Realistic Propagation Scenarios Research Articles

Agent‐based modeling of malware dynamics in heterogeneous environments

ABSTRACTThe increasing convergence of power‐law networks such as social networking and peer‐to‐peer applications, web‐delivered applications, and mobile platforms makes today's users highly vulnerable to entirely new generations of malware that exploit vulnerabilities in web applications and mobile platforms for new infections, while using the power‐law connectivity for finding new victims. The traditional epidemic models based on assumptions of homogeneity, average‐degree distributions, and perfect‐mixing are inadequate to model this type of malware propagation. In this paper, we study four aspects crucial to modeling malware propagation: application‐level interactions among users of such networks, local network structure, user mobility, and network coordination of malware such as botnets. Since closed‐form solutions of malware propagation considering these aspects are difficult to obtain, we describe an open‐source, flexible agent‐based emulation framework that can be used by malware researchers for studying today's complex malware. The framework, called Agent‐Based Malware Modeling (AMM), allows different applications, network structure, network coordination, and user mobility in either a geographic or a logical domain to study various infection and propagation scenarios. In addition to traditional worms and viruses, the framework also allows modeling network coordination of malware such as botnets. The majority of the parameters used in the framework can be derived from real‐life network traces collected from a network, and therefore, represent realistic malware propagation and infection scenarios. As representative examples, we examine two well‐known malware spreading mechanisms: (i) a malicious virus such as Cabir spreading among the subscribers of a cellular network using Bluetooth and (ii) a hybrid worm that exploit email and file‐sharing to infect users of a social network. In both cases, we identify the parameters most important to the spread of the epidemic based upon our extensive simulation results. Copyright © 2011 John Wiley & Sons, Ltd.

Blind and Efficient Serial Search Strategy for Ultrawideband Signal Initial Acquisition

The problem of initial acquisition of ultrawideband (UWB) signals in the dense multipath channel is addressed. We demonstrate the advantages of designing the acquisition system so that the size of the uncertainty region is a Fibonacci number and propose a simple search strategy for coarse synchronization that uses no channel knowledge, extending a previous work where we proposed a method based on the golden section, which practically achieved the minimum mean acquisition time (MAT) under a simplistic model. We derive the MAT of the new strategy for this model and compare it with simulation results for a realistic propagation scenario with a high signal-to-noise ratio (SNR). There is an agreement between the theoretical and simulated MATs, which is limited by the differences between the two models. Simulations from moderate to high SNRs confirm that the proposed strategy provides a simple way to achieve the performance of the best strategies for acquisition of wide-bandwidth signals. In particular, it is similar in terms of complexity and performance to the popular bit reversal search, thus providing alternatives in the choice of design parameters wherever the bit reversal search is advisable.

An Exact Solution for the Level-Crossing Rate of Shadow Fading Processes Modelled by Using the Sum-of-Sinusoids Principle

The focus of this paper is on the higher order statistics of spatial simulation models for shadowing processes. Such processes are generally assumed to follow the lognormal distribution. The proposed spatial simulation model is derived from a non-realizable lognormal reference model with given correlation properties by using Rice's sum-of-sinusoids. Both exact and approximate expressions are presented for the level-crossing rate (LCR) and the average duration of fades (ADF) of the simulation model. It is pointed out that Gudmundson's correlation model results in an infinite LCR. To avoid this problem, two alternative spatial correlation models are proposed. Illustrative examples of the dynamic behavior of shadow fading processes are presented for all three types of correlation models. Emphasis will be placed on two realistic propagation scenarios capturing the shadowing effects in suburban and urban areas.

Some Analysis in Distributed MIMO Systems

The predicted capacity gain of a traditional co- located MIMO system is often severely limited in realistic propagation scenarios, especially when the number of antennas becomes large. Recently, a generalized paradigm for multiple-antenna communications, distributed MIMO, is proposed as a remedy. In this paper, through asymptotic large-system analysis, we provide solid justifications on the advantages of distributed MIMO over co-located MIMO when communication channels are subject to spatial correlation and shadow fading. We also exploit inherent macrodiversity in distributed MIMO to devise a cost- effective link adaptation scheme that achieves significant performance gain.

Ordered Subcarrier Selection Algorithm for OFDM-Based High-Speed WLANs

In this letter, a low-complexity and low-overhead adaptive bit-loading algorithm for wireless multicarrier schemes is proposed and analyzed. It is based on the diversity gain obtained through the ordering and selection of the more reliable subcarriers. Higher order modulations are used to compensate for the reduced subcarrier utilization. On the contrary to other bit-loading algorithms, it does not require nonuniform bit and power level allocation among subcarriers, thus drastically reducing the modem hardware complexity and making it attractive as a possible extension of existing high-speed wireless local-area network standards. System performance is analyzed in different configurations and conditions, including a realistic 5-GHz propagation scenario. Comparison with optimal adapted and unadapted solutions is also made. Finally, the effect of unideal feedback of the channel state information is analyzed showing the robustness and the low overhead required of the new scheme.

Spatial and temporal equalization for broadband wireless indoor networks at millimeter waves

The combined use of adaptive antennas and decision feedback equalization (DFE) is analyzed in a realistic propagation scenario at millimeter waves, taking the direction of arrivals (DOA's) of the received paths into account. The joint antennas and DFE scheme, with one forward filter for each antenna and a single feedback filter (FBF), can be viewed as a spatial and temporal DFE (ST-DFE). The performance of this solution is compared with the cascade of adaptive antenna used for beamforming and DFE. It is found that ST-DFE achieves better performance since it combines the beamforming capability of the antenna array with the equalization properties of the DFE, with great advantages especially when rays arrive from similar angles. The mean square error (MSE) is analytically derived for infinitely long filters in a quasi-static environment with multiple rays having different DOAs, and compared (for the two-path model) with simulation results assuming filters with a small number of taps. Finally, service availability through coverage evaluation is developed and compared with that of a coded-orthogonal frequency division multiplexing (C-OFDM) system.