JP2571122B2 - Manchester M-sequence code modulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator for spread spectrum (SS) communication, in particular, to code shift keying (Code Shift Keying).
Keying = CSK).

2. Description of the Related Art In addition to satellite communication, mobile communication, and the like, the SS communication method has also been applied to power line communication. The conventional SS communication system will be described with reference to FIGS. 5 and 6. On the transmitting side, the output a of the PN (pseudo noise) code sequence generator 1 is subjected to an EX-OR operation by the EX-OR circuit 2 with the transmission data b (signal c).
The signal is transmitted to the transmission line by the amplifier 3 as a transmission signal. On the receiving side, the received signal is amplified by the amplifier 4 and then synchronized by the correlator 6.
Correlate with the output d of the PN code sequence generator 5, compare the correlation value (signal e) with a predetermined threshold in the comparator 7,
Is demodulated.

The transmission path may be a wireless, wired, or other transmission medium. Therefore, in many cases, the transmission signal is not only sent directly to the transmission medium, but also converted into a signal suitable for transmitting the transmission medium and sent. Also, power line communication requires an interface that is separated from commercial power. In the following, a connection section with a transmission medium that performs such signal conversion and separation functions is referred to as a reception interface or a transmission interface.

Problems to be Solved by the Invention In the conventional communication system, the PN sequence generated by the synchronous PN code sequence generator 5 on the receiving side must be synchronized with the PN sequence on the transmitting side. There is a need to. If there is no problem in the transmission characteristics of the transmission path, a peak is detected in the correlation waveform at the synchronization point. However, in the case of transmission lines with extremely poor transmission characteristics, such as power line communication, and in which there is a dip point in the transmission band, the correlation waveform deteriorates, and the positive / negative relationship of the correlation values is reversed, and the data 1 , 0 error. Further, there is a disadvantage that synchronization cannot be maintained due to deterioration of the waveform.

The present invention is to provide a modulator for a novel CSK communication system which overcomes the above-mentioned disadvantages of the conventional SS communication system.

Means for Solving the Problems A Manchester M-sequence code modulation device according to the present invention comprises:
First and second Manchester M-sequence generators each generating two Manchester M-sequences having the same code length with a low cross-correlation at a constant period, and generating a clock signal commonly driving the two Manchester M-sequence generators. A clock generation circuit, a phase synchronization circuit for detecting a specific phase of the first Manchester M-sequence generator, and setting a predetermined initial phase in the second Manchester M-sequence generator at the time of the detection; One of the transmission data
Or the first or second Manchester M according to 0
A switching circuit is provided for selecting one of the output signals of the sequence generator and transmitting it as a transmission signal.

The first and second Manchester M-sequence generators each include a plurality of shift registers driven by the clock signal, a feedback circuit for feeding back an output of a predetermined stage of the shift register to an input thereof, and the shift register. , And an exclusive-OR circuit which receives the output of the last stage and the clock signal as inputs. The first Manchester M-sequence generator and the second Manchester M-sequence generator feed back to the input by the feedback circuit. The stage of the shift register is different.

The exclusive OR circuit may be used as both the first Manchester M-sequence generator and the second Manchester M-sequence generator, and may be connected to the output side of the switching circuit.

CSK (Code Shift Keying) means that two low-cross-correlation binary PN code sequences of the same code length (including M sequence and Manchester M sequence) correspond to transmission data 1 and 0, respectively. It refers to a modulation method for transmitting one of the PN code sequences accordingly. This concept of CSK will become more apparent from the entire specification.

The M sequence refers to a code sequence having the maximum period among various code sequences that can be generated using a plurality of stages of shift registers and a linear operation circuit. When an n-stage shift register is used, the length of the generated M sequence is given by 2 ⁿ -1 bits.

The Manchester code is a code format in which one cycle of a rectangular wave having a specific phase is assigned to 1 of an input binary signal, and one cycle of an opposite phase is assigned to 0 of an input binary signal.

The first step including a multi-stage shift resist and its feedback circuit
When the M-sequence of the Manchester M-sequence generator reaches a specific phase, a predetermined initial phase is set in the second Manchester M-sequence generator having a similar configuration, so that these two Manchester M-sequence generators have the same phase. The sequence generator generates M sequences different from each other at a fixed cycle. The output signal of the first or second Manchester M-sequence generator is selected by the switching circuit in accordance with 1 or 0 of the transmission data and transmitted as a transmission signal at every predetermined period. As a result, CSK
The modulated transmission signal is sent out to a transmission path or a transmission medium.

1. Embodiment FIG. 1 shows an overall configuration of a CSK communication system using a Manchester code M sequence.

On the transmitting side, the modulation device (transmitted signal) 11 is provided with two Manchester M-sequence generators 31 and 32 for synchronizing and generating Manchester M-sequences having low correlation and the same code length, respectively. Is output to the switching circuit 33. The switching circuit 33 is controlled according to the binary transmission data (1 or 0). For example, when the transmission data is 0, the code output of the generator 31 is selected, and when the transmission data is 1, the code output of the generator 32 is selected. This switching circuit 33
Is the transmission signal TXO. The switching control in the switching circuit 33 is performed in synchronization with the cycle of the generated Manchester code M sequence, and one binary data (1 or 0) is represented by one cycle of the Manchester code M sequence.

Since the switching or selection of two different Manchester code M sequences is performed according to the code (1 or 0) of the data to be transmitted, this modulation method is called code shift keying (CSK).

The transmission signal TXO is transmitted to a transmission path or a transmission medium via the transmission interface 12A. Transmission interface 12A
As shown in the section of "Prior Art", is a connection part in a broad sense, and is a part for performing carrier modulation or mixing processing to a power line.

The receiving interface 12B also performs carrier demodulation, separation from a power line, A / D conversion, and the like, and converts a signal input from a transmission line or a transmission medium into a digital reception signal RXI and outputs the signal.

The receiver on the receiving side has two correlators 21 and 22 and a demodulator 2
3, a carrier detection circuit 24, a synchronization control circuit 25, and the like. The digital reception signal RXI output from the reception interface 12B is branched into two and input to the correlators 21 and 22, respectively. In one correlator 21, a Manchester code M sequence generated from one Manchester M sequence generator 31 is set, and a correlation between this set sequence and the received signal RXI is obtained. Similarly, a Manchester code M sequence generated from the other Manchester M sequence generator 32 is set in the other correlator 22, and the set sequence is correlated with the received signal RXI. Correlation outputs obtained from these correlators 21 and 22 are provided to a demodulation device 23, where a demodulation signal 1 or 0 is assigned according to the correlation value, and output as reception data RXD. That is, correlators 21 and 22
When the correlator 21 has a larger correlation peak value, the received data of 0 is received. When the correlator 22 has a larger correlation peak value, the received data of 1 is obtained. Data is generated respectively.

The correlation output is also input to a carrier detection circuit 24 and a synchronization control circuit 25. The carrier detection circuit 24 detects the presence or absence of a carrier based on the correlation output, and supplies the detection signal to the synchronization control circuit 25. The presence or absence of the carrier is used to determine whether or not the received signal RXI is being received. When a carrier is detected, the synchronization control circuit 25 generates a timing signal for demodulation and carrier detection based on the correlation output, and generates a demodulation device 23 and a carrier detection circuit.
Give 24.

As described above, in the CSK communication system, the two correlation outputs are compared on the receiving side, and the 0 of the received data is determined according to the magnitude of the correlation output.
Alternatively, since 1 is assigned, the Manchester M sequence on the receiving side does not need to be strictly synchronized with that on the transmitting side, and no data demodulation error occurs. Further, if an absolute value is taken as the output of the correlator, no error occurs even in the case of a transmission line having characteristic deterioration such that the transmission peak value is negative. Further, by using the Manchester code M sequence, it is possible to reduce the low-frequency component of the received signal and suppress the coupling loss with the transmission line.

FIG. 2 shows a specific configuration example of the CSK modulation device 11. FIG. 3 shows the output signal waveform of each part of this circuit.

Shift register FF ₁₁ to ff ₁₃ of each Manchester M series generator 31, 32 3 stages in this example _{(n = 3), FF 21} ~FF
₂₃ , these shift registers are clock generators 34
The data shift operation is performed at the timing of the clock signal CK output from. The feedback circuits of these shift registers are different from each other. That is, the shift register FF ₁₁
In to ff _13, while the sign of the second stage and the cell of the third stage is fed back to the input side through the exclusive OR circuit (EX-OR) 31a, the shift register FF ₂₁ to ff ₂₃ In the figure, the signs of the cells in the first and third stages are fed back via the EX-OR 32a. The shift register and its feedback circuit are an M-sequence generator (PN
Code generator, PN code = Pseude Noise Code = pseudo noise code). Then, the exclusive OR of the code output of the last stage of each shift register and the clock signal CK is taken by the EX-OR circuits 37 and 38, respectively, to create a Manchester code.

A phase synchronization circuit is provided so that the other Manchester M-sequence generator 32 always has a constant phase (initial phase) when one Manchester M-sequence generator 31 has a specific phase (all 1s). This phase synchronization circuit includes a NAND circuit 36 and an initial phase setting unit 35. Initial phase setting device 35 is for setting an initial code in each stage of the shift register FF ₂₁ ~FF _23, it can be set to any code. Shift register
L level signal is generated from the FF ₁₁ to ff all when the code becomes 1 stage (this state is caused once a period T of the Manchester code M series) NAND circuit 36 of the _13, clock code next set in the initial phase setting device 35 at the time of the rising edge of the signal CK is respectively loaded into each stage of the shift register FF ₂₁ ~FF _23.

As described above, the outputs of the Manchester M-sequence generators 31 and 32, that is, the outputs of the EX-OR circuits 37 and 38, are supplied to the switching circuit 33, and the transmission data TXD outputs one cycle (data section) T of the Manchester code M-sequence. A switching operation is performed.
The output of the NAND circuit 36 is provided to a transmission data processing unit (for example, a microprocessor) as a transmission request signal.
The transmission data processing section outputs one bit (1 or 0) of the transmission data TXD every time this transmission request signal is input, and gives it to the switching circuit 33.

FIG. 4 shows a modification. Compared to Fig. 2,
The EX-OR circuits 37 and 38 are removed from the Manchester M-sequence generators 31 and 32, respectively. Instead, the output of the switching circuit 33 and the clock signal CK are input to the output side of the switching circuit 33.
An EX-OR circuit 39 is provided, and a Manchester code is created. Reference numerals 31A and 32A indicate M-sequence generators, respectively.
These outputs (signs of the last stage of the shift register) are given to the switching circuit 33, respectively. This variant is
This has the advantage that the number of EX-OR circuits can be reduced by one.

The output side of the switching circuit 33 in FIG. 2 and the EX-OR in FIG.
It is preferable to provide a one-clock latch circuit on the output side of the circuit 39 to shape the waveform of the transmission signal TXO.

Effects of the Invention The Manchester M-sequence code modulation device according to the present invention
This is applied to a CSK communication system using Manchester codes. In the CSK communication system, two correlation outputs are compared on the receiving side, and 0 or 1 of the received data is assigned according to the magnitude. Therefore, the Manchester M sequence on the receiving side is strictly synchronized with that on the transmitting side. There is no need to take this, and no data demodulation error occurs. Further, if an absolute value is taken as the output of the correlator, no error occurs even in the case of a transmission line having characteristic deterioration such that the transmission peak value is negative. Further, by using the Manchester code M sequence, there is an effect that the low frequency component of the received signal can be reduced and the coupling loss with the transmission line can be suppressed low.

According to the present invention, as described above, when the M-sequence of the first Manchester M-sequence generator including a plurality of stages of shift registers and its return circuit has a specific phase, the second configuration having the same configuration Are set to have a predetermined initial phase, these two Manchester M-sequence generators have different M
Generate a sequence. The output signal of the first or second Manchester M-sequence generator is selected by the switching circuit in accordance with 1 or 0 of the transmission data and transmitted as a transmission signal at every predetermined period. As a result, the CSK-modulated transmission signal is sent out to the transmission path or the transmission medium, so that a modulation device suitable for the CSK modulation method can be realized with a relatively simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of the CSK communication system. FIG. 2 is a circuit diagram showing an embodiment of the modulation device according to the present invention, and FIG. 3 is a time chart showing the operation thereof. FIG. 4 is a circuit diagram showing another embodiment. FIGS. 5 and 6 show a conventional SS communication system.
FIG. 5 is a circuit diagram showing the configuration, and FIG. 6 is a time chart showing the operation. 11: Modulator, 31, 32: Manchester M-sequence generator, 31a, 32a: EX-OR circuit (feedback circuit), 33: Switching circuit, 34: Clock generator, 35: Initial phase setting vessel, 36 ...... NAND circuit, 37,38,39 ...... EX-OR _{circuit, FF 11 ~FF 13, FF 21} ~FF 23 ...... shift register.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Soichi Tsumura 3-5-24 Miyahara, Yodogawa-ku, Osaka-shi, Osaka NEC Home Electronics Co., Ltd.

Claims (2)

(57) [Claims] 1. A first and a second Manchester M-sequence generator for generating two Manchester M-sequences having a low cross-correlation and having the same code length at a fixed period, respectively, and commonly driving the two Manchester M-sequence generators. A clock generation circuit for generating a clock signal; a phase synchronization for detecting a specific phase of the first Manchester M-sequence generator and setting a predetermined initial phase in the second Manchester M-sequence generator at the time of the detection; A switching circuit for selecting one of the output signals of the first or second Manchester M-sequence generator in accordance with 1 or 0 of the transmission data and transmitting the transmission signal as a transmission signal for each of the predetermined periods. The first and second Manchester M-sequence generators each include a plurality of shift registers driven by the clock signal, The first Manchester M series, comprising a feedback circuit for feeding back the output of a predetermined stage of the shift register to the input thereof, and an exclusive OR circuit having the output of the last stage of the shift register and the clock signal as inputs. A Manchester M-sequence code modulator, wherein a generator and a second Manchester M-sequence generator have different stages of a shift register fed back to the input by the feedback circuit. 2. An exclusive OR circuit serving as both a first Manchester M-sequence generator and a second Manchester M-sequence generator, and connected to the output side of said switching circuit. 3. The Manchester M-sequence code modulator according to item 1.