JPH0396036A - Fsk demodulation circuit - Google Patents

Abstract

PURPOSE:To reduce disturbance given onto other paging terminal equipment of the direct.conversion system by shifting an oscillating frequency of a local oscillator in one direction from a transmission frequency. CONSTITUTION:Two carriers orthogonal to each other generated by using an output of an oscillator 4 are multiplied with an inputted FSK modulation wave. Then two orthogonal signal outputs Di, Dg whose phase varies with a modulation data are extracted by a detection section 3. A data reproduction section 2 samples other signal output at a leading point of one signal output in the 2 signal outputs to obtain a reproduction data. Then the output frequency of the oscillator 4 is shifted so as to minimize the deterioration in the error rate of the reproduction data obtained by other FSK demodulation circuit employing the direct.conversion system.

Description

[Detailed Description of the Invention] [Summary] Mobile communication system. For example, PSK used in paging terminals that use the direct conversion method
With regard to the demodulation circuit, this is a system that transmits data using the direct conversion method, with the aim of reducing interference caused by paging terminals using the direct conversion method to other paging terminals using the same method. A detection part that multiplies the FSX modulated wave by two mutually orthogonal carrier waves using the output of the oscillator to extract two orthogonal signal outputs whose phases change corresponding to the three modulated data; Another FSK demodulation circuit using the direct convergence method in an FSX modulation circuit having a data reproduction section that samples the other signal output at the rising point of one of the two signal outputs to obtain reproduced data. Care is taken to shift the output frequency of the oscillator so that the degradation of the error rate of reproduced data obtained by the circuit is minimized.

[Industrial application field]

The present invention relates to an FSK demodulation circuit used in a mobile communication system, for example, a paging terminal using a direct conversion method.

In recent years, mobile communication systems that provide communication means for moving objects have shown remarkable development, and among these systems is a paging system.

A paging system allows a person who goes out to receive information from the other party by holding a paging terminal (i.e., a receiver). Currently, the single conversion method is mainstream due to the structure of the receiver, but
From a future perspective, the direct conversion method used in some systems is more advantageous.

The former is a heterologous type, for example, approximately 280 MHz.
After frequency converting the FSX modulated received signal to an intermediate frequency band signal. It is designed to extract information.

On the other hand, the latter method extracts information directly from the received signal without frequency conversion, but since there is a high possibility that a paging terminal using the latter method will cause interference to other paging terminals using the same method, this method is not recommended. It is necessary to minimize this possibility as much as possible.

[Conventional technology]

FIG. 6 is a block diagram of a conventional example, and FIG. 7 is an explanatory diagram of the operation of FIG. 6. Here, the symbols on the left side of FIG. 7 indicate the waveforms of the portions with the same symbols in FIG.

The modulated data in FIG. 7 is used on the transmitting side (not shown), but is shown for comparison with FIG. 3 (1). The operation shown in FIG. 6 will be explained below with reference to FIG.

First, the received signal, which is an FSK modulated wave, is expressed as r(t)=cos (ωc+a5ωa)tωc. Angular frequency ωd of S transmission wave: Maximum angular frequency deviation ai: +l when data is 1, -1 when data is O.

In other words, when the data is 1, the angular frequency of the PSK modulated wave is ω
. ω is higher than ω4, and when O is ω.

ω4 is lower than that of ω4.

Now, this received signal is input to mixers 12 and 13 after being amplified by amplifier 1l. Here, a local oscillator 1 with a phase difference of 90 degrees is generated by a 90 degree hybrid l4.
Since the outputs sin ωct and cos ωct of 0 are also applied, the received signal is multiplied by the output of the local oscillator, and the multiplication result is passed through the corresponding low-pass filter 15 and 16 into two series (hereinafter, Ich, (referred to as lch) baseband signal dI(t)=-sin(ai ω=
t) = − at sin ω, 1 td
Q(t)= +cos(at ωa t)= +
at cos (tedt is obtained. When this is identified by discriminators 17 and 18, binary signals D, +
Dq is obtained, but this is added to the D and CK terminals of the D type flip-flop (hereinafter abbreviated as o-pp) constituting the phase detection circuit 2l, and the rising point of +oq (■ in Figure 7 is the , only the rising point of ) is expressed as D, by D-F
When the data is taken into F and the output is taken out from the Q terminal, the same data as the modulated data is reproduced (see Fig. 7-1-1).

Note that the relationship between +Di and DQ may be reversed.

[Problems to be Solved by the Invention] Here, in the case of the direct conversion method, the frequency f. (corresponding to the angular frequency ω of the unmodulated wave mentioned above) and the output frequency fL of the local oscillator match, but the received level of the FSK modulated wave is, for example, −120 dBm, and the output level of the local oscillator is, for example, (
-10 to -20) dam, and the output level of the local oscillator is in a higher state.

Therefore, other paging terminals that use the same direct conversion method. In other words, when a high-level output from the local oscillator in the FSK demodulation circuit (hereinafter abbreviated as interference wave) is input to the own station, the spectrum of the high-level interference wave (in the figure) appears as shown in Figure 8(a). FS received by (dotted line)
The entire spectrum of the K modulated wave, ie. Modulation data 1
, O, and the error rate deteriorates. Incidentally, FIG. 8 is an explanatory diagram of the problem.

Now, in Fig. 8) is the D-FF21 when there is an interference wave (
(shown in Figure 6).The frequencies of the received signal and the interference wave do not match completely, and the stability is also different, so there is a difference as shown in Figure 8 (b) 1 and ■. A frequency signal is applied to the D-FF as data. For this reason, data with many errors is sent out as reproduced data from the output side, as shown in FIG. 8(b) (1).

Note that FIG. 8(b) 1-2 shows only the rising point of D9.

Furthermore, although the above explanation shows a case in which the local station is interfered with by the output of the local oscillator from another paging terminal, in the reverse case as well, the error rate of the paging terminal that receives the interference is inferior, as in the above case.

That is, there is a problem in that a paging terminal using the direct conversion method is likely to interfere with other paging terminals using the same method.

An object of the present invention is to reduce the interference caused by a paging terminal using the direct comparison method to other paging terminals using the same method.

[Means to solve problems] FIG. 1 shows a block diagram of the principle of the present invention.

In the figure, 3 is for the manually generated FSK modulated wave. By multiplying two mutually orthogonal carrier waves using the output of an oscillator, two orthogonal carrier waves whose phase changes in accordance with the modulation data are generated.
A detection part extracts a signal output, and 2 is a data reproducing part which samples the other signal output at the rising point of one of the two signal outputs to obtain reproduced data.

Then, the output frequency of the oscillator is shifted so that the degradation of the error rate of reproduced data obtained by another FSK demodulation circuit using the direct conversion method is minimized.

[Function] As mentioned above, the FSK modulated wave has a transmission frequency f. Although the frequency shifts by +ΔF or -ΔF (corresponding to ai ω4) around , the probability that it becomes +ΔF or -ΔF is the same due to the randomness of the modulation data. Here, ΔF indicates frequency deviation.

Therefore, the present invention shifts the oscillation frequency f of the local oscillator by α from f8 to either one as shown in FIG. 2(a).

Due to this. Even if interference waves from a paging terminal using the direct conversion method are input to other paging terminals using the same method, the right half of the FSK modulation spectrum f, as shown in Figure 2 (a). Alternatively, the left half receives interference, but the interference on the left or right half of +fs is reduced, and as shown in FIG. 2 0)), the deterioration of the error rate is improved compared to the conventional example.

That is, the interference caused by a paging terminal using the direct conversion method to other paging terminals using the same method can be reduced.

〔Example〕

3 is a block diagram of an embodiment of the present invention, FIG. 4 is an explanatory diagram of the operation of FIG. 3, and FIG. 5 is an explanatory diagram of another operation of FIG. 3.

Here, an amplifier 31, a detector 32 . 33. 90 degree hybrid 34, low pass filter 35, 36. The discriminators 37 and 38 are components of the detection section 3 and the local oscillator 4.
1 represents a horizontal portion of the oscillator 4, and the phase detector 21 represents a component of the data reproducing portion 2.

below. The operation in FIG. 3 will be explained with reference to FIGS. 4 and 5.

(1) When there is no interference from other paging terminals First, as shown in the spectrum characteristic in Figure 4(a), the output frequency fL of the local oscillator is set by α (for example, α= ΔF/2).

Therefore, the PSK modulated wave whose frequency shifts by +ΔF or -ΔF with +fs as the center is multiplied by the output of the local oscillator 4l in mixers 32 and 33, and the frequency becomes ΔF+α, ΔF.
A baseband signal of 1α is obtained.

At this time, the low-pass filter 35. By changing the cutoff frequency of 36 to ΔF+α and ΔF−α as shown in FIG. 4, the shift in the oscillation frequency of the local oscillator is compensated for.

Now, the baseband signal is processed by the above low-pass filter.
Discriminator 37. 38, binary signals Di and Dq are obtained as shown in Figure 5(a) 1 and ■.These binary signals are processed by the phase detector 21 consisting of a D-FP.
By sampling Di, error-free reproduced data as shown in FIG. 5(a)-1 is obtained.

(2) When receiving interference from other paging terminals Next,
Suppose that a disturbance wave is manually generated at a position with frequency ft (·f5-α).

As mentioned above, the data l corresponding to the frequency (f.+ΔF) is hardly affected by the interference waves. For this reason, Fig. 5 (b
)1 ■. As shown in (2), 2{L! corresponding to the modulated data l sent from the discriminator! Signal D. , DQ have few errors, but the binary signal corresponding to the modulated data O has many errors because the signal of the difference frequency is added to the D-FF as data.

Therefore, the output of the phase detector has few errors in the reproduced data for modulated data 1, as shown in Figure 5(b)-1.
The reproduced data for 0 will have many errors.

That is, by shifting the output frequency of the local oscillator, the interference caused to other same systems is limited to one side, so that the interference caused to other paging terminals using the same system is reduced.

〔Effect of the invention〕

As described in detail above, according to the present invention, the effect of a paging terminal using the direct conversion method on other paging terminals using the same method can be reduced.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of the operation of Fig. 1, Fig. 3 is a block diagram of an embodiment of the present invention, Fig. 4 is an explanatory diagram of the operation of Fig. 3, and Fig. 5 6 is a block diagram of the conventional example, FIG. 7 is an explanatory diagram of the operation of FIG. 6, and FIG. 8 is an explanatory diagram of problems. In the figure, 2 indicates a data reproducing section 3 is a detection section, and 4 indicates an oscillator. Tomi 1 Figure 2 Figure i 3 Memo 3 That movement/) Theory ap Cooking rod 4 mouths

Claims (1)

[Claims] A system that transmits data using a direct conversion method, which transmits two mutually orthogonal carrier waves generated using the output of an oscillator (4) to an input FSK modulated wave. A detection part (3) that multiplies and extracts two orthogonal signal outputs (D_i, D_q) whose phases change in accordance with the modulation data, and a detection part (3) that extracts two orthogonal signal outputs (D_i, D_q) whose phases change in accordance with the modulation data; In an FSK modulation circuit having a data reproducing part (2) that samples the signal output of the
An FSK demodulation circuit characterized in that the output frequency of the oscillator is shifted so that deterioration in the error rate of reproduced data obtained by the demodulation circuit is minimized.