Where on the planet are you proposing to site this >?-the nearer the poles you go, the lower the 'midday sun' angle that the satellites reach, while southern Europe and central  USA enjoy satellites that are to all intents and purposes over head for some of the orbit, Northern UK and Scotland only see satellites rise and fall within a cone to the south and a max elevation of about 40- 50 deg. For a reliable fix you need 4 or more in simultaneous view  for a decent acquisition period.. For an accurate clock, a couple is usually enough.

Antenna siting advice written for Texas will not work so well in Yorkshire.

Mike

I'm planning for 5G network in Hong Kong (latitude: 22.4°). HK is a place full of high rises everywhere and difficult to find sky clearance. I'm just wandering if there's norm requirements for the GNSS antenna in my case. 

Ah well, .in HK you will get a reasonable no of satellite  passes more or less overhead, and not just to the south of you, unlike round here...

The only dead cert solution for any given location is to try it, but as you are only needing something to discipline a local clock, rather than to provide location for a fast moving target, you will not need anything like such a good view of the sky,

I presume the receivers are commercial , Ublox or modules similar, and not something bespoke, but in any case, yes you may get away with quite a lot of obstruction. There are dedicated 'timing' receiver algorithms, as opposed to the more common navigation ones, but I would expect this to have already been taken care of.

There are antennas designed to reject multi-path scatter from buildings and so on,and this may well be worth considering if timing jitter is problematic. Obviously averaged for long enough any GPS synchronized clock looks as good as an atomic standard, but the problem, if there is one, is the short and medium term jitter over seconds and minutes.

Mike.

Hi Mike,

During clocking synchronization, we need to track against at least 4 GNSS satellites. These satellites can be any combination from GPS, Galileo, GLONASS & Beidou? For instance, two from GPS & 2 from Beidou.

JW

From Hong Kong you wont have anything like as much problem achieving that as you would here. you just need to get a decent cone of sky in view  - in the UK that becomes a cone of sky laying on its side and pointing south - a harder target to meet.

If you want to calculate exactly  how bad you can get away with you will have to look in detail at the constellation patterns and consider how often do you do clock sync, and how long is at acceptable to wait, if you try and do it at a time when the stars are not in alignment as it were.  For GPS the orbital period is just under 12 hours, so the same satellite will be in view at at any given place not quite the same times twice per day. Glonass is a bit different, and the orbital period is 8/17 of a day, and each disk holds 8 satellites. For completeness the Beidou inclined disc (IGSO orbit) period is 7/13 of a day. but there are also some geostationary over China that provide infill. I'd expect that to be pretty solid over HK too.

I must admit that the 3d calcs are beyond my mental maths, and I tend to rely on published computer models if I really need to know how many will  be in view from any given place at a given time.

Mike

Thank for your advice. Get more on the Earth positioning.