U.S. patent application number 09/360048 was filed with the patent office on 2001-10-11 for paging of mobile station in a cellular radio system.
This patent application is currently assigned to NOKIA TELECOMMUNICATIONS OY. Invention is credited to VERKAMA, MARKKU.
Application Number | 20010029181 09/360048 |
Document ID | / |
Family ID | 8548150 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010029181 |
Kind Code |
A1 |
VERKAMA, MARKKU |
October 11, 2001 |
PAGING OF MOBILE STATION IN A CELLULAR RADIO SYSTEM
Abstract
In cellular radio systems re-paging of a mobile station (MS)
loads the mobile communications network very much, especially the
limited radio path resources of the network. The present invention
concerns a paging method in a cellular radio system including
several cells (C1-C10). In the method a first paging of the mobile
station (MS) is performed in all cells (C1-C10) of the area
according to the stored location information. According to the
invention, the paging method is characterized in that in the method
the area according to the location information is divided according
to the cell division into at least two sub-areas, each one of which
is formed of at least one cell, limitation values for the number of
pagings are defined for the cells on a sub-area basis and re-paging
of the mobile station is limited in each cell of the area based on
the said limitation values for the number of pagings.
Inventors: |
VERKAMA, MARKKU; (ESPOO,
FI) |
Correspondence
Address: |
MICHAEEL B. LASKY
ALTERA LAW GROUP, LLC
6500 CITY WEST PARKWAY
SUITE 100
MINNEAPOLIS
MN
55344-7701
US
|
Assignee: |
NOKIA TELECOMMUNICATIONS OY
|
Family ID: |
8548150 |
Appl. No.: |
09/360048 |
Filed: |
July 23, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09360048 |
Jul 23, 1999 |
|
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|
PCT/FI98/00101 |
Feb 3, 1998 |
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Current U.S.
Class: |
455/458 ;
340/10.1; 340/7.21 |
Current CPC
Class: |
H04W 68/00 20130101 |
Class at
Publication: |
455/426 ;
455/458; 455/456; 340/7.21; 340/10.1 |
International
Class: |
H04Q 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 1997 |
FI |
970555 |
Claims
1. A paging method in a cellular radio system including several
cells (C1-C10), mobile stations (MS) and a database, wherein
location information of the mobile station (MS) is stored, in which
method a first paging of the mobile station (MS) is performed in
all cells (C1-C10) of the area according to the stored location
information, characterized in that, in the method the area
according to the location information is divided according to the
cell division into at least two sub-areas, each one of which is
formed of at least one cell, limitation values for the number of
pagings are defined for the cells on a sub-area basis and re-paging
of the mobile station is performed so that the number of re-pagings
to be performed in each cell of the area according to the location
information is limited based on the said limitation values for the
number of pagings.
2. Method as defined in claim 1, characterized in that the area
according to the location information is divided according to the
cell division into at least two sub-areas, each one of which is
formed of one cell.
3. Method as defined in claim 1 or 2, characterized in that for
performing re-paging of the mobile station re-paging is started in
those cells of the area according to the location information
wherein the limitation values for the number of pagings allow
re-paging, and paging of the mobile station is interrupted when
re-paging is not allowed in any cell.
4. Method as defined in claim 1, 2 or 3, characterized in that for
performing re-paging of the mobile station the number of performed
pagings is calculated, the said number of performed pagings is
compared with the limitation values for the number of pagings of
the cells and a paging message is sent to the mobile station (MS)
in those cells of the area according to the location information
where the limitation value for the number of pagings exceeds the
number of performed pagings, until the limitation value for the
number of pagings does not exceed the number of performed pagings
in any cell.
5. Method as defined in claim 3 or 4, characterized in that for
performing re-paging of the mobile station a reply from the mobile
station (MS) is waited for a certain time after the sending of each
paging message and paging of the mobile station (MS) is interrupted
upon reception of the mobile station's reply to the paging.
6. Method as defined in claim 1 or 2, characterized in that
limitation values for the number of pagings are defined for the
cells based on statistics on successful pagings in the radio
system.
7. Arrangement in a cellular radio system, which cellular radio
system includes several cells (C1-C10), mobile stations (MS) and a
database, wherein location information of the mobile station (MS)
is stored, characterized in that the arrangement includes storing
means for storing limitation values for the number of pagings of
the cells and means for limiting re-pagings to be performed
according to the said limitation values for the number of
pagings.
8. Arrangement as defined in claim 7, characterized in that the
arrangement also includes means for defining limitation values for
the number of pagings in the cells.
9. Arrangement as defined in claim 7, characterized in that the
means for limiting re-pagings to be performed include calculating
means for counting the number of pagings to be performed, comparing
means for comparing the value of the calculating means with the
limitation values for the number of pagings in the cells and means
for relaying a re-paging command to the cells in the area according
to the location information based on the result of the comparison
by the said comparing means.
10. Arrangement as defined in claim 8, characterized in that the
means for defining limitation values for the number of pagings in
the cells include means of keeping statistics for forming
statistics on successful pagings in the radio system and means of
choosing limitation values for the number of pagings based on the
statistics formed by the said means of keeping statistics.
11. Arrangement as defined in any one of claims 7-10 in a cellular
radio system, which cellular radio system includes at least one
centre (MSC), having subordinated to itself at least one base
station controller (BSC) and several base transceiver stations
(BTS1-6), characterized in that at least a part of the arrangement
is located in the centre (MSC).
12. Arrangement as defined in any one of claims 7-11 in a cellular
radio system, which cellular radio system includes at least one
centre (MSC), having subordinated to itself at least one base
station controller (BSC) and several base transceiver stations
(BTS1-6), characterized in that at least a part of the arrangement
is located in the base station controller (BSC).
13. Arrangement as defined in any one of claims 7-12 in a cellular
radio system, which cellular radio system includes at least one
centre (MSC), having subordinated to itself at least one base
station controller (BSC) and several base transceiver stations
(BTS1-6), characterized in that at least a part of the arrangement
is located in the base transceiver station (BTS).
14. Arrangement according to claim 10 in a cellular radio system,
which cellular radio system includes an operation and maintenance
centre (OMC), characterized in that the said means of keeping
statistics is located in the operation and maintenance centre
(OMC).
15. Arrangement as defined in claim 10 or 14 in a cellular radio
system, which cellular radio system includes an operation and
maintenance centre (OMC), characterized in that the said means of
choosing limitation values for the number of pagings is located in
the operation and maintenance centre (OMC).
Description
FIELD OF APPLICATION OF THE INVENTION
[0001] The invention concerns a method of paging in a cellular
radio system including several cells, mobile stations and a
database wherein location information of the mobile station is
stored. In the method a first paging of the mobile station is
performed in all cells of an area according to the stored location
information.
[0002] In addition, the invention concerns an arrangement in a
cellular radio system.
BACKGROUND OF THE INVENTION
[0003] FIG. 1 in the appended drawing shows a block diagram of a
simplified GSM mobile communications system. The Mobile Station MS
is connected over the radio path with some Base Transceiver Station
BTS, which is BTSI in the example shown in FIG. 1. The Base Station
System BSS comprises a Base Station Controller BSC and subordinated
base transceiver stations BTS. Several Base Station Controllers BSC
are usually subordinated to a Mobile Services Switching Centre MSC.
The mobile services switching centre MSC is connected to other
mobile services switching centres and through a Gateway Mobile
Services Switching Centre GMSC the GSM network is connected to
other networks, such as a public telephone network PSTN, another
public land mobile network PLMN or an ISDN network. The operation
of the whole system is monitored by an Operation and Maintenance
Centre OMC. Subscriber information of the mobile station MS is
stored permanently in the Home Location Register HLR and
temporarily in that Visitor Location Register VLR in the area in
which the mobile station MS is located at each time. The location
information of the mobile station MS is stored in the visitor
location register VLR with the accuracy of a Location Area LA.
[0004] The geographical area monitored by the visitor location
register VLR is divided into one or more location areas LA, inside
each of which the MS may move freely without notifying the VLR. One
or more base transceiver stations BTS may operate within each
location area. The base transceiver stations BTS send constant
information about themselves and about their environment on their
broadcast channel, such as a Base Station Identity Code BSIC,
adjacent cell information and a Location Area Identifier LAI. Based
on the last-mentioned, the MS which has locked into the base
transceiver station BTS will know in which location area LA it is
located at each time. If when changing base transceiver station BTS
the mobile station notices that the location area identifier LAI of
the base transceiver station has changed, the mobile station will
send a location update request to the network. The location area of
the mobile station MS will be updated in that visitor location
register VLR, in the area of which the mobile station is located at
each time. Information indicating in which VLR's area the MS is
located is relayed to the home location register HLR.
[0005] The mobile station's location information stored in
registers of the mobile communications system is used e.g. in
routing of an incoming call. Based on location information of the
mobile station MS available from the home location register HLR and
from the visitor location register VLR, the incoming call is routed
to that mobile services switching centre MSC in the area of which
the mobile station MS of the called subscriber is located at each
time according to the location information. The mobile services
switching centre MSC asks its own visitor location register VLR for
information on the called subscriber for setting up the call. The
visitor location register VLR gives the required information on the
mobile station MS including e.g. the mobile station's MS location
area LA stored in the latest location update, which is LA1 in the
case shown in FIG. 1. Based on the location area information, the
mobile services switching centre MSC will send a paging message
provided with the mobile station's MS identifier on the paging
channels of all base transceiver stations of the location area in
question, in the case shown in FIG. 1 on the paging channels of
base transceiver stations BTS1, BTS2 and BTS3. Mobile stations MS
located in the coverage area of base transceiver station BTS
regularly receive the signal on Paging Channel PCH of the cell's
base transceiver station and they reply to the received paging on
Random Access Channel RACH of that BTS, in the coverage area of
which the mobile station MS is located when receiving, e.g. on the
RACH channel of base transceiver station BTS1 in FIG. 1. On
receiving the reply, the network reserves a traffic channel for the
call and sets up a speech connection for mobile station MS.
[0006] When base transceiver stations BTS send a paging message,
the mobile station MS may be momentarily in a shadow region of the
network, e.g. in a tunnel, or mobile station MS does not receive
the paging message correctly, e.g. due to interference or noise.
The paging message will hereby not reach the called subscriber,
even if the subscriber would otherwise be prepared to receive the
call. Paging will also fail, if the mobile station MS is turned off
unbeknownst to the mobile communications network or if the
transmission power of mobile station MS is not sufficient for
setting up a connection with the base transceiver station. If the
mobile station does not reply to paging, e.g. within a certain
period of time, it is generally known to perform re-paging of the
mobile station MS over the entire location area LA through all base
transceiver stations BTS in the location area. Typically, such
re-paging is done no more than two or three times.
[0007] The publication "Adaptive Paging Algorithms for Cellular
Systems", S. Madhavapeddy et al., Fifth WINLAB Workshop on Third
Generation Wireless Information Networks, 1995, pages 347-361,
presents the establishment and utilisation of a paging area based
on statistics kept on the mobile station's location. In the method
according to the publication, paging of the mobile station is first
done in the formed paging area, where the mobile station is
expected to be located most probably. If the mobile station does
not reply to the first paging, a new extended paging is performed,
either once more in the same paging area or through all base
transceiver stations in the location area. In another embodiment
presented in the publication, paging of the mobile station is first
done in the established paging area and next through all base
transceiver stations of the system, if the mobile station does not
reply to the first paging. If the mobile station does not reply
even to the second paging, a third paging will be sent through
those base transceiver stations which are not located within the
established paging area.
[0008] It is a problem with known re-paging methods that due to the
large paging area they load the network extensively, especially the
limited resources of the radio path, and will cause plenty of
signalling loads both on the radio path and between the radio
network's switching centre and base transceiver stations. Nor do
known paging methods take into account that shadow areas of cells
are of different size, whereby the need for re-paging will vary in
cells. In addition, when the mobile station is turned off or if the
transmission power of the mobile station is too low, re-paging will
not be successful, whereby network resources have been spent on
extended paging quite unnecessarily.
BRIEF DESCRIPTION OF THE INVENTION
[0009] It is a purpose of this invention to implement optimum
paging of a mobile station in a cellular radio system. In other
words, the objective is paging of the mobile station with as few
paging messages as possible, however, maintaining a good standard
of service.
[0010] This new type of mobile station paging is achieved in the
method according to the invention, which is characterised in that
in the method the area according to the location information is
divided according to the cell division into at least two sub-areas,
each one of which is made up of at least one cell, limitation
values for the number of pagings are defined on a sub-area basis
for the cells and re-paging of the mobile station is performed so
that the number of re-pagings to be performed in each area
according to the location information is limited based on the said
limitation values for the number of pagings.
[0011] The invention also concerns an arrangement in a cellular
radio system comprising several cells, mobile stations and a
database, wherein the mobile station's location information is
stored. According to the invention, the arrangement is
characterised in that it comprises storing means for storing
limitation values for the number of pagings in the cells and means
for limiting re-pagings to be performed based on the said
limitation values for the number of pagings.
[0012] The invention is based on the idea that re-paging of a
mobile station is performed within an area which is smaller than
the normal location area and wherein re-paging based on information
collected from the network is most likely to be successful.
Limitation values for the number of allowed pagings to be performed
are defined separately for each cell or group of cells. Based on
these limitation values, such cells are selected for each re-paging
round wherein re-paging may still be performed. Re-paging is
performed so many times in each cell as is indicated by the
limitation value defined for the number of pagings for the cell,
unless re-paging is found unnecessary e.g. if the mobile station
has already replied to a sent paging message.
[0013] It is an advantage of such a paging method that it minimises
network loading and, in particular, the use of radio resources in
re-paging.
[0014] Another advantage of the paging method according to the
invention is that re-paging may be targeted e.g. only at shadow
areas of the network's radio coverage or at poor signal areas of
the network.
[0015] It is another advantage of the paging method according to
the invention that in a radio network of a good quality, re-paging
which is probably unnecessary is avoided, whereby information on
failed paging can be forwarded more quickly, e.g. to subscriber A,
or the call can be connected more quickly to the voice mail of the
called subscriber.
LIST OF FIGURES
[0016] The invention will be described in greater detail in the
following in connection with advantageous embodiments and referring
to the appended drawings, wherein:
[0017] FIG. 1 shows a block diagram of the structure of a mobile
communications system;
[0018] FIG. 2 shows an example of the cellular structure of a radio
network;
[0019] FIG. 3 shows a flow chart of the paging method according to
a primary embodiment of the invention; and
[0020] FIG. 4 shows a flow chart of the paging method according to
a secondary embodiment of the invention; and
[0021] FIG. 5 shows a flow chart of the paging method according to
a third embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention may be applied in connection with any
mobile communications system of the cellular type. The system is
described hereinafter by way of example primarily in connection
with a GSM mobile communications system. FIG. 1 shows the
simplified structure of the GSM network which was mentioned
earlier. The GSM system is described in GSM recommendations and the
book "The GSM System for Mobile Communications", M. Mouly & M.
Pautet, Palaiseau, France, 1992, ISBN:2-9507190-0-7, where an
interested reader can find more background information.
[0023] FIG. 2 shows a simplified example of a cellular structure,
where the geographic area of the network shown in the figure is
divided into cells C1-C10 so that when located in each cell the
mobile station MS is in connection with the network through a base
transceiver station BTS1-10 (not shown in the figure) located in
the cell. Cells C1-C10 establish one location area LA10 in the
network.
[0024] The invention is described more closely in the following in
the light of a primary embodiment of the invention and referring to
FIG. 2. According to the present invention, a limitation value Ri
is determined for the number of pagings for each cell in the
network, e.g. based on the success of earlier pagings performed in
the cell, as will be described later in this application, or based
on the occurrence of shadows in cell coverages. The limitation
values Ri for the number of pagings established by the operator are
stored in connection with a unit controlling the paging process of
the mobile communications system, e.g. a mobile services switching
centre MSC or base station controllers BSC. In the example shown in
FIG. 2, limitation values R1-R10 for the number of pagings in cells
C1-C10 are stored as follows: R1, . . . , R8=1, R9=2 and R10=3,
whereby in cells C1-C8 only one paging is allowed, in cells C9
after the first paging one re-paging and in cell C10 no more than
three pagings.
[0025] When the location area LA10 has been stored in the
subscriber information of visitor location register VLR as the
mobile station's MS location information and when paging for mobile
station MS, state-of-the-art paging is first performed in all cells
C1-C10 of the location area LA10, that is, a paging message
provided with the mobile station's MS identifier is sent on the
paging channels of base transceiver stations BTS1-10. According to
the state of the art, the mobile station identifier used in the
paging message may be a Temporary Mobile Subscriber Identity TMSI
or an International Mobile Subscriber Identity IMSI. If the mobile
station MS does not reply to this first paging within a certain
period of time through any base transceiver station BTS1-10 which
has sent the paging message, those cells wherein re-paging will be
performed are chosen from the cells C1-C10 of location area LA10
according to the primary embodiment of the invention. This second
paging is performed in those cells, which have a limitation value
RI of at least two. In the case of the example shown in FIG. 2,
such cells are C9 and C10. The unit or units in control of the
paging process will relay to base transceiver stations BTS9 and
BTS10 a command to perform re-paging. A paging message provided
with the identifier of mobile station MS is thus sent once more on
the paging channels of base transceiver stations BTS9 and BTS10.
Again according to the state of the art, the mobile station
identifier used in the paging message may be either TMSI or IMSI.
The identifier used in re-paging may be a different one than the
identifier used in the first paging. If the mobile station MS now
replies to this paging, e.g. through base transceiver station BTS9,
the paging process will be stopped and a state-of-the-art call
setup will be performed. If the mobile station MS would not have
replied even to the second paging, paging for the mobile station MS
would have been performed a third time in cell C10. The mobile
station identifier used in the paging message may again be either
TMSI or IMSI irrespective of the identifiers used in the previous
pagings. Paging would be deemed unsuccessful if the mobile station
MS would not have replied to the paging message even after the
third paging.
[0026] FIG. 3 shows a flow chart of a primary embodiment of the
paging method according to the invention. At point 31 the operator
establishes limiting values Ri for the number of pagings separately
for either each cell or each cell group. Establishment of the
values Ri is performed at least once when the method is introduced,
whereupon the values Ri need not necessarily be re-established. The
limitation value Ri for the number of pagings is established for
all those cells, where it is desired to bring about a functionality
according to the invention. At point 32 in FIG. 3, the value
established for the counter is 1. Here the value of the counter
indicates which paging in succession is about to begin. According
to the state of the art, paging of mobile station MS is performed
at point 33 in all cells of the location area indicated by the
location information, in the case shown in FIG. 2 in cells C1-C10
of location area LA10. At point 34 in FIG. 3, the unit controlling
the paging process in the mobile communications system, e.g. the
mobile services switching centre MSC, will wait for a reply from
mobile station MS for a certain time. If mobile station MS does not
reply to the first paging message sent in the whole location area,
the counter value will be raised by one at point 35 in FIG. 3 in
accordance with the present invention. At point 36 the limitation
values Ri established for the number of pagings are compared to the
counter value, which according to the above presentation is 2 after
the first paging, and a check is made to find out if any limitation
value Ri for the number of pagings is at least equal to the counter
value. If even one such cell is found which meets the condition of
point 36, re-paging will be performed at point 37 in those cells
which have a limitation value Ri for the number of pagings which is
at least equal to the counter value. In the case shown in FIG. 2,
this second paging according to point 37 is performed in cells C9
and C10, which have limitation values R9=2 and R10=3 which are at
least equal to the counter value of 2. When the mobile services
switching centre MSC controls the paging process, it sends to the
base station controllers BSC, in the case of GSM information in a
BSSMAP_PAGING message indicating in which base transceiver stations
paging must be performed. If those base transceiver stations BTS
where re-paging is to be performed are located subordinated to
several different base station controllers BSC, then the mobile
services switching centre MSC will send to each base station
controller BSC an individual BSSMAP_PAGING message, indicating the
re-pagings to be performed under the base station controller BSC in
question. In the case shown in FIG. 2, the base station controller
BSC forwards to base transceiver stations BTS9 and BTS10 a command
to send a paging message to the mobile station MS. At point 38 in
FIG. 3 the process again waits to see if mobile station MS will
within a certain time respond after the paging message was sent. If
the mobile station does not reply even now, the process returns to
point 35 in FIG. 3 once again to raise the counter value by one.
The next step is the check at point 36 as was described above. If
such cells are still found which meet the condition of point 36,
that is, which allow re-paging, then re-paging at point 37 is
performed in those cells, in the case of FIG. 2 the third paging
would be performed in cell C10, whose R10=3 is at least equal to
the counter value of 3. Re-pagings are continued in the cells
allowing re-paging until mobile station MS responds or until no
more such cells are found which allow re-paging. If it is found as
a result of the check at point 36 in FIG. 3 that the limitation
value Ri of all cells Ci are below the counter value, then paging
for mobile station MS is discontinued and the paging is deemed a
failure (point 39). Any continued processing of a failed paging is
performed as state-of-the-art processing. E.g. subscriber A may be
informed that the called subscriber can not be reached or the call
may be directed to the voice mail of the called subscriber.
[0027] The functionality controlling the paging process of the
primary embodiment of the present invention is preferably located
in the mobile services switching centre MSC. If the functionality
according to the primary embodiment of the invention is located in
base station controller BSC, then the base station controller BSC
must be adapted to identify the mobile station's MS reply to the
paging message, so that the paging process may be interrupted after
the mobile station has replied. If in this case base transceiver
stations BTS in cells of some location area are in addition
controlled by more than one base station controller BSC, it is
advantageous to arrange between these base station controllers BSC
a signalling connection and to adapt the base station controllers
to identify such signalling, which may be used for informing other
base station controllers performing paging of the same mobile
station MS that the mobile station MS has replied to the paging
message through a base transceiver station subordinated to some
base station controller.
[0028] FIG. 4 shows a flow chart of a secondary embodiment of the
paging method according to the invention. In the secondary
embodiment of the invention control of the re-paging process
preferably takes place at base transceiver station BTS, which does
not wait for any reply from mobile station MS, but completes the
whole paging process in the cell whether the mobile replies or not.
At point 41 in FIG. 4 the operator establishes a limitation value
Ri for the number of pagings in the cell of base transceiver
station BTS in the same way as described above in connection with
the primary embodiment. At point 42 a value of 1 is established for
the counter counting the number of pagings to be started. At point
43 state-of-the-art paging of mobile station MS is performed in the
cell for the first time. At point 45 in FIG. 4 the value of the
counter is increased by one in accordance with the present
invention. At point 46 the established limitation value Ri is
compared with the counter value, which according to the above
presentation is 2 after the first paging, and a check is made to
find out whether the limitation value Ri is at least equal to the
counter value. When the condition at point 46 is fulfilled, the
process goes on to point 43 to perform a new paging in the cell,
whereupon the counter value is again increased at point 45.
Re-pagings are continued until the condition of the check at point
46 in FIG. 4 is no longer fulfilled, whereby paging is regarded as
completed. Further processing of a successful and an unsuccessful
paging is performed in a state-of-the-art manner.
[0029] In the secondary embodiment of the invention signalling load
between base station controller and base transceiver station BTS is
minimised, since for one paging round to be started the base
station controller BSC sends to base transceiver station BTS only
one paging command and base transceiver station BTS performs
re-pagings independently.
[0030] The paging process of the secondary embodiment of the
invention is generally completed in such a way that the number of
pagings allowed by the limitation value Ri for the number of
pagings in each cell is performed in all cells. Depending on the
load situation of the individual base transceiver station BTS,
re-pagings according to the invention may also be left unperformed
at some base transceiver station, if there is too much of other
call loading at the base transceiver station BTS. In this way
re-pagings according to the invention are prevented from blocking
the paging channel.
[0031] If required, the primary and secondary embodiments described
above may also be combined e.g. so that re-paging of mobile station
MS is performed independently at base transceiver station BTS
according to the limitation value R1i established for the number of
pagings at the base transceiver station whereas at the mobile
services switching centre MSC sending of re-paging commands is
performed at a slower rate to the mobile services switching centre
MSC according to the limitation value R2i for the number of pagings
in the cell of base transceiver station BTS. In this combined
embodiment, base transceiver station BTS thus performs its own
re-paging round independently for each paging command sent by
mobile services switching centre MSC, whereby more paging messages
pass across the radio interface than is expressed by the individual
limitation values for the number of pagings. Thus, re-pagings to be
performed in the process of paging mobile station MS can be limited
according to more than one limitation value Ri.
[0032] FIG. 5 shows a flow chart of a third embodiment of the
paging method according to the invention. In the third embodiment
of the invention, the unit controlling the paging process in the
mobile communications system, preferably a unit having several
subordinated base transceiver stations, does not wait for a reply
from mobile station MS, but completes the whole paging process
whether the mobile station replies or not. At point 51 in FIG. 5
the operator establishes limitation values Ri for the number of
pagings in the same way as described above in connection with the
primary embodiment. At point 52 a value of 1 is set for the counter
counting the number of pagings to be started. At point 53
state-of-the-art paging for mobile station MS is performed first in
all cells of the location area indicated by the subscriber
information, in the case of FIG. 2 in cells of location area LA10.
At point 55 in FIG. 5 the counter value is increased by one
according to the present invention. At point 56 the limitation
values Ri established for the number of pagings are compared with
the counter value, which according to the above description is 2
after the first paging, and a check is made to find out whether
some of the limitation values for the number of pagings is at least
equal to the counter value. In the same way as in the primary
embodiment, when the condition at point 56 is fulfilled, a new
paging is performed at point 57 in those cells, which have a
limitation value Ri which is at least equal to the counter value.
In the case shown in FIG. 2 this first re-paging according to point
57 is performed in cells C9 and C10, which have such limitation
values R9=2 and R10=3 which are at least equal to the counter value
of 2. Next, the process again proceeds to point 55 in FIG. 5 to
increase the counter value once more by one. The next step is the
check at point 56 as described above. If cells allowing paging are
still found, re-paging at point 57 will be performed in those
cells, in the case of FIG. 2 a second re-paging, that is, the third
paging is performed in cell C10, having a R10=3 at least equal to
the counter value of 3. Re-pagings are continued in cells allowing
re-paging, until cells allowing re-paging are no longer found, that
is, until the condition of the check at point 56 in FIG. 5 is no
longer fulfilled, whereby the paging is regarded as completed.
Further proceeding of a successful and an unsuccessful paging is in
a state-of-the-art manner.
[0033] The unit controlling the paging process in a third
embodiment of the invention is preferably a base station controller
BSC, which does not interpret reply messages of the mobile station
MS arriving from the base transceiver station BTS, but which only
relays them to the mobile services switching centre MSC. Control in
the third embodiment may in principle also be arranged from mobile
services switching centre MSC, if the mobile services switching
centre MSC does not use information on the reply arrived from
mobile station MS for controlling the re-paging process.
[0034] The limitation values and counter operation presented above
are arranged suitably in each operating environment so that the
limitation values are used for limiting the number of pagings to be
performed at the desired value. Thus, the counter can be set e.g.
to count pagings already performed, whereby the limitation value
check must be carried out e.g. so that the limitation values Ri for
the number of pagings are established at the value for the allowed
number of pagings, whereby re-pagings are in principle performed in
each cell, until the number of pagings performed in the cell is
equal to the limitation value Ri for the number of pagings in the
cell. The counter may also be arranged to count otherwise than in
steps of +1 described above.
[0035] With the aid of limitation value Ri for the number of
pagings according to the invention the paging load of the network
is reduced to a minimum, however, preserving a sufficient service
level especially from the viewpoint of successful pagings. The
establishment of limitation values Ri for the number of pagings may
be arranged in several ways. The operator may establish the
limitation values Ri he desires on a basis of different criteria.
Some ways of establishing limitation values will be presented in
the following.
[0036] Based on various parameters describing the operation of the
radio network it is possible to predict the future behaviour of the
network. For the paging method of the present invention it is
possible to estimate the success of paging and re-paging, e.g.
separately for each cell. For defining limitation values Ri those
mobile station pagings m.sub.1i are registered e.g. in each cell
over a certain period of time, to which the mobile station has
replied after the first paging message was sent, and those pagings
m.sub.2i are registered during the same period to which the mobile
station has replied after the second paging message was sent. This
information is advantageously obtained e.g. in the
BSSMAP_COMPLETE_LAYER.sub.--3_INFORMATION message sent by the base
station controller to the mobile services switching centre MSC, in
which the mobile services switching centre MSC learns if the mobile
station MS has replied to the paging and which also states through
which base transceiver station the mobile station MS sent its
reply. To compile representative statistics, the mobile
communications system must be operated for some time so that at
least one re-paging is sent in all cells, when the mobile station
has not replied to the first paging, for the number m.sub.2i of
pagings replied to in the second paging to be rational. In
addition, a registration period of sufficient length will guarantee
that enough replies to pagings are obtained, whereby statistics
will better correspond with the reality. The relation of numbers of
successful pagings .alpha..sub.i=m.sub.2i/m.sub.1i shows the
probability of failure of paging in the individual cell and it may
be used for optimising the number of re-pagings. If, for example,
there has never been any reply to the second paging in some cell,
it is very unlikely that any failure of pagings would be due to
shadow areas of the radio coverage or to interference/noise in the
area of the cell. Failure of paging is then more probably due to
the circumstance that the mobile station MS unbeknownst to the
mobile communications network has been turned off or to the
circumstance that the transmission power of the mobile station MS
is not sufficient for delivering a reply to base transceiver
station BTS. The probability a.sub.i of failure of paging in the
individual cell may thus be seen as describing the occurrence of
shadows in the cell, so that the higher the .alpha..sub.i the
larger is the total shadow area of the cell.
[0037] Re-paging in the area of a cell having a good radio coverage
will most probably not have any result. Thus in cells, where the
relation .alpha..sub.i calculated on a basis of statistical number
values m.sub.2i, m.sub.1i obtains a value of 0, paging of mobile
stations is preferably performed e.g. only once. Correspondingly,
on a basis of .alpha..sub.i values which may be obtained with
different m.sub.2i, m.sub.1i values it is possible to define a
suitable number of re-pagings for each cell. Limitation values Ri
for the number of pagings may be chosen e.g. on a basis of
threshold values defined for the value .alpha..sub.i, e.g. so that
with the value .alpha..sub.i=0 the limitation value Ri will allow
one paging only, with values 0<.alpha..sub.i.ltore- q.0.3 the
limitation value will allow no more than two pagings, that is, a
first paging and one re-paging, with values
0.3<.alpha..sub.i<0.6 the limitation value is set to allow no
more than three pagings, etc. The operator may define suitable
threshold values experimentally or by modelling the network in a
suitable manner.
[0038] A mathematical way of modelling is described in the
following for defining limitation values Ri based on network
parameters. Parameters occurring in the model are the probability
of failure of paging in the individual cell .alpha..sub.i which was
described above and the probability of failure of the call p.sub.0,
which is defined based on call setup statistics gathered from the
network from a certain geographical area e.g. the location area by
calculating the relation between the number of failed mobile
terminated call setup attempts over a certain period of time and
the number of all mobile terminated call setup attempts over the
same period of time. The probability p.sub.0 may also be defined as
covering the whole network. From this probability of failure of a
call p.sub.0 it is possible with a formula (1) and by assuming even
distribution to calculate the probability of failure of a paging in
the individual cell p.sub.i, that is, the probability of the mobile
station MS being located in the area of cell i. The term N
occurring in formula (1) is the number of cells in the examined
location area.
p.sub.i=(1-p.sub.0)/N, wherein i=1, . . . , N (1)
[0039] The probability of successful paging in the individual cell
pi could also be defined e.g. by calculating how often there are
replies from a cell to mobile terminated calls. The probability
p.sub.i may also be defined for individual calls or
subscribers.
[0040] If in optimising paging the only objective would be to
minimise paging costs, that is, the paging load, it would not be
worth while to page for the mobile station at all, as loading will
then be less. However, this is not an acceptable alternative from
the viewpoint of service quality. On the other hand, if the only
objective would be an optimum service quality, it would be worth
paging for the mobile station, until a reply is received. However,
when optimising paging in practice both the mutually opposed
objectives mentioned above must be taken into account. For
comparing these incommensurable parameters in the model to be
described herein, a certain penal parameter C is established for
failure of paging which represents the value of loss of the call as
commensurable with the value of loading of radio resources. By
increasing penal parameter C it is possible to increase the
limitation values Ri for the number of allowed pagings and vice
versa. The same penal parameter C may be used in all location areas
of the network, whereby the standard or quality of paging will be
uniform all over the network. The penal parameter C may also be
used for the individual area, call or subscriber, if it is
desirable to offer the subscriber e.g. different levels of service
in the network. In practice, the operator thus selects and
establishes the penal parameter C so that with the paging method
according to the invention such numbers of re-paging are achieved
in some area which have been found empirically sensible, e.g. a
suitable paging load is established in the network, whereupon the
same value may also be used elsewhere in the network.
[0041] The following formulas (2)-(5) may be used for solving the
optimum number s.sub.n of all pagings of the mobile station MS as
well as limitation values for the number of pagings for individual
cells. Using the optimum limitation value for the number of pagings
in the individual cell the use of radio resources is minimised with
the method according to the invention. Table 1 shows formulas
(2)-(5) where for the sake of simplicity and by way of example
calculation is performed for five cells only. The following values
are used as initial values in the calculation: p.sub.0=0.05,
.alpha..sub.1=.alpha..sub.2=.alpha..sub.5=0, .alpha..sub.3=0.01,
.alpha..sub.4=0.05. In the first line k=1 values p.sub.i are
calculated with formula (1). The function f.sub.n(p) in formula (2)
is a model of the expected value of paging costs. In formulas (2)
and (5) the occurring parameter n shows the level of precision of
the calculation. By increasing the value of parameter n the
precision in optimising may be improved. In Table 1 the expected
value of paging costs is calculated by using approximation
f.sub.2(p).
f.sub.0(p)=C,
[0042] 1 f 0 ( p ) = C , ( 2 ) f 1 ( p ) = min { C , min i [ 1 + (
1 - ( 1 - i ) p i ) C ] } , f n ( p ) = min { C , min i [ 1 + ( 1 -
( 1 - i ) p i ) f n - 1 ( T i p ) ] } , wherein n > 1 and T i p
= [ ( T i p ) 0 , ( T i p ) 1 , , ( T i p ) N ] ( T i p ) j = p j /
( 1 - ( 1 - i ) p i , when j i a i p i / ( 1 - ( 1 - i ) p i , when
j = i ( 3 ) .alpha..sub.i=m.sub.2i/m.sub.1i (4)
[0043] s.sub.n=min{k:f.sub.n(p(k+1))=C} (5)
[0044] The optimum paging end point s.sub.n is defined with formula
(5), wherein p(k+1)=(p.sub.1, k+1, . . . p.sub.N, k+1) is defined
as follows in the case of Table 1. Examining line k=1 in Table 1
calculation is done at each column pi of the figure
(1-.alpha..sub.i) p.sub.i and these figures are compared with one
another. As the value of column .delta.*.sub.k the index i of that
column pi is chosen, which will give the highest figure of the ones
mentioned. If more than one column will give the same higher
figure, any index of the columns in question may be chosen for
column .delta.*.sub.k. E.g. in Table 1 on line k=1 the highest
numerical value is obtained in columns p.sub.1, p.sub.2 and p.sub.5
and .delta.*.sub.1=1 is chosen of these.
[0045] Next, updated location probabilities may be calculated using
formula (3), wherein index j indicates the cell which the
calculation concerns and index i indicates the cell .delta.*.sub.1
mentioned above which gives the highest numerical value. The
results are shown in Table 1 on line k=2. Next, .delta.*.sub.2 can
be calculated using the new probability values p.sub.i thus
obtained, etc.
[0046] When probabilities p(k) of line k have been calculated, the
optimum paging cost f.sub.2(p(k)) may be calculated according to
formula (2). According to formula (5), when the calculation reaches
the situation f.sub.2(p(k))=C the conclusion is drawn that the
optimum moment of ending, that is, the number of all pagings, is
k-1. This shows that the optimum paging cost is equal to the
penalty for stopping paging, that is, it is no longer worth while
to continue the paging. Optimum limitation values Ri for the number
of pagings for individual cells may now be formed by calculating
the number of occurrences for each cell in column .delta.*.sub.k
until the moment of ending k.
1TABLE 1 k p.sub.1 P.sub.2 p.sub.3 p.sub.4 p.sub.5 .delta.*.sub.k
f.sub.2(p) 1 0.19 0.19 0.19 0.19 0.19 1 622 2 0 0.235 0.235 0.235
0.235 2 533 3 0 0 0.306 0.306 0.306 5 392 4 0 0 0.442 0.442 0 3 144
5 0 0 7.85E - 3 0.785 0 4 218 6 0 0 3.09E - 2 0.155 0 4 824 7 0 0
3.63E - 2 9.07E - 3 0 3 957 8 0 0 3.76E - 4 9.41E - 3 0 4 992 9 0 0
3.8E - 4 4.75E - 4 0 -- 1000
[0047] The value calculated for the expected value f.sub.2(p) of
paging costs with the value 9 of the last line k in Table 1 is no
longer less than the penal parameter C, so it is not worth while to
perform any further paging of this line. Thus the optimum
limitation values for the number of pagings which can be obtained
based on the calculations in Table 1 are R1=R2=R5=1, R3=2 and R4=3,
wherein the limitation values indicate that number of maximum
pagings which may be performed in each cell. Based on the results
of calculations shown in Table 1 limitation values Ri for the
number of pagings are stored for individual cells or cell groups in
the mobile communications system e.g. in connection with the unit
in control of the paging operation, e.g. in the form shown in Table
2. In the case of the secondary embodiment of the invention
described above, the limitation values Ri for the number of pagings
are stored in connection with each base transceiver station
BTS.
2TABLE 2 Limitation value Location area Cell identifier Ri for the
number of pagings LA10 C1 1 C2 1 . . . . . . C10 3
[0048] For the limitation values Ri defined by the operator, values
may be defined in advance and the values are stored in the network
or new values may be defined dynamically during operation of the
network based on new statistics gathered from the network. The
limitation values Ri are preferably stored in connection with the
unit controlling the paging process in the mobile communications
system, e.g. the mobile services switching centre MSC or the base
station controller BSC, as was described above in the primary and
third embodiments of the invention. When required, the limitation
values Ri may also be stored in base transceiver stations BTS, in
accordance with the secondary embodiment of the invention which was
described above. The values m.sub.1i and m.sub.2i needed for
calculating the limitation values are preferably formed in the
operation and maintenance centre OMC or in the mobile services
switching centre MSC using for each ending call attempt such
records formed in the mobile services switching centre MSC, wherein
the identifier of that base transceiver station BTS is stored from
which the mobile station MS has replied as well as the number of
performed pagings and any other information. Calculation of the
limiting values may preferably be performed in the same unit where
the values m.sub.1i and m.sub.2i are formed. If the limitation
values Ri are calculated in the operation and maintenance centre
OMC, they will be transferred from that centre to the concerned
units controlling re-paging, such as the mobile services switching
centre MSC or the base station controller BSC, corresponding with
the embodiments presented in the foregoing. Alternatively,
calculation of the limitation values Ri may be performed
independently in each re-paging control unit, in which case the
values m.sub.1i and m.sub.2i needed in the calculation will again
be transferred to the re-paging control units from the place where
the values m.sub.1i and m.sub.2i have been formed, e.g. from the
OMC. It is an explicit advantage of the latter alternative that the
limitation values may then be calculated in the re-paging control
unit separately for each call, if required.
[0049] The mobile communications system implementing paging
functionality according to the invention includes storing means
according to the invention, e.g. a register, for storing limitation
values for the number of pagings and means for limiting re-pagings
to be performed. The means for limiting re-pagings to be performed
comprise calculating means, e.g. counters, for counting the number
of pagings to be performed, comparing means for comparing the
values of the calculating means with the limitation values Ri for
the number of pagings in cells and means for relaying a re-paging
command to some of the cells of the area according to the location
information based on the result of the comparison made by the said
comparing means. The mobile communications system also preferably
comprises means for defining limitation values for the number of
pagings in the cells.
[0050] The method according to the invention is excellently
suitable for use both in connection with fixed and dynamic location
areas and also in such pagings where the set of cells to be paged
is formed on a subscriber basis or on a call basis utilising the
location information of the mobile station.
[0051] The results of the calculation in the presented optimum
paging alternative may be utilised in designing the capacity
required for the paging channels of the radio network. In radio
systems of the TDMA and FDMA type this could mean that e.g. in each
cell an individual and only necessary share of radio resources
would be allocated for the paging channels. In CDMA systems a lower
network noise level would be achieved by optimising the paging
channels.
[0052] Drawings and their related explanation are intended only to
illustrate the inventive idea. The details of the paging method and
mobile communications system according to the invention may vary
within the scope of the claims. Although the invention has been
described in the foregoing mainly in connection with the setting up
of a speech connection, the invention may also be used for some
other kind of mobile terminated radio connection, e.g. for
delivering short messages.
* * * * *