Re: [digitalradio] A question about spread spectrum
It is still valid, Ted, and is described such in the Wikipedia http://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrum. I think the FCC rules are definitely out of date, but identification is essential to being about to share frequencies, so any code that prevents that has no place on the ham bands. ROS is not like that, though, since the synchronization is apparently contained in the reception code, so anybody can copy. The FCC rules need to be amended, but that needs to be done by petition. Until that is done, we are required to follow the current rules whether we agree with them or not. The other possible problem is wide-spreading spread spectrum. There was a failed attempt about 5 years ago by the ARRL HSMM (High Speed Multi-Media) proponents to allow spread spectrum on the HF bands with the argument that the signal is spread so widely, each carrier appears at any given frequency only a short time, so it would not significantly interfere with other users of the frequency, and could, for example, be allowed to cover the entire 20m band. However, that assumes only one FHSS signal at a time. I think if you put on many at one time, in the resulting aggregate, there could be continuous interference over the entire width of the spectrum spread, since the spreading is pseudorandom. You can see what happens when just more than one ROS user tries to use the same frequency. They interfere with each other. A /million monkeys/ with typewriters will eventually write a Shakespeare play. 73 - Skip KH6TY theophilusofgenoa wrote: I had the idea that a reason spread spectrum was not legal was that the use of a psuedo-random spreading sequence lent itself to the development of an unbreakable code (or at least a difficult to break code) that would allow secret communications by people inimical to the good old USA. And I think that is a valid point. Ted Stone, WA2WQN
Re: [digitalradio] A question about spread spectrum
El 06/03/2010 9:01, KH6TY escribió: The other possible problem is wide-spreading spread spectrum. There was a failed attempt about 5 years ago by the ARRL HSMM (High Speed Multi-Media) proponents to allow spread spectrum on the HF bands with the argument that the signal is spread so widely, each carrier appears at any given frequency only a short time, so it would not significantly interfere with other users of the frequency, and could, for example, be allowed to cover the entire 20m band. However, that assumes only one FHSS signal at a time. I think if you put on many at one time, in the resulting aggregate, there could be continuous interference over the entire width of the spectrum spread, since the spreading is pseudorandom. You can see what happens when just more than one ROS user tries to use the same frequency. They interfere with each other. That is affectively a limit with CDMA cellphones. Even when using different codes, they are not 100% orthogonal and the result is a degradation of SNR. It requires a multiplicity of non overlapping cells and automatic power control to be viable. Using a single coding sequence, access method such as those used in packet to share the channel should be enforced as well. Not a simple matter, as the hidden station is a concrete fact. 73, Jose, CO2JA
Re: [digitalradio] A question about spread spectrum
The HSMM working group never proposed the use of spread spectrum. It was interested in getting the maximum data rate into limited bandwidths. SS does the opposite of what the HSMM WG was interested in. It spreads limited amounts of data over the maximum bandwidth. The actual proposal was to create small segments in the 80, 40, 20 and 15 meter bands for emissions up to 16 kHz wide -- matching what existed in the 10 meter band but on a much smaller scale. Many of us wanted that limited to 9 kHz -- the same as the ARRL allowed for AM. The goal was to preserve the priveledges that currently exist in the phone/image segments (AM equivalent bandwidth) as the ARRL was shrinking bandwidths in the RTTY/data segments (currently unlimited bandwidth). 73, John KD6OZH - Original Message - From: KH6TY To: digitalradio@yahoogroups.com Sent: Saturday, March 06, 2010 14:01 UTC Subject: Re: [digitalradio] A question about spread spectrum The other possible problem is wide-spreading spread spectrum. There was a failed attempt about 5 years ago by the ARRL HSMM (High Speed Multi-Media) proponents to allow spread spectrum on the HF bands with the argument that the signal is spread so widely, each carrier appears at any given frequency only a short time, so it would not significantly interfere with other users of the frequency, and could, for example, be allowed to cover the entire 20m band.
Re: [digitalradio] A question about spread spectrum
Thanks, John. I stand corrected. It has been quite a few years since that time and my recollection was that the argument was that the signal lasted such a short time on any one frequency that it would not create significant QRM, but that also may have been a misunderstanding on my part, or simply not what was proposed. 73 - Skip KH6TY John B. Stephensen wrote: The HSMM working group never proposed the use of spread spectrum. It was interested in getting the maximum data rate into limited bandwidths. SS does the opposite of what the HSMM WG was interested in. It spreads limited amounts of data over the maximum bandwidth. The actual proposal was to create small segments in the 80, 40, 20 and 15 meter bands for emissions up to 16 kHz wide -- matching what existed in the 10 meter band but on a much smaller scale. Many of us wanted that limited to 9 kHz -- the same as the ARRL allowed for AM. The goal was to preserve the priveledges that currently exist in the phone/image segments (AM equivalent bandwidth) as the ARRL was shrinking bandwidths in the RTTY/data segments (currently unlimited bandwidth). 73, John KD6OZH - Original Message - *From:* KH6TY mailto:kh...@comcast.net *To:* digitalradio@yahoogroups.com mailto:digitalradio@yahoogroups.com *Sent:* Saturday, March 06, 2010 14:01 UTC *Subject:* Re: [digitalradio] A question about spread spectrum The other possible problem is wide-spreading spread spectrum. There was a failed attempt about 5 years ago by the ARRL HSMM (High Speed Multi-Media) proponents to allow spread spectrum on the HF bands with the argument that the signal is spread so widely, each carrier appears at any given frequency only a short time, so it would not significantly interfere with other users of the frequency, and could, for example, be allowed to cover the entire 20m band.
