JP2000196501A - Spread spectrum transmission and reception system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an initial synchronization acquisition time in a spread spectrum signal receiver adopting the FH system. SOLUTION: For the initial synchronization acquisition, frequency signal of the receiver is fixed to bring a hopping frequency to a single state. When a transmission signal that receives frequency hopping and is transmitted has a prescribed frequency, an IF signal with a frequency Δf whose voltage is more than a reference voltage is generated and a comparator circuit 6 outputs an output signal. When a desired ID signal is detected from an output of a demodulation circuit 4, a CPU generates a detection signal. Then a control circuit 8 generates a control signal to activate a PN code generating circuit 9, which starts frequency hopping synchronously with that of the transmitter side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency hopping type spread spectrum transmission / reception system with improved initial synchronization acquisition.

[0002]

2. Description of the Related Art Generally, there are two broad types of transmission / reception systems for spread spectrum signals: a direct spread system and a frequency hopping system. In the direct spreading method, for example, FSK
Or spread-spectrum-modulated signal is transmitted after spread-spectrum with a spread code, the receiving side generates a receive spread code synchronized with the spread code in the spread-spectrum signal, and despreads the received spread-spectrum signal with the receive spread code. By doing so, an FSK or PSK modulated signal is obtained. On the other hand, the frequency hopping method does not spread an information modulation signal with a spreading code as in the direct spreading method, but changes the frequency at the same time between transmitting and receiving apparatuses. Hereinafter, the frequency hopping (FH) method will be described.

FIG. 6 shows a conventional spread spectrum transmitting / receiving system of the FH system. In the transmitting device 61 of FIG. 6, an information modulated signal that has been AM, FM, FSK or PSK modulated (hereinafter collectively referred to as information modulation) is frequency-converted by a mixer 63 into a transmission RF signal by a frequency signal. The frequency signal is generated from the frequency signal generating circuit 64, and the output frequency of the frequency signal generating circuit 64 is hopped by a PN code (spreading code) from outside in a predetermined pattern. When the output frequency of the frequency generation circuit 64 is hopped as described above, the hopped R
The F signal is transmitted from the transmitting device 61.

Then, the RF signal is received by the receiving device 65, and a predetermined IF
The signal is frequency-converted, and then the IF signal is demodulated.
In the receiving device 65, the frequency signal is
6, the frequency signal generating circuit 66 hops the frequency in a predetermined pattern according to the PN code, similarly to the transmitting side. When the frequency signal is hopped by the PN code, the frequency of the RF signal serving as a predetermined IF signal is also hopped.

FIG. 3 shows a PN code generation circuit used in the FH system. In FIG. 3, a shift register 31 is applied to a first-stage register which is composed of four-stage registers operated by the same clock, and to which the outputs of the first-stage and the fourth-stage are added. And a weighting circuit 32 for weighting the output of In the weighting circuit 32, in response from the first stage to the register of the fourth stage each present circuit from 2 ³ 2 ^0, for example, when the output of the first stage outputs a "1", the output of the 2 ³ = 8 Is the weighting circuit 3
From 2 Further, the output of the weighting circuit 32 is added by the addition circuit 33, a distance is calculated from the addition result, and this distance is applied to the frequency signal generation circuit as a PN code. The distance is defined as a value obtained by subtracting the sum of the output patterns of the adjacent shift registers 31.

FIG. 4 shows the output pattern of the shift register 31, the weighted sum corresponding to the output pattern, and the distance.
Every time the contents of the register are changed, the distance is changed.
In FIG. 3, the hopping frequency is determined according to the distance. Here, assuming that hopping frequencies corresponding to distances 1 to 8 are f1 to f8, the frequency hopping of the transmission signal proceeds in a pattern as shown in FIG.

By the way, in the receiving apparatus, in order to correctly demodulate the modulation signal, the RF signals on the transmitting side and the receiving side must have the same pattern and hop in synchronization. That is, it is necessary that the frequency pattern of the frequency signal is the same and the PN code is changed in synchronization with the same pattern. Therefore, at the start of transmission / reception, it is necessary to acquire the frequency hopping pattern synchronously.

In general, a receiving apparatus matches a hopping pattern with a transmission signal, and includes a synchronization acquisition circuit for acquiring synchronization for that purpose. Conventionally, initial synchronization has been performed by a sliding correlator. In the sliding correlation, assuming that the period in which one pattern circulates is one hopping cycle, the receiving apparatus performs one cycle of hopping according to the hopping pattern, compares the receiving side with the hopping pattern in the RF signal, and performs correlation. Get. If the correlation value cannot be obtained, the PN code pattern is shifted by one chip by sliding. Until the correlation value becomes maximum, the sliding is repeated to obtain the coincidence of the hopping patterns on the transmitting and receiving sides.

[0009]

However, in the case of the sliding correlator, if the hopping patterns on the transmitting and receiving sides are completely displaced by several chips or more, there is a problem that a great deal of acquisition time is required. Particularly, in a system in which signals are exchanged between the transmitting and receiving devices at a low speed, the use of the above-described sliding correlator significantly increases the synchronization acquisition time, and occupies most of the synchronization of signals during transmission and reception. However, the efficiency of signal transmission and reception was very poor.

[0010]

SUMMARY OF THE INVENTION The present invention provides a frequency hopping type spread spectrum transmission / reception system which uses a code sequence that hops a specific frequency only once.
A transmitting device that frequency-hops and transmits an information signal,
And a receiving device that stands by so as to receive the specific frequency at the time of initial synchronization acquisition.

In particular, the receiving apparatus includes a frequency signal generating circuit for generating a frequency signal for frequency hopping, a multiplying circuit for multiplying a transmission signal and the frequency signal, and a signal of a predetermined frequency among output signals of the multiplying circuit. Filter, a signal detection circuit for detecting the presence of a signal of a predetermined frequency from the output signal of the filter, and at the time of initial synchronization acquisition, the frequency signal is set to a fixed frequency, according to the output signal of the signal detection circuit And a control circuit for starting hopping of the frequency signal.

Further, an ID detection circuit for detecting an ID signal from the received signal is provided, and the control circuit includes a signal detection circuit and an ID detection circuit.
Frequency hopping is started when both output signals of the D detection circuit are detected.

Further, the signal detection circuit is characterized by comprising a comparison circuit for comparing the output level of the filter with a reference level. Still further, the signal detection circuit includes a PLL using an output signal of the filter as a reference signal.
And a lock / unlock detection circuit for detecting a locked state of the PLL.

According to the present invention, a transmission signal is transmitted from the transmission side in a sequence in which a specific frequency is hopped only once, and the reception side is set to a reception standby state at the specific frequency. In the frequency hopping pattern, the next hopping frequency after the specific frequency is uniquely determined, and the frequency hopping can be synchronized in a short time.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the present invention. 1 is a frequency signal generating circuit for outputting a frequency signal, and 2 is a frequency converter for converting a received RF signal into an IF signal according to the frequency signal. Mixer 3, BPF for passing an IF signal of a predetermined frequency out of IF signals, and 4, AM, FM, FS
A demodulation circuit that performs K or PSK demodulation to obtain an information signal, 5 is a level detection circuit that detects the output level of the BPF 3, and 6 is a comparison that compares whether the output level of the level detection circuit 5 is higher than a reference voltage. A circuit 7 for extracting data from the output signal of the demodulation circuit 4 and executing various controls;
U and 8 are control circuits for generating control signals based on the output signals of the comparison circuit 6 and the CPU 7, and 9 is a PN code generation circuit for hopping the frequency of the frequency signal by the control signals. Reference numerals 1 to 9 indicate spread spectrum signal receiving apparatuses.

Reference numeral 10 denotes an information modulation circuit for generating an information modulation signal; 11, a PN code generation circuit for generating a PN code of the same code sequence as the PN code generation circuit on the receiving side; A frequency signal generation circuit for generating a transmission frequency signal according to the PN code, and a mixer 13 for frequency-converting the information modulation signal according to the transmission frequency signal. Reference numerals 10 to 13 indicate spread spectrum transmitting apparatuses.
In FIG. 1, when communication is started, the spread spectrum transmitting apparatus transmits the transmitting apparatus while performing frequency hopping. The PN code generation circuit 11 is configured as shown in FIG. 3 as in the prior art, and the contents of the registers and the like change in a pattern as shown in FIG. Then, the transmission frequency signal hops due to the PN code, whereby the mixer 1
3 is hopped in a pattern as shown in FIG. As is clear from FIG. 5, this hopping pattern is a sequence in which the frequency f8 hops once, and the rest hops twice.

On the other hand, when communication is started, the spread spectrum signal receiving apparatus enters a standby state in which it waits for only a specific transmission signal f8. That is, in the standby state, the frequency signal is set to (f8 + Δf), and the frequency of the transmission signal is set to f8
Only in the case of, the IF signal having the frequency Δf is generated from the mixer 2.

When the transmission frequency is not f8, the output frequency from the mixer 2 is f8 + Δf ± fn (where n = 1 to
7) and not Δf. Therefore, this IF signal cannot pass through BPF3. IF signal is BP
If the signal cannot pass through F3, no output is generated from the level detection circuit 5, and as a result, no output signal is generated from the comparison circuit 6. Therefore, the control circuit 8 controls the control signal STA
Does not generate RT. Note that, as described later, the control signal ST
ART is a signal for starting frequency hopping on condition that both output signals of the comparison circuit 6 and the CPU 7 are generated.

While the control signal START is not generated, the receiving apparatus sets the fixed receiving frequency signal as it is,
A transmission signal whose frequency is hopping every moment is received. Then, when the transmission signal having the frequency f8 is received by the receiving device, an IF signal having the frequency Δf is generated from the mixer 2 by the frequency signal having the frequency (f8 + Δf).
This IF signal is level detected by the level detection circuit 5,
A detection signal having a level is generated. The detection signal is compared with a reference voltage by the comparison circuit 6. When the detection signal is higher than the reference voltage, an output signal is generated from the comparison circuit 6 and applied to the control circuit 8.

The IF signal is demodulated into an information signal by a demodulation circuit 4 and applied to a CPU 7. The CPU 7 detects an ID signal from the information signal and detects whether or not the signal is a desired ID signal. If the ID signal is a desired ID signal, the transmission RF signal is recognized as a signal from a desired station, and a detection signal ID is generated to the control circuit 8. When the control circuit 8 receives both output signals of the comparison circuit 6 and the CPU 7, the control signal S
TART occurs. After that, the PN code generation circuit 9
When the control signal is received, (f8 +
The PN code is changed so as to change the frequency of the frequency signal from Δf). Thereby, the receiving apparatus starts frequency hopping synchronized with the transmitting side. When the IF signal level is equal to or lower than the reference voltage or when a desired ID signal cannot be detected, the receiving device continues to be in a standby state. When the frequency hopping is started, the initial synchronization acquisition is completed, and normal communication is started between the transmitting and receiving apparatuses.

In FIG. 1, the reception frequency of the spread spectrum receiving apparatus at the time of initial synchronization acquisition is fixed at f8. In the PN code generation circuit 9, as shown in FIG.
While the frequencies f1 to f7 occur twice in one cycle,
The frequency f8 occurs only once. If the hopping frequency of the receiving device is set to f8 as the initial state, the next hopping frequency is uniquely determined to shift to f4. Therefore, if the receiving device can capture the transmission signal of f8, it can immediately shift to the frequency hopping state. . Therefore, it is possible to shorten the time required for completing the synchronization acquisition.

The frequency hopping pattern is not limited to those shown in FIGS. 4 and 5, but can be applied to the present invention as long as a specific pattern hops only once.

FIG. 2 is a diagram showing another embodiment of the present invention, in which a PLL is used as a signal detection circuit. However, other circuit configurations and operations are the same as those in FIG. In FIG. 2, the IF signal of Δf is applied to the phase comparison circuit 22, and the phase comparison between the IF signal and the output signal of the VCO 21 is performed. An output signal corresponding to the phase difference is generated from the phase comparison circuit 22, and the output signal of the phase comparison circuit 22 is smoothed by an LPF (low-pass filter) 23 and then applied to the VCO 21 as a control voltage. The output signal of the VCO 21 returns to the phase comparison circuit 22 and is compared with the IF signal again.
The phase comparison circuit 22, LPF 23 and VCO 21 constitute a PLL circuit using the IF signal as a reference signal. When the IF signal of Δf is applied to the phase comparison circuit 22, the PLL circuit operates so that the output frequency of the VCO 21 matches Δf.

The output signal of the LPF 23 is applied to a lock / unlock detection circuit 24, which detects whether or not the PLL circuit has locked at the frequency Δf based on the output signal of the LPF. When the VCO 21 generates an output signal of Δf, the output voltage of the LPF 23, which is the control voltage of the VCO 21, becomes Vc1. The output Vc1 is compared by the lock / unlock detection circuit 24 with reference voltages Vr1 and Vr2 satisfying the relationship of Vr1 <Vc1 <Vr2. Since the output Vc1 falls within the range of the reference voltages Vr1 and Vr2, the lock / unlock detection circuit 24 detects that the PLL circuit is locked at the frequency Δf. When locked, an output signal is generated from the lock / unlock detection circuit 24 and the control circuit 8
Is applied to

If no IF signal is generated or if it is not Δf, the PLL circuit locks to a frequency other than Δf. Therefore, the output signal of the LPF falls outside the range of the reference voltages Vr1 and Vr2, and the lock / unlock detection circuit 2
No. 4 is detected that the PLL circuit is not locked to the frequency Δf. In this state, the lock / unlock detection circuit 2
4 does not generate an output signal.

[0026]

According to the present invention, when capturing the initial synchronization,
Since the receiving device stands by at a single frequency and captures synchronization by the error frequency between the frequency of the transmission signal and the single frequency, the circuit configuration can be simplified. In addition, since synchronization can be acquired in one cycle of frequency hopping, the initial synchronization acquisition time can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram illustrating a specific example of a PN code generation circuit.

FIG. 4 is a state diagram showing an output state of each circuit of FIG. 3;

FIG. 5 is a characteristic diagram showing a frequency hopping pattern.

FIG. 6 is a block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 12 Frequency signal generation circuit 2, 13 Mixer 3 BPF 4 Demodulation circuit 5 Level detection circuit 6 Comparison circuit 7 CPU 8 Control circuit 9, 11 PN code generation circuit 10 Modulation circuit 21 VCO 22 Phase comparison circuit 23 LPF 24 Lock / Unlock Lock detection circuit

Claims (5)

[Claims] 1. A frequency hopping spread spectrum transmission / reception system, comprising: a transmission device for frequency-hopping and transmitting an information signal by a code sequence for hopping a specific frequency only once; and receiving the specific frequency during initial synchronization acquisition. And a standby receiving apparatus. 2. A receiving apparatus comprising: a frequency signal generating circuit for generating a frequency signal for frequency hopping; a multiplying circuit for multiplying a transmission signal and the frequency signal; and a signal of a predetermined frequency among output signals of the multiplying circuit. And a signal detection circuit for detecting the presence of a signal of a predetermined frequency from the output signal of the filter, at the time of initial synchronization acquisition, the frequency signal is fixed frequency,
The spread spectrum transmission / reception system according to claim 1, further comprising a control circuit that starts hopping of a frequency signal in accordance with an output signal of the signal detection circuit. 3. An ID detection circuit for detecting an ID signal from a received signal, wherein the control circuit starts frequency hopping when both the signal detection circuit and the output signal of the ID detection circuit are detected. The spread spectrum transmitting / receiving system according to claim 2, wherein 4. The spread spectrum transmission / reception system according to claim 2, wherein said signal detection circuit comprises a comparison circuit for comparing an output level of said filter with a reference level. 5. The signal detection circuit according to claim 2, wherein the signal detection circuit comprises a PLL that uses the output signal of the filter as a reference signal, and a lock / unlock detection circuit that detects a locked state of the PLL. The spread spectrum transmission / reception system as described.