Experimental evaluation of voiceband fractionally-spaced blind equalizer based on the constant modulus algorithm

We describe the results of simulation experiments that evaluated several alternative blind equalizers for use in a voiceband QAM constellation classifier. The test signals included simulated signals as well as recordings of real fax and V.32bis modem test signals made at a monitoring point in the public telephone network. V.32bis has five operating modes that use 4, 16, 32, 64, and 125-QAM symbol constellations to provide bit rates of 4.8, 7.2, 9.6, 12.0, and 14.4 kbits/sec, respectively. Several different timing recovery and fractionally-spaced blind equalizer configurations were considered in conjunction with Godard's (1978) constant modulus algorithm (CMA).