Showing papers in "IEEE Transactions on Vehicular Technology in 1978"
TL;DR: The spectral efficiency of the spread-spectrum scheme may exceed those of the narrow-band schemes by a factor of almost five, and more ambitious bit-rate-reducing speech digitization methods could improve still further on these figures.
Abstract: A spread-spectrum technique for cellular high-capacity mobile communications is described and some results from an analytic study are summarized. The technique uses a very large set of frequency-hopped signals which are designed for minimal mutual interference. No synchronization of the mobile units is required, and each user is permanently assigned his own signal, which serves as an identifying signal and as a carrier for the biphase-modulated digital message. The spectral efficiency of the spread-spectrum system is analyzed and compared with the efficiencies of developmental FM/channel reuse schemes currently under construction in the U.S. and Japan. It is concluded that even with relatively simple speech digitization schemes, the efficiency of the spread-spectrum scheme may exceed those of the narrow-band schemes by a factor of almost five. More ambitious bit-rate-reducing speech digitization methods could improve still further on these figures. Additional benefits of the spread-spectrum scheme include immunity from fading and interference, more consistent speech quality, simpler system control algorithms, and more flexible blocking properties under overload conditions.
330 citations
TL;DR: This paper describes an easily automated heuristic assignment technique in which the channel requirements that prove themselves to be "difficult," through repeated failures to be assigned channels, rise rapidly toward the top of the list of requirements.
Abstract: In preparing or revising an RF channel plan for a group of mobile radio nets operating in the same region, the order in which the nets are assigned channels can be crucial to success. One well-known principle for selecting such an assignment sequence is to rank the channel requirements of the various nets in descending order of "assignment difficulty." This paper describes an easily automated heuristic assignment technique in which the channel requirements that prove themselves to be "difficult," through repeated failures to be assigned channels, rise rapidly toward the top of the list of requirements. The heuristic technique is useful in solving complex frequency-assignment problems that involve cochannel, adjacent-channel, spurious and intermodulation interference; nonrepetitive zone structures; fixed pre-existing frequency assignments; and frequency-resource lists that contain gaps and vary from zone to zone.
192 citations
TL;DR: In this article, the correlation in mean received power from four non-cosited 900 MHz sources is studied as a function of angle of arrival difference (AAD) at the mobile.
Abstract: The correlation in mean received power from four non-cosited 900 MHz sources is studied as a function of angle of arrival difference (AAD) at the mobile. Two tests are examined, one in the Washington-Baltimore area, and the other in the Chicago-Schaumburg area. Three hundred meter power averages were taken in Washington while 20 meter averages were obtained in Chicago. Weighted correlation coefficients averaging in the order of 0.7 were obtained at small AAD's. Serial correlations are also examined. A table lookup model of correlation coefficient versus AAD was obtained from the measurements. This was applied to the cellular system simulation to show differences in estimated performance with and without AAD correlation taken into account. The example given was assumed to be in an urban propagation enviroment with a 19-mile separation between co-channel users. Differences in 〈C〉/〈I〉 of 2.7 dB with omni antennas and 4.7 dB with 60-degree sector antennas are obtained at the level achievable at 90% of the locations.
123 citations
AT&T1
TL;DR: In this paper, the authors presented results of UHF propagation measurements conducted at 820 MHz in urban Philadelphia, where the emphasis was placed on transmission from relatively low land-site antennas at heights of 40-70 feet above local ground level.
Abstract: Results are presented of UHF propagation measurements conducted at 820 MHz in urban Philadelphia. The Philadelphia tests departed from previous path-loss measurements in that emphasis was placed on transmission from relatively low land-site antennas at heights of 40-70 feet above local ground level. Composite path-loss statistics have been derived for transmissions from five separate locations covering local environments considered typical of an urban area. This paper describes the measurement configuration, summarizes the data processing techniques, and presents results of the analysis.
63 citations
TL;DR: An experimental study of the electromagnetic wave propagation in various tunnels at frequencies between 1 MHz and 1000 MHz is presented in this paper, which provides a better understanding of various propagation mechanisms in underground galleries.
Abstract: An experimental study of the electromagnetic wave propagation in various tunnels at frequencies between 1 MHz and 1000 MHz is presented. The results provide a better understanding of various propagation mechanisms in underground galleries. The analysis shows the existence of a cutoff frequency, and enables one to distinguish three different ranges of frequency characterized by three different modes of propagation. Experimental verification was made in road and mine tunnels of various shapes and sizes. The results show a strong correlation between the propagation characteristics and the transverse dimensions of the tunnel.
58 citations
TL;DR: In this article, the measured values of energy deposited in simulated human tissue exposed for one minute in the immediate vicinity of 800 MHz portable radio transmitters are presented, and the deposited RF energy was evaluated by temperature measurements.
Abstract: The measured values of energy deposited in simulated human tissue exposed for one minute in the immediate vicinity of 800 MHz portable radio transmitters are presented. The deposited RF energy was evaluated by temperature measurements. The portable radio used in the tests had a 6-W experimental transmitter operating at 840 MHz. Two different antennas were tested for energy deposition: a sleeve dipole and a resonant whip. The two antennas have given substantially different results indicating different field structures near the two radiators. The experiments with flat slabs have shown that the sleeve dipole deposits higher levels of power density than the resonant whip in the near field although the length of the latter radiator is about half the size of the former. The temperature profiles generated by both antennas inside the head of the simulated operator indicate the presence of a "hot spot" about 1 in below the surface of the temporal bone. This phenomenon was not detected previously at lower frequencies. The short antenna exposes the eye of the operator to more intense power deposition than the sleeve dipole. The temperature increases measured during the investigation are so small that no thermal damage to tissue should be caused by normal use of the portable radio.
56 citations
TL;DR: In this article, the measurement of vehicle magnetic moments and the results from use of a fluxgate magnetic sensor to actuate a lighting system from the magnetic fields of passing vehicles are reported.
Abstract: The measurement of vehicle magnetic moments and the results from use of a fluxgate magnetic sensor to actuate a lighting system from the magnetic fields of passing vehicles is reported. A typical U.S. automobile has a magnetic moment of about 200 A-m2(Ampere-meters2), while for a school bus it is about 2000 A-m2. When the vehicle is modeled as an ideal magnetic dipole with a moment of 200 A-m2, the predicted results from an analysis of the sensor-vehicle geometry agree closely with observations of the system response to automobiles.
54 citations
TL;DR: The results of the study indicate that the design of a dial that is located within the reach and sight of the driver has little effect on driving control.
Abstract: Concern about the effects of mobile telephone use on driving control led to the development of a methodology for evaluating driving performance. A summary of the methodology is presented along with the results of a study comparing the effects of dialing a telephone to the effects of adjusting the car radio. A detailed account of a study of the effects of alternative control unit designs is provided. Three types of dials were implemented for this study. They are a rotary dial, a pushbutton dial, and a pushbutton dial-in-handset. Three mounting locations for the pushbutton dial were studied: on the dashboard, in the dashboard, and in the visor area. The rotary dial and the dial-in-handset models were mounted on the transmission tunnel. The results of the study indicate that the design of a dial that is located within the reach and sight of the driver has little effect on driving control. User preferences favored a pushbutton dial mounted in the dashboard area.
53 citations
TL;DR: In this paper, a spread-spectrum waveform centered at 1370 MHz was used to measure urban and terrain conditions with high time-delay resolution, and a detailed analysis of the multipath structure was made for various terrain conditions.
Abstract: Measurements over a variety of urban and terrain conditions were made using a spread-spectrum waveform centered at 1370 MHz. Chip rates of 10 and 20 MHz were used, giving high time-delay resolution. The transmitter end of the measurement link was elevated and fixed while the receiver was mobile. A detailed analysis of the multipath structure was made for various terrain conditions. This included distributions of the number and spacing of individual multi-path components as a function of amplitude threshold and also distribution of total delay. Thresholds are referenced to both average signal level and the maximum level in each pulse interval. Some instances of spatial variation of the received signal are also presented.
49 citations
TL;DR: In this article, the results of a research project on the heating of simulated human tissue in the induction field of portable radios at VHF were summarized, where measurements made with commercially available field probes indicated that, in some cases, apparent power levels higher than 10 mW/cm2are incident on the operator.
Abstract: The results of a research project on the heating of simulated human tissue in the induction field of portable radios at VHF are summarized. The investigation was initiated because measurements made with commercially available field probes indicated that, in some cases, apparent power levels higher than 10 mW/cm2are incident on the operator. Two phantom models have been built for RF heating tests. The first is a parallelepiped of simulated muscle material 26 in long, 9 in wide, and 6.5 in high, topped by a 0.5 in layer of fat and bone composition. The other phantom is a human-size head and shoulders. This "dummy" is a 1/3-in thick shell of bone composition containing simulated brain material. The measurements of temperature increment due to radiation were performed with a digital thermometer having a sensitivity of 0.01°C. Temperature measurements on the parallelepipedal phantom have shown that the penetrating power densities in the simulated tissue are substantially lower than what could be expected from an incident plane wave with the same E-field intensity. The physical reason for this apparent discrepancy is that the strong fields of static nature emanating from a VHF helical antenna (commonly used with portable radios) are normally rather than tangentially directed to the surface of the phantom. These fields practically collapse at the air-body interface because of the high complex dielectric constant of human flesh. The results of the measurements performed on the head phantom have shown that a 6-W portable radio with a helical antenna held at 0.2 in from the operator's mouth causes very little heating of the simulated biological tissue (less than 0.1°C is highest temperature increase for one minute exposure). The maximum power density penetrating the dummy is less than 1 mW/cm2in the middle forehead. No detectable temperature increase is present in the immediate eye area. This is because in normal use, the eyes of the operator are exposed to the relatively low fields at the base of the antenna. A health hazard is present if the user places the tip of the antenna in the immediate vicinity of the eye (less than a 0.2-in distance) and then operates the transmitter. In this case, the possibility of damage is greatly reduced by a thick insulating cap at the tip of the antenna.
45 citations
TL;DR: In this paper, a method of predicting the loss in error performance in mobile radio data transmission is given in which the variation in local mean signal level (shadowing) is included as well as fading.
Abstract: A method of predicting the loss in error performance in mobile radio data transmission is given in which the variation in local mean signal level (shadowing) is included as well as fading. Also, the density function of the received signal envelope is found for the case of fading and shadowing. Field measurements are reported of error rates at VHF and UHF due to vehicle ignition noise, and the distribution of errors is plotted.
TL;DR: In this article, the performance of error detecting and correcting codes has been investigated and the effects of varying code parameters explored, and the advantages of using a high data rate are considered.
Abstract: Error patterns recorded during mobile radio data transmission experiments in London have been used to assess what error control strategies are required to achieve reliable data communication. The performance of error detecting and correcting codes has been investigated and the effects of varying code parameters explored. Results are given for transmission at 462 MHz using data rates of 1200 b/s and 4800 b/s, and the advantages of using a high data rate are considered. Bit interleaving is shown to be a useful way of dispersing bursts of errors, greatly improving the performance of an error correcting code. Fairly simple coding techniques can give a performance which is adequate for many applications, and a high performance is readily possible.
TL;DR: In this paper, an offset carrier frequency allocation method is proposed for a high capacity land-mobile telephone system which employs a small zone technique, and the simulation test results are presented which determine the design parameters.
Abstract: 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.
TL;DR: In this article, a simple and efficient diversity technique is proposed for use in a digital FM land mobile radio communication system, which receives two RF signals periodically by switching two antenna branches at a rate moderately higher than the bit rate.
Abstract: A simple and efficient diversity technique is proposed for use in a digital FM land mobile radio communication system. This technique receives two RF signals periodically by switching two antenna branches at a rate moderately higher than the bit rate. The improved bit error rate (BER) performance resulting from the use of diversity is shown to be the effect of transforming the probability density function of the signal energy per bit to noise power density ratio to a sharper distribution. Laboratory simulation test results show that in a Manchester-coded frequency-shift keying (FSK) system with a bit rate of 600 bit/s and a frequency deviation of ±5 kHz, the diversity gain at an average BER of 1 × 10-3is about 10 dB for an optimum switching rate of about 2 kHz. This diversity improvement is also verified by the field test performed in a suburban area.
TL;DR: The control channel frequency assignment method proposed decreases the required number of control channel frequencies by more than one half of the number in the existing assignment method.
Abstract: Control channel efficiency improvement techniques for an 800-MHz band high-capacity land mobile telephone system are described. Three interesting techniques, 1) the channel capacity increase technique under the random access mode from many mobiles, 2) a control channel division method which takes into account differences of control signal traffic behavior in land originated calls and mobile originated calls, and 3) a control channel frequency assignment method for efficient utilization of the radio frequency band, are studied by using computer simulations. The control channel frequency assignment method proposed decreases the required number of control channel frequencies by more than one half of the number in the existing assignment method.
TL;DR: The results of a comprehensive mesurement program at 820 MHz designed to determine propagation characterstics in flat suburban terrain are presented and show an environmental advantage of 11 dB for flat open suburban terrain.
Abstract: The results of a comprehensive mesurement program at 820 MHz designed to determine propagation characterstics in flat suburban terrain are presented. The data are organized to separate the effects of surface features, mobile antenna gain, and land-site antenna height, gain, and type (omnidirective and directive). The data have been collected using a digital data acquisition system to sample each of 18 variables once every three milliseconds. The mobile traveled over 500 route miles in the suburban Philadelphia/Camden, NJ area while probing an 11-square-mile measurement area in collecting these data. The results show propagation characteristics and relative antenna comparisons in flat suburban terrain. These results are compared to earlier urban data and show an environmental advantage of 11 dB for flat open suburban terrain.
TL;DR: The 800-MHz band land mobile telephone system which is going into service in Tokyo and other major cities is described, characterized by an ordered array of cells which allows each radio channel to be reused by spacing at an appropriate coordination distance.
Abstract: The 800-MHz band land mobile telephone system which is going into service in Tokyo and other major cities is described. This system is characterized by 1) an ordered array of cells which allows each radio channel to be reused by spacing at an appropriate coordination distance in a wide service area (cellular system), 2) development of a new higher frequency band, and 3) a fully automatic exchange system integrated with the ordinary telephone network. Field tests have been carried out in the Tokyo metropolitan area since 1975 and have now been brought to a successful completion.
TL;DR: In this paper, the performance of the two-branch equal-gain diversity system as a function of the cross-correlation between the two received signals from the diversity antennas is described.
Abstract: It has generally been accepted that in a two-branch diversity receiver a near maximum diversity advantage is realized when the cross correlation between the two branches is less than 0.7. Based on this figure, space diversity reception at the mobile presents little problem since the antenna separation distances that achieve this mount of decorrelation in the mobile environment are very small (≤20 cm at 850 MHz). However, the space diversity antenna separation requirement at the land site necessary to achieve the same amount of signal decorrelation is in the range of 10 wavelengths or more at antenna elevations of 150 ft or greater. Therefore, a comprehensive characterization of the effect of changing the cross correlation between the two received signals at the land site is important to effective system design. The performance of the two-branch equal-gain diversity system as a function of the cross-correlation between the two received signals from the diversity antennas is described. The cumulative probability distribution, level crossing rates, and duration of fades from a two-branch equal-gain combined diversity signal with variable correlation between the two branches are described also.
TL;DR: A method based on the application of modern solid state microwave Doppler radar for monitoring the velocity of agricultural tractors is described in this paper, where experimental results obtained during the field tests on different field surfaces are presented.
Abstract: A method based on the application of modern solid state microwave Doppler radar for monitoring the velocity of agricultural tractors is described. Experimental results obtained during the field tests on different field surfaces are presented.
TL;DR: Typical transmission channel configurations, various modulation methods, signal spectra, and bit error probabilities when transmitting data over a mobile radio channel are described.
Abstract: During the last few years data communication has become important in the mobile radio services. This tutorial paper introduces the reader to the basic concepts of data transmission. Typical transmission channel configurations, various modulation methods, signal spectra, and bit error probabilities when transmitting data over a mobile radio channel are described.
TL;DR: A sensor system is described which measures the on-board alcohol concentration so that carburetion and/or spark timing corrections can be made for optimal engine operation.
Abstract: Ethanol additions to the Brazilian fuel supply are seasonal and regionally variable. Thus cars in Brazil must now function with gasoline/alcohol mixtures ranging in alcohol content from 0 percent to 30 percent. A sensor system is described which measures the on-board alcohol concentration so that carburetion and/or spark timing corrections can be made for optimal engine operation.
TL;DR: In this article, the results of field measurements carried out in center city Philadelphia and in the Whippany/Morristown, NJ suburban area to assess the accuracy of a vehicle location technique at 820 MHz based on signal strength comparison are described.
Abstract: The results of field measurements carried out in center city Philadelphia and in the Whippany/Morristown, NJ suburban area to assess the accuracy of a vehicle location technique at 820 MHz based on signal strength comparison are described. Six co-sited directional antennas, each covering a 60° angular sector in azimuth, were used to detect the signal transmitted by the mobile. The angular location of the vehicle was determined by comparing the signal strengths received "simultaneously" through the directional antennas. The measured vehicle location was then compared against the true location of the vehicle at the time of the measurement to generate statistics on location accuracy. An estimate is made on the expected improvements in the locating accuracy when three co-sited directional antennas are used, each of which provides coverage for a 120° sector in the horizontal plane. Also described are the effects of signal sample "integration time" and antenna beam shaping on the accuracy of the position estimate. The measurement results presented put a bound on the expected range of accuracies in the signal-strength-based "angle-of-arrival" vehicle location technique.
TL;DR: In this paper, it was shown that the efficiency and the bandwidth of the antenna increase as the load is moved from the base of the monopole until a maximum, while the value of the inductance required to tune the antenna increases as the latter is moved away from its base.
Abstract: Theoretical studies have shown that the properties of electrically short monopole antennas are improved by placing an inductive load on the structure. The results obtained from the moment method are presented and compared with an experimental evaluation. The current distribution along the structure is computed and measured for various positions of the load. From this, the input admittance, efficiency, and bandwidth of the antenna are deduced. It is found that the efficiency and the bandwidth of the antenna increase as the load is moved from the base of the monopole until a maximum is reached. Simultaneously, the value of the inductance required to tune the monopole increases as the latter is moved away from the base.
TL;DR: The effect of periodic switching diversity on the bit error rate (BER) performance of a binary frequency-shift keying system in the presence of co-channel interference is described and the diversity effect on the BER performance in a Rayleigh fading environment is analyzed.
Abstract: The effect of periodic switching diversity on the bit error rate (BER) performance of a binary frequency-shift keying (FSK) system in the presence of co-channel interference is described. The distribution of the signal-to-interference energy ratio per bit presented to the FM detector is found and the diversity effect on the BER performance in a Rayleigh fading environment is analyzed. The diversity effect on the BER performance in a Manchester-coded FSK system with limiter-discriminator detection is verified by laboratory simulation tests using a Rayleigh fading simulator.
TL;DR: The characteristics and relative advantages of several types of electric vehicle control systems are discussed in this article, where an advanced electronic control system for a separately excited dc motor is described and performance characteristics of an electric vehicle using this control are discussed and recommendations for future systems are given.
Abstract: The characteristics and relative advantages of several types of electric vehicle control systems are discussed. An advanced electronic control system for a separately excited dc motor is described. Performance characteristics of an electric vehicle using this control are discussed and recommendations for future systems are given.
TL;DR: A narrow deviation voltage controlled crystal oscillator (VCXO) circuit has been developed that exhibits near-linear tuning characteristic and, unlike previously reported circuitry, is extremely simple and straightforward in design and highly economical with regard to material and fabrication costs.
Abstract: A narrow deviation voltage controlled crystal oscillator (VCXO) circuit has been developed that exhibits near-linear tuning characteristic and, unlike previously reported circuitry, is extremely simple and straightforward in design and highly economical with regard to material and fabrication costs. The design principle makes use of a linear reactance modulator incorporating abrupt junction varactor diode developed by M. Driscoll, and previously reported by Driscoll and Healey in connection with the design of a wide deviation VCXO for radar application. Because the total oscillator turning requirements are only on the order of 1 part in 105, however, much of the circuit complexity has been eliminated, and the problem of interdependence between linearity and center frequency adjustment has been solved. Network equivalence theorems have been utilized to reduce the total number of required circuit inductances to only one, and the composite resonator has been reconfigured to operate on the series resonance of its impedance characteristic allowing simple means for prevention of oscillation at spurious network resonances through the addition of a single resistor. Laboratory measurement of transmitter FM distortion using a number of FM oscillator modules reveals repeatable achievement of less than 0.5 percent distortion with linearity adjustment and less than 1½ percent without any adjustment. Also, the achievement of repeatable linear tuning characteristic has simplified the oscillator modules so that required temperature stability is obtained by addition of negative temperature coefficient (NTC) capacitors to the oscillator circuit and a single simple three-point thermistor compensation circuit that is easily designed and provides simultaneous temperature dependent compensating voltage for all radio oscillator modules. The oscillator design also allows for direct parallel connection of multiple modules (for multichannel operation) having commonly connected tuning input and signal output ports.
TL;DR: In this paper, a technique for obtaining synchronization signals from an engine's ignition system without significantly modifying the far field radio frequency interference (RFI) produced by the engine is described.
Abstract: A technique is described for obtaining synchronization signals from an engine's ignition system without significantly modifying the far field radio frequency interference (RFI) produced by the engine. These signals are used to view the output of an RFI receiver as a function of time, allowing for a correlation between RFI and individual arcing events in the ignition sequence. Examples of real time and statistical data obtained with the technique are given.
TL;DR: It is shown how if the time of arrival is known at certain locations, the traffic signals may be appropriately timed to remove this instability and enable the buses to adhere to their schedule with greater precision.
Abstract: Bus bunching causes uneven passenger loadings and increases the average passenger waiting time. Bunching is caused by an unstable relationship between delay in the actual bus arrival time and passenger loading time requirements. An appropriate mathematical representation of this process is provided, and the general mathematical requirements for stabilizing the process is described. It is shown how if the time of arrival is known at certain locations, the traffic signals may be appropriately timed to remove this instability and enable the buses to adhere to their schedule with greater precision. An example demonstrating the performance of the algorithm on a particular bus route is provided.
TL;DR: In this article, a method of generating continuous position information for use in the longitudinal control of ground transport systems is presented, which utilizes two specially excited four-wire helically wound transmission lines.
Abstract: A method of generating continuous position information for use in the longitudinal control of automated ground transport systems is presented. The technique utilizes two specially excited four-wire helically wound transmission lines. The method of excitation, the signal detection, and processing schemes necessary to obtain the control signal, and the results of laboratory tests are presented. The technique should provide accurate, easily implementable, and environmentally impervious means of generating information for longitudinal control.
TL;DR: An introduction to redundancy encoding as used in digital data communications is described, followed by a discussion of the binary symmetric channel, burst noise channels, and the use of interleaving to randomize burst errors.
Abstract: An introduction to redundancy encoding as used in digital data communications is described. The need for redundancy is first addressed, followed by a discussion of the binary symmetric channel, burst noise channels, and the use of interleaving to randomize burst errors. The concept of redundancy is presented next, showing how it is used to supply the highest possible degree of error detection or how it can be applied to provide for the detection and correction of a lesser number of errors. The use of some codes to correct some errors and also to detect, but not correct, additional errors is discussed. The properties of block codes are developed beginning with repetition codes then covering single-parity check codes, Hamming (single-error detection) codes, and Bose-Chadhuri-Hocquenghem (BCH)codes. The basic properties and structures of these codes are emphasized with examples of implementation procedures for both encoding and decoding.