JP2947638B2 - Spread spectrum communication system and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication system and apparatus suitable for communication using a power line as an information transmission path.

[0002]

2. Description of the Related Art Electric power lines are present in all households. Therefore, when viewed as an information transmission medium in a home, they are very effective and economically scalable. Is connected to a variety of electrical devices such as lighting, air conditioners, and TVs, and the transmission characteristics of the power lines sometimes change depending on the use / non-use (eg, power ON / OFF) of these electrical devices. The phase characteristics change every moment. For example, in the case of a device using a TV or a switching power supply, the phase characteristics change rapidly in synchronization with the power supply frequency.

As described above, the transmission characteristics of the power line are not flat and unstable, so that there is a problem that it is difficult to transmit high-quality data.

[0004] As countermeasures, for example, the literature “Power Line Communication (Data Transmission)”, Sekkei 2 Technical Report SSTA89-7 (1989), the document “High Performance SS Power Line Modem”, NEC Technical Report Vol.
As described in p.98-106 (1989), spread spectrum communication systems (hereinafter, referred to as
The introduction of an SS communication method) is being considered.

[0005]

In this SS communication system, there is a code modification method for inverting a PN (Pseudo Nois) sequence every time a transition from 1 to 0 or from 0 to 1 occurs in transmitted data. In order to demodulate the received signal, it is necessary to generate the same sequence synchronized with the PN sequence used on the transmission side on the receiver side. Therefore, the correlation between the received signal and the received PN sequence generated in the receiver is monitored, and synchronization acquisition (synchronization detection) is performed depending on whether or not the correlation value exceeds a certain threshold. Maintain synchronization (synchronization tracking). After synchronization is established, if the correlation value is on the + side with respect to the threshold value, it is demodulated to logic "1", and if it is on the-side, it is demodulated to logic "0".

[0006] A sliding correlator (Sl
In the case where an iding correlator is used, the timing of generating the correlator sequence is shifted by a minute frequency from the timing of generating the PN sequence on the transmitting side, and the correlation between the two PN sequences is obtained. Although there is an advantage that the configuration is simple, since the difference between the two PN sequence generation frequencies cannot be made so large, the sliding speed cannot be increased, it takes time to establish synchronization, and the effective transmission speed is significantly reduced.

In addition, when a digital DLL is used for maintaining the synchronization, in this system, when the transmission characteristic fluctuates at high speed, the shape of the correlation function is disturbed and changes suddenly. There is a problem that demodulation errors are likely to occur and reliability is low.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to establish synchronization in a short time, sufficiently follow a sudden change in transmission characteristics, and furthermore, to establish a connection with a transmission line. It is an object of the present invention to provide a spread spectrum communication system and device capable of suppressing coupling loss to a low level.

[0009]

According to the present invention, in order to achieve the above object, in the spread spectrum communication in which transmission data is subjected to code transformation with a PN sequence and communicated, a logic "1" and a logic " 0 ", a first PN sequence and a second PN sequence shifted by a predetermined phase with respect to the PN sequence are assigned. On the receiving side, the same PN sequence as the first PN sequence and the received signal are assigned. comparing the correlation output of the same PN sequence as the correlation output and the second PN sequence and the received signal
To select the larger correlation output,
The peak that appears every cycle of the PN sequence received from the
The peak was output from either of the above two correlation outputs
The peak is determined by the first PN
If it is obtained by the same PN sequence as the sequence,
The demodulation is performed by allocating the logic “1”, and the peak is equal to the second P
If it is obtained by the same PN sequence as the N sequence,
The configuration is such that logic "0" is assigned and demodulated .

According to a third aspect of the present invention, a PN sequence generator for generating a first PN sequence, a delay unit for inputting the first PN sequence and generating a second PN sequence shifted by a predetermined phase, and transmission data of 1 bit A transmission unit including a selector for selecting the first PN sequence or the second PN sequence in accordance with the logic of the above, and a first correlator for obtaining a first correlation value between the first PN sequence and a received signal And a second correlator for obtaining a second correlation value between the second PN sequence and the received signal. The second correlator compares the first correlation value with the second correlation value.
A comparator for generating a selection command for selecting the correlation value or the second correlation value, a selector for selecting the correlation value based on the output of the comparator, and inputting the output of the selector to detect the peak value and the peak position Peak detector, the above comparator and
One cycle of the PN sequence received from the selector and the peak detector
The peak that appears every time is output from either of the above two correlators
A flip-flop that assigns a logical “1” or a logical “0” to the binary output of the comparator, and performs a latch operation on the flip-flop in synchronization with the peak position And a receiving unit including a synchronization control unit that generates a clock to be synchronized and tracks the peak position.

In a preferred embodiment, a matched filter is used as the first and second correlators.

According to claim 5, the first PN sequence and the second PN sequence
Are configured to be Manchester-encoded M sequences.

[0013]

According to the present invention, on the transmitting side, the first PN sequence and the second PN sequence shifted by a predetermined phase with respect to the PN sequence in accordance with the logic "1" and the logic "0" of the transmission data, respectively.
A sequence is allocated and transmitted. On the receiving side, the PN of the correlation output between the received signal and the two PN sequences generated by the receiving unit is output.
Peaks appearing for each cycle of the sequence are detected, and it is determined which correlator the peak appears on, and the data of the received signal is demodulated to logic "1" or logic "0".

According to the present invention, even if the waveforms of the two correlation outputs suddenly change due to a sudden change in the transmission characteristics, it is only necessary to detect the peak of the correlation output (peak value and peak position). Good and stable synchronization acquisition, synchronization holding and data demodulation can be performed. Further, since the correlator uses a matched filter, synchronization acquisition can be performed at high speed.

Since the M-sequence encoded by Manchester encoding is used, the coupling loss between the transmission unit and the transmission path can be reduced.

[0016]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a transmitting unit, and FIG.
The receiving unit is shown in a block configuration.

In FIG. 1, 1 is a five-stage shift register,
An EXOR gate 2 constitutes a first PN sequence generator 3. The EXOR gate 2 receives the output of a specific stage of the shift register 1, and the output of the EXOR gate 2 is fed back to the input of the shift register 1. In this embodiment, the shift register 1 As an initial value, a value other than “00000” is set to obtain an M-sequence code having a code length of 31. The output of the PN sequence generator 3 is defined as PNO. The clock speed of the clock c supplied to the PN sequence generator 3 is assumed to be much higher than the data transmission speed. Reference numeral 4 denotes a second PN sequence generator, which includes a delay unit including a 15-stage shift register.
The output of the PN sequence generator 3 is input and the PN sequence generator 3
PN sequence (PNS), which is driven by the same clock c as the clock c applied to the PNO and has a phase delayed by 15 chips from the PNO. Numeral 5 is a timing signal generator, which is composed of an AND gate, which ANDs the outputs of all stages of the shift register 1 and outputs the output PT of the AND gate 5.
(A signal representing one cycle of the M-sequence code) is the transmission data D
, And a timing signal PT for synchronizing PNO and PNS. Reference numeral 6 denotes a selector, which is one of transmission data D.
When the logic is 1, the PNO is selected, and when the logic is 0, the PNS is selected and the SS signal is sent. This SS signal is band-limited by the low-pass filter LFP7 (in the case of a power line, After being amplified to a predetermined level by a transmission amplifier (not shown), it is sent out to the transmission line 10 via a coupler (not shown).

FIG. 5 shows PNO, PNS, PT and PT
The relationship between the transmission data D and the synchronized transmission data D is shown below.

FIG. 6 shows that the transmission data D is "0010".
An example of the SS signal in the case of "11" is shown.

In the receiving section of FIG. 2, reference numeral 11 denotes a PNO correlator (PNO. CORR, matching filter), which outputs a correlation value between a received signal and a PN series PNO. Reference numeral 12 denotes a PN1 correlator (PNS. CORR, matching filter), which outputs a correlation value between a received signal and a PN sequence PNS. The PNO correlator 11 and the PNS correlator 12
As shown in the figure, the value of each stage of the shift register 21 to which the A / D converted received signal is input is multiplied by the value of each stage of the PN code pattern generator 22, and the multiplied value is added. Vessel 2
3 is added.

Reference numeral 13 denotes a comparator, which is a PNO correlator 1
1 is compared with the output of the PNS correlator 12 and the output is supplied to the D input of the D-type flip-flop 14. Reference numeral 15 denotes an OR circuit, and reference numeral 16 denotes a selector. The selector 16 sets the output of the comparator 13 as a selection command signal S ₁ after the synchronization acquisition, and
The larger one of the outputs of the S correlator 12 is selected and supplied to the peak detector 17. The peak detector 17 detects a peak value V _P (V _po , V _PS ) and a peak position (synchronization point) T _P (T _Po , T _PS ) during one period of the PN sequence. It is sent to the synchronization control unit 18. Synchronization control unit 18, the pre-synchronization acquisition, and sends a selection command signal S _2, peak - click value V _P0 and Pi - click position T
_P0 is observed to perform synchronization acquisition. After synchronization acquisition, a clock ck synchronized with the peak positions T _PS and T _PO is supplied to the clock input ck of the flip-flop 14, and the peak positions T _PS , so as not to lose sight of T _PO (peak - as click position is at the center of the PN sequence one period), the peak to control the clock C _S applied to the PNO correlator 11, PNS correlator 12 - click position to track T _P.

Next, the operation of this embodiment will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 7 shows the transmission data "PNO, PN
S, PNO "(101), a waveform time chart of the correlation output of the PNO correlator 11 and the PNS correlator 12, and FIG. 8 shows the transmission data" PNS, PNS, PNO ".
PNO correlator 11, PNS when (001) is received
4 is a waveform time chart of the correlation output of the correlator 12 for use.

(1) Acquisition of Synchronization When performing SS communication, first, the transmission unit continuously transmits "1" as a synchronization signal. Synchronization at the stage where not achieved, the synchronization control unit 18 sends a selection command signal S ₂ as the selector 16 selects the output COR1 of PNO correlator 11. The peak detector 17 is a PNO correlator 1
Detects the click P ₁ peak - - Pi for each PN sequence one cycle of the first output COR1 enter the click information to the synchronization control unit 18, the synchronization control unit 18, this pin - over click P ₁ is a plurality of periods If the same peak position _TP0 occurs continuously, it is determined that communication has started. At this time, the output C of the PNS correlator 12
Since the click position T _PS enters the advanced position as the 15 clock against T _P0, this pin - - OR @ 2 of pins can be used click position T _PS to confirm the synchronization acquisition.

(2) Synchronization Tracking When the synchronization acquisition is completed, the selector 16 performs the selection operation in response to the selection command signal S ₁ of the comparator 13, and outputs the output COR ₁ of the PNO correlator 11 and the output of the PN 1 correlator 12. CO
The larger output of R2 is provided to peak detector 17.
The output COR1 the PNO correlator 11, peak - but click P 'appears - secondary peak between the click P ₁ - Pi such has to be tracking the click position - click P ₁ and pin (The same applies to the output COR2 of the PNS correlator 12), and the synchronization control unit 18 ignores this secondary peak P 'so as not to lose the synchronously captured peak positions T _PS and T _PO. to control the clock C _S to. Since this secondary peak P 'is generated at a position shifted by 15 or 16 chips from the _peak positions T _PS and T _PO requiring tracking, it can be easily identified, and the synchronous control can be performed. The section 18 sends out a clock ck synchronized with the peak positions T _PO and T _PS of the peaks P ₁ and P ₂ to the flip-flop 14, and the flip-flop 14 receives the clock ck every time the comparator 13 receives the clock ck. Latch output, COR1, COR
2 are demodulated as logic "1" and "0", respectively.

As described above, in this embodiment, the received PN
A peak appearing for each cycle of the series is detected and a synchronous operation is performed. When this peak appears in the output of the PNO correlator 11, it is demodulated to logic "1" and the PNS correlator 12 is demodulated. When it appears on the output, it is demodulated to logic "0", and if it is possible to determine which correlator the peak appears on, data can be demodulated. In the present embodiment, the correlation outputs COR1, COR2
The above determination is made by the comparator 13, the selector 16, and the peak detector 17 which compare the magnitudes of the two, and it is sufficient that only the peak value and the peak position of the two correlation outputs can be detected. Since the demodulation is not performed based on the magnitude relationship between the correlation output and the threshold value, even if the transmission characteristics suddenly change and the waveform of the correlation output suddenly changes,
Stable synchronization acquisition and synchronization holding can be performed, and thus stable communication can be performed.

In this embodiment, since matched filters are used as the correlators 11 and 12, synchronous acquisition can be performed at high speed.

In this embodiment, an M-sequence having a code length of 31 is used. However, in the M-sequence, as shown in FIG. This low-frequency component is preferably small from the viewpoint of coupling loss. This is because power line communication requires a coupler for separating commercial power between the communication device and the power line, and the coupler includes a low-pass filter for cutting the commercial power frequency. Therefore, when the M-sequence is used, this low-pass filter also cuts the low-frequency component of the M-sequence,
This is because a significant part of the signal component is lost. This is a Manchester-encoded M sequence (shown in FIG. 9A).
Is used, the low-frequency component can be reduced, and the coupling loss with the transmission line 10 can be reduced.

FIG. 10 and FIG. 11 show a transmitting section using an M-sequence encoded by Manchester.

In FIG. 10, 2A and 2B are EXO
R gate. The EXOR gate 2A receives the output of the shift register 1 and the clock c and generates a Manchester-encoded M series PNO. Shift register 1, EXO
The R gate 2 and EXOR gate 2A constitute a Manchester-coded M-sequence generator 3 '. The shift register 4 receives the output of the shift register 1 and performs EXOR
The gate 2B receives the output of the shift register 4 and the lock c and generates a Manchester-encoded M-sequence PNS. The shift register 4 and the EXOR gate 2B constitute a second Manchester-encoded M-sequence generator 4 '. The selector 6 selects the Manchester-encoded PNO when the logic is 1, and the Manchester-encoded PNS when the logic is 0 for one bit of the transmission data D.
Select Other configurations are the same as those in FIG.

As shown in FIG. 11, an EXOR gate 2C is provided at the subsequent stage of the selector 6 in FIG.
, The Manchester-encoded P
NO and PNS can be obtained.

Although the phase of the PNO is shifted by 15 clocks from the phase of the PNS, it is sufficient that the phase is shifted by ± 1 chip or more.
Only one N-sequence generator is required. Further, when the PNS is ahead of the PNO by four chips, for example, the shift register 4 for delaying becomes unnecessary. Can be substituted.

In this embodiment, the case where two correlators shown in FIG. 3 are used has been described as an example. However, as shown in FIG. 4, one shift register and one PN −
The two correlators 11, 1 are composed of a pattern generator and two adders.
2 can be configured. Further, in the present embodiment, instead of specifying and limiting the combination of codes of the two PN sequences, an arbitrary PN sequence can be selected and the two PN sequences need only be shifted by one shift register chip or more. In the case where an SS signal from another system is present on a transmission line during communication between SS modems of one system,
If different PN sequences having a small cross-correlation are used in both systems, demodulation can be performed with high probability even if a collision occurs.

Even when a plurality of communication terminals are present in one system, different PN sequences having a small cross-correlation are allocated to each communication terminal so that demodulation can be substantially performed even if a collision occurs. Can be. Furthermore, each PN
The sequence can be used as the address of each communication terminal,
In this case, each communication terminal can be identified by a PN sequence.
Of course, instead of different PN sequences having a small cross-correlation, those having the same PN sequence shifted in phase can be used. In this case, it is necessary that the phase shift amounts do not overlap each other.

In the above embodiment, the clock _CS is controlled for synchronization tracking. However, the peak position information is observed, and as shown in FIG.
Feedback may be applied from 8 to the peak detector 17 to control the timing of the observation.

An adder can be used instead of the selector 16 in FIG.

[0037]

As described above, according to the present invention, on the transmitting side, a first PN sequence and a second sequence obtained by passing this PN sequence through a delay unit are prepared, and data logic is made to correspond to each. On the receiving side, the correlation between the received signal and the two PN sequences generated on the receiving side is detected, and the logic is demodulated based on which correlation output has the peak value of the correlation output. Therefore, stable communication can be performed even when the transmission characteristic changes abruptly, as compared with the conventional case where demodulation is performed based on the magnitude relationship between the correlation output and the threshold value.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a transmission unit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a receiving unit in the embodiment.

FIG. 3 is a block diagram showing a correlator in the embodiment.

FIG. 4 is a block diagram showing a correlator in the embodiment.

FIG. 5 is a timing chart showing a relationship among a PNO, a PNS, and a timing signal PT in the embodiment.

FIG. 6 is a diagram illustrating an example of an SS signal transmitted by a transmission unit.

FIG. 7 is a diagram illustrating an example of a correlation output of a correlator in the embodiment.

FIG. 8 is a diagram showing an example of a correlation output of a correlator in the embodiment.

FIG. 9 is a diagram showing a spectrum of an M-sequence subjected to Manchester encoding and a spectrum of an M-sequence not subjected to Manchester encoding.

FIG. 10 is a block diagram showing an embodiment using an M-sequence encoded by Manchester encoding according to the present invention.

FIG. 11 is a block diagram showing another embodiment of the present invention using a Manchester-encoded M sequence.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 shift register 2 EXOR gate 2A, 2B, 2C EXOR gate 3 first PN sequence generator 4 delay device as second PN sequence generator 5 timing signal generator 6, 16─ selector 7 LPF 10 Power lines 11 and 12 correlator 13 comparator 14 flip-flop 17 peak detector 18 synchronization controller

Claims (5)

(57) [Claims] 1. In spread spectrum communication in which transmission data is subjected to code transformation with a PN sequence and communicated, a transmitting side uses a first PN sequence and a first PN sequence in accordance with a logic “1” and a logic “0” of the transmission data, respectively. A second PN sequence shifted by a predetermined phase is assigned to the PN sequence, and on the receiving side, a correlation output between the same PN sequence as the first PN sequence and the received signal and the same PN sequence as the second PN sequence are assigned. Correlation output with received signal
Compare the larger correlation output and select the selected correlation output.
Find the peak that appears every cycle of the PN sequence received from the force
The peak is output from either of the above two correlation outputs.
It is determined whether or not the peak is the first peak.
Field obtained from the same PN sequence as
In this case, a logic "1" is assigned and demodulated.
2 obtained by the same PN sequence as the PN sequence
A spread spectrum communication method characterized by assigning a logic "0" in the case and demodulating . 2. The spread spectrum communication system according to claim 1, wherein the first PN sequence and the second PN sequence are Manchester-encoded PN sequences. 3. A PN sequence generator for generating a first PN sequence, a delay device for inputting the first PN sequence and generating a second PN sequence shifted by a predetermined phase, and one bit of transmission data.
A transmission unit including a selector for selecting the first PN sequence or the second PN sequence in accordance with the logic of
A first correlator for obtaining a first correlation value between the PN sequence and the received signal, a second correlator for obtaining a second correlation value between the second PN sequence and the received signal, and the first correlation A comparator for comparing a value with a second correlation value and generating a selection command for selecting the first correlation value or the second correlation value in accordance with the magnitude thereof; Selector, a peak detector that receives the output of the selector and detects the peak value and the peak position, the comparator and the selector
Appears every cycle of the PN sequence received from the peak detector
Peaks output from either of the above two correlators
And a flip-flop that assigns a logical “1” or a logical “0” to the binary output of the comparator, and a clock that causes the flip-flop to perform a latch operation in synchronization with the peak position. A spread spectrum communication apparatus, comprising: a receiving unit that generates and tracks a peak position and includes a synchronization control unit. 4. The spread spectrum communication apparatus according to claim 3, wherein the first and second correlators are matched filters. 5. The spread spectrum communication apparatus according to claim 3, wherein said first PN sequence and said second PN sequence are Manchester-coded M sequences.