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Satellite Communications in the 5G Era
About the Authors of Satellite Communications
Shree Krishna Sharma holds a Ph.D. diploma in wi-fi communications from the College of Luxembourg, the M. Res. diploma in computing science from Staffordshire College, United Kingdom, and the M.Sc. diploma in info and communication engineering from the Institute of Engineering, Nepal.
He has greater than 3 years of postdoctoral analysis expertise at SnT, College of Luxembourg and at the College of Western Ontario, Canada in the areas of cognitive satellite tv for pc communications, 5G wi-fi and Web of Issues (IoT).
In the previous, he was with Nepal Telecom for over 4 years as a Telecom Engineer in the subject of data expertise and telecommunication.
He has revealed greater than 80 technical papers in scholarly journals and worldwide conferences and has over 1,200 Google Scholar citations. He’s the recipient of a number of awards together with the FNR Award for Excellent Ph.D. Thesis 2015, CROWNCOM 2015 Greatest Paper Award and 2018 EURASIP Greatest Paper Award.
He’s a senior member of IEEE and has been actively serving as a reviewer and a TPC member for a number of worldwide conferences together with IEEE ICC, IEEE GLOBECOM, IEEE VTC, and IEEE PIMRC.
Symeon Chatzinotas is the Deputy Head of the SITCOM Analysis Group, Interdisciplinary Centre for Safety, Reliability, and Belief (SnT), College of Luxembourg, Luxembourg and a Visiting Professor at the College of Parma, Italy.
He acquired the M. Eng. diploma in telecommunications from the Aristotle College of Thessaloniki, Thessaloniki, Greece, in 2003, and the M.Sc. and Ph.D. levels in digital engineering from the College of Surrey, Surrey, United Kingdom, in 2006 and 2009, respectively.
He has over 250 publications, 2,800 citations and an H-Index of 26 in response to Google Scholar. His analysis pursuits embody multiuser info principle, co-operative/cognitive communications and wi-fi networks optimization.
He’s the co-recipient of the 2014 Distinguished Contributions to Satellite Communications Award from the Satellite and Area Communications Technical Committee, IEEE Communications Society, the CROWNCOM 2015 Greatest Paper Award and 2018 EURASIP Greatest Paper Award.
Pantelis Daniel Arapoglou has been a communications system engineer with the European Area Company ESA/ESTEC since September 2011 the place he’s supporting R&D actions and developments in the areas of satellite tv for pc telecommunications, digital and optical communications, and high-data-rate telemetry for Earth commentary purposes.
He acquired the Dr. Eng. Diploma from the Nationwide Technical College of Athens (NTUA), Greece, in 2007 and the Diploma diploma in Electrical and Laptop Engineering in 2003.
He has participated in the work of Research Group 3 of the ITU-R in SatNEx III and in COST Motion IC0802. At the moment, he’s following SatNEx IV which is funded by ESA. He’s additionally concerned in the standardization work of the CCSDS optical working group.
Satellite Communications Contents
- Function of satellite tv for pc communications in 5G ecosystem: views and challenges
- Satellite use circumstances and situations for 5G eMBB
- SDN-enabled SatCom networks for satellite-terrestrial integration
- NFV-based situations for satellite-terrestrial integration
- Propagation and system dimensions in extraordinarily high-frequency broadband aeronautical SatCom methods
- Subsequent-generation non-geostationary satellite tv for pc communication methods: hyperlink characterization and system perspective
- Variety combining and handover strategies: enabling 5G utilizing MEO satellites
- Highly effective nonlinear countermeasures for multicarrier satellites: development to 5G
- Satellite multi-beam precoding software-defined radio demonstrator
- Beam-hopping methods for next-generation satellite tv for pc communication methods
- Optical on-off keying knowledge hyperlinks for low Earth orbit downlink purposes
- Extremely-high-speed knowledge relay methods
- On-board processing for satellite-terrestrial integration
- On-board interference detection and localization for satellite tv for pc communication
- Random entry in satellite tv for pc communications: background on the legacy and superior schemes
- Interference avoidance and mitigation strategies for hybrid satellite-terrestrial networks
- Dynamic spectrum sharing in hybrid satellite-terrestrial methods
- Two-way satellite tv for pc relaying
Preface to Satellite Communications in the 5G Era
Satellite Communication (SatCom) has been enjoying a significant function in the wi-fi world as a consequence of its functionality of broadcasting telecommunication providers to wider geographical areas and delivering broadband connectivity to sparsely populated distant areas, that are usually inaccessible or under-served by the terrestrial communication infrastructures.
SatCom applied sciences have been considerably helpful in bridging the digital hole in at this time’s info age by fostering the financial and social growth of rural communities and growing international locations.
Though there are a number of advances in the terrestrial wi-fi world in phrases of capability and protection enhancement, SatCom is the solely viable possibility for delivering telecommunication providers in a variety of sectors similar to aeronautical, maritime, army, rescue and catastrophe aid.
Furthermore, the demand for rising purposes similar to excessive definition tv, interactive multimedia providers and broadband web entry is quickly rising, thus resulting in the ever-increasing want of SatCom methods.
Extra importantly, in order to fulfill the client expectation of the seamless entry to any telecommunications providers anytime and wherever together with the situations like touring on cruise liners, planes, and high-speed trains, the satellite tv for pc ought to be an necessary element of the upcoming fifth-generation (5G) and past wi-fi architectures.
The upcoming 5G and past wi-fi communications are anticipated to help an enormous variety of good units, related sensors and large machine kind communication (MTC) units having numerous quality-of-service (QoS) necessities.
On this path, 5G wi-fi methods are envisioned to offer 1,000 occasions elevated capability, 10–100 occasions larger end-user data-rates, 5 occasions decrease latency, 10 occasions elevated power effectivity for low-power units and to help 10–100 occasions larger variety of related units as in comparison with the present 4G methods.
Additionally, varied rising wi-fi methods similar to broadband methods, Web of Issues (IoT) and MTC methods are anticipated to be built-in with the legacy networks to make the most of the already-deployed applied sciences similar to 2G, 3G, long-term evolution (LTE), LTE-advanced, Wi-Fi and satellite tv for pc.
Nevertheless, there are a number of challenges in assembly heterogeneous service necessities in phrases of achievable protection, knowledge charges, latency, reliability, and power consumption, and in delivering converged wi-fi options to the end-users.
Primarily, future wi-fi networks might want to present wherever, anytime and any machine connectivity in a variety of rising software situations together with industrial automation, related automotive, E-Healthcare, good metropolis, good house, good grid, communications-on-the-move and high-speed platforms similar to trains, airplanes and unmanned aerial automobiles (UAVs).
In the period of 5G wi-fi, SatCom options can complement terrestrial telecommunication options in all geographical areas together with rural/inaccessible locations and concrete/suburban areas in phrases of offering telecommunication providers to the end-users.
Satellite backhaul turns into a really perfect answer to ship telecommunication providers to the geographically difficult areas since it’s troublesome to deploy wired backhaul options similar to copper and optical fiber as a consequence of the value and implementation points.
As in comparison with the terrestrial backhaul, satellite tv for pc backhaul not solely can scale back the infrastructure value but in addition is usually a backup answer to the terrestrial backhaul hyperlinks in case of failure or for load balancing in the locations/occasions with excessive site visitors demand.
Moreover, in many purposes focused by 5G and past methods similar to distributed IoT/MTC networks, content material supply networks (CDNs), and extremely distributed small/medium dimension networks, satellite tv for pc networks are higher suited than the terrestrial solely options.
Due to this fact, SatComs could be thought-about as an necessary means to help the growth of 5G ecosystem towards extremely dependable and safe international networks.
The latest advances in Ku-band, Ka-band, further excessive frequency (EHF) band and free-space optical applied sciences have led to the new period of excessive throughput satellite tv for pc (HTS) methods.
These HTS are anticipated to considerably scale back the communication value of the next-generation satellite tv for pc methods and of the built-in satellite-terrestrial methods.
Nevertheless, the major problem in rising HTS methods and non-geostationary (NGSO) constellations is the integration of satellite tv for pc and terrestrial methods from an architectural perspective in order that SatCom methods turn out to be an energetic a part of the entry community quite than one other clear backhaul medium for the 5G and past methods.
On this regard, the ideas of using software-defined networking (SDN) and community operate virtualization (NFV) towards enabling the seamless integration of satellite-terrestrial are rising.
These SDN- and NFV-based options are envisioned to drastically shift the current hardware-based system design and implementation towards full notarization, thus enabling the versatile and adaptive implementation of the 5G ecosystem towards fulfilling the numerous QoS necessities of the end-users.
Satellite methods are challenged in assembly the latency necessities for some purposes similar to the tactile Web, and there are different challenges similar to enhancing reliability, effectivity, protection and lowering prices in the dense areas.
That is notably true for geostationary (GSO) satellites, whereas NGSO satellite tv for pc constellations are in a a lot better place in phrases of latency. On the different hand, terrestrial wi-fi can present connectivity to indoor and ground-mobile customers with low latency however is economically difficult in sparse or intermittent areas.
On this path, the convergence of cell, fastened and broadcasting methods with the risk of coexistence of satellite tv for pc networks with the terrestrial methods is one in every of the promising future instructions. Towards enabling this convergence, SatComs can play a key function in constructing heterogeneous architectures by means of hybrid and built-in satellite-terrestrial paradigms.
Moreover, the involvement of the satellite tv for pc makes the deployment of IoT involving sensors and M2M connections in large areas possible. Moreover, in order to allow the Web of every part, offering exact positioning and context capabilities is a vital side and could be achieved by the mixture of satellite tv for pc and mobile positioning methods.
Furthermore, the integration of SatComs with the mobile will result in higher availability in emergency and catastrophe purposes. For instance, the supply of real-time excessive definition video utilizing satellite tv for pc in the UAV surveillance purposes could be thought-about.
As well as, there’s a rising curiosity in satellite tv for pc supply in the transport sector security providers and vehicle-to-vehicle purposes.
The aforementioned features clearly spotlight the want of integrating satellite tv for pc in 5G and past wi-fi architectures towards enabling the elevated convergence as focused by the 5G neighborhood.
One promising manner of taking mutual advantages from satellite tv for pc and terrestrial applied sciences in the 5G ecosystem is to mix them in the identical platform in the type of hybrid/built-in networks. Nevertheless, satellite tv for pc methods have been largely used in an overlay method quite than an built-in kind besides in the S-band.
Additionally, enhancing the spectral effectivity in addition to the whole system throughput has been an necessary concern for future SatCom methods as a consequence of constantly rising demand for broadcast, multimedia, and interactive providers and the lack of usable satellite tv for pc spectrum.
Though SatCom methods have moved from the conventional monogram satellites to the multibeam platform and the rising full-frequency reuse idea can present important capability features as in comparison with the typical four-color reuse methodology, the drawback of cochannel interference must be addressed with the assist of superior precoding and multiuser detection schemes.
Moreover, as the variety of cochannel satellites (GSO and NGSO) in addition to different cochannel terrestrial methods will increase, dealing with inter-system interference turns into one other difficulty.
On this regard, the investigation of appropriate spectrum sharing, useful resource allocation, and interference avoidance/mitigation strategies has turn out to be essential towards realizing the subsequent era Terabit/s SatCom methods.
Motivated by the above-mentioned quite a few advantages and the function of SatComs in 5G methods and the related challenges, a number of tutorial establishments, regulators and industries are placing important efforts in investigating novel satellite-terrestrial built-in options and the subsequent era SatComs applied sciences/architectures.
Additionally, there are ongoing actions in the areas of dynamic spectrum sharing, cognitive and cooperative SatComs, useful resource allocation, superior interference mitigation strategies, multibeam joint processing, multiuser detection, superior precoding strategies, design of good antennas, optical inter-satellite/space-ground hyperlinks and the exploitation of high-frequency bands (Q/V/W/optical) for the gateway connections.
Though there are some latest books in the literature discussing the features of 5G mobile communications, the significance of SatComs in 5G and past wi-fi methods has been uncared for.
On this path, this ebook focuses on latest analysis efforts being carried out towards integrating SatCom methods in the upcoming 5G and past methods, and likewise on varied novel enabling applied sciences for the subsequent era of Terabit/s SatComs.
This ebook goals to offer important inputs to teachers, researchers, telecom engineers, industrial actors and policymakers similar to 5G stakeholders, regulators, and analysis businesses to stimulate future actions in strengthening the function of SatCom in the 5G and past wi-fi methods.
In the above context, this ebook discusses varied rising ideas/applied sciences/ architectures in the area of next-generation SatComs and built-in satellite-terrestrial methods.
The chapters included in this ebook are introduced in the logical sequence of 5G SatCom situations and providers/networking (Chapters 1–4), channel and propagation features (Chapters 5 and 6), physical- and system-level strategies (Chapters 7–10), optical technology-based satellite tv for pc methods (Chapters 11–12), onboard processing (OBP) methods and strategies (Chapters 13 and 14), superior collision/interference mitigation, spectrum sharing and latency discount strategies (Chapters 15–18).
The ebook begins with an outline of the function of SatCom in the 5G period and the associated use circumstances (Chapters 1 and 2) after which presents the rising ideas associated to SDN (Chapter 3) and NFV (Chapter 4) together with their purposes towards the seamless integration of satellite tv for pc and terrestrial networks.
Then, the ebook analyzes the feasibility of utilizing satellite tv for pc methods in EHF bands for aeronautical broadband purposes together with the traits of the aeronautical to satellite tv for pc channel (Chapter 5).
The ebook advances by presenting the major propagation traits of NGSO satellite tv for pc methods together with some promising capability enhancement strategies (Chapter 6).
Subsequently, varied features of MEO satellites similar to variety combining and handover strategies are mentioned and an SDN-based cost-effective handover structure is proposed together with some prototype-based check outcomes (Chapter 7).
Then, the ebook presents a number of superior compensation strategies that may mitigate the impact of nonlinear distortions in rising multicarrier satellite tv for pc methods (Chapter 8).
Subsequently, the ebook analyzes the feasibility of a softwaredefined radio (SDR)-based precoder for broadband multibeam satellite tv for pc methods with the assist of in-lab validation outcomes (Chapter 9).
The ebook then proceeds by presenting rising beamhopping applied sciences for the subsequent era satellite tv for pc methods with a selected give attention to the upcoming Eutelsat Quantum-class satellite tv for pc (Chapter 10).
In the context of rising optical applied sciences, the ebook discusses a number of features of optical on-off keying (OOK) knowledge hyperlinks for rising LEO downlink purposes together with an in depth evaluation of the laser communication channel (Chapter 11).
As well as, the major parts concerned in the design of optical technology-based ultra-high pace relay methods are mentioned and the hyperlink finances calculation of varied related hyperlinks is introduced (Chapter 12). Subsequent, the ebook contains two chapters associated to the promising OBP paradigm in the subsequent era satellite tv for pc methods.
Primarily, varied design features associated to OBP are introduced towards enabling the satellite-terrestrial integration together with an OBP instance use case by using LEO satellites (Chapter 13).
And, some promising onboard interference detection and localization strategies are introduced together with their efficiency analysis by way of numerical outcomes (Chapter 14).
The ebook then discusses varied typical and superior random entry (RA) schemes and analyzes their efficiency with respect to numerous system constraints (Chapter 15).
In the context of hybrid satellite-terrestrial cell backhaul (MBH) methods, varied interference avoidance and mitigation strategies together with user-level linear precoding schemes and symbol-level precoding (SLP) schemes are mentioned together with their efficiency evaluation (Chapter 16).
Furthermore, towards enabling dynamic sharing of the radio spectrum between satellite tv for pc and terrestrial methods, varied spectrum sharing strategies are mentioned together with a sensible coexistence instance of a set satellite tv for pc service (FSS) system and a terrestrial fastened service (FS) system (Chapter 17).
Lastly, the ebook discusses varied features of two-way satellite tv for pc relaying (TWSR) together with an in depth mathematical evaluation of beamforming and mixing strategies in TWSR communication methods (Chapter 18).
In the following paragraphs, an outline of the major contents of all the chapters is introduced. In Chapter 1, O. Onireti and M. A. Imran focus on a number of key areas the place satellites can play important roles in the 5G methods beginning with the highlights on the 5G imaginative and prescient.
The important thing areas mentioned embody offering ubiquitous connectivity to inaccessible areas similar to distant areas, passengers in plane/trains/vessels, emergency and demanding situations, huge MTCs, resilience provisioning, content material caching and multicasting, satellite-terrestrial built-in community (trunking and head-end feed, backhauling and communication on the transfer) and ultra-reliable communication.
Moreover, the authors highlighted and mentioned the latest advances in 5G SatComs methods together with some ongoing initiatives on satellite-terrestrial integration [Satellite and Terrestrial Network for 5G (SAT5G), SANSA and VITAL], spectral sharing between satellite tv for pc and terrestrial methods, mega-LEO constellation, OBP, gallium nitride expertise, SDN, multicasting, and built-in signaling.
Lastly, some analysis challenges and proposals related to the built-in satellite-terrestrial structure, built-in signaling and OBP are supplied.
In Chapter 2, Ok. Lillis et al. focus on varied promising use circumstances and situations for 5G enhanced Cellular Broadband (eMBB) outlined in the context of the European Fee H2020 5G PPP Part 2 undertaking SaT5G.
Beginning with a short dialogue on the function of satellite tv for pc in the 5G ecosystem and the SaT5G undertaking, the chapter presents 4 totally different use circumstances for the eMBB and gives their relevance to the key analysis pillars, the major 5G PPP Key Efficiency Indicators, the 3GPP SA1 SMARTER use case households and 5G market verticals.
The principle use circumstances included in this chapter embody supply and offloading of multimedia content material to the community edges, 5G fastened backhaul to offer broadband connectivity to the locations inaccessible by terrestrial communications, complementary connectivity to terrestrial networks in under-served areas and broadband connectivity to the platforms on the transfer.
Moreover, the chapter gives the qualitative market dimension evaluation for the chosen satellite tv for pc use circumstances for eMBB based mostly on the satellite tv for pc operators’ perspective and up to date industrial developments.
Furthermore, the chapter describes a set of situations for every of the chosen use circumstances together with their qualitative high-level description.
Lastly, the chapter concludes by highlighting the key features of the introduced use circumstances and situations.
In Chapter 3, F. Mendoza et al. focus on the function of SDN applied sciences in facilitating the seamless integration and operation of built-in satellite tv for pc and terrestrial networks. Specifically, the realization of end-to-end (E2E) site visitors engineering (TE) in a mixed terrestrial-satellite community through the use of SDN applied sciences is mentioned with a selected give attention to an MBH community situation.
Moreover, a system structure for an SDN-enabled floor section system is introduced, and a number of other candidate SDN knowledge fashions and interfaces are mentioned.
Furthermore, an built-in strategy for the realization of E2E SDN-based TE in satellite-terrestrial backhaul networks is introduced by abstracting the satellite tv for pc element as an open move change, and two central TE workflows are illustrated to validate the proposed built-in strategy with one workflow towards computing an optimum path and one other workflow to beat congestion/failures.
As well as, the efficiency of the proposed SDN-based TE software is analyzed by way of numerical simulations in varied situations together with homogeneous and heterogeneous load conditions, unavailability of terrestrial hyperlinks and the presence of transportable base stations that completely depend on the satellite tv for pc capability for backhauling.
Lastly, the chapter gives some concluding remarks and future suggestions. In Chapter 4, H. Koumaras et al. first present a short introduction to cloud computing and focus on the functionalities of AFVs.
Subsequently, the chapter presents the promising use case situations for the integration of cloud networking strategies into satellite tv for pc networks that are derived from the terrestrial NFV use circumstances and tailored to the SatCom context.
The mentioned situations embody digital CDN as-a-service, satellite tv for pc digital community operator situation, dynamic backhauling with edge processing-as-a-service situation, and buyer features virtualization situation.
For every of those situations, the related advantages and implementation challenges are mentioned. The chapter concludes by offering some future suggestions for the environment friendly implementation of NFV expertise in SatCom methods.
In Chapter 5, N. Jeannin et al. focus on the potentialities of utilizing EHF on satellite tv for pc methods for the provision of aeronautical broadband communication.
Beginning with an outline of current or deliberate methods devoted to broadband communication, the authors analyze the projected business aviation generated site visitors demand by contemplating present business aviation site visitors and the forecasted knowledge utilization.
Subsequently, the traits of the aeronautical to satellite tv for pc channel at the EHF bands are introduced with a selected give attention to the impression of the altitude on the tropospheric impairments.
Moreover, the authors current the newest ITU-R requirements which assess the impression of the troposphere on an aircraft-space hyperlink together with a dialogue on the related propagation traits.
Furthermore, the authors extrapolate the present aeronautical terminals and satellite tv for pc traits to EHF vary to exhibit the efficiency enchancment at the EHF bands and it’s proven that the capacities supplied could be enhanced by the use of conformal antennas and supply about 4–10 occasions capability enhancements over present Ka-band methods.
Lastly, the chapter concludes by demonstrating the feasibility of EHF satellite tv for pc methods to fulfill future Aero passenger necessities. In Chapter 6, C. Kourogiorgas et al. current varied hyperlink traits and system views of the subsequent era NGSO SatCom methods.
The chapter first discusses the major propagation traits for the hyperlinks between floor stations and NGSO satellites together with native environmental results and propagation traits by way of the ambiance.
The operation of NGSO methods in decrease bands (L-/S-bands) is usually affected by the native surroundings, whereas in excessive RF bands and optical vary, atmospheric results turn out to be dominant they usually should be thought-about for the system design.
Relating to atmospheric propagation options, authors present an in depth dialogue on propagation traits for RF methods at the Ka-band together with totally different current fashions for calculating whole atmospheric attenuation and rain attenuation.
Subsequently, the chapter discusses the propagation traits for optical NGSO methods by highlighting the results of clouds and turbulence. Moreover, the chapter presents some promising strategies to boost the capability of NGSO methods together with variable and adaptive coding and modulation, and spatial variety and a number of antenna strategies.
Lastly, the chapter gives a short dialogue on interference points and the perspective of NGSO–GSO cooperation.
In Chapter 7, beginning with the function of MEO satellites in 5G methods, Nicolò Mazzali et al. focus on the system structure, providers, purposes and challenges of MEO satellites with a selected give attention to the O3b satellite tv for pc community.
Subsequently, the chapter describes the key parts of the E2E channel of MEO satellites together with the uplink and downlink radio propagation results, payload results and consumer terminal results.
Moreover, an outline of the current handover strategies for MEO purposes is supplied together with the particulars on the seamless handover idea.
To deal with the shortcomings of the current handover options in attaining optimum efficiency and 0 packet loss, the chapter proposes an SDN-based cost-effective handover structure which allows the mixture of the ideas of “make-before-break” and “unidirectional switching.”
Additionally, the chapter describes a prototype constructed to exhibit the handover efficiency of the proposed answer together with some check outcomes.
Furthermore, the chapter gives an in depth evaluation of the variety combining strategies for MEO satellites together with their benefits, drawbacks, and trade-offs, and presents the efficiency of three basic combining algorithms in MEO purposes by contemplating reasonable sign and channel fashions.
Lastly, the chapter concludes by offering the major insights and future roadmap. In Chapter 8, B. F. Beidasfirst presents an analytical framework based mostly on Volterra collection illustration, which characterizes the distortion amongst carriers appropriate for multicarrier satellite tv for pc purposes.
Subsequently, a number of superior compensation strategies to be utilized at the transmitter and receiver to successfully decrease the linear and nonlinear distortion in SatCom methods are introduced.
As one in every of the promising options at the receiver, the writer describes the Turbo Volterra equalization methodology which iteratively exchanges delicate info between the equalizer and ahead error correcting (FEC) decoders.
Moreover, three various kinds of distortion options, particularly, Volterra-based knowledge distortion, Volterra-based successive sign predistortion and successive knowledge predistortion are mentioned for the transmitter aspect.
Furthermore, the software of orthogonal frequency division multiplexing (OFDM) signaling for broadband satellite tv for pc transmission in the ahead path (from the gateway to terminals) is mentioned and appropriate countermeasure methods are employed to mitigate the impact of nonlinear distortion in OFDM-based satellite tv for pc methods.
Lastly, the chapter concludes by offering suggestions for the purposes of the proposed nonlinear distortion countermeasures in precoding-based satellite tv for pc methods and cognitive satellite tv for pc methods.
In Chapter 9, Stefano et al. exhibit the functionality of an SDR-based precoder in enabling the operation of broadband multibeam satellite tv for pc methods with aggressive frequency reuse modes in the presence of sensible impairments.
Beginning with the dialogue of latest initiatives on precoding, the authors present a short evaluation of the associated works on precoding for SatComs.
Subsequently, an in depth evaluation of sensible constraints similar to instantaneous differential section distortion, timing misalignment and channel state info (CSI) estimation errors for precoding is supplied and attainable options are mentioned.
Moreover, the authors describe the sensible implementation of precoding strategies with a selected give attention to SLP.