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  • 101. Fodor, Gabor
    et al.
    Rácz, András
    Link-level flow control method for an ATM server1998Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A link level flow control method for serving ATM cell streams arriving from a number of packet sources determines a requested bandwidth share for each packet source and queues ATM cells arriving from the packet sources in a shared FIFO buffer. Based on the number of transmitted ATM cells during a pre-defined time period, non-violating packet sources and violating packet sources are identified. The non-violating packet sources are those packet sources that during the predefined time period do not require more than their requested bandwidth share, and the violating packet sources are those packet sources that during the same period require more than their requested bandwidth share. In order to maintain fairness among the packet sources, the non-violating packet sources are granted no more than their requested bandwidth share, with the remaining bandwidth not granted to the non-violating packet sources being granted to the violating packet sources.

  • 102.
    Fodor, Gabor
    et al.
    Ericsson Research, Sweden.
    Sorrentino, Stefano
    Ericsson Research, Sweden.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Soldati, Pablo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the impact of uplink power control in network MIMO systems with MMSE and SIC receivers2010In: 2010 IEEE International Symposium on 'A World of Wireless, Mobile and Multimedia Networks', 2010, Vol. WoWMoM 2010 - Digital ProceedingsConference paper (Refereed)
    Abstract [en]

    Network multiple input, multiple output (MIMO) systems are built around a broadband backbone network that allows for the fast communication of channel state information (CSI) as well as user data between different base stations. Previous works have shown that multicell channel adaptive (opportunistic) power control can minimize the sum power or maximize the sum rate when the backbone is used for the exchange of CSI in network MIMO systems. In this work we investigate the gains of multicell opportunistic power control under per user fairness constraints when both CSI and user data are shared between multiple sites. We find that multicell opportunistic power control working in concert with uplink joint signal detection is an efficient means both for the capacity and the power control problems that not only minimizes sum power or maximizes overall capacity, but is also able to provide arbitrary level of fairness.

  • 103. Fodor, Gabor
    et al.
    Telek, M
    Bounding the blocking probabilities in multirate CDMA networks supporting elastic services2007In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 15, no 4, p. 944-956Article in journal (Refereed)
    Abstract [en]

    Several previous contributions have proposed calculation methods that can be used to determine the steady state (and from it the blocking probabilities) of code-division multiple-access (CDMA) systems. This present work extends the classical Kaufman-Roberts formula such that it becomes applicable in CDMA systems in which elastic services with state-dependent instantaneous bit rate and average-bit-rate-dependent. residency time are supported. Our model captures the effect of soft blocking, that is, an arriving session may be blocked in virtually all system states but with a state dependent probability. The core of this method is to approximate the original irreversible Markov chain with a reversible one and to give lower and upper bounds on the so-called partially blocking macro states of the state space. We employ this extended formula to establish lower and upper bounds on the steady state and the classwise blocking probabilities.

  • 104.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Telek, Miklos
    Budapest University of Technoloy and Economics.
    Optimal Pilot-to-Data Power Ratio for Massive SIMO SystemsManuscript (preprint) (Other academic)
    Abstract [en]

    We consider a single cell single input multiple output (SIMO) system employing orthogonal frequencydivision multiplexing (OFDM). In such systems, setting the pilot-to-data power ratio (PDPR)has a large impact on the spectral and energy efficiency. In this paper we provide a closedform solution for the mean square error (MSE) of the received data as a function of thePDPR assuming Gaussian channels and minimum mean square error (MMSE) equalization.In numerical experiments we find that the MSE is a convex function of the PDPRand study the optimal PDPR as the number of antennas at the base station (BS) grows large.We find that the optimal PDPR heavilydepends on the number of antennas and the path loss between the mobile station and theBS. Specifically, as the number of antennas grows large, a larger portionof the total power budget needs to be allocated for pilot signals, especially for low pathloss users.

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  • 105.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems. KTH, School of Electrical Engineering (EES), Automatic Control.
    Telek, Miklos
    Di Marco, Piergiuseppe
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On the Impact of Antenna Correlation on the Pilot-Data Balance in Multiple Antenna Systems2014Report (Other academic)
    Abstract [en]

    We consider the uplink of a single cell single input multiple output (SIMO) system, in which the mobile stations use intra-cell orthogonal pilots to facilitate uplink channel estimation. In such systems, the problem of pilot-data transmission power balancing is known to have a large impact on the performance on the achievable uplink data rates. In this paper we derive a closed form expression for the mean square error (MSE) as a function of the pilot and data power levels under a per-user sum pilot-data power constraint. Our major contribution is the derivation of the MSE formula for Gaussian channels under arbitrary channel covariance matrices. For example, our model readily allows to study the MSE as a function of the number of antennas and antenna correlation structures, including the popular spatial channel model (SCM). Numerical results suggest that the impact of antenna spacing on the MSE is limited, but the angle of arrival (AoA) and angular spread have a more articulated impact on the MSE performance. We also find that as the number of antennas at the base station grows large, a higher percentage of the power budget should be allocated to pilot signals than with a low number of antennas.

     

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  • 106. Fodor, Gabor
    et al.
    Telek, Miklós
    A recursive formula to calculate the steady state of CDMA networks2005In: Performance Challenges for Efficient Next Generation Networks / [ed] XJ, Liang; ZH, Xin; GS, Kuo; VB, Iversen, Beijing: International Teletraffic Congress , 2005, p. 1285-1294Chapter in book (Other academic)
    Abstract [en]

    Several previous contributions have proposed calculation methods that can be used to calculate the steady state (and from it the blocking probabilities) in CDMA systems. To our best knowledge, this present work is the first one that extends the classical Kaufman-Roberts formula such that it becomes applicable in CDMA where elastic services (with state dependent instantaneous bit rate and average bit rate dependent residency time) are supported. The core of this method is to approximate the original irreversible Markov chain with a reversible one and to assign a proper blocking measure to the macro states of the system.

  • 107. Fodor, Gabor
    et al.
    Telek, Miklós
    Performance analysis of the uplink of a CDMA cell supporting elastic services2005In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 3462, p. 205-216Article in journal (Refereed)
    Abstract [en]

    We consider a single cell of a multi-service CDMA network, in which some of the service classes are explicit rate controlled. We call these elastic service classes. The instantaneous bit rate of elastic services is dynamically adjusted between a minimum and maximum value such that the system always remains work conserving. We develop a Markov model that allows us to study the impact of such state dependent (dynamic) rate control on the class-wise blocking probabilities and the first two moments of the holding times. We conclude that dynamic (state dependent) rate adjustment decreases the class-wise blocking probabilities and only moderately increases the expectation and the second moment of the time spent in the system.

  • 108. Fodor, Gabor
    et al.
    Telek, Miklós
    Badia, Leonardo
    On the tradeoff between blocking and dropping probabilities in CDMA networks supporting elastic services2006In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 3976, p. 954-965Article in journal (Refereed)
    Abstract [en]

    This paper is a sequel of previous work, in which we proposed a model and computational technique to calculate the Erlang capacity of a single CDMA cell that supports elastic services. The present paper extends that base model by taking into account two important features of CDMA. First, we capture the impact of soft blocking by modeling the neighbor cell interference as a lognormally distributed random variable. Secondly, we model the impact of the outage by taking into account that in-progress sessions can be dropped with a probability that depends on the current load in the system. We then consider a system with elastic and rigid service classes and analyze the trade-off between the total (soft and hard) blocking probabilities on the one hand and the throughput and the session drop probabilities on the other.

  • 109. Fodor, Gabor
    et al.
    Telek, Miklós
    Koutsimanis, Chrysostomos
    Performance analysis of scheduling and interference coordination policies for OFDMA networks2008In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 52, no 6, p. 1252-1271Article in journal (Refereed)
    Abstract [en]

    In orthogonal frequency division multiple access systems there is an intimate relationship between the packet scheduler and the inter-cell interference coordination (ICIC) functionalities: they determine the set of frequency channels (sub-carriers) that are used to carry the packets of in-progress sessions. In this paper we build on previous work - in which we compared the so called random and coordinated ICIC policies - and analyze three packet scheduling methods. The performance measures of interest are the session blocking probabilities and the overall throughput. We find that the performance of the so-called Fifty-Fifty and What-It-Wants scheduling policies is somewhat improved by coordinated sub-carrier allocation, especially in poor signal-to-noise-and-interference situations and at medium traffic load values. The performance of the All-Or-Nothing scheduler is practically insensitive to the choice of the sub-carrier allocation policy.

  • 110. Fodor, Gabor
    et al.
    Telek, Miklós
    Rácz, Sándor
    Link capacity sharing for throughput-blocking optimally in a mixed rigid-elastic traffic environment by dividing the bandwidth into common and dedicated parts1999Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention concerns an efficient strategy for sharing link bandwidth in a mixed rigid-elastic traffic environment, as well as a strategy for sharing bandwidth among elastic traffic flows. The idea according to the invention is to sharing the link bandwidth among rigid and elastic traffic by dividing the link bandwidth into a first common part CCOM for elastic as well as rigid traffic and a second part CELA dedicated for elastic traffic. Subsequently, one or more admission control parameters for the elastic traffic are determined in order to restrict the number of elastic traffic flows simultaneously present on the link. In particular, by formulating a call-level model for elastic traffic and determining a maximum number NELA of admissible elastic traffic flows based on call-level constraints for the elastic traffic related to throughput and/or blocking, the so-called throughput-to-blocking trade-off for elastic traffic can be fully considered.

  • 111. Fodor, Gabor
    et al.
    Tuoriniemi, Aimo
    A method for discovering the capabilities of a candidate access router2003Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A method for selecting a wireless network (8, 9) for a user terminal present in a multi access system, which comprises several wireless networks (8, 9) each with a technology respective access and each comprising access routers (2, 6) each associated with access points (14), exchanging access routers (2, 6) CARD information, capability discovery of candidate access router, using the CARD protocol on the control plane IP characterized by an operation, performed in an access router (2, 6), of translating CARD information protocol information messages of layer 2 and transmit information CARD protocol translated from each wireless network (8, 9) on at least one layer 2 wireless service to the user terminal (1); and operations performed in the user terminal (1), to hear the information CARD protocol broadcast that has been translated into the information layer 2 first, being held this listener in each wireless network (8, 9), and select then the wireless network (8, 9) that provides the capabilities that best meet the requirements of the user terminal (1).

  • 112. Fodor, Gabor
    et al.
    Tuoriniemi, Aimo
    Technology-independent access selection based on application requirements and network conditions2003Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A system and a method allowing a user terminal (18) in a network to simultaneously access a plurality of radio based access networks (19, 20) of diverse access technologies. Characteristic features of the invention are access selection adapters (22, 23), each one associated with a respective radio based access network, and an access technology independent access selector (26). An access adapter has means (32) for receiving access technology dependant information from its respective access network and means (31) for translating the information into access technology independent status information. The access selector comprises an access selection algorithm (33) interacting with applications (27) resident in the user terminal and with each access adapter for selection of a radio access network based on an individual QoS profile associated with each respective application and on said access technology independent status information. The invention also relates to a method for service scheduling.

  • 113.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Res, Kista, Sweden..
    Vinogradova, Julia
    Ericsson Res, Jorvas, Finland..
    Hammarberg, Peter
    Ericsson Res, Stockholm, Sweden..
    Nagalapur, Keerthi Kumar
    Ericsson Res, Stockholm, Sweden..
    Qi, Zhiqiang (Tyler)
    Ericsson Res, Beijing, Peoples R China..
    Do, Hieu
    Ericsson Res, Stockholm, Sweden..
    Blasco, Ricardo
    Ericsson Res, Jorvas, Finland..
    Baig, Mirza Uzair
    Ericsson Res, Stockholm, Sweden..
    5G New Radio for Automotive, Rail, and Air Transport2021In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 59, no 7, p. 22-28Article in journal (Refereed)
    Abstract [en]

    The recent and upcoming releases of the 3rd Generation Partnership Project's 5G New Radio (NR) specifications include features that are motivated by providing connectivity services to a broad set of verticals, including the automotive, rail, and air transport industries. Currently, several radio access network features are being further enhanced or newly introduced in NR to improve 5G's capability to provide fast, reliable, and non-limiting connectivity for transport applications. In this article, we review the most important characteristics and requirements of a wide range of services that are driven by the desire to help the transport sector to become more sustainable, economically viable, safe, and secure. These requirements will be supported by the evolving and entirely new features of 5G NR systems, including accurate positioning, reference signal design to enable multi-transmission and reception points, and service quality prediction.

  • 114. Fodor, Gabor
    et al.
    Östergaard, Jessica
    Method and arrangement in a wireless communication system2011Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The present invention relates to a method for enabling intercell interference coordination in a network node 112, 132, which is comprised in a wireless communications network 100. The network node 112, 132 comprises at least two antennas for multi-antenna transmission and/or reception. According to the method, the network node 112, 132 transmits an indication of an amount of spatially multiplexed streams for at least one block of radio resources to at least one receiving network node 122, which is also comprised in the wireless communications network 100. By indicating the amount of spatially multiplexed streams, it is made possible for the receiving network node 122 to take the intercell interference in the spatial domain into consideration, for instance in a scheduling and/or link adaptation decision.

  • 115. Fodor, Gábor
    et al.
    Koutsimanis, Chrysostomos
    Rácz, András
    Reider, Norbert
    Simonsson, Arne
    Müller, Walter
    Intercell Interference Coordination in OFDMA Networks and in the 3GPP Long Term Evolution System2009In: Journal of Communications, ISSN 1796-2021, E-ISSN 2374-4367, Vol. Vol. 4, no No. 7, p. 445-453Article in journal (Refereed)
    Abstract [en]

    Intercell interference coordination (ICIC) in or-thogonal frequency division multiple access (OFDMA) net¬works in general and in the 3GPP Long Term Evolution system in particular has received much attention both from the academia and the standardization communities. Under¬standing the trade-offs associated with ICIC mechanisms is important, because it helps identify the architecture and protocol support that allows practical systems to realize potential performance gains. In this paper we review some of the recent advances in ICIC research and discuss the assumptions, advantages and limitations of some of the proposed mechanisms. We then proceed to describe the architecture and protocol support for ICIC in the 3GPP LTE system. We make the point that the 3GPP standard is formed in a flexible way such that network operators can employ the most suitable ICIC mechanism tailored to their actual deployment scenario, traffic situation and preferred performance target.

  • 116.
    Fodor, Gábor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Sweden.
    Parkvall, S.
    Sorrentino, S.
    Wallentin, P.
    Lu, Q.
    Brahmi, N.
    Device-to-device communications for national security and public safety2014In: IEEE Access, E-ISSN 2169-3536, Vol. 2, p. 1510-1520, article id 6985517Article in journal (Refereed)
    Abstract [en]

    Device-to-device (D2D) communications have been proposed as an underlay to long-term evolution (LTE) networks as a means of harvesting the proximity, reuse, and hop gains. However, D2D communications can also serve as a technology component for providing public protection and disaster relief (PPDR) and national security and public safety (NSPS) services. In the United States, for example, spectrum has been reserved in the 700-MHz band for an LTE-based public safety network. The key requirement for the evolving broadband PPDR and NSPS services capable systems is to provide access to cellular services when the infrastructure is available and to efficiently support local services even if a subset or all of the network nodes become dysfunctional due to public disaster or emergency situations. This paper reviews some of the key requirements, technology challenges, and solution approaches that must be in place in order to enable LTE networks and, in particular, D2D communications, to meet PPDR and NSPS-related requirements. In particular, we propose a clustering-procedure-based approach to the design of a system that integrates cellular and ad hoc operation modes depending on the availability of infrastructure nodes. System simulations demonstrate the viability of the proposed design. The proposed scheme is currently considered as a technology component of the evolving 5G concept developed by the European 5G research project METIS.

  • 117. Fodor, Gábor
    et al.
    Reider, Norbert
    A Distributed Power Control Scheme for Cellular Network Assisted D2D Communications2011In: 2011 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE (GLOBECOM 2011): 54th Annual IEEE Global Telecommunications Conference (GLOBECOM), New York: IEEE conference proceedings, 2011Conference paper (Other academic)
    Abstract [en]

    Device-to-device (D2D) communications underlaying a cellular infrastructure has recently been proposed as a means of increasing the resource utilization, improving the user throughput and extending the battery lifetime of user equipments. In this paper we propose a new distributed power control algorithm that iteratively determines the signal- to-noise-and- interference-ratio (SINR) targets in a mixed cellular and D2D environment and allocates transmit powers such that the overall power consumption is minimized subject to a sum-rate constraint. The performance of the distributed power control algorithm is benchmarked with respect to the optimal SINR target setting that we obtain using the Augmented Lagrangian Penalty Function (ALPF) method. The proposed scheme shows consistently near optimum performance both in a single-input-multiple-output (SIMO) and a multiple-input-multiple-output (MIMO) setting.

  • 118.
    Fodor, Gábor
    et al.
    Ericsson Research, Sweden.
    Roger, Sandra
    Rajatheva, Nandana
    Ben Slimane, Slimane
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Svensson, Tommy
    Popovski, Petar
    B. da Silva Jr., Jose Mairton
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Ali, Samad
    An Overview of Device-to-Device Communications Technology Components in METIS2016In: IEEE Access, E-ISSN 2169-3536, Vol. 4, p. 3288-3299Article in journal (Refereed)
    Abstract [en]

    As the standardization of network-assisted deviceto-device (D2D) communications by the 3 rd Generation Partnership Project progresses, the research community has started to explore the technology potential of new advanced features that will largely impact the performance of 5G networks. For 5G, D2D is becoming an integrative term of emerging technologies that take advantage of the proximity of communicating entities in licensed and unlicensed spectra. The European 5G research project Mobile and Wireless Communication Enablers for the 2020 Information Society (METIS) has identified advanced D2D as a key enabler for a variety of 5G services, including cellular coverage extension, social proximity and communicating vehicles. In this paper, we review the METIS D2D technology components in three key areas of proximal communications – network-assisted multi-hop, full-duplex, and multi-antenna D2D communications – and argue that the advantages of properly combining cellular and ad hoc technologies help to meet the challenges of the information society beyond 2020.

  • 119. Fodor, Gábor
    et al.
    Rácz, András
    Reider, Norbert
    Temesváry, András
    Architecture and Protocol Support for Radio Resource Management (RRM)2009In: Long Term Evolution: 3GPP LTE Radio and Cellular Technology / [ed] Furht, Borko; Ahson, Syed A., New York: Auerbach Publications , 2009, p. 99-154Chapter in book (Other academic)
  • 120.
    Fodor, Gábor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Telek, Miklós
    On the Pilot-Data Power Trade Off in Single Input Multiple Output Systems2014In: 20th European Wireless Conference, EW 2014, 2014, p. 485-492Conference paper (Refereed)
    Abstract [en]

    We consider a single cell single input multiple output (SIMO) system employing orthogonal frequencydivision multiplexing (OFDM). In such systems, setting the pilot-to-data power ratio (PDPR)has a large impact on the spectral and energy efficiency. In this paper we provide a closedform solution for the mean square error (MSE) of the received data as a function of thePDPR assuming Gaussian channels and minimum mean square error (MMSE) equalization.In numerical experiments we find that the MSE is a convex function of the PDPRand study the optimal PDPR as the number of antennas at the base station (BS) grows large.We find that the optimal PDPR heavilydepends on the number of antennas and the path loss between the mobile station and theBS. Specifically, as the number of antennas grows large, a larger portionof the total power budget needs to be allocated for pilot signals, especially for low pathloss users.

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  • 121.
    Fodor, Sebastian
    et al.
    Jane Street Capital, London, U.K.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Stockholm, Sweden.
    Gurgunoglu, Doga
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Telek, Miklos
    Budapest University of Technology and Economics, Department of Networked Systems and Services, Budapest, Hungary; ELKH-BME Information Systems Research Group, Budapest, Hungary.
    Optimizing Pilot Spacing in MU-MIMO Systems Operating Over Aging Channels2023In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 71, no 6, p. 3708-3720Article in journal (Refereed)
    Abstract [en]

    In the uplink of multiuser multiple input multiple output (MU-MIMO) systems operating over aging channels, pilot spacing is crucial for acquiring channel state information and achieving high signal-to-interference-plus-noise ratio (SINR). Somewhat surprisingly, very few works examine the impact of pilot spacing on the correlation structure of subsequent channel estimates and the resulting quality of channel state information considering channel aging. In this paper, we consider a fast-fading environment characterized by its exponentially decaying autocorrelation function, and model pilot spacing as a sampling problem to capture the inherent trade-off between the quality of channel state information and the number of symbols available for information carrying data symbols. We first establish a quasi-closed form for the achievable deterministic equivalent SINR when the channel estimation algorithm utilizes multiple pilot signals. Next, we establish upper bounds on the achievable SINR and spectral efficiency, as a function of pilot spacing, which helps to find the optimum pilot spacing within a limited search space. Our key insight is that to maximize the achievable SINR and the spectral efficiency of MU-MIMO systems, proper pilot spacing must be applied to control the impact of the aging channel and to tune the trade-off between pilot and data symbols.

  • 122. G, Eneroth
    et al.
    G, Fodor
    G, Leijonhufvud
    A, Rácz
    I, Szabó
    Applying ATM/AAL2 as a switching technology in third-generation mobile access networks1999In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 37, no 6, p. 112-122Article in journal (Refereed)
    Abstract [en]

    In this article we focus on the transport and switching part of third-generation mobile access networks and outline some important aspects of applying ATM in these networks. In particular, we argue that in order for the mobile access network to support low-bit-rate delay-sensitive traffic consisting of short packets, the standardization of a new ATM adaptation layer, AAL2, and associated signaling protocol has been necessary. The AAL2 protocol has been designed to support low-bit-rate delay-sensitive services (typically compressed voice) where other adaptation layers fail to deliver the required QoS and maintain efficient resource utilization at the same time. Furthermore, in order to provide mobility and soft handover support in CDMA-based mobile networks such as UMTS or IMT-2000, there is also a strong demand for fast connection establishment and release. Therefore, when designing ATM-based cellular access networks some specific architectural and traffic management issues need to be addressed.

  • 123. G, Fodor
    On scheduling and interference coordination policies for multicell OFDMA networks2007In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 4479, p. 488-499Article in journal (Refereed)
    Abstract [en]

    In orthogonal frequency division multiple access systems there is an intimate relationship between the packet scheduler and the inter-cell interference coordination (ICIC) functionalities: they determine the set of frequency channels (sub-carriers) that are used to carry the packets of in-progress sessions. In this paper we build on previous work - in which we compared the so called random and coordinated ICIC policies - and analyze three packet scheduling methods. The performance measures of interest are the session blocking probabilities and the overall throughput. We find that the performance of the so-called Fifty-Fifty and What-It-Wants scheduling policies is improved by coordinated sub-carrier allocation, especially in poor signal-to-noise-and-interference situations. The performance of the All-Or-Nothing scheduler is practically insensitive to the choice of the sub-carrier allocation policy.

  • 124. G, Fodor
    Performance analysis of a reuse partitioning technique for OFDM based evolved UTRA2006In: 14th IEEE International Workshop on Quality of Service (IWQoS) / [ed] [sn], Piscataway: IEEE conference proceedings, 2006, p. 112-120Chapter in book (Other academic)
    Abstract [en]

    The current 3GPP working assumption on the evolved universal terrestrial radio access (E-UTRA) physical layer is that it will be based on single carrier frequency division multiple access (SC-FDMA) for the uplink and orthogonal frequency division multiple access (OFDMA) for the downlink. According to the concept specification, inter-cell interference mitigation techniques applicable to SC-FDMA and OFDMA systems are expected to be the key radio resource management techniques for E-UTRA. In this paper we propose and analyze a simple reuse partitioning technique (assuming coordinated sub-carrier allocation in the cells) that is able to minimize inter-cell interference. We propose a model that is able to take into account that sessions dynamically enter and leave the system. Rigid sessions require a class-specific fixed number of sub-carriers, while elastic sessions can enter the system if a minimum number of sub-carriers is allocated to them. In this rather general setting we analyze the system performance in terms of the expected number of sub-carrier collisions, the session blocking probabilities and the signal-to-noise-and-interference ratio performance. We present numerical results on the various trade-offs between these measures that provide insight into the behavior of OFDM based cellular systems and help dimension the parameters of a reuse partitioned system.

  • 125. G, Fodor
    Performance analysis of resource sharing policies in CDMA networks2007In: International Journal of Communication Systems, ISSN 1074-5351, E-ISSN 1099-1131, Vol. 20, no 2, p. 207-233Article in journal (Refereed)
    Abstract [en]

    We consider an interference-limited code division multiple access (CDMA) network, in which some of the service classes are explicit rate controlled. Such rate-controlled service classes include adaptive ones whose holding time does not depend on the sending rate, while the holding time of elastic services becomes longer when their sending rate is slowed down. We develop a Markov model that allows us to study the impact of employing service differentiation (prioritization) during admission control and rate control on the classwise blocking probabilities and throughputs. The admission control takes into account the interference from adjacent cells as a log-normally distributed random variable and employs service class and state-dependent (soft) blocking in addition to hard blocking. The state-dependent rate control algorithm takes into account the minimum and maximum requested rates of admitted sessions in a fairness policy-dependent manner. Our conclusion is that work conserving bandwidth sharing policies may have a major impact on the moments of the time spent in the system by elastic services, but only a minor one on the classwise blocking probabilities. When the admission control algorithm takes into account the neighbour cell caused interference, the blocking probability of all classes increases somewhat, but the throughput of the accepted sessions increases. Blocking prioritization in the soft blocking model affects the classwise total blocking probabilities but has little impact on the throughput of adaptive and elastic traffic.

  • 126. G, Fodor
    et al.
    A, Eriksson
    A, Tuoriniemi
    Providing quality of service in always best connected networks2003In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 41, no 7, p. 154-163Article in journal (Refereed)
  • 127. G, Fodor
    et al.
    A, Pradini
    A, Gattami
    On applying network coding in network assisted device-to-device communications2014In: European Wireless 2014; 20th European Wireless Conference (EW 2014), Berlin: IEEE conference proceedings, 2014, p. 651-656Conference paper (Other academic)
    Abstract [en]

    Device-to-device (D2D) communication has been shown to increase the spectrum and energy efficiency of local communication sessions in cellular networks. On the other hand, physical layer network coding (NWC) at a cellular base station ¿ which can be employed without D2D functionality ¿ can also improve the efficiency of a cellular network that carries local traffic. In this paper we study the joint application of D2D and NWC technologies with the purpose of further improving the performance of cellular networks that employ either D2D or NWC alone. We find that the joint D2D and NWC scheme yields additional gains, provided that the network exercises proper mode selection (MS) and resource allocation. Specifically, a cellular network that supports both D2D and NWC can achieve higher spectral and energy efficiency than a network that employs only one of these schemes.

  • 128. G, Fodor
    et al.
    A, Rácz
    S, Blaabjerg
    Simulative analysis of routing and link allocation strategies in ATM networks supporting ABR services1998In: IEICE transactions on communications, ISSN 0916-8516, E-ISSN 1745-1345, Vol. E81-B, no 5, p. 985-994Article in journal (Refereed)
  • 129. G, Fodor
    et al.
    C, Koutsimanis
    A low intercell interference variation scheduler for OFDMA networks2008In: 2008 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, PROCEEDINGS, VOLS 1-13 / [ed] IEEE, New York: IEEE conference proceedings, 2008, p. 3078-3084Chapter in book (Other academic)
    Abstract [en]

    In orthogonal frequency division multiple access networks, link adaptation (LA) selects the appropriate modulation and coding scheme for the upcoming transmission time interval. Since LA relies on measurements of the interference level and assumes that it remains similar during the next scheduling instance, the performance of LA depends on the variation (rather than simply the level) of intercell interference (ICI). In this paper we propose a minimum variance scheduler that allows for opportunistic scheduling - and thereby to take advantage of multi-user frequency diversity - but keeps the variation of intercell interference at a low level. We build on previously proposed collision models (detailed in own work and related other papers) and study the interplay between this scheduler and two intercell interference coordination (ICIC) methods that we call random and coordinated subcarrier allocation. We find that the proposed low variance scheduling scheme together with coordinated ICIC reduces ICI and its variance and is superior to other scheduling techniques in terms of the overall system throughput.

  • 130. G, Fodor
    et al.
    C, Koutsimanis
    On the impact of uplink interference coordination when using multiple antennas at the base station2008In: GLOBECOM 2008 - 2008 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE: IEEE Global Telecommunications Conference (GLOBECOM 08)(51st IEEE Global Telecommunications Conference) / [ed] IEEE, New York: IEEE conference proceedings, 2008, p. 5026-5031Chapter in book (Other academic)
    Abstract [en]

    We consider the uplink of a multi-cell orthogonal frequency division multiple access (OFDMA) system that employs multiple (M > 1) receive antennas and maximum ratio combining at the base station. We propose a model that captures the impact of intercell interference coordination on the modulation and coding scheme dependent bit error rate (BER) performance. We analyze this model in two steps. First, we find a closed form formula to calculate the BER under Rayleigh fading for a single subcarrier. Second, we calculate the subcarrier collision probabilities under random and coordinated subcarrier allocation. Combining these two steps allows us to derive the average BER performance (over all OFDM subcarriers) without/with intercell interference coordination (ICIC). We perform extensive Monte Carlo simulations in order to compare these two schemes when mobile stations are positioned randomly in multi-cell cell system. We find that at low and medium load coordinated allocation is superior (for various values of M), while at higher loads the two schemes perform similarly. We also find that at asymmetric load, it is beneficial to employ "asymmetric ICIC" as opposed to "symmetric ICIC". Finally, we explain a somewhat counterintuitive result that shows that the ICIC gain can be larger with multiple antennas at the base station than when there is only one antenna, although this gain is in the very low BER regime.

  • 131. G, Fodor
    et al.
    E, Nordstrom
    S, Blaabjerg
    Revenue optimization and fairness control of priced guaranteed and best effort services on an ATM transmission link1998In: ICC 98 - 1998 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS VOLS 1-3 / [ed] anon, New York: IEEE , 1998, p. 1696-1705Chapter in book (Other academic)
    Abstract [en]

    This paper is the sequel of two previous papers describing and analyzing partially blocking-queueing systems. In [1, 2] we proposed the extension of the classical multirate circuit switched loss model [11] in order to model and analyze on the call level ATM systems supporting best effort type service classes, such as the ABR or UBR service classes. After a brief review of the basic modelling concepts, in this paper we are concerned with optimal Call Admission Control, (CAC) of CBR/VBR and ABR/UBR calls in the sense that we want to maximize the revenue on a single ATM link when both QoS guaranteed and best effort service classes are present. We formulate the problem as a Markov Decision Problem [3, 4, 5, 11, 13, 15, 16] and find that the concept of intelligent blocking is useful in this context. We solve this optimization task by policy iteration to find the blocking states of the link. This modelling framework (in its present form and by extensions) allows to study the impact of pricing policies on CAC and fairness.

  • 132. G, Fodor
    et al.
    G, Leijonhufvud
    S, Malomsoky
    A, Racz
    Comparison of call admission control algorithms in ATM/AAL2 based 3/sup rd/ generation mobile access networks1999In: 1999 IEEE Wireless Communications and Networking Conference (WCNC) / [ed] IEEE, New York: IEEE , 1999, p. 1508-1512Chapter in book (Other academic)
  • 133. G, Fodor
    et al.
    G, Malicsko
    S, Malomsoky
    A joint radio-IP resource reservation scheme in All-IP 3rd generation networks2000In: Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC) / [ed] IEEE, New York: IEEE , 2000, p. 1286-1290Chapter in book (Other academic)
  • 134. G, Fodor
    et al.
    K, El-Malki
    D, Partain
    Closing the gap between industry, academia and users: Is there a need for QoS in wireless systems?2005In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 3552, p. 375-378Article in journal (Refereed)
    Abstract [en]

    In this short paper we make the point that although there may be a gap between academic and industrial research in the area of quality of service (QoS), this gap can be narrowed. In order for this to happen, it is important that the academic and industrial players jointly make an effort to better understand business drivers and end user needs and analyze how networks are used and how they are likely to evolve. That is, understanding the key drivers (the "why"-s) in the QoS area is the key in bringing academic and industrial research (that aims to answer the "how"-s) closer to each other.

  • 135. G, Fodor
    et al.
    M, Lindström
    On multi-cell admission control in CDMA networks2008In: International Journal of Communication Systems, ISSN 1074-5351, E-ISSN 1099-1131, Vol. 21, no 1, p. 25-50Article in journal (Refereed)
    Abstract [en]

    We consider a multi-cell (MC) code division multiple access (CDMA) system that supports multiple service classes, including peak rate allocated and elastic ones. Peak rate allocated sessions—when admitted into the system—transmit at a constant bit rate, while elastic sessions can be slowed down at the expense of increasing their residency time. Admitted sessions cause an instantaneous bit rate-dependent interference in neighbour cells. In this rather general setting, we propose a method to calculate the class-wise blocking probabilities as the functions of the estimated so-called inter-cell coupling factors. In the paper this coupling factor is the ratio between the uplink path gains to different Node-B:s (that can be easily obtained in a CDMA system from pilot measurement reports), but our model could include other coupling measures as well. We find that when these coupling factors are underestimated, the system may get into false states (FSs) or false rate states(FRSs) that lead to violating the noise rise threshold. As traffic becomes increasingly elastic, the probability of FSs decreases, but the probability of FRSs increases. Based on numerical results, we make the point that as the traffic becomes more elastic, avoiding the underestimation of these coupling factors as well as exercising MC admission control plays an increasingly important role in guaranteeing proper service quality.

  • 136. G, Fodor
    et al.
    P, Skillermark
    Performance analysis of a reuse partitioning technique for multi-channel cellular systems supporting elastic services2009In: International Journal of Communication Systems, ISSN 1074-5351, E-ISSN 1099-1131, Vol. 22, no 3, p. 307-342Article in journal (Refereed)
    Abstract [en]

    For multi-cell systems employing intra-cell orthogonal communication channels, inter-cell interference mitigation techniques are expected to be one of the key radio resource management functions. In this paper we propose and analyze a simple reuse partitioning technique (with random and coordinated resource block allocation in neighbor cells) that is able to reduce inter-cell interference. We propose a model that is able to take into account that sessions dynamically enter and leave the system. Rigid sessions require a class-specific fixed number of resource blocks, while elastic sessions can enter the system if a minimum number of resources are allocated to them. In this rather general setting (and using the example of a system employing frequency division for multiple access) we analyze the system performance in terms of the expected number of channel collisions, the session-blocking probabilities, the signal-to-interference-and-noise ratio (SINR) and packet error rate performance. We present numerical results on the various trade-offs between these measures (including the trade-off between the reuse factor and the SINR performance) that provide insight into the behavior of multi-channel cellular systems and help dimensionalize the parameters of a reuse partitioned system.

  • 137. G, Fodor
    et al.
    S, Sorrentino
    S, Sultana
    Network assisted device-to-device communications: Use cases, design approaches, and performance aspects2014In: Smart Device to Smart Device Communication / [ed] Mumtaz, Shahid; Rodriguez, Jonathan, Cham (Svájc): Springer, 2014, p. 135-163Chapter in book (Other academic)
    Abstract [en]

    Network assisted device-to-device (D2D) communications have emerged as a means of increasing spectral and energy efficiency, reducing latency and creating a platform for proximity-based services. Application areas of D2D communications include cellular network offloading and coverage extension, proximity-based social networking, and providing national security and public safety (NSPS) in infrastructure-less situations. This broad range of applications has led to a large set of technical requirements that must be taken into account when designing physical layer algorithms, user and control plane protocols, and network architecture. In this chapter we review the key requirements and current approaches to network assisted service and device discovery, radio resource management and tuning the performance of integrated D2D, and cellular networks.

  • 138.
    Gabor, Fodor
    et al.
    Ericsson Research.
    Miklos, Telek
    On the Tradeoff Between Blocking and Dropping Probabilities in Multi-cell Cdma Networks2007In: Journal of Communications, ISSN 1796-2021, E-ISSN 2374-4367, Vol. 2, no 1, p. 22-33Article in journal (Refereed)
    Abstract [en]

    This paper is a sequel of previous work, in which we proposed a model and computational technique to calculate the Erlang capacity of a single CDMA cell that supports elastic services. The present paper extends that base model by taking into account two important aspects of CDMA. First, we describe a simple and a refined multicell CDMA model that are able to capture the impact of the neighbor cells on important performance measures of the cell under study. These performance measures include the class-wise blocking probabilities and the mean time that elastic sessions spend in the system. Secondly, we model the impact of the outage by taking into account that in-progress sessions can be dropped with a probability that depends on the current load in the serving and neighbor cells. We then consider a system with elastic and rigid service classes and analyze the trade-off between the total (soft and hard) blocking probabilities on the one hand and the throughput and the session drop probabilities on the other.

  • 139. Ghauch, Hadi
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Skoglund, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Machine Learning for Spectrum Sharing in Millimeter‐Wave Cellular Networks2020In: Machine Learning for Future Wireless Communications / [ed] Fa‐Long Luo, John Wiley & Sons, 2020, p. 45-62Chapter in book (Refereed)
    Abstract [en]

    This chapter is devoted to the use of machine learning (ML) tools to address the spectrum‐sharing problem in cellular networks. The emphasis is on a hybrid approach that combines the traditional model‐based approach with a (ML) data‐driven approach. Taking millimeter‐wave cellular network as an application case, the theoretical analyses and experiments presented in the chapter show that the proposed hybrid approach is a very promising solution in dealing with the key technical aspects of spectrum sharing: the choice of beamforming, the level of information exchange for coordination and association, and the sharing architecture. The chapter then focuses on motivation and background related to spectrum sharing. It also presents the system model and problem formulation, and focuses on all technical aspects of the proposed hybrid approach. Finally, the chapter discusses further issues and conclusions.

  • 140. Gomes, P. R. B.
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Stockholm, Sweden.
    Freitas, W. C.
    De Almeida, A. L. F.
    Silva, Y. C. B.
    Tensor-Based Modeling and Processing for Channel Estimation in Two-Hop V2X MIMO Systems2019In: 2019 IEEE Conference on Standards for Communications and Networking, CSCN 2019, Institute of Electrical and Electronics Engineers (IEEE) , 2019Conference paper (Refereed)
    Abstract [en]

    Efficient vehicle-to-everything (V2X) communications improve traffic safety, enable autonomous driving and help to reduce environmental impacts. To achieve these objectives, accurate channel estimation in highly mobile scenarios becomes necessary. In this paper, we propose a tensor modeling-based approach for channel estimation and receiver design in a two-hop multiple-input multiple-output V2X communication system. Specifically, by exploiting a Tucker-2 modeling of the received signals, and relying on the joint estimation of the two-hop link, we formulate simple tensor-based closed-form and iterative semi-blind receivers. Furthermore, motivated by the parallel factor analysis (PARAFAC) structure of the time-varying multipath channel, we develop an iterative algorithm for estimating key parameters of the two-hop channel - including angles of departure, angles of arrival and path gains - from the factor matrices of the estimated channel tensors. Simulation results illustrate the performance of the proposed channel estimation and receiver algorithms in selected V2X communications scenarios.

  • 141.
    Gomes, Paulo R.B.
    et al.
    Federal University of Ceará, Wireless Telecom Research Group, Brazil.
    De Araujo, Gilderlan T.
    Federal University of Ceará, Wireless Telecom Research Group, Brazil.
    Sokal, Bruno
    Federal University of Ceará, Wireless Telecom Research Group, Brazil.
    De Almeida, Andre L.F.
    Federal University of Ceará, Wireless Telecom Research Group, Brazil.
    Makki, Behrooz
    Ericsson Research, Göteborg, Sweden.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Göteborg, Sweden.
    Tensor-Based Channel Estimation for RIS-Assisted Communications with Non-Ideal Phase Shift Responses2022In: 2022 Workshop on Communication Networks and Power Systems, WCNPS 2022, Institute of Electrical and Electronics Engineers (IEEE) , 2022Conference paper (Refereed)
    Abstract [en]

    Reconfigurable intelligent surface (RIS) is a candidate technology for future wireless networks. It is known that the promised gains of RIS-Assisted communications depend on the channel estimation performance. When the RIS is affected by imperfections, the associated phase shift responses present a non-ideal behavior, which translates into unknown, and possibly time-varying, phase deviations. Such perturbations can be caused by physical, electronic, or environmentalrelated conditions. In this scenario, traditional channel estimation schemes may fail to provide sufficiently accurate channel estimates. In this work, considering a time-varying RIS imperfection model, we propose an efficient and low-complexity tensor-based method to estimate the involved communication channels under unknown phase-shift responses. The proposed algorithm relies on a tensor modeling of the received signals and has a closed-form solution based on the higher order singular value decomposition. Simulation results show the effectiveness of our proposed solution in terms of estimation accuracy and computational complexity compared to the benchmark method.

  • 142. Guimaraes, F. R. V.
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Stockholm, Sweden.
    Freitas, W. C.
    Silva, Y. C. B.
    A Multi-Stream Pricing-Based Precoding and Power Control Algorithm for Dynamic TDD Networks2019In: 2019 IEEE Conference on Standards for Communications and Networking, CSCN 2019, Institute of Electrical and Electronics Engineers (IEEE) , 2019Conference paper (Refereed)
    Abstract [en]

    Dynamic time division duplexing (DTDD) cellular networks enable to adapt the number of uplink and downlink time slots to the prevailing traffic demands in each cell at the expense of base station (BS)-to-BS and user equipment (UE)-to-UE interference. Recognizing the importance of mitigating the effect of these additional interference types, previous works proposed multicell coordinated beamforming to realize the full potential of DTDD systems that employ multiple antennas at the BSs. Unfortunately, the previously proposed mechanisms suffer from slow convergence, which renders such schemes impractical in fast fading and highly mobile environments. In this paper, we formulate the multicell multi-stream DTDD beamforming problem as an optimization task, and propose a near-optimal pricing-based algorithm to determine the beam directions and transmit power levels for each stream at the BSs. The proposed distributed precoding and power control algorithm not only improves the downlink performance, but it also substantially mitigates the BS-to-BS interference levels, and thereby improves the uplink performance as well. Simulation results indicate that the proposed algorithm exhibits faster convergence than previously proposed near-optimal schemes at the expense of some small performance degradation in terms of the achieved signal-to-interference-plus-noise-ratio (SINR).

  • 143.
    Guimaraes, Francisco R. V.
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, CP 6005, BR-60440970 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Res, S-16483 Stockholm, Sweden.
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, CP 6005, BR-60440970 Fortaleza, Ceara, Brazil..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, CP 6005, BR-60440970 Fortaleza, Ceara, Brazil..
    Pricing-Based Distributed Beamforming for Dynamic Time Division Duplexing Systems2018In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, no 4, p. 3145-3157Article in journal (Refereed)
    Abstract [en]

    Multicell dynamic time division duplexing (TDD) systems make it possible to adapt the number of uplink and downlink time slots in each cell to the prevailing cell-wide traffic demand. Although dynamic TDD systems can be advantageously deployed in scenarios in which the uplink and downlink traffic demands are asymmetric and time varying, dynamic TDD systems give rise to base station to base station (BS-to-BS) interference and user equipment to user equipment (UE-to-UE) interference that negatively impact the system performance. In this paper, we propose employing a distributed beamforming scheme to mitigate the BS-to-BS interference and thereby to improve the uplink performance. Specifically, the proposed scheme uses interference pricing to find the appropriate precoder vectors at the BSs, which also improves the signal-to-interference-plus-noise ratio (SINR) performance in the downlink. We compare the performance of the pricing-based (PB) beamforming scheme with that of zero-forcing beamforming in an outdoor picocell environment specified by the 3rd Generation Partnership Project using a realistic system simulator. We find that the proposed PB scheme boosts the SINR in the uplink at the expense of a small degradation of the downlink SINR compared with the zero-forcing scheme. On the other hand, the PB beamforming approach can significantly reduce the downlink transmit power levels and thereby improve the overall energy efficiency of the system.

  • 144. Guo, K.
    et al.
    Dai, S.
    Zhang, C.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Sweden.
    Ascheid, G.
    Massive MIMO aided multi-pair relaying with underlaid D2D communications2017In: European Wireless 2017 - 23rd European Wireless Conference, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 8011348Conference paper (Refereed)
    Abstract [en]

    Device-to-device (D2D) communication underlaying a cellular infrastructure is an important technique, e.g. to offload traffic, but has a limit of short range, which can be overcome via relaying. In such context, the coexistence of D2D and multi-pair communications in massive MIMO aided relaying is considered in this paper. The direct D2D transmission reuses the source-torelay spectrum in the first hop, which leads to a rate loss at the destination users, due to the amplify-and-forward relaying. To evaluate this loss, a closed-form deterministic equivalent of the end-to-end (e2e) signal to interference-plus-noise ratio (SINR) is derived. Moreover, in case of failed direct transmissions, D2D receivers can perform the detection in the second hop, based on the signal forwarded by the relay. The associated deterministic D2D SINR equivalent is also derived. The asymptotic analysis indicates that the transmit power of source users can be made inversely proportional to the number of relay antennas, such that non-vanishing e2e rate at the destination users and relay assisted D2D rate exist. Simulations validate the analytical results and the feasibility of supporting underlaid D2D transmissions when deploying multi-pair relaying with massive MIMO.

  • 145. Guo, Kaifeng
    et al.
    Guo, Yan
    Fodor, Gabor
    Ascheid, Gerd
    Uplink power control with MMSE receiver in multi-cell MU-massive-MIMO systems2014In: 2014 IEEE International Conference on Communications (ICC), New York: IEEE conference proceedings, 2014, p. 5184-5190Conference paper (Other academic)
    Abstract [en]

    In the current literature considering multi-cell multi-user massive multiple-input multiple-output (MU-Massive-MIMO) systems, equal uplink power allocation among users is typically assumed, which does not exploit the potential of peruser power control. By contrast, in this paper we apply multi-cell uplink power control, assuming the minimum mean-square-error receiver based on the pilot contaminated channel estimation and a very large but finite number of antennas at the base station. We derive the lower bound on the average post-processing uplink signal to interference-plus-noise ratio (SINR) with individual power assignment between pilot and data transmissions for each user, which facilitates a joint iterative uplink pilot and data power control strategy that minimizes the sum transmit power of all users subject to the per-user SINR and per-user power constraints. The convergence of the proposed algorithm to a unique fixed point optimal solution is discussed for both single- and multi-user scenarios. Numerical results indicate the significance of uplink power control which further improves the energy efficiency in MU-Massive-MIMO systems.

  • 146.
    Hammarberg, Peter
    et al.
    Ericsson Research, Sweden.
    Vinogradova, Julia
    Ericsson Research, Sweden.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Finland.
    Shreevastav, Ritesh
    Ericsson Research, Sweden.
    Dwivedi, Satyam
    Ericsson Research, Sweden.
    Gunnarsson, Fredrik
    Ericsson Research, Sweden.
    Architecture, Protocols, and Algorithms for Location-Aware Services in beyond 5G Networks2022In: IEEE Communications Standards Magazine, E-ISSN 2471-2825, Vol. 6, no 4, p. 88-95Article in journal (Refereed)
    Abstract [en]

    The automotive and railway industries are rapidly transforming with a strong drive toward automation and digitalization, with the goal of increased convenience, safety, efficiency, and sustainability. Since assisted and fully automated automotive and train transport services increasingly rely on vehicle-to-everything communications and high-accuracy real-time positioning, it is necessary to continuously maintain high-accuracy localization, even in occlusion scenes such as tunnels, urban canyons, or areas covered by dense foliage. In this article, we review the 5G positioning framework of the 3rd Generation Partnership Project in terms of methods and architecture and propose enhancements to meet the stringent requirements imposed by the transport industry. In particular, we highlight the benefit of fusing cellular and sensor measurements, and discuss required architecture and protocol support for achieving this at the network side. We also propose a positioning framework to fuse cellular network measurements with measurements by onboard sensors. We illustrate the viability of the proposed fusion-based positioning approach using a numerical example.

  • 147. I, Cananéa
    et al.
    D, Mariz
    J, Kelner
    D, Sadok
    G, Fodor
    An on-line access selection algorithm for ABC networks supporting elastic services2008In: Wireless Communications and Networking Conference, 2008. WCNC 2008. IEEE, New York: IEEE conference proceedings, 2008, p. 2033-2038Conference paper (Refereed)
    Abstract [en]

    The problem of access selection (AS) for multi-access networks has for long been addressed by both the standardization and research communities. As a result, a number of papers have proposed efficient AS algorithms that can take into account radio resource efficiency, overall capacity and quality of service (QoS) requirements in a multi-service environment. However, only a few works have developed on-line AS algorithms that do not require a priori knowledge of the traffic mix when delay sensitive (e.g. voice) and best effort (data) applications are supported. In this work, we present an online AS algorithm that performs well in a multiaccess network supporting two service classes and specifically takes into account the elastic nature of data applications. We model AS as a binpacking problem and realize that the problem is NP-complete. Therefore, we develop a heuristic algorithm called LessDamage that calculates a damage parameter and uses it as a metric for the allocation strategy. Simulation results show that LessDamage performs better in terms of blocking probability and elastic data throughput than available online binpacking heuristics, independently of the number of the available access technologies.

  • 148. JMB, Da Silva
    et al.
    G, Fodor
    TF, Maciel
    Performance analysis of network-assisted two-hop D2D communications2014In: 2014 IEEE Globecom Workshops (GC Wkshps), New York: IEEE conference proceedings, 2014, p. 1050-1056Conference paper (Other academic)
    Abstract [en]

    Network-assisted single-hop device-to-device (D2D) communication can increase the spectral and energy efficiency of cellular networks by taking advantage of the proximity, reuse, and hop gains. In this paper we argue that D2D technology can be used to further increase the spectral and energy efficiency if the key D2D radio resource management algorithms are suitably extended to support network assisted multi-hop D2D communications. Specifically we propose a novel, distributed utility maximizing D2D power control (PC) scheme that is able to balance spectral and energy efficiency while taking into account mode selection and resource allocation constraints that are important in the integrated cellular-D2D environment. Our analysis and numerical results indicate that multi-hop D2D communications combined with the proposed PC scheme can be useful not only for harvesting the potential gains previously identified in the literature, but also for extending the coverage of cellular networks.

  • 149.
    Kant, Shashi
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering. Ericsson AB.
    Barros da Silva Jr., José Mairton
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering. Princeton University, Princeton, NJ, USA,.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson AB.
    Göransson, Bo
    KTH, School of Electrical Engineering and Computer Science (EECS). Ericsson AB.
    Bengtsson, Mats
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Federated Learning using Three-Operator ADMMManuscript (preprint) (Other academic)
  • 150.
    Kant, Shashi
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering. Ericsson AB.
    Barros da Silva Jr., José Mairton
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering. Princeton University, Princeton, NJ, USA.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson AB.
    Göransson, Bo
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering. Ericsson AB.
    Bengtsson, Mats
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Federated Learning Using Three-Operator ADMM2023In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, E-ISSN 1941-0484, Vol. 17, no 1, p. 205-221Article in journal (Refereed)
    Abstract [en]

    Federated learning (FL) has emerged as an instance of distributed machine learning paradigm that avoids the transmission of data generated on the users' side. Although data are not transmitted, edge devices have to deal with limited communication bandwidths, data heterogeneity, and straggler effects due to the limited computational resources of users' devices. A prominent approach to overcome such difficulties is FedADMM, which is based on the classical two-operator consensus alternating direction method of multipliers (ADMM). The common assumption of FL algorithms, including FedADMM, is that they learn a global model using data only on the users' side and not on the edge server. However, in edge learning, the server is expected to be near the base station and have direct access to rich datasets. In this paper, we argue that leveraging the rich data on the edge server is much more beneficial than utilizing only user datasets. Specifically, we show that the mere application of FL with an additional virtual user node representing the data on the edge server is inefficient. We propose FedTOP-ADMM, which generalizes FedADMM and is based on a three-operator ADMM-type technique that exploits a smooth cost function on the edge server to learn a global model parallel to the edge devices. Our numerical experiments indicate that FedTOP-ADMM has substantial gain up to 33% in communication efficiency to reach a desired test accuracy with respect to FedADMM, including a virtual user on the edge server.

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