If you surf the Internet all the time, you get the false impression that everyone around everyone owes everyone. Even if you do not go deep into politics, where in general everyone is as one experts and knows what to do, but, as the hero of one anecdote said, there is no time to do something yourself, because you need to "tax", then we are surrounded by crowds of dissatisfied people. In general, everyone is unhappy with mobile communications. I don't have a ready-made recipe for how to fix this discontent, but the good news is that if you understand how this damn mobile communication works, then you are much less nervous. For example, have you ever talked about the quality of communication with those who deal with it? I have certainly spoken like that more than once. And I have never met a dissatisfied specialist (although, of course, they also have communication problems). They do not fuss, do not get nervous, because they almost always have a clear idea of \u200b\u200bwhat (and why) is happening. And under what conditions the situation can change. Mastering this "kung fu" is actually not difficult, and you need to start by understanding how mobile communication works and what processes occur in it when we pick up the phone, make a call or use the phone for the Internet.
Radio signal
And you need to start with the banal: mobile communication actually (that's news, right?) Uses a radio signal, which, by definition, cannot be as reliable a connection as a thick copper cable safely hidden from any impact (well, except for an excavator bucket, of course) from the outside. The radio signal is subject to a bunch of other things in this unjust world. If only because we are constantly surrounded by a multitude of invisible transmissions that take place at various frequencies. Of course, we all know from a school physics course that a radio wave signal can be at different frequencies (and different power, I will add, but for our understanding of the situation this is already too difficult, we will not go so deep). And when we talk about our phones operating at 900, 1800 and 1900 MHz, they are actually frequency bands. And a specific base station and your phone can work on others close to them: 1799 or 1801 GHz. It is this kind of frequency division that allows thousands of people to use mobile communications in a modern city at the same time, and not wait until the free frequency becomes free. What makes the situation even more complicated if you think about the fact that we have more mobile operators than one. And they all work simultaneously too.
We also remember from the physics course (after all, we remember, right?) That when passing an obstacle, the signal weakens. Remember how things are with the Bluetooth signal if you go out into the next room. But the distance is less than 10 meters stated by the standard. So what are they lying to you? No, there is an obstacle in the way, and if the wall is also load-bearing, then inside it is not drywall, but iron reinforcement, which definitely only worsens the signal and certainly does not improve it in any way. The situation is similar with Wi-Fi and mobile communications. Because in both cases, a radio signal is used. Therefore, every time you enter the elevator or go down to the basement (for example, in a cafe), the connection may suddenly deteriorate. And that's okay, because it fully complies with the laws of physics, even if you don't know anything about them.
Base stations
Once a base station was installed in one village.
After a while, the operator who installed the base station,
complaints from local residents began to come
on the deteriorated state of health.
“What's that?” The operator's representatives replied.
"Here's what starts when we turn it on"
A popular joke among operators
Some (not all, of course) realize that base stations are also needed for mobile communication. These are rather complex (and expensive) complex structures, which include a different set of communication (and not only its) equipment. In the minimum configuration, the base station needs power, connection to other similar base stations and / or network routers that can correctly route data and instantly connect two subscribers. This connection can be via a fiber-optic cable (and then you will not even see it) or via a radio channel. And then you will see such large circular radio relay antennas working along a directional beam and connecting the base station with another (specific) station of the same. In the city, such base stations can be located on the roofs of administrative (mainly, it is easier to get permission to install them) buildings. Why on rooftops? Because the higher, the more open space and fewer obstacles to the radio signal. Outside the city (or where there are no tall buildings), a separate mast is installed for the base station, which looks like power transmission masts. The base station itself is also a box with smart electronics serving all this economy, as well as an air conditioner that cools its operation (especially needed, as we all understand, in the summer). In theory, each base station should also have a self-powered diesel generator that turns on automatically when the electricity is cut off. Otherwise, in case of any failures in the power grid, the mobile communication will be immediately disconnected, and so it can still work for some time (ideally, until the arrival of the repair team or the elimination of the power grid failure). Check it out? And we have not yet moved on to transmitters that directly link the base station with mobile phones. You see them most often - these are vertically installed panels, usually there are three of them - in a sector of 120 degrees each.
So that all this works like clockwork and different market players do not interfere with each other, there is government regulation. It concerns the power of the equipment used, the safety of mobile phones (that is why all legally sold phones undergo mandatory certification, which, albeit slightly, but increases their cost). By the way, this is why phones bought abroad may not work as well as we would like - they are designed for different conditions and meet other requirements. This is especially true of cheap models (as a rule, there are no such surprises with branded phones, because they are produced by companies that carefully monitor the compliance of their devices with the standards of those countries where they are officially sold). You can read about why the state does this, how and what benefits it brings to society in a separate article on this topic.
But we remember that radio communication and its quality still depends on many factors that are unstable. The data transfer rate at a specific location in a specific time interval can change significantly if the original data changes. Therefore, consumer testing is subjective, but it is they that can provide information to the consumer in a certain geographic point about the quality of the service provided. You can truly assess the quality of the network only with the help of special equipment and a whole team of specialists (and in each city - a separate one).
In addition to natural reasons (load on the network, for example) there is another problem: in the cities where we live, new facilities are constantly being built that can radically change the picture of network coverage and signal availability in a particular area. Therefore, the process of radio planning a network is a continuous process. It never stops, and the 3G rollout we are seeing now is just one episode in a long line of ongoing work that has been, is and will continue to be in the future. Always.
In addition to rather slow changes (the construction of a high-rise, you must agree, takes months or even years), there are also spontaneous surges in the consumption of mobile communications that can create peak loads that are many times greater than the capacity of the network in the current location. The simplest example is exhibitions, when thousands of people gather in one building or pavilion, each of whom has a mobile phone in their pockets. You have probably come across a situation when mobile communications did not work well at an exhibition (or stadium). Similar surges, for example, occur on New Year's Eve, for which all operators are carefully preparing. Because for them it is not only a certain challenge and satisfaction of consumers, but also (why hide) additional income.
If the event is known in advance, so-called mobile base stations are used to increase the network capacity. They represent a car with a bunch of expensive electronics inside that connect to the operator's network and increase the capacity of the network in a specific location. To deploy such a mobile base station, it takes from 3-4 hours to a day (depending on the complexity of the conditions - let me remind you that each operator has their own, and are determined by the presence of the nearest base stations, distance to them, line of sight, and so on). For example, according to Yuri Grigoriev, Head of the Department of Mobile Network Operation of the Central Region of lifecell, during the Euro 2012 football championship on Khreshchatyk, three mobile base stations were operating in the fan zone at once in different parts of the street (the whole Khreshchatyk was then a fan area with huge installed screens for spectators). Similar actions apply to seasonal events such as city days. The periods of vacations with resort places - sea summer and ski winter - make their own adjustments. All these actions are carried out imperceptibly for the majority of mobile subscribers, who are not even aware of the technical difficulties (yes, between us, they should not even suspect). But they are carried out by all operators, regardless of what you think about their work.
Equipment used to improve communication inside premises is a separate topic. In order not to complicate the story by listing different repeaters and femtocells, I'll just say that inside the building (it can be a cafe in the basement or a huge shopping center), equipment is installed that in one way or another increases the network capacity and transfers all traffic (voice and data) further into the network operator. In the metro, a special cable emitting radio signal is used for this, so we may (or may not) have mobile communication even in metro tunnels, although they are at a depth unattainable for conventional radio waves.
Support network
At first glance, the question seems strange, but we never think about where the signal from the mobile phone goes next. No, it is clear that it goes to the network of a mobile operator, but what is a “network”? In fact, a significant part of the mobile operator's network is in ... cable. Base stations connected to each other only by radio are not capable of transmitting all that volume of voice communication, and even more so data by radio signal. Moreover, the majority of mobile communication users are concentrated in separate cities that are not connected with each other by radio communications. And the signal between them travels through the backbone fiber optic cables that form the backbone of the telecommunications industry. There is the concept of a "backbone" or back bone, which can also be called a transmission due to its functions - the transfer of a huge data flow between key segments of the operator's network. Each city, in turn, can have its own "ring" that connects data streams from specific base stations or control points that accumulate traffic from several base stations. To manage the entire network, huge nodal switches are needed serving entire regions. These are huge data centers that manage all traffic and occupy a separate building. They, like any other data centers, have several independent connection channels, their own energy consumption systems. In less commercial cities there are also "remote" switches, smaller in size, designed to serve their region.
Now you understand that the operator's mobile network is a very complex system. And at every stage, at every link in the chain - from the user's mobile phone to the base station, switch and core network, a problem with the quality of communication may arise. We talked about these problems in more detail in a separate article, so I will briefly remind you that the quality of communication depends on three factors: coverage, capacity and quality of the network itself. Roughly speaking, coverage is where the signal of the base station "finishes", capacity is the ability of the network to receive more calls and / or transmit more data (by the way, this is the main benefit from the introduction of 4G networks, which allows to increase capacity and use more frequencies - this is its own separate problem, including related to the redistribution of frequencies and technological neutrality).
Billing
Speaking about mobile communications, how it works and where users may experience problems, we cannot but touch upon the issue of billing. Technically, this software determines the subscriber's tariff, takes into account all the user's costs included in it, and calculates his balance on the account. It is integrated into the operator's network and when any action is taken by the subscriber (call, SMS, Internet access), it first checks whether the user can perform this action, then either allows the system to provide the subscriber with the requested service, or gives him a message why this action should be performed it is impossible (for example, there is not enough funds in the account). All these numerous operations occur instantly and imperceptibly for the user, but for a general understanding of how mobile communication works, it is worth knowing about it.
How billing works was explained to us by Konstantin Zhilin, Head of the Department of Telecommunication Networks Operation of lifecell: “In order to make a call, the server defines a trigger: what needs to be done to give the subscriber the opportunity to call. The trigger can be "play some melody", sometimes it is the trigger "go and check the tariffication". In order for a subscriber to make a call, the billing system first needs to ask whether the subscriber has enough funds to make a call. The billing system looks at the subscriber's bill and answers: "please, I allow you to make a call of such and such duration." And only after that the traffic, routing and so on are connected. After the subscriber has used this call quota, for example, 150 seconds, the billing system makes a request for permission again and checks the balance on the account. The quota is issued based on the average time of making a call and the balance on the account and is calculated in minutes. "
The very withdrawal of money from the account (sacred moment) occurs when the call ends, when the billing system asks the system about the final duration of the call and rates it according to the actual duration, and not according to the volume of the allocated quota. From the point of view of the billing system, changing a subscriber's tariff plan simply means replacing one item in the operator's product catalog with another. The billing product plan contains a list of services available to the subscriber, some of which are basic (and provided within the tariff plan at no additional charge), and some are additional and, accordingly, paid separately. If one or the other changes, then something free of charge becomes paid for billing or vice versa. Or the cost of a specific service changes. This is how it works. All talk about money theft by operators is in fact a common misconception. That does not negate the active marketing activities of most operators. But it is physically impossible to steal something from the subscriber.
As they say, knowledge is power, so in all controversial cases you need to carefully read the terms of your tariff plan and do not hesitate to clarify all questions with the operator. Call center employees are stress-resistant, undergo special trainings and are always ready to calmly listen to the subscriber and try to help him. We will talk about this in more detail sometime next time.
For those who want to know more
Operators use their own slang words, which we found funny and worth your attention:
- "Saucepan" - radio relay antenna, which has a round shape and is designed to communicate between two base stations over a radio channel
- "Warm the air"- to work idle, as they say, when expensive equipment does not fully use its capabilities, has excess network capacity and, accordingly, does not bring the expected income for the operator
- "Cabinet" - a cabinet of a mobile base station with equipment: a chassis with a transceiver (contains up to 4 shelves, which accommodate up to 12 transceivers) and the "brains" of the base station - electronics that ensures the operation of the network itself
Do you know what happens after you have dialed a friend's number on your mobile phone? How does the cellular network find it in the mountains of Andalusia or on the coast of the distant Easter Island? Why is the conversation sometimes interrupted unexpectedly? Last week I visited Beeline and tried to figure out how cellular communication works ...
A large area of \u200b\u200bthe populated part of our country is covered by Base Stations (BS). In the field, they look like red and white towers, and in the city they are hidden on the roofs of non-residential buildings. Each station picks up a signal from mobile phones at a distance of up to 35 kilometers and communicates with a mobile phone via service or voice channels.
After you have dialed a friend's number, your phone contacts the base station (BS) nearest to you via the service channel and asks to select a voice channel. The base station sends a request to the controller (BSC), and that forwards it to the switch (MSC). If your friend is a subscriber of the same cellular network, then the switch will check with the Home Location Register (HLR), find out where the called subscriber is at the moment (at home, in Turkey or in Alaska), and will transfer the call to the appropriate switch, where he is from. will forward to the controller and then to the Base Station. The Base Station will connect to your mobile phone and connect you with a friend. If your friend is a subscriber of another network or you call a landline phone, then your switch will turn to the corresponding switch of the other network. Complicated? Let's take a closer look. The Base Station is a pair of iron cabinets locked in a well-air-conditioned room. Considering that in Moscow it was +40 on the street, I wanted to live a little in this room. Typically, the Base Station is located either in the attic of a building or in a container on the roof:
2. 
The Base Station antenna is divided into several sectors, each of which "shines" in its own direction. The vertical antenna communicates with telephones, the round antenna connects the Base Station with the controller:
3. 
Each sector can handle up to 72 calls simultaneously, depending on setup and configuration. A Base Station can have 6 sectors, so one Base Station can handle up to 432 calls, however, there are usually fewer transmitters and sectors installed on the station. Cellular operators prefer to install more base stations to improve the quality of communication. The base station can operate in three bands: 900 MHz - the signal on this frequency travels further and better penetrates into buildings 1800 MHz - the signal travels over shorter distances, but allows you to install more transmitters on 1 sector of 2100 MHz - 3G network This is what the cabinet looks like with 3G equipment:
4. 
900 MHz transmitters are installed at Base Stations in the fields and villages, and in the city, where Base Stations are stuck like a hedgehog's needles, basically, communication is carried out at a frequency of 1800 MHz, although transmitters of all three bands can be present at any Base Station simultaneously.
5. 
6. 
A 900 MHz signal can hit up to 35 kilometers, although the "range" of some Base Stations located along the routes can be up to 70 kilometers, by reducing the number of simultaneously served subscribers at the station by half. Accordingly, our phone, with its small built-in antenna, can also transmit signals up to 70 kilometers ... All Base Stations are designed to provide optimal radio coverage at ground level. Therefore, despite the range of 35 kilometers, the radio signal is simply not sent to the flight altitude of the aircraft. However, some airlines have already begun installing low-power base stations on their aircraft that provide coverage inside the aircraft. Such a BS is connected to a terrestrial cellular network using a satellite channel. The system is complemented by a control panel that allows the crew to turn the system on and off, as well as certain types of services, for example, turning off the voice on night flights. The phone can measure the signal strength from 32 Base Stations simultaneously. It sends information about the top 6 (by signal level) via the service channel, and the controller (BSC) decides which BS to transmit the current call (Handover) if you are on the move. Sometimes the phone can make a mistake and transfer you to the base station with the worst signal, in which case the conversation can be interrupted. It may also appear that all voice lines are busy at the Base Station that your phone has selected. In this case, the conversation will also be interrupted. They also told me about the so-called "upper floors problem." If you live in a penthouse, sometimes, when moving from one room to another, the conversation can be interrupted. This is because in one room the phone can "see" one BS, and in the second - the other if it goes to the other side of the house, and, at the same time, these 2 Base Stations are located at a great distance from each other and are not registered as " neighboring "from the mobile operator. In this case, the transfer of a call from one BS to another will not occur:
Communication in the metro is provided in the same way as on the street: Base Station - controller - switch, with the only difference that small Base Stations are used there, and in the tunnel the coverage is provided not by an ordinary antenna, but by a special radiating cable. As I wrote above, one BS can make up to 432 calls simultaneously. Usually this power is enough for the eyes, but, for example, during some holidays the BS may not cope with the number of people who want to call. This usually happens on New Years, when everyone starts congratulating each other. SMS are transmitted via service channels. On March 8 and February 23, people prefer to congratulate each other using SMS, sending funny rhymes, and the phones often cannot agree with the BS on the allocation of a voice channel. I was told an interesting case. From one district of Moscow, subscribers began to receive complaints that they could not get through to anywhere. The technicians began to figure it out. Most of the voice lines were free, and all service lines were busy. It turned out that next to this BS there was an institute in which exams were being held and students were constantly exchanging text messages. The phone divides long SMS into several short ones and sends each one separately. The technical service staff advise sending such greetings using MMS. It will be faster and cheaper. From the Base Station, the call goes to the controller. It looks as boring as the BS itself - it's just a set of cabinets:
7. 
Depending on the equipment, the controller can serve up to 60 Base Stations. Communication between the BS and the controller (BSC) can be carried out via a radio relay channel or via optics. The controller manages the operation of radio channels, incl. controls the movement of the subscriber, signal transmission from one BS to another. The switch looks much more interesting:
8. 
9. 
Each switch serves from 2 to 30 controllers. He already occupies a large hall, filled with various cabinets with equipment:
10. 
11. 
12. 
The switch handles traffic management. Remember the old films, where people first dialed up to the "girl", and then she already connected them with another subscriber, poking wires? Modern switches do the same:
13. 
To control the network, Beeline has several cars, which they affectionately call "hedgehogs". They move around the city and measure the signal strength of their own network, as well as the level of the network of colleagues from the Big Three:
14. 
The entire roof of such a car is studded with antennas:
15. 
Inside there is equipment that makes hundreds of calls and removes information:
16. 
Round-the-clock control over switches and controllers is carried out from the Flight Control Center of the Network Control Center (CCC):
17. 
There are 3 main areas of control over the cellular network: accidents, statistics and feedback from subscribers. Just like in airplanes, all the equipment of the cellular network has sensors that send a signal to the CCS and output information to the dispatcher's computers. If some equipment is out of order, then the light on the monitor will start blinking. MCC also keeps track of statistics for all switches and controllers. He analyzes it by comparing it with previous periods (hour, day, week, etc.). If the statistics of any of the nodes began to differ sharply from the previous indicators, then the light on the monitor will start blinking again. Subscriber service operators receive feedback. If they cannot solve the problem, then the call is transferred to a technician. If he also turns out to be powerless, then an "incident" is created in the company, which is decided by the engineers who operate the corresponding equipment. The switches are monitored by 2 engineers around the clock:
18. 
The graph shows the activity of Moscow switches. It is clearly seen that almost no one calls at night:
19. 
Control over the controllers (sorry for the tautology) is carried out from the second floor of the Network Control Center:
22. 
21. 
Looking at them, I realized that it was time to update the material - the second article was written at a time when Yota was working on Wimax technology, and 4g had just appeared, the first one even earlier.
The new article is not only about modems, but about the mobile Internet in general. It is designed primarily for those who have just begun to understand this topic, that is, "seasoned mobile Internet users" are unlikely to find something unknown here.
I want to chew on some of the fundamental subtleties associated with the mobile Internet, "sort things out," so to speak. Let's start.
What do you need to use mobile internet?
- an agreement (and a SIM card) with a certain cellular operator and a connected tariff (tariff option, package), which implies the presence of a certain amount of traffic or access to the network without restrictions;
- a device that will work with this operator and will directly "surf the Internet", and (or) will enable other devices to be connected to the network;
- everything should happen in the coverage area of \u200b\u200bthe selected operator's network.
It seems simple, but in reality - there are enough subtleties, let's figure it out in order.
Where will mobile internet work?
It will work in the coverage area of \u200b\u200bthe network of your chosen operator. Moreover, the better the signal level, the better it will work. Signal strength isn't the only thing that determines the speed you can get.
How will mobile internet work?
There are a number of technologies for transferring data over mobile networks - the speed depends on what technology is being used at the moment. Each specific technology must be supported by both the device and the operator base station with which it works. Don't forget about the signal level either.
The speed will depend on:
- what type of network the operator has in the place where you are;
- what data transmission technologies your device supports;
- what is the signal level in the place where you are (I wrote about it separately).
The speed depends both on the current load on the network (relevant primarily for cities) and on the weather (on the contrary, this is especially noticeable outside the city, when the distance to the base station is long).
What types of networks and data transmission technologies exist at the moment?
Second generation networks - 2g (GSM).They include two data transmission technologies:
GPRS is the slowest option. If we are talking about a smartphone or tablet, then when working with GPRS, next to the signal level indicator, the symbol "G" lights up. The "ceiling" of this technology in ideal conditions is only 171.2 kbps. And conditions are rarely ideal. You can't do much with GPRS - e-mail, surfing (better with disabled image loading - otherwise you will wait for each page to load for a very long time), instant messengers. You can safely forget about YouTube, listening to music online and other delights of the modern Internet.
EDGE - already better. With this technology, your smartphone or tablet will display an “E” next to the signal strength indicator. The theoretical "ceiling" for EDGE is 474 kbps. In real conditions, the speed will, of course, be lower, but nevertheless - you can count on 150-200 kilobits, and this will already allow you to surf (with angelic patience), play some games (many MMOs do not need a wide channel), and etc., but it will still be difficult with multimedia content.
Third generation networks - 3G (WCDMA):
This includes the actual 3G (UMTS), and when working in such networks, the smartphone or tablet will display “3g” symbols near the signal strength indicator. The theoretical maximum data transfer rate is 2048 kbps. This can already be called quite adequate network access speed. You can talk on Skype and watch a video on YouTube.
HSDPA - a more advanced option. The theoretically possible speed is as much as 84.4 Mbps. In "field" conditions, I was able to see figures in the region of 5 - 15 megabits. The smartphone, when working with HSDPA, will show you the "H" or "H +" symbol.
Fourth generation networks - 4g (LTE)
And so far the only technology in this category is 4g itself, or, if you use the "official" and not the marketing name - LTE (although - not only LTE. If you are interested, see Wikipedia). In theory, 4g supports speeds of up to 173 megabits per second for reception and 58 for upload. In practice, I was able to "intend" to receive 40 megabits (although on the network I often see talk about higher speeds).
About devices
Various devices can be used to access the network. This could be:
Modem. It connects to a computer via USB, some tablets also support connecting a modem - also via USB using an OTG cable (if there is a full USB port, then without any OTG). Allows you to access the network on the device to which it is connected. If you need to distribute the Internet, then there are several options. Connect the modem to the router (see next item). You can distribute from the computer to which the modem is connected, but this requires quite specific settings, especially if you plan to distribute via Wi-Fi. You can also distribute via Bluetooth, if necessary. Theoretically, the tablet to which the modem is connected can also distribute the Internet (additional programs may be required if there is no "portable access point" option in the settings).
If the modem is purchased in the salon of this or that operator and carries its identification marks on board, then, with a probability of 99.9%, the modem is "locked", that is, a software restriction is set, due to which the modem works only in the network of its operator. You can overcome this attack - the modem can be "unlocked". There is no universal recipe here, so we enter the model of the modem into Google, add the word "unlock", and read the found (most likely it will be all sorts of forums).
Turning not to a communications salon, but to an ordinary computer store, you can buy a modem that will work with the network of any operator. Keep in mind that it will cost more (maybe even much) - operators, quite often, sell modems, which is called "at a loss" and make money by selling traffic.
Router + modem. We connect the modem to the router, set up the router - it distributes the Internet - via Wi-Fi, by wire, etc. From the subtle points - the router must have a USB port, in addition, you must first clarify whether this or that particular router is working with one or another specific modem. You need to look for a list of supported modems on the router manufacturer's website, where you can also download the latest firmware, which can support new models of modems.
Special mobile router. These are sold in communication stores, and are a device that already combines both a modem and a router. Also, not uncommon, there is a battery - so that it can be used in the "field" conditions. Like modems, they can be locked to one operator. As is the case with modems, in computer stores you can find devices that are not tied to any particular operator.
Cellular telephone. Often it can also provide Internet access by connecting to a computer or tablet with a wire, or via Bluetooth.
Smartphone or tablet. Most smartphones and tablets (of course, those that support 3g or 4g and have a SIM card slot) can act both as a modem, when connected to a computer via a wire or Bluetooth, and as a router, distributing the Internet via Wi-Fi. Since we have touched on this topic above, I will mention that inexpensive smartphones sold in communication salons under the brands of certain operators are also not infrequently "locked", in two-SIM phones only one SIM card is often "locked".
Will a 3G modem work in a 4g network and vice versa?
The question is true not only for modems, but also for any other devices.
Operator networks rarely support only one particular technology. They are often supported by everything from 2g to 4g. In the outback, there are base stations without 4g, and sometimes without 3g. That is, with rare exceptions (consider below) if you see a certain cell tower, then it is most likely "2g or higher".
Various devices, more often than not, also support everything, although it is still quite possible to buy a smartphone or a modem in the store, which "knows" only 2g and 3g.
All other things being equal, there should be no problems. If you with a 4g modem (smartphone, tablet) get to where the operator has 3g coverage, it will just work in 3g. And even in 2g it will work if you get to where there is only such coverage.
If you get with a 3g modem (smartphone, tablet) where the operator has 4g coverage, the device will still work, but again only in 3g. Finally, if you take some older phone that can't even 3g, it will still work - just 2g.
There are exceptions to what is described above. For example, the Tele2 network in Moscow and the region is implemented only in 3g and 4g. Or here are Yota modems - they work only in 4g. And even if you insert a Yota modem SIM-card into a "non-Etova" modem that "knows" 3g, nothing will work - that's how they all work.
Let's take a closer look at the situation with Tele2 in Moscow: if you insert a Tele2 SIM card into any device that can only work in 2g networks, then nothing will work for you.
A more complex example is that almost all dual-SIM phones currently on the market have only one SIM-card that can work in 3g \\ 4g, while the second will work only in 2g. This means that when using Tele2 in the Moscow region, you must give the privilege of using 3g \\ 4g to this particular SIM card. Under these conditions, you can only use the Internet adequately through Tele2. If you want the Internet via a SIM card of another operator, you will have to switch it to 3g \\ 4g mode, while the Tele2 SIM card will enter the “only 2g” mode and simply stop working - I remind you, because Tele2 does not have a 2g network in Moscow.
Smartphones in which both SIM cards can simultaneously work in 3g \\ 4g while only a few (google and find it if you need one).
About SIM cards and different devices (will a SIM card from a modem work in a smartphone and vice versa)
Looking through the search queries through which visitors come to my site, I often see something like "is it possible to insert a SIM card from a smartphone into a modem" or vice versa "from a modem to a smartphone". At the time of this writing, both questions could be answered in the affirmative, now the situation has changed.
Technically, it is possible to insert a SIM card from a smartphone into a modem without any problems - both there and there are used exactly the same SIM-cards. Even if you have a micro-sim in your smartphone, and a full-size SIM in the modem, you can still insert it by simply pressing it to the contacts in the right position, since the contact pad is the same size there and there. You probably noticed that SIM cards are now being sold universal - initially they are full-sized, and using pre-saddled cuts, it can easily be turned into micro- and nano-SIMs. The remaining piece of plastic can be used as an adapter. We decided, from a technical point of view, there are no problems.
There are restrictions of a different nature - along with the appearance of tariffs offering unlimited Internet for a smartphone / tablet, there was also a restriction on the part of operators who are not interested in using SIM cards with such tariffs in modems and routers. As a rule, this is spelled out in the tariff itself - something like "The SIM card is intended for use in a smartphone / tablet, when using a modem, Internet access will be limited."
There are also modem tariffs, the use of which in smartphones is limited by the operator. And if not limited, then on some of them voice calls are not possible at all, on others high prices are set for "voice". Be careful!
The final answer to the questions "is it possible to insert a SIM-card from a smartphone into a modem" or "a SIM-mole from a modem into a smartphone" is as follows: depends on your carrier and tariff plan. If in doubt, call the operator and ask.
About sharing the Internet from a smartphone or tablet
If you have the Internet on a smartphone or tablet, using a wire, Wi-Fi or Bluetooth, you can provide access to the network to other devices - for example, a laptop. It is very convenient on the road. This is how I use the Internet at the dacha on weekends, and at home I use the Internet from my smartphone as a "backup channel" - if the wired Internet is disconnected, a couple of taps to start the access point on the smartphone - and I'm back online.
That's all. I hope this article was helpful to you :)
Almost everyone used a cell phone, but few people thought - how does it all work? In this literary opus, we will try to consider how communication occurs from the point of view of your telecom operator.
When you dial a number and start calling, well, or someone calls you, your device communicates over the radio channel with one of the antennas of the nearest base station.
Each of the base stations contains from one to twelve transmit-receive antennas directed in different directions to provide communication to subscribers from all directions. In professional jargon, antennas are also called "sectors". You yourself have probably seen them more than once - large gray rectangular blocks.
From the antenna, the signal is transmitted via the cable directly to the control unit of the base station. The combination of sectors and a control block is usually called - BS, Base Station, base station... Several base stations, whose antennas serve a specific territory or area of \u200b\u200bthe city, are connected to a special block - the so-called LAC, Local Area Controller, "local area controller"often called simply controller... Up to 15 base stations are usually connected to one controller.
In turn, the controllers, which can also be several, are connected to the most central "brain" unit - MSC, Mobile services Switching Center, Mobile Services Control Center, more commonly known as switch... The switch provides an exit (and entrance) to city telephone lines, to other cellular operators, and so on.
That is, in the end, the whole scheme looks something like this:
In small GSM networks, only one switch is used, in larger ones serving more than a million subscribers, two, three or more can be used MSCunited with each other.
Why so much complexity? It would seem that you can simply connect the antennas to the switch - and that's it, there would be no problems ... But it's not that simple. The point here is in one simple English word - handover... This term refers to handoff in cellular networks. That is, when you walk down the street or drive a car (electric train, bicycle, roller skates, asphalt paver ...) and at the same time are talking on the phone, then in order for the connection not to be interrupted (and it is not interrupted), it is necessary to switch Your phone is from one sector to another, from one BS to another, from one Local Area to another, and so on. Accordingly, if the sectors were directly connected to the switch, then all these switches would have to be managed by the switch, which already has something to do. A multi-level network scheme makes it possible to evenly distribute the load, which reduces the likelihood of equipment failure and, as a result, loss of communication.
Example - if you and your phone move from the coverage area of \u200b\u200bone sector to the coverage area of \u200b\u200banother, then the BS control unit is engaged in the transfer of the phone, without affecting the "higher" devices - LAC and MSC... Accordingly, if the transition occurs between different BS, then it is controlled by LAC etc.
Switch operation should be considered in more detail. A switch in a cellular network performs almost the same functions as a PBX in a wired telephone network. It is he who determines where you call, who is calling you, is responsible for the operation of additional services, and, in the end, in general, determines whether it is possible to call or not.
Let's dwell on the last point - what happens when you turn on your phone?
Here, you turn on your phone. Your SIM card has a special number, the so-called IMSI - International Subscriber Identification Number, International Subscriber Identification Number... This number is unique for every SIM-card in the world, and it is by this number that operators distinguish one subscriber from another. When the phone is turned on, it sends this code, the base station transmits it to LAC, LAC - to the switch, in turn. This is where two additional modules associated with the switch come into play - HLR, Home Location Register and VLR, Visitor Location Register... Respectively, Home Subscribers Register and Guest Subscriber Register... IN HLR are kept IMSI all subscribers who are connected to this operator. IN VLR in turn, contains data on all subscribers who are currently using the network of this operator. IMSI transmitted to HLR (of course, in a highly encrypted form; we will not go into details about encryption, we will only say that another block is responsible for this process - AuC, Authentication Center), HLR, in turn, checks whether he has such a subscriber and, if so, whether he is blocked, for example, for non-payment. If everything is in order, then this subscriber is registered in VLR and from that moment can make calls. Large operators may have not one, but several parallel operating HLR and VLR... Now let's try to display all of the above in the figure:
Here we briefly examined how the cellular network works. In fact, everything is much more complicated there, but if you describe everything as it is thoroughly, then this presentation in terms of volume may well exceed "War and Peace".
Next, we will consider how (and most importantly - for what!) The operator debits money from our account. As you have probably already heard, there are three different types of tariff plans - the so-called "credit", "advance" and "prepaid", from English Pre-Paid, that is, prepaid. What is the difference? Let's consider how money can be written off during a conversation:
Let's say you called somewhere. It was registered on the switchboard - subscriber such and such called there, talked, say, forty-five seconds.
The first case - you have a credit or advance payment system. In this case, the following happens: data about your and not only your calls are accumulated in the switchboard and then, in the order of the general queue, are transferred to a special block called Billing, from English to bill - pay bills. Billing Responsible for all issues related to subscribers' money - calculates the cost of calls, charges a subscription fee, charges money for services, and so on.
Information transfer rate from MSC in Billing depends on what the computing power is billing, or, in other words, how quickly he manages to translate technical data on the calls made into direct money. Accordingly, the more subscribers talk, or the more "slow" billing, the slower the queue will move, respectively, the greater the delay between the conversation itself and the actual write-off of money for this conversation. This fact is related to the dissatisfaction often expressed by some subscribers - “They say, money is being stolen! I didn’t speak for two days - they wrote off a certain amount ... ”. But at the same time, it is not at all taken into account that for conversations that took place, for example, three days ago, money was not immediately written off ... People try not to notice good things ... And these days, for example, billing could simply not work - because of an accident, or because it was somehow modernized.
In the opposite direction - from billing to MSC - there is another line in which billing informs the switchboard about the status of subscribers' accounts. Again, a fairly frequent case - the account debt can reach several tens of dollars, and you can still call by phone - this is precisely because the "return" queue has not yet arrived and the switchboard does not yet know that you are a malicious defaulter and You should be blocked for a long time.
Advance tariffs differ from credit tariffs only in the way they pay the subscriber - in the first case, a person deposits some amount into the account, and the money for calls is gradually deducted from this amount. This method is convenient in that it allows you to plan and limit your communication costs to some extent. The second option is credit, in which the total cost of all calls for a certain period (“ billing cycle»), Usually for a month, is issued in the form of an invoice that the subscriber must pay. The credit system is convenient in that it insures you against those cases when you urgently need to call, and the money on the account suddenly runs out and the phone is blocked.
The pripedes are arranged in a completely different way:
Prepaid billing as such is usually called " Prepaid platform».
Immediately at the start of the telephone connection, a direct connection is established between switch and prepaid platform... No queues, data is transmitted in both directions directly during the conversation, in real time. In this regard, the following characteristic features are inherent in the prepaid - this is the absence of a monthly fee (since there is no such thing as billing period), a limited set of additional services (it is technically difficult to charge them in "real time"), the impossibility of "going into the red" - the conversation will simply be interrupted as soon as the money in the account runs out. A clear dignity prepaids is the ability to accurately control the amount of money in the account, and, as a result, your expenses.
IN prepaid still sometimes there is some funny phenomenon - if prepaid platform refuses to work for any reason, for example, due to overload, then, accordingly, for subscribers prepaid tariffs at this time all calls become absolutely free. What, in fact, they - subscribers - can not but rejoice.
And how is our money calculated when we talk while in roaming? And how does the phone work in roaming? Well, let's try to answer these questions:
room IMSI consists of 15 digits, and the first 5 digits, the so-called CC - Country Code (3 digits) and NC - Network Code (5 digits) - clearly characterize the operator to which this subscriber is connected. By these five numbers VLR the guest operator finds HLR home operator and looks in it - but, in fact, can this subscriber use roaming with this operator? If yes, then IMSI prescribed by VLR guest operator, and in HLR home - link to the same guest VLRto know where to look for the caller.
The situation with writing off money in billing is also not very simple. Due to the fact that the calls are processed by the guest switchboard, but the money is calculated by its own, "home" billing, large delays in debiting funds are quite possible - up to a month. Although there are systems, for example, “ Camel2», Which work on the principle of prepaid in roaming, that is, write off money in real time.
Here another question arises - why are the money written off in roaming? If “at home” everything is clear - there are clearly defined tariff plans, then the situation with roaming is different - they write off a lot of money and it is not clear why. Well, let's try to figure it out:
All roaming phone calls are divided into 3 main categories:
Incoming calls - in this case, the cost of a call consists of:
Cost of an international call from home to the guest region
+
The cost of an incoming call from a guest operator
+
Some surcharge depending on the specific guest operator
Outgoing call home:
Cost of an international call from the guest region home
+
Outgoing call cost from a guest operator
Outgoing call in the guest region:
Outgoing call cost from a guest operator
+
Operator-specific markup
As you can see, the cost of calls in roaming depends only on two things - on which operator the subscriber is connected to at home and what operator the subscriber uses when visiting. At the same time, one very important thing is revealed - the cost of a minute in roaming does not depend on the tariff plan chosen by the subscriber.
I would like to add one more remark - if two phones of one operator are together in roaming with another operator (well, for example, two friends went to rest), then it will be very expensive for them to talk to each other - the caller pays as for an outgoing home, and the receiving a call - like an incoming call from home. This is one of the disadvantages of the GSM standard - in this case, communication goes through the house. Although it is technically quite realistic to arrange a connection "directly", but which of the operators will do it, if you can leave everything as it is and earn money?
Another question that has recently often interested the owners of more than one mobile phone - how much will the forwarded call from one phone to another cost? And the answer to this question is quite realistic:
Let's say that call forwarding is set from phone B to phone C. From phone A they call to phone B - accordingly, the call is forwarded to phone C. In this case, they pay
Phone A - as outgoing to phone B
(in fact, this is logical - after all, he calls him)
Phone B - pays the forwarding price
(usually a few cents per minute)
+
the cost of an international call from the region where B is registered to the region where C is registered
(if the phones are of the same region, then this component is equal to zero).
Phone C - pays as incoming from phone A
At the end of the topics, I would like to mention one more subtle point - how much will the call forwarding cost in roaming? And this is where the fun begins:
For example, the phone has call forwarding on condition of employment to a home number. Then, with an incoming call, the so-called " roaming loop"- the call will go to the home phone through the guest switch, respectively, the cost of such a forwarded call for roamer will be equal to the sum of the cost of incoming and outgoing calls to home, plus the cost of the forwarding itself. And what is funny at the same time - the roamer may not even know that such a call took place, and subsequently be surprised to see the communication bill.
Hence follows a practical advice - when traveling, it is advisable to turn off all types of forwarding (you can leave only unconditional - in this case, the "roaming loop" does not work), especially forwarding to voice mail - otherwise you can later be surprised for a long time - "Where did this money go? a?"
List of terms used in the text:
AuC - Autentification Center, Authentication Center, is responsible for encoding information when transmitting on the network and receiving from the network
Billing - Billing, operator's cash accounting system
BS - Base Station, base station, multiple transmit and receive antennas belonging to one control device.
Camel2 - one of the Prepaid systems, which implements instant debiting of funds in roaming
CC - Country Code, country code in the GSM standard (for Russia - 250)
GSM - Global System for Mobile Communications, the world's most widespread cellular standard
Handover - transfer control of a handset from one antenna / base station / LAC to another
HLR - Home Location Register, register of home subscribers, contains detailed information about all subscribers connected to a given operator.
IMEI - International Mobile Equipment Identification, the international serial number of equipment in the GSM standard, is unique for each device
IMSI - International Mobile Subscriber Identification, the international serial number of a subscriber for GSM services, is unique for each subscriber
LAC - Local Area Controller, a device that controls the operation of a number of base stations, whose antennas serve a specific area.
Local Area - Local area, territory served by BSs that are part of one LAC
MSC - Mobile services Switching Center, Mobile Services Control Center, switch is the central link of the GSM network.
NC - Network Code, Network Code, the code of a specific operator in a given country in the GSM standard (for MTS - 01, BeeLine - 99).
Prepaid - Prepaid, prepayment - billing system based on instant debiting of funds.
Roaming - Roaming, using the network of another, "guest" operator.
SIM - Subscriber Identification Module, Subscriber Identification Module, SIM card - an electronic unit inserted into the phone on which the subscriber's IMSI is recorded.
VLR - Visitor Location Register, register of active subscribers - contains information about all subscribers who are currently using the services of this operator.
Millions of people around the world use mobile phones because mobile phones have made it much easier to communicate with people around the world.
Mobile phones present a whole range of functions these days, and there are more and more of them every day. Depending on your mobile phone model, you can do the following:
Save important information
Take notes or make a list of tasks
Record important appointments and turn on an alarm for reminders
use a calculator for calculations
send or receive mail
search for information (news, statements, anecdotes and much more) on the Internet
play games
watch TV
send messages
use other devices such as MP3 player, PDA devices and GPS navigation system.
But haven't you ever wondered how a mobile phone works? And what makes it different from a simple landline phone? What do all these terms PCS, GSM, CDMA and TDMA mean? This article will focus on the new capabilities of mobile phones.
To begin with, a mobile phone is essentially a radio - a more advanced form, but a radio nonetheless. The telephone itself was created by Alexander Graham Bell in 1876, and wireless communication a little later by Nikolai Tesla in the 1880s (the Italian Guglielmo Marconi first began talking about wireless communication in 1894). It was destined for these two great technologies to come together.
In ancient times, when there were no mobile phones yet, people installed radio phones in their cars to communicate. This radiotelephone system was powered by a single main antenna mounted on a tower in the city border and supported about 25 channels. To connect to the main antenna, the phone had to have a powerful transmitter - with a radius of about 70 km.
But not many could use such radio phones due to the limited number of channels.
The genius of the mobile system lies in the division of the city into several elements ("honeycomb"). This promotes frequency reuse throughout the city, so millions of people can use mobile phones at the same time. "Honeycomb" was not chosen by chance, since it is precisely honeycombs (in the form of a hexagon) that can best cover the area.
In order to better understand the operation of a mobile phone, it is necessary to compare CB radio (i.e. conventional radio) and a radiotelephone ..
Full duplex handheld versus half duplex - a radiotelephone, like a simple radio, is a half duplex device. This means that two people are using the same frequency, so they can only speak in turn. A mobile phone is a full duplex device, which means that a person uses two frequencies: one frequency is for hearing the person on the other side, the other for speaking. Therefore, you can talk on mobile phones at the same time.
Channels - the radiotelephone uses only one channel, in the radio there are about 40 channels. A simple mobile phone can have 1,664 channels or more.
In half-duplex devices, both radio transmitters use the same frequency, so only one person can speak. In full duplex devices, the 2 transmitters use different frequencies, so people can talk at the same time. Mobile phones are considered full duplex devices.
In a typical US mobile system, a mobile phone user uses about 800 frequencies to talk around the city. A mobile phone divides the city into several hundred. Each cell is of a certain size and covers an area of \u200b\u200b26 km2. Honeycombs are like hexagons enclosed in a lattice.
Since mobile phones and stations use low power transmitters, non-adjacent cells can use the same frequencies. Two cells can use the same frequencies. The cellular network is powerful high-speed computers, base stations (multi-frequency VHF transceivers), distributed throughout the entire working area of \u200b\u200bthe cellular network, mobile phones and other high-tech equipment. We'll talk about base stations later, but now let's look at the "cells" that make up the cellular system.
One cell in an analog cellular system uses 1/7 of the available two-way communication channels. This means that each cell (out of 7 cells in the lattice) uses 1/7 of the available channels, which have their own set of frequencies and, due to this, do not overlap:
The mobile phone user usually receives 832 radio frequencies for city calls.
Each mobile phone uses 2 frequencies per call - the so-called. two-way channel - therefore, there are 395 communication channels for each mobile phone user (the remaining 42 frequencies are used by the main channel - we will talk about it later).
Thus, each cell has up to 56 available communication channels. This means that 56 people will be able to talk on their mobile phones at the same time. The first mobile technology 1G is considered an analogue of the cellular network. Since the introduction of digital transmission of information (2G), the number of channels has increased significantly.
Mobile phones have built-in low-power transmitters, so they operate at 2 signal levels: 0.6 watts and 3 watts (for comparison, we present a simple radio that operates at 4 watts). Base stations also use low-power transmitters, however, they have their advantages:
The transmission of the signal of the base station and the mobile phone within each cell does not allow you to go far from the cell. In this way, both cells can reuse the same 56 frequencies. The same frequencies can be used throughout the city.
The charge consumption of a mobile phone, which usually runs on battery power, is not significantly high. Low-power transmitters mean a small battery, which makes mobile phones more compact.
The cellular network needs a number of base stations, regardless of the size of the city. A small town should have several hundred towers. All mobile phone users in any city are managed by one main office, which is called the Mobile Telephone Switching Center. This center monitors all telephone calls and base stations in the area.
Mobile phone codes
The electronic serial number of the device (ESN) is a unique 32-bit number programmed into the mobile phone by the manufacturer.
Mobile Identification Number (MIN) is a 10-digit code derived from the mobile phone number.
The System Identification Code (SID) is a unique 5-digit code assigned to each FCC company. The last two codes, MIN and SID, are programmed into your mobile phone when you buy a card and turn on your phone.
Each mobile phone has its own code. Codes are needed to recognize phones, mobile phone owners and mobile operators. For example, you have a mobile phone, you turn it on and try to call. Here's what happens at this time:
When you just turn on the phone, it looks for an identification code on the main control channel. A channel is a special frequency that mobile phones and base stations use to transmit signals. If the phone cannot find the control channel, then it is out of reach and the message "no network" is displayed on the screen.
When the phone receives an identification code, it verifies it against its own code. If matched, the mobile phone is allowed to connect to the network.
Together with the code, the phone requests access to the network and the Mobile Phone Switching Center records the position of the phone in the database, so the Switching Center knows which phone you are using when it wants to send you a service message.
The switching center receives calls and can figure out your number. At any time, he can view your phone number in his database.
The switching center communicates with your mobile phone to tell you which frequency to use, and after the mobile phone contacts the antenna, the phone gains access to the network.
The cell phone and base station maintain constant radio contact. The cell phone periodically switches from one base station to another with a stronger signal. If the cell phone leaves the base station field while moving, then it establishes communication with another, nearest base station, even during a conversation. The two base stations "communicate" through the Switching Center, which sends a signal to your mobile phone to change the frequency.
There are times when, while moving, the signal moves from one cell to another belonging to another mobile operator. In this case, the signal does not disappear, but is transmitted to another mobile operator.
Most modern cell phones can operate in several standards, which allows using roaming services on different cellular networks. The wiring center you now use the cellphone connects to your wiring center and asks for a code confirmation. Your system transfers all data about your phone to another system and the Switching Center connects you to the cells of the new mobile operator. And the most amazing thing is that all this is done within a few seconds.
The most unpleasant thing about all this is that you can pay a pretty big sum for roaming calls. On most phones, when you just cross the border, the roaming service is displayed. Otherwise, you'd better check the mobile coverage map so that you don't have to pay "inflated" tariffs later. Therefore, check immediately the cost of this service.
Please note that the phone must operate in multiple bands if you want to use the roaming service, because different countries use different bands.
In 1983, the first analogue mobile standard, AMPS (Advanced Mobile Telephone Service), was developed. This analog mobile communication standard operates in the frequency range from 825 to 890 MHz. In order to maintain competition and keep prices in the marketplace, the US federal government required that there be at least two companies in the market, engaged in the same activity. One such company in the United States was the Local Telephone Company (LEC).
Each company had its own 832 frequencies: 790 for calls and 42 for data. To create one channel, two frequencies were used at once. The frequency range for an analog channel was typically 30 kHz. The range of transmission and reception of the voice channel is divided by 45 MHz, so that one channel does not overlap with another.
A version of the AMPS standard called NAMPS (Narrowband Advanced Communication System) uses new digital technologies to enable the system to triple its capabilities. But even despite the fact that it uses new digital technologies, this version remains just an analogue. Analog standards AMPS and NAMPS only operate at 800 MHz and cannot yet offer a wide variety of functions, such as Internet connection and mail handling.
Digital mobile phones are second generation (2G) mobile technologies. They use the same radio technology as analog phones, albeit in a slightly different way. Analog systems do not fully utilize the signal between the phone and the mobile network — analog signals cannot be suppressed or manipulated as easily as digital signals can. This is one of the reasons why many cable companies are migrating to digital, so they can use more channels in a given range. It's amazing how efficient a digital system can be.
Many digital mobile systems use frequency modulation (FSK) to transmit and receive data through the analog AMPS portal. Frequency modulation uses 2 frequencies, one for logic one and one for logic zero, choosing between the two when transmitting digital information between the tower and the mobile phone. In order to convert analog information into digital and vice versa, modulation and coding scheme are needed. This suggests that digital mobile phones need to be able to process data quickly.
In terms of "complexity per cubic inch," mobile phones are among the most sophisticated devices available today. Digital mobile phones can perform millions of calculations per second in order to encode or decode a voice stream.
Any ordinary phone consists of several parts:
Microcircuit (board), which is the brain for the phone
Antenna
Liquid crystal display (LCD)
Keyboard
Microphone
Speaker
Battery
The microcircuit is the center of the entire system. Next, we will look at what chips are there and how each of them works. A chip for converting analog information to digital and vice versa encodes the outgoing audio signal from the analog system to digital and the incoming signal from the digital system to the analog system.
A microprocessor is a central processing unit responsible for the bulk of information processing. It controls the keyboard and display, and many other processes.
The ROM chips and memory card chip can store the operating system data of the mobile phone and other user data such as phone book data. Radio frequency manages power and charge, and also works with hundreds of FM waves. The RF amplifier controls the signals that enter or reflect the antenna. The screen size has increased significantly since the mobile phone has more features. Many phones have notebooks, calculators, and games. And now many more phones connect to a PDA or Web browser.
Some phones save certain information, such as SID and MIN codes, in the built-in flash memory, while others use external cards such as SmartMedia cards.
Many phones have speakers and microphones so tiny that it's hard to imagine how they make any sound at all. As you can see, the speakers are the same size as a small coin, and the microphone is no bigger than a watch battery. By the way, such wristwatch batteries are used in the internal chip of a mobile phone to operate the watch.
The most amazing thing is that 30 years ago, many such details occupied an entire floor of a building, and now all this fits in the palm of a person.
There are three most common ways 2G mobile phones use radio frequencies to transmit information:
FDMA (English Frequency Division Multiple Access) TDMA (English Time Division Multiple Access) CDMA (English Code Division Multiple Access) - Code Division Multiple Access.
Although the names of these methods seem so confusing, you can easily guess how they work by simply breaking the name into separate words.
The first word, frequency, time, code, indicates the accessor method. The second word, division, refers to the fact that it separates calls based on the access method.
FDMA places each call on a separate frequency TDMA allocates a certain time to each call on the specified frequency CDMA assigns a unique code to each call and then transmits it to a free frequency.
The last word of each method “multiple” means that several people can use each cell.
FDMA
FDMA (Frequency Division Multiple Access) is a method of using radio frequencies, when there is only one subscriber in one frequency range, different subscribers use different frequencies within a cell. It is an application of frequency division multiplexing (FDM) in radio communications. In order to better understand how FDMA works, it is necessary to consider how radios work. Each radio station sends its signal to free frequency bands. The FDMA method is used primarily for the transmission of analog signals. And although this method can undoubtedly transmit digital information, it is not used, since it is considered less effective.
TDMA
TDMA (Time Division Multiple Access) is a method of using radio frequencies, when there are several subscribers in the same frequency slot, different subscribers use different time slots (slots) for transmission. It is an application of time division multiplexing (TDM) to radio communications. With TDMA, the narrow bandwidth (30 kHz wide and 6.7 milliseconds long) is split into three time slots.
Narrow bandwidth is commonly referred to as “channels”. Voice data converted into digital information is compressed so it takes up less space. Therefore, TDMA operates three times faster than an analog system using the same number of channels. TDMA systems operate on the 800 MHz (IS-54) or 1900 MHz (IS-136) frequency bands.
GSM
TDMA is currently the dominant technology for mobile cellular networks and is used in the GSM (Global System for Mobile Communications) (Russian SPS-900) standard - a global digital standard for mobile cellular communications, with channel division according to the TDMA principle and a high degree of security due to public key encryption. However, GSM uses TDMA and IS-136 access differently. Let's imagine that GSM and IS-136 are different operating systems that run on the same processor, for example, both Windows and Linux operating systems are based on Intel Pentium III. GSM systems use a coding method to encrypt phone calls from mobile phones. The GSM network in Europe and Asia operates at 900 MHz and 1800 MHz, and in the USA at 850 MHz and 1900 MHz and is used for mobile communications.
Blocking your GSM phone
GSM is an international standard in Europe, Australia, most of Asia and Africa. Mobile phone users can buy one phone that will work wherever this standard is supported. In order to connect to a specific mobile operator in different countries, GSM users simply change their SIM card. SIM cards store all information and identification numbers that are required to connect to a mobile operator.
Unfortunately, the 850MHz / 1900-MHz GSM frequencies used in the United States do not match those of the international system. Therefore, if you live in the USA, but you really need a mobile phone abroad, you can buy a three- or four-band GSM phone and use it at home and abroad, or just buy a mobile phone with GSM 900MHz / 1800MHz standard to travel abroad. ...
CDMA
CDMA (Code Division Multiple Access). Traffic channels with this method of dividing the medium are created by assigning each user a separate numeric code that spreads across the entire bandwidth. There is no time division, all subscribers constantly use the entire channel bandwidth. The frequency band of one channel is very wide, the broadcasting of subscribers is superimposed on each other, but since their codes are different, they can be differentiated. CDMA is the basis for IS-95 and operates in the 800 MHz and 1900 MHz bands.
Dual band and dual standard mobile phone
When you travel to travel, you undoubtedly want to find a phone that will work on several lanes, in several standards, or will combine both. Let's take a closer look at each of these possibilities:
A multiband phone can switch from one frequency to another. For example, a dual band TDMA telephone can use TDMA services in an 800 MHz or 1900 MHz system. A dual-band GSM phone can use the GSM service in three bands - 850 MHz, 900 MHz, 1800 MHz or 1900 MHz.
Multi-standard telephone. "Standard" in mobile phones means the type of signal transmission. Therefore, a phone with AMPS and TDMA standards can switch from one standard to another if necessary. For example, the AMPS standard allows you to use the analogue network in areas where the digital network is not supported.
The multiband / multistandard phone allows you to change the frequency band and transmission standard.
Phones that support this feature automatically change bands or standards. For example, if the phone supports two bands, then it connects to the 800 MHz network, if it cannot connect to the 1900 MHz band. When a phone has several standards, it first uses a digital standard, and if it is not available, it switches to an analog one.
Mobile phones come in two and three bands. However, the word "three-lane" can be deceiving. It can mean that the phone supports CDMA and TDMA standards, and an analog standard. And at the same time, it can mean that the phone supports one digital standard in two bands and an analog standard. For those traveling abroad, it is better to get a phone that operates on the 900 MHz GSM band for Europe and Asia and 1900 MHz for the US, and also supports the analog standard. In essence, it is a dual band phone with one of these modes (GSM) supporting 2 bands.
Cellular and Personal Communications Service
Personal Communications Service (PCS) is essentially a mobile phone service that emphasizes personal communications and mobility. The main feature of PCS is that the user's telephone number becomes his Personal Communication Number (PCN), which is "tied" to the user himself, and not to his phone or radio modem. A user traveling around the world with the PCS can freely receive phone calls and e-mails on their PCN.
Cellular communications were originally created for use in automobiles, while personal communications meant great possibilities. Compared to traditional cellular communications, PCS has several advantages. First, it is completely digital, which allows for faster data transfer rates and facilitates the use of data compression technologies. Secondly, the frequency range used for the PCS (1850-2200 MHz) reduces the cost of the communications infrastructure. (Since the overall dimensions of the PCS base station antennas are smaller than the dimensions of the cellular base station antennas, they are cheaper to manufacture and install).
In theory, the US mobile system operates in two frequency bands - 824 and 894 MHz; PCS operates at 1850 and 1990 MHz. And since this service is based on the TDMA standard, the PCS has 8 timeslots and the channel spacing is 200KHz, as opposed to the usual three timeslots and 30KHz between channels.
3G is the latest technology in mobile communications. 3G means the phone belongs to the third generation - the first generation is analog mobile phones, the second is digital. 3G technology is used in multimedia mobile phones, commonly referred to as smartphones. These phones have multiple bands and high speed data transmission.
3G uses several mobile standards. The most common are three of them:
CDMA2000 is a further development of the 2nd generation CDMA One standard.
WCDMA (Wideband Code Division Multiple Access - broadband CDMA) is the radio interface technology chosen by most cellular operators to provide broadband radio access to support 3G services.
TD-SCDMA (English Time Division - Synchronous Code Division Multiple Access) is a Chinese standard for third generation mobile networks.
The 3G network can transfer data at speeds up to 3 Mb / s (therefore, in order to download an MP3 song of 3 minutes duration, it takes only about 15 seconds). For comparison, here are second-generation mobile phones - the fastest 2G phone can reach data transfer rates up to 144 Kb / s (it takes about 8 hours to download a 3-minute song). High-speed 3G data transfer is ideal for downloading information from the Internet, sending and receiving large multimedia files. 3G phones are a kind of mini-laptops that can handle large applications such as receiving streaming video from the Internet, sending and receiving faxes, and downloading e-mail messages with applications.
Of course, this requires base stations that transmit radio signals from phone to phone.
Mobile phone base stations are cast metal or lattice structures that rise hundreds of feet. This picture shows a modern tower that "serves" 3 different mobile operators. If you look at the base of the base stations, you can see that each mobile operator has installed their own equipment, which nowadays takes up very little space (at the base of older towers, small rooms were built for such equipment).
Base station. photo from the site http://www.prattfamily.demon.co.uk
A radio transmitter and receiver are placed inside such a block, thanks to which the tower communicates with mobile phones. The radio receivers are connected to the antenna on the tower with several thick cables. If you look closely, you will notice that the tower itself, all cables and equipment of the companies at the base of the base stations are well grounded. For example, a plate with green wires attached to it is a copper ground plate.
A mobile phone, like any other electronic device, may have problems:
Most often, these include corrosion of parts caused by moisture entering the device. If the phone gets wet, make sure the phone is completely dry before turning it on.
Excessive temperatures (eg in a car) can damage the battery or the electronic board of the phone. If the temperature is too low, the screen may turn off.
Analog mobile phones often face the problem of "cloning". A phone is considered "cloned" when someone intercepts its identification number and can call other numbers for free.
Here's how "cloning" works: Before calling anyone, your phone sends its ESN and MIN codes to the network. These codes are unique and it is thanks to them that the company knows who to send invoices for calls. When your phone transmits MIN / ESN codes, someone can hear (using a special device) and intercept them. If you use these codes in another mobile phone, then you can call from it completely free of charge, since the owner of these codes will pay the bill.
