Accession Number:

ADA222995

Title:

Studies of ECCM Improvements for Frequency-Hopping CPFSK Systems

Descriptive Note:

Final rept.

Corporate Author:

LEE (J S) ASSOCIATES INC ARLINGTON VA

Personal Author(s):

Report Date:

1990-05-30

Pagination or Media Count:

130.0

Abstract:

The performance of frequency-hopping CPFSK modulations such as used in several Army radio systems in the presence of worst-case partial-band noise jamming WCPBNJ is derived for both limiter-discriminator and differential detector forms of receiver. The transmitter is assumed to repeat the data L times on different hops, and the receiver combines the L chips for each data symbol in a way to mitigate the effects of the jamming. Hard-decision combining simply makes a binary decision on each chip, then a majority decision on the whole symbol this limits a jammed chip to one vote. AGC combining weights each analog chip sample in inverse proportion to the received noise power and decides on the basis of the sum of weighted chip samples jammed chips tend to be weighted less. Analysis and computations show that either form of ECM combining can produce a 27 dB gain against WCPBNJ, and with error-control coding, a 31-33 dB gain. Coding alone can give a 28-29 dB gain. Soft decoding of hard-decision diversity combining gives 1.4 dB more gain than hard decoding. It is also shown that, due to the spectral attenuation characteristics of the receivers IF filter, the effects of the transient phase difference between the incoming hopping waveform and the receivers synthesizer are primarily confined to an interval of duration T ts tau, where T is the symbol duration inverse of IF bandwidth, ts is the synthesizer switching time, and tau is the offset in synchronization between the received signal and the receivers synthesizer.

Subject Categories:

  • Countermeasures

Distribution Statement:

APPROVED FOR PUBLIC RELEASE