Sharif Digital Repository

Cache memories constitute a large fraction of processor chip area and are highly vulnerable to soft errors caused by energetic particles. To protect these memories, most of the modern processors employ Error Detection Codes (EDCs) or Error Correction Codes (ECCs). EDCs/ECCs impose significant overheads in terms of area and energy; these overheads increase as a function of interleaving EDCs/ECCs to detect/correct multiple errors. This paper proposes a new cache architecture to minimize the area and energy overheads of EDCs/ECCs in set-associative L1-caches. Simulation results for a 4-way set-associative cache show that the proposed architecture reduces both the area and static power overheads... 

Scratchpad memory (SPM) is extensively used as the on-chip memory in modern embedded processors alongside of the cache memory or as its alternative. Soft errors in SPM are one of the major contributors to system failures, due to ever-increasing susceptibility of SPM cells to energetic particle strikes. Since a large fraction of soft errors occurs in the shape of Multiple-Bit Upsets (MBUs), traditional memory protection techniques, i.e., Error Correcting Code (ECCs), are not affordable for SPM protection; mainly because of their limited error coverage and/or their high overheads. This paper proposes a novel algorithm that efficiently protects SPM with high error correction capability and... 

In this paper, we study the problem of resistance drift in an MLC Phase Change Memory (PCM) and propose a solution to circumvent its thermally-affected accelerated rate in 3D CMPs. Our scheme is based on the observation that instead of alleviating the problem of resistance drift by using large margins or error correction codes, the PCM read circuit can be reconfigured for tolerating most of the resistance drift errors in a dynamic manner. Through detailed characterization of memory access patterns for 22 applications, we propose an efficient mechanism to facilitate such reliable read scheme via tolerating (a) early-cycle resistance drifts by using narrow margins so that considerably saving... 

Scratch Pad Memory (SPM) is an important part of most modern embedded processors. The use of embedded processors in safety-critical applications implies including fault tolerance in the design of SPM. This paper proposes a method, called FTSPM, which integrates a multi-priority mapping algorithm with a hybrid SPM structure. The proposed structure divides SPM into three parts: 1) a part is equipped with Non-Volatile Memory (NVM) which is immune against soft errors, 2) a part is equipped with Error-Correcting Code, and 3) a part is equipped with parity. The proposed mapping algorithm is responsible to distribute the program blocks among the above three parts with regards to their vulnerability... 

Infrared indoor wireless communications using nondirected links are subject to severe multipath distortion which causes intersymbol interference (ISI). To lessen multipath distortion effect and thereby to improve the system performance, in this paper, we consider a new time-hopping based multiple access scheme for this channel, in which one pulse is transmitted in each bit interval. The position of the pulse is determined based on the output of a low rate error correcting code along with the user's dedicated PN code. We evaluate the multiple access performance of the system for correlation receiver considering background noise, dark current, and thermal noise. We compare the performance of... 

The growth of data communication networks has made digital watermarking an important issue for copyright and content protection. Achieving high level of robustness and good transparency are the main objectives of developing every digital watermarking algorithm. From among transform domains as the basis of watermark hiding place, Discrete Cosine Transform (DCT), Discrete Wavelet Transform (DWT) and Singular Value Decomposition (SVD) are the most commonly used transforms in literature. In this paper we propose a new hybrid DWT-SVD domain watermarking scheme taking into account the energy content of every chosen block of the selected DWT sub-band coefficients. Before embedding, we append a... 

Spin-Transfer Torque RAM (STT-RAM) is a promising alternative to SRAM for implementing on-chip L2 and L3 caches. One of the most critical challenges in STT-RAM is reliability due to limited write endurance, which results in insufficient lifetime, as well as various types of errors. Previous studies have focused on either presenting various cache architectures/management techniques to improve the lifetime of STT-RAM caches or utilizing different Error Correcting Codes (ECCs) to protect against the permanent and transient errors. However, there is no quantitative analysis in the literature to determine the impact of ECCs on the lifetime of the STT-RAM caches. This paper formulates this impact... 

Due to serious problems of SRAM-based caches in nano-scale technologies, researchers seek for new alternatives. Among the existing options, STT-RAMseems to be themost promising alternative.With high density and negligible leakage power, STT-RAMs open a new door to respond to future demands of multi-core systems, i.e., large on-chip caches. However, several problems in STT-RAMs should be overcome to make it applicable in on-chip caches.High probability of write error due to stochastic switching is amajor problemin STT-RAMs. Conventional Error-CorrectingCodes (ECCs) impose significant area and energy consumption overheads to protect STT-RAMcaches. These overheads in multi-core processors with... 

Spin-Transfer Torque Random Access Memories (STT-RAMs) are a promising alternative to SRAMs in on-chip caches. STT-RAMs face with a high error rate in write operations due to stochastic switching. To alleviate this problem, Error-Correcting Codes (ECCs) are commonly used, which results in a significant area and energy consumption overhead. This paper proposes an efficient technique, so-called Adaptive Way Allocation for Reconfigurable ECCs (AWARE), to correct write errors in STT-RAM caches. AWARE exploits the asymmetric error rate in cell switching directions, which leads to data-dependent write error rates, to reduce the ECC overheads without compromising the reliability of the cache. To... 

The wear-out of flash-based Solid-State Drives (SSDs) is a main concern that significantly affects their reliability. One major parameter that accelerates SSD wear-out is the number of write-cycles committed to flash chips. The number of write-cycles in SSD-based disk subsystem is highly dependent on the erasure code implemented in Redundant Array of Independent Disks (RAIDs). In this paper, we investigate the impact of erasure codes and the configuration of storage subsystems (i.e., the number of disks participated in the RAID array and stripe unit size) on the endurance of storage systems. The number of write-cycles is considered as a metric to evaluate the endurance of storage system. We... 

Spin-Transfer Torque Magnetic Random Access Memory (STT-MRAM) is a promising alternative to SRAM in cache memories. However, STT-MRAMs face with high probability of write errors due to its stochastic switching behavior. To correct the write errors, Error-Correcting Codes (ECCs) used in SRAM caches are conventionally employed. A cache line consists of several codewords and the data bits are selected in such a way that the maximum correction capability is provided based on the error patterns in SRAMs. However, the different write error patterns in STT-MRAM caches leads to inefficiency of conventional ECC configurations. In this paper, first we investigate the efficiency of ECC configurations... 

Absolutely maximally entangled (AME) states are pure multi-partite generalizations of the bipartite maximally entangled states with the property that all reduced states of at most half the system size are in the maximally mixed state. AME states are of interest for multipartite teleportation and quantum secret sharing and have recently found new applications in the context of high-energy physics in toy models realizing the AdS/CFT-correspondence. We work out in detail the connection between AME states of minimal support and classical maximum distance separable (MDS) error correcting codes and, in particular, provide explicit closed form expressions for AME states of n parties with local... 

In Part I, a new internally coded time hoping optical code division multiple access (TH/OCDMA) scheme for fiber optic communication systems has been proposed and its multiple access performance has been evaluated using optical orthogonal code (OOC). Due to low cardinality of OOCs with a correlation value of 1, the capability of the proposed scheme could not be utilized effectively for an increasing number of simultaneous users. In this part, we consider applying the internally coded technique introduced in part one to the frame time hopping/OCDMA scheme. We evaluate the multiple access performance of the system for the three detectors introduced in Part I. Our results demonstrate the... 

Recently, a lot of research has been done on compressed sensing, capturing compressible signals using random linear projections to a space of radically lower dimension than the ambient dimension of the signal. The main impetus of this is that the radically dimension-lowering linear projection step can be done totally in analog hardware, in some cases even in constant time, to avoid the bottleneck in sensing and quantization steps where a large number of samples need to be sensed and quantized in short order, mandating the use of a large number of fast expensive sensors and A/D converters. Reconstruction algorithms from these projections have been found that come within distortion levels... 

We consider a combined time-hopping (TH) and spread-time (ST) multiple-access technique that uses an internal code. In this method, the duration of each bit is divided into Ns frames. The outputs of the encoder and a pseudorandom (PN) sequence specify the number of the frame in which the data bit is transmitted in ST code-division multiple-access (ST-CDMA) form using the second PN sequence. We consider the correlator receiver, followed by the channel decoder. We obtain the performance of the combined method in additive white Gaussian noise (AWGN) and fading channels in the presence of multiple-access interference (MAI) and narrowband interference (NBI). We also consider the conventional...