Hi, In general, the reciever upto the demodulator uses uniform quantization and step size in the powers of 2 while the Low Density Parity Check (LDPC) decoder uses uniform quantiztion and arbitrary step size. LDPC decoder using min-sum algorithm needs different quantization schemes based on the offset used. Offset varies based on code parameters. Say the soft output of demodulator is 16 bits. The output is in the format :2's complement,uniformly quantized and step size 2^-15. Let it be called y_q15. Say now I want to quantize the output of the demodulator before feeding it to a decoder for channel code. The number of bits I needed for the decoder input is 5 bits and step size 'beta'. The value of beta is optimized for each code the decoder supports. In matlab, I can achieve the above with the following. stepSize_inverse = 1/beta; (%pre computed) y_requantized = round(y_q15*stepSize_inverse); % has to be computed for every value However doing the above multiplication in hardware implementation is costly. I can implement a Look up table approach to avoid multiplication- but this is also cumbersome if I needed to parallel processing on a vector. Could you please let me know if there is any efficient way to tackle the re-quantization problem? Other alternative approach I came upon is filtering approach which is too expensive for what I need to solve. "On the re-quantization of data to implement high-order narrow-band filters using reconfigurable logic " Dick, C.H.; Harris, F.; Signals, Systems and Computers, 1995. 1995 Conference Record of the Twenty-Ninth Asilomar Conference on Volume 2, 30 Oct.-2 Nov. 1995 Page(s):1347 - 1351 vol.2 http://ieeexplore.ieee.org/iel3/3850/11241/00540918.pdf?tp=&arnumber=540918&isnumber=11241 Thanks for your time. Regards Kiran ps: This is the reference about the min-sum and the quantization issues. "Near optimum universal belief propagation based decoding of low-density parity check codes" Jinghu Chen; Fossorier, M.P.C.; Communications, IEEE Transactions on Volume 50, Issue 3, March 2002 Page(s):406 - 414 http://ieeexplore.ieee.org/iel5/26/21364/00990903.pdf?tp=&arnumber=990903&isnumber=21364

# re-quantization

Started by ●August 2, 2006