Quadrature amplitude modulation recording for digital VCRs

To improve recording efficiency and increase the channel bit rate of VCRs, the authors studied the application of quadrature amplitude modulation (QAM) to magnetic recording channels. Since QAM requires the channel to have a linear characteristic, bias recording was used to record the QAM signal. It was found with simulations that the QAM number `16´ (16QAM) was suitable for VCRs. To increase channel bit rate or decrease required SNR, the 16QAM was modified to 32QAM with coded modulation technique (Trellis coding). Coded 32QAM signals of 30 Mbps data rate were recorded and reproduced with a word error rate less than 10E-4 using an experimental VCR having head scanning speed of 5.8 m/s, and track width of 20 μm