Masato Saito

Novel Receive Diversity Scheme Using ESPAR Antenna and Arbitrary Frequency Band

This paper proposes a novel receive diversity scheme which uses Electronically Steerable Passive Array Radiator (ESPAR) antenna in which reactance connected to parasitic antenna element is oscillated by sinusoidal waveforms of arbitrary frequencies. By controlling the frequency applying to the reactance, we can use frequency bands both assigned and not assigned to the corresponding communication systems without causing any interference to the signals used in the band. We propose several receiver structures for Orthogonal Frequency Division Multiplexing (OFDM) systems and evaluate Bit Error Rate (BER) to confirm the effect of the proposed diversity scheme with Maximum Ratio Combining (MRC) and Selection Combining (SC).

Dual-Hop Non-regenerative OFDM Relay Systems with Chunk-Based Power Allocation

In this paper, we propose dual-hop non-regenerative Orthogonal Frequency Division Multiplexing (OFDM) relay systems without signal buffering and processing delay due to Fast Fourier Transform (FFT) and Inverse FFT (IFFT) at the Relay Node (RN). One scheme uses per subcarrier Power Allocation (PA) at Source Node (SN) and per chunk PA at RN to improve the achievable rate. Another scheme employs per chunk PA at both SN and RN. Numerical results in mobile communication environments show that both schemes improve the achievable rates compared to conventional simple amplify-and-forward relay systems with per subcarrier PA at RN. In particular, the latter scheme can obtain almost the same or slightly higher achievable rates by selecting an appropriate chunk size in severe frequency selective channel and by setting any chunk size in highly frequency-correlated channels. Therefore, chunk-based PA at both SN and RN can be found a beneficial PA for dual-hop OFDM relay systems in terms of competitive achievable rates and relatively small amount of required channel information to calculate allocated power.

Evaluation of clipping effect on OFDM signals for visible light communications

In this paper, we evaluate Orthogonal Frequency Division Multiplexing (OFDM) systems with clipping method for Visible Light Communications (VLCs). Clipping can efficiently reduce Peak-to-Average Power Ratio (PAPR), improve Signal-to-Noise power Ratio (SNR) by compensating the reduced transmit power, and prevent the necessity of estimating the bias value added at the transmitter to keep the signal real-positive. Besides, since usually VLC has no specific spectrum mask, the out-of-band components generated by clipping can be remained. Thus, there is no need to care peak regrowth which is a typical problem of Clipping And Filtering method (CAF). We show the proposed system can keep the bias constant and improve required SNR for Quadrature Phase Shift Keying (QPSK) modulation by 3 dB compared to the conventional method.

A study on received signal spectrum of antenna with periodically variable directivity

In this study, we obtain periodically time-variable antenna pattern of the antenna based on the equivalent weight vector method with approximated continuous reactance. According to the antenna pattern we analyze the received signal spectra which are frequency-shifted by the time-variable antenna pattern. We compare the spectra to those obtained by the experiments and verify the antenna pattern analysis.

Receiver structures of ESPAR antenna to realize receive diversity

In this paper, we propose receiver structures to achieve receive diversity which uses ESPAR (Electronically Steerable Passive Array Radiator) antenna. By applying a sinusoidal voltage to the parasitic element of the antenna, we can receive the received signals which have three different central frequencies and experience independent fading. Instead of the conventional idealized complex-valued voltage, we introduce to apply feasible real-valued voltage to the variable reactance element. To receive all the signal components with minimum additional operations and obtain higher diversity gain, we propose three receiver structures. According to the evaluation of BER (Bit Error Rate) performances, we can obtain almost the same diversity gain by a receiver structure as that by the receiver with idealized applying voltage.