Abhay Samant

High-resolution frequency analysis with a small data record

Fast Fourier transform-based implementations of the discrete Fourier transform have proven themselves the workhorses of discrete-time spectral analysis. Although these algorithms find widespread use, they have limitations. One problem is that frequency resolution is dependent on the number of samples available. For a given sampling frequency, the longer the data record, the better the frequency resolution. An alternative approach, model-based spectral analysis, is now being employed, as it derives a higher-resolution spectral detail from fewer samples. This approach was used by National Instruments Corp. in a portion of the design of a portable analyzer for the telephony industry. The analyzer is intended for technicians to use in diagnosing and locating faults on a standard twisted pair copper (plain old telephone system) line. In the software design phase, one option considered and tested for feasibility was employing model-based spectral analysis (MBSA) to decode a calling number delivery signal (better known as Caller ID). Not just applicable in this analyzer example, MBSA works in a variety of circumstances and offers a valuable addition to an engineers toolbox of software-based methods for spectral analysis. The technique might find an application wherever there is a lack of data, as in the case of analysis of a short time event, or where a restriction is imposed to ensure that the spectral characteristics of a signal do not change over the duration of a data set.

Trends in radar systems drive the need for smarter test systems

Active Electronically Scanned Array (AESA) technology will enable next generation radars achieve better jamming resistance capability and low probability of intercept by spreading their emissions over a wide frequency range. These radars systems consist of a large number of transmit/receive modules (TRMs) which are electronically scanned in a tight time-synchronized manner. This requires digital control to move closer to the radio front end on the antennas. Other emerging technologies, such as cognitive radars and MIMO radars, will continue to drive the need for complex timing, synchronization, and high mix RF and digital measurement requirements. To meet these challenges, radar engineers will need a platform based approach which delivers capabilities such as multi-channel phase aligned measurements over wide bandwidths and high-throughput streaming. This paper discusses the fundamentals of AESA radars and trends in radar systems. It analyzes the impact of these trends on test system architecture and explains how the advances in PXI modular instrumentation can meet these challenging requirements.

Modular Network Effects on Communicable Disease Models

Communicable disease models have been studied using classical mathematical differential equations for a long time now. However, these classical models do not always accurately represent the complex network behavior that governs the spread of any type of information, including communicable diseases. The paper presents a new modular network representation and shows how diseases generally spread in such a network. This paper also shows different simulation results, while looking at various observation parameters such as infection duration and number of modules. This paper then analyzes the 2009 H1N1 data for the Indian metropolitan cities of Delhi and Mumbai and states of Karnataka and Tamil Nadu in India and then discusses the correlation between the real-world data and the modular network results obtained through our simulations.

A design for software defined M-PSK radio on FPGA for low SNRs and symbol rates upto 10MS/s

In this paper we present an architecture for a software defined M-PSK (M=2, 4, 8) receiver which was prototyped to handle real world satellite signals of Eb/N0 up to 4dB for BPSK and QPSK and up to 6dB for 8-PSK using only 2 samples per symbol. This design supports symbol rates between 32kS/s and 10MS/s. We also present the BER curves of the demodulator designed and the approach we took to obtain them. This infrastructure is scalable to any kind of real time software radio development and aids rapid development on FPGA.

A land mobile channel modeling in LabVIEW

This paper presents a case study implementation of a fading channel model for a recently introduced Global Positioning System (GPS) simulator from National Instruments. Existing models are discussed and implementation aspects are presented for a model which combines statistical properties of different multipath channels. The NIs GPS simulator is implemented in an open development environment, LabVIEW, which allows an incorporation of user-defined models. Computational optimization issues are also discussed.

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.

Characterization and calibration techniques for multi-channel phase-coherent systems

Electronic Warfare (EW) and Radio Detection and Ranging (Radar) are two of the many applications that rely on multi-channel and phase-coherent configurations for signal processing. We provide herein an overview of the complexities and requirements of a multi-channel phase-coherent measurement system. Multiple Input Multiple Output [MIMO] systems have to overcome key technical challenges related to phase, time and frequency synchronization in order to coherently receive and process the data acquired/generated from each input/output. In practical MIMO systems, the radio hardware should be capable of acquiring and/or generating such phase coherent signals across the multiple channels. Further, the systems need to be able to sustain the phase coherence over considerable duration of time, depending on the sensitivity of the system. However, drifts will occur owing to the effects like temperature, thermal expansion, mismatched cable lengths, uncorrelated phase noise, ADC sample clock phase noise and quantization noise. Thus, a calibration process is required to compensate for the drift, whenever it crosses a particular threshold value that defines the accuracy of the phase-coherent system. In this paper, an FPGA based software-defined calibration method is presented for synchronizing the phase and magnitude across multiple channels of a system. This method allows the phase/magnitude drift over time to be periodically monitored and calibrated, when there is a need. With the FPGA built into the system, the calibration can take place remotely without the need of connecting the system to an external calibration kit. Also, measurement results are provided for a state of the art super heterodyne receiver system to show that the phase drift is lesser than ±1 degree across a 500MHz - 26.5GHz frequency range at 23°C ± 5°C for 2 and 4 channels configurations. Such systems can find use in a variety of real-world MIMO implementations such as Direction Finding, Beam Steering, Passive Radars, MIMO and Phased-Array Radar Systems, where phase coherence, alignment and /or synchronization has added advantages to multi-channel systems.

Traceable phase calibration of a wide-bandwidth microwave Vector Signal Analyzer

Numerous wide-bandwidth and multi-channel applications benefit from accurate test and measurement equipment which minimize the distortion of the generated and analyzed signals. Different techniques are described in literature to achieve this for Vector Signal Analyzers. This paper presents a simple traceable phase calibration technique for wide-bandwidth Vector Signal Analyzers using a comb generator which is able to realize a dense frequency grid up to 40 GHz and above. The comb generator itself is calibrated using a technique which is traceable to electro-optical sampling as primary standard. The calibration procedure is explained in detail showing the characterized phase distortion for different center frequencies and different IF bandwidths of a commercial VSA.

Cognitive radio testbed using reconfigurable PIFA antenna and energy detection sensing

This paper proposes a Cognitive Radio testbed setup. A reconfigurable PIFA antenna has been designed and simulated in AWR MWO. Then from these a look up table of different modes have been constructed in Labview Software. Then energy detection algorithm for wideband spectrum sensing was implemented in Labview and using NI PXI Chassis and NI VST the whole set up was tested and verified. Output is shown as LED indication which is the required PIN Diode switching configuration for reconfiguring the PIFA Antenna so as to achieve new transmission mode.