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  • 1.
    Axell, Erik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Optimal and Sub-Optimal Spectrum Sensing of OFDM Signals in Known and Unknown Noise Variance2011Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 29, nr 2, s. 290-304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider spectrum sensing of OFDM signals in an AWGN channel. For  the case of completely known noise and signal powers, we set up  a vector-matrix model for an OFDM signal with a cyclic prefix and  derive the optimal Neyman-Pearson detector from first  principles. The optimal detector exploits the inherent correlation  of the OFDM signal incurred by the repetition of data in the cyclic  prefix, using knowledge of the length of the cyclic prefix and the  length of the OFDM symbol. We compare the optimal detector to the energy  detector numerically. We show that the energy detector is  near-optimal (within 1 dB SNR) when the noise variance is  known. Thus, when the noise power is known, no substantial gain can  be achieved by using any other detector than the energy detector.

    For the case of completely unknown noise and signal powers, we  derive a generalized likelihood ratio test (GLRT) based onempirical second-order statistics of  the received data. The proposed GLRT detector exploits the  non-stationary correlation structure of the OFDM signal and does not  require any knowledge of the noise power or the signal power. The  GLRT detector is compared to state-of-the-art OFDM signal detectors,  and shown to improve the detection performance with 5 dB SNR in  relevant cases.

  • 2.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Sanguinetti, Luca
    University of Pisa, Italy; University of Paris Saclay, France.
    Kountouris, Marios
    Huawei Technology Co Ltd, France.
    Deploying Dense Networks for Maximal Energy Efficiency: Small Cells Meet Massive MIMO2016Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 34, nr 4, s. 832-847Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    What would a cellular network designed for maximal energy efficiency look like? To answer this fundamental question, tools from stochastic geometry are used in this paper to model future cellular networks and obtain a new lower bound on the average uplink spectral efficiency. This enables us to formulate a tractable uplink energy efficiency (EE) maximization problem and solve it analytically with respect to the density of base stations (BSs), the transmit power levels, the number of BS antennas and users per cell, and the pilot reuse factor. The closed-form expressions obtained from this general EE maximization framework provide valuable insights on the interplay between the optimization variables, hardware characteristics, and propagation environment. Small cells are proved to give high EE, but the EE improvement saturates quickly with the BS density. Interestingly, the maximal EE is achieved by also equipping the BSs with multiple antennas and operate in a "massive MIMO" fashion, where the array gain from coherent detection mitigates interference and the multiplexing of many users reduces the energy cost per user.

  • 3.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Dynamical Effects of Time Delays and Time Delay Compensation in Power Controlled DS-CDMA2001Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 19, nr 1, s. 141-151Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

  • 4.
    Larsson, Erik G.
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Jorswieck, Eduard
    Dresden University of Technology.
    Competition Versus Cooperation on the MISO Interference Channel2008Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 26, nr 7, s. 1059-1069Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the problem of coordinating two competingmultiple-antenna wireless systems (operators) that operatein the same spectral band. We formulate a rate region whichis achievable by scalar coding followed by power allocationand beamforming. We show that all interesting points on thePareto boundary correspond to transmit strategies where bothsystems use the maximum available power. We then argue thatthere is a fundamental need for base station cooperation whenperforming spectrum sharing with multiple transmit antennas.More precisely, we show that if the systems do not cooperate,there is a unique Nash equilibrium which is inefficient in the sensethat the achievable rate is bounded by a constant, regardless ofthe available transmit power. An extension of this result to thecase where the receivers use successive interference cancellation(SIC) is also provided.Next we model the problem of agreeing on beamformingvectors as a non-transferable utility (NTU) cooperative gametheoreticproblem, with the two operators as players. Specificallywe compute numerically the Nash bargaining solution, which isa likely resolution of the resource conflict assuming that theplayers are rational. Numerical experiments indicate that selfishbut cooperating operators may achieve a performance which isclose to the maximum-sum-rate bound.

  • 5.
    Li, Yuan
    et al.
    Lund University, Sweden.
    Pappas, Nikolaos
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
    Angelakis, Vangelis
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
    Pioro, Michal
    Lund University, Sweden; Warsaw University of Technology, Poland.
    Yuan, Di
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. University of Maryland, MD 20742 USA.
    Optimization of Free Space Optical Wireless Network for Cellular Backhauling2015Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 33, nr 9, s. 1841-1854Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With the densification of nodes in cellular networks, free space optic (FSO) connections are becoming an appealing low cost and high rate alternative to copper and fiber backhaul solutions for wireless communication systems. To ensure a reliable cellular backhaul, provisions for redundant disjoint paths between the nodes must be made in the design phase. This paper aims at finding a cost-effective solution to upgrade the cellular backhaul with pre-deployed optical fibers using FSO links and mirror components. Since the quality of the FSO links depends on several factors, such as transmission distance, power, and weather conditions, we adopt an elaborate formulation to calculate link reliability. We present a novel integer linear programming model to approach optimal FSO backhaul design, guaranteeing K-disjoint paths connecting each node pair. Next, we derive a column generation method to a path-oriented mathematical formulation. Applying the method in a sequential manner enables high computational scalability. We use realistic scenarios to demonstrate that our approaches efficiently provide optimal or near-optimal solutions, and thereby allow for accurately dealing with the trade-off between cost and reliability.

  • 6.
    Matthaiou, Michail
    et al.
    Chalmers, Sweden .
    Karagiannidis, George K.
    Aristotle University of Thessaloniki, Greece .
    Larsson, Erik G
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Marzetta, Thomas L.
    Alcatel Lucent, NJ USA .
    Schober, Robert
    University of British Columbia, Canada .
    Editorial Material: Large-Scale Multiple Antenna Wireless Systems2013Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 31, nr 2, s. 113-116Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    n/a

  • 7.
    Ngo, Hien Quoc
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Suraweera, Himal A.
    University of Peradeniya, Peradeniya 20400, Sri Lanka .
    Matthaiou, Michail
    Queen's University Belfast, Belfast, BT3 9DT, U.K..
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Multipair Full-Duplex Relaying with Massive Arrays and Linear Processing2014Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 32, nr 9, s. 1721-1737Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a multipair decode-and-forward relay channel, where multiple sources transmit simultaneously their signals to multiple destinations with the help of a full-duplex relay station. We assume that the relay station is equipped with massive arrays, while all sources and destinations have a single antenna. The relay station uses channel estimates obtained from received pilots and zero-forcing (ZF) or maximum-ratio combining/maximum-ratio transmission (MRC/MRT) to process the signals. To signicantly reduce the loop interference effect, we propose two techniques: i) using a massive receive antenna array; or ii) using a massive transmit antenna array together with very low transmit power at the relay station. We derive an exact achievable rate expression in closed-form for MRC/MRT processing and an analytical approximation of the achievable rate for ZF processing. This approximation is very tight, particularly for a large number of relay station antennas. These closed-form expressions enable us to determine the regions where the full-duplex mode outperforms the half-duplex mode, as well as to design an optimal power allocation scheme. This optimal power allocation scheme aims to maximize the energy efficiency for a given sum spectral efficiency and under peak power constraints at the relay station and sources. Numerical results verify the effectiveness of the optimal power allocation scheme. Furthermore, we show that, by doubling the number of transmit/receive antennas at the relay station, the transmit power of each source and of the relay station can be reduced by 1.5 dB if the pilot power is equal to the signal power, and by 3 dB if the pilot power is kept fixed, while maintaining a given quality of service.

  • 8.
    Studer, Christoph
    et al.
    Rice University, TX USA .
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    PAR-Aware Large-Scale Multi-User MIMO-OFDM Downlink2013Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 31, nr 2, s. 303-313Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate an orthogonal frequency-division multiplexing (OFDM)-based downlink transmission scheme for large-scale multi-user (MU) multiple-input multiple-output (MIMO) wireless systems. The use of OFDM causes a high peak-to-average (power) ratio (PAR), which necessitates expensive and power-inefficient radio-frequency (RF) components at the base station. In this paper, we present a novel downlink transmission scheme, which exploits the massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems to achieve low PAR. Specifically, we propose to jointly perform MU precoding, OFDM modulation, and PAR reduction by solving a convex optimization problem. We develop a corresponding fast iterative truncation algorithm (FITRA) and show numerical results to demonstrate tremendous PAR-reduction capabilities. The significantly reduced linearity requirements eventually enable the use of low-cost RF components for the large-scale MU-MIMO-OFDM downlink.

  • 9.
    Xiao, Ming
    et al.
    Royal Institute Technology, Sweden.
    Mumtaz, Shahid
    Institute Telecomunicacoes, Portugal.
    Huang, Yongming
    Southeast University, Peoples R China.
    Dai, Linglong
    Tsinghua University, Peoples R China.
    Li, Yonghui
    University of Sydney, Australia.
    Matthaiou, Michail
    Queens University of Belfast, North Ireland.
    Karagiannidis, George K.
    Aristotle University of Thessaloniki, Greece; Aristotle University of Thessaloniki, Greece.
    Björnson, Emil
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Yang, Kai
    Tongji University, Peoples R China.
    Chih-Lin, I.
    China Mobile, Peoples R China.
    Ghosh, Amitabha
    Nokia, IL 60004 USA.
    Editorial Material: Millimeter Wave Communications for Future Mobile Networks (Guest Editorial), Part I in IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, vol 35, issue 7, pp 1425-14312017Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, nr 7, s. 1425-1431Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    n/a

  • 10.
    Xiao, Ming
    et al.
    KTH Royal Institute Technology, Sweden.
    Mumtaz, Shahid
    Institute Telecomunicacoes, Portugal.
    Huang, Yongming
    Southeast University, Peoples R China.
    Dai, Linglong
    Tsinghua University, Peoples R China.
    Li, Yonghui
    University of Sydney, Australia; University of Sydney, Australia.
    Matthaiou, Michail
    Queens University of Belfast, North Ireland.
    Karagiannidis, George K.
    Aristotle University of Thessaloniki, Greece; Aristotle University of Thessaloniki, Greece.
    Björnson, Emil
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Yang, Kai
    Tongji University, Peoples R China.
    Chih-Lin, I
    China Mobile, Peoples R China.
    Ghosh, Amitabha
    Nokia Bell Labs, NJ USA.
    Millimeter Wave Communications for Future Mobile Networks2017Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, nr 9, s. 1909-1935Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Millimeter wave (mmWave) communications have recently attracted large research interest, since the huge available bandwidth can potentially lead to the rates of multiple gigabit per second per user. Though mmWave can be readily used in stationary scenarios, such as indoor hotspots or backhaul, it is challenging to use mmWave in mobile networks, where the transmitting/receiving nodes may be moving, channels may have a complicated structure, and the coordination among multiple nodes is difficult. To fully exploit the high potential rates of mmWave in mobile networks, lots of technical problems must be addressed. This paper presents a comprehensive survey of mmWave communications for future mobile networks (5G and beyond). We first summarize the recent channel measurement campaigns and modeling results. Then, we discuss in detail recent progresses in multiple input multiple output transceiver design for mmWave communications. After that, we provide an overview of the solution for multiple access and backhauling, followed by the analysis of coverage and connectivity. Finally, the progresses in the standardization and deployment of mmWave for mobile networks are discussed.

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