As the demand of wireless personal communications networks increases, detailed chracteristics of indoor radio propagation in UHF band are required. In this paper, multipath fading characteristics at 1 GHz in an indoor mobil (walking speed) channel are investigated. By using a computer-controlled antenna scanner, signal strength was measured at 1400 points with a quarter wavelength resolution, which forms a two-dimensional fading map. The fading characteristics were found to be mainly dominated by the signals through the LOS path and the reflected paths due to two side-walls and one front-wall. It is analytically shown that middle-scale (over three wavelengths) fading is caused by the reflection from the side-walls, and periodical small-scale (equal to or less than a wavelength) fading is caused by the reflection from the front-wall. A software simulator based on geometric optics was developed in order to predict the measured fades. A modified algorithm for the two-dimensional ray launching technique which removes the necessity of checking the "multiple-counted rays" is presented. Comparison between measurements and predictions shows good agreement highlighting the usefulness of the two-dimensional simulator as a tool for channel design.

The 4th harmonics of a Nd:YAG laser beam (266 nm) is applied to fabricate highly oriented Y1Ba2Cu3O7-δ -SrTiO3-Y1Ba2Cu3O7-δ multilayer structures. It has been shown that the emission temperature of a film surface will change during deposition, depending on deposition conditions, even though the heater temperature is constant. The change of substrate temperature is strongly correlated to film characteristics such as critical temperature, c-axis length, and resistivity. The insitu monitoring of the substrate temperature is useful for obtaining high-quality Y1Ba2Cu3O7-δ films reproducibly. It is also shown that a SrTiO3 layer prevents oxygen restoration in a Y1Ba2Cu3O7-δ underlayer. The relationship between oxygen deficiency and the annealing conditions is studied.

We have developed a strato-mesospheric ozone monitoring system with a low noise SIS mixer, which receives 110.836 GHz millimeter-wave emission due to the rotational transition of ozone molecules (J=61,560,6). The system is completely standalone. We derived the altitude profile of ozone density between 25 km and 80 km from the observed spectrum. The receiver noise temperature was as low as 17 K (DSB), so that the altitude profile could be obtained every 3-10 minutes. The monitoring system can operate continuously over one year without any maintenance work, because it utilizes a 4 K closed cycle helium refrigerator and reliable Nb/AIOx/Nb SIS junctions. We used two acousto-optical spectrometers (AOSs) as real-time spectrometers because of their high resolution and simple construction. In an up-to-date system, one AOS would have a band-width of 65 MHz and the other, a band-width of 250 MHz with resolutions of 40 kHz and 250 kHz, respectively. A computer controls the entire system and is also used to analyze measured data. In this paper, we present the principles of system operation, the latest performance and the construction of the system, and some observed data.

In this paper, oscillation modes produced in a Josephson circuit and its application to digital systems are described. The analysis is performed using an analog simulator to model the Josephson junction, in addition to computer simulation. The experimental results concerning oscillation modes agree well with the simulation results. The main advantage of the mapping for the oscillation modes is that it allows understanding of the relationships among oscillation modes and circuit parameters at first sight. In addition, a novel application of nonlinear oscillation to digital systems is described.

For Nakagami-Rice fading environment which seems to become a principle propagation environment in the next generation wideband and high-capacity mobile systems such as personal communications, we have previously proposed an approximated evaluation scheme for wideband digital transmission characteristics such as errors due to intersymbol interference of multipath waves. We called the scheme 'Equivalent Transmission-Path (ETP) Model.' In this paper, through a discussion about more general equivalent propagation channel expressions, we clarify a theoretical foundation of the ETP model and extend the model to have an ability of expression of instantaneous fading condition varying with time. Also the appropriateness of the instantaneous expression is examined by a computer simulation analysis. Based on this model, statistics of link quality and service availability in Nakagami-Rice fading environments are discussed.

For direct sequence spread spectrum systems, the performance of PN sequence acquisition can be significantly affected if data modulation is present. However, the data modulation often exists during the reacquisition of a PCS radio channel. This study proposes and analyzes two shemes which are designed to improve acquisition process for PN sequence under data modulation. Both designs are based upon a PN acquisition receiver with parallel I-Q matched filters. The first scheme employs a serial search strategy with verification mode. The second scheme, which is still based upon the same parallel acquisition receiver, employs the parallel search strategy. We show that the second scheme is capable of providing faster acquisition under data modulation than the first serial search scheme using the same number of I-Q matched filter. We believe it should become a very good alternative for the acquisition of data modulated PN sequences in personal communications.

In this paper, coded modulation techniques suitable for satellite broadcasting of digital high-definition TV are studied. An overview of current approaches to satellite broadcasting is presented. New constructions of coded modulation schemes for unequal error protection (UEP), based on both block and trellis codes, are introduced in this paper. The proposed schemes can achieve both better overall performance and enhanced graceful degradation of the received signal, in comparison with existing digital satellite broadcasting approaches.

An algorithm for finding the unequal error protection (UEP) capability of a q-ary image of a low-rate qm-ary cyclic code is presented by combining its concatenated structure with the UEP capability of concatenated codes. The results are independent of a choice of a basis to be used for expanding an element over GF (qm) into GF (q). A table of the UEP capability of binary images of low-rate Reed-Solomon codes over GF (26) is given. It is shown that the encoding and decoding algorithms for superimposed concatenated codes can be applied to a q-ary image as a linear UEP code.

In high-speed digital land mobile radio communication, communication quality is degraded by frequency selective fading that has intersymbol interference. It causes increase of bit error rate (BER). To decrease BER in the channel, this paper proposes a system with combined multilevel coding and adaptive equalization using interleaving. By using interleaving, the proposed system obtains time diversity effect. Furthermore the system realizes a type of decision feedback adaptive equalizer where signal after multilevel decoder is fed back. These features of the system cause decrease of BER. The proposed system is compared with a similar system with a feedback signal before multilevel decoder. The average bit error rate of the proposed system is less than 1/100 with that of the compared system at average Eb/No = 22 [dB] in a case of fading channel with one intersymbol interference.

This paper presents a new blind identification method of nonminimum phase FIR systems and an adaptive blind equalization for PAM/QAM inputs without employing higher-order statistics. They are based on the observation that the absolute mean of a second-order white sequence can measure whether the sequence is higher-order white or not. The proposed methods are new alternatives to many higher-order statistics approaches. Some computer simulations show that the absolute mean is exactly estimated and the proposed methods can overcome the disadvantages of the higher-order statistics approaches.

A channel coding which combines convolutional coding and M-ary PSK/orthogonal multi-carrier (MPSK/OMC) transmission is proposed. A coding gain is achieved without sacrificing the data rate or occupying extra bandwidth. The proposed coding formula is that the imformation data bits of bit interval Ts are serial to parallel converted to P parallel branches where each branch has a bit interval Tp = PTs. The data bits of the parallel branches are encoded through a rate nP/(n + 1)(2P - 1) convolutional encoding process and the total (n+1)(2P-1) symbol of the encoder output is transmitted by 2P - 1 OMCs where each carrier is modulated by MPSK/OMC (M = 2n + 1). Following performance analysis of a coding form using rate P/(2P - 1) convolutional encoder and BPSK/OMC modulation, a general channel coding combining convolutional coding and MPSK/OMC modulation is discussed.

The performance of APP (a posteriori probability) decoding algorithm which is well known as a soft decision decoding algorithm for majority logic decodable codes is further improved by iterating the algorithm one or more times. This letter shows that there exists the optimal non-zero threshold value of the decision function that minimizes the decoded error rate in two-pass APP decoding though the optimal threshold value in one-pass APP decoding is zero.

M-ary orthogonal keying (MOK) systems under carrier frequency offset (CFO) are investigated. It is shown that spurious signals are introduced by the offset frequency components of spectrum after multiplication in correlation detection process, and some conditions on robust orthogonal signal sets are derived. Walsh function sets are found to be very weak against CFO, since they produce large spurious signals. As robust orthogonal signal sets against CFO, the rows of circulant Hadamard matrices are proposed and their error performanses are evaluated. The results show that they are good M-ary orthogonal signal sets in the presence of CFO.

The performance of an M-ary spread-spectrum multiple-access (M-ary/SSMA) scheme in the presence of carrier frequency offset is discussed in this paper. The influence of carrier frequency offset on the non-coherent reception of M-ary/SSMA signals is examined and it is shown that the carrier frequency offset degrades the performance remarkably, yet. this influence has a distinctive property. Making use of this property, we propose a new M-ary/SSMA scheme that can mitigate the influence of the carrier frequency offset. The scheme is based on the assignment of two distinctive Hadamard codes to in-phase and quadrature components of the transmitted signal. The effect of simultaneous transmission is evaluated in terms of bit-error-rate performance with the carrier frequency offset. As the result, it is observed that the satisfactory bit-error-rate performance can be achieved in the presence of carrier frequendy offset.

The structure of an SST Viterbi decoder for general rate (n-1)/n convolutional codes is investigated in the light of syndrome decoding. Since the input to the main decoder is expressed as S(H-1)T (S: syndrome, H: dual encoder of G) for a general non-systematic convolutional code G if the inverse encoder G-1 is used as a pre-decoder, SST Viterbi decoding can be regarded as searching for the most likely error sequence through an extended syndrome trellis. We show that searching based on the extended syndrome trellis is equivalent to the original syndrome decoding by applying the invariant-factor theorem.

For the dependent protocols to perform the server-aided RSA secret computation, the damage caused by the active attacks is greater than that by the passive attacks. Though there are two dependent proposed protocols against active attacks, the cost of the two protocols is still high. In this paper, we propose two efficient dependent protocols. Even considering the low cost of these two protocols, they can also guard against the proposed active attacks.

Hybrid direct sequence/slow frequency hopping-time division duplex (DS/SFH-TDD) multiple access system has some good features of each system. However it has a problem of hit between multiple users. If the designed frequency hopping patterns are inadequate, the quality of the multiple access system is degraded due to the frequent hit. In this paper, we propose an adaptive hopping pattern control system which is able to avoid the multiple access interference of hit. The proposed system decreases the influence of hit and increases the user capacity in the cell. And this adaptive hopping pattern control is applied to both single-cell and multi-cell systems. By computer simulation to evaluate the performance of this system, we found that this system is effective in increasing the multiple access capability.

This paper proposes and investigates the adaptive multi-user equalizer based on the multi-dimensional IIR adaptive lattice filter in order to suppress the co-channel interference (CCI) in asynchronous DS/CDMA system. An asynchronous DS/CDMA system with multi-user receiver is modeled as multi-dimensional or multi-input/out system with cross-coupling that is co-channel interference. From the system model it is shown that the multi-user detection is reduced into a problem of multi-dimensional equalization for multiaccess interference as well as intersymbol interference. The proposed multi-user equalizer can improve the equalizing error of the filter, comparing with that of the multi-dimensional FIR transversal filter of which number of tap is finite. The multi-dimensional lattice filter can adaptively achieve fast and stable convergence with less taps. Since the filter can resolve correlative multiple input into orthogonal output stage by stage, CCI can be removed. Computer simulations show performance of the proposed scheme.

The p-collection problem is where to locate p sinks in a flow network such that the value of a maximum flow is maximum. In this paper we show complexity results of the p-collection problem. We prove that the decision problem corresponding to the p-collection problem is strongly NP-complete. Although location problems (the p-center problem and the p-median problem) in networks and flow networks with tree structure is solvable in polynomial time, we prove that the decision problem of the p-collection problem in networks with tree structure, is weakly NP-complete. And we show a polynomial time algorithm for the subproblem of the p-collection problem such that the degree sum of vertices with degree3 in a network, is bound to some constant K0.

In this paper, an efficient voice/data integrated access algorithm for future personal communication networks (PCNs) is proposed and analyzed based on an equilibrium point analysis (EPA) method. A practical wireless communication channel may be impaired by noise and multipath distortion, and thus corrupted real-time packets have to recompete immediately in order to be transmitted within the stringent delay constraint. Also, real-time traffic users have to transmit their packets irrespective of the amount of non real-time data messages so that heavy non real-time traffic does not degrade the quality of real-time traffic. In the proposed algorithm, request subslots are distributed in the beginning of every slot to reduce access delay of real-time traffic. Moreover, slots are assigned to real-time traffic first and the remaining idle slots are assigned later to non real-time traffic by using the scheme of contention separation. We analyze the throughput and delay characteristics of this system based on an EPA mothod, and validate their performances by simulations. This scheme can support different quality of services (QoSs) imposed by different services efficiently and show good quality of real-time traffic, especially voice packets, no matter how heavy non real-time traffic is.