Image sensor communication (ISC), a type of visible light communication, is an emerging wireless communication technology that uses LEDs to transmit a signal and uses an image sensor in a camera to receive the signal. This paper discusses the present status of and future trends in ISC by describing the essential characteristics and features of ISC. Moreover, we overview the products and expected future applications of ISC.

A new class of visible light communication (VLC) systems, namely image sensor (IS) based VLC systems, has emerged. An IS consists of a two-dimensional (2D) array of photodetectors (PDs), and then VLC systems with an IS receiver are capable of exploiting the spatial dimensions invoked for transmitting information. This paper aims for providing a brief survey of topics related to the IS-based VLC, and then provides a matrix representation of how to map a series of one dimensional (1D) symbols onto a set of 2D symbols for efficiently exploit the associate grade of freedom offered by 2D VLC systems. As an example, the matrix representation is applied to the symbol mapping of layered space-time coding (L-STC), which is presented to enlarge the coverage of IS-based VLC that is limited by pixel resolution of ISs.

The purpose of this study was to examine an efficient interval encoding method with a slow-frame-rate image sensor, and show that the encoding can work to capture heart rates from multiple persons. Visible light communication (VLC) with an image sensor is a powerful method for obtaining data from sensors distributed in the field with their positional information. However, the capturing speed of the camera is usually not fast enough to transfer interval information like the heart rate. To overcome this problem, we have developed an event timing (ET) encoding method. In ET encoding, sensor units detect the occurrence of heart beat event and send their timing through a sequence of flashing lights. The first flash signal provides the rough timing and subsequent signals give the precise timing. Our theoretical analysis shows that in most cases the ET encoding method performs better than simple encoding methods. Heart rate transfer from multiple persons was examined as an example of the method's capabilities. In the experimental setup, the developed system successfully monitored heart rates from several participants.

Spatial modulation (SM) is introduced into layered space-time coding (L-STC) used in image sensor (IS)-based visible light communication (VLC) systems. STC was basically investigated for extending the communication range of the IS-based VLC link [10], although it is out of the range when IS receivers are at the long distance from the LED array of the transmitter where the number of pixels capturing the transmitter on the image plane is less than the number of LEDs of the array. Furthermore, L-STC was done in [11] for increasing the reception rate with improving the pixel resolution while the receiver was approaching the transmitter. In this paper, SM is combined into L-STC by mapping additional information bits on the location of the pair of STC bit matrices of each layer. Experimental results show that additional SM bits are extracted with no error, without deteriorating the reception quality of and shrinking the transmission range of the original L-STC.

A power packet dispatching system is proposed to realize the function of power on demand. This system distributes electrical power in quantized form, which is called power processing. This system has extensibility and flexibility. Here, we propose to use the power packet dispatching system as the next generation power distribution system in self-established and closed system such as robots, cars, and aircrafts. This paper introduces the concept and the required researches to take the power packet dispatching system in practical phase from the total viewpoints of devices, circuits, power electronics, system control, computer network, and bio-inspired power consumption.

A new Internet Draft on benchmarking methodologies for IPv6 transition technologies including DNS64 was adopted by the Benchmarking Working Group of IETF. The aim of our effort is to design and implement a test program that complies with the draft and thus to create the world's first standard DNS64 benchmarking tool. In this paper, we disclose our design considerations and high-level implementation decisions. The precision of our special timing method is tested and found to be excellent. Due to the prudent design, the performance of our test program is also excellent: it can send more than 200,000 AAAA record requests using a single core of a desktop computer with a 3.2GHz Intel Core i5-4570 CPU. Its operation comprises all the functionalities required by the draft including checking the timeliness and validity of the answers of the tested DNS64 server. Our DNS64 benchmarking program, dns64perf++, is distributed as free software under GNU GPL v2 license for the benefit of the research, benchmarking and networking communities.

In this paper, we investigate a novel preamble channel estimation (CE) method based on the compressed sensing (CS) theory in the orthogonal frequency division multiplexing system with offset quadrature amplitude modulation (OQAM/OFDM) over a frequency selective fading channel. Most of the preamble based CE methods waste power by deploying the pilots in all the subcarriers. Inspired by the CS theory, we focus on using many fewer pilots than one of traditional CE methods and realize accurate reconstruction of the channel response. After describing and analyzing the concept of OQAM/OFDM and its traditional CE methods, we propose a novel channel estimation method based on CS that requires fewer pilots in the preamble, and we design the corresponding preamble pattern to meet the requirements of CS. Simulation results validate the efficiency and superior performance of the proposed method in wireless channel.

A flexible orthogonal frequency-division multiplexing optical network enables the bandwidth to be flexibly changed by changing the number of sub-carriers. We assume that users request to dynamically change the number of sub-carriers. Dynamic bandwidth changes allow the network resources to be used more efficiently but each change takes a significant amount of time to complete. Service centric resource allocation must be considered in terms of the waiting time needed to change the number of sub-carriers. If the user demands drastically increase such as just after a disaster, the waiting time due to a chain-change of bandwidth becomes excessive because disaster priority telephone services are time-critical. This paper proposes a Grouped-elastic spectrum allocation scheme to satisfy the tolerable waiting time of the service in an optical fiber link. Spectra are grouped to restrict a waiting time in the proposed scheme. In addition, the proposed scheme determines a bandwidth margin between neighbor spectra to spectra to prevent frequent reallocation by estimating real traffic behavior in each group. Numerical results show that the bandwidth requirements can be minimized while satisfying the waiting time constraints. Additionally measurement granularity and channel alignment are discussed.

Artificial lighting is responsible for a large portion of total energy consumption and has great potential for energy saving. This paper designs an LED light control algorithm based on users' localization using multiple battery-less binary human detection sensors. The proposed lighting control system focuses on reducing office lighting energy consumption and satisfying users' illumination requirement. Most current lighting control systems use infrared human detection sensors, but the poor detection probability, especially for a static user, makes it difficult to realize comfortable and effective lighting control. To improve the detection probability of each sensor, we proposed to locate sensors as close to each user as possible by using a battery-less wireless sensor network, in which all sensors can be placed freely in the space with high energy stability. We also proposed to use a multi-sensor-based user localization algorithm to capture user's position more accurately and realize fine lighting control which works even with static users. The system is actually implemented in an indoor office environment in a pilot project. A verification experiment is conducted by measuring the practical illumination and power consumption. The performance agrees with design expectations. It shows that the proposed LED lighting control system reduces the energy consumption significantly, 57% compared to the batch control scheme, and satisfies user's illumination requirement with 100% probability.

This paper addresses power saving for STAs (Wireless Stations) in WLANs (Wireless LANs). Mobile devices are increasingly used in situations in which they access WLANs. However, mobile devices consume large amounts of power when they communicate through a WLAN, and this shortens their battery lifetime. IEEE 802.11 specifies PSM (Power-Saving Mode) as the power-saving method for standard WLANs. However, the sleep conditions specified by PSM for STAs are not optimal in terms of power saving, except when the number of STAs is small, and this increases packet transfer delay. In this paper, we propose a power-saving method in which STAs reduce power consumption by sleeping for a period specified by the NAV (Network Allocation Vector) duration, which is set by an RTS/CTS handshake, and the duration of the NAV is extended by bidirectional burst transmission. To suppress the transfer delay caused by the bidirectional burst transmission, an AP (Access Point) manages the transmission deadline of each downlink packet on the basis of its acceptable value of delay and adapts the number of packets transferred in the bidirectional burst transmission. Although another existing method also uses the NAV duration to manage STA sleeping, the bidirectional burst transmission can only be initiated by the STAs themselves and the NAV is of an extremely limited duration. On the other hand, the proposed method specifies generalized bidirectional burst transmission without the limitations of the transmission initiator and the burst length within acceptable packet transfer delay. Moreover, we investigate the combination of the proposed method with PSM in order to improve the performance in situations in which the number of STAs is small by taking advantage of the combined properties of PSM and the proposed method. The evaluation results demonstrate that these proposed methods can reduce the power consumption of wireless stations and suppress packet transfer delay.

A novel real-valued ESPRIT (RV-ESPRIT) algorithm is proposed to estimate the direction of arrival (DOA) and direction of departure (DOD) for noncircular signals in bistatic MIMO radar. By exploiting the property of signal noncircularity and Euler's formula, a new virtual array data of bistatic MIMO radar, which is twice that of the MIMO virtual array data, is established with real-valued sine and cosine data. Then the receiving/transmitting selective matrices are constructed to obtain the receiving/transmitting rotationally invariant factors. Compared to the existing angle estimation methods, the proposed algorithm has lower computational load. Simulation results confirm the effectiveness of the RV-ESPRIT.

In this paper, a new effective C/N₀ theoretical model for global navigation satellite system (GNSS) receiver is proposed, in the presence of continuous wave interference (CWI). The proposed model is derived based on an interesting finding, correlator may output direct current (DC) in the presence of CWI. The DC introduced by CWI eventually leads to increase of carrier power estimation. It is totally different from current assumption that interference just causes noise power increase after correlation. The proposed model is verified by simulation.

For a multiuser multi-input multi-output (MU-MIMO) multicell network, the Han-Kobayashi strategy aims to improve the achievable rate region by splitting the data information intended to a serviced user (UE) into a common message and a private message. The common message is decodable by this UE and another UE from an adjacent cell so that the corresponding intercell interference is cancelled off. This work aims to design optimal precoders for both common and private messages to maximize the network sum-rate, which is a highly nonlinear and nonsmooth function in the precoder matrix variables. Existing approaches are unable to address this difficult problem. In this paper, we develop a successive convex quadratic programming algorithm that generates a sequence of improved points. We prove that the proposed algorithm converges to at least a local optimum of the considered problem. Numerical results confirm the advantages of our proposed algorithm over conventional coordinated precoding approaches where the intercell interference is treated as noise.

The 1-bit band-pass delta-sigma modulator (BP-DSM) achieves high resolution by using the oversampling technique. This method allows direct RF signal transmission from a digitally modulated signal, using a 1-bit digital pulse train. However, it has been previously reported that the adjacent channel leakage ratio (ACLR) in a target frequency band degrades due to the pulse transition mismatch between rising and falling waveforms in the time domain. This paper clarifies that the spurious distortion in BP-DSM is caused by the asymmetricity of the waveform about the center of an eye pattern in the time axis, and proposes a 1-bit BP-DSM with the compensator consisting of a fractional delay filter and a binary data differentiator to cancel out the asymmetry in the target frequency band. This can accurately provide a wideband cancellation signal with more than 100MHz bandwidth, including the adjacent channel, within 50dB power dynamic range. Using long term evolution (LTE) signals with 5MHz bandwidth at 0.8GHz, we simulated the spurious distortion, performing various combinations of rising and falling times in the eye pattern, and the proposed 1-bit BP-DSM always achieved high ACLR, up to 60dB, in 140MHz bandwidth, under all conditions.

In heterogenous networks (HetNets), the deployment of small cells with the reuse of limited frequency resources to improve the spectral efficiency results in cross- and co-tier interference. In addition, the excessive power usage in such networks is also a critical problem. In this paper, we propose precoding and postcoding schemes to tackle interference and energy efficiency (EE) challenges in the two-tier downlink multiple-input-multiple-output (MIMO) HetNets. We propose transmission strategies based on hierarchical partial coordination (HPC) of the macro cell and small cells to reduce channel state information (CSI) exchange and guarantee the quality of service (QoS) in the upper tier with any change of network deployment in the lower tier. We employ the interference alignment (IA) scheme to cancel cross- and co-tier interference. Additionally, to maximize the EE, power allocation schemes in each tier are proposed based on a combination of Dinkelbach's method and the bisection searching approach. To investigate insights on the optimization problem, a theoretical analysis on the relationship between the maximum achievable EE and the transmit power is derived. Simulation results prove the superior EE performance of the proposed EE maximization scheme over the sum rate maximization approach and confirm the validity of our theoretical findings.