Tadahiro Wada’s research while affiliated with Shizuoka University and other places

A digital signage image-sensor-based visible light communication (IS-VLC) system can transmit data information by embedding it on visual information. The use of a motion video as visual information makes it difficult to completely erase the visual information in this system. The extraction of data information is an important issue because the incomplete extraction will degrade the bit error rate performance. In this letter, we expand the IS-VLC system to overlay a motion video with data information by introducing a cell-position correction method and a noise elimination method. Experimental results clarify the effectiveness of the extended system.

In this paper, we propose an image-sensor-based visible light communication (IS-VLC) system that provides visual information in digital signage used for advertisements. One important issue of IS-VLC systems is the deterioration of visual information while transmitting the data information. Human eyes are sensitive to luminance but not to color difference; therefore, we propose the modulation of color difference. We evaluate the performance of the proposed system in terms of both the quality of visual information and communication quality of data information, and clarify the effectiveness of the proposed system.

The aim of the study is to explore the possibility of the use of Meteor Burst Communications (MBCs) in equatorial regions. We installed the master and the remote stations at Yogyakarta, Java Island and Jimbaran, Bali Island, Indonesia, respectively. As a preliminary experimental result, we confirmed that some packet transmissions between the two stations were achieved through meteor burst channels.

In this paper, we construct a new prototype of parallel-transmission wireless visible light communication (VLC) systems using Color-Shift Keying (CSK). The prototype consists of a Liquid Crystal Display as a transmitter and an Image Sensor as a receiver. We show the CSK scheme can improve information transmission capability of VLC systems compared with that using mono-color. We also show an effect of a forward error correction code for VLC systems.

Root raised cosine roll-off (RRC) filter is one of the most fundamental elements in modern digital communications. This paper proposes a new method to efficiently realize the RRC filter. The method employs cubic Hermite interpolation to obtain a piecewise-polynomial approximation for the impulse response of the RRC filter. Then, the approximated impulse response is efficiently realized by using a transversal filter with a very small number of taps followed by integrators with a simple recursive structure, named cascaded recursive finite impulse response (CR-FIR) filter. As an example, an RRC filter with roll-off factor 0.5 is constructed by using the CR-FIR filter with only nine multipliers. Performance of the RRC filter in matched filtering is examined by computer simulations. Then, it is shown that the constructed RRC matched filter has nearly the same performance as the ideal filter.

In this paper, we focus on a X channel; a system with two transmitters and two receivers each equipped with a single antenna, where independent messages need to be conveyed over channels from each transmitter to each receiver. A key concept of that arises in the context of the X channel is interference alignment (IA) that refers to an overlap of signal spaces occupied by undesired interference at each receiver while keeping desired signal spaces distinct. However, all the channel responses and the precise time synchronization are required at every transmitter and receiver to realize the IA, which are seriously demanding in practice. In this paper, we propose semi-blind IA (S-BIA) scheme exploiting frequency selectivity of wireless channels using orthogonal frequency division multiplexing (OFDM), which only requires channel responses corresponding to each transmitter. Numerical results confirm that proposed S-BIA can achieve the same degrees of freedom as conventional IA even in the presence of time synchronization errors.

In this paper, we propose a new automatic repeat request (ARQ) scheme, named Go-Back-i-symbol (GBi) ARQ scheme, suitable to Meteor Burst Communications (MBC). The scheme realizes symbol-wise ARQ by using the Viterbi decoding algorithm for convolutional codes. We also propose a practical transmission protocol for applying the GBi-ARQ scheme to packet communications over time varying short burst channels such as meteor burst channels. Fundamental performances of the GBi-ARQ scheme in MBC are evaluated by computer simulations. Effectiveness of the GBi-ARQ scheme is shown by comparing the performance with that of a conventional block-wise ARQ scheme.