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We study frame synchronization (FS) based on the transmission of known sequences (synchronization words) for M -PSK signals in the presence of additive white Gaussian noise and phase offset due to imperfect carrier phase estimation. In particular, we derive optimal and simple suboptimal metrics for noncoherent FS of M -PSK modulation with M ≥ 4. We show that a simple ℓ1-norm correction of the noncoherent correlation gives large improvements in terms of synchronization error probability. For example, more than 2 dB are gained with respect to usual correlation tests in terms of signal to noise ratio, assuming QPSK with a synchronization error probability 10 −3 . Finally, we illustrate that the proposed technique is better than correlation based metric also for M -QAM systems, as well as in the presence of small frequency offsets.

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Recent history demonstrates that threat has no borders, though risk does, due to national and regional differences in vulnerabilities and exposure landscapes. The difference between well and poorly managed threat is striking. Inequalities in preparing for threats as a function of their type are still apparent. Compared to more concerning electromagnetic interference threats, the impact of geomagnetic disturbance (GMD) on power grid operation is not well studied. The need for detailed research of GMD negative impacts is expected to broaden awareness. The amplitude of geomagnetically induced currents (GICs) is treated as a uniform measure of danger that can be processed by various stakeholders. Hence, methods for increasing the accuracy of GIC representation are presented in this paper. A low-entropy signal is defined and it is shown that the feature of low signal entropy can be used for increasing the accuracy of the measurement equipment. At the end, a full-system view of GMD impact on power grid operation is given.

The required block length in OFDM schemes (Orthogonal Frequency Division Multiplexing) can be very high when we have severely time-dispersive channels. This means that the channel variations from block to block or even within a given block can be substantial. In this paper we consider OFDM systems with fast-varying channels where the variations are due to phase/frequency errors between local oscillators at the transmitter and the receiver, as well as the effects associated to non-constant Doppler drifts. The overall phase error can be approximated by a Taylor polynomial with small degree. Suitable training sequences are multiplexed with data blocks and used for estimating the Taylor coefficients of the phase error. These are then used for predicting the evolution of the phase error for subsequent data blocks, which is compensated before detection. Our performance results show that our phase predicting method can lead to significant performance improvements when we have significant, nonlinear phase errors, reducing the required frequency of training blocks. KEY WORDSOFDM, phase variations, Doppler effects.