Yuma Inaba

Bio: Yuma Inaba is an academic researcher from Nagoya Institute of Technology. The author has contributed to research in topics: MIMO & Transmission (telecommunications). The author has an hindex of 3, co-authored 3 publications receiving 30 citations.

Multilevel modulated chaos MIMO transmission scheme with physical layer security

Abstract: Ensuring security at the physical layer in wireless communications is important and effective because it can omit upper-layer secure protocols in ad hoc or multi-hop relay transmissions, or it can enhance security together with upper-layer protocols. To realize this system, we have proposed a chaos-based multiple-input multiple-output (MIMO) transmis- sion scheme that enables both physical-layer security and a channel coding effect in a MIMO multiplexing transmission. However, the transmission rate is equivalent to binary phase shift keying (BPSK), that is, one bit/symbol, and multilevel modulations are needed to achieve higher-capacity communication. Moreover, the channel coding gain is limited, which needs to be improved. Therefore, in this paper, we propose a two- and four-bit/symbol chaos-MIMO scheme, equivalent to quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (16QAM) rate-efficiency, with an adaptive chaos processing scheme enhancing the channel coding gain. The improved performances of the proposed scheme are shown in the numerical results. In addition, we describe the concept of identification modulation using this chaos transmission.

Multi-user chaos MIMO-OFDM scheme for physical layer multi-access security

Abstract: Wireless multihop networks can be potentially used to realize a smart commu- nity that comprehensively controls social infrastructures. In a wireless multihop transmission, personal data are forwarded by a third party, so wireless security is indispensable. In current wireless systems, security is ensured by encryption in the upper layers. However, this encryption tends to require a complex protocol or processing, which is not suitable for a multihop protocol with a simple implementation. To solve this problem, we have proposed a chaos multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) scheme with phys- ical layer encryption and channel-coding abilities. On the other hand, an effective technique for wireless multihop transmission is point-to-multipoint (P-MP) communication, and recently, multi-user (MU)-MIMO has been proposed as an effective P-MP scheme. In MU-MIMO, wire- less security is also important. However, there are few studies considering MU-MIMO security in the physical layer. Therefore, in this paper, we propose a multiuser (MU) chaos MIMO- OFDM scheme that achieves physical layer security and channel-coding gain in MU-MIMO transmission. Additionally, the user distribution and propagation loss are taken into consider- ation. The improved performances are shown through computer simulations.

Generation of Uncorrelated Multichannel Chaos by Electrical Heterodyning for Multiple-Input–Multiple-Output Chaos Radar Application

Abstract: Multiple-input–multiple-output (MIMO) radar has received much attention in recent years for its great ability in imaging. However, the essence of MIMO radar has not been fully implemented due to the lack of proper transmission waveforms. In MIMO radar, the transmission waveform of each channel has to be uncorrelated with one another to avoid cross-interference between channels. To achieve this, we investigate the generation of uncorrelated multichannel chaos using electrical heterodyning for MIMO chaos radar (MIMO CRADAR) application. By electrically heterodyning a seed chaos source with multiple single-frequency local oscillators, chaos with different heterodyned spectra can be extracted and converted into multiple chaos channels. In this paper, the correlations between different channels of chaos generated are analyzed both numerically and experimentally. The minimal frequency spacing of the local oscillators for generating the largest amount of uncorrelated chaos channels is discussed. In our analysis, thousands of uncorrelated chaos channels can be simultaneously generated with a correlation time of several microseconds. Moreover, compared with those conventional waveform-designing methods that require complicated optimization and digital-to-analog conversion (DAC), the proposed heterodyned technique shows, for the first time, that multiple uncorrelated channels can be generated in real-time while breaking the bandwidth limitation of the DAC devices. A proof-of-concept experiment is successfully demonstrated to show the feasibility of using multichannel heterodyned chaos in the MIMO CRADAR application.

Performance improvement of chaos MIMO scheme using advanced stochastic characteristics

Abstract: Chaos multiple-input multiple-output (C-MIMO) is a transmission scheme that uses Gaussian signal transmission based on chaos, where physical-layer security and channel coding effect are obtained. However, because the Gaussian signals are generated according to the principle of central limit theorem, about ten independent chaos signals are needed, resulting in increased calculation complexity. In addition, the probability density function of the phase of transmit signals slightly deviates from uniform distribution, which degrades the bit error rate (BER) performance. Therefore, we propose a C-MIMO scheme with improved Gaussian modulation, in which the stochastic characteristic is improved by applying the Box–Muller method with only one chaos signal.

Sparse chaos code multiple access scheme achieving larger capacity and physical layer security

Abstract: Massive machine-type communications (mMTC) scenarios that can accommodate Internet of things (IoT) device communications are currently being considered for implementation in fifth generation mobile communication systems. To support the dynamic traffic present in mMTC systems, grant-free non-orthogonal multiple access schemes have been proposed. In these schemes, both system capacity enhancement and transmit protocol simplification are achieved, and an overloaded transmission of more than one hundred percent of the capacity of the number of transmit samples is conducted. However, demand still exists for more capacity to accommodate massive devices. On the other hand, a simple method for ensuring the security of mMTC systems is required to suppress the energy consumption of IoT devices and reduce the amount of signal processing required at the central receive stations. In this paper, to satisfy these requirements, we propose a novel grant-free sparse chaos code multiple access (GF-SCCMA) scheme for mMTC systems in which sparse code multiple access is supplied based on chaos signals and physical layer security is ensured. GF-SCCMA is a non-orthogonal multiple access scheme in which only pairs sharing common keys can decode data by utilizing a chaotic codebook of transmission sequences. Furthermore, the distribution of the output log likelihood ratio is improved by using chaos-based quasi-Gaussian modulation, and enhancement of the capacity is achieved for conventional schemes when the outer channel code is concatenated. The improved performances in terms of capacity and security are shown through numerical simulations.

Artificially Time-Varying Differential MIMO for Achieving Practical Physical Layer Security

Abstract: In this paper, we propose a differential multiple-input multiple-output (MIMO) scheme based on the novel concept of chaos-based time-varying unitary matrices to demonstrate—for the first time in the literature—the ability of differential encoding in achieving practical physical layer security even without the need for using channel estimation. In the proposed scheme, an erroneous secret key, which is extracted from the wireless nature, is used to initialize a chaos sequence that is responsible for generating artificially time-varying unitary matrices capable of obfuscating the transmitted data symbols from illegitimate eavesdroppers. Contrary to conventional studies, the key agreement ratio in this study is assumed to be imperfect, which is often true and very realistic in high-mobility scenarios. Following this, we conceive a new calibration algorithm for reconciling the chaotic sequence generated at the legitimate parties, thus making this calibration algorithm a unique, novel solution to the key sharing problem of conventional chaos-based communication techniques, which has been overlooked over the past few decades. It is found out that differential encoding obviates additional complexity and insecurity in dealing with channel estimation, whereas an eavesdropper must tackle the complicated differentially encoded patterns, which have an exponentially increasing complexity order. In addition, the obtained simulation results demonstrate that the proposed scheme can outperform conventional chaos-based MIMO schemes that assume perfect channel knowledge.