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  • 151. Reider, Norbert
    et al.
    Fodor, Gabor
    Ericsson Research, Stockholm, Sweden.
    On Opportunistic Power Control for MIMO-OFDM Systems2010In: 2010 IEEE Globecom Workshops, GC'10, Miami: IEEE Press, 2010, p. 793-798Chapter in book (Other academic)
    Abstract [en]

    Transmit antenna diversity and single user spatial multiplexing have become attractive in practical systems, because they achieve performance gains without requiring sophisticated channel state information (CSI) feedback mechanisms. On the other hand, when fast and accurate CSI at the transmitter is available, opportunistic power control (OPC) is an attractive alternative to signal-to-interference-and-noise ratio (SINR) target following approaches, because it maximizes throughput by taking advantage of fast channel variations. In this paper we examine the question whether OPC is worth the pain of obtaining fast CSI by evaluating the gains of OPC for the downlink of a system employing multiple input multiple output (MIMO) systems with Alamouti and open loop spatial multiplexing (SM). We formulate the OPC problem as a throughput maximization task subject to power budget and fairness constraints. We solve this task by the Augmented Lagrangian Penalty Function and find that without fairness constraints, OPC in concert with SM provides superior throughput. With increasingly tight fairness constraints, Alamouti along with equal power allocation becomes a viable alternative to the SM OPC scheme. Both from fairness and throughput perspectives, Alamouti along with OPC is particularly efficient when adaptive MCS is employed and users with large differences in channel qualities have to share the total transmit power.

  • 152. Reider, Norbert
    et al.
    Fodor, Gábor
    Ericsson Res., Stockholm, Sweden.
    Rácz, András
    Opportunistic Target SINR Setting for the MIMO Broadcast Channel2010In: 2010 European Wireless Conference (EW) / [ed] IEEE, New York: IEEE Press, 2010, p. 132-140Chapter in book (Other academic)
  • 153. Reider, Norbert
    et al.
    Rácz, András
    Fodor, Gábor
    Ericsson Res., Stockholm, Sweden.
    On Scheduling and Power Control in Multi-Cell Coordinated Clusters2009In: GLOBECOM 2009 - 52nd IEEE Global Telecommunications Conference / [ed] M, Ulema, New York: IEEE , 2009Chapter in book (Other academic)
    Abstract [en]

    Recently, tight network coordination in cellular systems has been demonstrated to improve the spectrum efficiency by means of signal processing methods. However, the performance of signal processing based multi-cell coordination is sensitive to backhaul delays, channel estimation errors and imperfections in fast link control. In this paper we consider tight network coordination for fast radio resource management (RRM) including packet scheduling, power control and modulation and coding scheme selection. We use a system level simulator to analyze the uplink performance of a multi-cell coordinated system that is built around a fast backhaul transport infrastructure for the purpose of enabling coordinated RRM rather than coordinated signal processing. We find that coordinated RRM alone can provide significant performance gains, up to 50% for cell edge and cell capacity as compared to traditional single-cell configurations and that multi-cell fast power control and modulation and coding scheme selection can significantly improve the accuracy of link adaptation in terms of signal-to-interference-and-noise (SINR) distribution, while imposing lower demands on the capacities of backhaul links compared to coordinated signal processing. Therefore RRM coordination can be an efficient complement to coordinated signal processing in multi-cell coordinated clusters.

  • 154. Rácz, András
    et al.
    Reider, Norbert
    Fodor, Gábor
    Ericsson Res., Stockholm, Sweden.
    On the Impact of Inter-Cell Interference in LTE2008In: GLOBECOM 2008 - 2008 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE: IEEE Global Telecommunications Conference (GLOBECOM 08)(51st IEEE Global Telecommunications Conference), New York: IEEE Press, 2008Chapter in book (Other academic)
  • 155. S, Racz
    et al.
    M, Telek
    Fodor, Gabor
    Mobile Networks- and Systems Research, Ericsson Radio Systems, Sweden.
    Link capacity sharing between guaranteed- and best effort services on an ATM transmission link under GoS constraints2001In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 17, no 1, p. 93-114Article in journal (Refereed)
    Abstract [en]

    While link allocation policies in multi-rate circuit switched loss models have drawn much attention in recent years, it is still an open question how to share the link capacity between service classes in a fair manner. In particular, when an ATM link is offered calls from service classes with/without strict QoS guarantees one is interested in link capacity sharing policies that maximize throughput and keep the per-class blocking probabilities under some GoS constraints. In this paper we propose a model and associated computational technique for an ATM transmission link to which CBR/VBR and ABR classes offer calls. We also propose a simple link allocation rule which takes into account blocking probability constraints for the CBR/VBR calls and a throughput constraint for the ABR calls and attempts to minimize the blocking probability of ABR calls. Numerical examples demonstrate the effectiveness of the policy and of the applied computational technique.

  • 156. S, Racz
    et al.
    M, Telek
    Fodor, Gábor
    Ericsson Res., Stockholm, Sweden.
    Call level performance analysis of 3(rd) generation mobile core networks2001In: 2001 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-10, CONFERENCE RECORD / [ed] IEEE, New York: IEEE Press, 2001, p. 456-461Chapter in book (Other academic)
  • 157. S, Rácz
    et al.
    BP, Gerö
    Fodor, Gabor
    Ericsson Research, Kista, Sweden.
    Flow level performance analysis of a multi-service system supporting elastic and adaptive services2002In: Performance evaluation (Print), ISSN 0166-5316, E-ISSN 1872-745X, Vol. 49, no 1-4, p. 451-469Article in journal (Refereed)
  • 158. S, Rácz
    et al.
    M, Telek
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Link capacity sharing between guaranteed and best effort services2000In: System Performance Evaluation: Methodologies and Applications / [ed] E, Gelenbe, Boca Raton FL: CRC Press , 2000, p. 69-79Chapter in book (Other academic)
  • 159. Saxena, V.
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Sweden.
    Karipidis, E.
    Mitigating pilot contamination by pilot reuse and power control schemes for massive MIMO systems2015In: IEEE Vehicular Technology Conference, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    The performance of massive multiple input multiple output systems may be limited by inter-cell pilot contamination (PC) unless appropriate PC mitigation or avoidance schemes are employed. In this paper we develop techniques based on existing long term evolution (LTE) measurements - open loop power control (OLPC) and pilot sequence reuse schemes, that avoid PC within a group of cells. We compare the performance of simple least-squares channel estimator with the higher-complexity minimum mean square error estimator, and evaluate the performance of the recently proposed coordinated pilot allocation (CPA) technique (which is appropriate in cooperative systems). The performance measures of interest include the normalized mean square error of channel estimation, the downlink signal-to-interference-plus-noise and spectral efficiency when employing maximum ratio transmission or zero forcing precoding at the base station. We find that for terminals moving at vehicular speeds, PC can be effectively mitigated in an operation and maintenance node using both the OLPC and the pilot reuse schemes. Additionally, greedy CPA provides performance gains only for a fraction of terminals, at the cost of degradation for the rest of the terminals and higher complexity. These results indicate that in practice, PC may be effectively mitigated without the need for second-order channel statistics or inter-cell cooperation.

  • 160.
    Shokri-Ghadikolaei, Hossein
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Boccardi, F.
    Erkip, E.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Kountouris, Marios
    Popovski, Petar
    Zorzi, Michele
    The Impact of beamforming and coordination on spectrum pooling in mmWave Cellular networks2016In: Signals, Systems and Computers, 2016 50th Asilomar Conference on, Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 7868986Conference paper (Refereed)
    Abstract [en]

    Spectrum pooling is not typically used in current cellular networks, because it only provides a slight performance improvement while requiring heavy coordination among different cellular operators. However, these problems can be potentially overcome in millimeter-wave (mmWave) networks, thanks to the use of beamforming both at base stations and at user equipments. In this paper, we develop a joint beamforming and cell association optimization problem to characterize the performance gain that can be obtained when spectrum pooling is used, as a function of the underlying beamforming and coordination strategies. Our performance analysis reveals that beamforming can substantially reduce the need for coordination and simplify the implementation of spectrum pooling. These benefits are more prominent at higher mmWave frequencies (for example, 73 GHz) due to the possibility of having antenna arrays with more elements within the radome. The results of this paper provides useful insights on the feasibility of spectrum pooling at mmWave networks.

  • 161.
    Shokri-Ghadikolaei, Hossein
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Boccardi, Federico
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zorzi, Michele
    Spectrum Sharing in mmWave Cellular Networks via Cell Association, Coordination, and Beamforming2016In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 34, no 11, p. 2902-2917Article in journal (Refereed)
    Abstract [en]

    This paper investigates the extent to which spectrum sharing in millimeter-wave (mmWave) networks with multiple cellular operators is a viable alternative to traditional dedicated spectrum allocation. Specifically, we develop a general mathematical framework to characterize the performance gain that can be obtained when spectrum sharing is used, as a function of the underlying beamforming, operator coordination, bandwidth, and infrastructure sharing scenarios. The framework is based on joint beamforming and cell association optimization, with the objective of maximizing the long-term throughput of the users. Our asymptotic and non-asymptotic performance analyses reveal five key points: 1) spectrum sharing with light on-demand intra-and inter-operator coordination is feasible, especially at higher mmWave frequencies (for example, 73 GHz); 2) directional communications at the user equipment substantially alleviate the potential disadvantages of spectrum sharing (such as higher multiuser interference); 3) large numbers of antenna elements can reduce the need for coordination and simplify the implementation of spectrum sharing; 4) while inter-operator coordination can be neglected in the large-antenna regime, intra-operator coordination can still bring gains by balancing the network load; and 5) critical control signals among base stations, operators, and user equipment should be protected from the adverse effects of spectrum sharing, for example by means of exclusive resource allocation. The results of this paper, and their extensions obtained by relaxing some ideal assumptions, can provide important insights for future standardization and spectrum policy.

  • 162.
    Shokri-Ghadikolaei, Hossein
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Res, Sweden.
    Popovski, Petar
    Aalborg Univ, Denmark.
    Zorzi, Michele
    Univ Padua, Italy.
    Millimeter Wave Cellular Networks: A MAC Layer Perspective2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 10, p. 3437-3458Article in journal (Refereed)
    Abstract [en]

    The millimeter wave (mmWave) frequency band is seen as a key enabler of multi-gigabit wireless access in future cellular networks. In order to overcome the propagation challenges, mmWave systems use a large number of antenna elements both at the base station and at the user equipment, which lead to high directivity gains, fully-directional communications, and possible noise-limited operations. The fundamental differences between mmWave networks and traditional ones challenge the classical design constraints, objectives, and available degrees of freedom. This paper addresses the implications that highly directional communication has on the design of an efficient medium access control (MAC) layer. The paper discusses key MAC layer issues, such as synchronization, random access, handover, channelization, interference management, scheduling, and association. The paper provides an integrated view on MAC layer issues for cellular networks, identifies new challenges and tradeoffs, and provides novel insights and solution approaches.

  • 163. Siomina, Iana
    et al.
    Furuskär, Anders
    Fodor, Gabor
    A mathematical framework for statistical QoS and capacity studies in OFDM networks2009In: 2009 IEEE 20TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, New York: IEEE conference proceedings, 2009Conference paper (Other academic)
    Abstract [en]

    This paper presents a mathematical modeling framework for studying the capacity of multi-cell orthogonal frequency division multiplexing networks in single- and multi-service scenarios with various quality of service (QoS) constraints. The framework is built around a feasible network load concept which relates cell resource utilization and interference-dependent resource demand generated by traffic. The feasible load problem is formulated for a general irregular network with non-uniform traffic distribution. Unlike in earlier works, the proposed model explicitly takes into account interference which is load- and service-dependent and models the service constraints on a time scale longer than the typical scheduling interval. A computationally efficient stochastic model is proposed for a regular network deployment with a user distribution pattern repeated over cells and then enhanced with QoS constraints. As an example application, the capacity region problem is studied and numerical results are presented for a realistic network setup. The framework can further be used, for example, for studying radio resource management algorithms or optimizing QoS parameters with respect to an operator QoS policy.

  • 164.
    Soldati, Pablo
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fodor, Gabor
    Ericsson Research, Sweden.
    Sorrentino, Stefano
    Ericsson Research, Sweden.
    On pilot dimensioning in multicell single input multiple output systems2011In: 2011 IEEE GLOBECOM Workshops, GC Wkshps 2011, IEEE , 2011, p. 1382-1387Conference paper (Refereed)
    Abstract [en]

    Resource management schemes in multicell orthogonal frequency division multiplexing (OFDM) networks typically assume perfect channel knowledge at the transmitter or employ a statistical channel estimation error. In this paper we propose a model that explicitly captures the inherent tradeoff between the power allocated to transmitting data and pilot signals in multicell single input multiple output (SIMO) systems. We first study the asymptotic behavior of the required data power to reach a predefined signal-to-noise ratio (SNR) target as a function of the employed pilot power in a single OFDM cell, then develop a distributed multicell algorithm that strives to minimize the multi-cell sum data power with respect to a predefined signal-to-interference-and-noise-ratio (SINR) target vector. The results provide new insights in dimensioning the pilot and data transmit power levels and serve as a basis for developing distributed power control schemes in multicell systems.

  • 165.
    van Dooren, Dirk
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson AB, Ericsson Res, Stockholm, Sweden..
    Gross, James
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Delay Analysis of Group Handover for Real-Time Control over Mobile Networks2018In: 2018 IEEE Global Communications Conference, GLOBECOM 2018 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8647501Conference paper (Refereed)
    Abstract [en]

    Future mobile networks will provide support for real-time control applications. The tight real-time and reliability constraints of these applications introduce novel challenges for mobility management. Legacy individual handover schemes do not sufficiently address these issues, as they do not consider physical interactions between mobile nodes. A novel group handover scheme is proposed which allows for the simultaneous handover of a group of nodes. Both the individual and the group handover are modeled as discrete-time Markov chains. Based on these models expressions for the stochastic handover delay are derived. The results are numerically evaluated in a vehicle platooning scenario. The group handover is shown to significantly reduce the handover delay in comparison to the individual handover. Furthermore, the group handover is shown to scale well when the number of vehicles increases. These improvements are shown to come at the cost of an increased messaging overhead.

  • 166. Widegren, Ina
    et al.
    Fodor, Gabor
    Williams, Brian
    Johnson, Oyama
    Application influenced policy for filtering and gating the data flow in a quality of service connection between a remote host and a host-user equipment session2001Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A method of filtering and gating data flow in a QoS connection between a remote host and user equipment in a packet data network using policy control mechanisms includes a remote host initiating an application in an application server and a corresponding session between the remote host and the user equipment (“UE”) via the application server. The UE requests, to a gateway support node (“GGSN”) of the network, establishment of a network bearer service between the UE and the remote host. A corresponding policy control function (“PCF”) in a policy server receives, from the application server, filtering data derived from session data received by the application server during the session. The GGSN interrogates the corresponding PCF in the policy server to initialize a gate using policy control filtering data at the GGSN. The gate then filters the data flow in the QoS connection according to the policy control filtering data.

  • 167. Y, Zhang
    et al.
    TM, Bohnert
    D, Moltchanov
    D, Staehle
    Fodor, Gabor
    Ericsson Research, Sweden.
    E, Knightly
    Broadband wireless access2009In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2009Article in journal (Refereed)
  • 168.
    Zhao, Peiyue
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Fodor, Gabor
    Ericsson Res, S-16480 Stockholm, Sweden..
    Dan, Gyorgy
    Budapest University of Technology and Economics, Budapest, Hungary.
    Telek, Miklos
    MTA BME Informat Syst Res Grp, H-1117 Budapest, Hungary.
    A Game Theoretic Approach to Setting the Pilot Power Ratio in Multi-User MIMO Systems2018In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 3, p. 999-1012Article in journal (Refereed)
    Abstract [en]

    We consider the uplink of a single cell multi-user multiple input multiple output (MU-MIMO) system, in which the base station acquires channel state information at the receiver by means of uplink pilot signals. Since each mobile station has a sum power budget that is used to transmit pilot and data symbols, the pilot power ratio (PPR) has a large impact on the system performance in terms of spectral and energy efficiency. We formulate the problem of PPR setting as a non-cooperative game, in which each mobile station aims at minimizing the mean squared error of the uplink received data symbols at the base station. We show that in this game a unique Nash equilibrium exists, and propose an iterative decentralized algorithm-termed best PPR algorithm (BPA)-that is guaranteed to converge to that Nash equilibrium. Since BPA dynamically responds to the measured interference, it outperforms widely used schemes that use a predetermined PPR. BPA also performs close to the global optimum, especially when mobile stations with similar path loss values are co-scheduled in the MU-MIMO system. Based on these insights, we propose a practical signaling mechanism for implementing BPA in MU-MIMO systems.

  • 169.
    Zhao, Peiyue
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Dán, György
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Telek, Miklos
    Budapest Univ Technol & Econ, H-1117 Budapest, Hungary.;MTA BME Informat Syst Res Grp, H-1117 Budapest, Hungary..
    A Game Theoretic Approach to Uplink Pilot and Data Power Control in Multi-Cell Multi-User MIMO Systems2019In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, no 9, p. 8707-8720Article in journal (Refereed)
    Abstract [en]

    In multi-user multiple-input-multiple-output (MU-MIMO) systems that employ pilot-symbol aided channel estimation, the pilot-to-data power ratio (PDPR) has a large impact on the system performance. In this paper, we consider the problem of setting the PDPR in multi-cell MU-MIMO systems in the presence of channel estimation errors, intercell interference and pilot contamination. To analyze and address this problem, we first develop a model of the multi-cell MU-MIMO system and derive a closed-form expression for the mean squared error of the uplink received data symbols. Building on this result, we then propose two decentralized PDPR-setting algorithms based on game theoretic approaches that are applicable in multi-cell systems. We find that both algorithms converge to a Nash equilibrium and provide performance improvements over systems that do not properly set the PDPR, while they maintain different levels of fairness.

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