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We consider a wireless ad hoc network where each node employs a single-beam directional antenna and is provisioned with limited energy. We are interested in an online routing algorithm for successive multicast communication requests with the aim of maximizing the network lifetime. The beam-forming property, which is associated with single-beam directional antennas, introduces some unique problems that do not exist for omnidirectional antennas and, therefore, significantly increases the design space for routing algorithms. The contributions of this paper are twofold. First, we provide some important theoretical understanding on various multicast problems and deduce that even an offline version of this problem is NP-hard. Second, we develop a highly competitive online routing algorithm that takes the network lifetime consideration directly into iterative calculations and show that an algorithm that is designed under this methodology provides consistently better performance than the current state-of-the-art algorithm that only considers remaining energy. The theoretical results and routing algorithm in this paper offer some important insights on algorithm design for energy-constrained wireless ad hoc networks with directional antennas. [ABSTRACT FROM AUTHOR]

In spectrum sensing and wireless communications analysis, signals of interest typically occupy only a few among several possible bands and do so for short-time bursts within a given observation interval. The frequency and time location of these signals may be known only approximately a priori (for instance, the nominal frequency of a wireless channel) or, in general, not accurately enough to set up more detailed measurements. In this paper, a compressive sensing (CS) algorithm is employed to provide accurate preliminary information and suitably preprocessed data for a vector signal analysis algorithm. The CS paradigm exploits sparsity, a feature common to several signals of interest, to allow the design of efficient data acquisition schemes. It is shown that the application of the sensing method called modulated wideband converter allows one to successfully extract specific signal bursts from a record of samples covering a longer time interval and a broader bandwidth. The accuracy of the extraction process is analyzed and the results referring to vector analysis are presented. This provides blind spectrum sensing and signal extraction capabilities that can effectively simplify the time-consuming process of setting up a spectrum analyzer for vector signal analysis. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a new two-way time synchronization (TS) method for orthogonal frequency division multiplexing (OFDM)-based wireless systems. It relies on the time-reversal (TR) technique to remove the effect of the channel phase after the signal round-trip. Thus, the method is named TR-TS. TR technique yields a linear phase rotation across subcarriers, regardless whether the channel is minimum, maximum, or mixed phase. This phase is proportional to the difference of the OFDM symbol-timing synchronization errors at the two receivers. Thus, the clock-offset between the radios is determined using the local reception times and the estimated linear phase resulting from the TR technique. A reliable low-complexity algorithm called fast Fourier transform-weighted least-squares is proposed to estimate the linear phase slope, and its mean-square error is compared with the Cramér-Rao Lower Bound (CRLB). The results show that the proposed algorithm attains the CRLB at low SNR, even when a single OFDM symbol is used. The OFDM packets are time-stamped at the medium access control layer, which allows eliminating errors caused by different and varying delays in the internal lower level processing of the data. Hence, an accurate estimate of the clock-offset is obtained. The impact of various nonidealities on the proposed algorithm is also studied. In addition, we propose a ranging method that employs the novel TS method and a first-path delay estimation technique. The performance of the proposed methods is studied in simulations, as well as using real-world measured channels. The results show that the proposed methods can be successfully applied in low to moderate mobility scenarios such as indoors despite harsh multipath, since they rely on channel reciprocity. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the accuracy of indoor localization measurement based on a wireless sensor network. The position estimation procedure is based on the received-signal-strength measurements collected in a real indoor environment. Two different classes of low-computational-effort algorithms based on the centroid concept are considered, i.e., the weighted centroid localization method and the relative-span exponential weighted localization method. In particular, different sources of measurement uncertainty are analyzed by means of theoretical simulations and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, we address the problem of nonlinear sensor dynamic compensation that will be performed on board wireless sensor network nodes. To this aim, we design suitable reduced-complexity learning-from-example algorithms and implement them on resource-constrained devices, namely, 8-bit microcontrollers. The proposed approach is validated with simulations on different examples of nonlinear sensor models. [ABSTRACT FROM AUTHOR]

The combined use of multitaper estimation and wavelet thresholding has proved to be a very powerful digital-signal-processing algorithm in achieving the true power spectrum of signals that are peculiar to digital wireless communication systems and in ultimately carrying out accurate and repeatable power measurements. Nevertheless, the induced computational burden is too heavy. This paper mainly shows that GRID, which is currently one of the key technologies in deploying global-scale computing infrastructures, can make the aforementioned algorithm enforceable in a real-time context. A GRID computing-based approach for power measurement in digital wireless communication systems is proposed, which allows high levels of accuracy and repeatability in a significantly reduced measurement time. After a concise outline of the measurement algorithm, all of the adopted hardware and software strategies are described in detail. Major results concerning performance assessment and actual measurements are also given and discussed. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of blind channel estimation for single-input-single-output (SISO) orthogonal frequency-division multiplexing (OFDM) system via second-order statistics only. Based on the assumption that the transmitted symbols are independent and identically distributed, we develop a simple blind channel estimation technique for OFDM systems by utilizing a generalized linear nonredundant block precoding. Instead of using partial information from the signal covariance matrix, as done in previous works where a specific precoder is designed and only one column of the signal covariance matrix is exploited, our work jointly considers all the information contained in the signal covariance matrix. Compared to the popular subspace-based blind channel estimation methods, the proposed algorithm is much more computationally efficient. A design criterion of the precoders by which the performance can be improved is provided, and the closed-form stochastic Cramér-Rao bound is derived. The numerical results clearly show the effectiveness of our proposed algorithm, as well as its improvement over the existing techniques. [ABSTRACT FROM AUTHOR]

This paper proposes a joint power and rate assignment (JPRA) algorithm to deal with multirate soft handoffs (SHOs) in mixed-size wideband code division multiple access cellular systems. This JPRA algorithm contains a link proportional power allocation scheme and an evolutionary computing rate assignment method to determine an appropriate allocation of transmission power and service rate for multirate SHOs. It can achieve power balancing among cells better than the conventional site-selection diversity transmission scheme with best effort rate allocation. Simulation results show that the JPRA algorithm can achieve better cell's service coverage and higher system capacity with and without the measurement errors during the active set selection. [ABSTRACT FROM AUTHOR]

This paper proposes task-scheduling algorithms designed to save energy in ad hoc networks by using a novel concept of "affinity" as the scheduling metric. This notion of affinity is used to represent the task-linking topology. For one-hop ad hoc networks, we define three types of affinity measures: node affinity, task affinity, and weighted affinity. Node affinity is defined as the weighted sum of incoming and outgoing task flows at each node, and task affinity as the sum of node affinities of source and destination nodes for each task. Based on these affinity measures, we consider three heuristic scheduling algorithms that are executable in real time: 1) affinity-first shortest task scheduling Qat; 2) task-size-first affinity-based scheduling Qta; and 3) task-size weighted-affinity scheduling Qwa. These algorithms have the advantage of making the total duration of the doze state of all the nodes in the network longer than in other conventional schemes, thereby achieving significant power saving (PS). Our simulation experiments suggest that the PS performance of Qwa is comparable to optimal scheduling (which is not implementable in practice for realistic link topologies). We also present a framework for a PS medium-access-control (MAC) protocol in which our scheduling algorithm can be deployed, and we describe how to enhance the existing 802.11 PS MAC to implement our framework. Simulation results demonstrate that our enhanced PS MAC protocol combined with affinity-based scheduling improves power efficiency and throughput significantly over other existing schemes. [ABSTRACT FROM AUTHOR]

In this paper, an advanced experimental plane-wave-based method (EPWBM) for evaluation of the performance of multiantenna systems is considered. The method enables a statistical antenna evaluation without performing long routes of radio-channel sounder measurements to be carried out separately for each antenna under test. The EPWBM utilizes the joint contribution of the estimated signal spectrum and the simulated or measured complex three-dimensional (3-D) radiation patterns of antennas under test. The proposed method enables more comprehensive antenna evaluation in a shorter time period compared to direct measurements. For validation purposes, the results obtained with the EPWBM are compared with the results of direct radio-channel measurements. The method is shown to be sufficiently accurate for comparing the performance of different antenna configurations. The average difference between the two methods is below 1 dB when estimating the diversity gain of two-element antennas. Further, the maximum difference between the methods in multiple-input multiple-output analysis is below 1 b/s/Hz in estimating mean capacity. [ABSTRACT FROM AUTHOR]