File Name: mobile cellular telecommunications analog and digital systems .zip
The cellular system connects mobile radios called mobile stations via radio channels to base stations. Some of the radio channels or portions of a digital radio channel are used for control purposes setup and disconnection of calls and some are used to transfer voice or customer data signals. Each base station contains transmitters and receivers that convert the radio signals to electrical signals that can be sent to and from the mobile switching center MSC.
The MSC contains communication controllers that adapt signals from base stations into a form that can be connected switched between other base stations or to lines that connect to the public telephone network. The switching system is connected to databases that contain active customers customers active in its system. The switching system in the MSC is coordinated by call processing software that receives requests for service and processes the steps to setup and maintain connections through the MSC to destination communication devices such as to other mobile telephones or to telephones that are connected to the public telephone network.
When linked together to cover an entire metro area, the radio coverage areas called cells form a cellular structure resembling that of a honeycomb. As a customer called a subscriber moves through a cellular system, the mobile switching center MSC coordinates and transfers calls from one cell to another and maintains call continuity.
Key drivers for the mobile telephone market growth include new wireless technology 3G service availability and the replacement market for mobile phones with new capabilities such as camera phones, color displays, and increased accessory capabilities. Ravinder puranamravinder gmail. Cellular systems allow reuse of the same channel frequencies many times within a geographic coverage area. The technique, called frequency reuse, makes it possible for a system to provide service to more customers called system capacity by reusing the channels that are available in a geographic area.
These handsets are capable of operating on an analog or digital radio channel, depending on whichever is available. Most dual mode phones prefer to use digital radio channels, in the event both are available. This allows them to take advantage of the additional capacity and new features such as short messaging and digital voice quality, as well as offering greater capacity.
Regardless of the size and type of radio channels, all cellular and PCS systems allow for full duplex operation. Full duplex operation is the ability to have simultaneous communications between the caller and the called person. This means a mobile telephone must be capable of simultaneously transmitting and receiving to the radio tower. The radio channel from the mobile telephone to the radio tower is called the uplink and the radio transmission channel from the base station to the mobile telephone is called the downlink.
The uplink and downlink radio channels are normally separated by 45 MHz to 80 MHz. One of the key characteristics of cellular systems is their ability to handoff also called handover calls from one radio tower to another while a call is in process.
Handoff is an automatic process that is a result of system monitoring and short control messages that are sent between the mobile phone and the system while the call is in progress. The control messages are so short that the customer usually cannot perceive that the handoff has occurred. Analog cellular systems are regularly characterized by their use of analog modulation commonly FM modulation to transfer voice information. Ironically, almost all analog cellular systems use separate radio channels for sending system control messages.
These are digital radio channels. In early mobile radio systems, a mobile telephone scanned the limited number of available channels until it found an unused one, which allowed it to initiate a call. Because the analog cellular systems in use today have hundreds of radio channels, a mobile telephone cannot scan them all in a reasonable amount of time. To quickly direct a mobile telephone to an available channel, some of the available radio channels are dedicated as control channels.
Most cellular systems use two types of radio channels, control channels and voice channels. Control channels Ravinder puranamravinder gmail. The basic operation of an analog cellular system involves initiation of the phone when it is powered on, listening for paging messages idle , attempting access when required and conversation or data mode. When a mobile telephone is first powered on, it initializes itself by searching scanning a predetermined set of control channels and then tuning to the strongest one.
During the initialization mode, it listens to messages on the control channel to retrieve system identification and setup information. After initialization, the mobile telephone enters the idle mode and waits to be paged for an incoming call and senses if the user has initiated dialed a call access. When a call begins to be received or initiated, the mobile telephone enters system access mode to try to access the system via a control channel.
When it gains access, the control channel sends an initial voice channel designation message indicating an open voice channel. The mobile telephone then tunes to the designated voice channel and enters the conversation mode. As the mobile telephone operates on a voice channel, the system uses Frequency Modulation FM similar to commercial broadcast FM radio.
To send control messages on the voice channel, the voice information is either replaced by a short burst blank and burst message or in some systems, control messages can be sent along with the audio signal. Mobile telephones compete on the control channel to obtain access from a cellular system. Access is attempted when a command is received by the mobile telephone indicating the system needs to service that mobile telephone such as a paging message indicating a call to be received or as a result of a request from the user to place a call.
Transmissions must begin within a prescribed time limit after the mobile station finds that the control channel access is free, or the access attempt is stopped on the assumption that another mobile telephone has possibly gained the attention of the base station control channel receiver.
If the access attempt succeeds, the system sends out a channel assignment message commanding the mobile telephone to tune to a cellular voice channel. A call origination access attempt message is sent to the cellular system that contains the dialed digits, identity information along with other information.
If the system allows service, the system will assign a voice channel by sending a voice channel designator message, if a voice channel is available. If the access attempt fails, the mobile telephone waits a random amount of time before trying again. The mobile station uses a random number generating algorithm internally to determine the random time to wait. The design of the system minimizes the chance of repeated collisions between different mobile stations which are both trying to access the control channel, since each one waits a different Ravinder puranamravinder gmail.
To receive calls, a mobile telephone is notified of an incoming call by a process called paging. When the telephone determines it has been paged, it responds automatically with a system access message that indicates its access attempt is the result of a page message and the mobile telephone begins to ring to alert the customer of an incoming telephone call.
It does this by sending the telephone number and an electronic serial number to provide the users identity. After a mobile telephone has been commanded to tune to a radio voice channel, it sends mostly voice or other customer information.
Periodically, control messages may be sent between the base station and the mobile telephone. Control messages may command the mobile telephone to adjust its power level, change frequencies, or request a special service such as three way calling. When there is silence, the mobile telephone may stop transmitting for brief periods of time several seconds. When the mobile telephone user begins to talk again, the transmitter is turned on again. This is called discontinuous transmission.
Analog Cellular Systems: There are many types of analog and digital cellular systems in use throughout the world. It is still in widespread use and by ; AMPS systems were operating in over 72 countries. The AMPS system continues to evolve to allow advanced features such as increased standby time, narrowband radio channels, and anti-fraud authentication procedures.
Its primary differences include changes to the radio channel frequencies, radio channel bandwidths, and data signaling rates. This narrower radio bandwidth reduced the data speed of the signaling channel.
The Nordic mobile telephone NMT system was developed by the telecommunications administrations of Sweden, Norway, Finland, and Denmark to create a compatible mobile telephone system in the Nordic countries. The first commercial NMT cellular system was available at the end of Due to the rapid success of the initial NMT system and limited capacity of the original system design, the NMT system version was introduced in There are now over 40 countries that have NMT service available.
Some of these countries use different frequency bands or reduced number of channels. The NMT system uses a lower frequency MHz and higher maximum transmitter power level which allows a larger cell site coverage areas while the NMT system uses a higher frequency approximately the same MHz band used for TACS and GSM and a lower maximum transmitter power which increases system capacity.
Because more of these narrower radio channels can be installed in each cell site, NAMPS systems can serve more subscribers than AMPS systems without adding new cell sites. NAMPS also shifts some control commands to the sub-audible frequency range to facilitate simultaneous voice and data transmissions.
Because this system had achieved great success, several different types of cellular systems have evolved in Japan. The system operates in the MHz band. The channel bandwidth is 25 kHz and the signaling is at bps.
The control channels are simulcast from all base stations in the local area. This limits the maximum capacity of the MCS-L1 system. It uses the same frequency bands as the MCS-L1 system. The radio Ravinder puranamravinder gmail. This gives the MCS-L2 system 2, channels. The control channels transfer information at 2, bps and the voice channels can use either in-band blank and burst signaling at 2, bps or sub-band digital audio signaling at bps.
MCS-L2 mobile telephones have diversity reception similar to diversity receive used in base stations. While this increases the cost and size of the mobile telephones, it also increases the performance and range of the cellular system.
Analog systems commonly use FM modulation to transfer voice information and digital systems use some form of phase modulation to transfer digital voice and data information. Although analog systems are capable of providing many of the services that digital systems offer, digital systems offer added flexibility as many of the features can be created by software changes. Digital cellular systems use two key types of communication channels, control channels and voice channels.
A control channel on a digital system is usually one of the sub-channels on the radio channel. This allows digital systems to combine a control channel and one or more voice channels on a single radio channel. The portions of the radio channel that is dedicated as a control channel carries only digital messages and signals that allow the mobile telephone to retrieve system control information and compete for access.
The other sub-channels on the radio channel carry voice or data information.
Special Mobile Analogue to Digital Converter. A reference that provides a complete technical description of the design, analysis, and maintenance of cellular systems, covering subjects such as cell-site antennas and mobile antennas, cochannel interference reduction, noncochannel interference, frequency management and channel assignment, and dat Schematic diagram of information flow in a digital communication system. Global System for designed to replace the incompatible analog systems. The development From the Publisher: Here's the second edition of the classic reference in the field,Mobile Cellular Telecommunications Systems.
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Я должен был знать. Да взять хотя бы его электронное имя. - Боже мой, Северная Дакота. Сокращенно NDAKOTA.
Энсей Танкадо - это Северная Дакота… Сьюзан попыталась расставить все фрагменты имеющейся у нее информации по своим местам. Если Танкадо - Северная Дакота, выходит, он посылал электронную почту самому себе… а это значит, что никакой Северной Дакоты не существует. Партнер Танкадо - призрак.
Она отдала это чертово кольцо.
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