JPS5823782B2 - Wireless communication system resistant to transmission intermodulation interference - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wireless communication system that is resistant to transmission intermodulation interference.

FIG. 1 shows an example of a telephone switching network in which the wireless communication system according to the present invention is used.

As shown in Fig. 1, a general wired telephone switching network consists of an exchange 1, subscriber telephones 2a, 2b, . . . , 2n, and local subscriber lines 3a, 3b connecting the subscriber telephones and the exchange.
,...

Toll lines 4a and 4 connecting 3n and exchange 1 with other exchanges
It is composed of b,...

However, if the subscriber is in a remote location or if it is difficult to set up a wired line, a multi-access wireless telephone system is used.

In the figure, the multi-access radio telephone system includes a shared antenna 11 and each channel radio 12a, 12b, . . .
12n and its control device 13, and slave stations A1, A2, . . . 5m located at remote locations.

As shown in detail in FIG. 2, the base station 10 connects each radio device 12a,
12b, . . . ++, are connected to the transmitter TX and receiver RX of 12n.

In the multi-access radio telephone system configured in this way, a plurality of radio channels are provided to the radio base station as shown in the figure.

When two or more transmitters transmit at the same time, the transmission output from the other transmitter enters through the antenna duplexer 11a, and transmission intermodulation due to nonlinear distortion is generated at the final stage of each transmitter.

For example, if two channels of frequencies fa and fb transmit at the same time, among the countless interference waves generated, frequencies fa and f
Those that fall in the same band as b are 2fa-fb and 2f
b-fa.

In addition, in the case of three waves of fa, fb, and fo, fa + fb - fo
etc.

Now, if the radio channels given to the base station are arranged at equal intervals on the f-axis, channels CH1 and CH
2 transmits, the frequency of channel CH3 is generated as 2XCH2-CH1=CH3.

When a slave station in a multi-access radio telephone system makes a call, it sequentially checks the radio channels given to the system (that is, given to the base station), transmits on an empty channel, and sends a call signal to the base station.

If all channels are not available, abandon the call and wait.

In such a system, if the frequency of channel CH3 is generated as described above, the slave station will switch to channel C.
I mistakenly thought that H3 was not available.

In order to avoid such inconveniences, conventional techniques have been to use transmitters that generate less intermodulation, and to devise channel assignments.

The latter is based on a method such as the Pubcock method, and taking the case of 8 channels as an example, CH1, CH2
, CH5, CHlo, CH16, CH23°CH33,
It's like CH35, and it makes the channel roar louder.

However, such a channel allocation method is extremely luxurious considering the recent wireless channel congestion.

On the other hand, the method of using a transmitter that generates a small amount of intermodulation is also uneconomical because it requires a large number of expensive isolators.

An object of the present invention is to provide an economical wireless communication system that is resistant to transmission intermodulation interference.

According to the present invention, in a wireless communication system in which m slave stations check whether the channel of a wireless base station having N channels (m>>N) is vacant and perform transmission using the vacant channel, If the base station has an empty channel, at least one of the empty channels transmits an empty line signal indicating that the channel is empty, and the empty line signal is a different signal that corresponds one-to-one to the channel number, A wireless communication system is proposed that is resistant to transmission intermodulation interference, characterized in that the slave station detects the idle line signal and transmits to the wireless base station.

Embodiments of the wireless communication system according to the present invention will be described in detail below.

The present invention eliminates the conventional drawbacks by the following means, taking economic efficiency in terms of both price and frequency spectrum into consideration.

Width) Transmits radio waves to empty channels as well.

(b) That is, a "blank line signal" indicating that the channel is "vacant" is transmitted to the vacant channel.

(c) This blank line signal is a different signal that corresponds one-to-one to the channel number.

(d) If the service life of the base station transmitter or the power consumption of the base station is an issue, do not send idle signals to all available channels and limit it to 1 or 2 channels.

(e) As a low-cost method for identifying the idle line signal of a slave station, for example, the signal type is a single continuous tone, and the tone frequency and channel frequency are associated in a 1:1 ratio.

The slave station detects this using a CR active band wave transducer whose tuning frequency changes by changing the resistance.

(f) In paragraph (d) above, the number of vacant channels on which the idle signal is transmitted is set so that the slave station can quickly search for a vacant channel, and to be able to rescue a slave station whose "specific channel has failed." channel.

The features of the present invention in the above means are as described above (
If the blank line signal in item c) is a different signal that corresponds one-to-one to the channel number, and there are many empty channels in items (d) and (f), the blank line signal may be sent to all or some of them. The decision on whether to send the data to the base station should be made by taking into consideration matters such as the power supply of the base station.

Generally, the idle line signal is acquired by scanning, so it goes without saying that if the idle line signal is sent to all idle channels, the idle channel can be acquired quickly.

According to this method as described above, for example, [channel CH,
When CH is busy and channel CH3 is vacant, channel CH3I due to intermodulation (■ means due to intermodulation) and channel CH3D (D means predetermined) transmitting the idle signal are simultaneously connected to the base station. The slave station can correctly determine that the channel CH3I, which is transmitted more frequently but is weaker, is suppressed and only the predetermined channel empty signal CH3D is received, and that channel CH3 is empty.

Also, for example, if channel CH2 is busy and channel CH1 is transmitting a blank line signal, a mixture of CH1 and CH2 is received on channel CH3, and channel CH2 is not talking, the blank line signal is sent. A signal is received, but since there is no correspondence with the channel number, no misjudgment will occur.

As described in detail above, the present invention is extremely effective against interference from other systems and interference caused by intermodulation between the transmission waves of other systems and the transmission waves of the own system.

In the above description, a multi-access radio telephone system has been explained as an example, but it goes without saying that the present invention can also be applied to a multi-frequency mobile radio system.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of a wireless communication system according to the present invention, and FIG. 2 is a detailed block diagram of a base station in FIG. 1. In the figure, 10 is a base station, 11 is a shared antenna, 12a,
[b, . . . , 12n is a channel radio, 13 is a control device, AI, A2 . ..., Am is a slave station.

Claims (1)

[Claims] 1. In a wireless communication system in which m slave stations check whether the channel of a wireless base station having N channels (m>N) is vacant and perform transmission using the vacant channel, the wireless base station is assigned a vacant channel. If there is, at least one of the vacant channels transmits a blank line signal indicating that the channel is occupied, and the blank line signal is a different signal that corresponds one-to-one to the channel number,
A wireless communication system resistant to transmission intermodulation interference, characterized in that the slave station detects the idle line signal and transmits to the wireless base station.