Basic design of a mobile phone. Block diagram of a GSM cell phone
Almost everyone used a cell phone, but few people thought about how it all works? 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 via radio channel with one of the antennas of the nearest base station.
Each of the base stations contains from one to twelve transceiver 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 many times - large gray rectangular blocks.
From the antenna, the signal is transmitted via cable directly to the control unit of the base station. The set 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 the city, are connected to a special unit - the so-called LAC, Local Area Controller, often called simply controller. Up to 15 base stations are usually connected to one controller.
In turn, the controllers, of which there may also be several, are connected to the very central “brain” unit - MSC, Mobile services Switching Center, Mobile Services Control Center, popularly known as switch. The switch provides access (and input) to city telephone lines, to other cellular operators, and so on.
That is, in the end the whole scheme looks something like this:
Small GSM networks use only one switch; larger ones, serving more than a million subscribers, can use two, three or more M.S.C., united with each other.
Why such complexity? It would seem that you could simply connect the antennas to the switch - and that’s it, there would be no problems... But it’s not so simple. It's all about one simple English word - handover. This term refers to handover in cellular networks. That is, when you are walking down the street or driving a car (train, bicycle, roller skates, asphalt paver...) and at the same time talking on the phone, then in order for the connection not to be interrupted (and it is not interrupted), you need to switch in time Your phone 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 switchings would have to be managed by the switch, which already has something to do. A multi-level network design 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 one sector to the coverage area of another, then the BS control unit handles the transfer of the phone, without affecting the “superior” devices - L.A.C. And M.S.C.. Accordingly, if the transition occurs between different B.S., then it is controlled L.A.C. and so on.
The operation of the switch should be considered in a little more detail. A switch in a cellular network performs almost the same functions as a PBX in wired telephone networks. It is he who determines where you are calling, who is calling you, is responsible for the operation of additional services, and, in the end, in general, determines whether you can call or not.
Let's stop at the last point - what happens when you turn on your phone?
Here, you turn on your phone. Your SIM card has a special number called IMSI – International Subscriber Identification Number. This number is unique for every SIM card in the world, and it is precisely by this number that operators distinguish one subscriber from another. When you turn on the phone, it sends this code, the base station transmits it to LAC, LAC– to the switch, in turn. Here two additional modules associated with the switch come into play - HLR, Home Location Register And VLR, Visitor Location Register. Respectively, Register of Home Subscribers And Register of Guest Subscribers. IN HLR are stored IMSI all subscribers who are connected to this operator. IN VLR in turn, it contains data about all subscribers who are currently using the network of a given operator. IMSI transferred to HLR(of course, in a highly encrypted form; we will not go into detail about the features of 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 now on can make calls. Large operators may have not one, but several working in parallel HLR And VLR. Now let’s try to display all of the above in the figure:
Here we briefly looked at how the cellular network works. In fact, everything there is much more complicated, but if we describe everything as it is in detail, then this presentation may well exceed “War and Peace” in volume.
Next, we will look at how (and most importantly, why!) the operator debits money from our account. As you’ve 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's the difference? Let's look at how money can be written off during a conversation:
Let's say you called somewhere. It was recorded on the switchboard that subscriber such and such called there and talked for, say, forty-five seconds.
The first case is that you have a credit or advance payment system. In this case, the following happens: data about your and not only your calls is accumulated in the switch and then, in the order of the general queue, is transferred to a special block called Billing, from English to bill - to pay bills. Billing is responsible for all issues related to subscribers' money - calculates the cost of calls, writes off subscription fees, writes off money for services, and so on.
Information transfer speed from M.S.C. V Billing depends on how much computing power you have billing, or, in other words, how quickly he manages to convert technical data about calls made into direct money. Accordingly, the more subscribers talk, or the more “slow” the billing, the slower the queue will move, and accordingly, the greater the delay between the conversation itself and the actual debiting of money for this conversation. This fact is associated with the dissatisfaction often expressed by some subscribers - “They say they are stealing money! I didn’t speak for two days - a certain amount was written off...” But it does not take into account at all that for conversations that took place, for example, three days ago, the money was not immediately written off... People try not to notice the good... 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 M.S.C.- there is another queue in which billing informs the switchboard about the status of subscribers' accounts. Again, a fairly common case - the debt on the account can reach several tens of dollars, but you can still make phone calls - this is precisely because the “reverse” queue has not yet arrived and the switchboard does not yet know that you are a malicious defaulter and You should have been blocked a long time ago.
Advance tariffs differ from credit tariffs only in the method of settlement with the subscriber - in the first case, a person deposits some amount into the account, and money for calls is gradually deducted from this amount. This method is convenient because 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 any period (“ billing cycle"), usually per month, is issued in the form of an invoice that the subscriber must pay. The credit system is convenient because it insures you against those cases when you urgently need to make a call, but the money in your account suddenly runs out and your phone is blocked.
Prepaids are designed completely differently:
In the prepaide billing as such is usually called " Pripad platform».
Immediately at the moment the telephone connection starts, 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 connection with this, prepaids have the following characteristic features - the absence of a subscription fee (since there is no such thing as billing period), a limited range of additional services (they are technically difficult to charge in “real time”), the inability to “go into the red” - the conversation will simply be interrupted as soon as the money in the account runs out. Clear dignity prepaids is the ability to accurately control the amount of money in the account, and, as a result, your expenses.
IN preipedes sometimes a funny phenomenon is observed - if prepaid platform for some reason refuses to work, for example, due to overload, then, accordingly, for subscribers prepaid tariffs at this time all calls become absolutely free. Which, in fact, makes them – the subscribers – happy.
But how is our money calculated when we talk while in roaming? And how does the phone generally work in roaming? Well, let's try to answer these questions:
Number IMSI consists of 15 digits, and the first 5 digits, the so-called СС – Country Code(3 digits) and NC – Network Code(5 digits) – clearly characterize the operator to which the subscriber is connected. According to these five numbers VLR finds the guest operator HLR home operator and looks in it - but, in fact, can this subscriber use roaming with this operator? If yes, then IMSI is registered with VLR guest operator, and in HLR home - link to the same guest VLR to know where to look for the subscriber.
The situation with writing off money in billing is also not very simple. Due to the fact that calls are processed by the guest switch, but the “home” switch counts the money billing, large delays in debiting funds are quite possible - up to a month. Although there are systems, for example, “ Camel2”, which even in roaming work on the prepaid principle, that is, they write off money in real time.
Here another question arises - what is the money written off for? roaming? If “at home” everything is clear - there are clearly defined tariff plans, then with roaming the situation is different - a lot of money is written off and it is not clear why. Well, let's try to figure it out:
All phone calls while roaming are divided into 3 main categories:
Incoming calls – in this case, the cost of the call consists of:
Cost of an international call from home to a guest region
+
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 to home
+
Cost of an outgoing call from a guest operator
Outgoing call to guest region:
Cost of an outgoing call from a guest operator
+
Some surcharge depending on the specific operator
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 which operator the subscriber uses when away. This reveals one very important thing - the cost of a minute in roaming absolutely 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 roaming together with another operator (well, for example, two friends went on vacation), then it will be very expensive for them to talk to each other - the caller pays as for outgoing home, and the recipient the call is like someone coming from home. This is one of the disadvantages of the GSM standard - that communication in this case goes through the house. Although technically it is quite possible to arrange a connection “directly”, which operator will do this if you can leave everything as it is and make money?
Another question that has recently often interested owners of more than one mobile phone is how much will it cost to forward a call from one phone to another? And it’s quite possible to answer this question:
Let’s say call forwarding is set from phone B to phone C. A call is made from phone A to phone B - accordingly, the call is forwarded to phone C. In this case, they pay:
Phone A – as for outgoing to phone B
(actually, this is logical - after all, that’s what he’s calling)
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 from the same region, then this component is zero).
Phone C – pays as for incoming calls from phone A
In conclusion, I would like to mention one more subtle point - how much will forwarding in roaming cost? And here's where the fun begins:
For example, your phone has a call forwarding to your home number due to busy conditions. Then, when an incoming call occurs, the so-called “ roaming loop" - the call will go to the home phone through the guest phone switch, accordingly, the cost of such a forwarded call for roamer will be equal to the sum of the costs of incoming and outgoing calls to home plus the cost of the forwarding itself. And what’s funny about this is that the roamer may not even know that such a call took place, and subsequently be surprised when he sees the bill for communication.
This leads to practical advice - when traveling, it is advisable to disable all types of forwarding (you can leave only unconditional - in this case, a “roaming loop” does not work), especially forwarding to voice mail - otherwise, later you can wonder for a long time - “Where did that money go, A?"
List of terms used in the text:
AuC– Authentification Center, Authentication Center, is responsible for encoding information when transmitted over the network and received from the network
Billing– Billing, operator’s cash accounting system
B.S.– Base Station, base station, several transceiver 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 most widespread cellular communication standard in the world
Handover – transfer of handset control from one antenna/base station/LAC to another
HLR– Home Location Register, a register of home subscribers, contains detailed information about all subscribers connected to a given operator.
IMEI– International Mobile Equipment Identification, international equipment serial number in the GSM standard, unique for each device
IMSI– International Mobile Subscriber Identification, the international serial number of a subscriber for GSM standard services, is unique for each subscriber
L.A.C.– Local Area Controller, Local Area Controller, a device that controls the operation of a certain number of base stations whose antennas serve a certain territory.
Local Area– Local zone, an area served by BSs that are part of the same LAC
M.S.C.- 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 – a 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, a register of active subscribers – contains information about all subscribers who are currently using the services of this operator.
In order to find out the phone device, find out GSM operating principle mobile communications wrote this review.
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Next, you can find and read about the structure of a cell phone and its main functional components. Find mobile device diagrams. Learn how a mobile phone works and how the GSM channel works. Design and circuitry of GSM standard cellular telephones.
Spare parts and repair of mobile phones.
Store spare parts and components for phones, tablets, smartphones
radiomaster.net- another Internet service that provides downloads to your computer or phone of phone device diagrams and instructions for simple and mobile phones and other equipment. Mobile phone diagrams are downloaded from the site for free, without advertising and SMS, directly from this site. At the time of writing this review, you can download free circuit diagrams for cell phones for more than 600 models of mobile devices.
market.yandex.ru- search and purchase of spare parts for mobile and cell phones through the irreplaceable Yandex.Market service. As always, for users of the service it is convenient to sort and search for phone parts by price and the nearest location of the cell phone spare parts store.
The mobile phone is an integral part of a modern, technologically advanced society. Despite the commonality and apparent simplicity of this device, very few people know how a mobile phone works.
Mobile phone device
Modern technologies and constantly moving forward progress make it possible to create phones with a huge number of functions and capabilities. With each new model, phones become thinner, more beautiful and more affordable. Despite the huge variety of models and manufacturers, all these devices are designed according to the same principle.
Essentially, a mobile phone is a receiving and transmitting device that has a receiver, transmitter and radio antenna in its body. The receiver receives a radio signal, converts it into electrical impulses and sends it to the speaker of your phone in the form of electrical waves. The speaker converts these electrical impulses into the sound that we hear when talking to the other person.
The microphone picks up your speech, converts it into electrical signals and sends it to the built-in transmitter. The transmitter's task is to convert electrical impulses into radio waves and transmit them to the nearest station via an antenna. The antenna serves to enhance the reception and transmission of radio waves from the phone to the nearest cellular station.
How does a landline phone work?
The design of a landline phone is not much different from a mobile phone. In a landline telephone there is no need to convert electrical impulses into radio waves, since contact with the subscriber occurs via a telephone cable through an Automatic Telephone Exchange (ATS). The station does not need to search for a device within its coverage area, and when you dial a number, it automatically connects you to the telephone set to which this number is registered.
How does mobile communication work?
Each of us has the opportunity to visually observe a large number of radio towers located in different parts of the city. These towers, as a rule, are installed on the highest possible places, on the roofs of high-rise buildings, on structures of other communications or on their own stationary towers. These radio towers are called base stations (BS). You may notice that in cities such stations are installed much more often than in intercity areas. This is due to the fact that in urban environments there is a lot of natural interference in the form of concrete buildings and various metal structures, which significantly degrade the signal quality. At the same time, a larger number of subscribers are concentrated in cities, which create a heavy load on the cellular network and in order to maintain good communication quality, increased coverage is required.
Your phone has its own identification in the form of your SIM card's mobile number. When turned on, the mobile phone constantly scans the area in search of a network and automatically selects the Base Station that provides the best signal quality. At the same time, it informs the station about its location and status, thus, the central computer of the cellular operator always knows which base station the phone is in coverage and whether it is ready to receive a call signal. As soon as another person calls your number, the computer detects your location and sends a ringing signal to your phone. If the phone is turned off or is not within range of the nearest Base Station, then the computer tells you that the subscriber is out of coverage and cannot receive a call.
Today I want to talk about how to correctly read mobile phone diagrams. I will try to tell you the most basic things that a master should know. So. Where to begin? The first thing you need to know. This is what the microcircuits are called and how they are designated on the diagrams.
1. Processor. The processor is usually signed on the CPU or RAP, RAPIDO circuit. They are most often square and most often the largest. If it is Nokia, then in most cases there is a “skirt” along the rim of the processor. In new Nokia models you can often find a processor mounted on a flash drive. They are called “sandwich”, this is the worst thing that can happen after the compound) what is the compound sometime later.
2. Flash drive. A flash drive on the diagrams is written as flash and somewhere I came across mem, memory. It is most often rectangular in shape. And remember, in Nokia phones the processor and flash drive can only be changed in pairs. And they only fit from an identical model. What I mean is that, for example, Nokia 6233 and 6300 phones have the same processor. But this is only in appearance! They won't work!
3. Power controller. It is signed on the diagrams with different “names”: it can be written retu, tahvo, betty, UEM - all this is a power controller. Most of them are small square chips.
4. Also, any mobile phone has a receiver and transmitter RF chip and GSM FEM. You need to be more careful when replacing transmitters. Some look identical but the last numbers in the markings are different. But they don't work on other phones. Others may be similar and fundamentally different numbers but will work. In the process of work, you can do it for yourself. Using your experience, build a model compatibility diagram.
These were the most basic ones in my opinion. If you have any questions about microcircuits and their designation. And in general any questions regarding mobile phone repair. Ask in the comments or write on Skype. The number can be found in my contacts 
Using the example of the Nokia 6233 phone, I’ll add a picture with the location of these parts 
I remembered! There are 2 more important details in phones. Not everything is true. Briefly speaking. This is a thermistor and fuse. The fuse is most often used for charging. But in some phones it can also be found on camera. It burns out very often. And then you have to install a jumper. And a thermistor. What is a thermistor? This is such an insidious nasty thing)) The thermistor is in the phone charging circuit and is responsible for overheating. Very often this thermistor bursts after an impact or rots after water. Then the phone, when connected to the charger, starts writing “invalid battery” or “charger not allowed” or something else. I don’t remember everything anymore. In this case, it is a thermistor. How can they be found on the diagram? Yes, very simple! The fuse is located immediately behind the connector and is called FUSE, and the thermistor is BTemp. We must also remember. that the thermistor cannot be replaced by anything. Only with a different thermistor. Jumpers are snot) in this case do not roll. That's all for today. I'm tired of writing))
While most of us take a landline phone for granted, having a telephone in your home is one of the most amazing devices ever created. If you want to talk to someone, all you have to do is pick up the phone and dial a few numbers. You can contact this person at any time and communicate with him.
The telephone network extends throughout the world, so you can reach almost everyone on the planet. If you remember that just 100 years ago or less, sending a written message to someone could take several weeks...
Surprisingly, the telephone is one of the simplest devices in your home. The principles of telephone communication have not changed for almost a century. If you have a vintage telephone from the 1930s, you can plug it into your telephone jack and it will work just fine!
Phone internals
The simplest telephone consists of three parts:
1. Switch, connecting and disconnecting a telephone from the network. This switch is usually called lever switch. It connects your phone to the network when you pick up the handset.
2. Dinamik. This is the most common speaker, the size of a 50 kopeck coin and a resistance of 8 ohms.
3. Microphone. In the past, telephone microphones were extremely simple and consisted of granules of activated carbon sandwiched between two thin metal plates. The sound waves from your voice compressed and unclenched the granules, changing their resistance and adjusting the current flowing through the microphone.
And it will work! You can dial a number on this phone by quickly pressing the lever switch - all telephone switches still recognize " pulse dialing" If you pick up the phone and quickly tap the switch four times, the phone company switchboard will know that you dialed “4.”
The only problem with such a phone is that during a call you will hear your voice through the speaker.
Wires and cables
The telephone network starts at your home. P ara copper wires runs from your phone to a thick cable containing many of these copper pairs. Depending on where you are, this thick cable will go directly into the telephone exchange switch in your area, or it will be connected into a box about the size of a refrigerator that acts as digital hub.
Digitization and voice delivery
The hub digitizes your voice at 8,000 samples per second and 8-bit resolution. It then collects your voice and dozens of others and sends them all onto a single wire (usually a coaxial cable or fiber optic cable) leading to the telephone exchange. Either way, your line connects to the line disconnect and you can hear a long dial tone when you pick up the handset.
If you call someone connected to the same station, the switch simply creates a closed circuit between your phone and the phone of the person you dialed. If it's a long-distance call, your voice is digitized and combined with millions of other voices. Your voice usually travels along a fiber optic line to the receiving end of the telephone exchange, but it can also be transmitted by satellite or communications towers.
Creating your own telephone network
The phone is not just a simple device. Communication between you and the telephone exchange is even easier. In fact, you can easily create your own telephone network using two phones, a 9-volt battery and a 300-ohm resistor, which can be purchased at the radio market. You can assemble all this equipment as follows: one wire connects both phones directly, and a power supply and resistor are connected in series to the second wire connecting the phones. If both people pick up the phone at the same time, they will be able to talk to each other normally over a distance of several kilometers.
The only thing your little intercom won't be able to do is call another phone and ask the person on the other end to pick up the phone. The bell signal is supplied by 90 volts alternating current with a frequency of 20 hertz.
The connection to the telephone exchange consists of two copper wires. One of them transmits 6 to 12 volts DC, approximately 30 mA. The microphone modulates the sound waves, the speaker at the other end reproduces this modulated signal. That's all.
If you go back to the days of the manual switchboard, it is easy to understand how a large telephone network once worked. In those days, there were many pairs of copper wires running from each house to the telephone exchange downtown. The switchboard operator sat in front of a large board with one slot for each subscriber. There was a small light above each connector. A large battery was connected through a resistor for each wire pair. When someone picked up the receiver on their telephone, a lever switch completed a circuit and sent current through the wires between the house and the telephone exchange. This turned on the light bulb above that socket on the switchboard. The operator would connect his headset to this jack and ask who the person would like to talk to. The operator would then send a ringing signal to the receiving party and wait for someone there to pick up the phone. Once the handset was picked up, the operator connected the two people together, just like a simple intercom connection. It's very simple!
Tone dialing
In modern telephone systems, operators have been replaced by electronic switch. When you pick up the handset, the switch senses the circuit and plays a long beep sound. This way you know the switch and your phone are working. The long beep sound is a combination of a 350 Hertz tone and a 440 Hertz tone. Dialing the digits of the number is also accompanied by sounds of different tones. If the number is busy, you hear an intermittent busy signal, which is made up of 480 Hertz and 620 Hertz tones.
Bandwidth
In order to ensure longer-distance calls, transmitted frequencies are limited bandwidth about 3000 Hertz. All frequencies in your voice below 400 Hertz and above 3400 Hertz are excluded. This makes the voice on a long-distance telephone have a characteristic sound.
Therefore, it is better not to organize musical performances over the phone, so as not to become the hero of a joke:
Petka and Vasily Ivanovich meet. Vasily Ivanovich says: “What do people find in these Beatles?! They sing monotonously!” Petka asks: “Vasily Ivanovich, where did you listen to the Beatles?!” Vasily Ivanovich: “Like where? Yesterday Furmanov sang a couple of their songs to me over the phone...”
