A novel beamformer for circular sonar arrays
A new Beamformer (BF) technique using Linear Deltamodulation (DM) on the spatially sampled circular array sensor signals is presented. In this method, the FIR-type of beam-former implementation for circular arrays results in an extremely simplified hardware which does away with multipliers and retains basically adders. Thus, the immediate problem of large word-size is considerably resolved. The DM-type of BF by virtue of the implementation, provides an additional advantage of beam-space interpolation. Various aspects of array gain, sidelobes and noise performance are dealt with the help of simulation studies. Hardware structures both for fixed and programmable beamformer coefficients are also proposed which bring out the potential of this technique for compact sonar systems.
Digital encoding and filtering using delta modulation
Digital filters are described which are based on delta modulation rather than pulse code modulation. It is shown that delta modulation encoding may be combined with digital filtering to realize either nonrecursive or recursive types. Conventional digital filter design techniques are applicable in both cases. Simulation of such filters on a small computer is discussed. Quantization noise is considered and comparisons made with the noise performance of the conventional digital filter.
Two Loop Adaptive Delta Modulation Systems
Two adaptive delta modulation (ADM) coders, one for A/D conversion of speech and the other for fiat spectrum signals, have been developed by incorporating a second adaptive feedback loop around the basic delta modulation (DM) coder. The dynamic range of the coder for integrated spectrum has been extended to more than 35 dB with a signal-to-noise ratio (SNR) > 28 dB, for a pulse-repetition frequency (PRF) of 32 kbits/s only, by using an adaptive circuit consisting of digital/analog slope detector and an FET expander. For flat spectrum signals, similar results with constant SNR over the band are obtained at a bit rate of 40 kbits/s. Thus the coders have performances equivalent to those of a 7-digit PCM, using only 32 and 40 kbits/s, respectively.