JP2593071B2 - Biphase code transmission method with error correction function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a code transmission method for correcting a code error on a transmission line caused by thermal noise or the like in a digital transmission system using an optical fiber.

(Prior art and its problems) Conventionally, various codes have been proposed as error correction codes, but Hamming codes whose codes and decoding configurations are relatively simple (Hideki Imai: "Information Theory" Shokodo Shuppan, (Refer to P.138)
Is well known. Generally, a Hamming code is configured by defining the following matrix and defining check bits.

However, {P _i , P _i2 ,..., P _ik } (i = 1 to m) have different patterns for all i and are not all zeros. Further, m (= nk) is the number of check bits, and n (= 2 ^m −
1) represents the code length, and k (= 2 ^m -1 -m) represents the number of information bits.

Check bits c ₁ , ……, _cm And Hamming code Is Is configured as On the other hand, decoding is Against By calculating the syndrome, the presence or absence of a bit error in the transmission path is detected, and if there is an error, the error bit is corrected using the result of the syndrome. This includes, for example, Peterson's decoding method. Specifically, an example of a configuration of a conventional error correction code will be described by taking a (7,4) Hamming code having a code length of 7 as an example. Information bits (x ₁ ,
x ₂ , x ₃ , x ₄ ), check bits satisfying the following relational expression:
Determine c ₁ , c ₂ , and c ₃ .

That is, the parity matrix Table 1 shows the configuration of the (7,4) Hamming code.

Codeword Received syndrome without error Becomes zero, The following relationship should hold:

So the received word For the following Ask for.

this According to the pattern (3), as shown in Table 2, the 3-bit syndrome value and the position of the error bit correspond one-to-one, so that a single error bit can be obtained and can be corrected.

In order to apply this code to normal data transmission, a synchronization problem first arises. Conventionally, apart from transcoding,
Had made up the frame. Therefore, the circuit configuration is complicated and large-scale. Also, a long same-code continuous pattern such as all “0” or all “1” may occur. Such a pattern causes loss of timing information in the repeater, and also causes an increase in intersymbol interference due to low-frequency step-up distortion, thereby deteriorating transmission quality. Therefore, in addition to the code conversion, use of scrambling or the like is indispensable in order to balance marks.

(Object of the Invention) It is an object of the present invention to provide a bi-phase code transmission method having an error correction function that solves the above-mentioned disadvantages while maintaining the error correction capability of a Hamming code.

(Features of the Invention) The present invention provides an error check bit and a complementary code bit.
The most significant feature is that an error correction code controlled so as to ensure the mark ratio balance in the block and also suppress the continuation of the same code is provided.

According to the present code transmission method, the frame structure required for synchronization is not conventionally required, the worst case of the same code continuous length can be specified, and the design margin for the timing system can be increased.

Conventionally, the error correction code has a configuration in which the balance of the mark is neglected. However, the present invention has made it possible to completely reduce the mark ratio to 1/2 in a block.

(Example) Table 3 shows a code configuration example in the present invention. Information bits, and 3 bits _{x 1, x 2, x 3} . The complement sign information bits x ₃ regarded as x ₄ and the pseudo information bits. In this case, the error check bits c _i (i = 1 to 4) are obtained by the following relational expressions.

x _i (i = 1 to 3): information bit x ₄ = ₃ : complementary code bit Here, since x ₄ = _3, c ₂ = x ₂ + 1 = ₂ , c ₃ = ₁ , c ₄
= ₁ , the error check bits (c ₄ , c ₂ ) are complementary to the information bit sequence (x ₁ , x ₂ ), respectively.
For information bits x _3, x ₄ is the complementary code relationship, also complement code relationship holds between the error check bits c ₁ and c _3. Therefore, as shown in Table 3, by sequentially arranging sequences that have a complementary code relationship with each other, the same sequence as a conventionally used biphase code can be generated. Therefore, the worst-case homocode continuous length is 2 bits. That is,
Channel coding method according to the invention with respect to the 3-bit information code _{(x 1, x 2, x} 3), x 4 = 3, c 1 = x 1 x 2 x 3, c 2 = x 2
A check bit is generated by x ₃ x ₄ , c ₃ = x ₁ x ₂ x ₄ , c ₄ = x ₁ x ₃ x _{4 and the} check bit is written as (x ₁ c ₄ x ₂ c ₂ x ₃ x ₄ c ₁ c ₃ ) In order of 8 bits.

On the receiving side, first, it is necessary to secure block synchronization for decoding. For this purpose, a method is conceivable in which a phase relationship established between information bits and other bits is used. For example, from the formula, However, it always holds at the correct synchronization position. Synchronization can be ensured by finding a phase in which these relationships are satisfied at the same time. Synchronized received words Against the syndrome Is calculated, and the result is compared with an error pattern as shown in Table 4 to enable error correction. However, the correspondence between the received word and the transmitted word is as follows.

_{y 1 ⇔x 1, y 2 ⇔x} 2, y 3 ⇔x 3, y 4 ⇔x 4 y 5 ⇔c 1, y 6 ⇔c 2, y 7 ⇔c 3, y 8 ⇔c 4 i.e., the code Although the output is performed in the order shown in Table 3 in the chemical method, the relationship shown in Table 4 is based on the assumption that (x ₁ x ₂ x ₃ x ₄ c ₁ c ₂ c ₃ c ₄ ) has been received. Therefore, in practice, computing the syndrome after conversion to _{(x 1 c 4 x 2 c} 2 x 3 x 4 c 1 c 3) once the _{(x 1 x 2 x 3 x} 4 c 1 c 2 c 3 c 4) Need to be done.

In the above description, the complement sign information bits x _3, only select as a fourth code but also as a target information bits x ₁ ~x ₃ throat, a change in the bit string complement code relationship holds, the , The relationship basically holds.

FIG. 1 shows the error correction capability of the code shown in the present invention. It shows the bit error rate at the time of decoding when error correction is performed on the bit error rate on the transmission path and when error correction is not performed. By performing error correction at a bit error rate of 10 ^-5 , which is an alarm occurrence condition on the transmission line, an improvement in the code error rate of four or more digits can be obtained.

Further, as an error detection method, since “1” and “0” in one block have the same number, x ₁ x ₂ x ₃ x ₄ c ₁ c ₂ c ₃ c ₄
Is calculated, and an odd error in one block can be detected. In addition, a method of detecting an error using a complementary code relationship between bits can be considered.

On the receiving side, a complementary code relationship established between information bits in one block and other bits, for example, x ₄ =
By examining the relationships of ₁ , c ₁ = ₂ , c ₃ = ₂ , c ₄ = ₃ , errors in one block can be detected.

(Effects of the Invention) As described above, according to the present invention, with a relatively simple configuration, the balance of the mark ratio is ensured, block synchronization utilizing the characteristics of the code is performed, and error detection is performed. A binary transmission system having a function of performing error correction can be realized. Therefore, in the digital transmission system, the signal-to-noise ratio is equivalently improved, and the relay gain is increased. It also leads to ensuring the reliability of the entire system.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the error correction capability of the transmission line code shown in the present invention.

Claims (3)

(57) [Claims] 1. A binary signal "1", in a digital transmission system in which a "0", the information sequence 1 sequence slow 3 sequence (x _1, x
₂ , x ₃ ), the complementary code of any one of these sequences is taken as the next sequence x _4, and x ₁ x ₂ x ₃ , x ₂ x
_{An operation of 3} x ₄ , x ₁ x ₂ x ₄ , x ₁ x ₃ x ₄ (exclusive OR) is performed to create four series (c ₁ , c ₂ , c ₃ , c ₄ ), The information sequence (x ₁ , x ₂ , x ₃ ), the complementary code sequence (x ₄ ),
A bi-phase code transmission method having an error correction function, further comprising multiplexing four sequences (c ₁ , c ₂ , c ₃ , c ₄ ) into one sequence and transmitting the multiplexed sequence. 2. One information sequence is divided into three low-speed sequences (x ₁ , x ₂ , x ₃ ).
After the division into the following series,
and x _4, with respect to their _{sequence, x 1 x 2 x 3,} x 2 x 3 x 4,
An operation of x ₁ x ₂ x ₄ , x ₁ x ₃ x ₄ (exclusive OR) is performed to create four sequences (c ₁ , c ₂ , c ₃ , c ₄ ), and the above information sequence (c ₁ , c ₂ , c ₃ , c ₄ ) x ₁ , x ₂ , x ₃ ), a complementary code sequence (x ₄ ), and 4
The sequences (c ₁ , c ₂ , c ₃ , c ₄ ) are multiplexed into one sequence and transmitted. On the receiving side, one received code sequence is distributed into eight sequences, block synchronization is established, and then information bits ( x ₁ , x ₂ , x ₃ ), complementary code bits (x ₄ ), and error check bits (c ₁ , c ₂ , c ₃ , c ₄ )
Error check formula s ₁ = x ₁ x ₂ x ₃ c ₁ , s ₂ = x
₂ x ₃ x ₄ c ₂ , s ₃ = x ₁ x ₂ x ₄ c ₃ , s ₄ = x ₁ x ₃ x ₄ c
_4. A bi-phase code transmission method having an error correction function, which calculates ₄ and corrects a bit error according to those patterns. 3. A correlation established between an information bit and a check bit, for example, c ₁ c ₂ = x ₁ as the block synchronization method.
_{x 4, c 3 c 4 =} x 2 x 3, c 1 c 3 = x 3 x 4 phase error correction range second claim of claims, characterized in that so as to ensure synchronization with the hold of such A bi-phase code transmission method having a function.