A new microcontroller-based technique for generating variable voltage/frequency sinusoidal PWM signals

This paper presents a flexible and robust microcontroller-based technique for generating the control signals of any sinusoidal pulse width modulation (SPWM) scheme for variable voltage/frequency output. The proposed technique exploits the fully static design of a high-speed microcontroller and generates the PWM control signals by varying the controller's clock, while keeping the number of the algorithm processing states constant. As the experimental results show, the technique can be used for transient-free frequency and/or voltage changes with very good resolution and a wide range of applications.     

Nanopositioning using the spiral of Archimedes: The probe-based storage case

Micro-Electro-Mechanical-Systems (MEMS)-based scanning probes appear as potential candidates for a wide variety of emerging nanoscale applications, including ultra-high-density data-storage and surface imaging. In this work, a spiral trajectory nanopositioning scheme is proposed as an alternative to the conventional raster positioning pattern. The resulting positioning signal has an extremely narrowband frequency content, which shifts very slowly over time. These properties enable enhanced tracking performance and offer potentially uninterrupted high-speed operation. The mathematical analysis of the spiral positioning signal as well as its properties are presented. Experimental results obtained from applying the new nanopositioning scheme on a MEMS-based scanning-probe data-storage setup for thermomechanical storage on polymer medium are illustrated.     

A New Data Allocation Method for Parallel Probe-Based Storage Devices

We present a new data allocation method for probe-based storage devices that use multiple, simultaneously accessed parallel data fields. Our method uses blocks of data of unequal length for allocating a sector in the various storage fields. The amount of data stored in each field depends on the sector's offset from the beginning of the allocation round and on the storage field used. Numerical results demonstrate the storage efficiency improvement that is achieved by the proposed method. We show that this method can be applied to atomic force microscopy-based probe storage devices.     

A new computationally efficient discrete bit-loading algorithm for DMT applications

This letter presents a new bit-loading algorithm for discrete multitone systems that converges faster to the same bit allocation as the optimal discrete bit-filling and bit-removal methods. The algorithm exploits the differences between the subchannel gain-to-noise ratios in order to determine an initial bit allocation and then performs a multiple-bits loading procedure for achieving the requested target rate. Numerical results using asymmetric digital subscriber test loops demonstrate the computational efficiency of the proposed algorithm.     

Design and implementation of a MAC controller for the IEEE802.11 wireless LAN

IEEE 802.11 wireless LANs have a tremendous market potential, as they support high data rates, work in the world-wide licence free 2.4 GHz ISM band and have high performance in terms of range and power consumption. Hence, the development of a communication processor that supports the IEEE 802.11 MAC functions has a significant potential, making very important the concept of having an ASIC ‘right from the first time’, in order to minimize development cost and to meet short time-to-market requirements. This paper presents the methodology of developing such a component with emphasis on the rapid prototyping approach. The chip architecture, which is based on an ARM processor core, is described in detail, focusing on the implementation of the protocol functions using custom hardware modules. Finally, the paper presents experimental results on the ASIC implementation.     

Multipath characterization of indoor power-line networks

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.     

The IEEE 802.11 Distributed Coordination Function in Small-Scale Ad-Hoc Wireless LANs

The IEEE 802.11 standards for wireless local area networks define how the stations of an ad-hoc wireless network coordinate in order to share the medium efficiently. This work investigates the performance of such a network by considering the two different access mechanisms proposed in these standards. The IEEE 802.11 access mechanisms are based on the carrier sense multiple access with collision avoidance (CSMA/CA) protocol using a binary slotted exponential backoff mechanism. The basic CSMA/CA mechanism uses an acknowledgment message at the end of each transmitted packet, whereas the request to send/clear to send (RTS/CTS) CSMA/CA mechanism also uses a RTS/CTS message exchange before transmitting a packet. In this work, we analyze these two access mechanisms in terms of throughput and delay. Extensive numerical results are presented to highlight the characteristics of each access mechanism and to define the dependence of each mechanism on the backoff procedure parameters.     

A new performance metric for M-APSK receivers

Synchronization is a critical function that determines the overall performance and complexity of the receiver of any communications system. The implementation and evaluation of effective synchronization algorithms still comprises a challenging task that requires accurate testing methods, which are based on measurements collected at various processing stages. M-ary Amplitude-Phase Shift Keying (M-APSK) constellations are used in modern communications systems, such as digital video broadcasting and interactive broadband satellite services, due to their bandwidth efficiency characteristics. This paper presents a new metric that can be associated with the signal quality at various synchronization mechanisms used in M-APSK receivers. Apart from the metric's mathematical derivation, the paper presents various experimental results based on single (QPSK, 8PSK), two (16APSK) and three (32APSK) ring M-APSK schemes employed in DVB-S2 systems.     

Implementation issues of the ATM cell delineation mechanism

The cell delineation mechanism (CDM) used in the asynchronous transfer mode (ATM) interfaces is based on the validation of the header error control (HEC) byte of the incoming cells, and is used for extracting the boundaries of the incoming cell stream. The CDM is analysed and an efficient implementation algorithm is derived, resulting in a hardware architecture, applicable at high data rates