The effect of a multitone jammer on frequency-hopped FSK is evaluated when the tones are generated by modulating a carrier by a sinusoidal waveform. Theoretical expressions are given for M-ary FSK, and numerical computations for the binary case are shown. The results indicate that such a tone jammer has nearly the same effect as an ideal tone jammer with an equivalent number of tones.

The spectral density of the sonic-boom N-wave pressure time function is derived simply. The analysis method employed herein is one that avoids the usual method of integration by parts in computing the Fourier transform of any function made up of straight line segments such as an ideal N-wave pressure signature. The dominant first peaks of the normalized energy spectral density are plotted for different sonic-boom durations. The results modify those given earlier by Young [J. Acoust. Soc. Am. 40, 496–498 (L) (1966)].

Reproduction in whole or in part is permitted for any purpose of the United States Government. "o: 17. DISTRIBUTION STATEMENT (of the abttract entered In Block 20. II dltttrant from Report) \:V'. r-.\ IS. SUPPLEMENTARY NOTES See Reverse Side 19. KEY WORDS (Continue on revet»* »Id* It neceetary and Identity by block number) Multiplicative Array Detection Receiver Operating Characteristics Bearing Estimation DISTHtBUiiC'NliTAtEMESf Ä"" 1 20. ABSTRACT (Continue on reverie eld* It neceeeary and Identity by block number) Investigation is made of a "multiplicative" receiver array to determine its capability as signal detector ard bearing estimator. The same analyses are made of the conventional square-law array for comparison purposes. The probability density functions for the filter outputs of array models are obtained for these arrays for the input signals consisting of monochromatic signals and narrowband additive Gaussian noise. The number of sensor elements, SNR, source bearing, and interelement noise correlation, are treated, as DD (J FORM AN 73 1473 EDITION OF 1 NOV 65 IS OBSOLETE

The function of the receiver in a binary digital communication system is to make a binary ("space", "mark" or "O", "'1") decision by comparing the signal values from the mark and space filters (or correlators) at known successive time intervals ("bit" or "baud" time intervals). When the signal value out of the mark filter is greater than that out of the space filter, it is decided that mark or 1 is transmitted, and vice versa. It is of fundamental importance to know the exact instant of time at which the two filter outputs are to be compared. This is the problem of synchronization between the transmitter and the receiver. In this paper, we assume a system that is perfectly synchronized. In a practical system, the difference between the two filter outputs must differ from a threshold by some finite amount in order to cause the device to respond reliably. The examination of the effects of this dead zone (finite-width decision threshold) on digital transmission systems is of important practical interest. Its effects on binary differentially coherent phase-shift-keying, and m-level phase-shift-keying systems have been investigated previously. In this paper we consider its effects on binary coherent phase-shiftkeying (CPSK), coherent orthogonal (CFSK), and noncoherent orthogonal (NCFSK) systems. The probability of bit error and the channel capacity of each system is obtained in terms of the dead zone threshold. For the error probability computation, a randomized decision rule is employed whenever the difference between the mark and space filter output at decision time is less than or equal to the dead zone threshold. The analyses are carried out based on the binary symmetric erasure channel (BSEC) model of each system.

The Jammed Hop Elimination (JHE) receiver is analyzed for a multiple ( L ) hops/bit frequency-hopping binary FSK spread spectrum (FH/BFSK/SS) communication system in the partial-band noise jamming channel. The basic structure of the JHE receiver is the standard diversity combiner modified to use "side information" on the presence or absence of jamming on each hop. The goal of this paper is to observe the performances of three different variations of the standard combiner, including the JHE receiver, that result from different assumptions about the use of side information, processing of jammed hops, and the presence or absence of system background noise. The receiver schemes considered are: