201 research outputs found
Dependability Assessment of NAND Flash-memory for Mission-critical Applications
It is a matter of fact that NAND flash memory devices are well established in consumer market. However, it is not true that the same architectures adopted in the consumer market are suitable for mission critical applications like space. In fact, USB flash drives, digital cameras, MP3 players are usually adopted to store "less significant" data which are not changing frequently (e.g., MP3s, pictures, etc.). Therefore, in spite of NAND flash's drawbacks, a modest complexity is usually needed in the logic of commercial flash drives. On the other hand, mission critical applications have different reliability requirements from commercial scenarios. Moreover, they are usually playing in a hostile environment (e.g., the space) which contributes to worsen all the issues. We aim at providing practical valuable guidelines, comparisons and tradeoffs among the huge number of dimensions of fault tolerant methodologies for NAND flash applied to critical environments. We hope that such guidelines will be useful for our ongoing research and for all the interested reader
Dependability Assessment of NAND Flash-memory for Mission-critical Applications
It is a matter of fact that NAND flash memory devices are well established in consumer market. However, it is not true that the same architectures adopted in the consumer market are suitable for mission critical applications like space. In fact, USB
flash drives, digital cameras, MP3 players are usually adopted to store "less significant" data which are not changing frequently (e.g., MP3s, pictures, etc.). Therefore, in spite
of NAND flash’s drawbacks, a modest complexity is usually needed in the logic of commercial flash drives. On the other hand, mission critical applications have different reliability requirements from commercial scenarios. Moreover, they are usually playing in a hostile environment (e.g., the space) which contributes to worsen all the issues.
We aim at providing practical valuable guidelines, comparisons and tradeoffs among the huge number of dimensions of fault tolerant methodologies for NAND flash applied to critical environments. We hope that such guidelines will be useful for our ongoing research and for all the interested readers
Error and Congestion Resilient Video Streaming over Broadband Wireless
In this paper, error resilience is achieved by adaptive, application-layer rateless channel coding, which is used to protect H.264/Advanced Video Coding (AVC) codec data-partitioned videos. A packetization strategy is an effective tool to control error rates and, in the paper, source-coded data partitioning serves to allocate smaller packets to more important compressed video data. The scheme for doing this is applied to real-time streaming across a broadband wireless link. The advantages of rateless code rate adaptivity are then demonstrated in the paper. Because the data partitions of a video slice are each assigned to different network packets, in congestion-prone wireless networks the increased number of packets per slice and their size disparity may increase the packet loss rate from buffer overflows. As a form of congestion resilience, this paper recommends packet-size dependent scheduling as a relatively simple way of alleviating the buffer-overflow problem arising from data-partitioned packets. The paper also contributes an analysis of data partitioning and packet sizes as a prelude to considering scheduling regimes. The combination of adaptive channel coding and prioritized packetization for error resilience with packet-size dependent packet scheduling results in a robust streaming scheme specialized for broadband wireless and real-time streaming applications such as video conferencing, video telephony, and telemedicine
A Comparative Analysis of ASCII and XML Logging Systems
This research compares XML and ASCII based event logging systems in terms of their storage and processing efficiency. XML has been an emerging technology, even for security. Therefore, it is researched as a logging system with the mitigation of its verbosity. Each system consists of source content, the network transmission, database storage, and querying which are all studied as individual parts. The ASCII logging system consists of the text file as source, FTP as transport, and a relational database system for storage and querying. The XML system has the XML files and XML files in binary form using Efficient XML Interchange encoding, FTP as transport using both XML and binary XML, and an XML database for storage and querying. Further comparisons are made between the XML itself and binary XML, as well as binary XML to ASCII text when comparing file sizes and transmission efficiency. XML itself is a poor choice for hard drive and network transport time compared to ASCII. However, in a binary form, it uses less hard drive space and network resources. Because no XML databases support a binary XML, it is loaded without any optimization. The ASCII loads into the relational database with less time than XML into its database. However, querying each database, neither outperforms the other as one query results in shorter time for one, and another query results in a shorter time for the other. Therefore, XML and/or its binary form, is a viable candidate for use as a comprehensive logging system
Design and Optimization of Adaptable BCH Codecs for NAND Flash Memories
NAND flash memories represent a key storage technology for solid-state storage systems. However, they suffer from serious reliability and endurance issues that must be mitigated by the use of proper error correction codes. This paper proposes the design and implementation of an optimized Bose-Chaudhuri-Hocquenghem hardware codec core able to adapt its correction capability in a range of predefined values. Code adaptability makes it possible to efficiently trade-off, in-field reliability and code complexity. This feature is very important considering that the reliability of a NAND flash memory continuously decreases over time, meaning that the required correction capability is not fixed during the life of the device. Experimental results show that the proposed architecture enables to save resources when the device is in the early stages of its lifecycle, while introducing a limited overhead in terms of are
A survey of digital television broadcast transmission techniques
This paper is a survey of the transmission techniques used in digital television (TV) standards worldwide. With the increase in the demand for High-Definition (HD) TV, video-on-demand and mobile TV services, there was a real need for more bandwidth-efficient, flawless and crisp video quality, which motivated the migration from analogue to digital broadcasting. In this paper we present a brief history of the development of TV and then we survey the transmission technology used in different digital terrestrial, satellite, cable and mobile TV standards in different parts of the world. First, we present the Digital Video Broadcasting standards developed in Europe for terrestrial (DVB-T/T2), for satellite (DVB-S/S2), for cable (DVB-C) and for hand-held transmission (DVB-H). We then describe the Advanced Television System Committee standards developed in the USA both for terrestrial (ATSC) and for hand-held transmission (ATSC-M/H). We continue by describing the Integrated Services Digital Broadcasting standards developed in Japan for Terrestrial (ISDB-T) and Satellite (ISDB-S) transmission and then present the International System for Digital Television (ISDTV), which was developed in Brazil by adopteding the ISDB-T physical layer architecture. Following the ISDTV, we describe the Digital Terrestrial television Multimedia Broadcast (DTMB) standard developed in China. Finally, as a design example, we highlight the physical layer implementation of the DVB-T2 standar
High Speed S-band Communications System for Nanosatellites
3Cat-3 is a nanosatellite based on the 6 unit cubesat standard. Its payload is an optical multispectral imager that imposes stringent downlink requirements for a nanosatellite. This TFG is based on the experience gained in 3Cat-1 and 3Cat-2 communications systems to develop a "high speed" (goal >= 5 Mbps) downlink for nanosatellites based on the TI CC3200.In order to accomplish the objectives of the next generation of nanosatellites high-speed downlinks have to be designed. This goal faces stringent design constraints as nanosatellites are limit in power, processing capabilities and dimensions. In the quest for higher bit rates the widely used VHF band has to be replaced for higher frequency bands and the link budged margin tightened, decreasing the SNR at reception. The proposed solution uses COTS 2.4 GHz WiFi adapters as transceivers. Range limitations imposed by the default 802.11 mode of operation are bypassed by using packet forging and injection at transmission jointly with monitor mode at reception. A loss-resilient unidirectional downlink is achieved by using application-layer encoding by means of LPDC-Staircase codes. This solution has been already implemented in 3CAT-2, a 6 unit cubesat GNSS-R mission to be launched in July 2016. In addition, bursts of errors are combated by using Reed-Solomon. The system has been tested under Doppler shift and scintillation effects, and a 188Km link between Barcelona and Mallorca has been performed, showing satisfactory results
The design and use of a digital radio telemetry system for measuring internal combustion engine piston parameters.
During the course of this project, a digital radio telemetry system has been
designed and shown to be capable of measuring parameters from the piston of
an internal combustion engine, under load. The impetus for the work stems
from the need to sample the appropriate data required for oil degradation
analysis and the unavailability of system to perform such sampling.
The prototype system was designed for installation within a small Norton
Villiers C-30 industrial engine. This choice of engine presented significant
design challenges due to the small size of the engine (components and
construction) and the crankcase environment. These challenges were manifest
in the choice of carrier frequency, antenna size and location, modulation
scheme, data encoding scheme, signal attenuation, error checking and
correction, choice of components, manufacturing techniques and physical
mounting to reciprocating parts. In order to overcome these challenges detailed
analysis of the radio frequency spectrum was undertaken in order to minimise
attenuation from mechanisms such as, absorption, reflection, motion, spatial
arrangement and noise.
Another aspect of the project concerned the development of a flexible modus
operandi in order to facilitate a number of sampling regimes. In order to
achieve such flexibility a two-way communication protocol was implemented
enabling the sampling system to be programmed into a particular mode of
operation, while in use. Additionally the system was designed to accommodate
the range of signals output from most transducer devices.
The sampling capabilities of the prototype system were extended by enabling
the system to support multiple transducers providing a mixture of output
signals; for example both analogue and digital signals have been sampled.
Additionally, a facility to sample data in response to triggering stimuli has been
tested; specifically a sampling trigger may be derived from the motion of the
piston via an accelerometer.
Ancillary components, such as interface hardware and software, have been
developed which are suitable for the recording of data accessed by the system.
This work has demonstrated that multi-transducer, mixed signal monitoring of
piston parameters, (such as temperature, acceleration etc.) using a two-way,
programmable, digital radio frequency telemetry system is not only possible
but provides a means for more advanced instrumentation
REAL TIME MICROPROCESSOR TECHNIQUES FOR A DIGITAL MULTITRACK TAPE RECORDER
Transport properties of a standard compact - cassette tape
system are measured and software techniques devised to configure
a low - cost,direct digital recording system.
Tape - velocity variation is typically ± 10% of standard speed
over tape lengths of 5 µm.with occasional variations of ±40%.
Static tape - skew can result due to axial movement of the tape
reel when it spools.Dynamic tape skew occurs and is primarily
caused by tape - edge curvature with a constant contribution
due to the transport mechanism.Spectral skew components range
from 0.32 Hz to 8 Hz with magnitude normally within one 10 kbit/
sec- bit cell.The pinch roller works against the friction of the
tape guides to cause tape deformation.Average values of tape
deformation are 0.67 µm,0.85 µm and 1.08 µm for C60,C90 and
C120 tape respectively.
Parallel,software encoding / decoding algorithms have been
developed for several channel codes.Adaptive software methods
permit track data rates up to 3.33 k bits/sec in a rnultitrack
system using a simple microcomputer.For a 4 - track system,raw
error rates vary from 10ˉ⁷ at 500 bits/sec/track to 10ˉ⁵ at 3.33
kbits/sec/track.Adaptive software reduces skew - induced errors
by 50%.A skew - correction technique has been developed and
implemented on an 8 - track system at a track data rate of 10 k
bits/sec.
Real - time error correction gives a theoretical corrected
error rate of 10ˉ¹¹for a raw error rate of 10ˉ⁷. Multiple track
errors can cause mis - correction and interleaving is advised.
Software algorithms have been devised for Reed - Solomon code.
With a more powerful microprocessor this code m ay be combined
with the above techniques in a layered error-correction scheme.
The software techniques developed may be applied to N tracks
with an N - bit computer.Recording density may be increased by
using thin - film,multitrack heads and a faster computer.British Broadcasting Corporatio
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