This paper presents a new offset-quadrature-phase-shift-keying (OQPSK) coherent demodulation scheme for wireless asynchronous transfer mode (WATM) systems that premise the Ricean fading communication channels (e.g., typically with derectional antennas). The presented demodulator is basically advanced from a simultaneous carrier and bit-timing recovery (SCBR) scheme by newly employing a phase compensated filter and a reverse-modulation scheme for OQPSK. This advancement aims to enhance the carrier phase tracking performance against the phase fluctuation due to the fading and/or the phase rotation caused by the carrier frequency error of the oscillator. Design consideration and performance evaluation of the demodulator are extensively carried out under Ricean fading channels typical of the WATM systems as well as additive white Gaussian noise (AWGN) channels. The evaluation ressults show that the advanced SCBR (ASCBR) scheme achieves a bit-error-rate/cell-error-rate (BER/CER) performance close to ideal coherent detection with a considerably short preamble, e.g., 8 symbols. Specifically, compared with differential detection (evaluated for QPSK with the hard-wired clock), the new coherent demodulator achieves a significant required E_b/N_o improvement, which becomes larger as the fading condition degrades. This paper concludes that the ASCBR scheme is a strong candidate for the Ricean-fading-premise WATM systems.

We propose a new bit timing recovery (BTR) scheme, what we call Step Sampled BTR (SSBTR), that can lower the sampling clock frequency and shorten the clock phase convergence time, for burst signals in high bit rate wireless access systems. The SSBTR scheme has the following characteristics. A sine wave resulting from the BTR code passing through a Nyquist Transmission System is always used, the sampling clock has a lower frequency than the system clock, and the clock phase of Intermediate Frequency (IF) signal input can be estimated from as few as 3 sampled data. The SSBTR scheme corrects the clock phase only once in a burst signal. Therefore, in some wireless access systems, some kind of operation must be performed after the SSBTR, in order to deal with long burst signals, instability of the system clock, and so on. In other wireless access systems that do not have these problems, clock phase can be fixed by the SSBTR scheme alone. The preformance of the SSBTR scheme with respect to additive white Gaussian noise (AWGN) was examined by computer simulation. In addition, when SSBTR is implemented in hardware, there are imperfections in the circuitry that lead to phase estimation error and thus deterioration, so we studied the effects of several such imperfections by computer simulation. The results of these simulations clarify the performance of the SSBTR scheme.

This paper presents an adaptive coding rate trellis-coded octal phase-shift keying system with rates of 1/3, 1/2, 2/3, and 5/6, under the restriction of a constant transmission bit rate, where the ratio between the informaion bits and error-correcting redundant bits varies according to channel conditions. This system has the advantage of using a simple modem configuration. Because it has no need to change modulation type, transmitter/receiver filters, and clock and carrier recovery circuits, and it can use a convenient Read-Only-Memory table encoder. As for code design, the trellis structures and its signal assignments for rates of 1/3, 1/2, and 5/6 are proposed and investigated, and their BER performances are estimated. As a result, when the system requirement is to keep the bit error rate of 10^-4, this system can operate at the lower Eb/No value of 1.5dB on the reduction of transmitting information bits.

This paper investigates the error rate performance of parallel combinatorial spread spectrum (PC/SS) communicaion systems that use coherent and differential multiphase modulation: multiphase parallel combinatorial spread spectrum (MPC/SS) communication systems. The PC/SS systems are multicode SS systems based on orthogonal pseudo-noise (PN) sequences. Data is transmitted by delivering a combination of multiple PN sequences among a set of pre-assigned PN sequences. In the MPC/SS systems, every PN sequence on transmission is modulated by q-ary coherent or differential phase shift keying (PSK). Symbol error rate (SER) and average bit error rate (BER) in coherent and differential MPC/SS systems are investigated. The BER comparison between the MPC/SS systems and simple multicode SS systems with q-ary coherent and differential PSK is also presented. Numerical results show that the MPC/SS systems are superior to the conventional q-ary PSK systems, if they have equal spectral efficiency.

It is highly desirable to develop an efficient and flexible dynamic channel assignment algorithm in order to realize an integrated traffic TDMA mobile radio communication network. In this paper, an integrated traffic TDMA system is studied in which transmission of voice and data are assumed to occupy one and n time slots in each TDMA frame, respectively. In general, there are two types of channel (time slot) assignment algorithms: the partitioning algorithm and the sharing algorithm. However, they are not well-suited to the multimedia traffic consisting of various information sources that occupy different number of slots per frame. In this paper, assuming that voice is much more sensitive to transmission delay than data, an algorithm based on the sharing algorithm with flexible tima slot management scheme is proposed. Our method tries to vary the number of data slots adaptively so as to improve the quality of servive of voice calls and the system capacity. Computer simulations show the good performance of the proposed algorithm when compared to conventional channel assignment algorithms.

In this paper, we propose a quasi-optimum multiuser detector using co-channel interference cancellation technique in an asynchronous code-division multiple-access communication system, and evaluate its performance by computer simulations. In the proposed detector, maximum likelihood sequence estimation is performed to compare the original received signal with replicas of the signal which are produced from the demodulation data bit sequence of a co-channel interference canceller. In several conditions, the proposed detector is compared with the co-channel interference canceller, and it is shown that the average bit error rate characteristics of the propose detector are improved considerably.

Macro/microcellular systems have recently been proposed to accommodate both fast and slow moving users. If macrocells and microcells reuse the same frequency band in a macro/microcellular system, the interference between both types of cells can become a critical problem and degrade system capacity, particularly in CDMA systems. In this paper, Frequency Division CDMA (FD-CDMA) is applied to CDMA macro/spot-microcellular systems and uplink capacity is evaluated. The CDMA frequency band is divided into several subbands and both macrocells and microcells reuse the same subbands simultaneously. Interference signals from both types of cells are dispersed by dividing the frequency band, and performance degradation resulting from interference is reduced at both the macrocell and microcell. By reusing the same frequency band for macrocells and microcells, the system capacities become more flexible and can be changed according to variations in traffic. This paper describes the detail of the FD-CDMA system. Uplink capacities are calculated for some cell conditions such as microcell size or location through simulation evaluations. A comparison with a non-reuse subband system as well as results of adaptive control of subbands are described.

This paper describes a delay control scheme for synchronous detection of an orthogonal coding multi-carrier CDMA (Code Division Multiple Access) system. The delay control scheme estimates transmission timing of data from each mobile station. At a base station, delay time is obtained by detecting phase shift value of the preamble signal from each mobile station. The estimated transmission timing information is sent from base station to each mobile station and the mobile station then adjusts its transmission timing. Simulation results clarified that Bit Error Rate (BER) is 2.510^-3 at 19dB of E_b/N_o under conditions of 29.4 msec initial delay time, 32kbit/sec data rate, 16 subchannels and 100Hz of fading frequency.

We propose a soft decision Viterbi decoding scheme and a self-interference cancellation method applicable to a Parallel Combinatory CDMA (PC-CDMA) system. In this decoding scheme, branch metric is calculated for every bit by weighting the output levels of the PC-CDMA correlators so as to enable an effective soft decision capability to the system. The effectivity of this scheme is then further enhanced by the use of a simple pseudo-random bit interleaving scheme. Moreover, to increase the capacity of the PC-CDMA system, we propose a simple self-interference cancellation method for self-induced cross-correlation arising from the multipath environment. This further enhances the efficacy of the decoding scheme because the false contributions of the self-induced cross-correlation component are removed from the branch metric prior to soft decision Viterbi decoding. Finally, we simulated a possible PC-CDMA system with a user data rate of 1.92Mbps, transmitting it at a chip rate of 3.84Mcps and at 7.68Mcps under a multipath-Rayleigh fading interference environment. For a chip rate of 7.68Mcps, BER after Viterbi decoding is less than 3.2e-7 even without the use of interference cancellation. For a chip rate of 3.84Mcps, BER after Viterbi decoding with interference cancellation is 1.0e-4.

In a radio network, while deploying microcells enhances spectral efficiency, it increases handoff in number and puts restriction on mobility of a terminal. As a solution of this contradictory matter, we propose a random access micro-cellular system (RAMCS). In the system deployed microcells produce higher system capacity, and "handoff on a terminal" isn't required. Therefore flexible mobility is given to terminals, and a terminal becomes simple. The aspect of the air interface is as follows. On uplink, packets are transmitted by means of random access (e.g., slotted ALOHA) at the same channel in any cell. On downlink, packets are broadcast at the same carrier in any cell and they are picked out conforming to TDMA. In this paper, a model of RAMCS is proposed. In addition, characters of RAMCS (e.g., throughput, system capacity, and delay) are clarified comparing it with a primary cellular system, where a spectrum can be reused repeatedly in different cells.

This paper presents the evaluation for personal communication systems (PCS). Two types of PCS are supposed for low and high degree of mobility. The service area with 30km radius is covered by a multiple hexagonal cells, which are micro cells and macro cells for the low mobility and high mobility planes respectively. As for a traffic distribution, uniform and exponentially tapered traffic distributions are assumed. After defining the system model, cost evaluation form along with capacity has been derived. The evaluation and discussions are made in terms of cost economy, capacity and spectrum usage in various conditions. It is shown that there exist the optimum cell radius for the prescribed subscriber numbers and the integration of two systems is desirable for the support of full mobility with cost-effectiveness and spectrum efficiency.

Dynamic Channel Assignment (DCA), which improves the efficiency of channel use in cellular mobile communication systems, requires finding an available channel for a new call after the call origination. This causes the delay which is defined as the time elapsing between call origination and completion of the channel search. For system planning, it is important to evaluate the delay characteristic of DCA because the delay corresponds to the waiting time of a call and influences service quality. It is, however, difficult to theoretically analyze the delay characteristics except its worst case behavior. The time delay of DCA has not been theoretically analyzed. The objective of this paper is analyzing the distribution and the mean value of the delay theoretically. The theoretical techniques in this paper are based on the techniques for analyzing the blocking rate performance of DCA.

This paper proposes the use, in integrated wireless systems, of the Reserved Idle Signal Multiple Access with Collision Resolution (R-ISMA/CR) protocol for applications in future multimedia mobile communications. It is applied to the integrated voice and data wireless system. Moreover, the consideration is made of the integrated voice and the low-bit video wireless system in R-ISMA/CR. To integrate video we employed not only a packed discard for video packets when the video packet delay is more than a threshold value, but also the connection packet (CP) technique for improving the channel utilization. Finally the integration of voice, data, and low-bit-video wireless system in R-ISMA/CR is considered. The performance are evaluated mainly by simulations.

In this paper, we propose a modified R-ISMA (reserved idle signal multiple access) protocol for a wireless local area network (WLAN) with a hybrid system construction. The protocol can support a basic service area as large as that supported by a centralized system and allows the direct transmission between neighbor stations as in a distributed system without the problem of hidden terminals. Since a polling scheme is used during transmission of information packets, an ARQ (auto repeat request) scheme is easily applied. A dynamic analysis using transient fluid approximation analysys is used for performance evaluation. In the analysis, we use Fritchman channel model to describe a burst error environment. Some numerical examples using a set of practical system parameters are given. It is shown that the system performance is improved compared with a centralized system with R-ISMA.

Applying ARQ to real time video communication can significantly increase transmission delay due its retransmission operations. We analyze this delay and propose an adaptive error control scheme that uses acknowledgment from the receiver to reduce the delay. We evaluate this scheme using a computer simulation and show that the proposed scheme can reduce the delay by controlling the amount of video data by changing the quantization step size and video frame skipping. It also offers acceptable video quality as confirmed by a subjective evaluation test.

The computers are connected with each other by the network as a result of the progress of technology in the field of the computer and network, and then all of the data to be processed are transferred quickly and at the real-time through the computer network. However the user can use the computer system at any time, the user must go to the location of the computer system to use the computer resources. The necessities for using the computer system occur anywhere and anytime in spite of the location of the computer system. For this requirement the mobile computing environment (MCE) is expected strongly. In this paper we introduce the model of MCE and discuss the need of the user authentication at entering and logging-in the network in MCE only with a user ID. We propose the method of a user ID assignment from which a server ID can be decided by a simple logical operation. Also, we propose a protocol for a user authentication in MCE and discuss the robustness of security against the various attacking on the route.

The paper provides the algorithm to estimate the deviation bound admitting to recovering irregularly sampled signals in wavelet subspaces, which does not need the symmetricity sampling constraint of Paley-Wiener's and relaxes the deviation bounds in some wavelet subspaces. Meanwhile the method does not need the continuity and decay constraints imposed on scaling functions by Liu-Walter and Chen-Itoh-Shiki.

A new method is proposed for estimating a single complex sinusoid and its parameters (frequency and amplitude) from measurements corrupted by white noise. This method is called the ECKF-SVD method, which is derived by applying an extended complex Kalman filter (ECKF) to a nonlinear stochastic system whose state variables consist of the AR coefficient (a function of frequency) and a sample of the original signal. Proof of the stability is given in the case of a single sinusoid. Simulations demonstrate that the proposed ECKF-SVD method is effective for estimating a single complex sinusoid and its frequency under a low signal-to-noise ratio (SNR). In addition, the amplitude estimation by means of the ECKF-SVD method is also discussed.

This study was conducted to assess the relationship between fatigue and pupillary responses. Pupillary responses, ECG and blood pressure were measured for 24 hours every 30 min in 8 subjects. A questionnaire was used to rate subjective feeling of fatigue. Twenty-four hours were divided equally into four 6-hour blocks. Subjective feeling of fatigue increased markedly in the fourth block, and the difference in subjective fatigue between fourth and first blocks was significant. Of nine pupillary responses, the pupil diameter was found to decrease with time. With respect to the function of the autonomic nervous system such as heart rate, systolic blood pressure and diastolic blood pressure, only heart rate was found to be sensitive to the increased subjective feeling of fatigue. A significant difference was found in the mean pupil diameter and mean heart rate between the last and first blocks. This result indicates that pupil diameter is related to fatigue and can be used to assess fatigue. Possible implications for fatigue assessment are discussed.

In this study, we show how changing a frequency in one of N chaotic circuits coupled by a resistor effects our system by means of both circuit experiment and computer calculation. In these N chaotic circuits, N-1 circuits are completely identical, and the remaining one has altered the value of the oscillation frequency. It is found that for the case of N = 3 when a value of a coupling resistor is gradually increased, only one circuit with different frequency exhibits bifurcation phenomena including inverse period-doubling bifurcation, and for larger value of coupling resistor, the chaotic circuit with different frequency suddenly stops oscillating and the remaining two chaotic circuits exhibit completely anti-phase synchronization.

We propose an interactive identification scheme based on the quadratic residue problem. Prover's identity can be proved without revealing his secret information with only one accreditation. The proposed scheme requires few computations in the verification process, and a small amount of memory to store the secret information, A digital signature based on this scheme is proposed, and its validity is then proved. Lastly, analysis about the proposed scheme is presented at the end of the paper.

The TLS method is an unbiased estimator for solving the overdetermined set of linear equations when errors occur in all data. However it doesn't show robustness while the errors have a heavy tailed pdf. In this letter we derive a robust method of TLS (ROTLS) based on the characteristics of TLS solution, where the performance of ROTLS is verified by applying it to the system identification problem.

In this article, a new type of diffusion template and an analogic CNN algorithm using this diffusion template for detecting some lung cancer symptoms in X-ray films are proposed. The performance of the diffusion template is investigated and our CNN algorithm is verified to detect some key lung cancer symptoms, successfully.