Anxiao (Andrew) Jiang's research while affiliated with Texas A&M University and other places

Publications (107)

Article
When neural networks (NeuralNets) are implemented in hardware, their weights need to be stored in memory devices. As noise accumulates in the stored weights, the NeuralNet’s performance will degrade. This paper studies how to use error correcting codes (ECCs) to protect the weights. Different from classic error correction in data storage, the optim...
Conference Paper
Full-text available
Clinical trials often require that patients meet eligibility criteria (e.g., have specific conditions) to ensure the safety and the effectiveness of studies. However, retrieving eligible patients for a trial from the electronic health record (EHR) database remains a challenging task for clinicians since it requires not only medical knowledge about...
Article
Deep Neural Networks (DNNs) are a revolutionary force in the ongoing information revolution, and yet their intrinsic properties remain a mystery. In particular, it is widely known that DNNs are highly sensitive to noise, whether adversarial or random. This poses a fundamental challenge for hardware implementations of DNNs, and for their deployment...
Conference Paper
Deep neural networks (DNNs) typically have many weights. When errors appear in their weights, which are usually stored in non-volatile memories, their performance can degrade significantly. We review two recently presented approaches that improve the robustness of DNNs in complementary ways. In the first approach, we use error-correcting codes as e...
Research
When the analog weights of a neural network are stored as analog values in hardware, noise will accumulate in the stored weights and degrade the performance of the neural network. This work explores the use of analog codes for protecting the analog weights from noise and improving neural networks' performance. Both linear and non-linear analog code...
Preprint
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The persistent storage of big data requires advanced error correction schemes. The classical approach is to use error correcting codes (ECCs). This work studies an alternative approach, which uses the redundancy inherent in data itself for error correction. This type of redundancy, called Natural Redundancy (NR), is abundant in many types of uncomp...
Conference Paper
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This work studies the Stopping-Set Elimination Problem, namely, given a stopping set, how to remove the fewest erasures so that the remaining erasures can be decoded by belief propagation in k iterations (including k =∞). The NP-hardness of the problem is proven. An approximation algorithm is presented for k = 1. And efficient exact algorithms are...
Conference Paper
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We consider a joint source-channel decoding (JSCD) problem where the source encoder leaves residual redundancy in the source. We first model the redundancy in the source encoder output as the output of a side information channel at the channel decoder, and show that this improves random error exponent. Then, we consider the use of polar codes in th...
Conference Paper
For the storage of big data, there are significant challenges with its long-term reliability. This paper studies how to use the natural redundancy in data for error correction, and how to combine it with error-correcting codes to effectively improve data reliability. It explores several aspects of natural redundancy, including the discovery of natu...
Conference Paper
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We propose a joint list decoder and language de-coder that exploits the redundancy of language-based sources during polar decoding. By judging the validity of decoded words in the decoded sequence with the help of a dictionary, the polar list decoder constantly detects erroneous paths after the decoding of every few bits. This path-pruning techniqu...
Article
Non-volatile memories suffer from two challenges due to their physical and system-level constraints. One challenge is limited memory lifetime, also called the endurance problem. The other is the difficulty in deleting data securely, called the insecure deletion problem. This work proposes a coding scheme that addresses both challenges jointly. It s...
Conference Paper
We propose efficient coding schemes for two communication settings: 1) asymmetric channels and 2) channels with an informed encoder. These settings are important in non-volatile memories, as well as optical and broadcast communication. The schemes are based on non-linear polar codes, and they build on and improve recent work on these settings. In a...
Conference Paper
The challenge of using inexpensive and high-density NAND flash for archival storage was posed recently for reducing data center costs. However, such flash memory is becoming more susceptible to noise, and its reliability issues has become the major concern for its adoption by long-term storage systems. This paper studies the system-level reliabilit...
Article
Full-text available
We exploit the redundancy of the language-based source to help polar decoding. By judging the validity of decoded words in the decoded sequence with the help of a dictionary, the polar list decoder constantly detects erroneous paths after every few bits are decoded. This path-pruning technique based on joint decoding has advantages over stand-alone...
Conference Paper
Secure Write-Efficient Memory (WEM) was proposed in [11] to solve the endurance and the insecure deletion problems in flash memories. Information theoretical results, i.e., the achievable region and the secrecy rewriting capacity, have been obtained. In this work, a code construction for secure WEM is presented and it is optimal for a large family...
Conference Paper
One serious challenge for flash memories is data reliability. In this work, we present the content-replication codeword problem, and it leads to our proposed joint decoder. We focus on joint decoding algorithms and study their theoretical decoding performances. The proposed scheme is novel for flash memories, and we show their reliability can be en...
Article
There are two fundamental approaches for error correction. One approach is to add external redundancy to data. The other approach is to use the redundancy inside data, even if it is only the residual redundancy after a data compression algorithm. The first approach, namely error-correcting codes (ECCs), has been studied actively over the past seven...
Conference Paper
There are two fundamental approaches for error correction. One approach is to add external redundancy to data. The other approach is to use the redundancy inside data, even if it is only the residual redundancy after a data compression algorithm. The first approach, namely error-correcting codes (ECCs), has been studied actively over the past seven...
Article
The increasing density of NAND flash memories makes data more prone to errors due to severe process variations and disturbance. The urgency to improve NAND flash reliability encourages searching for optimal channel coding methods. This paper reports our efforts towards a read channel for flash memories using polar coding. Our contributions include...
Conference Paper
The increasing density of NAND flash memories makes data more prone to errors due to severe process variations and disturbance. The urgency to improve NAND flash reliability encourages searching for optimal channel coding methods. This paper reports our efforts towards a read channel for flash memories using polar coding. Our contributions include...
Conference Paper
The classic approach for error correction is to add controlled external redundancy to data. This approach, called error-correcting codes, has been studied extensively. And the rates of ECCs are approaching theoretical limits. We explore a second approach for error correction in this work, which is to use the redundancy inside data, even if it is ju...
Article
Endurance and security are two serious challenges for non-volatile memories such as flash memories. Write-Efficient Memory (WEM) is an important rewriting code model to solve the endurance problem. Aiming at jointly solving the endurance and the security issues in non-volatile memories, this work focuses on rewriting code with a security constraint...
Article
Full-text available
We propose efficient coding schemes for two communication settings: 1. asymmetric channels, and 2. channels with an informed encoder. These settings are important in non-volatile memories, as well as optical and broadcast communication. The schemes are based on non-linear polar codes, and they build on and improve recent work on these settings. In...
Patent
Full-text available
A memory device having a plurality of cells, each of which stores a value, where the values of the cells are mapped to discrete levels and the discrete levels represent data, is programmed by determining a maximum number of cell levels in the memory device, and determining the set of values that are associated with each of the cell levels. The maxi...
Conference Paper
We consider the noisy write-once memory (WOM) model to capture the behavior of data-storage devices such as flash memories. The noisy WOM is an asymmetric channel model with non-causal state information at the encoder. We show that a nesting of non-linear polar codes achieves the corresponding Gelfand-Pinsker bound with polynomial complexity.
Conference Paper
For nonvolatile memories such as flash memories and phase-change memories, endurance and reliability are both important challenges. Write-Efficient Memory (WEM) is an important rewriting model to solve the endurance problem. An optimal rewriting code has been proposed to approach the rewriting capacity of WEM. Aiming at jointly solving the enduranc...
Conference Paper
Flash memories have become a significant storage technology. However, they have various types of error mechanisms, which are drastically different from traditional communication channels. Understanding the error models is necessary for developing better coding schemes in the complex practical settings. This paper endeavors to survey the noise and d...
Conference Paper
This paper considers the partial information rewriting problem for flash memories. In this problem, the state of information can only be updated to a limited number of new states, and errors may occur in memory cells between two adjacent updates. We propose two coding schemes based on the models of trajectory codes. The bounds on achievable code ra...
Article
Full-text available
This issue consists of 22 high-caliber papers with contributions from both academia and industry. The papers are organized into the following six sections: (i) Channel Modeling and Signal Processing Algorithms for Emerging Memory Technologies, (ii) Error Control Coding Techniques for Flash Memories, (iii) Algebraic Methods with Applications to Non-...
Conference Paper
Write-efficient memories (WEM) [1] were introduced by Ahswede and Zhang as a model for storing and updating information on a rewritable medium with constraints. A coding scheme for WEM using recently proposed polar codes is presented. The coding scheme achieves rewriting capacity, and the rewriting and decoding operation can be done in time O(N log...
Conference Paper
Current flash memory technology is focused on cost minimization of the stored capacity. However, the resulting approach supports a relatively small number of write-erase cycles. This technology is effective for consumer devices (smart-phones and cameras) where the number of write-erase cycles is small, however, it is not economical for enterprise s...
Conference Paper
Both rewriting and error correction are important technologies for non-volatile memories, especially flash memories. However, coding schemes that combine them have been limited. This paper presents a new coding scheme that combines rewriting and error correction for the write-once memory model. Its construction is based on polar codes, and it suppo...
Conference Paper
Full-text available
This work studies memories with the goal of exploring the concept of in-memory computing. Our point of departure is the 1972 classical study on logical arrays by Akers. We demonstrate a number of new ways for these arrays to simultaneously store information and perform logical operations. We first generalize these arrays to non-binary alphabets. We...
Conference Paper
Rank modulation is a technique for representing stored information in an ordered set of flash memory cells by a permutation that reflects the ranking of their voltage levels. In this paper, we consider two figures of merit that can be used to compare parallel programming algorithms for rank modulation. These two criteria represent different tradeof...
Article
This work analyzes the stochastic behavior of writing to embedded flash memory at voltages lower than recommended by a microcontroller’s specifications in order to reduce energy consumption. Flash memory integrated within a microcontroller typically requires the entire chip to operate on a common supply voltage almost twice as much as what the CPU...
Conference Paper
Flash memories have many distinct properties, which affect the design of error correcting codes. In this paper, we combine error correction with rewriting, and present such a code construction based on polar coding.
Conference Paper
Nonvolatile memories (NVMs) such as flash memories play a significant role in meeting the data storage requirements of today's computation activities. The rapid increase of storage density for NVMs however brings reliability issues due to closer alignment of adjacent cells on chip, and more levels that are programmed into a cell. We propose a new m...
Conference Paper
Codes that correct limited-magnitude errors for multi-level cell nonvolatile memories, such as flash memories and phase-change memories, have received interest in recent years. This work proposes a new coding scheme that generalizes a known result [2] and works for arbitrary error distributions. In this scheme, every cell's discrete level ℓ is mapp...
Conference Paper
Full-text available
The limited endurance of flash memories is a major design concern for enterprise storage systems. We propose a method to increase it by using relative (as opposed to fixed) cell levels and by representing the information with Write Asymmetric Memory (WAM) codes. Overall, our new method enables faster writes, improved reliability as well as improved...
Article
Full-text available
Flash memories are currently the most widely used type of nonvolatile memories. A flash memory consists of floating-gate cells as its storage elements, where the charge level stored in a cell is used to represent data. Compared to magnetic recording and optical recording, flash memories have the unique property that the cells are programmed using a...
Conference Paper
Full-text available
Rank modulation has been recently proposed as a scheme for storing information in flash memories. While rank modulation has advantages in improving write speed and endurance, the current encoding approach is based on the “push to the top” operation that is not efficient in the general case. We propose a new encoding procedure where a cell level is...
Conference Paper
Full-text available
Predetermined fixed thresholds are commonly used in nonvolatile memories for reading binary sequences, but they usually result in significant asymmetric errors after a long duration, due to voltage or resistance drift. This motivates us to construct error-correcting schemes with dynamic reading thresholds, so that the asymmetric component of errors...
Conference Paper
Full-text available
For many nonvolatile memories, - including flash memories, phase-change memories, etc., - maximizing the storage capacity is a key challenge. The existing method is to use multilevel cells (MLC) of more and more levels. The number of levels supported by MLC is seriously constrained by the worst-case performance of cell-programming noise and cell he...
Conference Paper
Full-text available
Phase-change memory (PCM) is an emerging nonvolatile memory technology that promises very high performance. It currently uses discrete cell levels to represent data, controlled by a single amorphous/crystalline domain in a cell. To improve data density, more levels per cell are needed. There exist a number of challenges, including cell programming...
Article
Network planarization has been an important technique in numerous sensornet protocols—such as Greedy Perimeter Stateless Routing (GPSR), topology discovery, data-centric storage, etc.—however the planarization process itself has been difficult. Known efficient planarization algorithms exist only for restrictive wireless network models: unit-disk gr...
Article
A write-once memory (wom) is a storage medium formed by a number of “write-once” bit positions (wits), where each wit initially is in a “0” state and can be changed to a “1” state irreversibly. Examples of write-once memories include SLC flash memories and optical disks. This paper presents a low complexity coding scheme for rewriting such write-on...
Article
Full-text available
Codes that correct asymmetric errors have important applications in storage systems, including optical disks and Read Only Memories. The construction of asymmetric error correcting codes is a topic that was studied extensively, however, the existing approach for code construction assumes that every codeword could sustain t asymmetric errors. Our ma...
Conference Paper
This work analyzes the stochastic behavior of writing to embedded flash memory at voltages lower than recommended by a microcontroller's specifications to reduce energy consumption. Flash memory integrated within a microcontroller typically requires the entire chip to operate on common supply voltage almost double what the CPU portion requires. Our...
Conference Paper
Rank modulation is a scheme that uses the relative order of cell levels to represent data. Its applications include flash memories, phase-change memories, etc. An extension of rank modulation is studied in this paper, where multiple cells can have the same rank. We focus on the rewriting of data based on this new scheme, and study its basic propert...
Article
Full-text available
A deep understanding of the structural properties of wireless networks is critical for evaluating the performance of network protocols and improving their designs. Many protocols for wireless networks — routing, topology control, information storage/retrieval and numerous other applications — have been based on the idealized unit-disk graph (UDG) n...
Article
Full-text available
Flash memory is a nonvolatile computer memory comprised of blocks of cells, wherein each cell is implemented as either NAND or NOR floating gate. NAND flash is currently the most widely used type of flash memory. In a NAND flash memory, every block of cells consists of numerous pages; rewriting even a single page requires the whole block to be eras...
Article
Full-text available
Memories whose storage cells transit irreversibly between states have been common since the start of the data storage technology. In recent years, flash memories have become a very important family of such memories. A flash memory cell has q states-state 0, 1, ..., q-1-and can only transit from a lower state to a higher state before the expensive e...
Conference Paper
Full-text available
Phase-change memories (PCMs) are an important emerging non-volatile memory technology that uses amorphous and crystalline cell states to store data. The cell states are switched using high temperatures. As the semi-stable states of PCM cells are sensitive to temperatures, scaling down cell sizes can bring significant challenges. We consider two pot...
Conference Paper
Full-text available
Parallel programming is an important tool used in flash memories to achieve high write speed. In parallel programming, a common programm voltage is applied to many cells for simultaneous charge injection. This property significantly simplifies the complexity of the memory hardware, and is a constraint that limits the storage capacity of flash memor...
Conference Paper
An LDPC code is proposed for flash memories based on rank modulation. In contrast to previous approaches, this enables the use of long ECCs with fixed-length modulation codes. For ECC design, the rank modulation scheme is treated as part of an equivalent channel. A probabilistic model of the equivalent channel is derived and a simple high-SNR appro...
Conference Paper
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NAND flash memories have become the most widely used type of non-volatile memories. In a NAND flash memory, every block of memory cells consists of numerous pages, and rewriting a single page requires the whole block to be erased. As block erasures significantly reduce the longevity, speed and power efficiency of flash memories, it is critical to m...
Article
Full-text available
We investigate error-correcting codes for a novel storage technology for flash memories, the rank-modulation scheme. In this scheme, a set of n cells stores information in the permutation induced by the different charge levels of the individual cells. The resulting scheme eliminates the need for discrete cell levels, overcomes overshoot errors when...
Chapter
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We would like to thank all our co-authors for their collaborative work in this area. In particular, we would like to thank Mike Langberg and Moshe Schwartz for many of the main results discussed in this chapter.
Conference Paper
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NAND flash memories are the most widely used non-volatile memories, and data movement is common in flash storage systems. We study data movement solutions that minimize the number of block erasures, which are very important for the efficiency and longevity of flash memories. To move data among n blocks with the help of Δ auxiliary blocks, where eve...
Conference Paper
Flash memory cells use the charge they store to represent data. The amount of charge injected into a cell is called the cell's level. Programming a cell is the process of increasing a cell's level to the target value via charge injection, and the storage capacity of flash memories is limited by the precision of cell programming. To optimize the pre...
Conference Paper
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Flash memories are a very widely used type of non-volatile memory. Like magnetic recording and optical recording, flash memories have their own distinct properties. These distinct properties introduce very interesting information-representation and coding problems, which address many aspects of a successful storage system. In this paper, we survey...
Article
Full-text available
Rank modulation has been recently introduced as a new information representation scheme for flash memories. Given the charge levels of a group of flash cells, sorting is used to induce a permutation, which in turn represents data. Motivated by the lower sorting complexity of smaller cell groups, we consider bounded rank modulation, where a sequence...
Conference Paper
Full-text available
NAND flash memories are currently the most widely used flash memories. In a NAND flash memory, although a cell block consists of many pages, to rewrite one page, the whole block needs to be erased and reprogrammed. Block erasures determine the longevity and efficiency of flash memories. So when data is frequently reorganized, which can be character...
Conference Paper
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A constrained memory is a storage device whose elements change their states under some constraints. A typical example is flash memories, in which cell levels are easy to increase but hard to decrease. In a general rewriting model, the stored data changes with some pattern determined by the application. In a constrained memory, an appropriate repres...
Article
Full-text available
We explore a novel data representation scheme for multi-level flash memory cells, in which a set of n cells stores information in the permutation induced by the different charge levels of the individual cells. The only allowed charge-placement mechanism is a "push-to-the-top" operation which takes a single cell of the set and makes it the top-charg...
Conference Paper
Flash memories are the most widely used type of non-volatile electronic memories. Every flash memory cell has q discrete levels for storing information. A prominent property of flash memories is that although it is easy to increase a cell level, to decrease any cell level, a whole block of cells have to be erased and reprogrammed. To minimize the n...
Conference Paper
Full-text available
Flash memories are the most widely used type of non-volatile electronic memories. Compared to magnetic recording and optical recording, flash memories have the unique property that their cell levels, which represent data, are programmed using an iterative procedure that monotonically shifts each cell level upward toward its target value. In this pa...
Article
Full-text available
Distributively storing widely shared files with redundancy is an important technique for high performance and fault-tolerance in information networks. This paper proposes a new file storage scheme for encoded files, aiming at satisfying highly varied QoS requirements and guaranteeing graceful performance-degradation while some data become inaccessi...
Conference Paper
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The rank modulation scheme has been proposed recently for efficiently writing and storing data in nonvolatile memories. Error-correcting codes are very important for rank modulation; however, existing results have bee limited. In this work, we explore a new approach, systematic error-correcting codes for rank modulation. Systematic codes have the...
Conference Paper
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Flash memory is an electronic non-volatile memory with wide applications. Due to the substantial impact of block erasure operations on the speed, reliability and longevity of flash memories, writing schemes that enable data to be modified numerous times without incurring the block erasure is desirable. This requirement is addressed by floating code...
Conference Paper
Data-centric storage (Shenker et al., 2002), which supports efficient in-network data query and processing, is an important concept for sensor networks. Previous approaches mostly use hash functions to store data, where data with the same key value are stored in sensors at or near the same geographic location. We propose a new data-centric storage...
Conference Paper
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Wireless sensor networks need very efficient network protocols due to the sensors' limited communication and computation capabilities. Network planarization - finding a planar subgraph of the network that contains all the nodes - has been a very important technique for many network protocols. It first became the foundation of various well known rou...