JPH02272943A - Demodulator - Google Patents

Abstract

PURPOSE:To prevent an error from being enlarged even when the error is generated in a transmission line by detecting a frame signal determined in advance between transmission and reception, calculating symbol difference between the transmission and reception from the detected frame signal and reproducing received data according to this symbol difference. CONSTITUTION:A frame detector 41 executes the synchronization decision of the frame signal, which is determined in advance between the transmission and reception, from a demodulation signal 39 and only when the frame signal is detected, a signal '1' is supplied to a computing element 43 as a frame synchronizing signal 47. The computing element 43 estimates the symbol difference between the transmission and reception from the frame synchronizing signal 47 and the symbol train of a signal inputted to each shift register and supplies symbol difference signals 49a-49c to a code converter 45. The code converter 49 executes the code conversion of the demodulation signal 39 based on the symbol difference signal. Then, received data 51a-51c are reproduced. Thus, even when the data are erroneously received, the error is not enlarged but the data can be received with high quality.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides 2) PSK on the l phase according to the agreement between the transmitter and the receiver.
The present invention relates to a demodulator that demodulates a modulated wave.

[Conventional technology]

Among the methods of digitally modulating and transmitting data, PSK (Phase 5hi
ft Keying) modulation method. This is a method in which transmitted data is modulated by changing the phase of a carrier wave. That is, when data to be transmitted is divided into groups of N bits each, there are 2N types of values that each group can take. For example, each combination of N=2 bits is “00”
There are four types: "01", "11", and "10". These N-bit information are transmitted by being assigned one-to-one to each of 2) one type of carrier wave whose phase differs from the reference phase.

Therefore, a large amount of information can be transmitted simultaneously with one modulation, that is, one phase change. That is, the transmission signal is converted into an N-channel code string divided into N bits, modulated to a phase corresponding to this code string, and transmitted. On the receiving side, the received symbol is demodulated by detecting the phase state of the received signal with respect to the reference phase.

Figure 7 shows the differences in methods due to differences in phase change: 4-phase type, 8-phase type,
This shows the phase equation. FIG. 7 Δ shows a four-phase type, and FIG. 7 B shows an eight-phase type.

The circle shown in this figure indicates the unit circle drawn by the end point of the unit vector when the phase of each carrier wave corresponding to each data in units of N bits is expressed by a unit vector. The numbers expressed on the outer periphery of this unit circle are data for each set of N focus units. In FIG. 7A, there is a phase difference of 2π/2', that is, 90°, between adjacent data, and in FIG. 7B, there is a 45° phase difference. The reference shown in the figure refers to the phase of a carrier wave that serves as a reference, and means the reference phase for determining how many times the phase of a general transmission wave is advanced or delayed from this phase.

However, how this reference phase is determined is arbitrary.

For convenience of explanation below, numbers 0, ■, 2.3, etc. are used as transmission symbols for each set of N bits.
... is given and shown inside each unit circle.

PSK modulation is performed using the method described above, but since this PSK modulated signal does not include information regarding the reference phase on the transmitting side, it must be transmitted to the receiving side by some means, or the receiving side must be able to determine the reference phase. It is necessary to be able to demodulate without knowing it.

Differential code modulation has been conventionally used as one method of transmitting the reference phase to the receiving side. Differential code modulation is a modulation in which the phase of a transmission symbol one time slot before is used as a reference phase, and the reference phase is changed. That is, the sum of the transmission symbol one time slot before and the transmission symbol to be transmitted next is calculated using the 2N system, and this is transmitted as the next transmission symbol. on the other hand,
On the receiving side, the position of the carrier wave received one time slot before is used as a reference, and the received data is reproduced from the phase difference with this reference phase. That is, the received data is reproduced by calculating the difference between the received symbol and the received symbol for one time slot using the binary system.

As an example, four-phase PSK will be explained. In 4-phase PSK, N is 2 and has four transmission symbols "00", "01", "11", and "10" indicated by a 2-bit code, and 22
That is, it performs summation and difference calculations using the quaternary system. Each transmission symbol follows FIG. 7A.

When sending data ``0101100111'',
Write this in 2-bit units as “01”01”10”01”11
”, the transmission symbols are “1”, “1”, and “3” respectively.
1"2" corresponds. For example, if the transmit symbol one time slot before this data was "3", in order to continue transmitting "1", the phase of transmit symbol "3" is used as a reference, and the phase of transmit symbol "1" is used as a reference. Transmit transmission symbols with corresponding phase differences. In other words, the transmission symbol "0" (3+1=O), which is found by performing a quaternary summation operation of the transmission symbol a3'' from one time slot before and the transmission symbol "1'" to be transmitted next, is the next transmission symbol. becomes. When further transmitting "l", the transmission symbol "1" (0+1=1) is transmitted by summation operation with "0". To continue sending the transmitted symbols "3"1"2", a summation operation is similarly performed between the transmitted symbols one time slot before, and on the receiving side, the phase of the received symbol and 1 are calculated.
The phase difference with the phase of the received symbol before the time slot is determined, and the transmitted symbol corresponding to this phase difference is reproduced. That is, the received data is reproduced by performing a difference calculation using a quaternary system with the received symbol one time front ago.

For example, assume that the symbol difference between transmission and reception due to a phase shift due to reception timing is 3 as a result of difference calculation using the quaternary system. In this case, the previous transmitted symbol “3”0”1”
0"1"3" are received on the receiving side in the order of "2"3"0"3"0""2".These are received by the received symbol one time slot before and the difference calculation (3-2=1.0- 3=1
．． 3-0=3.0-3=1.2-02), the same "1"■""3"1"2"' as the transmission symbol is obtained. This symbol allows the data "0101" before PSKS submodulation to be obtained.
100111” is played.

However, if an error occurs during modulation and demodulation, for example, the receiving side may change the transmitted symbol to "2"3""0" 0 (error) "0"'2
”, the difference is calculated as “1” 1” 0 (error) “0 (error)” “2”, and the error expands to 2 time slots. Also, the data reproduced from this will be “01010 ( Error) 000 (Error) 11
In other words, the differential code modulation method has the disadvantage that when an error occurs in the transmission path, the error increases by one time slot, and the required C/N (carrier pair Furthermore, when combined with an error correction code, the error correction effect cannot be fully exploited.

As a method to overcome this drawback, there is a modulation method that does not use differential code modulation and inserts a channel identification code into the modulated signal.

A radio frame signal and a channel identification code are determined in advance on both the transmitting side and the receiving side, and the transmitting side inserts the determined radio frame signal and 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 determining whether the demodulated signal is inverted from the radio frame signal and by determining whether the channel has changed from the channel identification symbol.

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

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

On the receiving side, PSK demodulation is performed based on the monthly difference by comparing it with an arbitrarily determined reference phase. Assume that as a result of demodulation, received symbols are received in the order of "3"l"1"3"1"3"2". Then, as shown in each channel of FIG. 8B, the 2nd channel is “100101
1” 1 channel is restored as “0110101”.

This is compared with the radio frame signal and channel identification code agreed upon in advance with the transmitting side. For 2 channels, the radio frame signal changes from “0” to “1” and from “1” to “0”.
Since the channel identification code is inverted, when the channel identification code is reversed, it becomes "00", indicating channel 1. Also, since the radio frame signal for channel 1 is not inverted, the channel identification code is "01" as it is, indicating channel 2. Therefore, subsequent received data can be demodulated by inverting all two channels to become the L channel, and by making the first channel into the second channel.

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

As shown in FIG. 9, the radio frame signal of each channel is "01101", the channel identification code of channel 1 is "00", and the channel identification code of channel 2 is "0".
Assume that the channel identification codes for channels 1 and 3 are set to 11. In this case, the transmitted symbols are 0, 5, 5, 0, 5, 3, and 4 from Figure 7B. Transmit.

On the receiving side, if the received symbols are received in the order of "2", "7", "7", "5n", and "6" with respect to the arbitrarily set reference phase, each channel is restored as shown in Figure 9. Similar to the four-phase case, this is compared with the radio frame signal and channel identification code agreed upon with the transmitting side.

For channel 3, the radio frame signal is inverted, and when reversed, the channel identification code becomes 01, indicating channel 2.For channel 2, the radio frame signal is not inverted, and the channel identification code is "11", indicating channel 3. Also, 1 channel indicates 1 channel because the radio frame signal is inverted and the channel identification code is "00" when reversed. Demodulation can be performed by inverting all the channels to make 2 channels, by inverting all the 2 channels to make 3 channels, and by inverting all the 1 channels to make 1 channel.

However, the previous transmitted symbol is "2""7" 7 on the receiving side.
If the channel identification codes are not received in the order of 2"7"5"6", the channel identification codes will have no meaning and demodulation will no longer be possible, as will be explained below.

In Fig. 9C, the previous transmitted symbol is “3” 0” 0” “3” “0” with respect to the reference phase arbitrarily set on the receiving side.
This shows the demodulated signals of each channel when received in the order of "6" and "7".

For channel 3, the radio frame signal is inverted, and when the channel identification code is reversed, it becomes "11", indicating channel 3. However, since 2-channel and 1-channel radio frame signals output data completely different from the radio frame signal agreed upon with the transmitting side, it is impossible to distinguish between inverted and non-inverted signals, and therefore the channel identification code has no meaning.

[Problem to be solved by the invention]

'As explained above, the conventional demodulator for demodulating a PSK modulated wave has the following drawbacks.

The differential code modulation method performs storage-type calculations that reproduce received data from information from one time slot 7) before, so if an error occurs in the transmission path, the error increases by one time slot 7). Ta.

The method of inserting a channel identification code has the drawback that it requires 2N frame synchronization circuits for detecting frame signals, resulting in an increase in the size of the device. Also, N
In polyphase PSK where is 3 or more, the channel identification code has no meaning, making it difficult to reproduce the received data.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a demodulation device that does not increase errors and can demodulate even polyphase PSK in which N is 2 or more without increasing the size of the device.

[Means to solve the problem]

The demodulation device of the present invention provides (i) a multiplexed signal obtained by multiplexing a frame signal with a length of M symbols and a transmission data signal transmitted as data, which is indicated by an N-bit encoded symbol agreed upon in advance between the transmitter and the receiver; PS to 2N phases from
(ii) a signal receiving means for receiving a K-modulated PSK modulated signal; (ii) a PSK demodulating means for demodulating a received symbol represented by an N-bit code from the PSK modulated signal received by the signal receiving means; (iii) this PSK. (iv) a frame signal detection means for detecting a frame signal from the received symbol string demodulated by the demodulation means; and (iv) a symbol for estimating the symbol difference between transmission and reception from the symbol string of the frame signal detected by the frame signal detection means. A difference estimation means, (
v) Received data reproducing means for reproducing received data by code-converting the demodulated symbol string according to the symbol difference between transmitting and receiving estimated by the symbol difference estimating means.

That is, the present invention detects a frame signal agreed upon in advance between the transmitter and the receiver, determines a symbol difference between the transmitter and the receiver from the detected frame signal, and reproduces received data according to this symbol difference.

:Example〕 Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 2 shows the PS received by an embodiment of the demodulator of the present invention.
The configuration of a modulation device that transmits a K-modulated signal is shown in blocks.

The modulation device 11 includes a frame signal generator 13.

The frame signal generator 13 supplies the multiplexer 17 with frame signals 15a, 15b, and 15c determined in advance between the transmitter and the receiver. The multiplexer 17 transmits transmission data 19a, 1.9b, 19
Frame signals 13a, 13 correspond to each channel of C.
b, 13C and modulated signals 21a, 21b, 21
C is supplied to the PSK modulator 23. The PSK modulator 23 performs 2N-phase PSK modulation on the modulation signal 21, and outputs a PSK modulation signal 25 from the modulation device ll.

FIG. 1 is a block diagram showing the configuration of a demodulation device according to an embodiment of the present invention, which demodulates the PSK modulated signal 25 sent out from the modulation device 11 shown in FIG.

The demodulation device 31 includes a PSK demodulation signal receiver 33 that receives the PSK modulation signal 25 sent out from the modulation device 11, and a PSK demodulator 37 that performs phase detection of the received signal using the synchronous carrier wave 35 as a reference phase wave. There is. Demodulated signals 39a, 39b, and 39c output from the PSK demodulator 37 are sent to a frame detector 41, an arithmetic unit 43, and a code converter 45.
is being supplied to.

The frame detector 41 determines synchronization of the frame signal from the demodulated signal 39 using a frame synchronization circuit (not shown), and supplies a signal "1" to the calculator 43 as a frame synchronization signal 47 only when a frame signal is detected. Arithmetic unit 4
3 is provided with N shift registers (not shown) each having the same number of digits as the frame signal length, that is, three 7-digit shift registers, into which the demodulated signal 39 is sequentially input manually.

The computing unit 43 estimates the symbol difference between transmitting and receiving from the frame synchronization signal 47 and the symbol string of the signal manually input to each shift register (not shown), and generates symbol difference signals 49a,
4.9b and 49C are supplied to the code converter 45. The code converter 45 converts the code of the demodulated signal 39 based on the symbol difference signal, and converts the code of the demodulated signal 39 into received data 51a, 51b.
, 51C.

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

FIG. 3 shows demodulated signals output in different synchronization states of a frame signal 15 and a predetermined synchronized carrier wave 45 determined in advance on both the transmitting side and the receiving side.

The modulation device 11 performs modulation where N is 3, that is, 8-phase PSK modulation. The frame signal generator 13 generates a transmission symbol ``2226626'' with a length of 7 symbols agreed upon between the transmitter and the receiver in advance.
” corresponding to each channel, frame signals 15a, 15
b, output as 15C. These frame signals 15a
, 15b, 15C are connected to 19a, 19b, 1 by the multiplexer 17.
The modulated signal 21 is multiplexed with the transmission data 19 indicated by 3 pins of 9C, and the modulated signal 21 after multiplexing is shown in FIG. 3A.

The modulated signal 21 is input to the PSK modulator 29, and the PSK modulated signal 25 is sent out from the modulation device 11.

FIG. 4 shows an 8-digit Gray code and shows the code arrangement of transmission symbols.

PSK modulator 23 performs PSK modulation of multiplexed modulated signal 21 according to this Gray code. This Gray code corresponds to the one shown in FIG. 7, and since there is a possibility of erroneously detecting adjacent phases when detecting phases, the combination is such that even if a mistake occurs, only a 1-bit error will occur. In addition, in the case of a four-digit system, it is desirable to use a Gray code corresponding to FIG. 7A.

A PSK modulated signal 25 modulated by the modulating device 11 shown in FIG. 1 is received by a PSK modulated signal receiving device 33. The received PSK modulated signal 25 is phase-detected by a PSK demodulator 37 using the synchronous carrier wave 35 as a reference phase wave, and the demodulated signal 3
9a, 39b, and 39C are output. This demodulated signal 39a
, 39b, and 39C correspond to 3-channel, 2-channel, and ■-channel signals, respectively. The synchronous carrier wave 35 has 23, ie, 8, synchronous states with respect to the received PSK modulated signal 25, and each outputs a different demodulated signal.

Assume that the transmission symbol "2226626" to FIG. 3 is transmitted from the modulation device 11, received by the PSK modulated signal receiver 33 of the demodulation device 31, and demodulated by the PSK demodulator 37 as the received symbol "2226626". In this case, the demodulated signal 39 becomes the same as the modulated signal 21, as shown in FIG.

On the other hand, the demodulator 31 changes from the state of received symbol 5 to “55”.
51151", the demodulated signal 39 is the third
It becomes like a plan. In this case, a demodulated signal 39 different from the modulated signal 21 is output from each channel. Therefore, the signal is demodulated as follows.

That is, a specific frame pattern is always output to one of the channels of the frame signal demodulated by the PSK IX modulator 37. For example, if the frame signal is a symbol of "2226626", either the 3rd channel or 2nd channel includes a signal of "1110010" or its inverted signal "0001101". Third
As shown in Figure C, the received symbol is “5551151”
If received, 111 is sent to channels 3 and 2.
A frame pattern of "0010" is output.

Therefore, in the frame detector 41, a frame synchronization circuit (not shown) detects a frame signal by synchronizing the frame patterns included in the 3-channel demodulated signal 39a and the 2-channel demodulated signal 39b. Upon detecting a frame signal, the frame detector 41 supplies a frame synchronization signal 47 to the arithmetic unit.

FIG. 5 shows the relationship between the symbol sequence of the demodulated signal 39 and the symbol difference between transmission and reception for a frame signal.

In the arithmetic unit 43, demodulated signals 39a, 39b, and 39c are sequentially input to each of three shift registers (not shown) each consisting of seven digits. When the frame synchronization signal 47 is supplied from the frame detector 41, the arithmetic unit 43 outputs in parallel the demodulated signal 39 input to a shift register (not shown). Since the signals output from each shift register correspond to frame signals 15a, 15b, and 15c, the symbol difference between transmitting and receiving is determined by comparing the symbols with the table shown in FIG. 5, etc. Arithmetic unit 43 supplies symbol difference signals 49a, 49b, and 49C to code converter 45 according to the determined symbol difference. The conversion table shown in FIG.
Memory).

The code converter 45 converts the codes of the demodulated signals 52a, 52b, 53C supplied from the PSK demodulator based on the symbol difference signal 49 supplied from the arithmetic unit 43 according to the conversion table shown in FIG. la, 5 lb,
Play 51c. The conversion table shown in FIG. 6 is stored, for example, in a ROM 1 (not shown).

In this way, in this embodiment, the frame signal is
26'', there is no need for a frame synchronization circuit for determining synchronization of inversion and ratio inversion for all channels.

That is, the frame synchronization circuit of the frame detector 41 is
The advantage is that only four are needed to detect two frame patterns for one channel.

In the embodiment described above, the demodulation of data subjected to PSK modulation in 8 phases has been explained, but demodulation can be similarly performed in other cases, for example, in the case of 4 phases.

In addition, in the embodiment described above, the frame signal is
6626'', but the content and length of the frame signal and the multiplexing method are not particularly limited.The length of one frame is also arbitrary, and the transmitting side as well as the wireless frame signal and the multiplexing method are not limited. This is determined in advance by both the receiver and receiver.For example, "246462" may be used as the frame signal.In this case, the frame pattern to be synchronized by the frame synchronization circuit of the frame detector is "110101" and "246462". This is the inverted signal, and is detected in the 3rd channel and the 2nd channel.

Further, when the frame signal is "1735175", the frame pattern is "0011001" and its inverted signal, and is detected from the 3rd channel and the 2nd channel.

Furthermore, in the arithmetic unit, the demodulated signal for determining the symbol difference between transmission and reception was manually input to three 7-digit shift registers, but the present invention is not limited to this, and for example, a RAM (Random Access (memory).

〔Effect of the invention〕

As described above, according to the present invention, even if data is received in error, it can be received with high quality without amplifying the error. Therefore, it is particularly effective when transmitting data over a transmission path with a lot of noise, etc., and when error correction is added, it can be used in combination with a differential encoder and an error correction encoder to reduce the coding gain of error correction. No consideration is required, and the coding gain is close to the ideal state.

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

Furthermore, since the code converter does not require complicated calculations and can be easily handled by table conversion using a ROM or the like, the number of circuits and parts increases very little. Therefore, since the device can be miniaturized, it is suitable for a semi-fixed type demodulator.

[Brief explanation of drawings]

1 to 6 are for explaining an embodiment of the present invention, and FIG. 1 shows an embodiment of the present invention in which a signal that has been subjected to 8-phase PSK modulation in a transmitting device is demodulated. Figure 2 is a block diagram of a modulator that performs 8-phase PSK modulation, and Figure 3 is a block diagram of a demodulator that performs 8-phase PSK modulation. Fig. 4 is a diagram showing the demodulated signal demodulated in different synchronization states based on the frame. 6 is a diagram showing a conversion table for converting a demodulated signal into received data, and FIGS. 7 to 9 are diagrams for explaining the conventional technology. The figure shows the difference in methods due to differences in phase change for 4-phase and 8-phase systems. Figure 8 shows the modulation and demodulation method when a channel identification code is inserted in 4-phase PSK. FIG. 9 is a diagram showing a modulation and demodulation method when a channel identification code is inserted in 8-phase PSK. 31... Demodulator, 33... PSK modulated signal receiver, 35...
...Synchronized carrier wave, 37...PSK demodulator, 41
... Frame detector, 43 ... Arithmetic unit, 45 ... Code converter.

Claims (1)

[Claims] 2^N from a multiplexed signal obtained by multiplexing a frame signal with a length of M symbols indicated by N-bit encoded symbols prearranged between the transmitter and receiver and a transmission data signal transmitted as data. a signal receiving means for receiving a PSK modulated signal that has been PSK-modulated into phases; a PSK demodulating means for demodulating a received symbol represented by an N-bit code from the PSK modulated signal received by the signal receiving means; and this PSK demodulating means a frame signal detecting means for detecting a frame signal from a received symbol string demodulated by the frame signal detecting means; a symbol difference estimating means for estimating a symbol difference between transmission and reception from the symbol string of the frame signal detected by the frame signal detecting means; 1. A demodulation device comprising: received data reproducing means for reproducing received data by code-converting a demodulated symbol string according to the symbol difference between transmission and reception estimated by the difference estimating means.