What is the maximum bits-per-symbol possible using FSK on telephone devices?
in [DSP]
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From: Green Xenon on 17 Dec 2009 22:48 >Green Xenon wrote: >>> Green Xenon wrote: >>>>> Green Xenon <green_xenon1(a)yahoo.com> wrote: >>>>> >>>>>> [glen writes] >>>>>>> All the FSK I know of are one bit/symbol. >>>>>> Isn't MFSK [Multiple Frequency Shift Keying] a form of FSK that uses >>>> more >>>>>> than 1-bit-per-symbol? >>>>> Does the M stand for Multiple or does it mean Minimal? >>>> M stands for multiple >>> Can you cite an example? >> >> Quote from http://en.wikipedia.org/wiki/Multiple_frequency-shift_keying : >> >> "Multiple frequency-shift keying (MFSK) is a variation of frequency-shift >> keying (FSK) that uses more than two frequencies." > >Thanks. > >You wrote in another post that 1 symbol/sec satisfies you. Since >sampling for a second theoretically yields 1 Hz resolution, that's a lot >of frequencies in the telephone voice band. Using a spacing of 2 Hz to >allow for less-than-ideal conditions, and taking the band to be 300 to >8,000 Hz, you can see that it is trivially simple to get 3,850 bits in a >symbol provided you can synchronize properly. Now, 2^3850 is a big >number, nearly 10^1159. What will you do with an alphabet of that many >letters? > If 3,580-bits-per-symbol can be done in FSK using telephone systems, then why isn't it already being done? You said it is "trivially simple".
From: glen herrmannsfeldt on 18 Dec 2009 01:48 Jerry Avins <jya(a)ieee.org> wrote: (snip) > Thanks. > You wrote in another post that 1 symbol/sec satisfies you. Since > sampling for a second theoretically yields 1 Hz resolution, that's a lot > of frequencies in the telephone voice band. Using a spacing of 2 Hz to > allow for less-than-ideal conditions, and taking the band to be 300 to > 8,000 Hz, you can see that it is trivially simple to get 3,850 bits in a > symbol provided you can synchronize properly. Now, 2^3850 is a big > number, nearly 10^1159. What will you do with an alphabet of that many > letters? That should be 4kHz. Also, the bits/symbol is log2(number of possible symbols), so log2(1850). Half the bandwidth might be enough to recover the clock. That is, to know when the symbol transitions occur. There needs to be enough (or sufficient) frequency changes such that the receiver can detect where they occur, and not lose sync. A more efficient way is to use multiple BFSK carriers not overlapping in frequency space. Then you do get a large number of bits. -- glen
From: Green Xenon on 18 Dec 2009 06:23 >Green Xenon wrote: >>> Green Xenon wrote: >>>>> Green Xenon wrote: >>>>>>> Green Xenon <green_xenon1(a)yahoo.com> wrote: >>>>>>> >>>>>>>> [glen writes] >>>>>>>>> All the FSK I know of are one bit/symbol. >>>>>>>> Isn't MFSK [Multiple Frequency Shift Keying] a form of FSK that >> uses >>>>>> more >>>>>>>> than 1-bit-per-symbol? >>>>>>> Does the M stand for Multiple or does it mean Minimal? >>>>>> M stands for multiple >>>>> Can you cite an example? >>>> Quote from http://en.wikipedia.org/wiki/Multiple_frequency-shift_keying >> : >>>> "Multiple frequency-shift keying (MFSK) is a variation of >> frequency-shift >>>> keying (FSK) that uses more than two frequencies." >>> Thanks. >>> >>> You wrote in another post that 1 symbol/sec satisfies you. Since >>> sampling for a second theoretically yields 1 Hz resolution, that's a lot >> >>> of frequencies in the telephone voice band. Using a spacing of 2 Hz to >>> allow for less-than-ideal conditions, and taking the band to be 300 to >>> 8,000 Hz, you can see that it is trivially simple to get 3,850 bits in a >> >>> symbol provided you can synchronize properly. Now, 2^3850 is a big >>> number, nearly 10^1159. What will you do with an alphabet of that many >>> letters? >>> >> >> If 3,580-bits-per-symbol can be done in FSK using telephone systems, then >> why isn't it already being done? You said it is "trivially simple". > >Now it's time to put those 154 I's ans Q's to work. See how those >numbers hang together -- or don't. What do you mean?
From: Green Xenon on 18 Dec 2009 06:26 >Green Xenon wrote: >>> Green Xenon wrote: >>>>> Green Xenon wrote: >>>>>>> Green Xenon <green_xenon1(a)yahoo.com> wrote: >>>>>>> >>>>>>>> [glen writes] >>>>>>>>> All the FSK I know of are one bit/symbol. >>>>>>>> Isn't MFSK [Multiple Frequency Shift Keying] a form of FSK that >> uses >>>>>> more >>>>>>>> than 1-bit-per-symbol? >>>>>>> Does the M stand for Multiple or does it mean Minimal? >>>>>> M stands for multiple >>>>> Can you cite an example? >>>> Quote from http://en.wikipedia.org/wiki/Multiple_frequency-shift_keying >> : >>>> "Multiple frequency-shift keying (MFSK) is a variation of >> frequency-shift >>>> keying (FSK) that uses more than two frequencies." >>> Thanks. >>> >>> You wrote in another post that 1 symbol/sec satisfies you. Since >>> sampling for a second theoretically yields 1 Hz resolution, that's a lot >> >>> of frequencies in the telephone voice band. Using a spacing of 2 Hz to >>> allow for less-than-ideal conditions, and taking the band to be 300 to >>> 8,000 Hz, you can see that it is trivially simple to get 3,850 bits in a >> >>> symbol provided you can synchronize properly. Now, 2^3850 is a big >>> number, nearly 10^1159. What will you do with an alphabet of that many >>> letters? >>> >> >> If 3,580-bits-per-symbol can be done in FSK using telephone systems, then >> why isn't it already being done? You said it is "trivially simple". > >Green, >you are using the term 'symbol' in a non-standard way. In >Data Comms, 'symbol' refers to the information being >conveyed e.g. the ASCII character set is made up of 128 >symbols and it takes 7 bits to represent each symbol. >The term you need instead of 'symbol' is 'state' which is a >combination of amplitude and either frequency and phase. >The related term 'Baud' is the number of state changes per >second. > >Regards, >John > Isn't baud the same thing symbol-per-second? 1 baud being 1-symbol-per-second? As for the term "symbol", QAM and PSK devices use it, so I thought FSK also uses it in a similar manner.
From: Clay on 18 Dec 2009 11:00
Flex - it is a Motorola propriatary paging standard. It uses 4 level FSK. It supports 4 mixes of rate and number of levels. Essentially the rates are 1600 or 3200 bauds and each baud can be either 1 or 2 bits. The header is always 1600 - 2 level and then may change to a higher data rate based upon the header's content. The 4 level data is grey encoded and FSK modulated on an RF carrier. The spec calls for a 10th order Bessel filter (IIRC cutoff = 3.8kHz) to be used to slew limit the modulation. The RF lives in a 25kHz wide channel, although the actuall spectral occupancy is much less. But the RF may be viewed as a 4 FSK. There's your example. Clay |