U.S. patent application number 10/752678 was filed with the patent office on 2004-12-30 for cell station, radio communication system, communication control method of cell station, and method of building radio communication network.
Invention is credited to Aratani, Koichi, Kawashima, Takeshi, Sasayama, Tsukasa, Sato, Hirofumi, Yanagi, Kenji.
Application Number | 20040264421 10/752678 |
Document ID | / |
Family ID | 33535273 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040264421 |
Kind Code |
A1 |
Sato, Hirofumi ; et
al. |
December 30, 2004 |
Cell station, radio communication system, communication control
method of cell station, and method of building radio communication
network
Abstract
Traffic that can be processed at a cell station is increased
without reducing communication quality. When a channel is allocated
to every time slot constituting a communication frame and radio
control section receives a link channel establishment request from
a personal station through a control channel allocated to any of
the time slots, a control section notifies the personal station
through the traffic channel of an allocation message indicating
that the time slot allocated to the control channel will be
allocated to a traffic channel. The transmission of the control
channel is stopped when a predetermined time (a control channel
transmission/reception duration) passes after the notification of
the allocation message.
Inventors: |
Sato, Hirofumi; (Yokohama,
JP) ; Sasayama, Tsukasa; (Yokohama, JP) ;
Kawashima, Takeshi; (Yokohama, JP) ; Aratani,
Koichi; (Yokohama, JP) ; Yanagi, Kenji;
(Yokohama, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
33535273 |
Appl. No.: |
10/752678 |
Filed: |
January 8, 2004 |
Current U.S.
Class: |
370/337 ;
370/347 |
Current CPC
Class: |
C07J 9/00 20130101; A61Q
19/00 20130101; A61K 8/671 20130101; A61Q 19/08 20130101; A61P
35/00 20180101; A61K 2800/92 20130101; A61P 17/00 20180101 |
Class at
Publication: |
370/337 ;
370/347 |
International
Class: |
H04J 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2003 |
JP |
2003-182782 |
Claims
What is claimed is:
1. A cell station accommodating a personal station by using a time
division multiple access method, comprising: communication unit
which transmits and receives a frame including a plurality of time
slots; and control unit which allocates a traffic channel or a
control channel to each of the time slots constituting the frame,
wherein, in the case that a channel is allocated to every time slot
constituting the frame and the communication unit receives a link
channel establishment request from the personal station through the
control channel allocated to any of the time slots, the control
unit notifies the personal station through the control channel that
the time slot allocated to the control channel will be allocated to
a traffic channel and stops transmission and reception of the
control channel when a predetermined time passes after the
notice.
2. A cell station according to claim 1, wherein the predetermined
time is set such that it is longer than an estimated time until the
reception of a link channel establishment re-request when the
re-request is sent as a response of the personal station to the
notice and is shorter than an estimated time until the reception of
a synchronization burst signal when the signal is set as the
response.
3. A cell station accommodating a personal station by using a time
division multiple access method, comprising: communication unit
which transmits and receives a frame including a plurality of time
slots; control unit which allocates a traffic channel or a control
channel to each of the time slots constituting the frame; and
timing storing unit which stores timing for transmitting and
receiving a frame including the control channel, wherein, in the
case that a traffic channel is allocated to every time slot
constituting the frame, when any of the traffic channels is
disconnected to make a time slot open, the control unit controls
the communication unit such that the control channel is transmitted
and received in the time slot which has become open in a frame
transmitted at said timing.
4. A cell station according to claim 3, wherein: the control unit
controls the communication unit to perform carrier sensing for the
control channel in the time slot which has become open in the frame
transmitted and received at said timing; when no interference is
detected, the control unit controls the communication unit to
transmit and receive the control channel in the time slot which has
become open in the frame transmitted and received at said timing;
and when interference is detected, the control unit controls the
communication unit such that it repeats a process of switching a
traffic channel allocated to another time slot to the time slot
which has become open and performing carrier sensing for the
control channel in the another time slot in a frame transmitted and
received at timing stored in the timing storing unit until no
interference is detected and it transmits and receives the control
channel in a time slot in which no interference has been detected
in the frame transmitted and received at said timing.
5. A cell station accommodating a personal station by using a time
division multiple access method, comprising: communication unit
which transmits and receives a frame including a plurality of time
slots; control unit which allocates a traffic channel or a control
channel to each of the time slots constituting the frame; and
traffic monitoring unit which monitors communication traffic,
wherein the control unit performs carrier sensing for the control
channel in a time slot to which the control channel is allocated
according to results of the monitoring by the traffic monitoring
unit and adjusts timing for transmitting and receiving a frame
including the control channel.
6. A cell station according to claim 5, wherein: the traffic
monitoring unit monitors the number of link channel establishment
requests received from the personal station through the control
channel within a predetermined time as the communication traffic;
and the control unit performs said adjustment when the
communication traffic monitored by the traffic monitoring unit is
equal to or smaller than a predetermined threshold.
7. A cell station accommodating a personal station by using a time
division multiple access method, comprising: communication unit
which transmits and receives a frame including a plurality of time
slots; control unit which allocates a traffic channel or a control
channel to each of the time slots constituting the frame; and
traffic monitoring unit which monitors communication traffic,
wherein: the control unit operates in either of a first mode in
which the control channel is always allocated to at least one of
the time slots constituting the frame and a second mode in which a
traffic channel can be allocated to every time slot constituting
the frame; and the operation modes are switched according to
results of the monitoring by the traffic monitoring unit.
8. A cell station according to claim 7, wherein: the traffic
monitoring unit monitors the number of rejections of link channel
establishment requests received from the personal station through
the control channel within a predetermined time as the
communication traffic; and the control unit switches the operation
mode to the second mode when the communication traffic monitored by
the traffic monitoring unit becomes equal to or greater than a
predetermined threshold during an operation in the first mode.
9. A radio communication system having a plurality of cell stations
and a communication network connecting the plurality of cell
stations, wherein at least one of the plurality of cell stations is
a cell station according to claims 1.
10. A communication control method for a cell station accommodating
a personal station by using a time division multiple access method,
wherein: in the case that a channel is allocated to every time slot
constituting the frame, when a link channel establishment request
is received from the personal station through the control channel
allocated to any of the time slots, the personal station is
notified through the control channel that the time slot allocated
to the control channel will be allocated to a traffic channel; and
transmission and reception of the control channel is stopped when a
predetermined time passes after the notice.
11. A communication control method for a cell station accommodating
a personal station by using a time division multiple access method,
wherein, in the case that a traffic channel is allocated to every
time slot constituting the frame, when any of the traffic channels
is disconnected to make a time slot open, the control channel is
transmitted and received in the time slot which has become open in
a frame transmitted and received at timing stored in advance in
storing unit.
12. A communication control method for a cell station accommodating
a personal station by using a time division multiple access method,
comprising the steps of: monitoring communication traffic; and
performing carrier sensing for a control channel in a time slot to
which the control channel is allocated and adjusting timing for
transmitting and receiving a frame including the control channel
when results of the monitoring becomes equal to or greater than a
predetermined threshold.
13. A communication control method for a cell station accommodating
a personal station by using a time division multiple access method,
comprising the steps of: monitoring communication traffic; and
switching the operation mode to a second mode in which a traffic
channel can be allocated to every time slot constituting a frame
when results of the monitoring becomes equal to or greater than a
predetermined threshold during an operation in a first mode in
which a control channel is always allocated to at least one of time
slots constituting a frame to be transmitted and received.
14. A method of constructing a radio communication network
utilizing a plurality of cell stations connected to each other
through a communication network, wherein at least one of the
plurality of cell stations carries out the communication control
method for a cell station according to claim 10.
15. A method of constructing a radio communication network
utilizing a plurality of cell stations connected to each other
through a communication network, wherein at least one of the
plurality of cell stations carries out the communication control
method for a cell station according to claim 11.
16. A method of constructing a radio communication network
utilizing a plurality of cell stations connected to each other
through a communication network, wherein at least one of the
plurality of cell stations carries out the communication control
method for a cell station according to claim 12.
17. A method of constructing a radio communication network
utilizing a plurality of cell stations connected to each other
through a communication network, wherein at least one of the
plurality of cell stations carries out the communication control
method for a cell station according to claim 13.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a communication control
technique and, more particularly, a technique for accommodating
personal stations by using the time division multiple access
method.
[0002] For example, one communication control technique for
accommodating personal stations by using the time division multiple
access method is the personal handyphone system defined in "Second
Generation Cordless Telephone system RCR STD-28", issued by
Research & Development Center for Radio System. Japanese Patent
Laid-Open Publication No. H10-136438 (hereinafter referred to as
Patent Document 1) is disclosed a technique for accommodating a
greater number of personal stations in such a radio communication
system using the time division multiple access method.
[0003] Referring to Patent Document 1, in the case that, when a
channel is allocated to every time slot constituting frames
transmitted and received, a cell station receives a link channel
establishment request from a personal station through a control
channel allocated to any time slot when a channel is allocated to
every time slot constituting frames transmitted and received, the
cell station stops transmission of the control channel and
allocates a time slot which has been allocated to the control
channel to a traffic channel. Thus, a greater number of personal
stations are accommodated.
[0004] Referring again to Patent Document 1, before a cell station
starts the service, the cell station checks from an identifier set
for itself whether the cell station can operate in both of a first
mode in which a control channel is always allocated to any time
slot constituting a frame and a second mode in which traffic
channels can be allocated to all of time slots constituting a
frame. When it can operate in both modes, the cell station obtains
identifiers informed from other cell stations located in the
neighborhood and checks whether there is any cell station operating
only in the first mode among those cell stations. The cell station
sets itself for operations in the second mode only when such a cell
station exists and sets itself for operations in the first mode
when no such cell station exists. Such an arrangement prevents a
situation wherein all cell stations belonging to the same service
area stop transmission over the control channel and personal
stations in a ready state are handled as location being outside the
area.
SUMMARY OF THE INVENTION
[0005] However, the technique disclosed in Patent Document 1 has
the following problems.
[0006] Let us assume that a time slot for a control channel is
allocated to a traffic channel of a certain personal station. In
the case that the personal station cannot recognize the allocated
traffic channel as a result of carrier sensing, the personal
station transmits a re-request for allocation to the cell station.
However, according to the technique disclosed in Patent Document 1,
the re-request for allocation cannot be received because the cell
station has already stopped transmission and reception of the
control channel. As a result, the personal station continues
transmitting the re-request for allocation until the personal
station becomes in a ready state for another cell station, and a
call to the personal station may not be connected.
[0007] Let us assume that, in the case that time slots constituting
a frame which have been allocated to respective traffic channels at
a cell station, a call is terminated and an open slot is produced.
In this case, carrier sensing for the control channel is performed
in the open slot, and the control channel is allocated to the open
slot after it is confirmed that there is no interference. However,
when a plurality of cell stations in the same service area perform
such an allocating process, a plurality of cell stations can
transmit and receive the control channel at close timing. In this
case, interference can be detected during the carrier sensing for
the control channel because of time lags in transmitting and
receiving the time slot attributable to an error in the operating
clock of each of the cell stations, and the control channel may not
be allocated to the open slot. This results in call loss and a
reduction in the traffic. No consideration to such a situation is
reflected in the technique disclosed in Patent Document 1.
[0008] Before starting a service, the cell station decides a mode
of operation, i.e., a first mode in which a control channel is
always allocated to any of time slots that constitute a frame or a
second mode in which a traffic channel can be allocated to every
time slot constituting a frame. However, the mode of operation
decided prior to the operation may not be appropriate for an actual
traffic. No consideration to this point is reflected in the
technique disclosed in Patent Document 1.
[0009] The present invention is made taking the above-described
situations into consideration, and it is an object of the present
invention to improve the traffic that can be processed at a cell
station without any reduction in communication quality.
[0010] In order to solve the above-described problems, in a first
aspect of a cell station according to the present invention, when a
time slot for a control channel is allocated to a traffic channel
of a certain personal station and the personal station cannot
recognize the allocated traffic channel, the cell station can
receive a re-request for allocation transmitted by the personal
station.
[0011] For example, a cell station in this aspect of the present
invention is a cell station accommodating a personal station by
using a time division multiple access method including
communication unit which transmits and receives a frame including a
plurality of time slots and control unit which allocates a traffic
channel or a control channel to each of the time slots constituting
the frame. In the case that a channel is allocated to every time
slot constituting the frame, when the communication unit receives a
link channel establishment request from the personal station
through the control channel allocated to any of the time slots, the
control unit notifies the personal station through the control
channel that the time slot allocated to the control channel will be
allocated to a traffic channel and stops transmission and reception
of the control channel when a predetermined time passes after the
notice.
[0012] In a second aspect of a cell station according to the
present invention, when a time slot which has been allocated to a
traffic channel is to be allocated to a control channel, the
control channel is allocated to the time slot at timing for
transmitting and receiving a frame including the control channel
which has been registered in advance. The frame
transmission/reception timing registered in advance is timing at
which no interference has been detected as a result of carrier
sensing for the control channel.
[0013] For example, a cell station in this aspect of the present
invention is a cell station accommodating a personal station by
using a time division multiple access method, including
communication unit which transmits and receives a frame including a
plurality of time slots, control unit which allocates a traffic
channel or a control channel to each of the time slots constituting
the frame, and timing storing unit which stores timing for
transmitting and receiving a frame including the control channel.
In the case that a traffic channel is allocated to every time slot
constituting the frame, when any of the traffic channels is
disconnected to make a time slot open, the control unit controls
the communication unit such that the control channel is transmitted
and received in the time slot which has become open in a frame
transmitted and received at the timing.
[0014] In a third aspect of a cell station according to the present
invention, when traffic is reduced, the cell station judges that
there is call loss attributable to interference with control
channels of other cell stations, and adjusts a timing for
transmitting and receiving a frame including the control channel is
adjusted.
[0015] For example, a cell station in this aspect of the present
invention is a cell station accommodating a personal station by
using a time division multiple access method, including
communication unit which transmits and receives a frame including a
plurality of time slots, control unit which allocates a traffic
channel or a control channel to each of the time slots constituting
the frame, and traffic monitoring unit which monitors communication
traffic. The control unit performs carrier sensing for the control
channel in a time slot to which the control channel is allocated
according to results of the monitoring by the traffic monitoring
unit and adjusts timing for transmitting and receiving a frame
including the control channel.
[0016] In a fourth aspect of a cell station according to the
present invention, the cell station automatically switches an
operation mode decided before service is started according to
actual traffic.
[0017] For example, a cell station in this aspect of the present
invention is a cell station accommodating a personal station by
using a time division multiple access method, including
communication unit which transmits and receives a frame including a
plurality of time slots, control unit which allocates a traffic
channel or a control channel to each of the time slots constituting
the frame, and traffic monitoring unit which monitors communication
traffic. The control unit operates in either of a first mode in
which the control channel is always allocated to at least one of
the time slots constituting the frame and a second mode in which a
traffic channel can be allocated to every time slot constituting
the frame, and switches the operation mode according to results of
the monitoring by the traffic monitoring unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram of a radio communication
system to which an embodiment of the present invention is
applied;
[0019] FIG. 2 shows an example of a format of communication frames
transmitted and received between a cell station 10 and a personal
station 30;
[0020] FIG. 3 is a schematic configuration diagram of the cell
station 10;
[0021] FIG. 4 is a flow chart for explaining an operation of a main
control section 105 performed when the cell station 10 is started
up;
[0022] FIG. 5 is a flow chart for explaining a process of canceling
allocation of a control channel to a time slot performed by the
main control section 105 at a call connecting process;
[0023] FIG. 6 is a sequence diagram showing a flow of processes
until a traffic channel is established between the cell station 10
whose operation is set in a high traffic mode and the personal
station 30;
[0024] FIG. 7 is a flow chart for explaining a process of
reallocating a control channel to a time slot performed by the main
control section 105 at a call disconnecting process;
[0025] FIG. 8 is a flow chart for explaining a process of adjusting
transmission/reception timing for a communication frame 60 carrying
a control channel performed by the main control section 105;
and
[0026] FIG. 9 is a flow chart for explaining an operation mode
switching process performed by the main control section 105.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] A preferred embodiment of the present invention will now be
described.
[0028] FIG. 1 is a schematic diagram of a radio communication
system to which an embodiment of the present invention is
applied.
[0029] For example, the radio communication system according to the
present embodiment is a personal handyphone system as defined in
"Second Generation Cordless Telephone System RCR STD-28" issued by
Research & Development Center for Radio System, and it is used
in a service area having a high traffic such as a flourishing town.
As illustrated, the system is configured by connecting a plurality
of cell stations 101 to 10.sub.n (hereinafter also simply referred
to as cell stations 10) and a maintenance terminal 20 which
monitors the states of operation of the cell stations 10 through a
communication network 50 such as a PSTN (Public Switched Telephone
Network)
[0030] The cell stations 10 accommodate a personal station 30 by
using the time division multiple access method. A plurality of the
cell station 10 forms a service area 40 in which the personal
station 30 can communicate with the communication network 50.
Although only one personal station 30 is shown in FIG. 1, it is
obvious that there may be a plurality of personal stations 30.
[0031] For example, the personal station 30 selects a cell station
10 in a good environment for communication based on receiving
condition of a control channel transmitted by each of the cell
stations 10. It performs communication by transmitting and
receiving communication frames to and from the selected cell
station 10.
[0032] FIG. 2 shows an example of a format of communication frames
transmitted and received between the cell station 10 and the
personal station 30. As illustrated, the cell station 10 performs
communication by sequentially transmitting and receiving
communication frames 60 formed by a plurality of time slots to and
from the personal station 30. A communication frame 60 has a
plurality of transmission slots 601 which are transmitted from the
cell station 10 to the personal station 30 and a plurality of
reception frames 602 which are received by the cell station 10 from
the personal station 30. The transmission slots 601 and the
reception slots 602 are equal in quantity. For example, in the case
of a personal handyphone system as described above, a communication
frame 60 is formed by eight time slots in total, i.e., four
transmission slots 601 and four reception slots 602, and it has a
frame period of 5 ms.
[0033] The cell stations 10 of the present embodiment operate in
either of a first mode in which a pair of a transmission slot 601
and a reception slot 602 in a communication frame 60 is always
allocated to a control channel (referred to as normal mode) and a
second mode in which all time slots in a communication frame 60 can
be allocated to the traffic channel (referred to as high traffic
mode). By way of example, FIG. 2 shows a case in which a pair of a
transmission slot (a third transmission slot) 601 and a reception
slot (a third reception slot) 602 in a communication frame 60 is
allocated to the traffic channel. It is not essential that the
traffic channel is stored in each of the communication frames 60.
The control channel may be transmitted or received by storing the
control channel in a predetermined transmission slot 601 and/or a
predetermined reception slot 602 of communication frames 60 which
are transmitted and received at an arbitrary frame period. In the
example shown in FIG. 2, the frame period of a control channel
transmission frame for transmission of the control channel from the
cell station 10 to the personal station 30 comes at every 5n-th (n
is a natural number, e.g., 20) frame.
[0034] The cell station 10 will be described in detail. An existing
personal station such as a personal handyphone system that
communicates with the cell station 10 by using the time division
multiple access method may be used as the personal station 30. The
maintenance terminal 20 is a common terminal which manages and
outputs various kinds of information transmitted thereto from the
cell station 10. Therefore, no detailed description is given on the
personal station 30 and the maintenance terminal 20.
[0035] FIG. 3 is a schematic configuration diagram of the cell
station 10.
[0036] As illustrated, the cell station 10 has a transmission
system radio device 102, a reception system radio device 103, a
radio control section 104, a main control section 105, a storage
section 106, a channel control section 107, and an antenna 108. For
example, the cell station 10 of the present embodiment is realized
through the execution of a program in a memory by a CPU of an
information processing apparatus which has the CPU, the memory, a
communication device, and a radio communication device. In this
case, the memory is used as the storage section 106.
[0037] The transmission system radio device 102 performs a
predetermined modulation process on transmission slots 601 received
from the radio control section 104 and transmits them from the
antenna 108. The reception system radio device 103 performs a
predetermined demodulation process on signals received by the
antenna 108 to restore reception slots 602 and passes the reception
slot 602 thus restored to the radio control section 104. The radio
control section 104 transmits and receives communication frames 60
to and from the personal station 30 through the transmission system
radio device 102 and the reception system radio device 103. The
channel control section 107 transmits and receives communication
data and control data to and from the communication network 50
according to a communication protocol adopted by the communication
network 50. Various kinds of information (such as the operation
mode of the cell station 10, information on whether the operation
mode can be switched or not, and a threshold for operation mode
switching) to be used by the main control section 105 are stored in
the storage section 106. The main control section 105 controls
operations of the cell station 10 as a whole.
[0038] Specifically, the main control section 105 transmits and
receives call control data to and from the communication network 50
through the channel control section 108. Whereby the main control
section 105 performs a call control process to establish a channel
to the communication network 50. The main control section 105 also
transmits and receives call control data to and from the personal
station 30 through the radio control section 104 using transmission
slots 601 for transmitting a control channel and reception slots
602 for receiving the control channel. Thus, a call control process
is performed to allocate a traffic channel with the personal
station 30 to a pair of a transmission slot 601 and a reception
slot 602 of a communication frame 60 to establish a radio channel
to the personal station 30. Timing for a control channel
transmission frame is instructed by the main control section 105 to
the radio control section 104. According to the instruction from
the main control section 105, the radio control section 104 stores
call control data in a predetermined transmission slot of the
control channel transmission frame and transmits the control
channel transmission frame by using the transmission system radio
device 102. The main control section 105 also exchanges
communication data transmitted and received through the channel
established between the channel control section 108 and the
communication network 50 and communication data transmitted and
received through the radio channel established between the radio
control section 104 and the personal station 30. Whereby, the
personal station 30 is connected to the communication network 50.
The main control section 105 also receives information on the
control channel transmitted by other cell stations 10 through the
reception system radio device 103.
[0039] In addition to the above-described processes, the main
control section 105 performs a process for increasing the traffic
that can be processed by the cell station 10 without reducing
communication quality.
[0040] First, the main control section 105 decides the operation
mode (either of the normal mode and high traffic mode) when the
cell station 10 is started up (initial operation). FIG. 4 is a flow
chart for explaining the operation of the main control section 105
performed when the cell station 10 is started up.
[0041] The main control section 105 sets an operation mode by
reading operation mode identification information for the cell
station 10 which has been set by an operator and stored in advance
in the storage section 106 (step S101). The main control section
105 receives control channel information transmitted by other cell
stations 10 located in the neighborhood of own cell station 10
through the reception system radio device 103 and the radio control
section 104 and stores the information in the storage section 106
(step S102).
[0042] Next, the main control section 105 judges which of the
normal mode and the high traffic mode has been set (step S103).
When the normal mode has been set, the process proceeds to step
S106. When the high traffic mode has been set, it is checked
whether the number of cell stations 10 transmitting the control
channel stored in the storage section 106 is equal to or greater
than a threshold which has been set by the operator and stored in
advance in the storage section 106 (step S104). When the number is
equal to or greater than the threshold, the process proceeds to
step S106. When the number is not equal to or greater than the
threshold, the main control section 105 changes the operation mode
setting from the high traffic mode to the normal mode (step S105),
and then the process proceeds to step S106.
[0043] Next, at step S106, the main control section 105 reads
operation mode switchability information for own cell station 10
which has been set by the operator and stored in advance in the
storage section 106 and makes a setting accordingly. The main
control section 105 then performs carrier sensing to determine
slots to be allocated to the control channel and frame
transmission/reception timing such that no interference with
control channels of the other cell stations 10 occurs (step S107).
Since existing techniques are used for determining slots to be
allocated to a control channel and frame transmission/reception
timing through carrier sensing, no detailed description will be
made in this regard.
[0044] When slots to be allocated to the control channel and frame
transmission/reception timing are determined as described above,
the main control section 105 controls the radio control section 104
such that communication frames having control channel information
stored in the allocated slots thereof are transmitted and received
at the frame transmission/reception timing (step S108). Then, the
operation of the cell station 10 is started.
[0045] When the flow shown in FIG. 4 terminates and the cell
station 10 enters an operating state, the main control section 105
performs a process of canceling the allocation of time slots to the
control channel and a process of reallocating time slots to the
control channel according to the operation mode which has been set,
the operation mode switchability information, and the state of
occupation of time slots that constitute a communication frame
60.
[0046] FIG. 5 is a flow chart for explaining the process of
canceling the allocation of time slots to the control channel that
is performed by the main control section 105 at a call connecting
process.
[0047] First, when a link channel establishment request is received
from the personal station 30 through a communication frame 60 for
transmitting and receiving the control channel (YES at step S201),
the main control section 105 checks whether there is a pair of open
slots (a transmission slot 601 and a reception slot 602) in the
communication frame 60 transmitted and received by the radio
control section 104 (step S202).
[0048] When it is found at step S202 that a pair of open slots
exists, the main control section 105 allocates the traffic channel
of the personal station 30 which has transmitted the link channel
establishment request to the pair of open slots and performs
carrier sensing in the open slots to determine the frequency of the
traffic channel (step S203). The main control section 105 then
performs a process of synchronizing the traffic channel between the
personal station 30 which has transmitted the link channel
establishment request (step S204) and own cell station 10. When the
synchronization process is successful and the traffic channel is
established (YES at step S205), the traffic channel synchronizing
process is followed by a call control process (step S206) that is
performed between the personal station 30 and own cell station 10
to establish a radio channel to the personal station 30. The
process then returns to step S201. When the synchronizing process
fails and the traffic channel is not established (NO at step S205),
the process returns to step S201.
[0049] When there is no pair of open slots at step S202 or when a
traffic channel or control channel has been allocated to every time
slot constituting the communication frame 60, the main control
section 105 checks whether the operation mode set for itself in the
flow shown in FIG. 4 is the high traffic mode (step S207).
[0050] When it is found at step S207 that the operation mode is not
the high traffic mode or when the operation mode is the normal
mode, the main control section 105 increments the value in a
counter which is, for example, automatically reset when a
predetermined time passes to update the number of rejections of
link establishment requests per the predetermined time (step S208).
Then, the main control section 105 notifies the personal station 30
of the rejection of the link establishment request through the
communication frame 60 for the transmission and reception of the
control channel (step S209), and the process thereafter returns to
step S201.
[0051] When it is found at step S207 that the operation mode is the
high traffic mode, the main control section 105 performs carrier
sensing in the time slots to which the control channel is allocated
to retrieve frequencies for traffic channels (step S210). When the
carrier sensing reveals that interference occurs at any frequency
that traffic channels can use in the time slots to which the
control channel is allocated and that no traffic channel can be
allocated to the times lots (NO at step S211), the main control
section 105 notifies the personal station 30 of there jection of
time slot allocation through the communication frame 60 for
transmitting and receiving the control channel (step S209), and the
process thereafter returns to step S201. On the contrary, when a
frequency that traffic channels can use is detected in the time
slots to which the control channel is allocated as a result of the
carrier sensing (YES at step S211), the main control section 105
notifies the personal station 30 of the allocation of time slots
through the communication frame 60 for transmitting and receiving
the control channel (step S212).
[0052] After notifying the personal station 30 of the time slot
allocation, the main control section 105 stores the timing of
transmission and reception of the communication frame 60 for
transmitting and receiving the control channel at the radio control
section 104 in the storage section 106 (step S213). Then, it waits
for transmission of a re-request for link channel establishment
from the personal station 30 (steps S214 and S215) for a
predetermined time. The predetermined time is set such that it is
longer than an estimated time until the reception of the re-request
for link channel establishment when the request is sent as a
response of the personal station 30 to the allocation notice and
such that it is shorter than an estimated time until the reception
of an up synchronization burst signal when the signal is
transmitted as the response. This makes it possible to process
either of a link channel establishment re-request and an up
synchronization burst signal using the same time slot.
[0053] When a link channel establishment re-request is sent from
the personal station 30 within the predetermined time (YES at step
S214), the process returns to step S210 to continue the retrieval
of frequencies for traffic channels. On the contrary, when no link
channel establishment re-request is sent from the personal station
30 within the predetermined time (YES at step S215, in which case
an up synchronization burst signal is sent as a response of the
personal station 30 to the allocation notice), the main control
section 105 causes the radio control section 104 to stop
transmitting and receiving the control channel and cancels the
allocation of the control channel to time slots (step S216). Then,
it instructs the radio control section 104 to perform a traffic
channel synchronizing process according the time slot and frequency
allocated to the personal station 30 (step S217). Whereby, the
radio control section 104 performs a traffic channel synchronizing
process by exchanging synchronization burst signals with the
personal station 30 through the transmission system radio device
102 and the reception system radio device 103.
[0054] When the synchronizing process at step S217 is successful
and a traffic channel is established (YES at step S218), the main
control section 105 performs a call control process with the
personal station 30 to establish a radio channel (S219). On the
contrary, when the synchronizing process at step S217 fails and no
traffic channel is established (NO at step S218), the main control
section 105 re-allocates the control channel to the time slots for
which control channel allocation has been canceled (step S220).
Then, the main control section 105 reads the timing for
transmission and reception of the communication frame 60 for
transmitting and receiving the control channel stored in the
storage section 106 and causes the radio control section 104 to
resume transmission and reception of the communication frame 60 for
transmitting and receiving the control channel at the timing for
transmission and reception (step S221).
[0055] FIG. 6 is a sequence diagram showing a flow of the process
performed until a traffic channel is established between the cell
station 10 whose operation mode is set to the high traffic mode and
the personal station 30. It is assumed that there is no open slot
in communication frames 60 transmitted and received by the cell
station 10.
[0056] First, the personal station 30 transmits a link channel
establishment request message to the cell station 10 (step SQ301).
Upon receipt of the link channel establishment request message, the
cell station 10 performs step S210 in FIG. 5 because there is no
open slot in the communication frames 60 transmitted and received
by itself and the high traffic mode is set as the operation mode.
That is, the time slot to which the control channel is allocated is
chosen as a time slot to be allocated to the traffic channel, and
carrier sensing is performed in the time slot to retrieve
frequencies for traffic channels (step SQ302). Then, an allocation
message including specification of the allocated times lot and
frequency is transmitted to the personal station 30 (step
SQ303).
[0057] When the allocation message from the cell station 10 is
received, the personal station 30 performs carrier sensing
according to the time slot and frequency specified by the
allocation message to check whether the time slot and frequency can
be used as a traffic channel (SQ304). When they cannot be used
because of reasons such as interference, a link channel
establishment re-request message is transmitted to the cell station
10 (step SQ305).
[0058] The cell station 10 receives the link channel establishment
re-request message transmitted by the personal station 30 within a
predetermined time (a control channel transmission/reception
duration 701) after the transmission of the allocation message in
the processes at steps S214 and S215 shown in FIG. 5. The cell
station 10 then performs step S210 in FIG. 5 to re-retrieve
frequencies for traffic channels (step SQ306) and transmits an
allocation message including specification of a time slot and a
frequency to be allocated to the personal station 30 again (step
SQ307) Upon receipt of the allocation message again from the cell
station 10, the personal station 30 performs a process similar to
step SQ304 to check whether the time slot and frequency specified
by the allocation message can be used as a traffic channel (step
SQ308). When they can be used, it transmits an up synchronization
burst signal to the cell station 10 using the time slot and
frequency (step SQ310).
[0059] Since the cell station 10 has not received the link channel
establishment re-request message transmitted by the personal
station 30 within the control channel transmission/reception
duration 701 after the transmission of the allocation message in
the processes at steps S214 and S215 shown in FIG. 5, it performs
the process at step S216 in FIG. 5 to stop transmission and
reception of the control channel and to cancel the allocation of
the control channel to a time slot (step SQ309). Thereafter, it
receives an up synchronization burst signal transmitted by the
personal station 30.
[0060] In the case of the above-described personal handyphone
system, the personal station 30 transmits the up synchronization
burst signal before time-out of an up synchronization burst signal
waiting timer (TR101C-1) 702 which is started after the
transmission of the allocation message at the cell station 10. The
time-out comes 100 ms after the timer is started. Upon receipt of
the allocation message, the personal station 30 performs carrier
sensing in four communication frames 60. Since a communication
frame 60 of the above-described personal handyphone system is 5 ms,
the carrier sensing is performed for 20 ms. Therefore, the timing
of transmission of the link channel establishment re-request
message from the personal station 30 comes at least 20 ms after the
reception of the allocation message. When no allocation message is
received from the cell station 10, the personal station 30
transmits another link channel establishment request message again
1200 ms after the transmission of the message requesting link
channel establishment request message. This process is repeated up
to three times.
[0061] Therefore, in the case of the personal handyphone system
described above, the control channel transmission/reception
duration 701 is set taking those points into consideration.
Specifically, the duration is to start 1200 ms after the
transmission of a link establishment request message and to end
within a time range between 20 ms and 100 ms after the transmission
of an allocation message. The duration is to be longer than an
estimated time until the reception of a re-request for link channel
establishment re-request message at the cell station 10 when the
link channel establishment re-request message is sent as a response
of the personal station 30 to the allocation message. The duration
is to be shorter than an estimated time until the reception of an
up synchronization burst signal at the cell station 10 when the up
synchronization burst signal is transmitted as the response of the
personal station 30 to the allocation message.
[0062] When the cell station 10 receives the up synchronization
burst signal before the time-out of the up synchronization burst
signal waiting timer 702, it transmits a down synchronization burst
signal to the personal station 30 (step SQ311). When the personal
station 30 receives the down synchronization burst signal before
time-out of a down synchronization burst signal waiting timer
(TR101P-1) 703 which is started after the transmission of the up
synchronization burst signal (the time out comes 100 ms after the
timer is started), it transmits a TCH (traffic channel) idle burst
signal to the cell station 10 (step SQ312). When the cell station
10 receives the TCH idle burst signal before time-out of a TCH idle
burst signal waiting timer (TR101C-2) 704 which is started after
the transmission of the down synchronization burst signal, it
transmits a TCH idle burst signal to the personal station 30 (step
SQ313). When the personal station 30 receives the TCH idle burst
signal before time-out of a TCH idle burst signal waiting timer
(TR101P-2) 705 which is started after the transmission of the TCH
idle burst signal, a traffic channel is established (step
SQ314).
[0063] FIG. 7 is a flow chart for explaining a process of
reallocating the control channel to a time slot that is performed
by the main control section 105 at a call disconnect process.
[0064] When the radio control section 104 receives a call
disconnect message from a certain personal station 30 through a
traffic channel, the main control section 105 transmits the call
disconnect message to the communication network 50 through the
channel control section 107 and cancels the allocation of the
traffic channel to a time slot is cancelled. When the cancellation
of the allocation of the traffic channel to a time slot results in
any open slot in communication frames 60 transmitted and received
by the radio control section 104 through the transmission system
radio device 102 and the reception system radio device 103 (YES at
step S401), the main control section 105 checks whether the
operation mode set for itself is the high traffic mode (step S402).
When the operation mode is the high traffic mode, the main control
section 105 further checks whether the transmission and reception
of the control channel is currently stopped by the radio control
section 104 (step S403).
[0065] When the transmission and reception of the control channel
is stopped by the radio control section 104 (YES at step S403), the
main control section 105 reads the timing of transmission and
reception of a communication frame 60 carrying the control channel
stored in the storage section 106 (step S404) Next, the main
control section 105 performs carrier sensing for the control
channel in the newly generated open slot at the read
transmission/reception timing of the communication frame 60 to
check whether there is any interference with the control channel
(step S405).
[0066] When it is found that there is interference with the control
channel as a result of the carrier sensing (YES at step S406), the
main control section 105 transmits, through any of the traffic
channels, a message to the personal station 30 that is
communicating using this traffic channel to notify the personal
station 30 that the time slot to which the traffic channel is
allocated will be changed to the open slot (a TCH switch message in
the case of the above-described personal handyphone system).
Whereby, the time slot to which the traffic channel has been
allocated is changed to the open slot (step S407). The process then
returns to step S405 at which the main control section 105 performs
carrier sensing for the control channel in the newly generated open
slot at the transmission/reception timing for the communication
frame 60 for transmitting and receiving the control channel read as
described above.
[0067] When it is found that there is no interference with the
control channel as a result of the carrier sensing (NO at step
S406), the main control section 105 allocates the control channel
to the open slot (step S408). Then, it causes the radio control
section 104 to resume the transmission and reception of the
communication frame 60 for transmitting and receiving the control
channel at the transmission/reception timing for the communication
frame 60 for transmitting and receiving the control channel read
from the storage section 106 (step S409).
[0068] When the flow shown in FIG. 4 is terminated and the cell
station 10 enters the operating state, the main control section 105
monitors the state of communication traffic. According to results
of the monitoring, it performs a process of adjusting the
transmission/reception timing of the communication frame 60
carrying the control channel and a process of switching the
operation modes.
[0069] FIG. 8 is a flow chart for explaining the process of
adjusting the transmission/reception timing of the communication
frame 60 carrying the control channel performed by the main control
section 105.
[0070] While the radio control section 104 transmits and receives
the control channel, the main control section 105 counts the number
of link channel establishment requests received by the radio
control section 104 through the control channel within a
predetermined time (e.g., one hour) (steps S501, S502, and S503).
It is judged whether the count value is equal to or smaller than a
predetermined threshold (referred to as adjustment reference value)
stored in the storage section 106 (step S504). For example, the
adjustment reference value is set at the number (an estimated
value) of received link channel establishment requests in a case
wherein it seems that proper transmission and reception of the
control channel is not performed because of interference.
[0071] When the count value within the predetermined time is equal
to or smaller than the adjustment reference value (YES at step
S504), the main control section 105 causes the radio control
section 104 to suspend the transmission and reception of the
control channel (step S505). Then the main control section 105
performs carrier sensing to decide again a slot to be allocated to
the control channel and frame transmission/reception timing at
which no interference with the control channels of other cell
stations 10 occurs (step S506). The radio control section 104 is
then caused to resume the transmission and reception of the
communication frame 60 for transmitting and receiving the control
channel at the slot and frame transmission/reception timing thus
decided again (step S507).
[0072] When the radio control section 104 stops transmitting and
receiving the control channel (NO at step S501), the count value is
cleared (step S508).
[0073] In the flow shown in FIG. 8, the transmission/reception
timing for the communication frame 60 carrying the control channel
is re-decided each time a predetermined time passes during the
transmission and reception of the control channel based on a value
counted within the predetermined time. For example, values counted
within the predetermined time may be stored in the storage section
106; an average of such count values may be obtained when the
number of the count values reaches a predetermined number (e.g.,
when the number of the count values is counted for a day); and the
processes at steps S504 to S507 may be performed on the average
value thus obtained.
[0074] FIG. 9 is a flow chart for explaining the operation mode
switching process performed by the main control section 105.
[0075] The main control section 105 counts the number of allocation
reject messages in response to link channel establishment requests
transmitted by the radio control section 104 within a predetermined
time (e.g., one hour) (steps S601 and S602). Then, the main control
section 105 judges whether the count value is equal to or greater
than a predetermined threshold (referred to as reference value for
switching to the high traffic mode) stored in the storage section
106 (step S603). The reference value for switching to the high
traffic mode is set at the number (an estimated value) of
allocation reject messages transmitted in a case wherein it seems
that possibility of rejection of a link channel establishment
request is higher because of an increase in the traffic.
[0076] When the count value within the predetermined time is equal
to or greater than the reference value for switching to the high
traffic mode (YES at step S603), the main control section 105
checks whether the operation mode switchability information read at
step S106 in FIG. 4 indicates that operation mode switching is
enabled (step S604). If the information indicates that operation
mode switching is enabled, the main control section 105 further
checks whether the operation mode set for own cell station 10 is
the normal mode (step S605). When the operation mode set for own
cell station 10 is the normal mode (YES at step S605), the main
control section 105 changes the operation mode from the normal mode
to the high traffic mode (step S606). The process thereafter
proceeds to step S611. When the operation mode switchability
information indicates that operation mode switching is disabled (NO
at step S604) or when the operation mode set for own cell station
10 is the high traffic mode (NO at step S605), the process proceeds
to step S611 without changing the operation mode.
[0077] When the count value within the predetermined time is not
equal to or greater than the reference value for switching to the
high traffic mode (NO at step S603), the main control section 105
judges whether the count value is equal to or smaller than a
predetermined threshold (referred to as reference value for
switching to the normal mode) stored in the storage section 106
(step S607). The reference value for switching to the normal mode
is set at the number (an estimated value) of allocation reject
messages transmitted in a case wherein it seems that possibility of
rejection of a link channel establishment request is lower because
of a reduction in the traffic.
[0078] When the count value within the predetermined time is not
equal to or smaller than the reference value for switching to the
normal mode (NO at step S607), the process returns to step S601.
When the count value is equal to or smaller than the reference
value for switching to the normal mode (YES at step S607), the main
control section 105 checks whether the operation mode switchability
information indicates that operation mode switching is enabled
(step S608). If the information indicates that operation mode
switching is enabled, the main control section 105 further checks
whether the operation mode set for own cell station 10 is the high
traffic mode (step S609). When the operation mode set for own cell
station 10 is the high traffic mode (YES at step S609), the main
control section 105 changes the operation mode from the high
traffic mode to the normal mode (step S610). The process thereafter
proceeds to step S611. When the operation mode switchability
information indicates that operation mode switching is disabled (NO
at step S608) or when the operation mode set for own cell station
10 is the normal mode (NO at step S609), the process proceeds to
step S611 without changing the operation mode.
[0079] At step S611, the main control section 105 controls the
channel control section 107 to transmit the operation mode set for
own cell station 10, the operation mode switchability information,
and the state of communication traffic (the number of allocation
reject messages within the predetermined time) to the maintenance
terminal 20 through the communication network 50. Then, the count
value is cleared (step S612), and the process returns to step S601.
Upon receipt of the above information, the maintenance terminal 20
notifies maintenance personnel of the operation mode, the operation
mode switchability information, and the state of communication
traffic notified by the cell station 10 by displaying them on a
display. This allows the maintenance personnel to judge the state
of service in the current operation mode and to reconsider the
installation place, the operation mode and operation mode
switchability information of own cell station 10.
[0080] In the flow shown in FIG. 9, whether to switch the operation
mode is judged each time a predetermined time passes based on a
value counted within the predetermined time. For example, values
counted within the predetermined time may be stored in the storage
section 106; an average of such count values may be obtained when
the number of the count values reaches a predetermined number
(e.g., when the number of the count values is counted for a day);
and the processes at steps S603 to S611 may be performed on the
average value thus obtained.
[0081] A preferred embodiment of the invention has been described
above.
[0082] In the embodiment, when the radio control section 104
receives a link channel establishment request message from the
personal station 30 through the control channel that is allocated
to any time slot in a state in which a channel is allocated to
every time slot constituting a communication frame 60, the main
control section 105 notifies the personal station 30 of an
allocation message through the control channel to indicate that the
time slot allocated to the control channel will be allocated to a
traffic channel. The transmission of the control channel is stopped
when a predetermined time (the control channel
transmission/reception duration 701) passes after the notification
of the allocation message. Therefore, in the present embodiment, in
a case wherein the time slot for the control channel is allocated
to the traffic channel of a certain personal station 30 and the
personal station 30 cannot recognize a traffic channel thus
allocated, a re-request for allocation transmitted by the personal
station 30 can be received. It is therefore possible to suppress
any reduction in connectability of a call from the personal station
30.
[0083] In the present embodiment, in a case wherein a traffic
channel is allocated to every time slot constituting a
communication frame 60 and any of the traffic channels is
disconnected to produce an open slot, the main control section 105
controls the radio control section 104 such that a control channel
is transmitted and received in the open slot in the communication
frame 60 that is transmitted and received at frame
transmission/reception timing stored in the storage section 106.
The frame transmission/reception timing is transmission/reception
timing of the communication frame 60 of a control channel in which
no interference has been detected during carrier sensing and which
has been properly transmitted and received. Therefore, the
possibility of detection of interference is reduced by performing
carrier sensing in the control channel at that
transmission/reception timing, and the possibility of successful
allocation of the control channel to the open slot is thus
increased.
[0084] Even if interference is detected, in the present embodiment,
the open slot is changed to a slot to which a traffic channel is
allocated, and another time slot is made open and is subjected to
carrier sensing for the control channel. Since the control channel
can be thus allocated to any time slot, the occurrence of call loss
and a resultant reduction of traffic can be prevented.
[0085] In the present embodiment, the main control section 105
monitors the number of link channel establishment request messages
received within a predetermined time. When the number of received
requests is equal to or smaller than a predetermined adjustment
reference value, carrier sensing for the control channel is
performed in the time slot to which the control channel is
allocated to adjust the timing for transmitting and receiving the
frame including the control channel. This makes it possible to
prevent proper transmission and reception of the control channel
from being disabled by interference, and the occurrence of call
loss and a resultant reduction in traffic can be prevented.
[0086] In the present embodiment, the main control section 105
monitors the number of link channel establishment request messages
transmitted within a predetermined time and controls the switching
of operation modes according to results of the monitoring.
Specifically, the operation mode is switched from the normal mode
to the high traffic mode when the number of transmitted messages is
equal to or greater than a predetermined reference value for
switching to the high traffic mode, and the operation mode is
switched from the high traffic mode to the normal mode when the
number of transmitted messages is equal to or smaller than a
predetermined reference value for switching to the normal mode
(provided that operation mode switchability information indicates
that switching is enabled). This allows an operation mode decided
before the starting of the service to be automatically switched to
another according to actual traffic.
[0087] The present embodiment thus makes it possible to increase
traffic that can be processed at a cell station without reducing
communication quality.
[0088] The invention is not limited to the above-described
embodiment and may be modified in various ways within the scope of
the teaching thereof. For example, the above-described functions of
the cell station 10 are not limited to implementation on a software
basis through execution of a program in a memory by a CPU in an
information processing apparatus having a CPU, a memory, and a
communication device. Alternatively, the functions may be provided
on a hardware basis using an integrated circuit such as an
ASIC.
[0089] As described above, the invention makes it possible to
increase traffic that can be processed by a cell station without
reducing communication quality.
* * * * *