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1. Sparsity-Based Channel Estimation Exploiting Deep Unrolling for Downlink Massive MIMO

   Chen, An; Xu, Wenbo; Lu, Liyang; Wang, Yue (December 2023, 2023 IEEE Global Communications Conference)

   Massive multiple-input multiple-output (MIMO) enjoys great advantage in 5G wireless communication systems owing to its spectrum and energy efficiency. However, hundreds of antennas require large volumes of pilot overhead to guarantee reliable channel estimation in FDD massive MIMO system. Compressive sensing (CS) has been applied for channel estimation by exploiting the inherent sparse structure of massive MIMO channel but suffer from high complexity. To overcome this challenge, this paper develops a hybrid channel estimation scheme by integrating the model-driven CS and data-driven deep unrolling technique. The proposed scheme consists of a coarse estimation part and a fine correction part to respectively exploit the inter- and intraframe sparsities of channels to greatly reduce the pilot overhead. Theoretical result is provided to indicate the convergence of the fine correction and coarse estimation net. Simulation results are provided to verify that our scheme can estimate MIMO channels with low pilot overhead while guaranteeing estimation accuracy with relatively low complexity. 

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2. Double Adjacent Error Correction in RRAM Matrix Multiplication using Weighted Checksums

   https://doi.org/10.1109/IOLTS60994.2024.10616083  

   Pinto, Kenrick Xavier; Kodali, Krishnaja; Das, Abhishek; Touba, Nur A (July 2024, Proceedings)

   Artificial Intelligence (AI) has permeated various domains but is limited by the bottlenecks imposed by data transfer latency inherent in contemporary memory technologies. Matrix multiplication, crucial for neural network training and inference, can be significantly expedited with a complexity of O(1) using Resistive RAM (RRAM) technology, instead of the conventional complexity of O(n2). This positions RRAM as a promising candidate for the efficient hardware implementation of machine learning and neural networks through in-memory computation. However, RRAM manufacturing technology remains in its infancy, rendering it susceptible to soft errors, potentially compromising neural network accuracy and reliability. In this paper, we propose a syndrome-based error correction scheme that employs selective weighted checksums to correct double adjacent column errors in RRAM. The error correction is done on the output of the matrix multiplication thus ensuring correct operation for any number of errors in two adjacent columns. The proposed codes have low redundancy and low decoding latency, making it suitable for high throughput applications. This schemeuses a repeating weight based structure that makes it scalable to large RRAM matrix sizes. 

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3. Combining Deep Learning and Verification for Precise Object Instance Detection

   Ancha, Siddharth; Nan, Junyu; Held, David (November 2019, Proceedings of Machine Learning Research)

   Deep learning object detectors often return false positives with very high confidence. Although they optimize generic detection performance, such as mean average precision (mAP), they are not designed for reliability. For a re- liable detection system, if a high confidence detection is made, we would want high certainty that the object has indeed been detected. To achieve this, we have developed a set of verification tests which a proposed detection must pass to be accepted. We develop a theoretical framework which proves that, under certain assumptions, our verification tests will not accept any false positives. Based on an approximation to this framework, we present a practical detection system that can verify, with high precision, whether each detection of a machine-learning based object detector is correct. We show that these tests can improve the overall accu- racy of a base detector and that accepted examples are highly likely to be correct. This allows the detector to operate in a high precision regime and can thus be used for robotic perception systems as a reliable instance detection method. 

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4. Floating-Point Formats and Arithmetic for Highly Accurate Multi-Layer Perceptrons

   https://doi.org/10.1109/NANO58406.2023.10231201  

   Niknia, Farzad; Wang, Ziheng; Liu, Shanshan; Reviriego, Pedro; Louri, Ahmed; Lombardi, Fabrizio (July 2023, IEEE)

   The data precision can significantly affect the accuracy and overhead metrics of hardware accelerators for different applications such as artificial neural networks (ANNs). This paper evaluates the inference and training of multi-layer perceptrons (MLPs), in which initially IEEE standard floating-point (FP) precisions (half, single and double) are utilized separately and then compared with mixed-precision FP formats. The mixed-precision calculations are investigated for three critical propagation modules (activation functions, weight updates, and accumulation units). Compared with applying a simple low-precision format, the mixed-precision format prevents an accuracy loss and the occurrence of overflow/underflow in the MLPs while potentially incurring in less hardware overhead in terms of area/power. As the multiply-accumulation is the most dominant operation in trending ANNs, a fully pipelined hardware implementation for the fused multiply-add units is proposed for different IEEE FP formats to achieve a very high operating frequency. 

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5. Optimal adaptive inspection and maintenance for redundant systems

   https://doi.org/10.1177/1748006X211020151  

   Lin, Chaochao; Pozzi, Matteo (May 2021, Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability)

   Optimal exploration of engineering systems can be guided by the principle of Value of Information (VoI), which accounts for the topological important of components, their reliability and the management costs. For series systems, in most cases higher inspection priority should be given to unreliable components. For redundant systems such as parallel systems, analysis of one-shot decision problems shows that higher inspection priority should be given to more reliable components. This paper investigates the optimal exploration of redundant systems in long-term decision making with sequential inspection and repairing. When the expected, cumulated, discounted cost is considered, it may become more efficient to give higher inspection priority to less reliable components, in order to preserve system redundancy. To investigate this problem, we develop a Partially Observable Markov Decision Process (POMDP) framework for sequential inspection and maintenance of redundant systems, where the VoI analysis is embedded in the optimal selection of exploratory actions. We investigate the use of alternative approximate POMDP solvers for parallel and more general systems, compare their computation complexities and performance, and show how the inspection priorities depend on the economic discount factor, the degradation rate, the inspection precision, and the repair cost. 

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