Land Mobile Systems Research Articles

Satellite Machine-Type Communication for Maritime Internet of Things: An Interference Perspective

Satellite machine-type communication plays a crucial role in the maritime Internet of Things. The realization of such a system, i.e., the VHF data exchange (VDES) satellite system, however, faces many technical challenges. Due to its global broadcasting nature, the interference generated from the emissions of the VDES satellite space stations to the incumbent or future land systems in the same band is of major concern to the International Telecommunication Union (ITU) spectrum allocation. However, neither regulatory rules nor related studies have been specified or made available in the literature regarding such interference. This paper utilizes the electromagnetic power flux density (PFD) mask concept for evaluating and constraining the emission onto earth from a satellite space station. The mathematical analysis and derivation are based on the principle that the actual interference from a space station that a land system experiences is no worse than that from any other land system allowed by the regulations. We demonstrate the derivation of such a PFD mask from three closely related regulations on the legacy land mobile systems by the Electronic Communications Committee (ECC) and ITU and present the corresponding constraints imposed on the VDES satellite system and their impacts on the performance of the system.

Emulation of Channel Model and Estimation for MIMO based Satellite Land Mobile System using Software Defined Radio

Land mobile satellite system (LMS) with multiantenna setup is explored in order to achieve better performance reliability and increase in capacity. The prime objective of this work is to emulate the channel accounting for channel effects for the geostationary satellite orbits with terrestrial fading conditions in the downlink segment. The three state channel model given by Loo consisting of Line of sight, Moderate shadowing, Deep shadowing conditions with its impact on determining the channel parameters i.e mean, standard deviation and multipath power is considered. Also the analysis of these parameters with respect to cross polar discrimination of antenna and cross polar coupling of an environment is performed. In addition to this, the impact of elevation angle on cross polar discrimination and cross polar coupling effect is also analyzed in order to have better link reliability. In this work a LMS channel model is developed considering all of the above conditions in GNU radio and validated using Universal Software Radio Peripheral. The bit error rate of the system is found to be 10-5 with perfect channel statistics known at the receiver.

Generalised three‐dimensional scattering channel model and its effects on compact multiple‐input and multiple‐output antenna receiving systems

The development of realistic channel models that can efficiently and accurately describe a wireless propagation channel is a key research area. In this study, a generalised three-dimensional (3D) scattering channel model for land mobile systems is proposed to simultaneously describe the angular arrival of multi-path signals in the azimuth and elevation planes. The model considers a base station located at the centre of a 3D semi-spheroid-shaped scattering region and a mobile station (MS) located within the region. Using this channel model, the authors first derive the closed-form expression for the joint and marginal probability density functions of the angle of arrival and time of arrival measured at the MS corresponding to the azimuth and elevation angles. Next, they derive an expression for the Doppler spectra distribution due to the motion of the MSs. Furthermore, they analyse the performance of multiple-input and multiple-output antenna systems and their numerical results. The results show that the proposed 3D scattering channel model performs better compared with previously proposed 2D models for outdoor and indoor environments. They compare the results with previous scattering channel models and measurement results to validate the generalisation of their model.

A comparison between APSK and QAM in wireless tactical scenarios for land mobile systems

We evaluate the performance of APSK modulation for wireless systems and compare it with the performance of more conventional QAM systems. In previous literature, the analysis of APSK has been mainly focused on the AWGN channel. This channel model provides useful insights when APSK is used in satellite systems, while it is important to consider more complex channel models for its use in terrestrial wireless applications. In particular, we consider wireless tactical scenarios for land mobile systems, that are of interest for military applications, and provide several numerical examples. First, we explore the effects on the total degradation of the reduced PAPR, typical of APSK, also taking into account the nonlinearity of HPAs and the need to use adaptive predistortion. Then, the bit error rate performance is assessed by simulation, for some typical multipath scenarios with decision feedback equalization, also including the presence of turbo channel coding. Our analysis shows that APSK can be a valid alternative to QAM in all cases in which the nonlinear effects due to HPAs cannot be neglected.

Improving the efficiency of measurement procedures for assessing human exposure in the vicinity of mobile phone (GSM/DCS/UMTS) base stations

Standards stipulate 6-min time interval of averaging for measurements of radio-frequency electromagnetic fields to assess human exposure to non-ionising radiation. Having in mind the base stations of public land mobile systems, the time interval defined in such a way noticeably limits the number of measuring points in practical applications. In this paper, based on the results of measurements in the vicinity of a multisystem base station (Global System for Mobile Communications [GSM], Digital Communication System [DCS] and Universal Mobile Telecommunications System [UMTS]), it was shown that the measurement process can be significantly accelerated by using shorter time intervals of averaging--15 s, 30 s and 1 min. It was found that measurement results differed from the 6-min root-mean-square mean by 10.5 %, 15.9 and 19 %, respectively, while the uncertainty of the measurements was increased by 3.0 %, 3.8 and 4.4 %, respectively. Shorter time-averaging intervals would reduce the total duration of the exposure assessment survey, while not compromising too much on measurement quality.

Ionospheric effects on satellite land mobile systems

Satellite-ground radio systems are now so sensitive that ionospheric changes can disrupt their performance. This paper discusses some satellite-to-ground propagation problems in the UHF and L bands caused by the Earth's ionosphere. Such problems include signal time delay, signal dispersion, Faraday rotation, and scintillation.

Dynamic characteristics of a narrowband land mobile communication channel

Land mobile communication signals are subject to propagation effects that result in variation of the received signal amplitude and phase. The most rapid signal variations are the result of multipath propagation and occur with sufficient severity to make reception difficult. At microwave frequencies, the narrowband (30-kHz) channel is considered nondispersive. It will experience flat amplitude fading and band-limited frequency distortion. An understanding of the dynamic nature of the communication channel is required to design land mobile systems that are tolerant of rapid multipath conditions. A model is presented to characterize the dynamic nature of multipath channels, and a new dynamic measure, fractional power change rate, is introduced. The distribution of the fractional power change rate, power change rate, and phase change rate are predicted by the model and validated by comparison to measured data. The research in this paper is part of an ongoing effort to develop multipath-tolerant demodulation techniques for higher order modulation types. The measures developed are of primary importance for specifying the dynamic requirements for such demodulators.

テレビ映像放送波の移動受信におけるフェージング解析

This paper analyzes the basic properties of reception of TV waves by land mobile systems. A precise TV wave propagation model is developed, fading is analyzed mathematically, and a received-signal equation is derived. This analysis treats all kinds of signals as well as TV signals. Doppler effects made by multipath distortion are introduced to both carrier and modulation signals for wide-band signal transmission. The resulting expression for the received signal is numerically evaluated. The characteristics of wide-band signals such as TV wave transmission are different from those of narrow-band signal tramsmission. The time correlation has almost zero value when the distance is half λc or less. (λc is the carrier wavelength); and the carrier frequency correlation has almost a constant value when the carrier frequency distance between received signals is further than a certain threshold. The correlation coefficient between wide-band received signals and narrow-band received signals has a low value. Therefore, for land mobile reception wide-band signals and narrow-band signals cannot be treated in the same way.

UMTS — mobile communications beyond the year 2000: Requirements, architecture and system options

To support the massive demand for mobile services third generation land mobile systems will be based on a new architecture concept and adaptive techniques. Moreover, these systems are expected to offer service quality comparable to that of fixed networks contemporary to their deployment. UMTS (universal mobile telecommunication system) is the developing pan-European concept for third generation mobile systems. The paper briefly overviews the requirements for and the emerging architecture of the UMTS as they appear at the transition between two RACE research phases and the beginning of dedicated standardisation activity in ETSI.

Digital signal processing in communications satellite payloads

Satellite on-board digital signal processing (DSP) offers the potential for significantly improved performance in certain satellite communications system scenarios in terms of system capacity and link quality. On-board DSP functions include digital beamforming, frequency multiplexing and demultiplexing, interference suppression, signal level control and, in a regenerative system, modems. The authors review the status of DSP in communications satellite payloads, focusing on the system advantages, some basic algorithms, and application specific IC implementation issues. As a specific illustrative example an advanced land mobile system is described which features digital beamforming and associated digital signal processing to achieve significant gains in power efficiency (and hence capacity), frequency reuse and flexibility to response to changing traffic scenarios.< >

Mobile satellite system for Europe—Which is the optimum orbit configuration?

This paper compares three possible orbit options for satellite mobile systems for Europe: (1) a geostationary system, (2) a 24 h Tundra orbit system and (3) a 12 h Molniya orbit system. A comparison of the traffic capacities and overall systems costs which would be applicable in a first and second generation land mobile system has been made. The estimated traffic capacity of these systems, which depend critically on both the propagation margin and the type of mobile antenna, indicate a clear advantage for inclined orbit systems over the geostationary approach. The CCIR prediction technique was used as the basis for establishing the system margins as a function of elevation angle. The orbit optimization for the elliptical orbit systems requires detailed consideration, as the satellite range, elevation angle and antenna beam patterns alter throughout the “useful part of the orbit” between hand-over points. Both the Molniya and Tundra situations require slightly different considerations. In the Molniya based system the particular case of the Loopus orbit was chosen, i.e. where the Earth tracks nearly touch at the hand-over point. The equivalent Tundra situation gives an impractical solution to coverage areas. Other considerations such as orbit life time, operational problems and radiation environment are also discussed. Comparative cost estimates were deduced for two satellite options.

Experimental evaluation of packet error rates for the 850 MHz mobile channel

A series of field measurements were conducted to examine the transmission characteristics of different digital land mobile systems in the VHF/UHF frequency bands. This paper briefly describes these measurements, and then focuses on the measured data that describe the bipolar coding/FM modulation with a bit rate of 4800 bit/s and an RF channel spacing of 25 kHz. The basic error characteristics of the channel are presented by (i) the average bit error rate, (ii) the gap length distribution and (iii) the error burst length distribution. The measured error pattern was used in conjunction with some known error control techniques, to examine their effectiveness in reducing the overall errors. In particular, the block coding techniques used in the AMPS system were evaluated and compared with other, simpler techniques having higher coding rates. The results are presented in the form of curves relating the packet error rate to the packet length.

Antenna systems for ESM applications—a land-mobile example

The design of antenna systems for ESM applications requires that a number of demanding requirements be met simultaneously, each of them imposing constraints on the possible solutions that may be adopted. The paper uses the design of a land-mobile system employing a quad-ridged horn to illustrate briefly the various constraints and the solutions that can be adopted, indicating how the requirements of, for example, aviation systems may differ. The effect on the overall design of having to meet requirements for DF capability and polarisation detection, in addition to those for ESM performance and, possibly, having to at the same time produce an antenna system suitable for high-power transmission or simultaneous transmission and reception, is also discussed.

Mobile and personal communications - Editors' comments [special issue intro.

The revolution has begun, if you believe the soothsayers and marketeers. The revolution is known by the name personal communications, and its existence is heralded by a plethora of new publications and popular media write-ups. What has been a rather sleepy industry, the land mobile business, is suddenly confronted with the exciting possibility of extending its services to the general public, not just the business people loolung for phones in their cars. The concept is to remove the wire from wireline communications and to offer information-age services over wireless terminals that are conveniently carried by individuals. we have organized t h s Special Issue to present results of work currently aimed at improving our understanding of the fundamentals of the technology. The issue gves no final answers and few specific implementations. Rather, it provides interim results of work undertaken to better understand the underlying principles of the technology. Particular emphasis is placed on digital technologies because most workers feel that the simple voice communications implemented in current land mobile systems will quickly be complemented by the need for data and more generalized information services.

A simulation study of high-capacity cellular land-mobile radio-communication systems

Considers the problem of channel assignment in Land-Mobile Radiocommunication systems. The performance of the hybrid assignment scheme under various loading conditions is evaluated by using simulation results of channel that has a cellular mobile communications system forty cells with Erlang-B service. In addition the hybrid system is compared to the fixed and dynamic systems with respect to the maximum transmission per cell that each system can support, while having a call rejection rate of no more than 2 per cent. For the same cellular system the minimum number of necessary channels (in order to establish a given quality of service for various traffic load. A conclusion is offered per cell) is determined. A conclusion reached regarding the spectral efficiency of hybrid systems with respect to the fixed systems.

Multitransmitter digital signal transmission by using offset frequency strategy in a land-mobile telephone system

In a high-capacity land-mobile telephone system which employs a small zone technique, it is advantageous to provide control channels separate from voice channels. We first review two control channel allocation methods: the individual control zone system and the multiple control zone system. From the viewpoints of efficient frequency utilization and reliable call processing, the multiple control zone system is shown to be preferable. It is experimently verified that an offset carrier frequency strategy is well suited to the realization of this system. Simulation test results are presented which determine the design parameters. Offset carrier frequency allocation methods concerning three types of fundamental zone configuration are derived. The carrier frequency synchronization and the phase adjustment of the modulation signals are investigated for the actual system construction.

Multiple radio zone plans in mobile radio systems

Multiple zone structure in a land mobile system seems to offer a flexibility in radio zone planning by using different interference distances conforming to the different system requirements in a system, thus improving the frequency utilization. A multiple zone structure can be formed by a tessellation of basic zone groups with an identical shape in parallel translation on a plane. To assure the possibility of the tessellation, two types of basic zone groups are investigated. One has several hexagonally shaped zones covered by an omnidirectional antenna beam from the zone center, while another is constructed as a subdivision of hexagons covered by a directive antenna beam. The former is expected to facilitate reduced interference distance between adjacent frequencies. An estimate of the latter type has shown better frequency economy than that in a conventional zone structure.

Mobile v.h.f. and u.h.f. radio systems in the UK

Mobile radio systems, operating in the v.h.f. and u.h.f. bands, are widely used in the United Kingdom for short-range land, maritime and aeronautical services. In tracing the growth of these services the preponderance of land-mobile units is evident, and the review concentrates on land-mobile aspects, referring to the others mainly when differences in equipment or practice are significant. Developments in equipment and systems are reviewed, and selected units and installations are briefly described. The market for new and replacement equipment is estimated, and possible savings through the use of mobile radio are discussed. Other systems such as paging, which use the same frequency bands or techniques as mobile radio, are enumerated, and their operation and merits examined. One Section is devoted to the design of selected sections of equipment and another to the estimation of range. Typical figures for land-mobile systems are tabulated. The ever present problems of frequency selection, interference and noise are reviewed. The two main, and several proposed, systems of modulation are compared, and their future possibilities discussed. Final Sections examine reliability and testing, possible future developments and problems. Some possible lines of progress are deduced. A carefully selected, rather than a comprehensive, list of references is given.

900 MHz Land Mobile Radio Improved Using Circular Polarization

Land mobile systems currently use vertically polarized antennas while trying to solve the problem of small sector signal variations, which are greater for vertical polarization than for either horizontal or circular polarization; This difference in small sector variations is shown from results of tests at 430 MHz. The variations at 900 MHz should be more rapid and have amplitudes at least as great as those shown for 450 MHz. At 900 MHz antennas can be made small for mobile service and the improvements noted here may spur developments in circularly polarized antennas.

900 MHz land mobile radio improved using circular polarization

Land mobile systems currently use vertically polarized antennas while trying to solve the problem of small sector signal variations, which are greater for vertical polarization than for either horizontal or circular polarization. This difference in small sector variations is shown from results of tests at 430 MHz. The variations at 900 MHz should be more rapid and have amplitudes at least as great as those shown for 450 MHz. At 900 MHz antennas can be made small for mobile service and the improvements noted here may spur developments in circularly polarized antennas.