Telephone Technology Here Is Often Quite Inline With Our Installation

A Phone From NOKIA

It would be helpful to allow an summary of the telephone technology here as this is often quite inline with our installation. let's examine however a telephone works? What makes it totally different from an everyday phone? What do all those confusing terms like PCS, GSM, CDMA and TDMA mean?






Let's begin with the basics: In essence, a telephone could be a radio. one in every of the foremost fascinating things a couple of telephone is that it's really a radio -- a particularly refined radio, however a radio even so. the phonephone was fictitious by Alexander Graham Bell in 1876, and wireless communication will trace its roots to the invention of the radio by Nikolai Tesla within the Eighties (formally given in 1894 by a young Italian named Guglielmo Marconi). it had been solely natural that these 2 nice technologies would eventually be combined!



In the age before cell phones, people that very required mobile-communications ability put in radio telephones in their cars. within the radio-telephone system, there was one central antenna tower per town, and maybe twenty five channels offered thereon tower. This central antenna meant that the phone in your automobile required a strong transmitter -- large enough to transmit forty or fifty miles (about seventy km). It additionally meant that not many of us might use radio telephones -- there simply weren't enough channels.



The genius of the cellular system is that the division of a town into tiny cells. this enables intensive frequency utilize across a town, in order that legion folks will use cell phones at the same time. during a typical analog cell-phone system within the u.  s., the cell-phone carrier receives regarding 800 frequencies to use across the town. The carrier chops up the town into cells. every cell is often sized at regarding ten sq. miles (26 sq. kilometers). Cells area unit ordinarily thought of as hexagons on a giant polygon grid.

Each cell features a base station that consists of a tower and atiny low building containing the radio instrumentation (more aboard stations later).

A single cell in AN analog system uses seventh of the offered duplex voice channels. That is, every cell (of the seven on a polygon grid) is exploitation seventh of the offered channels therefore it's a singular set of frequencies and there are not any collisions:

• A cell-phone carrier generally gets 832 radio frequencies to use during a town.
• Each telephone uses 2 frequencies per decision -- a duplex channel -- therefore there area unit generally 395 voice channels per carrier. (The different forty two frequencies area unit used for management channels -- additional on this on following page.)
• Therefore, every cell has regarding fifty six voice channels offered.

In different words, in any cell, fifty six folks is talking on their telephone at only once. With digital transmission strategies, the quantity of accessible channels will increase. as an example, a TDMA-based digital system will carry thrice as several calls as AN analog system, therefore every cell has regarding 168 channels offered (see this page for heaps additional info on TDMA, CDMA, GSM and different digital cell-phone techniques).

Cell phones have low-power transmitters in them. several cell phones have 2 signal strengths: zero.6 watts and three watts (for comparison, most CB radios transmit at four watts). the bottom station is additionally transmittal at low power. Low-power transmitters have 2 advantages:

• The transmissions of a base station and therefore the phones inside its cell don't build it terribly way outside that cell. Therefore, within the figure on top of, each of the purple cells will utilize identical fifty six frequencies. identical frequencies is reused extensively across the town.
• The power consumption of the telephone, that is generally battery-operated, is comparatively low. Low power suggests that tiny batteries, and this is often what has created hand-held cellular phones doable.

The cellular approach needs an oversized range of base stations during a town of any size. A typical massive town will have many towers. however as a result of such a big amount of folks area unit exploitation cell phones, prices stay low per user. every carrier in every town additionally runs one headquarters known as the Mobile phonephone change workplace (MTSO). This workplace handles all of the phone connections to the conventional land-based communication system, and controls all of the bottom stations within the region.Now let's analyses what happens we tend to as you (and your cell phone) move from cell to cell.

From Cell to Cell

All cell phones have special codes related to them. These codes area unit wont to determine the phone, the phone's owner and therefore the service supplier.

Let's say you've got a telephone, you switch it on and somebody tries to decision you. Here is what happens to the call:

• When you 1st power up the phone, it listens for AN SID (see sidebar) on the management channel. The management channel could be a special frequency that the phone and base station use to speak to 1 another regarding things like decision set-up and channel dynamic . If the phone cannot notice any management channels to pay attention to, it is aware of it's out of vary and displays a "no service" message.
• When it receives the SID, the phone compares it to the SID programmed into the phone. If the infant death match, the phone is aware of that the cell it's communication with is an element of its home system.
• Along with the SID, the phone additionally transmits a registration request, and therefore the MTSO keeps track of your phone's location during a info -- this fashion, the MTSO is aware of that cell you're in once it desires to ring your phone.
• The MTSO gets the decision, and it tries to seek out you. it's in its info to examine that cell you're in.
• The MTSO picks a frequency try that your phone can use in this cell to require the decision.
• The MTSO communicates together with your phone over the management channel to inform it that frequencies to use, and once your phone and therefore the tower put on those frequencies, the decision is connected. you're talking by two-way radio to a friend!
• As you progress toward the sting of your cell, your cell's base station notes that your signal strength is decreasing. Meanwhile, the bottom station within the cell you're moving toward (which is listening and activity signal strength on all frequencies, not simply its own one-seventh) sees your phone's signal strength increasing. the 2 base stations coordinate with one another through the MTSO, and at some purpose, your phone gets a proof on a sway channel telling it to vary frequencies. This hand off switches your phone to the new cell.

Roaming
If the SID on the management channel doesn't match the SID programmed into your phone, then the phone is aware of it's roaming. The MTSO of the cell that you just area unit roaming in contacts the MTSO of your home system, that then checks its info to verify that the SID of the phone you're exploitation is valid. Your home system verifies your phone to the native MTSO, that then tracks your phone as you progress through its cells. and therefore the wonderful factor is that each one of this happens inside seconds!

Cell Phones and CBs 
A good thanks to perceive the sophistication of a telephone is to match it to a CB radio or a radio link.

• Simplex vs. duplex - each walkie-talkies and CB radios area unit simplex devices. That is, 2 folks communication on a CB radio use identical frequency, therefore just one person will speak at a time. A telephone could be a duplex device. meaning that you just use one frequency for talking and a second, separate frequency for listening. each folks on the decision will speak right away.
• Channels - A radio link generally has one channel, and a CB radio has forty channels. A typical telephone will communicate on one,664 channels or more!
• Range - A radio link will transmit regarding one mile (1.6 km) employing a zero.25-watt transmitter. A CB radio, as a result of it's abundant higher power, will transmit regarding five miles (8 km) employing a 5-watt transmitter. Cell phones operate inside cells, and that they will switch cells as they move around. Cells provide cell phones unimaginable vary. somebody employing a telephone will drive many miles and maintain a spoken language the complete time owing to the cellular approach.

In simplex radio, each transmitters use identical frequency. just one party will speak at a time.

In duplex radio, the 2 transmitters use totally different frequencies, therefore each parties will speak at identical time.

Cell phones area unit duplex.

In the next section, you will get a decent look within a digital telephone.