A. Yardim

Offset windowing for FIR fractional-sample delay

Non-optimal FIR filters used for fractional-sample delay, despite their wideband nature, are shown to benefit significantly from application of windowing. Here simple raised-cosine windows prove to be very effective, particularly if they are cast as asymmetric modifications of their conventional forms. The offset von Hann window is surprisingly potent when the number of coefficients is large and window offset coincides with the fractional delay required of the overall filter.

Optimal Signal Selection for FIR Matched Filtering in Pole-Only Noise

With duration-limited signals there is the opportunity for perfect matched filtering by a suitable FIR filter whenever the accompanying noise has pole-only coloration. The maximal SNR value obtainable via matched filtering is itself sensitive to the signal pulse shape initially given. In some signaling situations (e.g. radar) we are unilaterally free to choose signal shape, and with this come prospects of further SNR improvement. Four distinct perspectives on optimizing signal selection are pursued, including a new single-frequency toneburst windowing approach that becomes a very good approximation for large signal sizes. Three of the approaches are capable of near-optimal SNR performance, but the whitener eigenvalue method introduced is recommended as the best possible way of selecting signals. Discussion is included of special multi-tonality issues which arise for smaller signals and for multiple maximum whitener eigenvalues.

Optimal signal and jamming dynamics embracing digital filter strictures

Dynamic jamming/evasion duels are described purely in terms of re-design iterations for three separate agile FIR digital filters. At the signal generation end of the contest an optimal pulse-shaping filter works in concert with an optimal detection filter. At the jamming end, two strategies are evaluated for the re-design of the noise coloration filter. One of these utilizes an optimal square-rooting filter which (ideally) neutralizes the selectivity of the detection filter, while the other gives slightly less impressive jamming effectiveness but shows an exploitation advantage if it is known that the receiver recklessly uses a simple flip-template filter for detection.

Pulsed interference mitigation employing periodic nonuniform decimation

Suppression of wideband signals contaminated by pulsed interference is undertaken using synchronous temporal blanking. This repetitive time gating of the raw signaling waveforms employed at physical level of communications, radar or sensor systems can sometimes largely remove interference, but leaves a waveform remnant that will often be insufficient to permit satisfactory restoration of the entire signal waveform through simple interpolatory filtering. If the interference is periodic the requisite gating of the digitized signal can be treated as periodic nonuniform decimation. We undertake restoration using the “alias unraveling” approach, introducing a digital filter design of the sampling pulse which leads to significantly better conditioning of the unraveling matrix, and affords a very considerable extension of resilience to interferer duty cycle.

A waveform-agile jamming duel demonstrator

A potent software-based demonstrator is described for agile pulse transmission in shaped noise jamming and clutter interference. Four distinct and interacting FIR digital filter coefficient sets accounting for prevailing signaling conditions are of central importance. The entity using its coefficients to shape its emitted noise power spectrum elicits the most-disruptive jamming currently possible. Likewise, the opposing entity undertakes optimal pulse-shaping/detection filtering aimed at countering the most recent jamming transmission. The optimal filter design algorithms underlying the demonstrator are emphasized, along with discussions of nonlinear design effects connected with clutter, static out-take plots of simulation runs and selectable suboptimal compromises.

Reducing pulse compression sidelobes by inversion-amenable code selection

Two alternative filtering approaches (dubbed ldquocode-inverserdquo and ldquoCodeACF-inverserdquo) for reduction of temporal sidelobes are evaluated and compared for practical engineeering application to pulse compression. It is seen that the optimal code pattern for each code length must be discovered as part of a tightly integrated search process that is sensitive to the inverse filter design algorithm and the number of coefficients budgeted. Re-use of codes derived in other contexts has been commonplace in earlier work, but rarely proves optimal. Hence unique application algorithm-specific codes must be sought, with codewords for CodeACF-inverse employment being obtained independently from those for Code-Inverse usage. If CodeACF-inversepsilas greater storage requirement can be accommodated, then it is found to be very significantly superior. A rule-of-thumb that filter length should be about three times the code length is confirmed by measured sidelobe performance when code sequences are chosen to be optimally amenable to inverse filtering.

Output-Energy Filters in Noncoherent Pulse-Event Detection

Digital matched filters are pivotal for detection of pulses in numerous applications. But compromises are necessary in situations of phase uncertainty, degrading the optimality matched filtering offers. The problem is compounded when (say, for avoidance of intersymbol interference) in colored noise the filter size is restricted below optimal length. In such circumstances energy detection can be attractive. Here we explore employment of so-called output-energy filters as candidate pre-filters for traditional square-law nonlinear energy detectors. We show conditions where an output-energy processor outperforms a length-deficient matched filter used in pulse arrival time location and in a quadrature receiver for noncoherent FSK detection. Peak response offsets in some length-deficient matched filter responses are encountered and shown to require care in interpreting even noisefree data records. In certain operating regimes output-energy processing has advantages, offering phase-blind detection ability unavailable with matched filters.

Classroom design demonstrations for complex IIR filters

An environment for exceptionally fast design of FIR and IIR filters by pushbutton and easy drag-and-drop manipulations is described. Filter gain and phase credentials are immediately available to the designer, along with the facility to simply sketch the desired filter characteristics. The design flow for a specimen complex FIR and IIR realization of an arbitrary combination of gain and group delay is presented in detail, and a subsequent phase compensation filter is also shown. A varied selection of other design examples emphasizes the flexibility and abundance of choice afforded the user.

Dynamic matched filtering - animating the action [educational aid]

A Simulink-based block diagram modelling environment is described which makes investigation of demanding DSP concepts such as FIR matched filtering easy and fun. Users interact with the experiment to a remarkable degree, watching scope displays while tuning parameter values or moving sliders to effect model changes during run time in a dynamic fashion. Instrumentation for achieved signal-to-noise ratio sits alongside displays advising the experimenter of theoretically optimal SNR for the current parameter settings. A small example problem using a single-pole noise-shaping filter is seen to be very enlightening, especially since a variable-coefficient matched filter block is employed which is self-designing in response to the prevailing pole radius and resonant frequency selection.

All-thru DSP provision, essential for the modern EE

DSP deserves to be a major focus of professional engineering education, with ready access points provided at virtually all stages of undergraduate, postgraduate, and continuing professional development study. The authors describe one institutions commitment to this concept, where entering undergraduates experience an electronic engineering curriculum designed around a 15% substrate of DSP, with an abundance of supporting project work available in two years of the program. A named DSP masters course is an important bridge to industry and permits simultaneous access to short courses serving both full-time postgraduates and industry-based engineers. A satellite outreach linking a 15-site network of leading European DSP groups via live, interactive tele-seminars is also described.<<ETX>>