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.
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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. 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.http://maisonducalvet.com/orozko-hombres-solteros.php
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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. 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. Fundamentals of Mobile Data Networks. Cambridge University Press. Retrieved 23 November Patent 3,, , issued 16 May Telecommunication Networks. The Reverse Phone. Archived from the original on 30 April Retrieved 2 April Nomor Research.
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