Ruffini's rule: Difference between revisions
en>Elizabeth Stapel m →External links: correcting spellling of external site's name |
en>JCSantos m Adding format of the reference |
||
| Line 1: | Line 1: | ||
'''Rain fade''' refers primarily to the [[absorption (optics)|absorption]] of a [[microwave]] [[radio frequency]] (RF) signal by atmospheric rain, snow or ice, and losses which are especially prevalent at frequencies above 11 [[GHz]]. It also refers to the degradation of a signal caused by the [[electromagnetic interference]] of the leading edge of a storm front. Rain fade can be caused by precipitation at the uplink or downlink location. However, it does not need to be raining at a location for it to be affected by rain fade, as the signal may pass through precipitation many miles away, especially if the [[satellite dish]] has a low [[look angle]]. From 5 to 20 percent of rain fade or satellite signal attenuation may also be caused by rain, snow or ice on the uplink or downlink antenna reflector, radome or feed horn. Rain fade is not limited to satellite uplinks or downlinks, it also can affect terrestrial point to point microwave links (those on the earth's surface). | |||
Possible ways to overcome the effects of rain fade are [[site diversity]], uplink power control, [[variable rate encoding]], receiving antennas larger (i.e. higher gain) than the required size for normal weather conditions, and [[hydrophobic]] coatings. Only [[superhydrophobic]], [[Lotus effect]] surfaces repel snow and ice. | |||
== Uplink power control == | |||
The simplest way to compensate the rain fade effect in [[satellite communications]] is to increase the transmission power: this dynamic fade countermeasure is called '''uplink power control''' (UPC). Until more recently, uplink power control had a limited use since it required more powerful transmitters - ones that could normally run at lower levels and could be run up in power level on command (i.e. automatically). Also uplink power control could not provide very large signal margins without compressing the transmitting amplifier. Modern amplifiers coupled with advanced uplink power control systems that offer automatic controls to prevent transponder saturation make uplink power control systems an effective, affordable and easy solution to rain fade in satellite signals. | |||
== Parallel fail-over links == | |||
In terrestrial point to point microwave systems ranging from 11 GHz to 80 GHz, a parallel backup link can be installed alongside a rain fade prone higher bandwidth connection. In this arrangement, a primary link such as an 80GHz 1 Gbit/s full duplex microwave bridge may be calculated to have a 99.9% availability rate over the period of one year. The calculated 99.9% availability rate means that the link may be down for a cumulative total of ten or more hours per year as the peaks of rain storms pass over the area. A secondary lower bandwidth link such as a 5.8 GHz based 100 Mbit/s bridge may be installed parallel to the primary link, with routers on both ends controlling automatic failover to the 100 Mbit/s bridge when the primary 1 Gbit/s link is down due to rain fade. Using this arrangement, high frequency point to point links (23GHz+) may be installed to service locations many kilometers farther than could be served with a single link requiring 99.99% uptime over the course of one year. | |||
== CCIR interpolation formula == | |||
It is possible to extrapolate the cumulative attenuation distribution at a given location by using | |||
the CCIR interpolation formula:<ref>CCIR [1990] Report 564-4 "Propagation data and prediction | |||
methods required for earth-space telecommunication systems"</ref> | |||
: ''A''<sub>''p''</sub> = ''A''<sub>001</sub> 0.12 ''p''<sup>−(0.546 − 0.0043 log<sub>10</sub> ''p'')</sup>. | |||
where ''A''<sub>''p''</sub> is the attenuation in dB exceeded for a ''p'' percentage of the time and ''A''<sub>001</sub> is the attenuation exceeded for 0.01% of the time. | |||
== ITU-R frequency scaling formula == | |||
According to the ITU-R,<ref>“Propagation Data and Prediction Methods Required for the Design of Earth-Space Telecommunication Systems,” Recommendations of the ITU-R, Rec. P.618-10, 2009.</ref> rain attenuation statistics can be scaled in frequency in the range 7 to 55 GHz by the formula | |||
:<math>\frac{A_2}{A_1} = \left(\frac{b_2}{b_1}\right) ^ {1-1.12 \cdot 10^{-3}\sqrt{b_2/b_1}(b_1A_1)^{0.55}}</math> | |||
where | |||
:<math>b_i = \frac{f_i^2}{1+10^{-4} f_i^2}</math> | |||
and ''f'' is the frequency in GHz. | |||
==See also== | |||
*[[Fresnel zone]] | |||
*[[Diversity scheme]] | |||
== References == | |||
<references/> | |||
{{radio spectrum}} | |||
[[Category:Radio frequency propagation fading]] | |||
[[Category:Satellite broadcasting]] | |||
Revision as of 17:33, 2 February 2014
Rain fade refers primarily to the absorption of a microwave radio frequency (RF) signal by atmospheric rain, snow or ice, and losses which are especially prevalent at frequencies above 11 GHz. It also refers to the degradation of a signal caused by the electromagnetic interference of the leading edge of a storm front. Rain fade can be caused by precipitation at the uplink or downlink location. However, it does not need to be raining at a location for it to be affected by rain fade, as the signal may pass through precipitation many miles away, especially if the satellite dish has a low look angle. From 5 to 20 percent of rain fade or satellite signal attenuation may also be caused by rain, snow or ice on the uplink or downlink antenna reflector, radome or feed horn. Rain fade is not limited to satellite uplinks or downlinks, it also can affect terrestrial point to point microwave links (those on the earth's surface).
Possible ways to overcome the effects of rain fade are site diversity, uplink power control, variable rate encoding, receiving antennas larger (i.e. higher gain) than the required size for normal weather conditions, and hydrophobic coatings. Only superhydrophobic, Lotus effect surfaces repel snow and ice.
Uplink power control
The simplest way to compensate the rain fade effect in satellite communications is to increase the transmission power: this dynamic fade countermeasure is called uplink power control (UPC). Until more recently, uplink power control had a limited use since it required more powerful transmitters - ones that could normally run at lower levels and could be run up in power level on command (i.e. automatically). Also uplink power control could not provide very large signal margins without compressing the transmitting amplifier. Modern amplifiers coupled with advanced uplink power control systems that offer automatic controls to prevent transponder saturation make uplink power control systems an effective, affordable and easy solution to rain fade in satellite signals.
Parallel fail-over links
In terrestrial point to point microwave systems ranging from 11 GHz to 80 GHz, a parallel backup link can be installed alongside a rain fade prone higher bandwidth connection. In this arrangement, a primary link such as an 80GHz 1 Gbit/s full duplex microwave bridge may be calculated to have a 99.9% availability rate over the period of one year. The calculated 99.9% availability rate means that the link may be down for a cumulative total of ten or more hours per year as the peaks of rain storms pass over the area. A secondary lower bandwidth link such as a 5.8 GHz based 100 Mbit/s bridge may be installed parallel to the primary link, with routers on both ends controlling automatic failover to the 100 Mbit/s bridge when the primary 1 Gbit/s link is down due to rain fade. Using this arrangement, high frequency point to point links (23GHz+) may be installed to service locations many kilometers farther than could be served with a single link requiring 99.99% uptime over the course of one year.
CCIR interpolation formula
It is possible to extrapolate the cumulative attenuation distribution at a given location by using the CCIR interpolation formula:[1]
- Ap = A001 0.12 p−(0.546 − 0.0043 log10 p).
where Ap is the attenuation in dB exceeded for a p percentage of the time and A001 is the attenuation exceeded for 0.01% of the time.
ITU-R frequency scaling formula
According to the ITU-R,[2] rain attenuation statistics can be scaled in frequency in the range 7 to 55 GHz by the formula
where
and f is the frequency in GHz.
See also
References
Hostgator Coupon Codes - http://dawonls.dothome.co.kr/db/?document_srl=404110.
google.deYou need to view this as an investment to start up a business. You can now customize your Wordpress theme and add content to your blog. Every company out there, from larger ones like iPage to the newest entrants on the hosting market, usually has something to offer (unless they're complete garbage to begin with) and you should check all the relevant reviews carefully to ensure that you're not missing out on a deal that can potentially work much better for you. If you are pondering of organising your individual website, then perhaps one of the first issues that you want to take into account is finding a great web hosting service that may cater to your on-line needs. offer, their price is the lowest among the major hosting providers. If you already have webhosting, you can often install wordpress with just a few clicks. To turn the serious profit, you need to invest time. And now I have taken on the target of creating an internet network marketing business. How to Use Quick Install ?Access your HostGator hosting control panel and scroll down the mouse to bottom and see the category "software/services" ?Here you can find the QuickInstall icon. You also have the option on which sort of reseller account you would like, you get the aluminum, copper, silver, gold as well as diamond plan.
Find blogs related to your niche, contact the owner and see if you can write a guest posts on their blog. Running a blog. If you have a private web site having a single domain and blog, you shouldn't be having to pay anymore than $10/mo. This would mean that your website will be up and operating with no distractions and no downs. So, you can get more than just a saving by using this excellent option. HostGator was founded by Brent Oxley in 2002 when he was still a student at University. Environment Friendly Lately Hostgator acquired turned eco-friendly by energizing and cooling their hosting server using wind flow power. That's ridiculous.