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Communications, IEEE Transactions on

Issue 11 • Date November 1973

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Displaying Results 1 - 25 of 27
  • [Front cover and table of contents]

    Publication Year: 1973 , Page(s): 0
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    Freely Available from IEEE
  • Guest editorial

    Publication Year: 1973 , Page(s): 1171
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    Freely Available from IEEE
  • [Back cover]

    Publication Year: 1973 , Page(s): 0
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    Freely Available from IEEE
  • Spectral and Economic Efficiencies of Land Mobile Radio Systems

    Publication Year: 1973 , Page(s): 1177 - 1187
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1256 KB)  

    A variety of land mobile radio systems are compared by their spectral and economic efficiencies in providing various user services, system types covered are private one-channel, shared repeater one channel, controlled-access one-channel, trunked multichannel, and cellular. Spectral efficiency is defined to be the number of mobile users that can be served per MHz of spectrum in a core urban area, while economic efficiency is the average system cost per mobile. Both efficiencies vary with the type of usage, hence they are calculated for three major usages-mobile telephone service, dispatch service emergency, and dispatch service nonemergency. Services are described via seven "service parameters," namely call holding time (average), tolerable average wait for channel access, peak busy hour utilization per mobile, audio quality (S/N), noise levels tolerable, and service range. Sensitivity of the basic results to variations in the service parameters are also computed and discussed. View full abstract»

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  • A Multipath Fading Simulator for Mobile Radio

    Publication Year: 1973 , Page(s): 1325 - 1328
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    A simple device to simulate the Rayleigh distributed fast fading encountered in mobile radio is described and evaluated. The Rayleigh envelope statistics are obtained by adding two independent Gaussian noise source in quadrature. The theoretical spectrum of the received signal is approximated by shaping the spectrum of the noise sources with filters. A design is given whose performance is shown to agree very closely with theory. View full abstract»

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  • 910 MHz Urban Mobile Radio Propagation: Multipath Characteristics in New York City

    Publication Year: 1973 , Page(s): 1188 - 1194
    Cited by:  Papers (59)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (960 KB)  

    Small scale statistics of multipath propagation in a heavily built-up urban mobile radio environment are presented. The statistics cover vehicle travel distances on the order of 30 m along streets. Measuring equipment time delay resolution is about 0.1 μs. In some locations, paths with significant amplitudes are observed with excess delays of 9 to 10 μs. The delay spreads ( \sqrt {\hbox{second central moment of power delay profile}} ) in this environment are on the order of 2 μs. Often the signal at fixed delays has a Rayleighdistributed amplitude but large departures from the Rayleigh distribution also occur. From the measurements it appears reasonable to model the urban mobile radio channel as a Gaussian quasi-wide-sense stationary uncorrelated scattering channel within a bandwidth of 10 MHz and for intervals along the street of up to 30 m. View full abstract»

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  • Increasing Channel Occupancy in Large-Scale Mobile Radio Systems: Dynamic Channel REassignment

    Publication Year: 1973 , Page(s): 1302 - 1306
    Cited by:  Papers (22)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Large-scale mobile radio systems using dynamic channel REassignment switch the channels assigned to some of the calls in progress to maintain a nearly optimum separation between coverage areas simultaneously using the same channel. Dynamic channel REassignment produces a significant increase in channel occupancy. For example, in the systems studied, which have a uniform distribution of their fixed channels and were operated against a uniform spatial distribution of offered traffic, the channel occupancy was increased by frac23 over a pure fixed channel assignment system at a blocking rate of one percent. This corresponds to a channel savings of about 40 percent for the same traffic carried at one percent blocking by the hybrid systems that were studied. View full abstract»

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  • Performance of Feedback and Switch Space Diversity 900 MHz FM Mobile Radio Systems with Rayleigh Fading

    Publication Year: 1973 , Page(s): 1257 - 1268
    Cited by:  Papers (23)  |  Patents (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    A theoretical and experimental comparison of performance has been made between two types of predetection switching space diversity mobile radio systems. This comparison was made at a frequency of 840 MHz using simulated Rayleigh fading for a vehicle speed of about 80 mi/h. The switch diversity system was a conventional receiver antenna switching technique with two simulated physically separated receiving antennas and a single transmitting antenna. The feedback diversity system used a single receiving antenna with two simulated physically separated transmitting antennas. The transmitting antennas were switched remotely from the receiver. The difference in the performance of the two systems was shown to be primarily due to time delay inherent in the remote antenna switching technique. View full abstract»

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  • Statistical Estimation of Mean Signal Strength in a Rayleigh-Fading Environment

    Publication Year: 1973 , Page(s): 1207 - 1213
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    A commonly used model for signal fading in many types of communication channels is that the amplitude of the received signal at a given time is a Rayleigh-distributed random variable. In this paper we show how classical statistical techniques may be applied to the problem of estimating the Rayleigh distribution parameter (i.e., the mean), given samples from the distribution. In particular, we first consider the problem of estimating the population mean, given a sequence of independent samples. We derive an unbiased maximum-likelihood estimator. We show that this estimator is unique, and since it is based on a sufficient statistic, it is therefore "best" in the Blackwell-Rao sense of minimizing expected loss. Using this estimator, we then develop confidence intervals whose length can be used as a guide in selecting the required sample size. We then consider the same estimation problem when the signal samples are obtained from the output of a logarithmic receiver. We derive an interval estimator which does not require taking the antilogs of the log samples, and which is not appreciably worse than the "best" estimator. View full abstract»

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  • New Concepts in Spectrum Usage

    Publication Year: 1973 , Page(s): 1172 - 1176
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    The author alleges that there is no shortage of radio spectrum, but rather, a shortage of new concepts in spectrum usage. The recent reallocation of additional frequencies to land mobile radio uses (FCC Dockets 18 261 and 18 262) provides new opportunities for innovative approaches, approaches that are free of the constraints of existing rules and regulations, existing manufacturing and engineering processes and concepts. Intending to be provocative and to initiate action and dialogue, the author challenges the technologists of this industry to come forward with innovative approaches based upon thorough, objective engineering analyses. The FCC, he contends, sorely needs factual, objective data from industry technologists in order to make the best decisions possible. View full abstract»

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  • A Mobile Wide-Band Measurement System for Urban Man-Made Noise

    Publication Year: 1973 , Page(s): 1224 - 1232
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB)  

    This paper describes in detail the criteria for the design of a mobile laboratory for the characterization and measurement of manmade 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. View full abstract»

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  • 900 MHz Land Mobile Radio Improved Using Circular Polarization

    Publication Year: 1973 , Page(s): 1321 - 1323
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    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. View full abstract»

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  • Switching Plan for a Cellular Mobile Telephone System

    Publication Year: 1973 , Page(s): 1281 - 1286
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    Federal Communication Commission Docket 18 262 allocated a 75-MHz band to the common carriers to implement high capacity mobile telephone systems. The Bell System has proposed a cellular arrangement of low-power transmitters/receivers that permits frequency reuse in a coverage area. This method of achieving spectrum efficiency will require extensive centralized coordination and control to properly administer channel assignments and to interconnect the mobiles with each other and with the direct distance dialing (DDD) network. This can be accomplished by means of an electronic switching system (ESS) with special data terminals and trunking arrangements, and a unique program. In the proposed plan the radio sites (base stations) act effectively as remote concentrators in the frequency domain under the control of ESS, which in turn acts primarily as a trunk-to-trunk switcher. In addition to the usual switching, signaling, and supervising functions, the switching office must also perform numerous special functions including paging of mobiles, location of mobiles (signal strength and ranging data analysis), channel reassignment of mobiles, and reswitching of mobiles to various base stations-these last three occurring while customers are talking. View full abstract»

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  • Effects on Correlation Between Two Mobile Radio Base-Station Antennas

    Publication Year: 1973 , Page(s): 1214 - 1224
    Cited by:  Papers (108)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The correlation between signals received by two mobile radio base-station antennas is investigated to determine spacing requirements for space diversity. Measurements of the fading of UHF signals received by two base-station horn antennas oriented at different angles with respect to the incoming mobile radio signal were made for different antenna spacings. The experimental results are compared with an analytical expression derived in this paper; they agree fairly well. A further experiment was made after removing the possible local scatterers surrounding the base station. Comparing these two experimental results, we find that the following are true. 1) Propagation in the direction of a line connecting the two base-station antennas is the critical case and requires a large separation of 70 wavelengths. As soon as the incoming wave is 10° away from the inline axis, the spacing requirement drops to 30 wavelengths. 2) Local scatterers at the base station tend to decrease the correlation between signals received at the two antennas. We conclude that an upper limit to the spacing of antennas used for diversity can be obtained and that it is within the achievable range. View full abstract»

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  • Single-Receiver Diversity Systems

    Publication Year: 1973 , Page(s): 1276 - 1280
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    Diversity reception techniques can help to combat fast fading in urban areas, and this paper describes some predetection combining systems designed to be compatible with existing standard receivers. Quantitative results show that a worthwhile improvement in quality of reception can be obtained with small numbers of antennas. There are advantages to be gained if, in future receiving systems, the diversity technique is incorporated directly into the receiver design. View full abstract»

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  • A Switched Diversity Receiving System for Mobile Radio

    Publication Year: 1973 , Page(s): 1269 - 1275
    Cited by:  Papers (10)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    A low cost switched diversity receiving system has been developed for use in UHF-FM mobile radio. The input of a single receiver is switched back and forth between two antennas upon command from a signal level sensing logic circuit. The system has been measured on simulated Rayleigh fading channels and has been found to give a significant improvement to both voice and data signals. View full abstract»

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  • Baseband Performance of a Pilot Diversity System with Simulated Rayleigh Fading Signals and Co-Channel Interference

    Publication Year: 1973 , Page(s): 1248 - 1257
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (976 KB)  

    Using simulated Rayleigh-fading FM signals, the baseband performance of a diversity system that uses a separate pilot is studied. The effect of various RF/audio bandwidth expansion ratios is included. These results show an approach to a constant asymptotic baseband SNR for large expansion ratios, with diversity increasing this asymptote by 5 dB in the case of moderate to large interference and/or RF noise levels (9 to 15 dB below the carrier), to over 10 dB in the case of lower impairment levels (21 to 27 dB below the signal level). Assuming the usual hex-cell radio coverage plan, and a propagation law of the form r^{-n}, n = 3 or 4, bandwidth expansion ratios of about three to six seem to yield the most efficient RF spectrum utilization in many practical situations. The number of required channel subsets (cells) is strongly influenced by the propagation law ranging from about 19 for n = 3 , to about 7 for n = 4 . View full abstract»

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  • The Elevation Angle of Mobile Radio Signal Arrival

    Publication Year: 1973 , Page(s): 1194 - 1197
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    Field measurements of mobile radio signals have shown that signal arrival is concentrated in elevation angles lower than 16°. This suggests use of an omnidirectional antenna with vertical directivity, instead of the usual whip antenna, to increase average signal strength as a further improvement in the advantages of diversity reception. View full abstract»

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  • Statistically-Optimum Dynamic Server Assignment in Systems with Interfering Servers

    Publication Year: 1973 , Page(s): 1287 - 1293
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Cellular mobile radio systems have been proposed that use many base stations to provide radio service over a large geographical area. In such systems, a stored-program processor assigns radio channels to base stations in real time, under certain interference constraints. The capacity and the queueing characteristics of the overall system are strongly dependent on the processor algorithms that are used. This paper presents three algorithms which are in a certain minimax sense statistically optimum. The procedures are quite general, and may be applied to any system that employs many servers, the use of some combinations of which is not allowed. The first algorithm provides for the preferential assignment of a "standard" channel. If all standard channels are busy, a "nonstandard" channel is selected in such a manner that the probability of blocking is minimized in that interferable facility most likely to suffer blocking. The second algorithm provides for the transfer of service from nonstandard to standard channels whenever standard channels become free. The choice of the particular nonstandard channel to be freed is again made in a manner which minimizes the maximum probability of future blockage. The third algorithm provides for the rearrangement of channel assignments in those instances when all assignable channels, both standard and nonstandard, are busy. Such rearrangement can cause channels to become available under certain circumstances. If more than one rearrangement is possible, again the choice of what particular action should be taken is governed by the goal of minimizing the maximum probability of future blockage. All three algorithms attain short-term optimality by enumeration; that is, each candidate for assignment is considered in turn. Under the condition that the given candidate is selected, the conditional probability of future blocking in each of the server groups is calculated, and the maximum of these probabilities is associated with the candidate. After all candidates have been considered, that candidate which has the minimum associated probability is assigned. These algorithms produce, by definition, an instantaneous system state which is always optimum in the above minimax sense. In systems with large numbers of servers, the- system changes state rapidly; thus, occasional short-term errors disappear rapidly, and short-term optimization tends to lead to peak performance in the long term as well. View full abstract»

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  • Traffic Engineering of Combined Mobile Telephone and Dispatch Systems

    Publication Year: 1973 , Page(s): 1307 - 1309
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    If a server group carrying short-holding-time queued traffic at high blocking probability is combined with another server group carrying normal blocked-calls-cleared traffic at low blocking probability, the resulting mixed group will in many cases operate at an intermediate blocking probability. Thus the mixed group provides better service to the queued traffic, while degrading the service of the cleared traffic. If the random arrival characteristics of the short-holding-time traffic are suitably modified by delaying calls an appropriate time before service, then the grades of service for both types of traffic may be engineered independently. An example of a possible use of this technique of induced delay, the combining of dispatch and mobile-telephone traffic on the same set of radio channels in the High-Capacity Mobile Telecommunications System, is discussed. View full abstract»

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  • The Statistics of the In-Phase Component of the Branch Signal in a Pilot-Derived Maximal Ratio Diversity Combiner

    Publication Year: 1973 , Page(s): 1319 - 1320
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    An often-discussed scheme for providing maximal ratio combining in mobile radio is to set the complex branch gain according to the amplitude and phase of a pilot sent with the carrier. The in-phase component of the branch signal in such a system has a simple doubleexponential distribution. These and other relevant statistics are derived. View full abstract»

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  • A Mobile Radio Single-Frequency "Two-Way" Diversity System Using Adaptive Retransmission from the Base

    Publication Year: 1973 , Page(s): 1241 - 1247
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "twoway diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches. View full abstract»

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  • Methods for Investigation and Simulation of Mobile Data Transmission

    Publication Year: 1973 , Page(s): 1323 - 1324
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    This paper deals with two aspects of the investigations of mobile data transmission. The first aspect shows the equipment for measuring and recording of parameters that influence the transmission. The second aspect shows the development of an analog simulation of the data transmission with the possibility of adjusting significant parameters independently. Finally the applicability of the model is verified by comparison between simulation and actual transmission. View full abstract»

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  • Some Propagation Experiments Relating Foliage Loss and Diffraction Loss at X-Band and UHF Frequencies

    Publication Year: 1973 , Page(s): 1198 - 1206
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    Measurements of signal attenuation were made from a suburban hilltop base station to a mobile vehicle on several streets in the surrounding countryside. Measurements of signal strength were simultaneously made in the winter of 1971 at frequencies of 836 MHz and 11.2 GHz and then repeated in the summer to determine the effects of foliage. The presence of foliage reduced the received signal strength and the effect was more pronounced at X -band than at UHF. In cases where the shadowing obstacle was tree covered, signal levels at UHF might typically be 10 dB lower when the trees were in full leaf, whereas at X -band this additional loss could be as high as 20 dB. The experimental data was compared to values predicted by knife-edge diffraction and reasonable agreement was found. View full abstract»

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  • Man-Made Noise in Urban Environments and Transportation Systems: Models and Measurements

    Publication Year: 1973 , Page(s): 1232 - 1241
    Cited by:  Papers (68)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (952 KB)  

    Analytically tractable statistical-physical models of manmade 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. Firstorder 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. View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia