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.
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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. The mobile unit then automatically switches from the current channel to the new channel and communication continues. The exact details of the mobile system's move from one base station to the other vary considerably from system to system see the example below for how a mobile phone network manages handover.
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.
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. 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.
Understanding Cellular Telephone Security
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. 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.
Mobile (Cellular) Technologies Explained
They range from wideband repeaters for consumer use in homes and offices to smart or digital repeaters for industrial needs. The following table shows the dependency of the coverage area of one cell on the frequency of a CDMA network: . From Wikipedia, the free encyclopedia. For history of mobile phones, including the history of cellular networks, see History of mobile phones.
Common types. Safety and regulation. Mobile phone radiation and health Wireless electronic devices and health International Telecommunication Union Radio Regulations. Beam steering Beam tilt Beamforming Small cell. Reconfiguration Spread spectrum. Main article: Small cell. Main article: Handover. Main article: Cellular frequencies.
CDMA vs. GSM: What’s the difference between these cellular standards?
Fundamentals of Mobile Data Networks. Cambridge University Press. Retrieved 23 November Patent 3,, , issued 16 May Telecommunication Networks. The Reverse Phone. The easiest way to arrange aggregation would be to use contiguous component carriers within the same operating frequency band as defined for LTE , so called intra-band contiguous.
This might not always be possible, due to operator frequency allocation scenarios.
For non-contiguous allocation it could either be intra-band, i. To specify different CA combinations some new definitions are used:. In R10 three CA configurations are defined, see table 1. In R11 a large number of additional CA configurations are defined, see table 2. The maximum aggregated bandwidth is still 40 MHz and maximum number of CC is 2. In later releases more configurations will be added. The coverage of the serving cells may differ, for example due to that CCs on different frequency bands will experience different pathloss, see figure 3.
Different component carriers can be planned to provide different coverage, i. In the case of inter-band carrier aggregation the component carriers will experience different pathloss, which increases with increasing frequency. In the example shown in figure 3 carrier aggregation on all three component carriers can only be used for the black UE, the white UE is not within the coverage area of the red component carrier. Introduction of carrier aggregation influences mainly MAC and the physical layer protocol, but also some new RRC messages are introduced. Basically each component carrier is treated as an R8 carrier.
Regarding scheduling there are two main alternatives for CA, either resources are scheduled on the same carrier as the grant is received, or so called cross-carrier scheduling may be used, see figure 5. For heterogeneous network planning the use of for example remote radio heads RRH is of importance. TR Please send any suggestions and comments about this article to: kevin. Early progress on Rel bands for 5G. New CT Chair looks to boost cooperation. TV and radio services over 3GPP systems. The Mobile Broadband Standard.
Figure 1. The CCs can be of different bandwidths. Figure 2. Carrier Aggregation; Intra-band and inter-band aggregation alternatives. For non-contiguous cases the CCs are separated by one, or more, frequency gap s.
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