Evolution of data transfer speed in Wi-Fi networks
- Why do you need nubuck?
- In order to dimensionlessly use the possibilities of bluetooth, and to switch with other subscribers throughout the region of Russia with the help of Wi-Fi!
(C) Ural Dumplings
The IEEE 802.11 working group was first announced in 1990, and for 25 years now, incessant work on wireless standards has been underway. The main trend is the constant increase in data rates. In this article, I will try to trace the path of technology development and show how the increase in productivity was ensured and what to expect in the near future. It is assumed that the reader is familiar with the basic principles of wireless communication: modulation types, modulation depth, spectrum width, etc. and knows the basic principles of Wi-Fi networks. In fact, there are not many ways to increase the bandwidth of the communication system, and most of them were implemented at different stages of improving the standards of the 802.11 group.
Standards defining the physical layer from a mutually compatible ruler a / b / g / n / ac will be considered. The standards 802.11af (Wi-Fi on terrestrial TV frequencies), 802.11ah (Wi-Fi in the range of 0.9 MHz, designed to implement the IoT concept) and 802.11ad (Wi-Fi for high-speed connection of peripheral devices like monitors and external drives) are incompatible on the other, they have different applications and are not suitable for analyzing the evolution of data transmission technologies over a long time interval. In addition, the standards defining security standards (802.11i), QoS (802.11e), roaming (802.11r), etc. will remain out of consideration, since they only indirectly affect the data transfer rate. Hereinafter we are talking about the channel, the so-called gross speed, which is obviously greater than the actual data transfer rate due to the large number of service packets in the radio.
The first wireless standard was 802.11 (without a letter). It provided for two types of transmission medium: a 2.4 GHz radio frequency and an infrared range of 850–950 nm. IR devices were not widely distributed and were not developed in the future. In the 2.4 GHz band, there were two ways of spreading the spectrum (spreading is an integral procedure in modern communication systems): spread spectrum hopping (FHSS) and direct sequence (DSSS). In the first case, all networks use the same frequency band, but with different rebuilding algorithms. In the second case, the frequency channels from 2412 MHz to 2472 MHz in 5 MHz increments already appear, which are still preserved. As an expanding sequence, a Barker sequence with a length of 11 chips is used. The maximum data transfer rate ranged from 1 to 2 Mbps. At that time, even taking into account the fact that in the most ideal conditions, the useful data transfer rate via Wi-Fi does not exceed 50% of the channel speed, such speeds looked very attractive compared to the speeds of modem access to the Internet.
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For signal transmission in 802.11, 2- and 4-position keying was used, which ensured the operation of the system even in adverse signal-to-noise conditions and did not require complicated receiving-transmitting modules.
For example, to implement an information speed of 2 Mbit / s, each transmitted symbol is replaced by a sequence of 11 characters.
Thus, the chip speed is 22 Mbps. In one transmission cycle, 2 bits are transmitted (4 signal levels). Thus, the speed of manipulation is 11 baud and the main lobe of the spectrum in this case occupies 22 MHz, the value that is applied to 802.11 is often called the channel width (in fact, the signal spectrum is infinite).
At the same time, according to the Nyquist criterion (the number of independent pulses per unit time is limited to twice the maximum channel bandwidth), a 5.5 MHz band is sufficient to transmit such a signal. Theoretically, 802.11 devices should work satisfactorily on channels that are 10 MHz apart (unlike later implementations of the standard, requiring broadcasting at frequencies that are not less than 20 MHz apart).
Very quickly, the speed of 1-2 Mbit / s was not enough, and 802.11b came to replace 802.11, in which the data transfer speed was increased to 5.5, 11 and 22 (optional) Mbit / s. The speed increase was achieved by reducing the redundancy of error-correcting coding from 1/11 to ½ and even 2/3 due to the introduction of block (CCK) and high-precision (PBCC) codes. In addition, the maximum number of modulation steps was increased to 8 by one transmitted symbol (3 bits per 1 baud). The channel width and frequencies used have not changed. But with a decrease in redundancy and an increase in the modulation depth, the requirements for the signal-to-noise ratio inevitably increased. Since it is not possible to increase the power of devices (due to the energy savings of mobile devices and legal restrictions), this restriction manifested itself in a slight reduction in the service area at new speeds. The service area at inherited speeds of 1-2 Mbit / s has not changed. It was decided to completely abandon the method of expanding the spectrum using the frequency hopping method. More in the Wi-Fi family, it was not used.
The next step to increase the speed to 54 Mbps was implemented in the 802.11a standard (this standard was developed earlier than the 802.11b standard, but the final version was released later). The increase in speed was mainly achieved by increasing the modulation depth to 64 levels per character (6 bits per 1 baud). In addition, the radio frequency part was radically revised: the direct sequence spread spectrum was replaced by the spread spectrum extension by the serial signal into parallel orthogonal substituting (OFDM). The use of parallel transmission on 48 subchannels made it possible to reduce intersymbol interference by increasing the duration of individual characters. Data transmission was carried out in the 5 GHz band. At the same time, the width of one channel is 20 MHz.
Unlike the 802.11 and 802.11b standards, even partial overlapping of this band can lead to transmission errors. Fortunately, in the 5 GHz band, the distance between the channels is the same 20 MHz.
The 802.11g standard was not a breakthrough in terms of data rate. In fact, this standard was a compilation of 802.11a and 802.11b in the 2.4 GHz band: it supported the speeds of both standards.
A significant increase in speed occurred in the 802.11n standard (in both 2.4 and 5 GHz bands): up to 72 Mbps due to a decrease in the guard intervals between the transmitted symbols. In addition, to increase the bandwidth, it was possible to combine two channels of 20 MHz and get 150 Mbps. However, this is not the best way to increase speed: in the 2.4 MHz band, only one extended channel at 40 MHz can fit. Another way to increase the speed was MIMO technology: the use of multiple transceivers operating on the same frequency. Channel separation occurs due to the spatial separation of antennas and mathematical operations on a signal received on different antennas: it will differ due to multipath propagation of radio waves. Ironically, it was the multipath effect that previously had a negative effect on the transmission of data on the network, but engineers were able to identify the ailment for the feat and make this parasitic factor work to increase speed. The 802.11n standard supports MIMO 4x4: 4 (four independent channels) and provides speeds of up to 600 Mbps.
However, this technology requires high quality manufacturing of the radio part of the device. In addition, these speeds are not fundamentally feasible on mobile terminals (the main target group of the Wi-Fi standard): the presence of 4 antennas at sufficient diversity cannot be realized in small-sized devices either for reasons of lack of space or due to lack of sufficient 4 transceiver energy.
In most cases, the speed of 600 Mbit / s is nothing more than a marketing ploy and is unrealizable in practice, since in fact it can only be achieved between stationary access points installed within the same room with a good signal-to-noise ratio.
The next step in the transmission speed was performed by the 802.11ac standard: the maximum speed stipulated by the standard is up to 6.93 Gbit / s, but in fact this speed has not yet been achieved on any equipment on the market. The speed increase is achieved by increasing the bandwidth to 80 and even up to 160 MHz. This band cannot be provided in the 2.4 GHz band; therefore, the 802.11ac standard only functions in the 5 GHz band. Another speed increase factor is an increase in the modulation depth up to 256 levels per character (8 bits per 1 baud). Unfortunately, this modulation depth can only be obtained near a point due to the increased signal-to-noise ratio requirements. These improvements made it possible to achieve an increase in speed of up to 867 Mbps. The remaining increase is due to the previously mentioned 8x8: 8 MIMO streams. 8678 = 6.93 Gbit / s. MIMO technology has been improved: for the first time in the Wi-Fi standard, information on the same network can be transmitted to two subscribers simultaneously using different spatial streams.
In a more visual form, the results in the table:
The table lists the main ways to increase throughput: “-” - the method is not applicable, “+” - the speed was increased due to this factor, “=” - this factor remained unchanged.
The redundancy reduction resources have already been exhausted: the maximum speed of the error-correcting 5/6 code was achieved in the 802.11a standard and has not increased since then. Increasing the modulation depth is theoretically possible, but the next step is 1024QAM, which is very demanding of the signal-to-noise ratio, which will extremely reduce the range of the access point at high speeds. This will increase the requirements for the performance of the hardware transceivers. Reducing the intersymbol guard interval is also unlikely to be a direction for improving the speed — reducing it threatens to increase the errors caused by intersymbol interference. An increase in the channel bandwidth above 160 MHz is also hardly possible, since the possibilities for organizing non-overlapping cells will be severely limited. Even less realistic is the increase in the number of MIMO channels: even 2 channels are a problem for mobile devices (due to power consumption and size).
Of the above methods for increasing the transmission speed, a large part takes the usable coverage area as payment for its use: the bandwidth of the waves decreases (transition from 2.4 to 5 GHz) and the requirements for the signal-to-noise ratio (increased modulation depth, increased code rate) increase. Therefore, in its development, Wi-Fi networks are constantly striving to reduce the area served by one point in favor of the data transfer speed.
The following improvement directions can be used: dynamic distribution of OFDM subcarriers between subscribers in wide channels, improvement of the medium access algorithm, aimed at reducing service traffic and using interference cancellation techniques.
Summarizing the above, I will try to predict the development trends of Wi-Fi networks: it is unlikely that the following standards will seriously increase the data transfer speed (I don’t think that it is more than 2-3 times) if there is no qualitative jump in wireless technologies: almost all possibilities quantitative growth exhausted. It will be possible to provide the growing needs of users for data transmission only by increasing the coverage density (reducing the range of points by controlling power) and by more rational distribution of the existing band between subscribers.
In general, the trend of decreasing service areas seems to be a major trend in modern wireless communications. Some experts believe that the LTE standard has reached the peak of its capacity and will not be able to further develop for fundamental reasons related to the limited frequency resource. Therefore, offload technologies are being developed in western mobile networks: at any opportunity, the phone connects to Wi-Fi from the same operator. This is called one of the main ways to save the mobile Internet. Accordingly, the role of Wi-Fi networks with the development of 4G networks not only does not fall, but increases. What puts in front of the technology all the new and new speed challenges.
- In order to dimensionlessly use the possibilities of bluetooth, and to switch with other subscribers throughout the region of Russia with the help of Wi-Fi!
(C) Ural Dumplings
The IEEE 802.11 working group was first announced in 1990, and for 25 years now, incessant work on wireless standards has been underway. The main trend is the constant increase in data rates. In this article, I will try to trace the path of technology development and show how the increase in productivity was ensured and what to expect in the near future. It is assumed that the reader is familiar with the basic principles of wireless communication: modulation types, modulation depth, spectrum width, etc. and knows the basic principles of Wi-Fi networks. In fact, there are not many ways to increase the bandwidth of the communication system, and most of them were implemented at different stages of improving the standards of the 802.11 group.
Standards defining the physical layer from a mutually compatible ruler a / b / g / n / ac will be considered. The standards 802.11af (Wi-Fi on terrestrial TV frequencies), 802.11ah (Wi-Fi in the range of 0.9 MHz, designed to implement the IoT concept) and 802.11ad (Wi-Fi for high-speed connection of peripheral devices like monitors and external drives) are incompatible on the other, they have different applications and are not suitable for analyzing the evolution of data transmission technologies over a long time interval. In addition, the standards defining security standards (802.11i), QoS (802.11e), roaming (802.11r), etc. will remain out of consideration, since they only indirectly affect the data transfer rate. Hereinafter we are talking about the channel, the so-called gross speed, which is obviously greater than the actual data transfer rate due to the large number of service packets in the radio.
The first wireless standard was 802.11 (without a letter). It provided for two types of transmission medium: a 2.4 GHz radio frequency and an infrared range of 850–950 nm. IR devices were not widely distributed and were not developed in the future. In the 2.4 GHz band, there were two ways of spreading the spectrum (spreading is an integral procedure in modern communication systems): spread spectrum hopping (FHSS) and direct sequence (DSSS). In the first case, all networks use the same frequency band, but with different rebuilding algorithms. In the second case, the frequency channels from 2412 MHz to 2472 MHz in 5 MHz increments already appear, which are still preserved. As an expanding sequence, a Barker sequence with a length of 11 chips is used. The maximum data transfer rate ranged from 1 to 2 Mbps. At that time, even taking into account the fact that in the most ideal conditions, the useful data transfer rate via Wi-Fi does not exceed 50% of the channel speed, such speeds looked very attractive compared to the speeds of modem access to the Internet.
')
For signal transmission in 802.11, 2- and 4-position keying was used, which ensured the operation of the system even in adverse signal-to-noise conditions and did not require complicated receiving-transmitting modules.
For example, to implement an information speed of 2 Mbit / s, each transmitted symbol is replaced by a sequence of 11 characters.
Thus, the chip speed is 22 Mbps. In one transmission cycle, 2 bits are transmitted (4 signal levels). Thus, the speed of manipulation is 11 baud and the main lobe of the spectrum in this case occupies 22 MHz, the value that is applied to 802.11 is often called the channel width (in fact, the signal spectrum is infinite).
At the same time, according to the Nyquist criterion (the number of independent pulses per unit time is limited to twice the maximum channel bandwidth), a 5.5 MHz band is sufficient to transmit such a signal. Theoretically, 802.11 devices should work satisfactorily on channels that are 10 MHz apart (unlike later implementations of the standard, requiring broadcasting at frequencies that are not less than 20 MHz apart).
Very quickly, the speed of 1-2 Mbit / s was not enough, and 802.11b came to replace 802.11, in which the data transfer speed was increased to 5.5, 11 and 22 (optional) Mbit / s. The speed increase was achieved by reducing the redundancy of error-correcting coding from 1/11 to ½ and even 2/3 due to the introduction of block (CCK) and high-precision (PBCC) codes. In addition, the maximum number of modulation steps was increased to 8 by one transmitted symbol (3 bits per 1 baud). The channel width and frequencies used have not changed. But with a decrease in redundancy and an increase in the modulation depth, the requirements for the signal-to-noise ratio inevitably increased. Since it is not possible to increase the power of devices (due to the energy savings of mobile devices and legal restrictions), this restriction manifested itself in a slight reduction in the service area at new speeds. The service area at inherited speeds of 1-2 Mbit / s has not changed. It was decided to completely abandon the method of expanding the spectrum using the frequency hopping method. More in the Wi-Fi family, it was not used.
The next step to increase the speed to 54 Mbps was implemented in the 802.11a standard (this standard was developed earlier than the 802.11b standard, but the final version was released later). The increase in speed was mainly achieved by increasing the modulation depth to 64 levels per character (6 bits per 1 baud). In addition, the radio frequency part was radically revised: the direct sequence spread spectrum was replaced by the spread spectrum extension by the serial signal into parallel orthogonal substituting (OFDM). The use of parallel transmission on 48 subchannels made it possible to reduce intersymbol interference by increasing the duration of individual characters. Data transmission was carried out in the 5 GHz band. At the same time, the width of one channel is 20 MHz.
Unlike the 802.11 and 802.11b standards, even partial overlapping of this band can lead to transmission errors. Fortunately, in the 5 GHz band, the distance between the channels is the same 20 MHz.
The 802.11g standard was not a breakthrough in terms of data rate. In fact, this standard was a compilation of 802.11a and 802.11b in the 2.4 GHz band: it supported the speeds of both standards.
A significant increase in speed occurred in the 802.11n standard (in both 2.4 and 5 GHz bands): up to 72 Mbps due to a decrease in the guard intervals between the transmitted symbols. In addition, to increase the bandwidth, it was possible to combine two channels of 20 MHz and get 150 Mbps. However, this is not the best way to increase speed: in the 2.4 MHz band, only one extended channel at 40 MHz can fit. Another way to increase the speed was MIMO technology: the use of multiple transceivers operating on the same frequency. Channel separation occurs due to the spatial separation of antennas and mathematical operations on a signal received on different antennas: it will differ due to multipath propagation of radio waves. Ironically, it was the multipath effect that previously had a negative effect on the transmission of data on the network, but engineers were able to identify the ailment for the feat and make this parasitic factor work to increase speed. The 802.11n standard supports MIMO 4x4: 4 (four independent channels) and provides speeds of up to 600 Mbps.
However, this technology requires high quality manufacturing of the radio part of the device. In addition, these speeds are not fundamentally feasible on mobile terminals (the main target group of the Wi-Fi standard): the presence of 4 antennas at sufficient diversity cannot be realized in small-sized devices either for reasons of lack of space or due to lack of sufficient 4 transceiver energy.
In most cases, the speed of 600 Mbit / s is nothing more than a marketing ploy and is unrealizable in practice, since in fact it can only be achieved between stationary access points installed within the same room with a good signal-to-noise ratio.
The next step in the transmission speed was performed by the 802.11ac standard: the maximum speed stipulated by the standard is up to 6.93 Gbit / s, but in fact this speed has not yet been achieved on any equipment on the market. The speed increase is achieved by increasing the bandwidth to 80 and even up to 160 MHz. This band cannot be provided in the 2.4 GHz band; therefore, the 802.11ac standard only functions in the 5 GHz band. Another speed increase factor is an increase in the modulation depth up to 256 levels per character (8 bits per 1 baud). Unfortunately, this modulation depth can only be obtained near a point due to the increased signal-to-noise ratio requirements. These improvements made it possible to achieve an increase in speed of up to 867 Mbps. The remaining increase is due to the previously mentioned 8x8: 8 MIMO streams. 8678 = 6.93 Gbit / s. MIMO technology has been improved: for the first time in the Wi-Fi standard, information on the same network can be transmitted to two subscribers simultaneously using different spatial streams.
In a more visual form, the results in the table:
The table lists the main ways to increase throughput: “-” - the method is not applicable, “+” - the speed was increased due to this factor, “=” - this factor remained unchanged.
The redundancy reduction resources have already been exhausted: the maximum speed of the error-correcting 5/6 code was achieved in the 802.11a standard and has not increased since then. Increasing the modulation depth is theoretically possible, but the next step is 1024QAM, which is very demanding of the signal-to-noise ratio, which will extremely reduce the range of the access point at high speeds. This will increase the requirements for the performance of the hardware transceivers. Reducing the intersymbol guard interval is also unlikely to be a direction for improving the speed — reducing it threatens to increase the errors caused by intersymbol interference. An increase in the channel bandwidth above 160 MHz is also hardly possible, since the possibilities for organizing non-overlapping cells will be severely limited. Even less realistic is the increase in the number of MIMO channels: even 2 channels are a problem for mobile devices (due to power consumption and size).
Of the above methods for increasing the transmission speed, a large part takes the usable coverage area as payment for its use: the bandwidth of the waves decreases (transition from 2.4 to 5 GHz) and the requirements for the signal-to-noise ratio (increased modulation depth, increased code rate) increase. Therefore, in its development, Wi-Fi networks are constantly striving to reduce the area served by one point in favor of the data transfer speed.
The following improvement directions can be used: dynamic distribution of OFDM subcarriers between subscribers in wide channels, improvement of the medium access algorithm, aimed at reducing service traffic and using interference cancellation techniques.
Summarizing the above, I will try to predict the development trends of Wi-Fi networks: it is unlikely that the following standards will seriously increase the data transfer speed (I don’t think that it is more than 2-3 times) if there is no qualitative jump in wireless technologies: almost all possibilities quantitative growth exhausted. It will be possible to provide the growing needs of users for data transmission only by increasing the coverage density (reducing the range of points by controlling power) and by more rational distribution of the existing band between subscribers.
In general, the trend of decreasing service areas seems to be a major trend in modern wireless communications. Some experts believe that the LTE standard has reached the peak of its capacity and will not be able to further develop for fundamental reasons related to the limited frequency resource. Therefore, offload technologies are being developed in western mobile networks: at any opportunity, the phone connects to Wi-Fi from the same operator. This is called one of the main ways to save the mobile Internet. Accordingly, the role of Wi-Fi networks with the development of 4G networks not only does not fall, but increases. What puts in front of the technology all the new and new speed challenges.
Source: https://habr.com/ru/post/254559/
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