A Study on AM-FM Combined Detection for Magnetic Recording Using STO Reading

A 3-D magnetic recording using microwave-assisted magnetic recording (MAMR) and a spin-torque oscillator (STO) as a reading sensor has been proposed as a candidate for the prospective recording technologies. In the STO reading system, the temporal magnetization dynamics of the STO vary not only in amplitude but also in frequency, depending on the recorded pattern. Therefore, we have constructed the STO signal model which considers both amplitude and frequency fluctuations to develop a combined signal processing using the detection of amplitude and frequency fluctuations. Furthermore, we have applied the STO signal model to the low-density parity-check (LDPC) coding and iterative decoding system with the detectors for amplitude modulation (AM) and frequency modulation (FM) and have proposed the AM–FM combined detection. Then, we have evaluated the bit error rate (BER) performances by computer simulation. The results show that the system with AM–FM combined detection improves the performance of the LDPC coding and iterative decoding system, which achieves “no errors” at the carrier-to-noise ratio for system noise (CNR $_{S}) = 15.9$ dB, whereas the AM and FM detections require CNR $_{S} = 21.2$ and 17.2 dB.