Arithmetic coding for joint source-channel coding

This paper presents a joint source-channel coding technique involving arithmetic coding. The work is based on an existing maximum a posteriori (MAP) estimation approach in which a forbidden symbol is introduced into the arithmetic coder to improve error-correction performance. Three improvements to the system are presented: the placement of the forbidden symbol is modified to decrease the delay from the introduction of an error to the detection of the error; the arithmetic decoder is modified for quicker detection by the introduction of a look-ahead technique; and the calculation of the MAP metric is modified for faster error detection. Experimental results show an improvement of up to 0.4 dB for soft decoding and 0.6 dB for hard decoding.