Our research covers a range of areas in wireless communications,
signal processing, networking, and antenna technology.
As quantum computers evolve, their integration with communication networks becomes increasingly feasible, driving the transition from quantum computing breakthroughs to the realization of a revolutionary "Quantum Internet." It is expected to work in synergy with the current classical Internet to enable unparalleled security, distributed computing, and information processing. Our "Quantum Internet in the Sky" concept employs free-space optical (FSO) systems to transmit photonic quantum bits across non-terrestrial platforms such as low-altitude platform stations (LAPS), high-altitude platform stations (HAPS), and low-Earth orbit (LEO) satellites, establishing a dynamic three-dimensional mesh network for quantum communications. By leveraging the quantum features of photons, we aim to forge ultra-secure connections that can instantly link any two points on Earth. Like SpaceX's Starlink, LEO satellites serve as quantum repeaters and routers, ensuring global secure communications with minimal signal loss.
P. V. Trinh and S. Sugiura, "Quantum Internet in the sky: Vision, challenges, solutions, and future directions," IEEE Communications Magazine, Oct. 2024 (DOI: 10.1109/MCOM.003.2300835).
While high frequencies such as millimeter and terahertz waves can provide wide bandwidth, they are not suitable for non-line-of-sight communication because they are vulnerable to distance attenuation and blockage by obstacles. Therefore, metasurface intelligent reflectors, which can flexibly control the characteristics of the reflected waves, are expected to combat these limitations. Here, we proposed an algorithm to achieve secure multi-user communication using intelligent reflectors in the presence of multiple eavesdroppers. We also developed metasurface hardware that can arbitrarily control a reflected wave's beam direction and polarization.
S. Sugiura, Y. Kawai, T. Matsui, T. Lee, and H. Iizuka, "Joint beam and polarization forming of intelligent reflecting surfaces for wireless communications," IEEE Transactions on Vehicular Technology, vol. 70, no. 2, pp. 1648-1657, Feb. 2021.
A novel secure buffer-aided decode-and-forward relay selection that amalgamates the benefits of buffer-state-based relay selection, the max-ratio criterion, simultaneous activation of multiple source-to-relay links, and cooperative beamforming is proposed in the context of dual-hop networks. More specifically, the proposed scheme is designed for selecting a single or multiple relay nodes for packet reception or transmission, based on the buffer states of relay nodes, while avoiding the detrimental effects of both an empty buffer state and a buffer overflow. Furthermore, analytical bounds on the secrecy outage probability and average delay are derived for our proposed scheme, based on a Markov chain process, in order to verify the system model of our proposed scheme. Furthermore, we introduce the concept of cooperative jamming into the proposed scheme, in order to interfere with an eavesdropper’s reception, while dispensing with full channel state information associated with an eavesdropper at a central coordinator.
R. Nakai and S. Sugiura, "Physical layer security in buffer-state-based max-ratio relay selection exploiting broadcasting with cooperative beamforming and jamming," IEEE Transactions on Information Forensics and Security, vol. 14, no. 2, pp. 431-444, Feb. 2019.
Motivated by the recent max-link protocol and the max-max protocol, both of which were developed for a simple dual-hop buffer-aided cooperative network, we present a novel hybrid buffer-aided cooperative protocol that attains the benefits of high reliability and reduced packet delay. by introducing a periodic Markov chain model, we derive the theoretical outage probability of our hybrid buffer-aided scheme under the realistic assumption of finite-buffer relays. Our analytical and simulation results demonstrate that the proposed protocol benefits from the aforementioned high-diversity reliable performance and the reduced end-to-end packet delay.
M. Oiwa, C. Tosa, and S. Sugiura, "Theoretical analysis of hybrid buffer-aided cooperative protocol based on max-max and max-link relay selections,” IEEE Transactions on Vehicular Technology, vol. 65, no. 11, pp. 9236-9246, Nov. 2016.
In the field of radio-frequency (RF) communications, the multiple-input multiple-output (MIMO) strategy allows us to attain a higher rate of data transfer due to the multipath-rich environment. In contrast, it is challenging to achieve the same rate in a highly correlated channel that is specific to optical wireless communications. In this paper, we propose the novel concept of an element-by-element optical MIMO system that enables the interference-free reception of parallel symbol streams; it achieves this by using an angular filter (AF) with a narrow transparent window. The AF consists of a one-dimensional photonic crystal, and the angular selectivity is obtained by using the extremely small wave vector regime. We demonstrate that the capacity of the proposed system increases linearly with the minimum number of transmit source elements and receive detectors, which is similar to conventional RF MIMO systems.
S. Sugiura and H. Iizuka, "Element-by-element full-rank optical wireless MIMO systems using narrow-window angular filter designed based on one-dimensional photonic crystal,” IEEE/OSA Journal of Lightwave Technology, vol. 34, no. 24, pp. 5601-5609, Dec. 2016.
A novel graphene-based multiple-input multiple-output (MIMO) concept is proposed for high-rate nanoscale wireless communications between transceivers, which are nano/micrometers apart from each other. In particular, the proposed MIMO architecture considers exploiting a deep-subwavelength propagation channel made of graphene. This allows us to increase the number of transmitted symbol streams, while using a deep-subwavelength arrangement of individual plasmonic nanotransmit/receive elements in which the spacing between the transmitters and/or the receivers is tens of times smaller than the wavelength. This exclusive benefit is achieved with the aid of the phenomenon of graphene plasmons, where graphene offers the extremely confined and low-loss plasmon propagation. Hence, the proposed graphene-based MIMO system is capable of combating the fundamental limitations imposed on the classic MIMO configuration. We also present a novel graphene-specific channel adaptation technique, where the chemical potential of the graphene channel is varied to improve the power of the received signals.
S. Sugiura and H. Iizuka, "Deep-subwavelength MIMO using graphene-based nanoscale communication channel,” IEEE Access, vol. 2, no. 1, pp. 1240-1247, Oct. 2014.
Wireless sensor networks (WSN) consist of unreliable devices, sensors or vehicles, which can be used for instance as a distributed storage system. Typically, the employment of an efficient Forward Error Correction (FEC) scheme is necessary for such a virtual storage system, in order to protect source information stored in distributed sensor nodes. Furthermore, it is desirable for WSNs to be able to complete the channel-encoding process in a decentralized and distributed manner, which is for the sake of avoiding any substantial overhead and energy consumption. The novel contribution of this research is that we first propose an efficient decentralized precoding aided rateless code, where source nodes generate redundant symbols in an uncoordinated manner. This enables us to eliminate an error floor, imposed on the Luby transform (LT) code based single layer fountain code.
S. Sugiura, “Decentralized-precoding aided rateless codes for wireless sensor networks,” IEEE Communications Letters, vol. 16, no. 4, pp. 506-509, April 2012.
In recent years, cooperative space-time coding schemes as well as the suite of related techniques were proposed, where a collection of single-antenna-aided nodes act as a virtual antenna array, having widely separated distributed antenna elements. This spatially dispersed mobilestation based distributed MIMO architecture enables us to exploit the maximum achievable diversity order, while avoiding the detrimental effects of the colocated MIMO’s interantenna correlation. In this study, we presented a cooperative STC protocol, intrinsically amalgamating the concepts of asynchronous cooperation, of noncoherent detection as well as of DTC, which is capable of achieving beneficial spatialdiversity and iterative-processing gains. More specifically, assuming the configuration of multiple relay nodes, which experience realistic synchronization errors among them as well as independent path-loss and Rayleigh fading effects.
S. Sugiura, S. X. Ng, L. Kong, S. Chen, and L. Hanzo, “Quasi-synchronous cooperative networks,” IEEE Vehicular Technology Magazine, vol. 7, no. 4, pp. 66-76, Dec. 2012.
Recently, a new concept of area-based collaborative distributed cache systems has been proposed, where local useful information can be stored in a wireless distributed storage system, which is situated in a specific geographic area of interest. More specifically, such a distributed storage system consists of a collection of wireless mobile nodes in an infrastructure-less manner, which allows us to operate diverse location-specific applications. For example, file/message sharing and advertising distribution are the promising candidates. We note, nevertheless, that it is quite a challenging task to manage the connection between stored data and its saved node in a decentralized manner. In this research, we propose a novel two-layered structured overlay, called a distributed Bloom filter table (DBFT), which is capable of substantially reducing overhead imposed by highly-dynamic peer-to-peer (P2P) distributed storage systems. More specifically, in our DBFT scheme, each node’s ID remains unchanged, when the associated cluster changes due to the physical movement of the node. This provides us with an exclusive enefit of maintaining the rule of structured overlay without imposing any additional overhead to reconfigure index between saved information and its stored node, which cannot be achieved by the previous P2P techniques designed for mobile ad hoc networks.
K. Sasaki, S. Sugiura, S. Makido, and N. Suzuki, “Bloom-filter aided two-layered structured overlay for highly dynamic distributed storage,” IEEE Communications Letters, vol. 17, no. 4, pp. 629-632, Apr. 2013.
AFTER the first proposal of the faster-than-Nyquist (FTN) concept in the 1970s, it has recently been rediscovered as a means of boosting a transmission rate beyond that defined by the Nyquist criterion, without imposing any additional bandwidth expansion. Naturally, this induces unavoidable ISI effects at the receiver and imposes a higher demodulating complexity in order to eliminate ISI. the novel contribution of this study is that we are the first to propose a low-complexity frequency-domain equalization (FDE) receiver structure, which can operate in the context of FTN signaling transmissions. Our proposed scheme is especially beneficial for a long-tap FTN scenario, where a delay spread associated with ISI is substantially large.
S. Sugiura, "Frequency-domain equalization of faster-than-Nyquist signaling," IEEE Wireless Communications Letters, vol. 2, no. 5, pp. 555-558, Oct. 2013.
STOCHASTIC resonance (SR) is a physical phenomenon, which has the potential of improving the receiver’s detection performance, upon increasing the power of the additive noise contaminating the signal. Typically, such an SR effect can be observed in non-linear (NL) systems. For these reasons, the SR is especially useful in a scenario, where a small signal is corrupted by additive noise and the NL effects imposed by the receiver are intrinsically unavoidable. However, owing to the presence of a NL component, it is a challenging task to theoretically characterize its achievable performance. the novel contributions are as follows. We first propose a channel-encoded SR system, which is capable of attaining a near-capacity performance. More specifically, a serially-concatenated turbo code, employing the NL component of a single-comparator, is optimized with the aid of EXIT charts.
S. Sugiura, A. Ichiki, and Y. Tadokoro, “Stochastic-resonance based iterative detection for serially-concatenated turbo codes,” IEEE Signal Processing Letters, vol. 19, no. 10, pp. 655-658, Oct. 2012.
Recently, the sophisticated concept of SM was proposed, which serves as a novel MIMO encoding principle, which is fundamentally different from that of the SDM scheme. In the SM scheme, the transmitter activates one out of M transmit AEs, whose antenna-activation process acts as an additional means of conveying information bits, and then only the activated antenna transmits a signal modulated with the aid of the classic L-point constellation, such as PSK and Quadrature Amplitude Modulation (QAM). Unlike BLAST, SM schemes do not transmit simultaneously via M AEs, hence single-antenna based low-complexity ML detection can be employed at the receiver, while dispensing with symbol-level Inter-Antenna Synchronization (IAS) at the transmitter.
- S. Sugiura, S. Chen, and L. Hanzo, “A universal space-time architecture for multiple-antenna aided systems,” IEEE Communications Surveys & Tutorials, vol. 14, no. 2, pp. 401-420, Second Quarter, 2012.
- M. Di Renzo, H. Haas, A. Ghrayeb, S. Sugiura and L. Hanzo, "Spatial modulation for generalized MIMO: Challenges, opportunities and implementation," Proceedings of the IEEE, 2014, in press.
A reactively steered ring antenna array and its beamforming concept have been proposed for forthcoming automotive applications. The antenna features a conformal and simple configuration composed of only one RF port with multiple variable reactance circuits. Strong mutual couplings among the feed and the reactance circuits have been realized, which contribute to beamforming performance.
S. Sugiura and H. Iizuka, “Reactively steered ring antenna array for automotive application,” IEEE Transactions on Antennas and Propagation, vol. 55, no. 7, pp. 1902?1908, July 2007.