JP2583401B2 - Adjacent channel interference wave detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a digital MCA for communicating with a plurality of mobile radios using a plurality of radio channels.
(Multi-channel access) Adjacent channel interference wave detection circuit suitable for a mobile communication system such as a system,
Especially included in the receiving circuit of the fixed radio for the purpose of obtaining a desired signal from the radio signal transmitted through the own radio channel which is one of the radio channels, from the adjacent radio channel adjacent to the own radio channel The present invention relates to an adjacent channel interference wave detection circuit that detects adjacent channel interference waves leaking into the desired signal.

[0002]

2. Description of the Related Art Conventionally, as an interference wave detection circuit for detecting an interference wave of the same frequency (channel) or an adjacent frequency in a receiver of a mobile communication system, Japanese Patent Laid-Open Publication No. Hei 4-31422 has been disclosed. . The interference wave detection circuit is a circuit that detects an interference wave in a receiver that receives an angle-modulated wireless signal. A reception signal output from the high-frequency unit of the receiver and including a desired wave corresponding to a radio signal from the own radio channel and an interference wave corresponding to a radio signal from an adjacent radio channel is first amplitude-limited by a limiter circuit, The output of the limiter circuit is band-limited by the required band of its own channel, and then subjected to envelope detection.

In this interference wave detecting circuit, a signal exceeding a threshold value of the limiter circuit is limited to a certain level, and a signal having an amplitude proportional to the level is output for a signal below the threshold value. Therefore, the output level of the desired wave having a large amplitude becomes constant, and the output level corresponding to the beat signal having a small amplitude caused by the interference wave is obtained. If the output of the limiter circuit is subjected to envelope detection, the level of the interference wave indicated by the level of the beat signal can be detected without being affected by the envelope fluctuation of the modulated wave due to the band limitation.

[0004]

The conventional interference wave detection circuit described above can effectively detect an interference wave level only when the level of the interference wave is smaller than the level of the desired wave. If the level is higher than the level, there is a problem that the desired wave is mistakenly regarded as an interference wave.

In this interference wave detection circuit, the limiter circuit limits the amplitude of a received signal.
(Multi-level amplitude modulation) There is a problem that it is inappropriate for detecting an interference wave of a radio signal requiring amplitude information such as a wave.

On the other hand, the level of an interference wave (interference wave) from an adjacent wireless channel that causes a bit error rate higher than the standard in a digital MCA system is generally much higher than the level of a desired wave.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an adjacent channel interference wave detection circuit which can detect an interference wave from an adjacent wireless channel regardless of the modulation method and has a simple configuration.

[0008]

According to the present invention, there is provided an adjacent channel interference wave detecting circuit for a fixed radio device which communicates with a plurality of mobile radio devices using a plurality of radio channels. Channel interference included in a receiving circuit for obtaining a desired signal from a wireless signal transmitted through the wireless channel and leaking from an adjacent wireless channel adjacent to the own wireless channel to the own wireless channel to interfere with the desired signal An adjacent channel interference wave detection circuit for detecting a wave, wherein a wireless signal transmitting each of the wireless channels has a non-modulation period and a modulation period, respectively, and the receiving circuit receives from the mobile wireless device. Band limiting that limits the wireless signal to a band corresponding to the own wireless channel to generate a superimposed signal of the desired signal and the adjacent channel interference wave. Having a path, the adjacent channel interference wave detection circuit detects a reception electric field level value of the superimposed signal, a reception electric field level value of the radio signal in the non-modulation period and the reception electric field level value of the modulation period An adjacent channel interference wave determination circuit that determines whether the level value of the adjacent channel interference wave is greater than the level value of the desired signal by a predetermined level or more by comparing the received electric field level value;

The adjacent channel interference wave detection circuit has a frame configuration in which the radio signal alternately repeats the predetermined non-modulation period and the modulation period, respectively. Discriminating the non-modulation period and the modulation period according to the timing signal of, the non-modulation period using the discrimination result of the non-modulation period and the modulation period and the reception electric field level value received from the reception electric field detection circuit Detecting the level difference between the received electric field level value and the received electric field level value during the modulation period, and determining from the level difference whether the level value of the adjacent channel interference wave is greater than the level value of the desired signal by the predetermined level or more. It is possible to adopt a configuration for judging whether or not.

The adjacent channel interference wave detection circuit is a circuit in which the reception electric field detection circuit obtains the reception electric field level value by performing envelope detection on the superimposed signal passing through the band limiting circuit. A wave detection circuit, a first latch circuit that latches the reception electric field level value in the non-modulation period indicated by the timing signal and sets the reception electric field level value in the non-modulation period, A second latch circuit that latches in the modulation period indicated by the timing signal and sets the reception electric field level value in the modulation period; and the reception electric field level value in the non-modulation period and the reception electric field level value in the modulation period. Whether the level value of the adjacent channel interference wave is greater than the level value of the desired signal by the predetermined level value or more in response to the reference voltage corresponding to the predetermined level. It can be the structure and a determining comparators.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. FIG. 2 is a signal configuration diagram of an example of a radio signal received by the present embodiment.

A digital MCA system to which this embodiment is applied is described in "RCR STD-32, Digital MC"
A system, issued by the Radio System Development Center, and includes a command station (not shown), a mobile station (not shown) including a mobile radio, and a relay station including a fixed radio partially shown in FIG. (Fixed station), and communication is basically performed between a command station and a mobile station or between mobile stations via a relay station. This system is basically composed of one relay station, a plurality of command stations, and mobile stations. The group of stations that can communicate with each other communicates on the radio channel specified by the relay station by the multi-channel access method in the service area. The wireless channel used for communication uses a 1.5 GHz band, and 25
M (M is plural) channels are prepared at a carrier interval of kHz. These radio channels are used in the TDM / TDMA scheme.

First, the signal configuration of the radio signal Sr received by the fixed radio receiver circuit (see FIG. 1) of the present embodiment from the mobile radio will be described with reference to FIG.

The radio signal Sr represents a radio signal transmitting M radio channels, such as radio signals Sr1 and Su arranged at intervals of 25 kHz. The wireless signals Sr1 and Su are signals of wireless channels adjacent to each other. Radio signal S
r is N = 6 slots as one frame. Each of the above slots has a non-modulation period T1 called an AGC preamble.
And a modulation period T2 modulated by 16-level QAM or the like including a synchronization signal, a pilot signal, a data symbol and the like at a transmission rate of 64 kbp (symbol time 250 μs). Each slot has, for example, a repetition of 15 ms, a non-modulation period T1 of 7 symbols, 1.75 ms, and a modulation period T2 of 5
Three symbols, 13.25 ms. All radio signals S
The frame timing and slot timing of r
Synchronous control is performed by a control unit (not shown) of the fixed wireless device.

Referring now to FIG. 1, this embodiment shows a receiving circuit of a fixed radio used in the digital MCA system. The fixed wireless device receives a radio signal Sr for M radio channels of the MCA system, such as a receiving circuit having the frequency conversion circuit 1 as a head, and receiving circuits (RX) 10B and 10M having substantially the same configuration as the receiving circuit. A receiving circuit is provided. The antenna 7 receives the radio signal Sr of the radio channel transmission from a plurality of mobile radios. The receiving circuit having the frequency conversion circuit 1 as a head has a wireless channel transmitting the wireless signal Sr1 among the wireless signals Sr as its own wireless channel, and aims to obtain a desired signal D (= D3 + D4) from the wireless signal Sr1. I have.
The receiving circuits 10B, 10M, and the like also aim to obtain a desired signal from a wireless signal that transmits their own wireless channel having different channels. Note that the radio signal Su
Is a wireless signal representative of an adjacent wireless channel adjacent to the wireless channel of the receiving circuit whose head is the frequency conversion circuit 1.

The radio signal Sr received by the antenna 7 is distributed to the frequency conversion circuit 1, the receiving circuits 10B, 10M and the like via a distribution circuit having or not having a radio channel demultiplexing function. Hereinafter, a reception circuit having the frequency conversion circuit 1 as a head will be described as a representative of the reception circuit of the fixed wireless device.

The frequency conversion circuit 1 frequency-converts the radio signal Sr1 transmitting the own radio channel and the adjacent channel radio signal Su transmitting the adjacent radio channel into an intermediate frequency signal S1. Here, the radio signal Sr1 is, for example, 450
The radio signal Su is converted into, for example, 450 ± 25 kHz, 450 kHz ±.
It is converted to an intermediate frequency signal S1 such as 50 kHz.

The intermediate frequency signal S 1 is band-limited by the IF filter 2. This IF filter 2 has an intermediate frequency signal S1 corresponding to the radio signal Sr1.
And the signal component corresponding to the radio signal Sr1 is not attenuated, but the adjacent channel radio signal Su
Is largely attenuated. Therefore, the 3 dB band of the IF filter 2 is equal to the channel interval of the radio channel, which is 2 in this MCA system.
It is desirable to set it to about 5 kHz. IF filter 2
As described above, the desired signal D in which the radio signal Sr1 of the own radio channel is band-limited to a desired band and the adjacent channel interference wave U (=) in which the intermediate frequency signal S1 corresponding to the adjacent radio channel radio signal Su is greatly attenuated. U3 + U4). The superimposed signal of the wireless signal Sr in the non-modulation period T1 is S2a, and the superimposed signal in the modulation period T2 is S2b.

A part of the superimposed signal S2 is demodulated by the demodulation circuit 3 to become a baseband demodulated signal S3. As the demodulation circuit 3, a digital demodulation circuit that converts the superimposed signal S2 into a digital signal and then demodulates the signal by a DSP (digital signal processor) can be used.

Here, the required transmission quality required in this MCA system is the bit error rate of the demodulated signal S3 of 3 × 10
^-2 or less. It has been confirmed that in order to obtain the required transmission quality, the ratio between the desired signal D and the adjacent-channel interference wave U and D / U should be approximately -30 dB or more in the intermediate frequency signal S1. An interference signal that is much larger than the desired signal D and degrades the required transmission quality from the standard value due to the wireless signal Su transmitting the adjacent wireless channel is called an adjacent channel interference wave U. The co-channel interference signal resulting from the transmission signal of the other station using the own radio channel has a bit error rate of 3 × 1 of the demodulated signal S3 even if the desired signal D / co-channel interference signal is about 20 dB.
About 0 ^-2 occurs.

The reception electric field detection circuit 4 further connected to the IF filter 2 and the determination circuit 5 connected thereto constitute an adjacent channel interference wave detection circuit for detecting the adjacent channel interference wave U.

The reception electric field detection circuit 4 performs envelope detection of the superimposition signal S2 and outputs a reception electric field level value S4 having a level value substantially proportional to the logarithm of the power of the superposition signal S2. Here, the reception electric field level value of the radio signal Sr during the non-modulation period T1 is represented by S
4a, the received electric field level value in the modulation period T2 is S4b. Further, the reception electric field detection circuit 4 obtains a reception electric field level value S4 through a low-pass filter having a cutoff frequency of 1 kHz or less for the signal obtained by performing the envelope detection. Therefore, the received electric field level value S4 does not respond to the beat signal of the desired signal and the adjacent channel interference wave and each symbol, and the average (power) level value of the non-modulation period T1 and the modulation period T2 of the radio signal Sr is Each will be shown. Note that a commercially available product such as μPC8000IC (manufactured by NEC) or the like can be used for the reception electric field detection circuit 4.

The decision circuit 5 responds to the received electric field level value S4 and a timing signal S6 indicating the frame timing of the radio signal Sr1 supplied from the control unit (not shown) of the fixed radio, and responds to the radio signal Sr1. Non-modulation period T
By comparing the received electric field level value S4a of No. 1 with the received electric field level value S4b of the modulation period T2, it is determined whether the level value of the adjacent channel interference wave U is higher than the level value of the desired signal D by a predetermined level X or more. When the level value of the adjacent channel interference wave U is larger than the level value of the desired signal D by X level or more, the determination circuit 5 determines that the adjacent channel interference wave U
Is determined to have leaked into its own wireless channel, and outputs an interference wave alarm signal S5.

FIG. 3 is a diagram for explaining the operation of this embodiment. Hereinafter, the operation of detecting the adjacent channel interference wave U in the present embodiment will be described with reference to FIGS. 1, 2 and 3.

FIG. 3A shows the signal spectrum of the intermediate frequency signal S1 input to the IF filter 2 during the non-modulation period T1. The desired signal D1 corresponds to the radio signal Sr1 of the own radio channel, and the adjacent channel interference wave U1 corresponds to the radio signal Su of the adjacent channel. Desired signal D1
Is a center frequency f0 and a level value A1. The adjacent channel interference wave U1 has a center frequency f1 away from the frequency f0 by a channel (carrier) interval Δf and a level value B
It is one. The level value B1 of the adjacent channel interference wave U1 is
It is considerably larger than the level value A1 of the desired signal D1. IF filter 2 has a center frequency f0, a 3 dB band Δf, a frequency f
Attenuation L0 ≒ 0 at 0 and attenuation LΔf at frequency f1.

FIG. 3B shows a signal spectrum of the superimposed signal S2 passed through the IF filter 2 during the non-modulation period T1. The desired signal D3 corresponds to the desired signal D1,
The adjacent channel interference wave U3 corresponds to the adjacent channel interference wave U1. Since the level value of the desired signal D3 is not attenuated by the IF filter 2, it is the same as the level value A1 of the desired signal D3. On the other hand, the level value B1a of the adjacent channel interference wave U3
Is a value attenuated from the level value B1 of the adjacent channel interference wave U1 by the amount of attenuation LΔf by the IF filter 2.

FIG. 3C shows the signal spectrum of the intermediate frequency signal S1 input to the IF filter 2 during the modulation period T2. The desired signal D2 corresponds to the radio signal Sr1 of the own radio channel, and the adjacent channel interference wave U2 corresponds to the radio signal Su of the adjacent channel. Since the desired signal D2 and the adjacent channel interference wave U2 are, for example, 16-level QAM modulated waves, the desired signals D1, D
3 and the adjacent channel interference waves U1 and U3, the spectrum is broadened, and the peak level values A2 and B2 are respectively lower than the level values A1 and B1 of the non-modulation period T1 by the same level.

FIG. 3D shows the signal spectrum of the superimposed signal S2 passed through the IF filter 2 during the modulation period T2. The desired signal D4 corresponds to the desired signal D2, and the adjacent channel interference wave U4 corresponds to the adjacent channel interference wave U2. Since the level value of the desired signal D4 is not attenuated by the IF filter 2, it is the same as the level value A2 of the desired signal D2. On the other hand, since the attenuation of the IF filter 2 increases from the frequency f0 to the frequency f1, the spectrum peak of the adjacent channel interference wave U4 occurs near the frequency f1, and the level value B2a changes from the level value A2 to the attenuation L
It is larger than the value obtained by subtracting Δf. Therefore, the attenuation of the average power of the adjacent channel interference wave U4 by the IF filter 2 is LΔ
less than f.

The superimposed signal S2a in the non-modulation period T1
Is the sum of the power of the desired signal D3 and the power of the adjacent channel interference wave U3. Further, the superimposed signal S2b in the modulation period T2 is composed of the power of the desired signal D4 and the adjacent channel interference wave U.
4 is the sum of the power and the power. Now, the relationship between the power of the superimposed signal S2a in the non-modulation period T1 and the power of the superimposed signal S2b in the modulation period T2 is expressed by a mathematical formula. In the following mathematical expressions and their descriptions, the signs D1 to D4, U1 to U4, S2a and S2b of each signal represent the power of each signal as it is.

S2b / S2a = (D4 + U4) / (D3 + U3) (1) Since D3 = D4, the equation (1) is transformed into the equation (2).

S2b / S2a = {1+ (U4 / D4)} / {1+ (U3 / D3)} (2) While U3 is greatly attenuated by the IF filter 2, the attenuation of U4 is Much smaller. Also, the level (power) of the adjacent channel interference wave U4 that substantially interferes with the demodulation of the desired signal D4 in the demodulation circuit 3.
Is greater than or equal to D4. That is, when an adjacent channel interference wave is to be detected, the expression (3) is established.

U4 >> U3, U4 => D4, U4 / D4 >> U3 / D3 (3) From the expressions (2) and (3), the reception electric field level value S2a and the modulation period T2 in the non-modulation period T1 are obtained. It can be seen that the ratio S2b / S2a with respect to the received electric field level value S2b is always larger than 1 as long as the adjacent channel interference waves U3 and U4 are present, and increases as the proportional relation U3 and U4 increases. Note that the superimposed signal S2 is only the desired signals D3 and D4, and the adjacent channel interference wave U
When 3 and U4 do not exist, the level ratio S2b /
S2a becomes 1.

Using the received electric field level values S4a and S4b which are the level detection results of the superimposed signals S2a and S2b, the demodulation circuit 3 uses the desired signal D2 in the superimposed signal S2.
The levels of adjacent channel interference waves U3 and U4, particularly the level of U4, which are problematic in demodulation of D3 and D4, can be calculated from the relationship of the above equation (2). That is,
The determination circuit 5 compares the received electric field level values S4a and S4b and determines that the level value of the adjacent channel interference wave U4 is the desired signal D4.
It is determined whether the level value is larger than the level value of No. 4 by a predetermined level X or more. The predetermined level X is a level determined to cause interference when demodulating the desired signal D4.

FIG. 4 is a detailed block diagram of the judgment circuit 5 used in this embodiment.

The latch circuit 51 latches the received electric field level S4a during the non-modulation period T1 of the radio signal Sr, and the latch circuit 53 latches the received electric field level S4b during the modulation period T2. The timing signal S6 is a signal for determining the latch timing of the latch circuits 51 and 52, and has a level of "L" in the non-modulation period T1 and a level of "H" in the modulation period T2. In the latch circuit 51,
The level of the timing signal S6 is inverted by the inverter 52 and input. The received electric field level value S4b latched by the latch circuit 53 is supplied to one of the input terminals of the differential amplifier 54. To another input terminal of the differential amplifier 54, an offset voltage x of a predetermined level is set from a level setting unit 55. Therefore, (S4
b−x) are output. The offset voltage x is a voltage corresponding to a predetermined level difference X between the adjacent channel interference wave U4 and the desired signal D4, and is a value calculated from the level ratio S2b / S2a using Expression (2) or an experimental value, and a demodulation circuit. 3, the input / output characteristics of the reception electric field detection circuit 4, the fading of the radio signal Sr1, and the like.

The non-modulation period T latched by the latch circuit 51
The received electric field level value (S4a) of 1 and the output of the differential amplifier 54 are compared by a comparator 56 using an operational amplifier or the like.
The comparator 56 outputs the output of the differential amplifier 54 to the latch circuit 51.
Is larger than the desired signal D4, it is determined that there is an adjacent channel interference wave U4 that is higher than the desired signal D4 by the level X or more, and an interference wave alarm signal S5 is output. In the non-modulation period T1 and the modulation period T2 of the radio signal Sr, there are rise and fall times of the signal, respectively, so that the received electric field level values S4a and S4b are averaged to a low level. To avoid this, the latch circuit 5
1 and 53 are reception electric field level values S4a and S4b
May be sampled at the center t1 of the non-modulation period T1 and the center t2 of the modulation period T2, respectively.

In the above-described embodiment, the determination circuit 5 compares the desired signal D4 and the adjacent channel interference wave U4 for each slot of the radio signal Sr, and detects the harmful adjacent channel interference wave U. However, the radio signal Sr
If the level of the desired signal D4 and the adjacent channel interference wave U4 fluctuates in a long period due to fading or the like, the levels of the desired signal D4 and the adjacent channel interference wave U4 are averaged in a number of slots in anticipation of this fluctuation period. It is good to make it.

[0039]

As described above, according to the present invention, a desired signal after passing through a band limiting circuit for band limiting a radio signal received from a mobile radio device to a band corresponding to its own radio channel and an adjacent channel interference wave are generated. From the superimposed signal, whether the level value of the adjacent channel interference wave is greater than the level value of the desired signal by a predetermined level or more by comparing the received electric field level value of the wireless signal with the received electric field level value of the unmodulated period and the modulated period. Therefore, even if the level of the adjacent channel interference wave is higher than the level of the desired signal, or if a QAM modulated wave requiring amplitude information is received, not only an angle modulated wave, but also a simple configuration, There is an effect that adjacent channel interference waves can be detected.

Therefore, the mobile communication system to which the present invention is applied can always provide good communication quality by controlling the transmission output of a mobile station communicating on an adjacent channel which is an interference wave, changing the frequency of the communication channel, and the like. Produces an effect.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a signal configuration diagram of an example of a radio signal received by the embodiment.

FIGS. 3A and 3B are diagrams illustrating the operation of the present embodiment, in which FIGS. 3A and 3B are diagrams illustrating signal spectra before and after passing through an IF filter 2 when a wireless signal is in a non-modulation section; FIGS.
(C) and (d) are diagrams showing a signal spectrum before and after passing through the IF filter 2 when a wireless signal is in a modulation section.

FIG. 4 is a detailed block diagram of a determination circuit 5 used in the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Frequency conversion circuit 2 IF filter 3 Demodulation circuit 4 Reception electric field detection circuit 5 Judgment circuit 7 Antenna 10B, 10M reception circuit (RX) 51, 53 Latch circuit 52 Inverter 54 Differential amplifier 55 Level setting unit 56 Comparator

Claims (3)

(57) [Claims] An object of the present invention is to obtain a desired signal from a radio signal transmitted through its own radio channel, which is one of the radio channels, in a fixed radio communicating with a plurality of mobile radios using a plurality of radio channels. An adjacent channel interference wave detection circuit that detects an adjacent channel interference wave that leaks into the own wireless channel from an adjacent wireless channel adjacent to the own wireless channel and interferes with the desired signal. The radio signal transmitting each of the radio channels has a non-modulation period and a modulation period, respectively, and the receiving circuit converts the radio signal received from the mobile radio into a band corresponding to the own radio channel. A band limiting circuit that limits and generates a superimposed signal of the desired signal and the adjacent channel interference wave, wherein the adjacent channel interference wave detection circuit A reception electric field detection circuit for detecting a reception electric field level value of a tatami mat signal; comparing the reception electric field level value of the wireless signal in the non-modulation period with the reception electric field level value of the modulation period; An adjacent channel interference wave detection circuit for determining whether or not the level value is higher than the level value of the desired signal by a predetermined level or more. 2. The wireless signal has a frame configuration in which the predetermined non-modulation period and the predetermined modulation period are alternately repeated, and the adjacent channel interference wave determination circuit performs the non-modulation in accordance with the timing signal of the frame. Discriminating the period and the modulation period, the reception electric field level value of the non-modulation period using the discrimination result between the non-modulation period and the modulation period and the reception electric field level value received from the reception electric field detection circuit. Detecting a level difference between the received electric field level value in the modulation period and the received electric field level value, and determining from the level difference whether a level value of the adjacent channel interference wave is greater than a level value of the desired signal by the predetermined level or more. Claim 1
The adjacent-channel interference wave detection circuit according to claim 1. 3. The reception electric field detection circuit is a circuit that obtains the reception electric field level value by performing envelope detection on the superimposed signal that has passed through the band limiting circuit. A first latch circuit that latches an electric field level value in the non-modulation period indicated by the timing signal and sets the reception electric field level value in the non-modulation period; and the modulation period in which the reception electric field level value is indicated by the timing signal. A second latch circuit that latches the received electric field level value during the modulation period, and a reference voltage corresponding to the received electric field level value during the non-modulation period, the received electric field level value during the modulation period, and the predetermined level. And a comparator for determining whether a level value of the adjacent channel interference wave is greater than a level value of the desired signal by the predetermined level value or more in response to Adjacent channel interference wave detection circuit according to claim 2, wherein.