Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-03-08
2001-10-23
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S561000, C455S273000
Reexamination Certificate
active
06308085
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a distributed antenna system for use in mobile communications, and more particularly to a distributed antenna system wherein a plurality of antenna units are widely distributed in a service area and controlled by a centralized controller. In addition, the present invention relates to a method of controlling the distributed antenna system.
As a method of constructing base stations for mobile communications with use of cellular phones, there has been proposed a method wherein a plurality of antenna units each comprising an antenna and a transmission/reception amplifier unit are provided in a communication service area and controlled by a centralized controller in a centralized manner.
FIG. 1
shows a conventional distributed antenna system. In the conventional distributed antenna system, as shown in
FIG. 1
, antenna units
101
,
102
and
103
are distributed and controlled by a centralized controller
100
. Cables or optical fibers are used to connect the centralized controller
100
and antenna units
101
,
102
and
103
. The centralized controller
100
performs such a control that radio frequencies are assigned for information transmission between the antenna unit
101
,
102
,
103
and terminals
104
in an associated zone Z
1
, Z
2
and Z
3
, and transmission/reception signals are modulated/demodulated. The processing of signals for the antenna units
101
,
102
and
103
is performed independently. With this structure, the control can be effected by the centralized controller
100
in a centralized manner. If a great number of antenna sections are provided, the cost for installation can advantageously be reduced.
In the conventional distributed antenna system, however, no countermeasure has been taken for a multipath, phasing, etc. which are problems at all times in mobile communication of cellular phones, etc. Specifically, in a case where only one antenna unit can be accessed by the terminal side within the service area in the distributed antenna system as shown in
FIG. 1
, communication may be interrupted on a time-axis due to multi-path, phasing, etc. or shifting of terminals.
As has been described above, in the conventional distributed antenna system, no countermeasure is taken for multi-path or phasing which are problems in mobile communications, and the reliability of communication is low.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems and its object is to provide a distributed antenna system which can maintain excellent communication links in a mobile communication environment in which multi-path or phasing is occurring.
In order to achieve the above object, there is provided a distributed antenna system comprising: a plurality of antenna units arranged in a distributed manner such that individual service areas partly overlap one another; and a centralized controller for controlling the plurality of antenna units. The centralized controller comprises, as basic elements, a selection circuit for selecting at least one of the antenna units, and a beam forming circuit for forming a beam by setting desired excitation conditions for the antenna units selected by the selection circuit.
Necessary antenna units alone are chosen in accordance with the condition at the time of communication, and beams can be efficiently formed toward user terminals such as mobile terminals. In addition, interference wave components can be suppressed. Specifically, if an unnecessary antenna is used, electric waves may be radiated in an undesired direction and a third party may be interfered with. Moreover, if a beam is formed in an undesired direction, unnecessary interference waves may be received. These problems do not arise in this invention. Excellent communication links can be maintained in the mobile communication environment in which multi-path or phasing occurs.
The centralized controller may have a plurality of beam forming circuits and form a plurality of transmission beams or reception beams. Thereby, many user terminals can communicate independently at the same time while the cost is limited to a minimum.
In the centralized controller, the choice of antenna units and the formation of beams are performed independently for transmission and reception. Specifically, the centralized controller comprises: a first selection circuit for selecting at least one of the antenna units; a transmission beam forming circuit for forming a transmission beam by setting desired excitation conditions for the antenna unit selected by the first selection circuit; a second selection circuit for selecting at least one of the antenna units; and a reception beam forming circuit for forming a reception beam by setting desired excitation conditions for the antenna units selected by the second selection circuit.
In the mobile communication, the environment of electric wave propagation varies between transmission and reception due to a difference in time and frequency between transmission and reception. However, according to the present invention, since the transmission beam and reception beam are controlled independently for the communication of the same terminal, thus, transmission and reception communications can be always performed in good condition.
The centralized controller may comprise, in addition to the first and second selection circuits, the transmission beam forming circuit and the reception beam forming circuit, a monitor section for activating the transmission beam forming circuit and the reception beam forming circuit at the same frequency and monitoring a reception level of a signal transmitted from the transmission-side antenna unit, in which the transmission beam is formed, and received by the reception-side antenna unit in which the reception beam is formed.
With the above structure, the individual service areas of the respective antenna units can be recognized even in the condition in which the environment of electric wave propagation varies depending on time periods. Based on the recognition, the practically effective individual service areas can be set and the frequency (channel) arrangement for using the same frequency can be designed with a maximum efficiency of use. Thus, there is a great merit in efficiently using the frequency.
The centralized controller may find and store a mutual coupling amount between the transmission-side antenna unit and the reception-side antenna unit on the basis of the reception level monitored by the monitoring section.
Thereby, the mutual coupling amount and the presence/absence of mutual interference between the antenna units can always be stored. When the frequencies and channels are assigned for actual communication, the same frequency and channel are assigned to, for example, non-interfering two antenna units each other on the basis of the stored data. Thus, the frequencies can be reused and there is a greater advantage in efficiently using the frequency resource. In addition, more user terminals can be accommodated in the communication system in which one centralized controller is used as a base station, and crowded communication can be relaxed. In this case, if the mutual coupling amounts stored in the memory is updated periodically, the optimal frequency assignment can be performed according to the environment of electric wave propagation which varies depending on time periods.
Moreover, using the stored mutual coupling amount between the antenna units, each of the first and second select circuits in the centralized controller may select at least one antenna unit, in which the mutual coupling amount is a predetermined value or less. Thereby, a plurality of antenna groups are formed.
With this structure, the antenna groups can be controlled independently, and coupling between antenna groups can be reduced. If each antenna group is operated at the same frequency, different beams can be formed at the same frequency and isolation between beams can be ensured.
Additional objects and advantages of the invention will be
Kabushiki Kaisha Toshiba
Maung Nay
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Trinh Sonny
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