Search

This paper begins with a discussion of multipath interference. The spatial description of the field impinging upon a mobile radio antenna is derived and the power spectrum and other properties of the signal envelope are considered. Next, large scale variations of the average signal are discussed. Measurements of observed attenuation on mobile paths over both smooth and irregular terrain are summarized. The paper concludes with a discussion of methods of predicting the area of coverage from a base station.

Analytically tractable statistical-physical models of man-made noise environments have been constructed [1]-[3]. These permit quantitative description of the various types of electromagnetic interference appearing in typical radio receivers and, in particular here, for the communication links employed in mobile transportation systems and urban environments generally. This paper presents a summary of some of the principal analytical results obtained to date [1], [4], and includes some suggested next steps for joint theoretical and experimental study of these increasingly important phenomena. First-order probability density functions (pdf's) and probability distributions (pd's) are obtained explicitly; (higher order pdf's and pd's may also be found by similar methods) [2]. These models are based on a Poisson distribution of sources in space. The approach is canonical, in that the results are, in form, independent of particular emitted waveforms, propagation conditions, source distributions, beam patterns, and specific system parameters, as long as the interference is narrow-band following (at least) the aperture and/or the RF stages of a typical receiver. Considered here only are the cases of communication interference, where source and receiver bandwidths are comparable. The paper concludes with a short discussion of some features of suggested future interaction between theory and experiment.

This paper is a digest of the electrical system section of a report [8] on the feasibility of using a hybrid heat engine/electrical propulsion system as a means of reducing exhaust emissions from street-operated vehicles. The electrical system is composed of an electric traction motor, a generator, control system, and batteries. Batteries are not covered in this paper, but the remainder of the items will be treated here. First, the electrical system parameters or characteristics that have the greatest impact on the total system are considered; next, details of the advantages and disadvantages of various approaches are summarized; and, finally, development efforts are recommended.

At the present time there is much interest in vehicle location systems [1]-[3]. For certain applications [4]-[7] precise location of the vehicle is not needed and determination that the vehicle is within a zonal area of the city is sufficient. This paper considers a vehicle location system in which an array of transmitters forms an "electronic fence" along the zone boundaries. As it passes throagh the electronic fence a suitably equipped vehicle receives and stores the zonal location information. This information is sent by the vehicle to a central location via a separate radio channel after receiving an interrogation message. The analysis of the communication performance of the short-range communications link between the zonal transmitters and the vehicle is the concern of this paper. Design curves and formulas are presented that allow performance calculations to be made. The implications of this predicted communication performance to a vehicle locator system are then considered. Most of the results obtained are directly applicable to a general class of vehicle location systems, which utilize the proximity of a vehicle to some coded electronic signpost to determine the vehicle's location. The electronic fence is a special case of the proximity-type system.

The Automatic Route Control System (ARCS) is a self-contained on-board system that directs the operation of a conventional motor vehicle over predetermined routes and controls activities (such as the delivery or pickup of items) performed along the route. In effect, the system continuously measures the vehicle's location coordinates, compares these with the route coordinates, and then issues audio, visual, and/or printed instructions appropriate to the location. The system also detects driver errors and prescribes corrective action. The routes to be followed and the actions to be taken are defined on interchangeable magnetic tape cartridges, which may be updated daily or as required from a computerized central file. ARCS enables a driver to operate efficiently over a complex route without reference to maps or lists and without prior knowledge of the route. It also eliminates tedious manual report preparation because computer-ready data for route accounting can be acquired on a magnetic tape cartridge. Although applicable to most types of operations carried out over routes that can be defined in advance, the prototype application is for the delivery of newspapers. Installed in a van with paper throwers stationed at special windows on each side, the system signals each thrower with a tone through headphones at the proper time to throw papers to individual subscribers while driving through residential areas at 15-30 mi/h.

In those radio communications applications where area coverage is not desired, a series of repeaters, each operating at low power, can be used to extend the radio over long distances. Microwave relay systems operate on this principle with each node representing a point of potential local distribution. Where it is desirable to have the nodes closely spaced, such as along a highway, it becomes desirable to utilize a single frequency for all transmissions in one direction in the interest of conserving spectrum. This paper covers such a system operating in the 935-MHz band. The system described provides both the "backbone" communications system which employs single-frequency repeaters and the "roadside" communications from the repeater node points to users in their vehicles. The functioning of the repeaters is described, and the relationship between signal levels, isolation, external noise levels, and thresholds is presented. Both analog and digital modulations are employed, and it is shown how each repeater is remotely switched between "backbone" and "roadside" communications modes. Extensions from current single-channel to multiple-channel operation is described in terms of the application to a variety of highway-related uses. The results of propagation experiments both along the "backbone" and on the "roadside" are described and related to theoretical models. From these data, conclusions can be drawn about the relationship between repeater spacing, height, and power level, as well as their relationship to user antenna height, output power, and receiver sensitivity.

This paper describes in detail the criteria for the design of a mobile laboratory for the characterization and measurement of man-made electromagnetic noise in the urban, suburban, and rural environment. A significant difference from previous similar measurements is the bandwidth of the receiving system, which is here of the order of 1 MHz. A simple model is proposed to describe the impulsive noise together with a series of experiments to validate the model and determine the significant necessary parameters. The detailed requirements for each of the subsystems of the mobile laboratory are discussed and some typical results obtained in trial runs are presented.

Advances in the design, development, and fabrication of key microwave components along with those in electronics have resulted in growing optimism about the application of radar technology to solving the automotive highway collision problem. However, before an automotive radar system can be fully realized, a major effort will be required to define the environment in which the system must operate, and to obtain a fundamental understanding of the influence of these RF parameters. One such parameter which will have a considerable effect on the design of automobile radars is that due to the presence of natural and man-made surfaces within the beamwidth of the antenna. Generally, the presence of such a surface will result in incident RF energy being reflected off the surface in a forward direction and some portion being scattered in a backward direction. This paper presents the results of a program which was designed to measure this type of reflectivity characteristic for common road surfaces. Measured data are presented along with a theoretical study demonstrating the influence that this phenomenon can have on highway collision radar systems.

Proper selection of the propulsion system to meet the requirements of an electric passenger vehicle is of prime importance. Choice may be made among alternating current, direct current, or combined systems. Each approach can be implemented by utilizing various control techniques and power elements. For instance, an ac system may use an adjustable voltage inverter (AVI) or a pulse-width-modulated inverter (PWMI) for the power processor, and an induction motor or a synchronous motor for the rotating element. Similar alternatives exist for a dc system. The choice of a suitable manner of implementation must be. based on information characterizing the various elements and tradeoffs matching them to the vehicle requirements. This paper describes various ac and dc techniques, characterizes AVI, PWM, and representative dc chopper power processors and examines their interface with a variety of motors such as series, shunt, induction, etc.

This paper reports some propagation and coverage prediction results using various models provided to the Federal Communications Commission, Spectrum Management Task Force.

The design of electronic fuel injection (EFI) controls for the automobile must take into account limitations imposed by the automotive environment and by mass production. This paper outlines the fundamentals of EFI controls and provides insight into the unique problems encountered in the design of a viable system. The impact of the electrical and physical automotive environment is analyzed, and the constraints arising from volume production and cost considerations are discussed.

In mobile radio systems, especially in urban mobile service, one fixed transmitting station is located at the center part of the area, while several fixed receiving stations are installed at different location. In such systems the receiving station with the highest signal-to-noise ratio should be selected at all times. This paper presents two methods to select the best receiving station. One is an analog processed switching system. The other is a digital processed system. The design objectives, circuit diagrams and characteristics are described in detail. The performance of these two systems were compared in a field test. It became clear that there were no essential differences in the performance. The analog system was adopted in the actual mobile system taking into consideration the advantage in cost.

A signal-to-interference ratio for the transmission of scanned images and digital data in the dynamic multipath environment was derived in an earlier paper. The dynamic case depends upon a Doppler environment-signal parameter ratio, while the static result is independent of the signal structure. The dynamic case is asymptotic to, but always worse than, the static one. For a Doppler-signal ratio of less than 10 percent the dynamic signal-to-noise ratio is essentially equal to the static one. Most real systems today fall in this region. This indicates why certain simple multipath analyses in use today have been successful. The method of designing a signal to fall below the 10-percent value is indicated. Signal-to-noise ratio curves are provided for system design purposes. These results permit system analysis and tradeoff studies to be based on earth reflection coefficient distributions and aircraft or satellite operation envelopes.

The design of future mobile radio systems will be based upon an estimated user demand. Systems probably will be engineered to serve the "average business day" spatial distribution of call attempts, which for the purpose of this study was assumed to be uniform. There will be day-to-day fluctuations about this long-term average, the magnitudes of which are only to be conjectured at this time. This paper compares the performance of computer simulated mobile radio systems operating with several demand profiles. The profiles were selected to give an indication of the effects on system performance of either uncompensated changes in average traffic or normal fluctuations which occur in the randomly offered traffic even when the long-term average value does not change. The dynamic channel assignment systems increased the traffic capacity at low blocking levels even over a perfectly designed fixed channel assignment system. In addition, it was found that the dynamic channel assignment systems were relatively insensitive to the periodic spatial demand distributions studied by this computer simulation. Even though new call attempts were made to fluctuate markedly between adjacent base stations within a reuse interval, the blocking rate of each base station remained constant. It appears that the blocking rate within a reuse interval depends (in the dynamic channel assignment systems) mainly on the average demand within that interval and not very strongly upon the distribution of that demand. In the fixed channel assignment system, uncompensated fluctuations in the spatial demand distribution away from the design value always degrade system performance.

The following fundamental technical questions concerning the use of the spectrum allocated to the land mobile radio service are discussed. 1) Is it technically feasible to increase the number of assignable channels within the allocated spectrum space? 2) Are other modulation methods more or less suitable for providing more channels? The primary resource material used to answer these questions is the response of the Land Mobile Section, Industrial Electronic Division, Electronic Industries Association [49]. Only the frequency spacing question is treated in this paper.

This paper describes the original VHF mobile radio system in the Indiana and Michigan Electric (I&ME) Company and how it operated with standard squelch. It points out some of the problems which were encountered at the relatively low operating frequency in the 37-MHz region and goes on to show the solution for most of these problems by converting the entire system of 19 base stations and 300 mobile units from standard squelch to a tone coded squelch. The entire changeover was done in an economical manner and without disrupting operation of the original system while the conversion was being made. The benefits ensuing from this conversion are covered in detail.

Electronic clocks are rapidly becoming practical for automotive applications. These digital clocks promise not only superior timekeeping in automotive clocks, but they also could be used for a myriad of timing functions throughout the car. These range from turn signal flashers to top-speed limiting and safety-monitoring checks. Integrated circuits utilizing complementary metal oxide semiconductor devices (CMOS and silicon gate CMOS) make several system approaches feasible. This paper outlines some possible system approaches and summarizes considerations for CMOS IC's, quartz crystals, and electronic readout devices.

Several approaches to the operation of automated ground transport systems for urban use are presented and evaluated. Such systems have been suggested principally in response to the problems of urban traffic congestian and are often proposed as solutions to such problems. Thus this paper, the first of a series of three, discusses the problems of urban transportation and their origins, identifying as the principal elements the institutional structure, urban geography, and design of facilities for urban automotive transport. Importantly, the origins of a significant portion of "the urban transportation problem" lie outside the transport sector. Six potential applications for automated transport systems are suggested, ranging from specialized single-link "horizontal elevators" to general-purpose wide-area networks.

Automobile headlamp illumination is of concern because uniformity and shape of the beam pattern are quite important for optimum road visibility and safety for oncoming drivers. The Society of Automotive Engineers' specification on headlamp illumination [1] designates the maximum and minimum intensities at several spots within the beam. Many states require inspection of vehicle-mounted headlamps for illumination and aiming, and this test is commonly performed using a device which clamps on the headlamp lens. This clamp-on device is limited to checking the maximum intensity at beam center, rather than checking the overall beam pattern to the SAE-J579a specifications. In addition, mechanical limitations of this device have often resulted in the mis-aiming of vehicle headlamps. Present instrumentation available for measuring light intensity per SAE-J579a is primarily of the photo-cell type device, and the point-to-point measurement of light intensities is quite tedious and time consuming. A technique is described in this paper which incorporates electronic signal processing into a closed-circuit television system for displaying contours of constant illumination intensity. The technique is capable of rapidly performing vehicle-mounted headlamp testing per SAE-J579a and could be adapted for use at state inspection stations.

Many agencies, both governmental and private, in the highway transportation field need a system which would automatically identify motor vehicles. The basic concept of such a system requires a vehicle-mounted coded device, a transponder, that uniquely identifies that vehicle. As this vehicle comes within the range of a system interrogator installed along or on the highway, the code is read by this interrogator and the identification of the vehicle is obtained. The ideal transponder is passive and requires no power; has no effect on, and is not affected by the vehicle; does not require physical contact with the interrogator, and requires no action by the vehicle operator. Sensing at a distance (noncontact) involves the detection of some type of energy; either radiated or reflected from the object being monitored. Many different sensing techniques, including magnetic, infrared, optical, sonic, radioactive, radio frequency (RF) transmission, microwaves, have been surveyed, investigated, and analyzed to determine their applicability for an automatic vehicle identification (AVI) system. This analysis has concluded that a low-frequency induction system is presently the most appropriate method for use on the highway environment, Several diverse systems differing in design details have been constructed and tested, utilizing this basic technique. This paper describes the design of these systems as well as the methods that have been proposed and/or developed using the other sensing technologies.

This paper presents some of the economic and technical considerations for development of future noncooperative vehicle-detector systems. Vehicle-detector accuracy requirements, installation cost, location, and the roadway environment are used to develop a set of preferred vehicle detector characteristics. In addition, a description of vehicle detectors, considered for development by the Bureau of Public Roads, and some of the current vehicle-detector concepts under development, are presented.

Radio equipment and systems designers face an alarming complexity of considerations, when they attempt to calculate probable interference rates. Only a computer is able to handle all of these variables and predict system performance to a meaningful degree of probability. Therefore, this paper describes a computer simulation approach which has been used to: (1) Explore the relation between interference rates and equipment characteristics; (2) Determine the manner in which channel loading affects the various types of interference; and (3) Analyze multi-system configurations of both the concentrated and the geographically spread types.

The IEEE Third Symposium on Vehicular Communications Systems was held on 13 May 1969, in Los Angeles, CA, USA, and treated the subject of electromagnetic spectrum utilization. This subject is very broad in scope and very timely in that the recent release of the JTAC report entitled "Spectrum engineering - the key to progress" should produce a long needed reevaluation of the approach to electromagnetic spectrum utilization. The content of the program is reviewed here either by the paper, an abstract, or comment by the Symposium Chairman.