1. A method for decoding tail-biting convolutional codes, comprising: initializing all beginning states of a trellis diagram; calculating forward Viterbi metrics for the states of the trellis diagram; tracing back from an ending state of the trellis diagram at a first time instance to a first sate where all surviving paths converge at a second time instance; calculating backward Viterbi metrics for a predetermined period of time from the first state at the second time instance to a second state at a third time instance; and tracing back from a designated state, which is equal to the second state, at the first time instance to determine a most likely path for the convolutional codes in the trellis diagram.