JPS5868330A - Detecting circuit for identical frequency interference - Google Patents

Abstract

PURPOSE:To an interference detecting signal corresponding to the electric power ratio of an interference wave to a desired wave under no influence of variation in reception level, by detecting the beat signal of the composite wave of the desired wave and interference wave. CONSTITUTION:In a receiver used for digital communication which employs an angle modulation system, a received signal applied to a terminal 10 is converted by a square-law detector 11 into a signal 17 showing momentary received electric power to obtain a signal showing the amplitude of the received signal, which is applied to an HPF12 and an LPF13. The HPF12 outputs a signal 18 showing momentary received electric power while the DC component of received electric power and the variation component due to fading are removed, and the LPF13 outputs a signal 19 showing mean received electric power which contains the variation component due to the fading to apply them to a divider 14 respectively. The output of the divider 14 is converted by an envelope detector 15 into an envelope voltage, so that an identical frequency interference detecting signal voltage corresponding to the electric power ratio of an interference wave to a desired wave is developed at a terminal 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides, for example, in a digital mobile communication system,
This invention relates to a co-frequency interference detection circuit that detects co-channel interference due to nine radio waves emitted from other stations using the same frequency.

Conventionally, in digital mobile communications, there has been no effective method to efficiently detect co-channel interference, and either only prohibits co-channel interference, or the level of interference waves is sufficiently low! ! There was no countermeasure against interference other than to avoid the occurrence of interference by allowing reuse of mutual channels in friend regions K at odd distances.

(9) As a method of detecting interference at the expense of transmission efficiency, a knee word is added to the signal sequence to be transmitted as a station identification code, and when this is detected on the receiving side, the desired wave is received. There is a way to determine whether it is possible or not. However, in this method, (I) rounding transmission efficiency for assigning a station identification code is reduced; α) It becomes necessary to provide a frame structure to the transmission signal series, and a new circuit such as 7-ray synchronization is added. (b) When the desired interference wave power ratio (CIR) is sufficiently lower than 1, the weak interference wave is stronger, and correct interference detection is possible only in state 11 where the interference wave is correctly received. There are 6 drawbacks such as:

In particular, (2) means that interference cannot be detected when the CIR is close to IK, and the major disadvantage of this method is that it is impossible to take some kind of zero interference countermeasure. It shows.

In order to eliminate these drawbacks, the present invention aims to combine and receive the desired wave and the interference wave from points where the instantaneous phases of the carrier waves are different, since the desired wave and the interference wave are usually modulated with different signals. This method utilizes the phenomenon in which a beat is generated in which the amplitude of a wave fluctuates at a frequency close to the frequency of the modulation signal, and detects the beat to detect interference, which will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing temporal changes in received signal amplitude. In mobile communications, the amplitude of a received signal fluctuates greatly from several Hz to several tens of wavenumbers due to phasing caused by multiple wave propagation. The broken line in the figure shows the amplitude fluctuation due to 7 aging of Jin. When interference waves of the same frequency exist, amplitude fluctuations of frequencies close to the modulation frequency and baseband signal frequency are added to the interference waves. The solid line in the figure shows the amplitude fluctuation due to aging and interference. In this invention, among this amplitude fluctuation component,
It is based on the JJA principle of extracting only the fluctuation component due to interference (therefore detecting interference. Usually, variation 11
The JIII wave number is explained using a sufficiently high acid compared to the 7 engineering station wave number.
*y1ng) Describe the RIll method. The desired wave is ・, rt), and the interference wave is ・*(1).

Each OSm is 1. A)
.

If we set the angular frequency of the conveyor axle as #R, the angular frequency deviation as Ω, and the interval of 2 times as 0@transmission phase, the following equation holds true.

j: Imaginary unit Since the received signal is a combination of the desired wave and the interference wave, the received voltage [1) becomes 8(t) opening [.to 1) +., a)]. However, the name ``kasa'' represents the inner part of the temple. The instantaneous received power S) is given by the following formula.

W(t) 5S(t) ” A4 +A4 +2AIAIm (-1-φlowφ
(t))-10'-00"←)mu, φ-Ω41 sanmu Al
The change in tAl tφ(1) is about the same speed as the 7 aging bit, and is sufficiently slow compared to the change in φhφSO (t/2 per 1 blt in M8). Therefore, the instantaneous received power W is the number of 7 aging bits 0111
It can be normalized by the time average value W-A of 10 people, but,
J-mAl/At, that is, the desired wave to interference wave power ratio ((J
R). From the above formula, by envelope-detecting w/w and removing the DC component, the CIRK-compatible output voltage map (t
)-zJj,, ix+A can be obtained.

In Figure 2, either the desired wave or the interference wave is all! −
FIG. 4 is a diagram showing a power spectrum of normalized amplitude fluctuation when one signal is modulated in all space, and the other is modulated in all space. This and IIW/W are expressed by the following formula.

Therefore, there are only the DC component (1) and the Wm component. sth
g is a diagram showing the change in Ma(1) with respect to CIR, jK.

As can be seen from the figure, Jin's invention is based on the voltage v(
It has the characteristic of rapidly increasing in a small area of $A, and has a sensitive interference detection ability.

In the fourth garden, the power spectrum of the normalized amplitude fluctuation when both the appropriation wave and the interference wave are modulated with KPM (pseudo-random) codes spreads as shown in this figure, but it is sufficiently large compared to the fluctuation due to aging. The 0IIs diagram in which a high frequency O variation component exists and interference detection is possible shows an embodiment of the present invention. The input terminal 10Km receiving signal 411f is converted into a signal 17 representing the instantaneous received power by a square law detector 11, and a signal representing the amplitude (level) of the received signal 4t is obtained, and a high frequency F signal is obtained. P wave 1) is added to the wave sensor 13 and image field P wave 1). The high-frequency r*@tzo output becomes a signal 1 (corresponding to W-W) representing the instantaneous received power after removing the DC component of the received power and the fluctuation component due to facing, and the low-frequency P
The output of the divider 13 becomes a signal 19 (corresponding to the WK phase) representing the average damaged power including a fluctuation component due to fading, and is added to the divider 14.The output signal of the divider 14 is sent to the envelope detector 15 to detect the envelope voltage. Interference detection signal voltage v(t)1 corresponding to CIRK and interference detection output terminal 1
6 is output.

FIG. 6 shows another embodiment of the invention. In this embodiment, the square law detection [111 of FIG.

Also, it would be better to replace the divider 14 with the subtracter 22.
The circuit is designed to operate at dB values.

In this embodiment, since the average received power O dB value is also obtained at the same time, it is advantageous when used in conjunction with control that requires detection of the same level of diversity.

As an example of actually using the present invention, a method can be considered in which, when the voltage of the interference detection signal exceeds a specified level, it is determined that interference is occurring, and corresponding measures are taken. 9. Although the above explanation applies to PgK, other modulation methods such as BP8K, QP8K,
Even in the digital I communication system using MfiK,
Since no beats occur due to same-frequency interference, this output Wj
The i40 interference detection circuit works well. In this way, the present invention detects the magnitude of co-frequency interference and detects the presence or absence of intermediate-frequency interference.

When detecting the presence or absence of interference, only the presence or absence of the output of the high-frequency r wave generator 12 may be detected.

As can be explained above, the present invention is applicable to co-frequency interference tIL.
exists, the amplitude of the received signal is at a sufficiently high modulation frequency (baseband No. 1 frequency) compared to the fading wave number.
Since this is an interference detection circuit that detects interference using fluctuations in frequencies close to K, (1) the interference detection signal corresponding to the desired signal to interference signal power ratio (CIR) K is not affected by fluctuations in the reception level. can be obtained. α) PgK, PgK,
Any digital angle f quality adjustment method (such as M8) can be applied.GID interference detection characteristics are sensitive and it operates extremely effectively even in areas where CIR is poor (near OdB). It has the advantage that it does not impose constraint condition 1 and does not affect transmission efficiency.

[Brief explanation of drawings]

Figure 1 is a diagram showing the temporal change in the amplitude of the received signal, Figures 2 and 4 are diagrams each showing an example of the power spectrum of reception number 1, and Figure 3 is the desired wave to interference wave power ratio and interference detection. 5 and 6 are block diagrams showing embodiments of the present invention, respectively. lO... Received signal input terminal, 11... Square law detector,
12-...High-frequency f-wave device, 13...Low-frequency f-wave device, 14.
... Divider, 15... Enveloping line detector, 16... Interference detection output terminal, 17... Signal representing received power, 18.
... a signal representing nine instantaneous received power after removing the average received power,
19... Signal representing average received power, 20... Logarithmic amplifier 1, 21... Envelope liquid analyzer, 22... Subtractor,
23... Interference detection output terminal ((IB value), 24...
Output terminal for a signal representing average received power (dB value). Patent application: Nippon Telegraph and Telephone Public Corporation agent Fu Kusano Figure 1 Time Figure 72 Figure 73

Claims (1)

[Claims] In a receiving device used in digital communication that uses the angle modulation method, there is a level detection circuit that detects the amplitude of the received signal, and a signal that indicates the amplitude of the received signal output from the level detection circuit. What is claimed is: 1. A co-frequency interference detection circuit, comprising: a beat detection circuit that extracts fluctuating components of a frequency close to a band signal, and detects co-frequency interference.