In this letter, we enhance Complementary Code Keying (CCK) modulation with Pseudo-Periodic Sequence. It has been proved that the new Pseudo-Periodic CCK modulation is more efficient and robust fighting against multi-path interference. In order to support our new scheme, we design and implement the corresponding simulation. The in-depth analysis of the reason why Pseudo-Periodic Sequence can do a favor to CCK is also presented and emphasized.

We show that the necessary and sufficient condition for the existence of a balanced bowtie decomposition of the symmetric complete multi-digraph is n 5 and λ(n-1) 0 (mod 6). Decomposition algorithms are also given.

Energy consumption is one of the most critical constraints in the design of portable embedded systems. This paper describes an empirical study about the impacts of compiler optimizations on the energy consumption of the address bus between processor and instruction memory. Experiments using a number of real-world applications are presented, and the results show that transitions on the instruction address bus can be significantly reduced (by 85% on the average) by the compiler optimizations together with bus encoding.

This paper describes a 0.13 µm CMOS Logic process compatible single poly gate type non-volatile (NV) memory with a differential cell architecture, which is tailored for a rewritable FUSE (CMOS-FUSE) for System-on-a Chip (SoC). This paper features the following points; 1) firstly quantified how much important is avoiding any additional process cost and area penalty rather than reducing the area of memory cell itself from the chip cost point of view for the new SoC applications. CMOS FUSE can provide cost-competitive than the high-density NV memories (50-fold higher density with 20% additional cost relative to CMOS FUSE) in the capacity range of 200 kbit for the SoC occupied the logic area of 40 mm2. 2) firstly discussed in detail how much the differential cell architecture can change a data retention characteristics including an activation energy (Ea), failure-rate, and tail-bits issues relative to the conventional one based on the measured data of 0.13 µm devices. Based on the measured data retention characteristics at 300, 250, and 200, it is found that the proposed differential approach makes it possible to increase Ea by 1.5 times (from 1.52 eV to 2.23 eV), which means it can be expected to realize a 20000-fold longer data retention characteristics at 105. Even if considering the tail-bit issues for mass-production, an over 700-fold longer data retention characteristics at 105 can be expected while keeping the same failure rate (0.01 ppm) relative to the conventional OR-logical architecture. No significant Vt shifts ( 140 mV and 200 mV) were observed even after applying surge stress of +2200 V from I/O pad and 1000-times cycling of write and erase operations, respectively. In addition, 1024-bit CMOS-FUSE module has been embedded in the SoC without any additional area penalty by being laid out just beneath the power ring for SRAM macro and the stable memory read operation was verified at VDD=1.0 V under a severe I/O switching noise and an unstable VDD/GND condition in the power up sequence.

In this paper, introducing a stochastic hill-climbing dynamics into an optimal competitive Hopfield network model (OCHOM), we propose a new algorithm that permits temporary energy increases, which helps the OCHOM escape from local minima. In graph theory, a clique is a completely connected subgraph and the maximum clique problem (MCP) is to find a clique of maximum size of a graph. The MCP is a classic optimization problem in computer science and in graph theory with many real-world applications, and is also known to be NP-complete. Recently, Galan-Marin et al. proposed the OCHOM for the MCP. It can guarantee convergence to a global/local minimum of energy function, and performs better than other competitive neural approaches. However, the OCHOM has no mechanism to escape from local minima. The proposed algorithm introduces stochastic hill-climbing dynamics which helps the OCHOM escape from local minima, and it is applied to the MCP. A number of instances have been simulated to verify the proposed algorithm.

The transformation of a data set using a second-order polynomial mapping to find statistically independent components is considered (quadratic independent component analysis or ICA). Based on overdetermined linear ICA, an algorithm together with separability conditions are given via linearization reduction. The linearization is achieved using a higher dimensional embedding defined by the linear parametrization of the monomials, which can also be applied for higher-order polynomials. The paper finishes with simulations for artificial data and natural images.

With the explosive growth of the Internet system, demands for broadband communication networks have rapidly increased to provide high quality network services. For this purpose, the IEEE 802.6 MAC standard protocol defines the distributed-queue dual bus (DQDB) for metropolitan area networks (MANs). The isochronous channel reuse problem (ICRP) has been studied for efficient use of DQDB by finding proper channel assignments to incoming connection requests. In this paper, we first define the generalized isochronous channel reuse problem (GICRP) as a generalization of ICRP, to afford demands of simultaneously satisfying plural connection requests such as for multicast applications, where certain sets of connection requests must be assigned channels simultaneously. We prove the NP-completeness of its decision problem. Then, we propose a minimum dead space (MDS) algorithm as a heuristic approach to GICRP. The extensive simulation results show that with shorter computation time, our MDS algorithm can always find better channel assignments reducing the waiting time for packet transmissions than the best existing algorithm for conventional ICRP.

Propagation modeling and advanced channel characterization techniques represent integral parts of significant impact in advancing progress in enabling next generation wireless communication technology and realizing its much anticipated broader application and economic benefits. In this paper we describe advances in developing computationally efficient ray-tracing channel modeling procedures, and also describe recent results in characterizing challenging propagation environments including transmission through windows and propagation through walls of complex structures. The impact of these realistic propagation environments as well as the antenna mutual coupling effects on the estimation of channel capacity in a MIMO-based communication system is also evaluated. Significant difference between realistic and statistical channel models are identified and quantified for the special cases of the channels modeled in this study.

We propose a robust edge detection method based on independent component analysis (ICA). It is known that most of the basis functions extracted from natural images by ICA are sparse and similar to localized and oriented receptive fields, and in the proposed edge detection method, a target image is first transformed by ICA basis functions and then the edges are detected or reconstructed with sparse components only. Furthermore, by applying a shrinkage algorithm to filter out the components of noise in the ICA domain, we can readily obtain the sparse components of the original image, resulting in a kind of robust edge detection even for a noisy image with a very low SN ratio. The efficiency of the proposed method is demonstrated by experiments with some natural images.

This paper presents a path compression protocol for on-demand ad hoc network routing protocols, which is called dynamic path shortening (DPS). In DPS, active route paths adapt dynamically to node mobility based on the "local" link quality estimation at each own node, without exchanging periodic control packets such as Hello messages. Each node monitors its own local link quality only when receiving packets and estimates whether to enter the "proximity" of the neighbor node to shorten active paths in a distributed manner. Simulation results of DPS in several scenarios of various node mobility and traffic flows reveal that adding DPS to DSR which is the conventional prominent on-demand ad hoc routing protocol significantly reduces the end-to-end packet latency up to 50-percent and also the number of routing packets up to 70-percent over the pure DSR, in heavy traffic cases. We also demonstrate the other simulation results obtained by using our two novel mobility models which generate more realistic node mobility than the standard random waypoint mobility model: Random Orientation Mobility and Random Escape Mobility models. Finally, simple performance experiments using DPS implementation on FreeBSD OS demonstrate that DPS shortens active routes in the order of milliseconds (about 5 ms).

This paper presents a new approach based on current mode circuits for fast and accurate optical level monitoring with wide dynamic range of a gigabit burst-mode laser driver chip. Our proposed solution overcomes the drawbacks that voltage mode implementations show at higher bit rates or in other technologies. The main speed-limiting factor of the level monitoring circuitry is the parasitic capacitance of the back facet monitor photodiode. We propose the use of an active-input current mirror to reduce the impact of this parasitic capacitance. The mirror produces two copies of the photo current, one to be used for the "0" level measurement and another for the "1" level measurement. The mirrored currents are compared to two reference currents by two current comparators. Every reference current needs only one calibration at room temperature. A pattern detection block scans the incoming data for patterns of sufficiently long consecutive 0's or 1's. At the end of such a pattern a valid measurement is present at the output of one of the current comparators. Based on these measurements the digital Automatic Power Control (APC) will adjust the bias (IBIAS) and modulation current (IMOD) setting of the laser driver. Tests show that the chip can stabilize and track the launched optical power with a tolerance of less than 1 dB. In these tests the pattern detection was programmed to sample the current comparators after 5 bytes (32 ns at 1.25 Gbps) of consecutive 1's and 0's. Automatic power control on such short strings of data has not been demonstrated before. Although this laser transmitter was developed for FSAN GPON applications at a speed of 1.25 Gbps upstream, the design concept is generic and can be applied for developing a wide range of burst mode laser transmitters. This chip was developed in a 0.35 µm SiGe BiCMOS process.

Broadcasting in wireless mobile computing environments is an effective technique to disseminate information to a massive number of clients equipped with powerful, battery operated devices. To conserve the usage of energy, which is scarce resource, the information to be broadcast must be organized so that the client can selectively tune in at the desired portion of the broadcast. In this letter, the power efficient behavior of a predeclaration-based transaction processing in mobile broadcast environments is examined. The analytical studies have been performed to observe the effectiveness of predeclaration-based transaction processing combined with selective tuning ability in mobile broadcast environments.

In this paper, we present the interlaced fast Fourier transform (FFT) method to parallelize the adaptive integral method (AIM) algorithm for the radar cross-section (RCS) computation of large scattering objects in free space. It is noted that the function obtained after convolution is smoother as compared to the original functions. Utilizing this concept, it is possible to interlace the grid current and charge sources in AIM and compute the potentials on each set of interlaced grid independently using FFT. Since the potentials on each interlaced grid are smooth functions in space, we can then interpolate the potentials to every other nodes on the original grid. The final solution of the potentials on the original grid is obtained by summing the total contributions of all the computed and interpolated potentials from every individual interlaced grid. Since the potentials of each interlaced grid can be computed independently without much communication overheads between the processes, such an algorithm is suitable for parallelizing the AIM solver to run on distributed parallel computer clusters. It is shown that the overall computation complexity of the newly proposed interlaced FFT scheme is still of O(N log N).

We describe elements of a fast integral equation solver for large periodic and partly periodic finite array systems. A key element of the algorithm is utilization (in a rigorous way) of a block-Toeplitz structure of the impedance matrix in conjunction with either conventional Method of Moments (MoM), Fast Multipole Method (FMM), or Fast Fourier Transform (FFT)-based Adaptive Integral Method (AIM) compression techniques. We refer to the resulting algorithms as the (block-)Toeplitz-MoM, (block-)Toeplitz-AIM, or (block-)Toeplitz-FMM algorithms. While the computational complexity of the Toeplitz-AIM and Toeplitz-FMM algorithms is comparable to that of their non-Toeplitz counterparts, they offer a very significant (about two orders of magnitude for problems of the order of five million unknowns) storage reduction. In particular, our comparisons demonstrate, that the Toeplitz-AIM algorithm offers significant advantages in problems of practical interest involving arrays with complex antenna elements. This result follows from the more favorable scaling of the Toeplitz-AIM algorithm for arrays characterized by large number of unknowns in a single array element and applicability of the AIM algorithm to problems requiring strongly sub-wavelength resolution.

This paper proposes two types of network architectures using UMTS Release 5 architecture and wireless LAN suitable for context-aware information delivery and personal communication services, and it reports on preliminary evaluations of their performance. The first type of network architecture is the NCA (network-centric architecture) and the second is the ECA (end-user-centric architecture). The two architectures are modeled with a queuing network and their response times are compared through theoretical analysis and simulation. The results indicate that with low-performance servers, the response times of the ECA are generally shorter or almost the same as those of the NCA. However with high-performance servers, the response times of the NCA are generally shorter except during high server utilization.

Scattering of the two dimensional electromagnetic waves is studied by the infinite sequences of zeros arising on the complex plane, which just correspond to the null points of the far field pattern given as a function of the azimuthal angle θ. The convergent sequences of zeros around the point of infinity are evaluated when the scattering objects are assumed to be N-polygonal cylinders. Every edge condition can be satisfied if the locations of zeros are determined appropriately. The parameters, which allow us to calculate the exact positions of zeros, are given by the asymptotic analysis. It is also shown that there are N-directions of convergence, which tend to infinity. An illustrative example is presented.

In this article, it is shown that Unified Complex Hadamard Transform (UCHT) can be derived from Walsh functions and through direct matrix operation. Unique properties of UCHT are analyzed. Recursive relations through Kronecker product can be applied to the basic matrices to obtain higher dimensions. These relations are the basis for the flow diagram of a constant-geometry iterative VLSI hardware architecture. New Normalized Complex Hadamard Transform (NCHT) matrices are introduced which are another class of complex Hadamard matrices. Relations of UCHT and NCHT with other discrete transforms are discussed.

The AMR wideband speech codec was recently developed for high-quality wideband speech communications. Although it has an excellent performance due to expanded bandwidth of speech signal, it requires a huge amount of computation especially in codebook search. To solve this problem, this paper proposes an efficient codebook search method for AMR wideband codec. Starting from a poorly performing initial codevector, the proposed method enhances the performance of the codevector iteratively by exchanging the worst pulse in the codevector with a better one after evaluating the role of each pulse. Simulations show that the AMR wideband codec adopting the proposed codebook search method provides better performance with much less computational load than that using the standard method.

Subgraph isomorphism problems have various important applications, while generally being NP-complete. Though Ullmann and Konishi proposed the custom circuit designs to accelerate subgraph isomorphism problem, they require many hardware resources for large problems. This study describes the design of data-dependent circuits for subgraph isomorphism problem with evaluation results on an actual FPGA platform. Data-dependent circuits are logic circuits specialized in specific input data. Such circuits are smaller and faster than the original circuit, although it is not reusable and involves circuit generation for each input. In the present study, the circuits were implemented on Xilinx XC2V3000 FPGA, and they successfully operated at a clock frequency 25 MHz. In the case of graphs with 16 vertices, the average execution time is about 7.0% of the software executed on an up-to-date microprocessor (Athlon XP 2600+ of 2.1 GHz clock). Even if the circuit generation time is included, data-dependent circuits are about 14.4 times faster than the software (for random graphs with 16 vertices). This performance advantage becomes larger for larger graphs. Two algorithms (Ullmann's and Konishi's) were examined, and the data-dependent approach was found to be equally effective for both algorithms. We also examined two types of input graph sets, and found that the data-dependent approach shows advantage in both cases.

We propose a new algorithm for overdetermined blind source separation (BSS) based on multistage independent component analysis (MSICA). To improve the separation performance, we have proposed MSICA in which frequency-domain ICA and time-domain ICA are cascaded. In the original MSICA, the specific mixing model, where the number of microphones is equal to that of sources, was assumed. However, additional microphones are required to achieve an improved separation performance under reverberant environments. This leads to alternative problems, e.g., a complication of the permutation problem. In order to solve them, we propose a new extended MSICA using subarray processing, where the number of microphones and that of sources are set to be the same in every subarray. The experimental results obtained under the real environment reveal that the separation performance of the proposed MSICA is improved as the number of microphones is increased.