N. Izuka and Y. Daido (Japan)
QAM, APSK, Honeycombed Constellation, CDMA, Interference Tolerance
This paper describes a proposed spreading method to improve a multiple access interference tolerance. The method is applied to a CDMA system down-link. The spreading process is a serial-to-parallel conversion of a transmitted data sequence, a regular exchange of the parallel sequences, Fourier transforms, a random exchange of the transformed sequences, inverse Fourier transforms, and a multi-carrier modulation. The primary modulation is a power efficient APSK signal with a honeycombed constellation. We conduct a computer simulation to estimate the interference tolerance of the proposed method with the multi-level APSK signal. The simulation results show that the method with the APSK signal has a better tolerance of the interference by 3 dB than a conventional method using a variable length orthogonal spreading code with a multi-level QAM signal. A CDMA system capacity or a user data rate is limited by the interference. Therefore, the proposed method with the APSK signal could increase the capacity or the data rate.
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