JP3287724B2 - Spread spectrum communication equipment - 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 apparatus.

[0002]

2. Description of the Related Art In spread-spectrum communication, a code division multiplex communication system has been conceived which utilizes a low cross-correlation characteristic of a spread code to multiplex a plurality of communication paths in the same band to increase the information transmission speed. A patent application related to a synchronous code division multiplex communication apparatus using phase shift modulation has already been filed (Japanese Patent Application No. 5-151219). In general, in a single-channel spread spectrum communication system, a receiver has as a replica the same spreading code used for spread spectrum of a transmission signal, and performs a periodic correlation operation between the replica and the reception signal. Accordingly, code synchronization can be maintained simultaneously with information transmission.

On the other hand, in the code division multiplex communication system described at the beginning, since information signals are multiplexed by a plurality of spreading codes, once code synchronization is established, the cross-correlation characteristics between the spreading codes at the synchronization point are reduced. Because of low correlation or orthogonality, each information symbol can be independently demodulated. However, since the periodic cross-correlation characteristics of the plurality of spreading codes are not always low correlation, even if the periodic correlation operation is performed using any one of the spreading codes, the correlator output is affected by the cross-correlation characteristics between channels. It is difficult to recognize a steep correlation peak, and it is difficult to constantly capture and maintain synchronization while transmitting information. Therefore, in such a code division multiplex communication system, the transmitter transmits a pilot signal spread as a preamble by a single spreading code as a preamble for a certain period of time prior to transmission of an information signal, in order to obtain synchronization at the receiver, After capturing the synchronization with the pilot signal, the receiver may capture and hold the code synchronization by, for example, holding the clock during the information transmission period.

FIG. 9 is a diagram showing a configuration of a demodulator of the code division multiplex communication apparatus of the prior application. In this example, the modulation method is phase shift keying, and the demodulation method is synchronous demodulation. In the figure, first, a received signal converted into an intermediate frequency signal 201 is multiplied by a carrier 102 reproduced by a carrier wave reproducing circuit 101 by a mixer 102, passed through a low-pass filter 103, and converted into a baseband signal. Further, this baseband signal is supplied to the AD converter 104.
Is converted into a digital multiplexed signal. The demodulation circuit of the receiver includes the same number of digital correlators 106 as the number of multiplexes, and performs a correlation demodulation process on the multiplexed digital signal using a plurality of spread codes generated from the code generator 105. To obtain the multiplexed information data of each channel. At this time, for example, when the received multiplexed data at the time of performing the correlation operation is expressed in a positive / negative signed binary number, in the two-phase modulation, the sign bit of the correlator output can be regarded as demodulated data. The low-speed parallel data 206 demodulated in this manner is finally converted into a high-speed serial data stream 207 by the parallel-serial converter 107.

Here, in order to recognize a change point from the reception period of the preamble to the start of the information signal in the data stream of such packet type data transfer, a unique bit pattern having a specific bit pattern in the data stream is required. It is necessary to take measures depending on the upper layer protocol, such as inserting a word and informing the receiver of the start timing of the information signal by the appearance of the word.

[0006]

However, as described above, a unique word is inserted into a data stream,
Means for recognizing the data start point in the upper layer of the communication system inevitably causes a decrease in data transmission efficiency, and such a decrease in efficiency is particularly remarkable in packet-type data transmission.

It is therefore an object of the present invention to reduce the overhead of upper layer protocols by recognizing the starting point of information signal transmission at the lower layer level of the communication system without using unique words in the data stream.
An object of the present invention is to provide a spread spectrum communication device having high data transmission efficiency.

[0008]

In order to achieve the above object, according to the present invention, there is provided a correlation means for performing a correlation demodulation by a spread code transmitted as a preamble before information transmission, and a correlation output of the correlation means. Comparing means with a reference value, and processing means for recognizing that the preamble has ended when the correlation output of the correlation means has become equal to or less than the reference value, based on the comparison output of the comparison means, and processing the received data. Is provided.

Further, in addition to the configuration of the present invention, a holding means for latching the code synchronization signal generated from the code synchronization circuit by the output of the comparison means is provided. This holding means has a function of masking an incorrect correlator output that appears when code synchronization is not established.

Further, in addition to the configuration of the present invention, there is provided a holding means for latching a carrier wave reproduction signal generated from the carrier wave reproduction circuit by the output of the comparison means. This holding means has a function of masking an incorrect correlator output that appears when carrier recovery is not established.

[0011]

FIG. 1 is a diagram showing a configuration of a receiver according to a first embodiment of the present invention. In the figure, a code generator 105 outputs a pilot code 301 in addition to a spreading code for correlation demodulation of each information channel, and a pilot signal correlator 302 performs correlation between a received signal and the pilot code. Perform demodulation.

Now, assuming that the noise has a negligible magnitude, the output of the correlator is 0 when there is no received signal. Here, when the transmitter transmits the pilot signal as a preamble, after code synchronization and carrier recovery are established, the received power obtained by correlating and demodulating the pilot signal as a preamble appears in the correlator output 303 of the receiver. FIG. 2 is a timing chart of the received signal and the correlator output at this time.

Further, when communication shifts to information transmission after the end of the preamble period, since the pilot signal is not transmitted, a cross-correlation value that the pilot code receives from the spreading code of another information channel appears in the correlator output. ,
This cross-correlation value in a code division multiplex communication system is
As shown in FIG. 2, the value is smaller than the preamble section.

Now, FIG.
When a comparator 304 for comparing with a reference value as shown in FIG. 2 is provided, the comparison output 305 of this comparator becomes high level only during the preamble period as shown in FIG. It recognizes that it is a transition point from the data transmission to the information transmission, and processes the serial data stream 207 thereafter.

In the above embodiment, the pilot signal is used only at the time of transmitting a preamble, and is not transmitted at the time of transmitting multiplexed information. However, a pilot code is transmitted during information transmission by spreading one of the multiplexed information channels. The present invention is effective even when used as a code.

FIG. 3 is a diagram showing the configuration of a receiver according to another embodiment of the present invention. In this figure, the code generator 10
5 among the spreading codes for correlation demodulation generated from
One spreading code is a pilot code, and this code is input to both the correlator 106 for demodulating information and the correlator for pilot signals. Here, the correlation output 3 of the pilot signal correlator 302 with respect to the reception signal of the receiver is shown.
Focusing on 03, a timing chart as shown in FIG. 4 is obtained. It should be noted here that the correlator for the pilot signal measures the received power of the pilot channel by taking the absolute value of the correlation value, rather than demodulating the information symbols of the pilot channel, It has a function different from that of the correlator 106 for demodulating information symbols.

In the present embodiment, the total transmission power at the time of preamble and at the time of information transmission are configured to be substantially equal.
That is, while the pilot signal is included in both the preamble and the multiplexed information signal, the pilot signal in the preamble has a signal power equal to the total transmission power, whereas the transmission power is Since the signal power is distributed to the information channel, the signal power of the pilot signal at this time has a smaller value than that at the time of the preamble.

Therefore, as shown in FIG. 4, the output of the correlator for the pilot signal has a small value compared to the preamble in the section where the multiplexed information signal including the pilot signal is received. By comparing the correlator output with a certain reference level, the start point of information signal transmission can be recognized at its falling edge, as in the previous embodiment.

FIG. 10 shows the configuration on the transmitting side. The transmission serial data is converted into low-speed parallel data by a serial / parallel converter 507, and a digital multiplier 506 is used by using a plurality of spread codes generated from a code generator 505.
And added by the digital adder 503. Then, the signal is converted into an analog signal by a digital / analog converter 504, converted into a radio frequency by a modulator 502, and transmitted from an antenna.

The control circuit 510 controls the adder 5 so that the total transmission power is substantially equal between the preamble transmission and the information transmission.
03 is bit-shifted before being converted to an analog signal. For example, if it is shifted by 3 bits, it becomes 8 times.

When performing correlation demodulation in a spread spectrum communication system, a proper demodulated output cannot be obtained as a correlator output until code synchronization is established. Even when the correlator output is unstable, if the correlation value is always smaller than the threshold value of the comparator, a desired information transmission start signal can be obtained with the configuration of the receiver shown in FIG. However, if these invalid correlation output levels become large enough to exceed the threshold, in order for this information transmission start signal to operate properly, the comparison output is masked by a status signal indicating that synchronization has been established. There must be.

FIG. 5 is a diagram showing a configuration of a receiver according to the second embodiment. Here, reference numeral 108 denotes a code synchronization circuit having a function of generating a code synchronization signal 307 when code synchronization is established. If a value exceeding the reference value of the comparator 304 appears in the pilot signal correlator output 303 during the period before synchronization is established, a comparison output 305 as shown in FIG. 6 is generated. Now, if the initial value of the holding circuit 309 is set to a low level, even if the comparison output is unstable at this time, the holding circuit 309 connected to the next stage is operated.
Latches the low-level synchronization establishment signal, so that its state does not change.

Thereafter, when code synchronization is established, the code synchronization signal goes high, and at the same time, the correlator output starts correlation demodulation of a valid preamble. In the section after this, the correlation output becomes larger than the threshold value, so that the comparison output is stabilized at a high level, and when information transmission starts, a falling edge is generated in the comparison output as in the principle of FIG. You. If the holding circuit 309 latches the high-level code synchronization establishment signal at the falling edge, the start point of the information transmission section can be recognized.

An object of the present invention is to allow the communication system to recognize the start point of information transmission. After the occurrence of the falling edge, the holding circuit 309 can be reset by a timer or an external signal 306 to return to the initial state. For example, the same operation is performed for the next packet. The other embodiment of FIG. 3 can be similarly applied to a system using a pilot signal as a spreading code for information transmission.

In a code division multiplex communication system using synchronous demodulation, in order to demodulate an information signal, it is essential that both code synchronization and carrier wave reproduction have been established. Depending on the configuration of the receiver, pull-in of carrier recovery may be started after code synchronization is established, and in a receiver having such a configuration, carrier recovery is established and baseband demodulation is performed. Otherwise, proper correlation demodulation is not performed. In such a case, as in the second embodiment, the start point of the information transmission can be correctly recognized by masking the correlator output with the carrier reproduction signal.

FIG. 7 is a diagram showing a configuration of a receiver according to a third embodiment of the present invention. Here, reference numeral 101 denotes a carrier recovery circuit having a function of generating a carrier recovery signal 308 when carrier recovery is established.

In the present embodiment, the carrier recovery establishment signal 308
Is replaced with the code synchronization signal 307 in the second embodiment, it is obvious that the start point of the valid information signal can be recognized in the timing chart as shown in FIG.

The embodiment shown in FIG. 3 can be similarly applied to a system using a pilot signal as a spreading code for information transmission.

In this embodiment, digital correlation demodulation is taken as an example. However, even when an analog demodulator is used,
It is possible to carry out the invention.

[0030]

As described above, according to the present invention,
It is possible to reliably recognize the end of the preamble and improve the information transmission efficiency.

Further, even for unstable output of the correlator for pilot signals before code synchronization or carrier wave recovery is established, the start point of information transmission can be recognized more accurately.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a receiving device according to a first embodiment of the present application.

FIG. 2 is a diagram showing a timing chart of a first embodiment according to the present application.

FIG. 3 is a diagram illustrating a configuration of a receiving apparatus according to another embodiment of the present application.

FIG. 4 is a diagram showing a timing chart of another embodiment related to the present application.

FIG. 5 is a diagram illustrating a configuration of a receiving apparatus according to a second embodiment of the present application.

FIG. 6 is a diagram showing a timing chart of a second embodiment according to the present application.

FIG. 7 is a diagram illustrating a configuration of a receiving apparatus according to a third embodiment of the present application.

FIG. 8 is a diagram showing a timing chart of a third embodiment according to the present application.

FIG. 9 is a diagram illustrating a configuration of a receiving device of a conventional code division multiplex communication system.

FIG. 10 is a diagram illustrating a configuration of a transmission device according to an embodiment of the present application.

[Explanation of symbols]

 Reference Signs List 105 Code generator 106 Digital correlator 107 Parallel-serial converter 108 Code synchronization circuit 302 Correlator for pilot signal 304 Comparator 306 Reset signal 307 Code synchronization establishment signal 308 Carrier reproduction establishment signal 309 Holding circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04J 13/00-13/06 H04B 1/69-1/713 H04L 7/00

Claims (4)

(57) [Claims] 1. A method for transmitting information as a preamble before information transmission.
Correlation to perform correlation demodulation with spreading codesmeans
And the correlationmeansComparator that compares the correlation output of
Based on the comparison output of the comparing means.The correlation means
That the correlation output ofPre
AmbleRecognizes thatProcess the received data.
Spread spectrum communication characterized by providing control means
apparatus. 2. A further have a receiving means for receiving the multiplexed signal using a plurality of different pseudo-random sequence as a spreading code, year processing means, the comparison output of the comparison means
And the correlation output of the correlation means is equal to or less than the reference value.
Recognizes that the preamble has ended,
2. The spread spectrum communication apparatus according to claim 1, wherein the multiplexed signal received by said receiving means is processed . 3. A code synchronization means for generating a synchronization establishment signal when code synchronization is established with respect to a received signal, and said synchronization establishment signal is generated by a falling edge of an output of said comparison means. 2. The spread spectrum communication apparatus according to claim 1, further comprising holding means for latching. 4. Carrier recovery is established for a received signal.
Carrier recovery that generates a carrier recovery establishment signal at a point in timemeans
And outputting the carrier recovery establishment signal to the output of the comparing means.Standing
Falling edgeFurther comprising holding means for latching by
2. The spread spectrum communication apparatus according to claim 1, wherein
Place.