V60s Millimeter Wave Radio Links
Specifications:
- Product: Vubiq Networks HaulPass V60sTM
- Frequency: 60 GHz
- Point-to-point link budget: 142 dB
- Range: 750 meters with a 5.2 dB margin
Product Usage Instructions:
1. Understanding Link Budget and Fade Margin:
The Vubiq Networks HaulPass V60sTM operates at 60 GHz with a
link budget of 142 dB. This means that under ideal conditions with
zero rain fade, the product can provide a range of 750 meters with
a margin of 5.2 dB.
2. Rain Fade Considerations:
When installing the link at a range of 500 meters, there will
still be a margin of 12.5 dB to handle rain fade effectively. Rain
fade can impact signal strength, so it’s crucial to consider this
when setting up the link.
3. Predicting Link Availability:
Rain attenuation due to different rain rates can affect the link
performance. By referencing the ITU rain zone map and understanding
rain attenuation values at specific frequencies, you can predict
link availability based on geographical location and rain
rates.
4. Operating the Product:
Ensure that the link is installed within the specified range
limits and take into account the rain fade margins to maintain
optimal performance. Regularly monitor rain rates in your area to
anticipate any potential impact on link availability.
FAQ:
Q: How can I determine the expected link availability under
varying rain conditions?
A: You can predict link availability by knowing the link budget,
fade margin, and referencing rain attenuation values at specific
frequencies. Utilize the ITU rain zone map to understand rain rates
in your area and assess the impact on link performance.
Rain Fade Considerations in the Design of Millimeter Wave
Radio Links White Paper
By Mike Pettus CTO and Founder Vubiq Networks, Inc.
Page 2
Abstract
Millimeter wave point-to-point radio links are gaining traction for transporting high-speed digital information, especially as data rates approach and exceed 1 Gbps. Proper planning and design for the millimeter wave link requires knowledge of the local environment to assure reliable operation. The fundamental concept used to determine link reliability is known as service availability. Rain fade can affect millimeter wave wireless link availability if the fade is severe enough to interrupt link service.
This paper outlines these concepts and provides a methodology to predict link availability, taking into consideration the impact of rain fade.
Millimeter Wave Link Budget and Fade Margin
Millimeter wave radio transmission is naturally attenuated by distance of the transmission, known as path loss. For a known millimeter wave link design, the transmit power, antenna gain, and receive sensitivity are factors that combine with the path loss to determine the maximum range or distance for the link. From these parameters in a given product design, a link budget is derived. It’s typical and most convenient to specify the link budget in decibels or dB. The link budget is the maximum allowed path loss under ideal conditions.
As an example, the Vubiq Networks HaulPass V60sTM 60 GHz point-to-point product has a link budget of 142 dB. With zero rain fade, this number yields a range of 750 meters with a 5.2 dB margin. If the link is installed at a range of 500 meters, then there will be a margin of 12.5 dB left to handle even more rain fade.
Figure 1. Range, Path Loss and Margin for the HaulPass V60s
Once the link budget and margin are known for given ranges of operation, rain fade can be taken into account to determine the expected link availability.
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Rain Attenuation
Signal fade due to rain attenuation is a wellknown and studied phenomenon. Figure 2 shows a graph of specific attenuation versus frequency at various rain rates, with 60 GHz and 80 GHz highlighted. Rain rate means how much rain falls in a given time period, and is measured in millimeters of rain per hour (mm/h). Divide these numbers by 25.4 if inches/hour is desired.
Predicting Link Availability
Rain rate probabilities for a given geographical location can easily be derived from the International Telecommunications Union (ITU) rain zone map. Figure 3 shows the global ITU rain zone map, and Figure 4 shows a close-up of the southwestern U.S. and Mexico. To predict the rain fade probabilities for a given location, the area is first located on the rain zone map.
Figure 3. ITU Rain Zones, Global2
Figure 2. Attenuation vs Frequency at Different Rain Rates1
For example, at 25 mm/h (close to 1″/h), the attenuation due to rain at 60 GHz is 10 dB. If a V60s link were installed at 350 meters range, from Figure 1 the margin at this range is 17.9 dB. At 25 mm/h the rain would not affect operation since the rain attenuation of 10 dB is less than the margin at 17.9 dB.
Figure 4. ITU Rain Zones, Southwestern U.S./Mexico Close-Up
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Figure 5. Rainfall Intensity Exceeded (mm/h) vs. Rain Zones
As an example, let’s design a 350 meter V60s link to be installed in southern California with an uptime availability of 99.99% (“four nines”). The rain zone for this area is ITU Zone E. There is a table of rain rate probabilities published in the ITU document, shown in Figure 5. A 99.99% availability means the unavailability or downtime allowed needs to be less than .01%. For Zone E, the 0.01% row shows that the rain rate will exceed a value of 22 mm/h. Checking back at Figure 2, a rain rate of 22 mm/h will produce an additional attenuation, or rain fade, of slightly less than 10 dB/km.
Since the desired range is 350 meters, or 0.35 km, the actual attenuation will be 0.35*10 dB = 3.5 dB (this is because the rain attenuation is specified in dB/km).
The link budget chart for the V60s at Figure 1 shows that a 350 meter link will have a margin of 12.6 dB. The example link should operate with greater than 99.99% uptime since the margin is greater than the rain fade of approximately 3.5 dB for this link at 22 mm/h rain rate.
Conclusion
Knowing the parameters for a millimeter wave link and understanding how to use the ITU rain zone data enables link design with predictable performance and availability.
Footnotes: 1. FCC Office of Engineering and Technology, Bulletin
Number 70 https://transition.fcc.gov/Bureaus/Engineering_ Technology/Documents/bulletins/oet70/oet70.pdf 2. Recommendation ITU-R PN.837-1 https://www.itu.int/dms_ pubrec/itu-r/rec/p/R-REC-P.837-1-199408-S!!PDF-E.pdf 3. Recommendation ITU-R PN.837-1 https://www.itu.int/dms_ pubrec/itu-r/rec/p/R-REC-P.837-1-199408-S!!PDF-E.pdf
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Documents / Resources
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VUBIQ NETWORKS V60s Millimeter Wave Radio Links [pdf] User Guide V60s Millimeter Wave Radio Links, V60s, Millimeter Wave Radio Links, Wave Radio Links, Radio Links |