December 19, 2009 at 16:40WiMAX How it works
In this article I will tell about technology repeatedly mentioned on Habré.
Worlwide Interoperability for Microwave Access. So decrypts WiMAX.
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 into our everyday world only now.
Initially, it was positioned as 4G due to its novelty and transmission speed, but in 2008 it definitely took its place among third-generation technologies. However, this fact did not stop salespeople, advertisers, and other unclean people from advertising it under the slogan “4G Internet” (what are they talking about?).
To begin with, I will briefly tell those who are far from telecommunications about generations of communication technologies. In the beginning wasAMPS (Advaced Mobile Phone Service) is an analog standard that you could listen to just by having a receiver. Not having lived for several years, he lost the lead to the 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 the 2.5G intermediate generation. WCDMA reborn into HSDPA(High-Speed Downlink Packet Access, later HSUPA - High Speed Uplink Packet Access), and CDMA 2000 1x in CDMA EVDO . This is the third generation, to which, roughly speaking, WiMAX approached from the side of IP networks.
In place of all this, LTE and WiMAX Release 2.0 are already on the verge . What else awaits us?
As you now understand, opposing WiMAX and 3G is somewhat incorrect.
Now in more detail. WiMAX - refers to the networks of the class MAN (Metropolitan Area Network), is developed and supported by the association WiMAX Forum .
In 2004, the 802.16d specification came out describing fixed WiMAX. Subscriber devices cannot move over considerable distances, there is no handover, but at the same time, work is ensured at a great distance (up to 50 km from the BS, according to the specification). In my opinion, a futile branch.
802.16e is coming out in 2005. This is already Mobile WiMAX, which you hear about regularly. It was he who prophesied a great future.
The technology operates in the frequency range of 2-6 GHz. The most convenient frequencies for ensuring mobility are 2.3-2.7 GHz, but obtaining permission for them is extremely difficult. The following range used in the equipment: 3.4-3.6 GHz - the golden mean. At frequencies close to 6 GHz, the so-called preWiMAX works, subscriber units should be in the direct line of sight of the base station, since the penetration of waves of such a frequency and the rounding of obstacles is very weak. In this regard, the same GSM-networks (800-1900 MHz), and even more so CDMA (450 MHz) is much simpler.
As a rule, devices do not support operation in several frequency ranges, therefore people often call and say: “But I purchased a modem Iota in Moscow. Tell me, will he work for you here? ”- they are refused.
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
The concept of the following interfaces is introduced for the WiMAX network:
R1 - interface between CPE and BS
R2 - virtual interface between CPE and CSN
R3 - interface between ASN-GW and CSN
R6 - interface between BSN and ASN-GW
Generally speaking, there can be more ASN and CSN networks. for instance, two ASNs in different cities connected to the same CSN or to different. Picture. Here R4 interfaces are added for communication between various ASNs and R5 for CSN communication.
If the article is relevant and interesting for someone, I will write several detailed articles on the functions of each node.
Of course, the diagram does not show such elements as switches, firewalls, it does not say about transport to the BS, because this is a completely different story.
The principle of operation is approximately as follows: a subscriber device tuned to the operator’s network sends a BS a request for allocation of radio resources; upon successful completion, an authentication request is sent to ASN-GW (using EAP-TTLS). He, in turn, by the domain name in the login parameter determines where the request should be redirected. Next, the desired AAA server gives Accept or Reject to the device. If authentication is successful, the modem is assigned an IP address, QoS, mode of operation, and other parameters. All. The device is ready to go.
In conclusion, I will give the main features and advantages of WiMAX.
TDD (Time Division Duplex). It is not necessary to use different frequencies for reception and transmission, which allows more optimal use of the allocated frequency band (for 802.16e it is 5, 7, 10 MHz, for 802.16d it is possible to use 20 MHz). Also, for more rational use of the band, OFDMA (Orthogonal Friquency-Division Multiple Access) technology is used .
CP (Cycle Prefix) - a small piece (1/4, 1 / 8.1 / 16, 1/32) from the end is inserted at the beginning of the OFDMA symbol to prevent interference from the direct and reflected signal. Usually used 1/8.
CC and CTC(Convolutional coding and Convolutional Turbo coding). I can’t give specific explanations; it is used to encode OFDMA characters.
AMC (Adaptive Modulation and Coding). To convert a digital signal to 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 modulation: QPSK, 16QAM, 64QAM. The better the signal, the higher the modulation is selected, the higher the data rate. Coding and cycle prefix are also selected.
Harq(Hybrid automatic repeat request) - a mechanism that allows you to track errors and send a request for retransmission.
MIMO (Multiple Input / Multiple Output) - the use of multiple antennas for reception and transmission.
AAS (Adaptive Antenna System) - an antenna system whose radiation pattern changes in accordance with the movement of subscriber devices.
WiMAX’s path is thorny: on the one hand, this is competition from mobile operators, on the other hand, it rushes towards him on all LTE pairs, and on the third, Russian managers.
PS In this article we accumulate issues that should be addressed in the following articles.
<What did I want to convey in this article? General information about WiMAX technology, operating principles and mechanisms used. What did I want to know? Do you need more details?>
Worlwide Interoperability for Microwave Access. So decrypts WiMAX.
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 into our everyday world only now.
Initially, it was positioned as 4G due to its novelty and transmission speed, but in 2008 it definitely took its place among third-generation technologies. However, this fact did not stop salespeople, advertisers, and other unclean people from advertising it under the slogan “4G Internet” (what are they talking about?).
To begin with, I will briefly tell those who are far from telecommunications about generations of communication technologies. In the beginning wasAMPS (Advaced Mobile Phone Service) is an analog standard that you could listen to just by having a receiver. Not having lived for several years, he lost the lead to the 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 the 2.5G intermediate generation. WCDMA reborn into HSDPA(High-Speed Downlink Packet Access, later HSUPA - High Speed Uplink Packet Access), and CDMA 2000 1x in CDMA EVDO . This is the third generation, to which, roughly speaking, WiMAX approached from the side of IP networks.
In place of all this, LTE and WiMAX Release 2.0 are already on the verge . What else awaits us?
As you now understand, opposing WiMAX and 3G is somewhat incorrect.
Now in more detail. WiMAX - refers to the networks of the class MAN (Metropolitan Area Network), is developed and supported by the association WiMAX Forum .
In 2004, the 802.16d specification came out describing fixed WiMAX. Subscriber devices cannot move over considerable distances, there is no handover, but at the same time, work is ensured at a great distance (up to 50 km from the BS, according to the specification). In my opinion, a futile branch.
802.16e is coming out in 2005. This is already Mobile WiMAX, which you hear about regularly. It was he who prophesied a great future.
The technology operates in the frequency range of 2-6 GHz. The most convenient frequencies for ensuring mobility are 2.3-2.7 GHz, but obtaining permission for them is extremely difficult. The following range used in the equipment: 3.4-3.6 GHz - the golden mean. At frequencies close to 6 GHz, the so-called preWiMAX works, subscriber units should be in the direct line of sight of the base station, since the penetration of waves of such a frequency and the rounding of obstacles is very weak. In this regard, the same GSM-networks (800-1900 MHz), and even more so CDMA (450 MHz) is much simpler.
As a rule, devices do not support operation in several frequency ranges, therefore people often call and say: “But I purchased a modem Iota in Moscow. Tell me, will he work for you here? ”- they are refused.
Network diagram
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
The concept of the following interfaces is introduced for the WiMAX network:
R1 - interface between CPE and BS
R2 - virtual interface between CPE and CSN
R3 - interface between ASN-GW and CSN
R6 - interface between BSN and ASN-GW
Generally speaking, there can be more ASN and CSN networks. for instance, two ASNs in different cities connected to the same CSN or to different. Picture. Here R4 interfaces are added for communication between various ASNs and R5 for CSN communication.
If the article is relevant and interesting for someone, I will write several detailed articles on the functions of each node.
Of course, the diagram does not show such elements as switches, firewalls, it 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: a subscriber device tuned to the operator’s network sends a BS a request for allocation of radio resources; upon successful completion, an authentication request is sent to ASN-GW (using EAP-TTLS). He, in turn, by the domain name in the login parameter determines where the request should be redirected. Next, the desired AAA server gives Accept or Reject to the device. If authentication is successful, the modem is assigned an IP address, QoS, mode of operation, and other parameters. All. The device is ready to go.
Technology features
In conclusion, I will give the main features and advantages of WiMAX.
TDD (Time Division Duplex). It is not necessary to use different frequencies for reception and transmission, which allows more optimal use of the allocated frequency band (for 802.16e it is 5, 7, 10 MHz, for 802.16d it is possible to use 20 MHz). Also, for more rational use of the band, OFDMA (Orthogonal Friquency-Division Multiple Access) technology is used .
CP (Cycle Prefix) - a small piece (1/4, 1 / 8.1 / 16, 1/32) from the end is inserted at the beginning of the OFDMA symbol to prevent interference from the direct and reflected signal. Usually used 1/8.
CC and CTC(Convolutional coding and Convolutional Turbo coding). I can’t give specific explanations; it is used to encode OFDMA characters.
AMC (Adaptive Modulation and Coding). To convert a digital signal to 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 modulation: QPSK, 16QAM, 64QAM. The better the signal, the higher the modulation is selected, the higher the data rate. Coding and cycle prefix are also selected.
Harq(Hybrid automatic repeat request) - a mechanism that allows you to track errors and send a request for retransmission.
MIMO (Multiple Input / Multiple Output) - the use of multiple antennas for reception and transmission.
AAS (Adaptive Antenna System) - an antenna system whose radiation pattern changes in accordance with the movement of subscriber devices.
WiMAX’s path is thorny: on the one hand, this is competition from mobile operators, on the other hand, it rushes towards him on all LTE pairs, and on the third, Russian managers.
PS In this article we accumulate issues that should be addressed in the following articles.
<What did I want to convey in this article? General information about WiMAX technology, operating principles and mechanisms used. What did I want to know? Do you need more details?>