Abstract
In this paper, a multiple-symbol combined differential Viterbi decoding algorithm which is insensitive to frequency offset is proposed. According to the theories of multiple-symbol differential detection and maximum-likelihood detection, we combine the multiple-order differential information with the Viterbi algorithm. The phase shift caused by the frequency offset is estimated and compensated from the above information in the process of decoding. The simulation results show that the bit error rate (BER) of 2 bits combined differential Viterbi algorithm is below 10−3 when the normalized signal-to-noise ratio (NSNR) is 11 dB, and the decoding performances approach those of the coherent detection as the length of the combined differential symbols increases. The proposed method is simple and its performance remains stable under different frequency offsets.
Highlights
Automatic Identification System (AIS) [1], as a new type of navigation and security ensuring system on the sea, can realize ship-to-ship and ship-to-shore station communications well
The phase shift caused by the frequency offset is estimated and compensated from the multiple-order combined differential information in the process of decoding
The results show that this algorithm has good performance over AWGN channel and is insensitive to frequency offset and constant phase shift
Summary
Automatic Identification System (AIS) [1], as a new type of navigation and security ensuring system on the sea, can realize ship-to-ship and ship-to-shore station communications well. The phase shift caused by the frequency offset is estimated and compensated from the multiple-order combined differential information in the process of decoding. As for the algorithm, when the length of the combined differential symbols is N, the cost function of state S at time nTb is defined as
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