The number of channels was expanded to pairs per carrier, but ultimately the number of RF channels limits the number of calls that a cell site could handle.
коммутируемой сети - Перевод на английский - примеры русский | Reverso Context
Note that FDMA is a familiar technology to telephone companies, that used frequency-division multiplexing to add channels to their point-to-point wireline plants before time-division multiplexing rendered FDM obsolete. With TDMA, the transmitting and receiving time slots used by different users in each cell are different from each other.
TDMA typically uses digital signaling to store and forward bursts of voice data that are fit into time slices for transmission, and expanded at the receiving end to produce a somewhat normal-sounding voice at the receiver. TDMA must introduce latency time delay into the audio signal. As long as the latency time is short enough that the delayed audio is not heard as an echo, it is not problematic.
Note that TDMA is a familiar technology for telephone companies, that used time-division multiplexing to add channels to their point-to-point wireline plants before packet switching rendered FDM obsolete. DSSS allows multiple simultaneous phone conversations to take place on a single wideband RF channel, without needing to channelize them in time or frequency. Although more sophisticated than older multiple access schemes and unfamiliar to legacy telephone companies because it was not developed by Bell Labs , CDMA has scaled well to become the basis for 3G cellular radio systems.
Other available methods of multiplexing such as MIMO , a more sophisticated version of antenna diversity , combined with active beamforming provides much greater spatial multiplexing ability compared to original AMPS cells, that typically only addressed one to three unique spaces. Massive MIMO deployment allows much greater channel re-use, thus increasing the number of subscribers per cell site, greater data throughput per user, or some combination thereof.
Quadrature Amplitude Modulation QAM modems offer an increasing number of bits per symbol, allowing more users per megahertz of bandwidth and decibels of SNR , greater data throughput per user, or some combination thereof. The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity. The elements that determine frequency reuse are the reuse distance and the reuse factor.
The reuse distance, D is calculated as. Cells may vary in radius from 1 to 30 kilometres 0. The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells. The frequency reuse factor is the rate at which the same frequency can be used in the network. In case of N sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. N is typically 3. In other words, adjacent base station sites use the same frequencies, and the different base stations and users are separated by codes rather than frequencies.
While N is shown as 1 in this example, that does not mean the CDMA cell has only one sector, but rather that the entire cell bandwidth is also available to each sector individually. Recently also orthogonal frequency-division multiple access based systems such as LTE are being deployed with a frequency reuse of 1.
Since such systems do not spread the signal across the frequency band, inter-cell radio resource management is important to coordinate resource allocation between different cell sites and to limit the inter-cell interference. Cell towers frequently use a directional signal to improve reception in higher-traffic areas. If the tower has directional antennas, the FCC allows the cell operator to broadcast up to watts of effective radiated power ERP.
Although the original cell towers created an even, omnidirectional signal, were at the centers of the cells and were omnidirectional, a cellular map can be redrawn with the cellular telephone towers located at the corners of the hexagons where three cells converge. This provides a minimum of three channels, and three towers for each cell and greatly increases the chances of receiving a usable signal from at least one direction. The numbers in the illustration are channel numbers, which repeat every 3 cells. Large cells can be subdivided into smaller cells for high volume areas. Cell phone companies also use this directional signal to improve reception along highways and inside buildings like stadiums and arenas.
Practically every cellular system has some kind of broadcast mechanism. This can be used directly for distributing information to multiple mobiles. Commonly, for example in mobile telephony systems, the most important use of broadcast information is to set up channels for one-to-one communication between the mobile transceiver and the base station. This is called paging. The three different paging procedures generally adopted are sequential, parallel and selective paging. The details of the process of paging vary somewhat from network to network, but normally we know a limited number of cells where the phone is located this group of cells is called a Location Area in the GSM or UMTS system, or Routing Area if a data packet session is involved; in LTE , cells are grouped into Tracking Areas.
Paging takes place by sending the broadcast message to all of those cells. Paging messages can be used for information transfer. In a primitive taxi system, when the taxi moved away from a first tower and closer to a second tower, the taxi driver manually switched from one frequency to another as needed.
If communication was interrupted due to a loss of a signal, the taxi driver asked the base station operator to repeat the message on a different frequency. In a cellular system, as the distributed mobile transceivers move from cell to cell during an ongoing continuous communication, switching from one cell frequency to a different cell frequency is done electronically without interruption and without a base station operator or manual switching. This is called the handover or handoff. Typically, a new channel is automatically selected for the mobile unit on the new base station which will serve it.
Сети GSM. Взгляд изнутри.
The mobile unit then automatically switches from the current channel to the new channel and communication continues. The most common example of a cellular network is a mobile phone cell phone network. A mobile phone is a portable telephone which receives or makes calls through a cell site base station or transmitting tower. Radio waves are used to transfer signals to and from the cell phone.
Modern mobile phone networks use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets change frequency under computer control and use low power transmitters so that the usually limited number of radio frequencies can be simultaneously used by many callers with less interference. A cellular network is used by the mobile phone operator to achieve both coverage and capacity for their subscribers.
Large geographic areas are split into smaller cells to avoid line-of-sight signal loss and to support a large number of active phones in that area. All of the cell sites are connected to telephone exchanges or switches , which in turn connect to the public telephone network. However, satellite phones are mobile phones that do not communicate directly with a ground-based cellular tower but may do so indirectly by way of a satellite.
The transition from existing analog to the digital standard followed a very different path in Europe and the US. This network is the foundation of the GSM system network. There are many functions that are performed by this network in order to make sure customers get the desired service including mobility management, registration, call set-up, and handover.
The link from a phone to the RBS is called an uplink while the other way is termed downlink. As the phone user moves from one cell area to another cell while a call is in progress, the mobile station will search for a new channel to attach to in order not to drop the call. Once a new channel is found, the network will command the mobile unit to switch to the new channel and at the same time switch the call onto the new channel.
The signals are separated by using a pseudonoise code PN code that is specific to each phone. As the user moves from one cell to another, the handset sets up radio links with multiple cell sites or sectors of the same site simultaneously. This is known as "soft handoff" because, unlike with traditional cellular technology , there is no one defined point where the phone switches to the new cell. In IS inter-frequency handovers and older analog systems such as NMT it will typically be impossible to test the target channel directly while communicating.
Мобильный словарь
In this case, other techniques have to be used such as pilot beacons in IS This means that there is almost always a brief break in the communication while searching for the new channel followed by the risk of an unexpected return to the old channel. If there is no ongoing communication or the communication can be interrupted, it is possible for the mobile unit to spontaneously move from one cell to another and then notify the base station with the strongest signal.
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The effect of frequency on cell coverage means that different frequencies serve better for different uses. GSM 1. UMTS , at 2.
Higher frequencies are a disadvantage when it comes to coverage, but it is a decided advantage when it comes to capacity. Picocells, covering e. Cell service area may also vary due to interference from transmitting systems, both within and around that cell. This is true especially in CDMA based systems. The receiver requires a certain signal-to-noise ratio , and the transmitter should not send with too high transmission power in view to not cause interference with other transmitters.
As the receiver moves away from the transmitter, the power received decreases, so the power control algorithm of the transmitter increases the power it transmits to restore the level of received power. As the interference noise rises above the received power from the transmitter, and the power of the transmitter cannot be increased anymore, the signal becomes corrupted and eventually unusable. In CDMA-based systems, the effect of interference from other mobile transmitters in the same cell on coverage area is very marked and has a special name, cell breathing.
One can see examples of cell coverage by studying some of the coverage maps provided by real operators on their web sites or by looking at independently crowdsourced maps such as OpenSignal or CellMapper. In certain cases they may mark the site of the transmitter, in others, it can be calculated by working out the point of strongest coverage.
A cellular repeater is used to extend cell coverage into larger areas. They range from wideband repeaters for consumer use in homes and offices to smart or digital repeaters for industrial needs. Всю необходимую информацию о подключении и оплате услуги можно узнать у оператора. Роумингом пользуются многие. Но это, так скажем, вынужденная необходимость, потому что стоимость подобного удовольствия весьма и весьма велика.
Роуминг может быть внутрисетевым и международным.
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Международный — возможность регистрации при нахождении заграницей. Внутрисетевой — при нахождении на территории своей страны. Синхронизация — соединение мобильного телефона, например, с ПК. Для этого необходимо определённое программное обеспечение и специальный кабель или наличие модуля беспроводной связи.