| Summary: | 碩士 === 國立成功大學 === 電機工程研究所 === 84 === In DS/CDMA system, each channel is given its own spreading code
as channel distinction in order to transmit signal on the same
bandwidth. The performance of a CDMA system depends mainly on
the multiple access interference coming from other channel. The
cross-correlation of spreading codes is an important fact that
results in the interference. Because the cross-correlation of
aligned orthogonal codes is zero. orthogonal codes are
introduced to construct spreading codes by QUALCOMM.Generally,
orthogonal codes can be derived by the Walsh-Hadamard matrix.In
this thesis, a Walsh encoder and a Walsh decoder are proposed.
They are used in a DS/CDMA prototype design. The spreading
codes are composed of msequence code, Gold code and Walsh code.
The proposed Walsh encoder can be used as a Walsh code
generator. Several such Walsh code generators can generate
aligned different Walsh code sequences. The generated Walsh
codes used in the forward link make the spreading codes
orthogonal and reduce the interference. The Walsh code encoding
used in the reverse link improves the transmitted signal's
orthogonality. Because the auto-correlation of the Walsh codes
is not good, acquisition of the orthogonal covering may depend
on the acquisition of the pilot PN code in the forward link. It
can be achieved by proper desgin for the spreading code
structure. Such a design makes the forward link receiver able
to access multiple channels simultaneously by a pilot PN code
synchroniza- tion device. It simplifies the mobile station's
receiver.
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