JPS6337539B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving apparatus, and particularly to a receiving apparatus in a frequency hopping communication system using a spread spectrum signal based on frequency hopping modulation.

When transmitting and receiving information using radio waves, the spread spectrum communication method, which modulates and transmits and receives signals over a much wider frequency band than the frequency band required to transmit the information to be transmitted, has recently been introduced. It's becoming well known.

Frequency hopping modulation is one of the modulation methods used in spread spectrum systems, and is a pattern that is determined by a code sequence specified in advance for the purpose of communication. The information to be sent is incorporated into the above-mentioned code sequence or hopping frequency.

In a receiving device that receives such a spread spectrum signal, it is necessary to demodulate this signal in two stages. The first step is to demodulate the spread spectrum modulation of the input signal spread by frequency hopping modulation to restore the spectrum and band, and then the second step is to demodulate the signal containing information to extract the information. There is a process corresponding to normal demodulation processing.

FIG. 1 is a diagram showing an example of the operating principle of a frequency hopping communication system. At the transmitting station, pseudo-noise codes (hereinafter referred to as PN codes), such as longest linear codes (hereinafter referred to as M-type sequence codes), and other M
An output composite code of a code generator 11 that generates an arbitrary composite code by combining sequences is modulated by an information input 111. In this code modulation, an information signal is included in the code, and is modulated in response to information input so that it can be understood only by a receiving station that knows the original composite code.

A in FIG. 1B is a composite code sequence modulated in this manner, and information is contained in this code sequence.

In this case, the speed of the information to be transmitted is often on the order of several megabits/s, and therefore, as is well known, in order to improve the processing gain determined by the bandwidth ratio, the speed of the information to be transmitted must be A high-speed code sequence must be generated by code generator 11 with a much wider bandwidth and rate than that of .

In the frequency hopping modulation method, the output frequency of the frequency synthesizer 12 is controlled and determined in response to such a high-speed code sequence generated by the code generator 11, and a plurality of hopping frequencies are generated and transmitted from the transmitting antenna 13. Send. This transmission signal contains a plurality of evenly spaced carrier frequencies ₁ , ₂ , _3, etc. such as b in each pulse of the high-speed code sequence a shown in FIG. Become something. In the case of Figure 1B, the frequencies included in each pulse of high-speed code sequence a are three waves, and the transmission order is ₁ , ₂ , ₃ , but the number and order of these frequencies may vary depending on the purpose of communication. Of course, this can be determined arbitrarily.

Further, the case shown in FIG. 1B shows an example of the operation, and it is of course possible to allocate a large number of hopping frequencies for transmission corresponding to the binary levels of the code sequence a.

The spread spectrum signal subjected to frequency spreading in this manner is transmitted from the transmitting antenna 13, and the receiving station receives this signal using the receiving antenna 14 and sends it to the frequency mixer 15.

As mentioned above, the demodulation of the spread spectrum signal is performed in two stages.

The first stage is spread spectrum modulation demodulation, and the second stage is demodulation to extract information.
Demodulation of frequency hopping modulation, like other spread spectrum modulation methods, basically involves mixing the received wave with a local reference wave that has the same structure as the received wave and is synchronized with the received wave, and then calculating the product of both. , that is, by correlating the two. This local reference wave can be generated by providing the receiving station with the same code generator 11 and frequency synthesizer 12 as those on the transmitting station. The received wave undergoes despreading, which converts the signal spread over a wide band into a small number of signals with a bandwidth sufficient to extract information, and bandwidth restoration, and then undergoes bandwidth restoration.
Step-by-step demodulation is performed, but in this case, the demodulated wave is usually converted to an intermediate frequency by the heterodyne method to prevent unnecessary waves from being mixed in as an information signal.
It is demodulated by a demodulator 17 via an IF amplifier 16 and outputs information.

In this type of spread spectrum communication system using frequency hopping modulation, carrier waves such as hopping frequencies ₁ , ₂ , and ₃ included in the transmitted and received signals can be arbitrarily set as desired, and the transmission sequence can also be freely set. Because you can choose
By appropriately combining and configuring these, selective communication that is resistant to interference, interference, etc. can be performed between a plurality of transmitting and receiving stations.

This communication system that uses spread spectrum using frequency hopping modulation enables multiplex communication using selective calling and frequency division multiplexing of composite codes.The low transmission power spectral density provides high signal secrecy and prevents interference and jamming. It has various characteristics that make it strong.

Conventionally, this type of frequency hopping communication system is generally performed as follows.

That is, the hopping frequency to be included in each pulse of the composite code sequence modulated by the information is set according to the hopping pattern as desired.
₁ , ₂ , ₃ ... _o , and the transmission order of these hopping frequencies is such that a different sequence is given to each receiving station as an identification signal for identifying the receiving station, and a predetermined interval is set between each of these n frequencies. and transmit with a selective delay time of .

The receiving station prepares n receiving channels equal to the number of hopping frequencies, and receives frequency hopping received waves containing these n hopping frequency groups, each transmitted in a specific sequence, and a local standard shifted by an intermediate frequency. After performing correlation by frequency mixing with the wave and demodulating the spread spectrum code to obtain n intermediate frequencies containing information,
The hopping frequency sequence of ₁ , ₂ , ₃ ... _o containing the detected information is passed through a delay line to cancel each other's delay amount, and then input to an AND circuit. Accordingly
₁ , ₂ , ₃ ... _o hopping frequencies whose sequences differ depending on the receiving station are input to the AND circuit, and when they are input in agreement, that is, if the local reference wave and the input signal are synchronized, An output is generated in the AND circuit, which outputs a single signal that is the sum of the simultaneous inputs of these hopping frequencies containing information, and by this output, synchronization is confirmed and the information contained in the sequence of this single signal is output. is extracted by demodulation.

However, according to such a method, the receiving station obviously requires n receiving channels equal to the number selected as the hopping frequency, and as the hopping frequency increases, the size of the receiving circuit configuration increases, and it essentially requires several thousand channels. In order to avoid this, the number of hopping frequencies to be received is fixed to several waves to simplify the process. If you try to do so, you will be obstructed.
It is vulnerable to interference, etc., and requires a delay line having a number of taps and a delay amount equal to the period of several thousand hopping patterns.

Furthermore, in order to synchronize the local reference wave of the receiving station with the hopping pattern of the input signal, a delay lock loop is usually used to force the hopping pattern into synchronization through a synchronization search mode. Also, prepare code sequences of two local reference signals, one of which is delayed by a specific time compared to the other, and use the output information from this to change the speed of the clock signal that drives the code generator so that synchronization can be achieved. This is a common method, which assumes the synchronization search mode for initial capture of synchronization errors, and when the level of the input signal is close to the threshold for the operation of this delay lock loop, the signal S Ratio of noise to N, S/N
This method has the disadvantage that it requires several times as much synchronization pull-in time as compared to a case where the condition is good.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to use a receiving device using a frequency hopping method, arbitrarily receive a plurality of hopping frequencies forming a hop pattern according to a transmission/reception sequence, and add these outputs to detect synchronization errors. By the simple means of obtaining an output signal with a level proportional to , and thereby controlling the local reference wave for demodulation in the receiver, synchronization can be achieved within the hop pattern period, and the number of receiver circuits and the delay line It is an object of the present invention to provide a receiving device which can be greatly reduced in number, is resistant to interference and interference, and has high functional flexibility.

The device of the present invention corresponds to the transmission speed of an input spread spectrum signal in a frequency hopping communication receiving device that communicates information by changing frequencies (hops) according to a predetermined time series (hopping pattern). a high-speed switching receiving circuit that switches and receives the hopping frequency at a high speed;
a plurality of selective receiving circuits capable of selectively receiving the plurality of hopping frequencies in accordance with a frequency hopping pattern and controlling the reception frequency from the outside; a plurality of delay circuits that apply a selected delay amount to each of the hopping frequencies to produce a single position modulation signal, an adder circuit that adds the outputs of the plurality of delay circuits, and a high-speed switching receiving circuit. a high-speed switching frequency synthesis circuit that switches and outputs a local reference wave for demodulating the spread spectrum signal by frequency mixing the input spread spectrum signal and performing despreading by correlation; ,
Under the control of a pre-installed program, the receiving frequencies of the plurality of selective receiving circuits are controlled and set in accordance with a known frequency hopping pattern, and the output of the adding circuit is detected to combine the local reference wave with the local reference wave. The local reference wave is controlled by controlling the phase of the hopping frequency fast switching pattern of the local reference wave output from the fast switching frequency synthesis circuit in accordance with the detection level that is proportional to the synchronization shift of the frequency hopping pattern of the spread spectrum signal. and a control circuit for synchronizing the input spread spectrum signal with the input spread spectrum signal.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention. A spread spectrum signal 101 input from the receiving antenna 1 is sent to three selective receiving circuits 5A and 5B along with the high-speed switching receiving circuit 2 which is the main receiving circuit.
and 5C are also input.

As mentioned above, the input spread spectrum signal is
It has a spread spectrum code that is pulse-modulated according to the information to be transmitted, and a hopping frequency signal that is included in each pulse of the code and is transmitted in a frequency hopping pattern specified in advance for each receiving station, Therefore, to demodulate this, a two-step demodulation operation is required: first demodulating the spread spectrum code, and then performing so-called baseband demodulation to extract the information signal, similar to the demodulation of normal AM and FM modulated waves. is necessary.

The high-speed switching receiving circuit 2 which is the main receiving circuit is a frequency mixer 2 using a double balanced frequency mixer circuit.
1. It is equipped with an IF amplifier circuit 22 and a demodulator 23 that performs baseband demodulation, and after demodulating a spread spectrum code, outputs information output 201 by baseband demodulation.

Frequency mixer 2 demodulates the spread spectrum code
1, the correlation is established by multiplying the input signal by a local reference wave 301 output from the fast switching frequency synthesizer 3, which will be described later. This local reference wave is used in the subsequent processing step. In order to suppress the mixing of frequencies other than signal waves due to interference etc., the input hopping frequency is set to an intermediate frequency _IF.
and the same code as the spread spectrum code before modulation by information.
It has a PN code.

The high-speed switching frequency synthesizer 3 has a code generator using a feedback shift register, a frequency synthesizer that outputs a desired frequency by frequency synthesis, and a clock generator that generates clock pulses to drive the code generator. A driving clock pulse is output from the device, and a PN code with the same pattern as the code before modulation with information is generated on the transmitting side, and a hopping frequency shifted by the intermediate frequency _IF is used as the hopping pattern.
Generated in correspondence with PN code.

Therefore, the hopping frequency of the local reference wave 301 can change the pattern speed, that is, the phase of the individual hopping frequencies, depending on the speed of the clock pulse. In addition, the code of the local reference wave is the same PN code as the original code before the code of the input spread spectrum signal undergoes phase modulation by information.
This code is demodulated by correlating with the spread code of the input spread spectrum signal, and the spread spectrum is despread and output from the frequency mixer 21 again as a narrowband baseband information signal before spreading. will be done. However, in this code demodulation, the hopping frequency is converted to an intermediate frequency _IF as described above. Therefore,
The frequency mixer 21 outputs an intermediate frequency signal sequence in a sequence corresponding to the hopping pattern and phase modulated by information. This output is amplified by an IF amplifier 22, then subjected to baseband demodulation by a demodulator 23 having a phase detection circuit, and is output as an information output 201.

As mentioned above, the spread spectrum signal 101
demodulation can be obtained by correlating this with the synchronized local reference wave 301, but in reality it is extremely rare that the two are always synchronized, and the arrival time of the input signal 101 and The signals are deviated due to the influence of the Doppler frequency, etc. Therefore, it is essential for reception to always maintain this synchronization.

Normally, this synchronization requires a complicated delay lock loop as described above, and it takes a long time to acquire the synchronization. Furthermore, in order to perform communication corresponding to all hopping frequencies, many problems arise, such as the need to prepare receiving circuits equal to the hopping frequencies.

In this embodiment, this synchronization is performed as follows. That is, three selective receiving circuits 5A, 5B
and 5C receive the input spread spectrum signal 101, demodulate it and output it. In this case, the reception frequencies of the three selective reception circuits 5A, 5B and 5C can be arbitrarily set under the control of a program built in the control circuit 4 which receives the signals via the bus line 402. A control circuit 4 that controls the overall synchronous operation receives a pattern setting signal 40 from a transmitting station.
1, three adjacent frequencies corresponding to the frequency hopping pattern to be transmitted, for example, if the hopping pattern is ₁ , ₂ , ₃ ... _o , the selective receiving circuit 5A receives ₁ , 5B receives ₂ , 5C is set as the reception frequency by shifting ₃ by the intermediate frequency _IF .

The selection receiving circuit 5A is the same circuit as 5B and 5C, and includes a frequency mixer 51A, a frequency synthesizer 52A,
The frequency synthesizer 52A has a buffer memory 53A, an IF amplifier _54A , and an envelope detector 55A.
Enter. The frequency synthesizer 52A has a frequency synthesizer, a clock signal generator, and a PN code synthesizer.The frequency synthesizer 52A has a frequency of ₁ + _IF according to the control signal of the control circuit 4 received via the buffer memory 53A, and spreads the input spread spectrum signal. A local reference wave having a PN code which is the same composite code as the code is output, and the frequency mixer 51A performs correlation with the input spread spectrum signal 101 to demodulate the spread code with respect to the hopping frequency ₁ of the input spread spectrum signal. and the intermediate frequency
The signal is converted to _IF and input to the IF amplifier 54A.

Therefore, the signal input to the IF amplifier 54A is a pulse train of an intermediate frequency that has a hopping period of hopping frequency ₁ of the input spread spectrum signal and whose frequency has been converted to _IF .
IF amplifier 54A amplifies these intermediate frequency pulse trains and sends the output to envelope detector 55A. The envelope detector 55A performs envelope detection of the input pulse train of these intermediate frequencies, and sends it to the delay circuit 6A as an output of the selective receiving circuit 5A.

In this way, a signal is input to the delay circuit 6A at a timing equal to the period of the hopping frequency ₁ of the input spread spectrum signal and having a magnitude corresponding to the level thereof.

In exactly the same way, the output of the selective receiving circuit 5B receives the hopping frequency ₂ of the input spread spectrum signal.
A signal with a timing equal to the period of the hopping frequency 3 and a magnitude corresponding to the level is outputted, and a signal with a timing equal to the period of the hopping frequency ₃ of the input spread spectrum signal and a signal having a magnitude corresponding to the level is outputted to the output of the selective receiving circuit 5C. A signal with a corresponding magnitude is output.

The hopping frequencies are transmitted in a sequence of ₁ , ₂ , _{3 ,} . Therefore, by applying a delay amount corresponding to this time interval to the selective receiving circuits 5A, 5B, 5C, etc. using a delay circuit, these three outputs can all be output at the same time and at the same time when the transmission and reception are synchronized. The signal has a certain level. That is, these signals are equal level signals with a single time deviation.

Delay circuits 6A and 6B using charge transfer elements CCD (Charge Coupled Device) as analog delay lines provide the above-mentioned delay amount.

In this embodiment, when hopping frequency ₃ is used as a reference, ₂ is ahead of ₃ in time, and ₁ is ahead of ₂ in time. Therefore, the outputs of the selective receiving circuits 5A and 5B may be delayed so as to cancel out this advance time. Delay circuits 6A and 6B provide this amount of delay.

Now, the hopping frequencies are in the sequence ₁ , ₂ , ₃ ... _o , but even if the hopping pattern changes, the above method can be applied to any three adjacent frequencies.

The outputs of the delay circuits 6A, 6B and the selection receiving circuit 5C are sent to an adder circuit 7, which performs an addition operation on these three inputs. The output 701 of the adder circuit 7 has a maximum level when the three inputs are completely in phase with each other in accordance with frequency hopping, and decreases in level as the synchronization goes out.

This means that the selective receiving circuits 5A, 5B and 5
When the receive hopping frequencies ₁ , ₂ , and ₃ input to C are synchronized with the transmit hopping frequency, the output 701 of the adder circuit 7 is at the maximum, and the output 701 of the adder circuit 7 increases depending on the degree of synchronization. This corresponds to the decrease.

The output 701 of the adder circuit 7 is sent to the control circuit 4. The control circuit 4 has a level detection circuit consisting of an integrating circuit and a Schmitt trigger circuit, and under the control of a pre-built-in program, compares it with a judgment threshold to determine the magnitude of the level, and detects a level corresponding to this amount. A synchronous correction signal having a correction amount is sent to the fast switching frequency synthesizer 3 via the bus line 402. The high-speed switching frequency synthesizer 3 changes the phase of the local reference wave 301 synthesized and output from the synthesizer by changing the speed of the built-in clock signal using this synchronization correction signal, thereby changing the frequency of the high-speed switching receiver 2. The signal is sent to the mixer 21 and synchronized with the input spread spectrum signal 101.

The synchronization correction signal output from the control circuit 4 is also sent to the selective receiving circuits 5A, 5B, and 5C via the bus line 402, and is sent to the frequency synthesizers 52A, 52B, and 52C via the buffer memories 53A, 53B, and 53C, respectively. Adjust the phase of the local reference wave output from the input signal to maintain synchronization with the input signal.

In this way, three selective receiving circuits 5A, 5B
A simple method of detecting and correcting the phase shift between three adjacent hop frequencies using the outputs of 5C and 5C enables quick synchronization within one hop pattern period.

In addition, in this embodiment, the selective receiving circuit is
However, the present invention is characterized in that a plurality of hopping frequencies in a hopping pattern are compared, and synchronization is corrected in response to a decrease in output level due to out of synchronization, interference, interference, etc. ,
The number of selective receiving circuits may be three or more, and it is clear that in this case, the synchronization pull-in performance can be further improved, and the system will be resistant to interference and interference, and the S/N ratio will be improved. It is also possible in principle to use two selective receiving circuits. In this embodiment, three minimum units for majority judgment are selected as the criteria for synchronization judgment.

In addition, the high-speed switching frequency synthesizer 3 and frequency synthesizers 51A, 52B, 53C in this embodiment
The code generator included in the system is a PN code, but if desired, any other composite code obtained by combining M sequences may be used.Furthermore, in this embodiment, it is assumed that the information is contained in a spread spectrum code. However, it is clear that the present invention can also be easily applied to the case of transmitting and receiving a spread spectrum signal corresponding to a spread spectrum code using a carrier wave modulated with information in advance as a hopping frequency.

Furthermore, in terms of configuration, the high-speed switching frequency synthesis circuit 3
may be included in the high-speed switching receiving circuit 2, and the above can be easily implemented without detracting from the gist of the present invention.

As explained above, according to the present invention, in a receiving device using a frequency hopping method, a plurality of hopping frequencies that form a hop pattern are arbitrarily received according to a transmission sequence, and the outputs of these are added up and calculated in proportion to the synchronization difference. By simply obtaining an output signal with a level of
In addition, the number of receiving circuits equal to the number of hopping frequencies and the number of delay lines having a number of taps and a delay amount equal to the period of the hop pattern can be greatly reduced. This has the effect that it is possible to realize a receiving device with high performance.

[Brief explanation of the drawing]

FIG. 1 is an operating principle diagram showing an example of the operating principle of a frequency hopping communication system, and FIG. 2 is a block diagram showing an embodiment of the present invention. In Fig. 2, 1...receiving antenna, 2...
High-speed switching receiving circuit, 3... High-speed switching frequency synthesizer, 4... Control circuit, 5A, 5B, 5C... Selective receiving circuit A, B, C, 6A, 6B... Delay circuit A, B, 7... Addition circuit.

Claims (1)

[Claims] 1. In a frequency hopping communication receiving device that performs information communication by changing (hopping) the frequency according to a predetermined time series (hopping pattern), the frequency hopping is performed at a high speed corresponding to the transmission speed of the input spread spectrum signal. a high-speed switching receiving circuit that switches and receives hopping frequencies at high speed; a plurality of selective receiving circuits capable of selectively receiving the plurality of hopping frequencies in accordance with a frequency hopping pattern and controlling the receiving frequencies from the outside; a plurality of delay circuits that give each output signal of the selected receiving circuit a selected delay amount for each of the hopping frequencies in accordance with the hopping pattern to produce a single position modulation signal, and outputs of the plurality of delay circuits; and a local reference wave for demodulating the spread spectrum signal by performing frequency mixing with the spread spectrum signal input to the high speed switching receiving circuit and despreading by correlation. A high-speed switching frequency synthesis circuit that switches and outputs at high speed; and controlling and setting the receiving frequencies of the plurality of selective receiving circuits in accordance with a frequency hopping pattern specified under the control of a pre-installed program; hopping the local reference wave, which detects the output of the adder circuit and outputs it from the high-speed switching frequency synthesis circuit in response to the detection level that is proportional to the synchronization difference between the frequency hopping patterns of the local reference wave and the spread spectrum signal; A receiving device comprising: a control circuit that synchronizes the local reference wave with the spread spectrum signal by controlling the phase of a high-speed frequency switching pattern.