What do you think about this airline vs 5G brouhaha?

Tue Jan 18 21:57:52 UTC 2022

Brandon,

Bo, it’s the radar altimeter, not the barometric altimeter. This is a radar distance measurement device for determine the precise height above the ground,  critical for low-visibility approaches. 

Where frequency interference is concerned, under FCC rules the existing users have priority, and are entitled to interference-free operation. 

-mel via cell

> On Jan 18, 2022, at 1:43 PM, Brandon Martin <lists.nanog at monmotha.net> wrote:
> 
> On 01/18/2022 15:29, Michael Thomas wrote:
>> I really don't know anything about it. It seems really late to be having this fight now, right?
> 
> The issue seems to be old aviation equipment that has poor receiver selectivity on its radio (not radar) altimeter.  This is, apparently, a secondary, but still very important, instrument for instrument approaches upon landing.
> 
> This older equipment can be subject to meaningful interference by signals as much as 500MHz outside the actual assigned radio altimeter band limit.  Note that the radio altimeter band is only about 500MHz wide itself, so even a naive single-conversion receiver could/should have better selectivity that this.  The reason for this poor selectivity seems to simply be that, at the time, there was nothing else using the RF spectrum nearby, so they could get away with it, and it made the receiver somewhat simpler.
> 
> The system apparently also responds poorly to both narrowband and wideband jammers i.e. it does not employ what we'd consider robust, modern error-correction or coding systems or even digital error checking techniques.
> 
> Both of these are basically issues with how old the system is and how old a large amount of deployed equipment using it is.  The former is probably hard to fix in a backwards compatible way, but the latter is mostly a matter of upgrading your instruments more than once every 25 years which, for planes that are actually routinely making use of this system (largely commercial and charter operators), doesn't really seem like that big of an ask.
> 
> I think the issue is that the FCC did some rulemaking assuming that existing service users were being reasonable with their equipment design, then a giant game of chicken got started, and nobody blinked in time for anything to get done until a collision was imminent.
> 
> The C-band spectrum at issue here has become very valuable, both economically and from a public usage perspective, for mid- and short-range wireless communications.  The FCC allocated some of it based on "reasonable" expectations of existing users and provided an ample (arguably rather large) guard band between services.
> 
> In the end, I'd say that aviation folks are in the wrong, here, but they also have a lot of history to contend with and a large install base of gear that, whether it "should" or not, apparently does need to be upgraded to prevent detrimental interference to an important flight safety and operations facility.  A pause in deployment seems reasonable in that light, though it would have been nice if folks could have gotten this resolved sooner.
> 
> --
> Brandon Martin