Su altı akustiğinde doğrudan dizili yayılı İzge tekniğini kullanarak düşük güç ile mesafe ölçümü

Performance of direct sequence spread spectrum modulation (DSSS) in underwater acoustical range fi nding is investigated in this thesis. Range estimation using low power DSSS codes is both analyzed theoretically and implemented at 400 kHz for experimental assessment, where the chip duration is 20 us and sequence type is maximal. The eff ect of sequence length on the required transmit power is measured for sequence lengths from 7 chips to 127 chips. The performance of this method is compared to the widely used tone burst pulse range estimation technique. It is found that at a sequence of 127 chips and a pulse sequence length of 2,54 ms, range is estimated with 1,5 cm resolution using source level of 132,8 dB re 1 uPa rms @ 1 m source level , while it is 190,5 cm for the same length and magnitude tone burst modulation, at a reference test range of 4.5 m. Moreover, spectral height of received DSSS signal is well below the ambient noise level so that signal to noise ratio (SNR) for received DSSS signal is -14,8 dB, while it is 12,2 dB for received tone burst pulse. Keywords: Echo Sounding, Direct Sequence Spread Spectrum, Modulation,Range Estimation, Tone Burst Pulse