WiMAX. How it works
In this article I will talk about the technology that was repeatedly mentioned in Habré.
Worlwide Interoperability for Microwave Access. So WiMAX is decrypted.
This technology does not have deep roots, such as GSM or CDMA. It appeared relatively recently: in 2004, the first standard for WiMAX was released, and it penetrates our everyday world just now.
Initially, it was positioned as 4G due to its novelty and transmission speed, but in 2008 it definitely took its place among the technologies of the third generation. However, this fact did not prevent sales people, advertisers and other unclean people from advertising it with the slogan “4G Internet” (what are they about?).
For a start, I will briefly tell those who are far from telecommunications about the generations of communication technologies. Initially, there was AMPS (Advaced Mobile Phone Service) - an analog standard that you could listen to just by having a receiver. Not having lived for several years, he gave way to the palm of technology, known as GSM (Global System for Mobile Communications). This is the 2nd generation. Along with it appeared CDMA One (Code Devision Multiple Access). These two branches gave rise to GPRS (General Packet Radio Service, later EDGE - Enhanced Data Rates for GSM Evolution), WCDMA (Wideband CDMA aka UMTS ) and CDMA 2000 1x, respectively, which are commonly referred to as intermediate generation 2.5G. WCDMA was reborn as HSDPA (High-Speed ​​Downlink Packet Access, later HSUPA High Speed ​​Uplink Packet Access), and CDMA 2000 1x as CDMA EVDO . This is the third generation, to which, roughly speaking, from the side of IP networks came WiMAX.
In place of all this, LTE and WiMAX Release 2.0 are already on the threshold. What else is waiting for us?
As you now understand, opposing WiMAX and 3G is somewhat incorrect.
Now more. WiMAX - belongs to the MAN class network (Metropolitan Area Network), developed and supported by the WiMAX Forum association.
In 2004, the 802.16d specification, which describes fixed WiMAX, appeared. Subscriber devices can not move over significant distances, there is no handover, but it also provides work at a long distance (up to 50 km from the base station, according to the specification). In my opinion unpromising branch.
In 2005, 802.16e comes out. This is Mobile WiMAX, which you regularly hear about. It was he who was predicted a great future.
The technology works in the frequency range 2-6 GHz. The most convenient frequencies for providing mobility are 2.3-2.7 GHz, but it is extremely difficult to obtain permission for them. The following equipment used in the equipment: 3.4-3.6 GHz - the golden mean. At frequencies close to 6 GHz, the so-called preWiMAX works, subscriber devices must be in the line of sight of the base station, since the penetration of waves of such a frequency and around the obstacles is very weak. In this regard, the same GSM-networks (800-1900 MHz), and even more CDMA (450 MHz) is much simpler.
As a rule, devices do not support operation in several frequency bands, so people often call and say: “But I purchased a Yota modem in Moscow. Tell me, will he work here for you? ”- what is the rejection for?
What is a WiMAX network? The simplest case is presented in the diagram.
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Small explanations to the scheme:
CPE = Customer Premises Equipment
BS = Base Station
ASN = Access Service Network
ASN-GW = Access Service Network GateWay
CSN = Connection Service Network
AAA = Authentification, Autorization, Accounting
For the WiMAX network, the concept of the following interfaces is introduced:
R1 - interface between CPE and BS
R2 - virtual interface between CPE and CSN
R3 - interface between ASN-GW and CSN
R6 - interface between BS and ASN-GW
Generally speaking, the ASN and CSN networks can be more. For example , two ASN networks in different cities connected to the same CSN network or to different. Picture. Here, R4 interfaces are added for connecting different ASNs and R5 for CSN communications.
If the article is relevant and interesting to someone, I will write a few detailed articles on the functions of each site.
Of course, the diagram does not show such elements as switches, firewalls, does not say about transport to the BS, because this is a completely different story.
The principle of operation is approximately as follows: the subscriber device configured on the operator’s network sends a request for radio resource allocation to the BS, upon successful completion an authentication request is sent to the ASN-GW (EAP-TTLS is used). He, in turn, by the name of the domain in the login parameter determines where to redirect the request. Next, the desired AAA server gives Accept or Reject to the device. If the authentication is successful, the modem is assigned an IP address, QoS, mode of operation, and other parameters. Everything. The device is ready for operation.
Finally, I will give the main features and advantages of WiMAX.
TDD (Time Division Duplex). You do not need to use different frequencies for reception and transmission, which allows you to more optimally use the allocated frequency band (for 802.16e this is 5, 7, 10 MHz, for 802.16d it is possible to use 20 MHz). Also, OFDMA (Orthogonal Friquency-Division Multiple Access) technology is used to make rational use of the band.
CP (Cycle Prefix) - a small piece (1/4, 1 / 8,1 / 16, 1/32) is inserted into the beginning of the OFDMA symbol from the end to prevent interference of the direct and reflected signals. Usually used 1/8.
CC and CTC (Convolutional coding and Convolutional Turbo coding). I can not give specific explanations, used to encode OFDMA-smvolov.
AMC (Adaptive Modulation and Coding). To convert a digital signal into an analog, the inverse Fourier transform is used (for me this is a particularly exciting moment, because at the university I hated this topic). Depending on the signal level (RSSI - Received signal strength indication) and noise level (CINR - Carrier to Interference + Noise Ratio), the number of members of the Fourier series is selected, respectively, and the modulation: QPSK, 16QAM, 64QAM. The better the signal, the higher the modulation chosen, the higher the data rate. Also coding and cycle prefix is ​​selected.
HARQ (Hybrid automatic repeat request) is a mechanism for tracking errors and sending a request for retransmission.
MIMO (Multiple Input / Multiple Output) - the use of multiple antennas for receiving and transmitting.
AAS (Adaptive Antenna System) is an antenna system whose radiation pattern changes in accordance with the movement of subscriber devices.
The WiMAX path is thorny: on the one hand, it is competition from cellular operators, on the other hand, there is no LTE to meet it on all pairs, and on the third, Russian managers.
PS In this article we accumulate questions that should be covered in the following articles.
<What did I want to convey in this article? General information about WiMAX technology, principles of operation and mechanisms used. What did I want to know? Is it necessary to continue in detail?>
Worlwide Interoperability for Microwave Access. So WiMAX is decrypted.
This technology does not have deep roots, such as GSM or CDMA. It appeared relatively recently: in 2004, the first standard for WiMAX was released, and it penetrates our everyday world just now.
Initially, it was positioned as 4G due to its novelty and transmission speed, but in 2008 it definitely took its place among the technologies of the third generation. However, this fact did not prevent sales people, advertisers and other unclean people from advertising it with the slogan “4G Internet” (what are they about?).
For a start, I will briefly tell those who are far from telecommunications about the generations of communication technologies. Initially, there was AMPS (Advaced Mobile Phone Service) - an analog standard that you could listen to just by having a receiver. Not having lived for several years, he gave way to the palm of technology, known as GSM (Global System for Mobile Communications). This is the 2nd generation. Along with it appeared CDMA One (Code Devision Multiple Access). These two branches gave rise to GPRS (General Packet Radio Service, later EDGE - Enhanced Data Rates for GSM Evolution), WCDMA (Wideband CDMA aka UMTS ) and CDMA 2000 1x, respectively, which are commonly referred to as intermediate generation 2.5G. WCDMA was reborn as HSDPA (High-Speed ​​Downlink Packet Access, later HSUPA High Speed ​​Uplink Packet Access), and CDMA 2000 1x as CDMA EVDO . This is the third generation, to which, roughly speaking, from the side of IP networks came WiMAX.
In place of all this, LTE and WiMAX Release 2.0 are already on the threshold. What else is waiting for us?
As you now understand, opposing WiMAX and 3G is somewhat incorrect.
Now more. WiMAX - belongs to the MAN class network (Metropolitan Area Network), developed and supported by the WiMAX Forum association.
In 2004, the 802.16d specification, which describes fixed WiMAX, appeared. Subscriber devices can not move over significant distances, there is no handover, but it also provides work at a long distance (up to 50 km from the base station, according to the specification). In my opinion unpromising branch.
In 2005, 802.16e comes out. This is Mobile WiMAX, which you regularly hear about. It was he who was predicted a great future.
The technology works in the frequency range 2-6 GHz. The most convenient frequencies for providing mobility are 2.3-2.7 GHz, but it is extremely difficult to obtain permission for them. The following equipment used in the equipment: 3.4-3.6 GHz - the golden mean. At frequencies close to 6 GHz, the so-called preWiMAX works, subscriber devices must be in the line of sight of the base station, since the penetration of waves of such a frequency and around the obstacles is very weak. In this regard, the same GSM-networks (800-1900 MHz), and even more CDMA (450 MHz) is much simpler.
As a rule, devices do not support operation in several frequency bands, so people often call and say: “But I purchased a Yota modem in Moscow. Tell me, will he work here for you? ”- what is the rejection for?
Network layout
What is a WiMAX network? The simplest case is presented in the diagram.
')
Small explanations to the scheme:
CPE = Customer Premises Equipment
BS = Base Station
ASN = Access Service Network
ASN-GW = Access Service Network GateWay
CSN = Connection Service Network
AAA = Authentification, Autorization, Accounting
For the WiMAX network, the concept of the following interfaces is introduced:
R1 - interface between CPE and BS
R2 - virtual interface between CPE and CSN
R3 - interface between ASN-GW and CSN
R6 - interface between BS and ASN-GW
Generally speaking, the ASN and CSN networks can be more. For example , two ASN networks in different cities connected to the same CSN network or to different. Picture. Here, R4 interfaces are added for connecting different ASNs and R5 for CSN communications.
If the article is relevant and interesting to someone, I will write a few detailed articles on the functions of each site.
Of course, the diagram does not show such elements as switches, firewalls, does not say about transport to the BS, because this is a completely different story.
Principle of operation
The principle of operation is approximately as follows: the subscriber device configured on the operator’s network sends a request for radio resource allocation to the BS, upon successful completion an authentication request is sent to the ASN-GW (EAP-TTLS is used). He, in turn, by the name of the domain in the login parameter determines where to redirect the request. Next, the desired AAA server gives Accept or Reject to the device. If the authentication is successful, the modem is assigned an IP address, QoS, mode of operation, and other parameters. Everything. The device is ready for operation.
Technology features
Finally, I will give the main features and advantages of WiMAX.
TDD (Time Division Duplex). You do not need to use different frequencies for reception and transmission, which allows you to more optimally use the allocated frequency band (for 802.16e this is 5, 7, 10 MHz, for 802.16d it is possible to use 20 MHz). Also, OFDMA (Orthogonal Friquency-Division Multiple Access) technology is used to make rational use of the band.
CP (Cycle Prefix) - a small piece (1/4, 1 / 8,1 / 16, 1/32) is inserted into the beginning of the OFDMA symbol from the end to prevent interference of the direct and reflected signals. Usually used 1/8.
CC and CTC (Convolutional coding and Convolutional Turbo coding). I can not give specific explanations, used to encode OFDMA-smvolov.
AMC (Adaptive Modulation and Coding). To convert a digital signal into an analog, the inverse Fourier transform is used (for me this is a particularly exciting moment, because at the university I hated this topic). Depending on the signal level (RSSI - Received signal strength indication) and noise level (CINR - Carrier to Interference + Noise Ratio), the number of members of the Fourier series is selected, respectively, and the modulation: QPSK, 16QAM, 64QAM. The better the signal, the higher the modulation chosen, the higher the data rate. Also coding and cycle prefix is ​​selected.
HARQ (Hybrid automatic repeat request) is a mechanism for tracking errors and sending a request for retransmission.
MIMO (Multiple Input / Multiple Output) - the use of multiple antennas for receiving and transmitting.
AAS (Adaptive Antenna System) is an antenna system whose radiation pattern changes in accordance with the movement of subscriber devices.
The WiMAX path is thorny: on the one hand, it is competition from cellular operators, on the other hand, there is no LTE to meet it on all pairs, and on the third, Russian managers.
PS In this article we accumulate questions that should be covered in the following articles.
<What did I want to convey in this article? General information about WiMAX technology, principles of operation and mechanisms used. What did I want to know? Is it necessary to continue in detail?>
Source: https://habr.com/ru/post/78743/
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