This paper proposes a general method of robotic imitation learning. In this method, robots learn inner common features of demonstrations, which are largely different from each other, by analyzing the similarities among the features of the demonstrations. Adaptive generation methods are related to each feature. At the generation stage, given new task-relevant constraints, robots can generate motion trajectories, which still have the common feature learned from the demonstrations, to achieve the task-goals. This methodology is an opened framework which enables researchers to design features and feature related generation methods according to the application requirements. Three experiments are designed for robots to learn behaviors from human teachers, and the demonstrations given at the teaching stage are largely different from each other. Experimental results are given in this paper to verify the effectiveness of our proposed methodology.

In this paper, a frequency-division counterpart of joint power control and sequence design problem for code- division multiple-access (CDMA) systems is solved. Total transmit and receive power minimizations are considered for frequency- division multiplexing (FDM) and frequency-division multiple- access (FDMA) communications over overloaded channels. After the definition of channel overloading for CDMA systems is extended to the frequency-division systems, the user admissibility is characterized by a necessary and sufficient condition for the existence of the optimal solution under unequal signal-to- interference-plus-noise ratio constraints at the output of linear receivers and asymmetric data transmission rate constraints among users. The optimal signal power, bandwidth, transmit waveform, and receive waveform are derived for each user as the decision parameters of the optimization problem. It is shown that, if this solution is applied for the uplink users to minimize the total receive power, the optimal FDMA system performs the same as the optimal CDMA system. It is also shown that, if this solution is applied for the downlink users to minimize the total transmit power, the optimal FDM system always outperforms the code-division system that minimizes the extended total squared correlation. Numerical results suggest that the optimal FDM system and the optimal downlink code-division system achieve the same performance when the total transmit power is minimized.

The design of ultra-wideband (UWB) communication systems has proven to be challenging. Coherent systems require a rake receiver with many taps that is difficult to train, and transmitted-reference (TR) schemes require a wideband analog delay line whose implementation has proven extremely difficult. In response to this challenge, we have recently proposed the frequency-shifted reference (FSR-UWB) system, which leads to the replacement of the delay line in the receiver of the standard TR-UWB system with a mixer, and the resulting system is easily implemented. In this paper, the FSR-UWB idea is extended to provide multiple-access, and a performance analysis is presented. This analysis and the corresponding numerical results reveal that, due to the large bandwidth expansion of the UWB system, the FSR-UWB single-user receiver can still be successfully employed in lightly loaded systems; in other words, successful multiple- access can be achieved without the need for the wideband analog delay line of TR-UWB or the despreading circuitry generally associated with conventional multiple-access spread-spectrum systems. The result is an extremely simple architecture for wideband multiple-access communications in the wireless environment.

A promising ultra-wideband (UWB) radio technique being widely considered for low-data-rate applications, such as those often encountered in sensor networks, is the transmitted reference (TR) UWB scheme. However, the standard TR-UWB scheme, while often motivated by the simplicity of its receiver, is still dogged by implementation concerns. In particular, the receiver requires an extremely wideband delay element, which is difficult to incorporate into low-power integrated systems. In this paper, a TR scheme is proposed in which the separation between the data and reference signals, rather than being a time delay, is a slow rotation over the symbol interval. This provides a (slightly) frequency-shifted reference that, while orthogonal to the data-bearing pulse, still goes through a nearly equal channel. A detailed analysis of the proposed scheme is provided. Simulation results demonstrate the expected result that frequency shifting of the reference in the proposed manner is not effective for high-data-rate systems that experience appreciable intersymbol interference. However, for the targeted low-to-moderate data-rate applications, numerical results demonstrate that the proposed system not only achieves the primary goal of providing a much simpler receiver architecture, but also that it outperforms the standard TR-UWB system

In this paper, the peak-to-average power ratio (PAPR) is evaluated for the uncoded orthogonal frequency division multiplexing (OFDM) signals generated by using the IDFT procedure. The power spectral density of the transmitted OFDM signal is derived, taking into account the effects of cyclic prefix, windowing, digital-to-analog converter, null-subcarriers, and analog transmit filter. The PAPR distribution is then analyzed based on the extreme value theory. It is shown that the PAPR distribution is parameterized only by the length of the observation interval and the root mean square bandwidth of the signal, whose computation requires the PSD of the transmitted signal. Numerical results confirm that the proposed analysis accurately predicts the PAPR distribution of practical OFDM signals.

An optimal power and bandwidth allocation problem is considered for multi-rate frequency-division multiplexing (FDM) and frequency-division multiple-access (FDMA) over overloaded channels. We have derived the optimum frequency-division system that minimizes the total transmitted power subject to the QoS of users defined in terms of the transmission rates and the SINR requirements. The necessary and sufficient condition is found for the admissibility of the users, and the optimum power, bandwidth, transmit waveform, and receive waveform are found for each user. It is shown that the optimum frequency-division system performs exactly the same as the optimum CDMA system when all the users have the same transmission rate and channel gain. It is also shown that the optimum frequency-division system always outperforms the ETSC-minimizing code-division system when all the overloading users have the same transmission rate.