**MATLAB class for EXIT charts computation**

Object-oriented programming capabilities of the MATLAB language have been introduced in R2008a. A possible application of these capabilities is represented by the implementation of a class containing methods allowing the computation of EXtrinsic Information Transfer (EXIT) charts [1].

EXIT charts are useful for characterizing the convergence properties and the performance of turbo receivers. Turbo receivers are generally constructed from two or more Soft Input Soft Output (SISO) modules. By simulating a single SISO module, the Transfer Characteristic (TC) of the SISO module can be obtained using the EXIT class. The TCs of two SISO modules represented on the same figure by switching the axes give the EXIT chart (Fig. 1).

The MATLAB class for EXIT charts computation is implemented into EXIT.m (see below). Two usage examples for computing the TC of the SISO module are given in TC_MAP.m and TC_SOVA.m. These examples use Maximum A Posteriori (MAP) algorithm and Soft Output Viterbi Algorithm (SOVA) implemented as SISO modules in C++ (see SISO modules for turbo reception).

[1] S. ten Brink, ''Convergence behavior of iteratively decoded parallel concatenated codes,`` IEEE Transactions on Communications, vol. 49, pp. 1727-1737, Oct. 2001

EXIT charts are useful for characterizing the convergence properties and the performance of turbo receivers. Turbo receivers are generally constructed from two or more Soft Input Soft Output (SISO) modules. By simulating a single SISO module, the Transfer Characteristic (TC) of the SISO module can be obtained using the EXIT class. The TCs of two SISO modules represented on the same figure by switching the axes give the EXIT chart (Fig. 1).

Fig. 1 EXIT chart for SISO module implementing the decoder for Recursive and Systematic Convolutional Codes (with generating polynomials [7 5] in octal form, first polynomial gives the recursion)

The MATLAB class for EXIT charts computation is implemented into EXIT.m (see below). Two usage examples for computing the TC of the SISO module are given in TC_MAP.m and TC_SOVA.m. These examples use Maximum A Posteriori (MAP) algorithm and Soft Output Viterbi Algorithm (SOVA) implemented as SISO modules in C++ (see SISO modules for turbo reception).

[1] S. ten Brink, ''Convergence behavior of iteratively decoded parallel concatenated codes,`` IEEE Transactions on Communications, vol. 49, pp. 1727-1737, Oct. 2001