JPH0888587A - Spread spectrum communication equipment - Google Patents

Abstract

PURPOSE: To adopt a pseudo noise PN code having a long code length and to acquire synchronism in a shorter time by using plural PN codes which are different in code speeds and have prescribed relations to periods of each other. CONSTITUTION: PN code generators 3 and 4 of a transmission equipment generate plural PN codes PN1 and PN2 which are different by code speeds, and the period of one of these codes is an integral multiple of that of the other, and the other code is stored in one chip of one code. Multipliers 5 and 6 successively multiply the information signal given from an information signal source l and codes PN1 and PN2 . A balanced modulator 8 combines outputs of multipliers 5 and 6 with the output or a carrier generator 7 to generate a spread spectrum signal. A reception equipment inversely spreads codes in order from the code PN2 having the higher code speed. Consequently, the time required to acquire the synchronism with the PN code having the higher code speed again is shortened after the synchronism with the PN code having the higher code speed is acquired, and the entire synchronism acquisition time is shortened.

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 device having a transmitter and a receiver.

[0002]

2. Description of the Related Art FIG. 7 shows the configuration of a typical direct sequence spread spectrum communication system. In the transmitter of FIG. 7,
The information signal supplied from the information signal source 21 is used as one input, and P supplied from the PN (pseudo noise) code generator 22.
The multiplier 23 multiplies these signals with the N code as the other input. The output of the multiplier 23 is input to the balanced modulator 25, where it is combined with the output of the carrier generator 24 to form a spread spectrum signal, which is radiated from the transmitting antenna.

In the receiving apparatus, the spread spectrum signal received by the receiving antenna is demodulated by the demodulator 26 into a signal having the same shape as the output of the multiplier 23, and the despreading circuit 2
8 is input. The despreading circuit 28 separates the information signal from the output of the demodulator 26 and the output of the PN code generator 27 that generates the same code as the PN code generator 22.

FIG. 8 shows P supplied from a PN code generator.
The waveform of N code and the output power spectrum of the spread spectrum signal radiated from the transmitting antenna are shown. It is known that the spread of the main lobe of the output power spectrum is inversely proportional to the chip length T _c of the PN code. By the way, the spread spectrum communication is characterized in that the confidential communication that is resistant to noise and interference can be performed by spreading and transmitting the spectrum of the information signal in a band sufficiently wider than its bandwidth.

Therefore, it is important to spread the information signal over a wider band, and for this purpose, the shorter the chip length T _c of the PN code is, the more advantageous it is. This means that when the period T _pn of the PN code is constant, that is, when the speed of the information signal is the same, the longer the code length of the PN code is, the more advantageous it is. On the other hand, if the code length of the PN code becomes long, there is a drawback that when the synchronization of the spread code sequence is captured in the receiving device, it takes time to capture the synchronization and the configuration of the device becomes complicated.

For example, in a despreading circuit, a sliding correlation method is used in which correlation calculation is performed between a received signal and a reference code sequence, and the reference code sequence is slid until the synchronization point is captured to continue the correlation calculation. If so, it takes a long time to acquire the synchronization. Therefore, when intermittent communication is performed between the transmission device and the reception device, or when synchronization is lost during communication, it takes time for synchronization acquisition or synchronization recovery, and the actual communication operation rate decreases. .

When a matching filter method for obtaining a correlation output by passing a received signal through a transversal type matched filter is adopted as the despreading circuit, the circuit becomes complicated and the cost increases accordingly. For example, code length 102
When despreading a 4-chip PN code with a matched filter using a general-purpose logic circuit, about 1024 registers are still required. Further, when a SAW matched filter, which is a kind of matched filter, is used, the device length becomes longer according to the code length, which exceeds the practical limit.

Therefore, conventionally, a proposal has been made to realize a spread spectrum communication apparatus which adopts a PN code having a longer code length, requires less time for synchronization acquisition, and has a simple circuit configuration ( (See JP-A-63-88924). According to this proposal, two or more types of PN codes (referred to as PN ₁ and PN ₂ ) having different PN code periods and having a non-integer multiple relation with each other are combined to form a PN with a longer period. It is used as a code.

Then, at the receiving device, the code PN on the transmitting side
₁Similar to, but with the same sign but slightly different period
No. PN '₁Despread using as a reference code, and
No. PN₁Component and code PN '₁When and match periodically
Output (code PN₂It should contain only ingredients),
Reference code PN₂By obtaining the correlation with ₂
(See page 3, lower right column of the same publication). Well
At the point where this correlation value has a peak, the code PN '₁Phase of
Initialize PN₁It also holds the synchronization of.

As a result, the beat phenomenon between PN codes having mutually different periods is utilized to substantially increase the code length of the PN code, and in the despreading circuit, the received signal and the reference code sequence are used. It is said that a relatively short correlation calculation can be performed between the two to realize accurate demodulation synchronization.

[0011]

However, in the invention according to the prior art, the code P is generated by utilizing the synchronization with the code PN ₁ which occurs periodically and lasts only for a short time.
Because of the synchronization with N ₂ , a high speed (eg SAW correlator) must be used as the correlation analyzer for the code PN ₂ , which is complex in construction and It is expensive.

The reason why the code PN ₁ cannot be directly synchronized is that the code combining method in the transmitting device combines PN codes (PN ₁ and PN ₂ ) whose cycles are non-integer multiples. Therefore, the code (PN ') formed by combining is not similar to the code PN ₁ (the correlation is small). If an inexpensive one such as a sliding correlator is used as the correlation analyzer, it is necessary to secure synchronization with the long-term code PN _{1, and} for that purpose, the code PN is required.
The periods of ₁ and the code PN ′ ₁ must be set to be very close to each other, and as a result, the period of opportunity for the phases of the code PN ₁ and the code PN ′ ₁ which appear periodically to become long, becomes long, There is a problem that the time for synchronous acquisition increases in a multiplicative manner.

Therefore, an object of the present invention is to solve the above-mentioned technical problems and to provide a spread spectrum communication apparatus capable of acquiring synchronization in a shorter time while adopting a PN code having a long code length. .

[0014]

A spread spectrum communication apparatus according to the present invention for achieving the above object comprises a transmitting apparatus and a receiving apparatus, wherein the transmitting apparatuses have different code rates from each other and a mutual cycle. A plurality of PN code generators for generating a plurality of PN (pseudo-noise) codes, one of which is in an integral multiple relationship and the other code is accommodated in one chip of the other code, and an information signal supplied from an information signal source or A multiplier that multiplies the one PN code as one input and the other PN code as the other input, and combines the output of the multiplier with the output of a carrier generator to generate a spread spectrum signal. The receiving device includes a demodulator for demodulating a spread spectrum signal in the form of a product of an information signal and a PN signal, and P generated by a plurality of PN code generators of the transmitting device.
A plurality of PN code generators that generate the same PN code as the N code, and a plurality of PNs that the plurality of PN code generators generate
The code has a plurality of despreading circuits that perform despreading in order from the PN code with the highest code rate.

Further, the present invention may be configured by the transmitting device and the receiving device alone. The despreading circuit of the receiving device may be composed of a sliding correlator or a matched filter.

[0016]

According to the above spread spectrum communication apparatus, the transmission apparatus has a plurality of code speeds which are different from each other, and have a cycle in which the mutual cycles are integral multiples, and one code is accommodated in one code of the other code. A PN code is generated, and an information signal given from an information signal source or a PN code given from the plurality of PN code generators and a PN code given from the PN code generator are sequentially multiplied to spread spectrum. Generate a signal. Since this spread spectrum signal is multiplied by a plurality of PN codes having different code rates, it is spread over a sufficiently wide frequency band.

The receiving device sequentially performs despreading with a PN code having a higher code rate among a plurality of PN codes. At this time, the plurality of PN codes have different code rates,
In addition, since the mutual cycles are in an integral multiple relation and one code is accommodated in one code of the other code, it can be considered that synchronization is established with each other. Therefore, a plurality of P
When despreading is performed in order from the PN code with the highest code rate among the plurality of PN codes generated by the N code generator, when the PN code with the highest code rate is synchronized, the PN code with the next highest code rate is obtained. As a result, the time required to synchronize with is reduced, and as a result, the overall synchronization acquisition time is reduced.

When the despreading circuit of the receiver is composed of a sliding correlator, if it is synchronized with the PN code with the highest code rate, then the PN with the next highest code rate will be used.
To synchronize with the code, the amount of change in the applied clock is 1
You can use each clock. To elaborate on this, a single P
In the conventional technique using the N code, it is necessary to change the clock by 1/2 clock. The reason why the clocks of the signal to be despread and the clock of the reference signal are deviated from each other by nearly 1/2 is to change the clock by 1/2 clock.
This is because if the clocks are changed by one clock, there is a possibility that synchronization will not be established forever. However, in the present invention, the plurality of PN codes have different code rates, and the mutual cycles are in the relationship of integral multiples, and one code is accommodated in the other code 1 chip. Since it is known on the receiving side that one chip of a code contains an integer number of codes with a higher code speed, the code speed synchronized with the clock obtained by the synchronous acquisition of the code with a higher code speed. Using the clock for the later reference of
It is possible to find a point where synchronization can be achieved by changing the clock by 1 clock, calculating the correlation value, and shifting the correlation value by an integral number of times. In other words, it is known that the beginning of the faster code always coincides with the beginning of any one chip of the slower code, so it is changed by one clock at a time to find synchronization. This is because it suffices to check how many chips of the faster code the time-wise code coincides with.

Therefore, the synchronization acquisition time can be shorter than in the conventional case. When the despreading circuit of the receiving device is composed of a matched filter, it is sufficient to have a logic circuit corresponding to the sum of the number of bits of a plurality of PN codes, so that the circuit scale can be reduced. In this respect, the conventional technique using a single PN code requires a circuit corresponding to the code bit number itself. In the present invention, a long code can be produced equivalently by a combination of short codes, and the relationship of (bit sum of short codes) <(bit length of equivalent long code) holds, so the circuit scale can be reduced. Can be done.

[0020]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is a functional block diagram of a transmitter of a spread spectrum communication device of the present invention. The transmitter uses an information signal source 1 and an information signal given from the information signal source 1 as one input, and generates a PN code. A PN code (hereinafter referred to as “PN ₁ ”) given from the multiplier 3 as the other input, and a multiplier 5 output signal as one input,
The PN code given from the PN code generator 4 (hereinafter referred to as "PN
₂ ”. ) As the other input
And a balanced modulator 8 that combines the output of the multiplier 6 with the output of the carrier generator 7 to generate a spread spectrum signal,
The transmission antenna 9 and the clock generator 2 for supplying a clock signal to the PN code generator 3 and the PN code generator 4 are provided.

Based on the clock signal supplied from the information signal source 1, the clock generator 2 synchronizes the PN ₁ 1 code output from the PN code generator 3 with one bit of the information signal. Then, a clock is applied to the PN code generator 3. The PN code generator 3 follows the clock to generate PN
_{Raises 1} . The multiplier 5 multiplies the information signal supplied from the information signal source 1 by PN ₁ , so that the band of the information signal is widened.

Similarly, the clock generator 2 uses the clock signal given to the PN code generator 3 to generate the PN code generator 3.
PN code generator 4 for each PN ₁ chip
A clock is supplied to the PN code generator 4 so that PN ₂ output from the PN ₂ can be set in synchronization. The PN code generator 4 generates PN ₂ according to this clock. Since the multiplier 6 multiplies the signal given from the multiplier 5 by PN ₂ ,
As a result, the band of the information signal is further expanded.

The output of the multiplier 6 is input to the balanced modulator 8 together with the carrier wave, becomes a spread spectrum signal, and is transmitted from the transmission antenna 9. FIG. 2 shows the waveform of each part when the code length of PN ₁ is 5 and the code length of PN ₂ is 7. In the figure, (a) is the information signal waveform given from the information signal source 1 to the multiplier 5, (b) is the PN ₁ , (c) is the output signal of the multiplier 5, and (d) is the PN. ₂ , (e) of the figure shows the output signal of the multiplier 6. As can be seen from FIGS. 2B and 2D, one code of PN ₁ contains 5 codes of PN ₂ .

Since the structure of such a transmitting device is adopted, it is possible to obtain a spread signal equivalent to that converted by the PN code having a long code length shown in (e). FIG. 3 is a functional block diagram of a receiving device corresponding to the transmitting device,
The receiving device includes a receiving antenna 10 and a demodulator 1 for demodulating a spread spectrum signal into a product of an information signal and a PN code.
1, a sliding correlator 16, a sliding correlator 17, a PN code generator 14, and a PN code generator 1
5, a clock generator 12, and a clock generator 13.

The PN code generator 14 is the clock generator 1.
The sliding correlator 1 uses the same code PN ₂ as the higher PN code of the two PN codes multiplied by the information signal in the transmitter according to the clock given from 2.
Give to 6. The sliding correlator 16 performs despreading on PN ₂ generated from the PN code generator 14, and also includes PN ₂ received from the PN code generator 14 and the PN code to be despread included in the output of the demodulator 11. The correlation between these two codes is synchronized by calculating the correlation value with and feeding back to the clock generator 12. The signal after despreading the PN code with the higher code rate in this way is input to the sliding correlator 17.

The sliding correlator 17 performs despreading on the PN ₁ code generated from the PN code generator 15 and also includes the inverse of the PN ₁ received from the PN code generator 15 and the output of the sliding correlator 16. The correlation value with the PN code to be spread is calculated and fed back to the clock generator 13 to establish synchronization between these two codes. In this way, the information signal is demodulated.

Generally, the sliding correlator does not provide sufficient correlation between the input signals, that is, when these signals are not synchronized with each other, only 1/2 clock is given to the PN code generator. By advancing or delaying, the correlation for one period of the PN code is obtained, and this is repeated until a sufficient correlation is obtained. Therefore, for a PN code with a code length m, it takes a maximum of 2 m chip cycles to acquire the synchronization.

Then, applying this embodiment,
As shown in FIG. 4, first, the PN with the faster code rate is used.
₂ sign It will take a maximum of 14 chip cycles to start the synchronization acquisition for. However, when this is converted into the number of data, it is only 3 bits or less. Then, after the synchronization for PN _{2 is} established, the synchronization acquisition for PN ₁ is started, but since PN ₁ and PN ₂ are synchronized in the transmitting device, PN ₁ is generated if the synchronization with PN ₂ is established. The change amount of the clock given to the PN code generator 15 may be one clock at a time, as described above. Therefore, the time required for the synchronization acquisition of PN ₁ is a maximum of 5 chip periods, which corresponds to 5 bits of data. As a result,
As a whole, the maximum time required for synchronization acquisition is 8 data.
Less than a bit.

On the other hand, by combining two types of PN codes in which the cycles of both PN codes are non-integer multiples, PN with a longer cycle is obtained.
Prior art used as a code (Japanese Patent Laid-Open No. 63-88924)
In the case of the Japanese patent publication), a code P having a different period from the code PN ₁ is used.
Using N _'1, since performing despreading, repeated slowly so that phases are substantially coincides with will periodically shift the PN code used by the transmitting apparatus over time. When the phases match, a component corresponding to PN ₂ remains in the output waveform, so that the phase difference with respect to PN ₂ can be specified.

Compared with the present invention, in the present invention, the code P
Since one code of PN ₂ is accommodated in one chip of N ₁ , the combined code is the PN code itself or a set of inverted codes of PN ₂ . Therefore, PN ₂
Will be easily synchronized with. That is, according to the present invention, it is not necessary to use the synchronization for the code PN ₁ that lasts only for a short time as in the prior art to obtain the synchronization for PN ₂ , so that the sliding correlator is not subject to the restrictions of the prior art. It becomes possible to acquire synchronization in a relatively short time using.

Next, another embodiment of the transmitting apparatus is shown in FIG. This transmitter differs from the transmitter shown in FIG. 1 in that
Instead of sequentially multiplying the information signal by the PN code, the multiplier 5 performs multiplication between the PN codes in advance, and the multiplier 6 multiplies the result by the information signal to obtain a spread spectrum signal. Even in this case, the same result as that of the transmitter of FIG. 1 can be obtained.

FIG. 6 shows another embodiment of the receiving apparatus using a matched filter as the despreading circuit. The receiving device includes a receiving antenna 10 and a spread spectrum signal as an information signal and a P signal.
A demodulator 11 for demodulating into a product of N signals, a matched filter 18, a matched filter 19, and a PN code generator 14
, A PN code generator 15 and a clock generator 12.

In this receiver, the PN code generator 14
Supplies the matched filter 18 with the same code PN ₂ as the PN code with the faster code speed out of the two PN codes multiplied by the information signal in the transmitter according to the clock supplied from the clock generator 12. Performs despreading on the PN code generated from the PN code generator 14. When synchronized, the matched filter 18 outputs a synchronization detection pulse. By applying this synchronization detection pulse to the PN code generator 15 as a synchronization signal, the matched filter 19 can perform despreading.

Since the synchronization detection pulse obtained by the matched filter 19 can be used as a demodulation clock of the final demodulation signal, when a device requiring a clock signal is connected after this receiving device, the clock The reproduction circuit is unnecessary. As described above, in the receiving circuit using the despreading circuit and the matched filter, the synchronization acquisition circuit is not required, and the feedback loop for the synchronization acquisition is not required. Therefore, it is possible to reduce the time until the synchronization is established. it can. On the other hand, the circuit scale increases as the code length used for spreading increases. However, in the present invention, the circuit scale is changed by replacing the PN code having a substantially long code length with a combination of PN codes having a short code length. Therefore, it is possible to suppress the increase in cost and the high cost associated therewith.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, two PN codes whose mutual cycles are integral multiples are used, but in general, n (n ≧ 3) PN codes are used and 1 bit of the information signal is used. One PN code having the lowest code rate is accommodated in the PN code, and one PN code having the second lowest code rate is accommodated in one chip of the PN code.
(3, 4, ..., N) PN code having the lowest code rate One m-th PN code having the lowest code rate may be repeatedly stored in one chip to provide synchronized clocks.

Other various modifications can be made without departing from the spirit of the present invention.

[0037]

As described above, according to the spread spectrum communication apparatus of the present invention, the code speeds are different from each other, and the cycles are in integral multiples, and one code is the other code 1.
Since spread spectrum communication is performed using a plurality of PN codes accommodated in a chip, the bandwidth of an information signal is expanded to the same extent as a PN code having a substantially long code length by a combination of PN codes having a short code length. Can be achieved. Therefore,
It is possible to realize a spread spectrum communication device that is highly resistant to noise and interference and has excellent confidentiality. In addition, since the plurality of PN codes have different code speeds and their mutual cycles are in integral multiples, it can be considered that synchronization is established with each other. Therefore, if the receiving device performs despreading in order from the PN code with the highest code rate, once the PN code with the highest code rate can be synchronized, the time required to synchronize with the PN code with the next highest code rate. As a result, the overall acquisition time is reduced. Therefore, when intermittent communication is performed between the transmission device and the reception device, or when synchronization is lost during communication, the time required for establishing or restoring synchronization can be shortened, and the actual operating time ratio can be reduced. The decrease can be reduced.

In particular, when the despreading circuit of the receiving device is constructed by a sliding correlator, if synchronization with a PN code having a high code rate is achieved, then P having a second highest code rate will be used.
Since synchronization with the N code only needs to be provided with the amount of change in the clocks one clock at a time, the synchronization acquisition time can be shorter than in the conventional case. When the despreading circuit of the receiving device is composed of a matched filter, it is sufficient to have a logic circuit corresponding to the sum of the number of bits of a plurality of PN codes, so that the circuit scale can be reduced. For example, code length 1024
When despreading a bit PN code by a matched filter using a general-purpose logic circuit, the same number of registers is required, but two types of PN with a code length of 32 bits are required.
By replacing with a code, a matching circuit can be configured with 64 registers. Further, when a SAW matched filter, which is a kind of matched filter, is used, the device length can be shortened.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a transmission device of a spread spectrum communication device of the present invention.

FIG. 2 is a diagram showing a waveform of each part of the transmission device when the code length of PN ₁ is 5 and the code length of PN ₂ is 7;
(a) is an information signal waveform given from the information signal source 1 to the multiplier 5, (b) is PN ₁ , (c) is the output signal of the multiplier 5, (d) is PN ₂ , FIG. 7E shows the output signal of the multiplier 6.

FIG. 3 is a functional block diagram of a receiving device corresponding to the transmitting device.

[FIG. 4] PN ₁ and P when the code length of PN ₁ is 5
It indicates the inclusion relation N _2, is a diagram showing a history of synchronization probability.

FIG. 5 is a block diagram showing another embodiment of a transmission device in which a multiplier 5 performs multiplication between PN codes in advance, and a multiplier 6 multiplies the result by an information signal to obtain a spread spectrum signal. is there.

FIG. 6 is a block diagram showing another embodiment of a receiving device using a matched filter as a despreading circuit.

FIG. 7 is a block diagram showing a configuration of a typical direct sequence spread spectrum communication system.

FIG. 8 is a diagram showing a waveform of a PN code given from a PN code generator and an output power spectrum of a spread spectrum signal radiated from a transmitting antenna.

[Explanation of symbols]

1 Information Signal Source 2 Clock Generator 3 PN (PN ₁ ) Code Generator 4 PN (PN ₂ ) Code Generator 5 Multiplier 6 Multiplier 12 Clock Generator 13 Clock Generator 14 PN (PN ₂ ) Code Generator 15 PN (PN ₁ ) code generator 16, 17 sliding correlator

Claims (5)

[Claims] 1. A spread spectrum communication device, comprising: a transmission device and a reception device, wherein the transmission devices have different code rates, and their cycles are in integral multiples, and one code is the other code. A plurality of PN code generators for generating a plurality of PN (pseudo noise) codes accommodated in one chip, an information signal given from an information signal source or the one PN code as one input, and the other And a multiplier that multiplies the PN code as the other input, and outputs the spread spectrum signal by combining the output of the multiplier with the output of the carrier wave generator. Information signal and P
A demodulator that demodulates into a product of N signals, a plurality of PN code generators that generate the same PN code as the PN code generated by the plurality of PN code generators of the transmitter, and a plurality of PN codes A spread spectrum communication device, comprising: a plurality of despreading circuits for performing despreading in order from a PN code having a higher code rate among a plurality of PN codes generated by a generator. 2. A transmission apparatus for spread spectrum communication, wherein a plurality of PNs (codes different in code rate and having a cycle of an integral multiple from each other and one code accommodated in one code of the other code) are provided. A plurality of PN code generators for generating (pseudo-noise) codes, and an information signal given from an information signal source or the one PN code as one input, and the other P
And a multiplier that multiplies the N code as the other input, and the output of the multiplier is combined with the output of a carrier generator to generate a spread spectrum signal. 3. A receiver for spread spectrum communication, comprising a demodulator for demodulating a spread spectrum signal into a product of an information signal and a PN signal, and a PN generated by a plurality of PN code generators of a transmitter. A plurality of PN code generators that generate the same PN code as that of the codes, and a plurality of inverse spreaders that perform despreading in order from the PN code with the highest code rate among the plurality of PN codes generated by the plurality of PN code generators. A receiver comprising a spreading circuit. 4. The receiving apparatus according to claim 3, wherein the despreading circuit of the receiving apparatus is composed of a sliding correlator. 5. The receiving apparatus according to claim 3, wherein the despreading circuit of the receiving apparatus comprises a matched filter.