IEEE Transactions on Communications

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{seco... View full abstract»

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... View full abstract»

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 ... View full abstract»

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... View full abstract»

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... View full abstract»

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 ... View full abstract»

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 wit... View full abstract»

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... View full abstract»

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»

Many mobile telephone and personal paging systems require signaling simultaneously from multiple transmitters. This paper analyzes the factors that cause paging errors due to interference when the signaling format consists of audio tones sent simultaneously from two FM transmitters. The factors considered are: drift in carrier and modulation frequencies, and misequalization of land-line amplitude ... View full abstract»

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 firs... View full abstract»

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»

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, w... View full abstract»

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»

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 re... View full abstract»

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 ... View full abstract»

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 di... View full abstract»

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... View full abstract»

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 ... View full abstract»

This paper reports the results of an investigation of the increase in traffic capacity in a cellular high capacity mobile telecommunications system attainable with dynamic instead of fixed channel assignment. Three dynamic channel assignment algorithms were studied by simulation using a 21-cell hexagonal array as a representative system layout. Detailed results for each algorithm are presented. Fo... View full abstract»

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... View full abstract»

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 o... View full abstract»