Showing papers in "Electronics and Communications in Japan Part I-communications in 1991"

Characteristics of CMA adaptive array for selective fading compensation in digital land mobile radio communications

Abstract: This paper considers CMA adaptive array for the high-speed TDMA transmission system using GMSK, which is the most ordinary constant-envelope modulation system in the digital mobile land communication. A computer simulation is executed for the case where a four-element adaptive array is applied to cope with the selective fading. CMA is employed as the array control algorithm, which is suited to the compensation of the constant-envelope modulated signal. Assuming a model with two arriving waves, the convergence and the BER performances of CMA are evaluated. It is shown that the BER is improved greatly up to the limit that no more error can be reduced, compared to the case without an adaptive array. It is seen also that the error rate is improved better when the delay difference between the two arriving waves is large. Thus, the proposed method is shown to be an effective technique to cope with selective fading.

Design of a directional diversity receiver using an adaptive array antenna

Abstract: In mobile communication, fading due to multipath is a major factor in the deterioration of communication quality. One strategy for this problem is the adaptive array which eliminates the effect of the delayed waves by beam-forming or controlling the radiation pattern adaptively. However, in the conventional method, the delayed waves simply are eliminated but are not utilized. It has been pointed out also that the directional diversity reception is effective in reducing the fading effect. In the conventional directional diversity reception method, the radiation pattern of the antenna is fixed. In this paper, it is pointed out that the information identical to that in the direct wave is contained in the delayed wave. A directional diversity method is proposed in which, by means of the radiation pattern of the adaptive array antenna, the direct wave and the delayed waves are separated adaptively or combined. In this system, two sets of antenna weights are included for unknown or time-varying waves and the radiation patterns of the antenna can be controlled adaptively so that the directions of arrival can be estimated individually. By adaptively combining the direct and delayed waves, the SN ratio can be improved. The basic evaluation of this system is carried out to indicate that the error rate can be improved over that for the conventional adaptive array antenna which does not make use of the delayed wave. A possibility of using the proposed system in mobile communication is discussed.

Mobile propagation loss prediction for arbitrary urban environments

Abstract: This paper describes the estimation of the propagation loss in an urban environment important for channel design of land mobile communication. Conventional methods for estimating the propagation loss in an urban environment gives a representative value of the propagation loss in the urban environment or the propagation loss (median value) within a 500 m × 800 m area obtained by introducing an area factor of occupied buildings. Such a method is not suitable for estimation of the propagation loss depending on the situation near the mobile station. In this paper, the relationship of the measured data of the propagation loss in the Tokyo Metropolitan area at 813 and 1433 MHz with the urban environment parameters such as the base station antenna height, distance, frequency, width of the street where the mobile station exists, direction, average building height, building height on the street side is derived by the multiple regression analysis method. A prediction formula for the propagation loss (median value in the section of about 80 m) including these parameters is derived. The parameter dependencies of the propagation loss, such as the antenna height dependence and the average building height dependence, are described. In addition, the distance dependencies of the propagation loss in this prediction formula and conventional method are compared with the measured values. The prediction formula is expressed in terms of the sum of simple functions of the foregoing parameters. Hence, the estimation of the propagation loss can be carried out easily, taking into consideration the urban environments such as the height of the buildings and width of the streets.

Analysis of correlation characteristics of antenna diversity in land mobile radio environments

Abstract: Antenna diversity reception can significantly alleviate fading with a relatively simple configuration. Hence, this technique will be indispensable in future portable radio systems. In the antenna diversity system installed in a portable transceiver, degradation of the diversity effect due to artificial variation of the radiation pattern (polarization characteristics) is expected. To design an effective diversity branch which reduces degradation by such variations, it is necessary to carry out an analysis of characteristics of the diversity branch in which the arrivals of both the co-polarization and cross polarization are taken into account. This paper presents a theoretical analysis method for the antenna diversity correlation characteristics which takes into account the statistical incident wave distributions of both the co-polarization and cross polarization. In addition, a theoretical study is carried out on the correlation between the cross dipole antenna branches, constituting a polarization diversity antenna. The theoretical analysis reveals that the correlation characteristics of the diversity branches depend strongly not only on the antenna directivity but also on the incident wave characteristics and that the correlation between the diversity branches becomes almost zero regardless of the antenna pattern variation and the incident wave characteristics if the cross-polarization power ratio (XPR) is -1.5 dB. Further, the validity of the present analysis is confirmed through 900-MHz band experiments in a metropolitan area.

Distributed self‐healing network and its optimum spare‐capacity assignment algorithm

Abstract: Rapid self-healing under link failure in high-capacity optical fiber is a basic issue in broadband networks. Failure restoration schemes are being studied which reroute failed paths using the control of path reconfiguration function of the Digital Cross Connect System (DCS). Distributed control schemes based on a flooding algorithm have been proposed to meet real-time requirements for large-scale transmission networks, but problems arise, such as message congestion at nodes and internode synchronization. The performance of the self-healing algorithm depends not only on the algorithm itself but also on physical network topology and spare capacity. In this paper, we propose a distributed restoration algorithm using a flooding technique and a centralized spare-capacity assignment algorithm minimizing total spare capacity in a network while meeting a given survivability objective. The failure restoration time, restoration ratio, and spare capacity cost of these algorithms will be evaluated by computer simulation.

Urban multipath propagation delay characteristics in mobile communications

Abstract: In this paper, propagation delay measurements were carried out in Tokyo (metropolitan urban area) where high rises and other buildings are concentrated on a plane and in Kofu (urban area adjacent to mountains) surrounded by tall mountains. The delay characteristics such as delay spread and wave numbers were found. The principal results obtained in these areas are as follows. (1) In a metropolitan urban area, i.e., Tokyo, (a) the average delay spread in a high-density residential district is less than about 1 μs and the delay profile consists of a group of direct waves arriving directly from the base station; and (b) the average delay spread in a location with high-rise buildings is also less than 1 μs and the average number of arriving waves is about five with the delay profile consisting of a direct wave group and a reflected wave group from reflecting object. (2) In an urban area adjacent to mountains, i.e., Kofu, the average delay spread is less than about 2 μs and the average number of arriving waves is four. The delay profile consists of a direct wave group and a reflected wave group. The level of the reflected wave group decreases exponentially with the delay time in the case of reflection from buildings, while the level is almost constant within a certain range of delay time and is of a spread shape (rectangular) in the case of reflection from mountains. From these measured results, a simple propagation model consisting of a direct wave group and a reflected wave group is proposed. It is shown that the distance dependence of the delay spread has a peak between the base station and a reflecting object.

Relation between spacing and receiving efficiency of finite rectenna array

Abstract: In the rectenna array used for rectification of the microwaves received on the ground in the solar power satellite system, it is required that the rectenna elements have a high dc power conversion efficiency and that the element spacing is optimized so that the arriving microwave power is received efficiently and the number of elements can be reduced. In this paper, a microwave rectifier is fabricated in an integrated form with a microstrip line on a teflon substrate. A circular microstrip patch antenna is used. A high rectification efficiency, 66.7 percent is obtained at a microwave input of 750 mW and 75.7 percent for input of 500 mW. With this rectenna element, a 7 × 7 lattice array is formed and the variation of the receiving efficiency (the ratio of the power converted to dc to the input microwave power) is measured by varying the element spacing. On the other hand, the receiving efficiency is calculated for a given element spacing of this rectenna array from the circuit equation of the antenna system by deriving the mutual coupling between the elements. The relationship between the element spacing of a finite array and the receiving efficiency is obtained both experimentally and theoretically. This computation method is extended to the case with many elements so that the change of the receiving efficiency is investigated.

Dual‐mode equalization for digital mobile radio

Abstract: The performance of digital mobile radio systems when transmitting at over several tens of kbit/s severely degrades with the onset of fast fading multipath propagation. This paper proposes a dual-mode equalization (DME) method to overcome the degradation and experimentally verifies the effectiveness of the method. The new method uses decision feedback equalizers (DFEs) in two modes simultaneously, a normal mode, and a time-reversal mode, and selects the best equalization result. The time-reversal equalization mode improves the characteristics of equalization and adaptation in the non-minimum phase condition. It converts the nonminimum phase to the minimum phase condition by the time-reversal operation. Principles of dual-mode equalization, an algorithm for mode output selection, and timing problems are discussed in detail. Experiments demonstrate average BER performance in two-path and typical multipath environments. The proposed dual-mode equalization technique improves average BER performance by 2 dB Eb/N0.

A digital signature scheme on a document for MH facsimile transmission

Abstract: This paper proposes a digital signature scheme for a facsimile document which embeds a signature directly onto the document. The scheme modifies each run of white or black pixels with a single bit of the signature data. It is designed to be compatible with CCITT G3 facsimile standards and to protect the document from the insertion, modification, replacement, overwriting or deletion of characters. Furthermore, the total amount of data to be transmitted is about the same as that of the original facsimile document. In this paper, an authentication scheme is shown with a prototype model under a one-key encryption system.

Frequency diversity effects in multicarrier digital radio systems

Abstract: Frequency diversity usually is employed in microwave radio systems, where protection channels with different frequencies are prepared and the transmitting data signal is switched to the protection channel to secure the channel reliability when the channel quality is deteriorated by the fading. In multicarrier radio systems, there can be various channel switching configurations, since the protection channel is composed of more than one primary carriers. This paper discusses the effects of the frequency diversity in various switching schemes in the multicarrier radio system. As the model for the theoretical analysis for the microwave fading, the three-ray multipath fading model is assumed which is close to the actual transmission path. The frequency correlation coefficient and the joint probability for the received power distribution in different radio channels also are derived by a simulation calculation. The effects of the frequency diversity of various switching schemes in the multicarrier system are evaluated. The validity of the presented result is verified by the simultaneous measurement of more than one channel with different frequencies in the actual over-water transmission path by the measurements of the frequency correlation coefficient and the joint probability distribution for the received power.

A study of vertical space diversity for a land mobile radio

Abstract: Vertical space diversity used for reduction of deep fading in the mobile propagation path is effective for the base station and mobile station for the future land mobile communications for which the installation conditions become increasingly more severe due to the smallness of the area occupied by the antenna in this system. In this paper, the correlation coefficient of the vertical space diversity is studied theoretically and experimentally in the case where the antenna height changes from the mobile station to the base station. Further, from the comparison of the computed and measured data of the correlation coefficient, the spatial divergence of the multiple waves arriving at the antenna has been studied due to its importance in finding the diversity effect. The divergence of the multiple wave vs. the antenna height is estimated. As a result, the antenna spacing needed to obtain the diversity effect for an arbitrary antenna height is obtained easily. For instance, in the case where the antenna height is 156 m, the standard deviation of the divergence of the arriving wave is 0.2 deg. If the correlation coefficient is assumed to be less than 0.6, the required antenna spacing is about 30 wavelengths. For the antenna height of 1.5 m, the standard deviation of the divergence of the arriving wave is about 11 deg and the required antenna spacing is about 0.3 wavelengths.

Null beam forming by phase control of selected elements in phased‐array antennas

Abstract: In phased-array antennas, nulls of the radiation pattern can be formed in the direction of undesired wave by controlling only the phase excitation without affecting the main beam. However, the computation time becomes very large when an antenna with a large number of elements is analyzed and it becomes very difficult to counteract the variation of wave boundary instantly. Here, based on the exact calculation of phase value by the method of plane-wave synthesis, the foremen-tioned elements are selected which contribute more to the null formation, and the method of controlling only the phase of the selected elements is presented. Using this method, the computation time can be reduced. Moreover, the depth of nulls and the gain of the main beam obtained in this way is the same as that produced by controlling the phase of all the antenna elements. As a result of numerical simulation and experiments of null forming in the phased-array antenna using a 5-bit phase shifter, deep nulls with the level of less than -40 dB could be formed without decreasing the gain of the main beam.

Study of fault‐location expert systems for paired cables

Abstract: No method has been reported for fault location in a length of paired cable which consists of branched cables and wire of different gauges. This paper proposes a fault-location expert system which comprises a new pulse echo detector and a fault-location estimation expert system. The new pulse echo detector can locate a fault by the correspondence between theoretical and measured reflected waves. However, there is some degree of error because the transmission characteristics of each paired cable vary slightly. A more precise fault-detection technique has also been developed. It is the fault-location estimation expert system which has a knowledge base including experimental field data and an inference technique based on probability theory. The knowledge is obtained from the fault rate of each cable part in the field. Field tests have clarified that the fault-location expert system can detect faults successfully.

Error-rate performance of block-coded M-ary modulation and hard decision decoding systems on rayleigh fading channel

Abstract: Error rates of block-coded MPSK and/or MQAM systems with hard-decision decoding are evaluated theoretically on the Rayleigh fading channel characterizing the land mobile channel. BCH codes are employed as the block codes and analysis is carried out both for nondiversity reception and for dual MRC diversity reception. It is shown that on the Rayleigh fading channel, in contrast to the AWGN channel, BCH-coded MPSK systems can achieve significant coding gain compared to uncoded BPSK even in the hard-decision decoding case without changing spectral efficiency. It is shown also that diversity reception is needed for sufficient large coding gain in higher spectral efficiency. Moreover, it is suggested that the code length longer than a threshold is necessary for large coding gain under the given number of multilevel modulation and given spectral efficiency.

Signaling protocol architecture for a digital mobile communications network

Abstract: This paper proposes a signaling protocol which can be applied to high-capacity digital mobile communications networks. First, a hierarchical network function model based on the Intelligent Network (IN) concept is described. In the model, the need for mobile transit switching capability and subscriber line signaling transfer capability is discussed. Second, interoffice signaling protocol and subscriber line signaling protocol are proposed. The interoffice signals consist of circuit-related signals which are based on the SS No. 7 ISDN User Part (ISUP) and noncircuit-related signals which apply SCCP and TCAP. The subscriber line layer-3 signals are designed for expansion and radio frequency efficiency. The layer-3 grouping function is applied for efficient use of radio frequency. Third, some examples of procedures using those signals and comparisons of signal number and signal volumes between the digital system and the present analog system are shown.

High-speed TDM photonic switching system

Abstract: Photonic switching, a technique for switching optical information from an optical fiber transmission line without optical-to-electrical and electrical-to-optical conversion, is currently under intense study. Large-scale and economical optical fiber transmission lines have been realized based on TDM. Therefore, TDM photonic switching is the key technology for the development of high-speed and large-scale switching devices when matching with transmission lines is considered. However, no satisfactory system or devices have developed. This paper examines the structure of space and time switches, which are channel structure elements of a TDM photonic switching system. An optical matrix switch structure is proposed that is the optimum space switch for high-speed and large-scale systems. It is shown that such a time switch can now be constructed. Also, a TDM photonic switching system was constructed that combines the optical switch and an optical bistability semiconductor laser. This system operates at 512 Mbit/s.

Propagation characteristics for mobile reception of satellite broadcasting in urban areas

Abstract: When various broadcasting radio waves in the 12-GHz band from a geostationary satellite such as a broadcasting satellite are received in an urban area by a mobile receiver, transmission and reception systems such as a temporal diversity system often are designed. In such instances, it is necessary to evaluate quantitatively the mobile receiving characteristics such as the areal visibility on an urban street. When driving on an urban street, one finds that the waves from satellites frequently are disturbed by buildings. The degree of disturbance depends on the direction of the street, the density, height and width of the building. This paper describes first characteristics of measured satellite areal visibility on a road using an airscape photographed at a time when the apparent locations of the satellite and the sun coincide. The histogram of the visibility length is modeled by a log normal distribution. Second, from these distributions and the measurement and analysis of the actual velocity characteristics of automobiles in the Tokyo metropolitan area, the histogram of the visibility duration time is estimated. Third, an estimation method of the satellite areal visibility on a road is proposed in which the statistical data are published by a governmental agency on the building distributions and on the road. The results obtained by these measurement and estimations can provide quantitatively the mobile receiving characteristics of satellite broadcasting at 12 GHz so that they can be effective guidelines in the design of various transmission and reception systems.

Double-stage phase-diversity (DSPD) scheme for coherent optical fiber communications—optical circuit imbalance and its compensation

Abstract: The double-stage phase-diversity (DSPD) scheme we have proposed features a phase-diversity-type optical homodyne detection followed by a phase-diversity-type electrical frequency up-conversion, giving a heterodyne-like intermediate frequency (IF) signal. It has the advantages of both heterodyning and homodyning. In this paper, we first calculate the sensitivity penalty due to the optical circuit (hybrid) imbalance in a DSPD receiver. It is shown that the penalty is as small as that in a conventional phase-diversity receiver and that the optical circuit requirement is not severe. The DSPD experiment with an adjustable imbalance is then performed to confirm the theory; experimental results are in good agreement with the theory. Finally, the possibility of compensation of the optical imbalance at the electronic stage of the receiver is shown.

Characteristics and prediction methods for the occurrence rate of SES in available time affected by tropospheric scintillation

Abstract: The unavailable time percentage and the SES (severely errored seconds) occurrence rate within available time was investigated according to CCITT definition using Ku band low elevation angles satellite system data obtained mainly at the Yamaguchi station. As a result, the CCITT unavailable time percentage was found to agree with the cumulative signal attenuation time percentage as determined by the traditional statistical treatment. This agreement held even in the case of low elevation angles. Further, the ratio of SES occurrence rate within CCITT available time to the conventional cumulative signal attenuation time percentage was found to be much larger than in the case of high elevation angles, and to have a high correlation with tropospheric scintillation. An experimental formula was developed for this ratio as an index of the degree to which tropospheric scintillation affects overall signal deterioration. Using this formula a formula was developed to predict the SES occurrence rate within CCITT available time from the index and the traditional cumulative signal attenuation time percentage. Also, it was confirmed that there was good agreement between the predicted value and the experimental value.

Relationship between array excitation distribution and radiation pattern ripple depth

Abstract: To develop a radiation pattern synthesis technique for array antennas, the relationship between the ripple depth of the radiation pattern and the flatness of the array excitation amplitude distribution is clarified analytically. The roots of the representation equation of the radiation pattern are shifted radially from Schelkunoff's unit circle so that the ripple depth is changed. The ripple depth of the radiation pattern and the flatness of the excitation amplitude distribution are expressed by approximate equations in terms of the amount of the shift of the root. If the amount of the shift of the root is eliminated from these two equations, the relationship between the ripple depth and the flatness of the excitation amplitude distribution can be derived. Approximate equations indicate that the relationship between the two is almost independent of the sidelobe level and is determined mainly by the number of elements. As a numerical example, an asymmetrically shaped pattern is generated for a 20-element array antenna with an element spacing of 0.5 wavelengths. The approximate equations and the rigorously calculated results are compared for error evaluation. It is confirmed that the approximate equations yield accurate evaluations if the ripple depth is more than 4 dB. Flatter excitation amplitude distributions reduce the influence of fabrication error and the mutual coupling of the elements and thereby improve the accuracy of the excitation coefficients. Useful design data also are obtained.

Trellis coded modulation for mobile-satellite communication using space diversity

Abstract: Most of the past studies concerning the decoding performance of trellis coded modulation (TCM) in a fading channel have been based on time diversity using interleaving/deinterleaving. One problem with time diversity is that a large decoding delay is produced due to the interleaving/deinterleaving which depends on the fading interval. This paper considers TCM signals using space diversity which can drastically improve the decoding delay and analyzes the decoding characteristics in Rice fading channels. An analysis is also made of the effect of the Euclidean distance (ED) and the Hamming distance (HD) of the trellis code on the average bit error rate (BER), and it is shown that a code design considering those two distance structures is needed in a channel with severe fading. This paper considers the major application of the proposed method to be digital voice transmission in mobile communication via satellite. Consequently, a simulation is made for the second-order space diversity decoding performance for the trellis coded 8-PSK signal. The optimal trellis coding at the transmitter is discussed for BER = 10−4.

Planar four‐direction antenna for antenna pattern diversity reception

Abstract: In digital mobile communication, the directional diversity method is useful against fading. In this method, the antennas are switched successively to the antenna directed toward the arrival of the desired signal. In this paper, a four-directional switching antenna is proposed for the directional diversity. The proposed planar antenna consists of a sectoral patch antenna and 3-dB hybrids. By means of the cavity model, the eigenvalue, radiation pattern and mutual coupling between the elements are calculated for this antenna. It is shown theoretically that this antenna has the necessary characteristics of a four-direction antenna. The radiation pattern and the mutual coupling between the elements were measured for the antenna fabricated on a dielectric substrate to confirm the validity of the computation.

Hierarchical service control scheme for intelligent network services

Abstract: With the introduction of communication services into business activities, such as telemarketing, customer requirements for these services are becoming more varied. Since communication service has become competitive, quick provision of services has become important. This paper proposes a hierarchical service control scheme aimed at achieving service specification independence and the software architecture of an experimental intelligent network service system based on this new scheme. In the proposed new scheme, elementary functional parts are prepared beforehand and a service is realized using interpreter control based on the information about an execution order of functional parts. To localize modifications in software when a new service is introduced, functional parts are arranged in a hierarchical manner. This experimental system can change complicated service specifications in a few minutes. Processing volume is about half of that for an existing system in which service specification is described by a programming language and service associated data are managed by a common data management program.

Transform image coding with edge compensation

Abstract: A method to prevent edge degradation caused by orthogonal transform image coding is proposed The method contains three processes: 1) obtain a differential image between the original and low-pass one; 2) extract significant pixels concerning the edge degradation; and 3) add these pixels to compensate for the edge degradation Since an edge has a spatial length, five or more connected pixels whose value exceeds a threshold are selected in the differential image as significant error pixels Furthermore, using human visual perception that is very sensitive to the existence of an edge but very loose in its exact value and its exact location, the additional information (overhead) for compensation is saved The significant edge information is quantized three levels corresponding to positive error, negative error, and no error Then edges are classified in four directions after slight geometric approximations Four one-dimensional images with three-level value are assigned by Huffman code Run-length coding is used jointly for the zero error pixels The additional information for the edge compensation requires a few bits, but the image is reconstructed very clearly

Adaptive equalization of selective fading channel based on AR-model of channel-impulse-response fluctuation

Abstract: As an adaptive equalization method for multipath fading in a high-speed mobile communication at 100 kbit/s or more, a decision feedback equalization method with a Kalman filter is proposed based on the time-variant model of the impulse response variation of the transmission path. In this paper, by means of this equalization method, the autoregressive (AR) model of the variation is derived from the measured values of the impulse response variations. The result of simulation of the equalization is described. First, a method is explained to derive an AR model to be set in the equalizer from a set of measured data of the impulse response. Next, the results of simulation are presented for the case in which the variation characteristics of the transmission path and the equalizer model correspond to each other. It is shown that the results have the error rate almost equal to the case of uniform fading without a delayed wave and are better than those from the LMS method. Further, since the variation of the transmission path is slower than the transmission speed, a model is introduced in which the pole of the AR model is approximated by 1. It is shown that the variation of the transmission path in a wide region can be equalized without significant degradation even if the equalizer model is fixed.

Wave impedance in the near field around the fundamental electromagnetic radiating elements

Abstract: Standards for electromagnetic protection taking into account human health have been established in a number of countries. Most of the present standards are expressed in terms of the intensities of electric and magnetic fields or the power density of the irradiating electromagnetic field. Usually, for conversion among these quantities, the relationship in the electromagnetic field at a distance far away (far field, plane wave) is used. However, near the electromagnetic source where the electromagnetic wave is the strongest, the relationship among the forementioned quantities varies depending on the location of the observation point or the type of the source. Therefore, there are recommendations to reconsider the standard values. The purpose of this paper is to provide fundamental references for modeling the electromagnetic sources in various electromagnetic equipment to reconsider the protection standard of the near field, and to develop the electromagnetic shielding theory in the near field. In this paper, the distance characteristics and the spatial distribution of the electromagnetic wave impedance characterizing the nature of the electromagnetic wave are studied near the elementary radiating elements such as the electric dipole, magnetic dipole, half-wave dipole antenna, small current loop and small helical antenna.

Design and performance of a repeater for CSMA/CD passive optical star network connection

Abstract: One method to expand a network is to employ repeaters operating at layer 1. When networks using the optical passive star coupler are connected through repeaters with only a relaying function, there arises the problem of “self-collision.” This problem occurs when the packet returned from the optical star coupler connected to the destination network is relayed unconditionally by the repeater to the originating network. As a means to avoid the self-collision, the authors have proposed a repeater with wavelength-division multiplex technique and gate control [1]. Through the design of the wavelength filter, it is shown that a satisfactory performance is obtained [3]. This paper shows further the results of studies, from the functional viewpoint, for the transmission design of the repeater, the control method for the gate, and the relaying method for the code rule violation. The repeater is built into a system constructed experimentally for the star configured optical transmission system with the transmission rate of 32 Mbit/s. The result of measurement of the transmission performance and the functional operation are described. The design for the repeater, which is applicable to the connection of the passive star network, is now described clearly.

Simple go-back-N ARQ scheme for satellite channels with double acknowledgements

Abstract: This paper discusses a simple go-back-N ARQ scheme in which the satellite is provided not only with the repeater function but also with the processing function. The satellite detects the error in the data block sent from the transmitter. It returns ACK/NACK to the transmitter and relays the correctly received data block to the receiver. The receiver detects the error in the received data block and returns ACK/NACK to the transmitter. The transmitter examines two acknowledgement signals returned from the satellite and the receiver, and transmits the data block based on the basic go-back-N ARQ protocol. This paper analyzes the scheme in which the hardware complexity of the satellite is minimized. It is shown that the throughput can be increased and the average transmission delay can be decreased.

Two-dimensional analysis for gain enhancement of dielectric loaded antenna with a ground plane

Abstract: A gain enhancement is shown by loading with a dielectric plate of permittivity ϵr for an antenna with a reflection plate placed parallel in front of the antenna. For an infinitely extended dielectric plate, for simplicity, a two-dimensional problem with a linear current of a delta-function type was treated. Fourier analyses and geometrical optics were applied and a detailed examination was made of the radiation characteristics, gain, the generation rate of surface waves and the near fields as functions of the separation distance between the reflection plate and the dielectric plate, thickness t of the dielectric plate and ϵr. In particular, the radiated beam was directed toward the frontal direction (θ = 0) for h = mλ/2 and tr = (2n-1)λ/4, (m and n are integers; λ is free space wavelength) for either TE or TM waves. The radiated power was multiplied by a factor of ϵr of the power by the antenna itself. Good agreement was obtained with experimental results.

Quality control at the cell level and its characteristics in the ATM network

Abstract: In the ATM network, information is transmitted by the continuous transmission from node to node of a fixed-length packet called a “cell.” The requirements of the cell on the traffic characteristics and the network depend on the kind of information source. The information from a video terminal arriving at a node, for example, is bursty, and a severe condition is imposed on the delay. When cells from more than one medium arrive in a mixed way at the network, a certain control mechanism will be needed to satisfy the respective requirements from the cells. On the other hand, this control mechanism should be realized by as simple a structure as possible. This paper discusses the necessity of the quality control at the cell level and the basic concept in the control for the node handling different kinds of calls. First, the characteristics for the case of a single kind of call source (such as voice, video or data) are analyzed. Then the necessity and usefulness of the control methods when various kinds of calls are mixed and arrive at the node are discussed for different control methods using numerical examples.