wireless communication system

Abstract

To increase the chances of accepting a handover request for a wideband call in a cordless communication device in which both a normal band call and a wideband call can be used between a handset and a base unit. [Solution] A plurality of cordless communication devices, each consisting of a base unit and one or more handset units, are connected to a main unit, and the base units and handset units are wirelessly connected using time division multiple access / time division duplex. When a base unit at the destination receives a handover request for a wideband call from a handset unit and there is no available space for a wideband call but there is available space for a normal band call, the base unit at the destination sends a request to change the wideband call to a normal band call via the main unit to the base unit at the source of the call, changing the wideband call of the handset unit that sent the handover request to a normal band call. The base unit at the destination allows the handover of the handset unit that has been changed from a wideband call to a normal band call.

Description

[Technical Field]

[0001] The present invention relates to a wireless communication system suitable for use in a digital cordless telephone. [Background technology]

[0002] Wireless communication systems have become widespread in which multiple cordless communication devices, each consisting of a base unit and one or more slave units, are connected to a main unit connected to one or more telephone lines (see, for example, Patent Document 1 (JP 2013-85154 A) and Patent Document 2 (JP 2015-177239 A)). These wireless communication systems are used in a variety of facilities, including companies, factories, hospitals, and offices.

[0003] In this type of wireless communication system, taking into consideration that the range in which the base unit and handset of a cordless communication device can communicate while maintaining call quality is limited, the system is equipped with a handover function to prevent the call from being interrupted even when the user moves around with the handset while talking on the phone, and the base units are placed in locations distant from each other so that the entire area of ​​the facility can be covered.

[0004] Here, the handover function is a function for switching the base unit with good communication quality when the slave unit moves and changes its location.

[0005] In some cordless telephone calls in this type of wireless communication system, different bands can be used as the transmission band for call information between the base unit and the handset. For example, in cordless telephone calls using the TDMA (Time Division Multiple Access) / TDD (Time Division Duplexing) system of the DECT (Digital Enhanced Cordless Telecommunications) wireless system, normal band calls (hereinafter referred to as normal band calls) using one slot each for downlink calls from the base unit to the handset and uplink calls from the handset to the base unit, for a total of two slots, and wideband calls (hereinafter referred to as wideband calls) using two slots each for calls from the base unit to the handset and from the handset to the base unit, for a total of four slots.

[0006] In telephone systems such as business phones, the main unit accommodates many cordless communication devices, so multiple wireless terminal devices are often connected in the same area and calls are made simultaneously. The number of devices that can be accommodated by the main unit is set within the number of slots because the number of simultaneous calls that can be made is determined by the number of slots. However, when using wideband calls with high sound quality, the number of devices that can be accommodated is less than the number of handsets that can be used for calls.

[0007] Therefore, when a wideband call using two slots is being conducted between a base unit and a handset, if there are few available slots, a technology has been provided that changes the wideband call to a normal band call, allowing other handset units to make calls (see, for example, Patent Document 3 (JP 2017-60028 A)). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-85154 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-177239 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-60028 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, in a cordless communication device that allows both normal bandwidth calls and wideband calls between a handset and a base unit, when a handset that is making a wideband call sends a handover request to another base unit, there is a problem in that even if the other base unit has availability that would allow it to accept a handover request for a normal bandwidth call, it cannot accept the handover request for a wideband call.

[0010] Furthermore, the technology of the above-mentioned Patent Document 3 is a technology that applies between a base unit and a handset that are conducting a call, and therefore cannot respond to a handover request from a handset that is conducting a wideband call with the base unit.

[0011] An object of the present invention is to provide a wireless communication system that can solve the above problems. [Means for solving the problem]

[0012] In order to solve the above problem, the invention of claim 1 is as follows: In a wireless communication system in which a plurality of cordless communication devices, each consisting of a base unit and one or more handset units, are connected to a main unit, the base unit and the handset units are wirelessly connected using a time division multiple access / time division duplex system, and wideband calls and normal band calls are possible, and a handset unit in a call can perform handover to switch between the base units to which it is wirelessly connected, The handset that is making the wideband call with the first base unit sends a handover request for the wideband call to the second base unit that will be wirelessly connected to the handset after the handover; the second base unit that has received the handover request for the wideband call sends a request to change the wideband call to the normal band call via the main unit to the first base unit when there is no available space for the wideband call but there is available space for the normal band call; The first base unit, which has received the request to change from the wideband call to the normal band call through the main unit, changes the call between itself and the handset that sent the handover request from the wideband call to the normal band call, The second base unit permits handover of the handset that has been changed from the wideband call to the normal band call. The present invention provides a wireless communication system.

[0013] In the wireless communication system according to the invention of claim 1 having the above-mentioned configuration, when the second base unit (the base unit to which the handover is to be made) receives a request for handover of a wideband call and there is no available space for a wideband call but there is available space for a normal band call, it sends a request to change from the wideband call to the normal band call to the first base unit (the base unit from which the handover is to be made) via the main unit.

[0014] The first base unit sends a request to change the call from a wideband call to a normal band call to the handset that sent the handover request, and changes the call between the first base unit and the handset that sent the handover request from the wideband call to the normal band call. The second base unit permits the handover of the handset that has been changed from the wideband call to the normal band call. [Effects of the Invention]

[0015] According to this invention, when a handover request for a broadband call is sent from a handset, even if the base unit at the destination does not allow broadband calls, if there is space for normal band calls, the handover can be performed, thereby increasing the chances of continuing the call without interruption. [Brief explanation of the drawings]

[0016] [Figure 1]1 is a block diagram for explaining an overview of an embodiment of a wireless communication system according to the present invention; [Figure 2] FIG. 1 is a diagram for explaining handover in an embodiment of a wireless communication system according to the present invention. [Figure 3] 10A and 10B are diagrams for explaining the availability of a master unit at the handover destination and how a handover request is handled in the embodiment of the wireless communication system according to the present invention. [Figure 4] 1 is a block diagram showing a detailed configuration example of a main device that constitutes a part of an embodiment of a wireless communication system according to the present invention. [Figure 5] 2 is a block diagram showing a detailed configuration example of a master unit constituting a part of an embodiment of a wireless communication system according to the present invention; [Figure 6] 2 is a block diagram showing a detailed configuration example of a slave unit that constitutes a part of an embodiment of a wireless communication system according to the present invention; [Figure 7] 1 is a diagram showing part of a flowchart for explaining the main part of the operation of the base unit of the cordless telephone device in the embodiment of the wireless communication system according to the present invention; [Figure 8] 1 is a diagram showing part of a flowchart for explaining the main part of the operation of the base unit of the cordless telephone device in the embodiment of the wireless communication system according to the present invention; [Figure 9] 1 is a diagram showing part of a flowchart for explaining the main part of the operation of the base unit of the cordless telephone device in the embodiment of the wireless communication system according to the present invention; [Figure 10] 1 is a diagram showing part of a flowchart for explaining the main part of the operation of the base unit of the cordless telephone device in the embodiment of the wireless communication system according to the present invention; [Figure 11] 1 is a diagram showing part of a flowchart for explaining the main part of the operation of the base unit of the cordless telephone device in the embodiment of the wireless communication system according to the present invention; [Figure 12]10 is a diagram showing a part of a flowchart for explaining the operation at the time of handover of a handset of a cordless telephone device in an embodiment of the wireless communication system according to the present invention; [Figure 13] 10 is a diagram showing a part of a flowchart for explaining the operation at the time of handover of a handset of a cordless telephone device in an embodiment of the wireless communication system according to the present invention; [Figure 14] FIG. 10 is a diagram showing a part of an example of a sequence at the time of handover in an embodiment of the wireless communication system according to the present invention. [Figure 15] FIG. 10 is a diagram showing the continuation of the example of the sequence during handover in the embodiment of the wireless communication system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of a wireless communication system according to the present invention will be described with reference to the drawings, taking as an example a case where the system is applied to a telephone system called a business phone.

[0018] 1 is a block diagram showing an example of the overall configuration of a telephone system 10 as an embodiment of a wireless communication system according to the present invention. In this example of telephone system 10, a plurality of cordless telephone devices 21, 22, ..., 2n (n is an integer of 2 or more; the same applies below) are connected as extension telephone devices to a main device 1 as an example of a higher-level device. Each of the cordless telephone devices 21 to 2n is an example of a cordless communication device, and is made up of a base unit CS1, CS2, ..., CSn, respectively, and a handset PS1, PS2, ..., PSm (m is an integer of 2 or more; the same applies below), and each of the base units CS1 to CSn and each of the handset PS1 to PSm are wirelessly connected.

[0019] In the wireless communication system of this embodiment, the base units constituting the cordless telephone devices 21, 22, ..., 2n are fixed as base units CS1, CS2, ..., CSn, respectively, but when handover is taken into consideration, any of the handset units PS1, PS2, ..., PSm can constitute the cordless telephone devices 21, 22, ..., 2n.

[0020] In this embodiment, wireless connections between the base units CS1 to CSn of the cordless telephone devices 21 to 2n and the handsets PS1 to PSm are established by the TDMA / TDD method using the DECT standard for digital cordless telephones.

[0021] The DECT radio system is a wireless communication standard that employs the TDMA / TDD method, which consists of 24 slots (12 slots for uplink and 12 slots for downlink) in one frame with a 10 ms period. Wireless communication that complies with the DECT system assigns a number to each slot used for wireless communication to control the slot position for communication. Furthermore, one frame consists of 24 slots, from slot #1 to slot #24, and communication is controlled by assigning a frame number to each frame, with one slot pair assigned as a control channel and 11 slot pairs assigned as call channels.

[0022] In this embodiment, wireless calls between each of the base units CS1 to CSn of the cordless telephone devices 21 to 2n and each of the handset units PS1 to PSm are configured to allow normal band calls, with one slot each for downlink calls from the base units CS1 to CSn to the handset units PS1 to PSm and uplink calls from the handset units PS1 to PSm to the base units CS1 to CSn, each using a total of two slots, and wideband calls, with two slots each for calls from the base units CS1 to CSn to the handset units PS1 to PSm and from the handset units PS1 to PSm to the base units CS1 to CSn, each using a total of four slots.

[0023] The wireless connection between each of the base units CS1 to CSn of the cordless telephone devices 21 to 2n and each of the handset units PS1 to PSm is not limited to the TDMA / TDD system using the DECT standard. For example, various wireless connection wireless communication system configurations are possible, such as a wireless LAN (Local Area Network) system in which the base unit is configured as an access point device and the handset is configured as a station device wirelessly connected to the access point device, and multiple access point devices are further connected to a main unit, or a PHS (Personal Handyphone System) system in which a frequency band of 1893.5 MHz to 1906.1 MHz is used and one frame has a 5 ms period and includes eight slots (four slots for uplink and four slots for downlink).

[0024] The main unit 1 can accommodate one or more telephone lines L1 to Li (i is an integer equal to or greater than 1). Base units CS1 to CSn of the cordless telephone units 21 to 2n are connected to the main unit 1 by, for example, a LAN. In the example of Fig. 1, the base units CS1 to CSn and the main unit 1 are connected by wire, but they may also be connected wirelessly.

[0025] The main unit 1 performs call control and circuit switching control for the cordless telephone devices 21 to 2n, as well as other business phone control functions, and also has the function of supplying a reference synchronization signal SYNC to each of the cordless telephone devices 21 to 2n. In this example, the reference synchronization signal SYNC is a signal with a period of 130 milliseconds (ms).

[0026] Each of base units CS1 to CSn of cordless telephone units 21 to 2n synchronizes with reference synchronization signal SYNC from main unit 1 to generate a frame synchronization signal as a synchronization signal with a period of one frame (10 milliseconds (ms)), which is the unit communication period of a DECT-standard digital cordless telephone, and performs TDMA / TDD wireless communication using the DECT standard with handset units PS1 to PSm based on the generated frame synchronization signal. Therefore, all of the multiple cordless telephone units 21 to 2n operate in synchronization with reference synchronization signal SYNC from main unit 1.

[0027] The main unit 1, each of the base units CS1 to CSn, and each of the terminal units PS1 to PSm of the telephone system 10 in this example have a function for performing a handover sequence as will be described later.

[0028] Fig. 2 is a diagram showing a state in which a handover occurs. As shown in Fig. 2, each of the master devices CS1 and CS2 can communicate wirelessly with each of the slave devices PS1 to PSm within a circular communication range of, for example, radius D, and the communication ranges of the master devices CS1 and CS2 are installed in a state in which they partially overlap each other.

[0029] In this state, if the handset PS1, which is wirelessly connected to the base unit CS1 and is in a call with the other party, moves and becomes capable of wireless communication with both the base unit CS1 and the base unit CS2, as shown in Figure 2, and moves closer to the base unit CS2, the handset PS1 will detect that the received field strength of the radio waves from the base unit CS2 has become stronger than the received field strength of the radio waves from the base unit CS1.

[0030] Then, based on the detected received field strength, the handset PS1 determines that wireless connection with the base unit CS2 will improve communication quality, and sends a handover request to the base unit CS2. In this case, in this embodiment, if the handset PS1 was conducting a normal band call with the base unit CS1 with which it was conducting wireless communication at the time the handover request was sent, the handover request for the normal band call is sent to the base unit CS2. If the handover request for the normal band call was conducted with the base unit CS1, the handover request for the wideband call is sent to the base unit CS2. The handover request for the normal band call includes information requesting that the normal band call be conducted with the base unit CS2, and the handover request for the wideband call includes information requesting that the wideband call be conducted with the base unit CS2. The information requesting a normal band call and the information requesting a wideband call may be any information as long as it is information that can distinguish between a normal band call and a wideband call.

[0031] In addition, the handover request for the broadband call including information requesting the broadband call may be sent to the base unit CS2 by the handover terminal PS1 only when the handover terminal PS1 is conducting a broadband call with the base unit CS1, and the handover request for the normal band call may not include information requesting the normal band call.

[0032] Upon receiving this handover request, the base station CS2 determines whether wireless communication between itself and the other terminals is available. In determining availability, the base station CS2 uses the result of determining whether the received handover request is for a normal bandwidth call or a wideband call.

[0033] If the received handover request is for a normal bandwidth call, the base unit CS2 determines whether there is at least one available slot (meaning one slot for uplink and one slot for downlink). If it determines that there is available slot, it receives information necessary for wireless connection with the handset PS1 from the base unit CS1 via the main unit 1, and after receiving the information, sends a handover permission notice to the handset PS1. Based on this handover sequence, the main unit 1 switches and manages the call of the handset PS1 from the base unit CS1 to the base unit CS2. As a result, the handover allows the handset PS1 to switch the base unit to which it is wirelessly connected from the base unit CS1 to the base unit CS2 and continue the call. If the base unit CS2 determines that there is no available slot, it rejects the handover request.

[0034] Furthermore, in this embodiment, if the received handover request is a handover request for a broadband call, the base units CS1 and CS2, the handset PS1, and the main unit 1 are configured to perform the processing operations described below so that the handover can be performed as much as possible depending on the availability status, which is the result of availability determination in the base unit CS2, as shown in the table of Figure 3.

[0035] In the table of Fig. 3, the base station CS1 that is wirelessly connected before the handover of the handset PS1 in a call with the other party in Fig. 2 is designated as the first base station, and the base station CS2 to which the handover request is sent from the handset PS1 is designated as the second base station. In the table of Fig. 3, five cases are assumed depending on the availability determination result of the second base station CS2 when the handset PS1 in a wideband call with the first base station CS1 sends a handover request to the second base station CS2.

[0036] <Case 1> Case 1 is a case where there are two or more free slots (two slots for uplink and two slots for downlink) in the second base unit CS2. In this case 1, the handover request of the handover terminal PS1 is accepted by the second base unit CS2 as is, and after the handover, the handover terminal PS1 is connected to the second base unit CS2 and can continue the broadband call.

[0037] However, in this case, the two slots used for wideband calls in the second base unit CS2 must be two consecutive slots (adjacent slots) on the time axis. Therefore, if the two available slots are not two consecutive slots on the time axis, the handover request from the mobile unit PS1 cannot be accepted as is. In this embodiment, assuming such a case, even if there are two available slots, a further determination is made as to whether wideband calls are possible. If wideband calls are possible, the handover request for the wideband call is accepted. If wideband calls are not possible, the wideband call being conducted between the mobile unit PS1 and the first base unit CS1 is changed to a normal band call, and the second base unit CS2 then handles the handover request from the mobile unit PS1 as a request for a normal band call.

[0038] In addition, when two free slots are not consecutive on the time axis, the second base unit CS2 may move a slot used by a handset making a normal band call to generate two consecutive slots on the time axis. Also, when there is no handset making a normal band call for which a slot can be moved in this way for the second base unit CS2, but there is another handset making a wideband call, and two consecutive slots can be made available by changing the other wideband call to a normal band call, the second base unit CS2 may execute a process to change the other wideband call to a normal band call, thereby generating two consecutive slots, and may accept a handover request for the wideband call of the handset PS1.

[0039] In this case, the second base unit CS2 has a function for monitoring the priority of calls, as described below, so that the second base unit CS2 can determine the priority of the call of the handset that has requested handover and the priority of the broadband call of the base unit CS2, and if the priority of the call of the handset that has requested handover is lower, or if the priority of the call of the handset that has requested handover has not been set, the process of changing the broadband call of the base unit CS2 to a normal band call can be omitted.

[0040] <Case 2> Case 2 is a case where there is one free slot in the second base unit CS2 and the second base unit CS2 is not currently conducting a broadband call. In this case 2, the second base unit CS2 cannot currently conduct a broadband call, so in this embodiment, the broadband call currently being conducted between the handset PS1 and the first base unit CS1 is changed to a normal band call, and then the second base unit CS2 accepts the handover request from the handset PS1 as a request for a normal band call.

[0041] <Case 3> Case 3 is a case where there is one free slot in the second base unit CS2 and a broadband call is being made on the second base unit CS2. The base unit in the cordless telephone device of the telephone system 10 of this embodiment has a priority determination function that determines the priority of a call. Upon receiving a handover request, the second base unit CS2 uses this priority determination function to determine the priority between the call made by the handover-requesting handset PS1 and the broadband call being made on the second base unit CS2. In Case 3, two cases, Case 3(1) and Case 3(2), are performed depending on the result of this priority determination.

[0042] Case 3(1) is a case where the second base unit CS2 determines that the priority of the call made by the handover requesting handset PS1 is not defined, or that the priority is lower than the priority of the wideband call made by the second base unit CS2. In this case 3(1), in this embodiment, the wideband call made between the handover requesting handset PS1 and the first base unit CS1 is changed to a normal band call, and then the second base unit CS2 accepts the handover request from the handset PS1 as a request for a normal band call.

[0043] Case 3(2) is a case where the second base unit CS2 determines that the priority of the call made by the handover requesting handset PS1 is higher than the priority of the wideband call being made by the second base unit CS2. In this case 3(2), in this embodiment, the second base unit CS2 changes the wideband call being made by itself to a normal band call and creates one additional free slot, creating two free slots for the wideband call together with the one already free slot. Then, the handover request from the handset PS1 is accepted, and after the handover, the wideband call is made between the second base unit CS2 and the handset PS1.

[0044] In this case 3(2), if two consecutive slots for a wideband call cannot be generated even if the wideband call being made on the second base unit CS2 is changed to a normal band call, the second base unit CS2 will not change the wideband call being made on the second base unit CS2 to a normal band call, and after changing the wideband call being made between the handset PS1 and the first base unit CS1 to a normal band call, the second base unit CS2 will accept the handover request from the handset PS1 as a request for a normal band call.

[0045] <Case 4> Case 4 is a case where there is not even one free slot in the second base station CS2 and no broadband call is being made in the second base station CS2. In this case 4, the second base station CS2 rejects the handover request from the handset PS1 because there is no free slot.

[0046] <Case 5> Case 5 is a case where there is not even a single free slot in the second base unit CS2, but a wideband call is in progress on the second base unit CS2. In this case 5, the second base unit CS2 changes the wideband call in progress with the second base unit CS2 to a normal band call to create one free slot, and then accepts the handover request from the mobile unit PS1 as a request for the normal band call. Also, if there are two wideband calls in progress with the second base unit CS2, and the second base unit CS2 can change the two wideband calls to normal band calls to create two consecutive free slots, it can also be made to accept a handover request for the wideband call from the mobile unit PS1.

[0047] In this case, as in case 3, the second base unit CS2 uses a priority determination function to determine the priority of the call made by the handset PS1 that has requested the handover and the wideband call being made by the second base unit CS2, and executes case 5 only if it determines that the priority of the call made by the handset PS1 that has requested the handover is higher than the priority of the wideband call being made by the second base unit CS2.If the priority of the call made by the handset PS1 that has requested the handover is low, the handover request may be rejected, as in case 4.

[0048] Next, detailed configuration examples of the main apparatus 1, the parent devices CS1 to CSn, and the child devices PS1 to PSn in FIG. 1 will be described.

[0049] [Configuration example of main unit 1; Figure 4] Fig. 4 is a block diagram showing an example of the configuration of main unit 1. As shown in Fig. 4, main unit 1 is configured to include line interface 11 to which telephone lines L1 to Lm are connected, control circuit 12 equipped with a computer for controlling the entire main unit 1, line LSI (Large Scale Integrated Circuit) unit 13, and reference oscillator 14.

[0050] Under the control of the control circuit 12, the line interface 11 supplies voice signals (received voice signals) from the lines L1 to Ln to the line LSI unit 13, and supplies control signals such as call control signals from the lines to the control circuit 12. Also, under the control of the control circuit 12, the line interface 11 transmits voice signals (transmitted voice signals) from the line LSI unit 13 to the other party via the lines L1 to Ln, and also transmits control signals such as call control signals from the control circuit 12 to the other party via the lines L1 to Ln.

[0051] The line LSI unit 13 includes n extension processing circuits 131, 132, . . . , 13n and a timing signal generating unit 130 corresponding to n extension telephone devices.

[0052] The timing signal generating unit 130 generates a transmission clock signal CK and a multiplexing / division timing signal TM from a reference clock signal from a high-precision reference oscillator 14 using a quartz crystal oscillator, and supplies them to n extension processing circuits 131 to 13n.

[0053] The n extension processing circuits 131 to 13n have the same configuration, and each comprises a voice signal processing unit 31, a control signal processing unit 32, a synchronization signal processing unit 33, and a multiplexing / division processing unit .

[0054] The audio signal processing unit 31 is connected to the line interface 11 and also to the multiplexing / division processing unit 34, and is a processing circuit for processing the received audio signal from the line interface 11 and the transmitted audio signal from the multiplexing / division processing unit 34. A transmission clock signal CK is supplied to this audio signal processing unit 31 from the timing signal generating unit 130.

[0055] The control signal processing unit 32 is connected to the control signal input / output terminal of the control circuit 12 and is also connected to the multiplexing / division processing unit 34, and is a processing circuit for control signals such as call control signals when making and receiving calls, when terminating a call, and control signals during handover sequences (both control signals from the main unit 1 to the cordless telephone devices 21-2n and control signals from the cordless telephone devices 21-2n to the main unit 1). The transmission clock signal CK from the timing signal generating unit 130 is also supplied to this control signal processing unit 32.

[0056] The synchronization signal processing unit 33 is connected to the synchronization signal output terminal of the control circuit 12 and also to the multiplexing / division processing unit 34, and is a processing circuit for the reference synchronization signal SYNC having a predetermined synchronization signal pattern from the control circuit 12. Similarly, the transmission clock signal CK from the timing signal generating unit 130 is also supplied to this synchronization signal processing unit 33.

[0057] The multiplexing / division processing unit 34 is connected to the audio signal processing unit 31, the control signal processing unit 32, and the synchronization signal processing unit 33, and is also connected to each of the base units CS1-CSn of the cordless telephone devices 21-2n. Based on the timing signal TM from the timing signal generating unit 130, the multiplexing / division processing unit 34 multiplexes (time-division multiplexes) the audio signal (received audio signal) from the audio signal processing unit 31, the control signal from the control signal processing unit 32, and the reference synchronization signal SYNC from the synchronization signal processing unit 33 to generate a multiplexed signal, and supplies the generated multiplexed signal to each of the base units CS1-CSn. Based on the timing signal TM from the timing signal generating unit 130, the multiplexing / division processing unit 34 also divides the multiplexed signal from each of the base units CS1-CSn into an audio signal and a control signal, and supplies the audio signal (transmitted audio signal) to the audio signal processing unit 31 and the control signal to the control signal processing unit 32.

[0058] [Configuration example of cordless telephone devices 21 to 2n] The base units CS1 to CSn and the handsets PS1 to PSn all have the same configuration. Therefore, in the following description, the base unit CS1 and the handset PS1 of the cordless telephone device 21 will be used as an example to describe an example of the configuration of the base unit and the handset.

[0059] <Configuration example of parent device; Figure 5> Fig. 5 is a block diagram showing an example of the configuration of the master CS1. As shown in Fig. 5, the master CS1 is configured to include a control circuit 41 for controlling the entire master CS1, a line LSI unit 42, a synchronization signal generating circuit 43, a wireless communication circuit 44, and oscillators 45 and 46.

[0060] The control circuit 41 is configured with a computer mounted thereon. The control circuit 41 has functions for controlling call control in the base unit CS1 and control (sequence) during handover. To perform the sequence for handover, the control circuit 41 has functions such as a means for determining availability, a means for sending a request to the base unit, which is in a wideband call state with the handset that sent the handover request, to change the wideband call with the handset to a normal band call, a means for changing the wideband call with the handset that is in a wireless communication state (call state) with the base unit CS1 itself to a normal band call, a function for determining the priority of the call with the handset that sent the handover request and the wideband call with the base unit CS2, and a slot management function for managing available slots and occupied slots.

[0061] In addition, when the control circuit 41 controls a handset that is currently in a wideband call with the base unit CS1 to change to a normal band call, the call between the base unit CS1 and the handset, which has been changed to a normal band call, is converted to a pseudo-wideband call by complementing voice packets, etc., and sent to the other party who was in the wideband call with the handset.

[0062] The priority determination function of the base unit CS1 will now be described. Priority is set based on the call history of each handset connected to the base unit CS1 for calls, for example, a higher priority is set for a handset that is connected to and calls relatively frequently or a handset that has a long call duration. Also, when the users of the handset PS1 to PSm are determined, a priority may be set for each of the handset PS1 to PSm.

[0063] Furthermore, a higher priority is set for external calls than for internal calls. When determining the priority, the base unit CS1 determines that a call has a high priority if the duration of the call connected to the base unit CS1 is equal to or longer than a predetermined time. Furthermore, the priority may be changed depending on whether the call recipient is a mobile phone or a landline phone. For example, a landline phone is set to have a higher priority. Whether the call is a mobile phone or a landline phone can be determined by the subscriber's telephone number.

[0064] The line LSI unit 42 is a circuit for exchanging audio signals, control signals, and synchronization signals with the main unit 1, and consists of a division / multiplexing processing unit 421, a control signal processing unit 422, an audio signal processing unit 423, a synchronization signal processing unit 424, and a PLL (Phase Locked Loop) unit 425.

[0065] The PLL unit 425 is supplied with an oscillation signal of a reference frequency from the oscillator 45, and is also supplied with a multiplexed signal from the main unit 1. In this example, the frequency of the oscillation signal from the oscillator 45 is set to, for example, 2048 MHz (0.488 nanoseconds (ns)).

[0066] The PLL unit 425 extracts the component of the clock signal CK from the timing signal generating unit 130 of the main unit 1 from the multiplexed signal from the main unit 1 by so-called self-clocking, compares the phase of the extracted clock signal CK component with the oscillation signal from the oscillator 45, and based on the comparison result, generates a system clock signal SCK for the parent unit CS1 that is synchronized with the clock signal CK component from the oscillation signal of the oscillator 45.

[0067] The PLL unit 425 then supplies the generated system clock signal SCK to each of the division / multiplexing processing unit 421, control signal processing unit 422, audio signal processing unit 423, and synchronization signal processing unit 424 as a clock signal for signal processing, and also supplies it to the synchronization signal generating circuit 43.

[0068] The division / multiplexing processing unit 421 is connected to the extension processing circuit 131 of the main unit 1, and is also connected to a control signal processing unit 422, an audio signal processing unit 423, and a synchronization signal processing unit 424. The division / multiplexing processing unit 421 divides the multiplexed signal from the main unit 1 into a control signal, an audio signal, and a reference synchronization signal SYNC, and supplies the control signal to the control signal processing unit 422, the audio signal to the audio signal processing unit 423, and the reference synchronization signal SYNC to the synchronization signal processing unit 424, respectively.

[0069] In addition, the division / multiplexing processing unit 421 multiplexes the control signal from the control signal processing unit 422 and the audio signal from the audio signal processing unit 423 to generate a multiplexed signal, and supplies the generated multiplexed signal to the main unit 1.

[0070] The control signal processing unit 422 is connected to the control signal input / output terminal of the control circuit 41 and also to the division / multiplexing processing unit 421, and is a processing circuit for control signals such as call control signals when making or receiving a call, when handing over, or when ending a call (both control signals from the main unit 1 to the cordless telephone device 21 and control signals from the cordless telephone device 21 to the main unit 1).

[0071] The audio signal processing unit 423 is connected to the wireless communication circuit 44 and also to the division / multiplexing processing unit 421, and as shown in Figure 5, it is equipped with a transmission audio signal processing circuit 4231 that processes a transmission audio signal received from the handset PS1 via the wireless communication circuit 44, and a reception audio signal processing circuit 4232 that processes a reception audio signal received from the other device via the division / multiplexing processing unit 421.

[0072] The synchronization signal processing unit 424 receives the reference synchronization signal SYNC from the division / multiplexing processing unit 421, detects a predetermined synchronization signal pattern included in the reference synchronization signal SYNC, and generates a reference synchronization pulse PS that is synchronized with the reference synchronization signal SYNC and has the same period (130 ms) as the reference synchronization signal SYNC as the signal at the time of detection.The synchronization signal processing unit 424 then supplies the generated reference synchronization pulse PS to the synchronization signal generating circuit 43.

[0073] The synchronization signal generating circuit 43 comprises a counter 431 and a synchronization signal generating unit 432. A reference synchronization pulse PS having a period of 130 ms is supplied to a preset terminal of the counter 431 from the synchronization signal processing unit 424 of the line LSI unit 42, and the system clock SCK is supplied as a count input from the PLL unit 425. The output count value CNT of the counter 431 is supplied to the synchronization signal generating unit 432.

[0074] The synchronization signal generation unit 432 generates a frame synchronization signal with a frame period (10 ms) of the DECT standard from the output count value CNT of the counter 431. The synchronization signal generation circuit 43 supplies the frame synchronization signal generated by the synchronization signal generation unit 432 to the wireless communication circuit 44.

[0075] Next, in this embodiment, a general-purpose base unit wireless communication LSI for performing DECT wireless communication is used as the wireless communication circuit 44. This wireless communication circuit 44 is configured to include a control unit 441, a TDMA modulation / demodulation unit 442, and a wireless communication unit 443. The wireless communication unit 443 is a circuit unit for performing wireless communication with the slave unit PS1.

[0076] The control unit 441 is connected to the TDMA modulation / demodulation unit 442 and the wireless communication unit 443, and is also connected to the control circuit 41. The control unit 441 controls the overall operation of the wireless communication circuit 44, and supplies a control signal based on a control signal obtained from the control circuit 41 to the TDMA modulation / demodulation unit 442.

[0077] The TDMA modulation / demodulation unit 442 is connected to the control unit 441 and the audio signal processing unit 423 of the line LSI unit 42, and is also connected to the wireless communication unit 443, and modulates the control signal from the control unit 441 and the audio signal from the audio signal processing unit 423 in order to transmit them to the slave PS1. The signals modulated by this TDMA modulation / demodulation unit 442 are transmitted to the slave PS1 via the wireless communication unit 443.

[0078] In addition, the TDMA modulation / demodulation unit 442 demodulates the received signal from the sub-unit PS1 received by the wireless communication unit 443 into an audio signal and a control signal, supplies the demodulated audio signal to the audio signal processing unit 423, and supplies the demodulated control signal to the control unit 441.

[0079] The TDMA modulation / demodulation unit 442 includes a PLL unit 4421 for clock generation. The PLL unit 4421 is supplied with an oscillation signal from the oscillator 46 and a frame synchronization signal from the synchronization signal generation circuit 43.

[0080] The PLL unit 4421 compares the phase of the frame synchronization signal from the synchronization signal generating circuit 43 with the oscillation signal from the oscillator 46, and based on the comparison result, generates a timing signal and a clock signal synchronized with the frame synchronization signal from the oscillation signal of the oscillator 46.

[0081] The TDMA modulation / demodulation unit 442 uses a timing signal and a clock signal synchronized with the frame synchronization signal to generate a transmission signal to the slave unit PS1 in a period corresponding to one of the slots in the downlink that can be allocated and used, and also processes a received signal from the slave unit PS1 using one of the slots in the uplink.

[0082] [Example of slave unit configuration; Figure 6] Fig. 6 is a block diagram showing an example of the configuration of the slave PS1. As shown in Fig. 6, the slave PS1 is configured to include a wireless communication circuit 51, a control circuit 52, a codec circuit 53, an oscillator 54, a microphone 55, and a speaker 56. The microphone 55 constitutes a transmitter, and the speaker 56 constitutes a receiver.

[0083] The wireless communication circuit 51 uses a general-purpose wireless communication LSI for a handset to perform wireless communication in the DECT system. The wireless communication circuit 51 is configured to include a control unit 511, a TDMA modulation / demodulation unit 512, and a wireless communication unit 513. The wireless communication unit 513 is a circuit unit for performing wireless communication with the master unit CS1.

[0084] Control unit 511 is connected to TDMA modulation / demodulation unit 512 and wireless communication unit 513, and is also connected to control circuit 52. Control unit 511 controls the overall operation of wireless communication circuit 51, and supplies a control signal to TDMA modulation / demodulation unit 512 based on a control signal obtained from control circuit 52. Control unit 511 also detects the reception field strength of radio waves from master units that can be received via wireless communication unit 513, and transmits information on the detected reception field strength of radio waves from master units that can be received to control circuit 52.

[0085] TDMA modulation / demodulation unit 512 is connected to control unit 511 and wireless communication unit 513, and is also connected to codec circuit 53, and modulates the control signal from control unit 511 and the audio signal from codec circuit 53 in order to transmit them to base unit CS1. The signals modulated by this TDMA modulation / demodulation unit 512 are transmitted to base unit CS1 via wireless communication unit 513.

[0086] In addition, the TDMA modulation / demodulation unit 512 demodulates the received signal from the parent unit CS1 received by the wireless communication unit 513 into an audio signal and a control signal, supplies the demodulated audio signal to the codec circuit 53, and supplies the demodulated control signal to the control unit 511.

[0087] TDMA modulation / demodulation unit 512 includes PLL unit 5121 for clock generation. This PLL unit 5121 is supplied with an oscillation signal from oscillator 54 and a demodulated signal of the received signal from wireless communication unit 513. PLL unit 5121 generates a clock signal synchronized with the clock component of the demodulated signal of the received signal, from the oscillation signal from oscillator 54. The clock signal from PLL unit 5121 is used as a processing clock signal in TDMA modulation / demodulation unit 512.

[0088] When a call is made from the handset PS1, the control circuit 52 transmits a call control signal to the base unit CS1 via the wireless communication circuit 51, and when a call control signal is received from the base unit CS1, the control circuit 52 performs processing such as emitting a ring tone from the speaker 56. When the control circuit 52 determines that switching the currently connected base unit for a call to another base unit will improve communication quality based on the received field strength of radio waves from a receivable base unit detected by the control unit 511 of the wireless communication circuit 51, the control circuit 52 sends a handover request to the other base unit that is expected to improve communication quality. As mentioned above, this handover request includes information on whether the call with the base unit CS1 is a normal bandwidth call or a wideband call. The control circuit 52 then performs a sequence for handover.

[0089] In addition, in this embodiment, the control circuit 52 also has a control function for controlling whether to make a wideband call or a normal band call and for controlling the change between wideband calls and normal band calls by working in cooperation with the base unit CS1.

[0090] The codec circuit 53 decodes the audio signal demodulated by the TDMA modulation / demodulation unit 512, converts it into an analog audio signal, and supplies the analog audio signal to the speaker 56 to emit it as received audio. The codec circuit 53 also encodes the analog audio signal picked up by the microphone 55 and supplies it to the TDMA modulation / demodulation unit 512.

[0091] The above explanation is about the base unit CS1 and the handset PS1 of the cordless telephone device 21, but as mentioned above, the base units CS2 to CSn and the handset PS2 to PSn of the other cordless telephone devices 22 to 2n also have the same configuration.

[0092] [Example of parent unit operation] The operations of the above-mentioned master devices CS1 to CSn will be described with reference to the flowcharts of Figures 7 to 11, focusing on the processing in response to a handover request. Each step of the flowcharts of Figures 7 to 11 will be described as being executed by the control circuit 41 of each master device CS1 to CSn.

[0093] The control circuit 41 determines whether or not a handover request has been received from the slave unit (step S1), and if it determines that a handover request has been received, determines whether the handover request is for a normal band call or a wideband call (step S2). If it determines in step S2 that the handover request is for a normal band call, the control circuit 41 determines the availability (step S3) and determines whether or not there is an availability (step S4).

[0094] If it is determined in step S4 that there is no available space, the control circuit 41 determines whether the base unit is making a wideband call (step S5), and if it is determined that the base unit is making a wideband call, it determines the priority of the call made by the handset that has requested handover and the call made by the handset that is making the wideband call, and determines whether the priority of the call made by the handset that has requested handover is higher (step S6).

[0095] If it is determined in step S6 that the call of the handover-requesting handset has a higher priority, the control circuit 41 changes the broadband call to a normal band call and creates an empty space (step S7).Then, the control circuit 41 sends to the main unit 1 a request for acquiring information about the handover-source base unit to which the handover-requesting handset is connected (abbreviated as "information acquisition request" in the flowcharts of FIGS. 7 to 11) (step S8).

[0096] The main device 1 forwards this request to acquire source parent device information to the source parent device, receives a source parent device information acquisition response (abbreviated as information acquisition response in the flowcharts of Figures 7 to 11) sent from the source parent device, which includes information about the source parent device necessary for handover, and forwards it to the parent device that sent the request to acquire source parent device information.

[0097] The control circuit 41 receives the source base unit information acquisition response sent from the main unit 1 (step S9). Then, the control circuit 41 sends a handover response permitting the handover to the handover requesting handover terminal, executes handover processing using the received source base unit information, and starts a normal band call with the handover requesting handover terminal (step S10). Then, the control circuit 41 returns the process to step S1 and repeats the process from step S1 onwards.

[0098] If it is determined in step S4 that there is an available channel, the control circuit 41 proceeds to step S8 and executes the processes from step S8 onwards. If it is determined in step S5 that a wideband call is not in progress, the control circuit 41 rejects the handover request (step S11) and returns to step S1. Furthermore, if it is determined in step S6 that the call of the handset that has requested the handover has a lower priority, or that no priority has been set for the call of the handset that has requested the handover, the control circuit 41 also rejects the handover request (step S11) and returns to step S1.

[0099] If it is determined in step S2 that the handover request is not for a normal band call but for a wideband call, the control circuit 41 checks the availability (step S21 in FIG. 8) and determines whether there is an available wideband call (step S22). If it is determined in step S22 that there is an available wideband call, the control circuit 41 sends a request to obtain information about the moving-source base unit to the main unit 1 (step S23), and receives a response to the request from the main unit 1 about the moving-source base unit (step S24).

[0100] Then, the control circuit 41 sends a handover response permitting the handover to the handover requesting device, executes handover processing using the received information of the parent device from which the handover was made, and starts a broadband call with the handover requesting device (step S25).Then, the control circuit 41 returns the processing to step S1, and repeats the processing from step S1 onwards.

[0101] If it is determined in step S22 that there is no available space for wideband calls, the control circuit 41 determines whether there is available space for normal band calls (step S31 in FIG. 9). If it is determined in step S31 that there is no available space for normal band calls, the control circuit 41 determines whether the base unit is currently using a wideband call (step S32), and if so, determines the priority of the call of the handset that has requested handover and the call of the handset that is currently using a wideband call, and determines whether the priority of the call of the handset that has requested handover is higher (step S33).

[0102] If it is determined in step S33 that the call of the handover-requesting handset has a higher priority, the control circuit 41 changes the broadband call to a normal band call to create an empty space (step S35).Then, the control circuit 41 sends to the main unit 1 a request to obtain information about the handover-source base unit, including a request to change the broadband call of the handover-requesting handset to a normal band call (a request to change to the normal band) (step S36).

[0103] Then, the control circuit 41 receives the source base unit information acquisition response sent from the main unit 1 (step S37). At the time when the source base unit information acquisition response is received, the broadband call for the handover requesting handover has been changed to a normal band call.

[0104] After step S37, the control circuit 41 sends a handover response permitting the handover to the handover requesting device, executes handover processing using the received information of the source base device, and starts normal band communication with the handover requesting device (step S38).Then, the control circuit 41 returns the processing to step S1, and repeats the processing from step S1 onwards.

[0105] If it is determined in step S32 that the base unit is not making a wideband call, or if it is determined in step S33 that the call of the handset that has requested handover has a lower priority, or that no priority has been set for the call of the handset that has requested handover, the control circuit 41 performs processing to reject the handover request (step S34).Then, the control circuit 41 returns the processing to step S1 and repeats the processing from step S1 onwards.

[0106] Furthermore, when it is determined in step S31 that there is an available normal bandwidth call, the control circuit 41 determines whether the base unit is making a wideband call or not (step S41 in FIG. 10), and if it is determined that a wideband call is being made, it determines the priority of the call made by the handset that has requested handover and the call made by the handset that is making the wideband call, and determines whether the priority of the call made by the handset that has requested handover is higher (step S42).

[0107] If it is determined in step S42 that the call of the handset that has requested handover has a higher priority, the control circuit 41 changes the wideband call to a normal band call and creates an available space (step S43).The control circuit 41 then determines whether a wideband call is possible based on whether the created available space (one slot) for the normal band call and the existing available space (one slot) for the normal band call are two consecutive slots on the time axis (step S44).If it is determined in step S44 that a wideband call is possible, the control circuit 41 proceeds to step S23 in FIG. 8 and performs the processes from step S23 onward.In other words, a handover is permitted while the wideband call remains the same for the handset that has requested wideband handover.

[0108] If it is determined in step S41 that the base unit is not making a wideband call, if it is determined in step S42 that the call of the handset that requested the handover has a lower priority or that no priority has been set for the call of the handset that requested the handover, or if it is determined in step S44 that the wideband call is not available, the control circuit 41 proceeds to step S36 in Fig. 9 and performs the processes from step S36 onwards. That is, a handover is permitted in a state in which the wideband call is changed to a normal band call for the handset that requested the wideband handover.

[0109] 7, when it is determined that a handover request has not been received from the slave unit, the control circuit 41 determines whether or not a request to acquire information about the transfer source parent unit has been received from the main unit 1 (step S51 in FIG. 11). When it is determined in this step S51 that a request to acquire information about the transfer source parent unit has not been received from the main unit 1, the control circuit 41 performs other processing (step S52), and then returns the processing to step S1 in FIG.

[0110] When it is determined in step S51 that a request for acquiring information about the handover source base unit has been received from the main unit 1, the control circuit 41 determines whether the request for acquiring information about the handover source base unit includes a request to change the broadband call of the handset that requested the handover to a normal band call (a request for change to a normal band call) (step S53). When it is determined in step S53 that the request for changing the broadband call of the handset that requested the handover to a normal band call includes a request to change the broadband call of the handset that requested the handover to a normal band call (step S54). Thereafter, the control circuit 41 returns a request for acquiring information about the handover source base unit to the main unit 1 (step S55). Then, the control circuit 41 disconnects the call path to the handset that performed the handover (step S56), and the process returns to step S1 in FIG. 7.

[0111] If it is determined in step S53 that the call does not include a request to change to a normal band call, the control circuit 41 bypasses step S54 and advances the process to step S55, where it performs the processes from step S55 onwards.

[0112] Although not shown in the flowcharts of Figures 7 to 11, when the control circuit 41 of the parent device accepts a handover request for a wideband call by changing the wideband call of the child device that sent the handover request to a normal band call, if thereafter, while the call is ongoing, another call ends, creating an open space, the control circuit 41 will change the normal band call back to a wideband call.

[0113] Furthermore, in order to accept a handover request for a wideband call or a normal band call, the control circuit 41 of the base unit generates an empty space by changing the wideband call to a normal band call when a wideband call is in progress, but the call path between the base unit and the handset that was changed to a normal band call to generate the empty space is also returned to a wideband call when an empty space is generated as a result of the other call being ended.

[0114] [Example of handover operation of a handset] The operations of the slave devices PS1 to PSm at the time of the above-mentioned handover will be described with reference to the flowcharts of Figures 12 and 13. Each step of the flowcharts of Figures 12 and 13 will be described as being executed by the control circuit 52 of each of the slave devices PS1 to PSm.

[0115] The control circuit 52 monitors the radio wave conditions between the base unit (step S61) and determines whether a situation has arisen in which handover is necessary (step S62). If it determines that a situation in which handover is necessary has not arisen, the control circuit 52 returns to step S61 and continues to monitor the radio wave conditions between the base unit and the base unit. If it determines that a situation in which handover is necessary has arisen, it determines whether a wideband call is in progress (step S63).

[0116] If it is determined in step S63 that the call was not in a wideband call but in a normal band call, the control circuit 52 sends a handover request for the normal band call to the parent unit that is the destination of the handover request (step S64).Then, the control circuit 52 determines whether or not a notification of denial of the handover has been received from the parent unit that is the destination of the handover request (step S65), and if a notification of denial has been received, the control circuit 52 performs processing corresponding to the denial of the handover (step S66), and ends this handover processing routine.

[0117] If it is determined in step S65 that a notification of handover refusal has not been received, the control circuit 52 determines whether or not a handover response indicating that the handover is permitted has been received from the parent device that is the target of the handover request (step S67). If it is determined in step S67 that a handover response has not been received, the control circuit 52 returns the process to step S65 and repeats step S65 and subsequent steps. If it is determined in step S67 that a handover response has been received, the control circuit 52 executes handover processing (step S68) and ends this handover processing routine.

[0118] If it is determined in step S63 that a broadband call was in progress, the control circuit 52 sends a handover request for the broadband call to the parent device that is the destination of the handover request (step S71 in FIG. 13). Then, the control circuit 52 determines whether or not a notification of handover refusal has been received from the parent device that is the destination of the handover request (step S72). If a notification of refusal has been received, the control circuit 52 proceeds to step S66 in FIG. 12, where it performs processing corresponding to the handover refusal, and ends this handover processing routine.

[0119] If it is determined in step S72 that a notification of handover refusal has not been received, the control circuit 52 determines whether a request to change to a normal band call has been received (step S73), and if it is determined that a request to change to a normal band call has been received, executes processing to change the wideband call to a normal band call with the parent unit from which the handover originated (step S74).

[0120] If it is determined in step S73 that a request to change to normal bandwidth communication has not been received, or after step S74, the control circuit 52 determines whether or not a handover response indicating permission for handover has been received from the parent device that is the target of the handover request (step S75). If the control circuit 52 determines in step S75 that a handover response has not been received, the control circuit 52 returns the process to step S72 and repeats step S72 and subsequent steps. If it is determined in step S75 that a handover response has been received, the control circuit 52 executes handover processing (step S76) and ends this handover processing routine.

[0121] [Example of handover sequence (Case 2)] In the telephone system 10 of this embodiment, when a handset that has been making a wideband call sends a handover request, the wideband call of the handset that sent the handover request is changed to a normal band call, and the handover request is accepted (case 2), an example of a sequence performed between the base unit and handset of the cordless telephone devices 21 to 2n, and between the base unit and the main unit, will be described below with reference to Figure 14 and its sequel, Figure 15. The correspondence between the main processes in the sequences of Figures 14 and 15 and the steps in the flowcharts of the operations of the base unit and handset explained using Figures 7 to 13 is shown in Figures 14 and 15, and in the following explanation, corresponding step numbers will be shown in parentheses.

[0122] 14 and 15 show an example in which a handover request for a broadband call is sent to another base unit CS2 while a handover is in progress between a handover station PS1 and a base unit CS1. In this case, the base unit CS2, which is the destination of the handover, has three available call channels, is connected via wireless communication with two of the other handover stations PS2 to PS4, and is conducting a call on two channels. There are no available channels for a broadband call, but there are available channels for a normal band call.

[0123] That is, as shown in Fig. 14, when a broadband call is being made between the handover source base unit CS1 and the handover source base unit CS1 under good radio wave reception conditions, if the handover source base unit PS1 moves and the radio wave reception conditions with the base unit CS1 become poor, but the radio wave reception conditions with the base unit CS2 become good instead (steps S61 to S63 in Fig. 12), the handover source base unit PS1, which is in a broadband call with the base unit CS1, sends a handover request for the broadband call to the base unit CS2 (step S71 in Fig. 13). Hereinafter, the base unit CS1 will be referred to as the source base unit, and the base unit CS2 will be referred to as the destination base unit.

[0124] Upon receiving the handover request for the broadband call, the destination base unit CS2 determines the availability (step S21 in FIG. 8) and determines that there is no availability for the broadband call but there is availability for the normal band call (step S22 in FIG. 8 and step S31 in FIG. 9).The destination base unit CS2 then sends a request to obtain information about the source base unit to the main unit 1, including a request to change the broadband call of the handover-requesting handset PS1 to a normal band call (request to change to a normal band call) (step S37 in FIG. 9).

[0125] The main unit 1 sends an information acquisition request including the received request to change to a normal band call to the base unit CS1 of the transfer source.

[0126] Based on the request to change to a normal band call (step S53 in FIG. 11) included in the received information acquisition request (step S51 in FIG. 11), the source base unit CS1 sends a change request to change the broadband call to a normal band call to the mobile unit PS1 (step S54 in FIG. 11). As a result, the broadband call between the mobile unit PS1 and the source base unit CS1 is changed to a normal band call.

[0127] Then, after confirming that the broadband call with the handover terminal PS1 has been changed to a normal bandwidth call, the base unit CS1 from which the transfer originated returns an information acquisition response (step S55 in FIG. 11) including the information necessary for handover to the main unit 1, as shown in FIG. 15.

[0128] Upon receiving this information acquisition response, the main unit 1 sends a parent unit information acquisition response of the transfer source to the parent unit CS2 of the transfer destination.

[0129] Upon receiving the source base unit information acquisition response from the main unit 1 (step S37 in FIG. 9), the destination base unit CS2 sends a handover response to the handover request to the handover unit PS1 (step S38 in FIG. 9), indicating that the handover request is permitted, and creates a normal bandwidth call path between the handover unit PS1 and the destination base unit CS2, thereby executing the call with the communication partner.

[0130] [Effects of the embodiment] As explained above, in the wireless communication system of the above embodiment, when a handover request for a wideband call is sent from a handset, even if wideband calls are not possible at the base unit at the destination, if there is space available for normal bandwidth calls, the wideband call of the handset that sent the handover request can be changed to a normal bandwidth call, thereby making it possible to perform the handover, thereby increasing the chances that the call will continue without interruption.

[0131] In the wireless communication system of the above embodiment, the base unit that receives a handover request from the handset is configured to create an available call by changing a wideband call to a normal band call, thereby increasing the chances of accepting a handover request without rejecting it. Furthermore, since the base unit is configured to change a wideband call to a normal band call in consideration of the priority of the call, the quality of high-priority calls can be maintained. [Explanation of symbols]

[0132] 1...main unit, 10...telephone system, 21 to 2n...cordless telephone devices, CS1 to CSn...base units, PS1 to PSm...handsets, 41...control circuit of base unit, 52...control circuit of handset

Claims

1. In a wireless communication system in which a plurality of cordless communication devices, each consisting of a base unit and one or more handset units, are connected to a main unit, the base unit and the handset units are wirelessly connected using a time division multiple access / time division duplex system, and wideband calls and normal band calls are possible, and a handset unit in a call can perform handover to switch between the base units to which it is wirelessly connected, The handset that is making the wideband call with the first base unit sends a handover request for the wideband call to the second base unit that will be wirelessly connected to the handset after the handover; the second base unit that has received the handover request for the wideband call sends a request to change the wideband call to the normal band call via the main unit to the first base unit when there is no available space for the wideband call but there is available space for the normal band call; The first base unit, which has received a request to change from the wideband call to the normal band call through the main unit, changes the call between the first base unit and the handset that sent the handover request from the wideband call to the normal band call, The second base unit permits handover of the handset that has been changed from the wideband call to the normal band call. A wireless communication system comprising:

2. The slave unit is a first sending means for sending a handover request for the wideband call to a second base unit that will be wirelessly connected to the handset after handover while the wideband call is being made with the first base unit; means for changing the wideband call with the first base unit to the normal band call when a change request from the wideband call to the normal band call is received from the first base unit; Equipped with The second base unit is a determination means for determining whether or not wireless communication with the handset is available when a handover request for the broadband call is received; a second sending means for sending information including a request to change from the wideband call to the normal band call to the main device when it is determined that there is no available space for the wideband call but there is available space for the normal band call; a third sending means for sending a response of handover permission to the handset that has sent the handover request when a response of information including a request to change from the wideband call to the normal band call is received from the main device; The main device is a fourth sending means for, when receiving information including a request to change from the wideband call to the normal band call from the second base unit, transferring information including a request to change from the wideband call to the normal band call to the first base unit; a fifth sending means for, when receiving a response to information including a request to change from the wideband call to the normal band call from the first base unit, sending a response to information including a request to change from the wideband call to the normal band call to the second base unit; Equipped with The first base unit a sixth sending means for, when receiving from the main device information including a request to change from the wideband call to the normal band call, sending to the main device a response of information including the request to change from the wideband call to the normal band call; means for sending a request to change the broadband call to the normal band call to the handset based on the received request to change the broadband call to the normal band call, thereby changing the call with the handset from the broadband call to the normal band call; 2. The wireless communication system according to claim 1, comprising:

3. The second base unit is a conversion means for converting the wideband call between the handset and the wirelessly connected handset into the normal band call; When a handover request for the wideband call is received and there is no available space for the wideband call, if the conversion means converts the wideband call of the wirelessly connected handset into the normal band call and an available space for the normal band call is generated, it is determined that there is no available space for the wideband call but there is an available space for the normal band call.

2. The wireless communication system according to claim 1.

4. The second base unit is a priority determination means for determining, when a handover request for the wideband call is received, a priority between the call of the handset that has sent the handover request and a call of the wirelessly connected handset that is making the wideband call through the second base unit; When the priority determination means determines that the call of the handset that has sent the handover request has a higher priority, the conversion means is executed.

4. The wireless communication system according to claim 3.

5. The second base unit is When a call of another handset is ended and an idle time occurs during a call of the handset that has changed the wideband call to the normal band call and sent the response to the handover permission, the call of the handset that sent the response to the handover permission is returned to the wideband call.

2. The wireless communication system according to claim 1.

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