10 gigabit Ethernet 80 GHz point-to-point bridges • Hacker News Board

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#51

Post by madengr » Sat, Apr 23, 2016, 2:21 AM UTC

walrus01 wrote: post #50

madengr wrote: post #48

Earlier quoted context omitted.

Back in 60's AT&T make lots and lots of circular waveguide, intending to bury it across the country. One of the circular modes is dispersionless; then fiber was invented; lot's of money lost on circular waveguide. Interesting that mmWavguide is still rectangular. Wonder if one could do a mmWave fiber? Don't see why not.

millimeter wave waveguide on the rear of a parabolic antenna (30, 60cm dish) is actually circular (cylindrical), supporting dual polarity operation (opposite H and V). Individual radio heads like this russian radio or other 80 GHz radios are still single polarity. In certain scenarios you can mount two radio heads on a T-shaped waveguide on the rear of one dish antenna, one in H, one in V.

Thanks for the info. I got to mess with W-band stuff years ago, but I'm mostly Ku and below now. Would love to tear down some 80 GHz hardware.

Have you seen anything come of the "angular momentum" polarization discovered a few years ago? Seemed specific for P2P microwave.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#52

Post by xahrepap » Sat, Apr 23, 2016, 2:31 AM UTC

SoftwareMaven wrote: post #46

ChuckMcM wrote: post #35

Crap, now I need to go buy a couple of these and lobby the nearest data center for some rooftop space. That is the short way of saying I had no idea you could get antenna this effective for wireless data transmission. I'd seen the 5mbps ones but nothing close to a gigabit much less 10 gigabits. Time to draw a 10km radius circle around my home address :-)

The NSA Bluffdale facility might just squeak in that line for me. Think they'd hook me up?

If they do, let me know ;) I'm just about there too.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#53

Post by walrus01 » Sat, Apr 23, 2016, 2:36 AM UTC

madengr wrote: post #51

walrus01 wrote: post #50

Earlier quoted context omitted.

millimeter wave waveguide on the rear of a parabolic antenna (30, 60cm dish) is actually circular (cylindrical), supporting dual polarity operation (opposite H and V). Individual radio heads like this russian radio or other 80 GHz radios are still single polarity. In certain scenarios you can mount two radio heads on a T-shaped waveguide on the rear of one dish antenna, one in H, one in V.

Thanks for the info. I got to mess with W-band stuff years ago, but I'm mostly Ku and below now. Would love to tear down some 80 GHz hardware. Have you seen anything come of the "angular momentum" polarization discovered a few years ago? Seemed specific for P2P microwave.

I've yet to see a product of any sort I can buy with a credit card or purchase order. Would also like to know if anything comes of it.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#54

Post by rasz_pl » Sat, Apr 23, 2016, 2:45 AM UTC

walrus01 wrote: post #8

mey wrote: post #2

• Secure communication due inability to intercept the laser-like beam transmission at free air I would not trust that as a security layer.

It's definitely not something to trust in, but intercepting (at a layer 1 level) a PTP 80 GHz link is actually harder than tapping fiber. You'd have to have Rx equipment either directly in the path or directly behind both ends of the radio link. As compared to the effort required to cut an aerial or underground singlemode cable and fusion splice in place a passive prism split tap (basically the same thing as insertin…

or a drone with a reflector

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#55

Post by wrigby » Sat, Apr 23, 2016, 3:04 AM UTC

madengr wrote: post #51

walrus01 wrote: post #50

Earlier quoted context omitted.

millimeter wave waveguide on the rear of a parabolic antenna (30, 60cm dish) is actually circular (cylindrical), supporting dual polarity operation (opposite H and V). Individual radio heads like this russian radio or other 80 GHz radios are still single polarity. In certain scenarios you can mount two radio heads on a T-shaped waveguide on the rear of one dish antenna, one in H, one in V.

Thanks for the info. I got to mess with W-band stuff years ago, but I'm mostly Ku and below now. Would love to tear down some 80 GHz hardware. Have you seen anything come of the "angular momentum" polarization discovered a few years ago? Seemed specific for P2P microwave.

I would love to hear more about that - have any links? From a quick google, all I can dig up makes it sound like it's normal circular polarization, which is used quite often in satellite. Not sure why it wouldn't make it into terrestrial, since it has some interesting advantages (no x-pol alignment issues!)

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#56

Post by ArkyBeagle » Sat, Apr 23, 2016, 3:11 AM UTC

walrus01 wrote: post #45

ArkyBeagle wrote: post #42

Earlier quoted context omitted.

The more general dividing line between microwave and infrared ( outside comms ) is 300 GHz, which was what I meant.

That is true. One of the fun things illustrating first-hand how microwave/millimeter wave and fiber are the same thing is if you ever get to handle a 120 GHz band waveguide/feed. Some radar and military stuff operates in the 120 band. It's so incredibly tiny and narrow compared to a 11 or 18 GHz microwave waveguide. Then imagine continuing to make it narrower while increasing the frequency, follow that to its logical…

But it's something of an apparently completely different... phenotype from a small waveguide.

The seemingly arbitrary 300Ghz line was probably more cultural than essential; the instrumentation was just very different. What's the analog for a prism for microwave?

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#57

Post by wrigby » Sat, Apr 23, 2016, 3:15 AM UTC

walrus01 wrote: post #17

wrigby wrote: post #15

It's interesting to see the huge channel bandwidths they're using to attain this. Advances like this are largely driven by higher sample rate ADCs and DACs becoming more viable in recent years. Edit for clarity: channel bandwidths in the datasheet are up to 2 GHz. Need to close the link at 32 QAM to hit 10 gb before error correction overhead at that bandwidth, which is certainly doable. Also, it's interesting to note…

terrestrial microwave engineer here: "80 GHz" is actually 71-86 GHz FDD. The original FCC band plan allowed for 5000 MHz wide channels each direction and basically OOK or BPSK level modulation. Newer radios use 250, 500 or 1000 MHZ wide FDD channels and QPSK or better. Incredibly wide channels can be used because it falls off in the atmosphere so rapidly after a few km, and the antennas are all very narrow parabolic…

Thanks for jumping in! Sounds like it's really nice for urban small-cell deployments, campus networks, etc. Do you experience a lot of issues with keeping links aligned at those tiny beamwidths?

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#58

Post by detaro » Sat, Apr 23, 2016, 3:20 AM UTC

ArkyBeagle wrote: post #56

walrus01 wrote: post #45

Earlier quoted context omitted.

That is true. One of the fun things illustrating first-hand how microwave/millimeter wave and fiber are the same thing is if you ever get to handle a 120 GHz band waveguide/feed. Some radar and military stuff operates in the 120 band. It's so incredibly tiny and narrow compared to a 11 or 18 GHz microwave waveguide. Then imagine continuing to make it narrower while increasing the frequency, follow that to its logical…

But it's something of an apparently completely different... phenotype from a small waveguide. The seemingly arbitrary 300Ghz line was probably more cultural than essential; the instrumentation was just very different. What's the analog for a prism for microwave?

Apparently a block of plastics like Delrin works:

http://www.physics.rutgers.edu/ugrad/205/manuals/micro.pdf

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#59

Post by Dwolb » Sat, Apr 23, 2016, 3:42 AM UTC

walrus01 wrote: post #20

e2phd wrote: post #18

Earlier quoted context omitted.

You can pack many bits into a constellation point. Think 1024 QAM.

Most new licensed band 6, 11, 18, 23 GHz radios these days are 1024QAM capable. For 80 GHz the hot new thing is radios capable of 16/64/256QAM at varying code rates.

What's the limiting factor when designing to a constellation? Otherwise, what's improved about the chip or firmware to be able to move from 256QAM to 512QAM?

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#60

Post by Dwolb » Sat, Apr 23, 2016, 3:42 AM UTC

walrus01 wrote: post #20

e2phd wrote: post #18

Earlier quoted context omitted.

You can pack many bits into a constellation point. Think 1024 QAM.

Most new licensed band 6, 11, 18, 23 GHz radios these days are 1024QAM capable. For 80 GHz the hot new thing is radios capable of 16/64/256QAM at varying code rates.

What's the limiting factor when designing to a constellation? Otherwise, what's improved about the chip or firmware to be able to move from 256QAM to 512QAM?