Phani K. Sagiraju

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.

Performance of two-stage massive correlator architecture for fast acquisition of GPS signals

A typical operation of GPS receivers assumes a search of the satellites visible on the sky by synchronizing locally generated replica with the transmitted pseudo-random noise (PRN) code sequence. This synchronization is initially performed by finding the highest correlation between the incoming signal and replica, a process known as “acquisition”. Highest correlation is observed as a correlator peak response which is compared with a certain threshold to identify availability and values of unknown code phase and frequency of a residual carrier modulation. If the peak is not detected or the decision is wrong then acquisition stage should be repeated many times which is quite a time consuming task. State-of-the-art advanced receivers use massive correlators which parallelize the acquisition process. While massive correlators improve significantly the sensitivity of the receivers, so-called multiple peak selection approach provides an opportunity to save computations by sharing tasks between the massive correlator and validation system [1]. In this paper we study a performance of two stage correlator consisting of massive and supplementary implementations. The massive correlator is not making firm decisions each time it finds a peak, but provides several possible options (a limited set of highest peaks) to supplementary system.

An assisted GPS support for GPS simulators for embedded mobile positioning

During recent years, location technologies have emerged as a research area with many possible applications in wireless communications, surveillance, military equipment, etc. Location Based Services (LBS) such as safety applications have become very popular. For example, US Federal Communication Commission Enhanced 911 (E911) Mandate seeks to provide emergency services personnel with location information that will enable them to dispatch assistance to wireless 911 callers much more quickly. Assisted GPS (A-GPS) is an extension of the conventional Global Positioning System (GPS) which increases start-up sensitivity by as much as 25dB relative to conventional GPS and reduces start times to less than six seconds. In A-GPS assistance data is delivered to the receiver through communication links. This paper addresses the generation of the assistance for GPS simulators for testing A-GPS receivers. The proposed approach is to use IP-based links and location support standards for assistance delivery avoiding network-specific signaling mechanisms so that GPS receiver developers can use this information for testing A-GPS capabilities using basic GPS simulators. The approach is implemented for the GPS simulator developed by the National InstrumentsTM.

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.

Implementation of an intrusion detection system based on wireless positioning

WLAN networks are widely deployed and can be used for testbed and application developments in academic environments. This paper presents wireless positioning testbed and a related application implementation methodology as a case study. Nowadays state-of-the-art WLAN positioning systems achieve high location estimation accuracy. In designated areas the signal profile map can be designed and used for such a positioning. Coverage of WLAN networks is typically wider than the authorized areas and there might be network intrusion attempts from the vicinity areas such as parking lots, cafeterias, etc. In addition to conventional verification and authorization methods, the network can locate the user, verify if his location is in the authorized area and apply additional checks to find the violators.

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.

Automatic Classification of Location Based Information

The modern mobile phones can do more than communicate voice and data. The support for different new technical capabilities in mobile devices represents a great opportunity for application developers to create compelling services that are widely used and highly valued. At the same time big volumes of communicated information will require more advanced organizing capabilities. In this paper we present an automatic classification approach of communicated data according to the preferences made by a transmitting source. The information can be structured according to many attributes such as the place, topic, importance, etc. The main idea is to have the information categorized as early as possible and enable automatic rerouting of data to designated data locations on a receiver side. As a case study a simple photo classification application is developed. This application can be extended to storing any information such as day to day life, landmarks, location data and much more, thereby providing a simple tool to sort out information automatically and efficiently. Location based services will benefit from the suggested approach as it will help to categorize the information already tagged according to the location and time. The paper begins by discussing the importance of location based information and services the mobile phone can provide with this location based information. Then we address a suitable development platform which is based on Symbian/Series60 architecture. Finally, the application developed for Symbian/Series60 mobile phones is presented

Fast DS-SS Acquisition Implementation for High Sensitivity Receivers

Pseudorandom codes are used in direct sequence spread spectrum (DSSS) receivers to synchronize the received signals with locally generated replica. A coarse synchronization called acquisition is followed by a finer synchronization, tracking. Both of these procedures bring received and replica signals to a small timing offset and find the residual frequency modulation which is left after carrier wipe-off. The acquisition stage is computationally challenging procedure for the receivers operating in weak signal conditions as the signal search space increases due to long integrations needed for high sensitivity. For example, these conditions can be observed indoors for satellite ranging and communication portable receivers. We present new very fast technique for acquiring signals indoors in conditions that require a significant number of computations. In our approach, many arithmetic operations are shared and external aid can be used to reduce the search space. Significant gains in arithmetic complexity are achieved