Spread spectrum FH-MFSK decoder

Claim 1

A decoding arrangement (32) for decoding one of one or more concurrent L-length frequency-hopped, Q-level frequency shift keyed input signals, each input signal being originally formed by modulating a particular user's L-length frequency-hopping address sequence with the particular user's message signal encoded as one of Q possible frequencies, where Q is a prime or an integer power of a prime; the decoding arrangement comprising: spectrum analyzing means (46) capable of generating an output signal indicative of the presence of each of the Q possible frequencies in the input signal thereto; and frequency-hopping address generating means (40) characterized in that the frequency-hopping address generating means (40) is capable of generating a first and a second L-length frequency-hopping address sequence associated with a particular user in the same and next lower band, respectively, of Q frequencies as the band of Q frequencies in the input signal to the decoding arrangement, the decoding arrangement further comprising: an image rejection mixer (36) capable of mixing frequencies of said first L-length address sequence and only the frequencies equal to or above said first address sequence in corresponding intervals in the input signal to the decoding arrangement for generating an output signal comprising difference frequencies within Q baseband frequency levels; a second mixer (38) capable of mixing frequencies of said second L-length address sequence and the frequencies in corresponding intervals in the input signal to the decoding arrangement for generating an output signal comprising difference frequencies within said Q baseband frequency levels; a combiner (44) capable of adding the output signals from said mixers and generating an output signal representative of such addition for subsequent spectral analysis by the spectrum analyzing means; and decision means (48) capable of determining which of the Q baseband frequency levels in the output signals of the spectrum analyzing means have a maximum value or length over said L-length sequence, and where more than one maximum value or length frequency level is found, choosing one of said maximum frequency levels.

Claim 5

A method of decoding one of one or more concurrently received L-length frequency-hopped, Q-level frequency shift keyed input signals, each input signal being originally formed by modulating a particular user's L-length frequency-hopping address sequence with the particular user's message signal encoded as one of Q possible frequencies, where Q is an integer characterized in that the method comprises the steps of: (a) mixing the frequencies of the particular user's frequency-hopping address sequence which are in the same band of Q frequencies as the input signal with the frequencies in the received input signal which are equal to or above the corresponding address sequence frequencies in each L-length sequence for generating a resultant signal comprising difference frequencies within Q baseband frequency levels; (b) concurrent with step (a) mixing the frequencies of the particular user's frequency-hopping address sequence which are in the next lower band of Q frequencies than the input signal with the frequencies in the received input signal for generating difference frequencies within the Q baseband frequency levels of step (a); and (c) combining the resultant signals generated in steps (a) and (b) for generating a demodulated and decoded output signal.

Claim 6

A method of decoding one of one or more concurrently received L-length frequency-hopped, Q-level frequency shift keyed input signals, each input signal being originally formed by modulating a particular user's L-length frequency-hopping address sequence with the particular user's message signal encoded as one of Q possible frequencies, where Q is an integer characterized in that the method comprises the steps of: (a) mixing the frequencies of the particular user's frequency-hopping address sequence which are in the same band of Q frequencies as the input signal with the frequencies in the received input signal which are equal to or above the corresponding address sequence frequencies in each L-length sequence for generating a resultant signal comprising difference frequencies within Q baseband frequency levels; (b) concurrent with step (a) mixing the frequencies of the particular user's frequency-hopping address sequence which are in the next lower band of Q frequencies than the input signal with the frequencies in the received input signal for generating difference frequencies within the Q baseband frequency levels of step (a); and (c) combining the resultant signals generated in steps (a) and (b) for generating a demodulated and decoded output signal.