Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-01-14
2001-04-24
To, Doris H. (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S062000, C455S437000
Reexamination Certificate
active
06223036
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital time division mobile communication system having separate time slots for transmission and reception at a mobile station, and more particularly to an adjacent cell monitoring method.
2. Description of the Related Art
As described for example in Japanese Patent Laid-open No. 327139/89, this type of adjacent cell monitoring is performed with the object of realizing a mobile communication method that enables constant optimum connection with a base station without deterioration in transmission quality as a mobile station moves from one zone to another.
FIG. 1
is a block diagram showing the channel switching method in mobile communication of the prior art. Mobile communication exchange
61
is connected to public switch telephone net work
60
, and base stations
62
,
63
, and
64
each having radio zones
65
,
66
, and
67
, respectively, are each connected to mobile communication exchange
61
.
While communicating with base station
63
, mobile station
68
sequentially scans the control channel signals of base station
63
with which it is currently communicating as well as of adjacent base stations
62
and
64
at times other than during the time slots assigned to mobile station
68
, receives signals, measures the reception quality of these signals, selects the optimum base station based on these measurement results, and transmits optimum base station information to base station
63
with which it is communicating. Based on this optimum base station information that it receives by way of base station
63
, mobile communication exchange
61
then switches the base station connected to mobile station
68
.
The above-described prior art has a disadvantage that a certain amount of time is required before the optimum base station is selected.
This delay arises from the necessity of measuring the reception quality of adjacent base stations before the optimum base station can be selected. Reception quality is found from the base station having the highest received signal strength after measuring the received signal strength of adjacent base stations. In order to eliminate the influence of fading, the measurement of received signal strength generally requires taking a plurality of measurements, for example, five measurements, spaced out by measurement intervals and calculating the average value. The number of received signal strength measurements required is therefore the product of the number of base stations in the vicinity and the number of received signal strength measurements per base station. Carrying out received signal strength measurements equal in number to this product in the time intervals outside the time slots assigned to the mobile station is time consuming.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an adjacent cell monitoring method in digital time division mobile communication system that allow a reduction in the time necessary for selecting the optimum base station.
The first mobile station according to the present invention is provided with a voice component effectiveness judging section and a controller. A digital voice signal from a voice A/D converter is resolved into its voice components in a voice component extracting section. As input, the voice component effectiveness judging section takes voice parameters from the voice component extracting section and determines whether or not the voice parameter includes an effective voice component sufficient for transmission to the communicating base station. The output of the voice component effectiveness judging section is transmitted to the controller. If the output includes a message that an effective voice component is included, the controller controls a modulator, a transmitter, and a synthesizer such that voice transmission is performed in the transmission time slot. If the output does not include a message that an effective voice component is not included, the controller effects control such that, in the transmission time slot, the synthesizer tunes to the radio frequency of the control channels of adjacent base stations and the receiver and demodulator measure the signal strength.
According to another embodiment of the present invention, in accordance with a signal indicating the presence or absence of call connection information sent to the communicating base station, the controller similarly effects measurement of received signal strength of adjacent base stations in the transmission time slot if there is no call connection information.
According to another embodiment of the present invention, in accordance with a signal indicating the presence or absence of user data sent to the communicating base station, the controller similarly effects measurement of received signal strength of adjacent base stations in the transmission time slot if there is no user data information.
The present invention can shorten the time required to select the optimum base station by taking advantage of transmission time slots not required for transmitting speech or data to measure the received signal strength of adjacent base stations, thus enabling more rapid switching to an adjacent base station. The reason for this more rapid switching is that the transmission time slot assigned to a mobile station can be used for measuring the received signal strength of adjacent base stations in cases in which the transmission time slot is not being used for transmission of speech or data, thereby allowing completion of the required number of received signal strength measurements in a shorter time.
In addition, the present invention enables an increase in the number of measurements of received signal strength of adjacent base stations per unit of time, thereby enabling a reduction in the influence of fading and an increase in the reliability of measured values of received signal strength. This is because the transmission time slot assigned to a mobile station can be used for measurement of received signal strength of adjacent base stations when the transmission time slot is not being used for transmission, thereby enabling an increase in the number of measurements of received signal strength of base stations per unit of time.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with references to the accompanying drawings which illustrate examples of the present invention.
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patent: 5157661 (1992-10-01), Kanai et al.
patent: 5404573 (1995-04-01), Yabe et al.
patent: 5539748 (1996-07-01), Raith
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NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
To Doris H.
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