This paper presents a comparison of the throughput performance employing hybrid automatic repeat request (HARQ) with packet combining, such as Type-I with packet combining (simply Chase combining hereafter) and Type-II (Incremental redundancy hereafter), using turbo coding in a multipath fading channel in high speed downlink packet access (HSDPA). We apply a multipath interference canceller (MPIC) to remove the influence of severe multipath interference. Link level simulation results show that the maximum throughput using Incremental redundancy with 64QAM is improved by approximately 5-8% compared to that using Chase combining, and that the required average received signal energy of 12 code channels per chip-to-background noise spectrum density (Ec/N0) at the throughput of 4 Mbps with Incremental redundancy is decreased by approximately 1.0 dB rather than that with Chase combining when the vehicular speed is higher than approximately 30 km/h. Furthermore, we elucidate based on the system level simulation that although no improvement is obtained in a slow mobility environment such as the average vehicular speed of 3 km/h, the achieved throughput of Incremental redundancy is increased by approximately 5-6% and 13% for the average vehicular speed of 30 km/h and 120 km/h, respectively, compared to that with Chase combining.

In an orthogonal frequency division multiplexing (OFDM) system, the bit error performance is degraded in the presence of multiple propagation paths whose excess delays are longer than the Guard Interval (GI), because the orthogonality between subcarriers cannot be maintained. Therefore, the GI has to be long enough for an expected delay spread of the channel. On the other hand, a long GI causes a decrease in transmission efficiency. In this paper, we propose a new OFDM demodulation method with a variable effective symbol duration, in order to improve the bit error performance in the presence of multipaths whose excess delays are longer than the GI. The proposed method can realize more stable radio communication systems under a multipath propagation environment even if a propagation path whose excess delay is longer than the GI exists. In other words, the proposed method can improve transmission efficiency without performance degradation by a shortened GI under the same environment. The principle of the proposed method is explained, and the bit error probability of the proposed method is analyzed theoretically in an AWGN channel and a multipath fading channel. The performance of the proposed method is then evaluated by computer simulation. The results show that the proposed method improves the system availability under more various multipath fading environments without changing the system parameters.

New methods for digital image watermarking based on the characteristics of vector quantization (VQ) are proposed. In contrast with conventional watermark embedding algorithms to embed only one watermark at a time into the original source, we present one algorithm to embed multiple watermarks for copyright protection. The embedding and extraction processes are efficient for implementing with conventional VQ techniques, and they can be accomplished in parallel to shorten the processing time. After embedding, embedder would output one watermarked reconstruction image and several secret keys associated with the embedded watermarks. These secret keys are then registered to the third party to preserve the ownership of the original source in order to prevent the attackers from inserting counterfeit watermarks. Simulation results show that under no attacks, the embedded watermarks could be perfectly extracted. If there are some intentional attacks in our simulation, all the watermarks could survive to protect the copyrights. Therefore, we are able to claim the robustness, usefulness, and ease of implementation of our algorithm.

In this paper, we propose a new coded orthogonal frequency division multiplex (COFDM)-based ubiquitous antenna system, which is composed of multiple radio base stations (RBSs) deployed over the service area and Radio-on-Fiber (RoF) link that connects RBSs to the central control station (CCS). The proposed system is capable of receiving multiple mobile terminals simultaneously operating at the same frequency by making effective use of joint detection. However, the propagation delay due to the RoF link could be a major problem for realizing the ubiquitous antenna system. In order to overcome this delay problem, we assume that the guard interval of COFDM is longer than the delay difference. Furthermore, in order to improve BER performance in a multipath Rayleigh fading channel, we also propose the MSE normalization scheme followed by the use of an MMSE-based joint detector. Computer simulation results show that the proposed system can improve the frequency utilization efficiency of the broadband wireless access system.

Dual-Banyan is a buffered banyan asynchronous transfer mode (ATM) switch encompassing bifurcated queueing as its buffering strategy. This paper describes an efficient analytical model, based on iterative calculations, for performance evaluation of the Dual-Banyan switch under uniform and non-uniform traffic patterns with much less time than the simulation. The efficiency of the given model is verified through a comparison with simulation results. Another benefit of our model is the possibility to adopt it in any non-uniform incoming traffic. At last, we compare performance of Dual-Banyan switch and Input Buffer Banyan, and show that Dual-Banyan switch has significant better performance levels.

Organic light emitting diodes (OLEDs) containing nanostructured cathode buffer layers were fabricated, and their electrical and emitting properties were investigated. The OLEDs have an ITO anode/CuPc/TPD/Alq3/buffer layer/Al cathode structure with the buffer layers made from nanostructured alternating layers Alq3 and Al. The driving voltage and the efficiency of the devices were improved by insertion of the buffer layer. It was estimated that some modulations of the Schottky barrier at the Alq3 and the Al cathode interface were induced due to the insertion of the buffer layer and it caused an enhancement of electron injection from the Al cathode.

Compared with much research in the spatial-domain and transform-domain watermarking techniques, VQ-based watermarking technique has not been fully treated. A digital image watermarking scheme based on vector quantisation (VQ) is proposed to improve the degree of spreading watermark information. By partitioning the codebook into 3 groups, the scheme tries to embed one binary information for each block. The scheme spreads the watermark information almost evenly over the image with little extra distortion. The experimental results prove the efficiency and effectiveness of the scheme.

In this paper, we discuss the applicability of H filtering algorithm for a decision feedback equalizer (DFE) in mobile communications environments. A comparison of bit error rate (BER) performance between a H2 filtering (recursive least squares) algorithm-based and an a priori H filtering algorithm-based fractionally-tap-spaced DFEs in various fading channels is presented. Against, our results are rather pessimistic of the H equalizer, namely, as compared with the H2 equalizer, at most the same or a little better BER performance of the H equalizer is obtained only when the ratio of the average received energy per bit to the white noise power spectral density and the normalized fading rate are large enough, especially in Rician fading channels. Moreover, the H equalizer has the problems of how to choose an appropriate prescribed positive value and computational complexity, therefore it may not be considered as an attractive alternative to the H2 equalizer for wireless communications systems.

A new MAC protocol using the Adaptive Weighted Round Robin with Delay Tolerance (AWRR/DT) is presented. The proposed protocol is a type of centralized MAC protocol where the base station performs most operations. By using the AWRR/DT scheduler, we can guarantee delay QoS to different traffics without the heavy overhead induced by packet-based tagging techniques. In order to enhance the efficiency of random access systems, the proposed protocol employs three novel contention methods: slotted ALOHA with threshold, contention method using adaptive contention period, and traffic-specific contention method. Simulation results show that the proposed protocol guarantees delay bounds by using the AWRR/DT. The slotted ALOHA with threshold suffers less collisions than the regular slotted ALOHA when mobile terminals request slots. The method using adaptive contention period adjusts the length of contention period of each frame to relieve the performance degradation by collisions. The traffic-specific contention method provides a priority handling mechanism to contention-based systems. Experimental results of each contention method are provided.

STM/STS measurements have been carried out for TTF-TCNQ complex films evaporated on hydrogen-terminated silicon substrates, and the variation of tunneling spectra has been investigated on morphologically different crystal grains. Very thin semiconductive adsorbed layers were found to cover the as-deposited film surfaces. By removing the adsorbed layers, the intrinsic electronic structures of two different phases were revealed. A 'needle phase' which appears at the early stage of film growth has a semiconductive character and a 'granular phase' which grows later has a metallic character similar to bulk crystals. The electronic structure of the needle phase is considered to be affected by the substrate although the crystallographic structure is similar to the bulk crystal of TTF-TCNQ.

A study of apple flavor, banana flavor, and their chemical components was performed using an array of quartz crystal microbalance (QCM) gas sensors coated with sensing films such as lipids or stationary phase materials for gas chromatography (GC). The steady state sensor responses measured by a static measurement system were used to evaluate the characteristics of the different samples by principal component analysis (PCA) method. Since the array has shown good discrimination properties for fruit flavor components providing useful information, it was used to investigate the components that primarily contribute to the odor of the flavors. The results obtained from principal components analysis aided by sensory test were also used for an attempt to synthesize apple and banana flavors using only three of its odor components.

A generic multilevel quality-of-service (QoS) model for distributed multimedia applications is presented. QoS mapping mechanisms are required to translate the QoS parameters among the hierarchical levels. One QoS mapping mechanism based on the spline functions is proposed, hence two splines are compared. One is natural splines and the other is B-splines. QoS measurement experiments were conducted, and it is found that the B-splines give more accurate mapping results than the natural splines once the knots for the splines are selected appropriately.

A new four-quadrant (4Q) Multiplier complementally using linear and saturation regions of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is proposed for the wide dynamic range and superior flexibility of the input range. This multiplier operates in the region except for the threshold voltage VT to zero. The validity of the proposed circuit is confirmed through HSPICE simulation.

In this paper, we present a new approach to the construction of a set of binary sequences with a zero-correlation zone. The set consists of n pairs of binary sequences and the length of each binary sequence is n2(m+2) for some integers m and n. The Hadamard sequences with length n are used to construct the set. Any sequence in the set has 2(m+1) subsequences, each of length 2n. The author proves that any two subsequences are orthogonal if they belong to different pairs of binary sequences in the set.

This letter presents a code which corrects single bit errors in any location of the word as well as l-bit burst errors occurred in an important part of the word. The proposed code is designed by product of the parity check matrix of the l-bit burst error correcting codes and the matrix which converts input unequal errors into equal errors. This letter also demonstrates the evaluation of the code, and presents the extended codes with two-level burst error correcting capabilities by interleaving.

This paper proposes a novel space diversity reception scheme suitable for packet-based orthogonal frequency division multiplexing (OFDM) wireless access systems that achieves large diversity gain by improving the accuracy of both carrier frequency synchronization and phase tracking. Phase tracking compensates the phase rotation caused by residual carrier frequency error and phase noise and is necessary for high data rate OFDM systems that use coherent detection. In the proposed scheme, the accuracy of carrier frequency synchronization is improved by combining the information of the carrier frequency offset detected on all diversity branches; the accuracy of phase tracking is improved by using pilot signals whose signal to noise ratio (SNR) is raised by maximal ratio combining of the pilot signals extracted from all branches. Computer simulation results show that the proposed scheme effectively improves the diversity gain even in severe environments such as those with low carrier to noise ratios (CNR) and large delay spreads.

The problem of finding a path with two additive constraints, in particular finding a path that satisfies both the cost and the delay constraints, is called multi-constrained path (MCP) problem in the literature. In this paper, we explore the MCP problem based on the idea of single mixed weight --a mixed weight for each link is first obtained by combining its delay and cost, and then Dijkstra's algorithm is used to find the corresponding shortest path. Given two infeasible paths, it can be theoretically proved that a better path can possibly be found if we choose an appropriate parameter to construct the mixed weight. An approximate algorithm is thus proposed to solve the MCP problem. Theoretical analysis demonstrates that this algorithm can make a correct judgment whether there is a feasible path or not with a very high probability even in the strict case where the delay bound is between the delays of the least delay path and the least cost path, while the cost bound is between the costs of the two paths. On the other hand, the time complexity of this algorithm is very small since it only needs to execute Dijkstra's algorithm a limited number of times. The excellent performance of the proposed algorithm is verified by a large number of experiments on networks of different sizes.

Nonlinear feedback shift registers (NFSRs), which can generate maximal-period sequences called de Bruijn sequences, are regarded as one-dimensional maps with finite bits by observing states of the registers at each time. Such one-dimensional maps are similar to the Bernoulli map which is a famous chaotic map. This implies that an NFSR is one of finite-word-length approximations to the Bernoulli map. Inversely, constructing such one-dimensional maps with finite bits based on other chaotic maps, we can design new types of NFSRs, called extended NFSRs, which can generate new maximal-period sequences. We design such extended NFSRs based on some well-known chaotic maps, which gives a new concept in sequence design. Some properties of maximal-period sequences generated by such NFSRs are investigated and discussed.

We consider the services of broadcasting short messages via forward signaling channels in wireless cellular networks. In the provision of such services, the negative effect of short messages on the delivery of delay-sensitive control messages must be restricted. On the other hand, it is desirable to accommodate the users' demands for service enhancements involving timeliness and informativeness. As a way to resolve such conflicting arguments, we present a generic scheme in which a short message may be rejected or removed according to the buffer occupancy at the base station and is split into a number of segments for the transmission across a forward signaling channel. However, the rejection, removal and segmentation exhibit a trade-off among several facets of service enhancements. Thus, for a quantitative evaluation of the scheme and efficient optimization of design parameters, we develop an analytical method to calculate the moments of delay times experienced by control and short messages at a base station. Using the analytical method, we investigate the delay and loss performance of control and short messages with respect to the message load and short message length.

We propose a new receiver structure to mitigate interpath interference (IPI) in W-CDMA systems. We model IPI in RAKE combining as intersymbol interference (ISI) and use a two-stage receiver structure. The first stage is a RAKE receiver and the second stage is an equalizer. In cases of multi-code transmission, interference among code channels causes extra impairments which can not be modelled as ISI. Under these circumstances, they are estimated by using decisions from the first stage and then subtracted from the input of the equalizer. The residual interference is equivalent to ISI and can be mitigated by the equalizer. Simulation results show that the proposed receiver provides very promising performance in low spreading factor W-CDMA.