Udayan Dasgupta

Digital timing recovery for communication systems

The paper presents a novel digital timing recovery mechanism for communication systems. The proposed approach jitters the ADC clock based on phase information obtained directly or indirectly from the received signal. The paper studies the effect of jitter resolution and its distribution on the timing SNR. It is demonstrated through simulations that the best SNR is achieved when the jitters are equally spaced. The proposed timing recovery scheme can be implemented by means of a numerically controlled oscillator (NCO), a tapped delay line, or a combination of the two. Practical aspects of all these schemes are presented. The resulting mechanism is able to achieve voltage controlled crystal oscillator (VCXO)-like performance at a much lower implementation cost. Although the proposed methodology can be applied to most communication systems, we focus on its application to asymmetric digital subscriber line (ADSL) modems.

Mapping spatio-temporal filtering algorithms used in fluoroscopy to single core and multicore DSP architectures

Low dose X-ray image sequences, as obtained in fluoroscopy, exhibit high levels of noise that must be suppressed in real-time, while preserving diagnostic structures. Multi-step adaptive filtering approaches, often involving spatio-temporal filters, are typically used to achieve this goal. In this work typical fluoroscopic image sequences, corrupted with Poisson noise, were processed using various filtering schemes. The noise suppression of the schemes was evaluated using objective image quality measures. Two adaptive spatio-temporal schemes, the first one using object detection and the second one using unsharp masking, were chosen as representative approaches for different fluoroscopy procedures and mapped on to Texas Instruments (TI) high performance digital signal processors (DSP). The paper explains the fixed point design of these algorithms and evaluates its impact on overall system performance. The fixed point versions of these algorithms are mapped onto the C64x+TM core using instruction-level parallelism to effectively use its VLIW architecture. The overall data flow was carefully planned to reduce cache and data movement overhead, while working with large medical data sets. Apart from mapping these algorithms on to TIs single core DSP architecture, this work also distributes the operations to leverage multi-core DSP architectures. The data arrangement and flow were optimized to minimize inter-processor messaging and data movement overhead.

Analysis of fixed point FFT for fourier domain optical coherence tomography systems

Optical coherence tomography (OCT) is a new imaging modality gaining popularity in the medical community. Its application includes ophthalmology, gastroenterology, dermatology etc. As the use of OCT increases, the need for portable, low power devices also increases. Digital signal processors (DSP) are well suited to meet the signal processing requirements of such a system. These processors usually operate on fixed precision. This paper analyzes the issues that a system implementer faces implementing signal processing algorithms on fixed point processor. Specifically, we show the effect of different fixed point precisions in the implementation of FFT on the sensitivity of Fourier domain OCT systems.