Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-07-21
2001-02-27
Bost, Dwayne D. (Department: 2744)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S440000, C455S442000, C370S331000, C370S332000
Reexamination Certificate
active
06195551
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cellular communication system, more particularly, to a method for controlling an idle handoff in a cellular communication system.
2. Prior Art
In a cellular communication environment, when a mobile station moves from a first cell to a second cell, it is necessary to transfer the mobile station's RF communication link with the first cell to the second cell. This operation is commonly called handoff. An idle handoff occurs when a mobile station such as a vehicle mounted telephone, a portable telephone, or a personal communication system handset has moved from the coverage area of one base station into the coverage area of another base station during the mobile station idle state.
If the mobile station detects a pilot channel signal from another base station, that is sufficiently stronger than that of the current base station, the mobile station determines that an idle handoff should occur. In the mobile station idle state, the mobile station continuously searches for the strongest pilot channel signal on the current code division multiple access (CDMA) frequency assignment whenever it monitors the paging channel. If the mobile station determines that one of the neighbor set or remaining set pilot channel signals is sufficiently stronger than the pilot channel of the active set, the mobile station should perform an idle handoff.
U.S. Pat. No. 5,436,956 (issued to Hirofumi Shiotsuki et al. on Jul. 25, 1995) discloses a method and arrangement for reducing the number of handoff requests in a cellular mobile communications system.
FIG. 1
illustrates a conventional idle handoff controlling method in a cellular communication system. In step S
101
, when a user powers on a mobile station(not shown), the mobile station searches for a first pilot channel having the strongest strength on a current CDMA frequency assignment transmitted from one of the plurality of base stations as an active base station and measures a strength A of the first pilot channel searched. That is, the radios of received pilot energy per chip, Ec, to total received spectral density(noise and signals), It. That is, A=Ec/It.
In step S
102
, the mobile station searches for a second pilot channel transmitted from one of the plurality of neighbor base stations (not shown) and measures a strength B of the second pilot channel searched. B=Ec1/It1. In step S
103
, the mobile station subtracts the first pilot channel strength A with respect to the active base station from the second pilot channel strength B with respect to the neighbor base station which are stored in the memory
206
to obtain a strength difference D. That is, D=B−A.
In step S
104
, the mobile station judges whether or not the strength difference D is greater than a threshold value C
TH
between 2dB and 3dB. As the result of the judgement in step S
104
, when the strength difference D is greater than the threshold value C
TH
, the mobile station starts to search for and monitor a paging channel of the neighbor base station so that the mobile station performs an idle handoff(step S
105
). Thus, the mobile station can communicate with other mobile stations (not shown) located in a service area of the neighboring base station. When it is judged that the strength difference D is less than or equal to the threshold value C
TH
, the routine returns to step S
101
and the above process with respect to other neighbor base stations except the neighbor base station already processed repeats.
In the conventional idle handoff controlling method, the threshold value is a fixed value from 2dB to 3dB. When the second pilot channel transmitted from one of the plurality of base stations is momentarily received stronger than the first pilot channel transmitted from an active base station, even when the strength of the first pilot channel is sufficiently strong, the mobile station should perform the idle handoff.
Accordingly, waste of a battery of the mobile station increases and arrival rate of the mobile station lowers due to frequent idle handoff. When the mobile station moves to another area, the mobile station should periodically provide the information about the position thereof to the base station in order to receive a terminated call from a base station. Thus, a load of a reverse control channel is increased and communication efficiency of a reverse control channel becomes lower. Particularly, when a paging zone is changed, arrival rate of the mobile station lowers due to frequent idle handoff. It is therefore highly desirable to reduce the number of handoffs in order to provide the service of good quality.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention, for the purpose of solving the above mentioned problems, to provide an idle handoff controlling method for effectively reducing the number of idle handoff processes in a cellular communication system.
In order to attain the object, according to the present invention, there is provided an idle handoff controlling method in a cellular mobile communication system, said method comprising the steps of:
a) searching a first pilot channel having the strongest strength transmitted from one of a plurality of base stations as an active base station and measuring a strength of the first pilot channel;
b) calculating a variable threshold value based on the first pilot channel strength measured in step a);
c) monitoring a paging channel having a neighbor list of the active base station having a plurality of neighbor base stations in synchronization with the first pilot channel;
d) measuring a strength of a second pilot signal transmitted from one of the plurality of neighbor base stations included on the neighbor list;
e) subtracting the first pilot channel strength from the second pilot channel strength to obtain a strength difference;
f) judging whether the strength difference is greater than the variable threshold value; and
g) controlling performance of an idle handoff according to the judgement result of step f).
Also, there is provided an idle handoff controlling method in a cellular communication system, said method comprising the steps of:
i) searching a first pilot channel having the strongest strength transmitted from one of the plurality of base stations as an active base station and measuring a strength of the first pilot channel;
ii) monitoring a paging channel having a neighbor list of the active base station which has a plurality of neighbor base stations in synchronization with the first pilot channel;
iii) measuring a strength of a second pilot signal transmitted from one of the plurality of neighbor base stations in the neighbor list neighboring the active base station;
iv) subtracting the first pilot channel strength from the second pilot channel strength to obtain a strength difference;
v) judging whether the strength difference is greater than a threshold value;
vi) judging whether a state that the strength difference is greater than the threshold value lasts for a predetermined time interval when the strength difference is greater than the threshold; and
vii) controlling performance of an idle handoff according to a judgement result of step vi).
Also, there is provided an idle handoff controlling method, said method comprising the steps of:
(A) searching a first pilot channel having the strongest strength transmitted from one of the plurality of base stations as an active base station and measuring a strength of the first pilot channel;
(B) monitoring a paging channel having a neighbor list of the active base station which has a plurality of neighbor base stations in synchronization with the first pilot channel and storing the neighbor list;
(C) measuring a strength of a second pilot signal transmitted from one of the plurality of neighbor base stations in the neighbor list neighboring the active base station;
(D) subtracting the strength of the first pilot signal from the strength of the second pilot signal to obtain a strength difference;
(E) judging wheth
Kim Dong-Woo
Kim Kyu-Nam
Banner & Witcoff , Ltd.
Bost Dwayne D.
Davis Temica M.
Shinsegi Telecomm, Inc.
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