JPH0328098B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field to which the Invention Pertains) The present invention is necessary for fading compensation because the received signal of a mobile body undergoes fading and its envelope component changes complicatedly when performing land mobile communication. The present invention relates to a circuit that detects the envelope component of a received signal.

(Prior art) Linear detectors or logarithmic detectors have been used for the above purpose, but linear detectors have a simple circuit but have narrow linearity (approximately 25 dB), and logarithmic detectors have a narrow linearity range. Although it has a wide range (approximately 70 dB), the disadvantage is that the circuit is complex, and it is difficult and expensive to adjust to obtain sufficient characteristics. Next, it will be explained more specifically.

Since communication with fading cannot be avoided in land mobile communications, various countermeasures against fading have been proposed. One of the important elements in implementing these measures is level detection of the received signal (that is, detection of the envelope component). FIG. 1 is a diagram showing an example of reception level fluctuation on the mobile device side, where A represents the median fluctuation and B represents the instantaneous fluctuation. This diagram A is a relatively slow fluctuation, which is called a long-period fluctuation, and the fluctuation period is several times.
Hz or less. Such level fluctuations can be adequately handled by conventional measures such as AGC. On the other hand, Diagram B corresponds to an enlarged version of the part of Diagram A where the median fluctuation is almost constant. In mobile communications, the variation in diagram B that has the greatest impact on the quality is called Rayleaf Aging.

Next, a linear detector and a logarithmic detector, which are conventionally used to detect the level of a received signal subjected to Rayleigh fading, that is, the envelope component of the signal, will be explained.

FIG. 2 shows an example of the configuration of a linear detector, and the amplifier is used to input a sufficient voltage to the diode detector in the next stage. Diode detectors usually require an input of at least 0.3V, and linearity deteriorates below that. Furthermore, since the upper limit of the circuit voltage is 10 to 20 V in current transistor circuits, the upper limit of the linearity range is about 35 dB (20/0.3≒67=36.5 dB).

Figure 3 shows an example of the configuration of a logarithmic detector.
4 is an amplitude limiting amplifier, and 5 is a current addition circuit. The operation of a logarithmic detector is well known and will therefore be omitted, but in principle a detector with desired linearity can be realized. However, when trying to obtain a linear output, an inverse logarithmic transformation is required and adjustment is difficult, which is a major drawback.

(Specific Object of the Invention) The present invention has features intermediate between the two conventional types of envelope detectors. In other words, the linearity is close to 50 dB, and although the circuit configuration is not as simple as a linear detector, it is simpler than a logarithmic detector, and it does not require any delicate adjustments.

(Structure and operation of the invention) FIG. 4 is a diagram showing an example of the structure of an envelope formation detection circuit embodying the invention. In this figure, 11 and 12 are signal distributors, 13 is a comparator, 14 is a delay element, and 1
5, 16 are phase shifters, 17, 18 are multipliers, 19,
Reference numeral 20 represents a low frequency wave generator, and reference numeral 21 represents a magnitude comparison selection circuit. The operation of the circuit shown in FIG. 4 will now be explained with reference to FIG. 5, which is a time chart of waveforms of various parts thereof. First, a signal input is divided into two by a divider 11, and the amplitude is limited by a comparator 13. Figure 4a shows the input of the comparator 13, and b shows its output after limiting the amplitude and truncating below a certain amplitude. It shows that there will be no output. Comparator 13
The output of
The waveform shown in Figure c is obtained.

On the other hand, the other signal output of the divider 11 is sent to the divider 12 and further divided into two parts, and the output of one of the signals is phase-corrected in the phase shifter 15, and then multiplied by the output of the comparator 13 in the multiplier 17. Ru. Similarly, the other output of the distributor 12 is sent to the delay line 14 by the multiplier 18 after its phase is corrected by the phase shifter 16.
is multiplied by the output of Phase shifters 15 and 16 correct the phases of the signals input to multipliers 17 and 18 so that they are in phase. The outputs of multipliers 17 and 18 are passed through LPFs 19 and 20, respectively, to extract only low frequency components. The outputs are each subjected to full-wave rectification in the magnitude comparison detection circuit 13, and then the one with a higher level is detected and becomes the output. Here, further explanation will be given using equations. Generally, the signal input is expressed by the following equation.

S(t)=a(t) cosω ₀ t...(1) a(t) is the signal represented by the envelope, ω ₀ is the angular frequency of the carrier wave, and the signal whose amplitude is limited by a comparator is It will look like this: V _TH is a constant amplitude voltage value that is the threshold of the comparator.

'g(t)=b(t)cos ω ₀ t...(2) When 0|a(t)|V _TH Where b(t)=[1|a(t)|>V _TH The output obtained by multiplying S(t) and g(t) is as shown in equation (3). Note that a double-balanced modulator is generally used as a multiplier, and its operation is to obtain a multiplication output in the desired band by changing the polarity of the input signal with a local signal and band-limiting the signal output. It is.

m(t) = S(t)・g(t) = a(t) b(t) cos ω ₀ t・cos ω ₀ t = a(t) b(t) (1tcos2ω ₀ t)/2
...(3) The output after passing this m(t) through the LPF is given by the following formula.

ml(t)=a(t)b(t)/2...(4) In equation (4), a(t) is the component of the envelope in Figure 5 a as mentioned above, and b(t) is This is because it becomes an intermittent wave that becomes 1 when this envelope is larger than the comparator's "threshold" value V _TH and 0 when it is smaller than V _TH .
ml(t) has an intermittent waveform as shown in FIG. 5d. Similarly, the signal expressed by equation (4) given by the product of the delayed signal g(t) (output c in Fig. 4, 14 and c in Fig. 5) and the input (output in Fig. 4, 20) is The waveform is shown in Figure 5 e. Figures 5 d and e obtained by the above procedure
A part of the waveform is missing to obtain the envelope component a(t), but most of the other parts are the same. Also, the missing portion of one waveform is supplemented by the other waveform. Therefore, by comparing the magnitudes of these two waveforms and selecting and outputting the one with the larger signal voltage as shown in FIG. 4, a correct envelope component can be obtained.

Note that the delay element 14 in FIG. 4 delays the binary signal (b in FIG. 5) that is the output of the comparator 13, and there is no need to use an analog delay line, which simplifies the circuit configuration.

FIG. 6 is a diagram illustrating a configuration example of an interference wave regeneration/elimination circuit showing an example of use of the circuit of the present invention. As a method for reducing interference waves in land mobile communications, a method has been proposed in which the interference waves are regenerated and the interference signals are subtracted from the composite signal of desired wave D and interference wave U, thereby removing the interference waves. The circuit of the present invention can be applied to such a circuit. 32 in FIG. 6 corresponds to the circuit of the present invention. Although the signal input in FIG. 6 is (D+U), this circuit operates effectively only when D<<U. In other words, in the bandpass filter (BPF) 30 of f _U , U》D, so U
only is extracted, and the circuit after that operates normally for U. On the other hand, if there is no subtractor 35, the output of BPF 36 for f _D is D《U, so BPF3
6, the circuit D does not operate normally because of the U wave output that cannot be completely removed. However, when the subtracter 35 is added, the U wave in the D wave demodulation system shown in the lower part of FIG. 6 is removed, and the D wave is demodulated normally. (For details of this circuit, please refer to Sanpei and Yokoyama, "Adjacent interference wave removal method in two-phase PSK," IEICE technical report CS85-26.) (Effects of the invention) The envelope component detection circuit uses fading compensation technology. It is used for certain diversity synthesis click noise suppression, interference wave reproduction removal, etc., but until now there has been no circuit with sufficient performance, relatively simple and inexpensive, and a circuit that satisfies these requirements has been desired. As mentioned above, the circuit of the present invention has a sufficiently large range of linearity;
A remarkable effect is obtained in that the circuit is relatively simple, there is no difficulty in adjustment, the operation is stable, and the circuit can be realized at low cost.

[Brief explanation of the drawing]

Figure 1 is an example of reception level fluctuation on the mobile device side.
Fig. 2 is an example configuration diagram of a linear detector, Fig. 3 is an example configuration diagram of a logarithmic detector, Fig. 4 is an example configuration diagram of an envelope detection circuit according to the present invention, and Fig. 5 is a waveform of each part of Fig. 4. 6 are diagrams illustrating an example of the configuration of an interference wave regeneration/elimination circuit using the circuit of the present invention. 1 to 4... Amplitude limiting amplifier, 5... Current addition circuit,
11-12...Signal distributor, 13...Comparator, 14...
Delay element, 15, 16... Phase shifter, 17, 18... Multiplier, 19, 20... Low frequency converter, 21... Size comparison selection circuit.

Claims (1)

[Claims] 1 A circuit that detects the envelope component of an amplitude modulated received signal, which divides the received signal into two, limits the upper and lower amplitudes of one of them to form a rectangular intermittent wave train of constant amplitude, and delays this rectangular intermittent wave. means for generating a delayed rectangular intermittent wave train that does not overlap with the intermittent rectangular wave through an element, and further dividing the other half of the received signal into two.
one of the multipliers multiplies its input signal by the rectangular intermittent wave train; The multiplier has means for multiplying the input signal by the delayed rectangular intermittent wave train and passing each product output to a low-frequency wave generator to extract a low-frequency component, and rectifying each of the low-frequency components. An envelope component detection circuit characterized by comprising means for comparing the magnitudes thereof and outputting the one having a higher signal level as an envelope detection output.