|Budget Amount *help
¥3,200,000 (Direct Cost : ¥3,200,000)
Fiscal Year 1998 : ¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1997 : ¥1,600,000 (Direct Cost : ¥1,600,000)
Code division multiple access (CDMA) is now being studied as the major system for future generations because of its high capacity, robustness against interference, and so on. ln asynchronous direct sequence (DS)/CDMA, each multiple access user communicates by using an individual pseudo noise (PN) sequence over a common channel. When multiple access interference (MM) arises from cross correlation between the desired user's sequence and other users' sequences, bit error rate (BER) performance will be degraded.
This paper proposes a novel asynchronous DS/CDMA communication system using analog PN sequences that have an orthogonal relation for all active users. Analog PN sequences are produced by an adaptive filter called "a code-orthogonalizing filter (COF)'. In a base station receiver, the tap coefficients of the COF can be adaptively controlled "to approach to orthogonalize" various received PN sequences. The elements of the analog PN sequences consist of the tap coefficients of the COF.The analog PN sequence produced is assigned to the transmitter of each user in order. As a result, MAI caused by other users can be reduced considerably.
First, good BER properties can be obtained for appropriate parameters (step size and convergence decision criterion of LMS algorithm in COF, and amplitude limiting level in the process of producing the analog PN sequence) in an AWGN environment. Second, fast convergence properties of COF are discussed. Third, as practical applications, several characteristics of the system performance in a Rayleigh fading environment are shown by computer simulations. Next, an influence of quantization error is discussed when the analog PN sequences are transmitted to users. Further, we modify the method of producing analog PN sequences, considering the moving of mobile. Finally, we evaluate the effect considering MAI from the neighboring cell by the proposed system.