Communication system

Abstract

In a communication system that uses wireless communication equipment consisting of a master unit and a slave unit that perform handover and roaming, the aim is to reduce the likelihood of radio interference. [Solution] When a master unit CS1 and a slave unit PS1 are making a call (two-way communication) in a normal communication area Ar1 that does not overlap with the normal communication area Ar2 of a nearby master unit CS2, and the slave unit PS1 moves, if the signal strength of the received signal from the slave unit PS1 in the master unit CS1 falls below a predetermined value, the transmission output is increased in the original master unit CS1 and the nearby master unit CS2, which is a candidate for the destination master unit controlled by the master unit CS1 via the main unit 1, to form two extended communication areas that overlap with each other, enabling a handover. After the handover is complete, the two extended communication areas are returned to the normal communication areas Ar1 and Ar2.

Description

Technical Field

[0001] This invention relates to a communication system configured by connecting a wireless communication device, such as a cordless telephone device, in which, for example, a master unit and a slave unit are wirelessly connected, to a higher-level device such as a master device or a SIP (Session Initiation Protocol) server.

Background Art

[0002] In recent years, a business phone system (push-button phone system) has been configured by connecting a cordless telephone device to a network control device such as a master device or a SIP (Session Initiation Protocol) server. The cordless telephone device functions as a single telephone device with a master unit and a slave unit wirelessly connected. For example, a communication method conforming to the DECT (Digital Enhanced Cordless Telecommunication) standard may be used between the master unit and the slave unit constituting the cordless telephone device.

[0003] In the DECT standard, it is defined that the communication method for the downlink from the master unit to the slave unit is a time-division multiplexing duplex method using a time-division multiplexing method, and the communication method for the uplink from the slave unit to the master unit is a time-division multiple access method. Further, in the DECT standard, the operating frequency band uses the "1.9 GHz band". Furthermore, in the DECT standard, as shown in FIG. 25, the number of channels is 5 channels, and 1 channel is divided into frames in units of 10 milliseconds (ms), and each frame is divided into 24 time slots. Note that the number of channels may increase in the future. Hereinafter, a time slot will simply be referred to as a slot. And 12 slots S0 to S11 in the first half 1 / 2 frame period of 1 frame are used for the downlink from the master unit to the slave unit, and 12 slots S12 to S23 in the second half 1 / 2 frame period are used for the uplink from the slave unit to the master unit.

[0004] In DECT standard cordless telephone systems used in business phone systems, unless the power is off, a single cordless telephone unit uses one of its 12 slots in standby (idle) mode to transmit various control information, including synchronization signals, from the base unit to the handset. This slot is called a dummy bearer. Normally, multiple handsets can be connected to the base unit. However, whether only one handset is connected to the base unit or multiple handsets are connected, in standby mode, control information is transmitted to each handset using one slot (dummy bearer). In this case, no information is transmitted from the handset to the base unit.

[0005] From this standby state, for example, if an incoming call is received and the telephone control unit notifies the base unit of the incoming call, the base unit uses a dummy bearer to notify each slave unit of a data session connection request. The slave units then search for an available slot and contact the base unit to attempt to acquire a slot for communication. The data session connection request is a request to create an environment in which the base unit and slave units can communicate with each other, and it does not result in an incoming call notification. Then, in response to the data session connection request, once a slot for mutual communication between the base unit and slave units has been acquired, the base unit releases the dummy bearer and uses the acquired downlink slot to notify the base unit of the incoming call. At the same time, the base unit also identifies an uplink slot so that it can receive information from the slave units.

[0006] Thus, a pair of downlink and uplink slots acquired for mutual communication between a master unit and a slave unit are called a traffic bearer. Various control information, including synchronization signals, is transmitted through the traffic bearer, and after a voice line is established with the communication partner, voice information is also transmitted. Since various control information is transmitted through the traffic bearer, the process of identifying (acquiring) a traffic bearer and releasing a dummy bearer is called merging the dummy bearer into a traffic bearer.

[0007] Thus, in business phone systems configured by connecting cordless telephone devices, an invention that enables easy and reliable roaming and handover of handsets is disclosed in Patent Document 1, which will be described later. Specifically, the invention disclosed in Patent Document 1 involves each base unit of the cordless telephone devices constituting the telephone system sharing necessary information such as pairing information. Using this pairing information, a virtual link corresponding to the handset that has moved is formed at the base unit to which the handset is moving. This ensures that a logical communication environment is also established between the moved handset and the base unit to which the handset is moving, in response to changes in the physical communication environment, enabling reliable and easy roaming and handover.

[0008] In Patent Document 1, roaming means that a handset in a standby state, not making calls or data communications, changes its connected base station by moving. Handover means that a handset making calls or data communications can maintain its call or data communication even when it changes its connected base station by moving. Standby state (idle state) means that both the base station and the handset are powered on and can receive or make calls, but no calls are being made; it is a so-called waiting state. In this specification as well, the above definitions will be used for roaming, handover, and standby state (idle state). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2021-119654 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] As mentioned above, in a telephone system configured using DECT standard cordless telephone equipment, in order to hand over the cordless telephone equipment, there must be an overlapping area of ​​the radio wave coverage (communication coverage area) between the base station at the destination and the base station at the origin. Here, the radio wave coverage area refers to the area where the transmission signal from the base station can reach. For example, as shown in Figure 26(A), if the radio wave coverage area Ara of base station CSa and the radio wave coverage area of ​​base station CSb overlap in part, base station CSa cannot receive the transmission signal from base station CSb, and base station CSb cannot receive the transmission signal from base station CSa. Therefore, if base station CSa and base station CSb are configured to use the same channel / slot, and their communication paths conflict in this way, the likelihood of malfunctions due to radio wave interference increases.

[0011] Furthermore, as shown in Figure 26(B), if the radio wave area Ara of base station CSa and the radio wave area of ​​base station CSb largely overlap, base station CSa can receive transmission signals from base station CSb, and base station CSb can receive transmission signals from base station CSa. In this case, since the channels and slots used by both base stations are known, they will not use the same channel and slot. However, if the overlapping area between radio wave area Ara and radio wave area Arb becomes large and base station CSa and base station CSb use adjacent slots, radio interference may occur. In other words, in either pattern shown in Figures 26(A) and (B), in the area where the radio wave area of ​​the destination base station and the radio wave area of ​​the source base station overlap, there is always a concern that various problems may occur due to radio interference, such as handover failures and call noise.

[0012] In view of the above, the present invention aims to reduce radio interference between neighboring base stations in a communication system that uses a wireless communication device consisting of a base station and a slave station where handover and roaming occur. [Means for solving the problem]

[0013] To solve the above problems, the communication system of the invention described in claim 1 is In a communication system in which a master unit of a wireless communication device, which is configured by wirelessly connecting a master unit and slave units, is connected to a higher-level device in multiple master units, The aforementioned higher-level device is Each of the aforementioned master units is provided with a neighboring master unit storage means that stores adjacent master units in an identifiable manner, When a movement occurrence notification is received from the master unit indicating that the slave unit has moved, a movement preparation request providing means forms and provides a movement preparation request to the master unit that sent the movement occurrence notification, based on the information stored in the neighboring master unit storage means, requesting the neighboring master unit to prepare for the movement of the slave unit. When a handover request is received from the aforementioned neighboring master unit, the circuit switching control means releases the communication path between the master unit that provided the movement notification and the higher-level device, and connects the communication path between the aforementioned neighboring master unit that sent the handover request and the higher-level device. Equipped with, The aforementioned master unit is One or more standard communication antennas, One or more area expansion antennas, A switching means for selecting between the aforementioned standard communication antenna and the aforementioned area expansion antenna, Amplification means for raising or lowering the radio wave output level of the transmission signal supplied to the conventional communication antenna or the area extension antenna, A field strength detection means for detecting the received signal strength of a signal received from the slave unit through the aforementioned normal communication antenna or through the aforementioned area extension antenna. Equipped with, A means that functions when the master unit is the source of the slave unit's movement, When the switching means is switched to select the normal communication antenna and bidirectional communication is being performed with the slave unit, and the electric field strength detection means detects that the signal strength of the signal received from the slave unit falls below a predetermined threshold, the movement occurrence notification providing means forms the movement occurrence notification and provides it to the host device, When the movement occurrence notification is provided through the movement occurrence notification providing means, a first antenna control means for switching the switching means to select the area expansion antenna; When the movement occurrence notification is provided through the movement occurrence notification providing means, a first radio wave output control means for controlling the amplification means so as to increase the radio wave output of the transmission signal supplied to the area expansion antenna and form an extended communication area; Comprising; Means that functions when the master unit becomes the destination of movement of the slave unit, When receiving the movement preparation request from the upper device, a second antenna control means for switching the switching means to select the area expansion antenna; When receiving the movement preparation request from the upper device, a second radio wave output control means for controlling the amplification means so as to increase the radio wave output of the transmission signal supplied to the area expansion antenna and form an extended communication area; A handover request providing means for forming the handover request and providing it to the upper device when the switching means is switched to use the area expansion antenna and the received signal strength of the signal from the slave unit becomes a predetermined value or more by the electric field strength detection means; Characterized by comprising

Effect of the Invention

[0014] According to the communication system of this invention, in a communication system configured by using a wireless communication device including a master unit and a slave unit in which handover and roaming occur, the state in which radio wave interference occurs is minimized between adjacent master units, and radio wave interference can be made difficult to occur.

Brief Description of the Drawings

[0015] [Figure 1] It is a figure for demonstrating the structural example of the business phone system of 1st, 2nd Embodiment. [Figure 2]It is a block diagram for explaining a configuration example of a main device used in the business phone system according to the first embodiment. [Figure 3] It is a diagram for explaining an example of stored data in the neighboring master device storage unit of the main device according to the first embodiment. [Figure 4] It is a diagram for explaining an example of stored data in the connection master device management file of the main device according to the first embodiment. [Figure 5] It is a block diagram for explaining a configuration example of the master unit of the cordless telephone device used in the business phone system according to the first embodiment. [Figure 6] It is a block diagram for explaining a detailed configuration of the master unit of the cordless telephone device used in the business phone system according to the first embodiment. [Figure 7] It is a block diagram for explaining a configuration example of the slave unit of the cordless telephone device used in the business phone system according to the first embodiment. [Figure 8] It is a diagram for explaining the normal communication area and the extended communication area during handover performed in the business phone system according to the first embodiment. [Figure 9] It is a diagram for explaining the normal communication area and the extended communication area during handover performed in the business phone system according to the first embodiment. [Figure 10] It is a diagram for explaining the normal communication area and the extended communication area during handover performed in the business phone system according to the first embodiment. [Figure 11] It is a sequence diagram for explaining the processing during handover performed in the business phone system according to the first embodiment. [Figure 12] It is a sequence diagram following FIG. 11. [Figure 13] It is a block diagram for explaining a configuration example of a main device used in the business phone system according to the second embodiment. [[ID=3~4]] [Figure 14] It is a block diagram for explaining a detailed configuration of the master unit of the cordless telephone device used in the business phone system according to the second embodiment. [Figure 15] This is a block diagram illustrating an example of the configuration of a cordless telephone handset used in a business phone system according to the second embodiment. [Figure 16] This figure illustrates an example of data stored in the information storage unit of the base unit of a cordless telephone device used in a business phone system of the second embodiment. [Figure 17] This figure illustrates an example of data stored in the destination storage unit of a cordless telephone handset used in a business phone system of the second embodiment. [Figure 18] This diagram illustrates the normal communication area and extended communication area during roaming in the business phone system of the second embodiment. [Figure 19] This diagram illustrates the normal communication area and extended communication area during roaming in the business phone system of the second embodiment. [Figure 20] This diagram illustrates the normal communication area and extended communication area during roaming in the business phone system of the second embodiment. [Figure 21] This is a sequence diagram illustrating the roaming process performed in the business phone system of the second embodiment. [Figure 22] This is a sequence diagram following Figure 21. [Figure 23] This diagram illustrates the normal communication area and extended communication area during handover in the business phone system of the first embodiment. [Figure 24] This diagram illustrates the normal communication area and extended communication area during roaming in the business phone system of the second embodiment. [Figure 25] This is a diagram illustrating the DECT communication standard. [Figure 26] This diagram illustrates problems that can occur in communication systems that enable handover and roaming. [Modes for carrying out the invention]

[0016] The embodiments of the communication system according to this invention will be described below with reference to the figures. In the embodiments described below, the case in which the communication system according to this invention is applied to a so-called business phone system formed in, for example, a company office will be used as an example. Accordingly, in the embodiments described below, the main unit corresponds to the higher-level device of the communication system according to this invention, and the cordless telephone device consisting of a base unit and a sub-unit corresponds to the wireless communication device of the communication system according to this invention.

[0017] [Examples of business phone system (communication system) configurations in the first and second embodiments] Figure 1 is a diagram illustrating the configuration examples of the business phone systems in the first and second embodiments. In the first and second embodiments described below, for the sake of simplicity, we will focus on the three sets of cordless telephone devices 21, 22, and 23 connected to the main unit 1, as shown in Figure 1. However, in reality, many cordless telephone devices are connected to the main unit 1, and a large-scale business phone system is constructed.

[0018] Each of the cordless telephone systems 21, 22, and 23 consists of a base unit (Cell Station) CS1, CS2, and CS3, and a handset (Personal Station) PS1, PS2, and PS3, respectively. Hereafter, the Cell Stations CS1, CS2, and CS3 will be referred to as base units CS1, CS2, and CS3, and the Personal Stations PS1, PS2, and PS3 will be referred to as handsets PS1, PS2, and PS3.

[0019] In this embodiment, the wireless connection between the base units CS1, CS2, and CS3 of the cordless telephone devices 21, 22, and 23 and the handset PS1, PS2, and PS3 is performed using the TDMA / TDD method based on the DECT standard (method) for digital cordless telephones described above. The main unit 1 can accommodate one or more telephone lines L1 to Lm (where m is an integer of 2 or more). The base units CS1, CS2, and CS3 of the cordless telephone devices 21, 22, and 23 are connected to the main unit 1. In the example in Figure 1, the base units CS1, CS2, and CS3 are connected to the main unit 1 by wire.

[0020] The main unit 1 controls call and circuit switching, as well as other business phone functions, for multiple cordless telephone devices 21, 22, and 23, and also has the function of supplying a reference synchronization signal SYNC to each of the multiple cordless telephone devices 21, 22, and 23. In this example, the reference synchronization signal SYNC is a signal with a period of 130 milliseconds (ms).

[0021] Each of the base units CS1, CS2, and CS3 of the cordless telephone devices 21, 22, and 23 generates a frame synchronization signal, which is a synchronization signal with a period of 1 frame (10 milliseconds (ms)), the unit communication period of a DECT standard digital cordless telephone, in synchronization with the reference synchronization signal SYNC from the main unit 1. Based on the generated frame synchronization signal, they perform TDMA / TDD wireless communication using the DECT standard with the slave units PS1, PS2, and PS3. Therefore, all of the cordless telephone devices 21, 22, and 23 operate in synchronization with the reference synchronization signal SYNC from the main unit 1.

[0022] As shown in Figure 1, each of the cordless telephone devices 21, 22, and 23 is a telephone terminal connected to the main unit 1, constituting a business phone system. Therefore, call control signals such as incoming call notification and outgoing call request, as well as other control signals, are sent and received between them and the main unit 1. Other control signals include, for example, control signals for controlling the LCD (Liquid Crystal Display) and LED (Light Emitting Diode) of cordless telephone devices 21, 22, and 23 in order to notify the user of the operating status of other cordless telephone devices connected to the main unit 1.

[0023] Typically, the master units CS1, CS2, and CS3 are installed in designated locations within the office. Each of the master units CS1, CS2, and CS3 transmits signals at a predetermined transmission power, creating a so-called radio wave area where communication with the slave units PS1, PS2, and PS3 is possible. Normally, in order to enable handover and roaming of the slave units PS1, PS2, and PS3, overlapping areas are created in the radio wave areas formed by adjacent master units. This allows the slave units to perform seamless handover and roaming.

[0024] However, in the first and second embodiments described in detail below, each of the base stations CS1, CS2, and CS3 is configured to use a normal communication area for making calls and an extended communication area for handover and roaming. In this case, the normal communication area formed by the base station does not overlap with the normal communication areas formed by neighboring base stations. In contrast, the extended normal communication area formed by the base station is a wider extended communication area than the normal communication area only when a handover or roaming occurs with a slave device, and it overlaps with the extended communication areas formed by other neighboring base stations.

[0025] As a result, in the business phone system of the embodiment described below, stable calls can be made without causing radio interference with nearby base stations during calls. Conversely, only during handover or roaming of handset units, an extended communication area wider than the normal communication area is formed to ensure reliable handover and roaming of handset units, thereby shortening the period during which radio interference occurs.

[0026] The configuration examples of the main unit 1 and the base units CS1, CS2, CS3 and handset PS1, PS2, PS3 of the cordless telephone devices 21, 22, 23 that constitute the business phone systems of the first and second embodiments that realize such functions will be specifically described. In the following, the embodiment of the business phone system when the handset performs a handover will be described as the first embodiment, and the embodiment of the business phone system when the handset performs roaming will be described as the second embodiment.

[0027] In this specification, the terms "neighboring base station" or "neighboring base station" refer to base stations located adjacent to each other at a predetermined distance, as shown in Figure 1. Therefore, adjacent base stations, being located adjacent to each other at a predetermined distance, are the base stations (the source base station and the destination base station) where handover or roaming of a slave device takes place.

[0028] [First Embodiment (Example of a case where the slave unit performs a handover)] As mentioned above, handover means that even if the handset making a call moves and changes the base station it is connected to, the call can be maintained. In other words, the base station and handset communicate bidirectionally, and this state can be quickly established even when moving to the new base station. Below, we will explain an example of the configuration of each component that makes up a business phone system when implementing handover.

[0029] <Example of main unit configuration> Figure 2 is a block diagram illustrating an example configuration of the main unit 1. As shown in Figure 2, the main unit 1 is configured with a line I / F (Interface) 11 to which telephone lines L1 to Lm are connected, a control unit 12 that incorporates a computer and controls the entire main unit 1, a line LSI (Large Scale Integration) unit 13, and a reference oscillator 14.

[0030] The line interface 11, under control from the control unit 12, supplies voice signals (received voice signals) from lines L1 to Lm to the line LSI unit 13, and supplies control signals such as call control signals from the lines to the control unit 12. Furthermore, the line interface 11, under control from the control unit 12, transmits voice signals (transmitted voice signals) from the line LSI unit 13 to the other party via lines L1 to Lm, and also transmits control signals such as call control signals from the control unit 12 to the other party via lines L1 to Lm.

[0031] The line LSI unit 13 includes n extension processing circuits 131, 132, ..., 13n and a timing signal generation unit 130, corresponding to n extension telephone devices. The subscript character n basically represents an integer of 1 or greater. However, in Figure 2, since extension processing circuits 131 and 132 already exist, the character n in Figure 2 represents an integer of 3 or greater.

[0032] The timing signal generation unit 130 generates a transmission clock signal CK and a multiplexing / splitting timing signal TM from a reference clock signal from a high-precision reference oscillator 14 using a crystal oscillator, and supplies them to n internal processing circuits 131 to 13n. The n internal processing circuits 131 to 13n have exactly the same configuration and consist of an audio signal processing unit 31, a control signal processing unit 32, a synchronization signal processing unit 33, and a multiplexing / splitting processing unit 34, respectively.

[0033] The audio signal processing unit 31 is connected to the line interface 11 and also to the multiplexing / splitting processing unit 34, and is a processing circuit for the received audio signal from the line interface 11 and the transmitted audio signal from the multiplexing / splitting processing unit 34. The audio signal processing unit 31 is supplied with a transmission clock signal CK from the timing signal generation unit 130.

[0034] The control signal processing unit 32 is connected to the control signal input / output terminal of the control unit 12 and also to the multiplexing / splitting processing unit 34. It is a control signal processing circuit that handles call control signals during outgoing and incoming calls, as well as call termination. In other words, the control signal processing unit 32 is a processing circuit that handles both control signals from the main unit 1 to the cordless telephone device and control signals from the cordless telephone device to the main unit 1. The control signal processing unit 32 is also supplied with a transmission clock signal CK from the timing signal generation unit 130.

[0035] The synchronization signal processing unit 33 is connected to the synchronization signal output terminal of the control unit 12 and also to the multiplexing / splitting processing unit 34. It is a processing circuit for the reference synchronization signal SYNC having a predetermined synchronization signal pattern from the control unit 12. Similarly, the transmission clock signal CK from the timing signal generation unit 130 is also supplied to this synchronization signal processing unit 33.

[0036] The multiplexing / splitting processing unit 34 is connected to the voice signal processing unit 31, the control signal processing unit 32, and the synchronization signal processing unit 33, as well as to each of the base stations CS1 to CSn of the cordless telephone devices 21 to 2n. The multiplexing / splitting processing unit 34 processes based on the timing signal TM from the timing signal generation unit 130. The multiplexing / splitting processing unit 34 generates a multiplexed signal by multiplexing (time-division multiplexing) the voice signal from the voice 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. The multiplexing / splitting processing unit 34 supplies the generated multiplexed signal to each of the base stations CS1 to CSn.

[0037] Furthermore, the multiplexing / splitting processing unit 34 splits (separates) the multiplexed signals from each of the master units CS1 to CSn into audio signals and control signals based on the timing signals TM from the timing signal generation unit 130. The multiplexing / splitting processing unit 34 supplies the split (separated) audio signals to the audio signal processing unit 31, and the split (separated) control signals to the control signal processing unit 32. In this way, the call audio signals and control signals are transmitted and received between each of the master units CS1, CS2, and CS3 via the line LSI unit 13, and the synchronization signals from the main unit 1 are also supplied to each of the master units CS1, CS2, and CS3 via the line LSI unit 13.

[0038] As shown in Figure 2, the control unit 12 of the main unit 1 includes a neighboring master unit storage unit 121, a preparation request provision unit 122, a line switching control unit 123, a completion notification provision unit 124, and a cancellation request provision unit 125. The neighboring master unit storage unit 121 functions as a neighboring master unit storage means that stores neighboring master units, which are master units located adjacent to each master unit connected to the main unit 1, in an identifiable manner. Figure 3 is a diagram illustrating an example of data stored in the neighboring master unit storage unit 121 of the main unit 1 in the first embodiment. As shown in Figure 3, the neighboring master unit storage unit 121 stores and holds identification information of master units (neighboring master units) located adjacent to each master unit connected to the main unit 1.

[0039] The example shown in Figure 3 corresponds to the business phone system example shown in Figure 1, where the neighboring base station CS1 is base station CS2, the neighboring base stations of base station CS2 are base station CS1 and base station CS3, and the neighboring base station of base station CS3 is base station CS2. In Figure 3, the reference codes CS1, CS2, and CS3 shown in the figure are used as identification information for each base station, but in reality, identification information that can uniquely identify each base station, such as a MAC (Media Access Control) address, is used.

[0040] Therefore, based on the information stored in the neighboring master unit memory unit 121, it can be determined that master unit CS2 is located near master unit CS1, master units CS1 and CS3 are located near master unit CS2, and master unit CS2 is located near master unit CS3. In other words, it can be determined that handover and roaming are possible from master unit CS1 to master unit CS2, from master unit CS2 to master unit CS1 and master unit CS3, and from master unit CS3 to master unit CS2.

[0041] The preparation request provision unit 122 functions when it receives a move occurrence notification from a subordinate master unit that notifies it of the occurrence of a move of a slave unit. Based on the information stored in the neighboring master unit storage unit 121, the preparation request provision unit 122 forms and provides a move preparation request to the neighboring master unit (the master unit of the candidate destination for the slave unit) that sent the move occurrence notification (the master unit from which the slave unit is moving), requesting that the master unit prepare for the move of the slave unit. In this way, the preparation request provision unit 122 realizes its function as a means of providing a move preparation request. Therefore, when the preparation request provision unit 122 receives a move occurrence notification from master unit CS1, it provides a move preparation request to master unit CS2, and when the preparation request provision unit 122 receives a move occurrence notification from master unit CS2, it provides a move preparation request to master unit CS1 and master unit CS3. Also, when the preparation request provision unit 122 receives a move occurrence notification from master unit CS3, it provides a move preparation request to master unit CS2.

[0042] When the nearby base station that provided the move preparation request (the base station to which the slave unit is moving) provides a handover request, the line switching control unit 123 releases the communication path between the base station that sent the move notification and the unit itself, and connects the communication path between the nearby base station that sent the handover request and the unit itself. This allows the slave unit to seamlessly hand over (transfer) the call it was making through the base station it was moving to to the base station it was moving to. In this way, the line switching control unit 123 realizes its function as a line switching control means. When the completion notification provision unit 124 receives a move completion notification from the nearby base station that provided the move preparation request, notifying that the slave unit has completed its move to the unit itself, it provides a move completion notification to the base station that provided the move notification (the base station to which the slave unit is moving). In this way, the completion notification provision unit 124 realizes its function as a completion notification provision means.

[0043] When the cancellation request provision unit 125 receives a cancellation notification from a subordinate master unit, it provides a cancellation request to the neighboring master unit that sent the move preparation request via the preparation request provision unit 122. This allows the preparation for a handover to be canceled if the possibility of a handover occurring due to a move of a slave unit has increased, but a handover does not actually occur.

[0044] In this manner, when the control unit 12 of the main unit 1 receives a move notification from a subordinate master unit, it provides a move preparation request to the neighboring master units of that master unit. When a handover request arrives from the neighboring master unit that provided the move preparation request, it releases the communication path that was connected to the master unit that sent the move notification and connects a communication path to the neighboring master unit that sent the handover request. As a result, the slave unit that has moved from the master unit to the master unit to the master unit to which it moved can switch the call that was being conducted through the master unit to the call that was being conducted through the master unit to be conducted through the master unit to which it moved, allowing the call to continue without interruption even when the slave unit moves.

[0045] After this, when a move completion notification arrives from the master unit that initiated the handover request (the master unit at the destination), a completion notification is sent to the master unit that sent the move occurrence notification that triggered the processing in main unit 1 (the master unit at the source of the move). This allows the master unit at the source of the move to release the registration of the slave unit that was registered in its location.

[0046] Furthermore, if preparations are made for a handover, but the handset does not actually move significantly and the handover does not occur, the preparations can be canceled and the system can return to its state before the preparations were made. Therefore, even if preparations are made to enable a handover because the likelihood of a handover has increased, but the handover does not actually occur, the system can automatically return to the original state of making a call in the normal communication area.

[0047] Furthermore, the transmission of control signals, etc., that identify the destination master unit from the main unit 1 can be configured such that the identification information of the destination master unit is added to the transmission data and transmitted to each master unit connected to the line LSI unit 13, and the master unit selects and receives the signal addressed to itself. In addition, by managing the master unit connected to each of the multiple connection lines between the line LSI unit 13 and the master unit, the line LSI unit 13 can be configured to switch the connection line to which signals are transmitted. Figure 4 is a diagram illustrating an example of the data stored in the connection master unit management file of the main unit 1 in the first embodiment.

[0048] As shown in Figure 4, the connection master management file manages the identification information of the master unit connected to each connection line between the line LSI unit 13 and the master unit. In the example shown in Figure 4, for example, it is indicated that master unit CS1 is connected to connection line LN001, master unit CS2 is connected to connection line LN002, master unit CS3 is connected to connection line LN003, and master unit CS4 is connected to connection line LN004. Based on the information stored in the connection master management file, the connection line to which the target master unit is connected may be identified, and the system may be configured to provide the target notification or request to the target master unit through the identified connection line.

[0049] <Example configuration of cordless telephone devices 21, 22, and 23 of the first embodiment> Next, we will describe the configuration examples of the base units CS1, CS2, and CS3 and the handset PS1, PS2, and PC3 that constitute the cordless telephone devices 21, 22, and 23 of the first embodiment. Since the base units CS1, CS2, and CS3 of the cordless telephone devices 21, 22, and 23 are all configured similarly, we will use the base unit CS1 as an example to specifically describe their configurations below. Similarly, since the handset PS1, PS2, and PS3 of the cordless telephone devices 21, 22, and 23 are all configured similarly, we will use the handset PS1 as an example to specifically describe its configuration below.

[0050] <Example of a master unit configuration> Figure 5 is a block diagram illustrating an example configuration of the base unit CS1 of the cordless telephone device 21. As shown in Figure 5, the base unit CS1 is configured to include a control circuit 41 for controlling the entire base unit CS1, a line LSI unit 42, a synchronization signal generation circuit 43, a wireless communication circuit 44, and oscillators 45 and 46. The control circuit 41 is configured to incorporate a computer and realizes functions such as call control in this base unit CS1.

[0051] The line LSI unit 42 is a circuit for exchanging audio signals, control signals, and synchronization signals with the main unit 1. The line LSI unit 42 consists of a division / multiplexing processing unit 421, a control signal processing unit 422, an audio signal processing unit 423, a synchronization signal detection unit 424, and a PLL (Phase Locked Loop) unit 425. The PLL unit 425 is supplied with an oscillation signal of a reference frequency from the oscillator 45, as well as a multiplexing signal from the main unit 1. In this example, the frequency of the oscillation signal from the oscillator 45 is, for example, 2048 MHz (0.488 nanoseconds (ns)).

[0052] The PLL unit 425 extracts the clock signal CK component from the timing signal generation unit of the main unit 1 from the multiplexed signal from the main unit 1 by so-called self-clocking. The PLL unit 425 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 the system clock signal SCK of the master unit CS1 synchronized with the clock signal CK component from the oscillation signal of the oscillator 45. The PLL unit 425 supplies the generated system clock signal SCK as a clock signal for signal processing to the splitting / multiplexing processing unit 421, the control signal processing unit 422, the audio signal processing unit 423, and the synchronization signal detection unit 424, respectively, and also supplies it to the synchronization signal generation circuit 43.

[0053] The splitting / multiplexing processing unit 421 is connected to the main unit 1, as well as to the control signal processing unit 422, the audio signal processing unit 423, and the synchronization signal detection unit 424. The splitting / multiplexing processing unit 421 splits (separates) the control signal, audio signal, and reference synchronization signal SYNC from the multiplexed signal from the main unit 1. The control signal, separated in the splitting / multiplexing processing unit 421, is supplied 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 detection unit 424.

[0054] Furthermore, the splitting / multiplexing processing unit 421 multiplexes the control signals from the control signal processing unit 422 and the voice signals from the voice signal processing unit 423 to generate a multiplexed signal, and supplies the generated multiplexed signal to the main unit 1. The control signal processing unit 422 is connected to the control signal input / output terminal of the control circuit 41 and is also connected to the splitting / multiplexing processing unit 421. The control signal processing unit 422 is a processing circuit for control signals such as call control signals during outgoing calls, incoming calls, and call termination (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).

[0055] The audio signal processing unit 423 is connected to the wireless communication circuit 44 and also to the division / multiplexing processing unit 421. It is a processing circuit for the transmitted audio signal received from the slave unit PS1 via the wireless communication circuit 44 and the received audio signal from the division / multiplexing processing unit 421. The synchronization signal detection unit 424 receives a reference synchronization signal SYNC from the division / multiplexing processing unit 421 and detects a predetermined synchronization signal pattern provided by the reference synchronization signal SYNC. As a result, the synchronization signal detection unit 424 generates a reference synchronization pulse PS as the signal at the time of detection, which is synchronized with the reference synchronization signal SYNC and has the same period (130ms) as the reference synchronization signal SYNC. The synchronization signal detection unit 424 supplies the generated reference synchronization pulse PS to the synchronization signal generation circuit 43.

[0056] The synchronization signal generation circuit 43 consists of a counter 431 and a synchronization signal generation unit 432. The counter 431 receives a reference synchronization pulse PS with a period of 130ms from the synchronization signal detection unit 424 of the line LSI unit 42 to the preset terminal PRE, and a system clock signal SCK from the PLL unit 425 as the count input. The output count value CNT of the counter 431 is supplied to the synchronization signal generation unit 432. The synchronization signal generation unit 432 generates a synchronization signal FL with a frame period (10ms) according to the DECT standard from the output count value CNT of the counter 431. The synchronization signal generation circuit 43 supplies the frame synchronization signal FL generated by the synchronization signal generation unit 432 to the wireless communication circuit 44.

[0057] The wireless communication circuit 44 comprises a control unit 441, a TDMA modulation / demodulation unit 442, and a wireless communication unit (labeled "RF" in Figure 4) 443. The wireless communication unit 443 is a circuit unit for performing wireless communication with the slave unit PS1. The control unit 441 is connected to the TDMA modulation / demodulation unit 442 and the wireless communication unit 443, as well as to the control circuit 41. The control unit 441 also has the function of supplying control signals to the TDMA modulation / demodulation unit 442 based on control signals obtained from the control circuit 41, and supplying information obtained from the TDMA modulation / demodulation unit 442 to the control circuit 41.

[0058] 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, as well as to the wireless communication unit 443. It modulates the control signals from the control unit 441 and the audio signals from the audio signal processing unit 423 in order to transmit them to the slave unit PS1. The signals modulated by this TDMA modulation / demodulation unit 442 are transmitted to the slave unit PS1 via the wireless communication unit 443. The TDMA modulation / demodulation unit 442 also demodulates the audio signals and control signals from the signals received from the slave unit PS1 by the wireless communication unit 443. The demodulated audio signals are supplied to the audio signal processing unit 423, and the demodulated control signals are supplied to the control unit 441.

[0059] 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 FL from the synchronization signal generation circuit 43. The PLL unit 4421 performs a phase comparison between the frame synchronization signal FL from the synchronization signal generation circuit 43 and 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 FL from the oscillation signal of the oscillator 46. The TDMA modulation / demodulation unit 442 uses the timing signal and clock signal synchronized with the frame synchronization signal FL to generate a transmission signal to the slave unit PS1 for a period corresponding to the downlink slot that is available for allocation, and uses the uplink slot to process the received signal from the slave unit PS1.

[0060] As mentioned above, when the master unit CS1 is connected to the main unit 1 and in standby mode, it starts the synchronization process for communication with the paired slave unit PS1, and constantly sends synchronization signals and control information to the slave unit PS1 through the dummy bearer, maintaining a state where communication is possible. When the master unit CS1 is notified of an incoming call, it forms a link connection request and sends it to the slave unit PS1 through the dummy bearer. When the slave unit PS1 receives the link connection request, it performs a search process for an available slot, identifies the slot (traffic bearer) to be used for communication, and notifies the master unit CS1. The master unit CS1 acquires the identified slot and uses it to connect the master unit CS1 and the slave unit PS1, creating a state where a call can be made.

[0061] In this way, between the master unit 1 and the master unit CS1, voice communication signals and control signals can be transmitted and received via the line LSI unit 42, and synchronization signals from the master unit 1 can also be received via the line LSI unit 42. Furthermore, between the master unit CS1 and the slave unit, voice communication signals and control signals are transmitted and received via the wireless communication circuit 44. In this first embodiment, the master unit CS1 is able to perform a handover when a slave unit whose location is registered to the master unit moves while an external or internal call is being made using the slave unit.

[0062] However, unlike when building a business phone system using conventional cordless telephone equipment, it is not necessary to have overlapping call areas between nearby base stations. In other words, the base stations CS1, CS2, and CS3 of this embodiment can switch between two areas: a normal communication area and an extended communication area. By using the normal communication area and the extended communication area separately, problems caused by radio interference, such as call noise and handover failures, are minimized. For this reason, the configuration of the control circuit 41 and the wireless communication circuit 44 of base station CS1 differs from that of conventional systems.

[0063] <Details of the control circuit 41 and wireless communication circuit 44 of the master unit CS1> Figure 6 is a block diagram illustrating the detailed configuration of the base unit CS1 of the cordless telephone device 21. The wireless communication unit (labeled "RF" in Figure 5) 443 of the base unit CS1, as explained using Figure 5, comprises a conversion circuit 4431, an amplification unit 4432, and a switching unit 4433, as shown in Figure 6. The conversion circuit 4431 comprises a receiving unit Rv and a transmitting unit Sd. The receiving unit Rv converts the received signal, which is a high-frequency signal from the switching unit 4433, into an intermediate-frequency signal and supplies it to the TDMA modulation / demodulation unit 442. The transmitting unit Sd converts the transmitted signal, which is an intermediate-frequency signal from the TDMA modulation / demodulation unit 442, into a high-frequency signal and supplies it to the switching unit 4433.

[0064] As shown in Figure 6, the normal communication antenna AT1 is connected to terminal a of the switching unit 4433, and the area expansion antenna AT2 is connected to terminal b of the switching unit 4433. The switching unit 4433 functions as an antenna switching means that switches between the normal communication antenna AT1 and the area expansion antenna AT2 to be used for communication, in accordance with the control of the antenna control unit 412, which will be described later. The amplification unit 4432 is provided between the transmitting unit Sd of the conversion circuit 4431 and the switching unit 4433, and changes the amplification level of the transmitted signal depending on whether the destination of the transmitted signal is the normal communication antenna AT1 or the area expansion antenna AT2, in accordance with the control of the radio wave output control unit 413, which will be described later.

[0065] For example, suppose the switching unit 4433 is switched to terminal a, and the normal communication antenna AT1 is used. In this case, the amplification unit 4432 amplifies the transmission signal to a first level to form a normal communication area and supplies it to the normal communication antenna AT1. As a result, the transmission signal is radiated from the normal communication antenna AT1, and a normal communication area can be formed. This normal communication area does not form an area that overlaps with the normal communication areas formed by other nearby base stations. In other words, the normal communication area has no overlapping portion with the communication areas formed by other nearby base stations.

[0066] Furthermore, suppose the switching unit 4433 is switched to terminal b, and the area expansion antenna AT2 is used. In this case, the amplification unit 4432 amplifies the transmission signal to a second level to form an expanded communication area and supplies this to the area expansion antenna AT2. As a result, the transmission signal is radiated from the area expansion antenna AT2, and an expanded communication area can be formed. In this case, the second level is higher than the first level described above. Therefore, the expanded communication area is wider than the normal communication area described above and may overlap with the expanded communication area formed by other nearby base stations. In other words, the expanded communication area is wider than the normal communication area and has overlapping portions with the expanded communication area formed by other nearby base stations. Therefore, the relationship first level < second level holds between the first level and the second level described above.

[0067] Furthermore, the TDMA modulation / demodulation unit 442 includes an RSSI (Received Signal Strength Indicator) detection unit 4422. The RSSI detection unit 4422 detects the signal strength (received signal strength) of the received signal supplied from the receiving unit Rv of the wireless communication unit 443. The received signal strength detected by the RSSI detection unit 4422 is supplied to the control circuit 41 through the control unit 441. The control circuit 41 connected to the control unit 441 of the wireless communication circuit 44 includes, as shown in Figure 6, a movement occurrence notification provision unit 411, an antenna control unit 412, a radio wave output control unit 413, a handover request provision unit 414, a movement completion notification provision unit 415, and a cancellation notification provision unit 416. Note that the handover request provision unit 414 is labeled as the HO request provision unit in Figure 6, and will be referred to as the HO request provision unit 414 hereafter.

[0068] In the control circuit 41, the movement notification provision unit 411, the antenna control unit 412, and the radio wave output control unit 413 function when the master unit CS1 becomes the source of movement for a slave unit that is communicating bidirectionally with the master unit CS1. The movement notification provision unit 411 functions when the switching unit 4433 of the wireless communication unit 443 is switched to use the normal communication antenna AT1 and is communicating bidirectionally with the slave unit. The movement notification provision unit 411 forms a movement notification and provides it to the main unit 1 when the received signal strength of the received signal from the slave unit, detected by the RSSI detection unit 4422, falls below a predetermined value. In other words, the movement notification provision unit 411 provides a function to notify the main unit 1 of the fact that the slave unit is moving and is about to move outside the normal communication area formed by the master unit CS1 when the slave unit is making a call or two-way data communication through the unit.

[0069] When the antenna control unit 412 provides a movement notification to the main unit 1 via the movement notification provision unit 411, it switches the switching unit 4433 of the wireless communication unit 443 to terminal b, enabling bidirectional communication with the slave unit via the area expansion antenna AT2. When the radio wave output control unit 413 provides a movement notification to the main unit 1 via the movement notification provision unit 411, it controls the amplification unit 4432 to increase the transmission level (radio wave output) of the transmission signal supplied to the area expansion antenna AT2. These antenna control units 412 and radio wave output control units 413 enable bidirectional communication between the master unit CS1 and the slave unit in the expanded communication area when the slave unit, which is communicating bidirectionally with the master unit CS1, moves and is about to move out of the master unit CS1's normal communication area. This enables handover to a nearby master unit.

[0070] The HO request provision unit 414 and the move completion notification provision unit 415 function when the master unit CS1 becomes the destination of a slave unit that is communicating bidirectionally with another master unit. The antenna control unit 412 and the radio wave output control unit 413 also function when the master unit CS1 becomes the destination of a slave unit that is communicating bidirectionally with another master unit. First, when the control circuit 41 of the master unit CS1 receives a move preparation request from the main unit 1, the antenna control unit 412 switches the switching unit 4433 of the wireless communication unit 443 to select the area expansion antenna AT2. Also, when the control circuit 41 of the master unit CS1 receives a move preparation request from the main unit 1, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 to increase the output level (radio wave output) of the transmission signal supplied to the area expansion antenna AT2.

[0071] The HO request provision unit 414 functions when the switching unit 4433 of the wireless communication unit 443 is switched to use the area expansion antenna AT2. In this case, when the received signal strength of the received signal from the slave unit detected by the RSSI detection unit 4422 exceeds a predetermined value, the HO request provision unit 414 forms a handover request and provides it to the main unit 1. In other words, the HO request provision unit 414 transmits a signal through the area expansion antenna AT2 to form an expanded communication area, and provides a handover request to the main unit 1 when a slave unit becomes capable of bidirectional communication in this expanded communication area.

[0072] The movement completion notification provision unit 415 functions when the switching unit 4433 of the wireless communication unit 443 is switched to use the area expansion antenna AT2. In this case, when the received signal strength of the signal from the slave unit detected by the RSSI detection unit 4422 becomes greater than or equal to a value indicating that communication is possible with normal radio wave output, the movement completion notification provision unit 415 forms a movement completion notification and provides it to the main unit 1. This notifies the main unit 1 that the slave unit is located within the normal communication area of ​​the destination master unit and that the handover is complete.

[0073] Furthermore, when the antenna control unit 412 provides a movement completion notification to the main unit 1 via the movement completion notification provision unit 415, it switches the switching unit of the wireless communication unit 443 to select the normal communication antenna AT1. Also, when the radio wave output control unit 413 provides a movement completion notification to the main unit 1 via the movement completion notification provision unit 415, it controls the amplification unit 4432 to reduce the radio wave output of the transmission signal supplied to the normal communication antenna AT1 to form a normal communication area.

[0074] The cancellation notification provision unit 416 functions when the master unit CS1 becomes the source of movement for a slave unit that is communicating bidirectionally with the master unit CS1. Specifically, the cancellation notification provision unit 416 functions when the switching unit 4433 of the wireless communication unit 443 is switched to use the area expansion antenna AT2. In this case, the RSSI detection unit 4422 detects that the received signal strength of the received signal from the slave unit received through the area expansion antenna AT2 has exceeded a predetermined value. In this case, the cancellation notification provision unit 416 forms a cancellation notification to cancel the movement occurrence notification provided through the movement occurrence notification provision unit 4411 and provides this to the main unit 1.

[0075] In other words, because the received signal strength of the signal from the slave unit that was communicating bidirectionally in the normal communication area of ​​the master unit CS1 decreased, a movement notification was provided to the main unit 1 to prepare an environment for handover. However, if the handover did not actually occur, the cancellation notification provision unit 416 provides a cancellation notification to the main unit 1 to cancel (cancel) the preparation. When a cancellation notification is provided through the cancellation notification provision unit 416, the antenna control unit 412 of the master unit CS1 switches the switching unit 4433 of the wireless communication unit 443 to select the normal communication antenna AT1. Also, when a cancellation notification is provided through the cancellation notification provision unit 416, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 to lower the transmission level (radio wave output) of the transmission signal supplied to the normal communication antenna AT1, thereby forming a normal communication area. As a result, bidirectional communication with the slave unit is performed in the normal communication area Ar1 through the normal communication antenna AT1.

[0076] Furthermore, if the master unit CS1 is the master unit to which the slave unit is moving to, and receives a cancellation request from the main unit 1, the antenna control unit 412 switches the switching unit 4433 of the wireless communication unit 443 to select the normal communication antenna AT1. Also, if a cancellation request is received from the main unit 1, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 to reduce the radio wave output of the transmission signal supplied to the normal communication antenna AT1, thereby forming a normal communication area. In this way, the likelihood of the slave unit performing a handover has increased, and an environment for handover has been prepared, but suppose the handover does not occur. In this case, at the master unit that was supposed to be the source unit, the cancellation notification provision unit 416, antenna control unit 412, and radio wave output control unit 413 function, canceling the handover preparation and returning to the normal communication environment. Similarly, at the master unit that was supposed to be the destination unit, the antenna control unit 412 and radio wave output control unit 413 function, canceling the handover preparation and returning to the normal communication environment.

[0077] As described above, the movement occurrence notification provision unit 411, the antenna control unit 412, the radio wave output control unit 413, and the cancellation notification provision unit 416 are processing units that function when the master unit CS1 becomes the master unit from which a slave unit is moving while communicating bidirectionally with the slave unit. In addition, the HO request provision unit 414, the movement completion notification provision unit, the antenna control unit 412, and the radio wave output control unit 413 also function when the master unit CS1 becomes the master unit to which the slave unit is moving. Therefore, when the master unit CS1 is the source of the slave unit's movement, the antenna control unit 412 and the radio wave output control unit 413 function as the first antenna control means and the first radio wave output control means. Also, when the master unit CS1 is the destination of the slave unit's movement, the antenna control unit 412 and the radio wave output control unit 413 function as the second and third antenna control means and the second and third radio wave output control means.

[0078] <Example configuration of the handset> Figure 7 is a block diagram showing an example configuration of the handset PS1 of the cordless telephone device 21. As shown in Figure 7, the handset PS1 is composed of a wireless communication circuit 51, a control circuit 52, a codec circuit 53, an oscillator 54, a microphone 55, and a speaker 56. The control circuit 52 is configured as a microprocessor equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), non-volatile memory, etc., and realizes the function of controlling each part of the handset PS1.

[0079] The microphone 55 constitutes the transmitter, and the speaker 56 constitutes the receiver. The wireless communication circuit 51 comprises a control unit 511, a TDMA modulation / demodulation unit 512, and a wireless communication unit (labeled "RF" in Figure 7) 513. The wireless communication unit 513 is a circuit unit for performing wireless communication with the master unit CS1. The control unit 511 is connected to the TDMA modulation / demodulation unit 512 and the wireless communication unit 513, and is also connected to the control circuit 52. The control unit 511 controls the overall operation of the wireless communication circuit 51 and supplies control signals to the TDMA modulation / demodulation unit 512 based on control signals obtained from the control circuit 52.

[0080] The TDMA modulation / demodulation unit 512 is connected to the control unit 511 and the wireless communication unit 513, as well as the codec circuit 53. It modulates the control signals from the control unit 511 and the audio signals from the codec circuit 53 in order to transmit them to the master unit CS1. The signals modulated by the TDMA modulation / demodulation unit 512 are transmitted to the master unit CS1 via the wireless communication unit 513. The TDMA modulation / demodulation unit 512 also demodulates the audio signals and control signals from the signals received from the master unit CS1 by the wireless communication unit 513. The demodulated audio signals are supplied to the codec circuit 53, and the demodulated control signals are supplied to the control unit 511.

[0081] The TDMA modulation / demodulation unit 512 includes a PLL unit 5121 for clock generation. The PLL unit 5121 is supplied with an oscillation signal from the oscillator 54 and a demodulated signal from the received signal from the wireless communication unit 513. The PLL unit 5121 generates a clock signal synchronized with the clock component of the demodulated signal from the oscillation signal from the oscillator 54. The clock signal from the PLL unit 5121 is used as the processing clock signal in the TDMA modulation / demodulation unit 512.

[0082] 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 this analog audio signal to the speaker 55 to emit it as received audio. The codec circuit 53 also encodes the analog audio signal picked up by the microphone 56 and supplies it to the TDMA modulation / demodulation unit 512. When a call is made from the slave unit PS1, the control circuit 52 transmits the call control signal for the call to the master unit CS1 via the wireless communication circuit 51. When it receives a call control signal from the master unit CS1 for an incoming call, it performs processing such as emitting an incoming call tone from the speaker 55.

[0083] Furthermore, the control unit 511 of the wireless communication circuit 51 controls the TDMA modulation / demodulation unit 512 in response to a control signal from the master unit CS1 corresponding to itself, and searches for and identifies slots to be used for communication in both the downlink and uplink, enabling reception / transmission processing. For example, when a mass call occurs and a mass call notification is sent from the main unit 1 to the slave unit PS1 via the master unit CS1, the slave unit PS1 performs a search for an available slot and obtains an available slot to be used for the call. Then, the slave unit PS1 works in cooperation with the master unit CS1 to use the obtained available slot as a traffic bearer to make the call.

[0084] As mentioned above, when in standby mode, the PS1 slave unit can receive synchronization and control signals from the master unit through a predetermined slot (dummy bearer) on the downlink. When an incoming or outgoing call occurs, as described above, the dummy bearer is merged into the traffic bearer, and the slots to be used for communication are determined for the downlink and uplink, allowing the call to proceed.

[0085] The above description pertains to the base unit CS1 and handset PS1 of the cordless telephone device 21. As mentioned above, the base units CS2 and CS3 and handset PS1 and PS2 of the other cordless telephone devices 22 and 23 have a similar configuration and function in the same way. The notifications and requests provided by each of the above-mentioned devices include identification information of the sending device and identification information of the receiving device.

[0086] [Explanation of normal and extended communication areas during handover] In the business phone system comprising the main unit 1 and cordless telephone devices 21, 22, and 23 of the first embodiment having the configuration described above, the method of distinguishing between the normal communication area and the extended communication area during handover of a handset will be specifically explained. In the following explanation, for simplicity, the case in which a handset PS1 making a call via the base unit CS1 performs a handover to a nearby base unit CS2 will be used as an example. Figures 8 to 10 are diagrams illustrating the normal communication area and the extended communication area during handover in the business phone system of the first embodiment.

[0087] <If a handover occurs> As shown in Figure 8(A), assume that a slave unit PS1 located within the normal communication area Ar1 formed by the master unit CS1 is making a call (either an external or internal call) through the master unit CS1. As shown in Figure 1, there is a neighboring master unit CS2, which also forms a normal communication area Ar2. Thus, the normal communication areas Ar1 and Ar2 formed by master units CS1 and CS2 do not overlap with the normal communication areas formed by neighboring master units. As a result, there is no radio interference between the normal communication area Ar1 formed by master unit CS1 and the normal communication area Ar2 formed by master unit CS2. Therefore, calls can be made smoothly both within the normal communication area Ar1 formed by master unit CS1 and within the normal communication area Ar2 formed by master unit CS2.

[0088] Suppose that, starting from the state shown in Figure 8(A), the slave unit PS1 moves away from the master unit CS1 and approaches the master unit CS2, as shown in Figure 8(B). In this case, the signal strength of the signal received from the slave unit PS1 at the master unit CS1 will decrease as the slave unit PS1 moves further away from the master unit CS1. Therefore, when the signal strength of the signal received from the slave unit PA1, which is communicating bidirectionally, drops to a predetermined threshold at the master unit CS1, the movement occurrence notification provision unit 411 at the master unit CS1 functions to form a movement occurrence notification and provides it to the main unit 1.

[0089] Furthermore, in the master unit CS1, the antenna control unit 412 controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to select the area expansion antenna AT2. Also, in the master unit CS1, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to amplify the transmission signal supplied to the area expansion antenna AT2 to a predetermined level. As a result, as shown in Figure 8(C), the master unit CS1 forms an expanded communication area Ep1 in place of the normal communication area Ar1, and the slave unit PS1 can communicate bidirectionally with the master unit CS1 in the expanded communication area Ep1.

[0090] Furthermore, when a movement notification is provided to the main unit 1 from the master unit CS1, the main unit 1 identifies the neighboring master unit of master unit CS1, which is the source of the movement notification, based on the information stored in the neighboring master unit storage unit 121. As explained using Figures 1 and 3, the neighboring master unit of master unit CS1 is master unit CS2. For this reason, the preparation request provision unit 122 of the main unit 1 functions to form a movement preparation request and provides it to the identified neighboring master unit CS2.

[0091] In this case, when the nearby base station CS2 receives the request to prepare for relocation, the antenna control unit 412 controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to select the area expansion antenna AT2. Also, in the base station CS2, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to amplify the transmission signal supplied to the area expansion antenna AT2 to a predetermined level.

[0092] As a result, as shown in Figure 8(C), the neighboring master unit CS2 forms an extended communication area Ep2 instead of the normal communication area Ar2, enabling communication with the slave unit in the extended communication area Ep2. As shown in Figure 8(C), there is an overlapping portion between the extended communication area Ep1 of the master unit CS1 and the extended communication area Ep2 of the neighboring master unit CS2, and through this portion, the slave unit PS1 can hand over to the neighboring master unit CS2.

[0093] Suppose that, as shown in Figure 9(A), the slave unit PS1 then moves further towards the neighboring master unit CS2 and enters the overlapping area between the extended communication area Ep1 formed by the master unit CS1 and the extended communication area Ep2 formed by the neighboring master unit CS2. In this case, the received signal strength of the signal from the slave unit PS1 detected by the RSSI detection unit 4422 of the neighboring master unit CS2 exceeds a predetermined threshold, so the HO request provision unit 414 of the neighboring master unit CS2 forms a handover request and provides it to the main unit 1. When the main unit 1 receives the handover request from the neighboring master unit CS2, the line switching control unit 123 functions, releasing the communication path connected between the main unit 1 and the master unit CS1, and connecting a communication path between the main unit 1 and the neighboring master unit CS2. As a result, the slave unit PS1 and the neighboring master unit CS2 can communicate bidirectionally, and the slave unit PS1 can continue the call via the neighboring master unit CS2. In other words, a handover of the slave unit PS1 to the neighboring master unit CS2 is performed.

[0094] Furthermore, suppose that the slave unit PS1 moves to the neighboring master unit CS2, and as shown in Figure 9(B), the received signal strength from the slave unit PS1 becomes greater than or equal to a value (greater than a predetermined threshold) indicating that it has entered the normal communication area Ar2 formed by the neighboring master unit CS2. In this case, the movement completion notification provision unit 415 of the neighboring master unit CS2 functions and forms a movement completion notification, which is provided to the main unit 1. At the same time, in the neighboring master unit CS2, the antenna control unit 412 controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44, and controls it to select the normal communication antenna AT1. Also, in the neighboring master unit CS2, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44, and reduces the level of the transmission signal supplied to the normal communication antenna AT1 to a level that forms the normal communication area Ar2.

[0095] Meanwhile, when a movement completion notification is provided to the main unit 1 from the nearby master unit CS2, the main unit 1's completion notification provision unit 124 functions and forms and provides a completion notification to the master unit CS1, the source of the movement occurrence notification. In this case, upon receiving the completion notification, the master unit CS1's antenna control unit 412 controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to select the normal communication antenna AT1. Also, in the master unit CS1, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to reduce the level of the transmission signal supplied to the normal communication antenna AT1 to a predetermined threshold. This threshold is a level value sufficient for the master unit CS1 to form the normal communication area Ar1.

[0096] As a result, as shown in Figure 9(C), the master unit CS1 returns to the state of forming the normal communication area Ar1, and the neighboring master unit CS2 also returns to the state of forming the normal communication area Ar2. Therefore, as can be seen from the states in Figures 8 and 9, when the slave unit PS1 moves and the possibility of a handover increases, the master unit CS1 and the neighboring master unit CS2 form extended communication areas Ep1 and Ep2, creating an overlapping area between the two areas. This allows the slave unit PS1 to perform a handover to the neighboring master unit CS2 from its position in the master unit CS1's normal communication area Ar1.

[0097] Once the handover is complete, as shown in Figure 9(C), both the base station CS1 and the neighboring base station CS2 return to the state of forming normal communication areas Ar1 and Ar2, allowing for smooth communication in an environment free from radio interference. Thus, once the handover of the slave unit PS1 is complete, in the example explained using Figures 1 and 3, the source of the handover becomes the base station CS2, and the base stations CS1 and CS3, which are neighboring base stations of base station CS2, become neighboring base stations CS1 and CS3, enabling further handovers.

[0098] <If a handover does not occur> Furthermore, there are cases where the slave unit PS1 does not completely move to the neighboring master unit CS2 side, but returns to the master unit CS1 side. For example, suppose that the slave unit PS1 moves away from the master unit CS1, so that the master unit CS1 and the neighboring master unit CS2 form extended communication areas Ep1 and Ep2, as described above. In this case, as shown in Figure 10(A), the slave unit PS1 may temporarily leave the master unit CS1's normal communication area Ar1, but as shown in Figure 10(B), it may move towards the master unit CS1 side and return to the master unit CS1's normal communication area Ar1.

[0099] In this case, the signal strength of the signal received from the slave unit PS1 detected by the RSSI detection unit 4422 in the master unit CS1 is above a predetermined threshold that allows it to determine that the slave unit is located within the normal communication area Ar1. In this case, the cancellation notification provision unit 416 of the master unit CS1 functions, forms a cancellation notification, and provides it to the main unit 1. At the same time, in the master unit CS1, the antenna control unit 412 controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44, and controls it to select the normal communication antenna AT1. Also, in the master unit CS1, the radio wave output control unit 413 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44, and reduces the level of the transmission signal supplied to the normal communication antenna AT1 to a level that forms the normal communication area Ar2.

[0100] On the other hand, when a cancellation notification is provided from the master unit CS1 to the main unit 1, the main unit 1's cancellation request provision unit 125 functions and forms and provides a cancellation request to the neighboring master unit CS2. In this case, the neighboring master unit CS2, upon receiving the cancellation request, controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to select the normal communication antenna AT1. In addition, the neighboring master unit CS2 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to reduce the level of the transmission signal supplied to the normal communication antenna AT1 to a predetermined threshold. This threshold is a level value sufficient for the master unit CS1 to form the normal communication area Ar1.

[0101] As a result, as shown in Figure 10(C), the master unit CS1 returns to the state of forming the normal communication area Ar1, and the neighboring master unit CS2 also returns to the state of forming the normal communication area Ar2. Therefore, the likelihood of the slave unit PS1 moving and performing a handover increases, and even if both the master unit CS1 and the neighboring master unit CS2 form extended communication areas Ep1 and Ep2, if the slave unit PS1 does not perform a handover, the handover preparation state can be canceled. This allows the extended communication areas Ep1 and Ep2 to be properly canceled, and the system can be properly returned to a state where no radio interference occurs.

[0102] [Processing performed in the business phone system of the first embodiment] Next, the processing performed in the business phone system of the first embodiment will be summarized with reference to the sequence diagrams in Figures 11 and 12. Figures 11 and 12 are sequence diagrams for explaining the processing during handover in the business phone system of the first embodiment. Similar to the explanation using Figures 8 to 10, the explanation will be given using the example of a handset PS1 that is making a call via base unit CS1 and then handing over to a nearby base unit CS2.

[0103] Mutual activation processing is performed between the slave unit PS1 and the base unit CS1 (step S1). As a result, the base unit CS1 registers that the slave unit is located within its normal communication area Ar1. Similarly, the slave unit PS1 registers that it is located within the base unit CS1's normal communication area Ar1. This puts the slave unit PS1 in a state where it can communicate bidirectionally with the base unit CS1. Subsequently, by making a call from the slave unit PS1, or by answering an incoming call using the slave unit PS1, a data link is formed between the slave unit PS1 and the base unit CS1, and a call is in progress (step S2).

[0104] In the master unit CS1, the RSSI detection unit 4422 of the TDMA modulation / demodulation unit 442 functions and starts measuring (detecting) the received signal strength of the signal from the slave unit PS1 (step S3). After this, suppose the user holding the slave unit PS1 starts moving (step S4). The movement occurrence notification provision unit 411 of the control circuit 41 of the master unit CS1 monitors the received signal strength from the RSSI detection unit 4422 provided through the control unit 441 of the wireless communication circuit 44. The movement occurrence notification provision unit 411 determines whether the received signal strength (RSSI) of the signal from the slave unit PS1 has become smaller than a threshold (step S5). The determination process in step S5 is to determine whether the slave unit PS1, which is located within the normal communication area Ar1 of the master unit CS1, is likely to move out of the normal communication area Ar1.

[0105] In the determination process of step S5, if it is determined that the received signal strength (RSSI) of the signal from the slave unit PS1 is not below the threshold, the likelihood of the slave unit PS1 leaving the normal communication area Ar1 is not high, so the process from step S5 is repeated. In the determination process of step S5, if it is determined that the received signal strength (RSSI) of the signal from the slave unit PS1 has fallen below the threshold, the movement notification provision unit 411 of the master unit CS1 determines whether or not the call is continuing (step S6). In the determination process of step S6, if it is determined that the call is not continuing, the movement notification provision unit 411 terminates the process for performing a handover because there is no call in progress.

[0106] In the determination process of step S6, if it is determined that the call is continuing, the mobile occurrence notification provision unit 411 forms a mobile occurrence notification and provides it to the main unit 1 (step S7). At the same time, the antenna control unit 412 and the radio wave output control unit 413 function and perform area expansion processing (step S8). The area expansion processing in step S8 consists of two parts: one is controlling the switching unit 4433 of the wireless communication unit 443 to switch to terminal b to select the area expansion antenna AT2; the other is controlling the amplification unit 4432 of the wireless communication unit 443 to amplify the signal level of the transmission signal supplied to the area expansion antenna AT2 to a predetermined level. As a result, the master unit CS1 forms an expanded communication area Ep1. Therefore, the slave unit PS1 becomes able to communicate with the master unit CS1 in the expanded communication area Ep1.

[0107] Upon receiving the movement notification, the main unit 1 activates the preparation request provision unit 122 to form a movement preparation request and provides it to the neighboring master unit CS2 of the master unit CS1 that provided the movement notification, according to the information stored in the neighboring master unit storage unit 121 (step S9). Upon receiving the movement preparation request, the neighboring master unit CS2 activates the antenna control unit 412 and the radio wave output control unit 413 to perform area expansion processing (step S10). Step S10 is the same process performed in the master unit CS1 in step S8, but performed in the neighboring master unit CS2.

[0108] In other words, the process in step S10 involves two steps: firstly, controlling the switching unit 4433 of the wireless communication unit 443 to switch to terminal b so that it selects the area expansion antenna AT2; and secondly, controlling the amplification unit 4432 of the wireless communication unit 443 to amplify the signal level of the transmission signal supplied to the area expansion antenna AT2 to a predetermined level. As a result, the nearby master unit CS2 also forms the expanded communication area Ep2. This creates an overlapping area between the expanded communication area Ep1 formed by the master unit CS1 and the expanded communication area Ep2 formed by the nearby master unit CS2, as shown in Figure 8(C), thus creating an environment where the handover of the slave unit PS1 is possible.

[0109] Next, the process shown in Figure 12 proceeds. When the slave unit PS1 enters the extended communication area Ep2 of the neighboring master unit CS2, communication takes place between the slave unit PS1 and the neighboring master unit CS2 to perform a handover (step S11). In this state, the slave unit PS1 is still making a call through the master unit CS1. The neighboring master unit CS2, now able to communicate with the slave unit PS1, activates the HO request provision unit 414, forms a handover request, and provides it to the main unit 1 (step S12). The main unit 1 activates the line switching control unit 123, which connects a communication path between itself and the neighboring master unit CS2 and performs a communication path switching process that releases the communication path that was connected between itself and the master unit CS1 (step S13). As a result, the slave unit PS1 forms a data link with the neighboring master unit CS2 (step S14), and can seamlessly continue the call via the neighboring master unit CS2.

[0110] After this, the neighboring master unit CS2's movement completion notification provision unit 415 functions to determine whether the received signal strength of the signal from the slave unit PS1 detected by the neighboring master unit CS2's RSSI detection unit 4422 has reached the value that would be expected when the unit is located within the normal communication area Ar2 (step S15). If the determination process in step S15 determines that the received signal strength of the signal from the slave unit PS1 has reached the value that would be expected when the unit is located within the normal communication area Ar2, the movement completion notification provision unit 415 forms a movement completion notification and provides it to the main unit 1 (step S16). At the same time, the neighboring master unit CS2's antenna control unit 412 and radio wave output control unit 413 function to terminate the area expansion (step S17). One of the processes in step S17 is to control the switching unit 4433 of the wireless communication unit 443 to switch to terminal a so that it selects the normal communication antenna AT1. Another process involves controlling the amplification unit 4432 of the wireless communication unit 443 to reduce the signal level of the transmission signal supplied to the normal communication antenna AT1 to a level that forms the normal communication area Ar2. As a result, the nearby master unit CS2 returns to a state that forms the normal communication area Ar1.

[0111] Meanwhile, the main unit 1, upon receiving the movement completion notification, detects the completion notification and provides it to the master unit CS1, the source of the movement occurrence notification (step S18). Upon receiving the completion notification, the master unit CS1 activates the antenna control unit 412 and the radio wave output control unit 413 to terminate the area expansion (step S19). Step S19 is the same process performed by the master unit CS2 in step S17, but performed by the neighboring master unit CS1.

[0112] Specifically, the process in step S19 involves two steps: firstly, controlling the switching unit 4433 of the wireless communication unit 443 to switch to terminal a, selecting the area expansion antenna AT2; and secondly, controlling the amplification unit 4432 of the wireless communication unit 443 to reduce the signal level of the transmission signal supplied to the normal communication antenna AT1 to a level that forms the normal communication area Ar1. As a result, the neighboring base station CS1 also forms the normal communication area Ar1. Consequently, as shown in Figure 9(C), the base station CS1 forms the normal communication area Ar1, and the neighboring base station CS2 returns to a state where it forms the normal communication area Ar2. This eliminates radio interference, and the slave unit PS1, which has handed over to base station CS2, can continue to communicate smoothly through base station CS2.

[0113] Note that while the sequence diagrams in Figures 11 and 12 describe the case where the slave unit PS1 always performs a handover, as mentioned above, there are also cases where the slave unit returns to the normal communication area of ​​the original master unit. Therefore, after the processing of steps S8, S9, and S10 shown in Figure 11, the original master unit CS1 monitors the received signal strength of the signal from the slave unit PS1 detected by the RSSI detection unit 4422, and activates the cancellation notification provision unit 416 when it returns to a predetermined level. This cancels the preparation state for enabling the handover and returns to the state before the handover was enabled. [Effects of the First Embodiment] As can be seen from the description of the first embodiment above, the normal communication area formed by the master unit does not overlap with the normal communication area formed by the neighboring master unit. Therefore, the normal communication area is an area where communication with the slave unit can be performed smoothly and stably without causing radio interference. When there is a high possibility of a slave unit handover occurring, the master unit of the originating unit and the neighboring master unit located near the originating unit form an extended communication area. Since the extended communication area formed by the originating master unit and the extended communication area formed by the neighboring master unit overlap, a slave unit handover can be made possible. After the handover is completed, the master unit of the originating unit and the neighboring master unit change the extended communication area back to the normal communication area, so that the condition in which radio interference may occur can be resolved in a short time.

[0114] [Second embodiment (example when the slave device performs roaming)] As mentioned above, roaming means that a cordless handset in standby mode, which is not currently making a call, changes the base station it is connected to by moving. In this embodiment of the business phone system, a DECT standard cordless telephone system is used. Therefore, when a handset is in standby mode, control information and other data are transmitted from the base station to the handset via a dummy bearer, but no information is transmitted from the handset to the base station. Consequently, the base station does not receive signals from the handset, requiring a different configuration than when performing handover in the first embodiment. Below, we will describe an example of the configuration of each device that makes up the business phone system when roaming is implemented.

[0115] <Example of main unit configuration> Figure 13 is a block diagram illustrating an example of the configuration of the main unit 1 used in the business phone system of the second embodiment. In Figure 13, parts that are configured similarly to the main unit 1 of the first embodiment shown in Figure 2 are given the same reference numerals, and explanations of those parts are omitted to avoid redundancy. As can be seen by comparing Figure 13 with Figure 2, the configuration of the control unit 12A is different from the control unit 12 of the main unit 1 of the first embodiment. The control unit 12A of the main unit 1 of the second embodiment does not have a line switching control unit 123. This is because, in standby mode, there is no need to switch the call line connected to the base unit as in call mode. The other parts are configured similarly to the control unit 12 of the main unit 1 of the first embodiment.

[0116] <Example configuration of cordless telephone devices 21, 22, and 23 of the second embodiment> Next, we will describe the configuration examples of the cordless telephone devices 21, 22, and 23 of the second embodiment. Since the base units CS1, CS2, and CS3 of the cordless telephone devices 21, 22, and 23 are configured similarly, we will use the base unit CS1 as an example to specifically describe its configuration below. Similarly, since the handsets PS1, PS2, and PS3 of the cordless telephone devices 21, 22, and 23 are configured similarly, we will use the handset PS1 as an example to specifically describe its configuration below.

[0117] <Example of a master unit configuration> The basic configuration of the master unit CS1 in the second embodiment is the same as that of the CS1 in the first embodiment, as explained with reference to Figure 5. However, in order to realize roaming of the slave units, the configuration of the control circuit 41A of the master unit CS1 in the first embodiment differs from that of the control circuit 41 of the master unit CS1 in the first embodiment. For this reason, the following description will focus mainly on the configuration of the control circuit 41A of the master unit CS1 in the second embodiment.

[0118] Figure 14 is a block diagram illustrating the detailed configuration of the base unit CS1 of the cordless telephone device 21 used in the business phone system of the second embodiment. In Figure 14, parts that are configured similarly to the base unit CS1 of the first embodiment shown in Figure 6 are denoted by the same reference numerals, and detailed explanations of those parts are omitted. That is, in the base unit CS1 of the first embodiment, the wireless communication circuit 44 is configured similarly to the wireless communication circuit 44 of the base unit CS1 of the first embodiment.

[0119] In Figure 14, the configuration of the control circuit 41A differs from that of the control circuit 41 of the master unit CS1 in the first embodiment shown in Figure 5. As shown in Figure 14, the control circuit 41A of the master unit CS1 includes a storage information storage unit 41A1, a movement occurrence notification provision unit 41A2, and a release processing unit 41A3. Furthermore, the control circuit 41A includes an antenna control unit 41A4, a radio wave output control unit 41A5, a storage processing unit 41A6, a storage permission notification provision unit 41A7, and a movement completion request provision unit 41A8. Furthermore, the control circuit 41A includes a timer unit 41T and a cancellation notification provision unit 41A9.

[0120] The storage information storage unit 41A1 is activated in relation to the slave unit and stores the identification information of the slave unit it has connected to. Activation is a process in which the master unit and the slave unit communicate with each other and recognize that they are capable of communicating with each other. Upon activation, the master unit connects to the slave unit that can communicate (registers the slave unit located in a position where it can communicate with itself (location registration)), and the slave unit registers the identification information of the master unit with which it can communicate. Here, the identification information of the slave unit is information that can uniquely identify each slave unit, such as the MAC address of the slave unit, and the identification information of the master unit is also information that can uniquely identify each master unit, such as the MAC address of the master unit.

[0121] Figure 16 is a diagram illustrating an example of data stored in the storage information storage unit 41A1. As shown in Figure 16, the storage information storage unit 41A1 includes a storage slave ID field and a storage date and time field for storing identification information of slaves stored in the main unit. In Figure 16, for the sake of simplicity, the slave's reference code is used as the identification information of the stored slave, but in reality, as described above, identification information unique to the slave, such as the MAC address, is used. Based on the data stored in this storage information storage unit 41A1, the main unit CS1 can understand that slave PS1 exists as a slave that has been registered in the main unit and is capable of bidirectional communication.

[0122] The movement notification provision unit 41A2 functions when the switching unit 4433 of the wireless communication unit 443 is switched to use the normal communication antenna AT1 and the system is in a standby state where only the transmission of signals from the master unit to the slave unit is taking place. The movement notification provision unit 41A2 receives a movement preparation notification from a slave unit whose identification information is stored in the storage information storage unit 41A1, and forms a movement notification and provides it to the main unit 1. The release processing unit 41A3 deletes the identification information of the slave unit from the storage information storage unit 41A1 when it receives a completion request from the main unit 1 that includes the identification information of the slave unit. These movement notification provision unit 41A2 and the release processing unit 41A3 are processing units that function when the master unit CS1 is the master unit from which the slave unit moved.

[0123] The antenna control unit 41A4, upon receiving a move preparation request from the main unit 1, switches the switching unit 4433 of the wireless communication unit 443 to select the area expansion antenna AT2. The radio wave output control unit 41A5, upon receiving a move preparation request from the main unit 1, controls the amplification unit 4432 of the wireless communication unit 443 to increase the radio wave output of the transmission signal supplied to the area expansion antenna AT2, thereby forming an expanded communication area. The accommodation processing unit 41A6, upon receiving an accommodation request from a slave unit while the switching unit 4433 of the wireless communication unit 443 is switched to use the area expansion antenna AT2, records the identification information of the slave unit in the accommodation information storage unit 41A1.

[0124] Furthermore, the accommodation permission notification provision unit 41A7, via the accommodation processing unit 41A6, forms an accommodation permission notification and provides it to the slave unit when it records the slave unit's identification information in the accommodation information storage unit 41A1. The move completion request provision unit 41A8, upon receiving a move completion notification from the slave unit, forms a move completion request and provides it to the main unit 1.

[0125] The antenna control unit 41A4, as described above, also performs the process of switching the switching unit 4433 of the wireless communication unit 443 to select the normal communication antenna AT1 when it provides a move completion request to the main unit 1 through the move completion request provision unit 41A8. Furthermore, suppose a move completion request is provided to the main unit 1 through the move completion request provision unit 41A8. In this case, the radio wave output control unit 426, as described above, also performs the process of controlling the amplification unit 4432 of the wireless communication unit 443 to reduce the radio wave output of the transmission signal supplied to the normal communication antenna AT1 and form a normal communication area. Thus, the antenna control unit 41A4, the radio wave output control unit 41A5, the accommodation processing unit 41A6, the accommodation permission notification provision unit 41A7, and the move completion request provision unit 41A8 all function when the master unit CS1 is the destination of the slave unit.

[0126] Furthermore, the timer unit 41T measures the time elapsed since the movement occurrence notification was provided to the main unit 1 via the movement occurrence notification provision unit 41A2. The cancellation notification provision unit 41A9 implements a function to form and provide a cancellation notification to the main unit 1 if the timer unit 41T has not received a completion notification from the main unit 1 within a predetermined time. This is because it can be determined that the roaming of the slave unit was not completed within the predetermined time. These timer unit and cancellation notification provision unit 41A9 are used when the master unit CS1 is the source of the slave unit's movement.

[0127] Furthermore, suppose a cancellation request is provided from the main unit 1. In this case, the antenna control unit 41A4 implements a function to switch the switching unit 4433 of the wireless communication unit 443 to select the normal communication antenna AT1. In addition, if a cancellation request is provided from the main unit 1, the radio wave output control unit 41A5 also implements a function to control the amplification unit 4432 of the wireless communication unit 443 so as to reduce the radio wave output of the transmission signal supplied to the normal communication antenna AT1 and form a normal communication area.

[0128] <Example configuration of the handset> Figure 15 is a block diagram illustrating an example configuration of the handset PS1 of a cordless telephone device 21 used in a business phone system. In Figure 15, the same reference numerals are used for parts that are configured similarly to the handset PS1 of the first embodiment shown in Figure 7, and a detailed explanation of these parts is omitted to avoid redundancy. As can be seen by comparing Figure 15 and Figure 7, the handset PS1 of the second embodiment differs in that the TDMA modulation / demodulation unit 512A of the wireless communication circuit 51A is equipped with an RSSI detection unit 5122. Furthermore, the handset PS1 of the second embodiment has a control circuit 52A that includes a destination storage unit 521, a move preparation notification provision unit 522, a connection request provision unit 523, an update unit 524, and a move completion notification provision unit 525.

[0129] The RSSI detection unit 5122 of the TDMA modulation / demodulation unit 512 detects the received signal strength of the transmission signal from the master unit. The received signal strength of the transmission signal from the master unit detected by the RSSI detection unit 5122 is provided to the control circuit 52A via the control unit 511. The storage location storage unit 521 of the control circuit 52A stores the identification information of the master unit in which the identification information of the local unit is stored. Here, the identification information of the master unit is information that can uniquely identify each master unit, such as the MAC address of the master unit.

[0130] Figure 17 is a diagram illustrating an example of data stored in the destination storage unit 521. As shown in Figure 17, the destination storage unit 521 includes a destination master ID field and a placement date and time field, which store the identification information of the master unit to which the user device is housed. In Figure 17, for the sake of simplicity, the master unit's reference code is used as the identification information of the destination master unit, but in reality, as described above, identification information unique to the master unit, such as the MAC address, is used. Based on the data stored in this destination storage unit 521, the user device PS1 can understand that the master unit CS1 exists as a master unit to which the user device is registered and with which bidirectional communication is possible.

[0131] The movement preparation notification provision unit 522 of the control circuit 52A functions when the RSSI detection unit 5122 detects that the received signal strength of a transmission signal from a master unit whose identification information is recorded in the destination storage unit 521 has fallen below a predetermined value. In this case, the movement preparation notification provision unit 522 functions to form and provide a movement preparation notification to the master unit that transmitted the transmission signal. The accommodation request provision unit 523 of the control circuit 52A functions when the RSSI detection unit 5122 detects that the received signal strength of a transmission signal from a master unit other than the master unit whose identification information is recorded in the destination storage unit 521 has fallen above a predetermined value. In this case, the accommodation request provision unit 523 functions to form and provide an accommodation request to the other master unit that transmitted the transmission signal.

[0132] The update unit 524 of the control circuit 52A updates the master unit identification information in the destination storage unit 521 when it receives a notification of permission to accommodate from another master unit that has provided an accommodation request through the accommodation request provision unit 523. In addition, the accommodation completion notification provision unit 525 forms the move completion notification and provides it to the destination master unit when the received signal strength of the signal from the destination master unit detected by the RSSI detection unit 512 exceeds a predetermined threshold.

[0133] The above description concerns the base unit CS1 and handset PS1 of the cordless telephone device 21 of the business phone system in the second embodiment. However, as mentioned above, the base units CS2 and CS3 and handset PS1 and PS2 of the other cordless telephone devices 22 and 23 of the second embodiment have a similar configuration and function in the same way. The notifications and requests provided by each of the above-mentioned devices include identification information of the sending device and identification information of the receiving device.

[0134] [Explanation of normal and extended communication areas during roaming] In the business phone system comprising the main unit 1 and cordless telephone devices 21, 22, and 23 of the second embodiment having the configuration described above, the method of distinguishing between the normal communication area and the extended communication area when a handset is roaming will be specifically explained below. In order to simplify the explanation, the case in which a handset PS1 whose location is registered with the base unit CS1 roams to a nearby base unit CS2 will be used as an example. Figures 18 to 20 are diagrams illustrating the normal communication area and the extended communication area when roaming in the business phone system of the second embodiment.

[0135] <If roaming occurs> As shown in Figure 18(A), the master unit CS1 and the slave unit PS1, located within the master unit CS1's normal communication area Ar1, have been activated. The slave unit PS1's location has been registered with the master unit CS1, and the slave unit PS1 has registered that it can communicate with the master unit CS1. However, the slave unit PS1 is not currently being used for calls and is in a standby state (idle state). As mentioned above, one-way communication is taking place, with the master unit CS1 sending control information etc. to the slave unit PS1 via a dummy bearer. Therefore, the master unit CS1 is not receiving any signals from the slave unit PS1. In addition, the neighboring master unit CS2 forms the normal communication area Ar2, but is not in a positional relationship with the slave unit PS1 that allows for communication. Therefore, the master unit CS2 is unaware of the slave unit PS1's location.

[0136] In this second embodiment, as in the first embodiment described above, the normal communication areas Ar1 and Ar2 formed by the master units CS1 and CS2 do not overlap with the normal communication areas formed by neighboring master units. As a result, there is no radio interference between the normal communication area Ar1 formed by master unit CS1 and the normal communication area Ar2 formed by master unit CS2, and smooth communication can be performed between the master unit and the slave unit.

[0137] Suppose that, starting from the state shown in Figure 18(A), the slave unit PS1 moves away from the master unit CS1 and approaches the master unit CS2, as shown in Figure 18(B). In this case, the signal strength of the signal received by the slave unit PS1 from the master unit CS1 decreases as the slave unit PS1 moves further away from the master unit CS1. Suppose that the signal strength of the signal received by the slave unit PS1 from the master unit CS1, which is communicating in one direction through the dummy bearer, drops to a predetermined threshold, which is detected by the RSSI detection unit 5122 and notified to the control circuit 52A via the control unit 511. In this case, the movement preparation notification provision unit 522 of the control circuit 52A of the slave unit PS1 forms a movement preparation notification and provides it to the master unit CS1 whose position is registered.

[0138] Upon receiving the movement preparation notification, the master unit CS1 activates the movement occurrence notification provision unit 411 to form a movement occurrence notification and provides it to the main unit 1. When the main unit 1 receives the movement occurrence notification from the master unit CS1, it refers to the data stored in the neighboring master unit storage unit 121 and forms and provides a movement occurrence notification to the neighboring master unit CS2 for master unit CS1. Upon receiving the movement occurrence notification, the master unit CS2's antenna control unit 41A4 controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to select the area expansion antenna AT2. Also, in the master unit CS2, the radio wave output control unit 41A5 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44 to amplify the transmission signal supplied to the area expansion antenna AT2 to a predetermined level, thereby forming the expanded communication area Ep2.

[0139] As a result, as shown in Figure 18(C), the neighboring master unit CS2 forms an extended communication area Ep2 instead of the normal communication area Ar2, enabling communication with the slave unit in the extended communication area Ep2. In this case, as shown in Figure 18(C), the extended communication area Ep2 of the neighboring master unit CS2 is formed in the vicinity of the normal communication area Ar1 of the master unit CS1, allowing communication with the slave unit PS1, which has left the normal communication area Ar1 of the master unit CS1, to start quickly.

[0140] Suppose that, as shown in Figure 19(A), the slave unit PS1 then moves further towards the neighboring master unit CS2 and enters the extended communication area Ep2 of the neighboring master unit CS2. In this case, the slave unit PS1 becomes able to receive control signals, etc., from the neighboring master unit CS2 through the dummy bearer. Therefore, when the signal strength of the received signal from the neighboring master unit CS2 detected by the RSSI detection unit 5122 in the slave unit PS1 exceeds a predetermined threshold, the accommodation request provision unit 523 forms an accommodation request and provides it to the neighboring master unit CS2.

[0141] When the neighboring master unit CS2 receives an access request from the slave unit PS1, the access processing unit 41A6 functions to record the identification information of the slave unit PS1 in the access information storage unit 41A1. The access permission notification provision unit 41A7 of the neighboring master unit CS2 also functions to form an access permission notification and provides it to the slave unit PS1, the source of the access request. After this, when the signal strength received from the access master unit CS2 in the slave unit PS1 exceeds a predetermined threshold, the move completion notification provision unit 525 functions to send a move completion notification. Upon receiving the move completion notification from the slave unit, the neighboring master unit CS2 functions to form a move completion request, which it provides to the main unit 1. Upon receiving the move completion request, the main unit 1 forms and provides a completion notification to the master unit CS1, the source of the move occurrence notification.

[0142] Furthermore, in the master unit CS2, after providing a movement completion request to the main unit 1 via the movement completion request provision unit 41A8, the antenna control unit 41A4 switches the switching unit 4433 via the control unit 441 to select the normal communication antenna AT1. In addition, in the master unit CS2, after providing a movement completion request to the main unit 1 via the movement completion request provision unit 41A8, the radio wave output control unit 41A5 also functions. In this case, the radio wave output control unit 41A5 controls the amplification unit 4432 of the wireless communication unit 443 via the wireless control unit 441, reducing the transmission signal supplied to the normal communication antenna AT1 to a predetermined level. As a result, the master unit CS2 forms the normal communication area Ar2.

[0143] Meanwhile, when the slave unit PS1 receives an access permission notification from the nearby master unit CS2, it performs an update process to delete the identification information of the master unit CS1 already recorded in the access destination storage unit 521 and record the identification information of the nearby master unit CS2. Also, when the original master unit CS1 receives a completion notification from the main unit 1, the release processing unit 41A3 functions to delete the identification information of the slave unit PS1 recorded in the access information storage unit 41A1. As a result, as shown in Figure 9(B), the slave unit PS1, which was registered in the master unit CS1, is registered in the nearby master unit CS2, and an environment is set up for communication via the nearby master unit CS2 in the nearby master unit CS2's normal communication area Ar2.

[0144] <If roaming does not occur> Furthermore, there are cases where the slave unit PS1 does not completely move towards the neighboring master unit CS2, but instead returns to the master unit CS1. For example, suppose that the slave unit PS1 moves away from the master unit CS1, causing the neighboring master unit CS2 to form an extended communication area Ep2, as described above. In this case, as shown in Figure 20(A), the slave unit PS1 initially moves out of the master unit CS1's normal communication area Ar1, but as shown in Figure 20(B), it may move towards the master unit CS1 and return to the master unit CS1's normal communication area Ar1.

[0145] In this case, the originating master unit CS1 uses the timer unit 41T to measure the elapsed time since it formed a movement notification and provided it to the main unit 1. If the main unit 1 does not provide a completion notification within this time, the cancellation notification provision unit 41A9 functions to form a cancellation notification and provides it to the main unit 1. When the main unit 1 receives a cancellation notification from the master unit CS1, it forms a cancellation request and provides it to the neighboring master unit CS2.

[0146] Upon receiving a cancellation request, the neighboring base station CS2 controls the switching unit 4433 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44, switching it to select the normal communication antenna AT1. Furthermore, the neighboring base station CS2 controls the amplification unit 4432 of the wireless communication unit 443 via the control unit 441 of the wireless communication circuit 44, reducing the level of the transmission signal supplied to the normal communication antenna AT1 to a predetermined threshold. This threshold is a level sufficient for the base station CS1 to form the normal communication area Ar1.

[0147] As a result, as shown in Figure 20(B), the master unit CS1 returns to the state of forming the normal communication area Ar1, and the neighboring master unit CS2 also returns to the state of forming the normal communication area Ar2. Therefore, the likelihood of the slave unit PS1 moving and roaming occurring increases, and even if the neighboring master unit CS2 forms the extended communication area Ep2, if the slave unit PS1 does not roam, the roaming readiness state can be canceled. This allows the extended communication area Ep2 to be properly canceled and the system to return to a state where no radio interference occurs. In this case, the slave unit can continue to receive control information, etc., from the master unit CS1 through the dummy bearer.

[0148] [Processing performed in the business phone system of the second embodiment] Next, the processing performed in the business phone system of the second embodiment will be summarized with reference to the sequence diagrams in Figures 21 and 22. Figures 21 and 22 are sequence diagrams for explaining the roaming process performed in the business phone system of the second embodiment. As explained using Figures 18 to 20, the example will be that PS1, whose location is registered in base unit CS1, roams to a nearby base unit CS2.

[0149] Mutual activation occurs between the slave unit PS1 and the master unit CS1 (step S21). As a result, the master unit CS1 registers that the slave unit is located within its normal communication area Ar1. Similarly, the slave unit PS1 registers that it is located within the master unit CS1's normal communication area Ar1. This creates an environment where the slave unit PS1 can communicate with the master unit CS1. The master unit CS1 notifies the slave unit PS1 of the threshold for received signal strength (RSSI) within its normal communication area Ar1 (step S22). This threshold is used to determine whether or not the slave unit PS1 is within the master unit CS1's normal communication area Ar1. In other words, if the received signal strength from the master unit CS1 at the slave unit PS1 is lower than this threshold, it is determined to be out of range; if it is above this threshold, it is determined to be within range.

[0150] Furthermore, although the slave unit PS1 is in an environment where bidirectional communication with the master unit CS1 is possible, the slave unit PS1 is in a standby state, so the master unit CS1 starts transmitting control signals etc. to the slave unit PS1 via a dummy bearer (one-way communication from the master unit to the slave unit) (step S23). The RSSI detection unit 5122 in the slave unit PS1 starts detecting the signal strength of the received signal from the master unit CS1, and sequentially notifies the control circuit 52A of the detected values ​​via the control unit 511 (step S24).

[0151] Suppose the user possessing the slave unit PS1 then begins to move (step S25). The movement preparation notification provision unit 522 of the control circuit 52A of the slave unit PS1 monitors the detected value of the RSSI detection unit 5122 (step S26). In step S26, if it is determined that the received signal strength (RSSI) has become smaller than the threshold notified in step S22, the movement preparation notification provision unit 522 of the slave unit PS1 forms a movement preparation notification and provides it to the master unit CS1 (step S27).

[0152] In the master unit CS1, the movement occurrence notification provision unit 41A2 functions to form a movement occurrence notification and provides it to the main unit 1 (step S28). In the main unit 1, the preparation request provision unit 122 functions to form a movement preparation request, and based on the information stored in the neighboring master unit storage unit 121, identifies the neighboring master unit CS2 located near master unit CS1 and provides the movement preparation request to the neighboring master unit CS2 (step S29). Upon receiving the movement preparation request, the neighboring master unit CS2 starts area expansion (step S30). The process in step S30 is the process in which the antenna control unit 41A4 controls the switching unit 4433 and the radio wave output control unit 41A5 controls the amplification unit 4432 to form the expanded communication area Ep2.

[0153] Next, the process shown in Figure 22 is performed. Assume that the slave unit PS1 moves further away from the master unit CS1, and is outside the range of the master unit CS1's normal communication area Ar1, and can no longer receive signals from the master unit CS1 (step S31). On the other hand, assume that it is now within the range of the neighboring master unit CS2's extended communication area Ep2, and can now receive signals from the neighboring master unit CS2 (step S32). In this case, the slave unit PS1 and the neighboring master unit CS2 are activated (step S33).

[0154] The activation process in step S33 is carried out in coordination between the slave unit PS1 and the neighboring master unit CS2. Specifically, first, the accommodation request provision unit 523 of the slave unit PS1 functions to provide an accommodation request to the neighboring master unit CS2. Upon receiving the accommodation request, the neighboring master unit CS2 functions its accommodation processing unit 41A6 to register the identification information of the slave unit PS1 in the accommodation information storage unit 41A1, and the neighboring master unit CS2 functions its accommodation permission notification provision unit 41A7 to form an accommodation permission notification and provide it to the slave unit PS1. Upon receiving the accommodation permission notification, the slave unit PS1 functions its update unit 524 to delete the previous primary destination information (identification information of the master unit CS1) in the destination storage unit and record the identification information of the neighboring master unit CS2. As a result, the location of the slave unit PS1 is registered with the neighboring master unit CS2, and the slave unit PS1 is also aware that its location has been registered with the neighboring master unit CS2.

[0155] This creates an environment where the slave unit PS1 can communicate bidirectionally with the master unit CS1. The master unit CS2 notifies the slave unit PS1 of the threshold for received signal strength (RSSI) in its normal communication area Ar2 (step S34). This threshold is used to determine whether or not the slave unit PS1 is within the master unit CS2's normal communication area Ar2. In other words, if the received signal strength from the master unit CS2 at the slave unit PS1 is lower than this threshold, it is determined to be out of range, and if it is above this threshold, it is determined to be within range.

[0156] Furthermore, although the slave unit PS1 is in an environment where bidirectional communication with the master unit CS1 is possible, the slave unit PS1 is in a standby state, so the master unit CS2 starts transmitting control signals etc. to the slave unit PS1 via a dummy bearer (one-way communication from the master unit to the slave unit) (step S35). The movement preparation notification provision unit 522 of the control circuit 52A of the slave unit PS1 monitors the detected value of the RSSI detection unit 5122 (step S36). In step S36, if it is determined that the received signal strength (RSSI) has become greater than the threshold notified in step S34, the movement completion notification provision unit 525 of the slave unit PS1 forms a movement completion notification and provides it to the master unit CS2 (step S37).

[0157] When the master unit CS2 receives a move completion notification from the slave unit PS1, the move completion request provision unit 41A8 functions to form a move completion request and provides it to the main unit 1 (step S38). Also, when the master unit CS2 receives a move completion notification from the slave unit PS1, it terminates the area expansion (step S39). The process in step S39 is one in which the antenna control unit 41A4 controls the switching unit 4433 and the radio wave output control unit 41A5 controls the amplification unit 4432 to terminate the formation of the expanded communication area Ep2 and form the normal communication area Ar2.

[0158] Meanwhile, in the main unit 1, the completion notification provision unit 124 functions to form a completion notification and provides it to the master unit CS1 from which the device was moved (step S40). Upon receiving the completion notification from the main unit, the master unit CS1 functions the release processing unit 41A3 to perform a slave unit release process, which deletes the identification information of the slave unit PS1 stored in the storage information storage unit 41A1 (step S41). As a result, the slave unit PS1, master unit CS1, and neighboring master unit CS2 are in the state shown in Figure 19(B), and the slave unit PS1 is in a waiting state under the master unit CS2. In this case, master unit CS2 becomes the master unit from which the device was moved, and master unit CS1 becomes the neighboring master unit of master unit CS2.

[0159] Note that while the sequence diagrams in Figures 21 and 22 describe the case where the slave unit PS1 always performs roaming, as mentioned above, there are also cases where the slave unit returns to the normal communication area of ​​the original master unit. Therefore, after the processing in step S30 of Figure 21, the timer unit 41T and the cancellation notification provision unit 41A9 should be activated in the master unit CS1 that moved from the slave unit. This will provide a cancellation notification to the neighboring master unit CS2 through the main unit 1, ending the area expansion in the neighboring master unit CS2 and returning it to the state where the normal communication area Ar2 is formed.

[0160] [Effects of the second embodiment] As can be seen from the description of the second embodiment above, the normal communication area formed by the base station does not overlap with the normal communication area formed by the neighboring base station. Therefore, the normal communication area is an area where communication with the slave device can be performed smoothly and stably without causing radio interference. When there is a high possibility of the slave device roaming, the neighboring base station located near the base station from which the device is moving forms an extended communication area. Unlike the case where handover is enabled in the first embodiment described above, the base station from which the device is moving does not detect the extended communication area itself. As a result, during roaming, the cases in which an extended communication area is formed are further restricted, reducing the occurrence of radio interference and ensuring reliable roaming of the slave device.

[0161] [Ease of handling situations when multiple nearby base stations exist] In the first embodiment described above, the case in which the slave unit PS1 hands over from the master unit CS1 to the master unit CS2 was explained as an example, and in the second embodiment described above, the case in which the slave unit PS1 roams from the master unit CS1 to the master unit CS2 was explained as an example. However, in both the first and second embodiments described above, it is possible to handle cases where there are multiple neighboring master units. This is because the main unit 1 is equipped with a neighboring master unit storage unit 121.

[0162] Figure 23 is a diagram illustrating the normal communication area and extended communication area during handover in the business phone system of the first embodiment. In Figure 23, it is assumed that the only nearby base station CS1 is base station CS2, the only nearby base stations for base station CS2 are base station CS1 and base station CS3, and the only nearby base station for base station CS3 is base station CS2. In this case, as shown in Figure 23(A), when the handset PS1, which is making a call through base station CS1, performs a handover, as described above, base station CS1 and the nearby base station CS2 form extended communication areas Ep1 and Ep2, enabling the handover.

[0163] Furthermore, as shown in Figure 23(B), when a slave unit PS1 making a call through the master unit CS2 performs a handover, the storage data (Figure 3) in the neighboring master unit storage unit 121 of the main unit 1 indicates that there are two neighboring master units, master unit CS1 and master unit CS2. Therefore, as shown in Figure 23(B), the original master unit CS2 and the neighboring master units CS1 and CS3 form extended communication areas Ep1, Ep2, and Ep3, enabling the handover. In this case, the slave unit PS1 can hand over to master unit CS1, and it can also hand over to master unit CS3.

[0164] Figure 24 is a diagram illustrating the normal communication area and extended communication area during roaming in the business phone system of the second embodiment. In Figure 24, as in Figure 23, the only neighboring base station CS1 is base station CS2, the only neighboring base stations for base station CS2 are base station CS1 and base station CS3, and the only neighboring base station for base station CS3 is base station CS2. In this case, as shown in Figure 24(A), when the slave unit PS1, which is in standby mode via base station CS1, roams, as described above, the neighboring base station CS2 forms the extended communication area Ep2, enabling roaming.

[0165] Furthermore, as shown in Figure 24(B), when the slave unit PS1, which is in standby mode via the master unit CS2, roams, it can be determined from the data stored in the neighboring master unit storage unit 121 of the main unit 1 (Figure 3) that there are two neighboring master units, master unit CS1 and master unit CS2. Therefore, as shown in Figure 24(B), neighboring master units CS1 and CS3 form extended communication areas Ep1 and Ep3, enabling roaming. In this case, the slave unit PS1 can roam to both the master unit CS1 side and the master unit CS3 side.

[0166] [Differentiation] Furthermore, in the above-described embodiment, when roaming is performed, the originating base station measures the time elapsed since sending the move preparation notification, and if it determines that a timeout has occurred, the originating base station provides a cancellation notification to the main unit. This allows the main unit 1 to send a cancellation request to the nearby base station that has become a candidate for the destination, thereby canceling the roaming preparation state and returning to the original state. However, this is not the only possible solution. For example, if a slave unit that has registered its location with the originating base station leaves the base station's normal communication area, and then the slave unit requests activation again (a request for location registration), the originating base station may provide a cancellation notification to the main unit. In this case as well, the main unit 1 can send a cancellation request to the nearby base station that has become a candidate for the destination, canceling the roaming preparation state and returning to the original state.

[0167] Furthermore, the first embodiment described above explained the case where the slave unit performs a handover, and the second embodiment described the case where the slave unit performs roaming. However, by having the main unit, master unit, and slave unit each possess both the functions described in the first embodiment and the functions described in the second embodiment, a communication system capable of supporting both handover and roaming can be constructed.

[0168] Furthermore, although the cordless telephone equipment used to construct the business phone system in the above-described embodiment was described as employing the DECT method, it is not limited to this. For example, this invention can also be applied when constructing a telephone system using cordless telephone equipment employing the PHS (Personal Handy-phone System) method or cordless telephone equipment employing the SXGP (Shared eXtended Global Platform) method.

[0169] Furthermore, although the above-described embodiment explained the case where the communication system according to this invention is provided to a business phone system, it is not limited to this. For example, this invention can also be applied when a LAN (Local Area Network) system is formed by connecting multiple access points to a server device and wirelessly connecting these access points to a mobile communication terminal. In this case, the server device corresponds to the host device (main unit), the access points correspond to the master unit, and the mobile communication terminal corresponds to the slave unit. The slave unit can be a notebook PC (Personal Computer), a tablet PC, a smartphone, etc. [Explanation of Symbols]

[0170] 1...Main unit, 11...Line I / F, 12...Control circuit, 121...Nearby master unit memory unit, 122...Preparation request provision unit, 123...Line switching control unit, 124...Completion notification provision unit, 125...Cancellation request provision unit, 13...Line LSI unit, 14...Reference transmitting device, 21, 22, 23...Cordless telephone device, CS1, CS2, CS3...Master unit, 41...Control circuit, 411...Movement occurrence notification provision unit, 412...Antenna control unit, 413...Radio wave output control unit 414...HO request provision unit, 415...Movement completion notification provision unit, 416...Cancellation notification provision unit, 41A...Control circuit, 41A1...Accommodation information storage unit, 41A2...Movement occurrence notification provision unit, 41A3...Release processing unit, 41A4...Antenna control unit, 41A5...Radio wave output control unit, 41A6...Accommodation processing unit, 41A7...Accommodation permission notification provision unit, 41A8...Movement completion request provision unit, 41A9...Cancellation notification provision unit, 41T...Timer unit, 42...Line L SI section, 43...Synchronization signal generation circuit, 44...Wireless communication circuit, 441...Control unit, 442...TDMA modulation / demodulation unit, 4421...PLL circuit, 4422...RSSI detection unit, 443...Wireless communication unit, 4431...Conversion circuit, Rv...Receiver unit, Sd...Transmitter unit, 4432...Amplifier unit, 4433...Switching unit, AT1...Antenna for normal communication, AT2...Antenna for area expansion, PS1, PS2, PS3...Slave unit, 51...Wireless communication circuit, 511...Control 512...TDMA modulation / demodulation unit, 512A...TDMA modulation / demodulation unit, 5122...RSSI detection unit, 5121...PLL unit, 513...Wireless communication unit, 52...Control circuit, 52A...Control circuit, 521...Main destination memory unit, 522...Movement preparation notification provision unit, 523...Accommodation request provision unit, 524...Update unit, 525...Movement completion notification provision unit, 53...Codec circuit, 54...Transmitter, 55...Handset (microphone), 56...Handset (speaker)

Claims

1. In a communication system in which a master unit of a wireless communication device, which is configured by wirelessly connecting a master unit and slave units, is connected to a higher-level device in multiple master units, The aforementioned higher-level device is Each of the aforementioned master units is provided with a neighboring master unit storage means that stores adjacent master units in an identifiable manner, When a movement occurrence notification is received from the master unit indicating that the slave unit has moved, a movement preparation request providing means forms and provides a movement preparation request to the master unit that sent the movement occurrence notification, based on the information stored in the neighboring master unit storage means, requesting the neighboring master unit to prepare for the movement of the slave unit. When a handover request is received from the aforementioned neighboring master unit, the circuit switching control means releases the communication path between the master unit that provided the movement notification and the higher-level device, and connects the communication path between the aforementioned neighboring master unit that sent the handover request and the higher-level device. Equipped with, The aforementioned master unit is One or more standard communication antennas, One or more area expansion antennas, A switching means for selecting between the aforementioned standard communication antenna and the aforementioned area expansion antenna, Amplification means for raising or lowering the radio wave output level of the transmission signal supplied to the conventional communication antenna or the area extension antenna, A field strength detection means for detecting the received signal strength of a signal received from the slave unit through the aforementioned normal communication antenna or through the aforementioned area extension antenna. Equipped with, A means that functions when the master unit is the source of the slave unit's movement, When the switching means is switched to select the normal communication antenna and bidirectional communication is being performed with the slave unit, and the electric field strength detection means detects that the signal strength of the signal received from the slave unit falls below a predetermined threshold, the movement occurrence notification providing means forms the movement occurrence notification and provides it to the host device, When the movement occurrence notification is provided through the movement occurrence notification provision means, the first antenna control means switches the switching means to select the area expansion antenna, When the movement occurrence notification is provided through the movement occurrence notification provision means, a first radio wave output control means controls the amplification means to increase the radio wave output of the transmission signal supplied to the area expansion antenna to form an expanded communication area. Equipped with, A means that functions when the master unit becomes the destination of the slave unit, A second antenna control means, which, upon receiving the aforementioned movement preparation request from the aforementioned higher-level device, switches the switching means to select the area expansion antenna, A second radio wave output control means controls the amplification means to increase the radio wave output of the transmission signal supplied to the area expansion antenna in the event that the movement preparation request is received from the above-level device, thereby forming an expanded communication area. When the switching means is switched to use the area expansion antenna, and the electric field strength detection means detects that the signal strength of the received signal from the slave unit exceeds a predetermined value, the handover request providing means forms the handover request and provides it to the host device. A communication system characterized by comprising the following features.

2. A communication system according to claim 1, The aforementioned higher-level device is When a move completion notification is received indicating that the move of the slave unit from the nearby master unit to the higher-level device has been completed, the completion notification providing means provides the master unit that provided the move occurrence notification with a move completion notification for the slave unit. Equipped with, The aforementioned master unit is A means that functions when the master unit is the source of the slave unit's movement, A third antenna control means that, upon receiving the completion notification from the above-level device, switches the switching means to select the normal communication antenna, A third radio wave output control means controls the amplification means to reduce the radio wave output of the transmission signal supplied to the normal communication antenna when it receives the completion notification from the higher-level device, in order to form a normal communication area. Equipped with, A means that functions when the master unit becomes the destination of the slave unit, When the switching means is switched to use the area expansion antenna, and the electric field strength detection means determines that the received signal strength of the signal from the slave unit is equal to or greater than a value indicating that communication is possible with normal radio wave output, the movement completion notification providing means forms the movement completion notification and provides it to the host device, When the movement completion notification is provided to the higher-level device through the movement completion notification provision means, a fourth antenna control means switches the switching means to select the normal communication antenna, When the movement completion notification is provided to the higher-level device through the movement completion notification providing means, a fourth radio wave output control means controls the amplification means to reduce the radio wave output of the transmission signal supplied to the normal communication antenna in order to form a normal communication area. A communication system characterized by comprising the following features.

3. A communication system according to claim 1, The aforementioned higher-level device is Cancellation request providing means: When a cancellation notice is received from the master unit that provided the movement notification, provides the cancellation request to the nearby master unit that sent the movement preparation request. Equipped with, The aforementioned master unit is A means that functions when the master unit is the source of the slave unit's movement, The first antenna control means switches the switching means to select the area expansion antenna, and when the electric field strength detection means detects that the received signal strength of the signal from the slave unit received through the area expansion antenna has exceeded a predetermined value, the system provides a cancellation notification provision means to cancel the movement occurrence notification and provide it to the host device. When the cancellation notice is provided through the cancellation notice provision means, the first antenna control means switches the switching means to select the normal communication antenna. When the cancellation notice is provided through the cancellation notice provision means, the first radio wave output control means controls the amplification means to reduce the radio wave output of the transmission signal supplied to the normal communication antenna in order to form a normal communication area. A means that functions when the master unit is the source of the slave unit's movement, When the cancellation request is received from the higher-level device, the second antenna control means switches the switching means to select the normal communication antenna. When the cancellation request is received from the higher-level device, the second radio wave output control means controls the amplification means to reduce the radio wave output of the transmission signal supplied to the normal communication antenna in order to form a normal communication area. A communication system characterized by the following features.

4. In a communication system in which a master unit of a wireless communication device, which is configured by wirelessly connecting a master unit and slave units, is connected to a higher-level device in multiple master units, The aforementioned higher-level device is Each of the aforementioned master units is provided with a neighboring master unit storage means that stores adjacent master units in an identifiable manner, When a movement occurrence notification is received from the master unit indicating that the slave unit has moved, a movement preparation request providing means forms and provides a movement preparation request to the master unit that sent the movement occurrence notification, based on the information stored in the neighboring master unit storage means, requesting the neighboring master unit to prepare for the movement of the slave unit. Equipped with, The aforementioned master unit is One or more standard communication antennas, One or more area expansion antennas, A switching means for selecting between the aforementioned standard communication antenna and the aforementioned area expansion antenna, Amplification means for raising or lowering the radio wave output level of the transmission signal supplied to the conventional communication antenna or the area extension antenna, A storage information storage means for storing identification information of slave units housed in the master unit, and Equipped with, A means that functions when the master unit is the source of the slave unit's movement, When the switching means is switched to select the normal communication antenna, and the system is in a standby state where only the transmission of signals from the master unit to the slave unit is taking place, and the system receives a movement preparation notification from the slave unit whose identification information is stored in the storage information storage means, the system forms the movement occurrence notification and provides it to the host device. Equipped with, A means that functions when the master unit becomes the destination of the slave unit, When the above-level device receives the above-level device's request for preparation for movement, the switching means is configured to select the area expansion antenna, and the antenna control means is configured to switch the switching means to select the area expansion antenna. When the aforementioned mobile preparation request is received from the aforementioned higher-level device, a radio wave output control means controls the amplification means to increase the radio wave output of the transmission signal supplied to the area expansion antenna, When the switching means is switched to use the area expansion antenna, and a pickup request is received from the slave unit, the pickup processing means records the identification information of the slave unit in the pickup information storage means. When the identification information of the slave unit is recorded in the storage information storage means through the storage processing means, a storage permission notice is formed and provided to the slave unit by a storage permission notice provision means. Equipped with, The aforementioned sub-unit is A slave unit-side electric field strength detection means for detecting the received signal strength of the transmission signal from the master unit, A storage destination storage means that stores the identification information of the master unit in which the identification information of the slave unit is stored, When the receiving signal strength of a transmission signal from the master unit, whose identification information is recorded in the storage destination storage means, is detected by the slave unit-side electric field strength detection means to fall below a predetermined threshold, the movement preparation notification providing means forms and provides the movement preparation notification to the master unit, which is the source of the transmission signal, When the receiving signal strength of a transmission signal from another master unit other than the master unit, whose identification information is recorded in the storage destination storage means, is detected by the slave unit side field strength detection means to be above a predetermined value, the storage request provision means provides the other master unit that is the source of the transmission signal with the storage request, When an accommodation permission notification is provided from the other master unit that provided the accommodation request through the accommodation request provision means, an update means updates the master unit identification information of the accommodation destination storage means. A communication system characterized by comprising the following features.

5. A communication system according to claim 4, The aforementioned higher-level device is Completion notification providing means: When a move completion request is received from the neighboring master unit indicating that the move of the slave unit from the neighboring master unit to the neighboring master unit has been completed, the master unit that sent the move occurrence notification transmits a move completion notification for the slave unit. Equipped with, The aforementioned master unit is A means that functions when the master unit is the source of the slave unit's movement, Release processing means that deletes the identification information of the slave unit in the storage information storage means when it receives the completion request from the higher-level device, which includes the identification information of the slave unit. Equipped with, A means that functions when the master unit becomes the destination of the slave unit, The system includes a means for providing a move completion request, which, upon receiving a move completion notification from the aforementioned sub-unit, forms a move completion request and provides it to the higher-level device. When the antenna control means receives a notification of completion of movement from the sub-unit, it switches the switching means to select the normal communication antenna. When the sub-unit receives a notification of completion of movement, the radio wave output control means controls the amplification means to reduce the radio wave output of the transmission signal supplied to the normal communication antenna in order to form a normal communication area. The aforementioned sub-unit is When the signal strength of the signal received from the master unit at the destination, as detected by the slave unit-side received signal strength detection means, exceeds a predetermined threshold, the move completion notification is formed and provided to the master unit at the destination. A communication system characterized by comprising the following features.

6. A communication system according to claim 4, The aforementioned higher-level device is When a cancellation notice is received from the aforementioned master unit, the system is equipped with a cancellation request provision means that provides a cancellation request to the nearby master unit that provided the move preparation request. The aforementioned master unit is A means that functions when the master unit is the source of the slave unit's movement, A timer means for measuring the time elapsed since the aforementioned movement occurrence notification was provided to the higher-level device, If the completion notification from the higher-level device is not received within a predetermined time elapsed by the timer means, or if a second accommodation request arrives from the slave device whose identification information is stored in the accommodation information storage means, the cancellation request provision means forms the cancellation notification and provides it to the higher-level device. Equipped with, A means that functions when the master unit becomes the destination of the slave unit, When the aforementioned cancellation request is received from the aforementioned higher-level device, the antenna control means switches the switching means to select the aforementioned normal communication antenna. When the aforementioned cancellation request is received from the aforementioned higher-level device, the radio wave output control means controls the amplification means to reduce the radio wave output of the transmission signal supplied to the normal communication antenna in order to form a normal communication area. A communication system characterized by the following features.

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