JPH0336357B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a channel switching control method in a portable communication system in which the same frequency is commonly used in a plurality of wireless communication zones. In particular, it relates to a method of reducing interference of the same frequency from other zones.

[Description of prior art]

In the mobile communication system, a method is known in which a zone is set around one base station in which it can effectively communicate with mobile stations, and this base station and mobile stations communicate by specifying a channel. . In order to make effective use of frequencies in such a system, a method is adopted in which the radius of the zone is made small and the same radio frequency is commonly allocated to different zones for use.

On the other hand, fluctuations in the radio wave propagation characteristics of land mobile communications include short-term fluctuations due to short-range movement of a mobile station (for example, within several tens of meters in the case of an 800 MHz band car phone system), and long-term median values of these short-range fluctuations. There are long-range fluctuations for movement over a range (for example, several kilometers). Furthermore, the median value of this long-term variation is defined by a distance characteristic that varies depending on the distance to the base station.
In most cases, short-term fluctuations follow a Lehre distribution, and short-term median fluctuations follow a lognormal distribution. Further, the distance characteristic exhibits a characteristic as shown in FIG. In FIG. 1, the horizontal axis shows the distance between the base station and the mobile station, and the vertical axis shows the propagation loss.

For example, in order to manage call quality, if the median desired signal-to-interfering signal ratio (hereinafter referred to as "D/U") in a long period of short period median fluctuation is required to be 20 dB or more, use the same frequency. The distance between base stations is determined as follows. That is, referring to FIG. 2, the mobile station determines that the D/U satisfies 20 dB at point A around the desired wave zone and closest to the interfering wave zone. For example, the wireless zone radius r is 5 km.
In this case, the propagation loss at the 5 km point is 137 dB from Figure 1, but in order to make the propagation loss of the interference wave 157 dB or more so that D/U > 20 dB, the interference wave must be generated as shown in Figure 1. The distance d between the base station in the zone and point A must be 20 km or more.

In this way, when the same frequency is used in common in multiple zones, the distance between base stations can be determined so that there is no interference problem, but this is just a matter of setting it so that interference does not occur on average. In reality, if the desired wave is low in the center of the short section and the interference wave is high, interference will occur. For this reason, in the past, when using a certain channel, the presence or absence of interference waves was checked, and if the interference waves exceeded a certain value, the channel was not used. It was not possible to deal with cases where the interference wave level was low but then changed to become high.

[Purpose of the invention]

The present invention solves these drawbacks, and aims to provide a control method that can ensure a predetermined communication quality for all channels and also make effective use of channels with interference waves.

[Features of the invention]

The present invention sweeps each channel, measures the desired wave level and the interference wave level, calculates the desired wave level and interference wave level ratio, and when the ratio is less than a predetermined value, selects a channel with a lower interference wave level. It is characterized by controlling to switch between calls.

Furthermore, regarding the channel made vacant by this switching, if the desired signal level among calls communicating on other channels is sufficiently high and the ratio of this vacant channel to the interference signal level exceeds a predetermined value, then , the call is switched to the vacant channel, and control is performed to increase channel utilization efficiency.

According to the present invention, a base station is equipped with a control device using a microcomputer, and is configured to automatically execute measurement control, calculation, and switching control according to a program.

[Explanation based on examples]

N channels for communication are assigned to one zone, and a large number of mobile stations (mobile phone subscribers) within the zone communicate with the base station of the zone. Since the calling from the mobile station side or the calling from the base station side is a well-known technique, a detailed explanation will be omitted.

The base station is equipped with a control device using a microcomputer, and controls sweep measurement, calculation, and switching of each channel according to its program.
FIG. 3 is a flowchart of the main part of the control procedure. i, j, and k are each channel numbers, and the first channel according to the claims,
Corresponding to the second channel and the third channel. In Figure 3, i+1→i j+1→j k+1→k indicates that i, j, and k are each incremented by 1, and i, j, and k are each n
It is configured so that when n+1=1 is reached.

The channel control method of the present invention will be explained with reference to FIG. 3. First, i is set to 1, and it is checked whether the i-th channel is in use. If a call is not in progress, i is incremented by 1, and when a call is detected on a channel, the desired wave level Di and interference wave level Ui are measured for the i-th channel. The method of this measurement will be explained in detail later. Next, the ratio of the desired signal level to the interference signal level
Di/Ui is calculated and it is determined whether this is less than a predetermined value of 20 dB. If it exceeds 20 dB, it is assumed that there is no problem with the call, so i is incremented and the same check is repeated for the next channel.

If there is a value lower than the predetermined value of 20 dB, a vacant j-th channel other than the i channel is searched.
The level of interference for that jth channel
Measure Uj and obtain the desired wave level of the i-th channel.
The ratio between Di and the level Uj of the interference wave of the j-th channel is calculated to find the j-th channel that has a predetermined value of 20 dB or more. Once it is found, the call on the i-th channel is switched to its j-th channel.

Here, the i-th channel is now vacant, but even though the level of interference waves in this i-th channel is high, if the desired signal level is sufficiently large, the desired signal level and the interference wave level are ratio is a predetermined value
It is thought that the signal may exceed 20 dB, and we will search to see if there are any other signals with such a desired wave level. That is, the desired signal level (Dk) is measured for the k-th channel, and the ratio of this desired signal level Dk to the interference signal level Ui of the i-th channel, which is currently an empty channel, is calculated, and this is determined to be the predetermined value of 20 dB. If the number of calls on the kth channel is
Switch to the second channel.

In this way, the call on the kth channel is
Although the call quality is worse than before, communication that satisfies the predetermined quality is possible, and the newly empty channel k can be used for signals with even lower desired wave levels. It becomes like this.

By repeatedly performing the above control for i, j, and k from 1 to n, the quality of each channel is always ensured to be above a predetermined value, and the channels can be used effectively.

Next, a method of measuring the desired wave level and interference wave level of each channel will be explained.

FIG. 4 shows an example of the configuration of a mobile station transmitting circuit for distinguishing between desired waves and interference waves. 1 is an audio input terminal, 2 is a modulator, 3 is a pilot signal generation circuit,
4 is an intermediate frequency band synthesizer, 5 is a mixing circuit, 6 is a local oscillation circuit, 7 is an amplifier, and 8 is an output terminal to an antenna or a duplexer. An audio signal input from terminal 1 is modulated by modulator 2 and becomes an intermediate frequency band signal. The pilot signal generated by the pilot signal generation circuit 3 is synthesized by the intermediate frequency band synthesizer 4, and mixed with the output frequency of the local oscillation circuit 6 by the mixing circuit 5 to become a radio frequency band signal. This signal is amplified by an amplifier 7 and guided from an output terminal 8 to an antenna.

FIG. 5 is a diagram showing an example of a transmission wave spectrum of a mobile station. S is the spectrum of the audio signal, and P is the pilot signal. Here, the frequency of the pilot signal is set to a different frequency for each base station in each zone that uses the same frequency, and based on the designation from the base station, the mobile station uses the pilot signal frequency P designated for that zone. configured to send.

FIG. 6 is a diagram showing an example of the configuration of a base station receiver for detecting the levels of desired waves and interfering waves. 11
is the input terminal from the antenna or duplexer, 1
2 is a mixing circuit, 13 is a local oscillation circuit, 14 is a bandpass filter for extracting the audio modulation spectrum, 15 is a demodulator, 18 is a demodulation output terminal, 16 is a receiving circuit for pilot signal f ₁ , 17 is pilot signal f ₂ This is the receiving circuit.

Figure 7 shows the spectrum of the received wave at the base station when there is an interference wave, where S _D is the voice signal spectrum of the desired wave, S _U is the voice modulation spectrum of the interference wave,
P _D is the pilot signal spectrum of the desired wave, and P _U is the pilot signal spectrum of the desired wave and the interference wave. As mentioned above, the pilot signal frequencies assigned to the mobile station in each zone are different frequencies, so the pilot signal frequencies f ₁ and f ₂ of the desired wave and the interference wave are different from each other.

A base station received wave is inputted from a terminal 11 and mixed with a local frequency signal from a local oscillation circuit 13 in a mixing circuit 12 to become an intermediate frequency band signal. This intermediate frequency band signal is split into three branches, one passes through a bandpass filter 14 that passes the audio modulation spectrum, and one passes through a demodulator 15.
The audio signal is demodulated by. This is terminal 18
is output to. As for the signals in the other intermediate frequency bands, components of frequencies f ₁ and f ₂ are received by receiving circuits 16 and 17, respectively, and the desired wave level and the interference wave level can be determined from the levels thereof.

Although the method for inserting the pilot signal in the intermediate frequency band has been described above, the present invention is not limited to this, and other methods such as inserting the pilot signal in the baseband are also applicable.

To switch a call in progress to another channel, it is possible to apply the call channel switching procedure for switching the channel in progress in the current car telephone system as is.

[Explanation of effects]

As explained above, according to the present invention, a channel in which the communication quality has deteriorated due to an increase in the interference wave level is automatically detected, and switched to a channel that can ensure communication quality equal to or higher than a predetermined value. That is, when a base station and a mobile station receive strong interference from a distant station using the same frequency during communication, this interference is detected and the channel is switched to another channel within the same base station with less interference. This results in
The quality of communication between a base station and a mobile station within a wireless zone within the same base station can be maintained at a predetermined value or higher. Further, as a result of this switching, a call having a sufficiently high desired signal level can be switched and used for a channel that has become an empty channel. Therefore, an increase in noise due to same-channel interference can be avoided, and channels can be used effectively and frequency usage efficiency can be increased while always maintaining a predetermined communication quality for all channels.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of radio wave propagation loss characteristics in land mobile communication. FIG. 2 is a diagram explaining the relationship between the desired wave zone and the zone where interference waves are generated. FIG. 3 is a flowchart of the main part of the control procedure according to the embodiment of the present invention. FIG. 4 is a configuration diagram of main parts of the mobile station device of the present invention.
FIG. 5 is a diagram showing an example of the spectrum of a transmission signal from a mobile station. FIG. 6 is a block diagram of the main parts of the base station receiving device.
FIG. 7 is a diagram showing an example of the spectrum of a base station received wave. DESCRIPTION OF SYMBOLS 1...Audio signal input terminal, 2...Modulator, 3...Pilot signal generation circuit, 4...Synthesizer, 5...Mixing circuit, 6...Local oscillation circuit, 7...Amplifier, 8...Output terminal, 11...Input terminal, 12 ... mixer, 13 ... local oscillation circuit, 14 ... bandpass filter, 15 ... demodulator, 1
6, 17...Pilot signal receiving circuit, 18...Output terminal.

Claims (1)

[Claims] 1. A plurality of zones each having one base station at the center are arranged, and a mobile station in each zone is configured to communicate with the base station in that zone, In a mobile radio communication system in which channels of the same frequency are commonly assigned for a zone, the base station mentioned above uses one channel (hereinafter referred to as the "first channel") to transmit the desired wave in the zone and the other channels. The level of interference waves of the same frequency generated in a zone and received in that zone is measured, and when the ratio of the level of the desired wave and the level of the interference wave is less than a predetermined value, the interference wave is assigned to that zone. Measure the level of interference waves on a channel other than the first channel that is not in communication (hereinafter referred to as the "second channel"), and measure the level of the desired signal of the first channel and its level. A mobile radio communication system characterized in that when a ratio of the level of interference waves of the second channel to the level of interference waves is equal to or higher than a predetermined value, the call of the first channel is controlled to be switched to the second communication channel. Channel control method used. 2. In the channel control method for the mobile radio communication system recited in claim 1, the channels in use other than the first and second channels among the channels assigned to the zone (hereinafter referred to as the "first and second channels") When the ratio of the desired signal level to the interference signal level of the first channel exceeds the predetermined value, the call of the third channel is transmitted as described above. A channel control method for a mobile radio communication system, characterized in that the channel is controlled to switch to a first channel.