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This paper describes and clarifies a configuration and its performance of estimation and compensation of phase rotation in radio propagation using a pilot channel for the SS (spread spectrum) modulation and demodulation. Coherent radio transmission scheme is composed as follows: (i) Continuous pilot signal is transmitted through a pilot channel, (ii) the pilot channel is composed of O-QPSK and QPSK for reverse and forward links, respectively, (iii) pilot signal is added in each I channel of O-QPSK and QPSK, and (iv) coherent demodulation is achieved by estimation and compensation of phase rotation using the pilot channel. Phase rotation and its linearity has been estimated for QPSK and O-QPSK data modulation methods. The constellation on the complex plane is used for the evaluation of phase rotation and the Eye pattern for the demodulated waveforms. The bit-error-rate (BER) versus Eb/N0 is used for the characteristics of data modulation/demodulation and SS modulation/demodulation of the proposed radio system. A proposed scheme proved that (i) estimation of rapid phase rotation caused by multipath radio propagation with high-speed Doppler shift in frequency is well realized by the use of continuous pilot transmission (pilot channel), (ii) compensation of rapid phase rotation is well done by simplified logic operations, and (iii) high performance for high speed data transmission is realized by coherent demodulation. This system will be applied to wireless LANs with high performances and simplified configurations.

Multiple users communicate with individually-assigned codes on a single radio carrier frequency in a DS-CDMA system. Mutual interference among codes limits the capacity of the system. Conventional detectors of receivers are designed for a single-user neglecting the mutual interference. Multi-user detection is expected to enhance the capacity by removing the interference factors. In this paper, a new scheme is proposed corresponding to solving a huge matrix equation under multiple access interference (MAI) environments. This scheme is obtained by the mathematical approach to solve a huge matrix equation. The modeling of multi-user detection is shown, and the algorithm is given based on mathematical approach: the Conjugate Gradient Method (CGM). The characteristics of the proposed scheme are evaluated with comparison to the conventional single-user detector. The proposed scheme has been shown to be three times in capacity against single user detection with reduced complexity comparing conventional technologies based on serial and parallel configurations.