Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-09-16
2002-01-29
Bost, Dwayne (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C370S335000
Reexamination Certificate
active
06343218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a mobile station and a base station in a mobile communication system with transmission power control, a transmission power control method for mobile stations, and a recording medium containing a program for achieving this transmission power control method.
2. Background Art
In mobile radio systems, a service area is formed by providing a number of radio zones, which are circular areas centered around base stations. For the purposes of covering the service area fully, the base stations are provided so that a plurality of radio zones will overlap at the edges of the radio zones.
Since the radio zones are centered around base stations, the intensity of a desired signal to be received by a mobile station in a service area will be high in the vicinity of the base station but low near the radio zone edges. Since the communication quality will be reduced if an interfering signal is stronger than the desired signal, efforts have been made in existing mobile radio systems to retain the service quality by performing handover to another radio zone capable of achieving better communication quality when a mobile station has moved to the edge of a radio zone.
On the other hand, in CDMA (code division multiple access) systems, transmission power control is performed to always keep the transmission power of mobile stations as low as possible, for the purposes of retaining capacity and quality and reducing interference with other stations. The transmission power control in these mobile stations is achieved by closed-loop control, wherein the transmission power is increased and decreased in accordance with instructions given by the content of a single-bit transmission power control signal (hereinafter referred to as a TPC bit) sent from the base station.
Additionally, in the case of so-called soft handover, the mobile station simultaneously connects to a plurality of connectable base stations, and begins control of the switching between radio zones. At this time, the mobile station detects the TPC bits sent from the plurality of base stations by the above-mentioned closed-loop control, and decides and controls its own transmission power based on the content of the detected TPC bits. Here, an example of the transmission power control during soft handover in a mobile station is shown in FIG.
13
. In the example shown in
FIG. 13
, the transmission power is increased only when the content of the TPC bits from all of the connected base stations gives instructions for a transmission power increase (the value of the TPC bit is “1”), and otherwise, the transmission power is decreased.
However, during soft handover, the mobile station is not capable of receiving the signals from all of the connected base stations with the same quality. That is, there is a possibility of the reception quality of the signal from a certain base station being degraded. Degradations in the signal reception quality from a base station mean an increase in the error rate for transfer of the TPC bit from that base station. As described above, since a substance of the transmission power control of a conventional mobile station is decided by combining the contents of all TPC bits detected by the mobile station, an increase in the error rate for transfer of the TPC bit from one base station will directly lead to an increase in the probability that inappropriate transmission power control will be performed.
Moreover, in the above-described example, wherein the transmission power is increased only when the contents of the TPC bits from all of the connected base stations are “1” (when the TPC bits from all of the connected base stations give instructions for transmission power increase) as shown in
FIG. 13
, the probability that the transmission power will be made smaller than necessary will rise when the error rate for transfer of a TPC bit from a single base station increases. This is due to the fact that if an error arises in a TPC bit from a base station B when the combination of TPC bits sent from a base station A and base station B is “11” (transmission power increase), the reception pattern will become “10”, and will result in a transmission power decrease, whereas if an error arises in the a TPC bit from base station B when the combination of TPC bits sent from base station A and base station B is “00”, “10” or “01” (transmission power decrease), the reception pattern will become “01”, “11” or “00”, and will not always result in a transmission power increase. This effect can be expected to become more pronounced when the number of connected base stations is large.
In the end, as is clear from what is described above, the transmission power control of a conventional mobile station has a problem in that when the reception quality of the signals from any one of the base stations is low, then appropriate power control cannot be performed during soft handover, and the communication quality is reduced.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in view of the above background, and has the object of offering a mobile station and a base station, a transmission power control method for a mobile station, and a recording medium containing a program for achieving this transmission power control method, which are capable of appropriately controlling the transmission power of the mobile station during soft handover, even if the reception qualities of the signals from the connected base stations are not the same.
In order to resolve the above-mentioned problems, in a first aspect, the present invention comprises a transmission power control method for a mobile station simultaneously connected to a plurality of base stations. The method comprises a receiving step for receiving a transmission power control signal from each of said plurality of base stations in said mobile station; a reliability level acquiring step for acquiring a reliability level for each of said plurality of base stations; an object signal acquiring step for determining an object signal from said reliability levels acquired in said reliability level acquiring step and said plurality of transmission power control signals received in said receiving step; a control content deciding step for deciding a control content of the transmission power of said mobile station based on said object signal determined in said object signal acquiring step; and a control step for controlling the transmission power of said mobile station in accordance with the control content decided in said control content deciding step. According to this transmission power control method, the object signal is determined in the mobile station in consideration of not only the plurality of transmission power control signals, but also of the reliability level of each of the plurality of base stations, and the transmission power control is performed on the basis of this object signal. Therefore, the influence of a transmission power control signal for which an error has occurred during transfer can be made small. As a result, transmission power control can be performed with high precision, and the degradation of the communication quality and the degradation of the subscriber capacity can be prevented.
Additionally, in the above-described transmission power control method, it is possible, in said mobile station, to acquire a parameter based on a downward signal from each of said plurality of base stations, and generate a reliability level with respect to each of said plurality of base stations in accordance with said parameter; or in each of said plurality of base stations, to acquire a parameter based on an upward signal from said mobile station, and send said parameter to said mobile station, and in said mobile station, generate a reliability level with respect to each of said plurality of base stations in accordance with the parameter sent from each of said plurality of base stations; or in each of said plurality of base stations, to acquire a parameter based on an upward signal from said mobile station, g
Hagiwara Seiji
Higashi Akihiro
Kaneda Ryusuke
Bost Dwayne
Brinks Hofer Gilson & Lione
Green Miguel D.
NTT Docomo Inc.
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