This paper describes a method of test data compression for a given test set using statistical encoding. In order to maximize the effectiveness of statistical encoding, the method first converts some specified input values in the test set to unspecified ones without losing fault coverage, and then reassigns appropriate logic values to the unspecified inputs. Experimental results for ISCAS-89 benchmark circuits show that the proposed method can on the average reduce the test data volume to less than 25% of that required for the original test set.

In this paper, we propose two fast codebook generation algorithms for entropy-constrained vector quantization. The first algorithm uses the angular constraint to reduce the search area and to accelerate the search process in the codebook design. It employs the projection angles of the vectors to a reference line. The second algorithm has feature of using a suitable hyperplane to partition the codebook and image data. These algorithms allow significant acceleration in codebook design process. Experimental results are presented on image block data. These results show that our new algorithms perform better than the previously known methods.

In this paper, we propose an extension to the image transport protocol (ITP). When images are transmitted through the Internet, TCP is generally used because it ensures the reliable transmission. However, interactivity will largely affected because of its acknowledgement scheme. This becomes remarkable in the network where packet-loss rate is relatively higher like wireless LANs. For more efficient image transmission, ITP was proposed. Like UDP, in ITP transmission, packets can be transmitted without acknowledgement of the reception. This contributes to improve the interactivity, on the other hand, some of packets may lost during transmission. ITP has a mechanism that the receiver-side can control the retransmission of the lost packets to maintain the quality of the received image. However, it is a hard task for the receiver to select which packets to be retransmitted. In this paper, we propose an extension to ITP by which the server can mark the importance of each packet. This helps the receivers to select important packets for requesting retransmission for server.

This paper investigates modified random timers based on uniform and exponentially distributed timers for feedback scalability for large groups. We observe the widely-used probability distribution functions and propose new ones that are aware of network delays. The awareness of network delays of our proposed modified p.d.fs proves to be able to achieve lower expected number of messages compared to the original ones given that the parameters are optimized for the network variables: the number of receivers, and the network delay. In our analysis we derive an equation to estimate the optimized parameter based on these network variables. We also simulate the p.d.fs for heterogenous network delays and find that each receiver only needs to be aware of its network delay.

This paper presents a scalable and efficient quota-based admission control scheme for the 3rd generation (3G) operator's IP backbone network, where quota denotes a chunk of bandwidth. This research is motivated by the 3G operator's need for guaranteeing end-to-end IP QoS of mobile-to-mobile and mobile-to-server multimedia sessions. In the proposed scheme, the quota size of a path implies the proper amount of allocated and released resources on the path condition. Employing the quota size makes the job of allocating or releasing resources at nodes in a path simple so that it becomes scalable. Moreover, with this simple scheme, an edge node can be allowed not only to initiate the allocation/release request but also to perform admission control function. To maximize the efficiency, the path quota size varies depending on the bottleneck link condition in the path. In high offered load, the proposed scheme decreases the path quota size and retains higher utilization while it requires lower signaling cost than the fixed scheme using a fixed size aggregation. As the load lessens, it increases the path quota size and reduces the signaling cost significantly.

Interval arithmetic is able to be applied when we include the ranges of various functions. When we include them applying the interval arithmetic, the serious problem that the widths of the range inclusions increase extremely exists. In range inclusion of polynomials particularly, Horner's method and Alefeld's method are well known as the conventional methods which mitigates this problem. The purpose of this paper is to propose the new methods which are able to mitigate this problem more efficiently than the conventional methods. And in this paper, we show and compare the efficiencies of the new methods by some numerical examples.

The bi-level digital video, because of its simplicity and compactness, can be utilized to provide for a quick and faithful preview of its original content. The proposed bi-level digital video compression technique exploits the context-based probabilistic estimation model towards adaptive pixel prediction which can be used towards generating residual image frames which may then be Run-Length-Rice coded. Towards promoting error-resiliency and random-access, each bi-level digital video frame may be typed into either intra- or inter- picture format. The proposed technique can be seen, in comparison to existing JBIG compression technologies in simulation runs, to provide added temporal redundancy removal.

We propose binary-quantized and spatio-temporally discretized network models of linear diffusion systems and investigate their filtering effect on single-bit sigma-delta (ΣΔ) modulated signals. The network consists of only one kind of elements that add ΣΔ modulated signals and quantize the sum in the form of single-bit signal. A basic one-dimensional network is constructed first. Then, the network is extended into two dimensions. These networks have characteristics equivalent to those of linear diffusion systems in both time and frequency domains. In addition, network noise caused by the quantization in the elements contains low-level low-frequency components and high-level high-frequency components. Therefore, the proposed networks have possibility to be used as signal propagation and diffusion media of ΣΔ domain filters.

This letter introduces a novel multi-user detection method, successive interference cancellation based on the order of log-likelihood-ratio(LLR-SIC), for code division multiple access (CDMA) systems. Unlike the conventional successive interference cancellation (SIC) based on the order of correlation, LLR-SIC operates on the fact that the user with the largest absolute value of log-likelihood ratio (LLR) should be first detected and cancelled from received signal. Simulation results show that LLR-SIC significantly outperforms the conventional SIC and partial parallel interference cancellation (P-PIC) over Rayleigh fading channels, and that LLR-SIC performance is not sensitive to channel estimation error at medium Eb/N0.

This paper proposes a new decision feedback decoding scheme for Alamouti-based space-time block coding (STBC) transmission over time-selective fading channels. In wireless channels, time-selective fading effects arise mainly due to Doppler shift and carrier frequency offset. Modelling the time-selective fading channels as the first-order Gauss-Markov processes, we use recursive algorithms such as Kalman filtering, LMS and RLS algorithms for channel tracking. The proposed scheme consists of the symbol decoding stage and channel tracking algorithms. Computer simulations confirm that the proposed scheme shows the better performance and robustness to time-selectivity.

We propose a new approach associated with the use of some selected sets of Walsh Hadamard codes for joint estimation of channels and the number of transmit antennas by employing only one OFDM pilot symbol. This allows transmit antenna diversity to be applied in systems which have a limited number of training symbols (preambles), e.g. HIPERLAN/2. The proposed approach does not require any a priori knowledge about the number of transmit antennas, providing flexibility in the number of antennas to be used. In addition, adaptive scheme associated with the proposed approach provides more accurate estimations of the channels. The effectiveness of the proposed approach is evaluated through simulation. Results show that the proposed scheme provides significant improvement over previous channel estimation schemes and has almost the same performance as the ideal system with the full knowledge of the channel state information.

Group mutual exclusion is an interesting generalization of the mutual exclusion problem. This problem was introduced by Joung, and some algorithms for the problem have been proposed by incorporating mutual exclusion algorithms. Group mutual exclusion occurs naturally in a situation where a resource can be shared by processes of the same group, but not by processes of a different group. It is also called the congenial talking philosophers problem. In this paper we propose two algorithms based on ticket orders for the group mutual exclusion problem on the asynchronous shared memory model. These algorithms are some modifications of the Bakery algorithm. They satisfy lockout freedom and a high degree of concurrency performance. Each of these algorithms uses single-writer shared variables together with two multi-writer shared variables that are never concurrently written. One of these algorithms has another desirable property, called smooth admission. By this property, during the period that the resource is occupied by the leader (called the chair), a process wishing to join the same group as the leader's group can be granted use of the resource in constant time.

We study relationships between the class of Boolean formulas called exclusive-or expansions based on monotone DNF formulas (MDNF formulas, for short) and the class of Horn DNF formulas. An MDNF formula f is a Boolean formula represented by f = f1fd , where f1 > > fd are monotone DNF formulas and no terms appear more than once. A Horn DNF formula is a DNF formula where each term contains at most one negative literal. We show that the class of double Horn functions, where both f and its negation can be represented by Horn DNF formulas, coincides with a subclass of MDNF formulas such that each DNF formula fi consists of a single term. Furthermore, we give an incrementally polynomial time algorithm that transforms a given Horn DNF formula into the MDNF representation.

This paper describes synthesis of a complex RiCR filter with a finite transmission zero except zero frequency. The frequency response of the proposed filter is similar to the conventional elliptic filter. The proposed filter can be composed of fewer elements than the conventional one. A new kernel function is proposed. As an example, a fifth-order RiCR filter is designed. We compare the proposed filter with the conventional complex elliptic filter from the viewpoint of the frequency response and the number of the required elements.

We describe the first highly nonlinear dispersion-flattened polarization-maintaining photonic crystal fiber designed for nonlinear optics applications in the 1.55 µm region. The nonlinear coefficient of the fiber is 19 (W-1km-1), which is ten times that of dispersion shifted fiber. The chromatic dispersion and dispersion slope of the fiber at 1.55 µm are -0.23 ps/km/nm and 0.01 ps/km/nm2, respectively. We demonstrate the generation of a supercontinuum using the photonic crystal fiber. A symmetrical supercontinuum over 40 nm is obtained by injecting 1562 nm, 2.2 ps, and 40 GHz optical pulses into the 200 m-long photonic crystal fiber.

A simple and efficient context modeling technique (CM-WDR) is proposed to improve the performance of the wavelet difference reduction (WDR) algorithm for image compression. The CM-WDR employs an adaptive scanning order by context modeling. The PSNR improvement over WDR ranges from 0.1 to 1.5 dB at various bitrates.

An Ad Hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. The choice of medium access is difficult in Ad Hoc networks due to the time-varying network topology and the lack of centralized control. In this paper, we propose a novel multichannel schedule-based Medium Access Control (MAC) protocol for Ad Hoc networks named Multichannel Reservation Protocol for TDMA-based networks (MRPT). MRPT ensures collision free in successfully reserved data links, even when hidden terminals exist. The reservation of MRPT is based a control channel and in order to improve throughput we propose Four-Phase-Two-Division (FPTD) as a media access scheme of the control channel for broadcasting control or reservation messages. In FPTD, the collision can be solved rapidly with an efficient backoff algorithm which results in that system block is avoided in case of high traffic. In this paper, we also present the throughput performance of MRPT, which shows a high value and no system block even in case of high traffic load.

IEEE 802.11 standard and the enhanced amendments have defined several transmission rates for mobile stations to transmit and receive data frames. With the characteristic of modulation schemes, a higher network throughput can be expected by using higher level modulation scheme, but frame error probability will also become higher. Doubtlessly, it is an open issue of selecting a proper modulation scheme for a pair of mobile stations in time-varying indoor environment. This paper proposes a safe multiple access-rates transmission (SMART) scheme to enhance the reliability of data transmission in IEEE 802.11 multi-rate infrastructure wireless networks. SMART scheme provides reliable transmission by reserving a retransmission period which immediately follows the transmitted frame and is estimated by a lower transmission rate according to the transmitted frame. The performance of SMART scheme is evaluated by analytical model and simulation experiment, which show that the proposed scheme is significantly better than the IEEE 802.11 standard under the real environment with asymmetric traffic load. An enhanced SMART (ESMART) scheme is also proposed especially to improve bandwidth waste for long packet length at access point (AP). The performance measurements, such as goodput, throughput, average access delay, and service rate, are obtained and compared for the different schemes.

This paper describes feasibility of a proposed fixed wireless access system with CDMA technology. The system adopts a primary modulation of 16 QAM and the same frequency allocation in all cells to improve spectral efficiency. The system capacity is 1 Gbps per cell within 120 MHz bandwidth. The number of available orthogonal codes corresponds to the orthogonal code length in the system. All subscribers can attain an error free condition with output power control in the presence of inter-cell interference. The following two items are considered to examine the proposed system feasibility. 1) A test modem is fabricated, and a back-to-back modem BER performance is measured. An inter-symbol interference (ISI) level of the modem is estimated with the measured performance. 2) A computer simulation of down-link power control is carried out considering inter-cell interference and impairment factors of the power control such as intra-sector interference caused by the ISI and limited ranges of total and relative output power controls. The simulation results show that the proposed system would be feasible because the obtained power penalties caused by the above impairment factors are negligible.

This paper presents a novel wavelet compression technique to increase compression of images. Based on zerotree entropy coding method, this technique initially uses only two symbols (significant and zerotree) to compress image data for each level. Additionally, sign bit is used for newly significant coefficients to indicate them being positive or negative. Contrary to isolated zero symbols used in conventional zerotree algorithms, the proposed algorithm changes them to significant coefficients and saves its location, they are then treated just like other significant coefficients. This is done to decrease number of symbols and hence, decrease number of bits to represent the symbols used. In the end, algorithm indicates isolated zero coordinates that are used to change the value back to original during reconstruction. Noticeably high compression ratio is achieved for most of the images, without changing image quality.