Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
1999-07-30
2004-05-25
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S063300, C455S425000, C375S227000
Reexamination Certificate
active
06741837
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an inter-radio communications system interference avoidance method applicable to the case where a plurality of radio communications systems using different frequencies are installed in the same area.
BACKGROUND ART
When a plurality of radio communications systems are installed in the same area, the frequencies assigned to them must be divided to avoid interference between their radio signals. On the other hand, transmitters for performing radio communications cannot perfectly prevent transmitted signals from leaking to the outside of their frequencies, thereby producing leakage power to the frequencies outside their own. This is illustrated in FIG.
1
. As is seen from
FIG. 1
, although the leakage power is much smaller than the total transmission power, it can provide very large interference to adjacent frequencies depending on the locations of base stations and mobile stations. This will be described with reference to FIG.
2
.
In
FIG. 2
, a first radio communications system
110
and a second radio communications system
120
are installed in the same area, and employ adjacent frequencies. A mobile station
114
belonging to the first radio communications system
110
is very close to a base station
122
of the second radio communications system, and transmits to a base station
112
of the first radio communications system
110
which is farther away from it than from the base station
122
of the second radio communications system
120
. The mobile station
114
cannot change its belonging from the first radio communications system
110
to the second radio communications system
120
during its communication.
In this case, the leakage power even from the adjacent frequency brings about very large interference to the base station
122
of the second radio communications system
120
. Because of the interference, the base station
122
of the second radio communications system
120
may be unable to receive transmitted data from a mobile station
124
of the second radio communications system
120
.
In view of this, the conventional radio communications system assigns an unassigned frequency band called a guard band between the frequency bands employed by the two radio communications systems as illustrated in
FIG. 3
, thereby preventing the interference from taking place even in the case as shown in FIG.
2
.
However, frequency resources are limited, and the guard band has a disadvantage of decreasing the frequency utility efficiency. In particular, in broadband radio communications systems such as a CDMA (Code Division Multiple Access) system, the guard bands required become broad, resulting in marked reduction in the frequency utility efficiency. On the contrary, eliminating the guard band will reduce the capacity in terms of the number of subscribers because of the interference.
DISCLOSURE OF THE INVENTION
An object of the present invention is to avoid the inter-radio communications system interference by halting the transmission of a mobile station causing the inter-radio communications system interference rather than by assigning the guard bands.
To accomplish the object of the present invention, there is provided an entire radio communications system containing at least two radio communications systems in one geographical area, each radio communication system including at least one base station and at least one mobile station, and uses different frequencies, in which a mobile station belongs to one of the radio communications systems in a communication mode, and cannot change that radio communications system during the communication mode, wherein the base station comprises means for intentionally transmitting an interfering signal at a frequency different from a frequency assigned to the base station; and the mobile station comprises means for monitoring received signal quality of a downlink channel, and means for halting its transmission when the received signal quality monitored drops below an acceptable level.
Such a configuration makes effective use of the frequencies possible because the interference between the systems is avoidable without the guard band between the frequency bands needed for the conventional radio communications systems.
Generally, the mobile station in the radio communications system has a function to terminate its communication when communication quality is degraded. Hence, the frequencies can be effective by only adding to the base station a function of transmitting an interfering signal, without adding any special control function.
The transmission of the interfering signal from the base station can be carried out by utilizing leakage power or by equipping an interfering signal transmitter.
The base station may comprise a receiver for measuring a received signal level at the adjacent frequency; and transmit the interfering signal at the adjacent frequency only when the uplink received signal level exceeds an acceptable level.
With such a configuration, since the base station performs its transmission at the adjacent frequency only when necessary, the downlink interference to the adjacent radio communications system is reduced.
Furthermore, since the base station monitors directly the frequency band causing the interference, the accuracy of the estimation of the interference is improved. As a result, the possibility of undue termination of the communication, or the possibility of causing large interference is reduced.
The base station can measure the uplink interference level at the receiving frequency band, and transmit the interfering signal at the adjacent frequency only when the uplink interference level exceeds an acceptable level.
This configuration can reduce the downlink interference to the radio communications system using the adjacent frequency because the base station carries out its transmission at the adjacent frequency only when necessary, and can obviate the necessity of providing the base station with any additional receiver because the base station makes a decision as to whether to start or terminate the transmission of the interfering signal by measuring the interference level at the frequency assigned to the base station.
According to a second aspect of the present invention, there is provided a mobile station in an entire radio communications system containing at least two radio communications systems in one geographical area, each of which includes at least one base station and at least one mobile station, and uses different frequencies, in which a mobile station belongs to one of the radio communications systems in a communication mode, and cannot change that radio communications system during the communication mode, wherein the mobile station measures a signal level of a received signal at a frequency adjacent to its own assigned frequency, and halts its transmission when the received signal level exceeds an acceptable level.
This configuration can prevent the downlink interference from being increased because the base station does not transmit any interfering signal.
In addition, since the mobile station measures the level of the adjacent frequency in a straightforward manner, the accuracy of estimating the effect of the interference increases, and the possibility of unduly terminating the communication is reduced.
The mobile station can comprise a receiver for measuring a received signal level at the adjacent frequency, and terminate its transmission when the received signal level exceeds an acceptable level.
The mobile station can also measure the received signal level at an adjacent frequency by switching its receiving frequency when reception is not required in a standby mode or communication mode, and halt its transmission when the received signal level exceeds the acceptable level.
This configuration can obviate the receiver for measuring the received signal level at the adjacent frequency, making it possible to reduce the size of the mobile station.
REFERENCES:
patent: 5430761 (1995-07-01), Bruckert et al.
patent: 5437054 (1995-07-01), Rappaport et al.
pa
Hata Masafumi
Ishii Minami
Ishikawa Yoshihiro
Nakano Etsuhiro
Onoe Seizo
Brown & Raysman Millstein Felder & Steiner LLP
Chin Vivian
Craver Charles
NTT Mobile Communications Network Inc.
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