Method and apparatus for decoding M-PSK turbo code using new approximation technique

An apparatus for decoding a received symbol representing data bits including message bits and parity-check bits, said apparatus comprising:

• means for mapping said symbol onto a received signal point in a signal space, said signal point having an in-phase component (I) and a quadrature phase component (Q) in said signal space;
• means for computing reliability information for each data bit, said reliability information associated with a distance di={square root over ((I−Ii)2+(Q−Qi)2)} between said received signal point (I, Q) and a reference constellation point (Ii, Qi) in said signal space, where i=0, 1, . . . , M−1 (for M an integer), by replacing calculation of (I−Ii)2+(Q−Qi)2 with calculation of −2(Ii×I+Qi×Q);
• means for decoding said received symbol using said reliability information and a priori information to produce estimated message bits, said a priori information having a predetermined value in a first decoding;
• means for calculating difference between received message bits and said estimated message bits to produce extrinsic information of estimated bits;
• and
• mans for repeating at least once said mapping, computing, decoding and calculating, using said extrinsic information produced in a preceding calculating as said a priori information.

A decoding module for performing an iteration of decoding a received symbol, said received symbol representing data bits including message bits and parity-check bits, said decoding module comprising:

• a first input for inputting said data bits of said received symbol;
• a second input for inputting extrinsic information of estimated message bits;
• an output for outputting extrinsic information of estimated message bits;
• a reliability information determiner for mapping said data bits onto a received signal point in a signal space, said signal point having an in-phase component (I) and a quadrature phase component (Q) in said signal space, and for computing reliability information for each data bit, said reliability information associated with a distance di={square root over ((I−Ii)2+(Q−Qi)2)} between said received signal point (I, Q) and a reference constellation point (Ii, Qi) in said signal space, where i=0, 1, . . . , M−1 (for M an integer), by replacing calculation of (I−Ii)2+(Q−Qi)2 with calculation of −2(Ii×I+Qi×Q);
• and
• a decoder for decoding said received symbol using said reliability information and a priori information to produce estimated message bits, said a priori information being said extrinsic information of estimated message bits input from said second input, and for calculating difference between received message bits and said estimated message bits to produce extrinsic information of said estimated message bits.

A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform a method for decoding a received symbol representing data bits including message bits and parity-check bits, said method including:

• mapping said symbol onto a received signal point in a signal space, said signal point having an in-phase component (I) and a quadrature phase component (Q) in said signal space;
• computing reliability information for each data bit, said reliability information associated with a distance di={square root over ((I−Ii)2+(Q−Qi)2)} between said received signal point (I, Q) and a reference constellation point (Ii, Qi) in said signal space, where i=0, 1, . . . , M−1 (for M an integer), by replacing calculation of (I−Ii)2+(Q−Qi)2 with calculation of −2(Ii×I+Qi×Q);
• decoding said received symbol using said reliability information and a priori information to produce estimated message bits, said a priori information having a predetermined value in a first decoding;
• calculating difference between received message bits and said estimated message bits to produce extrinsic information of estimated message bits;
• and
• repeating at least once said mapping, computing, decoding and calculating, using said extrinsic information produced in a preceding calculating as said a priori information.