JP3250730B2 - Time division multiplex wireless communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division multiplex radio communication system, and more particularly to a time division multiplex radio communication system for shortening a handover time for switching a base station with which a terminal communicates when moving.

[0002]

2. Description of the Related Art In a mobile communication system, it is necessary for a terminal to switch a communication base station due to deterioration of reception quality during communication or the like, but in a system using a time division multiplexing system, communication with a new base station is required. Call is interrupted for a short period of time because it is necessary to disconnect the call with the base station that is currently in the call and take steps to establish a new call. There was a problem.

For example, in a PHS (Personal Handy Phone System), a handover time takes about 1 to 5 seconds. Since the PHS terminal usually has only one transmission / reception circuit as shown in FIG. 6, the PHS terminal disconnects from the base station which is once in a call and switches to the base station as shown in FIG. Follow the steps to establish a call. More specifically, a handover time of about 1 to 5 seconds is required since the communication state is entered for the first time after processing such as synchronization establishment, authentication confirmation, radio wave state confirmation, and assignment of a communication channel is performed. However, since only one set of transmission circuit and reception circuit of the radio section is required, the configuration is relatively inexpensive. Since the terminal uses only one communication channel, it is used in a high traffic area where the communication volume is large. There is an advantage that it can be used.

As a system with a short handover time, DECT (DIGITAL
EUROPEAN CODELESS TELEHPONE), but despite the same time division multiplexing method, the handover time is extremely short, less than 1 second. This corresponds to 2 as shown in FIG.
One transmission circuit / reception circuit, always establishes a call with two base stations, and when the communication state with the base station during a call deteriorates, the other set of transmission circuits / reception circuits talks with the base station. This is because it is not necessary to cut off the call with the base station that is currently talking and then establish a call with a new base station. Therefore, the time as shown in FIG. 7 described in the PHS is not required, and the handover can be performed in a very short time because only switching to another base station which is already in a call is performed. However, since two sets of transmission circuits / reception circuits are required in the terminal, the cost is high, and the reduction in size and weight is disadvantageous for a mobile terminal, which is an important commercial value. In addition, since the terminal always talks with two base stations, it cannot use the limited radio channel effectively, and has the disadvantage that it is difficult to use it in high traffic areas where there is a lot of traffic. ing.

Another conventional example is disclosed in Japanese Patent Laid-Open No. 60-0533.
No. 43, a switching method in the time division multiplexing method is exemplified. This is because the terminal has two receiving circuits, thereby simultaneously receiving the main base station and the backup base station, thereby shortening the switching time. However, it is necessary to have two receiving circuits. , Resulting in an expensive configuration.

Japanese Patent Application Laid-Open No. Sho 63-2 is another conventional example.
In the technology disclosed in Japanese Patent Application Laid-Open No. 96529, it is mentioned that a communication state is maintained and switched between a main base station and a backup base station in a time-division manner, but one terminal communicates with the main base station. Since two standby base stations are in communication with each other, one terminal always uses two timeslots of the base station, which is a fatal disadvantage in a high traffic system. Become.

[0007]

As described above, the conventional P
HS has the disadvantage that the handover time is long. In addition, the DECT method has disadvantages that the cost of the terminal increases and it is difficult to use the terminal in a high traffic area. Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 60-053343 has a disadvantage that the terminal needs to have two receiving circuits and the cost of the terminal increases. Further, JP-A-63-
The technique of 296529 has a disadvantage that it is difficult to use it in a high traffic area.

[0008] In addition, by maintaining a communication state with the spare base station for a fixed period of time while the terminal is in communication with one base station, the quality of the communication with the base station during communication deteriorates due to the terminal moving. However, by switching the call to the standby base station when it is confirmed that the call state with the standby base station is good, an extremely short handover time can be realized. In doing so, one terminal needs to occupy one slot of the spare base station in addition to one slot of the main base station.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a time division multiplex radio communication system capable of shortening a handover time in a high traffic area and not increasing the cost of a terminal.

[0010]

According to the time division multiplex radio communication system according to the present invention, one radio terminal uses a frame group consisting of a series of frames each consisting of a plurality of slots.
In a time-division multiplexing wireless communication system in which time-division communication is performed between a wireless base station and another wireless terminal in a time-division manner and preliminary communication for handover is performed with another wireless base station, a predetermined number of slots in one frame are reserved. A plurality of remaining slots in the one frame are allocated to a call communication; a slot allocated to a preliminary communication in a different frame is used by a different wireless terminal for the preliminary communication; Each wireless terminal uses a part of the plurality of slots allocated to a plurality of frames for call communication over a plurality of frames.

Further, the time division multiplex radio communication system according to the present invention is the above time division multiplex radio communication system,
The predetermined number of slots in the frame is one transmission slot and one reception slot.

Further, the time division multiplex radio communication system according to the present invention is characterized in that, in the time division multiplex radio communication system described above, each radio terminal does not perform a call communication in a frame for performing a preliminary communication.

Further, in the time-division multiplex radio communication system according to the present invention, one radio terminal uses one frame consisting of a plurality of consecutive frames composed of a plurality of slots to form one radio base station and another radio terminal. In a time-division multiplex radio communication system in which communication is performed in a time-division manner and preliminary communication for handover is performed with another radio base station, a predetermined number of slots in one frame are allocated to the preliminary communication, The remaining plurality of slots are allocated to the call communication, and each wireless terminal uses the slot allocated to the preliminary communication of the predetermined frame for the preliminary communication, and the plurality of wireless terminals are allocated to the communication communication of the frame other than the predetermined frame. The telephone communication is performed by using a part of the slots.

Further, the time division multiplex radio communication system according to the present invention is the time division multiplex radio communication system described above,
The predetermined number of slots in the frame is one transmission slot and one reception slot.

[0015] A wireless terminal according to the present invention comprises: a predetermined number of slots to which preliminary communication for handover is allocated;
Using a group of frames consisting of a plurality of slots consecutively allocated to speech communication, speech communication is performed in time division between one wireless base station and another wireless terminal, and handover with another wireless base station is performed. A wireless terminal that performs preliminary communication for a predetermined frame, wherein a plurality of slots allocated to call communication of a frame other than the predetermined frame using a slot allocated to preliminary communication of a predetermined frame for preliminary communication. The communication communication is performed by using a part of the communication.

In the wireless terminal according to the present invention, in the above wireless terminal, the predetermined number of slots is one transmission slot and one reception slot.

The radio base station according to the present invention uses a predetermined number of slots to which preliminary communication for handover is allocated, and a frame group in which a frame composed of a plurality of slots allocated to speech communication is continuous. A radio base station that performs time-division communication with a plurality of wireless terminals and performs preliminary communication with another plurality of wireless terminals. The communication is performed, and the communication with each wireless terminal is performed using a part of the plurality of slots allocated to the communication in each frame over the plurality of frames.

Further, in the radio base station according to the present invention, in the above radio base station, the predetermined number of slots is one transmission slot and one reception slot.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a plurality of terminals share one slot of one spare base station as a slot for spare communication, utilizing the fact that the use ratio of the spare base station is low.

FIG. 1 and FIG. 2 show an embodiment of the present invention. In FIG. 1, the terminal 6 is in a call state with the base station 1, and the communication state between the terminal 6 and the base station 2 is a case where the base station 2 is positioned as a backup base station. Terminal 7
Is in a call state with the base station 3, and the communication state between the terminal 7 and the base station 2 is a case where the base station 2 is positioned as a backup base station. FIG. 2 shows a state that has changed from the state of FIG. 1. After the terminal 6 moves, the state of communication between the terminal 6 and the base station 1 has deteriorated. Of the terminal 6 and the terminal 7 of FIG. In FIG. 2, the terminal 6 is in a call state with the base station 2, and the communication state between the terminal 6 and the base station 4 is:
This is a case where the base station 4 is positioned as a spare base station. The terminal 7 is in a call state with the base station 3, and the communication state between the terminal 7 and the base station 5 is a case where the base station 5 is positioned as a backup base station.

This will be described in more detail. Terminal 6 is base station 1
When the terminal 6 moves during the call communication with the terminal 6, the communication state between the terminal 6 and the base station 1 is degraded. Since the preliminary communication has already been established with the base station 2 as the base station, the terminal 6 transmits the base station 1 to the base station 1 when it is confirmed that the communication state with the base station 2 has not deteriorated. Station 2
You can instantly switch the communication destination. Terminal 6
Since the base station 2 which was the spare base station was set as the main base station, when the main call communication with the base station 2 was established,
A spare base station is searched, and as a result, preliminary communication with the base station 4 is started with the base station 4 as the spare base station. Also, the terminal 7 is in a call state with the base station 3 and is performing preliminary communication with the base station 2 using the base station 2 as a standby base station. Since the call communication is started as the base station, the preliminary communication between the terminal 7 and the base station 2 cannot be performed in the same time slot as the call communication. Therefore, the terminal 7 needs to change the spare base station. Therefore, the terminal 7
A search is made for another base station as a spare base station, and spare communication is established with the base station 5 using the base station 5 as a spare base station.

This embodiment employs a TDMA (time division multiplex) system in which a terminal is constituted by one transmission circuit / reception circuit. In a telephone communication state, which is a main communication state, telephone communication is performed between a terminal and a base station in a time slot at an assigned frequency. Since base station 2 as a spare base station in FIG. 1 has established communication as a spare base station for both terminal 6 and terminal 7 in the same one time slot, the spare base station It becomes possible to share the same for communication with one communication terminal, and it is possible to effectively utilize a finite radio channel time slot. For example, the rate at which the terminal communicates with the standby base station is 5% of the total communication of the terminal (a value in the case of a 20-frame configuration described later,
Frame), the communication ratio of the terminal with the main base station is reduced to about 95%. However, since communication has been established with the standby base station, the communication from the main base station to the standby base station is not performed. Switching of communication can be performed instantaneously. However, since 95% of the time slots (the same time slot of 19 frames out of 20 frames) are used for the communication between the terminal and the main base station, the time slot used for the main base station communication is used. Cannot be used as a time slot for preliminary communication with another terminal. Therefore, when a base station that has been shared as a spare base station of a plurality of terminals by sharing the same time slot is used as a main base station of any of the plurality of terminals, The other terminal of the plurality of terminals must newly establish preliminary communication with another base station. Alternatively, a spare communication must be newly established in a time slot that is not used for another call communication of the same base station.

Here, the use rate of the time slot for the preliminary communication is tentatively set to 5% because, based on experience, if this rate is used, the communication quality can be maintained. In FIG. 1, only one time slot is required for the terminals 6 and 7 to perform preliminary communication with the base station 2 serving as a standby base station.
It is possible to alleviate the reduction of the radio wave use efficiency for the backup base station. Assuming that the use ratio of the time slot by the backup communication is 5%, in one time slot of the backup base station, at most 100% ÷ 5% =
Twenty terminals can share the spare base station. Alternatively, it can be used as a maximum of 20 spare base stations in one time slot of the base station 2.
Therefore, it is understood that the influence on the use efficiency of radio waves is small.

Next, the operation of this embodiment shown in FIGS. 1 and 2 will be described with reference to FIGS. 3, 4 and 5. FIG.

FIG. 3 is a diagram showing a frame composed of a transmission slot and a reception slot and constituting a frame group, and
FIG. 4 is a diagram illustrating allocation of a call slot and a control slot.

First, with reference to FIG. 3, the operation when the terminal establishes a call with the base station and shifts to the call state will be described with reference to time slots. In the TDMA system of the present embodiment, signals are transmitted and received between a base station and a terminal using a frame configured with four transmission slots and four reception slots as basic units.

Transmission slot TX1 and reception slot RX1
Are communicated between the terminal and the base station. Similarly, the transmission slot TX2 and the reception slot RX2, the transmission slot TX3 and the reception slot RX3 are paired, and the transmission slot TX4 and the reception slot RX4 are paired. One base station can simultaneously communicate with four terminals. Configuration. However, since one of the four transmission / reception slots is a control slot, three terminals per base station can simultaneously communicate for a call. Here, it is assumed that the control slot is TX1 / RX1 and the other slots are communication slots. However, the assignment of control slots may be fixed in time or may change. 1
Focusing on calls for one terminal, one per frame
Times (1 frame TX2 / RX2, TX3 / RX3
Alternatively, transmission / reception of one time in TX4 / RX4 is repeated, and continuous frames (for example, from the first frame to the nineteenth frame) are repeated.
A call is established by frames (excluding the 20th frame). Each slot is composed of data necessary for a call.

Next, a description will be given of the operation from when the terminal searches for a base station to when the terminal shifts to a call state. The preliminary communication between one terminal and the base station is based on the control slot (T
X1 / RX1), for example, as shown in FIG. 3, a control slot (TX1 / RX1) of one frame in 20 frames (the first frame in the example of FIG. 3) as shown in FIG.
This is performed using 1). Therefore, if multiple base stations transmit control slots at different timings,
The terminal can confirm the communication state with a plurality of base stations only by looking at the control slot. In the present embodiment, one mobile station only confirms the control slot by sequentially shifting the frame of the control slot to be confirmed, and changes the communication state with a maximum of 20 (20 timing) base stations. You can check. Assuming that the control timing is not limited to TX1 / RX1, TX1 / RX1, TX2
/ RX2, TX3 / RX3, and TX4 / RX4, a maximum of 20 (timing) × 4 = 80 (8
0 timing). In FIG. 1, the terminal 6 confirms the control slot by the above-described method and selects the base station 1 having the best communication state, thereby establishing the communication with the base station 1. The terminal 7 performs the same operation as the terminal 6, so that the terminal 7 and the base station 3 establish a call communication.

FIG. 4 is a diagram showing the use state of the time slots in the state of FIG. FIG. 4 shows a communication state from the first frame to the twentieth frame, and 19 sets of upward and downward arrows between the base station 1 and the terminal 6 indicate TX2 / TX between the first frame and the nineteenth frame. RX2, T
Indicates that call communication is being performed between the base station 1 and the terminal 6 using either X3 / RX3 or TX4 / RX4, and indicates a set of upward communication between the terminal 6 and the base station 2. The downward arrow indicates that transmission / reception (preliminary communication) is performed between the terminal 6 and the base station 2 using TX1 / RX1 of the twentieth frame. One pair of upward and downward arrows is TX1 / RX of the 15th frame.
1 indicates that transmission / reception (preliminary communication) is being performed between the base station 2 and the terminal 7, and 19 upward and downward arrows between the terminal 7 and the base station 3 are the first arrows. From the frame to the 14th frame and from the 16th frame to the 20th frame
Until the frame, it indicates that telephone communication is being performed between the terminal 7 and the base station 3 using any of TX2 / RX2, TX3 / RX3, or TX4 / RX4. In addition,
In one frame, only one set of TXn / RXn
Only (n = 1, 2, 3, or 4) is used for communication based on the PHS specification.

Referring to FIG. 4, terminal 6 enters a communication state with base station 1 as a main base station, establishes a communication state with one slot per frame, and then establishes a communication with base station 2 as a standby base station. Perform communication. The terminal 6 searches for a base station capable of preliminary communication in the control slot of the twentieth frame, and as a result of the search, uses the base station 2 as a standby base station.
In frame 0, communication with the base station 2 is started. Therefore, the call communication with the base station 1 is interrupted at a frequency of 1 frame every 20 frames. However, there is no effect if the call quality is not a problem. Here, the order of establishing call communication between the terminal 6 and the base station 1 as the main base station and the order of establishing the preliminary communication between the terminal 6 and the base station 2 as the standby base station may be reversed. no problem.

The terminal 7 is in a call state with the base station 3, and the call is maintained in a call communication state of one slot per frame. In addition, although preliminary communication is established between the terminal 7 and the base station 2 at a rate of one frame for every 20 frames, the timing of the preliminary communication between the terminal 7 and the base station 2 and the timing of the preliminary communication between the terminal 7 and the base station 2 Since the timing of the preliminary communication between the terminal 6 and the base station 2 is different, it is possible for both the terminal 6 and the terminal 7 to perform the preliminary communication with the base station 2 as the standby base station using one set of slots.

FIG. 5 is a diagram showing the use state of the time slot in the state of FIG. FIG. 5 shows the communication state from the first frame to the twentieth frame. The 19 sets of upward and downward arrows between the base station 2 and the terminal 6 indicate the communication states between the first frame to the fourteenth frame and the sixteenth frame. From the frame to the twentieth frame, TX1 / RX1 is used to indicate that speech communication is being performed between the base station 2 and the terminal 6, and a set of upward communication between the terminal 6 and the base station 4 And downward arrows indicate TX2 / RX2, TX3 /
Terminal 6 and base station 4 using RX3 or TX4 / RX4
Indicates that transmission / reception (preliminary communication) is being performed between the base station 3 and the terminal 7, and a pair of upward and downward arrows between the base station 3 and the terminal 7 indicate TX1 / RX1 to TX4 / RX in the nineteenth frame.
4 indicates that transmission / reception (preliminary communication) is being performed between the base station 3 and the terminal 7 using any one of the four arrows, and 19 pairs of upward and downward arrows between the terminal 7 and the base station 5 Is a terminal using any one of TX1 / RX1 to TX4 / RX4 and not used in the preliminary communication between the base station 3 and the terminal 7 from the TX1 / RX1 to the TX4 / RX4 in the twentieth frame. 7 indicates that communication between the base station 5 and the base station 5 is being performed. TX1 between the base station 3 and the terminal 7
Which of the slots / RX1 to TX4 / RX4 is used for preliminary communication is determined by the availability of communication slots in the base station 3.

Although the terminal 6 was in a call state with the base station 1 as shown in FIG. 1, communication with the base station 1 became difficult due to movement, so that the terminal 6 was a spare base station as shown in FIG. Call communication is established using the base station 2 as the main base station.
The spare base station for the terminal 6 includes the base station 2 to the base station 4
And the terminal 6 and the base station 4, which is a backup base station,
In order to perform preliminary communication at a rate of 1 frame to 20 frames,
The call communication between the terminal 6 and the base station 2 as the main base station is 2
Although only one frame is cut off for every 0 frames, there is no problem in call quality.

In the state of FIG. 1, the terminal 7 uses the base station 2 as a spare base station. However, in the state of FIG. 2, the terminal 6 uses the base station 2 as a main base station. Since the terminal 7 cannot use the base station 2 as a spare base station, the base station 5 is used as a spare base station.
Has established a preliminary communication with However, the terminal 7 has established the preliminary communication with the base station 5 using the base station 5 as a spare base station. May be established. The empty call slot is TX2 /
Any of RX2, TX3 / RX3 or TX4 / RX4.

In the description of FIG. 4, it is assumed that the slots used for the preliminary communication are dynamically changing. The terminal 6 uses the slot previously used for the preliminary communication for the call communication after the handover. In this case, the terminal 7 determines that there is no longer any possibility of performing a call communication using the slot with the base station 2 and changes the slot used for the preliminary communication to another slot of the base station (if it is not used for the call communication). ) Or the base station of the other party of the preliminary communication is switched to another base station.

According to the present embodiment, it is possible to instantaneously perform base station switching that occurs at the time of handover,
Further, since the communication channel / time slot of the spare base station can be shared by a plurality of terminals, the communication channel can be used effectively.

[0037]

As described above, according to the present invention,
Since the terminal only needs to include one set of a transmission circuit and a reception circuit, it is possible to instantaneously perform base station switching that occurs at the time of handover with an inexpensive configuration.

Further, according to the present invention, since the communication channel / time slot of the spare base station can be shared by a plurality of terminals, the communication channel can be effectively used even in an area with high traffic.

Further, according to the present invention, the problems of the conventional system in the time division multiplexing system, such as shortening of the handover time, reduction of the cost of the mobile terminal, downsizing by a relatively simple circuit configuration, and finite The use in a high traffic area due to the effective use of a certain wireless channel can be solved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a state in which a terminal 6 performs a call communication with a base station 1 and a terminal 7 performs a call communication with the base station 3 according to the embodiment of the present invention. .

FIG. 2 is a diagram illustrating a state in which a terminal 6 performs a call communication with a base station 2 and a terminal 7 performs a call communication with the base station 3 according to the embodiment of the present invention. .

FIG. 3 is a diagram showing a frame configuration including a transmission slot and a reception slot according to an embodiment of the present invention and constituting a frame group, and an allocation of a communication slot and a control slot.

FIG. 4 is a diagram illustrating a use state of a time slot in the state of FIG. 1 according to the embodiment of the present invention;

FIG. 5 is a diagram illustrating a use state of a time slot in the state of FIG. 2 according to the embodiment of the present invention;

FIG. 6 is a diagram illustrating a configuration of a PHS terminal.

FIG. 7 is a diagram showing a communication probability procedure at the time of handover of a conventional PHS.

FIG. 8 is a diagram showing a configuration of a terminal of the DECT system.

[Explanation of symbols]

 1, 2, 3, 4, 5, base station 6, 7 terminal

Claims (9)

(57) [Claims] 1. One wireless terminal performs a time-division call communication with one wireless base station and another wireless terminal using a frame group in which a plurality of slots are continuously arranged,
In a time division multiplex radio communication system for performing preliminary communication for handover with another radio base station, a predetermined number of slots in one frame are allocated to preliminary communication, and a plurality of remaining slots in the one frame are used for telephone communication. Allocated, different wireless terminals use the slots allocated to the preliminary communication of different frames for preliminary communication, and each wireless terminal uses a part of the multiple slots allocated to the telephone communication in each frame for the telephone communication. A time-division multiplex radio communication system characterized by using over a plurality of frames. 2. The time-division multiplex radio communication system according to claim 1, wherein the predetermined number of slots in one frame is one.
A time-division multiplex radio communication system comprising one transmission slot and one reception slot. 3. The time-division multiplex wireless communication system according to claim 1, wherein each wireless terminal does not perform a telephone communication in a frame for performing a preliminary communication. 4. One wireless terminal performs time-division call communication with one wireless base station and another wireless terminal using a frame group in which a plurality of frames each consisting of a plurality of slots are continuous,
In a time division multiplex radio communication system for performing preliminary communication for handover with another radio base station, a predetermined number of slots in one frame are allocated to preliminary communication, and a plurality of remaining slots in the one frame are used for telephone communication. Allocating, each wireless terminal uses a slot allocated for preliminary communication of a predetermined frame for preliminary communication, and uses a part of a plurality of slots allocated for speech communication of a frame other than the predetermined frame. A time-division multiplex wireless communication system characterized by performing telephone communication. 5. The time-division multiplex radio communication system according to claim 4, wherein the predetermined number of slots in the one frame is one.
A time-division multiplex radio communication system comprising one transmission slot and one reception slot. 6. One radio base station using a predetermined number of slots to which preliminary communication for handover is allocated and a frame group consisting of a plurality of frames each consisting of a plurality of slots allocated to speech communication. And a wireless terminal performing time-division call communication with another wireless terminal and performing preliminary communication for handover with another wireless base station, wherein a slot allocated to preliminary communication of a predetermined frame is used for preliminary communication. A wireless terminal for performing a call communication using a part of a plurality of slots allocated to the call communication of a frame other than the predetermined frame. 7. The wireless terminal according to claim 6, wherein the predetermined number of slots is one transmission slot and one reception slot. 8. A plurality of wireless terminals using a predetermined number of slots to which preliminary communication for handover is allocated and a frame group including a plurality of frames each including a plurality of slots allocated to speech communication. A radio base station that performs call communication in a time-sharing manner and performs preliminary communication with a plurality of other wireless terminals, performs preliminary communication with a different wireless terminal in a slot allocated to the preliminary communication of a different frame, and performs each frame. A base station for performing a call communication with each wireless terminal by using a part of a plurality of slots allocated to a call communication in a plurality of frames. 9. The radio base station according to claim 8, wherein
The radio base station according to claim 1, wherein the predetermined number of slots is one transmission slot and one reception slot.