Box-minus operation and application in sum-product algorithm

A new formula for box-minus operation, which separates the box-minus operation into sign and reliability operations, was derived. Its application in the sum-product algorithm (SPA) was also investigated. Both box-plus operation and box-minus operation were divided into sign operation and reliability operation. The results show that on using the box-minus operation, SPA can be implemented with less decoding latency and complexity.