JP2567253B2 - Code hopping spread spectrum communication system - Google Patents

Description

The present invention relates to the field of spread spectrum communication systems. The spread spectrum communication method is to spread a baseband information signal in a spectrum band that is several hundred to several thousand times its bandwidth and send it out, and on the receiving side, compress that spectrum band to the band of the original baseband signal. It is a communication system that demodulates by using

According to the present invention, when a signal other than any signal other than the information signal to be transmitted is used to broaden (spread) the spectrum as a spread spectrum signal for modulation, the bit rate is considerably higher than the information signal bandwidth. The present invention relates to a direct sequence (DS) modulation method using a code modulation signal (carrier).

[Summary of the Invention] The present invention relates to a code hopping technique for improving the confidentiality and anti-jamming property of a spread spectrum communication device including a direct spread system.

[Prior Art] Spread spectrum communication is known to be excellent in external interference and confidentiality, but a simple direct spread spectrum method using a fixed spread code intends to actively eavesdrop or interfere. In general, it is easy for the other party who has the information to understand the nature of the code, and therefore, in a special application, it is customary to change the spread modulation code in order to avoid eavesdropping and interference.

[Problems to be Solved by the Invention] The present invention is intended to realize a spread spectrum communication system capable of performing a reliable and rapid modulation spread code change, that is, a code hopping operation between a transmitter and a receiver.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a plurality of transmitting side pseudo noise generating means and a plurality of transmitting side pseudo noises generated by the transmitting side pseudo noise generating means. A transmission side code multiplexer that selects and synthesizes a transmission side pseudo noise and outputs a transmission side spreading code; a transmission means that code-modulates an input signal by the transmission side spreading code to obtain and transmit a spread spectrum signal; And a receiving means for receiving the spread spectrum signal, and a signal for processing the received spread spectrum signal to obtain a pulse train signal corresponding to the code change of the spread code used in the spreading process of the code modulation. Processing means, a plurality of reception side pseudo noise generation means, and the reception side pseudo noise generation means in response to the pulse train signal Synchronization detecting means for detecting the synchronization between the receiving side pseudo noise and the transmitting side pseudo noise, and a system synchronization monitor for outputting receiving side spreading code selection data in response to a synchronization detecting signal from the synchronization detecting means. A receiving-side code multiplexer that selects receiving-side pseudo noise synchronized with the transmitting-side pseudo noise from the plurality of receiving-side pseudo noises according to the spreading code selection data, synthesizes the receiving-side pseudo noise, and outputs a receiving-side spreading code; A receiving device having demodulation means for demodulating the input signal from the received spread spectrum signal by a side spreading code, and the transmitting side multiplexer has a specific relationship according to transmitting side spreading code selection data. It is characterized in that a combination of the pseudo noises on the transmitting side is selected and combined according to a predetermined sequence. Provide code hopping multiplexing spread spectrum communication system to.

[Operation] The present invention can preferably apply the principle of the multiple spread spectrum communication system (Japanese Patent Application No. 61-234183 (Japanese Patent Laid-Open No. 63-88924)) previously proposed by the present applicant. That is, according to the present invention, the PN code selected in a certain sequence on the transmission side is combined by, for example, an exclusive OR circuit or the like, and this combined code is code-modulated with respect to the input signal and is transmitted. On the other hand, the receiver simultaneously generates reference signals corresponding to a predetermined number of PN codes that are supposed to be used on the transmission side, and thereby, the matching with the received signal is monitored separately. Since the reference signals that have been matched enter the tracking loops at that time, when synchronization is finally obtained for all reference signals used for code modulation, the pseudo noise that combines these reference signals is the received signal. Can be completely demodulated. Therefore, the present invention can exhibit not only the operation and effect peculiar to the multiple spread spectrum communication system but also the operation and effect peculiar to the code hopping technique.

[Embodiment] FIG. 1 is a schematic diagram of a spread spectrum communication system incorporating the principle of the present invention, in which the transmitting side is indicated by 100 and the receiving side is indicated by 200. The transmitting side is 101 and has a transmitting antenna 101, and the receiving side is 20
1 indicates the receiving antenna. At the transmitting side 100, a pseudo noise generator (PNG1, PNG2, PNG3, ... PNGn) 102-1 and 102-corresponding to generate n pseudo noise (PN) codes.
2, 102-3, ... 102-n are provided. From these
The PN code is provided to the code multiplexer 104. The code multiplexer 104 can be composed of, for example, a logic circuit including an exclusive OR gate, and is in the form of a code synthesizer for selecting at least one output and at most n outputs from these codes to perform code synthesis. There is. Input 106 receives pseudo noise (PN) code selection data, eg, code hopping schedule data described below. The output of the code multiplexer 104 is mixed with the carrier (f ₁ ) in the double balanced modulator (DBM) 106, further mixed with the input transmission signal (Tx signal) in the next DBM 108, and transmitted from the antenna 101.

An embodiment of the present invention has been previously proposed by the applicant of the present invention when, for example, a plurality of PN codes are used on the transmission side, for example, Showa 61
Filed on Oct. 1, 2014 (Japanese Patent Application No. 61-234183 (JP-A-63-88)
The multi-spread spectrum communication system of Japanese Patent No. 924)) can be preferably used. The summary is as follows. That is, in the conventional direct spread spectrum communication method, in order to realize a spreading process with higher performance, it is necessary to shorten the chip time as much as possible and use a spreading code having a large number of constituent bits, that is, shoe noise (PN). , As this request,
In particular, in order to increase the number of bits, the cost increases due to the sophistication on the receiving side and the complicated device. In order to solve such a problem, the above-mentioned prior patent application discloses two or more PNs having different circulation cycles.
By utilizing the beat phenomenon between codes, the spread code bit length is substantially expanded to perform more effective spectrum spreading, and accurate demodulation synchronization is realized by a combination of two or more types of relatively short correlation detection means. To do. A more detailed description is given in the above application and will not be described further here. Embodiments of the present invention may use the principles of such multiple spread spectrum communication schemes.

The input terminal 10 of the receiver 200 in FIG. 1 receives a spread spectrum signal, which is modulated by using N PN codes and transmitted by the transmitter, received by the antenna 201. This is given to the frequency demodulator 12 and converted into a code signal having a rising edge and a falling edge corresponding to the modulation code. In the situation where other direct spread spectrum signals using almost the same or close modulation frequencies are mixed, naturally, a code signal in which a signal indicating rising and falling, which is different from the above, is superimposed on this signal is obtained. . When a differentiation process is applied to this code signal, a pulse train-like signal can be obtained at each time when it is considered that there is a code change including the code change point of the code used in the spreading process.

In the figure, the output of the frequency modulator is applied to the differentiator 14 and then to the absolute value generator 16. This absolute value generator 16 outputs the pulse train signal from the differentiator 14 as one polarity without changing its time axis.

When code demodulating the above received signal, a reference code corresponding to the spreading code is generated by a PN generator, and demodulation is achieved under the condition that this phase substantially matches the transmitting side. The rising and falling timings are theoretically all overlapped with a series of pulse groups included in the pulse train. Therefore, if the pulse rate of this group of pulses is monitored within a finite time range by intentionally shifting the chip rate of the PN generator and the chip rate of the transmitting side, the point in time at which demodulation synchronization is achieved is determined. It becomes possible to grasp accurately. If it is further expanded and considered, according to this method, even if the signal is code-composite-modulated with a plurality of pseudo noises (for example, the above-mentioned multiple spreading method), one of the pseudo noises will be different. Since it is possible to know the time point when the synchronization is achieved, it is possible to maintain the overall synchronization as a set of tracking loops formed by independently feeding back each PN generator clock. At this time, even if the modulation code exception codes used in the system are mixed, the influence is greatly reduced in the process of checking the match with the reference signal.

In the figure, the signal on the line 17 from the absolute value generator 16 has a number of "S" corresponding to the number of PN codes used for transmission.
Unit "18-1 to 18-N are commonly provided. This S
The unit has a PN generator for detecting and tracking its synchronism, as described in more detail in connection with FIG. The sync detection signal from each S unit 18 is a line 19-
1, 19-2, 19-3, 19-4 ... 19-N to the system synchronization monitor 20. The system sync monitor 20 provides a control code output on line 22 which is described below.

S units 18-1 to 18-N are provided with PN
The outputs PN-1 to PN-N of the generator are applied to the code multiplexer 26 via lines 24-1 to 24-N, respectively. The sign multiplexer 26 is a logic circuit including an exclusive OR circuit,
The PN code selection data is received from the system synchronization monitor 20 via the line 28, and the line 30 is provided with the PN code obtained by selectively combining the PN-1 to PN-N codes. This is a balanced modulator 32,34
It is used in the final demodulation process in. Here, since the signal from the unit S indicating whether or not it is in the synchronous state is sent back to the transmitting side via the line 28, the transmitting side can also know the communication environment, and change the combination of the modulation code according to the situation. It is possible to take the measures described in (1) above, and it is possible to reliably handle jamming.

FIG. 2 shows a specific configuration of one S unit 18. In the figure, 40 is a voltage controlled crystal oscillator, and the chip clock rate is controlled according to a control voltage applied to an input 44 connected to a switch 42. The switch 42 supplies the Vslide voltage to the control input 44 so that the oscillator 40 generates a clock corresponding to a chip rate slightly different from the chip rate on the transmitting side during the acquisition process.

Reference numeral 46 is a pseudo noise generator that generates pseudo noise (PN) based on the chip clock output of the oscillator 40. This output is given to the code multiplexer 26 of FIG. And a transfer pulse generator 52 consisting of an exclusive OR circuit 50 and a delay device (d ') 51. The output D _S ′ of this transfer pulse generator 52
Is the output D _S of the absolute value generator 16 on line 17 in FIG.
It is given to the D circuit 54. In the synchronization acquisition process, as described above, the oscillator 40 normally generates a clock having a chip rate slightly different from the chip rate on the transmission side, and therefore, a pulse pulse for generating a code pulse train representing the transition timing of pseudo noise of the PN generator 46 is generated. The container 52 occurs as D _S ′. A synchronous state is periodically created between D _S ′ and the corresponding reception pulse train D _S on the transmission side according to the degree of their deviation. In this state, the output pulse train of a portion D _S 'of the pulse train of the D _S is generally consistent. Chip rate, and D _S and D _S of D _S to the adder 56 and the coherent integrator 60 consisting of delay device 58 '
Pulses having a predetermined interval determined by the difference in the chip rate of the PN generator are gradually accumulated, and conversely, the pulse train component that is not related to the output of the PN generator 46 has only irregular matching pulses, and thus only a very small amount is accumulated.

The output of the coherent integrator 60 is provided to the phase detector 62 together with the output of the oscillator 40. Therefore, as is clear from the above description, the output pulse train of the coherent integrator 60 accurately indicates the clock timing of the code component in question included in the received signal, and this and the current PN
If the clock frequency is fed back via the voltage controlled crystal oscillator 40 according to the amount of deviation of the clock phase supplied to the generator 46, the correct clock phase can be continuously maintained. In this embodiment, the analog switch 42 is switched to the feedback side due to the occurrence of a later-described sync detection signal on the line 19.
That is, normally, the above-mentioned Vslide is the control input 44 of the oscillator 40.
However, after the synchronization is detected, the switch 42 is switched so that the oscillator 40 can generate a clock almost matched to the chip timing on the transmitting side.
Plus the feedback voltage from phase detector 62 on line 66 is provided to the control input of oscillator 40.

As a method of detecting the synchronization, a method of judging from the output level of the coherent integrator 60, a method of judging from the frequency of the coincidence pulse of D _S / D _S ′ and the like can be considered. In the present embodiment, more accurate synchronization detection is performed. Scales also the frequency of matching pulses with sign change and the D _S output signals in the frequency at the same time of the reference signal and the complementary relationship between the match pulses D _S / D _S 'for, it is determined synchronization from these comparisons Things.

In FIG. 2, the output of the voltage-controlled crystal oscillator 40 (FIG. 3a) is given to the T flip-flop or the JK flip-flop 70, and its output is the output of the PN generator 46 (third FIG.
B) together with the exclusive OR gate 72, the output of which is complementary to the output of the reference signal or PN generator 46. That is, a complementary signal (FIG. 3c) is obtained that is a sequence that causes a code change only when there is no code change at the same time in the PN generator outputs among the code change timings determined by the clock. This is via a delay 73 similar to 51,
The pulse train D _S ″ (FIG. 3e) representing the transition point of the complementary signal is provided to the output of the transition pulse detection circuit 74 having the same configuration as the above-mentioned transition pulse detection circuit 52. This is described above. D _S '(Figure 3 d) is like the match pulse and D _S in the aND gate 54 is detected. counter 78 these aND gates consistent pulse of the D _S in the aND gate 76 is detected 5
Receives 4,76 outputs.

Figure 4 is D _S signal (Fig. 4 a) and AND in asynchronous state
Shows the D _S / D _S 'of matching pulses (Fig. 4 b) from the gate 54, D _S / D _S of the D _S signal (FIG. 5 a), the AND gate 54 in FIG. 5 is a synchronous state 'Match pulse (Fig. 5b) and AND
The D _S / D _S ″ match pulse from gate 76 is shown (FIG. 5c).

Figure 6 is 'is intended to illustrate the conditions example for determining synchronization by matching the pulse frequency comparison / D _S ", the horizontal axis _{D S / D S' D S} / D S by the counter 78 pulses (regular match the pulse) count on the vertical axis indicate taking D _S / D _S "pulse (invalid matching pulse) count.

As is apparent from the configuration of the above-described embodiment, the transmitting side 10
With 0 and n pseudo noise generators 102,
At the receiving side 200, pseudo noise (n = N) that is supposed to be used at the transmitting side can be constantly generated. The reference signals that have been matched enter the tracking loops at that point in time, so when synchronization is finally obtained for all the reference signals used for code modulation, pseudo noise that combines these reference signals is received. The signal can be completely demodulated.

In the embodiment of the present invention, in the code multiplexer 104 on the transmission side, data regarding a schedule of pseudo noise selection from a hopping scheduler described later is shown via an input 106 thereof. FIG. 7 shows an example of a code hopping scheduler. FIG. 7a shows the case of simple code hopping with a constant period, and eight pseudo noises PN-1.
~ One pseudo noise from PN-8 at a specific cycle
Select PN sequentially. In this example, PN-3, PN-5, PN-
2, PN-6, PN-4, PN-1, PN-8, PN-7, PN-3 are selected in this order. FIG. 7b shows the case of random code hopping with a non-uniform period, and four pseudo noises PN-1 to PN-4.
Is an example of. That is, the schedule is (PN-2), (PN-
1, PN-3, PN-4), (PN-2, PN-4), (PN-1),
(PN-2, PN-3), (PN-1, PN-4), (PN-3),
(PN-2, PN-3), (PN-1), (PN-1, PN-2, PN-
3), (PN-1), (PN-1, PN-2), (PN-1, PN-2,
The sequence is (PN-4), (PN-1, PN-2), (PN-4). FIG. 7c shows an example of a mutual complementary code whose period is not constant, and is a case where the sum of the numbers of eight PN codes is set to 13. That is, in this schedule
(PN-2, PN-4, PN-7), (PN-3, PN-4, PN-6),
(PN-1, PN-5, PN-7), (PN-2, PN-3, PN-8),
(PN-2, PN-5, PN-6), (PN-1, PN-4, PN-8),
The sequence is (PN-3, PN-4, PN-5). In the example of FIG. 7c, the combination of pseudo noises used at the time of transmission is given a specific relationship as in this embodiment, and when synchronization is not achieved for at least one type of pseudo noise, selection is made at the same timing. It is possible to determine this missing pseudo-noise from other pseudo-noises of the specified relationship and combine it in the receiver. For example, the pseudo noise generators 102-1 to 102-n on the transmission side are S units 18
It is assumed that there is a one-to-one correspondence with -1 to N, respectively, and in FIG.
PN-1 (102-1), PN-5 (102-5), PN-7 (102-
In the case of one selection sequence of 7), the system synchronization monitor of FIG. 1 sends the signal of the synchronization state from the S units 18-1, 18-5, 18-7 to the respective lines 19-1, 19-5, It can be received via 19-7. The combination of these sequences, or the timetable of the combination, can be stored in advance in the system synchronization monitor. Or data line 21
It may be given from an appropriate external circuit via. In this case, if at least one synchronization is not obtained in the S unit within a predetermined period from the start of the sequence, for example, S
Even if the synchronization of the unit 18-7 is not established, the system synchronization monitor 20 still receives the PN− signal via the PN code selection data line 28.
Data for selecting 1 (24-1), PN-5 (24-5), PN-7 (24-7) is given to the code multiplexer 26.

Is the PN code selection data given to the code multiplexer 104 on the transmission side via the input data line 106 stored in advance in a storage device such as a ROM or randomly generated and at least one PN code is predetermined? Alternatively, it is selected according to a time schedule of a short time unit of several hundred milliseconds or less, which is determined at any time.

In the case of the method of FIG. 1 between the transmitters and receivers in communication, it is necessary to re-synchronize the code after the change of the selection sequence, and generally time is required for this, but this synchronization It is desirable to shorten the time as much as possible to maintain the quality of communication. For this purpose, it is certain that the pilot signal is transmitted to the receiving side in advance prior to the code change, provisional synchronization is established, and the code change is executed while confirming this, and the synchronization is shortened. Is effective for.

FIG. 8 shows one configuration for doing this using pilot signals. In FIG. 8, elements similar to those in FIG. 1 use the same reference numbers. In FIG. 8, the transmitter 100 of FIG. 1 has a receiver 300 on the same side, and
The receiver 200 in the figure has a receiver 400 on the same side corresponding to the receiver 300. Transmitter 100 and corresponding receiver
200 constitutes a transmission / reception unit # 1, and the transmitter 400 and the receiver 300 corresponding thereto constitute a transmission / reception unit # 2. Site # 1 (transmitter 100 and receiver 300) has n
A code multiplexer 104 is provided for receiving the PN codes of the PN generators 102-1 to 102-n, and a code hopping scheduler 110 provides PN code selection data via line 106. In the example,
The code hopping scheduler 110 normally performs code hop according to the master scheduler, but changes the schedule when a channel out of synchronization is formed between PN-1 to n. Code hopping scheduler 110 also includes a line 112 for transmitting an instruction signal for generating a pilot signal associated with each PN generator 102-1 to 10-n. PN
When the code is changed, a code change pulse train corresponding to the code may be transmitted as a pilot signal prior to the start of the modulation with the regular code.

Receiver 200 at Site # 2 (receiver 200 and transmitter 400)
Receives a pilot signal sent from the transmitter 100 in advance before changing the PN code. This occurs on line 17 as a code transfer pulse in the same manner as described above. The corresponding S unit (Fig. 2) AND gate 80 this transfer pulse.
And 82. The AND gate 80 receives the code transfer pulse of the output of the PN generator 46 at the other input, and the AND gate 82 receives the code transfer pulse of the delayed output of the PN generator 46 (2 × d ′ delay time). Counters 84 and 86 are both enabled by the sync instruction pulse on line 19 to count the match pulses on each AND circuit, respectively. Therefore, the output of OR gate 88
90 provides a signal for identifying the pilot signal. S unit
The lines 90-1 to 90-N of 18-1 to N are provided to the system synchronization monitor 20. System synchronization monitor 20 is the applicable S
The identification signal of the pilot signal from the unit is received, and the PN code selection data is given to the line 28.
Let 26 do it. The combined PN code on line 30 is provided as a transmission modulation code for transmitter 400 having antenna 401 at the same site (site # 2). Site # 1 antenna
The receiver 300 having 301 has a portion 302 having the same structure as the portion 202 surrounded by the dotted line of the receiver 200 at the site # 2.
However, the circuitry corresponding to system sync monitor 20 in portion 302 has line 303 extending to code hopping scheduler 110. Therefore, transceiver unit # 2 (4
00, 300) confirms the presence of the retransmitted pilot signal and causes the receiver 100 to begin modulating the pilot signal with the associated regular PN code. The code hopping scheduler 110 also compares the received code code or pilot signal received via the transceiver unit # 2 with the code code or pilot signal used for transmission at the same site. It is possible to identify a code code that is out of synchronization with the other site and perform control such as changing the code code or changing the schedule.

FIG. 9 shows a code change between two sets of transmitters / receivers (unit # 1 and unit # 2) by a method of selecting two out of five PN codes (PN-1 to 5) and performing code modulation. It is a figure which shows a process. The code hopping scheduler 110 uses the PN−
When there is a channel that cannot be synchronized between 1 to n (corresponding to n = 5 in the explanatory view of FIG. 9), the schedule is changed. The example of FIG. 9 shows a state in which PN-5 due to external jamming is out of synchronization. In the figure, the hatched portion indicates the pilot signal portion. The time interval I is the case of the (PN-1, PN-2) selection mode to the (PN-3, PN-5) selection mode at the timing of the start process of the PN code change according to the normal schedule. Since time period II became out of synchronization with PN-5, the schedule was changed and the process of transition from the selection mode of (PN-3, PN-5) to the selection mode of (PN-3, PN-4) Indicates.

[Effects of the Invention] As described above, according to the present invention, in the spread spectrum communication method that selectively uses a plurality of pseudo noises, the transmitter and the receiver perform reliable and rapid spread code change, that is, code hopping. Therefore, it is possible to effectively prevent eavesdropping and obstruction in special applications.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram of an embodiment of the present invention, FIG. 2 is a more concrete view of a part of the elements of FIG. 1, and FIGS. 3 to 7 show the operation of FIG. 1 and FIG. 8 is a schematic circuit diagram showing a configuration in which the embodiment of FIG. 1 is applied to a transmission / reception mutual communication system, and FIG. 9 is a diagram showing an operation related to the configuration of FIG. is there. In the figure, 102-1 to n are pseudo noise generators, 104 is a code multiplexer, 106 and 108 are DBMs, 110 is a code hopping scheduler, 18-1 to N are S units, 20 is a system synchronization monitor, and 26 is a code multiplexer. .

Claims (1)

(57) [Claims] 1. A transmission side pseudo noise is selected from a plurality of transmission side pseudo noise generation means and a plurality of transmission side pseudo noises generated by the transmission side pseudo noise generation means in a predetermined relationship, is synthesized, and transmission side diffusion is performed. A transmitting side code multiplexer that outputs a code, a transmitting means that code-modulates an input signal with the transmitting side spreading code to obtain and transmit a spread spectrum signal, and a receiving means that receives the spread spectrum signal. A signal processing means for processing the received spread spectrum signal to obtain a pulse train signal corresponding to the code change of the spreading code used in the spreading process of the code modulation; a plurality of receiving side pseudo noise generating means; Receiving side pseudo noise generated by the receiving side pseudo noise generating means in response to the pulse train signal and the transmission Synchronization detection means for detecting synchronization with the receiving side pseudo noise, a system synchronization monitor for outputting reception side spreading code selection data in response to the synchronization detection signal from the synchronization detecting means, and in accordance with the spreading code selection data A receiving-side code multiplexer that selects receiving-side pseudo noise synchronized with the transmitting-side pseudo noise from the plurality of receiving-side pseudo noises, synthesizes it, and outputs a receiving-side spreading code; and the spread spectrum received by the receiving-side spreading code. Demodulation means for demodulating the input signal from a signal, and a receiver having: wherein the transmitter multiplexer predetermines a combination of transmitter pseudo noise having a specific relationship in accordance with transmitter spread code selection data. Code-hopping multi-spread spectrum characterized by selecting and synthesizing according to specified sequence Communication system.