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Ultrahigh storage densities can be achieved by using a thermomechanical scanning-probe-based data-storage approach to write, read back, and erase data in very thin polymer films. High data rates are achieved by parallel operation of large twodimensional arrays of cantilevers that can be batch fabricated by silicon-surface micromachining techniques. The very high precision required to navigate the storage medium relative to the array of probes is achieved by microelectromechanical system (MEMS)based x and y actuators. The ultrahigh storage densities offered by probe-storage devices pose a significant challenge in terms of both control design for nanoscale positioning and read-channel design for reliable signal detection. Moreover, the high parallelism necessitates new dataflow architectures to ensure high performance and reliability of the system. In this paper, we present a small-scale prototype system of a storage device that we built based on scanning-probe technology. Experimental results of multiple sectors, recorded using multiple levers at 840 Gb/in 2 and read back without errors, demonstrate the functionality of the prototype system. This is the first time a scanning-probe recording technology has reached this level of technical maturity, demonstrating the joint operation of all building blocks of a storage device.

Absfracf-Ultrahigh storage densities of up to 1 Thitlin? or more can be achieved by local-probe techniques to write, read back, and erase data in very thin polymer films. The thermomechanical scanning-probe-based data-storage concept called Millipede combines ultrahigh density, small form factor, and high data rate. After illustrating the principles of operation of the Millipede, we introduce system aspects related to the read-back process, multiplexing, and position-error-signal generation for tracking.

Multicarrier modulation is a powerful transmission technique that provides improved performance in various communication fields. A fundamental topic of multicarrier communication systems is the bit and power loading, which is addressed in this article as a constrained multivariable nonlinear optimization problem. In particular, we present the main classes of loading problems, namely, rate maximization and margin maximization, and we discuss their optimal solutions for the single-user case. Initially, the classical water-filling solution subject to a total power constraint is presented using the Lagrange multipliers optimization approach. Next, the peak-power constraint is included and the concept of cup-limited waterfilling is introduced. The loading problem is also addressed subject to the integer-bit restriction and the optimal discrete solution is examined using combinatorial optimization methods. Furthermore, we investigate the duality conditions of the rate maximization and margin maximization problems and we highlight various ideas for low-complexity loading algorithms. This article surveys and reviews existing results on resource allocation in constrained multicarrier systems and presents new trends in this area.

Abstract-The time-and frequency-varying behavior of an indoor power-line network is the result of variable impedance loads connected to its termination points. In fact, any signal transmitted through such a communications network is subject to time-varying multipath fading. In this paper, an analytical calculation method is presented, which can be used to determine the multipath components of any point-to-point channel in the indoor power-line environment. The method calculates all transmission characteristics of the network and, therefore, it can be exploited in the process of designing proper transmission algorithms for optimizing system performance. The proposed method is applied to an example network to demonstrate its usefulness in explaining the network's time-dependent behavior and in estimating channel parameters, such as subchannel bandwidth, multipath delay spread, fading conditions, etc.