G. V. S. Raju

Enhancing Security in Wireless Networks Using Positioning Techniques

Security is a key issue in any wireless environment. This paper considers the problem of using two alternative positioning technologies for secure authentications in wireless networks. Two different positioning techniques namely, Global Positioning System (GPS) and network-based positioning technique are merged for this purpose. For validation purposes network-based positioning is achieved through Ekahau location-enabling enterprise for Wi-Fi networks. The authentication approach for any new node that wishes to enter the wireless network, requests from the node its position which can be computed using user-centric GPS receiver. Then the network identifies user position using network-centric approach and compares the results. In case user tries to mislead the network on its true location the network will identify the unauthorized access attempt. Doing so, shall improve the security of the network from unknown intruders who claim to be in the network.

A novel BER-feedback power control algorithm for Personal Area Network Devices

Personal Area Network (PAN) Devices are often components of communication systems which opportunistically access the wireless spectrum. As such, they must operate without presenting interference to licensed users, while meeting their individual, varied Quality of Service (QoS) requirements. In this paper we use a novel Transmit Power Control (TPC) algorithm to reduce interference. In theory, over the life of a Secondary Users (SUs) transmission, there is an optimal power time curve reflective of the minimum amount of power necessary with which a device can transmit while maintaining acceptable BER, and practicing Interference Avoidance (IA). Using the response of the algorithm to instantaneous channel conditions as well as an iteratively updated QoS benchmark, we obtain a quadratic approximation of the desired power-time curve. Stability of the quadratic approximation is demonstrated through Matlab simulations using critical valued inputs to the approximator. From our results, we also show that our quadratic approximator outperforms others of different orders in terms of reduction in sensitivities to relatively small changes in inputs, and better tracking performance in following reference desired power curves used in the simulations. Our algorithm reduces transmit power (and thus interference) by approximately 3.5 dB compared to conventional methods while maintaining the required QoS.

A Closed-Loop Transmission Power Control System Using a Nonlinear Approximation of Power-Time Curve

In wireless communication networks, it is desirable to achieve energy efficiency, while maintaining quality of service. Overall, energy efficiency can be achieved by minimizing the power output for each communication device. This paper presents a novel energy-saving adaptive transmit power control (TPC) algorithm based on bit error rate (BER) feedback (BER-TPC) that outperforms conventional approaches based on signal-to-interference-plus-noise ratio (SINR) feedback (SINR-TPC). It is a distributed algorithm deployed in both transmitting and receiving devices that can be applied for various wireless network topologies and protocols. This paper addresses the power efficiency of adaptive TPC, in terms of reduced total transmit power of the network by smoothing transmit power transients during adaptive iterations. It is achieved using a distributed closed-loop power control system that applies heuristically estimated dual-rate power adjustments during adaptive iterations. Because the proposed system uses a mathematical formula for power adjustment, operational bounds for stability can be provided using simple analysis. It is demonstrated that the proposed system provides adequate tradeoff between performance and complexity, in terms of reduction in sensitivities and better tracking performance in following the desired reference power curves used in the simulations. Case scenarios are simulated demonstrating approximately 1.39-dB transmit power savings compared to conventional methods.

Development of Software GPS+ Receiver Testbed

In recent years many algorithms and implementations have been proposed for software GPS receivers. A software defined radio provides a flexible architecture that allows the receiver to be reconfigured to implement different processing scenarios for different operational environments. Most of the suggested receivers have pre-assigned set of algorithms performing receiver tasks limiting their attractiveness for the research community. This is because many receiver tasks can be implemented using different algorithms and we develop a receiver testbed allowing users to include and/or select different algorithmic options, and test their comparative performances. Such an approach allows more optimal algorithm selection for different computational platforms and simplifies their study. Thus the main goal of this effort is to develop a research platform for testing various algorithms rather than to suggest a specific software receiver solution.

A reduced complexity frequency domain acquisition of DS-SS signals for embedded applications

Most of the current wireless communication devices use embedded processors for performing different tasks such as physical layer signal processing and multimedia applications. Embedded processors provide a reasonable trade-off between application specific implementation and hardware sharing by different algorithms for more optimal design and flexibility. At the same time the widespread popularity of these processors drives the development of algorithms specifically tailored for embedded environments. Fast Fourier Transform (FFT) is a universal tool, which has found many applications in communications and many application specific architectures and Digital Signal Processor (DSP) implementations are available for FFT. In this paper our focus is in embedded algorithms for spread spectrum communication receivers, which are using FFT as an engine to compute convolutions. Using FFT-based correlators one can search over all possible so-called code phases of direct sequence spread spectrum (DS-SS) signal in parallel with fewer operations than conventional correlators do. However in many real-life scenarios the receiver is provided with a timing assistance which confines the uncertainty in code phase within a limited area. The FFT based search is becoming redundant and a reasonable strategy is to modify the FFT based methods for better utilization of embedded processor resources. In this paper we suggest a reduced complexity frequency domain convolution approach for the search over limited number of code phases.

Closed Loop Power Control Using Third Order Quadratic Approximator

AbstractIn this paper we introduce a novel bit error rate (BER) feedback transmit power control (TPC) system using a first-time third order quadratic approximation of the power–time curve. This approximation improves the power efficiency of a dual-rate TPC algorithm in terms of reduced total transmit power by smoothing transmit power transients during adaptive iterations. We show that the third order approximator outperforms linear and second order approximators in terms of transmit power savings, sensitivities, error magnitude, and better tracking performance in following reference desired power curves. For the approximator, we determine operational bounds for stability, and demonstrate algorithm behavior using critical valued inputs. In addition we demonstrate value in using a dynamic, rather than static, performance benchmark for quality of service approximation (obtained used scaled maximum acceptable BER), and provide heuristic estimates for the input parameters for the dynamic benchmark.

An adaptive stochastic-based M-ary Modulation extension algorithm for short range wireless CRs

Increasingly, unlicensed devices demand access to the licensed wireless spectrum, raising the problem of spectrum scarcity. This problem can be addressed by allowing unlicensed devices opportunistic access. Because opportunistic devices regard licensed users as interference, channel Signal to Interference Noise Ratio (SINR) is an important consideration for transmission. Cognitive Radio (CR) technology allows devices to sense spectrum and dynamically allocate bits to channels with good SINR. In this paper we introduce a stochastic modulation algorithm called the Cognitive Radio Stochastic Modulation (CRSM), for use as an extension to established M-ary Modulation schemes in underlay channels with poor SINR. In this modulation scheme, in additive channels, both the transmitting and receiving CR sense the magnitude and variance of the interference energy in the channel. The transmitter uses deterministic signals as unique identifiers in manipulating the variance of the signal detected at the receiver. The detected change in variance, measured at the receiver, is indicative of the presence or absence of a signal. In this paper we determine the critical regions for the CRSM and introduce a probability of error model.

A Software GPS+Receiver Toolkit

In recent years, due to the increasing demand of accuracy in GPS receivers and advancements in software technologies many algorithms and implementations have been proposed for software GPS receivers. The software receiver provides a flexible architecture that allows the receiver to be reconfigured so as to implement different processing scenarios for different operational environments. . In reality many receiver tasks can be implemented using different known algorithms. Most of the suggested receivers have pre-assigned set of algorithms performing receiver tasks limiting their attractiveness for the research community. Hence we came up with an idea of a system, which allows users to include and/or select different algorithmic options, and test their comparative performances. Such an approach allows more optimal algorithm selection for different computational platforms and simplifies their study. Thus the main goal of this effort is to develop a software receiver which can be used for testing various algorithms rather than suggesting a single specific software receiver solution.