N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 9 - Wireless Systems and Technologies                                                                                   Slide 3 of 80                                                                                                    ________________

         Wireless Communications Concepts

                                Radio Waves Used to Transmit Information in Space

                                Radio Waves Generated by Inducing Current into an
                                  Antenna

                                Radio Signals can be Generated Uniformly or Directed
                                  as a Beam of Energy

                                Radio Waves Travel at 186,000 miles per second in a
                                  Vacuum

                                                                                                   ________________

Radio waves, like fiber, coax-cable and twisted copper-wire pair, are another means of transmitting information. This type of communication is known as wireless communications. Wireless communications systems are used to send messages between two locations using radio waves which travel across free space.

Messages of all types, voice, music, image, video and text, are usually converted to digital form and are represented as a stream of 1's and 0's. Voice messages can be represented by 16,000 bps, CD quality music needs about 100,000 bps, and TV quality video messages require 1,000,000 bps.

Radio waves are electromagnetic waves used to carry a message over a distance. A radio wave is also known as a carrier wave. It looks like a sine wave and moves at a very high speed, cycles per second The electromagnetic waves of different frequencies and wavelengths have different properties. Radio waves can travel through walls, but light waves can't. Lower frequency waves travel further, and can bend around corners. Higher frequency waves travel in line of sight.

The radio frequency spectrum covers extremely low, below 300 HZ, to Tremendously High Frequencies (THF), 300 G Hz - 3 T Hz band. Terrestrial radio-link systems carry a substantial part of all telephone, data and television traffic. There are four type of radio waves: Ground, Space, Sky and Satellite.

Ground Wave - propagates along earth's surface - usually low frequency bands (30 K Hz - 300 K Hz). The medium frequency band (300 K Hz - 3 M Hz) is used for radio broadcasting.

Space Wave - travels in a straight line between a transmitting and a receiving antenna. This wave is used to broadcast TV signals in VHF (30 M Hz - 300 M Hz), UHF (300 M Hz - # G Hz) and SHF (3G Hz - 30 G Hz) bands.

Sky Wave - is transmitted upwards into the ionosphere and a portion of it is reflected to the ground. It uses 3M Hz - 30 M Hz frequency band. It is extensively used by radio broadcasting and long distance telephone systems.

Satellite Waves - are transmitted to a satellite station, amplified and transmitted back to a ground station.

Most wireless networks use infrared or radio frequency signals to transmit data. The application of radio frequencies is licensed and regulated by Federal Communications Commission (FCC) rules in the U.S. and  Industry Canada rules in Canada.

The specific parts of the radio spectrum are better suited for certain type of telecommunications. The carrier frequencies in the range of 1 to 5 G Hz are suited for indoor wireless communications through walls over a distance of several hundred feet or outdoor communications over several miles over line of sight.