JPH09312875A - Radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid interference and to obtain high quality communication with no complicated channel switching operation by switching the channel of a station of interference object when a base station which occupies plural slots for communication receives interference during communication. SOLUTION: When interference amount increases more than threshold in communication with a mobile station 21 at a base station 22, the base station 22 decides whether it occupies plural slots in communication with the mobile station 21. If it does not occupy them, the base station avoids the interference by performing radio channel exchange in communication with the mobile station 21. When it occupies them, the base station 22 searches base or mobile stations which give interference to the communication with the mobile station 21 and selects the base/mobile station which communicates with the fewest occupied slots of all the stations. The base station 22 can perform a high quality communication without increasing forced release ratio by sending an exchange request to the station or performing exchange with the mobile station 21 at the base station 22 according to the number of the slots of the selected station.

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to a wireless communication system.

[0002]

2. Description of the Related Art In recent years, wireless communication systems such as mobile phones and cordless phones have rapidly become popular. Digital mobile phone system, simplified mobile phone system (PHS: Pe
In rsonalHandy-phone System, etc., TDMA (Time Division Multiple Acces
s) method is used. The TDMA method is a method of dividing one radio wave carrier into time slots, allocating a user to each time slot, and multiplexing in time. The TDMA method has high frequency utilization efficiency and good compatibility with the digital method.

FIG. 8 shows a 4-channel multi-carrier TDMA / TDD (Time Division Multiple Access) which is a radio access method in a simplified mobile phone system.
/ Time Division Duplex) method. A digital signal on one radio wave carrier is divided into TDMA frames of 5 ms each, and one frame is further divided into eight time slots. Of the eight time slots, the first four slots # 1T, # 2T, # 3T, # 4
T is assigned as a transmission from the base station to the mobile station, and the latter four slots # 1R, # 2R, # 3R, # 4R are assigned as transmissions from the mobile station to the base station. The base station and mobile station communicate with each other in the assigned time slots,
With one communication carrier, the base station can simultaneously communicate with four mobile stations at a transmission rate of 32 kbit / s. Further, the base station and the mobile station have a function of detecting an interference wave on a time slot basis, and automatically assign a channel with less interference, and when interference is received during communication, it is possible to avoid interference on a time slot basis. . For these standards,
Radio System Development Center: Second Generation Cordless Telephone System Standard 1st Edition (RCR STD-28) (December 1993)
Month).

Further, in recent years, in addition to voice communication, there has been an increasing demand for wireless multimedia communication that centrally handles various types of media such as data and images. In communication of data, images, etc., higher speed data transmission is expected as compared with communication of only voice. As a method for performing high-speed data transmission, a method is known in which the same mobile station occupies and uses a plurality of slots in one TDMA frame.

FIG. 9 shows a TDMA frame and time slot arrangement when a plurality of slots are assigned to the same mobile station. Time slot # 1 is used between the base station 22 and the mobile station 21, time slots # 2 and # 3 are used between the base station 22 and the mobile station 23, and the base station 22 and the mobile station are moved. Communication with the station 24 is performed using the time slot # 4. The mobile station 23 occupies two sets of time slots to perform communication, so that the mobile station 23 can obtain a double transmission rate as compared with the normal use of one slot.
Thus, by occupying and using a plurality of slots in one TDMA frame for the same mobile station, high-speed data transmission can be performed. Note that one related to this type of slot allocation method is disclosed in
6-204943 is mentioned.

[0006]

When a base station or a mobile station receives interference during communication, the base station / mobile station that has received interference switches the communication channel in time slot units to avoid interference. As a result, good communication quality can be continued during a call. However, when the same mobile station occupies a plurality of slots in one TDMA frame for communication, it is more susceptible to interference than when occupying one conventional slot.

FIG. 7 is an explanatory diagram showing how interference is received when the same mobile station occupies one slot in one TDMA frame and when it occupies two slots. 1
For the mobile station 21 occupying the slot, FIG.
As shown in (a), interference is received from stations communicating using the same slot position and the same frequency. When the interference waves from these other stations exceed a threshold value, the mobile station 21 avoids interference by switching channels by changing its slot position or frequency.
When two slots are occupied, the station 2 communicating using the same slot position and the same frequency as the first slot position of the mobile station 21 as shown in FIG. 7B.
3 and a station 24 communicating with the same slot position and frequency as the second slot position of the mobile station 21.
Receive interference from Therefore, a mobile station occupying two slots has a higher probability of occurrence of interference than a case where communication is performed by occupying one slot.

For a mobile station that occupies two slots, radio channel switching is performed by changing the slot position or frequency in order to avoid interference when the conventional one slot is occupied. At the same time, the processing becomes complicated, and at the same time, there is a high possibility that an empty slot or frequency for switching cannot be secured and forced disconnection occurs. On the other hand, in data communication, the loss of one data may cause a big error, so
Ensuring reliable and high quality communications is important.

The object of the present invention is to provide the same mobile station with
An object of the present invention is to provide a wireless communication system capable of performing high-quality wireless communication without increasing the forced disconnection rate even when a plurality of slots in one TDMA frame are allocated.

[0010]

In order to achieve the above object, in the radio communication system of the present invention, the interference amount of a mobile station which occupies a plurality of slots in one TDMA frame and performs communication is equal to or more than a threshold value. In this case, the interference can be avoided by switching the radio channel of the station giving the interference.

Alternatively, when a base station which occupies a plurality of slots with respect to the same mobile station and receives interference during communication, interference can be avoided by switching the radio channel of the station giving the interference. It is characterized by enabling.

[0012]

1 is an operation sequence in a base station showing a wireless communication system according to an embodiment of the present invention. When the amount of interference in communication with the mobile station 21 at the base station 22 increases above a threshold value, or when the mobile station 21 reports that the amount of interference increases above the threshold value at the mobile station 21 (step 11), the base station 22 determines whether or not the communication with the mobile station 21 occupies a plurality of slots (step 12). If the base station 22 does not occupy the plurality of slots, the base station 22 performs wireless communication in the communication with the mobile station 21. Interference is avoided by switching channels (step 16). When it occupies a plurality of slots, it searches for a base station or a mobile station that interferes with the communication with the mobile station 21 (step 13), and selects the smallest occupied slot number from those base stations / mobile stations. The base station / mobile station communicating with is selected (step 14).

Thereafter, it is determined whether the number of occupied slots of the selected base station / mobile station is smaller than the number of occupied slots of the mobile station 21 (step 15). The base station is requested to switch the channel (step 17). If the number of occupied slots of the selected base station / mobile station is larger than the number of occupied slots of the mobile station 21, the base station 22 performs wireless channel switching with the mobile station 21 (step 16).

The feature of the present embodiment is that when the amount of interference increases in the mobile station 21 that occupies a plurality of slots with the base station 22 and the amount of interference increases, the radio channel is switched between the base station / mobile station that is giving the interference. To avoid interference in the mobile station 21. As a result, even when a plurality of slots are assigned to the same mobile station, high-quality wireless channel switching can be performed without increasing the forced disconnection rate.

Here, in the embodiment of FIG. 1, selection of the base station / mobile station for switching the radio channel (step 13,
14 and 15) can be appropriately changed according to the priority of the mobile station 21 or the station giving interference, the attribute of data, and the like. For example, step 15 may be deleted, and in step 14, one occupying one slot per mobile station and performing communication may be appropriately selected. Further, as shown in FIG. 6, the base station / mobile station that performs wireless channel switching may be performed to the station that has most recently made a call connection among the stations giving interference. Further, these may be combined.

Further, when the amount of interference of the base station 22 or the mobile station 21 does not drop below the threshold value only by switching the radio channel of one of the stations giving interference / the mobile station, further The interference can be avoided by switching the radio channel of the station giving the interference in the procedure of 1.

Further, the selection of the station which performs the radio channel switching is performed by the mobile station by always receiving the slot information of the base station from another base station which can obtain a reception electric field higher than the threshold value. Alternatively, it may be performed by the control station by managing slot information of a plurality of base stations by the control station.

In any case, it is possible to minimize forced disconnection or temporary suspension of transmission due to deterioration of speech quality in a mobile station occupying a plurality of slots, so that high quality wireless communication can be performed.

Here, in order to explain this embodiment in detail, FIG. 2 shows a schematic diagram of an example of radio channel switching in the embodiment of FIG. For example, the mobile station 21 occupies two sets of slots per TDMA frame with the base station 22, and uses the carrier frequency fb to communicate at a transmission rate of 64 kbits per second. Also, the mobile station 23 and the base station 24 occupy one set of slots per TDMA frame, use the carrier frequency fb, and 32 kbit / s.
Communicate at the transmission rate of.

Here, since the occupied slot position in the communication with the mobile station 21 / base station 22 and the occupied slot position in the communication with the mobile station 23 / base station 24 are the same, the base station 24 does not communicate with the mobile station 21. The interference wave 25 is given. Similarly, the mobile station 26 and the base station 27 also occupy one set of slots and communicate at a transmission rate of 32 kbits per second using the carrier frequency fb.
To the interference wave 28. Here, further, when the mobile station 29 and the base station 30 start communication, the interference wave 31 is also given from the base station 28 to the mobile station 21, and the interference amount in the mobile station 21 becomes equal to or larger than the threshold value. Then, the base station 22 performs the wireless channel switching with the mobile station 26 for the base station 27 among the base station 24, the base station 27, and the base station 30 that interfere with the communication with the mobile station 21. Request. The base station 27 that has received the request switches the wireless channel in communication with the mobile station 26 and thereby occupies 2 slots to communicate with the mobile station 2
The increase in the amount of interference with 1 is avoided, and the mobile station 21 and the base station 22 can continue communication. Thus, 1TD
When the amount of interference increases with respect to a station that occupies a plurality of slots in the MA frame and communicates, the amount of interference increases by switching the wireless channel of a third station that is causing interference to the station. It is possible to reduce the amount of interference of the stations that have failed. As a result, it is possible to efficiently avoid interference even for a station which occupies a plurality of slots and communicates, and it is possible to maintain the communication quality.

Next, referring to FIG. 3, an example of the TDMA frame and the time slot by the wireless communication system in the embodiment of FIG. 1 will be shown. In FIG. 3, time slots # 2 and # 3 are used between the base station 22 and the mobile station 21, and communication is performed using the carrier frequency fb. Mobile station 21
If the amount of interference from the third station increases and the communication quality deteriorates, the base station 22 searches for a station that interferes with the communication with the mobile station 21, and selects the least occupied slot from among those stations. Select the base station / mobile station that is communicating by number. After confirming that the number of occupied slots is smaller than the number of occupied slots in communication between the base station 22 and the mobile station 21,
The base station 22 notifies the base station so that the selected base station / mobile station switches the radio channel.

Upon receipt of this request, the base station switches the radio channel by moving the position of the slot giving interference from, for example, # 2 to # 4, as shown in FIG. 3 (B). Then, the mobile station 21 avoids interference. In this way, when the amount of interference of the mobile station 21 occupying two slots and performing communication increases, the interference of the mobile station 21 can be avoided by switching the slot position of the station giving interference. The mobile station occupying two slots can efficiently avoid interference without performing complicated radio channel switching.

Next, referring to FIG. 4, an example of the TDMA frame and the time slot by the wireless communication system in the embodiment of FIG. 1 will be shown. Communication is performed between the base station 22 and the mobile station 21 using the time slots # 2 and # 3 and using the carrier frequency fb. When the amount of interference from the third station increases in the mobile station 21 and the communication quality deteriorates,
Similar to the case of FIG. 3, the base station 22 searches for a station that interferes with the communication with the mobile station 21, and selects a base station / mobile station that communicates with the smallest occupied slot number from among them. select. The number of occupied slots is the base station 22 and the mobile station 2.
After confirming that it is smaller than the number of occupied slots in the communication with 1, the base station 22 informs the base station so that the selected base station / mobile station switches the radio channel.

Upon receipt of this request, the base station switches the carrier frequency used, for example, from fb to fd to switch the radio channel, as shown in FIG. 21 to avoid interference. In this way, when the amount of interference of the mobile station 21 occupying 2 slots and performing communication increases, the mobile station occupying 2 slots can also be changed by switching the carrier frequency of the station giving interference. The interference at 21 can be effectively avoided. Further, when the wireless channel is switched, the carrier frequency and the slot position of the station giving the interference may be switched at the same time.

Next, referring to FIG. 5, an example of the TDMA frame and the time slot by the wireless communication system in the embodiment of FIG. 1 will be shown. Communication is performed between the base station 22 and the mobile station 21 using the time slots # 2 and # 3 and using the carrier frequency fb. When the mobile station 21 deteriorates in communication quality due to an increase in the amount of interference, the base station 22 searches for a station that is interfering with the communication with the mobile station 21, as in the case of FIG. , A base station communicating with the smallest number of occupied slots per mobile station /
Select a mobile station. After confirming that the number of occupied slots is smaller than the number of occupied slots in the communication between the base station 22 and the mobile station 21, the base station 22 changes the wireless channel at the selected base station / mobile station. To the base station. The base station receiving this request is shown in FIG.
As shown in (b), the mobile station 21 avoids interference by switching the carrier frequency used in time slot # 2 from fb to fg. FIG. 5 shows a TDMA frame and a time slot by the wireless communication system in the embodiment of FIG. 1 in a state where both the burst and the frame are completely synchronized. The burst is synchronized but the frame phase is shifted. Even in the state, or in the case where the burst and the frame are in the asynchronous state, efficient interference avoidance can be performed by the same method.

3 to 5, the mobile station 21 uses the base station 22 and the two slots # 2 and # 3, and both f
It is assumed that communication is performed using the frequency of b, but 1TDMA
Occupation of multiple slots in a frame may occupy adjacent slots using the same carrier frequency, and
Adjacent slots may be occupied using different carrier frequencies. Alternatively, the slots may be arranged so as to be separated from each other by one slot or more so as not to be adjacent to each other, and may be occupied by using the same or different carrier frequencies. When occupying adjacent slots by using the same carrier frequency, or when occupying a plurality of slots so as not to be adjacent to each other by separating them by one or more slots, the mobile station can perform frequency allocation by one receiving unit. In the case where adjacent slots are occupied by a plurality of slots using different carrier frequencies, the mobile station may, for example, install two or more receiving units to accommodate each slot in order to cope with carrier frequency variations between the slots. It corresponds to the sequential switching of the reception frequency. Also,
The number of occupied slots in one TDMA frame is not limited to two sets, but can be applied to any case when a plurality of slots are used.

Further, in the radio channel switching in the selected base station / mobile station, the radio channel switching may be performed in the own base station with which the selected mobile station is currently communicating, and the selected mobile station is The wireless channel may be switched by switching to communication with another base station in the vicinity. In any case, it is possible to minimize the increase in the forced disconnection rate when the same mobile station allocates a plurality of slots in one TDMA frame for communication and to perform high-quality wireless communication.

[0028]

According to the present invention, a mobile station occupying a plurality of slots for communication or a base station occupying a plurality of slots for communication with the same mobile station interferes during communication. When receiving the interference, by switching the radio channel of the station giving interference, it is possible to avoid the interference without switching the radio channel to the mobile station occupying a plurality of slots. It is possible to avoid interference without performing a channel switching operation. Further, as a result, even when communication is performed by allocating a plurality of slots to the same mobile station, high-quality wireless communication can be performed without increasing the forced disconnection rate.

[Brief description of drawings]

FIG. 1 is a flowchart of the operation of a base station showing an embodiment of a wireless communication system according to the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of a wireless communication system according to the present invention.

3 is an explanatory diagram showing a TDMA frame and a time slot arrangement according to the embodiment of FIG. 1. FIG.

FIG. 4 is an explanatory diagram showing a TDMA frame and time slot arrangement according to the embodiment of FIG.

5 is an explanatory diagram showing a TDMA frame and time slot arrangement according to the embodiment of FIG. 1. FIG.

FIG. 6 is a flowchart of the operation of the base station showing another embodiment of the wireless communication system according to the present invention.

FIG. 7 is an explanatory diagram of an increase in interference amount when two slots are occupied.

FIG. 8: TDM of TDMA / TDD system in PHS
Explanatory drawing which shows the structure of A frame, and a time slot.

FIG. 9 is an explanatory diagram showing a time slot configuration when a plurality of slots are assigned to the same mobile station.

[Explanation of symbols]

21, 23, 26, 29 ... Mobile station, 22, 24, 27,
30 ... Base station, 25, 28, 31 ... Interference wave.

Claims (12)

[Claims] 1. In a radio communication system in which a base station and a plurality of mobile stations communicate with each other by a TDMA communication method in which one frame is composed of a plurality of slots using a plurality of carrier frequencies, the same mobile station is a plurality of TDMA frames within one TDMA frame. When the amount of interference of a station when occupying a slot and performing communication exceeds a threshold value, the radio is characterized by avoiding the interference by switching the radio channel of the station giving the interference. Communication method. 2. A radio for avoiding interference by switching a radio channel of a station communicating with occupying the smallest number of slots per mobile station among stations giving interference. Communication method. 3. The station according to claim 1, wherein among the stations giving interference, the station occupies a smaller number of slots than the occupied slots of a station whose interference amount is equal to or more than a threshold value and performs communication. A wireless communication method that avoids interference by switching the wireless channel of. 4. The wireless communication system according to claim 1, wherein among the stations giving interference, the station having the most recent call connection switches the wireless channel to avoid the interference. 5. In a wireless communication system in which a base station and a plurality of mobile stations communicate with each other by a TDMA communication system in which one frame is composed of a plurality of slots using a plurality of carrier frequencies, the same mobile station is a plurality in one TDMA frame. When the amount of interference of a station occupying a slot and performing communication exceeds a threshold value, the smallest slot per mobile station from the station causing interference and the station giving interference. A wireless communication system characterized by avoiding interference by switching the wireless channel of a station that occupies a number and communicates. 6. A wireless communication system in which the wireless communication system according to claim 2 or 4 is combined. 7. A wireless communication system in which the wireless communication system according to claim 3 or 4 is combined. 8. A wireless communication system in which the wireless communication system according to claim 4 or 5 is combined. 9. A wireless communication system according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the station whose interference amount is equal to or greater than a threshold is a base station. 10. The wireless communication system according to claim 1, wherein the station whose interference amount is equal to or more than a threshold value is a mobile station. 11. The method according to any one of claims 1 to 10,
A wireless communication method in which a mobile station that receives slot information by radio waves emitted from the base station selects the base station / mobile station that switches the radio channel. 12. The method according to any one of claims 1 to 10,
A wireless communication system in which a base station / mobile station that performs wireless channel switching is selected by a control station that manages a plurality of base stations.