A near union bound decoding algorithm for BCH code of Beidou B1I navigation signal

A near union bound decoding algorithm for BCH code of Beidou B1I navigation signal was proposed. The error correlation capability and union bound of BCH (15, 11) was established, which is accordant to Beidou B1I open service signal ICD file. An improved decoding algorithm was designed to overcome the low coding gain and high decoding fail threshold of standard decoding algorithm in ICD file. The new soft-decision decoding algorithm was considered based on Chase algorithm. The complexity of syndromes computing was reduced based on Gray code ordering in test code set. The equivalence of maximum correlation and minimum Euclidean distance was proved. The complexity of optimized soft-decision decoding algorithm reduces 50% without coding gain lost. Simulation results indicate that the different of union bound and the proposed scheme less than 0.01 dB at BER=10^-5. More than 2.5 dB coding gain is provided by the new decoding algorithm and the decoding failure threshold decreases from 4.4 dB to 1.2 dB.