JP2700980B2 - Spread spectrum communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication system, and more particularly to a spread spectrum communication system using frequency hopping.

[0002]

2. Description of the Related Art Generally, data communication is modulated and demodulated using a narrow band modulation method (BPSK, QPSK, etc.). These communications can be realized with relatively small circuits,
For example, when there are multiple multipath waves in indoor use, fading called multipath fading occurs, and the line may not be maintained.

In order to avoid this, in recent years, spread spectrum communication systems have attracted attention. Among them, the frequency hopping method is particularly strong in multipath fading and is promising.

FIG. 4 shows a power spectrum.
In particular, FIG. 4 (a) shows a frequency propagation characteristics in the propagation path of the chamber in FIG. 4 (b) shows a case of transmitting a narrowband modulated wave band B _1, FIG. 4 (c) Frequency Hopping Shows the spectrum by As shown in FIG.
In a propagation path in a certain room, there are frequencies that are strengthened and frequencies that are weakened by multipath. In a propagation path having such propagation characteristics, a band B shown in FIG.
Consider the case of transmitting _one narrow-band modulated wave. At this frequency, the frequency is in a frequency range where dimensions are weakening, and as a result, C / N is deteriorated, and the error rate of the line is significantly deteriorated.

On the other hand, in the frequency hopping method as shown in FIG. 4C, the frequencies f _{1 to} f ₂ are divided into several slots of the band B ₁ or more, and several tens to several hundreds of them are prepared. The frequency used is changed for each bit. In this case, even if the C / N of some of the slots is degraded, the remaining slots have a high C / N, and some of the bits that statistically cause an error are part. Further, an error that is continuous for several slots can be corrected by employing an error correction method that is strong against interleaving and burst errors. As a result, in a propagation path with rapid changes as shown in FIG. Also, a stable line can be secured.

[0006] As described above, the frequency hopping method is as follows.
Although it has a strong characteristic in a propagation path with multipath fading, its circuit, especially a demodulation system, is a complicated and large-scale circuit, and thus has not been adopted except for some special systems.

FIG. 5 is a block diagram of a synchronous circuit for initial acquisition by a conventional frequency hopping method. This synchronization circuit for initial acquisition is described in "Spread Spectrum Communication System" by Mitsuteru Yokoyama, published by Science and Technology Publishing Company, and is a circuit for capturing an initial signal at the start of line connection. In FIG. 5, a frequency hopping synthesizer 31 generates a local oscillation signal having a local frequency corresponding to the hopping frequency. This local oscillation signal is supplied to a mixing circuit 32 and mixed with a reception signal received by an antenna 33. , Into an intermediate frequency signal. A predetermined band component is extracted from the intermediate frequency signal by a band pass filter (BPF) 34, squared by a squarer 35, and integrated by an integrator 36 to detect the energy of the signal.

A search control logic 37 performs control for eliminating uncertainties in the time domain and the frequency domain.
In addition to controlling the oscillation frequency of the clock 39, a control signal is supplied to the clock control circuit 40 to control the clock frequency from the clock generation circuit 41. The oscillation output of VCO 39 is provided to frequency hopping synthesizer 31, and the clock signal from clock generator 41 is provided to PN sequence generator 42. The PN sequence generator 42 is a clock generator 41
A control signal is provided to the frequency hopping synthesizer 31 based on the clock signal from

In the synchronization circuit for initial acquisition shown in FIG. 5, the hopping frequency is determined in accordance with the pattern of the PN sequence. For this purpose, a control signal is supplied from the PN sequence generator 42 to the frequency hopping synthesizer 31, If the synchronization is not established and the timings do not match, the phase of the PN sequence is shifted by チ ッ プ chip, the switching of the hopping frequency is advanced, and the search in the time domain is performed.
On the other hand, when the frequency is shifted, an offset is applied to the main oscillator of the frequency hopping synthesizer 31, and a search in the frequency domain is performed.

FIG. 6 is a block diagram of the tracking circuit. This tracking circuit is for keeping the synchronization after the circuit is initially captured by the synchronization circuit for initial acquisition shown in FIG. The tracking circuit includes a frequency correlation network 50, which receives the received signal r from the frequency hopping synthesizer 51.
The local oscillation signal l _E (t), which is advanced more temporally than (t)
And the local oscillation signal l _L (t) delayed in time are supplied to the mixing circuits 52 and 53, and the received signal r (t) is frequency-converted. Then, the band is limited by band-pass filters 54 and 55, squared by squarers 56 and 57, and added by an adder 58.
And is provided to the loop filter 59. The loop filter 59 removes harmonics having the cycle of the hopping frequency as a fundamental component. The output is supplied to the VCC circuit 60, and the control signal is supplied to the FH sequence generation record 11. F
The H sequence generation record 11 provides a control signal to the frequency hopping synthesizer 51 based on the control signal from the VCC circuit 60. The tracking circuit shown in FIG. 6 is the same as the above-described synchronization circuit for initial acquisition and is described in the above-mentioned document, and detailed description thereof will be omitted.

[0011]

As described above, in the conventional spread spectrum communication system, the synchronization circuit for initial acquisition shown in FIG. 5 and the tracking circuit shown in FIG. 6 are required. There is a disadvantage that it is difficult to change the frequency at high speed. Furthermore, although it is resistant to multipath fading due to indoor use, if a line is broken, synchronization is lost, so it is necessary to recapture from the beginning, it takes time for that, and the signal during that time However, there is a drawback that demodulation cannot be performed.

Furthermore, since the phase becomes discontinuous after the frequency slot is changed, it is difficult to use phase modulation such as PSK modulation, and there is a limitation on the use. As described above, the conventional spread spectrum communication system using frequency hopping has various problems and has been a major obstacle to practical use.

SUMMARY OF THE INVENTION It is, therefore, a main object of the present invention to provide a spread spectrum communication system which can be constituted by a simple circuit, requires no time for synchronization, and can be applied to phase modulation.

[0014]

The invention according to claim 1 is
In a spread spectrum communication system using frequency hopping, a transmitting side generates two waves of a signal obtained by modulating a carrier wave with data and a signal consisting of only a carrier wave, and generates any one of the signals for an arbitrary time longer than one frequency stationary time of frequency hopping. After delaying one, the two waves are combined and transmitted, and on the receiving side, the received signal is distributed to two paths, and one of the distributed signals is delayed by the same delay amount as the transmitting side, and the delayed signal is It is configured to perform despreading by multiplying by the other distributed signal.

[0015] According to a second aspect of the present invention, on the transmitting side,
A dipulse-coded signal is used as the modulation signal.
On the other hand, the receiving side demodulates after removing the DC component. Claim
The invention according to the third aspect is characterized in that the transmission side multiplies a local oscillation signal before delaying either a signal obtained by modulating a carrier wave with data or a signal consisting of only a carrier wave, and converts the multiplied signal into an intermediate frequency band on the reception side. And demodulate the despread data modulated wave.

In the invention according to claim 4 , the delay amount is selected to be any time equal to or longer than the frequency hopping stop time.

[0017]

In the spread spectrum communication system according to the present invention, a signal obtained by modulating data with a carrier and a signal consisting of only a carrier are transmitted from a transmitting side with a delay of one of them, and a receiving signal is divided into two by a receiving side. By delaying one again and multiplying it by the other, all the frequency-hopping carriers become baseband signals and can be despread.

[0018]

FIG. 1 is a block diagram of an embodiment of the present invention. In particular, FIG. 1A shows a transmitter, and FIG. 1B shows a receiver. In FIG. 1A, a data generator 1 generates data to which an interleave or an error correction code is added. This data is provided to modulator 3. The modulator 3 modulates the carrier generated by the carrier generator 4 with data. Here, it is assumed that BPSK modulation (phase modulation) is performed. The frequency of the carrier generator 4 is changed in accordance with the FH (frequency hopping) controller 2 for each data bit number. This frequency changes in a predetermined pattern using a spreading code according to the number of slots prepared in advance.

On the other hand, the carrier is also input to the delay element 5,
The modulated signal 9 output from the modulator 3 and the unmodulated signal 1 delayed by the delay time z
0 is multiplexed. Then, the signal is converted into a high-frequency signal by the frequency converter 7 and transmitted from the antenna 8.

In the receiver shown in FIG. 1B, a signal input from an antenna 11 is converted by a frequency converter 12 into an intermediate frequency band. The intermediate frequency signal is splitter 1
3, one is delayed by the delay element 14, the delayed signal 15 and the undelayed signal 16 are multiplied by the multiplier 17, only the necessary band is extracted by the filter 18, and the data demodulation unit 19 Demodulated by

Next, more specific operations of the transmitter and the receiver shown in FIG. 1 will be described. Assuming that the data from the data generator 1 is d (t) and the carrier angular frequency is ω _C (t), the modulation signal 9 output from the modulator 3 is expressed by the following equation (1).

S ₁ (t) = d (t) cosω _{c (t)} t (1) On the other hand, if the delay amount of the signal delayed by the delay element 5 is z, the following equation (2) Becomes

S ₂ (t) = cosω _{C (tz)} (t−z) (2) Therefore, the signal formed by the multiplexer 6 is the sum of the signals and is represented by the following equation (3).

S ₀ = d (t) cosωc _(t) t + cosωc _(t−z) (t−z) (3) On the other hand, in the receiver, the signal 16 divided by the splitter 13 is divided into 16 Is expressed by the following equation (4), assuming that the signal propagation time is t ₀ ignoring the amplitude value.

R ₁ = d (t−t ₀ ) cosω _{C (t−t0)} (t−t ₀ ) + cosωC _(t−t0−z) (t−t ₀ −z) (4) The signal that has passed through the delay element 5 is expressed by the following equation (5).

[0026] _{R 2 = d (t-t} 0 -z) cosω C (t-t0- z) (t-t 0 -z) + cosω C (t-t0-2z) (t-t 0 -2z) (5) Therefore, the output of the multiplier 17 is a product of R ₁ and R ₂ .

R₀= R₁× R_Two= D (tt₀) Cosω_{C (t-t0)}(Tt₀) + Cosω _{C (t-t0- z)} (Tt₀−z) × d (tt)₀−z) cosω_{C (t-t0- z)}(Tt ₀ −z) + cosω_{C (t-t0-2z)}(Tt₀−2z) = d (tt)₀) · D (tt₀−z) cosω_{C (t-t0)}(Tt₀) ・ Co sω_{C (t-t0- z)}(Tt₀−z) + d (tt)₀) Cosω_{C (t-t0)}cosω_{C ( t-t0-2z)} (Tt₀−2z) + d (tt)₀−z) cosω_{C (t-t0-z)}(Tt ₀ −z) cosω_{C (t-t0- z)}(Tt₀−z) + cosω_{C (t-t0- z)}(Tt₀ −z) · cosω_{C (t-t0-2z)}(Tt₀-2z) (6)

Of these, ω_{C (t-t0)}And ω_{C (t-t0- z)}You
And ω_{C (t-t0)}And ω_{C (t-t0-2z)}, Ω _{C (t-t0-z)}And ω
_{C (t-t0-2z)}Where, z is one frequency dwell time of frequency hopping
Because they are longer, they have different frequencies. Therefore, multiplication
The frequency after multiplication by the multiplier 17 is the sum and difference frequency components
And does not fall into baseband.

On the other hand, cosω _{C (t−t0−z)} and cosω
By multiplying _{C (t−t0−z)} , it falls into a second harmonic and a baseband signal component. That is, d (t−t ₀ −z) cosω _{C (t−t0−z)} (t−t ₀ −z) · cosω _{C (t−t0−z )} (t−t ₀ −z) = d (t −t ₀ −z) {｛cosω _{C (t−t0−z)} (2t−2t ₀ −2z + cosωC _(t−t0−z) (0)} Therefore, after the filter, The output is d
(T−t ₀ −z), and data can be demodulated. That is, despreading is performed.

As described above, by using an embodiment of the present invention, demodulation of frequency hopping can be performed with a very simple circuit, and the conventional problems can be solved.

When attention is paid to synchronization, since two waves are always transmitted and the time z is sufficiently short, it is considered that they have substantially the same propagation path characteristics. Therefore, the output of the multiplier 17 is always in a despread state, and the circuit breaks or
Demodulation can be performed instantaneously even when the initial circuit is connected,
Conventional problems can be solved.

Focusing on the phase, as shown in the expansion of equation (6), since the phase term ω _{C (t−t0 −z)} is completely the same and no phase difference occurs, It can be seen that the phase continuity is obtained even if Further, as the effect of this embodiment, it is shown that the frequency accuracy and the transition time of ω _C (t) do not depend on the carrier wave generator 4.
This makes it easier to design, and the circuit load and price on the transmitting side can be reduced as compared with the conventional case.

In the embodiment of the present invention, the circuit can be constituted by either an analog or digital circuit.
It is also possible to output the output of the above by calculation, and the generality is not lost. Although the delay element 5 is connected to the output side of the carrier generator 4 in FIG. 1, the same operation can be performed even if a delay element is inserted on the output side of the modulator 3. It is clear from the above equations that either the output of the modulator 3 or the output of the carrier generator 4 may be delayed.

Next, as a second embodiment of the present invention, consider using a code having no DC component, such as a Manchester code, for the data generator 1.

FIG. 2 is a diagram showing a spectrum of a dipulse code such as a general NRZ code and a Manchester code. As can be seen from FIG. 2, if a dipulse code is used, since there is no DC component, the DC term can be cut by a filter. In the above-described first embodiment, a case where a CW interference wave is mixed will be considered. Assuming that the CW wave is cosω _N (t), the output of the multiplier 17 is as shown in the following equation (7).

Cos ω _N (t) × cos ω _N (t−z) = ｛· {cos ω _N (2t−z) + cos ω _N ( z )} (7) In this case, cos ω _N ( z ) A component is generated. Therefore, the DC component can be cut by changing the code from the NRZ code to the dipulse code and transmitting. If the present invention is used in a band where CW interference may enter, the following second embodiment is effective.

Here, a dipulse code such as a Manchester code is shown as a code having no DC component.
In addition to this, generality is not lost even if any code having a small spectral component is used for the DC term.

FIG. 3 is a block diagram showing a third embodiment of the present invention. In particular, FIG. 3A shows a transmitter, and FIG.
(B) shows a receiver. The transmitter shown in FIG. 3A has a frequency converter 20 on the output side of the modulator 3 shown in FIG.
And a local oscillator 21 for providing a local oscillation signal to the frequency conversion unit 20. The other configuration is the same as that of FIG. The carrier signal modulated by the data in the modulator 3 is provided to the frequency conversion unit 20, converted into a signal having a different frequency depending on the frequency of the local oscillation signal from the local oscillator 21, and multiplexed in the multiplexer 6.

On the other hand, on the receiver side, when the same processing as that of FIG. 1B is performed, the output of the multiplier 17 has the demodulation term of the above-mentioned equation (6) as d (t−t ₀ −z ) _Is transmitted as an intermediate frequency signal that is multiplied by the local oscillation frequency ω _{IF (t− t0−z)} . A filter 23 is connected to the output of the multiplier 17. The filter 23 takes out the intermediate frequency signal as a band pass filter, and the data demodulation unit 24 demodulates the BPSK wave by modulating a general intermediate frequency signal. I do. Further, among the terms generated by the multiplier 17,
What passes through the filter 23 can be selected by selecting the frequency and the hopping pattern of the local oscillator 21 as described in the first term.

In this embodiment, CW interference can be suppressed in the second embodiment described above, but an interference wave having a relatively wide band is generated with a spectrum which is considerably wider than that of DC, and a signal is generated. May interfere. Therefore, by shifting a desired signal to the intermediate frequency band as in the third embodiment, it is possible to remove these interference waves. The transmitter and the receiver according to this embodiment are effective when used in a frequency band in which the above-mentioned interference wave may exist.

In FIG. 3A, the local oscillator 2
Although the local oscillation signal from 1 is multiplied by the modulation signal, the same result can be obtained by multiplying the modulation signal by the carrier signal alone. Never lose generality.

Next, a fourth embodiment of the present invention will be described. Generally, in spread spectrum, multi-access is one feature. In the system according to the present invention, multi-access is performed based on the delay time z. In other words, another user that the user has received that using the delay time z ₁ radio waves transmitted with a delay time of z _2. The transmission wave at this time is expressed by the following equation (8).

[0043] _{R 1 = d (t-t} 1) cosω C (t-t1) (t-t 1) + cosω C (t-t1- z2) (t-t 1 -z 2) ... (8) On the other hand, The delayed wave is represented by the following equation (9).

[0044] _{R 2 = d (t-t} 1 -z 1) cosω C (t-t1- z1) (t-t 1 -z 1) + cos ω C (t-t1- z2-z1) (t-t ₁₋ z ₂ −z ₁ ) (9) Accordingly, the output of the multiplier 17 is given by the following equation (10).

[0045] _{R 0 = R 1 × R 2} = (d (t-t 1) cosω C (t-t1) (t-t 1) + cos ω C (t-t1- z2) (t-t 1 -z _{2)) × d (t-} t 1 -z 1) cosω C (t-t1- z1) (t-t 1 -z 1) + cosω C (t-t1- z2-z1) (t-t 1 -z ₂ −z ₁ ) (10) Considering the same as above, ω _{C (t−t1)} and ω _{C (t−t0−z2)} , ω _{C (t−t1)} and ω _{C (tt 1−z1)} , Ω
_{C (t-t0- z2)} and _{ω C (t-t0- z2-} z1) is the z _1, z ₂ longer than 1 frequency dwell time of frequency hopping, the frequency unrelated.

On the other hand, only ω _{C (t−t0−z2)} and ω _{C (t−t1−z1)} remain. When | z ₂ −z ₁ |> (one frequency underflow time), this signal is Without falling into the baseband, users can be distinguished and multi-access can be performed.

Therefore, multi-access for multiple users can be performed only by z, and a fourth embodiment of the present invention is to provide a fixed z for each user.

In this embodiment, it is apparent that the encoding shown in the second embodiment and the combined use of the intermediate frequency signal shown in the third embodiment can be performed simultaneously.

Further, in this embodiment, several bits of data are set at the time of stopping at one frequency. However, this may be any number of bits, or may be 1 bit or less. Further, it may be asynchronous.

[0050]

As described above, according to the present invention, on the transmitting side, either a signal obtained by modulating data with a carrier or a signal consisting of only a carrier is transmitted with a delay, and the receiving side transmits
By dividing the received signal into two, delaying one again and multiplying the other by the other, a frequency hopping system can be realized with a relatively simple circuit configuration. In addition, the problem that the conventional frequency hopping system requires a long time for synchronization and the problem that the phase is not continuous can also be solved, and a stable line can be supplied to indoor propagation with many multipaths.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a power spectrum distribution of an NRZ code and a dipulse code.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a power spectrum.

FIG. 5 is a block diagram showing a conventional synchronous circuit for initial acquisition for frequency hopping.

FIG. 6 is a block diagram showing a conventional tracking circuit.

[Description of Signs] 1 Data generation unit 2 Frequency hopping controller 3 Modulator 4 Carrier generator 5, 14 Delay element 6 Multiplexer 7 Frequency conversion unit 8, 11 Antenna 12, 20 Frequency conversion unit 13 Divider 17 Multiplier 18 , 23 Filter 19, 24 Data demodulation unit 21 Local oscillator

Claims (4)

(57) [Claims] 1. In a spread spectrum communication system using frequency hopping, a transmitting side generates two waves of a signal obtained by modulating a carrier with data and a signal of only the carrier, and calculates a frequency hopping one frequency dwell time. After delaying one of them for an arbitrary long time, the two waves are combined and transmitted. At the receiving side, the received signal is distributed to two paths, and one of the distributed signals is the same delay amount as the transmitting side. A spread spectrum communication system characterized in that despreading is performed by multiplying the delayed signal by the other signal distributed by the delayed signal. 2. The transmitting side, wherein the modulated signal includes
The impulse-coded signal is used, while on the receiving side, D
2. The demodulation method according to claim 1, wherein demodulation is performed after removing a C component.
Spread spectrum communication system. 3. The transmission side multiplies a local oscillation signal before delaying either a signal obtained by modulating a carrier with the data or a signal of the carrier alone, and the reception side multiplies the multiplied signal. 3. The spread spectrum communication system according to claim 1, wherein the data modulation wave is converted into an intermediate frequency band, and the demodulated data modulated wave is demodulated. 4. In multi-access for multi-pole users,
Delay of each station, and wherein each selected in the frequency hopping dwell time over a given time, spread spectrum communication system according to claim 1 or 2 or 3.