The Experts below are selected from a list of 37611 Experts worldwide ranked by ideXlab platform
Tommy Svensson - One of the best experts on this subject based on the ideXlab platform.
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precoder design with incomplete feedback for Joint Transmission
2016Co-Authors: Tilak Rajesh Lakshmana, Antti Tolli, Rahul Devassy, Tommy SvenssonAbstract:A centralized coordinated multipoint downlink Joint Transmission in a frequency division duplex system requires channel state information (CSI) to be fed back from the cell-edge users to their serving BS, and aggregated at the central coordination node for precoding, so that interference can be mitigated. The control signals comprising of CSI and the precoding weights can easily overwhelm the backhaul resources. Relative thresholding has been proposed to alleviate the burden; however, this is at the cost of reduction in throughput. In this paper, we propose utilizing the long-term channel statistics comprising of pathloss and shadow fading in the precoder design to model the statistical interference for the unknown CSI. In this regard, a successive second-order cone programming (SSOCP)-based precoder for maximizing the weighted sum rate is proposed. The accuracy of the solution obtained is bounded with the branch and bound technique. An alternative optimization framework via weighted mean square error minimization is also derived. Both these approaches provide an efficient solution close to the optimal, and also achieve efficient backhauling, in a sense that the precoding weights are generated only for the active links. For comparison, a stochastic approach based on particle swarm optimization is also considered.
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The role of small cells, coordinated multipoint, and massive MIMO in 5G
2014Co-Authors: Volker Jungnickel, Moritz Lossow, Wolfgang Zirwas, Rikke Apelfröjd, Konstantinos Manolakis, Volker Braun, Mikael Sternad, Berthold Panzner, Tommy SvenssonAbstract:5G will have to support a multitude of new applications with a wide variety of requirements, including higher peak and user data rates, reduced latency, enhanced indoor coverage, increased number of devices, and so on. The expected traffic growth in 10 or more years from now can be satisfied by the combined use of more spectrum, higher spectral efficiency, and densification of cells. The focus of the present article is on advanced techniques for higher spectral efficiency and improved coverage for cell edge users. We propose a smart combination of small cells, Joint Transmission coordinated multipoint (JT CoMP), and massive MIMO to enhance the spectral efficiency with affordable complexity. We review recent achievements in the transition from theoretical to practical concepts and note future research directions. We show in measurements with macro-plus-smallcell scenarios that spectral efficiency can be improved by flexible clustering and efficient user selection, and that adaptive feedback compression is beneficial to reduce the overhead significantly. Moreover, we show in measurements that fast feedback reporting combined with advanced channel prediction are able to mitigate the impairment effects of JT CoMP.
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Joint scheduling and power control in coordinated multi point clusters
2011Co-Authors: Tommy Svensson, Carmen Botella, Thomas Eriksson, Xin ChenAbstract:In this paper, we address the problem of designing a Joint scheduling and power control algorithm in a downlink coordinated multi-point (CoMP) cluster supporting CoMP Joint Transmission. The objective is to maximize the cell-edge throughput under per-point power constraints. By an analytical derivation, binary power control is proved to be the optimal solution for any given selected user group. Utilizing this analytical result, a centralized and a semi-distributed version of Joint user selection and power control algorithms are proposed. Compared to algorithms without considering Joint Transmission and algorithms without considering power control, simulation results show that the proposed algorithms achieve a good trade-off between Joint Transmission and interference coordination, which helps to improve the cell-edge performance.
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a novel frequency reuse scheme for coordinated multi point Transmission
2010Co-Authors: Hui Zhang, Tommy Svensson, Xiaofeng Tao, Carmen Botella, Baoling LiuAbstract:Coordinated Multi-Point (CoMP) Transmission is considered in 3GPP LTE-Advanced as a key technique to improve the cell-edge performance. In order to support Joint resource allocation among coordinate cells in CoMP systems, efficient frequency reuse schemes need to be designed. However, most of the existing frequency reuse schemes are not suitable for CoMP Transmission due to not considering multi-cell Joint Transmission scenario in their frequency reuse rule. To solve this problem, a cooperative frequency reuse (CFR) scheme is proposed in this paper, which divides the cell-edge area of each cell into two types of zones, and defines a frequency reuse rule to support CoMP Transmission for users in these zones. Compared with the conventional soft frequency reuse (SFR) scheme, simulation results demonstrate that the CFR scheme reduces the blocking probability by more than 50%, and improves the cell-edge throughput by 30~40%, with 5~9% additional cell-average throughput.
Wolfgang Zirwas - One of the best experts on this subject based on the ideXlab platform.
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opportunistic comp for 5g massive mimo multilayer networks
2015Co-Authors: Wolfgang ZirwasAbstract:In the FP7 project METIS we investigate suitable combinations of massive MIMO, Joint Transmission coordinated multipoint and small cells for future 5G systems. Challenging is a tight integration over small and macro layers. Straight forward is to ensure orthogonality between small and macro cell layers by allocation to different RF frequency bands like e.g. 2.6 and 3.5GHz respectively. Here within the macro layer frequency band an opportunistic tight cooperation between macro and small cell radio stations is being proposed. This requires dual band small cell radio stations operating in a traditional local area frequency band like 3.5GHz for data off loading and simultaneously - and on a need basis - at e.g. 2.6GHz as performance booster for macro UEs. First high level evaluations indicate significant spectral efficiency, capacity and coverage gains for macro cell users benefiting from higher Rx power and rank enhancement.
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The role of small cells, coordinated multipoint, and massive MIMO in 5G
2014Co-Authors: Volker Jungnickel, Moritz Lossow, Wolfgang Zirwas, Rikke Apelfröjd, Konstantinos Manolakis, Volker Braun, Mikael Sternad, Berthold Panzner, Tommy SvenssonAbstract:5G will have to support a multitude of new applications with a wide variety of requirements, including higher peak and user data rates, reduced latency, enhanced indoor coverage, increased number of devices, and so on. The expected traffic growth in 10 or more years from now can be satisfied by the combined use of more spectrum, higher spectral efficiency, and densification of cells. The focus of the present article is on advanced techniques for higher spectral efficiency and improved coverage for cell edge users. We propose a smart combination of small cells, Joint Transmission coordinated multipoint (JT CoMP), and massive MIMO to enhance the spectral efficiency with affordable complexity. We review recent achievements in the transition from theoretical to practical concepts and note future research directions. We show in measurements with macro-plus-smallcell scenarios that spectral efficiency can be improved by flexible clustering and efficient user selection, and that adaptive feedback compression is beneficial to reduce the overhead significantly. Moreover, we show in measurements that fast feedback reporting combined with advanced channel prediction are able to mitigate the impairment effects of JT CoMP.
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Multi-Cell Channel Estimation using Virtual Pilots
2008Co-Authors: Lars Thiele, Stefan Schiffermuller, Malte Schellmann, Volker Jungnickel, Wolfgang ZirwasAbstract:Multicellular radio systems are often limited due to the presence of cochannel interference. Proposed physical layer concepts, e.g. coordinated Joint Transmission and interference rejection combining, try to strengthen the signal while combating the interference. However, the performance may be limited by the available channel knowledge. We provide a concept for multi-cell channel estimation in the downlink applicable for for both physical layer concepts. This concept uses virtual pilots based on block-orthogonal sequences, e.g. Hadamard.
Wen Chen - One of the best experts on this subject based on the ideXlab platform.
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sequential and incremental precoder design for Joint Transmission network mimo systems with imperfect backhaul
2020Co-Authors: Ming Ding, Jun Zou, Zeng Yang, Hanwen Luo, Wen ChenAbstract:In this paper, we propose a sequential and incremental precoder design for downlink Joint Transmission (JT) network MIMO systems with imperfect backhaul links. The objective of our design is to minimize the maximum of the sub-stream mean square errors (MSE), which dominates the average bit error rate (BER) performance of the system. In the proposed scheme,we first optimize the precoder at the serving base station (BS), and then sequentially optimize the precoders of non-serving BSs in the JT set according to the descending order of their probabilities of participating in JT. The BS-wise sequential optimization process can improve the system performance when some BSs have to temporarily quit the JT operations because of poor instant backhaul conditions. Besides, the precoder of an additional BS is derived in an incremental way, i.e., the sequentially optimized precoders of previous BSs are fixed, thus the additional precoder plays an incremental part in the multi-BS JT operations. An iterative algorithm is designed to Jointly optimize the sub-stream precoder and sub-stream power allocation for each additional BS in the proposed sequential and incremental optimization scheme. Simulations show that, under the practical backhaul link conditions, our scheme significantly outperforms the autonomous global precoding (AGP) scheme in terms of BER performance.
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sequential and incremental precoder design for Joint Transmission network mimo systems with imperfect backhaul
2012Co-Authors: Ming Ding, Jun Zou, Zeng Yang, Hanwen Luo, Wen ChenAbstract:In this paper, we propose a sequential and incremental precoder design for downlink Joint Transmission (JT) network multiple-input-multiple-output (MIMO) systems with imperfect backhaul links. The objective of our design is to minimize the maximum of the substream mean square errors, which dominates the average bit error rate (BER) performance of the system. In the proposed scheme, we first optimize the precoder at the serving base station (BS) and then sequentially optimize the precoders of nonserving BSs in the JT set according to the descending order of their probabilities of participating in the JT. The BS-wise sequential optimization process can improve system performance when some BSs have to temporarily quit the JT operations because of poor instant backhaul conditions. In addition, the precoder of an additional BS is derived in an incremental way, i.e., the sequentially optimized precoders of the previous BSs are fixed, and thus, the additional precoder plays an incremental part in multi-BS JT operations. An iterative algorithm is designed to Jointly optimize the substream precoder and substream power allocation for each additional BS in the proposed sequential and incremental optimization scheme. Simulations show that, under the practical backhaul link conditions, our scheme significantly outperforms the autonomous global precoding scheme in terms of BER performance.
Volker Jungnickel - One of the best experts on this subject based on the ideXlab platform.
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The role of small cells, coordinated multipoint, and massive MIMO in 5G
2014Co-Authors: Volker Jungnickel, Moritz Lossow, Wolfgang Zirwas, Rikke Apelfröjd, Konstantinos Manolakis, Volker Braun, Mikael Sternad, Berthold Panzner, Tommy SvenssonAbstract:5G will have to support a multitude of new applications with a wide variety of requirements, including higher peak and user data rates, reduced latency, enhanced indoor coverage, increased number of devices, and so on. The expected traffic growth in 10 or more years from now can be satisfied by the combined use of more spectrum, higher spectral efficiency, and densification of cells. The focus of the present article is on advanced techniques for higher spectral efficiency and improved coverage for cell edge users. We propose a smart combination of small cells, Joint Transmission coordinated multipoint (JT CoMP), and massive MIMO to enhance the spectral efficiency with affordable complexity. We review recent achievements in the transition from theoretical to practical concepts and note future research directions. We show in measurements with macro-plus-smallcell scenarios that spectral efficiency can be improved by flexible clustering and efficient user selection, and that adaptive feedback compression is beneficial to reduce the overhead significantly. Moreover, we show in measurements that fast feedback reporting combined with advanced channel prediction are able to mitigate the impairment effects of JT CoMP.
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interference management for future cellular ofdma systems using coordinated multi point Transmission
2010Co-Authors: L. Thiele, Volker Jungnickel, Thomas HausteinAbstract:SUMMARY Todays cellular systems reach their limits for data rate due to the continuously increasing amount of subscribers using wireless service for business purposes or in leisure time (smartphone effect). Thus, recent research focuses on concepts for interference management for cellular OFDMA systems. This paper addresses various techniques related to this topic, while considering the concepts with lowest complexity and backhaul costs as promising candidates to be applied first. Starting from interference canceling receivers over multi-user MIMO using fixed precoding to multicell interference estimation, which improves the precision of link adaptation, we discuss closed-loop cooperative transmit beamforming using multiple base stations grouped into a wireless distributed network (WDN), which is denoted as coordinated multi-point Joint Transmission in the 3GPP LTE-Advanced standardization. It is obvious, the more sophisticated these techniques are, the higher the demands for feedback and backhaul become. Performance results are provided by employing multi-cell simulations according to recommendations from 3GPP. In addition, feasibility of coordinated multi-point Joint Transmission is demonstrated in a real-time prototype setup, i.e. in the Berlin LTE-Advance Testbed.
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cooperative multi user mimo based on limited feedback in downlink ofdm systems
2008Co-Authors: Lars Thiele, Malte Schellmann, Thomas Wirth, Volker JungnickelAbstract:Multi-cellular radio systems are often limited due to the presence of cochannel interference. Physical layer concepts as e.g. interference rejection combining, optimize the receiver side and thus strengthen the signal while combating the interference at the terminal side only. It is well known that Joint transceiver optimization, i.e. coordinated Joint Transmission from several base stations, yields large capacity improvement for downlink Transmission. However, the performance highly depends on the available channel knowledge. We focus on how to realize a decentralized and limited cooperative downlink Transmission in a multi-cellular network. This yields the crucial question: Is an efficient cooperative Transmission possible by using simple channel quality identifiers, or is channel state information at the transmitter mandatory? Further, we use minimum mean square error equalization at the terminal side to combat residual cochannel interference. For baseline we apply receiver optimization only and compare these results with those obtained from cooperative Transmission. We demonstrate potential capacity gains in a cellular orthogonal frequency division multiplexing system and their scaling with the number of cooperating antenna arrays.
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Multi-Cell Channel Estimation using Virtual Pilots
2008Co-Authors: Lars Thiele, Stefan Schiffermuller, Malte Schellmann, Volker Jungnickel, Wolfgang ZirwasAbstract:Multicellular radio systems are often limited due to the presence of cochannel interference. Proposed physical layer concepts, e.g. coordinated Joint Transmission and interference rejection combining, try to strengthen the signal while combating the interference. However, the performance may be limited by the available channel knowledge. We provide a concept for multi-cell channel estimation in the downlink applicable for for both physical layer concepts. This concept uses virtual pilots based on block-orthogonal sequences, e.g. Hadamard.
Martin Haenggi - One of the best experts on this subject based on the ideXlab platform.
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the sir meta distribution in poisson cellular networks with base station cooperation
2018Co-Authors: Qimei Cui, Yuanjie Wang, Martin HaenggiAbstract:The meta distribution provides fine-grained information on the signal-to-interference ratio (SIR) compared with the SIR distribution at the typical user. This paper first derives the meta distribution of the SIR in heterogeneous cellular networks with downlink coordinated multipoint Transmission/reception, including Joint Transmission (JT), dynamic point blanking (DPB), and dynamic point selection/dynamic point blanking (DPS/DPB), for the general typical user and the worst-case user (the typical user located at the Voronoi vertex in a single-tier network). A more general scheme called JT-DPB, which is the combination of JT and DPB, is studied. The moments of the conditional success probability are derived for the calculation of the meta distribution and the mean local delay. An exact analytical expression, the beta approximation, and simulation results of the meta distribution are provided. From the theoretical results, we gain insights on the benefits of different cooperation schemes and the impact of the number of cooperating base stations and other network parameters.
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coordinated multipoint Joint Transmission in heterogeneous networks
2014Co-Authors: Gaurav Nigam, Paolo Minero, Martin HaenggiAbstract:Motivated by the ongoing discussion on coordinated multipoint in wireless cellular standard bodies, this paper considers the problem of base station cooperation in the downlink of heterogeneous cellular networks. The focus of this paper is the Joint Transmission scenario, where an ideal backhaul network allows a set of randomly located base stations, possibly belonging to different network tiers, to Jointly transmit data, to mitigate intercell interference and hence improve coverage and spectral efficiency. Using tools from stochastic geometry, an integral expression for the network coverage probability is derived in the scenario where the typical user located at an arbitrary location, i.e., the general user, receives data from a pool of base stations that are selected based on their average received power levels. An expression for the coverage probability is also derived for the typical user located at the point equidistant from three base stations, which we refer to as the worst case user. In the special case where cooperation is limited to two base stations, numerical evaluations illustrate absolute gains in coverage probability of up to 17% for the general user and 24% for the worst case user compared with the noncooperative case. It is also shown that no diversity gain is achieved using noncoherent Joint Transmission, whereas full diversity gain can be achieved at the receiver if the transmitting base stations have channel state information.
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Coordinated multipoint in heterogeneous networks: A stochastic geometry approach
2013Co-Authors: Gaurav Nigam, Paolo Minero, Martin HaenggiAbstract:Motivated by the ongoing discussion on coordinated multipoint in wireless cellular standard bodies, this papercon- siders the problem of base station cooperation in the downlink of heterogeneous cellular networks. The focus of the paper is the Joint Transmission scenario, where an ideal backhaul network allows a set of randomly located base stations, possibly belonging to different network tiers, to Jointly transmit data, so as to mitigate intercell interference and hence improve coverageand spectral efficiency. Using tools from stochastic geometry, an exact integral expression for the network coverage probability is derived in the scenario where a typical user can coherently combine the received signal from a pool of base stations, that are selected based on their average received power strengthsor distance from the receiver. In the special case where cooperation is limited to two base stations, numerical evaluations illustrate relative gains in coverage probability of up to about 30% compared to the non-cooperative case.
