Space Division Multiple Access (SDMA) will form an important part of the new Wideband Code Division Multiple Access (WCDMA) standard that will realize the Universal Mobile Telephone System (UMTS). This paper addresses a few issues of importance when SDMA techniques are used in a cellular CDMA system. Firstly, a brief overview of SDMA techniques are presented followed by a theoretical analysis of a SDMA/CDMA system. The analysis is focused on a single cell, multipath Rayleigh fading scenario with imperfect power control. As system performance measure Bit Error Rate (BER) is used to investigate the influence of user location, number of antennas and power control error. An important parameter in a SDMA system is the antenna array element spacing. In our analysis a Uniform Linear Array (ULA) is considered and a measure is defined to determine the optimal antenna element spacing in a CDMA cellular environment. Normally the mobile users in a cell are assumed to be uniformly distributed in cellular performance calculations. To reflect a more realistic situation, we propose a novel probability density function for the non-uniform distribution of the mobile users in the cell. It is shown that multipath and imperfect power control, even with antenna arrays, reduces the system performance substantially.

The performance of AC plasma displays has been improved in the area of brightness and contrast, while significant advances in image quality are still required for the HDTV quality. In particular, in full color motion video, motion artifacts and lack of color depth are still visible in some situations. These motional artifacts are mitigated as the number of the subfields increases, usually at the cost of losing brightness or increasing driving circuitry. Therefore, it is still one of our great concerns to find out the optimized subfield configuration through weighting and order of each subfield, and their coding of combination. For evaluation and improvement of motion picture disturbance, we have established a procedure that fully simulates the image quality of displays which utilize the subfield driving scheme. The simulation features virtually located sensor pixels on human retina, eye-tracking sensor windows, and a built-in spatial low pass filter. The model pixelizes the observers retina like a sensor chip in a CCD camera. An eye-tracking sensor window is assigned to every light emission from the display, to calculate the emissions from one to four adjoining pixels along the trajectory of motion. Through this model, a scene from original motion picture without disturbance is transformed into the still image with simulated disturbance. The integration of the light emission from adjoining pixels through the window, also functions as a built-in spatial low pass filter to secure the robust output, considering the MTF of the human eye. Both simulation and actual 42-in-diagonal PDPs showed close results under various conditions, showing that the model is simple, but reasonable. Through the simulation, general properties of the subfield driving scheme for gray scale have been elucidated. For example, a PWM-like coding offers a better performance than an MSB-split coding in many cases. The simulation also exemplifies the motion picture disturbance as a non-linear filter process caused by the dislocation of bit weightings, suggesting that tradeoffs between disturbance and resolution in motion area are mandatory.

In this paper, a new overload control strategy is proposed for a call control processor (CCP) in the base station controller (BSC) and processor utilization is measured. The proposed overload control strategy can regulate the call attempts by adopting measured processor utilization. A function, specifically a linear interpolation function based on Inverse Transform theory is used to convert controlled predictive average load rate in a call rejection rate. Then a call admission rate is obtained from the call rejection rate. Simulation shows that the proposed algorithm yields better performance than the conventional algorithm does under the heavy transient overload status in terms of call admission rate.

A method to improve the reflection efficiency of holographic polymer dispersed liquid crystal (HPDLC) is proposed and its effectiveness is confirmed. Controlling the alignment of liquid crystal (LC) in tiny droplets of HPDLC can increase the refractive-index difference between the LC droplet layer and the polymer layer, causing the peak reflectance and reflective spectral width to expand. We observed experimentally that 96% of the light components excluding the scattering loss can be diffracted in a transmission HPDLC device by ordering the LC. In a reflection HPDLC, we found that reflection could be improved by ordering through an applied shear force. Our findings should lead to an improvement in the quality of reflective display devices.

This paper proposes a novel asynchronous direct sequence/code division multiple access (DS/CDMA) communication system using analog pseudo noise (PN) sequences that have an orthogonal relation for all active users. Analog PN sequences are produced by an adaptive filter called a "code-orthogonalizing filter" (COF). In a base station receiver, the tap coefficients of the COF can be adaptively controlled "to orthogonalize" or "to approach to orthogonalize" various received PN sequences. The elements of the analog PN sequences consist of the tap coefficients of the COF. The analog PN sequence produced is assigned to the transmitter of each user in order. As a result, multiple access interference (MAI) caused by other users can be reduced considerably, and multiple access capacity increased by the proposed system compared with matched filter (MF) reception and COF reception.

In this paper, the bit error rate (BER) performance of the Spread Spectrum communication with Constrained Spreading Code system is studied under the synchronous CDMA system. Particularly, BER considering the tracking error is derived by theoretical analysis. The synchronizing spreading sequence is employed to track the signals in the receiver. As the result, the BER performance is degraded by increasing the number of users. However, the BER performance can be improved by canceling the co-channel interference and by suppressing the cross-correlation value between the information spreading sequence and the synchronizing spreading sequence.

In mobile communications, power is a very important factor and nonlinear amplification of power amplifiers cannot be avoided due to their high power efficiency. This article presents the performance of π/2-shift BPSK modulation scheme used in DS/SS/CDMA wireless communications over multipath Rayleigh fading channel and compares the performance with the performance of conventional BPSK and offset QPSK CDMA systems. The performance parameters: Out-of-Band power, average Bit Error Rate (BER) and Spectral Efficiency have been evaluated. In order to obtain improved performance on fading channels, a RAKE receiver has been employed. Finally it is shown that π/2-shift BPSK outperforms conventional BPSK and offset QPSK in the presence of nonlinear amplification.

M-ary/SS systems are compared with DS/SS systems applied the multicarrier systems and the RAKE receiver in the presence of AWGN, frequency selective Rayleigh fading and partial-band interference. In particular, the BER performance and SSMA capability are evaluated. Consequently, the M-ary/SSMA system using the multicarrier techniques is subject to the M-ary/SSMA system with the RAKE receiver in the presence of partial-band interference. The BER performance of the M-ary/SSMA system is better than that of the DS/SSMA system when the number of users is smaller than 20. And the spectral efficiency of the multicarrier M-ary/SSMA system is best in the four systems when JSR=20 [dB] and BER=10-3.

This paper describes code assignment and the multicode sense scheme for an inter-vehicle CDMA communication network. When considering an inter-vehicle broadcasting CDMA communication network, spreading code assignment and notification problems arise. In such a CDMA network, the use of common codes is a solution. Then an objective function of common code assignment in an IVCN is formulated as a combinatorial optimization problem. In addition, a multicode sense (MCS)/CDMA system is proposed as a simple code assignment scheme. Computer simulations show that the MCS/CDMA system can autonomously perform spatial rearrangement of the common codes using only local information that each vehicle can obtain by sensing the code channels.

In the ITS (Intelligent Transport Systems), it is an essential condition (mixed environment) that vehicles that have communication equipment and vehicles that do not have it simultaneously run in the same road. In this paper, a vehicular driving assistant system that is applicable to the mixed environment is proposed. The proposed system uses spread spectrum techniques and consists of several new systems such as a PN code assignment system, new vehicle position systems, and a vehicle map update system. In the proposed system, the wireless broadcast CDMA is used for inter-vehicle communications. This paper also shows preexaminations of the proposed system by using an autonomous traffic flow simulator including inter-vehicle communications. It is shown that the traffic safety can be improved by using inter-vehicle communications.

A new identification algorithm based on output over-sampling scheme is proposed for a IIR model whose input signal can not be available directly. By using only an output signal sampled at higher rate than unknown input, parameters of the IIR model can be identified. It is clarified that the consistency of the obtained parameter estimates is assured under some specified conditions. Further an efficient recursive algorithm for blind parameter estimation is also given for practical applications. Simulation results demonstrate its effectiveness in both system and channel identification.

This paper presents a variant of the "Third-Order Recursion (TOR)" method for bispectral estimation of transfer-function parameters of a non-minimum-phase all-poles system. The modification is based on the segmentation of system-output data into coupled records, instead of independent records. It consists of considering the available data at the left and the right of each record as not null and taking them as the data corresponding to the preceding and succeeding record respectively. The proposed variant can also be interpreted as a "Constrained Third-Order Mean (CTOM)" method with a new segmentation in overlap records. Simulation results show that this new segmentation procedure gives more precise system parameters than the TOR and CTOM methods, to be obtained. Finally, in order to justify the use of bispectral techniques, the influence of added white and colored Gaussian noise on the parameter estimation is also considered.

The fact that bounded interval band orthonormal scaling function shows oversampling property is demonstrated. The truncation error is estimated when scaling function with oversampling property is used to recover signals from their discrete samples.

This paper formulates problems of fitting two corresponding sets of points by translation, rotation and scaling, and proposes efficient algorithms for the fitting. The algorithms are based on the theory of lower envelopes, or Davenport-Schinzel sequences, and linearization techniques in computational geometry, and are related to dynamic furthest Voronoi diagrams.

A method is presented for determining the minimum weight of cyclic codes. It is a probabilistic algorithm. This algorithm is used to find, the minimum weight of codes far too large to be treated by any known algorithm. It is based on a probabilistic algorithm for determining the minimum weight of linear code by Jeffrey S. Leon. By using this method, the minimum weight of cyclic codes is computed efficiently.

This paper presents a new approach to computing symbol error probability of fast frequency-hopped M-ary frequency shift keying (FFH/MFSK) systems with majority vote under multitone jamming. For illustrating the applications, we first consider the case in which the source data rate is fixed and the hopping rate is allowed to vary. In this case, the optimum orders of diversity for several values of M are examined. Results show that M=4 outperforms other values. Then, we treat another case in which the hopping rate is fixed and the data rate is adjusted so as to obtain maximum throughput under a given constraint of error probability. In addition to the case of diversity alone, we also evaluate the performances of the fixed hopping rate case with channel coding using convolutional code and BCH code.

A fuzzy Kohonen clustering network was proposed which integrates the Fuzzy c-means (FCM) model into the learning rate and updating strategies of the Kohonen network. This yields an optimization problem related to FCM, and the numerical results show improved convergence as well as reduced labeling error. However, the clusters may be either hyperspherical-shaped or hyperellipsoidal-shaped, we use a generalized objective function involving a collection of linear varieties. In this way the model is distributed and consists of a series of `local' linear-type models (based on the revealed clusters). We propose a method to generalize the fuzzy Kohonen clustering networks. Anderson's IRIS data and the artificial data set are used to illustrate this method; and results are compared with the standard Kohonen approach and the fuzzy Kohonen clustering networks.

In this paper the performance of the Block Sorting algorithm proposed by Burrows and Wheeler is evaluated theoretically. It is proved that the Block Sorting algorithm is asymptotically optimal for stationary ergodic finite order Markov sources. Our proof is based on the facts that symbols with the same Markov state (or context) in an original data sequence are grouped together in the output sequence obtained by Burrows-Wheeler transform, and the codeword length of each group can be bounded by a function described with the frequencies of symbols included in the group.

A key distribution system is a system in which users securely generate a common key. One kind of identity-based key distribution system was proposed by E. Okamoto. Its security depends on the difficulty of factoring a composite number of two large primes like RSA public-key cryptosystem. Another kind of identity-based key distribution system was proposed by K. Nyberg, R. A. Rueppel. Its security depends on the difficulty of the discrete logarithm problem. On the other hand, Koblitz and Miller described how a group of points on an elliptic curve over a finite field can be used to construct a public key cryptosystem. In 1997, we proposed an ID-based key distribution system over an elliptic curve, as well as those over the ring Z/nZ. Its security depends on the difficulty of factoring a composite number of two large primes. We showed that this system over an elliptic curve is more suitable for the implementation than those over the ring Z/nZ. In this paper, we apply the Nyberg-Rueppel ID-based key distribution system to an elliptic curve. It provides relatively small block size and high security. This public key distribution system can be efficiently implemented. However the Nyberg-Rueppel's scheme requires relatively large data transmission. As a solution to this problem, we improve the scheme. This improved scheme is very efficient since data transferred for the common key generation is reduced to half of those in the Nyberg-Rueppel's scheme.

Reentrant delay line memories using narrow YBa2Cu3O7-δ (YBCO) coplanar transmission lines are proposed. The proposed memory is composed of a looped YBCO coplanar delay line and a 22 semiconductor crossbar switch. This type of memory is superior to semiconductor memories in operating speed, the number of logic gates, power dissipation, and so on. We have also developed narrow and low-loss YBCO coplanar transmission lines for use in these reentrant delay line memories. Etch-back planarization and a patterning process combining Ar-ion milling and wet-etching enabled us to fabricate 18-cm-long YBCO coplanar transmission lines as narrow as 5 µm, and these lines did not suffer from electrical shorts even when the spacing was only 2. 5 µm. The surface resistances calculated from the attenuation constants of 5-, 10-, and 25-µm-wide lines provide similar low values of 0. 18-0. 26 mΩ at 10 GHz and 55 K. This indicates that the process damage was sufficiently suppressed despite the narrow line widths. The 5-µm-wide line attained a low attenuation constant of 2. 7 dB/m, which is similar to that in Cu coaxial cables. Even in the 5-µm-wide line, no significant increase in transmission loss was observed up to an input power level of 16 mW at 10 GHz and 55 K. This input power is comparable to that required to propagate digital signals from semiconductor circuits. Therefore high-speed digital signals can propagate through these narrow YBCO coplanar lines without significant attenuation of the signal pulses. Thus, these narrow YBCO coplanar lines can be used in the reentrant delay line memories.