Shoichiro Yamasaki

A visible-light communication system using optical CDMA with inverted MPSC

Visible-light communication systems are suitable to realize secure indoor networks. In this paper, an optical CDMA scheme employing EWO signaling with inverted sequences of MPSC or GMPSC is proposed for visible-light communication systems. The proposed scheme has the property of canceling MUI as well as the conventional EWO-MPSC scheme. Average light intensity and normalized intensity fluctuation of multiplexed optical signals are investigated by computer simulation. It is shown that the proposed scheme is more suitable for visible light communication, since it has lower intensity fluctuation and higher average light intensity, in comparison with the conventional scheme which adopts non-inverted sequences. Then, the authors implemented a visible-light CDM system with several LEDs. It has four channels on each of which 31.25KHz MIDI data, coded with a generalized MPSC with a length of 64, is transmitted. It is confirmed that the system can correctly decode every MIDI data transmitted simultaneously.

Secure wireless communications using secret sharing and vector coding

A secret sharing is a method to protect the information for security. The information is divided into n shares, and the information is reconstructed from any k shares but no knowledge of it is revealed from k - 1 shares. A physical layer security is a method to yield a favorable receive condition to the destination terminal in wireless communications. In this study, we propose a security scheme using the secret sharing based on systematic Reed Solomon (RS) codes and the physical layer security based on vector coding. The vector coding realizes the physical layer security in one-antenna system over multi-path channels and the secret sharing with systematic RS codes enhances the security.

Error correction scheme for Multi-carrier CDMA with bi-orthogonal modulation

In order to reduce out-of-band emission and PAPR for Multi-carrier (MC) CDMA system, bi-orthogonal modulation is one of the efficient schemes. However the performance of the scheme rapidly degrades if Hadamard code selection errors are occurred at the receiver. We propose and examine a frequency domain error correction scheme for the system employing Reed-Solomon (RS) code. This basic concept is that a Forward Error Correction (FEC) code corrects the code selection errors for all the subcarriers. An efficient decoding method that not only code selection error but the transmitted bit error can correct is also examined.

A reconstruction method of damaged two-dimensional signal blocks using error correction coding based on DFT

This study presents a signal restoration method in a block-coded still image and video, to cope with a block-loss problem at a decoder arising from an imperfect transmission through a communication channel. The feature of the proposal is that it applies a two-dimensional error correction coding technique not to the bit stream error correction, but to the signal restoration at the image plane.

A visible-light communication system using optical CDMA with RGB multi-chip LEDs

White light-emitting diodes (LEDs) are attracting attention as a light source in developing a visible-light communication system. Optical code division multiple access (CDMA) is one of the solutions to transmit several data streams simultaneously in the system. We propose a visible-light communication system using optical CDMA with red-green-blue (RGB) multichip LEDs. The proposed method has advantages of reducing the number of LEDs since each multi-chip device includes three light sources and of cancelling multi-user interferences without using colored filters. Computer simulation shows the validity of the proposed scheme.

A compression scheme of secret sharing

A secret sharing is a scheme to protect the data for security, in which the source data is divided into n shares and the source data is reconstructed from any k shares but no knowledge of the source data is not revealed from k - 1 shares. This algorithm is called (k, n) threshold scheme. In this study, we propose a scheme to compress the data of the (2, 5) threshold secret sharing, in which the source data is divided into five secret shared data in the first step and each shared data is compressed in the second step. This scheme has a merit such that the original source information is not revealed in the compression step, since the original source data is converted to the protected data in the initial step. The compression and decompression adopt a method used in distributed video coding which is based on error correction encoding and decoding. Any two compressed shares reconstruct the lossless source data assuming the ideal decoding. The compressed shares reconstruct the lossy source data assuming the non-ideal decoding. In such a case, using more than three compressed shares enhances the quality of the data reconstruction. Computer simulations show the validity of the scheme.

A study on multi-carrier CDMA with adaptive trellis coded modulation

A Generalized Symbol-rate-increased (GSRI) Pragmatic Adaptive Trellis Coded Modulation (ATCM) applied to a Multi-carrier CDMA system with bi-orthogonal keying is analyzed. In [7], an efficient ATCM scheme using GSRI-TCM has been proposed. However, since the modulation and coding selection is based on the ideal SNR estimation method, performance evaluations employing practical channel estimation scheme is desired. In this paper, we investigate the performance of the Multi-carrier CDMA with GSRI ATCM employing practical SNR estimation. The performance evaluations on a multi-path fading channel are presented.

Performance improvement of simplified structure based adaptive trellis coded multi-carrier DS-CDMA with bi-orthogonal keying

A performance analysis on a simplified transmitter structure for Generalized Symbol-rate-increased (GSRI) Adaptive Trellis Coded Modulation (ATCM) scheme applied to RS coded Multi-carrier DS-CDMA with Bi-orthogonal Keying is presented. The generic structure for a full ATCM has been proposed and evaluated [2]. In order to reduce the transmitter complexity, a simplified structure was proposed [4]. In [4], the performance degradation in both BER and throughput was an issue to be resolved. In this paper, an efficient scheme using discriminant analysis method for selecting the modulation parameter is proposed. It was shown that the proposed scheme improves both BER and throughput performance compared with those in [4].

Performance evaluation of single carrier transmission using frequency domain equalization

Frequency domain equalization (FDE) has attracted a great deal of attention as a broadband wireless access technique. The conventional single-carrier (SC) method using FDE requires the insertion of a cyclic prefix (CP) as the guard interval (GI) to avoid inter-block interference (IBI). However, CP insertion reduces the transmission efficiency. On the other hand, overlap FDE is an equalization technique for use with the SC method that avoids the need for CP insertion. We have proposed an overlap FDE with coherent averaging that suppresses the residual interferences of the conventional overlap FDE outputs and improves the equalization performance. In the present study, we evaluate and compare the bit error rate (BER) performances of the SC using FDE with a CP and without a CP under the same transmission efficiency. Computer simulations demonstrate that the proposed scheme has superior performance to various modulation methods.

Error resilient 3D DWT video transmission using invertible codes

There have been many studies that apply three-dimensional discrete wavelet transform (3D DWT) to video coding. It is known that lowest frequency sub-band coefficients of 3D DWT outputs affect the visual quality of video. In order to maintain image quality of video that is transmitted over channel with error such as a wireless, it is necessary to development of error resilient transmission scheme for protecting the lowest subband coefficients. Coauthors of the study proposed the method (conventional method), which adopted duplication scheme of lowest frequency sub-band coefficients of 3D DWT. The objective of this study is to indicate improvement of error resilience by replacing the duplication scheme of conventional method with the error correction scheme using invertible codes. In addition, conventional study is assumed the packet loss channel model that packets are lost or received without bit errors. However, in wireless communications of the actual, the packet is often received with errors, and errors occur in bursty. The simulation evaluations compare the performances of the proposed method with those of the conventional one over burst error channel.