Proposal of multiphase partial response method for optical disc readout systems

Optical disc systems usually have several detection channels in order to obtain information and objective lens control signals. As well as used in the area of wireless communication known as Multiple-Input Multiple-Output (MIMO) or the diversity technique, these multiple-channel signals should bring a higher quality of the information for the optical disc systems. Partial Response (PR) signal processing is an effective method to increase the recording density for the current optical disc systems. In this report, dual-input channels, sum and tangential push-pull detections are considered. Different PR classes can be adapted to the dual-input channels. Three kinds of signal modulation methods, the 1-7 RLL, the Eight-Fourteen Modulation (EFM) and un-modulated signals are examined. The qualities of the dual-channel signals are expressed by drawing the constellation maps. Compare to the conventional single-channel detection case, dual- channel one tend to indicate smaller signal level deviations normalized by the detection window. The normalized signal level deviation in multiple-channel detection is defined as the deviation in the channel dimension space normalized by the minimum distance between the average levels of the states. In many cases, levels of states are separated in dual- channel detection case though those are degenerated in single-channel detection case. The signal levels of the additional channel increase the number of states. It should enhance the performance of the later signal processing part such as maximum likelihood (ML) method.