| Research Abstract |
The demand for wireless LAN for office automation, factory automation, security control system, computer communication, telecontrol, etc. has continued to increase. Spread spectrum (SS) communication system is the most promising for the wireless LAN, because of its excellent performance known as multiple access, anti-jamming, low probability of intercept, security and anti-detecting. Since the transmission bandwidth of a message in the SS system is spread far in excess of the information bandwidth using a fast PN code, S/N recovery so called process gain can be obtained. Spreading the spectrum causes the difficulty in correlating and synchronizing the PN codes between transmitter and a receiver. Using SAW (Surface Acoustic Wave) devices such as a convolver or correlator, the SS system can be implemented simply and compactly because the synchronization and correlation can be carried out asynchronously.
The purpose of this work is (1) to develop a new compact asynchronous SS modems using
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a highly efficient SAW convolver, which has been developed by one of the investigators, and (2) to develop a fundamental one-chip demodulator on the basis ofAlN/Al_2O_3 combination.
2.4 GHz band has been recently approved for SS communication in Japan as well as in USA.In this work, in order to improve the performance of the asynchronous SS modem using the SAW convolver, we have proposed, designed and evaluated (1) a DBM demodulation method, (2) a time window detection method, and (3) a base band error correction method. On the basis of these results, we have designed and implemented 2.4GHz full-duplex asynchronous SS modem using the SAW convolver. We progress toward the new SS modems for telecontrol, wireless digital voice communication and wireless handy terminals, etc.
We have successfully deposited on epitaxial AlN films on 2-in.-diam. alpha-Al_2O_3 substrate by MOCVD.AlN features the high SAW velocity (5910m/s), moderate mechanical coupling coefficient (1%) and zero-temperature-coefficient-of-delay characteristics. The SAW correlator and SAW delay line on a AlN/alpha-Al_2O_3 substrate were designed and fabricated. We have demonstrated direct detection of 2.4GHz SS signal to base band data.
The SS wireless modem using the SAW convolver and correlator has a great potential for wireless LAN. Less
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