JPH043535A - Method for preventing interference due to same frequency - Google Patents

Abstract

PURPOSE:To eliminate interference due to a disturbing wave by obtaining a reception level ratio between a reception level of a communication channel and a reception level of a control channel at a mobile station and allowing a base station making communication to convert the communication channel frequency when the ratio is less than a prescribed value. CONSTITUTION:A channel control section 42 receives a reception level of a desired wave f1 from a communication level detection section 40 and receives a reception level of control channel frequencies fb, fc of an interference base station from an interference level detection section 43. Then a ratio D/U is obtained from each of the frequencies, where D is a reception level of a desired wave and U is a reception level of disturbing waves and whether or not the reception level ratio D/U is less than a predetermined reference value is discriminated. When the D/U is less than the reference level, a request signal revising the communication channel frequency f1 of a desired base station 11 into other frequency is sent so as to revise the frequency of the desired wave into a frequency different from those of the disturbing waves. Thus, the interference due to the disturbing wave is prevented with simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a co-frequency interference prevention method, and more particularly, to a co-frequency interference prevention method for preventing interference caused by interference waves having the same frequency as a desired wave in mobile communication.

[Conventional technology]

BACKGROUND ART Conventionally, communication channels and control channels are assigned to each of a plurality of base stations, and mobile communications are performed using the same communication channel frequency at geographically distant base stations.

As countermeasures against co-frequency interference in mobile communications, there are techniques such as increasing the frequency repetition distance, that is, the distance between base stations that use the same frequency, and using beam tilt antennas. When increasing the frequency repetition distance, the level of interference waves can be reduced because the same frequency is used in far-distant base station areas, or the frequency usage efficiency will deteriorate. When using a beam tilt antenna, the level of interference waves can be reduced by directing the main beam of the antenna downward rather than horizontally so that the radio waves do not spread beyond the necessary range.

These techniques aim to reduce interference by devising a method for forming a base station's wireless area, and are not techniques for dealing with interference when it occurs. In order to detect and reduce co-frequency interference during communication, the mobile station must use interference waves, that is, the control channel frequency of the co-channel base station (when the base station is in its area Detects the reception level (U: Undesired) of the channel frequency (used to call a mobile station and control communication channel settings, etc.), and detects the reception level of the desired wave (D: Buzzer).
A method has been considered in which the desired base station is requested to transmit on a different frequency when the required D/U ratio is not satisfied.

[Invention or problem to be solved]

However, since multiple base stations use the same control channel frequency within the same control zone, the mobile station receives a composite wave of the signals of the control channel frequencies of these base stations. There is a problem in that it is not possible to detect the reception level of the control channel frequency of a single base station that is transmitting interfering waves.

Another method for preventing co-frequency interference is to detect the code error rate in addition to the reception level of the signal transmitted from the base station (desired base station) with which the mobile station is communicating, and to detect the code error rate even if the reception level is high. One possible method is to request the base station to transmit on a different frequency when the error rate is high. However, this method has a problem in that it is necessary to detect the error rate in addition to the communication signal, and therefore the error rate detection signal must be constantly transmitted.

The present invention has been made in view of the above points, and is a co-frequency interference prevention method that can detect the reception level of interference waves of the same frequency as the communication channel frequency of a desired communication station and prevents interference due to interference waves with a simple configuration. The purpose is to provide

[Means to solve the problem]

The present invention allocates a communication channel and a control channel to each of a plurality of base stations, and enables geographically distant base stations to communicate with mobile stations using the same communication channel frequency. In a frequency interference prevention method, the control channel frequencies of base stations that use the same communication channel are made different from each other, and each base station moves the control channel frequency of the base station whose communication channel frequency is the same as that of its own station. The control channel frequency of the base station with the same frequency as the base station with which the mobile station is communicating is monitored, and the reception level of the communication channel with which the mobile station is communicating is monitored. A reception level ratio between the reception level of the monitored control channel and the reception level of the monitored control channel is determined, and when the reception level ratio is less than a predetermined value, the communicating base station is caused to convert the communication channel frequency to prevent co-frequency interference.

In addition, when a mobile station communicates using a time division multiple access method, the control channel frequency of the base station whose communication channel is the same as that of the base station with which the mobile station is communicating is assigned to the own station communication. Monitor at the timing of an empty slot other than the time slot.

[Effect]

In the present invention, the control channel frequencies of base stations that use the same communication channel are different from each other, and the reception level of interference waves from an interfering station is detected based on the reception level of the control channel frequency, and the influence of the interference waves is detected. When the communication channel of the desired station is large, the same frequency interference can be prevented by changing the communication channel of the desired station, and the reception level of the interference wave can be detected with a simple configuration without the need to constantly transmit an error rate detection signal.

〔Example〕

FIG. 1 shows a line configuration diagram of the method of the present invention.

In the figure, 11, 21, and 31 are mobile stations, and 12.2
2.32 each is a base station. For the mobile station 11, the base station 12 is the desired base station, that is, the communication partner station, and the base station 2
2.32 is an interfering base station. The base station 12 is the mobile station 11
The base stations 22 and 22 communicate with the mobile stations 21 and 31 using the same communication channel frequency f1. The base stations 12, 22, and 32 each have different control channel frequencies fa and fb.

I am using fc.

FIG. 2 shows a block diagram of a first embodiment of an interference prevention section of a mobile station. In the figure, taking the mobile station 11 as an example, the communication level detection unit 40 detects the reception level of the communication channel frequency f1 of the desired base station 12 among the signals received by the antenna 41, and notifies the channel control unit 42. . The interference level detection unit 43 detects the reception level of each of the control channel frequencies fb and fc of the interfering base stations 22 and 23 notified by the channel designation signal in the control channel of the desired base station 12, and controls the channel control unit. 42.

The channel control unit 42 executes the processing shown in FIG. In the figure, in step 50, the channel designation signal of the control channel of the desired base station 11 is used to report the communication channel frequency f1 of the desired wave and the control channel frequencies fb and fc of the interfering base station having the communication channel of the same frequency. and communicates on the reported frequency f1 (step 51).
. Unless the communication ends here (step 52), the process moves to step 53 and the desired wave f is detected by the communication level detection unit 40.
1 is read, and further the reception levels of control channel frequencies fb and fc of the interfering base station are read from the interference level detection unit 43 (step 54). Interfering base station 22.3
2 each transmits the control channel frequencies fb and fc with the same output from the same antenna as the respective communication channel frequency f (i.e., interference waves), so the interference is lower than the reception level of each control channel frequency fb and fc. The frequency f which is a wave
You can see the reception level of +.

Therefore, in step 55, the reception level ratio D/U of each of the desired waves is determined as D, and the reception level of each interference wave is determined as U, and this reception level ratio D/U is determined as a predetermined reference value. Determine whether it is less than or equal to. D/U
If D/U is greater than the reference value, it is assumed that there is no influence of interference waves and the process moves to step 51. If D/U is less than the reference value, the influence of interference waves is large, so in step 56 the desired signal, that is, the desired base station 11 is detected. A request signal for changing the communication channel frequency f to another frequency is sent from the transmitter 44 to the desired base station 11, and the process moves to step 50.

As a result, when the influence of the interference wave is large, the frequency of the desired wave is changed to be different from the interference wave, and interference by interference waves having the same frequency as the desired wave is prevented.

In FIG. 1, TDM (time division multiplex) transmission is performed from base stations 12, 22, 32 to mobile stations 11, 21, 31, respectively, and from mobile stations 11, 21, 31 to base station 12.
．． A case will be described in which TDMA (time division multiple access) transmission is performed for each of 22 and 32. In this case, the TDMA time slots of frequencies fa and f+, which are transmitted from the desired base station 12 to the mobile station 11 in its own area, are as shown in FIGS. 4(A) and 4(B). Similarly, the interfering base station 22 has a frequency f shown in FIGS. 4(C) and 4(D), respectively.
The interfering base station 32 transmits TDMA time slots b and f, respectively, in FIG. 4(E).

(F) Transmit TDMA time slots of frequencies fc and f+ shown respectively. Here, slot Ca.

Cb and Cc each represent a control signal slot for each base station to call a mobile station, set a communication frequency, etc.
Slot R+ + R2*Rs + R4+R5 represents a slot in which the desired base station 12 transmits a communication signal to each mobile station in its own area. Similarly, slot R+ +
Rz * R2' + R4' + Rs represents a slot in which the base station 22 transmits a communication signal to each mobile station in its own area, R,, R2R5, Ra, Rs
” represents a slot in which the base station 32 transmits a communication signal to each mobile station in its own area.

For example, as shown in FIG. 4(G), the mobile station 11 receives slot R3 assigned to its own communication using the communication channel frequency f1, and transmits at the communication channel frequency f1 in the next slot T3. The X slot is an empty slot, and the mobile station 11 does not use it for communication.

The interference prevention section of the mobile station in this case has the configuration shown in FIG. In the figure, taking the mobile station 11 as an example, a slot determination unit 60 determines the slots of frequencies fa and f+ received by the antenna 61, and notifies the reception level inspection unit 62 and channel control unit 63. The reception level detection unit 62 detects the reception level for each received slot and notifies the channel control unit 63 of the reception level.

The channel control unit 63 executes the processing shown in FIG. In the figure, in step 70, a report of the frequency f of the communication channel of the desired wave and the control channel frequencies fb and fc of the interfering base station having the communication channel of the same frequency is received from the slot Ca from the desired base station 11. , and communicates using the reported frequency f (step 71). Unless the communication ends here (step 72), the process moves to step 73. In step 73, it is determined whether it is the timing of slot R8 assigned to own station communication or the empty slot X, and at the timing of slot R2, the frequency f1
(step 74), and at the timing of empty slot X, the frequency fb is detected as shown in FIG. 4(D).
, fc are sequentially detected (step 75).

In step 76, the reception level of the desired wave of frequency f1 in slot R2 is set to D, and frequencies fb, f of vacant slot
The received level ratio D/U of each interference wave is determined as U, and it is determined whether this D/U is less than a predetermined reference value. If D/U is greater than or equal to the reference value, it is assumed that there is no influence of interference waves, and the process moves to step 71. If D/U is less than the reference value, the influence of interference waves is large, so step 77 is performed and slot R3 of the desired signal is selected. The slot transmitter 64 sends out a request signal requesting the desired base station 11 to change the communication channel frequency f to another frequency, and the process moves to step 70.

As a result, if the influence of the interference wave is large, the frequency of the slot R1 of the desired wave is changed to be different from the frequency f1 of the interference wave slot R,,R,'', and the interference wave of the slot with the same frequency as the slot of the desired wave is changed. Interference is prevented.

In this embodiment, slot R3 of the interference wave is empty slot X.
Since the reception levels of the control channel frequencies fb and fc of the base stations 21.31 that transmit R2 are detected, there is no need to provide a receiver for detecting the interference wave reception level in addition to the communication receiver.

〔Effect of the invention〕

As described above, in the configuration of claim (1), the method for preventing co-frequency interference of the present invention is capable of detecting the reception level of interference waves with a simple configuration, and does not require transmitting an error rate detection signal from each base station. This method prevents interference caused by jamming waves with a simple configuration, and is extremely useful in practice.

Furthermore, the configuration of claim (2) does not require a receiver for detecting the level of received interference waves, and can have a simpler configuration, which is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 is a line configuration diagram of the method of the present invention, FIGS. 2 and 5 are block diagrams of respective embodiments of the interference prevention section of a mobile station of the method of the present invention, and FIGS. FIG. 5 is a flowchart of the processing executed by the respective control units, and FIG. 4 is a diagram for explaining TDMA time slots of each base station and mobile station. 11.21.31...mobile station, 12. 22. 32
...Base station, 40...Communication level detection section, 42.6
3... Channel control section, 43... Interference level detection section, 44... Transmission section, 50 to 56. 70 to 77... Step, 60... Slot determination section, 62... Reception level Detection unit, 64...Slot transmission unit. Figure 2 Figure 3 Figure 5 1000 steps of work
v-) Figure 6

Claims (2)

[Claims] (1) The same frequency for mobile communication in which a communication channel and a control channel are assigned to each of multiple base stations, and geographically distant base stations use the same communication channel frequency to communicate with mobile stations. In the interference prevention method, the control channel frequencies of base stations that use the same communication channel frequency are made different from each other, and each base station uses the control channel frequency of the base station whose communication channel frequency is the same as that of its own station. It notifies the mobile station, monitors the control channel frequency of the base station whose communication channel frequency is the same as that of the base station with which the mobile station is communicating, and monitors the reception level of the communication channel with which the mobile station is communicating. A reception level ratio between the reception level of the monitored control channel and the reception level of the monitored control channel is determined, and when the reception level ratio is less than a predetermined value, the base station communicating with the base station changes the communication channel frequency to prevent co-frequency interference. Same frequency interference prevention method. (2) Allocate communication channels and control channels to each of multiple base stations, and use the same communication channel frequency at geographically distant base stations to perform time division multiple access communication from mobile stations. In a method for preventing co-frequency interference in mobile communications, the control channel frequencies of base stations that use the same communication channel are made different from each other, and each base station controls the base station whose communication channel frequency is the same as that of its own station. The control channel frequency of the base station whose communication channel frequency is the same as that of the base station with which the mobile station is communicating is broadcast to the mobile station in an empty slot other than the time slot assigned for own station communication Calculate the reception level ratio between the reception level of the communication channel with which the monitoring mobile station is communicating and the reception level of the monitored control channel at the timing of , and when the reception level ratio is less than a predetermined value, the mobile station performs communication. A method for preventing co-frequency interference, the method comprising: requesting a base station located in the station to change its communication channel frequency to prevent co-frequency interference.