JPH0120817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to detection of the amount of co-frequency interference in a wireless communication system.

(Background technology) Conventional interference detection, for example, in the 900 MHz band car phone system, involves informing the base station of the channel to be used through the control channel, and measuring the reception level at the receiver for the frequency to be used before starting a call. If it is less than the value, it is determined that there is no interference wave and communication is started. If the reception level exceeded a certain value, it was determined that there was an interference wave, and another channel was used. In other systems, in order to detect interference on the transmitting side, signals of different frequencies are sent out of the communication band for each station and the radio waves are sent out. On the receiving side, a receiver capable of receiving multiple interference detection frequencies outside the communication band was prepared, and when an interference detection frequency other than that of the other station was received, it was determined that there was an interference wave.

Of these methods, the former has a problem when interference occurs during a call. The latter method had the disadvantage of requiring additional equipment to be attached to the transmitter/receiver, as it required interfering signals to be transmitted and received outside the communication band in addition to information signals.

In addition, since conventional interference detection could only determine the presence or absence of interference, if the amount of interference that falls below the call quality determined by quantitatively detecting the amount of interference occurs, in order to maintain high quality communication, The drawback was that advanced control such as switching channels was not possible.

(Problems to be solved by the invention) In order to eliminate these drawbacks, the present invention makes it possible to quantitatively detect the amount of interference during communication.The present invention is characterized by the ability to detect desired waves and interference waves in a wireless communication system using angle modulation. means for detecting a low frequency component corresponding to the sum of the desired wave and the interfering wave, which has a band approximately the same as the spectral band of fading that occurs in the envelope detection output when simultaneously received, and has a band higher than the spectral band of fading. means for detecting a high frequency component corresponding to the product of the desired wave and the interference wave, which is a beat corresponding to the desired wave and the interference wave, and provides a ratio of the desired wave and the interference wave from the low frequency component and the high frequency component. It's in the detection method.

(Structure and operation of the invention) The interference amount detection principle and embodiments are shown below. Assuming that the desired wave (hereinafter referred to as D wave) and the interfering wave (hereinafter referred to as U wave) are FM modulated and are expressed by equations (1) and (2), their combined wave e is expressed by equation (3).

D wave e ₁ = E ₁ sin (ω ₁ t + Δω ₁ /P ₁ sinP ₁ t) (1) U wave e ₂ = E ₂ sin (ω ₂ t + Δω ₂ /P ₂ sinP ₂ t + ψ) (2) Combined wave e = e ₁ + e ₂ = (E ² ₁ + E ² ₂ + 2E ₁ E ₂ cosφ) ^1/2 × sin (ω ₁ t + Δω ₁ /P ₁ sinP ₁ t +tan ^-1 Λsinψ(t)/1+Λcosψ(t))(
3) However, E ₁ and E ₂ are the amplitudes of the D wave and U wave and change depending on the propagation path conditions, and since the propagation paths of the D wave and U wave are generally different, their fluctuations are independent of each other. ω ₁ ,
ω ₂ is the carrier frequency of the D wave and U wave, and φ is the phase difference. P ₁ and P ₂ are frequencies of modulated waves of D wave and U wave. Δω ₁ and Δω ₂ are frequency shifts of the D wave and U wave.

ψ(t)=(ω ₂ −ω ₁ )t+φ+Δω ₂ /P ₂ sin(P ₂ t+
θ) −Δω ₁ /P ₁ sinP ₁ t (4) Λ＝E ₁ /E _2When the composite wave e is square-law detected, its envelope R(t)
is R(t)=E ² ₁ +E ² ₂ +2E ₁ E ₂ cosψ(t) (5). E ₁ and E ₂ are the amplitudes of D wave and U wave,
It is generally subject to fading and fluctuates around its average value. In the present invention, ψ
The speed of fluctuation of (t) is set to be greater than the speed of fluctuation of fading. An example of the waveform of R(t) in this case is shown in FIG. 1 (detector output (envelope)). Curve 1 (E ² ₁ + E ² ₂ ) of R(t) is a low frequency component (fading) that varies depending on the propagation path conditions, and curve 2
(2E ₁ E ₂ cosψ(t)) is (ω ₁
-ω ₂ )/2π, a high frequency component with a beat frequency determined by the modulation factor, topple, etc., and changes at a frequency that is orders of magnitude higher than the low frequency component. Moreover, the low frequency component contains information about the sum of squares of the amplitudes of the D wave and the U wave, and the amplitude of the high frequency component contains information about the product of the D wave and the U wave. This interference amount detection method uses frequency characteristics to separate the amplitude sum and amplitude product of the D wave and U wave occurring in the envelope of the receiver IF, and detects the amount of interference.

FIG. 2A shows an embodiment of the present invention, in which 3 is an antenna, 4 is a receiver, 5 is a wave detector (square), 6 and 7 are analog-digital converters (A/D converters),
8 is an arithmetic unit, and 9 is a delay circuit.

The composite wave e of D wave and U wave passes through antenna 3,
The signal is received by receiver No. 4 and input to detector No. 5. The detector output R(t) has the waveform shown in FIG. For example, in the 900MHz band car phone system,
When the mobile station travels at 40 km/h, the low frequency component E ² ₁ +
E ² ₂ is a change of about 40Hz. high frequency component
2E ₁ E ₂ cosψ(t) changes at a rate of 1 KHz, for example, assuming that the frequency difference between the D wave and the U wave is 1 KHz. R(t) having such frequency characteristics is sampled by 6 and 7 A/D converters as follows,
The averages <E ² ₁ +E ² ₂ > and <4E ² ₁ +E ² ₂ > within T time are calculated using 8 calculators.

If T is sufficiently larger than the fluctuation period of ψ(t) and N is sufficiently large, the low frequency component will be as follows: .

X=1/N〓(E ² _1i +E ² _2i +2E _1i E _2i cosψ _i )=＜E ² ₁ +
E ² ₂ >=<E ² ₁ >+<E ² ₂ >(11) The sampling time of the A/D converter No. 7 is delayed by Δt from the A/D converter No. 6 by the delay circuit No. 9. do. However, the delay time Δt is
The value is selected to be smaller than the fading period of E ₁ and E ₂ and larger than the fluctuation period of ψ(t). For example, in the above-mentioned car telephone system, the delay time is on the order of 1/10 msec. Further, the time T is a value longer than the time at which X can be meaningful as a statistical quantity when determining X, and in the case of the above-mentioned car telephone system, it is about 1 second or more.

6, 7 sampling values R(t), R(t+Δt)
By squaring the difference and taking the average, the square mean Y of the amplitude of the high frequency component can be found.

Y=〈[R(t)-R(t+Δt)] ² 〉 Y=〈[R(t)-R(t+Δt)] ² 〉=〈〔(E ² ₁ +E ² ₂ +2E ₁ E ₂ cosψ(t) −(E ² ₁ 〓 _t +E ² ₂ 〓
_t +2E ₁ 〓 _t E ₂ 〓 _t cosψ(t+Δt)〕 ² 〉 Y=〈[R(t)−R(t+Δt)] ² 〉 =〈〔(E ² ₁ +E ² ₂ +2E ₁ E ₂ cosψ( t)−(E ² ₁ 〓 _t +E ² ₂ 〓
_t +2E ₁ 〓 _t E ₂ 〓 _t cosψ(t+Δt)〕 ² 〉 =〈4〔E ₁ E ₂ cosψ(t)−E ₁ 〓 _t E ₂ 〓 _t cosψ(t+Δ
t）〕 ² 〉 = 4〈E ² ₁ E ² ₂ (cosψ−cosψ(t+Δt)) ² 〉 (12) (13) ψ(t) is not a periodic signal but random for N samples of T seconds If it can be considered as, Equation (13)
becomes as follows.

Y=4〈E ² ₁ 〉〈E ² ₂ 〉 (14) When ψ(t) is a periodic signal, equation (14) can be obtained by randomly taking Δt under the above-mentioned conditions. Here, if the power average D/U ratio Γ is Γ=〈E ² ₁ 〉/〈E ² ₂ 〉 (15), then from equations (11) and (14), Γ=−k+√ ² −1 (16 ) becomes.

However, k=1−2X ² /Y (17) Here, Γ in equation (16) is 6, 7 A/D converters, 8
The amount of interference can be quantitatively detected.

FIG. 2B shows an operation flowchart of the computer 8. The number of samples N and the delay time Δt are set, and i for counting sampling is set to i=1. A/
It is sampled by D converters 6 and 7, and the sum 〓A _i and the square sum of the differences 〓 (A _i −B _i ) ² are obtained. If i=N,
Furthermore, sampling is performed using an A/D converter. i=N
When , calculate X and Y, and then calculate k. k ² −
If 1>0, the amount of interference Γ is calculated. If k ² −1<0
If so, Γ is not calculated, the value returns to i=1, and a new calculation of Γ is started.

FIG. 3 shows the relationship between the D/U setting value and the actual measurement value when the fading frequency F _d is used as a parameter. As shown in FIG. 3, in the embodiment, Δt is as small as 0.2, so the D/U ratio is not affected by the fading frequency.

FIG. 4 shows an embodiment in which the functions of the arithmetic machine of the embodiment are performed by a circuit. In Fig. 4, 10 is an antenna, 11 is a receiver, 12 is a detector, 13 is a smoothing circuit, 14 is a square circuit, 15 is a division circuit,
16 is a level meter, 17 is a delay circuit, 18 is a differential amplifier, 19 is a square circuit, and 20 is a smoothing circuit.

A composite wave e of D waves and U waves passes through 10 antennas and enters 11 receivers. When the IF output No. 11 is branched and one is input to the smoothing circuit No. 13 and smoothed, the output corresponds to the low frequency component X of equation (11) shown in the embodiment. When this output is further passed through a 14 square circuit and squared, equation (18)X is obtained.

X=(〈E ² ₁ 〉+〈E ² ₂ 〉) ² =〈E ² ₁ 〉 ² +2〈E ² ₁ 〉〈E ² ₂ 〉＋〈E ² ₂ 〉 ² (18) The others are input to 18 differential amplifiers and 17 delay circuits. 17 causes a delay corresponding to Δt in the embodiment, and is input to 18. 18 performs differential amplification of the undelayed signal and the delayed signal from 12, and passes it through a square circuit of 19 and 20 and a smoothing circuit to obtain a high frequency component Y corresponding to equation (14) of the embodiment. . Furthermore, 1
When the outputs of 4 and 20 are input to the division circuit 15, the output Z is expressed by equation (19) including the power average D/U ratio Γ from equations (13) and (18).

Ζ=〈E ² / ₁ 〉 ² + 2〈E ² / ₁ 〉〈E ² / ₂ 〉 +〈E ² /
₂ 〉 ² / 4〈E ² / ₁ 〉〈E ² / ₂ 〉=1/4 (Γ+2+1/Γ
)(19) By measuring Ζ with 16 level meters, the amount of interference can be known quantitatively.

FIG. 5 shows an embodiment of the present invention, 21 is an antenna, 22 is a receiver, 23 is an AGC, 24 is a detector (square), 25 is an amplifier, 26 is a filter (HPF), 27 is a detector, 28 is a filter (LPF), 29 is a smoothing circuit, 30 is a smoothing circuit,
31 is a level meter. Figure 6 shows the observed waveforms of each part of the interference detection device, where 32 is the output of 24 detectors, 3
3 indicates the output of the filter 26, 34 the output of the detector 27, and 35 the output of the smoothing circuit 30.

The composite wave e of D wave and U wave is received by 22 receivers through 21 antennas and dropped to an intermediate frequency.
Output from IF-OUT. This output is 23
When the envelope is detected by 24 detectors through AGC, 32 waveforms shown in FIG. 6 are obtained. This is a waveform corresponding to equation (5) described in the interference detection principle.
By amplifying signal 32 with signal 25 and passing it through a filter (HPF) 26 to cut out low frequency components, high frequency component 33 can be obtained. 33 is
2E ₁ E ₂ cosψ(t), which is expressed as 27, 28
When envelope detection is performed through
0) is obtained.

Y'=2E ₁・E ₂ (20) Since Y' is an instantaneous value and changes at a frequency of fading order, it is passed through 30 smoothing circuits, and 31 level meters are used to measure the square root Y of the root mean square value. give instructions.

Y=2 (〈E ² ₁ 〉・〈E ² ₂ 〉) ^1/2 (21) On the other hand, as shown in Fig. 5, the outputs of the 24 detectors are divided to sufficiently average out the fluctuations due to fading. The average value of the received level is detected by 29 smoothing circuits with the time constant set. AGC with this average value
so that the output of the detector (short interval median value) becomes constant. In other words, the sum of the squares of the D wave and the U wave is made constant.

X=〈E ² ₁ +E ² ₂ 〉=〈E ² ₁ 〉+〈E ² ₂ 〉=C (constant) (22) From equations (21) and (22) Since Y has a certain relationship with the D/U ratio Γ (power ratio), Γ can be estimated from Y.

FIG. 7 shows the output relationship between Γ and Y, where the solid line shows the theoretical value (formula (23)) and the cross mark shows the measured value Y.

In addition, 27 detectors are replaced with square law detectors, and 31
Even if Y is used as an average value indicating type level meter, Y has a constant relationship with Γ, and Γ can be estimated.

(Effects of the Invention) As explained above, this interference amount detection method can quantitatively detect the amount of interference during communication, so if the amount of interference exceeds a certain set value, it switches to another channel and improves the call quality. This has the advantage that calls can be continued without deterioration.

In addition, in systems that aim to improve frequency utilization using a small radio zone system of 3 to 5 km, such as car telephones, this method can further reduce the frequency repetition distance, improving frequency utilization. This can contribute to increasing subscriber capacity.

[Brief explanation of drawings]

FIG. 1 is an example of the detector output R(t), FIG. 2A is a block diagram of the first embodiment of the present invention, FIG. 2B is the operation flow of the computer 8 in FIG. 2A, and FIG. The figures are diagrams showing experimental results using the circuit of Fig. 2, Fig. 4 is a block diagram of the second embodiment of the present invention, Fig. 5 is a block diagram of the third embodiment of the present invention, and Fig. 6 is a diagram showing the results of an experiment using the circuit of Fig. 2. An example of waveforms observed at various parts of the apparatus according to the present invention, FIG. 7 is a diagram showing experimental results for the circuit of FIG. 5. (Explanation of symbols (Figure 2)) 3; antenna; 4;
Receiver, 5; Detector, 6, 7; A/D converter,
8; arithmetic machine, 9; delay circuit.

Claims (1)

[Claims] 1. In a wireless communication system using angle modulation, outputs of a desired wave and an interfering wave that have almost the same spectral band as the spectral band of fading that occurs in the envelope detection output when a desired wave and an interfering wave are simultaneously received. The sum of (=<
E ₁ ² ＞+<E ₂ ² ＞) Product of wave outputs (=<E ₁ ²
＞<E ₂ ^{2 >} )= means for detecting the ^high frequency component by _filtering the information consisting of _:
>)= and high frequency component (=Y=4<E ₁ ² ><E ₂ ² >)=
A method for measuring the amount of co-frequency interference characterized by determining the amount of interference Γ (==<E ₁ ² >/<E ₂ ² >)= from . 2. The co-frequency interference amount detection method according to claim 1, wherein the high frequency component due to the beat is generated by slightly detuning the carrier frequencies of the desired wave and the interfering wave on the transmitting side. 3. Making the high frequency components caused by the beat different in amplitude or frequency of the modulation signals of the desired wave and the interference wave,
2. A method for detecting the amount of co-frequency interference according to claim 1, which is caused by varying the signal information of the modulated waves or by varying the degree of modulation of the modulated waves. 4 The low frequency component is obtained by averaging the sampling using an analog-to-digital converter and an arithmetic unit, and the high frequency component is determined by two values sampled within a small delay time that can be regarded as the same value for the low frequency component. A co-frequency interference detection method according to claim 1, wherein the co-frequency interference amount is determined by taking the square of the difference or the average of the absolute values. 5 The low frequency component is obtained by a smoothing circuit that can sufficiently smooth the high frequency component, and the high frequency component is obtained by a delay circuit,
A method for detecting the amount of co-frequency interference according to claim 1, which is obtained from a differential amplifier and a smoothing circuit. 6. Claim 1, in which the low frequency component is smoothed, AGC is applied so that the average value of the low frequency component becomes constant, the high frequency component is determined by a filter and a detector, and the high frequency component is determined by smoothing it. Co-frequency interference detection method described in .