ame way within a given set. Since a maximum is sought in each symbol interval, the ordering is unimportant and thus in each case a decision is made among M energy detections corresponding to an input of Ts sec of a given MFSK tone and T sec of the adjacent transmitted tone. For the last symbol of that hop, however, only Ts - T sec of the corre- sponding MFSK tone is available for energy detection, the remaining T sec corresponding to noise only. As T increases beyond Ts sec, fewer and fewer symbol decisions will be based upon a full Ts sec of input signal. Finally, when T = Th, the entire mixer difference signal will contain noise only. For SFH/MFSK with diversity m, the appropriate serial search acquisition system reverts back to one resembling Figure 3.5, where the outputs of the M non-coherent demodulators are now individually summed over the m chips (one per hop) corresponding to a given symbol. As such, the integrate- and-dumps in each non-coherent demodulator operate over a chip interval NON-COHERENT DEMODULATOR IF-'s SELECT NON-COHERENT DEMODULATOR LARGEST FIF $2 Ts sec RECEIVED SIGNAL FILTER NON-COHERENT DEMODULATOR FREQUENCY fIF-SM SYNTHESIZER COUNT GENERATOR ThiTs EPOCH STEP SEARCH THRESHOLD CONTROL (CLOCK) COMPARISON END SEARCH Figure 3.7. A serial search acquisition system for SFH/MFSK. NON-COHERENT DEMODULATOR M 52 sin 2(fif-si)t ( ) 2 Figure 3.7. (continued) MFSK SEQUENCE FA(2) q(13) 1/131 TRANSMITTED HOP SEQUENCE RECEIVED SFH/MFSK f2+1;(2)+81 f2+fk(2)+8f f3+f;(3)+8f SEQUENCE FH SYNTHESIZER f++IF f2+f/F 13+fIF SEQUENCE MIXER DIFFERENCE INDICATES COMPONENTS NOT EFFECTIVE FOR CORRELATION DETECTION Figure 3.8. Received SFH/MFSK signal and local hop signal misaligned by less than a single hop interval. FH Acquisition Techniques corresponding to Tlm and the demodulator outputs must be delayed by intervals of Th sec before accumulation. To evaluate the performance of the various serial search FH/MFSK acqui- sition systems in the presence of noise, we must determine their operating characteristic, i.e., th