The document that the author of ROS originally published, "Introduction to ROS: The Spread Spectrum", contains a good description of frequency-hopping spread-spectrum (FHSS) techniques. Section 4 describes taking a 250 Hz wide mode (MFSK16) and spreading it over 2 kHz by shifting the center frequency in a pseuorandom sequence. The receiver changes frequencies in the same sequence and the logic used to detect a special tone sequence to obtain synchronization is described in section 5. The amount of spectrum occupied increases by a factor of 8. FHSS is one way to minimize the effects of multipath spread but there are also other techniques that occupy less spectrum.
Note that the author of ROS published a second doucument,"ROS Technical Description", that contains elements of the original but does not mention FHSS and omits any description of how data is mapped to tones. Users comparing the original and later versions of the code haven't seen a difference in the transmitted spectrum. 73, John KD6OZH ----- Original Message ----- From: Rein A To: [email protected] Sent: Friday, March 05, 2010 19:16 UTC Subject: [digitalradio] What is SS? Here is a reprint that for my limited mental capacities defines the core quite well. I have asked Mike the author for some references, no lack of trust though. --------------------------------------------------------- > -----Original Message----- > >From: n4qlb <n4...@...> > >Sent: Mar 5, 2010 1:15 PM > >To: [email protected] > >Subject: [ROSDIGITALMODEMGROUP] Re: How do you like ROS Now? > > > >Thank You for your comments Sig. Let me explain what SS is. Spread spectrum is a method by which a bank of channels (Frequencies)are designated between a Transmitter and Receiver and are shared or (Frequency Hopped) to facilitate a clear Transmisson. The Transmitter actually signals the Receiver to Hop from one frequency to another. A good example is a 900mhz digital cordless telephone or a 800Mhz digital radio truncking system. (Motorla Astro). A frequency in Ham radio consist of a 3kh wide channel. Ros does not signal a receiver to hop outside of that channel (3 Khz) therefore it is not SS and is just like anyother FSK mode used in the amatuer radio service. The ease of obtaining a License in the U.S. by people that are not technically qualified to hold one is the main culprit regarding the controversy over new modes such as ROS. I am confident that all variations of ROS are perfectly legal in the U.S. > > >
