SatCom on-the-move 7.2-8.4 gHz electrical experience

[Higgler]

Anyone here been involved in SatCom transceiver design in the recent past. Looking for some answers and guidance on receiver technology for processing satellite signals in the 7.2-8.4 gHz band for on the move vehicles.

Thanks

 

[IRstuff]

Not sure that on the move is that different from stationary.

Unless your vehicles are going a substantial fraction of 7km/s, your vehicles would appear to be stationary relative to the satellite. GPS receivers work in planes going Mach 1+, albeit at lower frequency.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[VEBill]

At a system level, two things that have a direct and major impact on the hardware are the following: Doppler shift is a pretty obvious issue for on-the-move systems. And if it's a two-way link, the issue other is frame timing that may force full-duplex operation (i.e. not a transceiver).

Make friends with the person in charge of the antenna system (including choice of cables). ;-)

 

[Higgler]

On the move is a whole lot different and much more difficult.

The major concern on talking with these geosynchronous satellites is that if you hit a bump in your vehicle, or you change direction, your antenna can't point towards the next satellite 2 degrees in angle away from the one you're targeting.

If you point towards the other satellite, you need to drop your Tx power X dB. It's very challenging to keep pointed properly to not interfere with neighboring satellites.

I'm looking for someone who's been involved in the design and processing of SatCom on the move systems. Also if someone has worked on ground based SatCom equipment too.

 

[VEBill]

Are you working just on the receiver/transceiver section? Or are you also getting dragged into the system design as well?

 

[Higgler]

We are tasked with investigating going from one antenna to multiple (4 ish) smaller antennas (flat ones, low profile) spread across the vehicle to see if that can work. Real estate on vehicles are tough to come bye and things that stick out get rudely treated.
Are you active Military VE1BLL?

 

[VEBill]

No - not active military. We provide engineering support to them.

One technology to investigate is Luneberg Lens antenna systems. DTV downlink (receive) antennas can be installed on aircraft as they're about four or five inches thick. They use four dielectric hemispheres mounted on a groundplane. The entire assembly rotates in azimuth, and little feeds on rotating bails move up and down for elevation. Other than e-steerable arrays, it's the lowest profile technology I've seen.

I wonder if the FCC (or equivalent) has any requirements for satellite uplink from a moving platform? I assume that one would not be permitted to 'give it a go' without some strict regulatory supervision.

 

[VEBill]

Look up 'Blue Yonder' too. It's a commercial network setup by ViaSat and other partners. They use commercial transponders to support comms on the move.

 

[VEBill]

Yonder (not blue).

http://www.viasat.com/broadband-satellite-networks/mobile-broadband

 

[Higgler]

I think downlink is relatively easy, you look for a signal. Uplink is critical you don't radiate towards other satellites. RV's have Satcom OTM dishes for DirecTV commercially.
Our requirements needs a large aperture, so phased arrays is the gameplan. There are other mechanical and half Mechanical & half Phased Array solutions too.

I looked at the viasat Yonder link, seems it's a Rx antenna systems only, and needs onboard internet link to upload.

 

[VEBill]

Yonder is a two-way system. "Up to" 1 Mbps uplink from the mobile platform, and much more downlink to the mobile platform. It varies widely depending on which satellite they're using to provide coverage in a given area. Some of the elderly satellite re-use is actually quite funny.

Ku-band uplink from aircraft is a fully-solved problem (Yonder and perhaps others). But I'm not so sure about ground vehicles. Aircraft have very good on-board navigation systems, and they don't bounce around quite as much as trucks. It's not something I've followed.


Inmarsat BGAN has much less requirement for tight uplink beam aiming control and is thus "easier" in most respects than commercial ku-band birds. 432 kbps is a basic rate (other options available).


If someone is getting you involved in a bottom-up system design (as hinted by your most-recent post), then they better have very deep pockets. And the time.

 

[IRstuff]

Boeing's Connexions planned on using a conformal antenna for 2-way internet service on planes, and they sunk a big chunk of money on it before giving up. At one point in time, they had a over a hundred people working on it.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[VEBill]

Conformal antennas are available for Inmarsat BGAN, but I've not seen any that have enough gain (tight beamwidth) suitable for commercial ku satcom where the satellites are so tightly packed. Sidelobes might be a big technical challenge for e-steerable arrays, as applies to ku-band.

Depending on the required data rate, Iridium is another option. Single channel get you 2400 bits (!) per second. But they've now got multi-channel systems that provide 8, 16, or 32 times. Still sloooow, but it does provide true global coverage.

The mid-term future will bring more options.

 

[VEBill]

Here's a link to a datasheet for a Luneburg Lens antenna array:

http://www.l-3com.com/datron/pdf/d_L-3_DBS-2400.pdf

Doesn't presently fit the 7.2 - 8.4 GHz range, but there's no reason it couldn't be scaled up in size.