JP4558046B2 - Method for woven spreading code - Google Patents

Description

  The present invention relates to a woven spreading code such as a Barker code used for pulse compression or pulse encoding. This weaving spread code can be used for, for example, direct sequence spread spectrum communication.

  Although the present invention will be described mainly with reference to direct sequence spread spectrum signals, the present invention is not limited to specific aspects of Barker codes, and other spread codes can be used in other aspects, particularly high. The present invention can be applied to a use related to a low noise signal environment.

  In a spread spectrum system, the signal occupies a larger bandwidth than the minimum bandwidth required to transmit information. The baseband is propagated by using a code that is unrelated to the data to be transmitted. The direct sequence is a type of technique performed by multiplying a data signal by a code signal. This code may be a Barker code.

  At the receiver, the original data signal is recovered by correlation of the received signal using a synchronized replica of the coded signal used to propagate the baseband. In this way, Barker codes can be used for the spreading method.

  A Barker code can be defined as a sequence of length N, for which a non-periodic autocorrelation function is between 0 and 1 / N. The Barker code may be given as a binary code or a non-binary code. Binary Barker codes with lengths of 2, 3, 4, 5, 7, 11, 13 are known. Here, the Barker code is a code in which +1 and −1 are given as a sequence of length (number) of N> = 2.

  Barker codes are used in the process of pulse compression and pulse coding. A Barker code can be used to compare two signals, giving the maximum output if the two signals match, otherwise giving a zero or constant minimum value. This comparison process is generally referred to as correlation.

  One bit of each input line is examined at a time, multiplied by these bits, and added to the individual result. Barker codes are not the only type of codes used for spreading, and other spreading codes can be used.

  While having these benefits, there are also problems. One of the most serious problems when using Barker codes is that the pulse envelope becomes non-uniform when the bandwidth needs to be limited. If this envelope becomes non-uniform, the energy per transmitted pulse will be small and the sensitivity of the receiver will be reduced.

  Therefore, the main object, feature or advantage of the present invention is to improve the above-mentioned prior art.

  Another object, feature or advantage of the present invention is to provide a code that achieves improved amplitude uniformity, thereby improving envelope uniformity even when bandwidth needs to be limited. is there.

  Yet another object, feature or advantage of the present invention is to provide a code which increases the energy per generated pulse.

  Yet another object, feature or advantage of the present invention is to provide a code that provides approximately the same autocorrelation as the properties associated with Barker codes.

  Other objects, features, or advantages of the present invention will become apparent from the description and the claims.

  The present invention provides for the generation and use of interwoven spreading codes. According to one aspect of the invention, the communication method includes the steps of adding a woven spreading code such as a Barker code to digital data to generate a signal and transmitting the signal. The woven spreading code is formed from an extended spreading code string at the first frequency, and is formed from a mirror of the extended spreading code string at the second frequency.

  In accordance with another aspect of the present invention, digital data is extracted from a signal containing data to be encoded using a woven spreading code. The spreading code used here is preferably a Barker code, but other spreading codes having appropriate autocorrelation characteristics may be used.

  The present invention provides a method of using a woven spreading code in a method of using a woven spreading code and a communication system.

  The present invention is not limited to the specific examples described herein. For the sake of explanation, a Barker code is used here. However, the present invention also includes embodiments in which other types of spreading codes, in particular spreading codes that provide the desired autocorrelation properties, can be used.

  The inventors have studied the relationship between the Barker column and its mirror image and found that these two columns alternately build and destroy each other. For purposes of explanation, here we use 13 rows of barkers, but any barker row can be used.

  Note that in the sum of these two columns, 2 and 0 appear alternately for each number. The alternating 2 indicates construction and 0 indicates destruction. This alternating pattern can be counteracted by constructing a new column where each element is the average of two consecutive elements in the Barker 13 column.

  The two vectors obtained are independent of each other. When the extended barker 13 is 1, the mirror is 0. When the mirror is 1, the extended barker 13 is 0. It should be noted that the resulting sum vector has this property.

  Furthermore, the envelope of the columns is almost uniform. This makes it possible to increase the energy per transmitted pulse.

  In a mathematical way, a new sequence is constructed by convolution of 13 columns of Barker with the vector [0.5,0.5]. This numerical operation ensures that the autocorrelation obtained by the above sequence does not change significantly. Furthermore, the signal bandwidth becomes narrower as the operating time becomes longer.

  Since these two columns are mirror images of each other, both columns are required to have symmetry that produces an autocorrelation at exactly the same time. By centering each sequence of different frequencies and entangle them, a signal with uniform amplitude and well-defined autocorrelation is obtained.

  The numbers in bold are generated from the extended barker 13 rows and are represented by the first frequency. The elements shown in italics are derived from the reverse sequence and are represented by the second frequency. Here, the sum of these two columns is a code called “weaving Barker code”.

  There are woven Barker codes that can be constructed from each Barker code in the manner described above. For convenience, FIG. 8 also illustrates how a woven Barker code can be determined from a Barker sequence.

  1 and 2 illustrate useful properties of a woven Barker code. In FIG. 1, the autocorrelation form of Barker 13 rows is indicated by row A. Also, the extended barker 13 row or its autocorrelation form is shown by row B. The autocorrelation form of the sum of the 13 extended barker rows and the mirror (13 woven barker rows) is shown by column C.

  It is noteworthy that the autocorrelation form of woven Barker 13 row C is about the same as the autocorrelation form for Barker 13 row A, and thus this advantage of Barker row is maintained.

  FIG. 2 illustrates one useful advantage of a woven Barker code. In particular, FIG. 2 shows that this woven Barker code has a more uniform amplitude than the Barker 13 row. Since the amplitude of the woven Barker code is uniform, the energy per generated pulse is increased.

  For woven Barker codes, including woven Barker 13 codes, it can be performed using surface acoustic wave (SAW) technology. This is disclosed, for example, in US Pat. No. 6,535,545, the disclosure of which is hereby incorporated by reference.

  In one embodiment of the invention, each of the two weaving sequences is encoded using BPSK (two-phase sequence keying) at a separate frequency. For example, the first column may be set at 482 MHz and the second column may be set at 494 MHz.

  The obtained signal was transmitted and observed on an oscilloscope. It was observed that the uniformity of the PA (pulse amplitude) compression envelope was higher than predicted by simulation. This is illustrated in FIG. The spectrum of the resulting woven Barker 13 code is shown in FIG. It is noted that the center frequency is set to 2.438 GHz and the signal bandwidth is relatively limited.

  FIG. 5 illustrates an autocorrelation signal with a woven Barker 13 code equal to the autocorrelation signal from the simulation.

  The present invention provides a method for using a woven Barker code in all applications, including applications where Barker codes are currently used, and applications where high uniformity of amplitude and a narrow bandwidth are advantageous. is there.

  FIG. 6 illustrates a block diagram of one embodiment of a transmitter that uses a woven Barker code. As shown in FIG. 6, an extended Barker sequence and a mirror extended Barker sequence are added to the input digital data bits (for example, by using an exclusive OR function (XOR function)). The resulting signal is modulated by modulator 12 to generate a transmission signal.

  FIG. 7 shows the receiver 20. The received signal is input to the demodulator 22. The resulting signal, after filtering, is transmitted to the correlator 24, where digital data is determined using the extended Barker train and the mirror extended Barker train. One skilled in the art will appreciate the advantage that the woven Barker code of the present invention can be used with any device hardware or software.

  While specific embodiments of the present invention have been described above, the present invention includes many other specific examples and variations. For example, the present invention provides for the use of a wide variety of spreading codes that are recognized to provide an effective autocorrelation signal when mirrored, including Barker codes or other spreading codes.

  The present invention also includes interwoven spreading codes having different lengths, and the present invention also includes an aspect in which interwoven spreading codes are used for purposes other than extended spectrum digital communication, and the difference in modulation format and frequency, Other changes and modifications apparent to those skilled in the art having the benefit of the disclosure are also included in the invention. Therefore, these modifications and other modifications are included in the scope of the present invention.

It is a graph which shows the autocorrelation form of Barker 13 row | line | column, extended Barker 13 row | line | column, or its mirror, and the autocorrelation form (weaving Barker row | line | column) of the sum of an expansion number sequence | sequence and its mirror. FIG. 6 is a graph illustrating a comparison between a simulated Barker 13 and a weave Barker 13 transmission signal and a difference in amplitude uniformity; FIG. It is a graph which illustrates the measurement transmission signal of the woven Barker 13 code | symbol, and shows a uniform envelope. It is a figure which illustrates the power spectrum of the woven Barker 13 code | symbol. It is a figure which illustrates the measured value of the autocorrelation type signal of the woven Barker 13 code | symbol. It is a block diagram which illustrates one specific example of the transmitter suitable for use of a woven Barker code | cord | chord. It is a block diagram which illustrates one specific example of the receiver suitable for use of a woven Barker code | symbol. It is a figure which illustrates one specific example which derives | leads-out the woven Barker code | symbol of this invention.

Explanation of symbols

12 Modulator 13 Extended Barker 20 Receiver 22 Demodulator 24 Correlator

Claims (9)

A communication method,
Providing a spreading code A comprising elements 1 to n;
a process of obtaining an extension code B in which the i-th element is an average of the (i−1) -th element and the i-th element in the code A;
The process of obtaining the code C by inverting the position of the element of B by mirroring the code B;
A process of obtaining a weaving code D by summing the code B and the code C;
And a process of generating a signal by extending data using a weaving code.   2. The communication method according to claim 1, wherein the weaving spread code is formed from the code B at the first frequency and the code C at the second frequency.   The communication method according to claim 1, further comprising a step of transmitting a signal.   The communication method according to claim 1, further comprising a step of receiving a signal.   5. The communication method according to claim 4, further comprising a step of detecting a correlation peak in the signal and extracting digital data. A system for encoding digital data using interwoven spreading codes,
Means for providing a signal by adding a weaving spread code to the digital data;
A modulator operatively connected to the means and modulating a signal;
Providing a spreading code A comprising elements 1 to n, obtaining an extension code B in which the i-th element is the average of the (i-1) -th element and the i-th element in the code A; The process of obtaining the code C by inverting the position of the element of B by mirroring the code B, the process of obtaining the weaving code D by summing the code B and the code C, and extending the data using the weaving code And a woven spreading code is obtained by the process of generating a signal. The system of claim 6, wherein the spreading code is a Barker code. A system for extracting digital data from a signal to be encoded by a woven spreading code,
A demodulator that provides a demodulated signal;
A correlator operatively connected to the demodulator and configured to correlate the woven spreading code with the demodulated signal;
Providing a spreading code A comprising elements 1 to n, obtaining an extension code B in which the i-th element is the average of the (i-1) -th element and the i-th element in the code A; The process of obtaining the code C by inverting the position of the element of B by mirroring the code B, the process of obtaining the weaving code D by summing the code B and the code C, and extending the data using the weaving code And a weaving spread code is obtained by the process of generating a signal. The system of claim 8, wherein the spreading code is a Barker code.

Images