JP2900397B2 - Radio circuit selection method for distributed wireless systems - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radio communication system, and more particularly to a radio channel selection method of a radio communication system for selecting a radio channel by distributed control such as a cordless telephone system.

(Prior Art) In a cordless telephone system, the level of an interference signal from another system on a wireless line is measured by a connecting device and a cordless telephone before starting communication, and only when the value is equal to or less than a threshold value, is the wireless line connected to that device. Communication avoids interference with other systems (NTT issued “Facilities” “New cordless telephones” Vol. 36, No. 3, pp. 134-14
1,1984). This measurement of the interference signal level is generally called carrier sense.

The lower the carrier sense threshold, the wider the interval between systems that use the same frequency. Even if the interference signal level increases or the desired signal level decreases as the telephone moves, the communication quality deteriorates due to interference. To do less. For this reason, the current carrier sense threshold value is very low (-6 dBμV to 6 dBμ) which is very close to the noise level.
V) (Gazette Gazette No. 25, issued on March 14, 1984, Notification of Ministry of Posts and Telecommunications, Daiichi 180).

(Problems to be Solved by the Invention) Even if the threshold value of the carrier sense is very close to the noise level, at the present time when cordless telephones are not so popular, the distribution density of the system is low, so that a plurality of From among them, it is possible to easily find and communicate with a radio line whose interference signal level is equal to or less than a threshold value. However, with the spread of cordless telephones and the high-density distribution of systems, if the carrier sense threshold value remains very close to the noise level, the interference signal level of any wireless line will almost always exceed the threshold value. Significantly deteriorates, and practical system operation becomes impossible.

It is an object of the present invention that even if the distribution density of the system fluctuates,
It is an object of the present invention to provide a radio channel selection method for a distributed radio communication system that secures a constant call loss rate.

(Means for Solving the Problems) A radio channel selection method for a distributed radio system according to the present invention is a distributed radio system in which a plurality of radio systems independently select radio channels and perform communication by distributed control,
Each system sets a threshold 1 and a threshold 2 which is larger than the threshold 1 by a certain value, measures a desired signal level at the start of communication,
A wireless line is set and its interference signal level is measured. If the interference signal level is equal to or less than a threshold value 1 and the desired signal level is equal to or greater than a threshold value 2, it is determined that the wireless line is usable and communication is started. If the interference signal level is equal to or higher than the threshold value 1 or the desired signal level is equal to or lower than the threshold value 2, it is determined that the wireless line is unusable, and the next wireless line is set. A means for rejecting the connection is provided if possible, and when the interference signal levels of all the wireless lines are equal to or higher than the threshold value 1, the threshold values 1 and 2 are increased, and the interference signal level is reduced in at least one wireless line. If the desired signal level is equal to or smaller than the threshold 1 but the desired signal level is equal to or smaller than the threshold 2 in all the wireless channels, the thresholds 1 and 2 are reduced.

(Operation) Even if the system is distributed at a high density, in order to secure a constant call blocking rate, it is necessary to start communication even if there is some possibility of interference. This will be described with reference to FIG. FIG. 2 schematically shows the relationship between the distance from the connection device of each system and the signal level.

FIG. 2 (a) shows a case where the distribution density of the system is low, and the connecting devices using the same frequency are located at points X1 and X2.
Are located in The transmission level of the connection device is P,
The reception level in a cordless telephone decreases as the distance from the connection device increases. In the case where the distribution density of the system is low and the connecting device that gives interference is located at a sufficiently distant place like X2, even if the threshold value of the carrier sense is set to a very low level (T) for the noise level N, the interference signal level is low. It is possible to easily find a wireless line where is less than or equal to the threshold.
The service area in this case is from point X1 to point Y where the difference between the desired signal level and the noise level is equal to or more than the value (A) necessary for communication.

On the other hand, FIG. 2 (b) shows a case where the distribution of the systems becomes dense and the interval between the systems decreases. Connection devices using the same frequency are located at points X1 and X3. In this case, since the interference signal level increases, if the threshold value of the carrier sense is kept fixed at T, a free radio line is hardly found, and the call blocking rate is significantly deteriorated. However, in actuality, in the range from the point X1 to the point Y ', the difference between the desired signal level and the interference signal level exceeds the value (A) necessary for communication, and communication can be performed without interference. Therefore, in such a case, if communication is permitted, a certain call loss rate can be secured.

In the present invention, as shown in FIG. 2 (b), two threshold values, a threshold value T1 for an interference signal level and a threshold value T2 for a desired signal level, are provided, and the difference between these threshold values ( Fixed to A). When the interference signal level is equal to or higher than the threshold T1 in all the wireless lines, the threshold T1 is determined to be too low with respect to the system density, and the threshold T1 and the threshold T2 are determined.
Raise. If there is a wireless line where the interference signal level is equal to or less than the threshold T1, if the desired signal level is equal to or less than the threshold T2 in all the wireless lines, it is determined that the threshold is too high for the system density, and the threshold T1 and the threshold T2 Lower. Also, in at least one wireless line, the desired signal level is equal to the threshold T2.
In the case described above, the threshold T1 and the threshold T2 may be reduced in order to avoid the influence of interference as much as possible without determining that the threshold is appropriate for the system density and not changing the threshold. In order to keep the call loss rate below a few percent, it is only necessary to increase the threshold when raising the threshold than when decreasing the control amount. In this way, a threshold value is set according to the distribution density of the system, so that a constant call blocking rate can be secured.

(Embodiment) FIG. 1 shows a flowchart of a radio channel selection system according to the present invention. The flowchart in FIG. 1 is an algorithm executed in a cordless telephone or a connection device. In this specification, a case will be described in which this algorithm is applied to a cordless telephone.

When there is a connection request, the cordless telephone first sets a flag indicating that there is a radio line whose interference signal level is equal to or lower than the threshold value T1 to 0. Next, the cordless telephone transmits and receives a control signal for connection control on the control line with the connection device, measures the reception level of the signal transmitted by the connection device at this time, and sets this as a desired signal level D.

Next, the first wireless channel is set, and the interference signal level of the wireless channel is measured. The cordless telephone compares this to a threshold T1. If U is larger than T1, it is determined that the wireless channel is unusable, and the next wireless channel is set. If U is smaller than T1, a flag indicating that there is a radio channel whose interference signal level is equal to or lower than the threshold T1 is set to 1, and the desired signal level is set to the threshold T2.
If it is larger, the communication is started on the wireless line. In this case, in this embodiment, the threshold T1 and the threshold T2 are not changed.
The threshold may be reduced to avoid interference as much as possible. If the desired signal level is smaller than the threshold T2, it is determined that the wireless line is unusable, and the next wireless line is set.

If it is determined that the last wireless line cannot be used, the connection is rejected. At this time, the cordless telephone
If the flag is 0, that is, if the interference signal levels of all the radio lines are equal to or greater than the threshold T1, the threshold T1 and the threshold T2 are increased by α,
If the flag is 1, that is, if the interference signal level of at least one wireless channel is equal to or less than the threshold T1, the threshold T1 and the threshold T2 are decreased by δ.

By performing such control, the thresholds T1 and T2 gradually decrease as long as the interference signal level of at least one wireless channel is equal to or lower than the threshold T1. Then, when the interference signal levels of all the radio lines are equal to or higher than the threshold T1, the threshold T1 and the threshold T2
Increases. Therefore, the threshold values T1 and T2 are set to values according to the distribution density of the system.

Incidentally, it is of course possible to set the upper and lower limits of the threshold T1 and the threshold T2, and to limit the values of the threshold T1 and the threshold T2 within the range, and in this case, the situation where the threshold T1 is lower than the noise level may occur. Can be avoided. It is also possible to execute the same algorithm in the connection device, or to implement and confirm this algorithm in both the connection device and the cordless telephone.

FIG. 3 shows an embodiment of the present invention. In this embodiment, the configuration of the entire wireless device is shown. However, since the portion related to the present invention is the portion denoted by reference numeral 10, this portion will be mainly described. The signal received from antenna 100 is input to mixer 60 via duplexer 20. Here, the signal is mixed with the carrier signal from the synthesizer 70 and converted into an IF signal. this
After the IF signal is converted to a signal level by the level measurement device 11,
The signal is input to the desired signal level memory 12 and the switch 13. The desired signal level memory 12 includes a microprocessor 18
And stores the level of the desired signal, and inputs the value to the switch 13. The interference signal threshold memory 16 and the desired signal threshold memory 17 store a threshold T1 for the interference signal and a threshold 2 for the desired signal, respectively. The outputs of the switch 13 and the switch 15 are compared by the comparator 14. The microprocessor 18 controls the switches 13 and 15, changes the frequency of the synthesizer 70,
By changing the contents of the desired signal threshold memory 17 or rewriting a flag indicating that there is a wireless line in which the level of the internal interference signal is below the threshold for the interference signal, the algorithm shown in FIG. Execute.
At the same time, the IF signal is demodulated by the demodulator 30 and output from the terminal 101. The signal input from the terminal 102 is modulated by the modulator 40, converted into an RF signal by the mixer 50, and transmitted from the antenna 100 via the duplexer 20.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to provide a radio channel selection method for a distributed radio communication system that ensures a constant call blocking rate even when the distribution density of the system fluctuates. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an algorithm of the radio channel selection system of the present invention, FIG. 2 is a diagram for explaining the operation of the entire system of the present invention, and FIG. 3 is a diagram showing a configuration of a radio device for implementing the present invention. is there.

Claims (1)

(57) [Claims] In a distributed wireless system in which a plurality of wireless systems independently select a wireless channel by distributed control and perform communication, each system provides a threshold 1 and a threshold 2 which is larger than the threshold 1 by a fixed value. At the start, a desired signal level is measured, a wireless line is set, and an interference signal level of the wireless line is measured. If the interference signal level is equal to or less than a threshold value 1 and the desired signal level is equal to or more than a threshold value 2, the wireless If the interference signal level is equal to or higher than the threshold value 1 or the desired signal level is equal to or lower than the threshold value 2, the wireless line is determined to be unusable and the next wireless communication is started. It has a means for setting a line and rejecting connection if all wireless lines are unavailable, and a threshold 1 and a threshold when the interference signal level of all the wireless lines is above threshold 1. Is increased, and when the interference signal level is equal to or less than the threshold value 1 in at least one wireless channel but the desired signal level is equal to or less than the threshold value 2 in all wireless channels, the threshold value 1 and the threshold value 2 are decreased. Wireless channel selection method for distributed wireless systems.