Tetsuhiko Miyatani

A reduced-complexity path timing detection method for DS-CDMA

The DS-CDMA system is a strong candidate for the third generation mobile communication system. The RAKE receiver is a key technology to implement DS-CDMA systems: it is an effective countermeasure to improve the channel quality under multipath fading. It is important for the RAKE receiver to detect all available paths for path diversity, since the BER characteristics depends on the number of detected paths. The path detection affects also the capacity of the CDMA system under the quality (SIR) based power control, since false detection will increase the transmission power required to avoid degradation of the channel quality. This paper proposes a new path detection method which requires no A/D converters or DSP to interface with either analog or digital matched filter (MFs). The circuit and algorithm of the proposed system is first described, then the performance obtained by computer simulation is shown.

A predistorter for a power amplifier affected by the even-order distortion [W-CDMA base station applications]

The even-order distortion at baseband perturbs bias conditions of a power amplifier (PA), and creates a new odd-order distortion, which shows a hysteresis effect on AM-AM and AM-PM characteristics. This effect combined with the original odd-order distortion generates imbalanced inter modulation distortion (IMD) outside of the signal bandwidth, which depends on frequency separation. The imbalanced IMD limits the compensation performance of conventional predistorters. We propose a new predistorter for W-CDMA base stations. The predistorter compensates the distortion to less than 60 dBc, even if the PA is affected by even-order distortion. The PA model and the adaptive algorithm are also shown.