In this paper, we propose an analytical approach for adaptive decode-and-forward (ADF) relaying schemes consisting of burst data transmission based on pilot symbol assisted-channel estimation (PSA-CE) methods over quasi-static Rayleigh fading channels. At first, we focus on the error-event at relay nodes in which the transmission mode switching is carried out burst by burst, whereas previous studies assumed the transmission mode switching symbol-by-symbol, thus showing lower error rate bound. Under consideration of burst transmission for ADF relay systems, we derive exact error rate expressions which better estimate the performance of actual systems. Then, the average bit and burst error rates are derived in approximated expressions for an arbitrary link signal-to-noise ratio (SNR) related with channel estimation errors. Their accuracy is confirmed by comparison with simulation results. Furthermore, ADF relay systems with PSA-CE schemes are confirmed to select correctly decoded relay nodes without additional signaling between relay nodes and the destination node and it is verified to achieve the performance at a cost of negligible SNR loss.

This paper extends our previously proposed non-orthogonal multiple access (NOMA) scheme to the base station (BS) cooperative multiple-input multiple-output (MIMO) cellular downlink for future radio access. The proposed NOMA scheme employs intra-beam superposition coding of a multiuser signal at the transmitter and the spatial filtering of inter-beam interference followed by the intra-beam successive interference canceller (SIC) at the user terminal receiver. The intra-beam SIC cancels out the inter-user interference within a beam. This configuration achieves reduced overhead for the downlink reference signaling for channel estimation at the user terminal in the case of non-orthogonal user multiplexing and enables the use of the SIC receiver in the MIMO downlink. The transmitter beamforming (precoding) matrix is controlled based on open loop-type random beamforming using a block-diagonalized beamforming matrix, which is very efficient in terms of the amount of feedback information from the user terminal. Simulation results show that the proposed NOMA scheme with block-diagonalized random beamforming in BS cooperative multiuser MIMO and the intra-beam SIC achieves better system-level throughput than orthogonal multiple access (OMA), which is assumed in LTE-Advanced. We also show that BS cooperative operation along with the proposed NOMA further enhances the cell-edge user throughput gain which implies better user fairness and universal connectivity.

In this paper, we analyze the rollback traffic in polar-orbit satellite networks that use the snapshot routing algorithm. The concept of diamond rollback links and polar rollback links are presented for the first time, and the numbers of diamond and polar rollback links in polar-orbit satellite networks are concisely formulated. Simulations are performed based on the Iridium and Teledesic system in NS2, and the results finally confirm our analysis. With this work, we can not only simplify the rollback loops avoidance scheme, but also provide guidance for future satellite network routing optimization and topology design.

In wireless LANs, wireless clients are associated with one of access points (APs) to obtain network connectivity, and the AP performs network traffic relay between the wired infrastructure and wireless clients. If a client with a low transmission rate is associated with an AP, the throughput performance of all the clients that are associated with the AP is significantly degraded because of the long channel usage time of the low-rate client. Therefore, it is important to select an appropriate AP when a new client joins the wireless LAN to prevent the performance degradation. In this paper, we propose a traffic control that determines the feasible data traffic from an AP to the clients on the basis of the trade-off relationship between the equal-throughput and equal-airtime traffic allocation policies. We then propose a network-wide association algorithm that allows a client to be associated with the AP that can provide the highest throughput improvement. Simulation results indicate that the proposed algorithm achieves the better aggregate throughput and throughput fairness performances in IEEE 802.11 WLANs.

In this paper, a threshold-based I-Q diversity combining scheme for ultra-high frequency (UHF) radio frequency identification (RFID) readers with a quadrature receiver is proposed in the aspect of improving the tag detection performance. In addition, the performance of the proposed scheme is evaluated as the closed-form expressions. In particular, its statistical characteristics are detailed and its performance is compared to that of conventional schemes over independent and identically distributed Rician fading conditions in terms of average signal-to-noise ratio (SNR), bit error rate (BER), and the average number of required combining process. Numerical results indicate that the proposed scheme enables processing power control through threshold control while meeting the required quality of service compared to conventional schemes.

The Earth's ionosphere can hinder radio propagation with two serious problems: group delay and phase advance. Ionospheric irregularities are significantly troublesome since they make the amplitude and phase of the radio signals fluctuate rapidly, which is known as ionospheric scintillation. Severe ionospheric scintillation could cause loss of phase lock, which would degrade the positioning accuracy and affect the performance of navigation systems. Based on the phase screen model, this paper presents a novel power spectrum model of phase scintillation and a model of amplitude scintillation. Preliminary results show that, when scintillation intensity increases, the random phase and amplitude fluctuations become stronger, coinciding with the observations. Simulations of the scintillation effects on the acquisition of Beidou signals predict acquisition probability. In addition, acquisition probabilities of GPS and Beidou signals under different scintillation intensities are presented. And by the same SNR the acquisition probability decreases when the scintillation intensity increases. The simulation result shows that scintillation could cause the loss of the acquisition performance of Beidou navigation system. According to the comparison of Beidou and GPS simulations, the code length and code rate of satellite signals have an effect on the acquisition performance of navigation system.

A regional protection system based on a wireless Ad-Hoc network has been in operation since 2008 in Shiojiri City, Japan. Wireless terminals transmit data packets to a server via transponders situated around the city. In this paper, a new routing algorithm that takes into account the level of congestion of the transponders is proposed. Using computer simulations, the proposed algorithm is shown to reduce the packet loss rate compared to the previous algorithm which is based on minimization of the number of hops to the server. Also, the proposed algorithm is shown be have almost the same packet loss rate as the best routing decisions obtained by an exhaustive search. Furthermore, the simulations used recreate the actual movement of terminals, so the results show what will happen in a realistic environment.

Although Quasi Orthogonal Space Time Block Code (QOSTBC) is capable of achieving a full rate transmission for more than two transmit antennas, its generation entails a complex algorithm to create the transmission matrix for a very large number of antennas. This paper presents a simplified generation scheme of QOSTBC, which can be generalized to 2k antennas for any positive integer k. In addition, under a realistic massive MIMO with up to 16 transmit and receive antennas, the performance evaluation is conducted. It is verified that the proposed scheme provides significant performance with BPSK and QPSK modulation formats in Rayleigh fading channels.

This letter presents performance analysis in the high signal-to-noise ratio (SNR) region for matched filter (MF) precoding in single cell Massive MIMO systems. The outage probability function is derived in closed form, and the data rate of each user is also given. We have also presented asymptotic analysis in terms of data rate for MF when the number of users and the number of antennas grow without bounds. The expressions of these analytical results are rather simple and are thus convenient for overall performance evaluation. The simulation results show that the analysis are very accurate.

This paper presents a particle swarm optimization network (PSON) to improve the search capability of PSO. In PSON, multi-PSOs are connected for the purpose of communication. A variety of network topology can be realized by varying the number of connected PSOs of each PSO. The solving performance and convergence speed can be controlled by changing the network topology. Furthermore, high parallelism is can be realized by assigning PSO to single processor. The stability condition analysis and performance of PSON are shown.

The built-in Pseudo Random Number Generator (PRNG) of OpenSSL on Android platform is important for producing the encryption keys and nonce needed for SSL/TLS communication. In addition, it is also widely used in generating random numbers for many applications irrelevant to SSL. We demonstrated that the initial OpenSSL PRNG state of Android apps can be restored practically, and claimed that a PreMasterSecret (PMS) can be recovered in certain apps using the RSA key agreement scheme at CCS2013. In this paper, we investigate more deeply the practical effect of the predictability of OpenSSL PRNG. First, we precisely analyze, and reduce the complexity of a PMS recovery attack on SSL with the RSA key exchange by analyzing the ASLR mechanism of Android. As a result, we show that the PMS can be recovered in O(246) computations with a probability of 25%. Next, we show that the attack is also applicable to the PMS of the ECDH key exchange by analyzing the heap memory pattern. We confirmed experimentally that the PMS can be recovered in real-time with a probability of 20%. Finally, we show the relation between the predictability of OpenSSL PRNG and the vulnerability of Android SecureRandom java class.

In this article, we study skew cyclic codes over $R=mathbb{F}_{q}+vmathbb{F}_{q}+v^{2}mathbb{F}_{q}$, where $q=p^{m}$, $p$ is an odd prime and v3=v. We describe the generator polynomials of skew cyclic codes over this ring and investigate the structural properties of skew cyclic codes over R by a decomposition theorem. We also describe the generator polynomial of the dual of a skew cyclic code over R. Moreover, the idempotent generators of skew cyclic codes over $mathbb{F}_{q}$ and R are considered.

Ultra high definition (UHD) imaging systems have attracted much attention as a next generation television (TV) broadcasting service and video streaming service. However, the state of the art video coding standards including H.265/HEVC has not enough compression rate for streaming, broadcasting and storing UHD. Existing coding standard such as H.265/HEVC normaly use RGB-YCbCr color transform before compressing RGB color image since that procedure can decorrelate color components well. However, there is room for improvement on the coding efficiency for color image based on an observation that the luminance and chrominance components changes in same locations. This observation inspired us to propose a new post-processing method for compressed images by using weighted least square (WLS) filter with coded luminance component as a guide image, for refining the edges of chrominance components. Since the computational cost of WLS tends to superlinearly increase with increasing image size, it is difficult to apply it to UHD images. To overcome this problem, we propose slightly overlapped block partitioning and a new variant of WLS (constrained WLS, CWLS). Experimental results of objective quality comparison and subjective assessment test using 4K images show that our proposed method can outperform the conventional method and reduce the bit amount for chrominance component drastically with preserving the subjective quality.

Recently, Intelligent Transport Systems (ITS) are being researched and developed briskly. As a part of ITS, detecting vehicles from images taken by a camera loaded on a vehicle are conducted. From such backgrounds, authors have been conducting vehicle detection in nighttime. To evaluate the accuracy of this detection, gold standards of the detection are required. At present, gold standards are created manually, but manually detecting vehicles take time. Accordingly, a system which detects vehicles accurately without human help is needed to evaluate the accuracy of the vehicle detection in real time. Therefore the purpose of this study is to automatically detect vehicles in nighttime images, taken by an in-vehicle camera, with high accuracy in offline processing. To detect vehicles we focused on the brightness of the headlights and taillights, because it is difficult to detect vehicles from their shape in nighttime driving scenes. The method we propose uses Center Surround Extremas, called CenSurE for short, to detect blobs. CenSurE is a method that uses the difference in brightness between the lights and the surroundings. However, blobs obtained by CenSurE will also include objects other than headlights and taillights. For example, streetlights and delineators would be detected. To distinguish such blobs, they are tracked in inverse time and vehicles are detected using tags based on the characteristics of each object. Although every object appears from the same point in forward time process, each object appears from different places in images in inverse time processing, allowing it to track and tag blobs easily. To evaluate the effectiveness of this proposed method, experiment of detecting vehicles was conducted using nighttime driving scenes taken by a camera loaded on a vehicle. Experimental results of the proposed method were nearly equivalent to manual detection.

The present study proposes a method for estimation of subjective image quality, for combinations of display physical factors, based on the Mahalanobis-Taguchi system in the field of quality engineering. The proposed method estimates subjective image quality by the estimated equation based on the Mahalanobis-Taguchi System and subjective evaluation experiments using the method of successive categories for images of which parameters are combinations of gamma, maximum luminance and minimum luminance. The estimated image quality is in good agreement with the experimental subjective image quality.

Multi-hop networks have been proposed to increase the data transmission rate in wireless mobile networks, and consequently improve the quality of experience of cell-edge users. A successive resource allocation scheme (SAS) has been proposed for a 2-hop virtual cellular network (VCN). In a multi-cell environment, the performance of SAS degrades because of intra-cell and inter-cell interference. In order to alleviate the effect of intra-cell and inter-cell interference and consequently increase the channel capacity of the VCN, this paper proposes the sequential iterative allocation scheme (SIS). Computer simulation results show that, compared to SAS, SIS can improve the fairness, the ergodic, and the outage channel capacity per mobile terminal (MT) of the VCN in a multi-cell environment. This paper also analyzes the performance of the VCN compared to that of the single hop network (SHN) when SIS is applied in a multi-cell environment. Using SIS, VCN can provide higher ergodic channel capacity, and better degree of fairness than SHN in a multi-cell environment. The effect of the number of wireless ports (WPs) in the VCN is also investigated, and the results suggest that adding more WPs per virtual cell in the VCN can enhance the outage channel capacity per MT and the degree of fairness of the VCN.

Compressive sensing (CS)-based channel estimation considerably reduces pilot symbols usage by exploiting the sparsity of the propagation channel in the delay-Doppler domain. In this paper, we consider the application of Bayesian approaches to the sparse channel estimation in orthogonal frequency division multiplexing (OFDM) systems. Taking advantage of the block-sparse structure and statistical properties of time-frequency selective channels, the proposed Bayesian method provides a more efficient and accurate estimation of the channel status information (CSI) than do conventional CS-based methods. Moreover, our estimation scheme is not limited to the Gaussian scenario but is also available for channels that have non-Gaussian priors or unknown probability density functions. This characteristic is notably useful when the prior statistics of channel coefficients cannot be precisely estimated. We also design a combo pilot pattern to improve the performance of the proposed estimation scheme. Simulation results demonstrate that our method performs well at high Doppler frequencies.

Nowadays, many individuals and organizations tend to outsource their data to a cloud storage for reducing the burden of data storage and maintenance. However, a cloud provider may be untrustworthy. The cloud thus leads to a numerous security challenges: data availability, data integrity, and data confidentiality. In this paper, we focus on data availability and data integrity because they are the prerequisites of the existence of a cloud system. The approach of this paper is the network coding-based Proof of Retrievability (POR) scheme which allows a client to check whether his/her data stored on the cloud servers are intact. Although many existing network coding-based PORs have been proposed, most of them still incur high costs in data check and data repair, and cannot prevent the small corruption attack which is a common attack in the POR scheme. This paper proposes a new network coding-based POR using the dispersal coding technique, named the ND-POR (Network coding - Dispersal coding POR) to improve the efficiency in data check and data repair and to protect against the small corruption attack.

An electro-optic (EO) modulator integrated with the microwave planar circuit directly formed on a LiNbO3 (LN) substrate for low frequency-chirp performance and compact configuration is introduced. Frequency chirp of EO intensity modulators was investigated and a dual-electrode Mach-Zehnder (MZ) modulator combined with a microwave rat-race (RR) circuit was considered for the low-chirp modulation. The RR circuit, which operates as a 180-degree hybrid, was designed on a z-cut LN substrate to create two modulation signals of the same amplitude in anti-phase with each other from a single input signal. Output ports of the RR were connected to the modulation electrodes on the substrate. The two signals of the equal amplitude drive two phase modulation parts of the modulator so that the symmetric interference are realized to obtain intensity modulation of low frequency-chirp. The modulator was designed and fabricated on a single LN substrate for around 10 GHz modulation frequencies and 1550 nm light wavelength. The chirp parameters were measured to be less than 0.2 in the frequency range between 8 and 12 GHz. By compensating imbalance of the light power splitting in the waveguide MZ interferometer the chirp could be reduced even more.

We investigate a quantization error improvement technique using a dual rail configuration for optical quantization. Our proposed optical quantization uses intensity-to-wavelength conversion based on soliton self-frequency shift and spectral compression based on self-phase modulation. However, some unfavorable input peak power regions exist due to stagnations of wavelength shift or distortions of spectral compression. These phenomena could induce a serious quantization error and degrade the effective number of bit (ENOB). In this work, we propose a quantization error improvement technique which can make up for the unfavorable input peak power regions. We experimentally verify the quantization error improvement effect by the proposed technique in 6 bit optical quantization. The estimated ENOB is improved from 5.35 bit to 5.66 bit. In addition, we examine the XPM influence between counter-propagating pulses at high sampling rate. Experimental results and numerical simulation show that the XPM influence is negligible under ∼40 GS/s conditions.