[amsat-bb] Re: Two hundred 437 MHz satallites launch March 16 + WebSDR

[Howie DeFelice]

Hi Wouter,

I personally agree with the ITU recommendations and think that CDMA/ spread spectrum techniques can be useful for amateur satellite communications. Unfortunately individual national regulatory entities (especially the U.S. FCC) can take a very long time to adopt ITU recommendations.  Current FCC rules define three spreading sequences based on defined tapped linear sequence generators; one 7 bit, one 13 bit and one 19 bit. That makes it difficult to deploy an effective CDMA system. I am sure provisions could be made for a STA ( special temporary authority) but I would anticipate this to be an involved process. 

I believe the current efforts by the ARRL to give amateurs more flexibility by adopting maximum bandwidth restrictions vs maximum symbol rate restrictions is a move in the right direction. If the purpose of amateur radio is to advance the state of the art, the rules need to be flexible enough to accommodate innovation. 

Of course, these are just the opinions of one person. I am sure there are as many opinions as there are subscribers to this list :) And yes, politics can be a great attenuator to progress... 

Howie, AB2S

Date: Sun, 9 Mar 2014 11:48:40 +0100
Subject: Re: [amsat-bb] Re: Two hundred 437 MHz satallites launch March 16 + WebSDR
From: wouterweg at gmail.com
To: howied231 at hotmail.com
CC: damonwa4hfn at gmail.com; amsat-bb at amsat.org

Howie,

CDMA is actually actively promoted by the ITU. Indeed all the details have to be published before launch, so everyone can demodulate it.

Citing from the ITU satellite-amateur
handbook: 
"Amateur
and amateur-satellite systems should have technical characteristics
that provide worldwide interoperability, and allow origination, relay
and termination of communications independent of other radio
services. Design emphasis should be placed on reliability, robustness
and flexibility of reconfiguration for efficient emergency
communications. Multiple access techniques (FDMA, TDMA and CDMA)
should be selected for optimum spectrum efficiency and frequency
reuse. The selection of modulation techniques should take into
account resistance to interference and immunity to adverse
propagation conditions."


I have been researching this for the QB50 mission, but strong pressures (mainly from the US) within the project killed the idea early on.

The US is now actively putting satellites in 70cm with experimental licenses, which unfortunately means they could use CDMA without providing the spreading codes. The (majority of the) rest of the world is still using the amateur satellite service.


Using CDMA would be beneficial for sharing the spectrum, but required coordination as well. I was trying to standardize the parameters (for QB50), so the IARU could be handing out orthogonal codes to satellite teams, so avoid clashes. But welcome to politics.....


Wouter PA3WEG


On Tue, Mar 4, 2014 at 10:16 PM, Howie DeFelice <howied231 at hotmail.com> wrote:

Yes, that is true, so are these licensed under an authority other than amateur radio ? If they aren't then my questions stand.




Date: Tue, 4 Mar 2014 14:55:52 -0600

Subject: Re: [amsat-bb] Re: Two hundred 437 MHz satallites launch March 16 + WebSDR

From: damonwa4hfn at gmail.com

To: howied231 at hotmail.com

CC: amsat-bb at amsat.org



70 CM is not just for the ham bands, it is a shared band check the ruleswa4hfn Damon



On Tue, Mar 4, 2014 at 2:30 PM, Howie DeFelice <howied231 at hotmail.com> wrote:



Is CDMA an authorized emission type for the Amateur service? What is the chipping rate/bandwidth of these? Don't the PRN sequences need to be made public so as not to be classified as "encryption" ? Detailed specs on the Sprites is in short supply. Has anyone done a link budget, seems like allot of spreading gain is required to hear 10mW form a 300km orbit which translates into allot of bandwidth in a part of the band usually reserved for narrow band modes. The lack of transparency on many of these projects that use the amateur bands seems to run against the spirit of amateur radio in my opinion.










Howie



AB2S



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