Spread spectrum FH-MFSK transmitter and receiver

A transmitter for use in a spread spectrum radio system for generating a frequency-hopping, multilevel frequency shift keyed (FH-MFSK) signal, the transmitter comprising:

• a Q level encoder (12), where Q is a prime or an integer power of a prime, capable of converting either one of a periodic sample of an analog message signal and a group of K sequential message bits of a binary signal into an equivalent level of a Q level code and generating an output signal indicative of such equivalent level;
• and
• a frequency-hopping address generating means (16) capable of generating as an output signal an L-length frequency-hopping address sequence which is associated with a particular user whose message signals were converted by the Q level encoder, where the address sequences of all users have a common algebraic structure and the particular address of each user is determined by that user's unique parameter
• characterized in that
• the transmitter further comprises:
• adding means (20) capable of adding corresponding elements of the output signals of the Q level encoder and the frequency-hopping address generating means in accordance with the rules of algebra for finite fields during each period of the L-length sequence and generating an output signal indicative of such addition;
• and
• a frequency generator (22) capable of generating a FH-MFSK output signal representative of the output signal from said adding means.

A method of decoding one or more concurrently received frequency-hopping, multilevel frequency shift keyed (FH-MFSK) signals which were originally generated by modulating a separate one of a plurality of different L-length frequency-hopping address sequences with each user's separate signal sample where each signal sample is encoded as one of Q possible frequencies where Q is a prime or an integer power of a prime and the address sequences of all users have a common algebraic structure and the particular address of each user is determined by that user's unique parameter, the method comprising the steps of:

• (a) spectrum analyzing the received signals for determining which of the possible Q frequencies are preent in the received FH-MFSK signals during each period of the L-length sequence
• characterized in that
• the received FH-MFSK signals were originally formed by adding corresponding elements of each user's signal sample and each user's associated frequency-hopping address sequence in accordance with the rules of algebra for finite fields during each period of the L-length sequence, the method comprising the further step of:
• (b) decoding the received signals by adding the binary value of the Q frequencies determined as present in step (a) with a desired user's frequency-hopping address sequence during each period of the L-length sequence in accordance with the rules of algebra for finite fields to generate a Q level by L-length set of decoded signals.