Hertz) and the wavelength in metres (or centimeters). The different types of waves in the electromagnetic spectrum are defined by the frequency range that they utilise in the electromagnetic spectrum.

Thus radio waves utilise the frequency range 10⁶ hertz and microwave utilizes 10⁹ hertz. Of course, these frequencies are more or less mid-point frequencies and the transmission can use frequencies slightly higher than or slightly lower than this. Fibre Optics, incidentally, operates at the frequency of about 10¹⁴ hertz.

Radio transmission has certain special characteristics. They are omnidirectional, they tend to get absorbed by rain and at low frequencies they pass through objects well, but power dissipates very sharply with increase in distance (roughly in the inverse of the cube of the distance from the source). At high frequencies, however, they tend to travel straight and get bounced off objects.

They also tend to face interference from electrical devices (most users must have noticed this). They also use a narrow frequency band for transmission.

They can, however, be used effectively for data transmission over relatively shorter distances. Generally, they are used for distances of up to 50 km for data transmission. Beyond that, they require repeaters. Since these repeaters are fairly expensive, they are not desired very often.

The cost of a repeater is almost the same as that of the original equipment; therefore, every time a repeater is used, the cost of establishing a radio link goes up by 100%. That is why, for data transmission, radio transmission is rarely, if ever, used for distances beyond 100 km.

The bandwidth available for data transmission is generally felt to be adequate, but increasing bandwidth is usually an expensive proposition since it invariably means that the original transmission equipment has to be totally scrapped and replaced by new equipment which can deliver higher bandwidths.

At the same time, radio transmission has very low operating cost (air waves are after all free). Radio transmission, because of its limitations, will never become the primary mode of data communication in Information Technology; however, because of its many advantages, it will always be in use.

2. Microwave Transmission:

Microwave transmission formed the heart of long-distance transmission until the use of Fibre Optics started to develop.

In fact, the US long-distance Communications Company MCI (Microwave Commu­nications Incorporated) came into existence to exploit the use of Microwave Technology for commu­nications. Microwave communication is based on the fact that in the electromagnetic spectrum waves at frequencies higher than 100 MHz travel in a straight line.

Waves being transmitted in the form of a beam can be narrowly focused using a parabolic antenna. As a result, for the transmission of microwave signals, merely one tower is required, from the top of which transmission in a fixed direction can take place.

At the receiving end, a similar tower is used, with the receiving equipment being mounted on top of this receiving tower. Obviously, the distance between the sending and the receiving tower is depen­dent upon the heights of the towers.

Of course, the curvature of the earth does come into the picture and because of this transmission over long distances, requires several repeaters. There are, however, some problems with microwave transmission. Unlike radio waves, microwaves do not pass through objects; they tend to get reflected.

Secondly, even though the beam may be well focused, there is a certain amount of dispersion in space so that there are some losses.

Thirdly, some of the waves get refracted by the lower layers of the atmosphere and may arrive at the receiving station out of phase with the rest of the wave.

This tends to disturb the signal being received and the signal may partly or totally get wiped off at the receiving end. Fourthly, rain may absorb some of the transmitted signal and thereby reduce the signal strength causing problems at the receiving end.

However, in spite of these difficulties, microwave transmission offers some advantages over Fibre Optics. It must be clear that most of the advantages, provided by microwave transmission over Fibre Optics, are not technological. They invariably refer to people’s perception of transmission technology.

This lends some credence to ones belief that with the passage of time, microwave transmission will be superseded by Fibre Optics because of the innumerable advantages offered by the latter.

The major perceived advantages are summed up below:

1. Setting up of microwave transmission facilities is less expensive than setting up a Fibre Optic link, because the former merely requires two plots of land, each say 10 sq. metres in area, in which the transmission and receiving towers can be built.

For laying down Fibre Optic cables, on the other hand, one may require stretches of hundreds of kilometers of land (albeit a very narrow strip) under very crowded localities or over inaccessible and inhospitable terrain.

2. Microwave transmission does not require any “right of way”; Fibre Optic cables may require per­mission from local authorities, individual land-owners and may be central and state governments. Based on the above discussion, it must be obvious that while most forms of transmission have reached “the end of the road” of their development life cycles, that of Fibre Optics is just beginning.

We should see tremendous growth in the development and use of Fibre Optics in the coming years. My own view is that, in the coming years, Fibre Optics will wipe out all the other transmission media from all but the most mundane uses in communications and networking.