Communication Circumstances Research Articles

Secure communication: quantum cryptography with a photon turnstile.

Quantum cryptography generates unbreakable cryptographic codes by encoding information using single photons, which until now have relied on highly attenuated lasers as sources1,2. But these sources can create pulses that contain more than one photon, making them vulnerable to eavesdropping by photon splitting3,4. Here we present an experimental demonstration of quantum cryptography that uses a photon turnstile device, which is more reliable for delivering photons one at a time. This device allows completely secure communication in circumstances under which this would be impossible with an attenuated laser.

The perception of Chinese speech sounds in masking noise and frequency distortion

The intelligibility tests of Chinese speech sounds were taken under five masking conditions, namely white noise, pink noise, speech noise, meaningful speech interference, and reverberation masking in auditorium, as well as under a quiet studio condition. To simulate the actual communication circumstances, the noise was introduced to input and output ends, respectively. The signal to noise ratios were varied with a fixed speech level about 80 dB at 1 m from the loudspeaker. In addition, the speech and noise were processed with high-pass, low-pass, or band-pass filtering except in reverberation. A set of simplified but rather sensitive word lists which were based on varying the initial consonants because of the higher sensitivity of initials to masking than finals were used. The effects of masking and frequency distortion on the perception of individual Chinese speech sounds will be presented in this report, with the conclusion that monosyllabic Chinese words or “characters” should be considered as an integral part of sound unit. The tones (or inflection of pitch) with patterns preserved are demonstrated by tape recordings.