Showing papers in "IEEE Transactions on Vehicular Technology in 1971"
TL;DR: In this paper, a variety of space diversity system techniques have been considered for the purpose of reducing the rapid fading encountered in microwave mobile radio systems, and tradeoffs between performance properties and system parameters are indicated.
Abstract: Over the past few years a variety of space diversity system techniques have been considered for the purpose of reducing the rapid fading encountered in microwave mobile radio systems. Basic diversity methods are first reviewed in the framework of mobile propagation effects, and then specific techniques are compared from the standpoint of transmitter power required to achieve a certain performance. Criteria of comparison used included baseband SNR while moving and reliability when the vehicle stops at random. System parameters are type and order of diversity and transmission bandwidth. Tradeoffs between performance properties and system parameters are indicated. The calculations show that relatively modest use of diversity techniques can afford savings in transmitter power of 10-20 dB. For example, at a range of 2 mi, to obtain 30-dB baseband SNR while moving and 99.9-percent reliability when stopped requires a transmitted power of 8 W for a conventional FM system with no diversity. Two-branch selection diversity provides the same performance for a transmitter power of only 300 mW.
95 citations
TL;DR: The concept of a small-zone system plan for mobile telephone service is reviewed, as are the advantages of spectrum economy, flexible growth, low power requirements, and wide channel spacing and the disadvantages of locating mobiles and establishing base-station sites.
Abstract: The concept of a small-zone system plan for mobile telephone service is reviewed, as are the advantages of spectrum economy, flexible growth, low power requirements, and wide channel spacing and the disadvantages of locating mobiles and establishing base-station sites. The functions which such a system must perform are enumerated. A call processing sequence and a mobile block diagram which perform the basic functions are outlined, followed with a proposed plan for locating mobiles with respect to the small-zone grid.
23 citations
TL;DR: In this article, the antenna spacing between two adjacent antennas in a space diversity array is greater than 0.5λ, and the array configuration does not affect the cumulative distribution curves nor the shapes of the level-crossing-rate (LCR) curves, and only slightly affects the signal level at which the maximum LCR occurs.
Abstract: The theoretical analysis in this paper is based on the assumption that the angles of signal arrival on the mobile receiver are uniformly distributed. From the analysis and experimental studies, we find that if the antenna spacing between two adjacent antennas in a space diversity array is greater than 0.5λ the array configuration does not affect the cumulative distribution curves nor the shapes of the level-crossing-rate (LCR) curves, and only slightly affects the signal level at which the maximum LCR occurs. Hence a three-element array with a triangular shape or a four-element array with a rectangular shape can be considered a good arrangement, provided each side (antenna spacing) is greater than 0.5λ. Two slightly better arrangements than those we just mentioned for improving the signal fading are also proposed for three-branch and four-branch diversity signals, respectively.
22 citations
TL;DR: The results of experimental tests of an automatic longitudinal control system in various lead-car overtaking, emergency braking, and car-following situations are reported and an examination of the data shows that this system can safely, efficiently, and comfortably control a vehicle during such maneuvers.
Abstract: It appears that both substantial improvement in high-speed high-density traffic flow and a decrease in highway accidents can be achieved by highway automation. An essential part of any approach to such automation is a method for the automatic longitudinal control of vehicles. The results of experimental tests of an automatic longitudinal control system in various lead-car overtaking, emergency braking, and car-following situations are reported. An examination of the data shows that this system can safely, efficiently, and comfortably control a vehicle during such maneuvers. The results of these tests corresponded to those predicted from previous theoretical and simulator studies.
18 citations
TL;DR: In this paper, a description and statistical analysis of radio propagation data over irregular terrain is presented with emphasis on communications between low antennas in VHF and UHF bands. But the analysis results provide first estimates of propagation parameters in many terrain types and information regarding applicability of the propagation model.
Abstract: Descriptive and statistical analyses of radio propagation data over irregular terrain are presented with emphasis on communications between low antennas in VHF and UHF bands. Measured data are evaluated for medians and ranges of basic transmission loss and height gain, and results are compared with estimates from a propagation model developed by the Institute for Telecommunication Sciences. Effects of vegetation near the path terminals are demonstrated. Analysis results provide first estimates of propagation parameters in many terrain types and information regarding applicability of the propagation model.
14 citations
TL;DR: The results obtained show that systematic errors introduced by the system far outweigh random errors and that this concept is feasible as a location interpolator between fixed known reference sites.
Abstract: Optimum utilization of patrolling vehicles requires that the central controller be continuously informed about their location. To meet this need, a purely mechanical analog computer was designed, built, and tested. The results obtained show that systematic errors introduced by the system far outweigh random errors and that this concept is feasible as a location interpolator between fixed known reference sites. Guidelines for the next generation system design were obtained.
13 citations
TL;DR: It is shown here that the use of diversity in a mobile radio system also will result in better utilization of the frequency spectrum, and that a diversity system utilizes the frequency Spectrum more efficiently than an equivalent nondiversity system.
Abstract: Diversity is often used in radio systems to alleviate the problem of fading. It is shown here that the use of diversity in a mobile radio system also will result in better utilization of the frequency spectrum. In a system which reuses channels in physically separated areas, probability distributions of signal-to-cochannel interference ratios in 1-, 2-, and 4-branch diversity systems are developed by Monte Carlo methods. We consider two cases: first, we assume signal strength to be Rayleigh distributed, which is a valid model for reception within a small localized area; second, we take shadow losses into account by assuming a more realistic long-term fading model. The effect of using diversity in a mobile radio system is considerable with either model. Assuming a hexagonal cell pattern of frequency reuse, it is shown that frequencies may be reassigned more often in a diversity system than in a system which does not use diversity. The conclusion, therefore, is that a diversity system utilizes the frequency spectrum more efficiently than an equivalent nondiversity system.
10 citations
TL;DR: Curves presented indicate that baseband distortion power as large as 20 percent of baseband signal power may occur for an RF carrier amplitude ratio of 0.7 and an unequalized delay of the order of 200 µs when the minimum rms transmitter phase deviation is 2 rad.
Abstract: The baseband distortion resulting from the cochannel interference of two FM carriers nominally carrying the same modulation is considered. Such distortion was observed to plague VHF mobile telephone service in Phoenix, Ariz. This distortion arises when the landline audio delay and modulation indices of the two transmitters are not closely equalized. Both sinusoidal and Gaussian modulation age analyzed. Curves presented indicate that baseband distortion power as large as 20 percent of baseband signal power may occur for an RF carrier amplitude ratio of 0.7 and an unequalized delay of the order of 200 µs when the minimum rms transmitter phase deviation is 2 rad. Increasing the deviation to 4 rad reduces the distortion to the 5-percent range. The desirability of large index modulation in this context is thus apparent.
9 citations
TL;DR: In this article, a dual-chamber electric car with two conventional choppers operating in parallel is presented, where the duty cycle generated by the firing circuit is feedback controlled so that the load current remains proportional to control output.
Abstract: Despite recent advances in solid-state controls for electric cars, chopper-induced problems still exist: commutation and ac losses are significantly high, the chopping action induces losses within the power source, and large ripple components in the chopper output cause increased rms losses at the motor. The author's dual chopper, two conventional choppers in parallel, reduces these problems. The duty cycle generated by the firing circuit is feedback controlled so that the load current remains proportional to control output. The dual chopper operates in a three-in-one system: in the first mode, the batteries charge at high rates; the second mode controls the amount of power flowing from battery to motor; and in the third or regenerative braking mode, the chopper transfers energy from the motor to the battery.
5 citations
TL;DR: A method of calculating the effect of supports on the amplitude characteristics of a Goubau line agrees well with experimental data and thus predictions for a line one mile in length were made.
Abstract: A method of calculating the effect of supports on the amplitude characteristics of a Goubau line is given in this paper. The results from this method agree well with experimental data and thus predictions for a line one mile in length were made. It is shown that supports can cause limitations in the line length and in the available bandwidth.
5 citations
TL;DR: This paper considers a vehicle location system in which an array of transmitters forms an "electronic fence" along the zone boundaries, and analyses the communication performance of the short-range communications link between the zonal transmitters and the vehicle.
Abstract: 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.
TL;DR: The guidance cable for automatic driving vehicles can be utilized as a communication medium between the road authority of a highway and vehicles on it and enables a warning to be issued to a vehicle that my swerve from the course.
Abstract: The guidance cable for automatic driving vehicles can be utilized as a communication medium between the road authority of a highway and vehicles on it. This highway communication system consists of two cables laid along both shoulders of a roadway, two detecting coils attached to the front bumper of a vehicle, and a transmitting-receiving coil mounted on the top of a vehicle. This system enables voice communication between the road authority and road vehicle drivers, and enables a warning to be issued to a vehicle that my swerve from the course.
TL;DR: Two types of frequency multiplexing are theoretically analyzed for their applicability as a form of modulation in the land mobile radio service (LMRS) and conclusions are drawn on the spectrum efficiency of a multiplex system compared to the present system.
Abstract: Two types of frequency multiplexing are theoretically analyzed for their applicability as a form of modulation in the land mobile radio service (LMRS). Both SSB/FM and FM/FM are analyzed for their signal-to-noise ratio (SNR) versus modulation index. These results are normalized to the signal-to-noise performances of the existing 5-kHz deviation system for comparison purposes. The latter performance is developed using the actual Electronic Industries Association (EIA) response of a LMRS receiver. The spectrum of the multiplex system for the case of equal subchannel signal-to-noise is developed using a computer. The spectrum is used to determine the spectrmm occupancy of multiplex systems. Based on the tradeoffs of transmit power and spectrum occupancy, a discussion of the interference characteristics of the multiplex systems compared to the existing system is presented. Finally, conclusions are drawn on the spectrum efficiency of a multiplex system compared to the present system.
TL;DR: The basis for design criteria for buried antennas is delineated and attention here is directed toward those problems occurring in the transmission aspect of the system, particularly the antenna design.
Abstract: The density of present and projected private vehicular traffic indicates a need for increasingly sophisticated techniques for the detection of, surveillance of, and communication with vehicles. Given these techniques, systems can be implemented to improve traffic flow and service to the motorist. All systems involve the function of data generation, processing and modulation, and transmission. Attention here is directed toward those problems occurring in the transmission aspect of the system, particularly the antenna design. Factors unique to vehicular communication for traffic control suggest, a priori, the use of antennas buried in the roadway. The basis for design criteria for buried antennas is delineated.