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  • 101.
    Wolkerstorfer, Martin
    et al.
    FTW Telecommunications Research Center Vienna.
    Jaldén, Joakim
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Nordström, Tomas
    Column generation for discrete-rate multi-user and multi-carrier power control2012Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 60, nr 9, s. 2712-2722Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a constrained multi-carrier power allocation problem in interference-limited multi-user systems with a finite set of transmission rates. The Lagrange relaxation is a common technique for decomposing such problems into independently solvable per-subcarrier problems. Deviating from this approach our main contribution is the proposal of a novel spectrum management framework based on a Nonlinear Dantzig-Wolfe problem decomposition. It allows for suboptimal initialization and suboptimal power allocation methods with low complexity. While we show that the combinatorial per-subcarrier problems have polynomial complexity in the number of users, we find that such suboptimal methods are indispensable in large systems. Thus we give an overview of various basic dual heuristics and provide simulation results on a set of thousand digital subscriber line (DSL) networks which show the superior performance of our framework compared to previous power control algorithms.

  • 102.
    Wosinska, Lena
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Fotonik.
    Thylen, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Fotonik.
    Reliability performances of optical ATM switches based on different routing and buffering schemes1999Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 47, s. 472-475Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reliability performances of seven equal-capacity optical asynchronous transfer mode switches based on different routing and buffering schemes are compared. Calculations are based on available reliability data for commercial components as well as expected life lengths for new components and systems. In general, for switching systems, the average downtime is required to be held below 3 min/year. However, our results indicate that the average downtime for the proposed configurations is much longer than requested, over ten times longer for the best case and over 1500 times longer for the worst case. Therefore, the multiplane structures (i.e., multiplying of the entire systems) have to be provided for the switching systems investigated here in order to satisfy reliability requirements

  • 103. Wyrembelski, Rafael F.
    et al.
    Bjelakovic, Igor
    Oechtering, Tobias J.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Boche, Holger
    Optimal Coding Strategies for Bidirectional Broadcast Channels Under Channel Uncertainty2010Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, nr 10, s. 2984-2994Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bidirectional relaying is a promising approach to improve the performance in wireless networks such as sensor, ad-hoc, and even cellular systems. Bidirectional relaying applies to three-node networks, where a relay establishes a bidirectional communication between two other nodes using a decode-and-forward protocol. First, the two nodes transmit their messages to the relay which decodes them. Then, the relay broadcasts a re-encoded message in such a way that both nodes can decode their intended message using their own message as side information. We consider uncertainty in the channel state information (CSI) and assume that all nodes only know that the channel over which the transmission takes place is from a pre-specified set of channels. In this work, we concentrate on the second phase, which is called the compound bidirectional broadcast channel. We present a robust coding strategy which enables reliable communication under channel uncertainty and show that this strategy actually achieves the compound capacity. Further, we analyze scenarios where either the receivers or the transmitter have perfect CSI. We show that CSI at the receivers does not affect the maximal achievable rates, while CSI at the transmitter improves the capacity region. A numerical example and a game-theoretic interpretation complete this work.

  • 104. Xiao, L.
    et al.
    Johansson, Mikael
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Boyd, S. P.
    Simultaneous routing and resource allocation via dual decomposition2004Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 52, nr 7, s. 1136-1144Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In wireless data networks, the optimal routing of data depends on the link capacities which, in turn, are determined by the allocation of communications resources (such as transmit powers and bandwidths) to the links. The optimal performance of the network can only be achieved by simultaneous optimization of routing and resource allocation. In this paper, we formulate the simultaneous routing and resource allocation (SRRA) problem, and exploit problem structure to derive efficient solution methods. We use a capacitated multicommodity now model to describe the data flows in the network. We assume that the capacity of a wireless link is a concave and increasing function of the communications resources allocated to the link, and the communications resources for groups of links are limited. These assumptions allow us to formulate the SRRA problem as a convex optimization problem over the network flow variables and the communications variables. These two sets of variables are coupled only through the link capacity constraints. We exploit this separable structure by dual decomposition. The resulting solution method attains the optimal coordination of data routing in the network layer and resource allocation in the radio control layer via pricing on the link capacities.

  • 105.
    Xiao, Ming
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Aulin, Tor
    Chalmers University of Technology.
    Optimal Decoding and Performance analysis of a Noisy Channel Network with Network Coding2009Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 57, nr 5, s. 1402-1412Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate sink decoding approaches and performance analysis for a network with intermediate node encoding (coded network). The network consists of statistically independent noisy channels. The sink bit error probability (BEP) is the performance measure. First, we investigate soft-decision decoding without statistical information on the upstream channels (the channels not directly connected to the sink). Numerical results show that the decoder cannot significantly improve the performance from a hard-decision decoder. We develop union bounds for analysis. The bounds show the asymptotic (regarding SNR: signal-to-noise ratio) performance of the decoder. Using statistical information about the upstream channels, we can find the error patterns of final hop channels (channels directly connected to sinks).With the error patterns, maximum-likelihood (ML) decoding can be performed, and a significant improvement in the BEP is obtained. To evaluate the union bound for the ML decoder, we use an equivalent point procedure. It is reduced to the least-squares problem with a linear constraint in the medium-to-high SNR region. With deterministic knowledge of the errors in the upstream channels, a genie-aided decoder can further improve the performance. We give the union bound for the genie decoder, which is straightforward to evaluate. By analyzing these decoders, we find that knowledge about the upstream channels is essential for good sink decoding.

  • 106.
    Xiao, Ming
    et al.
    Telecommunication Theory, Department of Computer Engineering, Chalmers University of Technology.
    Aulin, Tor M.
    Telecommunication Theory, Department of Computer Engineering, Chalmers University of Technology.
    Serially concatenated continuous phase modulation with convolutional codes over rings2006Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 54, nr 8, s. 1387-1396Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we investigate serially concatenated continuous phase modulation (SCCPM) with convolutional codes (CC) over rings. The transmitted signals are disturbed by additive white Gaussian noise. The properties for systems with both infinite and finite block lengths are investigated. For an infinite-length system, we check the convergence threshold using the extrinsic information transfer chart. For a finite-length system, we use union-bound techniques to estimate the error floors. In the union-bound analysis, we consider both the order and the position of nonzero permuted symbols. A simple method for determining a CPM error event through the sum of the input symbol sequence is shown. Thus, we can determine if the output symbol sequence of an error event in the ring CC can form an error event in CPM. Two properties concerning the interleaver gain (IG) are investigated. A recursive search algorithm for the maximal IG is shown. Compared with previous SCCPM with a binary CC, the proposed system shows an improvement concerning the convergence threshold or error floors.

  • 107.
    Xiao, Ming
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Kliewer, Joerg
    the Klipsch School of Electrical and Computer Engineering, New Mexico State University, U.S.A.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Design of network codes for multiple-user multiple-relay wireless networks2012Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 60, nr 12, s. 3755-3766Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the design of network codes for multiple-user multiple-relay (MUMR) wireless networks with slow fading (quasi-static) channels. In these networks, M users have independent information to be transmitted to a common base station (BS) with the help of N relays, where M ≥ 2 and N ≥ 1 are arbitrary integers. We investigate such networks in terms of diversity order to measure asymptotic performance. For networks with orthogonal channels, we show that network codes based on maximum distance separable (MDS) codes can achieve the maximum diversity order of N+1. We further show that the MDS coding construction of network codes is also necessary to obtain full diversity for linear finite field network coding (FFNC). Then, we compare the performance of the FFNC approach with superposition coding (SC) at the relays. The results show that the FFNC based on MDS codes has better performance than SC in both the high rate and the high SNR regime. Further, we discuss networks without direct source-to-BS channels for N ≥ M. We show that the proposed FFNC can obtain the diversity order N-M+1, which is equivalent to achieving the Singleton bound for network error-correction codes. Finally, we study the network with nonorthogonal channels and show our codes can still achieve a diversity order of N+1, which cannot be achieved by a scheme based on SC.

  • 108.
    Xiao, Ming
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Medard, Muriel
    MIT EECS.
    Aulin, Tor
    Chalmers University of Technology.
    Cross-Layer Design of Rateless Random Network Codes for Delay Optimization2011Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 59, nr 12, s. 331-3322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study joint network and channel code design to optimize delay performance. Here the delay is the transmission time of information packets from a source to sinks without considering queuing effects. In our systems, network codes (network layer) are on top of channel codes (physical layer) which are disturbed by noise. Network codes run in a rateless random method, and thus have erasure-correction capability. For the constraint of finite transmission time, transmission errors are inevitable in the physical layer. A detection error in the physical layer means an erasure of network codewords. For the analysis, we model the delay of each information generation in the network layer as independent, identically distributed random variables. The calculation approaches for delay measures are investigated for coded erasure networks. We show how to evaluate the rate and erasure probability of a set of channels belonging to one cut. We also show that the min-cut determines the decoding error probability in the sinks if the number of information packets is large. We observe that for a given amount of source information, larger packet length leads to fewer packets to be transmitted but higher physical-layer detection error probabilities. Further, longer transmission time (delay) in the physical-layer causes smaller detection error probability at the physical layer. Thus, both parameters have opposite impacts on the physical and network layer, considering delay. We should find the optimal values of them in a cross-layer approach. We then formulate the problems of optimizing delay performance, and discuss solutions for them.

  • 109.
    Xiao, Ming
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Multiple-User Cooperative Communications Based on Linear Network Coding2010Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, nr 12, s. 3345-3351Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a new scheme for cooperative wireless networking based on linear network codes. The network consists of multiple (M >= 2) users having independent information to be transmitted to a common basestation ( BS), assuming block-fading channels with independent fading for different codewords. The users collaborate in relaying messages. Because of potential transmission errors in links, resulting in erasures, the network topology is dynamic. To efficiently exploit the diversity available by cooperation and time-varying fading, we propose the use of diversity network codes (DNCs) over finite fields. These codes are designed such that the BS is able to rebuild the user information from a minimum possible set of coded blocks conveyed through the dynamic network. We show the existence of deterministic DNCs. We also show that the resulting diversity order using the proposed DNCs is 2M - 1, which is higher than schemes without network coding or with binary network coding. Numerical results from simulations also show substantial improvement by the proposed DNCs over the benchmark schemes. We also propose simplified versions of the DNCs, which have much lower design complexity and still achieve the diversity order 2M - 1.

  • 110.
    Xue, Qing
    et al.
    Southwest Jiaotong Univ, Key Lab Informat Coding & Transmiss, Chengdu 610031, Sichuan, Peoples R China.;Chongqing Univ Posts & Telecommun, Sch Commun & Informat Engn, Chongqing 400065, Peoples R China..
    Fang, Xuming
    Southwest Jiaotong Univ, Key Lab Informat Coding & Transmiss, Chengdu 610031, Sichuan, Peoples R China..
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Mumtaz, Shahid
    Inst Telecomunicacoes, P-3810193 Aveiro, Portugal..
    Rodriguez, Jonathan
    Univ South Wales, Mobile Commun, Pontypridd CF37 1DL, M Glam, Wales..
    Beam Management for Millimeter-Wave Beamspace MU-MIMO Systems2019Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, nr 1, s. 205-217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Millimeter-wave (mm-wave) communication has attracted increasing attention as a promising technology for 5G networks. One of the key architectural features of mm-wave is the possibility of using large antenna arrays at both the transmitter and receiver sides. Therefore, by employing directional beamforming, both mm-wave base stations (MBSs) and mm-wave user equipments (MUEs) are capable of supporting multi-beam simultaneous transmissions. However, most of the existing research results have only considered a single beam. Thus, the potentials of mm-wave have not been fully exploited yet. In this context, in order to improve the performance of short-range indoor mm-wave networks with multiple reflections, we investigate the challenges and potential solutions of downlink multi-user multi-beam transmission, which can be described as a beamspace multi-user multiple-input multiple-output (MU-MIMO) technique. We first exploit the characteristic of MBS/MUEs supporting multiple beams simultaneously to improve the efficiency of multi-user BF training. Then, we analyze the inter-user interference to avoid beam selection conflicts. Furthermore, we propose blockage control strategies and multi-user multi-beam power allocation solutions for the beamspace MU-MIMO. The theoretical and numerical results demonstrate that the beamspace MU-MIMO compared with single beam transmission can largely improve the rate performance and robustness of mm-wave networks.

  • 111.
    Yang, Guang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Du, Jinfeng
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. MIT.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Maximum Throughput Path Selection with Random Blockage for Indoor 60 GHz Relay Networks2015Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, nr 10, s. 3511-3524Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Indoor communications in the 60 GHz band is capable to support multi-gigabit wireless access thanks to the abundant spectrum and the possibility of using dense antenna arrays. However, the high directivity and penetration loss make it vulnerable to blockage events which can be frequent in indoor environments. Given network topology information in sufficient precision, we investigate the average throughput and outage probability when the connection between any two nodes can be established either via the line-of-sight (LOS) link, through a reflection link, or by a half-duplex relay node. We model the reflection link as an LOS with extra power loss and derive the closed-form expression for the relative reflection loss. For networks with a central coordinator and multiple relays, we also propose a generic algorithm, maximum throughput path selection (MTPS), to select the optimal path that maximizes the throughput. The complexity of the MTPS algorithm is O(n2) for networks equipped with n relays, whereas a brute-forced algorithm has complexity of O(n · n!). Numerical results show that increasing the number of relays can significantly increase the average throughput and decrease the outage probability, and resorting to reflection paths provides significant gains when the probability of link blockage is high.

  • 112.
    Yang, Guang
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Haenggi, Martin
    Univ Notre Dame, Dept Elect Engn, Notre Dame, IN 46556 USA..
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Traffic Allocation for Low-Latency Multi-Hop Networks With Buffers2018Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, nr 9, s. 3999-4013Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For buffer-aided tandem networks consisting of relay nodes and multiple channels per hop, we consider two traffic allocation schemes, namely local allocation and global allocation, and investigate the end-to-end latency of a file transfer. We formulate the problem for generic multi-hop queuing systems and subsequently derive closed-form expressions of the end-to-end latency. We quantify the advantages of the global allocation scheme relative to its local allocation counterpart, and we conduct an asymptotic analysis on the performance gain when the number of channels in each hops increases to infinity. The traffic allocations and the analytical delay performance are validated through simulations. Furthermore, taking a specific two-hop network with millimeter-wave (mm-wave) as an example, we derive lower bounds on the average end-to-end latency, where Nakagami-m fading is considered. Numerical results demonstrate that, compared with the local allocation scheme, the advantage of global allocation grows as the number of relay nodes increases, at the expense of higher complexity that linearly increases with the number of relay nodes. It is also demonstrated that a proper deployment of relay nodes in a linear mm-wave network plays an important role in reducing the average end-to-end latency, and the average latency decays as the mm-wave channels become more deterministic. These findings provide insights for designing multi-hop mm-wave networks with low end-to-end latency.

  • 113.
    Yang, Guang
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Ming, Xiao
    Vincent, H.
    Low-Latency Millimeter-Wave Communications: Traffic Dispersion or Network Densification2018Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, nr 8, s. 3526-3539Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Low latency is critical for many applications in wireless communications, e.g., vehicle-to-vehicle (V2V), multimedia, and industrial control networks. Meanwhile, for the capability of providing multi-gigabits per second (Gbps) rates, millimeter-wave (mm-wave) communication has attracted substantial research interest recently. This paper investigates two strategies to reduce the communication delay in future wireless networks: traffic dispersion and network densification. A hybrid scheme that combines these two strategies is also considered. The probabilistic delay and effective capacity are used to evaluate performance. For probabilistic delay, the violation probability of delay, i.e., the probability that the delay exceeds a given tolerance level, is characterized in terms of upper bounds, which are derived by applying stochastic network calculus theory. In addition, to characterize the maximum affordable arrival traffic for mmwave systems, the effective capacity, i.e., the service capability with a given quality-of-service (QoS) requirement, is studied. The derived bounds on the probabilistic delay and effective capacity are validated through simulations. These numerical results show that, for a given sum power budget, traffic dispersion, network densification, and the hybrid scheme exhibit different potentials to reduce the end-to-end communication delay. For instance, traffic dispersion outperforms network densification when high sum power budget and arrival rate are given, while it could be the worst option, otherwise. Furthermore, it is revealed that, increasing the number of independent paths and/or relay density is always beneficial, while the performance gain is related to the arrival rate and sum power, jointly. Therefore, a proper transmission scheme should be selected to optimize the delay performance, according to the given conditions on arrival traffic and system service capability.

  • 114.
    Yang, Guang
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Performance Analysis of Millimeter-Wave Relaying: Impacts of Beamwidth and Self-Interference2018Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, nr 2, s. 589-600Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the maximum achievable rate of a two-hop amplified-and-forward (AF) relaying millimeter-wave (mm-wave) system, where two AF relaying schemes, i.e., half-duplex (HD) and full-duplex (FD) are discussed. By considering the two-ray mm-wave channel and the Gaussian-type directional antenna, jointly, the impacts of the beamwidth and the self-interference coefficient on maximum achievable rates are investigated. Results show that, under a sum-power constraint, the rate of FD-AF mm-wave relaying outperforms its HD counterpart only when antennas with narrower beamwidth and smaller self-interference coefficient are applied. However, when the sum-power budget is sufficiently high or the beamwidth of directional antenna is sufficiently small, direct transmission becomes the best strategy, rather than the AF relaying schemes. For both relaying schemes, we show that the rates of both AF relaying schemes scale as O(min{theta(-1)(m),theta(-2)(m)})with respect to beamwidth theta(m), and the rate of FD-AF relaying scales as O(mu(-(1/2))) with respect to self-interference coefficient mu. Also, we show that ground reflections may significantly affect the performance of mm-wave communications, constructively or destructively. Thus, the impact of ground reflections deserves careful considerations for analyzing or designing future mm-wave wireless networks.

  • 115.
    Yao, Sha
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Analog Network Coding Mappings in Gaussian Multiple-Access Relay Channels2010Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, nr 7, s. 1973-1983Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the multiple-access relay channel with two source nodes, one relay node and one destination node. For practical simplicity, we consider orthogonal transmission of the source messages and half-duplex relaying. We also assume that the relay is memoryless and is implemented based on a two-to-one deterministic mapping. Our focus is on proposing and investigating such mappings. Essentially, the proposed relaying functions combine the two incoming analog signals and forward them to the destination, thus we term them as analog network coding mappings. Both linear and non-linear relaying are investigated for the multiple-access relay channel and the special case of the multiple-access two-hop channel. In particular, we suggest to use mappings based on the Archimedean spiral for analog non-linear combining. In addition, we propose to couple spiral mappings with sawtooth-like mappings to exploit the potential side information provided by the direct links of the multiple-access relay channel. In the case of symmetric topology, our proposed scheme can be seen as an extension to the amplify-and-forward scheme, where the asymmetric input/output dimensionality in the relay node is handled before amplifying. We investigate the resulting achievable rate regions and sum rates, and demonstrate significant gains over conventional relaying schemes.

  • 116.
    Zander, Jens
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Jamming in slotted ALOHA multihop packet radio networks1991Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 39, nr 10, s. 1525-1531Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of a packet radio network in the presence of active interference are discussed. Both the jammer and the network nodes are subject to an average power constraint. The network uses slotted ALOHA multiple access schemes and some simple fixed routing strategies with constant transmitter power. By using a game-theoretic approach the situation is considered as a two-person constant-sum game. The author defines network performance as the values of the game in terms of the expected forward progress of a packet. Both the performance and the optimum strategies for access and jamming are investigated.

  • 117.
    Zhan, Zhengquan
    et al.
    Southwest Jiaotong Univ, Key Lab Informat Coding & Transmiss, Chengdu 610031, Sichuan, Peoples R China..
    Ma, Zheng
    Southwest Jiaotong Univ, Key Lab Informat Coding & Transmiss, Chengdu 610031, Sichuan, Peoples R China..
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. Royal Inst Technol, Sch Elect Engn, Dept Informat Sci & Engn, SE-10044 Stockholm, Sweden..
    Lei, Xianfu
    Southwest Jiaotong Univ, Inst Mobile Commun, Chengdu 610031, Sichuan, Peoples R China.;Southeast Univ, Natl Mobile Commun Res Lab, Nanjing 210096, Jiangsu, Peoples R China..
    Ding, Zhiguo
    Univ Lancaster, Sch Comp & Commun, Lancaster LA1 4YW, England..
    Fan, Pingzhi
    Southwest Jiaotong Univ, Key Lab Informat Coding & Transmiss, Chengdu 610031, Sichuan, Peoples R China..
    Fundamental Tradeoffs of Non-Orthogonal Multicast, Multicast, and Unicast in Ultra-Dense Networks2018Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, nr 8, s. 3555-3570Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ultra-dense networks (UDNs) are the promising technology for the fifth-generation wireless networks and beyond to significantly boost network capacity and improve network coverage by exploiting spatial spectrum reuse through the deployment of massive base stations (BSs). In this paper, the fundamental tradeoffs of non-orthogonal multicast, multicast, and unicast in the UDN are studied, to understand the impact of network densitification on them and provide some insights on UDN deployment. Non-orthogonal multicast with imperfect channel estimation and successive interference cancellation is also investigated. To evaluate the performance, a tractable model for performance analysis is developed by using stochastic geometry, and then the analytical expressions for downlink signal-to-interference-plus-noise ratio coverage probability, spectrum efficiency, area traffic capacity, and energy efficiency are derived. The numerical results together with the Monte Carlo simulations are also provided. The results demonstrate that non-orthogonal multicast can further improve the performance of multicast and achieve higher spectrum efficiency, area traffic capacity, and energy efficiency than unicast from the low-to-high BS density regions, but suffers from inferior performance to unicast in the very high BS density region. The results also show that the non-orthogonal multicast and multicast exhibit different performance trends from unicast.

  • 118.
    Zhang, Guoqiang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Ljud- och bildbehandling.
    Østergaard, Jan
    Klejsa, Janusz
    KTH, Skolan för elektro- och systemteknik (EES), Ljud- och bildbehandling.
    Kleijn, W. Bastiaan
    KTH, Skolan för elektro- och systemteknik (EES), Ljud- och bildbehandling.
    High-Rate Analysis of Symmetric L-Channel Multiple Description Coding2011Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 59, nr 7, s. 1846-1856Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper studies the tight rate-distortion bound for L-channel sym-metric multiple-description coding of a vector Gaussian source with twolevels of receivers. Each of the first-level receivers obtains κ (κ < L) ofthe L descriptions. The second-level receiver obtains all L descriptions.We find that when the theory is applied to the scalar Gaussian source, theproduct of a function of the side distortions (corresponding to the first-level receivers) and the central distortion (corresponding to the second-levelreceiver) is asymptotically independent of the redundancy among the de-scriptions. Using this property, we analyze the asymptotic behavior of apractical multiple-description lattice vector quantizer (MDLVQ). Our anal-ysis includes the treatment of the MDLVQ system from a new geometricviewpoint, which results in an expression for the side distortions using thenormalized second moment of a sphere of higher dimensionality than thequantization space. The expression of the distortion product derived fromthe lower bound is then applied as a criterion to assess the performance lossof the considered MDLVQ system. In principle, the efficiency of other prac-tical MD systems can also be evaluated using the derived distortion product.

  • 119. Zhang, Lin
    et al.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Wu, Gang
    Li, Shaoqian
    Efficient Scheduling and Power Allocation for D2D-Assisted Wireless Caching Networks2016Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, nr 6, s. 2438-2452Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study a one-hop device-to-device (D2D)-assisted wireless caching network, where popular files are randomly and independently cached in the memory of end users. Each user may obtain the requested files from its own memory without any transmission, or from a helper through a one-hop D2D transmission, or from the base station. We formulate a joint D2D link scheduling and power allocation problem to maximize the system throughput. However, the problem is non-convex, and obtaining an optimal solution is computationally hard. Alternatively, we decompose the problem into a D2D link-scheduling problem and an optimal power allocation problem. To solve the two subproblems, we first develop a D2D link-scheduling algorithm to select the largest number of D2D links satisfying both the signal to interference plus noise ratio and the transmit power constraints. Then, we develop an optimal power allocation algorithm to maximize the minimum transmission rate of the scheduled D2D links. Numerical results indicate that both the number of the scheduled D2D links and the system throughput can be improved simultaneously with the Zipf-distribution caching scheme, the proposed D2D link-scheduling algorithm, and the proposed optimal power allocation algorithm compared with the state of the arts.

  • 120. Zhang, Zhengquan
    et al.
    Ma, Zheng
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Karagiannidis, George K.
    Ding, Zhiguo
    Fan, Pingzhi
    Two-Timeslot Two-Way Full-Duplex Relaying for 5G Wireless Communication Networks2016Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, nr 7, s. 2873-2887Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a novel two-timeslot two-way full-duplex (FD) relaying scheme, in which the access link and the backhaul link are divided in the time domain, and we study the average end-to-end rate and the outage performance. According to the user equipment capability and services, we investigate two scenarios: three-node I-and four-node Y-relaying channels. Among various relaying protocols, the well-known amplify-and-forward and decode-and-forward are considered. Closed-form expressions for the average end-to-end rate and the outage probability, under the effect of residual self-interference and inter-user interference, are presented. The results show that the proposed two-timeslot two-way FD relaying scheme can achieve higher rate and better outage performance than the half-duplex one, when residual self-interference is below a certain level. Therefore, this relaying scheme presents a reasonable tradeoff between performance and complexity, and so, it could be efficiently used in the fifth-generation wireless networks.

  • 121.
    Zhao, David Yuheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Ljud- och bildbehandling.
    Samuelsson, Jonas
    Dolby Labs, Stockholm.
    Nilsson, Mattias
    KTH, Skolan för elektro- och systemteknik (EES), Ljud- och bildbehandling.
    On entropy-constrained vector quantization using gaussian mixture models2008Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 56, nr 12, s. 2094-2104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A flexible and low-complexity entropy-constrained vector quantizer (ECVQ) scheme based on Gaussian mixture models (GMMs), lattice quantization, and arithmetic coding is presented. The source is assumed to have a probability density function of a GMM. An input vector is first classified to one of the mixture components, and the Karhunen-Loeve transform of the selected mixture component is applied to the vector, followed by quantization using a lattice structured codebook. Finally, the scalar elements of the quantized vector are entropy coded sequentially using a specially designed arithmetic coder. The computational complexity of the proposed scheme is low, and independent of the coding rate in both the encoder and the decoder. Therefore, the proposed scheme serves as a lower complexity alternative to the GMM based ECVQ proposed by Gardner, Subramaniam and Rao [1]. The performance of the proposed scheme is analyzed under a high-rate assumption, and quantified for a given GMM. The practical performance of the scheme was evaluated through simulations on both synthetic and speech line spectral frequency (LSF) vectors. For LSF quantization, the proposed scheme has a comparable performance to [1] at rates relevant for speech coding (20-28 bits per vector) with lower computational complexity.

  • 122.
    Zhao, Peiyue
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    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 Systems2018Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, nr 3, s. 999-1012Artikel i tidskrift (Refereegranskat)
    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.

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