JP2860614B2 - Spread spectrum communication equipment - 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 (S)
S) The present invention relates to a communication apparatus, and more particularly, to an improvement of an SS communication apparatus that includes a CPSK modulation / demodulation unit and employs a burst transmission method.

[0002]

2. Description of the Related Art Spread-spectrum communication methods use the RCD method.
As described in “Spread Spectrum Systems” by ixon, it is resistant to interference, noise, and fading, has signal confidentiality and confidentiality, and is capable of asynchronous random access. ing. In this spread communication method, one important requirement is that initial synchronization (establish high-speed synchronization between a PN code included in a received signal and a PN code string prepared inside the receiver) is required.

As an example of the means for providing the above-mentioned initial synchronization,
Reference 1: Japanese Patent Publication No. 64-11178 is known.
The means of the above document 1 is of a type using a convolver as correlation means of a receiver. As can be seen from the receiver circuit of FIG. The time difference between the start time of the reference PN code sequence and the start time of the convolver output is measured, and from this time difference, the phase difference between the PN code sequence included in the received signal and the reference PN code sequence is known, and The phase of the reference PN code sequence is adjusted so that the phase difference becomes zero.

[0004]

This method of initial synchronization is effective in principle, but when used in an actual radio channel, a. When performing the initial synchronization, it may not be possible to supplement the correlation output due to the influence of noise or interference. b. There was a problem that a malfunction occurred due to a correlator output other than the target signal.

Accordingly, the present applicant has previously filed Japanese Patent Application No. 2-331.
No. 399 was filed and proposed a spread spectrum communication method and apparatus capable of realizing more reliable supplementation of the correlation output and initial synchronization required for data demodulation with a simple circuit.

[0006] In the spread spectrum communication method according to the invention of the prior application, the transmitting side includes: a) a first modulation output portion that is spread spectrum modulated not including data to be transmitted, and the first modulation output portion following the first modulation output portion; Generating a spread-spectrum modulated output comprising: a second spread-spectrum modulated output comprising data to be transmitted;
The spread spectrum modulation output is transmitted at a low power at the second modulation output portion and at a high power at the first modulation output portion. Generating a demodulated output; b) from the correlated demodulated output, a first correlated demodulated output portion corresponding to the first modulated output portion and a second correlated demodulated output portion corresponding to the second modulated output portion.
Detecting the first correlation demodulation output portion among the correlation demodulation output portions; and c) generating a timing signal from the first correlation demodulation output portion which is a reference for the operation of the receiving side.

[0007] In the above-mentioned invention of the prior application,
The spread spectrum communication method when using the modulation and demodulation method is as follows.
On the transmitting side, a first PN code sequence composed of a repetition of a first PN code of a predetermined period and a second PN code sequence shifted from the code sequence by a predetermined phase are generated. One of the first and second PN code strings is selected according to each bit of data to be transmitted to generate a spread spectrum modulation output, thereby CPSK modulating each bit of the transmission data, and On the side, a)
The received input is subjected to correlation demodulation with a third PN code sequence consisting of a repetition of a second PN code of the predetermined period, which is time-inverted from the first PN code, to generate a correlation demodulated output. 3.) CPSK demodulation of the correlation demodulation output. This C
The PSK demodulation includes: i) a first time window composed of a pulse train having a half cycle of the predetermined period, synchronized with the correlation demodulation output, and a second time window consisting of a pulse train shifted by the predetermined phase from the pulse train. Generating a time window pulse train and a bit period indication signal indicating a period of each bit of the transmitted data; and ii) outputting a binarized pulse output obtained by binarizing the correlation demodulation output with a predetermined threshold value. Iii) within each bit period, the first of the binarized pulse outputs
Detecting the difference between the number of pulses in the time window and the number of pulses in the second time window, and iv) determining the state of each bit according to the polarity of the difference.

One of the features of the invention of the prior application is that a burst transmission system is employed. In this system, the transmission format includes a burst portion containing no data and a data portion containing data to be transmitted. In the form of a packet. The waveform of this burst transmission is as shown in FIG. 2. On the transmitting side, prior to all transmissions, a burst portion T that is spread spectrum modulated with a PN code is transmitted.
The transmission is performed after the peak power of B is increased, and then the data portion TD is transmitted at a lower power than TB to transmit one packet.

According to such a burst transmission system, 1
Since the power of the burst portion of the packet is higher than that of the data portion, the receiver can easily perform the initial synchronization at high speed and with high reliability. Although the above-mentioned burst transmission method of the prior application is basically excellent, it has been found that the following problems are encountered when actually implemented.

For example, upon reception, if the burst portion is overlooked due to the influence of high frequency noise and the data portion is synchronized, the received data at that time is as follows. (B) Part of the received data is missing. (B) Since the phase of the data clock reproduced by the receiving unit is not synchronized, errors increase. Therefore, in this case, the packet received as a result is almost always determined to be "error" and is discarded, and all the series of reception processing becomes meaningless. In addition, the reception processing of the next packet arriving during the meaningless reception processing cannot be performed, resulting in a decrease in throughput.

[0011] An object of the present invention is to provide a spread spectrum communication apparatus as described in the above-mentioned prior application, in which, when a burst part is missed as described above, synchronization is not achieved in a data part, so that a packet of the missed packet is lost. Restoration is not possible,
A purpose of the present invention is to avoid useless reception processing and to immediately respond to the reception processing of the next packet so as to improve the overall throughput.

[0012]

To achieve the above object, a spread spectrum communication apparatus according to the present invention switches between a burst period not including data to be transmitted and a data period including transmission data following the burst period. First switching means for switching and outputting different PN codes in response to a switching signal; and first spread-spectrum-modulated data not including data to be transmitted corresponding to the burst period based on one of the different PN codes. Modulation means for generating a spread-spectrum modulated output comprising a modulated output part and a second spread-spectrum modulated output part based on the other of the PN codes and subsequently containing the data to be transmitted; In response to the first spread spectrum modulation output and the second modulation output portion with low power and the first
A transmitter having transmission power control means for controlling the modulation output portion to transmit with high power, and a correlation means for inputting a received signal and a reference signal to generate a correlation output; and Burst detection means for detecting a first correlation output part corresponding to one modulation output part; demodulation means for detecting a second correlation output part corresponding to the second modulation output part from the correlation output and demodulating the data; PN in the transmitter in response to the output of the burst detecting means.
A second switching unit for switching and outputting a different PN code whose code has been inverted in time from a PN code corresponding to the burst period to a PN code corresponding to a data period, and a PN code output from the second switching unit And a reference signal generating means for generating the reference signal based on the reference signal.

[0013]

In the SS communication device of the present invention, the transmitter
The burst part and the data part are spread-modulated with different PN codes. In the receiver, the PN code of the burst portion is correlated with the burst portion with a time-reversed reference PN code, and when the burst portion is received, the PN code of the data portion is changed to the time-reversed reference PN code. After the switching, the subsequent reception processing is performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in the drawings will be described below.
1A and 1B show an embodiment of a transmitter and a receiver of a spread spectrum communication apparatus according to the present invention.

In the transmitter of FIG. 1A, 1 and 2 are first and second PN code generators, 3 is first switching means,
4 is a spread spectrum modulation circuit (for example, a CPSK modulation circuit), 5 is a double balanced modulator (multiplier), 6 is a high frequency signal (carrier) generator, 7 is a transmission power control circuit, and B / D is a burst period and data. A switching signal for switching between the periods, Data, is transmission data.

The first output from the first PN code generator
Is a PN code for spread spectrum modulation of the burst part, a second PN code PN2 output from a second PN code generator is a PN code for spread spectrum modulation of the data part, and The first switching means 3 driven by the switching signal B / D outputs the first PN code PN1 during the burst period and the second P code during the data period.
The N code PN2 is switched to each other and output to the spread spectrum modulation circuit 4.

In the modulation circuit 4, the burst section and the data section are spread-modulated with the first and second PN codes PN1 and PN2 different from each other as shown in FIG. Is modulated. The modulation output of the modulator 5 is supplied to a transmission power control circuit 7, which controls the burst section power so as to be larger than the data section as shown in FIG. I do.

Next, in the receiver shown in FIG. 1B, 10 is a high-frequency amplifier, 11 is a frequency conversion circuit, 12 is a local oscillator, 13 is an intermediate frequency amplifier, and 14 is a correlator (for example, S
AW convolver), 15 is a detection circuit, 16 is a demodulation circuit (for example, a CPSK demodulation circuit), 17 is a voltage comparison circuit,
Reference numeral 18 denotes a D-type flip-flop, 19 denotes second switching means, and 20 and 21 denote third and fourth PN codes PN1 and PN2 obtained by inverting the first and second PN codes PN1 and PN2 in the transmitter. Third and fourth PN generated
A code generator, 22 is a high-frequency oscillator, and 23 is a double balanced modulator (multiplier). At the start of one-packet communication, the correlator 14 receives a received signal from the intermediate frequency amplifier 13 and a reference signal generated from a third PN code PN1 to be described later from the modulator 23. The correlation is obtained, and the correlation output is applied to the detection circuit 15. A detection output from the detection circuit 15 is applied to one input of a voltage comparator 17 and a demodulation circuit 16.

On the other hand, a predetermined reference voltage is applied to the other input of the voltage comparator 17, and the burst section is controlled so that its power becomes larger than that of the data section as described above. , And a burst detection pulse is output from the voltage comparator 17 and applied to the flip-flop 18.

On the other hand, the flip-flop 18 is preset so as to generate an "H" output by a preset input at the start of communication of one packet.
At the output, the second switching means 19 is driven so as to select the third PN code PN1 corresponding to the burst period.

In this state, when a burst detection pulse is input, the output of the flip-flop 18 changes to "L" as shown in FIG. 2, and the second switching means 19 sets this "L".
By output, a fourth PN code P corresponding to the data period
Switching is performed to select N2. These PN codes are supplied to a modulator 23, which modulates a high frequency signal and outputs reference signals corresponding to a burst portion and a data portion to the correlator 14.

The demodulation circuit 16 demodulates data from the detection output corresponding to the correlation output between the reference signal generated from the fourth PN code PN2 and the data part.

Now, in the communication state as described above,
If the burst part cannot be detected by the receiver for some reason, the third PN code PN1 is still given to the correlator 14 because the burst detection pulse is not obtained, and therefore the burst part is not transmitted. Even if the data portion is subsequently input, the PN codes PN2 and PN1 have small correlation values and cannot be detected. Therefore, the initial synchronization is not performed in the data section.

[0024]

As described above, according to the present invention, since the burst part and the data part are spread-modulated with different PN codes in the transmitter, even if the burst part is missed on the receiving side, Since the correlation value between the PN code of the data portion following the PN code at that time and the (standby) reference PN code at that time is small and cannot be detected, the data portion is not erroneously detected as the burst portion, and the meaningless reception processing is performed. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a spread spectrum modulation communication apparatus according to the present invention.

FIG. 2 is an operation explanatory diagram of the above embodiment.

[Explanation of symbols]

 1, 2 PN code generator 3 first switching means 4 modulation circuit 5 modulator 7 transmission power control circuit 14 correlator 15 detection circuit 16 demodulation circuit 17 voltage comparison circuit 18 D-type flip-flop 19 second switching means 20, 21 PN code generator

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-199927 (JP, A) JP-A-64-11178 (JP, A) JP-A-54-72615 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04J 13/00

Claims (1)

(57) [Claims] A first switching unit that switches and outputs different PN codes in response to a switching signal for switching between a burst period that does not include data to be transmitted and a data period that includes subsequent transmission data. A first modulated output portion that does not include data to be transmitted corresponding to the burst period based on one of the different PN codes and that is to be transmitted following the other of the PN codes; A modulating means for generating a spread spectrum modulated output comprising a second spread spectrum modulated output section including data; and a low power transmitting means for converting the spread spectrum modulated output in response to the switching signal to a second modulated output section. And the first
A transmitter having transmission power control means for controlling the modulation output portion to transmit at a high power, and a correlation means for inputting a received signal and a reference signal to generate a correlation output; and The first corresponding to one modulation output part
Burst detection means for detecting a correlation output portion; a second burst output portion corresponding to the second modulation output portion from the correlation output;
A demodulation means for detecting a correlation output portion and demodulating the data; and responding to an output of the burst detection means, a time-inverted different PN code of the PN code in the transmitter from a PN code corresponding to the burst period. A receiver comprising: a second switching unit that switches and outputs a PN code corresponding to a data period; and a reference signal generation unit that generates the reference signal based on the PN code output from the second switching unit. A spread spectrum communication device comprising: