What are the characteristics of the router? Maximum distance, confident reception.


    Each range has its own characteristics. Thus, the 5 GHz band has a smaller coverage area, but at the same time greater throughput compared to 2.4 GHz. IN different countries Yes, there are restrictions on the use of the frequency spectrum and transmitter power. This is how different regulatory domains emerged. Here are the main ones:

    The manufacturer has an obligation to produce products that comply with the laws of different countries, that is, certification in certain regulatory domains.

    There are three sub-bands in the 5 GHz band:

    1.Band 5150-5250 MHz has the following channels:

    2. Band 5250-5350 MHz has the following channels:

    3.Band 5650-5825 MHz has the following channels:

    149: 5745 MHz

    153: 5765 MHz

    157: 5785 MHz

    161: 5805 MHz

    1. Basic terms and quantities

    dB (dB). A decibel is the logarithmic ratio of a signal to a conventional unit. For example, the table below compares with 1 W

    dBm. A decibel milliWatt is the logarithmic ratio of a signal to 1 mW

    With an increase in power by 9 dBm, the indoor coverage area increases by approximately 2 times. Accordingly, when the power decreases by 9 dBm, it decreases by approximately 2 times.

    dBi (dBi). A unit of measurement for antenna gain relative to a “reference” antenna. The so-called isotropic emitter is taken as such a reference antenna - an ideal antenna, the radiation pattern of which is a sphere, the gain of which equal to one and whose efficiency is 100%.

    The total radiated power is equal to the sum of the transmitter power and the antenna gain.

    This raises the answer to one of the questions that interests many: why Cisco Systems supplies access points to Russia with a power limit of 18 dBm (63 mW). The answer is this. The antenna gain varies from 2 (for built-in antennas) to 6 dBi (for directional external antennas). That is, the resulting output power will be from 20 dBm (100 mW) to 24 dBm (250 mW).

    When planning, one should not forget the feature of the emitter of the client device: as a rule, the transmitter power network card client does not exceed 50mW. Accordingly, the client device will “hear” perfectly, but its power will not be enough for the access point to “hear” it. Thus, in general, setting the power at the access point to more than 50 mW (17 dBm) is not advisable.

    In addition to the transmitter power, the sensitivity of the receiver is also measured in dBm, the values ​​will be negative numbers. The sensitivity of the receiver is minimum level signal, at which the connection will still be established at a minimum speed.

    RSSI (Received Signal Strength Indicatio)– this is the value of the received signal power converted into integers (from 0 to 255). For each manufacturer, translation can be carried out differently.

    SNR (Signal-to-Noise Ratio)- ratio of signal level to noise level, in dB. Typically, the signal-to-noise ratio should not exceed 5 dB for data transmission and 25 dB for voice transmission.

    2. RF Wi-Fi scheduling

    When unfolding wireless network There is no general template, everything is individual in each installation. However, there are a set of basic rules that should be followed. Below are the basic inputs for RF planning.

    When planning RF, you should consider the following key characteristics of a wireless network:

    1. Selecting the network type (data, voice or positioning)
    2. User Density
    3. Coverage and data rate requirements
    4. Features of client devices (transmitter powers, supported bands and channels, supported data rates)
    5. Network security requirements

    These characteristics can be achieved by manipulating the following physical quantities:

    1. Band (2.4 GHz or 5 GHz)
    2. Used channels of the selected range
    3. Transmitter power
    4. Antenna type and gain
    5. Allowed data rates

    In the 5 GHz band there are a larger number of non-overlapping channels and greater throughput, but at this moment Not all client devices support this range. In the 2.4 GHz band there are only 3 non-overlapping channels: 1, 6 and 11. Accordingly, RF planning must be done with this in mind. You should not place two access points nearby that will operate on the same frequency, this will lead to a high signal-to-noise value. In places high density users (for example, a conference room) can be installed up to three access points in order to increase bandwidth networks, they will work on different channels and not interfere with each other. It should be noted that the coverage radius in the 5 GHz band is significantly smaller than in the 2.4 GHz band.

    For a data transmission network, it is necessary to determine the minimum data transmission rate at the edges of the coverage area and plan the network taking this data into account. So, for example, for the same office, you may need 6 access points to cover at a speed of at least 11 Mbit/s and 12 access points to cover at a speed of at least 24 Mbit/s. If you need to limit the range of the access point, but not reduce power or lose speed, you can prohibit a number of speeds, for example, from 1 to 11 Mbit/s on the controller. Then at the edges of the network the speed will be at least 11 Mbit/s.

    For a voice network, it is necessary to overlap the coverage areas of neighboring access points by at least 15-20 percent with a signal level of at least -67 dBm, this will ensure continuous communication while roaming. In this case, the recommended power values ​​of access points are in the range of 35-50 mW.

    For positioning systems, a more complex approach to network construction is used, since here the basis is not optimal radio coverage, but optimal location access points.

    Antennas allow you to increase the communication range without increasing the power of the access point transmitter, as well as the client transmitter. Thus, if there is a problem covering enough large space or a long corridor with low user density, you can use external antennas with a high gain, both directional (for corridors) and omnidirectional (for large rooms).

    It is important to remember that you should plan the placement of access points with the condition that it is not recommended simultaneous connection more than 25 clients to one access point. In case of high client density or high throughput requirements, it is necessary to reduce the transmitter power and install access points more densely.

    3. Radio interface settings in WLC

    Let's move on to the practical part.

    On the WIRELESS tab, 802.11b/g/n menu, Network item, you can enable, disable, and make data transfer rates mandatory. In the case when it is necessary to limit the range of the network, which would not extend beyond the office, you can prohibit a number of low speeds, as in the example below.

    On the WIRELESS tab, menu 802.11b/g/n, TCP item, you can set the minimum and maximum transmitter power if automatic setting power. You can also change the Power Threshold parameter, which is involved in calculating the transmission power of the access point. The Power Threshold parameter specifies the maximum power level at which access points can listen to each other on overlapping channels from three access points. Accordingly, the power of the access point will increase until it hears a neighbor with the power specified in the Power Threshold parameter. This was done for reasons of building the largest possible coverage area with an optimal signal-to-noise ratio.

    On the WIRELWSS tab, menu 802.11b/g/n, DCA item, you can control automatic channel assignment. With careful planning and a small network size, you can assign channels manually at access points. With large network sizes, it is much more convenient to delegate this task to the controller. The figure below shows that auto channel selection occurs every 10 minutes, and the list available channels: 1, 6 and 11. Don’t forget to enable CleanAir technology, which will automatically rebuild channels at the hardware level in case of interference with third-party devices.

    For the 5 GHz band it will look like this. There is also the ability to select channels allowed for use. For example, this will be relevant for OUTDOOR solutions, where there are restrictions on the channels used. Here it is recommended to contact legislative framework RF to clarify permissions for the bands and channels used.

    Conclusion

    Increasing transmitter power will not always lead to increased coverage due to the client's limited transmitter power. The client will see the network, but will not be able to send packets to the access point

    Installing an antenna with a b O a higher gain will increase the coverage area

    Increasing the coverage area, as well as the number of clients in it, leads to a decrease in the capacity of the wireless network

    Increasing the capacity of a wireless network is achieved by reducing power and increasing the number of access points (reducing the size of micro cells)

    Coverage radius in the 5 GHz range is approximately 2 times smaller

    Limiting the cell range is achieved by prohibiting the use of minimum speeds

    Increasing the number of SSIDs leads to a significant decrease in network capacity. For example, 8 SSIDs will occupy 50% of the network capacity, while 2 SSIDs will occupy less than 10% of the network capacity. The reason is that the SSID is broadcast at minimal speeds. For this reason, it is not recommended to create a large number of SSID

At first glance, all Internet routers look the same - sort of flat boxes with antennas and blinking indicators. But in reality there are a lot of different WI models FI routers with certain characteristics.

Currently there are routers on the market with ADSL connection(Internet via telephone line), and there are also compatible with 3G/4G modems. In some cases, a router with support mobile internet may be the only option, since summing up wired internet may not be feasible for one reason or another.

Sellers often write “access point,” pointing to a router (WR), which distributes a signal wirelessly (not to be confused with a WI-FI adapter - a device for those devices that do not have a WIFI module), although an access point is fundamentally different from WIFI -router (Wifi-Router)

Below we will provide an educational program on choosing the right router - specifically for your requirements.

A Wi-Fi router can organize traffic (data transfer) between different network segments. With its help, regardless of the Internet service provider, you can register different network devices- create your own internal network. This is valuable in the aspect that many devices connected to a specific router (PC, for example) will be “visible” to everyone on the Internet and to the provider - under the same IP address, that is, the user does not have to pay for connecting to the Internet for each of his devices.Routers have 2 or more LAN interfaces. Created by routers internal network completely independent from the service provider.
These same access points - wireless access points - do not have these powers. They are just a link between wired network and wireless, devices for creating a Wi-Fi network or for repeating Signal loss.

Key parameters of WI FI router:

Data transfer rate

Wireless routers usually attract users with this parameter - speed. How many megabits per second can they transmit? Outdated models offer 11 Mbps, mid-budget 802.11g - 54 Mbps, and the most modern, 802.11n standard - 450 Mbps. Of course, the highest speed ones are attractive, but the actual performance you can get will be slightly lower than the maximum indicated by the manufacturer. Why? Because the capabilities of the router are one thing, and what your Internet provider offers is another. Typical offers from mass providers are 50 Mbit/s, or even less. In addition, you need to take into account advertising tricks from vendors - understand that if a speed of 150 Mbit/s is indicated, you need to understand that this is only in theory. In practice, the speed is within 100 Mbit/s.

Please note that 15 Mbps is 15 megabits per second, not megabytes, and this value will be equivalent to only 2 megabytes per second. Distance also affects the data transfer speed. Therefore, the parameter is also important range:

Radius of action

The router must “finish” the Internet to all your points where you would like to be located with your device. The range may be stated to be quite large - but this is under ideal conditions. For example, there are models with a range of up to 150 meters. But there may be some interference indoors that can shorten the signal range. And at the exit the speed will lose 40-50%. Therefore, power parameters are also important transmitter and antenna:

Transmitter power and antenna type

The main thing you should know regular user router - good power starts at 20dMB. If there is more power, you should not overpay, since the power will still be reduced in accordance with the permitted ranges, which border 2.4 GHz, that is, 20 dBm. A power of less than 17 dBm can be considered if there are no walls and you will be using the router in one small room without partitions. The number of antennas only affects the stability of the signal, but not its amplification. 2 antennas are preferable to one. The presence of three antennas is necessary for the signal to reach the floors.

The signal amplification itself is determined by the antenna signal gain characteristic, which enhances the signal transmission to the sides, “taking away” the signal propagation up and down. That is, the signal range at one level will be ensured by a high antenna coefficient, but it will not spread to floors (up and down). That is, for a house with 2-3 floors, each floor needs its own router signal amplifier. Or a router with three antennas.

Router class

This means that the selected router must be compatible with your PC, where the signal will be transmitted. This is important because WIFI data transmission standards are behind Lately have changed, and now, for example, 802.11n is used, although 802.11g was widespread recently. Before choosing a router, check what class your PC or laptop has. If your laptop supports G - class, there is no point in paying more and buy a router latest generation with class N – the router will reduce the speed, “adjusting” to the capabilities of the laptop.

Number of ports and inputs


Modern routers are equipped not only with several ethernet- inputs, but also USB ports, and sometimes SD card inputs. The USB connection is valuable in the case that you can directly distribute a t the contents, for example, of a hard drive to one of the devices “over the air”. With, of course, the appropriate software on the router. But this is most often implemented on expensive models. If you need such functionality, then also take into account this parameter on the router.

So, brief conclusions:

For a one-room apartment with a minimum of partitions, you can choose a single-antenna router with an average gain, preferably class N, theoretical speed 150 Mbit/s, power 17 dBm.

For an apartment with several rooms - a two-antenna one, preferably with a power of 20 dBm.

Remember that cheap models have one significant drawback- they are very unstable and often break the connection. The solution is to simply restart the router every time.

Read in the specifications whether the router can be used outdoors and what the range will be. The location of the router is very important - with a good location, even a simple class G router can output a signal to all rooms, for example, of a 2-room apartment.

Standards in routers:

802.11ac designed for speeds of up to 1300 Mbit/s, this is the same 5G WiFi

802.11n— speed up to 450 Mbit/s

802.11g— speed up to 54 Mbit/s

Therefore, before choosing a WIFI router, check the speed from the provider and the level of modernity of your laptop.

Many people go to the store and buy the most cheap devices, but immediately encounter a lot of troubles that they didn’t even think about, for example, the router slows down the speed, constantly freezes, gets very hot, the connection constantly breaks, or in general, the provider refuses to connect this device. We will try to help you making the right choice router for the home, we’ll tell you what characteristics you need to pay attention to.

Connection speed

The first thing the buyer pays attention to, although this is a very deceptive parameter. Theoretical maximum speed even the most inexpensive budget routers are 150 Mbit/s (megabits per second), while not all providers can provide real at least 50 Mbit/s, so it becomes clear that phrases like “up to 300 Mbit/s” are tempting or even “up to 1300 Mbit/s” in practical conditions means that when working on the Internet there will be almost no difference in speed between expensive and cheap Wi-Fi routers.

Radius of action

It would seem that everything is simple, because they usually indicate the distance outside and inside the premises, everything is clear and understandable. But these values ​​are very relative, especially indoors, since a couple of good reinforced concrete walls will nullify the signal of even the most powerful router, so the following three characteristics are truly important.

Transmitter power

Here the name speaks for itself and this is really very important. Many budget routers have a transmitter power of about 17 dBm or even less, which is usually enough to more or less confidently “break through” only 2 walls. The maximum power allowed by the legislation of most countries for the 2.4 GHz band is 20 dBm - they are recommended for purchase. It is worth keeping in mind that some Wi-Fi routers have technical feasibility operate at much higher power (typically up to 27 dBm), so they artificially reduce their power to comply with local regulations.

Receiver sensitivity

Unfortunately, most manufacturers do not indicate this parameter in the characteristics of their devices, and buyers rarely even pay attention to the transmitter power, not to mention the sensitivity of the receiver. Without going into details, we can say that the most important is the sensitivity at minimum speed, since in places with very low level signal allows you to maintain communication between the router and the device without interruption. Most mainstream Wi-Fi routers have a sensitivity value of -90 dBm at 1 Mbps at 8% PER, but lower values ​​are preferable (-92, -94, -98)

Antenna gain

The antenna gain misleads many users, since in reality the antennas themselves are passive devices and do not amplify anything themselves, they can only more narrowly direct and receive the signal. For example, the higher the gain of an omnidirectional antenna, the more transmitter energy goes to sides perpendicular to the antenna axis, and the less transmitter energy goes up and down. Thus, more powerful antenna is not universal solution, since it makes it possible to “punch” the signal much further to the sides, but at the same time “taking” it from above and below.

Number and type of antennas

When using several antennas, their energy does not add up, as many buyers believe, so three antennas will not be able to “break through” three times as many walls; they will only make the connection more stable and the coverage more uniform. Usually, the difference in the quality of coverage between routers with one antenna and two antennas is significant, but the difference between two- and three-antenna devices is often almost absent, although a lot depends on the chip used. It is worth noting that it is not recommended to buy cheap multi-antenna routers from an unknown manufacturer, since the deadline stable operation they are unknown, and very often even a single-antenna router with a good chip at the same price works much better.

Built-in antennas have low gain, so they distribute the signal almost evenly in all directions and can be useful only in small rooms or for accessing the network from adjacent floors. For a stable signal in a one-story house or apartment, it is recommended to buy Wi-Fi routers with 2-3 antennas with a gain of at least 5 dBi. To cover as much space as possible in a one-story house or apartment, it is necessary to install the antennas vertically or at a slight angle to one another.

Stability and firmware

Programmers - ordinary people and can make mistakes, and all their errors can only be identified by users during the work process. Therefore, updates are constantly released for each router software(firmware, firmware), which usually correct bugs and sometimes expand functionality. To avoid ending up with unstable “raw” firmware, it is recommended not to buy the newest, very rare or exclusive router models. The likelihood that a mass model that has been in production for several years contains fatal errors tends to zero.

Design

The last thing you need to pay attention to when choosing a Wi-Fi router for your home, since very often models that are beautiful in appearance have built-in omnidirectional antennas, which, in principle, cannot be very good.

Optimal location of a Wi-Fi router

The correct location of the router is of utmost importance, sometimes even more important than the transmitter power and antenna gain combined. Incorrect choice installation location can negate all the advantages of even the most best router and be the cause of outrage over why such an expensive device works so poorly.

Signal propagation

The main thing you need to know is wifi signal is weakly reflected and mainly spreads in a straight line, allowing you to work without obstacles at distances of 200-300 meters and even further, but it is very much lost when passing through walls, especially solid and reinforced concrete ones. Therefore, when choosing a location for installing a Wi-Fi router, it is necessary to imagine direct lines to those places in the apartment or house where clients will most often be located:

  • laptop table in the room;
  • SmartTV in the living room;
  • a kitchen table, where many people like to sit with a tablet, etc.

It is important that there are as few walls and other large objects in the path of these straight lines as possible, or that they intersect at as right an angle as possible. In addition, it is worth considering that large metal or metal-containing objects (refrigerators, washing machines, mirrors in now fashionable wardrobes, etc.) are absolutely opaque to radio waves, so the signal will pass behind them only due to reflection from the side walls, i.e. much weaker and of poor quality. It is also recommended to place the router at a distance of at least 20 cm from the walls.

The optimal location of the Wi-Fi router is in the center

Other Features

Naturally, routers, adapters in clients, and walls can be very different, but the general observation is that most laptops begin to receive signals unstably through 3 walls, and tablets and phones begin to receive signals through 2 walls. This rule is often observed, but still not an axiom, since there are cases when, even through 5 walls, by turning the laptop a little, it was possible to use the Internet relatively stably. Moreover, in dense urban environments, the density of closely spaced active devices is often so high that even the most best antennas and powerful Wi-Fi routers will not always be able to significantly improve the situation. In this case, it is recommended to scan the network (for example, with a very simple program for Android WiFi Analyzer) and occupy a channel where the signal from other routers will be as low as possible. Most often, channels 12 and 13 are the most free; only some client devices (laptops, tablets, phones) will not be able to connect to the access point on these frequencies.

Now many people are buying 802.11n access points, but good speeds Not everyone can achieve it. In this post we’ll talk about not very obvious small nuances that can significantly improve (or worsen) Wi-Fi work. Everything described below applies to both home Wi-Fi routers with standard and advanced (DD-WRT & Co.) firmware, and to corporate hardware and networks. Therefore, as an example, let’s take the “home” theme, as it is more native and closer to the body. Because even the most administrative of admins and the most technical of engineers live in apartment buildings (or villages with a sufficient density of neighbors), and everyone wants fast and reliable Wi-Fi.
[Attention!]:After comments regarding publication, the article was posted in full. This article is left as an example of how not to publish. Sorry for the confusion :)

1. How to live well yourself and not disturb your neighbors.

It would seem - what is there? Turn the point to full power, get the maximum possible coverage - and rejoice. Now let's think: not only the access point signal must reach the client, but the client signal must also reach the point. The TD transmitter power is usually up to 100 mW (20 dBm). Now look at the datasheet for your laptop/phone/tablet and find the power of its Wi-Fi transmitter there. Found it? You are very lucky! Often it is not indicated at all (you can search by FCC ID). However, it can be confidently stated that the power of typical mobile clients is in the range of 30-50 mW. Thus, if the AP broadcasts at 100 mW, and the client broadcasts only at 50 mW, there will be places in the coverage area where the client will hear the point well, but the client’s AP will hear poorly (or will not hear at all) - asymmetry. There is a signal, but there is no connection. Or downlink is fast and uplink is slow. This is true if you use Wi-Fi for online games or Skype; for regular Internet access this is not so important (only if you are not at the edge of the coverage). And we will complain about a wretched provider, a buggy point, crooked drivers, but not about illiterate network planning.

Conclusion: it may turn out that in order to obtain a more stable connection, the power of the point will have to be reduced. Which, you see, is not entirely obvious :)

Rationale (for those interested in details):
Our task is to provide the most symmetrical communication channel between the client (STA) and the point (AP) in order to equalize the speeds of uplink and downlink. To do this, we will rely on SNR (signal-to-noise ratio).
SNR(STA) = Rx(AP) - RxSens(STA); SNR (AP) - Rx(STA) - RxSens(AP)
where Rx(AP/STA) - power received signal from point/client, RxSens(AP/STA) - reception sensitivity of point/client. To simplify, we assume that the threshold background noise below the sensitivity threshold of the AP/STA receiver. Such a simplification is quite acceptable, because if the background noise level for AP and STA is the same, it does not affect the channel symmetry in any way.
Further,
Rx(AP) = Tx(AP)[point transmitter power at antenna port] + TxGain(AP)[transmission gain of a point antenna taking into account all losses, gains and directivity] -PathLoss[signal loss on the way from point to client] + RxGain(STA)[reception gain of the client's antenna, taking into account all losses, gains and directivity].
Likewise, Rx(STA) = Tx(STA) + TxGain(STA) - PathLoss + RxGain(AP).
It is worth noting the following:

  • PathLoss is the same in both directions
  • TxGain and RxGain antennas in case conventional antennas is the same (true for both AP and STA). Cases with MIMO, MRC, TxBF and other tricks are not considered here. So you can accept: TxGain(AP) === RxGain(AP) = Gain(AP), similar for STA.
  • Rx/Tx Gain of the client antenna is rarely known. Client devices are usually equipped with non-replaceable antennas, which allows you to specify the transmitter power and receiver sensitivity immediately taking into account the antenna. We will note this in our calculations below.
In total we get:
SNR(AP) = Tx*(STA) [including antenna] - PathLoss + Gain(AP) - RxSens(AP)
SNR(STA)=Tx(AP) + Gain(AP) - PathLoss -RxSens*(STA) [including antenna]

The difference between the SNR at both ends will be the channel asymmetry, we apply arithmetic: D = SNR(STA)-SNR(AP) = Tx*(STA) - Tx(AP) - (RxSens*(STA) - (RxSens(AP)).

Thus, the channel asymmetry does not depend on the type of antenna at the point and at the client (again, it depends if you use MIMO, MRC, etc., but it will be quite difficult to calculate anything here), but depends on the difference in power and sensitivity of the receivers. At D<0 точка будет слышать клиента лучше, чем клиент точку. В зависимости от расстояния это будет значить либо, что поток данных от клиента к точке будет медленнее, чем от точки к клиенту, либо клиент до точки достучаться не сможет вовсе.
For the power of the point (100mW=20dBm) and the client (30-50mW ~= 15-17dBm) we took, the power difference will be 3-5dB. As long as the point's receiver is more sensitive than the client's receiver by this same 3-5dB, problems will not arise. Unfortunately, this is not always the case. Let's carry out calculations for an HP 8440p laptop and a D-Link point DIR-615 for 802.11g@54Mbps:

  • 8440p : Tx*(STA) = 17dBm, RxSens*(STA) = -76dBm@54Mbps
  • DIR-615: Tx(AP) = 20dBm, RxSens(AP) = -65dBm@54Mbps.
  • D = (17 - 20) - (-76 +65) = 3 - 11 = -7dB.
Thus, problems may occur in the work, moreover, due to the fault of the point.

Also, a far from well-known fact that adds to the asymmetry is that most client devices have reduced transmitter power on the “extreme” channels (1 and 11/13 for 2.4 GHz). Here's an iPhone example from the FCC documentation (power at the antenna port).


As you can see, on the extreme channels the transmitter power is ~2.3 times lower than on the middle ones. The reason is that Wi-Fi is a broadband connection; it will not be possible to keep the signal clearly within the channel frame. So you have to reduce the power in “borderline” cases so as not to affect the bands adjacent to the ISM. Conclusion: if your tablet does not work well in the toilet, try moving to channel 6.

Since we're talking about channels, next time we'll talk about them in more detail.

UPD: I have already been told that the note is too short. I already understood everything. But if I add the rest of the text here, many will no longer see it. In the next post I will post everything in its entirety (I will remove the first part under the cut). Additional comments are welcome if they expand on the topic of “competent” posting on Habré. For emotions there is this hub. Thanks for understanding.

For beginners, a few words about the units of measurement adopted in antenna technology and high-frequency radio engineering, which are not clear to many.

    dBmSometimes it is convenient to take some value as a standard (zero level) and measure the level relative to it in decibels. So, if we take 1 mW as the zero level and measure the power relative to it on a logarithmic decibel scale, then the unit of measurement appears as dBm (1 mW = 0 dBm). It already has a very significant physical meaning, unlike impersonal decibels, dBm is a measure of power. It measures the level of weak signals (in the same “palmometer” of the modem), the sensitivity of receivers, the power of transmitters, etc. For example, a level of 50 μV at a 50-ohm receiver input corresponds to a power level of 5·10 -8 mW or -73 dBm. Measuring sensitivity in power units is more convenient than in voltage units, since we have to deal with signals of different shapes, including noise. In addition, we get rid of the need to specify each time what the input impedance of the receiver is. For example, the threshold power of most “whistles”, at which they still connect to the base station, is about -110 dBm. Transmitter power can also be measured in dBm. For example, the power of a Wi-Fi router of 100 mW is 20 dbm. You can use our online calculator to convert mW to dBm and vice versa. In many devices you will find the signal level at asu. This is another unit of measurement of signal level, designed to drive the anonymous person into a stupor with its incomprehensibility. It stands for "Arbitrary Strength Unit" - an average unit of signal strength. The fact is that in different ranges we use channels with different modulations, different frequency bands, etc. Therefore equal dBm V3G And 4G- are not equivalent to the same sensitivity in terms of signal-to-noise ratio in the channel. To bring sensitivity to a common denominator, they came up with asu. Connection between asu And dBm for different ranges the following:

    • GSM: dBm = 2 × ASU - 113, ASU in the range of values 0..31 And 99 (network not defined).
    • UMTS: dBm = ASU - 116, ASU in the range of values -5..91 And 255 (network not defined).
    • LTE: (ASU - 141) ≤ dBm< (ASU - 140)

  • dBi (dBi).A unit of measurement for antenna gain relative to a “reference” antenna. The so-calledisotropic emitter- an ideal antenna, the radiation pattern of which is a sphere, the gain of which is equal to unity and the efficiency of which is 100%. The signal is emitted by such an emitter with uniform intensity in all directions. Such an antenna does not exist in nature; it is a virtual object, however, it is very convenient as a standard for measuring the parameters of real antennas. There is one more unit: dBd- here a half-wave dipole is taken as the standard. However, the use dBi preferable because in this case, it is easier to calculate the energy balance of the radio communication path. dBi- this is a relative unit, essentially indistinguishable from a simple decibel, except for the definition of the standard, relative to which the countdown takes place. There is no fundamental difference between dBi and dBd - dBi gain = dBd gain + 2.15 dB . In old amateur radio books and magazines, antenna gain is simply measured in decibels. In this case, what is most often meant is the gain relative to a half-wave vibrator, i.e. it is equivalent dBd. The measurement of a relative isotropic radiator was originally used only in the United States, but has recently spread throughout the world, so to avoid confusion, it is now good practice to use a decibel with the suffix - dBi or dBd when talking about antenna gain.

In principle, any value can be taken as the “zero level”. This is how such animals as “dBmkV” (voltage - the ratio to one microvolt), “dBW” (power - the ratio to one watt) are born. In acoustics, the zero sound level is taken to be a sound pressure of 2 10 -5 Pa - hearing threshold. At the same time, they didn’t bother with the addition to “dB”, but just measured the sound level in decibels. This happened historically, because decibels were first used in the field of acoustics. But we must keep in mind that these are not “pure” relative decibels, but “sound” - absolute ones. For example, the noise of a jet plane from a distance of 25 m is 140 dB, and 0 dB is the threshold of audibility. You can often find a unit called dBA. It is specially designed for measuring noise intensity. The dBA value is the sound pressure level measured in “sound” decibels using a sound level meter containing a correction chain that imitates the sensitivity of the human ear, which makes it possible to obtain readings more consistent with the actual audibility of noise.

In general, people started using decibels to measure various things for a reason. Back in the 19th century, psychophysiologists Ernst Weber and Gustav Fechner established that “the strength of sensation p is proportional to the logarithm of the intensity of the stimulus S.” This applies to sound, lighting, tactile sensations.
In wire communication technology, another unit is used - Neper. Nepers are determined not through the decimal, but through the natural logarithm. Maybe this is more correct, because many laws of nature are based on the Euler number, which is the base of the natural logarithm. But we still use decibels. (1 neper = 8.686 dB)

When calculating all these dB, dBi, dBm in essence, all are decibels, i.e. are summed (if amplification) or subtracted (if attenuation), but dBm takes precedence as a measure of signal strength. For example:

Receiver input level(dBm) = Transmitter power(dBm) + Antenna gain(dBi) - Signal attenuation(dB)

An inexperienced anonymous person is usually lost at the sight of such an abundance of varieties of decibels. But then comes the understanding that this brings simplification in calculations. For example, in calculating Wi-Fi communication range. Many people find it difficult to visualize the “decibel” scale, especially in the negative area. In fact, this is easy to do by analogy with the familiar thermometer. The higher the power in dBm, the “warmer” the number. In other words, -75dBm is larger (higher on the scale, “warmer”) than -95dBm. A more negative number in the sensitivity parameter means that the receiver is able to receive a weaker (colder) signal.

That's how it's all confused in this decibel kingdom. And finally... Keep in mind that decibel and imbecile are completely different concepts.







2024 gtavrl.ru.