TW513874B - Coding and spreading technique for communications systems - Google Patents

Abstract

A method and apparatus are provided for generating a code having both coding gain and spreading factor. An information bit is first encoded using a rate r encoder. A repetition pattern is then applied to a first codeword generated by the rate r encoder to obtain a second codeword having a redundancy factor of L. A cover code is applied to the second codeword to spread the spectrum occupied by the second codeword. The combination of error correction codes, repetition codes and cover or spreading codes provides both coding gain and spreading factor and can result in a signal having the distance spectrum otherwise achievable by more complex codes.

Description

Qiu Fan B7 V. Description of the invention (1) Background of the invention In communication systems, especially in multiple access systems, it is often useful to extend the frequency spectrum of a transmission signal to improve the reliability or shared spectrum of a communication system in a noisy environment. . In a spread spectrum system, a pseudo-random (PN) sequence is generally used to extend the band width of a transmission signal through a band width that is much larger than the width of the basic band signal. Spectrum spreading generally results in a processing gain that is directly related to the spreading factor. Another well-known method of improving transmission reliability is the use of error correction codes such as convolution or linear block codes, which can provide a coding gain through an uncoded system. According to the system using the convolutional code, by increasing the code's limit length, the coding gain is typically maximized, but in terms of potential factors, calculations and memory are sacrificed to implement more complex systems. It is well known in the channel coding theory that the coding gain achieved through convolutional coding is related to the free distance of the code. By a code division multiple access (CDMA) system, a pseudo-random sequence can be used to randomly select a user's waveform using an orthogonal convolutional code based on a Hadamard code that can provide a low ratio code, as discussed in Viterbi, Andrew J. ”Spread Spectrum Spectrum Multiple Access Channels The Maximum Theoretical Performance of Very Low Ratio Roundabout Codes”, JSAC vol. 8, No. 4, May 1990. Joint PN sequences can also be used based on repeated roundabout codes or nested roundabout codes as Discussed in Lefrancois, S. and Haccoun, D. " Very low ratio of CDMA is similar to the optimal round-robin code ", with memoirs 1994 Canadian Electrical and Computer Engineering Conference, pp. 210-213. September 1994. Although this combination results in low spectral efficiency, there is no spreading characteristic of O: \ 70 \ 70130-910920.DOC, 4-4 · This paper size applies to China National Standard (CNS) A4 specification (210X 297 mm) ) 513874 V. Description of the invention (2) Defined by Massey, James L., "Information Theory on Spread Spectrum System", Multiple Code Access Communication, Boston, Dordrecht and London: Kluwer, 1995 〇 Hope joint coding To obtain the benefits of spread spectrum, this system has a low complexity and high performance. For the above reasons, there is a need for a method and device that can support encoding and spreading so that the minimum distance between two codewords is maximized and the complexity of the decoding structure is minimized. SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for generating a code having a coding gain and a spreading factor. According to a preferred example, an information bit can be encoded convolutionally using a binary round-robin code (BCC) at a ratio of one of the forms k / n. Reveal the output of BCC to a repeating encoder that can apply a repeating pattern with a redundancy factor of 2. The output of a repeating encoder can be extended by using a coverage code synchronized with the repeating encoder. As an example, a ratio of 1/2 to 4-state BCC with a free distance of 5 can be used. After the BCC is a repeating encoder with a redundancy factor of 12 and a repeating pattern equal to (4,8). According to this example, a code generated by the cover code (0001, 0010001〇) generates a code with the same Hamming distance of 32 °. According to another example, a repetition pattern (5,5,5) is combined. The repetitive encoder and the masking sequence (00001, 100,000, 10, 10) which are synchronized to the repetitive pattern to perform an encoding operation can use a ratio L = 1/3 16- State O: \ 70 \ 70130-910920.DOC, 4-5-This paper size applies to China National Standard (CNS) A4 specification (210 x 297 mm) A7 B7 V. Description of invention (3) BCC. Another example is used to show a circuit used in a communication system. This circuit includes a Γ ratio L encoder that generates the first codeword from one or more information bits as an output, and applies a _repetition pattern to the first-repeated encoder to generate a second codeword as an output. This wire also includes the first-covering code to the first-codeword that the spreader can synchronize with the repeating pattern. This includes a projection module, so that the received signal is associated with the second coverage code to despread the received signal spread-spectrum code modulation signal; and a decoder that decodes the output of the projection module. These other features and objects of the present invention will be more fully understood from the following detailed description of a preferred example which should be readable from the P diagram. Brief description of the drawings are the drawings incorporated in the specification and forming a part of it, which can illustrate the examples of the invention and, together with the illustrations, can be used to clarify the principles of the invention. According to the drawings: Figure 1 is a general digital communication system using the method of the present invention; Figure 2 is a ratio 1/2 4-state binary round-robin code; Figures 3A and 3B show one of a repeat encoder and spectrum spreading Coverage code; Figure 4 shows a spreading spectrum coding modulation method to resolve one of the spreading projections; and Figures 5A and 5B show parameter tables associated with the spreading code modulation system. Light Examples In detail, the preferred embodiments of the present invention will be described as described in the accompanying drawings. For understanding, specific terms may be used. However, the present invention is not intended to limit the specific term selected and O: \ 70 \ 70130-910920.DOC \ 4-6 · I paper size applies Chinese National Standard (CNS) A4 specifications (210 X 297 public love) 513874.

It should be understood that each-specific term includes all technical applications that can be used for the same purpose. F. Completion of the general reference drawings, especially with reference to Wang] "The installation of the present invention is shown in Fig. 0, which shows the digital communication system that enables the method of the present invention. According to a better example, the error code can be used in conjunction with repeated codes and masking or spreading sequences. This combination provides the code gain (code decoder) with the same coding gain and spreading factor and has a distance spectrum that can be achieved in other ways by more complex codes. According to a preferred example, a ratio L in the form of k / n binary round-robin code (BCC) i00 can encode k information bits (k = 1 in this example) into a codeword c of size n. Alternatively, the ratio £ _ linear block code can be used to perform the channel encoding process. Codeword C is presented at the input of repetition encoder 120, which can apply a repetition pattern to codeword C. According to a fake example, the constituent parts of the codeword C may be repeated differently. As an example, the repeating encoder 120 can apply a repeating pattern (5, 5, 5) to a codeword C composed of (C !, C2, CD. The following describes an example of the repeating encoder 120 according to FIG. 3A and the The table of Figures 5A and 5B shows a set of repetition patterns. The total coding rate generated by BCC and repetition coding is equal to 1 / L. The parameter L is referred to below as the redundancy factor and is the size of the code thus obtained after repetition. Measured values. Although the application of repeated codes to linear codes can reduce the overall coding rate and improve the minimum distance, repeated codes, by themselves, are not spreadable as shown in the above-mentioned document by James L. Massey. "Information Theory" was published in the Code Division Multiple Access Newsletter, Boston, Dordrecht, and

London: Kluwer, 1995 (incorporated and modified by this article) This spectrum is defined by O: \ 70 \ 70130-910920.DOO 4 This paper size applies the Chinese National Standard (CNS) A4 specification (210X297 mm)

Binding

0,513874 '(day correction supplement A7 B7 V. Description of the invention (5) According to a preferred example, the spread spectrum can be performed through the coverage code 140 with a narrow automatic correlation function. An example of the coverage code 140 can be explained according to FIG. 3B The output of the coverage code 140 is presented to the modulator 160 that can draw the signal S to the BPSK or PAM signal represented by the signal X. This modulator 160 can draw the binary 0 to + 1 and the binary 1 to -1 The QPSK format can also be used by drawing the signal S into a QPSK constellation. A signal X (not shown) can be sent through a communication channel and the signal can be corrupted by additional noise, such as Gaussian noise represented by the signal W. At the other end of the communication system, the demodulator 170 can demodulate the received signal Y and can estimate the signal S as represented by the signal R to a projection function 150 that can perform a despreading function. The projection function 150 enables the estimated signal R Despread the frequency to obtain a sufficient statistic of the signal R. This sufficient statistic is the signal T and can be added to the BCC decoder 110 as a software input. According to this example, the BCC decoder 110 can also use the codeword C to represent Sufficient statistics T to recover information bits Press the system using the hardware input decoder to make the signal T quantize before it is displayed to the hardware input decoding to recover the information bits. The combination of error control coding, repeating code and spread spectrum is referred to as the development Frequency code modulation. As an example, a BCC encoder can be used as the error control code. Figure 2 illustrates a ratio 1/2 4-state BCC encoder used in the present invention. Other BCC encoders such as ratio 1 / 3 16-state BCC encoder has multiple generators G equal to (25, 33, 37). The encoder in Figure 2 has multiple generators G equal to (1 + D2, 1 + D + D2) or, as indicated by the line, (5 , 7) and has a free distance of 5. The BCC encoder takes the information bit U as the input and the output is a codeword C (Ci, C2) combined with the convolutions of the past and present information bits. Use binary back to O: \ 70 \ 70130-910920.DOC \ 4-8-This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

Binding

6 Spin codes are familiar to skilled artisans. ^ ~ Examples, add a repeating pattern to codeword C. Figure 3A shows the application of the (4,8) repeating pattern to a codeword c having two components Ci and c2. According to this example, the bit Ci represented by "&" is not repeated four times, and the bit C2 represented by 0 is repeated 8 times. Other repeating patterns can also be used. Figure 5 contains the display Different repetition patterns of different BCC encoders. Figure 3B shows that according to the spread spectrum function using a masking sequence, which in this case is equal to the sequence (0001, 00100010) or, according to the bipolar, a redundancy factor L 12 of (ΗΗ + ^ ΙΗ + ΐ-ΐ + ΐ + ΐ + ΐ-ΐ + ΐ). Use one as shown by the output of the covering code 140, or use "(乂 〇 magic operation to add the masking sequence to the repeated encoding The output of the generator 120 can also use other masking sequences that can display the characteristics of the auto-correlation degree. The spreading factor as defined in the first seven is linked to the modulation format and the redundancy factor L. The list in Figure 5 shows different encoding ratios 1 / Different spreading factors of n. Fig. 4 illustrates the use of a correlator 400 that is a spread spectrum function of the spread spectrum coding modulation system. The projection function 15 of Fig. 1 can be performed, for example, using the correlator 400 shown in Fig. 4 Correlation function represented. As shown in Fig. 4, demodulation "pay number (RhRhRhR4)" And (1 ^, 乂 6, 7, 118, 119, 111〇, 11, 1 ^) groups, go to the correlator 400 to calculate the sufficient statistics of the demodulated signal (Ti, T2). According to this example, the correlator 400 If the input is related to the masking sequence shown in Figure 4, a sufficient statistic for each group of symbols can be calculated at its input. The full statistic (Ti, T2) to B (:(: decoder 110 to generate an estimate of the information bit U) Figure 5A shows-the list contains the different parameters of the spread spectrum coding and modulation system with a redundancy factor L equal to 12. This parameter includes parameters O: \ 70 \ 70130-910920.DOC \ 4 · Θ · 5 mil · year.) Corrected supplementary A7 B7 on the month π V. Description of the invention (7) Such as the output number η, BCC memory element number v and polynomial generator G. The parameter (li) is detailed by the repeated encoder The repeating pattern used at 120. The table also details the spreading factor P and Hamming distance d obtained after the spreading. Figure 5B shows that the spreading code modulates the same parameter with the same redundancy factor L equal to 15.

As explained in the present invention, the combination of linear codes and repetitive codes using spread spectrum technology can improve the distance spectrum of linear codes. As an example, the combination of a ratio of 1/3 16_state BCC and a factor of 5 spread spectrum can produce a total code with the ratio of 1/15 and a binary Hamming distance of 60. By applying the repeat pattern (5,5,5) and the same coverage code (00010,00010,00010), you can get a factor 5 spread spectrum. According to previous techniques, a binary Hamming distance of 60 can be obtained by using a composite code such as a ratio of 1/15 16-state BCC code.

The present invention can be practiced in many different ways, including software, hardware, or a combination thereof, which are well known to those skilled in the art. In particular, the present invention can be implemented by software embedded in a digital signal processor. The invention can also be practiced as part of an application specific integrated circuit (ASIC). Although the present invention has been described with reference to specific examples, it will be apparent to those skilled in the art that various changes and modifications can be obviously made within the scope of the present invention. The present invention is intended to be broadly protected within the scope and spirit of the attached patent application. O: \ 70 \ 70n0-910920.DOC \ 4-10 This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

Claims (1)

513874 范围 、 Scope of patent application 1 · A method for encoding data with an error control code in a communication system, including the following steps: (a) Encoding at least one: Bayesian bit encoding, using a ratio r encoder to generate a first Codewords; (b) applying a repeating pattern to the first codeword, wherein the repeating pattern can produce a second codeword with a redundancy factor L; and (c) using a first coverage of length l synchronized with the repeating pattern Code to spread the second codeword. 2 · The method according to item 1 of the patent application scope includes the following one-step steps: (d) Despread the received spread-spectrum coded modulation signal at the projection module, where the projection module can make the received signal and The second coverage code is correlated to generate a despread signal as output; and (e) decode the despread signal. 3. The method according to item 1 of the patent application range, wherein the ratio Γ encoder is a ratio 1/3 16-state binary round-robin code. 4. The method according to the scope of patent application, wherein the repeating pattern is (5,5,5). 5. The method according to item 1 of the scope of patent application, wherein the spreading step (c) can use a covered sequence (00001, 100001, 00001 ()). 6-A device for encoding data with error control codes, including ... (a) a ratio of one of the first codewords generated from at least one information bit "encoder; (b) applying a repeating pattern to one of the first codewords A repetitive encoder, wherein the repetitive encoder can generate a second codeword with a redundancy factor L as O: \ 70 \ 70130-910920.DOC \ 5 Λ Λ This paper size applies to China National Standard (CNS) Α4 specifications (2ι〇χ 4 7 mm) 513874 A BCD Patent application scope output; and (c) applying a spreading code of length L to one of the second codewords, where the cover code is synchronized with the repeating pattern. 7. The device according to item 6 of the scope of patent application, further comprising: (d) — a projection module that despreads the received spread-spectrum coded modulation signal, wherein the projection module correlates the received signal with the second coverage code; And (e) a decoder that decodes the output of the projection module. 8 · The device according to item 6 of the patent application range, in which the ratio ^ encoder is a ratio 1/3 16-state binary rotary encoder. 9. The device according to item 6 of the patent application, wherein the repeating encoder applies a repeating pattern equal to (5,5,5). 10. If the device in the scope of the patent application is item 6, the spreader can use a coverage code equal to (00010,00010,00010). O: \ 70 \ 70130-910920.DOC \ 5-12 · This paper size applies to China National Standard (CNS) A4 (210 χ 297 mm)