Research on Quasi-Synchronous Spread Spectrum Wireless LAN

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This Project has been performed from 1994 to 1995, for the purpose of investigating the applicability to an indoor wireless LAN of a quasi-synchronous spread spectrum communication system using real-valued orthogonal pseudonoise sequences to bring more communication channels than any other system and of offering an option of indoor wireless LANs. The codes that each terminal should communicate without interchannel crosstalk in a limited shift range are constructed by combining an orthogonal set of real-valued cyclic pseudonoise sequences and a shift-orthogonal real-valued finite-length pseudonoise sequence, are used for the experiment of indoor optical wireless LAN.It is shown that the interchannel and intersymbol crosstalks in the optical quasi-synchronous multiple access of narrow-or wide-band spread spectrum are suppressed to the similar low level as the theory suggests. The formation of digital ccorrelator, also investigated in this project, is expected to be useful for realizing t … More his system by ASICs. The achievements of this project are the followings.(1) Examination of the multi-path in the indoor wireless LANThe effcts of pillars and walls on radio wave propagation are examined by simulation. The 0.8mu-wavelength spread spectrum signal, reflected upon the walls and ceiling under fluorescent lamp illumination, is detected at the sufficient level.(2) Construction of the codes for multiple accessThe orthogonal set of the real-valued sequences, inserted by zero values, modulated by data, convolved with the real-valued finite-length sequence and leads to the codes to supress interchannel and interssymbol crosstalks.(3) Performance analysis of the quasi-synchronous multiple accessErrors of digital signal processing and noise effect on correlation output are analized.(4) Rating experiment of the indoor wireless LANThe experiment of the spread specrum optical wireless LAN designed in order that 128 terminals communicate within -1 to +1 chip shift, shows the 44-dB improvement of desired to undesired signal ratio. Less