Herschel H. Loomis

Computationally efficient algorithms for cyclic spectral analysis

Two computationally efficient algorithms for digital cyclic spectral analysis, the FFT accumulation method (FAM) and the strip spectral correlation algorithm (SSCA), are developed from a series of modifications on a simple time smoothing algorithm. The signal processing, computational, and structural attributes of time smoothing algorithms are presented with emphasis on the FAM and SSCA. As a vehicle for examining the algorithms the problem of estimating the cyclic cross spectrum of two complex-valued sequences is considered. Simplifications of the resulting expressions to special cases of the cross cyclic spectrum of two complex-valued sequences, such as the cyclic spectrum of a single real-valued sequence, are easily found. Computational and structural simplifications arising from the specialization are described.<<ETX>>

High-Speed Recursive Digital Filter Realization

Pipeline techniques have been successfully applied to speeding up processing in both general- and special-purpose digital computers. Application of these techniques to nonrecursive (FIR) filters has been suggested and is quite straightforward. Application to recursive (IIR) filters has not previously been shown. In this paper, the technique for applying pipeline techniques to recursive filters is shown and the advantages and disadvantages of the technique are discussed. Using these techniques, recursive digital filters operating at hitherto impossibly high rates can be designed.

Elimination of narrow-band interference in BPSK-modulated signal reception

Four different classes of adaptive signal cancelers can be used to eliminate narrowband interference, from a broadband signal. The adaptive algorithm for these filters has been proposed by Kwan and Martin (1989) and modified by Petraglia, Mitra and Szczupak. The authors propose a modification of the structure to improve the adaptation and simplify the hardware. The new structure is applied to narrowband biphase shift-key (BPSK) interference in broadband BPSK signals with and without background noise.<<ETX>>

Challenges of Remote FPGA Configuration for Space Applications

There are many unique challenges associated with providing remote access to space experimental payloads. The limited bandwidth to the space craft, the inability to physically monitor and probe the payload, and the management of access time for various researchers working on the project all compound to create a challenging work environment. The configurable fault tolerant processor (CFTP) project aims to alleviate many of the difficulties associated with remote payload operation. We have made use of modular FPGA design, which allows us to transfer only small application modules rather than full configuration files. This dramatically reduces the bandwidth required to upload new applications as we discover new experiments for the CFTP after launch. Another unique aspect of the CFTP project is the collaborative effort in its development. We must manage access time for universities and research institutions across the country for running experiments on the CFTP, downloading CFTP documents, and analyzing telemetry after launch

Geolocation of LTE subscriber stations based on the timing advance ranging parameter

This paper investigates geolocating a Long Term Evolution (LTE) subscriber station based on the timing advance ranging parameter within the network signal internals. The basic approach to geolocation based on radial distances from multiple base stations is outlined. Specifics of the timing parameters used during LTE network entry are examined as they relate to calculating these distances. Computer simulation is used to demonstrate expected geolocation accuracy in multiple base station networks when estimating likely locations of subscriber stations on a two-dimensional coordinate mapping system. Computer simulation is further refined to demonstrate expected geolocation accuracy in multiple base station networks when estimating likely locations of subscriber stations on a three-dimensional coordinate mapping scheme. Results show the possibility of fixes with ten times greater accuracy than in previous results in the literature when applying timing advance techniques to Global System for Mobile communications networks when using a two-dimensional coordinate mapping scheme, and accuracy approaching fifty centimeters when using a three-dimensional coordinate mapping scheme, accuracy that is comparable to the accuracy in Global Positioning System technologies.

Digital implementations of spectral correlation analyzers

A variety of quadratic system implementations of spectral correlation analyzers using pipeline digital techniques is studied. The authors analyze in detail three realizations, each with different advantages. One approach is based on the frequency-smoothing method of cross-spectral analysis. The remaining approaches are variants of the time-smoothing method in which the time-smoothing operation is replaced by a Fourier transform operation. In each of these realizations, the characteristics kernel in the fundamental equation is shown, and the digital realization is developed. Also, detailed complexity analyses are presented for each form.<<ETX>>

Parallel computation structures for a class of cyclic spectral analysis algorithms

A digital frequency smoothing algorithm for cyclic spectral analysis is described. Partitioning schemes are presented that have properties amenable to parallel implementation. Parallel computation structures, based on the partitioning schemes, are described and system architectures proposed.

Television as a Tool in Off-Campus Engineering Education

Television has recently been very successfully applied to Engineering Extended Learning. This paper will review the use of this medium by the University of Florida, Colorado State University, Stanford University and the University of California, Davis Campus. Factors examined in the paper are: 1. Extent and type of system 2. Need served 3. Number and type of students 4. Cost of system a. total per student served b. cost to student 5. Results and reaction to the system The paper particularly emphasizes the University of California system and includes a report on the results of the first year of operation of a singularly successful system for bringing graduate education to the full time working engineer at reasonable cost and high quality.

Reduced Precision Redundancy in a Radix-4 FFT implementation on a Field Programmable Gate Array

Reduced Precision Redundancy (RPR) is demonstrated as a new method for improving fault tolerance in Field Programmable Gate Arrays (FPGAs) replacing Triple Modular Redundancy (TMR) to protect against the Single Event Effects due to radiation in arithmetic processes.12 As a test of this approach, the RPR technique was used to implement a Radix-4 Fast Fourier Transform (FFT). This design was implemented in a Xilinx Virtex 2® FPGA in order to find the possible gain in speed and reduction in power and resources as compared to the TMR method. Simulation of different degrees of RPR explore the impact on speed and power on the FPGA performance at various levels of precision reduction.

Computational balance in real-time cyclic spectral analysis

Real-time cyclic spectral analysis is useful in many applications, but is difficult to achieve because of its computational complexity. This paper studies the distribution of complex multipliers in multiprocessor cyclic spectrum analyzers, with the objective of obtaining computational balance. Computationally balanced implementations efficiently use hardware so that computational bottlenecks are reduced and a smooth flow of data between computational sections of the analyzer is maintained. Tables are presented that give the number of complex multipliers required in each section of the analyzer to obtain computational balance.<<ETX>>