JPH09135232A - Spread spectrum communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a bit error rate by reducing combination error of a primary demodulator and an inversely spread signal by multiplying a specific primary modulation signal without fail with a specific spread code when the specific spread code is selected. SOLUTION: Spread series of r-sets selected by a spread series selection section 22 corresponds to r-sets of primary modulation signals to be multiplied. In the case of selection of PN1 , PN2 , PN3 , they are respectively outputted to modulation sections 231, 232, 233 without fail. Furthermore, in the case of selection of a PN4 without selection of the PN1 , the PN4 is outputted to the modulation section 321 without fail, in the case of selection of a PN5 without selection of the PN2 , the PN4 is outputted to the modulation section 321 without fail, and in the case of selection of a PN6 without selection of the PN3 , the PN4 is outputted to the modulation section 321 without fail. When an error in reception series selection by a reception series selection section 26 is one series, a mean error of the correspondence between a modulation section and a demodulation section is 1.48 and the number of combinations of errors of three series is 6 ways. Thus, a bit error rate is reduced by reducing the error of the correspondence between a modulation section and a demodulation section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a spread spectrum communication apparatus for converting communication into a signal having a band wider than a band normally required for this communication and performing communication.

[0002]

2. Description of the Related Art Spread spectrum (SS) technology is a technology that spreads the transmission bandwidth by several tens of times the bandwidth of an information signal and transmits it. However, there is a concealment that it is difficult for others to understand that communication is being performed because the transmission power density is low. Furthermore, it has the advantage of being able to measure the communication distance, and has been often used for military communication so far.

However, the number of channels per frequency can be increased, interference from other communication or interference is less likely to occur, interference to other communication channels is less likely to occur, influence of multipath or fading is less likely, and confidentiality is not provided. Therefore, the excellent feature that it can be used not only for communication but also for measuring distance and direction at the same time has been attracting attention as a target for private use.

Conventional frequency division multiple access (FDM)
There is also a movement to adopt the code division multiple access (CDMA or SSMA) method by the SS method instead of the A) method and the time division multiple access (TDMA) method. Especially in the US, since 1985, ISM (Industrial Scien
tific and Medical band is released to SS system.

In Japan, the frequency allocation for wireless LAN is 1
It was approved at the end of 992. This is 26 in the 2.4 GHz band
It can output a maximum of 260 mW in the bandwidth of MHz. (From “Data compression and digital modulation”, Nikkei Electronics Books, pp. 237-252, Nikkei PB (1993)) The most important problem when considering the SS communication system is the problem of frequency utilization efficiency. is there. When the usable bandwidth for SS communication is determined, the upper limit of the chip rate of the spread code is determined.
The chip rate is represented by the product of the information transmission rate of the transmission data and the spreading ratio. Therefore, if the transmission data information transmission rate is increased, the spreading ratio cannot be obtained and the processing gain decreases.
The merit of the S method is reduced.

[0006] Therefore, it is necessary to study to improve the frequency utilization efficiency without deteriorating the characteristics of the SS system. As a method for increasing the frequency utilization efficiency, N spreading codes PN corresponding to the input k bits are input.
_{1 to} PN _N are selected, each of which is a primary modulation signal S
There is a parallel combination spread spectrum communication system in which _{1 to} S _r are multiplied, multiplexed and transmitted.

In such a parallel combination transmission method, it is necessary that the primary modulator on the transmitting side and the primary demodulator on the receiving side have a one-to-one correspondence. However, when the correspondence between the spreading sequence and the modulator as shown in FIG.
Even though N ₁ , PN ₂ , and PN ₃ are transmitted, if PN ₁ is mistaken as PN ₄ on the receiving side, it is an error of only one sequence, but PN ₂ , PN ₃ , and PN ₄ on the receiving side.
Since it is judged that the primary modulation signal spread in step 2 was received and the correspondence between the primary modulator on the transmitting side and the primary demodulator on the receiving side is all different, there is a problem that all primary modulated signals cause demodulation errors. there were.

[0008]

As described above, in the conventional method, there is a possibility that a demodulation error will occur in all primary modulation signals when the selection of the spread sequence transmitted on the receiving side is erroneous.

Therefore, according to the present invention, by applying a certain constraint to the combination of the selected r spread sequences and the primary modulation signal to be multiplied, even if the spread sequence transmitted on the receiving side is erroneously selected, the reverse sequence is reversed. It is an object of the present invention to realize a spread spectrum communication device capable of minimizing an error in a combination of a spread signal and a primary demodulator and reducing a bit error rate.

[0010]

To achieve the above object, the present invention represents a digital signal consisting of a bit string by selecting r spreading codes from _N spreading codes PN _{1 to} PN _N , and In a spread spectrum communication apparatus that multiplies each of them by primary modulation signals S _{1 to} S _r , multiplexes them, and transmits, a specific spreading code PN _i (i is a natural number 1 ≦ i of the spreading codes PN _{1 to} PN _N. ≤r), the specific spreading code PN _i is always the spreading code PN _i.
Is multiplied by the primary modulation signal S _i .

A specific spreading code PN _{m × r + i} among the spreading codes PN _{1 to} PN _N (i and m are natural numbers and 1 ≦ i ≦
r) and a specific spreading code PN _{n × r + i} (n
Is a natural number, and n <m) is not selected, the specific spreading code PN _{m × r + i} is always set to the spreading code PN.
It is characterized in that the primary modulated signal S _i corresponding to _{m × r + i} is multiplied.

According to the present invention as described above, the combination of the selected r spreading sequences and the primary modulation signal to be multiplied has a certain correspondence relationship. As a result, even if the spread sequence transmitted on the receiving side is erroneously selected, the error in the combination of the despread signal and the primary demodulator can be minimized and the bit error rate can be reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A spread spectrum communication apparatus according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the spread spectrum communication apparatus of the present invention.

The device comprises a digital interface 10, a control unit 11, a spread modulation / demodulation unit 12, a synchronization unit 13, and a radio unit 14.
And an antenna 15.

Signals from various terminal devices (voice, image, data terminal, etc.) not shown are digital interfaces 1.
When 0, the level, speed, etc. are converted, spread modulation / demodulation unit 12 performs spread modulation, radio unit 14 modulates a radio signal, and the signal is transmitted from antenna 15. On the other hand, the reception signal received by the antenna 15 is demodulated by the radio unit 14, spread and demodulated by the spread modulation / demodulation unit 12, the level, speed, etc. are converted by the digital interface 10 and output to various terminal devices not shown.

The digital interface 10 is an interface between various terminal devices and the spread modulation / demodulation unit 12, and performs data level conversion between the various terminal devices and the spread modulation / demodulation unit 12.
It performs frame synchronization and speed conversion, and outputs a timing signal to the control unit 11.

The control unit 11 is a digital interface 1
0 and the timing signal output from the synchronization unit 13 are sent to the spread modulation / demodulation unit 12 to control the device.

The spread modulation / demodulation unit 12 is a unit for performing spread modulation / demodulation. As shown in FIG. 2, the serial / parallel conversion unit 20, the spreading sequence generating units 211 to 217, the spreading sequence selecting unit 22, the modulating units 231 to 233, and the combining unit. Parts 241, 242, despreading part 25
1 to 257, reception sequence selection unit 26, demodulation units 271 to 27
3 and the parallel-serial conversion unit 28.

On the transmission side, the serial / parallel converter 20 is connected to the controller 1
On the basis of the timing signal output by 1, the bit sequence output by the digital interface 10 is divided into 11 bits, 5 bits of which are output to the spreading sequence selection unit 22, and the remaining 6 bits are each modulated by 2 bits. Part 23
1 to 233.

Spreading sequence generators 211 to 217 generate spreading sequences PN _{1 to} PN ₇ as shown in FIG. 6 based on the timing signals output from control unit 11, respectively, and spread sequence selecting unit 22 and despreading unit. It is output to the units 251 to 257. The spreading sequences PN _{1 to} PN ₇ are codes that are orthogonal to each other.

The spreading sequence selection unit 22 is a serial / parallel conversion unit 20.
Corresponding to the 5 bits output by the spreading sequence generator 211
3 to 217 out of the spreading sequences PN _{1 to} PN _7.
One of them is selected and output to the modulators 231 to 233, respectively. The serial-parallel converter 20 shown as an input bit string in FIG.
5 shows the correspondence relationship between the 5 bits output from the above and the spreading sequences PN _{1 to} PN ₇ output to the modulators 231 to 233.

A characteristic feature here is that, as shown in FIG. 7, when PN ₁ is selected, the modulation unit 231 always receives
When PN ₂ is selected, the PN
_This means that when ₃ is selected, it is always output to the modulator 233. When PN ₁ is not selected and PN ₄ is selected, PN ₄ is always output to modulator 231.
Similarly, when PN ₂ is not selected and PN ₅ is selected, PN ₅ is always output to the modulator 232, and when PN ₃ is not selected and PN ₆ is selected, PN ₆ is always modulated. It is output to the unit 233.

The modulators 231 to 233 are composed of a primary modulator 30 and multipliers 311 and 312 as shown in FIG.

The primary modulator 30 baseband-modulates the two bits output from the serial / parallel converter 20 to obtain the I component and the Q component.
The components are output to the multipliers 311 and 312, respectively.

The multipliers 311 and 312 have the primary modulator 30.
And the spreading sequence output from the spreading sequence selection unit 22 are multiplied and output to the combining units 241 and 242, respectively.

The synthesizers 241 and 242 are modulators 231 to 231.
The output signal of 233 is linearly combined and output to the wireless unit 14 as a communication signal.

On the other hand, on the receiving side, despreading units 251 to 257 are provided.
Is composed of multipliers 401 and 402 and integrators 411 and 412, as shown in FIG.

Multipliers 401 and 402 multiply the output signal from the radio section 14 and the spreading sequences PN _{1 to} PN ₇ generated by the spreading sequence generating sections 211 to 217, and integrator 41 respectively.
Output to 1, 412.

The integrators 411 and 412 integrate the signals sent from the multipliers 401 and 402 over the length of the period of the spread signal based on the timing signal output from the control unit 11, and the reception sequence selection unit. To 26.

The reception sequence selection unit 26, based on the timing signal output from the control unit 11, despreading units 251 to 25.
Three spreading sequences PN _{1 to} PN ₇ are selected in descending order of the sum of absolute values of the I component and the Q component of the output of ₇ . Then, 5 bits are output to the parallel-serial conversion unit 28 according to the correspondence relationship shown in FIG. Further, the despreading units 251 and 252 corresponding to the PN sequence selected from the spreading sequences PN _{1 to} PN _7.
The outputs (I, Q) of 57 are output to the demodulation units 271 to 273 according to the correspondence relationship shown in FIG.

The demodulators 271 to 273 perform baseband demodulation of the output signal of the reception sequence selector 26 based on the timing signal output from the controller 11, and output the obtained 2 bits to the parallel-serial converter 28. .

The parallel / serial conversion unit 28 includes a reception sequence selection unit 26.
Then, a total of 11 bits output from the demodulation units 271 to 273 are parallel-serial converted based on the timing signal output from the control unit 11 and output to the digital interface 10.

As shown in FIG. 5, the radio section 14 includes the low-pass filters 501 to 504, the carrier wave generator 51, the π / 2 phase shifter 52, the multipliers 531 to 534, the combiner 54, and the bandpass filter. It is composed of the devices 551 and 552, the amplifiers 561 and 562, the circulator 57, and the carrier synchronization unit 58.

On the transmitting side, low-pass filters 501 and 502
Limits the band of the output signal of the spread modulation / demodulation unit 12.

The carrier wave generator 51 outputs a radio frequency sine wave. At the time of reception, the output is controlled based on the carrier wave phase control signal output from the carrier synchronization unit 58.

The π / 2 phase shifter 52 delays the phase of the sine wave output from the carrier wave generator 51 by π / 2.

The multiplier 531 multiplies the output signal from the low-pass filter 501 and the sine wave output from the carrier wave generator 51. The multiplier 532 multiplies the output signal from the low-pass filter 502 and the sine wave output from the π / 2 phase shifter 52.

The synthesizer 54 includes a multiplier 531 and a multiplier 53.
The two output signals are combined.

The bandpass filter 551 band-limits the output signal of the combiner 54.

The amplifier 561 power-amplifies the output of the bandpass filter 551.

The circulator 57 outputs the output of the amplifier 561 which is a transmission signal to the antenna 15, and the antenna 1
The signal received by 5 is output to the bandpass filter 552.

On the receiving side, the bandpass filter 552 limits the band of the signal received from the antenna 15.

The amplifier 562 amplifies the output signal of the bandpass filter 552.

The multiplier 533 multiplies the output signal of the amplifier 562 by the sine wave output from the carrier wave generator 51, and the multiplier 534 multiplies the output signal of the amplifier 562 by the π / 2 phase shifter 52.
Multiply the sine wave output by.

The low-pass filters 503 and 504 are multipliers 53.
The band of the output signals of 3, 534 is limited. Low-pass filter 5
The outputs of 03 and 504 are the despreading unit 25 of the spreading modulation / demodulation unit 12.
1 to 257 are input to the synchronization unit 13.

The carrier synchronizing section 58 is composed of a multiplier, a loop filter, etc., which are not shown, and the low-pass filter 5 is provided.
The carrier wave phase control signal is output to the carrier wave generator 51 based on the output signals of 03 and 504.

The synchronizing section 13 includes low-pass filters 503 and 504.
The timing of the clock and the period of the spread code is extracted from the output signal of 1 and the timing signal is output to the control unit 11. At this time, the timing of the spread code is obtained by transmitting a specific spread code before data transmission and receiving it.

A feature of the present invention is a method of associating the r spreading sequences selected by the spreading sequence selecting unit 22 with the r primary modulation signals multiplied by these.

In the corresponding method of FIG. 7 to which the present invention is applied, P
When N ₁ , PN ₂ and PN ₃ are selected, they are always output to the modulators 231, 232 and 233, respectively. When PN ₁ is not selected and PN ₄ is selected, PN ₂ is not selected for the modulation unit 231, and when PN ₅ is selected, PN ₃ is selected for the modulation unit 232 without exception. However, when PN ₆ is selected, it is always output to the modulator 233. The signal modulated by the modulator 231 must be demodulated by the demodulator 271, the signal modulated by the modulator 232 must be demodulated by the demodulator 272, and the signal modulated by the modulator 233 must be demodulated by the demodulator 273.

Here, most of the errors in the reception sequence selection in the reception sequence selection unit 26 are errors in only one sequence.
Therefore, the error of only one sequence will be considered here.

For example, when the corresponding method as shown in FIG. 8 to which the present invention is not applied is used, PN ₁ , P on the transmitting side are used.
Even if N ₂ and PN ₃ are selected (input bit string 0000000), if it is determined that PN ₂ , PN ₃ , and PN ₄ (input bit string 01111) are received on the receiving side, P
Although the error is only one sequence of N ₁ and PN ₄ , the correspondence between the modulation unit and the demodulation unit is incorrect. Therefore, when the correspondence method shown in FIG. 8 is used, the correspondence error of the modulation unit and the demodulation unit when the reception sequence selection unit 26 has one reception sequence selection error is 1.65 on average, and all three are erroneous. There are 60 possible combinations.

On the other hand, when the correspondence method of FIG. 7 to which the present invention is applied is used, when the reception sequence selection error in the reception sequence selection unit 26 is one sequence, the correspondence between the modulation unit and the demodulation unit is obtained. The average number of errors is 1.48, and there are 6 combinations in which 3 are incorrect. Therefore, the bit error rate can be lowered by reducing the errors in the correspondence between the modulation unit and the demodulation unit.

[0054]

As described above, according to the present invention, a digital signal consisting of bit strings is converted into n spread codes PN _{1 to} P.
Select and represent r spreading codes from N _N , each of which is 1
A spread spectrum communication device that multiplies the next modulated signals S _{1 to} S _r , multiplexes the signals, and transmits the signals. A specific spread code PN _i (i is a natural number 1 ≦ i ≦ r) of the spread codes PN _{1 to} PN _N.
When is selected, the specific spreading code PN _i is always multiplied by the specific primary modulation signal S _i .

Further, among the spreading codes PN _{1 to} PN _N, a specific spreading code PN _{m × r + i} (i and m are natural numbers 1 ≦ i
≦ r) is selected and the specific spreading code PN _{n × r + i}
If (n is a natural number and n <m) is not selected,
The specific spreading code PN _{m × r + i} is always multiplied by the specific primary modulation signal S _i .

By this means, it is possible to reduce the number of combinations of errors corresponding to the modulation unit and the demodulation unit when there is an error in the reception sequence selection, that is, to reduce the errors of the combination of the despread signal and the primary demodulator. It is possible to reduce the bit error rate.

[Brief description of the drawings]

FIG. 1 is a block diagram of a spread spectrum communication device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a spread modulator / demodulator of the embodiment shown in FIG.

3 is a block diagram showing a configuration of a modulation unit of the spread modulation / demodulation unit shown in FIG.

FIG. 4 is a block diagram showing a configuration of a despreading unit of the spreading modulation / demodulation unit shown in FIG.

5 is a block diagram showing a configuration of a wireless unit of the embodiment shown in FIG.

FIG. 6 is a waveform diagram of a spreading sequence output from a spreading sequence generation unit of the spreading modulation / demodulation unit shown in FIG.

7 is an example of a correspondence table of spreading sequences selected for an input bit sequence in a spreading sequence selection unit of the spreading modulation / demodulation unit shown in FIG.

8 is another example of a correspondence table of spreading sequences selected with respect to an input bit sequence in the spreading sequence selection unit of the spreading modulation / demodulation unit shown in FIG.

[Explanation of symbols]

 10 Digital Interface 11 Control Section 12 Spreading Modulation / Demodulation Section 13 Synchronization Section 14 Radio Section 15 Antenna 20 Serial / Parallel Conversion Section 22 Spreading Sequence Selection Section 26 Received Sequence Selection Section 28 Parallel / Serial Conversion Section 30 Primary Modulation Section 51 Carrier Generator 52 π / 2 phase shifter 54 combiner 57 circulator 58 carrier synchronization part 211-217 spreading sequence generating part 231-233 modulating part 241,242 combining part 251-257 despreading part 271-273 demodulating part 311,312 multiplier 401, 402 multiplication 411, 412 Integrators 501-504 Low-pass filters 531-534 Multipliers 551, 552 Band-pass filters 561, 562 Amplifiers

Claims (2)

[Claims] 1. A digital signal comprising a bit string is represented by selecting r spread codes from _N spread codes PN _{1 to} PN _N , each of which is multiplied by a primary modulated signal S _{1 to} S _r , In a spread spectrum communication device for multiplexing and transmitting, a specific spread code P among the spread codes PN _{1 to} PN _N is used.
When N _i (i is a natural number 1 ≦ i ≦ r) is selected, the specific spreading code PN _i is always multiplied by the primary modulation signal S _i corresponding to the spreading code PN _i. Spread spectrum communication device. 2. A specific spreading code PN _{m × r + i} among the spreading codes PN _{1 to} PN _N (i and m are natural numbers and 1 ≦ i
≤r) and a specific spreading code PN
_{When n × r + i} (n is a natural number and n <m) is not selected, the specific spreading code PN _{m × r + i} is always set to the spreading code PN.
_The spread spectrum communication device according to claim 1, wherein the primary modulated signal S _i corresponding to _{m × r + i} is multiplied.