The Construction of Variable Length Codes With Good Synchronization Properties

Variable length codes offer advantages for data compression, but are susceptible to loss of synchronization if a bit error occurs. This can be mitigated by the use of variable length codes with specific mechanisms for resynchronization. Such mechanisms exist in the codes known as Huffman Equivalent (HE) codes and T-codes. These have been extensively studied in the literature. For optimal compression a length vector is obtained from the probabilities of the symbols of the alphabet used. However, HE-codes and T-codes do not exist for all length vectors. In this paper, a new class of variable length codes with good synchronization properties is developed. These are referred to as ordered termination (OT) codes. OT-codes do exist for all length vectors. Experimental results and some theoretical support suggest that OT-codes compare favorably with HE- and T-codes.