Land Mobile Communication Research Articles

Land mobile satellite communication channel model for simultaneous transmission from A land mobile terminal via two separate satellites

AbstractThere are certain data services that could use transmit‐only land‐mobile satellite communication terminals. Such terminals would not be able to receive acknowledged messages and transmit them onward. Thus it is of interest to study alternative means of improving the system reliability. In this paper we propose the use of transmission to two satellites separated in azimuth and elevation in order to improve the reliability of throughput.We have investigated the improvements by building upon the model proposed by Lutz for land mobile satellite communications via one satellite, and extended this using measurements of the shadowing coefficient in different areas (suburban, countryside and city) to two separated satellites. The measured data is used to produce an empirical model of the equivalent shadowing coefficient variations with the separation angle variation between two satellites.The results show good agreement with the shadowing coefficients produced by the Lutz model for a single satellite. The degree of improvement produced by using two separated satellites in the different environments, in terms of bit rate and probability of the received power is given.

Study of multidimensional coded modulation in land mobile radio communication

A high reliability in communication is required in data transmission, such as personal computer communication and facsimile, in the digital land mobile communication. One means to cope with this problem is the coded modulation. This paper discusses the multidimensional coded modulation which is one such coded modulation method. Little consideration has been given to the application of this method to land mobile communication. In this study, 16 QAM is employed, applying the fading distortion compensation to the modulation method. The interleaving method is combined, and the bit-error rate of the multidimensional coded modulation system under the fading environment is investigated. The four-, eight-, and 16-dimensional cases are investigated by computer simulation, and a gain of approximately 3 dB is indicated for the eight- and 16-dimensional cases. The reason for such a small improvement is due to the unbalance of the error-rate performance in the coded symbol block. From such a viewpoint, the bit-error rate is analyzed by dividing the bit sequence in the symbol block into three parts, considering only the eight-dimensional case. As a result of the effort to reduce the unbalance of the bit-error rate performance under fading, the improvement of approximately 6 dB is realized for the bit-error rate of 103, thereby increasing the performance improvement.

Pereormance analysis of slotted ALOHA for land mobile satellite networks

AbstractThe ALOHA protocol has been proposed for accessing reservation channels in demand‐assigned channel access protocols for land mobile satellite communications networks. This paper provides a rigorous performance analysis of both the slotted ALOHA protocol and two‐packet replication ALOHA protocol taking into account the effects of the fading multipath communications environment. Throughput, delay and stability of these two protocols are determined using a Gilbert channel error model with memory. Comparison of slotted ALOHA and two‐packet replication ALOHA shows that a smaller average delay can be achieved by replication. Moreover average throughput is improved in some cases. However replication reduces stability.

A new carrier recovery circuit for land mobile satellite communication

A DCF (dual carrier filter) reverse-modulation-type carrier recovery circuit is proposed to achieve a low carrier skipping rate and satisfactory phase tracking performance for coherent detection of PSK (phase shift keying) signals in fast Rician fading channels. The proposed scheme employs both narrow and wide bandwidth carrier filters simultaneously for the reverse-modulation-type carrier recovery circuit. It is clarified by computer simulation that the Pe performance of a QPSK (quadriphase shift keying) modem employing the proposed scheme shows an improvement of 1.5 dB in required E/sub s//N/sub O/ at Pe=10/sup 4/ (after Viterbi decoding (R=7/8, K=7), C/M (direct-to-multipath signal power ratio)=10 dB, interleaving size=64*64), compared with conventional coherent detection employing the reverse modulation tank-limiter scheme or the Costas loop scheme. >

Mobile satellite communications - current status of maritime systems

Any review of the development of maritime satellite communications is essentially the history of Inmarsat and its predecessor system, Marisat. With perhaps two qualifications, one might extend the definition to mobile satellite communications generally. In the land mobile satellite communications domain two companies, Geostar and Qualcomm, have also made their mark. Geostar was recently declared bankrupt but Qualcomm continues to go from strength to strength.We are frequently asked ‘what is Inmarsat?'. The term Inmarsat is generally used, and used herein, to mean the permanent staff (the Directorate), Land Earth Station (LES) operators, manufacturers and value-added service providers who offer mobile satellite communications products or services via the satellites and other infrastructure which makes up the Inmarsat system. It is, essentially, a partnership but within it there is also internal competition. LES operators compete in the provision of telecommunications services (quality is consistently high, but they each decide what services to offer and at what tariffs). Manufacturers compete to secure market dominance and profitabilty for their products. Not all will be equally successful. More than anything, Inmarsat is a global partnership dedicated to meeting mankind's need to communicate while on the move. It aims to do so cost-effectively and using satellites.

Investigation of a compartment-mounted diversity antenna for land mobile radios

When constructing a compartment-mounted diversity antenna for land mobile communication, it is important to provide an antenna branch with a small correlation factor and to improve the receiving level degradation due to the effect of the vehicle body. To solve these problems, a directivity diversity antenna is proposed which is in a hybrid circuit form with antennas placed near the front and rear windows of a passenger sedan with respect to the direction of motion. This antenna was studied theoretically and experimentally. If the antenna element has a beamwidth of 180° in the horizontal plane and a gain of 3 dBd, a receiving level almost identical to that of an omnidirectional 0-dBd gain antenna in the horizontal plane installed outside the vehicle was attained in an urban area. The correlation coefficient was small between the terminals.

A study of vertical space diversity for a land mobile radio

AbstractVertical 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.

Mobile propagation loss prediction for arbitrary urban environments

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.

Reed-Solomon codes for land mobile satellite channels

The performance of Reed-Solomon codes is determined for land mobile satellite communications where a shadowed Rician channel model is used. An effective coding/interleaving scheme is proposed which uses the multipath fading and shadowing statistics of the channel.

The land mobile satellite communication channel-recording, statistics, and channel model

The communication channel between the MARECS satellite at 26 degrees W and a cruising van was measured and recorded in European areas exhibiting satellite elevations from 13 to 43 degrees . Different environments and mobile antennas were tested. The results of an extensive statistical evaluation include spectra of the fading amplitude; probability density, and distribution of the received signal power; and the percentage of time for fade and nonfade periods. Based on the physical phenomena of multipath fading and signal shadowing, an analog model of the land mobile satellite channel which can readily be used for software and hardware fading simulation is developed. The most important parameter of this model is the time-share of shadowing. The Rice factor which characterizes the channel during unshadowed periods, can vary from 3.9 to 18.1 dB. Block error probability density, error gap distribution, and block error probability are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fully digital M-ary psk and M-ary qam demodulators for land mobile satellite communications

A fully digital implementations of digital modems is the preferred option of system designers because high performance can be achieved at reasonable cost. The paper explains the beneficial features inherent in fully digital demodulator implementations. Other features which are required for land mobile satellite communication systems are also discussed. Recently reported techniques for the synchronisation and detection of M-ary PSK and M-ary QAM modulation schemes are reviewed with emphasis placed on those which are well suited to digital implementation.

Received signal level characteristics with adaptive transmitter power control in mobile communications

AbstractThe adaptive transmitter power control (ATPC) which controls the transmitter power in accordance with the propagation loss between the base station and a mobile station in the land mobile communication is effective in reducing the interference within a channel and that between the adjacent channels of the base station. Also, the portable mobile station which must be small and lightweight is required to reduce the average power consumption. One of the ATPC methods is the ATPC feedback control in which the up‐ and downlinks can be controlled independently.In this paper, the receiving level probability density function is derived theoretically as the basic characteristics in the case of an ATPC feedback. Finally, the effects on the receiving level profile from the control parameters such as the controlled delay time, maximum amount of control, control step width and control level setting are investigated theoretically and experimentally.

Performance of a decision feedback equalizer under frequency‐selective fading in land mobile communications

AbstractSome means to cope with frequency‐selective fading is indispensable to the realization of a wideband digital mobile communication, and various investigations have been made to this end. For example, the decision feedback equalizer (DFE) is considered promising, since it requires smaller‐scale equipment and is versatile in applications.The application of DFE to mobile communication requires tracking to the time‐varying channel as well as the fast initial adaptation. Thus, comprehensive investigations, including the construction of the equalizer and tap‐updating algorithm are needed.The Kalman algorithm is employed as the tap‐updating algorithm. By introducing the memory factor into the algorithm, the tracking performance to the time‐varying channel is improved as well as the speed of the initial adaptation.A computer simulation is made for the proposed method based on the model of 256 kbit/s TDMA system with QPSK modulation. It is verified that DFE is useful in compensating for the frequency‐selective fading in mobile communication.

Error rate performance in high‐speed gmsk transmission on mobile satellite channel

AbstractIn high‐speed digital transmission in mobile satellite and land mobile communications, one of the serious problems is the effect of waveform distortion due to the frequency‐selective fading. This paper considers the GMSK modulation system, which is considered as useful as the modulation scheme for digital mobile communication.The effect of the waveform distortion produced by the time‐delay spread of the scattered interfering waves in the Nakagami‐Rice fading channel is considered and the bit error rate is calculated theoretically. Numerical examples of bit error rate performance are illustrated. It is shown that the bit error rate is improved when there is an average delay time or a time‐delay spread in the scattered interfering wave, compared with the case without a delay. However, the effect is relatively small.

A new millimetre wave satellite system for land mobile communications

AbstractCellular systems are gaining wide acceptance. In Europe the GSM system is expected to provide service to more than 10 million users by the year 2000. Assuming that a demand for additional services at 64 kbit/s or so will not easily be satisfied either by the present GSM system or by advanced satellite systems at L‐band, this paper proposes a new satellite system at EHF (40150 GHz) to be integrated at the end of the decade with the GSM system or its descendants. First, the paper describes the main obstacles for the new system, in terms of channel characteristics and technology developments, and then illustrates a preliminary system design to show the technical feasibility in the proposed ten years time scale.

Digital transmission through a land mobile satellite channel

An analytical derivation of the probability of bit error noncoherent frequency-shift keying (FSK) and coherent phase-shift keying (PSK) signals transmitted through a land-mobile satellite channel is described. The channel characteristics used in the analysis are based on a recently developed model which includes the combined effects of fading and shadowing. Analytical expressions for the probability of bit error of FSK and coherent phase-shift keying (CPSK) signals are obtained. The results show that large amounts of signal-to-noise ratio (SNR) are required to compensate for the combined effect of fading and shadowing. An analytical expression for the irreducible probability of bit error of a CPSK signal due to phase variations caused by fading and shadowing is derived. The results described should be useful in the design of land mobile satellite communication systems. >

Rayleigh fading compensation method for 16qam modem in digital land mobile radio systems

AbstractTo cope with the increasing demands for the land mobile communication with a limited frequency band, it is necessary to improve the spectral efficiency beyond the present state. QAM (quadrature amplitude modulation) is one of the effective means for this purpose. When QAM is applied to land mobile communication, however, a great distortion is produced in the envelope and the phase due to fading fluctuation. Because of this property, few discussions have been made on the application of QAM to land mobile communication. This paper proposes the following system for such an application. The fading distortion is measured from the periodically inserted known frame symbol. By interpolating the obtained time‐series, the fading distortion for all symbols is estimated. Then the distortion is compensated. The performance when the proposed method is applied to 16QAM is examined by computer simulation. It is seen as a result that the fading distortion can be compensated with high accuracy, making 16QAM applicable to land mobile communications.

Land mobile communications in Ku‐band. Results of a test campaign on eutelsat I‐F1

AbstractThis paper presents and discusses the results of technical tests on land mobile communications conducted in June and July 1989 in Europe using a EUTELSAT satellite. The land mobile communication system under test was that already operated by QUALCOMM in the U.S.A. under the registered name OmniTRACS.The field trial was organized in conjunction with the Signatories who expressed to EUTELSAT an interest in a full‐scale technical investigation of the system. The aim of the field trial was to evaluate the technical characteristics of the system and test its performance in different operating conditions.The results establish the relationship between transmission performance (i.e. essentially the required number of transmission attempts in order to get a message through the communication channel), and the environment of the land mobile, the satellite transponder's mode of operations and the interference conditions.

SYCOMORES concept

Most organizations consider that the extension of satellite applications to new areas, such as land mobile communications, will be in a rapid worldwide growth phase, up to the end of the century. The land environment and the geometrical link properties, the economical aspects with the projected saturation of the frequency allocation lead to consider non-conventional orbits for near future new communications services. This paper presents both a report of an analysis effort of the fundamental problems and a statement of the short-dated technical solutions within the particular framework of a general land mobile communication mission. The results of these efforts lead to propose the SYCOMORES concept, studied and briefly described in the paper, which is, at last, a two satellite system located on particular inclined elliptical geosynchronous orbits.

Sycomores concept

AbstractMost organisations predict that the expansion of satellite applications to new areas, such as land mobile communications, will be in a rapid worldwide growth phase up to the end of the century. The geographical and geometrical link properties along with the economic aspects (with the projected saturation of the frequency allocation), have led communications services to consider non-conventional orbits for the near future. This paper presents an analysis of the fundamental problems and a statement on the short-term technical solutions within the particular framework of a general land mobile communication mission. The results of these efforts led the authors to propose the Sycomores concept, which is at least a twin satellite system located on particular inclined elliptical geosynchronous orbits.