Wireless Technologies

The diffusion of wireless systems globally has greatly affected the use of cable technology. This is due apparently to the inherent characteristics of this system: physical connection is unnecessary, wireless systems function well with other applications, such as mobile telephony, which is impossible with the cable system. The wireless transmission system works by transmitting messages through the electromagnetic spectrum. The wireless transmission technologies include radio system, microwave systems and satellites systems. The radio system allows transmission in the form of radio waves. There are different types of waves arranged according to their frequencies. They vary from the extremely low frequency (ELF) to tremendously high frequency (THF) and within this range are UHF (ultra-high frequency) and the VHF (very high frequency). The radio systems, apart from transmission of messages, are used for broadcasting. Broadcast channels are located according to the different frequency ranges. The radio communication systems play an important role in mobile communication in our society, especially in local municipalities where police and fire services are critical. For a clearer understanding of the importance of radio communication, especially two way radio communication, one just needs to look at day-to-day examples: ship-to shore communication, police officer on patrol; the fire-fighter on an emergency call, the police on daily routine and etcetera.

Microwave

Microwave systems are high volume transmission systems that provide long-distance communication without wires. "Microwave systems transmit voice and data through the atmosphere as super-high-frequency radio waves" (Williams et al. 1999: 369). One particular characteristic of the microwave system is that it cannot bend around corners; therefore microwave antennas must be in "line of sight" of each other - that is, unobstructed. Microwave dishes and relay towers may be on the ground, however, they are usually situated atop high places, such as mountains or tall building, so that signals can be beamed over uneven terrain (ibid). Microwave systems can be very efficient in areas that are too remote to economically construct wired system.

The following are some of the characteristics of the microwave system:

1. High Volume
2. Long distance transmission
3. Point to point transmission
4. High frequency radio signals are transmitted from one terrestrial transmitter to another
5. Satellites serve as a relay station for transmitting microwave signals over very long distances. See figure 1.2

Fig 1.2: Low-Orbit Satellite and Microwave Transmission

Source: Telecom Networks. http://myphliputil.pearsoncmg.com/student/bp_laudon_mis_7/ch08.ppt

Satellite System

Satellite technology plays an important role in communication globally. Satellites work by receiving and transmitting radio signals from one earth station to another. Satellite technology operates in a three-step approach: Messages are sent from one earth station to the satellite and from the satellite down to another receiving earth station. There are three main types of satellites: The geosynchronous satellites, these satellites remain in a fixed position and are about 36,000 km from earth; the Low Earth Orbital satellites (LEO's) are positioned closer to earth and the third is the Very Small Aperture Terminals Satellites (VSAT).

Satellite systems have the advantages of transmission from point to multipoint systems, which means transmissions can be beamed to areas that are geographically dispersed. Over the years, satellite communication has improved tremendously, especially the expansion of the capacity of transponders. Transponders are the devices that receive signals from earth and retransmit these signals across stations within its 'footprint'. This expansion of capacity has strengthened the signals emitted by satellite; consequently, satellite-receiving dishes have been reduced considerably in size. Satellite technology has the potential to beam signals across different countries; this has improved international telephony enormously. It has also improved television signal transmission as well; programmes are transmitted to television operators from one country to another through satellite technology (Bitner, 1985). Over the years satellite transmission for telephony has been considered inappropriate. This is due to the fact that the time taken to beam the signal to space and back to earth creates a short delay in the exchange of conversations; this also leads to an echo in telephonic conversations.

Satellite voice communication, for a long time was out of reach for rural subscribers in developing countries. However, developments over the years have made direct access voice services available on a large scale, even to rural subscribers. For example, these services can be accessed through a briefcase size potable terminal (Westerveild, 1994). Perhaps, the most interesting development from this scenario is the development of a fixed cellular system. This system is very beneficial to rural subscribers. This system uses the existing cellular mobile telecommunications system with fixed rural subscribers. Westerveild (1994: 205) notes that "rural subscribers in the vicinity of large urban areas and roads could be connected to a CMTS (cellular mobile telecommunication systems) and use the excess capacity of that system".

The fixed cellular system, using satellite technology, has improved access to telecommunications tremendously in Africa. It has circumvented the physical connection through the laying of cables. This technology has become very appropriate for most developing countries, it comprises a briefcase-sized terminal connected to a telephone, which enables subscribers to make and receive calls irrespective of their geographical location. In South Africa, Vodacom, a private telecommunication provider in the country, is providing a fixed cellular facility in rural areas. The popularity of this technology in Africa is based on one inherent problem, which is associated with most developing regions of the world: the disparity in access to social amenities and infrastructure. This disparity is as a result of the inequality in economic power. A large percentage of the population in developing countries resides in the rural areas and they are confined to these areas due to the lack of economic power. Satellite communication, as stated earlier has the advantages of connecting points to points communication irrespective of the geographical location. That is, the arduous and capital-intensive task of laying cables up hill and down hill around the country can be circumvented. Secondly, satellite systems also enhance communication and mobility. Figure 1.3 provides information about the types of telecommunications transmission media, their speed and cost.

Fig 1.3: Speed and cost of telecommunications transmission media

Source: Telecom Networks. http://myphliputil.pearsoncmg.com/student/bp_laudon_mis_7/ch08.ppt