Showing papers on "Base station published in 1972"

A power-spectral theory of propagation in the mobile-radio environment

Abstract: The statistical properties of radio propagation between a mobile unit and a base-station terminal are derived. The power spectrum of the transmission coefficient in the multipath medium is used to determine probability distributions of amplitude and phase, correlations of fields versus time and space at mobile and base stations, level-crossing rates and durations of fades, and random frequency modulation. Duality between the power spectrum and density of time delays is shown. The correlations versus frequency and the coherence bandwidth then follow from the density of time delays. The performance of standard diversity systems is then predicted. There is a review of results previously presented by Clarke [1], however, the derivations given herein utilize expressions of the power spectrum rather than expressions of the component waves. The power-spectral approach, used throughout, allows direct application of previous statistical analyses, particularly those of Rice [2].

Polarization Diversity System for Mobile Radio

Abstract: Conventional space diversity reception at typical elevated base locations requites separation of 30λ for broadside incidence and even more for in-line incidence and is therefore difficult to implement. A polarization diversity system for mobile radio is proposed. This is a two-branch receiver diversity system with the advantage that the base station antennas can be spaced as closely as desired. An experimental program has been carried out to obtain the statistical properties of vertically and horizontally polarized electromagnetic waves in a suburban environment at 836 MHz. It was observed that signals of both polarizations were Rayleigh plus log normal, where one is uncorrelated and other is correlated irrespective of base or mobile antenna spacings. The local means of the two signals were highly correlated and were with ± 3 dB for almost 90 percent of the time. Variation of base transmitter heights appeared to have little effect on the ratio of the local means of the two signals. The analysis and experiment demonstrated the feasibility of providing two diversity branches at UHF by polarization diversity.

A Comparison of Some Channel Assignment Strategies in Large-Scale Mobile Communications Systems

Abstract: When more than one radio channel is available to serve a mobile customer in a large-scale mobile communications system the strategy used to make the assignment has an effect on system performance. Performance characteristics for five different assignment strategies obtained from a computer simulation are compared in this paper. It was found that the strategy that chooses a channel to be assigned at a base station so that the distance to the next base station using the same channel is a minimum, performs better than a strategy that minimizes the mean square distance to the next "in use" base stations on both sides. Also, it was found that choosing the first available channel encountered in a channel search is a strategy that produces reasonably good system performance.

Some characteristics of mobile radio propagation at 836 MHz in the Philadelphia area

Abstract: Mobile radio propagation tests were carried out at 836 MHz from a base station in downtown Philadelphia, Pa., to a mobile which traveled on the city streets. It was found that the median signal power tends to fall off as R-3for distances greater than 1 to 2 mi from the base station antenna. The mean received-signal level was found to be approximately log-normally distributed with a standard deviation varying from 5 to 10 dB, where the higher values were observed close to the base station.

Mobile telephone cellular switching system

Abstract: A high capacity cellular mobile communication system arranged to maintain a mobile station communication path by transferring the mobile station from a shadowed serving base station to a clear base station A multiport trunk circuit is utilized to establish the communication path between a switching central office and the mobile station through a serving base station The deterioration of the serving base station radio carrier communication link, brought about by the shadowing of the serving base station, enables the trunk circuit to test continuity of communication channels through other base stations to the mobile station Once continuity of a new communication channel has been established through a clear base station, the trunk transfers the communication path to the tested communication channel in order that a continuous communication path may be maintained between the switching central office and the mobile station

Mobile radio extension interface for converting conventional transmit/receive to a repeater

Abstract: A unit connectable to a conventional transmitter and receiver to convert them for use as a repeater or transponder with provision for automatically inhibiting multiple transmissions by units within range of one another. The unit is particularly useful for using a mobile transceiver as a repeater to form communications links in both directions between a base station and a hand held portable unit in the proximity of the mobile transceiver.

Statistically-optimum dynamic server assignment in systems with interfering servers

Abstract: In a mobile radio system which uses many base stations to provide radio service over a large geographical area, and which has a stored-program processor to assign radio channels to base stations in real time, the queueing characteristics of the overall system are strongly dependent on the processor algorithms which are used. Three algorithms, which are in a certain minimax sense statistically optimum, are described below. The procedures are quite general, and may be usefully applied to any system which employs many servers, the use of some combinations of which is not allowed.

Effects of some nonuniform spatial demand profiles on mobile radio system performance

Abstract: 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 Behavior of Dynamic Channel-Assignment Mobile Communications Systems as a Function of Numbers of Radio Channels

Abstract: Dynamic channel assignment in mobile communications systems is able to cope with varying nonuniform spatial user demand. It also readily handles the normal randomness in offered traffic. This study presents system performance data for radio systems having 8, 20, 40, 80, and 120 radio channels available and a radio-channel reuse interval of 4 base-station coverage areas. Data are also presented that compare performance of a 30 radiochannel system with a reuse interval of 3 base stations, a 40 radiochannel system with a reuse interval of 4 base stations, and a 50 radio-channel system with a reuse interval of 5 base stations. The results are obtained from a computer simulation of a onedimensional network laid out along a line. As the number of radio channels available to a communication system increases, the system becomes more efficient in handling the fluctuations in offered traffic. Changing the radio-channel reuse interval also affects the per-channel traffic carried by a dynamic-channel-assignment system.

Effects of Some Nonuniform Spatial Demand Profiles on Mobile Radio System Performance

Abstract: signal output from the energy-density antenna system and that from a single unipole antenna are obtained as expressions which depend on the angle of incidence and the magnitude and the direction of vehicle velocity in a general way. From these general expressions the fading frequency and the maximum range of output variation are found. The extent of amplitude fluctuation for the energy-density antenna system is always smaller than that for the single antenna. When the incident Abstruct-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 magni- tudes of which are only to be conjectured at this time. This paper com- pares the performance of computer simulated mobile radio systems op- erating with several demand profiies. The profiles were selected to give an indication of the effects on system performance of either uncom- pensated 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 fiied 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 simula- tion. Even though new call attempts were made to fluctuate markedly between adjacent base stations within a reuse interval, the blocking rate