Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1997-08-26
2001-02-13
Bost, Dwayne D. (Department: 2744)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C342S359000, C342S372000, C343S824000
Reexamination Certificate
active
06188913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Application
The present invention relates to a directivity control antenna apparatus for use in base stations and mobile stations of a mobile communication system such as a radio paging system, cellular telephone system, etc.
2. Prior Art
In the prior art, methods such as time division multiplexing (TDMA), frequency division multiplexing (FDMA), code division multiplexing (CDMA), etc., have been used in the field of mobile communication, as methods for communicating with a plurality of mobile stations within areas which have been allocated to respective base stations of a mobile communication system. With time division multiplexing, a channel having a single frequency is divided into equidistant intervals along the time axis to provide communication slots, for enabling communication between a plurality of mobile stations and a base station, while with frequency division multiplexing this is accumplished by using a plurality of different frequency channels, Alternatively, with code division multiplexing, a plurality of mobile stations execute spectrum dispersion modulation by using data encoded such as to ensure there is no mutual correlation between the respective received signals which are obtained by a base station from the various mobile stations, to thereby enable communication between the mobile stations and the base station within the same frequency band.
With such a prior art system, in general communication is only possible between a base station and those mobile stations which are located within the service area of the base station, i.e. an area of nominally predetermined size. In practice, the level of signal strength received by a base station from a mobile station is usually employed as an indication of whether the mobile station is within the service area of that base station. Also, in general, the radio transmission frequencies which are used by a base station and by the mobile stations which are located within the service area of that base station are predetermined such that these will not result in interference with communication between any adjacent base station and those mobile stations which are within the service area of the adjacent base station.
When such prior art technology is used, the number of mobile stations which can be accommodated by the service area of a single base station is limited to the total number of communication slots that are allocated to the mobile stations, in the case of time division multiplexing, while that number of mobile stations is limited to the total number of frequency channels, in the case of frequency division multiplexing, and is limited by the degree of effectiveness of interference prevention (which is determined by the ratio of the data transfer rate to the spectrum dispersion chip rate) in the case of code division multiplexing. There are limitations on frequency resources, so that there are limitations on the number of channel frequencies and frequency bandwidth which can be allocated to mobile communication systems, and this places an upper limit on the number of mobile stations which can be accommodated by a mobile communication system. Moreover since the service area of a base station and the frequencies or number of TDMA slots which can be used by a base station for communication with mobile stations are fixed, cases can occur in which one of the base stations has communication channels available, while the slots or communication channels of an adjacent base station are completely filled. In the prior art, in such a case, i.e. in which there is communication channel capacity available in the overall system, it may not be possible to achieve communication in some instances due to lack of communication channel capacity in one or more base stations.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the above problems, by providing a mobile communication system having a high efficiency of utilizing communication channel resources.
To achieve the above objective, the present invention provides a mobile communication system whereby each base station includes incoming direction estimation means for estimating the incoming direction of radio waves which are received from a mobile station, to thereby estimate the direction of the mobile station with respect to the antenna of the base station. Based on the results of such estimation, the radiation pattern of the antenna of the base station is formed with a directivity peak which is oriented in the direction of that mobile station by antenna directivity control means. To achieve this, the antenna directivity control means appropriately controls the phase and amplitude of respective transmission/received signals that are supplied to/received from the array elements constituting the array antenna.
The emission of radio waves from a base station towards mobile stations other than those with which communication is being conducted can thereby be suppressed, thus enabling interference with other base stations and mobile stations to be eliminated, and enabling each base station to communicate with the respective mobile stations which are within its service area by using only a low level of transmission power, while enabling the number of communication channel frequencies which are required within the overall mobile communication system to be reduced. That is to say, with a prior art mobile communication system which uses FDM for example, it has been necessary to assign respectively different sets of frequency channels to base stations which are closely adjacent within the system, although identical sets of frequency channels can be assigned to base stations which are spaced sufficiently far apart to eliminate the danger of mutual interference.
In addition, the shaping of the antenna directivity is adaptively performed. That is to say, while a base station is in communication with a specific mobile station, the direction of the mobile station can be estimated during each of successive periods in which a signal is being received by the base station from that mobile station, so that the orientation of the antenna peak can be adaptively changed in accordance with successively estimated directions of that base station, while communication with a mobile station is in progress.
With the present invention, it is possible to utilize a simple linear array antenna (or set of array antennas, disposed to provide 360° of azimuth coverage) at each base station, to obtain the incoming direction of radio waves received from a mobile station, and assume that the (azimuth) direction of the mobile station with respect to the antenna is identical to that incoming direction of radio waves. The direction information thus obtained is then used to orient a corresponding directivity peak of the antenna. With such operation, the antenna directivity is shaped irrespective of the distance between the mobile station and the base station. Such operation provides substantially accurate direction information if the angle of elevation of the mobile station with respect to the base station is relatively small, for example if the mobile station is located at a sufficient distance from the base station.
Alternatively, in order to to achieve greater accuracy of shaping the radiation pattern of the base station, and to thereby obtain greater effectiveness in reducing the danger of interference with communication executed by adjacent base stations, it is possible with the present invention to estimate the actual position of a mobile station with respect to the base station, e.g. with the position expressed as an azimuth angle and line-of-sight distance, and to form a peak of the antenna directivity which is shaped in accordance with that position. In that case, more accurate estimation of mobile station directions can be achieved, and more accurate shaping can be performed of the antenna directivity, to ensure that the directivity peak is of appropriate magnitude for communication with a specific mobile station, while minimizing the danger of inter
Adachi Naoki
Fukagawa Takashi
Hasegawa Makoto
Matsuoka Akihiko
Bost Dwayne D.
Craver Charles R
Matsushita Electric - Industrial Co., Ltd.
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