wireless means without the use of any physical media in transfer of data. For example if data and information are transferred using physical cables like, twisted pair cables or optical cables, then that type of transmission cannot be called as wireless.
Common types of wireless transmission uses microwaves, Wi-Fi, Bluetooth, and other types of electromagnetic waves.
network refers to a group of computing devices which are connected together or which shares a common set of services and peripherals together.
In wireless networking, usually this refers to group of devices like computers, mobiles and other network hardware which communicate with each other to connect themselves together.
Information is, that which is distributed or exchanged by communication, is created by or used in, virtually every human activity and machine operation. Although the word information is self- explanatory, in the science of telecommunications, it is necessary to quantify the information content of messages conveyed over communication systems.
Information in telecommunications is carried by signals, which are time-varying electrical, electromagnetic, or light waveforms created by the information source.
For example, a microphone creates an electrical signal corresponding to the voice of the speaker. This signal carries the information contained in the speaker’s voice, which includes not only the content of the speech, but also information uniquely identifying the speaker, the feelings with which he/she is talking etc.
A communication channel carries the information over the distance. Therefore, it acts as a conduit for information. While carrying information, the channel also causes impairments to the signal. In wireless network this impairment is comparatively high.
Communication services refer to applications that are implemented on telecommunication systems. A telecommunications system will be useless without any services. A variety of communication services have been developed over a period of more than 150 years to satisfy the needs of the time, using the technology available at the time.
Starting from the earliest service, the primitive telegraph, all aspects of electronics and telecommunication technologies have advanced to make today’s sophisticated services possible. In today’s wireless context, there are so many sophisticated services like, voice calls, channeling services, bill payments, 3G, 4G and 4.5G internet, entertainment services like TV channels, movies and so on.
A continuous function that assumes smooth changes in value, and rates of change are finite. Analog signals are the natural forms of signals generated by many physical processes.
The microphone is a good example of a source for an analog signal. When we speak, voice generated is an analog signal.
A function that assumes a limited set of discrete values for constant durations of time is called a digital signal. Changes of values are instantaneous, and the rate of change at that instant is infinite.
At all other times it is zero. A binary waveform is one that has only two allowable values, and are commonly used for the communication of digital data. Binary signals are the natural form of signals generated by computers and similar devices.
The range of frequencies that just encompasses all of the energy present in a signal is known as the Bandwidth of that signal. In wireless engineering, Fourier transformation is vital in finding the bandwidth.
In any telecommunication system, whatever the transmission media used, there is unwanted electrical energy present as well as that of the wanted information signal. This unwanted electrical energy is generally referred to as noise. Noise arises from a number of different sources.
The most predominant type of noise is generated in electronic components due to the random motion of electrons. This type of noise is called thermal noise. Since external interferences are severe in wireless communication, noise is higher in these networks compared to wired networks.
Attenuation and distortion as signals travel along a channel, its amplitude or power is progressively reduced because of losses in the channel. These losses, called attenuation, may be due to heat dissipation by the resistance of the channel, dielectric losses or due to distribution of signal power in space.
In wireless networking, heat dissipation is very less and so is the dielectric loss. So it is basically due to the spread of signal power. A designer of a wireless communication system must ensure that a sufficient signal level is present at the receiver, for it to detect the signal accurately.
Hence he/she must take the attenuation into account when the transmit power is determined.
This is the set of frequencies is allocated to all stations offering a specific service. Frequency allocations are administered by the International Telecommunication Union (ITU) with the help of information gathered at periodic Regional and Worldwide Administrative radio Conferences (RARCs and WARCs).
We will examine the frequency bands and their designated usage internationally in the next section
This is the specific frequency or frequency band on which a particular station must operate to provide the service. A telecommunication regulatory authority in each country is responsible for this task. The US frequency assignment is handled by the Federal Communications Commission (FCC).
In addition to specific frequency assignment and authorization to provide services, operating licenses usually include restrictions as to permissible radiated power, type of signal to be used and may limit times of operation etc.
The license is provided for an annual fee and if an operator violates the conditions of his license, it may be cancelled. This is a very important paper for all wireless service providers.
frequencies from about 300 Hz to 300 GHz. This is the range of electromagnetic waves that are used in communications. Radio waves are further subdivided into different bands.
Ground wave propagation
Ground wave propagation is the wireless propagation method which is dominant for frequencies below 2 MHz. Here, the electromagnetic wave tends to follow the contour of the earth due to diffraction. This is the main propagation method for AM broadcasting.
Sky wave propagation
Sky wave propagation is the dominant method of propagation in the frequency range 2 to 30 MHz. Here, long-distance coverage is obtained by reflecting the wave at the ionosphere. The ionosphere is the part of the atmosphere at high altitudes, where ionization is caused by ultraviolet radiation from the sun.
The amount of ionization caused by ultraviolet radiation from the sun is highly dependent on the time of the day, season of the year and sunspot activity. This results in changing propagation characteristics. HF (short-wave) broadcasting operates in this frequency range. Hence, the reception is highly variable.
Tropospheric propagation is the dominant mode for frequencies above 30 MHz. Here, the electromagnetic wave propagates in a straight line, either through the atmosphere as in the case of satellite communications, or inside the atmosphere as in other terrestrial microwave communication systems.
Many communications systems in this frequency region uses line-of- sight (LOS) propagation of tropospheric waves between the transmitter and the receiver.
The process of bundling many signals together in order to transmit them simultaneously over a telecommunication link is called multiplexing. The frequency shifting characteristics of AM and FM and the digital encoding of signals using techniques such as PCM form the basis of multiplexing.
The bundled signals are separated at the receiving end by a process called demultiplexing.
One of the principles of cellular systems is to divide a large geographic service area into cells with diameters from about 2 to 50 km, each of which is allocated a number of RF channels.
Transmitters in adjacent cells operate on different frequencies to avoid interference. Since, however, the transmit power and antenna height in each cell are relatively low, cells that are sufficiently far apart can reuse the same set of frequencies without causing co-channel interference.
This is the cutting edge wireless technology which is used to transmit high bandwidth data. It is several times faster than the Bluetooth and infrared transmission.
Since the bandwidth is comparatively high, large number of users can utilize the same server at once. This communication technology employs 2.4 GHz UHF and 5 GHZ SHF radio waves. Its name is a trademark name and is a play on the audiophile terminology Hi-Fi.
This is a fundamental cellular idea is hand-off. In a cellular system, not all mobile calls may be completed within the boundaries of a single, relatively small cell.
To deal with this, the cellular system is equipped with its own system level switching and control capability. Through continuous monitoring of signal strength and other parameters received from individual cell sites, the cellular system can sense when a mobile unit with a call in progress passes from one cell to another and can switch the call to the new cell without interruption.