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Wireless communication involves the transmission of information over a distance without the help of wires, cables or any other forms of electrical conductors. Wireless communication is a broad term that incorporates all procedures and forms of connecting and communicating between two or more devices using a wireless signal through wireless communication technologies and devices. Features of Wireless Communication The evolution of wireless technology has brought many advancements with its effective features. The transmitted distance can be anywhere between a few meters (for example, a television's remote control) and thousands of kilometers (for example, radio communication). Wireless communication can be used for cellular telephony, wireless access to the internet, wireless home networking, and so on. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones. Wireless - Advantages Wireless communication involves transfer of information without any physical connection between two or more points. Because of this absence of any 'physical infrastructure', wireless communication has certain advantages. This would often include collapsing distance or space. Wireless communication has several advantages; the most important ones are discussed below − Cost effectiveness Wired communication entails the use of connection wires. In wireless networks, communication does not require elaborate physical infrastructure or maintenance practices. Hence the cost is reduced. Example − Any company providing wireless communication services does not incur a lot of costs, and as a result, it is able to charge cheaply with regard to its customer fees. Flexibility Wireless communication enables people to communicate regardless of their location. It is not necessary to be in an office or some telephone booth in order to pass and receive messages. Miners in the outback can rely on satellite phones to call their loved ones, and thus, help improve their general welfare by keeping them in touch with the people who mean the most to them.
Convenience Wireless communication devices like mobile phones are quite simple and therefore allow anyone to use them, wherever they may be. There is no need to physically connect anything in order to receive or pass messages. Example − Wireless communications services can also be seen in Internet technologies such as Wi-Fi. With no network cables hampering movement, we can now connect with almost anyone, anywhere, anytime. Speed Improvements can also be seen in speed. The network connectivity or the accessibility were much improved in accuracy and speed. Example − A wireless remote can operate a system faster than a wired one. The wireless control of a machine can easily stop its working if something goes wrong, whereas direct operation can’t act so fast. Accessibility The wireless technology helps easy accessibility as the remote areas where ground lines can’t be properly laid, are being easily connected to the network. Example − In rural regions, online education is now possible. Educators no longer need to travel to far-flung areas to teach their lessons. Thanks to live streaming of their educational modules. Constant connectivity Constant connectivity also ensures that people can respond to emergencies relatively quickly. Example − A wireless mobile can ensure you a constant connectivity though you move from place to place or while you travel, whereas a wired land line can’t. Among the various terms used in Mobile telephony, the most used ones will be discussed here. Mobile Station (MS) − The Mobile Station (MS) communicates the information with the user and modifies it to the transmission protocols of the air interface to communicate with the BSS. The user information communicates with the MS through a microphone and speaker for the speech, keyboard and display for short messaging and the cable connection for other data terminals. The mobile station has two elements Mobile Equipment (ME) and Subscriber Identity Module (SIM). Mobile Equipment (ME) − ME is a piece of hardware that the customer purchases from the equipment manufacturer. The hardware piece contains all the components needed for the implementation of the protocols to interface with the user and the air-interface to the base stations. Subscriber Identity Module (SIM) − This is a smart card issued at the subscription to identify the specifications of a user such as address and type
In wireless communication systems, it is often desirable to allow the subscriber to send information simultaneously from the mobile station to the base station while receiving information from the base station to the mobile station. A cellular system divides any given area into cells where a mobile unit in each cell communicates with a base station. The main aim in the cellular system design is to be able to increase the capacity of the channel , i.e., to handle as many calls as possible in a given bandwidth with a sufficient level of quality of service. There are several different ways to allow access to the channel. These includes mainly the following − Frequency division multiple-access (FDMA) Time division multiple-access (TDMA) Code division multiple-access (CDMA) Space division multiple access (SDMA) Depending on how the available bandwidth is allocated to the users, these techniques can be classified as narrowband and wideband systems. Narrowband Systems Systems operating with channels substantially narrower than the coherence bandwidth are called as Narrow band systems. Narrow band TDMA allows users to use the same channel but allocates a unique time slot to each user on the channel, thus separating a small number of users in time on a single channel. Wideband Systems In wideband systems, the transmission bandwidth of a single channel is much larger than the coherence bandwidth of the channel. Thus, multipath fading doesn’t greatly affect the received signal within a wideband channel, and frequency selective fades occur only in a small fraction of the signal bandwidth. Frequency Division Multiple Access (FDMA) FDMA is the basic technology for advanced mobile phone services. The features of FDMA are as follows. FDMA allots a different sub-band of frequency to each different user to access the network. If FDMA is not in use, the channel is left idle instead of allotting to the other users. FDMA is implemented in Narrowband systems and it is less complex than TDMA. Tight filtering is done here to reduce adjacent channel interference. The base station BS and mobile station MS, transmit and receive simultaneously and continuously in FDMA.
Time Division Multiple Access (TDMA) In the cases where continuous transmission is not required, there TDMA is used instead of FDMA. The features of TDMA include the following. TDMA shares a single carrier frequency with several users where each users makes use of non-overlapping time slots. Data transmission in TDMA is not continuous, but occurs in bursts. Hence handsoff process is simpler. TDMA uses different time slots for transmission and reception thus duplexers are not required. TDMA has an advantage that is possible to allocate different numbers of time slots per frame to different users. Bandwidth can be supplied on demand to different users by concatenating or reassigning time slot based on priority. Code Division Multiple Access (CDMA) Code division multiple access technique is an example of multiple access where several transmitters use a single channel to send information simultaneously. Its features are as follows. In CDMA every user uses the full available spectrum instead of getting allotted by separate frequency. CDMA is much recommended for voice and data communications. While multiple codes occupy the same channel in CDMA, the users having same code can communicate with each other. CDMA offers more air-space capacity than TDMA. The hands-off between base stations is very well handled by CDMA. Space Division Multiple Access (SDMA) Space division multiple access or spatial division multiple access is a technique which is MIMO (multiple-input multiple-output) architecture and used mostly in wireless and satellite communication. It has the following features. All users can communicate at the same time using the same channel. SDMA is completely free from interference. A single satellite can communicate with more satellites receivers of the same frequency. The directional spot-beam antennas are used and hence the base station in SDMA, can track a moving user. Controls the radiated energy for each user in space. Spread Spectrum Multiple Access Spread spectrum multiple access (SSMA) uses signals which have a transmission bandwidth whose magnitude is greater than the minimum required RF bandwidth.
The Coverage area is very high than that of terrestrial systems. The transmission cost is independent of the coverage area. Higher bandwidths are possible. Disadvantages of Satellite The disadvantages of Satellite Communications are as follows − Launching satellites into orbits is a costly process. The bandwidths are gradually used up. High propagation delay for satellite systems than the conventional terrestrial systems. Satellite Communication Basics The process of satellite communication begins at an earth station. Here an installation is designed to transmit and receive signals from a satellite in orbit around the earth. Earth stations send information to satellites in the form of high powered, high frequency (GHz range) signals. The satellites receive and retransmit the signals back to earth where they are received by other earth stations in the coverage area of the satellite. Satellite's footprint is the area which receives a signal of useful strength from the satellite. The transmission system from the earth station to the satellite through a channel is called the uplink. The system from the satellite to the earth station through the channel is called the downlink. Satellite Frequency Bands The satellite frequency bands which are commonly used for communication are the Cband, Ku-band, and Ka-band. C-band and Ku-band are the commonly used frequency spectrums by today's satellites. It is important to note that there is an inverse relationship between frequency and wavelength i.e. when frequency increases, wavelength decreases this helps to understand the relationship between antenna diameter and transmission frequency. Larger antennas (satellite dishes) are necessary to gather the signal with increasing wavelength. Earth Orbits A satellite when launched into space, needs to be placed in certain orbit to provide a particular way for its revolution, so as to maintain accessibility and serve its purpose whether scientific, military or commercial. Such orbits which are assigned to satellites, with respect to earth are called as Earth Orbits. The satellites in these orbits are Earth Orbit Satellites. The important kinds of Earth Orbits are − Geo-synchronous Earth Orbit Geo-stationary Earth Orbit Medium Earth Orbit
Low Earth Orbit Geo-synchronous Earth Orbit (GEO) Satellites A Geo-synchronous Earth orbit Satellite is one which is placed at an altitude of 22,300 miles above the Earth. This orbit is synchronized with a side real day (i.e., 23hours 56minutes). This orbit can have inclination and eccentricity. It may not be circular. This orbit can be tilted at the poles of the earth. But it appears stationary when observed from the Earth. The same geo-synchronous orbit, if it is circular and in the plane of equator, it is called as geo-stationary orbit. These Satellites are placed at 35,900kms (same as geosynchronous) above the Earth’s Equator and they keep on rotating with respect to earth’s direction (west to east). These satellites are considered stationary with respect to earth and hence the name implies. Geo-Stationary Earth Orbit Satellites are used for weather forecasting, satellite TV, satellite radio and other types of global communications. The above figure shows the difference between Geo-synchronous and Geo- Stationary orbits. The Axis of rotation indicates the movement of Earth. The main point to note here is that every Geo-Stationary orbit is a Geo- Synchronous orbit. But every Geo-Synchronous orbit is NOT a Geo- stationary orbit. Medium Earth Orbit (MEO) Satellites Medium earth orbit (MEO) satellite networks will orbit at distances of about 8000 miles from earth's surface. Signals transmitted from a MEO satellite travel a shorter distance. This translates to improved signal strength at the receiving end. This shows that smaller, more lightweight receiving terminals can be used at the receiving end. Since the signal is travelling a shorter distance to and from the satellite, there is less transmission delay. Transmission delay can be defined as the time it takes for a signal to travel up to a satellite and back down to a receiving station. For real-time communications, the shorter the transmission delay, the better will be the communication system. As an example, if a GEO satellite requires 0.25 seconds for a round trip, then MEO satellite requires less than
different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell When joined together, these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, tablets and laptops equipped with mobile broadband modems, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission. Cellular networks offer a number of desirable features: More capacity than a single large transmitter, since the same frequency can be used for multiple links as long as they are in different cells Mobile devices use less power than with a single transmitter or satellite since the cell towers are closer Larger coverage area than a single terrestrial transmitter, since additional cell towers can be added indefinitely and are not limited by the horizon Major telecommunications providers have deployed voice and data cellular networks over most of the inhabited land area of Earth. This allows mobile phones and mobile computing devices to be connected to the public switched telephone network and public Internet. Private cellular networks can be used for research[2]^ or for large organizations and fleets, such as dispatch for local public safety agencies or a taxicab company. 1G 1G or (1-G) refers to the first generation of wireless telephone technology (mobile telecommunications). These are the analog telecommunications standards that were introduced in 1979 and the early to mid-1980s and continued until being replaced by 2G digital telecommunications. The main difference between the two mobile telephone systems (1G and 2G), is that the radio signals used by 1G network are analog, while 2G networks are digital. 2G 2G (or 2-G) provides three primary benefits over their predecessors: phone conversations are digitally encrypted; 2G systems are significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with SMS (Short Message Service) plain text-based messages. 2G technologies enable the various mobile phone networks to provide the services such as text messages, picture messages and MMS (Multimedia Message Service). It has 3 main services: Bearer services is one of them which is also known as data services. Second generation 2G cellular telecom networks were commercially launched on the GSM standard 3G
3G technology provides an information transfer rate of at least 200 kbit/s. Later 3G releases, often denoted 3.5G and 3.75G, also provide mobile broadband access of several Mbit/s to smartphones and mobile modems in laptop computers. This ensures it can be applied to wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and mobile TV technologies. A new generation of cellular standards has appeared approximately every tenth year since 1G systems were introduced in 1981/1982. Each generation is characterized by new frequency bands, higher data rates and non– backward-compatible transmission technology. The first 3G networks were introduced in 1998 and fourth generation 4G networks in 2008. 3.5G 3.5G is a grouping of disparate mobile telephony and data technologies designed to provide better performance than 3G systems, as an interim step towards the deployment of full 4G capability. The technology includes: High-Speed Downlink Packet Access 3GPP Long Term Evolution, precursor of LTE Advanced Evolved HSPA 4G 4G provides, in addition to the usual voice and other services of 3G, mobile broadband Internet access, for example to laptops with wireless modems, to smartphones, and to other mobile devices. Potential and current applications include amended mobile web access, IP telephony, gaming services, high- definitionmobile TV, video conferencing, 3D television, and cloud computing. 4.5G 4.5G provides better performance than 4G systems, as an interim step towards deployment of full 5G capability. The technology includes: 5G 5G is a generation currently under development. It denotes the next major phase of mobile telecommunications standards beyond the current 4G/IMT- Advancedstandards. NGMN Alliance or Next Generation Mobile Networks Alliance define 5G network requirements as: Data rates of several tens of Mb/s should be supported for tens of thousands of users. 1 Gbit/s to be offered, simultaneously to tens of workers on the same office floor. Several hundreds of thousands of simultaneous connections to be supported for massive sensor deployments. Spectral efficiency should be significantly enhanced compared to 4G. Coverage should be improved.
