This paper describes an overview of demands on wireless communications from the point of view of robotics, oceanics and aviation technologies. These technologies are mostly applied to extreme environments, where humans cannot easily approach and directly operate equipment. In such environments, reliable and robust wireless communications are highly required to perform missions perfectly. However, there are many issues for wireless technologies to meet those requirements due to poor propagation and large delay conditions. This paper discusses wireless communication technologies required in land-sea-and-air environments based on the recent development challenges of unmanned ground and marine robots and next-generation air-transportation systems. This paper will contribute future wireless communication techniques for unmanned robots and next-generation aviations.

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This paper studies stabilization of uncertain systems over finite data rate and lossy channels. Limitations on data rate and packet loss probability are derived, characterized by the product of the eigenvalues of the plant. It is worth noting that even if we assume the most conservative plant dynamics, existing limitations for nominal plants are looser than those given in this paper. This fact implies that plant uncertainties cause strictly higher requirements in communication. We consider linear discrete-time systems with parametric uncertainties and employ uniform quantizers, which have the simplest quantization structure. Under the setup, a necessary condition and a sufficient condition for stability are derived. In particular, for scalar plants case, the conditions are exact. They coincide with the existing results for nominal plants as a special case and hence generalize them to the uncertain case.

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Self-triggered control is a control method that the control input and the sampling period are computed simultaneously in sampled-data control systems, and is studied in the field of networked control systems. In this paper, a new approach for self-triggered control is proposed based on the model predictive control (MPC) method. First, self-triggered MPC with delay compensation in which the delay-compensation input is introduced is newly formulated. Next, in order to efficiently solve this MPC problem, the optimal control problem with horizon one is formulated, and an approximate solution method is derived. Finally, the effectiveness of the proposed approach is shown by a numerical example.

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This paper discusses the reduction of the amount of transmitted information for the efficient use of frequency resources in wireless feedback control systems, and clarify the effect of the reduction of the amount of transmitted information. As a typical example of the underactuated controlled object, a rotary inverted pendulum is considered. We propose a reduction method for state information fed back from the controller to the controlled object. It estimates angle or velocity state from the previous state. In addition, we propose a reduction method that temporally omits less important control information and state information. Numerical examples clarify the effect of the reduction methods on the control quality. And we show that the reduction methods achieve large reduction of the amount of transmitted information with small disadvantage of the control quality.

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We consider a multi-hop control network where a wireless network is used for transmissions of input and output data between a plant and a computing system. We formulate a co-scheduling problem of sampling of the plant's outputs, execution of control tasks, and the routing of data transmissions in the network. Several constraints on control tasks and data transmission are described by logical formulae. By using a SAT solver, we obtain a scheduling satisfying the constraints. Through simulation, we investigate the relationship between the computation time in the SAT solver and the number of nodes in the network.

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A smart meter, a component of smart grid systems, has low computational capability. This is in contrast to data collection units (DCUs) and meter data management servers (MDMSs). In this study, we propose a lightweight signature scheme and an authentication and report protocol that can reduce computational overhead and facilitate efficient operation of these three components in smart grid systems. The proposed signature scheme, called the linear map digital signature scheme (LMDSS), uses properties of linear maps and matrix operations; hence, it has low computational requirements. The proposed protocol is a delegation-based authentication protocol that uses an intermediate node, DCU. Using the proposed protocol, authentication of a DCU can be completed by a hash function. To evaluate the performance of the scheme and protocol, we implemented signature schemes, ours and others, and simulated the proposed protocol to obtain analytical results. We also proved that the scheme is secure by using a random oracle and analyzing the security of the protocol based on possible attack scenarios.

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It is known that demand and supply power balancing is an essential method to operate power delivery system and prevent blackouts caused by power shortage. In this paper, we focus on the implementation of demand response strategy to save power during peak hours by using Smart Grid. It is obviously impractical with centralized power control network to realize the real-time control performance, where a single central controller measures the huge metering data and sends control command back to all customers. For that purpose, we propose a new architecture of hierarchical distributed power control network which is scalable regardless of the network size. The sub-controllers are introduced to partition the large system into smaller distributed clusters where low-latency local feedback power control loops are conducted to guarantee control stability. Furthermore, sub-controllers are stacked up in an hierarchical manner such that data are fed back layer-by-layer in the inbound while in the outbound control responses are decentralized in each local sub-controller for realizing the global objectives. Numerical simulations in a realistic scenario of up to 5000 consumers show the effectiveness of the proposed scheme to achieve a desired 10% peak power saving by using off-the-shelf wireless devices with IEEE802.15.4g standard. In addition, a small-scale power control system for green building test-bed is implemented to demonstrate the potential use of the proposed scheme for power saving in real life.

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This paper presents an independent sleep scheduling protocol for energy-efficient wireless body area networks. We designed the proposed protocol based on the IEEE 802.15.6 standard that is flexible to cover various application requirements for WBAN. The target of the proposed protocol is applications that generate aperiodic and intermittent traffic. Thus, the node providing these applications wakes up only when a new event occurs. We perform the numerical analysis and the simulation to compare the IEEE 802.15.6 without and with the independent sleep scheduling protocol. The results show that the proposed protocol increases energy-efficiency in case of large data size as well as long data occurrence interval.

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In forthcoming sensor networks, a multitude of sensor nodes deployed over a large geographical area for monitoring traffic, climate, etc. are expected to become an inevitable infrastructure. Clustering algorithms play an important role in aggregating a large volume of data that are produced continuously by the huge number of sensor nodes. In such networks, equal-sized multi-hop clusters which include an equal number of nodes are useful for efficiency and resiliency. In addition, scalability is important in such large-scale networks. In this paper, we mathematically design a decentralized equal-sized clustering algorithm using a partial differential equation based on the Fourier transform technique, and then design its protocol by discretizing the equation. We evaluated through simulations the equality of cluster sizes and the resiliency against packet loss and node failure in two-dimensional perturbed grid topologies.

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A use of ultra wideband (UWB) technology within spacecrafts has been proposed with a view to partially replacing wired interface buses with wireless connections. Adoption of wireless technologies within the spacecrafts could contribute to reduction in cable weight (and launching cost as a result), reduction in the cost of manufacture, more flexibility in layout of spacecraft subsystems, and reliable connections at rotary, moving, and sliding joints. However, multipath propagation in semi-closed conductive enclosures, such as spacecrafts, restricts the link performance. In this paper, UWB and narrowband propagation were measured in a UWB frequency band (from 3.1 to 10.6GHz, the full-band UWB approved in the United States) within a small spacecrafts and a shield box of the same size. While narrowband propagation resulted in considerable spatial variations in propagation gain due to interferences caused by multipath environments, UWB yielded none. This implies that the UWB systems have an advantage over narrowband from a viewpoint of reducing fading margins. Throughputs exceeding 80Mb/s were obtained by means of commercially-available UWB devices in the spacecraft. Path gains and throughputs were also measured for various antenna settings and polarizations. Polarization configurations were found to produce almost no effect on average power delay profiles and substantially small effects on the throughputs. Significantly long delay spreads and thus limited link performance are caused by a conductive enclosure (the shield box) without apertures on the surfaces. Even in such an environment, it was found that delay spreads can be suppressed by partially paneling a radio absorber on the inner surfaces. More than 96Mb/s throughputs were attained when the absorber panel covered typically 4% of the total inner surface area.

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This work proposes an exponential computation with low-computational complexity and applies this technique to the expectation-maximization (EM) algorithm for Gaussian mixture model (GMM). For certain machine-learning techniques, such as the EM algorithm for the GMM, fast and low-cost implementations are preferred over high precision ones. Since the exponential function is frequently used in machine-learning algorithms, this work proposes reducing computational complexity by transforming the function into powers of two and introducing a look-up table. Moreover, to improve efficiency the look-up table is scaled. To verify the validity of the proposed technique, this work obtains simulation results for the EM algorithm used for parameter estimation and evaluates the performances of the results in terms of the mean absolute error and computational time. This work compares our proposed method against the Taylor expansion and the exp() function in a standard C library, and shows that the computational time of the EM algorithm is reduced while maintaining comparable precision in the estimation results.

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This paper presents a method of designing transmission line couplers (TLCs) and a mixer-based receiver for dicode partial response communications. The channel design method results in the optimum TLC design. The receiver with mixers and DC balancing circuits reduces the threshold control circuits and digital circuits to decode dicode partial response signals. Our techniques enable low inter-symbol interference (ISI) dicode partial response communications without three level decision circuits and complex threshold control circuits. The techniques were evaluated in a simulation with an EM solver and a transistor level simulation. The circuit was designed in the 90-nm CMOS process. The simulation results show 12-Gb/s operation and 52mW power consumption at 1.2V.

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Due to the increasing need for low-power circuits in mobile applications, numerous leakage and performance optimization techniques are being used in modern ICs. In the present paper, we propose a novel transistor-level technique to reduce leakage current while maintaining drive current. By slightly increasing the channel length at the edge of a device that exploits the edge effect, a leakage-optimized transistor can be produced. By using TCAD simulations, we analyze edge-length-biased transistors and then propose the optimal transistor shape for minimizing I_off with the same or higher I_on current. Results show that by replacing all standard cells with their leakage-optimized counterparts, we can save up to 17% of the leakage in average for a set of benchmark circuits.

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A method of calculating the exact top event probability of a fault tree with dynamic gates and repeated basic events is proposed. The top event probability of such a dynamic fault tree is obtained by converting the tree into an equivalent Markov model. However, the Markov-based method is not realistic for a complex system model because the number of states that should be considered in the Markov analysis increases explosively as the number of basic events in the model increases. To overcome this shortcoming, we propose an alternative method in this paper. It is a hybrid of a Bayesian network (BN) and an algebraic technique. First, modularization is applied to a dynamic fault tree. The detected modules are classified into two types: one satisfies the parental Markov condition and the other does not. The module without the parental Markov condition is replaced with an equivalent single event. The occurrence probability of this event is obtained as the sum of disjoint sequence probabilities. After the contraction of modules without parent Markov condition, the BN algorithm is applied to the dynamic fault tree. The conditional probability tables for dynamic gates are presented. The BN is a standard one and has hierarchical and modular features. Numerical example shows that our method works well for complex systems.

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In modern cryptographic systems, physical unclonable functions (PUFs) are efficient mechanisms for many security applications, which extract intrinsic random physical variations to generate secret keys. The classical PUFs mainly exhibit static challenge-response behaviors and generate static keys, while many practical cryptographic systems need reconfigurable PUFs which allow dynamic keys derived from the same circuit. In this paper, the concept of reconfigurable multi-port PUFs (RM-PUFs) is proposed. RM-PUFs not only allow updating the keys without physically replacement, but also generate multiple keys from different ports in one clock cycle. A practical RM-PUFs construction is designed based on asynchronous clock and fabricated in TSMC low-power 65nm CMOS process. The area of test chip is 1.1mm², and the maximum clock frequency is 0.8GHz at 1.2V. The average power consumption is 27.6mW at 27°C. Finally, test results show that the RM-PUFs generate four reconfigurable 128-bit secret keys, and the keys are secure and reliable over a range of environmental variations such as supply voltage and temperature.

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This paper presents a novel color descriptor based on the proposed Color Barycenter Hexagon (CBH) model for automatic Road-Sign (RS) detection. In the visual Driver Assistance System (DAS), RS detection is one of the most important factors. The system provides drivers with important information on driving safety. Different color combinations of RS indicate different functionalities; hence a robust color detector should be designed to address color changes in natural surroundings. The CBH model is constructed with barycenter distribution in the created color triangle, which represents RS colors in a more compact way. For detecting RS, the CBH model is used to segment color information at the initial step. Furthermore, a judgment process is applied to verify each RS candidate through the size, aspect ratio, and color ratio. Experimental results show that the proposed method is able to detect RS with robust, accurate performance and is invariant to light and scale in more complex surroundings.

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Recursive least squares-based online nonnegative matrix factorization (RLS-ONMF), an NMF algorithm based on the RLS method, was developed to solve the NMF problem online. However, this method suffers from a partial-data problem. In this study, the partial-data problem is resolved by developing an improved online NMF algorithm using RLS and a sparsity constraint. The proposed method, RLS-based online sparse NMF (RLS-OSNMF), consists of two steps; an estimation step that optimizes the Euclidean NMF cost function, and a shaping step that satisfies the sparsity constraint. The proposed algorithm was evaluated with recorded speech and music data and with the RWC music database. The results show that the proposed algorithm performs better than conventional RLS-ONMF, especially during the adaptation process.

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The wideband noise controlling performance of the delayless subband adaptive filtering technique is affected by the group delay and in-band aliasing distortion of analysis filter banks. A method of recursive second-order cone programming is proposed to design the uniform DFT modulated analysis filter banks, with a small in-band aliasing error and low group delay. Simulation results show that the noise controlling performance is improved with small residual noise power spectra, a high noise attenuation level and fast convergence rate.

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Recent interest in wireless power transfer research has been attracting a great deal of attention. To transfer power efficiently and safely in wireless power transfer system, information, such as frequency, required power and element values, need to be transmitted reliably. However, the bandwidth, which is used for exchanging information, is affected by the change of load at the receiver when it is charging. This paper investigates the effect of load fluctuation in data communication using orthogonal frequency division multiplexing (OFDM) modulation in resonant-type wireless power transfer systems. The equivalent circuit used in the transmitting and receiving antennas is a band pass filter (BPF) and its bandwidth is evaluated through circuit simulations. Numerical results obtained through computer simulation show that the bit error rate (BER) performance is affected by the load fluctuation and the efficiency of power transfer.

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In this letter, a design of inverse discrete cosine transform for energy-efficient watermarking mechanism based on DS-CDMA with significant energy and area reduction is presented. Taking advantage of converged input data value set as a precomputation concept, the proposed one-dimensional IDCT is a multiplierless hardware which differs from Loeffler architecture and has benefits of low complexity and low power consumption. The experimental results show that our design can reduce 85.2% energy consumption and 58.6% area. Various spectrum and spatial attacks are also tested to corroborate the robustness.

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The linear complexity of quaternary sequences plays an important role in cryptology. In this paper, the minimal polynomial of a class of quaternary sequences with low autocorrelation constructed by generalized cyclotomic sequences pairs is determined, and the linear complexity of the sequences is also obtained.

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In this letter, we first introduce a new generalized cyclotomic sequence of order two of length pq, then we calculate its linear complexity and minimal polynomial. Our results show that this sequence possesses both high linear complexity and optimal balance on 1s and 0s, which may be attractive for use in stream cipher cryptosystems.

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Turbo equalization is an iterative equalization and decoding technique that can achieve impressive performance gains for communication systems. In this letter, we investigate the turbo equalization method for the decoding of the Davey-MacKay (DM) construction over the IDS-AWGN channels, which indicates a cascaded insertion, deletion, substitution (IDS) channel and an additive white Gaussian noise (AWGN) channel. The inner decoder for the DM construction can be seen as an maximum a-posteriori (MAP) detector. It receives the beliefs generated by the outer LDPC decoder when turbo equalization is used. Two decoding schemes with different kinds of inner decoders, namely hard-input inner decoder and soft-input inner decoder, are investigated. Simulation results show that significant performance gains are obtained for both decoders with respect to the insertion/deletion probability at different SNR values.

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The average Hamming correlation is an important performance indicator of frequency-hopping sequences (FHSs). In this letter, the average partial Hamming correlation (APHC) properties of FHSs are discussed. Firstly, the theoretical bound on the average partial Hamming correlation of FHSs is established. It works for any correlation window with length 1≤ω≤v, where v is the sequence period, and generalizes the bound developed by Peng et al which is valid only when ω=v. A sufficient and necessary condition for a set of FHSs having optimal APHC for any correlation window is then given. Finally, sets of FHSs with optimal APHC are presented.

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In this letter, we present a joint blind adaptive scheme to suppress inter-block interference and estimate a carrier frequency offset (CFO) in downlink OFDMA systems. The proposed scheme is a combination of a channel shortening method and a CFO estimator, both based on the carrier nulling criterion. Simulation results demonstrate the effectiveness of the proposed scheme.

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To mitigate the inter-cell interference in multicell downlink systems, this letter consider the robust precoder design for multicell cooperation where the knowledge of channel state available at the base station is imperfect. Assuming that imperfect channel state information (CSI) can be exchanged among cells but with no data sharing, we investigate the worst-case performance optimization problem with bounded CSI error. Our objective is to minimize the weighted sum mean-square-error (MSE) subject to per-base-station power constraints. A distributed solution is obtained by reformulating the upper bound of MSE and exploiting the Lagrangian method for the optimal problem. Simulation results demonstrate that the proposed algorithm is robust to guarantee the worst-case sum rate performance and has lower computational complexity than the SINR-based design.

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