Re: 2.4GHz broadband router on satellite?
Lee Maisel wrote:
James French wrote:
What are the possibilities of building a satellite that uses a Linksys WRT54GL router with a modified DD-wrt or HSMM-Mesh software as a store and forward BBS, to route a received request from one station to another station, or even to connect to a on board networked camera to receive images?
What kind of uplink power would be needed from the home station?
How fast could the speed(s) get theoretically?
How big would the antenna have to be on the craft and for the ground station to even be able to do this adequately?
Would the doppler be too much to even consider this?
Would the space environment be too harsh for something like this?
This is just something I was thinking about this morning and thought I would toss it out.
James W8ISS
THAT is an AWESOME Idea!
I don't see why it wouldn't work, I don't know if doppler is an issue though, it may not be if the modulation is FM. The antenna would not have to be big, it's 2.4Ghz
Why don't you post this on the HSMM-MESH.org web forums and get ideas?
73 Lee W5LMM
Hi James, Lee,
If you are thinking of using standard Wi-Fi as the link protocol, be aware that the timers that drive the protocol don't well work over long distances (few miles). Something about the speed of light not being fast enough. Real bummer. These would need to be adjusted, though I think the implications for a point-point connection may not be too severe.
Besides doppler shift, which could be a problem depending on how agile the ground station is, the modulation scheme (it's NOT simply FM) uses about 20 mhz of bandwidth, so you will need significant power to get the 20db S/N needed to decode anything halfway reliably. Remember, a typical AP runs 100mw on 2.4 ghz, and gets reliable communication over distances of 100's of FEET with omni antennas. Add some gain on both ends (so now you need attitude control on the satellite!), and you can go a few miles. But 100's of miles to orbit? I need someone to "do the numbers", but I bet it's not too good.
Greg KO6TH
Hi all,
wifi over long distance is a reality on earth-based point-to-point links, with distances up to 200miles. The long distance means long latencies, thus the standard wifi protocol needs to be modified. It exists today implementations of the modified protocols for the WRT54G router.
To cope with the link budget you need higher power (i.e power amplifier) and high gain antennas, and this should not be a big deal even on a spacecraft, although I am a bit concerned on the possibility of fitting a high gain antenna on top of a cubesat. Maybe it would be feasible at 5GHz, but in any case you would need 3 axes stabilization of the spacecraft.
What looks more difficult to me is the Doppler shift compensation, as the wifi transceivers do not have (at least to my knowledge) the possibility to fine tune the channel frequency.
I know that long range wifi has been investigated on south america to help connecting isolated villages in the jungle, and by a group of Italian researchers (http://www.ixem.polito.it/index_e.htm), and a high datarate link has been established with a stratospheric balloon.
It is an interesting discussion topic, and I hope somebody with more experience on the topic will jump into the discussion.
Simone IW1FYV
2013/2/22 Greg D ko6th.greg@gmail.com
Lee Maisel wrote:
James French wrote:
What are the possibilities of building a satellite that uses a Linksys WRT54GL router with a modified DD-wrt or HSMM-Mesh software as a store and forward BBS, to route a received request from one station to another station, or even to connect to a on board networked camera to receive images?
What kind of uplink power would be needed from the home station?
How fast could the speed(s) get theoretically?
How big would the antenna have to be on the craft and for the ground station to even be able to do this adequately?
Would the doppler be too much to even consider this?
Would the space environment be too harsh for something like this?
This is just something I was thinking about this morning and thought I would toss it out.
James W8ISS
______________________________**_________________
THAT is an AWESOME Idea!
I don't see why it wouldn't work, I don't know if doppler is an issue though, it may not be if the modulation is FM. The antenna would not have to be big, it's 2.4Ghz
Why don't you post this on the HSMM-MESH.org web forums and get ideas?
73 Lee W5LMM
Hi James, Lee,
If you are thinking of using standard Wi-Fi as the link protocol, be aware that the timers that drive the protocol don't well work over long distances (few miles). Something about the speed of light not being fast enough. Real bummer. These would need to be adjusted, though I think the implications for a point-point connection may not be too severe.
Besides doppler shift, which could be a problem depending on how agile the ground station is, the modulation scheme (it's NOT simply FM) uses about 20 mhz of bandwidth, so you will need significant power to get the 20db S/N needed to decode anything halfway reliably. Remember, a typical AP runs 100mw on 2.4 ghz, and gets reliable communication over distances of 100's of FEET with omni antennas. Add some gain on both ends (so now you need attitude control on the satellite!), and you can go a few miles. But 100's of miles to orbit? I need someone to "do the numbers", but I bet it's not too good.
Greg KO6TH
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Apart from power budget issues and Doppler the real killer will be the very high noise level on 2.4 GHz.
In urban areas you can expected to receive strong WiFi signals across all of 2402-2450 almost regardless of where you beam.
Any signals from a satellite would need to be strong enough to overcome this interference. 5 GHz is likely to suffer a similar problem in a few years as more use is made of that band for WiFi etc.
73 Trevor M5AKA
Maybe Drew KO4MA will reply--but I thought he did some "global listening" on 2.4GHz with AO-51 (frequency agile receiver). Seems like he published some plots in The Journal?
Take home from what I recall--it was very noisy!
Mark N8MH
On Fri, Feb 22, 2013 at 10:49 AM, Trevor . m5aka@yahoo.co.uk wrote:
Apart from power budget issues and Doppler the real killer will be the very high noise level on 2.4 GHz.
In urban areas you can expected to receive strong WiFi signals across all of 2402-2450 almost regardless of where you beam.
Any signals from a satellite would need to be strong enough to overcome this interference. 5 GHz is likely to suffer a similar problem in a few years as more use is made of that band for WiFi etc.
73 Trevor M5AKA
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Yes, 2.4 GHz was very noisy. AMSAT Eagle was to use a 3.4 GHz high-speed (0.5-1 Mbps) BPSK downlink. BPSK was chosen for maximum efficiency in the PA. WiFi and WiMAX use complex modulation schemes that are optimized for terrestrial applications where the signal is diffused and scattered by nearby objects. This results in a PA DC to RF conversion efficiency of less than 20%.
73,
John KD6OZH
----- Original Message ----- From: "Mark L. Hammond" marklhammond@gmail.com To: "Trevor ." m5aka@yahoo.co.uk Cc: "amsat-bb" amsat-bb@amsat.org Sent: Friday, February 22, 2013 16:20 UTC Subject: [amsat-bb] Re: 2.4GHz broadband router on satellite?
Maybe Drew KO4MA will reply--but I thought he did some "global listening" on 2.4GHz with AO-51 (frequency agile receiver). Seems like he published some plots in The Journal?
Take home from what I recall--it was very noisy!
Mark N8MH
On Fri, Feb 22, 2013 at 10:49 AM, Trevor . m5aka@yahoo.co.uk wrote:
Apart from power budget issues and Doppler the real killer will be the very high noise level on 2.4 GHz.
In urban areas you can expected to receive strong WiFi signals across all of 2402-2450 almost regardless of where you beam.
Any signals from a satellite would need to be strong enough to overcome this interference. 5 GHz is likely to suffer a similar problem in a few years as more use is made of that band for WiFi etc.
73 Trevor M5AKA
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
-- Mark L. Hammond [N8MH] _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
--- On Wed, 27/2/13, John Stephensen kd6ozh@comcast.net wrote:
Yes, 2.4 GHz was very noisy. AMSAT Eagle was to use a 3.4 GHz high-speed (0.5-1 Mbps) BPSK downlink.
In terms of noise a 3400-3410 MHz satellite band would have a lot going for it, unfortunately it isn't a Global Amateur-satellite allocation - it's not available in 1/3 of the World (Region 1).
73 Trevor M5AKA
participants (5)
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Greg D -
John Stephensen -
Mark L. Hammond -
Simone -
Trevor .