Experimental Benchmarks and Initial Evaluation of the Performance of the PASM System Prototype

The work reported here represents experiences with the PASM parallel processing system prototype during its first operational year. Most of the experiments were performed by students in the Fall semester of 1987. The first programming, and the first timing measurements, were made during the summer of 1987 by Sam Fineberg. The goal of the collection of experiments presented here was to undertake an Application-driven Architecture Study of the PASM system as a paradigm for parallel architecture evaluation in general. PASM was an excellent vehicle for experimenting with this evaluation technique due to its unique architectural features. Among these are: 1. A reconfigurable, partitionable multistage circuit-switched network. 2. Support for both SIMD and MIMD programs. 3. Ability to execute hybrid SIMD/MIMD programs. 4. An instruction queue which allows overlap of control-flow and data manipulation between micro-control (MC) units and processing elements (PE). It had been hypothesized that superlinear speed-up over the number of PEs could be attained with this feature, and experimental results verified this. 5. Support for barrier synchronization of MIMD tasks. This feature was exploited in some non-standard ways to show the ability to decouple variant length SIMD instructions into multiple MIMD streams for an overall performance benefit. This type of study is expected to continue in the future on PASM and other parallel machines at Purdue. This report should serve as a guide for this future work as well

Concatenated coding and iterative decoding for magnetic and optical recording

Ph.D.Steven W. McLaughli

Precoded PRML, serial concatenation, and iterative (turbo) decoding for digital magnetic recording

We show that a high rate serially concatenated code used in conjunction with a precoded partial response equalized magnetic recording channel and iterative decoding can provide similar performance to a turbo code on the same channel. The precoded partial response maximum-likelihood (PRML) read channel is incorporated as the inner code of the concatenated coding scheme and the outer code is a high rate convolutional code. Gains of 4.8 dB above conventional PRML at a bit error rate of 10 \Gamma5 for a rate 13/14 code can be achieved. Index Terms---Iterative decoding, precoded PRML, serial concatenated codes, turbo codes. I. Introduction Recently [1], [2], [3], have shown that high rate turbo codes [4] can provide 4-6 dB of coding gain when applied to PR4 and EPR4 equalized magnetic recording. In this paper we show that this outstanding performance is achievable without the use of turbo codes per se. That is, we show that a high rate serially concatenated code used in conjunction wi..

Integrating Language Models with Speech Recognition

The question of how to integrate language models with speech recognition systems is becoming more important as speech recognition technology matures. For the purposes of this paper, we have classified the level of integration of current and past approaches into three categories: tightly-coupled, loosely-coupled, or semicoupled systems. We then argue that loose coupling is more appropriate given the current state of the art and given that it allows one to measure more precisely which components of the language model are most important. We will detail how the speech component in our approach interacts with the language model and discuss why we chose our language model. 1 Introduction State of the art speech recognition systems achieve high recognition accuracies only on tasks that have low perplexities. The perplexity of a task is, roughly speaking, the average number of choices at any decision point. The perplexity of a task is at a minimum when the true language model is known and co..