Date of Completion

8-24-2015

Embargo Period

2-14-2016

Advisors

Jiong Tang, Xu Chen

Field of Study

Mechanical Engineering

Degree

Master of Science

Open Access

Campus Access

Abstract

Spread-spectrum communication, with its inherent interference attenuation capability, has become an increasingly popular technique in many different systems. Applications range from anti-jam systems, code division multiple access systems (CDMA), and systems designed to combat multi-path. Specific to the CDMA, it has strong anti-interference ability in which other communication system can not be compared with. Due to the broadband transmission, CDMA has strong anti-fading ability which makes the ratio of the useful signals much lower than the interference signal in the transmission channel.

To realize the CDMA System of Spread-spectrum communication, I incorporate a piezoelectric transducer to send spread spectrum code obtained from the M sequence ( the longest linear feedback shift register sequence). Also, for the future research of Spread-spectrum underwater communication, the underwater piezoelectric transducer is applied as the transmitting and receiving device whose frequency should be from 30KHz-300KHz， considering the attenuation and absorption of underwater sound wave. As a result, 50KHz or 200Khz is selected as the test frequency. In order to test the reliability and the accuracy of the piezoelectric transducer, the simulation of the transducer is needed. KLM model is applied in the research for model and simulation.

The design of spread sequence is the key technology of spectrum communication. White noise is a random process, which has excellent correlation characteristics. However amplification, detection, modulation, synchronization and control of the white noise are still unable to be realized up to now [1]. Therefore, the pseudo random sequence which has similar statistical characteristic can be regarded as the spread spectrum sequence in the spread spectrum system. There are several pseudo random sequences such as M sequence, Walsh sequence, Gold sequence and other [2]. Since the M sequence has good auto-correlation ability and cross-correlation characteristic, as well its easy generation, it was employed in this research finally.

To meet the frequency requirement of the transducer, the baseband signal needs to be translated into high frequency, which means that the modulation technology is essential. Modulation is able to move signal spectrum to any location, which is convenient to transmit the signal and make full use of spectrum resources. Also, the binary baseband digital signal without coding just shows the constant change of level. Low level and high level all can replace 1 or 0. For this kind of simplest baseband signal which has a long series of 1 or 0, the synchronization signal can not be extracted from the bit stream in the receiving end. To resolve both problems above, Manchester coding is applied [2]. Meanwhile, when the signal is translated by Manchester coding, the anti-interference ability and bandwidth are also improved.

To realize the full data transmission process, the data acquisition part is essential. Compared with varieties of data acquisition cards, the DAQ card PCIE-1816h is applied in the research, due to simple interface, easy testing, various programming support and moderate price.

Keywords: spread-spectrum communication, CDMA, piezoelectric transducer, KLM model, M sequence, Manchester coding, data transmission.

Major Advisor

Chengyu Cao

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