Guest Editorial: The Future of Wi-Fi and Wireless Technologies in Unlicensed Spectra

Importance of spectrum regulation and management was first revealed on May of 1985 after the release of unlicensed ISM bands resulting in emergence of Wi-Fi, Bluetooth and many other wireless technologies that has affected our daily lives by enabling the emergence of the smart world and IoT era. Today, the idea of a liberated spectrum is circulating around, which can potentially direct wireless networking industry into another revolution by enabling a new paradigm in intelligent spectrum regulation and management. The RF signal radiated from IoT devices as well as other wireless technologies create an RF cloud causing co- and cross-interference to each other. Lack of a science and technology for understanding, measurement, and modeling of the RF cloud interference in near real-time results in inefficient utilization of the precious spectrum, a unique natural resource shared among all wireless devices of the universe in frequency, time, and space. Near real time forecasting of the RF cloud interference is essential to pursue the path to the optimal utilization of spectrum and a liberated spectrum management. This paper presents a historical perspective on the evolution of spectrum regulation and management, explains the diversified meanings of interference for different sectors of the wireless industry, and presents a path for implementing a theoretical foundation for interference monitoring and forecasting to enable the emergence of a liberated spectrum industry and a new paradigm in spectrum management and regulations.

The articles in this special section focus on the deployment of Long Term Evolution in unlicensed spectrum. These articles cover various design issues such as network architecture, protocol development, network coexistence, unlicensed spectrum access, and practical implementation. Fifth generation (5G) cellular networks will face a rigorous challenge in the ever increasing data rate requirement. To meet such anticipated data growth demand, the industry and academia have developed many cutting edge techniques to improve spectrum utilization. However, the scarcity of spectral resources is still a fundamental bottleneck for network capacity enhancement. Recently, the rich available bandwidth on the 5.8 GHz unlicensed national information infrastructure (U-NII) spectrum has stimulated substantial interest from cellular operators to use the unlicensed spectrum for LTE. In 2015, the LTE-Unlicensed (LTE-U) Forum formally launched the LTE-U specification, and the Third Generation Partnership Project (3GPP) has pushed the standardization of licensed assisted access (LAA)into its Releases 13 and 14. However, the LTE-U technology is still in its infancy, and there are lots of challenges that need to be solved, such as network coexistence among different radio access technologies, unlicensed spectrum sharing and access, and quality of service (QoS) provision on unlicensed spectrum. This Feature Topic aims to provide a comprehensive overview of this appealing technology, harmonizing recent results and key challenges, as well as highlighting future important directions.

Current and planned solutions used in the ICT infrastructure are largely based on Photonic and RF Communications Systems. Rapid advances in photonic and RF photonic technologies have significantly accelerated the introduction of these new technologies in access storage, backbone and grid networks, defining and building the rules to ensure transfer of multi Tera-bit volumes of data. The purpose of this volume is to provide a vehicle for directing research in this area from multiple lenses in the selected areas of investigation. Following an introduction by the editors, reviews of research will be clustered into two sections. The first part of this Special Issue focuses on the Photonic and RF Communications systems technologies and this Section comprises 7 articles. Recent solutions in wideband and multi-band RF circuits are presented in the articles 7 through 9 in the second part of the Special Issue. The first article, by Arash Bahrami , et al., present an experimental evaluation of a radio-over-fiber system. In the paper, the authors proposed an optical microwave radio-over-fiber system in which an integrated dual-parallel Mach-Zehnder modulator is biased at the maximum transmission biasing point. The authors consider the two following modulation schemes: binary phase shift keying (BSK) and quadrature phase shift keying (QPSK) over fiber spans of 10 and 25 km of standard single mode fiber. The obtained results show that the second order sideband of optical microwave has the potential to provide error-free transmission for BPSK and QPSK. John S. Vardakas , et al. in the next article, analyse the delay of converged Wavelength Division Multiplexing Ethernet Passive Optical Network and WiMax networks. In such access networks, the provision of Quality of Service (QoS) support is a challenging issue, mainly due to the different bandwidth allocation mechanisms of the two access technologies. In the paper, the authors analyse the delay performance by considering multiple service-classes with different priorities. The proposed analytical model allows the calculation of the average end-to-end packet delay of each service-class as the sum of the queuing delay in both domains. The accuracy of the analysis was verified by simulation. Ioannis Mamounakis , et al., propose a novel traffic prediction method to minimize packet delay in Ethernet Passive Optical Networks. The authors utilise traffic information to predict the accumulated burst size of each respective optical network unit in the following cycle. The paper demonstrates and proves that a significant delay enhancement can be accomplished by reporting the predicted burst size, rather than the current one, to the Optical Line Terminal (OLT). The simulation experiments carried out by the authors show that a significant decrease in the delay can be obtained without any changes to the dynamic bandwidth assignment scheme at the OLT. The paper by Mariusz Głąbowski , et al. proposes an analytical model of a multi-service switching network with overflow links with finite capacity in the first stage of the network. This model can be used to evaluate the QoS parameters which are closely interrelated with the method of operation of the large capacity optical nodes. The proposed method allows their traffic capacity to be increased through a significant decrease in the phenomenon of internal blocking in switching networks which is the basic element of the node. The proposed calculation method is validated by the authors via simulation. Aboagela Dogman , et al. present an integrated QoS management process for multimedia traffic in wire and wireless networks. In the proposed process, the statistics of traffic are determined and then used as an input to a fuzzy interface system (FIZ). FIZ allows the traffic to be accurately sampled and this traffic is in the next step pre-processed using a fuzzy c-means (FCM). FIZ identifies clusters representing poor, average and good QoS. This information is then used in a multilayer perceptron neural network to assess the overall QoS for multimedia traffic. The authors showed that the developed adaptive statistical sampling represents traffic more correctly than systematic, stratified and random non-adaptive sampling methods. The article by Adam Kaliszan , et al. provides a generalised convolution algorithm for modelling state-dependent systems. This model corresponds to the system that uses one or many physical resources, e.g. one or a set of lambda channels in DWDM optical networks. The proposed calculation method can be used for the analysis and dimensioning of optical networks and systems. This method is also useful for an optical system in which advanced traffic management mechanism have been applied, e.g. bandwidth reservation or threshold mechanism. The accuracy of the proposed model is validated by simulation experiments. From their onset RF Communications Systems have been critical to the development of ICT infrastructure. In mobile and satellite communication systems, wideband and multi-band RF circuits are important for achieving high-date wireless transmission and supporting a large number of standards (e.g. UMTS, WiFi, WiMAX, or LTE). A wideband or multi-band RF circuit can replace a number of single-band RF circuits, leading to a significant reduction of size, weight and cost of modern wireless systems. There have been a great number of recent developments in the above areas over the past years. The articles that outline these solutions are in the latter part of this Special Issue, i.e. comprise articles from Article 7 through Article 9. The article by Bingo Wing-Kuen Ling , et al. discusses the frequency spectrum of a pulse for ultra wideband impulse radio systems as the frequency response of a real valued causal rational infinite impulse response filter. The pulse design problem is formulated as a functional inequality constrained optimization problem that can be solved by the method proposed by the authors. This pulse can be generated via an excitation of a simple circuit. Numerical simulation results confirm that the energy compaction performance defined in the frequency domain of the proposed pulse outperforms that of existing pulses. It is worth emphasizing that the pulse can be generated via an excitation of a simple circuit. In their article, Xue Li and , et al. present the WiFi leakage problem that appears in the users' equipment that simultaneously use both LTE and WiFi technologies. The authors propose WiFi leakage detection algorithms for successful detection of the weak WiFi leakage in the presence of both LTE signal and Gaussian noise. The algorithms include energy ratio detection, entropy ratio detection and cyclostationary detection based on spectral correlation function. The effectiveness and efficiency of the proposed WiFi leakage detection techniques have been confirmed by simulations performed for different scenarios. The article by Piotr Remlein discusses the performance of Intelligent Transportation Systems (ITS) that consists of satellite mesh networks. In the paper the author analyses a new power-limited and energy-efficient systems employing coded continuous phase modulation signals and with multiuser Frequency Division Multiplexed transmission. The results obtained by the author show that good performance of the proposed solution can be achieved by reducing the inter-carrier frequency spacing and using simple iterative ICI cancellation algorithm at the receiver. Based on the results, it can be concluded that this system might constitute a desirable option in ITS satellite mesh, ad-hoc networks. The objective of this Special Issue is to bring together the state-of-the-art research contributions that address challenges in emerging devices and architecture for photonic systems and RF circuits for wideband and multi-band communications systems. Due to the complexity and scope of the subject area, the set of articles presented attempts to address only some selected relevant issues. The Guest Editors believe though that the contributions included in the Special Issue will inspire the research activities of leading authors and scholars worldwide. The Guest Editors also expect this Special Issue to provide insight into the questions that they address as the presented articles expose important contributions to each of the relevant subject areas. Piotr Zwierzykowski received MSc and PhD (Hons) degrees in telecommunications from Poznan University of Technology, Poland, in 1995 and 2002, respectively. Since 1995 he has been working at the Poznan University of Technology, where he is currently an Assistant Professor. Piotr Zwierzykowski is the author, or co-author, of over 200 journals and conference publications and three books in the area of computer and communication networks. His research covers modelling and dimensioning of optical networks, teletraffic engineering and routing. He is a Senior Member of IEEE and the Secretary in the IEICE Europe Section. Steven Gao received a PhD degree from Shanghai University, P.R. China. He is a Professor and Chair in RF and Microwave Engineering at University of Kent, UK. His research covers smart antennas, satellite antennas, phased arrays, RF and microwave circuits (power amplifiers), satellite communications, UWB radars, synthetic-aperture radars and mobile communications. From 2007 to 2012, he was a Senior Lecturer and Head of Space Antennas and Microwave System Group at Surrey Space Centre, University of Surrey, UK. He has two books including “Space Antenna Handbook” (Wiley, 2012) and “Circularly Polarized Antennas” (IEEE-Wiley, 2014), published over 200 papers and holds several patents in smart antennas and RF. He is an IEEE AP-S Distinguished Lecturer and a Chair of LAPC 2013. He is an Invited Speaker at IWAT'2014 (Sydney), SOMIRES'2013 (Japan), APCAP'2014 (China), etc. He is an Associate Editor of Radio Science and the Editor-in-Chief for Wiley Book Series on "Microwave and Wireless Technologies". He is a Fellow of the IET. Wai Pang Ng received his BEng (Hons) Communication and Electronic Engineering and IEE Prize from Northumbria University, UK and PhD in Electronic Engineering from University of Wales Swansea, UK in 1997 and 2001, respectively. He is a Reader of Optical Communications at Northumbria University. From 2001 to 2004, he was a Senior Networking Software Engineer at Intel Corporation, before starting his academic career at Northumbria University. He has published over 80 journals and conference publications in the area of optical switching, optical signal processing and radio-over-fiber. He is a Chartered Engineer of the Engineering Council UK and a Senior Member of the IEEE. Currently he serves as the Chair of the IEEE UK&RI Communication Chapter. He was also the Co-Chair of the Signal Processing for Communications Symposium in IEEE International Conference on Communications (ICC) 2009 (Dresden, Germany) and now serves as the Publicity Chair of ICC 2015 in London. Zuqing Zhu received a PhD degree from the Department of Electrical and Computer Engineering, University of California, Davis, in 2007. From July 2007 to January 2011, he worked in the Service Provider Technology Group of Cisco Systems, San Jose, as a senior R&D engineer. In January 2011, he joined the University of Science and Technology of China (USTC), where he is currently an Associate Professor. He has published more than 100 papers in peer-reviewed journals and conferences. He has been in the technical program committees (TPC) of INFOCOM, ICC, GLOBECOM, ICCCN and etc. He is also an editorial board member of Elsevier Journal of Optical Switching and Networking, Springer Telecommunication Systems Journal, Springer Photonic Network Communications Journal and Wiley European Transactions on Emerging Telecommunications Technologies amongst others. He has received the Best Paper Awards from the IEEE International Conference on Communications (ICC) 2013, the IEEE Global Communications Conference (GLOBECOM) 2013, and the IEEE International Conference on Networking and Communications (ICNC) 2014. He is a Senior Member of IEEE and OSA.

In this paper, based on the analyzed emerging challenges encountered by the future radio network, we focus on several candidate techniques targeting at a more spectrum-efficient and cost-effective solution. Among them, spectrum management is one special topic covering fields of technique, regulation and politics. We point out the high tendency of spectrum liberation in terms of spectrum allocation for services and radio technologies even between different network providers. In the network planning topic, we address a number of solutions w.r.t. some typical dominating factors. A solution reducing the risk of high expenditure in conjunction with the flexibility of spectrum management is also given. To further enhance the efficiency, advanced radio resource management allowing interworking among heterogeneous radio technologies is also presented. I. Introduction Furthering the big success of the GSM system (Global System forMobile communications) with the population of subscribers reaches over 250 million worldwide, the international mobile and wireless market turns out to the evolution of third Generation Mobile Communication System termed as the UMTS (Universal MobileT elecommunication System) and the system beyond it. Future radio network faces practical challenges such as the higher throughput and more elastic traffic demand based on the exploiting multimedia services, the scarcity and deployment difficulty, the heterogeneity of different radio air interface and the high cost of network deployment and operation. To achieve high spectrum efficiency with high coverage is always the goal to design a radio network. After the significant contribution from Shannon in the late 50’s, people research on radio transmission technology targeting at approaching the Shannon bounds for different scenarios like AWGN noise-limited channel, fading channel, multi-user communication environment, etc. Several technologies achieve significant improvement of spectrum efficiency, such as the advanced channel coding schemes, diversity approach, digital modulation schemes, joint source-channel coding schemes, accurate channel estimation and joint detection techniques, antenna techniques like MIMO (Multiple Input and Multiple Output), etc. From higher layer mechanism viewpoint, one can see the performance improvements given by a number of mechanisms like Medium Access Control P rotocol (MAC), Data Link Control P rotocols (DLC), Radio Link Control P rotocols (RLC) as well as Radio Resource Control P rotocols (RRC). In the network layer and beyond, mechanisms enhancing the performance for TCP (T ransport control protocol) and UDP (User Diagram protocol) over IP protocol are required for the wireless communication. From the system level, advanced network planning and management techniques are needed catering for the heterogeneity and therefore facilitating the interoperability of the co-existing Radio Access T echnologies (RATs). Apart from the cellular technologies, kinds of Broadband W ireless Access (BWA) technology have been emerged for years. Typical examples are the WLAN (W ireless Local Area Network) represented by IEEE 802.11 family, Hiperlan in Europe and WiMAX (W orldwide interoperability for Microwave Access) represented by IEEE 802.16 family. In order to offer ubiquitous wireless access, the interworking and harmonization among heterogeneous networks are considered as primary important in the coming years. One aspect of it is to design the wireless local network as a complementarity to the cellular radio network, which must be considered in the network planning phase for such heterogeneous networks. Different to the classical network planning scheme, network co-planning for heterogeneous networks is not only based on the carrier strength that the mobile terminals can receive, traffic distribution, networks’ deployment costs, their interoperability, and the terminal capabilities and spectrum management are tightly associated topics.

Technology recognition and traffic characterization for wireless technologies in ITS band

In light of recent interests and activities by cellular networks operators to exploit the unlicensed bands to boost network capacity, never has the issue of fair coexistence and spectrum sharing been at the heart of most feasibility and performance studies of radio access technologies coexisting in unlicensed bands. This has been the case because overall system performance by incumbent radio access technologies is not expected to be compromised in the spirit of fairness. Therefore, fair coexistence or spectrum sharing has become a key performance metric in evaluating the performance of most solutions proposed to permit radio access technology coexistence in the unlicensed bands. Time- based fairness, the focus of this thesis, refers to a mechanism which can by adopted to evaluate fairness performance among coexisting radio access technologies in the time domain, however, limited studies have been conducted and practical implementation solutions are still out of reach. In this thesis, the objectives are to address existing gaps in accessing practical time-based fairness solutions. Firstly, a review of the state of the art on fairness issues, metrics and approaches are discussed, providing an overview of current approaches and solutions and identifies their shortcomings to practical implementation. Secondly, the estimation of number of nodes contending over the unlicensed spectrum, which is a requirement for many fairness oriented schemes proposed for radio access technologies coexisting in unlicensed bands, is addressed. A novel technology-neutral estimation method for node numbers is proposed. The transmission interval observed over the unlicensed channel represents a probabilistic distribution, which can be obtained via the uniform difference distribution. The characteristic features of the uniform difference distribution are exploited to aid estimation of node numbers in scenarios where nodes contend for the channel within the same contention window and under multiple contention windows. The benefit of the proposed method over existing methods is the level of accuracy and its ability to provide a tighter estimate to small increase in numbers of contenders on the channel. Thirdly, two approaches to achieving time-based fairness are proposed. The first being a deterministic approach and the second a probabilistic one. The deterministic approach aims to study the upper bound performance of time-based fairness utilizing the estimation method for node numbers proposed in this thesis. An optimal value is computed as a backoff value for each transmission cycle while keeping the transmission opportunity of all coexisting radio access technologies the same. The results show time-based fairness improves spectrum utilization and overall throughput performance. The probabilistic approach seeks for a practical and implementable solution to achieving time-based fairness based on the proven performance benefits shown from the deterministic approach. The transmission interval distribution obtained from observation of the channel activity during the node number estimation serves as the building block towards a practical solution. The distribution is continually monitored and mapping of the occurrence of transmission intervals to its probability density functions are performed. The mean of the distribution is then optimized to provide a balance between the channel access probabilities in order to achieve approximately equal transmission time by all nodes contending over the channel. Two parameters are adjusted to attain time-based fairness, which are the contention window sizes and transmission opportunity. Simulation results show that time-based fairness under the proposed scheme can improve spectrum utilization, reduce the disparity in throughput performance and guarantee fairness among coexisting radio access technologies.

The exponential growth in mobile services demand, along with the scarce licensed spectrum in the sub-6GHz bands, mandate the exploitation of bands other than the traditionally used by mobile broadband technologies. An example of such operation is the opportunistic access of the unlicensed bands by the LTE technology, as a means to increase the delivered end-user capacity and enhancing the overall quality of experience. In this paper, we present some extensive testbed measurements used for modeling the coexistence of LTE and WiFi technologies when operating within the same unlicensed environment. The experiments deal with different bandwidth settings for both the WiFi and LTE technologies, when LTE is operating closely or inside the primary or secondary channels of IEEE 802.11, taking into account the different threshold values for the Clear Channel Assessment functions that WiFi entails. We present exhaustive experimental measurements, collected under a real testbed setup, and present a cognitive algorithm for minimizing the impact of the two technologies to each other.

This paper addresses the channel occupation and the channel selection problem for the Long Term Evolution Unlicensed (LTE-U) technology when coexisting with the WiFi system on the unlicensed spectrum (typically the 5 GHz band). For instance, LTE is a communication standard developed by the 3GPP corporation based on the GSM/EDGE and the UMTP/HSPA technologies and conceived for high-spaced wireless communications. If we focus on LTE-U, it is an extension of the LTE-A (LTE-Advanced) scheme in unlicensed bands. In this paper, we will discuss the coexistence matters between the WiFi and LTE-U technologies. Therefore, we review the different solutions discussed in literature that addressed the coexistence issue. These works are either based on fair spectrum allocation between LTE-U and WiFi technologies or on the game theory paradigm where multi channel access and inter-dependance scenarios are discussed. As a future work, we intend to further investigate the coexistence issues between LTE-U and WiFi systems, especially in the case of inter-dependance scenarios and other configurations including hidden/exposed terminal problem in WiFi networks.

In order to meet the exponential rise in mobile data demand, it is proposed to supplement existing licensed bandwidth with the unlicensed spectrum, where a part of cellular data demand is served in the unlicensed spectrum. This deployment of LTE technology in unlicensed spectrum is termed as LTE in unlicensed spectrum (LTE-U). However, deploying LTE technology in the unlicensed 2.4/5 GHz band will greatly cause interference to the already existing technologies such as WiFi and Zigbee due to the stark differences in their channel access mechanisms. For LTE-U to become a reality, it is necessary for LTE to fairly coexist with the existing technologies. Therefore, in this paper, we propose a Q-Learning based Dynamic Frame Selection (DFS) algorithm which ensures fair coexistence between LTE-U and WiFi technologies. Furthermore, we propose the use of reduced power subframe to limit interference to the co-channel users and increase the channel utilization. By extensive simulation we show the effectiveness of our proposed DFS algorithm when compared to existing algorithms in the literature.

With the massive and growing number of wireless devices, the scarcity of the available frequency spectrum is a serious concern. The QoS requirements of most contemporary networking applications exacerbate this issue. Through opportunistic utilization of the available frequency spectrum, Cognitive Radio (CR) technology can offer some appropriate solutions to this problem. Unlicensed spectrum is shared very efficiently by Wi-Fi devices. To improve the availability of frequency spectrum and their efficient use, integration of CR and Wi-Fi technologies appear to be a promising approach. This combination forms the so-called White-Fi. This paper discusses the relevant spectrum assignment and sensing issues in White-Fi implementations. We also report the results of our simulation studies on the effects of sensing variations in the QoS levels of several typical applications. These studies show the effects of an intelligent sensing strategy that is aware of the application requirements on White-Fi QoS. Based on those, we propose some sensing improvements that may mitigate such effects on QoS. Our works indicate that while such an approach can result in a more efficient use of the available spectrum, the burden of sensing and the inevitable delays may result in some QoS degradations.

On the road towards 5G, a proliferation of Heterogeneous Networks (HetNets) is expected. Sensor networks are of great importance in this new wireless era, as they allow interaction with the environment. Additionally, the establishment of the Internet of Things (IoT) has incredibly increased the number of interconnected devices and consequently the already massive wirelessly transmitted traffic. The exponential growth of wireless traffic is pushing the wireless community to investigate solutions that maximally exploit the available spectrum. Recently, 3rd Generation Partnership Project (3GPP) announced standards that permit the operation of Long Term Evolution (LTE) in the unlicensed spectrum in addition to the exclusive use of the licensed spectrum owned by a mobile operator. Alternatively, leading wireless technology developers examine standalone LTE operation in the unlicensed spectrum without any involvement of a mobile operator. In this article, we present a classification of different techniques that can be applied on co-located LTE and Wi-Fi networks. Up to today, Wi-Fi is the most widely-used wireless technology in the unlicensed spectrum. A review of the current state of the art further reveals the lack of cooperation schemes among co-located networks that can lead to more optimal usage of the available spectrum. This article fills this gap in the literature by conceptually describing different classes of cooperation between LTE and Wi-Fi. For each class, we provide a detailed presentation of possible cooperation techniques that can provide spectral efficiency in a fair manner.

The escalating deployment of wireless networking technology as well as other wireless technologies in the same unlicensed spectrum is rapidly increasing the radio frequency (RF) interference for IEEE 802.11 products. These interferences involve a high error rate in the channel, leading to degrade considerably the Wireless LAN (WLAN) performances. This paper focuses on the problems associated with the IEEE 802.11 in presence of high errors in channel, and ways to improve its performance in this situation. The actual MAC layer has no mechanism to differentiate random losses on wireless link from collisions, and therefore treats all losses as collision. Besides demonstrate link errors effect over IEEE 802.11 performances, our contribution consists of enhancing the RTS/CTS handshake mechanism in order to improve the IEEE 802.11 behaviors under a noisy channel. We compare the performance of our proposition with the actual MAC protocol and demonstrate considerable throughput gains with our approach.

Trend of internet of things (IoT) creates new innovation in wireless technology. Low power wide area (LPWA) technology is one of the emerging technology that support IoT paradigm. Low power and long range characteristic of LPWA enables connectivity for low power device in large geographical area. LPWA as wireless communication technology require radio spectrum in its operation. LPWA can run both in licensed and unlicensed spectrum, but LPWA in licensed spectrum can give service assurance. As a limited resource, the use of the frequency spectrum is regulated by the government by applying a licensing system. This research will calculate the price of spectrum license in LPWA according to Indonesian regulation. NB-IoT system will be used as input parameter in calculating the spectrum price in Indonesia. The spectrum price then inserted into economical analysis as a component in operational cost and initial investment. As a result of this research, NPV analysis will be conducted to see profitability of investment in LPWA NB-IoT technology.

Chapter 2 - Communications Policy and Spectrum Management

U-LTE is a new wireless technology that is currently being developed by industry and academia to offer LTE service in unlicensed spectrum. U-LTE addresses spectrum shortage from 4G LTE cellular networks by allowing them to operate in unlicensed bands. To ensure fair spectrum sharing among different wireless technologies (LTE and WiFi in particular), a number of coexistence mechanisms have been proposed. These mechanisms operate in the time, frequency, or power domains to minimize potential adverse effects from LTE. Based on these mechanisms, a number of U-LTE standards are being developed by industry. In this article, we present recent advances in this exciting area by reviewing the state-of-the-art LTE/WiFi coexistence mechanisms and show how they are incorporated into industry standards. We also point out several key challenges and open problems for future research.