It is a non-commercial service that uses a press-to-talk switch. It can be amplitude modulated having double-sideband suppressed carrier or single-sideband suppressed carrier. Public land mobile radio is a two way FM radio system, used in police, fire and municipal agencies. It is limited to small geographical areas. Mobile telephones offer full-duplex transmission. These are one-to-one systems that permit two simultaneous transmissions. For privacy, each mobile unit carries a unique telephone number. Amateur HAM radios cover a broad frequency band from 1. Before I narrate the journey from 1G to 4G, let me explain the important technologies behind the phenomenal growth of mobile communication systems.
Since the commercial introduction of the advanced mobile phone system AMPS service in , mobile communication systems have witnessed explosive growth. The most important breakthrough was the cellular concept. The advent of cellular operation brought frequency reuse capabilities. Advances in wireless access, digital signal processing , integrated circuits, increased battery life, etc led to exponential growth of personal communication services. The cellular system works as follows: An available frequency spectrum is divided into discrete channels, which are assigned in groups to geographic cells covering a service area.
The discrete channels are capable of being reused in different cells with diameters ranging from 2 to 50 km. The service area is allotted a radio frequency RF transmitter, whereas adjacent cells operate on different frequencies to avoid interference. Cellular telephones began as a simple two-way analogue communication system using frequency modulation for voice and frequency-shift keying for transporting control and signalling information. Other cellular systems are a digital cellular system, cordless telephony, satellite mobile and paging.
Analogue cellular systems fall in the first-generation 1G category and digital cellular low-power wireless fall in the second-generation 2G category. Subscribers are assigned a pair of voice channels forward and reverse for the duration of their call. Analogue cellular channels carry both voices using FM and digital signalling information using binary FSK. It provides improvements in both capacity and performance. FDMA uses a frequency canalisation approach to spectrum management, while time-division multiple access TDMA utilises a time-division approach.
The entire available cellular RF spectrum is sub-divided into narrow-band radio channels to be used as a one-way communication link between cellular mobile units and base stations. Generally, a fixed amount of frequency spectrum is allocated to a cellular system. Multiple access techniques are deployed so that the users can share the available spectrum in an efficient manner. In TDMA the available spectrum is partitioned into narrow frequency bands or frequency channels, which, in turn, are divided into a number of time slots. In case of North American digital cellular standard IS, each frequency channel 30 kHz is divided into three-time slots, whereas in European digital cellular system GSM each frequency channel kHz is divided into eight time slots.
Guard bands are needed both between frequency channels and time slots. In FDMA, users share the available spectrum in a frequency band called traffic channel. Different users are assigned different channels on demand basis.
ETSI - Mobile Communications Technologies - GPRS, GSMA & UMTS
All the analogue cellular systems used FDMA system. OFDM is a multi-cellular transmission technique where a data stream is carried with many lower-rate subcarrier tones. It has been adopted in mobile communications to combat hostile frequency-selective fading and has been incorporated into wireless network standards. OFDM is a multi-cellular transmission technique where a data stream is carried with many lower-rate sub-carrier tones.
OFDM combines the advantages of coherent detection and OFDM modulation and has many merits that are critical for future high-speed transmission systems. Communication systems often involve the modulation of a carrier, which results in a bandpass waveform. A digital signal can be used to modulate the amplitude, frequency or phase of a sinusoidal carrier producing three different forms of digital modulation: amplitude-shift keying ASK , frequency-shift keying FSK and phase-shift keying PSK.
In addition to these basic techniques, there are some modulation schemes that employ a combination of amplitude and phase modulation.
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Digital modulation techniques mentioned above are spectrally inefficient in the sense that the available channel bandwidth is not fully used. Spectral efficiency can be improved by using QPSK. It is a system for two message sources. In this system modulation carriers in phase quadrature are combined to form the output waveform.
In QPSK the amplitude of the modulator waveform and modulator gains are made as nearly equal as possible. It is an ingenious technique whereby the carrier reference is derived from the received waveform in the preceding bit interval by use of a 1-bit delay. In essence, the received waveform delayed by 1-bit duration serves as its own reference. This is done by supplying various addressed packets, which are interconnected to have the conversation.
New dedicated paths are created for sending the data. From the multiple paths to the destination, any path can be used to send data. Cellular digital packet data was designed for optimal operation with an analogue cellular system, especially AMPS. For message transfer between relevant network entities, control and signalling channels instead of normal traffic channels are generally used for data transmission. GPRS essentially represents add-on capabilities to the basic voice-optimised cellular network that nevertheless maintain the essential characteristics of radio-access technology.
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In order to enhance the data handling capabilities of 2G service, the radio-access portion had to be modified. EDGE also supports a link adaptation mechanism that selects the best combination of modulation and encoding schemes based on the time varying link quality. EDGE concept applies to both circuit-mode and packet-mode data and is sufficiently generic for application to other digital cellular systems.
It works in the kHz bandwidth with one or more high-level modulation schemes and a range of efficient coding methods. It is a special communication technique that purposefully uses much more RF bandwidth than necessary to transmit a signal. The main advantages of this technique are secure communication and resistance to intentional jamming. There are 75 channels in the For other uses, see GSM disambiguation. Main article: GSM services. Main article: Base station subsystem.
Main article: GSM frequency bands. Retrieved 23 November Archived from the original on 8 February Retrieved CBS Interactive. Archived from the original on 5 May Retrieved 5 May Before GSM, Europe had a disastrous mishmash of national analogue standards in phones and TV, designed to protect national industries but instead creating fragmented markets vulnerable to big guns from abroad. European Telecommunications Standards Institute.
Features of Mobile Communication
GSM was designed principally for voice telephony, but a range of bearer services was defined GSM Association. Stephen Temple. Retrieved 7 April Yelisradio OY. Harri Holkeri made the first call on the Radiolinja Elisa's subsidiary network, at the opening ceremony in Helsinki on Archived from the original on 21 May Retrieved 8 June Retrieved 7 November Retrieved 2 December ATT Mobility.
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Retrieved 10 August Retrieved 1 August Retrieved 22 October December Retrieved 5 September The New York Times. Retrieved 2 February Retrieved 3 November O'Brien 28 December New York Times. Archived from the original on 25 December Retrieved 30 December Archived from the original on 28 December Retrieved 27 Dec Nohl said that he was able to intercept voice and text conversations by impersonating another user to listen to their voice mails or make calls or send text messages.
Even more troubling was that he was able to pull this off using a seven-year-old Motorola cellphone and decryption software available free off the Internet. High capacity load balancing means, when one access point is overloaded, the system will actively shift users from one access point to another depending on the capacity which is available.
Scalability: The growth in popularity of new wireless devices continuously increasing day by day. The wireless networks have the ability to start small if necessary, but expand in terms of coverage and capacity as needed - without having to overhaul or build an entirely new network.
Network management system: Now a day, wireless networks are much more complex and may consist of hundreds or even thousands of access points, firewalls, switches, managed power and various other components. The wireless networks have a smarter way of managing the entire network from a centralized point. Role based access control: Role based access control RBAC allows you to assign roles based on what, who, where, when and how a user or device is trying to access your network.
Once the end user or role of the devices is defined, access control policies or rules can be enforced. Indoor as well as outdoor coverage options: It is important that your wireless system has the capability of adding indoor coverage as well as outdoor coverage. Network access control: Network access control can also be called as mobile device registration. It is essential to have a secure registration. Network access control NAC controls the role of the user and enforces policies. NAC can allow your users to register themselves to the network.
It is a helpful feature that enhances the user experience. Mobile device management: Suppose, many mobile devices are accessing your wireless network; now think about the thousands of applications are running on those mobile devices. How do you plan on managing all of these devices and their applications, especially as devices come and go from your business?
Mobile device management can provide control of how you will manage access to programs and applications. Even you can remotely wipe the device if it is lost or stolen. Roaming: You don't need to worry about dropped connections, slower speeds or any disruption in service as you move throughout your office or even from building to building wireless needs to be mobile first. Roaming allows your end-users to successfully move from one access point to another without ever noticing a dip in a performance. For example, allowing a student to check their mail as they walk from one class to the next.
Redundancy: The level or amount of redundancy your wireless system requires depends on your specific environment and needs.