Julian,
By definition, it is SS "if" the pattern is independently generated from
the data. The original intent of FHSS was to make third-party decoding
impossible without knowledge of the code that generated the tones or
carriers. FCC rules disallow encryption because we are required to
police the bands ourselves. As long as there is not a pattern to the
frequencies generated, that is independent of the data, one of the
necessary and sufficient conditions to qualify as FHSS is missing.
However, in the case of ROS, the repeated pattern is not there, so,
until the regulations are changed, ROS is illegal FHSS, even though the
spreading is limited and capable of third-party monitoring. That is a
result of a historical attempt to prevent encryption, but this can
probably be changed through the petition process with public comment.
Until then, hams in the US have no choice but to abide by the
regulations as written.
In the author's own words, three necessary and sufficient elements make
it SS, and a search of the literature says the same:
1. The signal occupies a bandwidth much in excess of the minimum
bandwidth necessary to send the information.
2. Spreading is accomplished by means of a spreading signal, often
called a code signal, which is independent of the data.
3. At the receiver, despreading (recovering the original data) is
accomplished by the correlation of the received spread signal with a
synchronized replica of the spreading signal used to spread the information.
The operative phase here is "independent of the data".
It is just unfortunate that the FCC regulations, as currently written,
do not allow ROS on HF and that they really need to be updated. Note
that SS is already permittted above 222 MHz, where there is plenty of
space to use for spreading that does not exist on HF. In fact, the
encryption aspect is not even mentioned, except in other parts of the
regulations disallowing encryption. The regulations were obviously
written to prevent extremely wide SS signals from interfering with other
users. Since ROS is no wider than a phone signal, there is no reason the
regulations should not be modified to allow it (perhaps with other
necessary limitations), but until then, and right now, ROS is illegal
below 222 Mhz. It is that simple!
Compare the repeated pattern of MFSK64 to the random pattern of ROS as
data is applied. Substituting a 2- page "technical description" which is
COMPLETELY different from the 7-page description of ROS as FHSS in an
obvious attempt to circumvent FCC regulations is simply not believable,
as an apparent twisting of the FCC's statement of illegality was
apparently not true either. Which "version" is to be believed? Well, we
don't need to decide that, and you apparently cannot believe anything
the author claims since he keeps claiming something else! Anyone,
including the FCC, can simply observe the differences in the spectral
footprint of each, which is plainly shown here in a comparison of MFSK64
and ROS 1 baud at 2200 Hz width:
http://home.comcast.net/~hteller/compare.zip
Note how the repetitive sending of data (........) does not result in
any repetitive pattern on ROS, but it does in MFSK64, and MFSK64 idles
with a repeated pattern, but ROS does not. The ROS tones are obviously
not determined by the data and are also pseudo-randomly generated -
definitely FHSS.
The FCC regulations describe permitted and not permitted (i.e. SS and
others) emissions. They could care less about what a mode is called or
how it is described by someone, because in the final analysis, we are
required to maintain our EMISSIONS per the regulations, or have the
regulations changed through the petition and public comment process.
Had the author not tried so hard to convince everyone that ROS was
Spread Spectrum, this debate would probably never have occurred. It was
the term, "Spread Spectrum" that raised red flags among US hams who are
knowledgeable of the regulations we operate under, and they were right
in realizing that, as a result, ROS is illegal on HF unless the
regulations are changed. The FCC then confirmed that through the ARRL.
73 - Skip KH6TY
g4ilo wrote:
Is the random or pseudo-random manner of generating the tones or
carriers an essential element of spread-spectrum? If so, and if the
aim of using such a method is not to obfuscate the message but only to
provide better immunity to interference and path variations, would you
be any worse off using a repeated pattern of tones instead of a
pseudo-randomly generated one? And if you did that, would it still be
spread-spectrum?
Julian, G4ILO
--- In digitalradio@yahoogroups.com
<mailto:digitalradio%40yahoogroups.com>, KH6TY <kh...@...> wrote:
>
> I can't fathom the reason for doing that, but if the tone frequencies
> are pseudo-randomly generated and then modulated by either on/off
keying
> or some other way, you will have a spread spectrum system, similar to
> what is done in the ROS 2200 Hz-wide modes. The tones in a ssb
> transmitter simply generate rf carriers, so varying the tone
frequencies
> is no different than varying a vfo frequency as far as the outside
world
> sees. The distinction in spread spectrum is the generation of the tone
> frequencies independently of the data. I.e., you first generate a tone
> frequency in a psudo-random manner and then convey intelligence by
> modulating the resulting rf carriers.
>
> 73 - Skip KH6TY
