Takanori Iwamatsu

A simple predistorter in fixed microwave radio system with the transmission power control

This paper presents an orthogonal look up tables (LUTs) based predistorter (PD) whose coefficients are generated adaptively to minimize the out-band distortion power. It has low complexity and high robustness to impairments from the feedback circuit, with the drawback of slow convergence meanwhile. To counteract the performance degradation in the case of fast transmission power control (TPC) due to the slow convergence, a selection mechanism between on-line generated and memorized coefficients is proposed. The orthogonal LUTs based perdistorter and its TPC countermeasure were implemented in a fixed microwave radio system, where 14 dB reduction of adjacent channel leakage ratio (ACLR) was verified relying on experiments. In addition, the performance in the case of 100 dB/s TPC was also confirmed to satisfy the ACLR requirement of -45 dB.

Modified orthogonal matching pursuit based ISDB-T channel estimation over fractional delay channel

Integrated Service Digital Broadcasting for Terrestrial (ISDB-T) is a Japanese standard for digital television that uses a multi-subcarrier systems called Orthogonal Frequency Division Multiplexing (OFDM). A solution for compressed sensing called Modified Orthogonal Matching Pursuit (MOMP) is capable of reducing the computational cost for channel estimation. This paper extends the capability of MOMP in fractional multipath delay channel. The simulation results shows that the proposed method is robust against fractional delay by obtaining a good Bit-Error-Rate Performance in rayleigh fading channel.

Configurations and performance evaluations for a long-delay multipath interference based on the combinational use of an adaptive array antenna and multipath equalizers

Long-delay multipath interference is defined as a delayed signal located outside the guard interval of OFDM systems. An adaptive array antenna is often used to suppress long-delay multipath interference; however, the performance degrades when the desired and interference signals come from nearly the same direction. In these situations, a multipath equalizer in the time domain is very effective for suppressing the interference signal. In this paper, we propose three configurations based on a combinational use of an adaptive array antenna and a multipath equalizer as a remedy for long-delay multipath interference. We evaluated the performance using a computer simulation. The results show that excellent performance can be achieved even when the directions of desired and interference signals are close as well as when the interference signal comes from arbitrary directions.

An OFDM channel estimation based on a simultaneous use of liner interpolation and feedback channel estimation

In Orthogonal Frequency Division Multiplexing (OFDM), multiple pilot subcarriers are dispersed for propagation channel estimation. Our study suggests a method to reduce the number of pilot subcarriers to 1/15 while maintaining fading tolerance. This can be realized by estimating the propagation channel parameters with combined implementation of sequential feedback estimation for the time direction and linear interpolation for the frequency direction.