Realization method of low complexity performance limit approximate Turbo decoder

Abstract

The invention discloses a realization method of a low complexity performance limit approximate Turbo decoder, mainly solves the problems that a traditional Turbo decoder based on a searching table is high in complexity and a decoder based on a Max-Log-MAP algorithm is poor in performance. The method comprises following steps: demultiplexing input soft information streams; storing in an RAM; selecting data from the RAM by an SISO (soft input soft output) decoder according to decoder station indication signals; iteratively calculating backward measurement, forward measurement and a log-likelihood ratio, wherein a Log-MAP algorithm based on linear approximation is adopted, the same SISO decoder is iteratively multiplexed in front and back stages; reversely accessing an interleaving address unit; and interleaving and de-interleaving external information. According to the method of the invention, through carrying out linear approximation to the Log-MAP algorithm, compared with a traditional approximate scheme, a better error correction performance is obtained; compared with a scheme based on the searching table, the complexity is greatly reduced; and the method is applicable to an LTE system.

Description

technical field [0001] The invention belongs to the field of wireless communication, relates to an error control encoding technology, in particular to an implementation method of a low-complexity turbo decoder close to the performance limit, which can be used in LTE and satellite communication systems. Background technique [0002] Error control coding technology is one of the key technologies to ensure reliable transmission of information in wireless communication systems. In 1948, Shannon proposed the famous channel coding theorem, which laid the theoretical foundation for error-correcting code technology. Since then, scholars and technicians have been making unremitting efforts to find coding schemes that approach channel capacity. [0003] In 1993, C.Berrou et al. proposed parallel concatenated convolutional codes, namely Turbo codes, which opened up a new path for channel coding techniques approaching the Shannon limit. A large number of computer simulations show that...

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Problems solved by technology

[0004] The optimal decoding algorithm of Turbo code is an algorithm based on maximum a posteriori probability, referred to as MAP algorithm. However, there are a large number of multiplication and nonlinear operations in the algorithm, making it almost impossible to implement it directly by hardware.

The Log-MAP algorithm is the mapping of the MAP algorithm in the logarithmic domain. It converts the multiplication operation in the MAP algorithm into the addition operation in the logarithmic domain with almost no performance loss. Although the complexity is reduced, the hardware implementation of the logarithmic operation is still a challenge. problem

The Max-Log-MAP algorithm is an approximation to the Log-MAP algorithm. Because of its simple implementation, it has been widely used in the engineering field. However, the simulation shows that the Max-Log-MAP algorithm has a bit error rate of 10 -6 When , the coding gain is 0.4dB lower than that of the Log-MAP algorithm

[0005] The traditional turbo decoder implementation scheme based on MAP algorithm usually adopts the implementation method based on the lookup table. However, the scale of the lookup table increases exponentially with the increase of the internal information bit width of the decoder, which will increase the chip area and affect the processing speed

However, although the implementation scheme based on the Max-Log-MAP algorithm has low complexity, it loses performance.

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