JP2799533B2 - 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 an improvement in a direct spread spectrum spread communication system.

[0002]

2. Description of the Related Art In conventional data communication, communication using a narrow band modulation system (AM, FM, BPSK, etc.) is generally used. These can realize demodulation in a receiver with a relatively small circuit, but also have a disadvantage that they are weak against multipath and narrow band noise.

[0003] On the other hand, in the spread spectrum communication system, the transmitter side spreads the spectrum of data by a spread code, and the receiver side synchronizes the time with the spread code to obtain multipath and narrowband. It has the feature of reducing the effect of noise, and is attracting attention as an important technology.

[0004] Spread spectrum techniques include direct spreading, frequency hopping, time hopping, and hybrid schemes combining some of them, among which direct spread schemes provide a chip rate much faster than the data rate. A method of spreading the spectrum by exchanging the spread code and the data with each other, which can be easily realized in terms of circuits as compared with other methods, and multiplex communication in the same band can be realized by distinguishing the spread code. It becomes possible. Such a multiplexing method is referred to as CDMA (Code Division Multiple Access) or SSMA (Spread Spectrum).
m Multiple Access: Spread Spectrum Multiple Access).

FIGS. 7A and 7B are schematic block diagrams of a spread spectrum communication system using the direct spread system. (A) relates to the transmission system,
(B) relates to the receiving system.

On the transmitter side, as shown in FIG.
The information 57 as a (t) is modulated by the information modulator 58 to generate a signal b (t), and then a spreading code (PN) generator 60 by a spreading modulator (multiplier) 59.
Is multiplied by the spreading code c (t) generated in. The spreading code generator 60 is driven by the clock of the reference clock oscillator 61. Here, since the chip rate of the spread code c (t) is very high compared to the data rate of the data a (t), the spectrum band of the multiplied output signal s (t) is spread compared to b (t). You. The spread multiplied output signal s (t) is converted to an RF band by the frequency converter 62, amplified by the power amplifier 63, and transmitted from the antenna 64.

On the receiver side, as shown in FIG.
The signal received by the antenna 65 is transmitted to the RF amplifier 66
, And converted to an intermediate frequency by the frequency conversion unit 67. The signal s (t) converted to the intermediate frequency is
A spreading code (PN) is generated by a spreading demodulation unit (multiplier) 68.
It is multiplied by a spreading code c (t) having the same sequence as the transmitter side c (t) generated by the generator 69. Here, the spread code generated by the spread code generator 69 needs to be temporally synchronized with the spread code included in the received signal input to the spread demodulation unit (multiplier) 68. For this purpose, a time discrimination control circuit 70 having a loop structure is prepared, and constitutes a synchronization unit S together with the spread code generator 69. When the spreading code is removed by the spreading demodulation unit 68, the output b (t) of the spreading demodulator 68 returns to a narrow band signal modulated only by data. The information demodulation unit 71
, The information 72 of a (t) can be obtained.

[0008] The spread demodulation unit 68 on the receiver side synchronizes the time, so that the influence of multipath which is delayed in time can be reduced, and the spread code generator 69 is added to the received signal.
By multiplying by the spreading code generated in step (1), the narrow-band noise input to the receiving antenna is spread, and this effect is reduced.

[0009] By spreading the spectrum in this manner, communication is performed in a wide bandwidth, so that the communication is strengthened against multipath and narrowband communication, and more effective communication can be performed.

[0010] The spread spectrum communication system and FIG. 7 are described in detail in "Spread Spectrum Communication Systems", p10 to p16, published by Science and Technology Publishing Company.

[0011]

As described above, the direct spread spectrum spread communication system is more resistant to multipath and narrow band noise than the conventional narrow band communication, but on the other hand, a circuit for spread spectrum and despread is required. Required, and
The circuit of the synchronizing unit used for this generally has a loop structure, so that the circuit is larger and more complicated than a narrow band communication receiver.

As a method of confirming the synchronization of the spread code, a spread code of a received signal is multiplied by a spread code generated in a receiver, and the result is integrated.
Despreading is performed depending on whether the integration result reaches a certain level. In other words, it takes a certain amount of time to confirm synchronization, although there is a difference depending on the integration time. For example, if the integration time is t seconds (s) and the code length is n chips, and synchronization is to be confirmed by shifting by 1/2 chip, a maximum time of 2n × t (s) is required.

[0013]

In a communication system according to the present invention, a signal obtained by multiplying a spread code and data is used as a modulation signal and a carrier wave is BPSK-modulated, and only the spread code is used as a modulation signal and the carrier wave is used as a BPSK signal. A transmitter having means for combining the modulated wave with a signal obtained by delaying the modulated wave by at least one chip of the spreading code, and a delay unit having a delay amount equal to the delay time on the transmission side; And a receiver having means for despreading by multiplying the received signal passing through the delay unit and the received signal not passing through the delay unit. Further, the spreading code repetition period is set to be at least twice the system of the data to be transmitted. Further, a reference signal is added to data to be transmitted. Also,
Use frequency hopping together.

[0014]

According to the present invention, on the transmitter side, a signal modulated with a spreading code (which takes a value of either 1 or -1) and data, and a signal modulated with only the spreading code and the signal are used. And a signal delayed by an arbitrary time (one chip or more of the spreading code) is transmitted, and a delay circuit having the same delay amount as that of the transmitter is provided on the receiver side. Despreading can be performed by multiplying a received signal that does not pass through a delay circuit.

[0015]

1A and 1B are block diagrams of an embodiment of the present invention. (A) shows a transmission system and (b) shows a reception system.

The transmission system will be described with reference to FIG. Let information 1 be d (t), which is a digital signal represented by 1, -1. The spread code signal p (t) is output from the PN generator 3 by the clock from the reference clock oscillator 4.
Occurs. The signal p (t) is split into two paths, one of which is sent to the multiplier 2. The bit rate of the signal p (t) is d
It is much faster than (t). The multiplier 2 multiplies the signal d (t) by the signal p (t). here,
p (t) is also a code that takes 1, -1 in a pseudo-random manner,
As a result, the spectrum is spread to a width of (p (t) chip rate) / (data bit rate) times as compared with the case of only data. The output d (t) · p (t) of the multiplier 2 is converted by the BPSK modulator 5 into B
PSK modulation is performed to obtain d (t) · p (t) · cos ω _i t. Where ω _i is the local frequency and d (t) · p
(T) takes one of 1 and -1.

The signal p (t) passes through the other path as follows. After passing through the BPSK modulator 6, p (t) · co
s ω _i t, and then passes through the delay unit 8 and p (t−τ)
cosω _i (t−τ). Here, τ is a delay time and is a time equal to or longer than one chip of the spreading code. The output signals of these two paths are multiplexed by the multiplexer 7 to be {d (t) · p (t) · cos ω _i + p (t−τ) · cos ω _i (t−τ)}. This is designated as A (t). This signal A (t) is
The frequency is converted to the RF band by the frequency converter 9 and B (t)
Becomes This signal B (t) is amplified by the power amplifier 10 and transmitted from the antenna 11.

On the receiver side, as shown in FIG. 1B, the signal received by the antenna 12 is amplified by the RF amplifier 13 and frequency-converted by the frequency converter 14 to an intermediate frequency band. This signal is split by the splitter 15 into two paths. Assuming that the propagation time between the transmitter and the receiver is Δt, one is input to the multiplier 17 as A (t−Δt), and the other is a delay unit 16 having the same delay time τ as the delay unit 8 placed on the transmitter side. A (t−τ−Δt) is input to the multiplier 17. Here, A (t−Δt)
Represents ｛d (t−Δt) · p (t−Δt) · cos ω _i (t−Δt) + p (t−Δt−τ) · cos ω _i (t−Δt−τ) 、 (T−Δt−τ) is ｛d (t−Δt−τ) · p (t−Δt−τ) · cos ω _i (t−Δt−τ) + p (t−Δt−2τ) · cos ω since it represents the _{i (t-Δt-2τ)} }, output by the multiplier 17, except double frequency components of _{ω i, {d (t-} Δt) · d (t-Δt-τ) · p (t -Δt) ・ p (t-Δt-τ) ・ cos ω _i τ + d (t-Δt) ・ p (t-Δt) ・ p (t-Δt-2τ) ・ cos2ω _i τ + d (t-Δt -τ) ・ p (t-Δt-τ) ・ p (t-Δt-τ) ・ cos0 + p (t-Δt-τ) ・ p (t-Δt-2τ) ・ cos ω _i τ｝ and 4 terms It is shown by the sum of However, the spreading code term p (t)
Focusing on, except for the synchronized third term ｛d (t-Δt-τ) · p (t-Δt-τ) · p (t-Δt-τ) · cos0｝ , The spectrum remains spread and the data component d (t) can be extracted.

As described above, according to the above-described embodiment, by transmitting a composite wave from the transmitter, despreading can be easily performed on the receiver side. In addition, the synchronization is performed almost simultaneously when the power switch is turned on, so that the time required for the synchronization is almost zero. Since the phase of the carrier is also delayed on the transmitter side, the carrier is also removed from the output of the multiplier 17 on the receiver side, and information demodulation becomes easier.

FIGS. 2A and 2B are block diagrams of the second embodiment. (A) shows a transmission system, and (b) shows a reception system. This is an example in which information modulation is performed by analog modulation. The difference from FIG. 1 is that the information is analog information, the information modulator 20 is analog modulation, and the BPSK modulator 5 in FIG.

In FIG. 2A, the analog signal a ₁ (t) of the information 19 is subjected to analog modulation by the information modulator 20 to become a signal A ₁ (t). This can be any modulation, such as AM, FM or PM. The signal A ₁ (t) modulated here is output from the multiplier 21 to the PN generator 2.
3 is multiplied by the spread code signal p (t), and A ₁ (t) · p (t) is obtained. Where the signal p (t)
Takes a value of either 1 or -1. After this, the AM modulator 2
2 In the AM _{modulation, A 1 (t) · p} (t) · cosω i t
And input to the multiplexer 25.

The spread code signal p (t) generated by the PN generator 23 driven by the reference clock oscillator 24
Is BPSK-modulated by the BPSK modulator 26, and p
(T) · cos ω _i t, which is passed through the delay unit 27, where p (t−τ) · cos ω _{i where} τ is the delay time
(T−τ).

These two signals are combined by the multiplexer 25 and become C (t). Here, C (t) is {p (t) · A ₁ (t) · cos ω _i t + p (t−τ) · cos ω _i (t−τ)}. This is frequency-converted into an RF band by a frequency conversion unit 28, is converted into D (t), is amplified by a power amplification unit 29, and is transmitted from an antenna 30.

On the receiver side, as shown in FIG.
The combined signal is received by the antenna 31, amplified by the RF force amplifier 32, and frequency-converted to the IF band by the frequency converter 33. Thereafter, the signal is split into two paths by a divider 34, one of which is directly input to a multiplier 35, and the other is passed through a delay unit 36 and delayed by the same delay amount as the delay unit 27 on the transmitter side. Is input to Here, the distributor 3
4 is Ct, where the propagation time between the transmitter and the receiver is Δt.
(T−Δt), which is ｛p (t−Δt) · A ₁ (t−Δt) · cos ω _i (t−Δt) + p (t−Δt−τ) · cos ω _i (t− Δt-τ). Also, the output C (t−Δt−τ) of the delay unit 36
Is ｛p (t-Δt-τ) ・ A ₁ (t-Δt-τ) ・ cos ω _i (t-Δt-τ) + p (t-Δt-2τ) ・ cos ω _i (t-Δt- 2τ)｝. Therefore, the output of the multiplier 35 is expressed by the four terms if the double component of the carrier is removed, and the spreading code is synchronized, as in the first embodiment, ｛p (t−Δt) ) · P (t−Δt−τ) · A ₁ (t−Δt−τ) · cos0｝ The level is low, and the output is A ₁ (t−Δt−
τ). By passing this through the information demodulation unit 37, the information 3
8 is obtained.

By using this method, FM, A
For signals using M, PM, etc., a system resistant to multipath and narrow-band noise can be obtained by adding the above simple spread spectrum communication circuit.

FIGS. 3A and 3B are block diagrams of the third embodiment. FIG. 1A shows a transmission system, and FIG. 1B shows a reception system. This is for a case where an analog signal (such as an audio signal) is spread as it is.

In FIG. 3A, information 39 is an analog signal, which is referred to as a ₂ (t). This is multiplied by the spreading code signal p (t) generated by the PN generator 41 driven by the reference clock oscillator 45 by the multiplier 40 and a
₂ (t) · p (t), and the AM
Modulated. This signal is defined as A ₂ (t). Also, PN
Similarly, the spread code signal p (t) generated by the generator 41 is AM-modulated by the AM modulator 43 (equivalent to BPSK modulation here), and the signal B ₁ (t), that is, p (t) · cos
ω _i t, and is delayed by τ by the delay unit 45 as in the first and second embodiments, and the signal B ₁ (t−τ), that is, p
(T−τ) · cosω _i (t−τ). The two signals are multiplexed by the multiplexer 44. This signal is defined as C ₁ (t). Then, as in the first and second embodiments, the frequency is converted into the RF band by the frequency conversion unit 47, and D ₁ (t) is obtained.
The signal is amplified by the power amplifier 48 and transmitted from the antenna 49.

As shown in FIG. 3B, the receiver has the same system configuration as the first and second embodiments. The signal received by the receiving antenna 50 is transmitted to the RF amplifier 51
, And is frequency-converted into an IF band by the frequency converter 52, and is split into two paths by the distributor 53.

Assuming that the propagation time between the transmitter and the receiver is Δt, one becomes C ₁ (t−Δt) and is input to the multiplier 55.
Here, C ₁ (t−Δt) is expressed as: ｛a ₂ (t−Δt) · p (t−Δt) · cos ω _i (t−Δt) + p (t−Δt−τ) · cos ω _i (t -Δt-τ)｝. The other passes through the delay unit 54 having the same delay amount as the transmitter-side delay unit 45 as in the first and second embodiments.
C ₁ (t−Δt−τ) is input to the multiplier 55. Here, C ₁ (t−Δt−τ) is expressed as: ｛a ₂ (t−Δt−τ) · p (t−Δt−τ) · cos ω _i (t−Δt−τ) + p (t−Δt− 2τ) · cos ω _i (t-Δt-2τ)｝. Therefore, the output of the multiplier is obtained by synchronizing the spreading codes for the same reason as in the first and second embodiments. ｛P (t−Δt−τ) · p (t−Δt−τ) · a ₂ (t−Δt -τ) · cos0｝ and data is obtained. Therefore, even with this method, by adding a simple spread spectrum circuit, it is resistant to multipath and narrow band noise, and by shifting the delay time τ, the same band multiplex communication becomes possible.

In the first, second and third embodiments, among the four terms of the output of the receiver-side multiplier, three of the terms whose spreading codes are not synchronized are multiplied by cos ω _i τ as coefficients. There are two terms, and one term is multiplied by cos 2ω _i τ as a coefficient. This is set to A _n = A ₁ · cos ω _i τ + A ₂ · cos ω ₁ τ + A ₃ · cos 2ω _i τ, and by selecting ω _i and τ appropriately so that _An is minimized, more effect is obtained. Communication becomes possible.

Further, the spectrum of the spread spectrum signal is represented by the first null point where the chip rate of the spread code is f _{P N} (bps), the code length is L (chip), and the center frequency is f _c (H _Z ). f _c ± f _PN (sin x
/ X) with ² envelope (f _{P N} / L) (represented by a line spectrum of H _Z) intervals. Also, each line spectrum is a data-modulated line spectrum,
The spectral component in f _c (H _Z) is suppressed in the power basis as compared to the level before spreading (1 / L ^2). The spectrum spread in this way is concentrated in the center wave frequency portion by performing the despreading operation, and the components of the other line spectra become zero.

[0032] and 2f _D the spectrum band before spreading here. This is diffused and if 2f _D > f _PN / L If a, f _c portion and _{{f c ± (f p N} / L )｝ The spectrum of the portion overlaps for the above-mentioned reason. So CD
Perform the MA multiplexing, performs despreading operation for a line, to concentrate power to f _c portion, when taking out the band of 2f _D, the other line _{{f c ± (f p N} / L C) The C / N is degraded because some of the spectrum in the｝ portion enters the band.

Therefore, 2f _D <(fp _N / L) ) Enables more effective communication.

FIGS. 4A and 4B are block diagrams of the fourth embodiment. FIG. 2A shows a transmission system.
(B) shows a receiving system. This is a modification of the third embodiment shown in FIG.
A reference signal is added to data depending on the amplitude, etc., and then spread and transmitted.

In FIG. 4A, information 39 depending on amplitude such as baseband data or AM modulated wave and a reference signal 60 such as a narrow band signal or a sine wave outside the data band are combined by a multiplexer 61. Multiplex. For the reference signal, frequency information that does not affect the data band is selected. This is performed by the same method as described in the third embodiment.
The signal is transmitted from the antenna 49.

In FIG. 4B, various conversions are performed as in the third embodiment, and the despreading operation is performed by the multiplier 55. The signal after despreading is distributed by a distributor 62, and one of the signals is extracted only by a band-pass filter 63 and input to a gain control amplifier 64. On the other hand, the band-pass filter 67 extracts only the gain control reference signal,
6, the output of which controls the gain of the gain control amplifier 64. The output of the gain control amplifier 64 obtained by these operations is demodulated by the information demodulation unit 65 to obtain information 56.

[0037] The input of the receiver side of the multiplier 55, obviously, {a (t) + r (t)} · cos ω c t and p (t-Δt) · cos ω
_c (t-Δt) is input. Here, a (t) is a data component, p (t) is a spreading code, ω _c is a carrier frequency, r
(T) is a reference signal, and Δt is a delay time of a delay circuit in the transmitter.

The output of the multiplier 55 is as follows: i) {a (t) + r (t) {a (t-Δt) + r (t-Δt)} · p (t) · p (t-Δt)・ Cos ω _c t ・ cos ω _c (t- Δt) ii) ｛a (t) + r (t)｝ ・ p (t) ・ p (t-2 Δt) ・ cos ω _c t ・ cos ω _c ( t-2Δt) iii) ｛a (t-Δt) + r (t-Δt)｝ ・ p (t-Δt) ・ p (t-Δt) ・ cos ω _c (t-Δt) ・ cos ω _c (t - Δt) iv) p (t- Δt) · p (t-2 Δt) · cos ω c (t- Δt) · cos consists 4 wherein ω _c (t-2Δt), the inner iii) only the spreading code Is removed,
The desired components can be removed. In addition, all other components are also diffused. If the number of chips is set to 127 chips, the gain control signal is at least about 21 dB lower than the desired component, so that there is no particular problem in the gain control signal. With this method, a system that can receive data having amplitude information at a uniform level can be realized.

FIGS. 5A and 5B are block diagrams of the fifth embodiment. FIG. 2A shows a transmission system.
(B) shows a receiving system.

The transmission system shown in FIG. 5A is the same as that shown in FIG. Information 1 is set as d (t). In the case of FIG. 1, the case of a digital signal has been described, but this may be either an analog signal or a digital signal. PN
The spreading code p (t) at the chip rate f _s (chips / sec) generated by the generator 3 is multiplied by the multiplier 2 and modulated by the BPS modulator 5 (AM modulator if the information is an analog signal). Are input to the multiplexer 7. The spread code generated by the PM generator 3 is directly modulated by the BPS system modulator 6 on the other path, delayed by the delay amount τ, and input to the multiplexer 7.

The output A (t) of the multiplexer 7 is A (t) = d (t) · p (t) · cos ω _i t + p (t−), as described with reference to FIG. τ) · cos ω _i (t- τ). Here, ω _i represents the local frequency as in the case of FIG.

This signal is frequency-converted to the RF band by the frequency converter 9 as in the previous embodiment, becomes a signal B (t), is power-amplified by the current amplifier 10, and
Sent by

On the receiver side, as in the previous embodiment, the signal received by the antenna 12 is power-amplified by the RF amplifier 13 and frequency-converted to the intermediate frequency band by the frequency converter 14 to obtain A '(t ). Here, the propagation time between the transmitter and the receiver is ignored. Thereafter, the distributor 15
Distributed to the route. One passes through the delay unit 16 and A ′ (t−
τ) and the other passes through the comb filter 80 and the multiplier 17
Is input to Here, the input signal A ′ (t) of the comb filter 80 and the signal A ′ (t−
τ), respectively, A '(t) = d (t) · p (t) · cos ω i t + p (t-τ) · cos ω i (t- τ) A' (t- τ) = d (t−τ) · p (t−τ) cos ω _i (t−τ) + p (t−2τ) · cos ω _i (t−2τ), of which A ′ (t) Right side second
The data d (t-τ) is demodulated by multiplying the term by the first term on the right side of the equation for A ′ (t−τ). Where A '
The first term on the right side of the equation for (t) and the channel noise are:
Since the demodulation result is adversely affected, in order to remove the demodulation result, a second filter on the right-hand side of the equation relating to A '(t) passes through a comb filter 80 so as to pass only the spread code line spectrum group. 80 outputs and A '(t-
τ) is multiplied by the multiplier 17 to remove the spreading code and the carrier, thereby obtaining information.

The total pass band of the comb filter 80 is
Assuming that white noise is dominant in the reception noise when the spread transmission band is 1%, the signal after passing through the comb filter 80 is improved by 20 dB in C / N with respect to A '(t). become.

FIG. 6 is a block diagram of the sixth embodiment, which is more effective against interfering waves. this is,
This is an improvement of the transmission system of FIG. 1A in the first embodiment, in which both direct spreading and frequency hopping are used.

The receiving system uses the receiver shown in FIG. In FIG. 6, data information 1 is set as d (t). This is multiplied by a multiplier 4 by a PN code from a PN generator 3 and then primary-modulated by a BPSK modulator 5. The PN code from the PN generator 3 is sent to the other path, and is multiplexed by the multiplexer 7 through the BPSK modulator 6 and the delay unit 8 using only the PN code. The signals on both paths are
At this time, the carrier is secondarily modulated by a carrier generated by a carrier generator 82 controlled by an FH (frequency hopping) controller 81. The frequency of the carrier generation unit 82 changes synchronously or asynchronously with data every several bits to several tens of bits.

This operation will be described below. PN code is p
Assuming that (t), data is d (t), the carrier to be frequency-hopped is cosω _{c (t)} , and the delay amount is τ, the output of the BPSK modulator 5 is d (t) · p (t) · cosω _{c ( t)} t
Becomes

On the other hand, the output of the delay unit 8 is

[0049]

(Equation 1)

Is as follows. Therefore, the output of the multiplexer 7 is given by the following equation.

[0051]

(Equation 2)

When this is put into a receiving system as shown in FIG. 1B, the one without delay is A ″ (t−Δt),
The delayed one is A ″ (t−Δt−τ), where Δt is the propagation time between the transmitter and the receiver.

Therefore, the output of the multiplier 17 is as follows.

[0054]

(Equation 3)

Among them, the following is obtained except for the double frequency component of ω _{c (t)} .

[0056]

(Equation 4)

However, paying attention to the spreading code p (t), only the second term is synchronized, and the other terms remain spread.

Therefore, the despreading is caused by d in the second term.
(t-τ) p (t-τ) p (t-τ) cos0 = d (t-τ)
Becomes

As described above, the same result as in the first embodiment of the present invention is obtained, and it is understood that the generality is not lost at all even if the carrier is changed to ω _{c (t)} which is a variable of t by frequency hopping. Therefore, in the sixth embodiment of the present invention, the receiver of FIG. 1B performs a demodulation operation by multiplying the undelayed signal and the delayed signal by the multiplier 17 on the receiving side. Regardless of the modulated carrier frequency, it is converted to a despread baseband signal. Therefore, even if frequency hopping is performed on the transmission side and the carrier changes with time, the baseband signal is despread by multiplying with a delay, so that a carrier tracking circuit for hopping is not required.

In the method of the sixth embodiment, since the secondary demodulation is performed by delaying, the secondary demodulation can be performed even if the secondary demodulation is not synchronized with the data. Therefore, the modulation on the transmitting side does not necessarily need to be synchronized with the data.

This method uses frequency hopping,
Since the used band changes at any time, even when there is a strong CW interference and the spreading gain of direct spreading is insufficient, it can be avoided by changing the frequency, and the advantages of both frequency hopping and direct spreading can be achieved. While receiving, it can be seen that the demodulator can be easily demodulated without any load.

[0062]

According to the present invention, in addition to a signal modulated with a spreading code and data on the transmission side, a spreading code of 1
By transmitting a composite signal delayed by more than a chip, despreading can be easily performed on the receiving side. This makes the circuit smaller and less expensive. Another advantage is that no synchronization time is required. Further, a spread spectrum communication system can be easily added to the conventional communication system, and more effective communication can be performed with respect to multipath and narrow band noise.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention;
(A) shows a transmission system and (b) shows a reception system.

FIG. 2 is a block diagram of a second embodiment of the present invention;
(A) shows a transmission system and (b) shows a reception system.

FIG. 3 is a block diagram of a third embodiment of the present invention;
(A) shows a transmission system and (b) shows a reception system.

FIG. 4 is a block diagram of a fourth embodiment of the present invention;
(A) shows a transmission system and (b) shows a reception system.

FIG. 5 is a block diagram of a fifth embodiment of the present invention, where (a) shows a transmission system and (b) shows a reception system.

FIG. 6 is a block diagram of a sixth embodiment.

FIG. 7 is a block diagram of a conventional direct spread spectrum spread communication system, where (a) shows a transmission system and (b) shows a reception system.

[Explanation of symbols]

 2, 17, 21, 35, 40, 55 multiplier 3, 23, 41 spreading code generator 4, 24, 45 reference clock oscillator 5, 6, 26 BPSK modulator 7, 25, 44 multiplexer 8, 16, 27, 36, 45, 54 Delay section 9, 14, 28, 33, 47, 52 Frequency conversion section 10, 29, 48 Power amplification section 13, 32, 51 RF amplification section 11, 12, 30, 31, 49, 50 Antennas 15, 34, 53 Distributor 80 Comb filter 81 FH controller 82 Carrier generator 80 Comb filter 81 FH controller 82 Carrier generator

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-4340 (JP, A) JP-A-58-197934 (JP, A) JP-A-62-257224 (JP, A) JP-A 61-1979 89739 (JP, A) JP-A-64-48545 (JP, A) JP-A-2-81529 (JP, A) JP-A-4-8028 (JP, A) (58) Fields investigated (Int. ⁶ , DB name) H04J 13/00

Claims (6)

(57) [Claims] 1. A modulation signal obtained by multiplying a signal obtained by multiplying a spreading code and data as a modulation signal and a modulation wave obtained by BPSK modulation of a carrier and a modulation signal obtained by BPSK modulating the carrier using only the spreading code as a modulation signal. A transmitter having means for combining a time-delayed signal of at least one chip of the spreading code, and a delay unit having the same delay amount as the delay time on the transmission side;
A spread spectrum communication system comprising: a receiver having means for multiplying a received signal that has passed through a delay unit and a received signal that has not passed through a delay unit and despreading the received signal. 2. An intermediate frequency of a receiver and delay times set in a transmitter and a receiver are selected so that unnecessary components of a multiplier output in the receiver represented by these two variables are minimized. The direct spread spectrum spread communication system according to claim 1, wherein: 3. The transmitter for a direct spread spectrum communication system according to claim 1, wherein the repetition period of the spread code is at least twice as large as the band of the data to be transmitted. 4. The apparatus according to claim 1, wherein a signal obtained by adding a reference signal to data dependent on the amplitude is spread.
Direct spread spectrum spread communication system as described. 5. The direct spread spectrum communication system according to claim 1, wherein a comb filter is connected in parallel with the delay unit between the distributor and the multiplier of the receiver. 6. A modulated wave obtained by BPSK-modulating a frequency-hopped carrier using a signal obtained by multiplying a spread code and data as a modulation signal, and a BPSK-modulated frequency-hopped modulated wave using only the spread code as a modulation signal. A transmitter having means for combining a signal delayed by one or more chips of the spreading code with respect to the modulated wave, and a delay unit having a delay amount equal to the delay time on the transmission side;
A spread spectrum communication system, comprising: a receiver having means for multiplying a received signal that has undergone frequency hopping through a delay unit and a received signal that does not pass through a delay unit to perform despreading.