JP2571123B2 - 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, code shift keying (Cods Shift keying).
The present invention relates to a modulation device using a keying (CSK) modulation method.

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. 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, and
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 deterioration of the correlation waveform progresses, 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 signal length with a low cross-correlation at fixed intervals, respectively,
According to 1 or 0 of the transmission data, the first or second
Of the Manchester M-sequence generator for selecting one of the output signals.

The first and second Manchester M-sequence generators include:
A clock generation circuit for generating a commonly used clock signal, a commonly used multi-stage shift register,
A first feedback circuit for the first Manchester M-sequence generator that feeds back an output of a predetermined stage of the shift register to its input, and an output of a stage different from the first feedback circuit of the shift register. An exclusive OR that is used in common with the second feedback circuit for the second Manchester M-sequence generator that feeds back to its input, and that receives the output of the last stage of the shift register and the clock signal as inputs And an output of the first and second feedback circuits is provided as an input of the switching circuit, and an output of the switching circuit is fed back to an input of the shift register. The output signal of the OR circuit is transmitted as a transmission signal.

Preferably, there is further provided a circuit for detecting a specific phase of the shift register, and a timing circuit for fetching transmission data in response to a detection signal of the detection circuit and controlling switching 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 two shift circuits are connected to a shift register that also serves as two Manchester M-sequence generators, and two feedback circuits corresponding to the respective Manchester M-sequence generators are selectively switched by a switching circuit according to transmission data. Is fed back to the input of the above, the above-mentioned 2
One of the Manchester M-sequence generators corresponding to the transmission data is established. As a result, the CSK-modulated transmission signal is sent out to the transmission path or the transmission medium from the exclusive OR circuit connected to the output of the shift register.

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

On the transmitting side, the modulator (transmitter) 11 is provided with two Manchester M-sequence generators 31 and 32 for synchronizing and generating Manchester code M-sequences having low cross-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.

The Manchester M-sequence generator includes a multi-stage shift register, a feedback circuit provided in the shift register, an EX-OR circuit for generating an exclusive OR of a shift register output and a clock signal, and a Manchester code. Can be composed of In the CSK modulator 11 shown in FIG.
One Manchester M-sequence generator 31 is a shift register
FF _{1 to} FF ₃ , an EX-OR circuit 31 a as a feedback circuit, and an EX-OR circuit 39 for Manchester code generation. The other Manchester M-sequence generator 32 includes a shift register FF.
_{1 to} FF ₃ , an EX-OR circuit 31b as a feedback circuit, and an EX-OR circuit 39 for Manchester code generation. That is, the shift registers FF _{1 to} FF ₃ (three stages in this embodiment; n = 3) are connected to two Manchester M-sequence generators 31.
The EX-OR circuit 39 for generating Manchester codes is also used in the same manner. A shift register FF ₁ to ff ₃ and EX-OR circuit 31a first M sequence generator (PN code generator, PN code = Pseude Noise Code = pseudo noise) is constructed, the shift register FF ₁ to ff ₃ and EX -OR circuit
It may be considered that the second M-sequence generator is constituted by 31b. Then, the first M-sequence generator and the EX-OR circuit 39
Thus, a Manchester M-sequence generator 31 is constituted, and a Manchester M-sequence generator 32 is constituted by the second M-sequence generator and the EX-OR circuit 39.

The EX-OR circuit 31a as a feedback circuit is provided with a shift register FF ₁
Is intended to return the sign of the second stage and the cell of the third stage to ff ₃ to its input, EX-OR circuit 31b is for feeding back the sign of cells of the first and second stages. Thus, the feedback circuits of the two Manchester M-sequence generators 31 and 32 are different from each other. A switching circuit 33 is provided in this feedback loop. That is, the outputs D ₁ and D _{2 of} the EX-OR circuits 31a and 31b are input to the switching circuit 33, and the output of the switching circuit 33 is
It applied to the input of _{1 ~FF 3.}

The switching circuit 33 is controlled by the Q output (SW signal) of the D flip-flop 30 in each cycle T (data section) of the Manchester code M sequence according to the transmission data TXD.
In other words, controls the shifting operation timing clock signal CK output from the clock generator 34 is given to the shift register FF ₁ ~FF _3, D flip-flop
Enter 30. On the other hand, when the sign of all the stages of the shift register FF ₁ to ff ₃ is 1 (this state is the one period T
The output of the NAND circuit 36 becomes L level, which is given to the D flip-flop 30 as the enable signal EN. Therefore, when the enable signal EN is at the L level, D
The flip-flop takes in the input transmission data TXD,
This is given to the switching circuit 33 as a switching control SW. Switching circuit
Depending on the switching of 33, the Manchester M-sequence generator 31 or
32 because one of the feedback circuit (first or second M sequence generator) is established, the output of the established M outputs of the sequence generator (the last stage of the shift register FF ₁ to ff ₃ cell of the feedback circuit ) Is input to the EX-OR circuit 39. EX-OR circuit
The clock signal CK is also given to 39, and the output of the M-sequence generator is Manchester-coded and output as a transmission signal TXO.

If necessary, the output of the NAND circuit 36 is supplied as a transmission request signal to a transmission data processing unit (for example, a microprocessor), and in response to this, the transmission data processing unit generates the next one bit of transmission data TXD. Good. Also, EX
-One clock latch circuit is provided on the output side of the OR circuit 39,
The waveform of the transmission signal TXO may be shaped.

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, two feedback circuits connected to a shift register also used for two Manchester M-sequence generators and corresponding to each Manchester M-sequence generator are selectively switched by a switching circuit according to transmission data. By being fed back to the input of the shift register, one of the two Manchester M-sequence generators corresponding to the transmission data is established for each of the predetermined periods. As a result, the CSK-modulated transmission signal is sent out from the exclusive-OR circuit connected to the output of the shift register to the transmission line or the transmission medium. A suitable modulation device is realized. In particular, according to the present invention, the clock generation circuit, the shift register, and the exclusive OR circuit are commonly used by the two Manchester M-sequence generators, so that the circuit configuration can be simplified.

[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. FIGS. 4 and 5 show a conventional SS communication system.
FIG. 4 is a circuit diagram showing the configuration, and FIG. 5 is a time chart showing the operation. 11: Modulator, 30: D flip-flop, 31, 32: Manchester M-sequence generator, 31a, 32a: EX-OR circuit (feedback circuit), 33: Switching circuit, 34: Clock generator , 36 ...... NAND circuit, 39 ...... EX-OR circuit, FF ₁ ~FF ₃ ...... 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] A first and 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; A switching circuit for selecting one of the first and second Manchester M-sequence generators in response to 0, wherein the first and second Manchester M-sequence generators are commonly used A clock generation circuit for generating a clock signal; a plurality of commonly used shift registers; and a first Manchester M-sequence generator for feeding back an output of a predetermined stage of the shift register to an input thereof. A feedback circuit, and the second Manchester M that feeds back an output of a different stage of the shift register from the first feedback circuit to its input.
A second feedback circuit for the sequence generator; and an exclusive-OR circuit commonly used and having the output of the last stage of the shift register and the clock signal as inputs. 2 is provided as an input of the switching circuit, an output of the switching circuit is fed back to an input of the shift register, and an output signal of the exclusive OR circuit is transmitted as a transmission signal. , Manchester M-sequence code modulator. 2. A circuit for detecting a specific phase of the shift register, and a timing circuit for receiving transmission data in response to a detection signal of the detection circuit and controlling switching of the switching circuit. Item (1). The Manchester M-sequence code modulator.