JPH04250752A - Msk demodulating circuit - Google Patents

Abstract

PURPOSE:To easily demodulate even an MSK modulation wave whose phase rotation direction is forward or backward. CONSTITUTION:The MSK demodulator 20 is a known demodulator and has output ports of two channels I,Q and demodulates an MSK modulation wave to output a data series in a same time slot from each output port. An inverter 21 outputs inversely a data series of either the I or Q channel. A selector 22 uses an external control signal to select and output an output data of an inverter 22 or an input data.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MSK demodulation circuit.

0002

[Background Art] When converting the frequency of orthogonally modulated waves, for example, when converting a modulated wave in an intermediate frequency band (IF band) to a radio frequency band (RF band), the phase rotation of the orthogonally modulated wave is performed depending on the local frequency used. The direction changes. For example, if a quadrature modulated wave with a center frequency of 70MHz is
When frequency converting to Hz, the local frequency is 930M
If the frequency is converted to Hz and the upper sideband wave is selected from the obtained both sideband waves, the desired modulated wave with a center of 1 GHz can be obtained. Further, even if the local frequency is set to 1070 MHz and the lower side band wave is selected from the obtained both side band waves, a modulated wave with a 1 GHz center can be obtained. Both methods are often used depending on the convenience of implementing the device. However, the modulated waves in the RF band obtained by both methods have different phase rotation directions. That is, the RF band modulated wave obtained by the former method has the same phase rotation direction as the IF band modulated wave, but in the latter case, the phase rotation direction is opposite.

[0003] As is well known, the effect when a demodulator demodulates a modulated wave whose phase rotation direction is opposite is as follows when the modulation method is QPSK. That is, QPS
If the I and Q channel input data sequences of the K modulator are I and Q, respectively, and the modulated wave with the phase rotation in the opposite direction of the modulated wave of the modulator output is demodulated by the QPSK demodulator, the Q than the I channel is output, and from the Q channel I
is output.

Therefore, conventionally, when attempting to construct a versatile demodulation circuit that can demodulate modulated waves processed by any method, a demodulator 30 as shown in FIG.
2-input, 1-output selectors 31 and 32 were installed in the output of the . That is, when demodulating a modulated wave in the same phase rotation direction as the modulated wave of the modulator output (hereinafter referred to as a modulated wave with forward phase rotation), the selectors 31 and 32 select the I and Q of the demodulator 30. When the channel output is directly output to the baseband processing unit as the demodulation circuit output, and the modulated wave in the opposite phase rotation direction from the modulated wave of the modulator output (hereinafter referred to as the modulated wave with phase rotation in the opposite direction) is demodulated. , selector 31,3
2 uses the I channel output as the Q channel demodulation output,
The Q channel output is output to the baseband processing section as an I channel demodulated output.

[0005]

[Problem to be Solved by the Invention] When the modulation method is QPSK, the above-mentioned method has been used to construct a demodulation circuit that can demodulate a modulated wave whose phase rotation is in either direction. In this case, due to its unique signal processing, the handling method is different from that in the case of QPSK, and the specific circuit configuration was not known.

An object of the present invention is to provide an MSK modulated wave that can be easily demodulated in both forward and reverse phase rotation directions.
The object of the present invention is to provide a demodulation circuit.

[0007]

[Means for Solving the Problems] The MSK demodulation circuit of the present invention includes an MSK demodulator that has two output ports, an I channel and a Q channel, and outputs data sequences from these output ports in mutually identical time slots; An inverter that inverts and outputs the data series from either one of the two output ports, and a selector that selects and outputs either the output data or the input data of the inverter based on a control signal from the outside. There is.

[0008]

[Example] QPSK as a modulation and demodulation method in satellite communication
is widely used, but it is well known that the MSK modulation/demodulation method exhibits superior characteristics compared to QPSK, especially in systems to which nonlinear circuits are applied.

First, regarding the MSK modulation and demodulation system, FIGS.
, 4 will be briefly explained.

FIG. 2 is a block diagram of the basic configuration of a general MSK modulation/demodulation system, and FIG. 3 shows a time chart of each part signal in FIG.

In FIG. 2, TXI and TXQ are data sequences to be transmitted each having a bit rate of fs. The data series TXI, TXQ are shown in FIG. 3A. The data series TXI is supplied as is to the multiplier 1, and the data series TXQ is delayed by half a bit in the flip-flop 3 and then supplied to the multiplier 2. In multiplier 1, data series T
XI is multiplied by a cosine wave of frequency fs/2, and multiplier 2 multiplies the half-symbol delayed data of data series TXQ by a sine wave of frequency fs/2. The output signals of these multipliers 1 and 2 are TXII and T, respectively.
XQQ, and they are shown in B of FIG. 3 (these waveforms are analog signals and are not rectangular waves, but are represented here as rectangular waves for convenience). Note that multiplier 1,
The phase relationship in multiplication of data with a cosine wave and a sine wave in No. 2 is shown in A of FIG. Signal TXII, TXQ
Q is then orthogonally modulated in the same manner as QPSK by multipliers 4 and 5, and an MSK modulated wave is output. The above is MS
This is the main operation of the K modulator.

On the other hand, the MSK demodulator that receives the MSK modulated wave first performs orthogonal demodulation in multipliers 8 and 9 in the same manner as QPSK, and then performs A/D conversion in A/D converters 10 and 11 to generate a demodulated digital signal. Outputs data RXII and RXQQ. It should be noted here that the phase term α is added to the cosine waves and sine waves of the multipliers 8 and 9 in the orthogonal demodulator. This is an effect due to the well-known phase ambiguity of the recovered carrier wave that occurs during orthogonal synchronous detection, and has a value of 0, π/2, π, or -π/2. There are four types of data series obtained depending on the value of α. The state of the output here is shown in FIG. 3C. The demodulated digital data RXII, RXQQ are
The signals are supplied to multipliers (exclusive OR gates) 12 and 13, respectively, and are multiplied by a cosine wave and a sine wave similarly to the transmitting side. Note that since RXII and RXQQ are already digital signals, the multiplier is composed of exclusive OR gates 12 and 1.
3, the cosine wave and sine wave are replaced by a clock with a frequency of fs/2. The phase relationship during multiplication of the data and the sine wave in the exclusive OR gates 12 and 13 is shown in FIG. 4B. Since the data sequence on the Q channel side was delayed in the flip-flop 3 on the transmitting side, it is necessary to perform the opposite operation this time. For that reason, exclusive OR gate 1
The two outputs are delayed by half a bit in the flip-flop 14 and then output as a data sequence RXI. The output of the exclusive OR gate 13 is directly outputted as a data series RXQ without any operation. data series RXI,
RXQ is shown in FIG. 3D. The above are the main operations of the MSK demodulator.

Now, based on the above, MSK
The effect when the phase rotation direction of the MSK modulated wave in the demodulator is reversed will be considered using FIGS. 2 and 5.

When a modulated wave whose phase rotation direction is opposite is input to the input of the MSK demodulator, the demodulated digital data RXII, RXQQ in the demodulator becomes the same as that shown in A of FIG. 5 because the data sequences of the I and Q channels are swapped. It will be like that. This corresponds to C in FIG. After further signal processing, the data series RXI and RXQ become B in FIG. This corresponds to D in FIG.

[0015] If D in FIG. 3 is compared with B in FIG. 5, the following will be found. i.e. I channel, or
It can be seen that if the data series of either Q channel is inverted, they become the same data series.

Therefore, one of the I and Q channel output ports of the MSK demodulator 20 having the same function as the above-mentioned MSK demodulator, for example, the I channel output port, is connected to the inverter 21 and the inverter 21 depending on the control signal. The circuit shown in FIG. 1, which is connected to a selector 22 that selects and outputs either input data or output data, is the intended MSK demodulation circuit.

[0017]

[Effects of the Invention] As explained above, the present invention adds a simple circuit to the MSK modulation method in the same way as the QPSK modulation method, so that it can easily handle whether the rotation direction of the modulated wave is forward or reverse. This has the effect that it is possible to configure a demodulation circuit that can perform

[Brief explanation of the drawing]

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

FIG. 2 is a block diagram showing the basic configuration of the MSK modulation and demodulation method.

FIG. 3 is a time chart A, B, C, and D of data series at points a, b, c, and d in FIG. 2;

[Figure 4] Data and cosine waves of multipliers 1 and 2 in Figure 2,
A time chart A showing the phase relationship with the sine wave, and a time chart B showing the phase relationship between the data of the exclusive OR gates 12 and 13 and the cosine wave and the sine wave clock.

[Fig. 5] c in Fig. 2 when the MSK demodulator in Fig. 2 demodulates an MSK modulated wave whose phase rotation direction is opposite;
These are time charts A and B of the data series at point d.

FIG. 6 is a block diagram showing an example of a circuit in a conventionally used QPSK demodulator.

[Explanation of symbols]

20 MSK demodulator 21 Inverter 22 Selector

Claims (1)

[Claims] [Claim 1] Two channels, an I channel and a Q channel.
an MSK demodulator that has two output ports and outputs data sequences from these output ports in the same time slot; an inverter that inverts and outputs the data sequence from either one of the two output ports; and an inverter that is externally controlled. An MSK demodulation circuit comprising: a selector that selects and outputs either output data or input data of the inverter based on a signal.