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Experimental validation of the usability of Wi-Fi over redundant paths for streaming phasor data
Abstract
Applications performing streaming of phasor-measurement data require low latency and losses from the communication network. Traditionally, such requirements are realized through wired infrastructure. Recently, wireless infrastructure has gained attention due to its low-cost and ease of deployment, but its poor quality-of-service is a strong deterrent for use in mission-critical applications. Recent studies have used measurements to explore the use of packet replication over redundant Wi-Fi paths, for obtaining the desired loss performance without hampering the end-to-end latency. However, these studies are done in a controlled, laboratory environment and do not reflect the real, in-field performance. In this paper, we perform extensive measurements using two co-located directional Wi-Fi links in a real-life setting, to experimentally validate the use of packet replication over Wi-Fi for streaming phasor data. In the setting that we evaluated, we find that the two channels are not fail-independent but the performance achieved with replication is very close to what it would be if they were to be independent. From the loss and latency statistics after replication, we conclude that replicating the phasor data over redundant Wi-Fi paths is a viable option for achieving the desired quality-of-service.
... As shown in recent literature, the adoption of seamless redundancy at the data-link layer of wireless networks improves their behavior significantly, under the basic assumption that disturbance and interference on physical channels are statistically independent. In [12] and [13], such a hypothesis was experimentally checked for redundant links based on real Wi-Fi equipment. While tangible improvements were achieved in typical operating conditions, channels were found not to be completely independent. ...
... Several proposals have appeared in the past few years where seamless redundancy is exploited in specific application scenarios. In [16], a hybrid wired-wireless redundancy scheme was envisaged to improve reliability in electrical substations, while redundant wireless paths were used in [12] for streaming phasor data over Wi-Fi. The IP parallel redundancy protocol (iPRP), introduced in [17], applies the same concepts to geographic networks for use with smart grids. ...
... As shown in [12] and [13], the most benefits can be obtained from seamless redundancy when phenomena that affect transmissions on distinct physical channels are completely independent. In this case, in fact, the probability that a packet is lost (or that it misses a certain deadline) on the redundant link can be obtained by multiplying the relevant probabilities, evaluated separately on each physical channel. ...
p>Reliability and determinism of Wi-Fi can be tangibly improved by means of seamless redundancy, to the point of making this technology suitable for industrial environments. As pointed out in recent papers, the most benefits can be achieved when no phenomena can simultaneously affect transmissions on all channels of a redundant link. In this paper, several aspects are analyzed which, if not properly counteracted, may worsen seamless redundancy effectiveness. Effects they cause on communication have been experimentally evaluated in real testbeds, which rely on commercial Wi-Fi devices. Then, practical guidelines are provided, which aim at preventing joint interference through a careful system design. Results show that measured communication quality can be made as good as expected in theory.</p
... As shown in recent literature, the adoption of seamless redundancy at the data-link layer of wireless networks improves their behavior significantly, under the basic assumption that disturbance and interference on physical channels are statistically independent. In [12] and [13], such a hypothesis was experimentally checked for redundant links based on real Wi-Fi equipment. While tangible improvements were achieved in typical operating conditions, channels were found not to be completely independent. ...
... Several proposals have appeared in the past few years where seamless redundancy is exploited in specific application scenarios. In [16], a hybrid wired-wireless redundancy scheme was envisaged to improve reliability in electrical substations, while redundant wireless paths were used in [12] for streaming phasor data over Wi-Fi. The IP parallel redundancy protocol (iPRP), introduced in [17], applies the same concepts to geographic networks for use with smart grids. ...
... As shown in [12] and [13], the most benefits can be obtained from seamless redundancy when phenomena that affect transmissions on distinct physical channels are completely independent. In this case, in fact, the probability that a packet is lost (or that it misses a certain deadline) on the redundant link can be obtained by multiplying the relevant probabilities, evaluated separately on each physical channel. ...
p>Reliability and determinism of Wi-Fi can be tangibly improved by means of seamless redundancy, to the point of making this technology suitable for industrial environments. As pointed out in recent papers, the most benefits can be achieved when no phenomena can simultaneously affect transmissions on all channels of a redundant link. In this paper, several aspects are analyzed which, if not properly counteracted, may worsen seamless redundancy effectiveness. Effects they cause on communication have been experimentally evaluated in real testbeds, which rely on commercial Wi-Fi devices. Then, practical guidelines are provided, which aim at preventing joint interference through a careful system design. Results show that measured communication quality can be made as good as expected in theory.</p
... As shown in recent literature, the adoption of seamless redundancy at the data-link layer of wireless networks improves their behavior significantly, under the basic assumption that disturbance and interference on physical channels are statistically independent. In [12] and [13], such a hypothesis was experimentally checked for redundant links based on real Wi-Fi equipment. While tangible improvements were achieved in typical operating conditions, channels were found not to be completely independent. ...
... Several proposals have appeared in the past few years where seamless redundancy is exploited in specific application scenarios. In [16], a hybrid wired-wireless redundancy scheme was envisaged to improve reliability in electrical substations, while redundant wireless paths were used in [12] for streaming phasor data over Wi-Fi. The IP parallel redundancy protocol (iPRP), introduced in [17], applies the same concepts to geographic networks for use with smart grids. ...
... As shown in [12] and [13], the most benefits can be ob- tained from seamless redundancy when phenomena that affect transmissions on distinct physical channels are completely independent. In this case, in fact, the probability that a packet is lost (or that it misses a certain deadline) on the redundant link can be obtained by multiplying the relevant probabilities, evaluated separately on each physical channel. ...
Reliability and determinism of Wi-Fi can be tangibly improved by means of seamless redundancy, to the point of making this technology suitable for industrial environments. As pointed out in recent papers, the most benefits can be achieved when no phenomena can simultaneously affect transmissions on all channels of a redundant link. In this paper, several aspects are analyzed which, if not properly counteracted, may worsen seamless redundancy effectiveness. Effects they cause on communication have been experimentally evaluated in real testbeds, which rely on commercial Wi-Fi devices. Then, practical guidelines are provided, which aim at preventing joint interference through a careful system design. Results show that measured communication quality can be made as good as expected in theory.
... Its performance could also be compromised if none of the links provide a sufficiently good quality by themselves. Recent studies have demonstrated that diversity and redundancy can improve the reliability of industrial wireless communications ( [8], [9]). These studies have focused to date on wireless communications between fixed nodes in a factory. ...
... This was confirmed in [10] where authors analyzed the performance of PRP over WiFi by means of simulations. Experimental studies were also presented in [8] and [9]. In [9], authors evaluate the reliability and latency achieved when streaming mission-critical phasor data is duplicated and transmitted over two independent IEEE 802.11b links. ...
... Experimental studies were also presented in [8] and [9]. In [9], authors evaluate the reliability and latency achieved when streaming mission-critical phasor data is duplicated and transmitted over two independent IEEE 802.11b links. The transmission takes place between two fixed transmitters and one receiver that integrates two wireless interfaces. ...
Factories are evolving into fully digitalized and networked structures for more adaptive and agile production ecosystems in the context of the Industry 4.0. Wireless communications will be a technical pillar of this evolution as it improves the reconfigurability of factories and the integration of mobile robots and objects. The integration of industrial wireless networks into the Industry 4.0 requires solutions capable to support highly reliable and deterministic low latency communications. This is particularly challenging for mobile industrial applications with constantly changing link quality conditions. This study experimentally evaluates for the first time the capacity of diversity and redundancy to improve the reliability and latency of wireless networks for mobile industrial applications. To this aim, a prototype is built in a collaborative robotics experimental facility. The prototype wirelessly connects a dual-arm robot and a mobile robot that collects and supplies components to the dual-arm robot. The prototype implements redundancy and diversity (using multipath TCP) for the wireless connections between both robots. The conducted trials show that both techniques improve the reliability of mobile industrial wireless communications even under the presence of interference. However, redundancy achieves lower latency levels and represents then the most attractive solution to support mobile industrial applications.
... Behavior, in terms of the fraction of frames delivered to destination correctly and timely, was experimentally shown to improve substantially. Similar approaches were proposed for streaming phasor measurements in smart grids [16]. ...
p>Seamless redundancy layered atop Wi-Fi has been shown able to tangibly increase communication quality, hence offering industry-grade reliability. However, it also implies much higher network traffic, which is often unbearable as the wireless spectrum is a shared and scarce resource. To deal with this drawback the Wi-Red proposal includes suitable duplication avoidance mechanisms, which reduce spectrum consumption by preventing transmission on air of inessential frame duplicates.
In this paper, the ability of such mechanisms to save wireless bandwidth is experimentally evaluated. To this purpose, specific post-analysis techniques have been defined, which permit to carry out such an assessment on a simple testbed that relies on plain redundancy and do not require any changes to the adapters' firmware. As results show, spectrum consumption decreases noticeably without communication quality is impaired. Further saving can be obtained if a slight worsening is tolerated for latencies.</p
... Behavior, in terms of the fraction of frames delivered to destination correctly and timely, was experimentally shown to improve substantially. Similar approaches were proposed for streaming phasor measurements in smart grids [16]. ...
p>Seamless redundancy layered atop Wi-Fi has been shown able to tangibly increase communication quality, hence offering industry-grade reliability. However, it also implies much higher network traffic, which is often unbearable as the wireless spectrum is a shared and scarce resource. To deal with this drawback the Wi-Red proposal includes suitable duplication avoidance mechanisms, which reduce spectrum consumption by preventing transmission on air of inessential frame duplicates.
In this paper, the ability of such mechanisms to save wireless bandwidth is experimentally evaluated. To this purpose, specific post-analysis techniques have been defined, which permit to carry out such an assessment on a simple testbed that relies on plain redundancy and do not require any changes to the adapters' firmware. As results show, spectrum consumption decreases noticeably without communication quality is impaired. Further saving can be obtained if a slight worsening is tolerated for latencies.</p
... Behavior, in terms of the fraction of frames delivered to destination correctly and timely, was experimentally shown to improve substantially. Similar approaches were proposed for streaming phasor measurements in smart grids [16]. ...
Seamless redundancy layered atop Wi-Fi has been shown able to tangibly increase communication quality, hence offering industry-grade reliability. However, it also implies much higher network traffic, which is often unbearable as the wireless spectrum is a shared and scarce resource. To deal with this drawback the Wi-Red proposal includes suitable duplication avoidance mechanisms, which reduce spectrum consumption by preventing transmission on air of inessential frame duplicates. In this paper, the ability of such mechanisms to save wireless bandwidth is experimentally evaluated. To this purpose, specific post-analysis techniques have been defined, which permit to carry out such an assessment on a simple testbed that relies on plain redundancy and do not require any changes to the adapters' firmware. As results show, spectrum consumption decreases noticeably without communication quality is impaired. Further saving can be obtained if a slight worsening is tolerated for latencies.
... However, the exploitation of different sources of diversity was identified as a promising enabler to achieve the challenging reliability and requirements [13]. One of these sources is multi-connectivity, which enables the transfer of redundant data through multiple wireless links belonging to the same radio-access technology (RAT) (either operating on licensed or unlicensed frequency bands [14]- [16]) or to different ones [17], [18]. Here, we focus on the former type of multi-connectivity leveraging 3GPP technologies by considering two active connections in the DL direction, i.e., DC towards terminals from two serving base stations. ...
Data duplication is studied as a fundamental enabler for ultra-reliable low-latency communication (URLLC) in fifth-generation cellular systems. It entails the simultaneous usage of multiple radio links delivering redundant data between a terminal and the network to boost the transmission reliability. However, the improved reliability comes at a cost of reduced spectral efficiency, since the transmission of multiple instances of the data message on different links occupies more radio resources as compared to sending only one instance using a single link. It is therefore crucial to improve the performance of data duplication schemes, with the aim of reducing the radio resource consumption without degrading the reliability gain provided by this transmission paradigm. In this paper, we propose several methods to increase the downlink URLLC capacity supported by data duplication in fifth-generation cellular networks based on the New Radio standard. A single-user analytical model is derived to evaluate a combination of the proposed enhancements. The most promising solution, namely selective data duplication upon failure which entails a massive reduction of the overall number of duplicate transmissions, is finally evaluated by means of extensive multi-user system-level simulation campaigns. The simulation results with background mobile broadband traffic show that, in the investigated scenario, the proposed solution with 4 Mbps offered URLLC traffic outperforms the baseline approach for data duplication with 1 Mbps offered URLLC traffic, thus increasing the amount of URLLC user equipments that can be effectively sustained by the network.
Seamless redundancy layered atop Wi-Fi has been shown able to tangibly increase communication quality, hence offering industry-grade reliability. However, it also implies much higher network traffic, which is often unbearable as the wireless spectrum is a shared and scarce resource. To deal with this drawback the Wi-Red proposal includes suitable duplication avoidance mechanisms, which reduce spectrum consumption by preventing transmission on air of inessential frame duplicates. In this paper, the ability of such mechanisms to save wireless bandwidth is experimentally evaluated. To this purpose, specific post-analysis techniques have been defined, which permit to carry out such an assessment on a simple testbed that relies on plain redundancy and do not require any changes to the adapters’ firmware. As results show, spectrum consumption decreases noticeably without communication quality is impaired. Further saving can be obtained if a slight worsening is tolerated for latencies.
Reliability and determinism of Wi-Fi can be tangibly improved by means of seamless redundancy, to the point of making this technology suitable for industrial environments. As pointed out in recent papers, the most benefits can be achieved when no phenomena can simultaneously affect transmissions on all channels of a redundant link. In this paper several aspects are analyzed which, if not properly counteracted, may worsen seamless redundancy effectiveness. Effects they cause on communication have been experimentally evaluated in real testbeds, which rely on commercial Wi-Fi devices. Then, practical guidelines are provided, which aim at preventing joint interference through a careful system design. Results show that measured communication quality can be made as good as expected in theory.
Reliable packet delivery within stringent delay constraints is of primal importance to industrial processes with hard real-time constraints, such as electrical grid monitoring. Because retransmission and coding techniques counteract the delay requirements, reliability is achieved through replication over multiple fail-independent paths. Existing solutions such as parallel redundancy protocol (PRP) replicate all packets at the MAC layer over parallel paths. PRP works best in local area networks, e.g., sub-station networks. However, it is not viable for IP layer wide area networks, a key element of emerging smart grids. Such a limitation on scalability, coupled with lack of security, and diagnostic inability, renders it unsuitable for reliable data delivery in smart grids. To address this issue, we present a transport-layer design: IP parallel redundancy protocol (iPRP). Designing iPRP poses non-trivial challenges in the form of selective packet replication, soft-state and multicast support. Besides unicast, iPRP supports multicast, which is widely using in smart grid networks. It duplicates only time-critical UDP traffic. iPRP only requires a simple software installation on the end-devices. No other modification to the existing monitoring application, end-device operating system or intermediate network devices is needed. iPRP has a set of diagnostic tools for network debugging. With our implementation of iPRP in Linux, we show that iPRP supports multiple flows with minimal processing and delay overhead. It is being installed in our campus smart grid network and is publicly available.
We describe the real-time monitoring infrastructure of the smart-grid pilot on the EPFL campus. We experimentally validate the concept of a real-time state-estimation for a 20 kV active distribution network. We designed and put into operation the whole infrastructure composed by the following main elements: (1) dedicated PMUs connected on the medium-voltage side of the network secondary substations by means of specific current/voltage transducers; (2) a dedicated communication network engineered to support stringent time limits and (3) an innovative state estimation process for real-time monitoring that incorporates phasor-data concentration and state estimation processes. Special care was taken to make the whole chain resilient to cyber-attacks, equipment failures and power outages. The achieved latency is within 65ms. The refresh rate of the estimated state is 20ms. The real-time visualization of the state estimator output is made publicly available, as well as the historical data (PMU measurements and estimated states). To the best of our knowledge, the work presented here is the first operational system that provides low-latency real-time state-estimation by using PMU measurements of a real active distribution network.
WLAN according to standard IEEE 802.11 is widely regarded unsuitable as communication channel for real-time and safety applications. Non-determinism and interference liability leads to packet loss, exceeded and variable latency times due to retransmissions. This work proposes a method that compensates such consequences of stochastic channel fading by the parallel operation of diverse wireless channels, applying frequency and space diversity techniques. A fault-tolerant wireless “black channel” is achieved that is able to fulfill soft real-time availability plus providing redundancy. This is realized with standard WLAN components and the “Parallel Redundancy Protocol” (PRP) according to IEC 62439-3. Reliability and performance characteristics are derived from measurements on an experimental setup with SafetyNET p nodes.
Applying multiple redundant and diverse communication channels is an established method to achieve an improved overall communication channel. When applied for packet-based data transmission over channels with strongly nondeterministic behaviour due to environmental influence, such as Wireless Communications, timing performance can be greatly improved by this approach. The central element in such a system is the so called “Combiner” on the receiving side. In this work, a new specific type named “Timing Combiner” is described. The Parallel Redundancy Protocol (PRP) according to IEC 62439-3 realizes such a Timing Combiner on the Ethernet level. In this work, an OPNET simulation model is created and analysed for its performance characteristics. Also a quantitative analysis of the effect of different interference models in an industrial environment is presented.
The "Parallel Redundancy Protocol" (PRP) according to IEC 62439-3 realizes active network redundancy by packet duplication over two independent networks that operate in parallel. It has been specifically designed for industrial networks to meet highest availability requirements. In case of a single network failure, seamless redundancy is provided for data communication between PRP nodes that are connected to both networks. However, PRP was designed as a layer 2 Ethernet protocol that is transparent to higher protocol layers. In its current version, PRP is not able to support IP routing. This is because an IP router would change the source MAC address field of the Ethernet header which is used by a PRP receiver node for duplicate detection. In this work we propose and discuss a novel approach that keeps the PRP duplicate identification information across IP router boundaries.
The application of the "Parallel Redundancy Protocol" (PRP) according to IEC 62439-3 with two diverse redundant wireless channels achieves an improved overall wireless communication channel. Performance parameter like jitter and reliability increase significantly compared to the single wireless channels. In this work, a series of measurements on a redundant setup with two parallel WLANs according to IEEE 802.11n in diverse configuration settings is conducted and the results presented. A Markov model for the parallel redundant system is developed and the analytical results compared against the measurements.
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.
Availability of automation networks can be increased by providing redundant links and nodes. Although many specifications of industrial Ethernet have been submitted to the International Electrotechnical Committee (IEC), they do not disclose methods to implement network redundancy. The IEC SC65C worked out a standard for implementing redundancy in switched Ethernet networks applicable to a variety of industrial networks, with different solutions depending on the grace time of the plant and on the level of redundancy desired. This paper describes IEC 62439's parallel redundancy protocol (PRP), a redundancy method applicable to hard real time systems, based on full duplication and parallel operation of two redundant networks. PRP nodes send on both networks at the same time, and receive from both, providing bumpless recovery. Duplicate discarding and management functions complement the standard.
Smart Grid is designed to integrate advanced communication/networking technologies into electrical power grids to make them “smarter”. Current situation is that most of the blackouts and voltage sags could be prevented if we have better and faster communication devices and technologies for the electrical grid. In order to make the current electrical power grid a Smart Grid, the design and implementation of a new communication infrastructure for the grid are two important fields of research. However, Smart Grid projects have only been proposed in recent years and only a few proposals for forward-looking requirements and initial research work have been offered in this field. No any systematic reviews of communication/networking in Smart Grids have been conducted yet. Therefore, we conduct a systematic review of communication/networking technologies in Smart Grid in this paper, including communication/networking architecture, different communication technologies that would be employed into this architecture, quality of service (QoS), optimizing utilization of assets, control and management, etc.
The design and simulation of coding schemes, medium access control (MAC), and link-layer protocols for future industrial wireless local area networks can be supported by some understanding of the statistical properties of the bit error patterns delivered by a wireless link (which is an ensemble of transmitter, channel, receiver, modems). The authors present results of bit error measurements taken with an IEEE 802.11-compliant radio modem in an industrial environment. In addition to reporting the most important results, they draw some conclusions for the design of MAC and link-layer protocols. Furthermore, they show that the popular Gilbert/Elliot model and a modified version of it are a useful tool for simulating bit errors on a wireless link, despite their simplicity and failure to match certain measured statistics.
A 21st century clean energy economy demands a 21st century electricity grid, yet the communication networks of many utilities today are ill-equipped for smart grid evolution.
This must-read text/reference presents an application-centric approach to the development of smart grid communication architecture and network transformation. The coverage includes in-depth reviews of such cutting-edge applications as advanced metering infrastructure, distribution automation, demand response, and synchrophasors as well as more traditional utility applications like SCADA systems. Providing detailed insights derived from the authors’ pivotal research on smart grid communications and extensive consulting experience, the book explains how electric power companies can transform their networks to best meet the challenges of tomorrow’s smart grids.
Topics and features:
• Examines a range of exciting utility applications made possible through smart grid evolution
• Describes the core-edge network architecture for smart grids, introducing the concept of wide area and field area networks (WANs and FANs)
• Explains how the network design paradigm for smart grids differs from that for more established data networks, and discusses network security in smart grids
• Provides an overview of communication network technologies for WANs and FANs, covering OPGW, PLC, and LTE and MPLS technology
• Investigates secure data-centric data management and data analytics for smart grids
• Discusses the transformation of a network from conventional modes of utility operation to an integrated network based on the smart grid architecture framework
This comprehensive and practical guide will be of great interest to all professionals engaged in the planning, operation, and regulation of smart grids. Students studying courses on smart grids will also find the book to be an invaluable resource.
Seamless redundancy can be profitably exploited to improve predictability of wireless networks, including IEEE 802.11. Packets are sent on two channels at the same time and duplicate copies are discarded by receivers. As long as behavior of channels is reasonably uncorrelated, both transmission latencies and the frame loss ratio improve noticeably. In this paper, such an assumption has been analyzed by means of experimental measurements carried out on real devices. Results confirm that, in typical operating conditions, independence reasonably holds.
Reliable packet delivery within stringent delay-constraints is of paramount importance to mission-critical computer applications with hard real-time constraints. Because retransmission and coding techniques counteract the delay requirements, reliability may be achieved through replication over multiple fail-independent paths. Existing solutions, such as the parallel redundancy protocol (PRP), replicate all packets at the MAC layer over parallel paths. PRP works best in local area networks. However, it is not viable for IP networks that are a key element of emerging mission-critical systems. This limitation, coupled with diagnostic inability and lack of security, renders PRP unsuitable for reliable data-delivery in these IP networks. To address this issue, we present a transport-layer solution: the IP parallel redundancy protocol (iPRP). Designing iPRP poses non-trivial challenges in the form of selective packet replication, soft-state and multicast support. iPRP replicates only time-critical unicast or multicast UDP traffic. iPRP requires no modifications to the existing monitoring application, end-device operating system or to the intermediate network devices. It only requires a simple software installation on the end-devices. iPRP has a set of diagnostic tools for network debugging. With our implementation of iPRP in Linux, we show that iPRP supports multiple flows with minimal processing-and-delay overhead. It is being installed in our campus smart-grid network and is publicly available.
A powerful approach to improve the performance of wireless communication is the parallel redundant transmission with dual-radio wireless devices. To further verify this approach in this work, an OPNET simulation is performed on a star-topology WNCS workcell with 30 sensor and actuator pairs that are equipped with dual-radios for parallel redundancy. The applied wireless simulation model is based on IEEE 802.11g (Wi-Fi) standard and a quantitative analysis of the effect of interference in an industrial environment, is presented. This study proved that parallel redundancy improves system performance under different interference environments.
A model of a burst-noise binary channel uses a Markov chain with two states G and B. In state G, transmission is error-free. In state B, the channel has only probability h of transmitting a digit correctly. For suitably small values of the probabilities, p, P of the B rA B transitions, the model simulates burst-noise channels. Probability formulas relate the parameters p, P, h to easily measured statistics and provide run distributions for comparison with experimental measurements. The capacity C of the model channel exceeds the capacity C(sym. bin.) of a memoryless symmetric binary channel with the same error probability. However, the difference is slight for some values of h, p, P; then, time-division encoding schemes may be fairly efficient.
Wireless data communications are becoming widespread in many industries, since they offer significant benefits over wired communications, including low cost installations, rapid deployment, easy user access, and mobility. At the same time, the use of wireless technologies in power system environments presents a number of security and reliability concerns. These concerns include the impact of noisy electrical environments on the wireless media, the reliability of the currently available commercial wireless equipment, the overloading of the available bandwidth (particularly during emergency conditions), and the security of communications. Utilities are therefore wisely skeptical and cautious about introducing wireless communications in their substations. Nonetheless, the potential advantages of wireless technologies cannot be ignored. The possible uses of wireless technologies in power system operations therefore should be analyzed to determine where wireless could be a viable and attractive alternative to wired solutions, and what additional development of wireless technologies are needed
This book is the set of lecture notes for a course given at EPFL. It contains all the material needed by an engineer who wishes to evaluate the performance of a computer or communication system.
Transmitting large packets over wireless networks helps to reduce header overhead, but may have an adverse effect on loss rate due to corruptions in a radio link. Packet loss in lower layers, however, is typically hidden from the upper protocol layers by link or MAC layer protocols. For this reason, errors in the physical layer are observed by the application as higher variance in end-to-end delay rather than increased packet loss rate. We study the effect of packet size on loss rate and delay characteristics in a wireless real-time application. We derive an analytical model for the dependency between packet length and delay characteristics. We validate our theoretical analysis through experiments in an ad hoc network using WLAN technologies. We show that careful design of packetization schemes in the application layer may significantly improve radio link resource utilization in delay sensitive media streaming under difficult wireless network conditions.
Assessment of Wireless Technologies in Substation Functions- Part II: Substation Monitoring and Management Technologies
- T Kropp