The online unit clustering problem is one of the most basic clustering problems proposed by Chan and Zarrabi-Zadeh (WAOA2007 and Theory of Computing Systems 45(3), 2009). Several variants of this problem have been extensively studied. In this letter, we propose a new variant of the online unit clustering problem, called the online unit clustering problem with capacity constraints. For this problem, we use competitive analysis to evaluate the performance of an online algorithm. Then, we develop an online algorithm whose competitive ratio is at most 3.178, and show that a lower bound on the competitive ratio of any online algorithm is 2.

This letter proposes a Light Space Partitioned Shadow Maps (LSPSMs) algorithm which implements shadow rendering based on a novel partitioning scheme in light space. In stead of splitting the view frustum like traditional Z-partitioning methods, we split partitions from the projection of refined view frustum in light space. The partitioning scheme is performed dual-directionally while limiting the wasted space. Partitions are created in dynamic number corresponding to the light and view directions. Experiments demonstrate that high quality shadows can be rendered in high efficiency with our algorithm.

Recently, computer speed and memory capacity have been advanced. Therefore, applicable space size or equivalently the frequency in the FDTD method has been increased similar as the ray-tracing method for radio wave propagation. The ray-tracing method can obtain easily important parameters such as path loss, delay profile and angular profile. On the other hand, the FDTD method seems difficult to obtain an angular profile. We can overcome this problem by applying the DOA estimation method to the FDTD method. In this paper, we show that the FDTD method can be used as a counterpart of the ray-tracing method to analyze radio wave propagation of large space by using DOA estimation method such as MUSIC method.

Mutipath matching pursuit (MMP) is a new reconstruction algorithm based on compressed sensing (CS). In this letter, we applied the MMP algorithm to channel estimation in orthogonal frequency division multiplexing (OFDM) communication systems, and then proposed an improved MMP algorithm. The improved method adjusted the number of children generated by candidates. It can greatly reduce the complexity. The simulation results demonstrate that the improved method can reduce the running time under the premise of guaranteeing the performance of channel estimation.

In color image processing, hue-preserving is necessary for human being. In order to preserve the hue component, the perceptual color spaces such as HSI and HSV were used for the color image processing. The Hue-Saturation-Intensity (HSI) color space is important for color image processing and many color applications are commonly based on this color space. However, the gamut of conventional HSI color space is larger than that of RGB color space. Thus, the gamut problem is often occurred after the processing intensity and saturation in the HSI color space. In this paper, a new HSI color space with completely same gamut of RGB color space is developed. The gamut problem is solved by the proposed HSI color space.

Theoretical maximum radiation efficiency of electrically small spherical surface antennas has been derived in this study. The current on the antenna surface is described in terms of vector spherical harmonics, and the radiated and the dissipated powers are calculated to obtain the radiation efficiency. It has been found that non-resonant TM1m mode shows the best radiation efficiency, and a proper combination of TM10 and TE10 modes establishes a resonant spherical surface antenna whose radiation efficiency is bounded by those values of non-resonant TM10 and TE10 modes. As a practical example of the spherical surface antennas, the radiation efficiency of the spherical helix antennas has also been computed to check the validity of our formulation.

The Time Domain Boundary Element Method (TDBEM) has its advantages in the analysis of transient electromagnetic fields (wake fields) induced by a charged particle beam with curved trajectory in a particle accelerator. On the other hand, the TDBEM has disadvantages of huge required memory and computation time compared with those of the Finite Difference Time Domain (FDTD) method or the Finite Integration Technique (FIT). This paper presents a comparison of the FDTD method and 4-D domain decomposition method of the TDBEM based on an initial value problem formulation for the curved trajectory electron beam, and application to a full model simulation of the bunch compressor section of the high-energy particle accelerators.

Packages are re-usable components for faster and effective software maintenance. To promote the re-use in object-oriented systems and maintenance tasks easier, packages should be organized to depict compact design. Therefore, understanding and assessing package organization is primordial for maintenance tasks like Re-usability and Changeability. We believe that additional investigations of prevalent basic design principles such as defined by R.C. Martin are required to explore different aspects of package organization. In this study, we propose package-organization framework based on reachable components that measures re-usability index. Package re-usability index measures common effect of change taking place over dependent elements of a package in an object-oriented design paradigm. A detailed quality assessment on different versions of open source software systems is presented which evaluates capability of the proposed package re-usability index and other traditional package-level metrics to predict fault-proneness in software. The experimental study shows that proposed index captures different aspects of package-design which can be practically integrated with best practices of software development. Furthermore, the results provide insights on organization of feasible software design to counter potential faults appearing due to complex package dependencies.

We fabricated silicon solar cells with spin-coated sol-gel alumina passivation layers on the rear side. Spin-coated alumina passivation films have moderate passivation quality and are inferior to atomic layer deposited passivation films. However, low-cost and low temperature process of the sol-gel deposition is still beneficial for the cells using commercially available Cz silicon wafers. Thus, we consider an applicability of the spin-coated alumina passivation layer for rear side passivation. Dependence of cell efficiency on contact spacing and contact diameter of a rear electrode was investigated by both experiments and numerical calculation. The experimental results indicated that conversion efficiency of the cell is enhanced from 9.1% to 11.1% by optimizing an aperture ratio and contact spacing of the rear passivation layers. Numerical calculation indicated that small contact diameter with low aperture ratio of a rear passivation layer is preferable to achieve good cell performance in our experimental condition. We confirmed the effectivity of the spin-coated alumina passivation films for rear surface passivation of the low-cost silicon solar cells.

In multi user multiple input multiple output systems, spatial precoding is typically employed as an interference cancellation technique. This technique, however, requires accurate channel state information at the transmitter and limits the mobility of the mobile station (MS). Instead of spatial precoding, this letter implements collaborative interference cancellation (CIC) for interference suppression. In CIC, neighboring MSs share their received signals without decoding and equivalently increase the number of received antennas. The performance is evaluated through a field experiment using a vehicle that is equipped with seven MSs and moves around an urban area.

Single-instruction multiple-data (SIMD) extension provides an energy-efficient platform to scale the performance of media and scientific applications while still retaining post-programmability. However, the major challenge is to translate the parallel resources of the SIMD hardware into real application performance. Currently, all the slots in the vector register are used when compilers exploit SIMD parallelism of programs, which can be called sufficient vectorization. Sufficient vectorization means all the data in the vector register is valid. Because all the slots which vector register provides must be used, the chances of vectorizing programs with low SIMD parallelism are abandoned by sufficient vectorization method. In addition, the speedup obtained by full use of vector register sometimes is not as great as that obtained by partial use. Specifically, the length of vector register provided by SIMD extension becomes longer, sufficient vectorization method cannot exploit the SIMD parallelism of programs completely. Therefore, insufficient vectorization method is proposed, which refer to partial use of vector register. First, the adaptation scene of insufficient vectorization is analyzed. Second, the methods of computing inter-iteration and intra-iteration SIMD parallelism for loops are put forward. Furthermore, according to the relationship between the parallelism and vector factor a method is established to make the choice of vectorization method, in order to vectorize programs as well as possible. Finally, code generation strategy for insufficient vectorization is presented. Benchmark test results show that insufficient vectorization method vectorized more programs than sufficient vectorization method by 107.5% and the performance achieved by insufficient vectorization method is 12.1% higher than that achieved by sufficient vectorization method.

The RC4 stream cipher is widely used including WEP and WPA, which are the security protocols for IEEE 802.11 wireless standard. WPA improved a construction of the RC4 key setting known as TKIP to avoid the known WEP attacks. The first 3-byte RC4 keys generated by IV in WPA are known since IV can be obtained by observing packets. The weaknesses in TKIP using the known IV were reported by Sen Gupta et al. at FSE 2014 and by Ito and Miyaji at FSE 2015. Both showed that TKIP induces many RC4 key correlations including the keystream bytes or the unknown internal states. Ideally TKIP should be constructed in such a way that it can keep the security level of generic RC4. In the first part of this paper, we will provide newly theoretical proofs of 17 correlations remain unproven in our previous work theoretically. Our theoretical analysis can make clear how TKIP induces biases of internal states in generic RC4. In the second part of this paper, we will further provide a refined construction of the RC4 key setting. As a result, we can reduce the number of correlations in the refined construction by about 70% in comparison with that in the original setting.

This paper proposes an effective signal processing scheme using a modulation code with two-dimensional (2D) run-length limited (RLL) constraints for bit-patterned media magnetic recording (BPMR). This 2D signal processing scheme is applied to be one of two-dimensional magnetic recording (TDMR) schemes for shingled magnetic recording on bit patterned media (BPM). A TDMR scheme has been pointed out an important key technology for increasing areal density toward 10Tb/in2. From the viewpoint of 2D signal processing for TDMR, multi-track joint decoding scheme is desirable to increase an effective transfer rate because this scheme gets readback signals from several adjacent parallel tracks and detect recorded data written in these tracks simultaneously. Actually, the proposed signal processing scheme for BPMR gets mixed readback signal sequences from the parallel tracks using a single reading head and these readback signal sequences are equalized to a frequency response given by a desired 2D generalized partial response system. In the decoding process, it leads to an increase in the effective transfer rate by using a single maximum likelihood (ML) sequence detector because the recorded data on the parallel tracks are decoded for each time slot. Furthermore, a new joint pattern-dependent noise-predictive (PDNP) sequence detection scheme is investigated for multi-track recording with media noise. This joint PDNP detection is embed in a ML detector and can be useful to eliminate media noise. Using computer simulation, it is shown that the joint PDNP detection scheme is able to compensate media noise in the equalizer output which is correlated and data-dependent.

This paper presents a test pattern compaction algorithm applicable for large scale circuits. The proposed methods formalizes the test pattern compaction problem as a problem finding minimum set of compatible fault groups. Also, an efficient algorithm checking compatibility of fault group is proposed. The experimental results show that the proposed algorithm achieves similar or better results against a couple of existing methods, especially for middle circuits.

Power packet is a unit of electric power transferred by a pulse with an information tag. This letter discusses up-stream dispatching of required power at loads to sources through density modulation of power packet. Here, power is adjusted at a proposed router which dispatches power packets according to the tags. It is analyzed by averaging method and numerically verified.

High peak-to-average power ratio (PAPR) and spectral leakage are two main problems of orthogonal frequency division multiplexing (OFDM) systems. For alleviating the above problems, this paper proposes a joint model which efficiently suppresses both PAPR and spectral leakage, by combining serial peak cancellation (SPC) and time-domain N-continuous OFDM (TD-NC-OFDM) in an iterative way. Furthermore, we give an analytical expression of the proposed joint model to analyze the mutual effects between SPC and TD-NC-OFDM. Lastly, simulation results also support that the joint optimization model can obtain notable PAPR reduction and sidelobe suppression performance with low implementation cost.

In this paper a hardware-efficient local extrema detection (LED) method used for scale-space extrema detection in the SIFT algorithm is proposed. By reformulating the reuse of the intermediate results in taking the local maximum and minimum, the necessary operations in LED are reduced without degrading the detection accuracy. The proposed method requires 25% to 35% less logic resources than the conventional method when implemented in an FPGA with a slight increase in latency.

In this paper, we present a GPU implementation of bulk multiple-length multiplications. The idea of our GPU implementation is to adopt a warp-synchronous programming technique. We assign each multiple-length multiplication to one warp that consists of 32 threads. In parallel processing using multiple threads, usually, it is costly to synchronize execution of threads and communicate within threads. In warp-synchronous programming technique, however, execution of threads in a warp can be synchronized instruction by instruction without any barrier synchronous operations. Also, inter-thread communication can be performed by warp shuffle functions without accessing shared memory. The experimental results show that our GPU implementation on NVIDIA GeForce GTX 980 attains a speed-up factor of 52 for 1024-bit multiple-length multiplication over the sequential CPU implementation. Moreover, we use this 1024-bit multiple-length multiplication for larger size of bits as a sub-routine. The GPU implementation attains a speed-up factor of 21 for 65536-bit multiple-length multiplication.

This letter considers a cognitive radio (CR) network where multiple secondary downlinks coexist with a primary network. The primary user (PU) is assumed to be protected by the interference outage constraint with only channel distribution information (CDI) being available at the secondary users (SUs). The power allocation problem to maximize the sum outage capacity of the SUs under the interference outage constraint and the transmit power constraint is investigated. Due to the difficulty in obtaining the optimal solution, we propose a heuristic power allocation algorithm based on the bisection search method that can guarantee to satisfy both the interference outage and the transmit power constraints. It is shown that the proposed algorithm converges fast and outperforms other reference algorithms.

Write once memory (WOM) codes allow reuse of a write-once medium. This paper focuses on applying WOM codes to the binary symmetric asymmetric multiple access channel (BS-AMAC). At one specific rate pair, WOM codes can achieve the BS-AMAC maximum sum-rate. Further, any achievable rate pair for a two-write WOM code is also an achievable rate pair for the BS-AMAC. Compared to the uniform input distribution of linear codes, the non-uniform WOM input distribution is helpful for a BS-AMAC. In addition, WOM codes enable “symbol-wise estimation”, resulting in the decomposition to two distinct channels. This scheme does not achieve the BS-AMAC maximum sum-rate if the channel has errors, however leads to reduced-complexity decoding by enabling independent decoding of two codewords. Achievable rates for this decomposed system are also given. The AMAC has practical application to the relay channel and we briefly discuss the relay channel with block Markov encoding using WOM codes. This scheme may be effective for cooperative wireless communications despite the fact that WOM codes are designed for data storage.