JP3641414B2 - Digital cordless telephone system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a telephone system, and more particularly to a digital cordless telephone system using a plurality of radio base stations such as a PHS (Personal Handy Phone System) and a mobile phone and a plurality of mobile terminals.
[0002]
[Prior art]
Such digital cordless telephone systems are rapidly spreading due to their convenience. Further, conventional techniques relating to such a digital cordless telephone system are disclosed in, for example, “TDMA mobile communication system” in Japanese Patent Laid-Open No. 5-235835, “Channel allocation system” in Japanese Patent Laid-Open No. 7-38940, and Japanese Patent Laid-Open No. 8-26536. "Multiple slot allocation method" disclosed in Japanese Patent Laid-Open No. 10-304437, "Radio section synchronization monitoring system and radio base station apparatus using the system", and "Digital cordless telephone system" disclosed in Japanese Patent Laid-Open No. 11-187131 Has been. In particular, in the last publication, in a digital cordless telephone system of TDMA / TDD (Time Division Multiple Access / Time Division Duplex), that is, a time division multiple access method / time division bidirectional transmission method, a mobile terminal in a call is separated. When a call is transferred to the mobile terminal, another slot is used for the call at the transfer destination, and the use efficiency of the radio channel is poor. Therefore, a technique for solving this is disclosed.
[0003]
Digital radio communication between a radio base station and a mobile terminal using the TDMA / TDD scheme is generally performed as shown in FIG. That is, the first to eighth radio signal time slots 10 are defined as 1 TDMA / TDD frames 11. The radio signal time slots 1 to 4 are defined as radio base station side transmission / terminal side reception slots 12. Radio signal time slots 5 to 8 are defined as radio base station side reception / terminal side transmission slots 13. These slots 12 are composed of four slots T1, T2, T3 and T4, and each slot T1 to T4 is 0.625 mS, and thus the total of the four slots is 2.5 mS. Similarly, the slot 13 is composed of four slots of R1 to R4 of 0.625 mS, respectively, for a total of 2.5 mS. As described above, TDD communication is alternately performed every 2.5 mS between the transmission timings T1 to T4 of the four slots and the reception timings R1 to R4 of the four slots. Further, a plurality of mobile terminals can be communicated with one radio base station by multiplex communication using the TDMA digital communication system.
[0004]
Next, FIG. 7 shows a detailed timing chart of communication between the radio base station and the mobile terminal. 7A shows a radio base station time slot 20 (this corresponds to the radio signal time slot 10 of FIG. 6 described above). FIG. 7B shows radio base station transmission timing or mobile terminal reception timing 21. On the other hand, FIG. 7C shows the radio base station reception timing or the mobile terminal transmission timing 22. As shown in FIGS. 7A to 7C, the communication between the radio base station and the mobile terminal is performed with one reception slot (first slot in the illustrated example) and one transmission slot (illustrated) per TDMA / TDD frame. In the example of FIG. 5, the fifth slot) is assigned. In these slots, the radio base station and the mobile terminal perform transmission and reception operations.
[0005]
In this example, since one radio base station has a maximum of four transmission slots and reception slots, the radio base station can theoretically communicate with four mobile terminals simultaneously. However, since one slot is used as broadcast information and a control command, the number of mobile terminals that can simultaneously communicate with one radio base station is limited to three. 8, (a) is the time slot 30, (b) is the reception timing 31 of the first mobile terminal, (c) is the reception timing 32 of the second mobile terminal, and (d) is the third mobile terminal. (E) is a transmission timing for control information 34 of the radio base station, (f) is a transmission timing 35 of the first mobile terminal, (g) is a transmission timing 36 of the second mobile terminal, and (h) is The transmission timing 37 and (i) of the third mobile terminal are the control information reception timing 38 of the radio base station.
[0006]
In the time slot 30 shown in FIG. 8A, the first slot T1 of each TDMA / TDD frame is received from the reception timing 31 of the first mobile terminal shown in FIG. 8B or from the radio base station to the first mobile terminal. Transmission timing 31. The second slot T2 is the reception timing 32 of the second mobile terminal shown in (c), that is, the transmission timing from the radio base station to the second mobile terminal. The third slot T3 is the reception timing 33 of the third mobile terminal shown in (d), that is, the transmission timing from the radio base station to the third mobile terminal. The fourth slot T4 is the transmission timing 34 of control information from the radio base station shown in (e). On the other hand, the fifth slot R1 is the transmission timing 35 from the first mobile terminal to the radio base station shown in (f). The sixth slot R2 is the transmission timing 36 from the second mobile terminal to the radio base station shown in (g). The seventh slot R3 is a transmission timing 37 from the third mobile terminal to the radio base station shown in (h). The eighth slot R4 is a control information reception timing 38 by the radio base station shown in (i).
[0007]
As described above, only up to three mobile terminals per radio base station can be used simultaneously. Therefore, a state in which three mobile terminals are simultaneously using the radio base station, that is, communication time slots of all radio base stations (10 in FIG. 6, 20 in FIG. 7, and 30 in FIG. 3) are used. In this state, no more mobile terminals can be used.
[0008]
[Problems to be solved by the invention]
Since the radio base station of the digital cordless telephone system has only three communication slots as described above, only one mobile base station can use a maximum of three mobile terminals simultaneously. However, there are generally four or more mobile terminals per radio base station, and in an environment where communication traffic is relatively high, a large number of mobile terminals are connected to one radio base station. There is a tendency to be biased. For this reason, it is often the case that a newer (or another) mobile terminal sends a call request while all the communication slots of the mobile base station are used, and as a result, the radio line cannot be used. . In order to avoid such a situation, it is conceivable to install a plurality of radio base stations. However, even if other radio base stations use only three or less mobile terminals, the same situation will occur if a large number (four or more) of mobile terminals concentrate on a specific radio base station.
[0009]
OBJECT OF THE INVENTION
Accordingly, an object of the present invention is to provide a digital cordless telephone system that can improve the use efficiency of a finite wireless line and suppress the occurrence of the situation that the wireless line cannot be used.
[0010]
[Means for Solving the Problems]
The digital cordless telephone system according to the present invention communicates between a plurality of mobile terminals via a plurality of radio base stations each having a limited communication slot and having at least partially overlapping service areas between adjacent ones. In the digital cordless telephone system to be enabled, a control command for silent incoming call is sent from each radio base station to the mobile terminal, and the service areas of the radio base stations and the plurality of radio base stations are transmitted based on information returned from the mobile terminal. Is obtained when a new mobile terminal joins communication in a state where there is no empty communication slot of a specific radio base station among the plurality of radio base stations. It was based on the location registration information already other radio base station of the mobile terminal in use the specific radio base station Switching the one mobile terminal belonging to a service area to the other wireless base station, to make available the specific communication slots of a radio base station to the new mobile terminal.
[0011]
In addition, according to a preferred embodiment of the digital cordless telephone system of the present invention, it comprises an exchange body having a storage unit for storing location registration information . The switch body includes a BS interface unit that interfaces with a plurality of radio base stations (BS), a time division switch that switches a communication path of these BS interface units, and a control unit that controls the switch body .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration and operation of a preferred embodiment of a digital cordless telephone system according to the present invention will be described in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a diagram for explaining the basic principle of a digital cordless telephone system according to the present invention. In FIG. 1, two radio base stations (hereinafter referred to as BS) 44b and 47b and service areas of these BSs 44b and 47b are indicated by circles. Further, in FIG. 1, the location relationship between four mobile terminals (hereinafter referred to as PSs) 44c, 45c, 46c and 47c and their respective PSs 44c to 47c is located in the service area of these BSs 44b and 47b. Show.
[0014]
Here, when a call is made to or received from the PSs 45c to 47c, each PS 45c to 47c is connected to the BS 44b that is closest and has good radio conditions. Even if the PS 44c performs an off-hook operation for making a call in this state, the PS 44c cannot be used because the BS 44b already uses all the communication slots for the three PSs. Incidentally, as is apparent from FIG. 1, the two PSs 46 and 47c are also in the service area of the BS 47b. Therefore, if BS 47b is available, one (or both) of PS 46c or 47c can be disconnected from BS 44b, and the call can continue as it is even if it is reconnected to BS 47b, and the communication request of BS 44b is freed and a call request is made. The problem can be solved by using the existing PS44c. It is the present invention that achieves this.
[0015]
When performing the above-described control, it is important to manage the location registration of PSs that are present (or located) in the service area of each BS. This location registration management is solved by periodically sending a ringing incoming command from each BS to each PS, and performing location registration management of the PS based on a response to the incoming command sent from each PS. These series of controls are performed by an exchange as will be described later with reference to FIG.
[0016]
Next, FIG. 2 is a block diagram of a preferred embodiment of a digital cordless telephone system according to the present invention. This digital cordless telephone system includes a PBX (switch body) 40, a plurality of BSs (radio base stations) 44b, 45b,..., BS47b, BS48b and a plurality of PSs (mobile terminals) 44c, PS45c, PS46c, PS47 and PS48c. Is done. As described above with reference to FIG. 1, it is assumed that PSs 44c-47c are within the service area of BS 44b, while PSs 46c, 47c are also within the service area of BS 47b. In the digital cordless telephone system shown in FIG. 2, the PBX 40 includes a TDSW (time division switch) 41, a control unit 42, BS interface units 44a to 48a with the BSs 44b to 48b described above, and a storage unit 43.
[0017]
In the digital cordless telephone system according to the present invention shown in FIG. 2, the PBX 40 is an exchange main body, and connects (switches) the BSs 44b to 48b and the PSs 44c to 48c. The BS interface units 44a to 48a transmit and receive signals such as calls and data with the corresponding BSs 44b to 48b. The TDSW 41 is a time-division switch that switches the communication path of the BS interface units 44a to 48a. Further, the control unit 42 controls the PBX 40. The storage unit 43 stores location registration management information (data) of PSs 44c to 48c. The control unit 42 of the PBX 40 controls the TDSW 41, controls the connection of the speech path for each BS interface unit 44a to 48a, and sends control commands to the PSs 44c to 48c through the BS interface units 44a to 48a and BS 44b to 48b. The information sent from the PSs 44c to 48c is processed.
[0018]
For example, a case where the dial operation to PS48c is performed in PS44c will be described. The dial information is sent to the control unit 42 through the BS 44b and the BS interface unit 44a. Based on the connection request, the control unit 42 sends an incoming call control command to the PS 48c through the BS interface 48a and the BS 48b. In response to this incoming call control command, the corresponding PS 48c rings and the user of the PS 48c performs a response (off-hook) operation, etc., so that the BS interface units 44a and 48a are connected by the TDSW 41, thereby making a call between the PSs. It becomes possible.
[0019]
First, the operation of the preferred embodiment of the digital cordless telephone system according to the present invention shown in FIG. 2 will be described. According to FIG. 2, four PSs PS44c to 47c are present in the service area of the BS 44b, and at the same time, two PSs 46c and 47c are present in the BS 47b. The positional relationship between the PSs 44c to 47c and the BSs 44b and 47b is in the state shown in FIG. 1, and from the distance between the PSs 44c to 47c and the BSs 44b and 47b, the PSs 44c to 47c are easily connected to the BS 44b. The control unit 42 periodically transmits a ringing incoming control command from the BSs 44b to 48b to the PSs 44c to 48c via the BS interface units 44a to 48a. This control sequence is shown in FIG.
[0020]
Next, a description will be given with reference to the control sequence diagram of FIG. The “SETUP” command sent from the control unit 42 is converted to a radio signal via the BS interface units 44a to 48a and BSn, and then notified to the PSn as control information of an “incoming call” command for instructing a silent incoming call. The The corresponding PSn that has received this makes a “link channel establishment request” for the radio channel to BSn, and receives “link channel assignment” based on this request. Thereafter, after performing call setting processing, concealment, and authentication processing using a communication slot based on channel information, the PSs 44c to 48c send out “calls” indicating that they have responded. In a normal case, PS44c-48c rings with this series of processing, but since it is an “incoming call” instruction with no ringing designation, no ringing operation occurs and the user of PS44c-48c has received a call. That is not recognized.
[0021]
Next, the control unit 42 stores the location registration management information for each of the BSs 44b to 48b in the storage unit 43 based on the “calling” information returned from the PSs 44c to 48c. For management of this information, as shown in FIG. 4, the PSs 44c to 48c that have responded to the “SETUP” command transmitted from the BSs 44b to 48b are registered. In other words, all PSs within the service area for each of the BSs 44b to 48b are stored in the storage unit 43 as location registration management data. According to FIG. 4, PSs 44c to 47c are registered in the BS 44b, and PSs 46c and 47c are registered in the BS 47b. According to FIG. 5, after storing the location registration information in the storage unit 43, the control unit 42 sends “disconnect” to the PSs 44 c to 48 c to disconnect the radio channel between the BS and PS, thereby registering the location. Terminate the management process. With the above control, PS location registration management information existing in the service area for each BS is registered in the storage unit 43.
[0022]
Now, it is assumed that the PSs 45c to 47c are in a call state using the BS 44b. In this state, the case where the PS 44c goes off-hook to make a call will be described with reference to the communication control sequence diagram of FIG. A “link channel establishment request” is transmitted to the BS 44b by the off-hook of the PS 44c. Based on this request, the BS 44b determines the availability of the wireless slot (see (1) in FIG. 3). If there is an empty channel, “link channel allocation” (see (2) in FIG. 3) is performed on the PS 44c. In this case, since all the communication slots of the BS 44b are used, the BS 44b sends a “call switching request” to the PBX 40. This information is taken into the control unit 42 of the PBX 40. The control unit 42 refers to the data in the storage unit 43, searches for all PSs 44c to 48c connected to the BS 44b that has requested link channel establishment, and finds other PSs connected to the corresponding BS. A process is performed to determine whether there is a BS that can be used.
[0023]
Here, if there is no other BS that can be used by this search processing, a “switch rejection” is sent to the BS 44b. As a result, the PS 44c sends a busy tone (busy sound) from the speaker to notify the user that the line cannot be used.
[0024]
By the way, according to the location registration management data of FIG. 4, among the mobile terminals connected to the BS 44b, the PSs 46c and 47c are within the service area of another BS 47b and can be used. Therefore, the control unit 42 sends a “call switching instruction” to the BS 44b (see (3) in FIG. 3). By this command, the BS 44b disconnects the radio channel with the PS 46c (see (5) in FIG. 3). Then, “link channel assignment” is transmitted to the PS 44c using the free communication slot. The PS 44c establishes synchronization with the BS 44b, performs call setting processing and authentication processing based on this “link channel assignment”, and establishes a call state with the BS 44b.
[0025]
On the other hand, in the PS 46c in which the radio channel with the BS 44b is disconnected, the handover process is started due to a decrease in the electric field level in the radio signal and an increase in data code error (Frame Error Rate). Through this handover process, the PS 46c searches for another BS and sends a “link channel establishment request” to the connectable BS 47b (see (6) in FIG. 3). Thereafter, a sequence process similar to that described above is performed, and a call state is entered with the BS 47b, and the call is resumed.
[0026]
In the above description of the embodiment, the case where the PS performs the calling operation has been described. However, even if there is an incoming call to the PS, it is possible to make the incoming call in the same manner as described above. Easy to understand.
[0027]
The configuration and operation of the preferred embodiment of the digital cordless telephone system according to the present invention have been described in detail above. However, it should be noted that the above-described embodiments are merely examples of the present invention and do not limit the present invention. Those skilled in the art will readily understand that various modifications and changes can be made without departing from the spirit of the present invention.
[0028]
【The invention's effect】
As is apparent from the above description, the digital cordless telephone system of the present invention has the following remarkable practical effects. That is, even if all the communication slots of the BS (wireless base station) are in use and cannot communicate with other PSs (mobile terminals), other BSs that are in the service area and have free slots in the communication slots By using it, another PS can be used for communication, and the utilization efficiency of the wireless line can be improved. In general, BSs are provided so that their service areas overlap each other, and at the same time, it is rare that all BS communication slots are full (in other words, full), in other words, a specific BS communication slot is empty. Even if there is not, there are many cases where there is a vacancy in the communication slot of another adjacent BS. Therefore, since more PSs can be used without unduly providing a large number of BSs or unreasonably waiting for PS users, the facility utilization efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between a radio base station and a mobile terminal for explaining the basic principle of a digital cordless telephone system according to the present invention.
FIG. 2 is a block diagram showing a configuration of a preferred embodiment of a digital cordless telephone system according to the present invention.
FIG. 3 is a call control sequence diagram of the digital cordless telephone system shown in FIG. 2;
4 is a configuration example of mobile terminal location registration management data of the digital cordless telephone system shown in FIG. 2;
FIG. 5 is a control sequence diagram of mobile terminal location registration in the digital cordless telephone system shown in FIG. 2;
FIG. 6 is an explanatory diagram of transmission / reception operation timing according to a general TDMA / TDD system.
FIG. 7 is an explanatory diagram of call timing according to a general TDMA / TDD system.
8 is a call timing diagram similar to FIG. 7 during maximum communication. FIG.
[Explanation of symbols]
40 Switch body (PBX)
41 Time division switch (TDSW)
42 Control Unit 43 Storage Units 44a to 48a BS Interface Units 44b to 48b Radio Base Station (BS)
44c-48c Mobile terminal (PS)

Claims (3)

In a digital cordless telephone system that enables communication between a plurality of mobile terminals via a plurality of radio base stations each having a limited communication slot and at least partially overlapping service areas between adjacent ones.
A position indicating the positional relationship between the service areas of the plurality of radio base stations and the plurality of mobile terminals based on the information sent back from each mobile base station to the mobile terminal and a control command for ringing without ringing. Get registration information
When a new mobile terminal joins communication in a state where there is no available communication slot of a specific radio base station among the plurality of radio base stations, the specific radio base is already based on the obtained location registration information other one of the mobile terminals belonging to the service area of the radio base station switches to the other radio base station, the new mobile terminal to said specific communication slots of a radio base station of the mobile terminal in use the station A digital cordless telephone system characterized by being made available to the public.   The digital cordless telephone system according to claim 1, further comprising an exchange main body having a storage unit for storing the location registration information.   The switch body includes a BS interface unit that interfaces with the plurality of radio base stations, a time division switch that switches a communication path of the BS interface unit, and a control unit that controls the switch body. The digital cordless telephone system according to claim 1 or 2.

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