The goal of this research is to develop a compact system for improving the understandability of speech signals sent over military radio handsets from battlefield ground forces to nearby air support personnel. Interfering background noises in battle situations can include short, high intensity gunshot sounds from both friend and foe, as well as the more slowly varying sounds of helicopters, planes, tanks, trucks, wind, rain, etc. Acentech designed a noise cancellation device that effectively limits interference from transient gunshot noise without also limiting or distorting the transient speech signals themselves. The slowly varying background noises are more easily removed.

Our approach uses a small, closely spaced, 3-element microphone array and loudspeaker, along with digital signal processing elements, to provide an enhanced voice signal for radio transmission. This new technology, termed “PrivacyFone”, takes advantage of the array being in the acoustic near (induction) field of the talker and in the far field of the interfering sources. Differences in the directions of incidence between gunfire, other background noise, and the talker relative to the microphone array are also exploited by using array beam-forming to provide spatial discrimination that distinguishes the talker from background noise. The loudspeaker generates an acoustic signal at the array that adaptively reinforces the talker signal relative to noises from other directions. A further enhancement in the form of an adaptive interference canceller digitally cancels noise from directions other than along the array axis, which typically faces the talker. The adaptive filters maintain performance within a battlefield’s changing noise environment. These combined features enhance the talker signal and reject gunfire and other background noises.

Simulations of the resulting signal processing schemes demonstrate the ability of the system to recover intelligible voice signals, even when the voice is originally inaudible due to the presence of much louder gunshot and other battlefield sounds. The physical elements are to be incorporated within a small module that has been configured as an add-on to the mouthpiece of a standard military handset.