Takehisa Kohda

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In this paper, we investigate the locomotor behaviors of a biped robot on a splitbelt treadmill using a locomotion-control system composed of nonlinear oscillators with phase resetting. Our results show that the robot establishes stable walking on the treadmill at various speeds of the belts due to modulation of the rhythm and phase by phase resetting. In(More)
In this paper, we investigated the locomotion of a quadruped robot, whose legs are controlled by an oscillator network system. In our previous work, simulation studies revealed that a quadruped robot produces walk and trot patterns through dynamic interactions among the robot's mechanical system, the oscillator network system, and the environment. These(More)
Multiple-access interference (MAI) depends on chip pulse shapes in chip-asynchronous direct sequence/code division multiple access (DS/CDMA) systems. The mean squared MAI averaged over relative time delays is expressed in a quadratic form, where a coefficient matrix is derived from the pulse shapes, while a variable vector consists of aperiodic(More)
Typical methods for solving reinforcement learning problems iterate two steps, policy evaluation and policy improvement. This paper proposes algorithms for the policy evaluation to improve learning efficiency. The proposed algorithms are based on the Krylov Subspace Method (KSM), which is a nonstationary iterative method. The algorithms based on KSM are(More)
In this paper, we investigated the dynamic locomotion of a quadruped robot. This robot is controlled by a locomotion control system composed of nonlinear oscillators, which was constructed based on the physiological concept of central pattern generator and phase resetting. In our previous work, we revealed that the quadruped robot produces the walk and trot(More)
A Gaussian pulse has intersymbol-interference, which degrades signal to interference ratio (SIR). In asynchronous CDMA system, however, Markov codes with negative correlation recover the SIR of Gaussian pulses. The improvement over i.i.d. codes is 2.3 dB and Gaussian pulse achieves almost same SIR and bandwidth as a root raised cosine (RRC) pulse. The(More)
Pulse shaping filters are commonly implemented by FIR filters. Motivated by Slepian's philosophy of discrete prolate spheroidal sequences (DPSS), we investigate Welch's lower bound on aperiodic auto- and cross-correlations for oversampled sequences. An oversampled sequence set having minimum cross-correlations in chip-asynchronous CDMA system is provided(More)
In spread spectrum (SS)-based digital watermarking systems, watermark information is spread by a pseudorandom code and added to the original information signal. On the other hand, we have proposed another watermarking system having one watermark channel and several image transmission channels. Information data is modulated by SS codes with variable code(More)