The effect of Unbalanced-Magnetic-Pull (UMP) on vibration and run-outs has become stringent in the design for high performance HDD spindle motors. In this paper, reducing the UMP and also minimizing its variability for an 8-pole 9-slot spindle motor to achieve robustness in the performance is described and illustrated using novel robust design methods. A screening experiment identifies the key design parameters. Using Design of experiment (DOE) and Analysis of Variance (ANOVA), the parameter design reduces the amplitude of UMP and minimizes its variability by product parameter optimization. The tolerance design improves the quality by tightening tolerances on product or process parameters to reduce the performance variation. The optimal design process includes considerations of manufacturing and process noises, such as manufacturing tolerances for the slot opening and variation of the rotor magnet magnetization distribution due to the magnetization fixture and process. The optimal design procedure is briefly introduced and the results are presented.

In this letter, we consider an Orthogonal Frequency Division Multiplexing (OFDM) system without cyclic prefix (CP), i.e. with full spectral efficiency and present an optimum frequency-domain filtering scheme for mitigating inter-symbol interference (ISI) and inter-carrier interference (ICI). Simulation results show the signal to interference and noise ratio (SINR) improvement.

In OFDM systems, employing a cyclic prefix (CP) as the guard interval is a simple way to combat the inter-symbol interference (ISI) and the inter-carrier interference (ICI), however it reduces the transmission efficiency of the system, especially for some channels with a very long delay spread. In this paper, we consider the OFDM system with insufficient CP, much more efficient than conventional OFDM systems. First, we present the system mathematical model and give the ISI and ICI analysis. Then the signal-to-interference power ratio (SIR) performance is presented. To reduce the ISI and ICI due to the insufficient CP, we develop a minimum-mean-square-error decision feedback equalizer (MMSE_DFE). Based on the MMSE criterion, the optimum feedforward and feedback filter coefficients are derived. For time-varying channel, to avoid brute force matrix inversion in conventional schemes, we propose an adaptive LMS based solution to update the filtering coefficients by tracing the channel variation. Since the high complexity of MMSE_DFE, a reduced complexity scheme, ordered successive partial interference cancellation DFE (OSPIC_DFE), is developed. From the performance comparison between the MMSE_DFE and the OSPIC_DFE, we see that the latter is very near to the former. Finally the simulation shows these proposed methods are highly effective in combating ISI and ICI with low complexity.