Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02489812 1998-06-03
SPECIFICATION
TITLE OF THE INVENTION
MOBILE RADIO COMMUNICATION SYSTEM, MOBILE
STATION, AND METHOD FOR CONTROLLING DIVERSITY
HAND-OVER BRANCH
TECHNICAL FIELD
The present invention relates to a branch
candidate selecting method in a mobile station in
the case where the mobile station detects a
plurality of addition branch candidates and deletion
branch candidates, and to a diversity handover
branch control method on a network side in executing
diversity handover.
BACKGROUND ART
Recently, code division multiple access (CDMA)
technology has been proposed as one of promising
radio transmission methods for implementing
multimedia communications in the next generation
mobile communication network systems. A CDMA system
carries out diversity handover (DHO) that
- 1 -
CA 02489812 1998-06-03
establishes multiple communication links (branches)
between a mobile station and a plurality of base
stations while the mobile station is moving near a
boundary of a radio area, and communicates by
performing signal combining (selection combining) on
the multiple communication links. In the diversity
condition, it is possible to increase a radio
capacity by controlling such that the mobile station
and the base stations can communicate at minimum
transmission power (transmission power control).
Furthermore, it is possible in the diversity
condition to eliminate instantaneous chopping during
handover, which can occur in the conventional time
division multiple access (TDMA).
Establishing a new branch in the DHO is
specifically referred to as "addition DHO" in the
DHO, and deleting a communication branch not
contributing to the communications in the diversity
condition is specifically referred to as "deletion
DHO" in the DHO. To carry out the addition DHO and
deletion DHO, the mobile station normally detects a
candidate of the addition DHO (called "addition DHO
candidate" or "addition branch candidate"), and a
candidate of the deletion DHO (called "deletion DHO
candidate" or "deletion branch candidate").
Detecting an addition or deletion branch candidate
- 2 -
CA 02489812 1998-06-03
by monitoring a radio condition (transmission loss,
for example) of a perch in the current sector or
peripheral sectors, the mobile station notifies the
network side of the detected candidate. The network
side performs the DHO (addition DHO or deletion DHO)
based on the notified candidate. The term "network
side" usually refers to a switching center or a
control center of base stations, it is possible to
provide this function to the base stations.
The mobile station communicates with the base
stations using individual radio links (radio
branches) associated with the base stations. A
switching center comprises cable links (cable
branches) connecting it with the base stations that
are communicating with the mobile station, and
carries out, with a handover .(HO) processor or a
diversity handover trunk (DHT), the selection
combining of the signals sent from the base
stations. The fundamental operation of the
diversity handover branch is disclosed in Japanese
Patent Application Laid-open No. 9-508773 (1997),
and network configurations and control methods of
the diversity handover trunks are disclosed in
Japanese Patent Application No. 8-348900 (1996).
Because of hardware implementation or the like,
there are provided an upper limit to the number of
3 -
CA 02489812 1998-06-03
radio branches (a maximum radio branch number) that
the mobile station can establish simultaneously, and
an upper limit to the number of cable branches (a
maximum cable branch number) that the DHT in the
switching center can connect or process
simultaneously. The upper limit to the number of
communication branches (the maximum communication
branch number) that can be established in the
diversity condition equals the smaller one of the
maximum numbers of the radio branches and cable
branches. In ordinary systems, it is designed that
the maximum radio branch number becomes equal to the
maximum communication branch number to make
effective use of radio resources by giving priority
to them.
However, conventional papers (for example,
Shimizu, et al. "Handover equipment and control
method in next generation mobile communication
systems", General assembly of the Institute of
Electronics, Information and Communication Engineers
of Japan, 1997) handle the subject only under the
assumption that the control of branches to be added
or deleted is limited to a single branch, and do not
handle simultaneous control of a plurality of
addition branches and deletion branches. It is not
- 4 -
CA 02489812 1998-06-03
specified in ITU-T recommendation Q.FIF version 6,
as well.
As mentioned above, since the control of the
branches to be added and deleted is carried out on
one by one basis in the prior art, N times of
control is required in principle to control N
branches. However, the mobile station can detect a
plurality of deletion branch candidates and addition
branch candidates at the same time, because their
detection depends on the ambient radio condition.
In such a case, a number of times of similar
control operations are repeated between the mobile
station and the switching center, which is not only
inefficient, but also takes an extra time for the
control until the entire handover control is
completed.
Taking account of the addition DHO of a single
branch, the prior art sets the maximum cable branch
number at the maximum radio branch number plus one.
Thus, the network side can prepare the branches in
cable sections by the number greater than the
maximum radio branch number by one. This enables a
simple switching operation in the radio sections to
complete the addition DHO by adding one cable branch
from among the prepared cable branches without
deleting the communication branch even in the case
- 5 -
CA 02489812 1998-06-03
where one branch is added to the maximum number of
branches.
However, such a method that follows the prior
art, in which the maximum cable branch number is set
at the number greater than the maximum radio branch
number by one, has a problem of impairing effective
control because of the network side control repeated
by the number of addition branch candidates.
Furthermore, no prior art takes account of handling
any addition branch candidates that have not been
prepared in the cable section, even though they have
higher DHO priority than the communication branches,
because the control unit is for a single branch and
the maximum cable branch number is limited.
DISCLOSURE OF THE INVENTION
Therefore, the present invention is implemented
to solve the foregoing problems. An object of the
present invention is to provide a branch candidate
selecting method in a mobile station and a control
method of diversity handover branches on a network
side, considering a maximum cable branch number and
a maximum radio branch number of the mobile station
in the case where the mobile station detects a
- 6 -
CA 02489812 1998-06-03
plurality of addition branch candidates and deletion
branch candidates.
In the first aspect of the present invention,
there is provided a mobile communication system
comprising a mobile station, a base station
connected to the mobile station, and a switching
center connected to the base station, wherein
the mobile station notifies the switching center
of information on one or more addition branch
candidates between the mobile station and the base
station, and of information indicative of precedence
of the addition branch candidates; and
the switching center performs handover control
in accordance with the information notified.
Here, information transmitted from the mobile
station to the switching center may further include
information on one or more communicating branches
between the mobile station and the base station.
The switching center may establish a
communication branch between the mobile station and
the switching center using information on one or
more communicating branches between the mobile
station and the base station, the transmitted
information on one or more addition branch
candidates between the mobile station and the base
- 7 -
CA 02489812 1998-06-03
station, and the information on the precedence of
the addition branch candidates.
The switching center may establish, when a sum
total of a number of communicating branches and a
number of the addition branch candidates exceeds a
maximum radio branch number simultaneously
establishable in communications between the mobile
station and the base station, a communication branch
in order of precedence up to a maximum cable branch
number that can be processed simultaneously by the
switching center.
In the second aspect of the present invention,
there is provided a mobile station of a mobile
communication system comprising the mobile station,
a base station connected to the mobile station, and
a switching center connected to the base station,
wherein
information transmitted from the mobile station
to the switching center includes information on one
or more deletion branch candidates between the
mobile station and the base station.
In the third aspect of the present invention,
there is provided a mobile communication system
including a mobile station, a base station connected
to the mobile station, and a switching center
connected to the base station, wherein
- 8 -
CA 02489812 1998-06-03
the switching center creates settings for
deleting one or more communicating branches.
In the fourth aspect of the present invention,
there is provided a mobile station of a mobile
communication system including the mobile station, a
base station connected to the mobile station, and a
switching center connected to the base station,
wherein
the mobile station notifies the switching center
of information on one or more addition branch
candidates between the mobile station and the base
station, and of information indicative of precedence
of the addition branch candidates.
Here, the mobile station may notify, while
communicating with the base station using a maximum
number of radio branches simultaneously
establishable, the switching center of addition of
the addition branch candidates, when precedence of
an addition branch candidate to be added exceeds, by
an amount of a predetermined threshold value,
precedence of a communicating branch with lowest
precedence.
Information transmitted from the mobile station
to the switching center may further include
information on one or more communicating branches
between the mobile station and the base station.
9 -
CA 02489812 1998-06-03
In the fifth aspect of the present invention,
there is provided a diversity handover branch
control method in a mobile communication system
including a mobile station, a base station connected
to the mobile station, and a switching center
connected to the base station, wherein
information transmitted from the mobile station
to the switching center includes information on one
or more deletion branch candidates between the
mobile station and the base station.
In the sixth aspect of the present invention,
there is provided a diversity handover branch
control method, in which a mobile station detects
one or more addition branch candidates constituting
handover candidates in communications between the
mobile station and a base station connected to the
mobile station, and notifies a switching center
connected to the base station of the addition branch
candidates, wherein
information transmitted from the mobile station
to the switching center includes information on one
or more addition branch candidates between the
mobile station and the base station, and information
indicative of precedence of the addition branch
candidates.
- 10 -
CA 02489812 1998-06-03
Here, the information transmitted from the
mobile station to the switching center may further
include information on one or more communicating
branches between the mobile station and the base
station.
The information indicative of precedence may be
an order of arrangement of information on the
communicating branches and information on the
addition branch candidates.
The information indicative of precedence may
consist of numerals representing information on the
communicating branches and information on the
addition branch candidates.
The information indicative of precedence may be
an order of arrangement of information on the
addition branch candidates.
The order of arrangement may be a decreasing
order of transmission losses.
The information indicative of precedence may
consist of numerals representing information on the
addition branch candidates.
The switching center may establish the
communication branches between the mobile station
and the switching center using information on one or
more communicating branches between the mobile
station and the base station, transmitted
- 11 -
CA 02489812 1998-06-03
information on the one or more addition branch
candidates, and information indicative of precedence
of the addition branch candidates.
The switching center may establishe, when a sum
total of a number of communicating branches and a
number of the addition branch candidates exceeds a
maximum radio branch number simultaneously
establishable in communications between the mobile
station and the base station, a communication branch
in order of precedence up to a maximum cable branch
number that can be processed simultaneously by the
switching center.
The maximum cable branch number may be greater
than the maximum radio branch number by N, where N
is an integer equal to or greater than one.
The mobile station may make a decision of the
addition branch candidates again and notify the
switching center of the addition branch candidates,
when a total sum of a communicating branch number
and an addition branch number exceeds the maximum
cable branch number, and hence the addition branch
candidates are not added because of restrictions on
an upper limit of the maximum cable branch number.
The switching center may store, when the
addition branch candidates are not added because of
the upper limit of the maximum cable branch number,
- 12 -
CA 02489812 1998-06-03
branch candidates that cannot be added because of
the upper limit of the maximum cable branch number,
and autonomously carries out control.
In the seventh aspect of the present invention,
there is provided a mobile communication system
including a mobile station, a base station connected
to the mobile station, and a switching center
connected to the base station, wherein
information transmitted from the mobile station
to the switching center includes information on one
or more deletion branch candidates between the
mobile station and the base station.
In the eighth aspect of the present invention,
there is provided a diversity handover branch
control method in a mobile communication system
comprising a mobile station, a base station
connected to the mobile station, and a switching
center connected to the base station, wherein
the switching center creates settings for
deleting one or more communication branches.
In the ninth aspect of the present invention,
there is provided a diversity handover branch
control method in a mobile communication system
including a mobile station, a base station connected
to the mobile station, and a switching center
connected to the base station, wherein
- 13 -
CA 02489812 1998-06-03
the mobile station autonomously creates settings
for deleting one or more communication branches.
In the tenth aspect of the present invention,
there is provided a diversity handover branch
control method, in which a mobile station detects
one or more communication branches constituting
handover candidates, and notifies a switching center
of the communication branches, wherein
the mobile station autonomously deletes one or
more communication branches, and subsequently
notifies the switching center of the deleted
branches via a remaining communication branch.
In the eleventh aspect of the present invention,
there is provided a diversity handover branch
control method, in which a mobile station detects
one or more communication branches constituting
handover candidates, wherein
the mobile station autonomously deletes one or
more communication branches, and subsequently a
switching center, which is connected with the mobile
station through a base station, deletes a
corresponding cable branches by detecting
disconnection of the radio branch.
In the twelfth aspect of the present invention,
there is provided a diversity.handover branch
control method, in which a mobile station detects
- 14 -
CA 02489812 1998-06-03
one or more addition branch candidates constituting
handover candidates in communications between the
mobile station and a base station connected to the
mobile station, and notifies a switching center
connected to the base station of the addition branch
candidates, wherein
the mobile station does not notify, when a
communicating branch number equals a simultaneously
establishable maximum radio branch number between
the mobile station and the base station, the
switching center of information on addition branch
candidates that are unlikely to be added in
diversity handover.
In the thirteenth aspect of the present
invention, there is provided a diversity handover
branch control method, in which a mobile station
detects one or more addition branch candidates
constituting handover candidates in communications
between the mobile station and a base station
connected to the mobile station, and notifies a
switching center connected to the base station of
the addition branch candidates, wherein
the mobile station notifies, when a sum total of
a communicating branch number and an addition branch
candidate number is equal to or less than a
simultaneously establishable maximum radio branch
- 15 -
CA 02489812 1998-06-03
number between the mobile station and the base
station, the switching center of the addition branch
candidates.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram illustrating an
embodiment of a diversity handover branch control
method in accordance with the present invention;
Fig. 2 is a diagram illustrating images of
branch connection and release on a mobile station
side and a network side in respective DHO
operations;
Fig. 3 is a diagram illustrating images of an
addition DHO threshold value and a deletion DHO
threshold value;
Fig. 4A is a diagram showing a format of
addition information parameters;
Fig. 4B is a diagram showing a format of
deletion information parameters;
Fig. 5 is a diagram illustrating an image of the
DHO performance in terms of a threshold value;
Fig. 6 is a diagram illustrating relationships
between the branch numbers on a network side;
- 16 -
CA 02489812 1998-06-03
Fig. 7 is a flowchart illustrating the details
of handover trigger signal transmission algorithm in
a mobile station;
Fig. 8 is a diagram illustrating an example, in
which no addition branch candidate is notified
during maximum radio branch communications;
Fig. 9A is a diagram illustrating an oscillation
inhibiting threshold value in the case where the
addition branch candidate is added;
Fig. 9B is a diagram illustrating an oscillation
inhibiting threshold value in the case where no
addition branch candidate is added;
Fig. 10 is a flowchart illustrating the details
of DHO performance algorithm in a network;
Fig. 11 is a diagram illustrating branches for
activating a DHO sequence;
Fig. 12 is a diagram illustrating the
relationship between Figs. 12A, 12B and 12C linked
in this order;
Fig. 12A is a diagram illustrating a DHO
processing sequence when the radio condition as
illustrated in Fig. 11 takes place in a mobile
station;
Fig. 12B is a diagram illustrating the DHO
processing sequence when the radio condition as
- 17 -
CA 02489812 1998-06-03
illustrated in Fig. 11 takes place in the mobile
station;
Fig. 12C is a diagram illustrating the DHO
processing sequence when the radio condition as
illustrated in Fig. 11 takes place in the mobile
station;
Fig. 13 is a diagram illustrating an example of
candidates that cannot be added because of
restrictions on a maximum cable branch number;
Fig. 14 is a diagram illustrating a deletion
sequence;
Fig. 15 is a diagram illustrating a deletion
sequence; and
Fig. 16 is a diagram illustrating a deletion
sequence.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention will now be described with
reference to the accompanying drawings.
Fig. 1 is a schematic diagram illustrating an
embodiment of a diversity handover branch control
method in accordance with the present invention.
In Fig. 1, a mobile station (MS) 20 is a device
such as a mobile phone and a mobile information
terminal, which has radio communication functions,
- 18 -
CA 02489812 1998-06-03
and base stations (BS's) 10, 14 and 16 are radio
stations that communicate with the mobile station
20. The mobile station communicates with the base
stations 10, 14 and 16 at first. Mobile services
switching center (MSC) 30, 32 or 34, which is
connected with one of the base stations 10, 12, 14,
16 and 18 through a cable, has base station control
functions that perform radio control of the base
stations 10 and others, and a paging control
function that provides the mobile station 20 and
others with communication services through the base
stations 10 and others. It will be needless to say
that the mobile switching center 30, 32 or 34 can be
connected with the base station 10, 12, 14, 16 or 18
through fixed radio channels instead of the cable.
One mobile switching center can handle a plurality
of base stations. Although the base station 10 is
connected double through cable channels to both the
mobile services switching centers 30 and 32 in Fig.
1, this is for the purpose of load distribution or
switching between operating and standby systems, and
each base station is connected to one of the mobile
services switching centers during a single
communication term. When the mobile station 20
moves to the area of the mobile station 22, and
acquires quality communication condition with the
- 19 -
CA 02489812 1998-06-03
base stations 12 and 18, the base stations 12 and 18
each become an addition branch candidate. In this
case, if the radio condition between the mobile
station 20 and the base stations 10 and 14
deteriorates, the base stations 10 and 14 each
become a deletion branch candidate. Thus, because
the addition branch candidate is present, it does
not necessarily follow that the deletion branch
candidate is present. The mobile services switching
centers 30, 32 and 34 are interconnected through a
trunk circuit network.
Next, types of control of the DHO the present
invention employs will be described.
The DHO is roughly divided into the addition
DHO, deletion DHO and addition deletion DHO which is
a special case of the addition DHO. The addition
DHO is one that adds a new branch candidate, whereas
the deletion DHO is one that deletes a branch
candidate under communications which does not
contribute to any communications. Control
procedures of these DHO will now be described.
(Addition DHO]
Fig. 2 illustrates images of the branch
connection and release on the mobile station side
and network side in the respective DHO operations.
- 20 -
CA 02489812 1998-06-03
The radio branch connection and release image of
the addition DHO in Fig. 2 indicates that a new
radio branch 52 is added at a time 60 in the
presence of a communicating branch 50. The cable
branch connection and release image of the addition
DHO indicates that a new cable branch 54 is added.
In the branch control sequence in the addition DHO,
the addition (cable) branch 54 comes first, and then
the addition (radio) branch 52.
The mobile station monitors radio conditions
(for example, monitors transmission losses on the
perch) of peripheral sectors, and selects addition
branch candidates from among the branches that meet
the addition branch candidate decision conditions,
that is, the mobile station's detection conditions
of the addition branch candidate.
Fig. 3 shows an image of an addition DHO
threshold value and a deletion DHO threshold value.
In Fig. 3, the vertical axis indicates the
transmission loss level, and the horizontal axis
represents the distance the mobile station travels.
As shown in Fig. 3, when the mobile station
moves from left to right on the horizontal axis and
reaches the DHO area, it enters the diversity
condition, and communicates through two branches at
the same time. During this state, the handover (HO)
- 21 -
CA 02489812 1998-06-03
is carried out. The mobile station is communicating
through one branch on the left-hand side of the DHO
area. Thus, one addition branch candidate takes
place when the mobile station enters the DHO area
during one branch communications, and one deletion
branch candidate appears when it passes through the
DHO area to the right-hand side during the two
branch communications. The mobile station detects
the addition and deletion branch candidates in
accordance with the difference between the HO
(handover) source BS transmission loss and the HO
destination BS transmission loss (addition/deletion
branch candidate decision conditions). If the
difference becomes smaller than the addition DHO
threshold value (meets the addition branch candidate
decision condition), the mobile station detects the
addition branch candidate, whereas if the difference
becomes greater than the deletion DHO threshold
value (meets the deletion branch candidate decision
condition), it detects the deletion branch
candidate. In both the DHO operations (the addition
and deletion DHO operations), the least transmission
loss among the branches is used as a reference HO
source BS transmission loss during communications
through a plurality of communication branches. The
deletion DHO threshold value is made greater than
- 22 -
CA 02489812 1998-06-03
the addition DHO threshold value, so that a
difference (hysteresis) is provided to the two
threshold values, thereby preventing the deletion
DHO branch from being added soon again depending on
changes in the radio conditions.
The mobile station notifies the network of both
the addition branch candidates and communicating
branches in such a manner that they are arranged in
ascending order of the transmission loss, or in a
given order with information indicative of the order
of precedence, and are added to addition information
parameters in a handover trigger signal. The
deletion branch candidates, it there is any, are
also notified in a similar manner in the form of
deletion information parameters.
It is possible for the mobile services switching
center to acquire information about the
communicating branches, and this will make it
unnecessary for the mobile station to transmit the
information on the communicating branches to the
mobile services switching center.
The information indicative of the order of
precedence may be the foregoing arranged orders of
the transmission losses of the addition branch
candidates, or their absolute values or relative
values. For example, values indicative of the
- 23 -
CA 02489812 1998-06-03
lowness of the transmission losses can be
transmitted in connection with the information about
the branches independently of the arranged orders.
Fig. 4A illustrates an example of the format of
the addition information parameters, and Fig. 4B
illustrates an example of the format of the deletion
information parameters.
In Fig. 4A, the communicating visitor location
sector number indicates the number of sectors in DHO
communications when the mobile station sends the
handover trigger signal; the addition DHO candidate
sector number indicates the number of sectors that
can be added newly as the DHO candidates; a base
station number indicates the number of a base
station in DHO communications with the mobile
station, or that of a base station of an addition
branch candidate; a sector number indicates the
number of a sector within the service area of the
base station; a perch channel received SIR indicates
the received SIR of a broadcasting control channel;
and a perch channel transmission power level
indicates the transmission power level of the
broadcasting control channel. In the parameter
list, sets of the base station number, sector
number, perch channel received SIR and perch channel
transmission power level are repeated by the number
- 24 -
CA 02489812 1998-06-03
of times of the sum total of the communicating
visitor location sector number and the addition DHO
candidate sector number.
In Fig. 4B, the deletion DHO candidate sector
number indicates the number of sectors of the DHO
candidates that can be newly deleted, and sets of a
base station number and a sector number are repeated
by the number of times of the deletion DHO candidate
sector number as in Fig. 4A.
Fig. 5 illustrates a DHO performance image in
terms of the threshold values.
In Fig. 5, the highest priority communicating
branch is a branch 110, and the next highest one is
a branch 112. Threshold values 120 and 122 are
based on the highest priority branch 110 in the
communicating branches. The threshold value 120
designates the deletion DHO threshold value, and the
threshold value 122 designates the addition DHO
threshold value. The network side extracts branches
in order of the addition DHO precedence (in order of
the branches 114, 116 and 118) by the number of
branches the network side can handle, considering
the number of branches in communications at present,
and carries out the addition DHO. It is clear that
since the addition DHO branch candidate 114 has a
lower transmission loss than the communicating
- 25 -
CA 02489812 1998-06-03
branch 110, it satisfies the addition branch
decision conditions. Even the branch 116, which has
a greater transmission loss than the branch 110 with
a minimum transmission loss among the communicating
branches, can be considered to have a higher
precedence than the branch 118. In other words, the
high priority means that the branch is given higher
precedence in the addition processing.
The branch candidate selection by the mobile
station in accordance with the present invention
means that the mobile station carries out its
control such that it does not notify the network
side of the candidates that are unlikely to be
subjected to the addition DHO among the addition
branch candidates detected by the mobile station.
[Deletion DHO]
The radio branch connection and release image of
the deletion DHO in Fig. 2 indicates that a radio
branch 72 is deleted at a time 80 in the presence of
a communicating branch 70. The cable branch
connection and release image of the deletion DHO
indicates that a cable branch 74 is deleted. In the
branch control sequence in the deletion DHO, the
deletion (radio) branch 72 is deleted first, and
then the deletion (cable) branch 74 is deleted.
- 26 -
CA 02489812 1998-06-03
The mobile station monitors the radio conditions
(for example, monitors the transmission losses on
the perch) of the communicating sectors, and selects
all the branches that meet the deletion branch
candidate decision conditions as the deletion DHO
candidates. In the deletion DHO, the DHO precedence
is not considered. The deletion DHO candidates are
deleted as soon as they are detected, because they
do not contribute to the communications. The mobile
station notifies the network side of the deletion
DHO candidates by placing them into the deletion
information parameters in the handover trigger
signal. The deletion information parameters include
the deletion DHO sector number, and the sets of the
base station number and sector number which are
repeated by the number of times of the deletion DHO
sector number (see, the deletion information
parameter format of Fig. 4B). As illustrated in
Fig. 5, the network side carries out the deletion
DHO, and deletes the deletion DHO candidates, the
branch 113, for example. Alternatively, since the
deletion DHO candidates are sure to be deleted when
detected, the mobile station can autonomously delete
them and notify the network side of that.
[Addition deletion DHO]
- 27 -
CA 02489812 1998-06-03
The addition deletion DHO is one of the addition
DHO operations based on the restrictions on the
maximum radio branch number, and is activated when
the sum total of the communicating branches and
addition branches exceeds the maximum radio branch
number. To achieve the addition deletion DHO
effectively, the maximum cable branch number is set
greater than the maximum radio branch number.
Higher priority branches are added up to the maximum
cable branch number in order of decreasing
precedence in the addition deletion DHO.
Fig. 6 illustrates relationships between these
branch numbers seen from the network side.
As illustrated in Fig. 6, a (transitional) cable
branch number 126, which is the sum total of the
communicating branch number 128 and the addition
branch number 127, exceeds the maximum radio branch
number 125. The cable branches corresponding to the
excess, that is, the (transitional) cable branch
number 126 - the maximum radio branch number 125 = M
cable branches, are provided transitionally for
carrying out effective addition DHO. The network
side eventually deletes M branches in order of
increasing precedence (in order of decreasing
transmission loss, for example) within the
(transitional) cable branches, inclusive of
- 28 -
CA 02489812 1998-06-03
communicating branches, where M is equal to or less
than N, where N equals the maximum cable branch
number 124 - the maximum radio branch number 125.
In the radio section, addition of the radio branches
and switching of them are carried out in response to
the finally selected cable branches. It is also
possible to take such a control method that omits
the addition of those candidates which are most
likely to be deleted because of their lower
precedence than the communicating branches even
though they are added as the cable branches.
The radio branch connection and release image of
the addition deletion DHO in Fig. 2 indicates that a
new branch 92 is added in the presence of branches
90 and 91 at a time 100, the branch 91 is deleted by
switching at a time 102, and then a branch 93 is
added by switching after the time 102. The point of
intersection of the time 102 and the branch 93 is
represented by an open circle because the maximum
radio branch number is set at three. On the other
hand, the cable branch connection and release image
indicates that cable branches 96 and 98 are added,
and a cable branch 94 is deleted. The branch
control sequence in the addition deletion DHO takes
place in order of (1) the addition of the branches
96 and 98; (2) addition of the branch 92; (3)
- 29 -
CA 02489812 1998-06-03
deletion of the branch 91 by switching; (4) addition
of the branch 93 by switching; and (5) deletion of
the branch 94.
Fig. 7 is a flowchart illustrating the details
of handover trigger signal transmission algorithm in
the mobile station.
In Fig. 7, the mobile station monitors the radio
conditions of its current sector and peripheral
sectors to detect addition branch candidates and
deletion branch candidates at step S10. The mobile
station places the communicating branches and
addition branch candidates into the addition
information parameters in the handover trigger
signal, and the deletion branch candidates into the
deletion information parameters in the same signal.
The mobile station sets the addition information
parameters in the following conditions, and sends
them through steps S20-S90.
When one or more deletion branch candidates are
present (step S20), the mobile station places all
the communicating branches and addition branch
candidates into the addition information parameters,
and sends them through steps S40 and S50 (Condition
1) .
When no deletion branch candidate is present and
the number of the communicating radio branches is
- 30 -
CA 02489812 1998-06-03
less than the maximum value (step S30), the mobile
station places all the detected addition branch
candidates and the communicating branches in the
addition information parameters, and sends them
through steps S40 and S50 (Condition 2).
If the number of the communicating radio
branches equals the maximum value (step S30), the
mobile station decides as to the communicating
branches and the addition branch candidates whether
their difference (in the transmission loss, for
example) is greater than the oscillation inhibiting
threshold value by comparing them at step S60, and
sends only the addition branch candidates with a
difference greater than the oscillation inhibiting
threshold value by placing them into the handover
trigger signal through steps S80 and S90 (Condition
3), without sending them otherwise (step S70).
A first reason for imposing a rigid condition
such as the condition 3 on the candidate
transmission when the number of communicating radio
branches is maximum is that it is known beforehand
that those addition branch candidates which meet the
normal addition branch decision conditions but have
lower precedence than any other communicating
branches are not subjected the addition processing
even though they are sent to the network side.
- 31 -
CA 02489812 1998-06-03
Thus, notifying the network side of them as the
addition branch candidates is avoided.
Fig. 8 illustrates an example that does not
notify the network side of the addition branch
candidates during communications using the maximum
number of radio branches.
In Fig. 8, branches 130, 132 and 134 are
communicating branches, and the threshold value 142
indicates an addition DHO threshold value. Although
the branches 136 and 138 are addition branch
candidates because they meet the addition branch
candidate decision conditions (because the
differences in the transmission losses between them
and the branch 130 are less than the addition DHO
threshold value 142), they are highly unlikely to be
added because their precedence is lower than the
lowest communicating branch 134. Furthermore, the
oscillation inhibiting threshold value is set to
prevent the repetition of the addition and deletion,
that is, "oscillation", by imposing more strict
condition (second reason). Those branches that are
deleted at the start of the addition deletion DHO
are deleted not because they meet the deletion
branch candidate conditions, but because they become
lower than other branches. If a branch that meets
the requirements for a communication branch and
- 32 -
CA 02489812 1998-06-03
contributes communications is replaced by an
addition branch candidate with a slightly higher
priority, it is very likely that the replaced branch
is added again instead of the added addition branch
candidate because of fluctuations in the radio
section. Such an operation, if repeated, will
increase the control load of the network side. To
prevent such oscillation, the oscillation inhibiting
threshold value is set. The oscillation inhibiting
threshold value is set under the assumption that the
differences are considered between the addition
branch candidates and the communicating branch with
the lowest priority (because of a large transmission
loss, for example) during the communications using
the maximum number of radio branches, and the
decision is made by comparing the differences with
the threshold value so that the addition is made if
the differences are greater than the oscillation
inhibiting threshold value.
Figs. 9A and 9B are diagrams illustrating the
oscillation inhibiting threshold value. Fig. 9A
illustrates a case when an addition branch candidate
is added, whereas Fig. 9B illustrates a case when it
is not added. An addition branch candidate lower in
precedence than the communicating branches, that is,
lower than the lowest priority communicating branch
- 33 -
CA 02489812 1998-06-03
among them is not added because it is unlikely to be
added. If it has a slightly higher priority, it is
not added because it will cause the oscillation.
In Fig. 9A, branches 150, 152 and 154 are
communicating branches and a branch 156 is an
addition branch candidate with precedence above the
oscillation inhibiting threshold value 157.
In Fig. 9B, branches 160, 162 and 164 are
communicating branches and a branch 166 is an
addition branch candidate with precedence below the
oscillation inhibiting threshold value 167.
When one or more deletion branch candidates are
present, or when the number of the communicating
branches is less than maximum, the mobile station
notifies the network side of all the candidates. In
this way, the network side can obtain alternative
addition branch candidate, even if it rejects a
particular addition branch candidate owing to some
reason.
It will be obvious for those skilled in the art
that such control can be implemented without any
inconvenience that adds only addition branch
candidates which are very likely to be added. This
is analogous to the foregoing case in which it is
possible to circumvent any cable branch addition
processing of the candidates which are very likely
- 34 -
CA 02489812 1998-06-03
to be deleted because of their lower precedence than
the communicating branches even though they are
added as the cable branch candidates.
Fig. 10 is a flowchart illustrating the details
of the DHO performance algorithm in the network.
In Fig. 10, receiving the handover trigger
signal at step S100, the network side carries out
the deletion DHO first at step 5110, and then the
addition DHO at step S130 after completing the
deletion DHO. The deletion DHO sequence (step S200)
is for increasing the number of branches that are
available simultaneously in the addition DHO by
releasing beforehand those branches not contributing
to the communications by performing the deletion DHO
prior to the addition DHO. When the mobile station
carries out the deletion DHO autonomously, it can
perform the deletion DHO independently of the
addition DHO which is carried out after receiving
the handover trigger. It is preferable, however, to
carry out the deletion DHO before triggering the
addition DHO. The procedure of the addition DHO is
divided depending on whether the sum total of the
communicating branch number (#Br) - the deletion DHO
branch number (#Del) (that is, the communicating
branch number after completing the deletion DHO) and
- 35 -
CA 02489812 1998-06-03
the addition DHO branch number (#Add) exceeds the
maximum radio branch number (#Brmax) or not.
First, when the sum total (#Br - #Del + #Add) of
the communicating branch number and the addition
branch candidate number does not exceed the maximum
radio branch number (#Brmax), the network side
carried out the addition DHO in a normal procedure
(steps S120 and S130 of the addition DHO sequence
S210).
In contrast, when the sum total (#Br - #Del +
#Add) of the communicating branch number and the
addition branch candidate number exceeds the maximum
radio branch number (#Brmax), the network side
carried out the addition deletion DHO (the addition
deletion DHO sequence S220). The cable branches are
added up to the maximum cable branch number (step
S140). Subsequently, the addition and switching of
the radio branches are carried out up to the maximum
radio branch number #Brmax) (step S150). Finally,
unneeded cable branches exceeding the maximum radio
branch number (#Brmax) is released (step S160).
Fig. 11 is a branch diagram for activating the
DHO sequence.
In Fig. 11, a branch 1 (190), branch 2 (191) and
branch 3 (196) are communicating branches, in which
the branch 3 (196) is below a deletion DHO threshold
- 36 -
CA 02489812 1998-06-03
value 194. A branch 4 (192) and branch 5 (193) are
addition branch candidates, in which the branch 5
(193) is within an addition DHO threshold value 195,
and the branch 4 (192) has higher precedence than
the branch 2 (191).
Figs. 12A, 12B and 12C are linked in this order,
and illustrate the DHO processing sequence of
performing under the control of the network the
addition deletion DHO after the deletion DHO in the
case where the precedence of the branches is as
shown in Fig. 11, where it is assumed that the
maximum radio branch number is three and the maximum
cable branch number is four.
Fig. 12A shows the deletion DHO sequence, in
which an unneeded radio branch is deleted.
Fig. 12A shows three radio branches 1-3, three
cable branches 1-3, and five base stations with base
station numbers 1-5. A mobile station 500 detects
addition DHO candidates and deletion DHO candidates
(501), and decides addition DHO candidates and
deletion DHO candidates (505). The mobile station
500 sends to a network 503 a handover trigger
request (branch deletion or branch addition) (510).
The network 503 extracts the deletion DHO candidates
(517), and sends to the mobile station 500 a
handover execution request (deletion of the branch
- 37 -
CA 02489812 1998-06-03
3) (515). The mobile 500 sends back to the network
503 a handover execution response (520). Then, the
mobile station 500 deletes the radio branch 3 (525),
and suspends the maximal ratio combining of the
radio branch 3 (530), as represented by the deletion
of the line of the radio branch 3 at 530 as
indicated by a broken line.
The network 503 sends to the base station with
the base station number 3 a radio and cable bearer
release request (535). The base station with the
base station number 3 halts the reception of the
reverse radio channel (540), halts the transmission
of the forward radio channel (545), releases base
station number resources (550), and sends back to
the network 503 a radio and cable bearer release
response (560). The network 503 deletes the DHT
cable branch 3 (565).
Figs. 12B and 12C illustrate an addition
deletion DHO sequence which adds cable branches 4
and 5 in advance, adds a radio branch 4
corresponding to the added cable branches, carries
out switching between the radio branches 1 and 5,
and finally deletes the cable branch 1 that becomes
unnecessary.
In Fig. 12B, the network 503 detects addition
DHO candidates (600), decides an addition DHO
- 38 -
CA 02489812 2010-02-04
destination (605), and adds the cable branches 4 and
(610). The addition of the cable branches 4 and 5
is represented in Fig. 12B by lines of the cable
branches 4 and 5 appearing from the position
5 indicated by a broken line. The network 503 sends
to the base stations with the base station numbers 4
and 5 a radio and cable bearer establishing request
(615 and 620). The base stations with the base
station numbers 4 and 5 each send to the mobile
station 500 a forward radio channel transmission
start (625 and 630), receive a reverse radio channel
reception start (635 and 640), and sends to the
network 503 a radio and cable bearer establishment
response (645 and 650).
In Fig. 12C, the network 503 checks the cable
branches 4 and 5 (700). The network 503 sends to
the mobile station 500 a handover execution request
(for adding the branch 4 and switching between the
branches 1 and 5) (705), and the mobile station 500
sends back to the network 503 a handover execution
response (710). The mobile station 500 adds the
radio branch 4 (715), establishes synchronization of
the new branch 4 (720), starts the maximal ratio
combining of the radio branch 4 (725), switches the
radio branches 1 and 5 (730), and establishes the
synchronization of the new branch 5 (735).
- 39 -
CA 02489812 2010-02-04
The base station with the base
station number 4 detects the reverse radio channel
synchronization (740), and sends back to the network
503 a radio and cable bearer establishment response
(745). The base station with the base station
number 5 detects the reverse radio channel
synchronization (750), and sends back to the network
503 a radio and cable bearer establishment response
(755). The network 503 adds the radio branch 4 and
checks the switching between the radio branches 1
and 5 (757), and sends to the base station with the
base station number 1 a radio and cable bearer
release request (760). The base station with the
base station number 1 halts the reception of the
reverse radio channel (765,), halts the transmission
of the forward radio channel (770), releases the
base station number resources (775), and sends back
to the network 503 a radio and cable bearer release
response (780). The network 503 deletes the DHT
cable branch 1 (785).
Next, control will be described of a candidate
which is not added because of the restrictions on
the cable branch number (maximum cable branch
number), though the mobile station notifies the
network side of the candidate. The maximum number
- 40
CA 02489812 1998-06-03
of branches that can be handled in single network
control is limited to the maximum cable branch
number. Thus, when the sum total of the
communicating branches and the addition branch
candidates exceeds the maximum cable branches, it is
probable that the single control cannot add some
addition branch candidates although they have higher
precedence than the communicating branches.
Fig. 13 illustrates such addition candidates
which cannot be added because of the maximum cable
branch number.
In Fig. 13, branches 170, 172 and 174 are
communicating branches, and branches 176, 178 and
180 are addition branch candidates. Although the
branches 178 and 180 have higher precedence than the
communicating branch 170, they are not added because
of the maximum cable branch number of four. Only
the addition candidate branch 176 with the highest
precedence is added by the single control.
In such a case, a control method can be
introduced that notifies the network again of the
unadded addition branch candidates 178 and 180 by
putting them into the handover trigger signal in
response to the measurement on the mobile station
side. The network side can perform the addition DHO
of the addition branch candidates 178 and 180 that
- 41 -
CA 02489812 1998-06-03
are not added in the first control, at the point of
time it receives the handover trigger signal
including them. Alternatively, the network side can
choose a method that stores the addition branch
candidates 178 and 180, and successively carries out
the addition DHO for those candidates that are
omitted in the first control after completing the
series of the operations as shown in Fig. 10.
In the present invention, selecting the branch
candidates considering the maximum cable branch
number and the maximum radio branch number, the
mobile station notifies the network side of only the
candidates that are most likely to undergo the DHO
processing by excluding in advance the branch
candidates that are unlikely to be handled in the
DHO processing even though the mobile station
notifies the network side of them. In this case,
the following two methods can be employed.
First, considering the case where the network
side cannot add an addition branch candidate of a
higher precedence because of some reason, the mobile
station notifies the network side of alternative
addition branch candidates that are unlikely to be
added if the branch candidate of a higher precedence
is added. Thus, all the addition branch candidates
are notified of. Nevertheless, the mobile station
- 42 -
CA 02489812 1998-06-03
keeps performing the control that does not notify
the network side of the addition branch candidates
with lower precedence than the communicating
branches during communications using the maximum
number of the communicating branches. This is
because it cannot be expected that these branches
with the lower precedence than the communicating
branches are added because the maximum number of
communicating branches are already used.
Second, the mobile station notifies the network
side of only the addition branch candidates that are
likely to be added in the normal DHO processing
without notifying of the alternative addition branch
candidates. Although this method has an advantage
over the first method of being able to reduce an
amount of signals, the mobile station must consider
the relationships between the number of the
communicating branches and the number of the
deletion branch candidates. That is, since the
deletion DHO is carried out previously, such control
is required that selects only addition branch
candidates that are most likely to be added after
the deletion DHO which is executed beforehand.
In the present invention, the mobile station
notifies the network side not only of the addition
branch candidates by putting them into the
43 -
CA 02489812 1998-06-03
notification signal (handover trigger signal), but
also of the communicating branches in combination
with the information about the precedence by putting
them into the handover trigger signal. For example,
magnitudes of the transmission loss are retained in
the notification signal in order of precedence as an
indicator of the precedence. It is not necessary to
notify the network side of the deletion branch
candidates because they do not contribute to the
communications. Thus, they are detected and deleted
without being sent to the network side with the
communicating branches that are transmitted in
combination with the information about their
precedence. Since the network side can compared the
precedence between the communicating branches and
the addition branch candidates, it can decide the
addition branch candidates to be added, and the
communicating branches to be retained or deleted as
needed.
The mobile station places into one handover
trigger signal all the DHO candidates, that is, a
plurality of addition branch candidates and deletion
branch candidates, and notifies the network side of
them. More specifically, the addition branch
candidates are put into the addition information
parameters in the handover trigger signal, and the
- 44 -
CA 02489812 1998-06-03
deletion branch candidates are inserted into the
deletion information parameters. It is needless to
say that the communicating branches are put into the
addition information parameters together with the
addition branch candidates. This will make it
possible to reduce the number of transmission of the
handover trigger signal, enabling effective use of
the radio resources. To simplify the processing,
the network side separates the addition branch
candidates from the deletion branch candidates, and
sequentially carries out their DHO independently.
Carrying out the deletion DHO in advance to delete
unneeded branches makes it possible to add more
addition branch candidates through a single
transmission operation of the handover trigger
signal, enabling more effective use of the radio and
cable resources.
To achieve the deletion DHO under the control of
the mobile station, the mobile station puts the
deletion branch candidates into the handover trigger
signal, notifies the network side of them, and
releases the radio branches. Detecting the break of
the radio channels associated with the deletion
branch candidates notified, the network side
releases the cable branches corresponding thereto.
- 45 -
CA 02489812 1998-06-03
Fig. 14 illustrates the deletion DHO sequence
under the control of the mobile station. The
addition DHO is carried out independently of this
sequence.
By setting the maximum cable branch number at
the maximum radio branch number plus N (N>_1), it
becomes possible to add a greater number of cable
branches in advance than when the maximum cable
branch number is set at the maximum radio branch
number plus one. This makes it possible to achieve
more efficient control of the addition operation of
a plurality of multiple addition branch candidates.
In the foregoing control, it is likely that the
restrictions on the maximum cable branch number may
result in an addition branch candidates to which no
cable branch is added. In this case, the present
invention can propose the following two methods.
1. The network side does not carry out any
special control. The mobile station decides the
addition branch candidates again in the condition of
using new communication branches, notifies the
network of the handover signal again so that the
addition DHO of the unexecuted candidates is carried
out.
2. The network side stores the addition branch
candidates that are not handled by the first
- 46 -
CA 02489812 1998-06-03
control, and autonomously carries out the second
control.
Fig. 15 shows an embodiment of a configuration
of base stations, a switching center and so on in
accordance with the present invention.
In Fig. 15, a base station (BS1) 200 and a base
station (BS2) 210 are connected to a MSC (Mobile
services switching center) 220, to which a diversity
handover trunk (DHT) 230, a voice encoder (VXC) 240,
data service controller (DSC) 250 and processor
(PRC) 260 are connected.
Fig. 16 shows another embodiment of a
configuration of the base stations, switching
centers and so on in accordance with the present
invention.
In Fig. 16, blocks having the same functions as
those of Fig. 15 are designated by the same
reference numerals, and the description thereof is
omitted here. The configuration of Fig. 16 differs
from that of Fig. 15 in that it comprises a new
additional base station control office (MSC1) 320
.with a function of controlling the base stations,
which is connected to a mobile services switching
center (MSC2) 330 with a normal switching function.
The base station control office (MSC1) 320 can be
installed near the base station BS1 or BS2. It is
- 47 -
CA 02489812 1998-06-03
also possible to utilize a switching center of a
fixed network as the switching center (MSC2) 330
without any change. The DHT 230 and PRC 260 are
connected to the base station control office (MSC1)
320, and the VXC 240, DSC 250 and PRC 260 are
connected to the switching center (MSC2).
As described above, the present invention
provides a diversity handover branch control method
in the DHO performance, in which a mobile station
selects, when it detects a plurality of addition
branch candidates and deletion branch candidates,
branch candidates considering the maximum cable
branch number and maximum radio branch number.
48 -
