Wireless Communication: Cordless Phones

Abstract:

The transfer of information from one place to another place by signals not by wires is called wireless communication. Wireless itself means “without wires”. Radio and electromagnetic waves are used for all kind of information. Smoke signals were also used for this purpose before the invention of radio signals. There are many types of wireless communication e.g. cordless telephone, cellular telephone system, Bluetooth, satellite networks and wireless LANs. Cordless telephones were very famous in US and Europe. Cordless telephone were designed were designed to provide low cost communication for the users. Now they based on digital technology and their bandwidth is 1.9 GHz where they provide good voice quality. Cellular telephone system

Cordless telephones were planned to provide low cost communication for the users instead of wire connecting telephone. In these days, the usage of cordless phones is less because they have low coverage capacity. Cordless phones are limited within the same area, in an office or the working place. In Europe and Asia, these cordless telephones are advanced to provide wider coverage within the working place or outside the place. The system of cordless phone is same as the landline phone. They remain in their base unit and the movement of cordless phones is limited. In the past, they have single voice channel that’s why the interference was increased between the systems due to high density in a small area. Today they have multiple voice channels for better quality of voice and to reduce the interference. In 21st century, cordless phones are based on digital technology. Digital technology is providing clear voice and less interference between base stations. Mostly cordless phones work on a single base station but can be add more additional base stations and because of this people can conference calls. Manufactures designed high frequency bandwidth products to improve voice quality. The typical frequency bandwidth is 3.6 GHz where the voice quality of cordless phones is not good. The good quality frequency bandwidth is 1.9 GHz instead of 2.4GHz, 5.8GHz and

But wireless LANs is stationery or moving at a very low speed. Wireless LANs uses ISM (Industrial, scientific and medical frequency bands) frequency bands and their range is 900MHz, 2.4GHz and 5.8MHz. Some other systems also operate between these bands for the same purpose which causing interference between systems. Federal Communication Commission is trying to solve interference problem by limiting power per unit for ISM band system. Many Wireless LANs companies started working in 1990 for high speed data system.

Satellite Networks:

Satellite system provides broadcast services and better coverage to the users in worldwide. Their architecture is same as cellular system. Their characterization is done by measuring distance from the earth. Satellites can be divided into three types: low-earth orbit at 500-2000km, medium-earth orbit at 10,000km and synchronous-earth orbit at 35800km. Synchronous satellite has large coverage area, the earth and satellite orbits are synchronous. The satellites that have lower orbits have smaller coverage area and this area is changed with time, so satellite handoff is necessary for stationary users.