JPH0618345B2 - Transmission right control method - Google Patents

Description

The present invention relates to a communication system in which a plurality of stations share a plurality of channels, and more particularly, a plurality of stations form a plurality of communication zones and share frequency channels for reuse. The present invention relates to a transmission right control method for a wireless communication system.

(Prior Art) In a mobile communication system, in order to effectively use a frequency, a communication zone is set for each base station, different communication channels are designated to be used in adjacent communication zones, and the same frequency is specified. When used, a method of allocating a zone that is far enough away and does not cause interference is adopted. In order to meet the increasing demand for mobile communications, it is necessary to reduce this zone to further promote spatial spatial reuse of frequencies. However, when the zone becomes smaller, zone design becomes dramatically difficult due to the influence of buildings and other factors. In order to deal with such a problem, a method of observing a channel in each system before using it and using it only when it is determined that the channel is vacant is being studied. In order to further reduce the probability of causing interference, there is a method in which priorities are set for each channel based on the past history of the usage status of each channel and the channels are used based on the priority. A transmission right control method for determining such a priority is described in detail in Japanese Patent Application No. 60-231652 [Transmission right control method] (Reference 1) filed on October 16, 1985.

(Problems to be Solved by the Invention) In order to realize the above transmission right control method, a big problem is a method of determining whether or not a channel is vacant. In general, the strength of the radio wave to be interfered with is lower than the received electric field, and therefore the threshold value for channel vacancy detection must be set to a level lower than the received power in the service zone. Furthermore, in mobile communication, the strength of the received signal varies due to fading, so the power of the interference wave cannot be correctly estimated. Therefore, at the time of observation, even if the received signal has a level that does not receive interference, there is a possibility that interference will start during communication. In order to avoid such interference, it is necessary to set the threshold value for channel vacancy detection lower than the threshold value that is actually allowed. However, in this way, although interference can be avoided, a signal of a lower level than necessary is detected, and spatial spatial reuse efficiency of frequency becomes poor.

An object of the present invention is to provide a transmission right control method that overcomes the problems of the above-mentioned conventional transmission right control methods, can efficiently reuse frequencies, and does not cause interference.

(Means for Solving the Problems) According to the present invention, in a wireless communication system in which a plurality of stations share a plurality of channels, each station receives information about whether or not the channel is available before using the channel. A means for starting transmission only when it is determined by comparison between the electric field strength and a threshold value that it is determined to be free, and a priority order for each channel is determined based on past history. A transmission right control method having means for sequentially using the channels in descending order, wherein the threshold value is set for each channel, and means for varying the threshold value depending on whether interference has occurred during communication. A transmission right control method can be provided.

(Principle of the Invention) In order to reduce the probability of causing interference and to realize efficient spatial reuse of frequencies, a channel that is liable to cause interference is lowered by setting a threshold value as a vacant channel to cause a margin. A margin should be taken for difficult channels. For this purpose, it is sufficient to lower not only the priority order but also the threshold value for a channel that has been interfered with during operation. If the priorities are set for the channels to be used according to the past history, after a certain amount of time, the respective radio base stations will preferentially use different channels within a distance causing interference. The past history in this case is highly reliable because it is measured over a long period of time. Therefore, the threshold cannot be lowered because the probability of causing interference decreases at least for the channels with high priority. On the other hand, a channel with a low priority has a high probability of being used within a distance causing interference, and is likely to be interfered with. Therefore, the threshold is lowered during operation and automatic control is performed so as to reduce the interference probability. In the present invention, in this way interference-free and efficient spatial reuse of frequencies can be realized.

(Example) Next, this invention is demonstrated in detail with reference to drawings.

FIG. 2 shows the relationship between the threshold value and the communication zone. The allowable interference wave level is lower than the received electric field level at the service area limit of each zone. In order to reduce the error of electric field detection due to fading, it is necessary to set the threshold level for judging the line usage status to a value lower than that. However, this threshold value must be higher than the noise level so that the judgment is not mistaken due to noise. The size of the zone when the threshold is set in this way is shown in FIG. 2 (b). The interference zone is larger than the communication zone from the central wireless base station, and the interference detection zone is even larger than that. In reality, the same frequency can be reused outside the interference zone, but if it is attempted not to make a mistake in determining the channel utilization, the same frequency can be reused only outside the interference detection zone. As a countermeasure against this, the present invention adopts a method of changing the determination threshold value for each channel and adaptively changing each.

FIG. 1 shows an algorithm of an embodiment of the transmission right control system of the present invention. When a transmission request arrives, the radio must first observe the channel with the highest priority. This observation is called carrier sense. First, set the synthesizer to the channel with the highest priority and perform carrier sense. The channel set here is referred to as channel K. Next, the threshold value T (K) for determining whether the channel is in use is read. Received signal level is T
If it is (K) or more, it is determined that the channel is in use, the channel having the next priority is set, and the same operation is repeated. If the received signal level is lower than T (K), it is determined that the channel is idle and communication is started. At this time, the priority between channels is changed by using the information as to whether or not each channel is in use. By varying the channel priority in this way, each base station will use a different channel if it is within the distance of mutual interference, and there is a high probability of vacancy and a low probability of causing interference. It is described in detail in Reference 1 that the observation is performed in order from the channel.

Even if the interference signal level is low at the time of performing carrier sense, interference may occur due to movement of the terminal after starting communication. In particular, when the interference is observed to be small due to fading even though the average interference is large, the interference occurs with a very high probability. The communication is terminated by lowering the threshold value T (K) of the channel so that such a situation is unlikely to occur in the future if interference occurs. If no interference occurs until the end of communication, the threshold value T (K) of the channel is increased and the communication is ended. If the maximum value of T (K) is set to the allowable interference wave level and fluctuates below that level, the concrete T
(K) can be changed in any way. In this way, the threshold of the interfered channel is lowered, and the probability that it is determined to be in use increases, so the priority automatically decreases. On the other hand, the threshold value of the channel that is not interfered with is increased and becomes a channel with high priority. Since such a channel is used almost exclusively by the base station, it is effective to increase the threshold for such a channel to realize frequency reuse in the interference zone of FIG. Very important for use. On the other hand, the channel with low priority has a margin in the threshold value, and the probability of causing interference is small.

Although the communication is terminated when the interference is detected in this embodiment, it is of course possible to move to another channel and continue the communication. Further, it is obvious that the present invention can be applied to any method of interference detection.

(Effect of the Invention) As described in detail above, according to the present invention, it is possible to apply a transmission right control method that has a low probability of causing interference and efficiently realizes spatial frequency reuse.

[Brief description of drawings]

FIG. 1 is a diagram showing an algorithm in a transmission right control system according to an embodiment of the present invention, and FIG. 2 is a diagram showing a relationship between a signal level and a communication area.

Claims (1)

[Claims] 1. In a wireless communication system in which a plurality of stations share a plurality of channels, each station determines whether or not the channel is available by comparing the received electric field strength with a threshold value. Transmission having means for starting transmission only when it is determined that the channel is vacant, and means for setting priority for each channel based on the past history and using the channels in descending order of priority A transmission right control method, wherein the threshold value is determined for each channel, and there is provided means for varying the threshold value depending on whether interference is received during communication.