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Wide-band Characterization of Multi-Layer Coding Techniques to Achieve Electromagnetic Resilient Communication Networks
In this article, symbol diversity is presented for the pulse amplitude modulation PAM-4 encoding scheme. This technique is implemented in order to incorporate electromagnetic resilience in a triple modular redundant communication channel that is subjected to electromagnetic disturbances in reverberant environments. An in-depth numerical study is carried out in light of new electromagnetic disturbance condition monitoring definitions that provide a better insight into the actual state of the system. An explanation of the different fault mechanisms based on the new definitions is provided for the proposed PAM-4 symbol diversity setup and is compared with an undiverse PAM-4 system with a two-out-of-three majority voter. The results show that the proposed symbol diversity technique is quite an effective measure for incorporating fault tolerance in the system design.
In this paper, time diversity is used as a technique
to achieve EM resilience in a redundant communication channel
that is subjected to multi-frequency electromagnetic disturbances.
The geometry under study is subjected to strong incident fields
consisting of random angles of incidence and polarizations. Time
diversity is used as a measure to achieve fault tolerance in
the system. The effects of a multi-harmonic Electromagnetic
Interference (EMI) on the functional transmission signal inside a
redundant three-channel system with time diversity is compared
to the base case with no time diversity.
The study shows that time diversity proves to be quite an
effective measure to incorporate fault tolerance in redundant
systems which are interfered by multi-frequency disturbances.
The results reflect a clear improvement in performance in terms
of the Bit Error Rates (BERs). Furthermore, results show that
time diversity when suitably employed for a particular EMI
disturbance can lead to optimal improvement in performance.
Redundancy techniques based on the combination of multiple diverse communication channels are an established countermeasure to improve performance characteristics of wireless communication systems. Besides parallel redundancy in the space and frequency domain, serial redundancy in the time domain can be utilized. It is known that the parallel approaches can significantly improve performance characteristics like jitter and reliability, when applied for wireless packet-based data transmission. In this work, an investigation on the performance impact of additional time diversity on top of the parallel redundancy approaches is performed. An OPNET simulation model is created and analysed for its performance characteristics.
An M-FSK modulation and time-diversity permutation coding scheme for narrow-band power-line communications combined with the soft-decision technique is investigated in this paper. A process to identify the errors caused by impulse noise and narrow-band interference, and to mitigate the error effects is proposed. We further present a permutation decoding algorithm and a majority-logic decoding process to correct the remaining additive errors. Due to its simplicity and low encoding/decoding complexities, this scheme therefore can be suitable for a simple but robust narrow-band power-line communications system of practical interest.
A new method for the numerical simulation of the stochastic electromagnetic environment of a mode-stirred chamber is presented in this paper. This method is based on the plane-wave integral representation for the fields and uses a Monte Carlo simulation to replace the analytical integration by numerical summation. Therefore, a field generator is implemented as a program. The numerically generated field distributions and spatial correlation functions are compared to the analytical solutions for the validation of the field generator. With this generator, the field coupling to a simple transmission-line structure can be numerically simulated. The coupled current or voltage has to be regarded as a stochastic value as well, and therefore, parameters like the mean value and the standard deviation along the line are calculated. For the special case of a matched line, an analytic solution is introduced in order to validate the numerical results. The simulation also allows for investigating the statistical distribution and correlation of the coupled current along the transmission line. Numerous simulated results are compared with measurements.
Daily mitigation of and planning for intentional or unintentional EMI should be a part of a medical facilities ongoing spectrum management just as annual condition and risk assessments are performed at other facilities. A reasonable supply of spare electronic components should be stored safely on site and readily available (network switches, wireless access points, disks, computers, instrumentation). Although some planning can rely on good-faith compliance, protection and planning for noncompliance and electronic device failure is a necessity.
In this paper we discuss the condition assessment
definitions previously used to analyze the effectiveness of EMI
detectors/correctors. It is shown that those definitions do not
resemble the correct condition and an expansion is needed. New
expanded condition assessment definitions are presented and
evaluated in comparison with the old ones for a two out of three
majority voter system used in an EM diverse system. The new
definitions provide a better insight into the effectiveness of EMI
detectors on its own or in correctors. We also discuss the use of
the new definitions in a multi-layer error detection and correction
system.
This article investigates the effectiveness of frequency diversity, the usage of three different frequencies inside a triple modular redundant data transmission system, to cope with harsh electro-magnetic disturbances. Such a triple modular redundant system uses three different data channels to transmit data after which majority voting is applied to conclude one final output. Using a Monte-Carlo based simulation framework calculates the influence of harsh electromagnetic disturbances on the communication channel. The bit error rate and the amount of undetectable dangerous failures are calculated, and serve as a quality measure for our study. In addition, this article describes a semianalytical model that implements the critical factors that are necessary to get comparable results to the Monte-Carlo simulation framework, with less computational effort. To find the bit frequencies that optimize the bit error rate (BER), and minimize the amount of dangerous failures, a sweep is performed over two out of three data frequencies while fixing the third data frequency, and the electromagnetic interference (EMI) frequency. Notable relationships are recognized in the visual results and further studied. This results in six equations visualizing the relationships between the data and EMI frequencies. Finally, three equations predict the prospective BER, and undetectable failures, which is confirmed using the Monte-Carlo simulation framework.
Modern safety-critical systems rely heavily on robust communication channels. Even though these communication channels can be protected by error detection and correction codes, vulnerabilities caused by false negatives still exist. These false negatives can be caused by harsh electromagnetic disruptions and are detrimental to overall safety. This article considers the construction and structure of triplication-based error correction codes to find the most electromagnetic interference (EMI)-resilient code. Each code is tested and simulated in terms of the occurrence rate of false negatives under single-frequency disturbances. It is found that a code with inversion is significantly more robust to these disturbances. Furthermore, a systematic fault injection is also performed to search for vulnerabilities within the code itself. The systematic approach allows us to reverse engineer the expected vulnerabilities to real-world disturbances.
In this paper, different techniques and measures are described and discussed that are effective to reduce risks related to electromagnetic disturbances in mission- or safety-critical systems. The aim of these techniques and measures is to make a system EMI-resilient or fault-tolerant with respect to EMI. Whenever a fault occurs within the system, the techniques and measures should either allow that the system continues to work in a safe manner (possibly with reduced performance) or trigger that the system is switched to a safe-state. The techniques and measures align with the well-proven techniques and measures described in IEC 61508, the main standard in the field of Functional Safety. It is described how they have to be modified or optimized to be effective for EMI. At the end of the paper, the use of inversion and spatial diversity is studied in more detail, thereby giving guidance on possible pitfalls.
In the most recent IET Guide on ElectroMagnetic Compatibiliy (EMC) for Functional Safety [1], diverse redundancy is indicated as one of the techniques to cope with the effects ElectroMagnetic (EM) disturbances within safety-or mission-critical applications. Unfortunately, up to now, little or no research is available on how to implement such EM-diverse redundant system. This paper studies the effectiveness of spatial diversity to cope with EM disturbances caused by strong incident fields under reverberation room conditions. Here, reverberation room conditions refers to the situation where multiple plane waves are incident onto the system-under-study, each with a random angle-of-incidence, polarization and phase. Four different geometries are compared: a non-redundant system comprising a single trace on a PCB, a redundant system comprising three parallel traces on a single PCB, a redundant system comprising three non-parallel traces on a single PCB, and a redundant system comprising three differently oriented PCBs. A reciprocity-based technique is used to efficiently calculate the induced voltages and the resulting bit error probability in the different geometries. It is shown that only when using three differently oriented PCBs a significant reduction in the bit error probability is obtained.
Safety depends on 4 factors, anyone of which can cause problems:A)
The users of the system.
B)
Software.
C)
Hardware.
D)
The physical environment in which the system is used.
The author was led to the study given in this paper from a consideration of large scale computing machines in which a large number of operations must be performed without a single error in the end result. This problem of “doing things right” on a large scale is not essentially new; in a telephone central office, for example, a very large number of operations are performed while the errors leading to wrong numbers are kept well under control, though they have not been completely eliminated. This has been achieved, in part, through the use of self-checking circuits. The occasional failure that escapes routine checking is still detected by the customer and will, if it persists, result in customer complaint, while if it is transient it will produce only occasional wrong numbers. At the same time the rest of the central office functions satisfactorily. In a digital computer, on the other hand, a single failure usually means the complete failure, in the sense that if it is detected no more computing can be done until the failure is located and corrected, while if it escapes detection then it invalidates all subsequent operations of the machine. Put in other words, in a telephone central office there are a number of parallel paths which are more or less independent of each other; in a digital machine there is usually a single long path which passes through the same piece of equipment many, many times before the answer is obtained.
In this paper, an efficient reciprocity-based algorithm is proposed to predict the worst-case voltages and currents induced by an external plane wave at the ports of a multi-transmission line system by means of full-wave EM simulations. The proposed algorithm consists of two main steps. In the first step, the far-field radiation of the multi-transmisson line system is fully characterized by a mimimal set of full-wave simulations. In the second step, this information is used to efficiently evaluate the induced voltages and currents by a plane wave with arbitrary angles of incidence and polarization after which their worst-case can be found easily. The main novelty of the proposed algorithm is that no new full-wave simulations are required if different sets of terminations at the ports of the MTL system are considered. Both single port as well as common/differential mode voltages and currents are considered.
One of the proposed techniques for meeting the severe reliability requirements inherent in certain future computer applications is described. This technique involves the use of triple-modular redundancy, which is essentially the use of the two-out-of-three voting concept at a low level. Effects of imperfect voting circuitry and of various interconnections of logical elements are assessed. A hypothetical triple-modular redundant computer is subjected to a Monte Carlo program on the IBM 704, which simulates component failures. Reliability is thereby determined and compared with reliability obtained by analytical calculations based on simplifying assumptions.
Communication networks in the railway sector are critical to the operation of the system and have stringent requirements for reliability and safety. These types of networks are commonly characterized as “mission critical.” Further, rail communication networks have requirements for interoperability with legacy technology and long life cycle support. Many of the European railways operate trackside Global System for Mobile Communications-Railway (GSM-R) wireless networks; GSM-R is based on the GSM standard with railway-specific features. The railways have started to look at Long Term Evolution (LTE) as a potential future replacement system for GSM-R. This paper presents the role of communication networks in railway operations, the resulting unique requirements for mission critical rail networks, and current trends in railway telecommunications. A brief tutorial on GSM-R is provided. We then present the LTE network architecture and assess the suitability of LTE to meet the requirements of the railway sector, with a special focus on reliability. The paper focuses primarily on mainline rail networks; however, much of what is presented also is applicable to urban rail networks.
This paper provides analyses of three types of diversity combining systems in practical use. These are: selection diversity, maximal-ratio diversity, and equal-gain diversity systems. Quantitative measures of the relative performance (under realistic conditions) of the three systems are provided. The effects of various departures from ideal conditions, such as non-Rayleigh fading and partially coherent signal or noise voltages, are considered. Some discussion is also included of the relative merits of predetection and postdetection combining and of the problems in determining and using long-term distributions. The principal results are given in graphs and tables, useful in system design. It is seen that the simplest possible combiner, the equal-gain system, will generally yield performance essentially equivalent to the maximum obtainable from any quasi-linear system. The principal application of the results is to diversity communication systems and the discussion is set in that context, but many of the results are also applicable to certain radar and navigation systems.
A plane-wave integral representation is used to derive
spatial-correlation functions for the complex electric and magnetic
field components, and the results agree with previously published
results derived by volume averaging of a mode sum. Results are also
presented for the correlation functions of squared electric and magnetic
field components and electric, magnetic, and total energy densities. The
theory for the spatial correlation function of the squared transverse
electric field is shown to agree well with published measurements of the
power received by transverse monopole antennas
EMC testing and EMI mitigation for safety critical aerospace systems
- R J Perez
- I Majid
System-level hardware-based design techniques for EM Resilience: a necessity for safe and reliable programmable electronics
- J Lannoo