JP2903539B2 - Demodulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a demodulator for demodulating a ^2N- phase PSK-modulated wave in accordance with an agreement between transmission and reception.

[Conventional technology]

Among the methods of digitally modulating and transmitting data, PSK (Phase Shift Keying) is a modulation method that is often used because it has high transmission efficiency and bandwidth utilization and is strong against noise.
There is a modulation method. This is a method of modulating transmitted data by changing the phase of a carrier. That is, when data to be transmitted is divided into sets of N bits, there are 2 ^N possible values for each set. For example, each combination of N = 2 bits is four kinds of “00”, “01”, “11”, and “10”. The information in units of N bits is assigned to each of 2 ^N types of carrier waves that differ in phase with respect to a reference phase, and transmitted one by one. Therefore, a large amount of information can be transmitted simultaneously by one modulation, that is, one phase change. That is, the transmission signal is converted into an N-channel code string divided into N bits, and modulated and transmitted to a phase corresponding to the code string.
The receiving side demodulates the received symbol by detecting the phase state of the received signal with respect to the reference phase.

Fig. 7 shows the difference of the system due to the difference of the phase change,
This is for an eight-phase system. FIG. 7A is a four-phase type,
FIG. 6B shows an eight-phase system.

The circle shown in this figure indicates a unit circle drawn by the end point of the unit vector when the phase of each carrier corresponding to each data in N bits is represented by a unit vector. The numbers shown on the outer circumference of this unit circle are the data of each set in N-bit units. In FIG. 7A, there is a phase difference of 2π / 2 ^N, that is, 90 ° with respect to the adjacent data, and in FIG. B, there is a phase difference of 45 °.
The reference shown in the figure is the phase of a reference carrier wave, and means a reference phase when the phase of the carrier wave is advanced or delayed from this phase. However, how to take this reference phase is arbitrary. For convenience of the following description, numbers 0, 1, 2, 3,... Are given as transmission symbols to each set in units of N bits, and these are shown inside each unit circle.

PSK modulation is performed by the above method, but since this PSK modulated signal does not include information on the reference phase of the transmission side, it is transmitted to the reception side by some means, or the reception side does not know the reference phase. It must be able to demodulate.

As one method of transmitting the reference phase to the receiving side, differential code modulation has been conventionally used. Differential code modulation is modulation in which the phase of a transmission symbol one time slot before is used as a reference phase, and in which the reference phase changes. That is, a sum operation of a transmission symbol one time slot before and a transmission symbol to be transmitted next is performed by a ^2N- ary method, and this is transmitted as the next transmission symbol. on the other hand,
The receiving side uses the phase of the carrier received one time slot before as a reference, and reproduces the received data from the phase difference from the reference phase. That is, the received data is reproduced by calculating the difference between the received symbol and the received symbol one time slot before by the ^2N- ary method.

As an example, 4-phase PSK will be described. Four-phase PSK is
N is 2 and has four transmission symbols “00”, “01”, “11”, and “10” indicated by a 2-bit code, and performs 2 ^2, that is, sum and difference operation by the quaternary method. . FIG. 7A shows each transmission symbol.

When transmitting data “0101100111”, if this is divided into “01”, “01”, “10”, “01”, and “11” in 2-bit units, the transmission symbols “1”, “1”, “3”, “1”, 2 "corresponds.
Assuming that the transmission symbol one time slot before this data is, for example, “3”, in order to continue transmitting “1”, the phase of the transmission symbol “3” is used as a reference, and the transmission symbol “1” is used. A transmission symbol having a corresponding phase difference is transmitted. That is, the transmission symbol “3” one time slot before
Transmission symbol "0" (3 + 1 = 0) obtained by performing a quadrature operation on the transmission symbol "1" to be transmitted next and the transmission symbol "1" to be transmitted next
Becomes the next transmission symbol. Furthermore, when sending “1”,
The transmission symbol “1” (0 + 1 =
Transmit 1). In order to continuously transmit the transmission symbols “3”, “1”, and “2”, similarly, a sum operation is performed between the transmission symbol one time slot before and the reception side calculates the phase of the reception symbol and the time symbol one time slot before. A phase difference from the phase of the received symbol is obtained, and a transmission symbol corresponding to the phase difference is reproduced.
That is, the received data is reproduced by calculating the difference between the received symbol one time slot before and the quaternary method. For example, it is assumed that the symbol difference between transmission and reception due to the phase shift due to the reception timing is the result 3 of the difference calculation by the quaternary method. In this case, the previous transmission symbol “3” “0”
“1” “0” “1” “3” is “2” “3” “0” “3” “0” on the receiving side
Received in the order of “2”. These are differentially calculated with the received symbol one time slot before (3-2 = 1, 0-3 = 1,
3-0 = 3, 0-3 = 1, 2-0 = 2), the same "1", "1", "3", "1", and "2" as the transmission symbol are obtained. With this symbol, the original data “0101100111” before PSK modulation is reproduced.

However, when an error occurs in modulation and demodulation, for example, if the receiving side erroneously receives a transmission symbol in the order of “2” “3” “0” “0 (error)” “0” “2”, “1” “1” ",“ 0 (error) ”
The difference operation is performed with “0 (error)” and “2”, and the error expands to two time slots. Also, the data reproduced from this is “01
A two-bit error such as 010 (error) 000 (error) 11 "occurs. That is, the differential code modulation method has a disadvantage that if an error occurs in the transmission path, the error is enlarged by one time slot. There is a drawback in that the required C / N (carrier-to-noise power ratio) increases, and when combined with an error correction code, the error correction effect cannot be sufficiently obtained.

In order to solve this drawback, without using differential code modulation,
There is a modulation method for inserting a channel identification code into a modulation signal. The radio frame signal and the channel identification code are determined in advance on both the transmission side and the reception side, and the transmission side inserts the determined radio frame signal and the channel identification code at the beginning of transmission data and transmits the data. On the other hand, on the receiving side, the received data is reproduced by judging whether or not the demodulated signal is inverted from the radio frame signal, and judging the switching of the channel from the channel identification symbol.

FIG. 8 is a diagram for explaining a modulation and demodulation method when a channel identification code is inserted in 4-phase PSK.

Although the number of bits N of the 4-phase PSK is 2, for convenience of explanation,
The first bit of the data divided every two bits is one channel, and the second bit is two channels. “01101” is added as a radio frame signal for each channel. Also, “00” is used as the channel identification code of one channel,
It is assumed that “01” is added as a channel identification code of the channel. In this case, from FIG. 7A, the transmission symbols of the transmission data are "0", "2", "2", "0", "2", "0", and "3", which are PSK-modulated and transmitted.

On the receiving side, PSK demodulation is performed from the phase difference obtained by comparing with an arbitrarily determined reference phase. As a result of demodulation, it is assumed that received symbols “3”, “1”, “1”, “3”, “1”, “3”, and “2” are received in this order. Then, as shown in each channel of FIG. 8B, two channels are restored to “1001011” and one channel is restored to “0110101”. This is compared with a radio frame signal and a channel identification code that have been previously determined with the transmitting side. In channel 2, since the radio frame signal is inverted from “0” to “1” and “1” to “0”, when the channel identification code is inverted, “0” is returned.
The channel identification code is “01” because the radio frame signal is non-inverted, indicating two channels. Therefore, the received data following this is one channel. The demodulation can be performed by inverting all of the two channels to make one channel and changing one channel to two channels as it is.

Here, a total of four frame synchronization circuits for detecting a frame signal are used because it is necessary to determine inversion and non-inversion synchronization for two channels.

FIG. 9 is for explaining a method of modulation and demodulation when a channel identification code is inserted in 8-phase PSK.

As shown in FIG. 9A, the radio frame signal of each channel is “01101”, the channel identification code of one channel is “00”, the channel identification code of two channels is “01”, and the channel identification code of three channels Is assumed to be “11”. The transmission symbol in this case is “0” “5” from FIG. 7B.
"5", "0", "5", "3", "4" are transmitted.

Assuming that the receiving side receives the received symbols “2”, “7”, “7”, “2”, “7”, “5”, and “6” in order with respect to the arbitrarily set reference phase, each channel is shown in FIG. Is restored as shown in This is compared with a radio frame signal and a channel identification code agreed with the transmitting side as in the case of four phases. When the radio frame signal of channel 3 is inverted and the channel identification code is inverted, the channel identification code becomes "01", indicating channel 2. 2
The channel is a non-inverted radio frame signal, and the channel identification code is "11", indicating three channels. Also, one channel indicates one channel because the radio frame signal is inverted and the channel identification code is “00” when the inverted one is returned. Therefore, on the receiving side, the subsequent received data is 3
The demodulation can be performed by inverting all the channels, changing the two channels to three channels, changing the two channels to three channels, and inverting all the channels to one channel as it is.

The frame synchronization circuit in this case, like 4-phase PSK,
Since inversion / non-inversion synchronization determination is required for three channels, a total of six frame synchronization circuits are used.

However, the previous transmission symbol is converted to “2” “7” “7”
If not received in the order of “2” “7” “5” “6”, the channel identification code has no meaning as described below,
Demodulation cannot be performed.

FIG. 9C shows a case where the previous transmission symbol is received in the order of “3” “0” “0” “3” “0” “6” “7” with respect to the reference phase arbitrarily set on the receiving side. This shows a demodulated signal of each channel.

For the three channels, the radio frame signal is inverted, and the channel identification code is "11" when the inversion is reversed, indicating three channels. However, since the radio frame signals of two channels and one channel output completely different data from the radio frame signal decided on the transmitting side, it is not possible to distinguish between inverted and non-inverted, and the channel identification code has no meaning.

[Problems to be solved by the invention]

As described above, the conventional demodulator for demodulating a PSK-modulated wave has the following disadvantages.

That is, in the differential code modulation system, since a storage type operation for reproducing received data from information before one time slot is performed, if a transmission line error occurs, the error is enlarged by one time slot extra. there were.

The method of inserting the channel identification code has a drawback that the apparatus becomes large because 2N frame synchronization circuits for detecting a frame signal are required. Further, in the case of polyphase PSK in which N is 3 or more, there is a disadvantage that the channel identification code has no meaning and it becomes difficult to reproduce the received data.

Therefore, an object of the present invention is to make sure that errors do not increase and N is 2
An object of the present invention is to provide a demodulation device that can demodulate even the above-described polyphase PSK without increasing the size of the device.

[Means for solving the problem]

The demodulator of the present invention comprises: (i) a signal obtained by performing a summation operation by a ^2N- ary method except for a predetermined coded symbol in a frame signal having a length M indicated by a coded symbol of N bits; Signal receiving means for receiving a PSK modulated signal PSK-modulated to ^2N phases from a multiplexed signal obtained by multiplexing a transmission data signal transmitted as data, and (ii) PSK modulation received by the signal receiving means PSK demodulation means for demodulating a received symbol represented by an N-bit code from a signal;
(Iv) a difference arithmetic unit for calculating a difference of the received symbol demodulated by the PSK demodulation unit by a ^2N- ary method, and (iv) a frame signal detection unit for detecting a frame signal from a composite signal obtained by the calculation of the difference arithmetic unit. (V) a symbol difference estimator for estimating a symbol difference between transmission and reception from a predetermined reception symbol of the frame signal detected by the frame signal detector, and (vi) a symbol difference between transmission and reception estimated by the symbol difference estimator. Receiving data reproducing means for reproducing the received data by performing code conversion of the demodulated symbol sequence in accordance with (1).

That is, the present invention receives a frame signal determined in advance between transmission and reception, a signal transmitted by a modulation method, and performs a differential operation on the received signal on the receiving side, regardless of a symbol difference. , A frame signal is detected from the symbol.

On the other hand, a symbol difference between transmission and reception is estimated from a received symbol of a portion of the detected frame signal where no difference operation is performed on the transmission side, and the received data is reproduced according to the symbol difference.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 2 is a diagram showing a PS received by one embodiment of the demodulation device of the present invention.
FIG. 2 is a block diagram showing a configuration of a modulation device that transmits a K-modulated signal.

The modulation device 11 includes a frame signal generator 13. Frame signals 15a, 1 output from the frame signal generator 13
5b and 15c are summed by the frame timer 17 and the summing calculator 19 except for the first symbol. The coded frame signals 21a, 21b, and 21c that have undergone the sum operation in the sum operation unit 23 are supplied to the multiplexer 23. The multiplexer 23 multiplexes the coded frame signal 21 with the transmission data 25a, 25b, and 25c corresponding to each channel, and modulates the modulated signals 27a, 27b, and 27c with P.
Supply to SK modulator. The PSK modulator 29 performs ^2N- phase PSK modulation on the modulation signal 27, and sends out the PSK modulation signal 31 from the modulation device 11.

FIG. 1 is a block diagram showing a configuration of a demodulation device according to an embodiment of the present invention for demodulating a PSK modulation signal transmitted from the modulation device 11 of FIG.

The demodulation device 41 includes a PSK demodulation signal receiver 43 that receives the PSK modulation signal 31 transmitted from the modulation device 11, and a PSK demodulator 47 that performs phase detection on the received signal using the synchronization carrier 45 as a reference phase wave. I have. The difference calculator 49 is a PSK demodulator 47
Receive the demodulated signals 51a, 51b, and 51c from the multiplexed signal 53, and perform an octal difference operation on the symbols of the demodulated signal to obtain the decoded signal 53.
a, 53b and 53c are supplied to the frame detector 55. The frame detector 55 determines the synchronization of the frame signal from the decoded signal 53, and outputs the signal “1” as the synchronization signal 57 only when the frame signal is detected. The frame synchronization determination is performed with M−1, that is, 7 symbols, excluding the first symbol of the frame signal determined in advance between transmission and reception, as the verification target.

The demodulation device 41 also includes a symbol difference estimator 61. The symbol difference estimating unit 61 includes a delay circuit 63 for delaying the demodulated signal 51 by eight symbols, and a delay circuit 63 supplied from the delay circuit.
An arithmetic circuit 65 for calculating a symbol difference from the demodulated signal before the symbol and the synchronization signal 57 supplied from the frame detector 55
It is composed of The code modulator 69 reproduces the received data 71a, 71b, 71c from the demodulated signals 51a, 51b, 51c based on the symbol difference signals 67a, 67b, 67c output based on the symbol differences estimated by the calculator 65. ing.

Next, transmission and reception of data performed between the modulation device 11 configured as described above and the demodulation device 41 of the present embodiment will be described.

FIG. 3 shows a frame signal 15 determined in advance on both the transmitting side and the receiving side, and a demodulated signal output in a different synchronous state of a predetermined synchronous carrier 45.

The modulation device 11 performs N = 3 modulation, that is, 8-phase PSK modulation. The frame signal generator 13 outputs frame signals 15a, 15b, and 15c having an eight-symbol length indicated by three bits of three channels, two channels, and one channel, which are determined in advance between transmission and reception as shown in FIG. 3A. These frame signals 15
The first symbol is removed by the frame timer 17, and only the remaining seven symbols are summed by the sum operator 19 in octal with the coded symbol one time slot before. The coded frame signals 21a, 21b, and 21c after the addition operation output from the addition operation unit 19 are output from the multiplexer 23 by 25a, 25b, and 2
It is multiplexed with transmission data 25 indicated by 3 bits of 5c.
FIG. 3B shows the state after multiplexing. The multiplexed modulated signals 27a, 27b, and 27c are input to the PSK modulator 29, and the PSK modulated signal 31 is transmitted from the modulator 11.

FIG. 4 shows an 8-phase gray code, and shows a code arrangement of transmission symbols.

The PSK modulator 29 performs PSK modulation of the multiplexed modulated signal 27 according to the Gray code. The gray code shown in FIG. 4 corresponds to FIG. 7B, and may be erroneously detected as adjacent phases when detecting a phase.
It is a combination that requires only bit errors.
In the case of the four-phase system, it is desirable to use a Gray code corresponding to FIG. 7A.

A PSK modulation signal 31 modulated by the modulation device 11 shown in FIG.
Are received by the PSK modulation signal receiving device 43. This received signal 3
1 is phase-detected by the PSK demodulator 47 using the synchronous carrier 45 as a reference phase wave, and outputs demodulated signals 51a, 51b, 51c. The demodulated signals 51a, 51b, and 51c correspond to three-channel, two-channel, and one-channel signals, respectively. Synchronization carrier 45, 2 ^3, that is eight synchronous state exists with respect to PSK modulation signal 31 received, and outputs each different demodulated signals, respectively.

The transmission symbol “05277744” of FIG. 3B is transmitted from the modulation device 11 and is transmitted to the PSK modulation signal receiver 43 of the demodulation device 41.
In the received symbol by the PSK demodulator 47.
4 ". In this case, the demodulated signal 51 is shown in FIG.
As shown in FIG. Meanwhile, demodulator
Assuming that 41 receives “30522277” from the state of the received symbol 3, the demodulated signal 51 becomes as shown in FIG. 3D. In this case, each channel has a demodulated signal 51 different from the modulated signal 27.
Is output. Therefore, the signal is demodulated as follows.

In the difference calculator 49, the symbol of the demodulated signal 51 is
2 ^N , that is, an octal difference operation is performed, and a composite signal is calculated.
Output 53a, 53b, 53c. That is, the symbol “30522277” of the demodulated signal demodulated by the PSK demodulator 47 is used for the difference operation (3-X = Y, 0−3 = 5, 5−0 = 5, 2−5 = 5,
2-2 = 0, 2-2 = 0, 7-2 = 5, 7-7 = 0), and the symbol of the decoded signal is obtained as “Y5550050”. Here, the transmission data X received before the first symbol “3” of the demodulated signal is one of symbols 0 to 7. Therefore, Y is also an arbitrary value from 0 to 7.

FIG. 5 shows the relationship between the demodulated signal 51 and the composite signal 53 with respect to the symbol difference between transmission and reception when the PSK modulation signal receiver 43 receives the PSK modulation signal 31.

As shown in this figure, the decoded signal 53 after the difference operation by the difference operation unit 49 is the same as the frame signal in which all the symbols except the first symbol are determined regardless of the symbol difference between transmission and reception. Is the same. Therefore, the frame detector 55 takes in the demodulated signal “30522277” and outputs the first
A frame synchronization determination is performed with the remaining seven symbols excluding the th symbol as targets of frame detection. When a frame signal of 7 symbols is detected, the frame detector 55 outputs a synchronization signal.
57 is output to the computing unit 65.

The delay circuit 64 delays the demodulated signal by 8 symbols and computes
Supply to 49. That is, when the synchronization signal 57 is supplied to the arithmetic circuit 65 upon completion of the synchronization determination of the eighth symbol by the frame detector 55, the first symbol of the demodulated signal shown in FIG. It is supplied from the delay circuit 63. The arithmetic circuit 65 estimates the symbol difference between transmission and reception based on the symbol of the demodulated signal supplied from the delay circuit when the synchronization signal is received, that is, the first symbol of the received frame signal. The symbol difference between transmission and reception is calculated by performing an octal difference calculation between the first symbol of the frame signal supplied from the delay circuit and the first symbol of the frame signal determined in advance between transmission and reception. Estimate by However, when the first frame signal between transmission and reception is set to “0” as in the present embodiment, the symbol supplied from the delay circuit becomes the symbol difference between transmission and reception as it is. It becomes unnecessary.

FIG. 6 shows the reception data 71a, demodulated signals 51a, 51b, 51c.
7 shows a conversion table for conversion into 71b and 71c.

On the basis of the symbol difference between transmission and reception estimated by the arithmetic unit 65, the code converter 69 generates a demodulated signal 52 supplied from the PSK demodulator.
a, 52b, and 53c are code-converted and the received data 71a, 71b, and 71c are reproduced. The conversion table shown in FIG. 6 is stored in, for example, a ROM (Read Only Memory) not shown.

In the embodiment described above, the demodulation of data that has been subjected to PSK modulation in eight phases has been described. However, the demodulation can be similarly performed in the case of four phases.

Further, in the above-described embodiment, the frame signal is set to “0550050” by a symbol, but the content of the frame signal, its length, and the multiplexing method are not particularly limited.
Further, the length of one frame is also arbitrary, and is determined in advance on both the transmitting side and the receiving side together with the radio frame signal and the multiplexing method.

〔The invention's effect〕

As described above, according to the present invention, even when data is erroneously received, high-quality reception can be performed without expanding the error.
Therefore, it is particularly effective when data is transmitted on a transmission line with a lot of noise, etc., and when the error correction is added, consideration is given to the reduction of the coding gain of the error correction due to the combined use of the differential encoder and the error correction encoder. Becomes unnecessary, and a coding gain close to an ideal state is obtained.

Further, it is possible to demodulate a PSK modulated signal not only when N is 2 but also when it is 3 or more.

Furthermore, a single frame synchronization circuit is required for the frame detection circuit, and the code converter does not require complicated calculations, and can be easily handled by table conversion using a ROM or the like. The increase is extremely small. Therefore, since the device can be downsized, it is suitable for a semi-fixed demodulator.

[Brief description of the drawings]

FIGS. 1 to 6 are diagrams for explaining an embodiment of the present invention. Among them, FIG. 1 shows an embodiment of the present invention for demodulating a signal which has been subjected to 8-phase PSK modulation by a transmitter. FIG. 2 is a block diagram of a modulator that performs 8-phase PSK modulation, and FIG. 3 is a block diagram of a frame signal predetermined on both the transmitting side and the receiving side, and a predetermined synchronous carrier. FIG. 4 is a diagram showing a demodulated signal demodulated in different synchronization states based on FIG. 4, FIG. 4 is a diagram showing an 8-phase gray code,
FIG. 5 is a correspondence diagram showing a relationship between a demodulated signal and a composite signal with respect to a symbol difference between transmission and reception when a PSK modulated signal is received by a PSK modulated signal receiver, and FIG. 6 converts the demodulated signal into received data. FIG. 7 to FIG. 9 are diagrams for explaining the prior art, and FIG. 7 shows a four-phase system in which the difference in the system due to the difference in phase change is shown in FIG.
FIG. 8 is a diagram showing a phase equation, FIG. 8 is a diagram showing a modulation and demodulation method when a channel identification code is inserted in 4-phase PSK, and FIG. 9 is a modulation when a channel identification code is inserted in 8-phase PSK. FIG. 4 is a diagram illustrating a demodulation method. 41 demodulator, 43 PSK modulated signal receiver, 45 synchronous carrier, 47 PSK demodulator, 49 difference calculator 55
... frame detector, 61 ... symbol difference estimator, 69 ... code converter.

Claims (1)

(57) [Claims] 1. A signal subjected to a sum operation by a ^2N- ary method except for a predetermined coded symbol in a frame signal of length M indicated by a coded symbol of N bits, and transmitted as data. shown a transmission data signal and the signal receiving means for receiving a PSK modulated PSK modulated signal from the multiplexed multiplexed signal to the 2 ^N phase, in N-bit code from the PSK modulation signal received by the signal receiving means PSK demodulation means for demodulating a received symbol; a difference arithmetic unit for calculating a difference of the received symbol demodulated by the PSK demodulation means in a ^2N- ary system; and a frame signal obtained from a decoded signal obtained by the arithmetic operation of the difference arithmetic unit. And a symbol difference estimator for estimating a symbol difference between transmission and reception from the predetermined reception symbol of the frame signal detected by the frame signal detector. A demodulation device characterized in that the demodulation device further comprises: a received data reproducing unit that reproduces received data by performing code conversion of a demodulated symbol sequence according to the symbol difference between transmission and reception estimated by the symbol difference estimating unit.