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  • 1.
    Alabbasi, Abdulrahman
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Shihada, Basem
    Optimal Cross-Layer Design for Energy Efficient D2D Sharing Systems2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 2, p. 839-855Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose a cross-layer design, which optimizes the energy efficiency of a potential future 5G spectrum-sharing environment, in two sharing scenarios. In the first scenario, underlying sharing is considered. We propose and minimize a modified energy per good bit (MEPG) metric, with respect to the spectrum sharing user's transmission power and media access frame length. The cellular users, legacy users, are protected by an outage probability constraint. To optimize the non-convex targeted problem, we utilize the generalized convexity theory and verify the problem's strictly pseudoconvex structure. We also derive analytical expressions of the optimal resources. In the second scenario, we minimize a generalized MEPG function while considering a probabilistic activity of cellular users and its impact on the MEPG performance of the spectrum sharing users. Finally, we derive the associated optimal resource allocation of this problem. Selected numerical results show the improvement of the proposed system compared with other systems.

  • 2. Arnau, J.
    et al.
    Christopoulos, D.
    Chatzinotas, S.
    Mosquera, C.
    Ottersten, Björn
    Performance of the multibeam satellite return link with correlated rain attenuation2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 11, p. 6286-6299Article in journal (Refereed)
    Abstract [en]

    Rain attenuation is among the major impairments for satellite systems operating in the K-band and above. In this paper, we investigate the impact of spatially correlated rain attenuation on the performance of a multibeam satellite return link. For a comprehensive assessment, an analytical model for the antenna pattern that generates the beams is also proposed. We focus on the outage capacity of the link and obtain analytical approximations at high and low signal-to-noise ratio. The derived approximations provide insights into the effect of key system parameters such as the interuser distance, the satellite beam radius, or the rain intensity, and simulation results show that it fits tightly with the Monte Carlo results. Additionally, the derived expressions can be easily particularized for the single-user case, providing some novel insights.

  • 3.
    Asplund, Henrik
    et al.
    Ericsson Research.
    Alayon Glazunov, Andres
    Ericsson Research.
    Molisch, Andreas F.
    Nachrichtentechnik und Höchfrequenztechnik (INTHF) of the TU Wien.
    Pedersen, Klaus I.
    Aalborg University.
    Steinbauer, Martin
    Nachrichtentechnik und Höchfrequenztechnik (INTHF) of the TU Wien.
    The COST 259 Directional Channel Model-Part II: Macrocells2006In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 5, no 12, p. 3434-3450Article in journal (Refereed)
    Abstract [en]

    This paper describes the attributes of the COST 259 directional channel model that are applicable for use in the design and implementation of macrocellular mobile and portable radio systems and associated technology. Special care has been taken to model all propagation mechanisms that are currently understood to contribute to the characteristics of practical macrocellular channels and confirm that large scale, small scale, anddirectional characteristics of implemented models are realistic through their comparison with available measured data. The model that is described makes full use of previously published work, as well as incorporating some new results. It is considered that its implementation should contribute to a tool that can be used for simulations and comparison of different aspects of a large variety of wireless communication systems, including those that exploit the spatial aspects of radio channels, as, for example, throughthe use of adaptive antenna systems. 

  • 4.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fast-Lipschitz Power Control and User-Frequency Assignment in Full-Duplex Cellular Networks2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 10, p. 6672-6687Article in journal (Refereed)
    Abstract [en]

    In cellular networks, the three-node full-duplex transmission mode has the po-tential to increase spectral efficiency without requiring full-duplex capability ofusers. Consequently, three-node full-duplex in cellular networks must deal with self-interference and user-to-user interference, which can be managed by power controland user-frequency assignment techniques. This paper investigates the problem ofmaximizing the sum spectral efficiency by jointly determining the transmit powersin a distributed fashion, and assigning users to frequency channels. The problem is for-mulated as a mixed-integer nonlinear problem, which is shown to be non-deterministicpolynomial-time hard. We investigate a close-to-optimal solution approach by dividingthe joint problem into a power control problem and an assignment problem. The powercontrol problem is solved by Fast-Lipschitz optimization, while a greedy solution withguaranteed performance is developed for the assignment problem. Numerical resultsindicate that compared with the half-duplex mode, both spectral and energy efficienciesof the system are increased by the proposed algorithm. Moreover, results show that thepower control and assignment solutions have important, but opposite roles in scenarioswith low or high self-interference cancellation. When the self-interference cancellationis high, user-frequency assignment is more important than power control, while powercontrol is essential at low self-interference cancellation.

  • 5.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Spectral Efficient and Fair User Pairing for Full-Duplex Communication in Cellular Networks2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 11, p. 7578-7593Article in journal (Refereed)
    Abstract [en]

    —A promising new transmission mode in cellular networks is the three-node full-duplex mode, which involves a base station with full-duplex capability and two half-duplex user transmissions on the same frequency channel for uplink and downlink. The three-node full-duplex mode can increase spectral efficiency, especially in the low transmit power regime, without requiring full-duplex capability at user devices. However, when a large set of users is scheduled in this mode, self-interference at the base station and user-to-user interference can substantially hinder the potential gains of full-duplex communications. This paper investigates the problem of grouping users to pairs and assigning frequency channels to each pair in a spectral efficient and fair manner. Specifically, the joint problem of user uplink/downlink frequency channel pairing and power allocation is formulated as a mixed integer nonlinear problem that is solved by a novel joint fairness assignment maximization algorithm. Realistic system level simulations indicate that the spectral efficiency of the users having the lowest spectral efficiency is increased by the proposed algorithm, while a high ratio of connected users in different loads and self-interference levels is maintained.

  • 6.
    Berggren, Fredrik
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Jäntti, Riku
    Faculty of Computer Science Department of Information Technology University of Vaasa FIN-65101, Vaasa, FINLAND.
    Asymptotically Fair Transmission Scheduling over Fading Channels2004In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 3, no 1, p. 326-336Article in journal (Refereed)
    Abstract [en]

    In this work, the problem of scheduling delay insensitive data over a DS-CDMA downlink fading channel is considered. We consider the case where only one user at a time is allowed to transmit. As the channels can be considered to vary asynchronously among the users, multiuser diversity gains can be obtained by exploiting channel adaptive scheduling. For this, schedulers of different adaptation rate are suggested and compared. In particular we analyze a simple fast scheduler that schedules a user to transmit when its channel is good relative to its mean. This scheduler is resource fair in the sense it can provide the users with the same asymptotical channel access. We show that the achievable scheduling gain compared to round robin is equal to the gain of a selection diversity scheme. The scheduling gain is determined, both on closed-form and by numerical integration, for several scenarios, including multicellular systems and the effect of time delayed channel estimates. The results show that the scheduling gain is larger for channels with low average quality.

  • 7.
    Berggren, Fredrik
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Kim, Seong-Lyun
    Radio Resource Management & Optimization Laboratory Informations and Communications University School of Engineering Yusong P.O. Box 77, Taejon, 305-600, KOREA.
    Energy-Effcient Control of Rate and Power in DS-CDMA Systems2004In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 3, no 3, p. 725-733Article in journal (Refereed)
    Abstract [en]

    The quality of service in DS-CDMA can be controlled by a suitable selection of processing gain and transmission powers. In this paper, distributed control of rate and power for best effort data services is considered. In particular, we elaborate on the problem of how to control the transmission rates for maximizing system throughput while simultaneously minimizing the transmission powers. We assume a practical scenario, where every user has a finite set of discrete transmission rates and propose a simple heuristic rate allocation scheme, greedy rate packing (GRP), applicable in both upand downlink. The scheme can be interpreted as a practical form of water-filling, in the sense that high transmission rates are allocated to users having high link gains and low interference. We show that under certain conditions, GRP will give maximum throughput and that it can be extended to guarantee a minimum data rate while maximizing network excess capacity. We suggest and analyze a distributed power control control algorithm to control the intercell interference when GRP is applied to a multicellular system. Numerical results show that the proposed transmission scheme can significantly decrease the power levels while maintaining high throughput.

  • 8. Bhattacharjee, P S
    et al.
    Saha, D
    Mukherjee, Amitava
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    An approach for location area planning in a personal communication services network (PCSN)2004In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 3, no 4, p. 1176-1187Article in journal (Refereed)
    Abstract [en]

    This paper deals with an approach for planning location areas (LAs) in a personal communication services network (PCSN) to be overlaid on an existing wired network. Given the average speed of mobile terminals, the number of mobile switching centers (MSCs), their locations, call handling capacity of each MSC, handoff cost between adjacent cells and call arrival rate, an important consideration in a PCSN is to identify the cells in every LA to be connected to the corresponding NISC in a cost effective manner. In this work, while planning a location area, we present a two-step approach, namely optimization of total system recurring cost (subproblem I) and optimization of hybrid cost (subproblem II). The planning first determines the optimum number of cells in an LA from subproblem I. Then, it finds out the exact LAs by assigning cells to the switches, while optimizing the hybrid cost which comprises the handoff cost and the cable cost, in subproblem II. This divide-and-conquer strategy provides a practical way for designing LAs. As our approach toward LA planning takes into accounts both cost and network planning factors, this unique combination will be of great interest to PCSN designers. It develops an optimum network planning method for a wide range of call-to-mobility ratios that minimizes the total system recurring cost while still ensuring a good system performance. Our study shows that acceptable results are achievable with a reasonable computational effort, which supports the engineered planning of a PCSN.

  • 9.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jorswieck, Eduard A.
    Dresden University of Technology (TUD), Germany.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Impact of Spatial Correlation and Precoding Design in OSTBC MIMO Systems2010In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 9, no 11, p. 3578-3589Article in journal (Refereed)
    Abstract [en]

    The impact of transmission design and spatial correlation on the symbol error rate (SER) is analyzed for multi-antenna communication links. The receiver has perfect channel state information (CSI), while the transmitter has either statistical or no CSI. The transmission is based on orthogonal space-time block codes (OSTBCs) and linear precoding. The precoding strategy that minimizes the worst-case SER is derived for the case when the transmitter has no CSI. Based on this strategy, the intuitive result that spatial correlation degrades the SER performance is proved mathematically. In the case when the transmitter knows the channel statistics, the correlation matrix is assumed to be jointly-correlated (a generalization of the Kronecker model). The eigenvectors of the SER-optimal precoding matrix are shown to originate from the correlation matrix and the remaining power allocation is a convex problem. Equal power allocation is SER-optimal at high SNR. Beamforming is SER-optimal at low SNR, or for increasing constellation sizes, and its optimality range is characterized. A heuristic low-complexity power allocation is proposed and evaluated numerically. Finally, it is proved analytically that receive-side correlation always degrades the SER. Transmit-side correlation will however improve the SER at low to medium SNR, while its impact is negligible at high SNR.

  • 10.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. Supélec, France; Linköping University, Sweden.
    Matthaiou, Michail
    Debbah, Merouane
    Massive MIMO with Non-Ideal Arbitrary Arrays: Hardware Scaling Laws and Circuit-Aware Design2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 8, p. 4353-4368Article in journal (Refereed)
    Abstract [en]

    Massive multiple-input multiple-output (MIMO) systems are cellular networks where the base stations (BSs) are equipped with unconventionally many antennas, deployed on co-located or distributed arrays. Huge spatial degrees-of-freedom are achieved by coherent processing over these massive arrays, which provide strong signal gains, resilience to imperfect channel knowledge, and low interference. This comes at the price of more infrastructure; the hardware cost and circuit power consumption scale linearly/affinely with the number of BS antennas N. Hence, the key to cost-efficient deployment of large arrays is low-cost antenna branches with low circuit power, in contrast to today's conventional expensive and power-hungry BS antenna branches. Such low-cost transceivers are prone to hardware imperfections, but it has been conjectured that the huge degrees-of-freedom would bring robustness to such imperfections. We prove this claim for a generalized uplink system with multiplicative phase-drifts, additive distortion noise, and noise amplification. Specifically, we derive closed-form expressions for the user rates and a scaling law that shows how fast the hardware imperfections can increase with N while maintaining high rates. The connection between this scaling law and the power consumption of different transceiver circuits is rigorously exemplified. This reveals that one can make the circuit power increase as root N, instead of linearly, by careful circuit-aware system design.

  • 11. Björnson, Emil
    et al.
    Sanguinetti, Luca
    Hoydis, Jakob
    Debbah, Merouane
    Optimal Design of Energy-Efficient Multi-User MIMO Systems: Is Massive MIMO the Answer?2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 6, p. 3059-3075Article in journal (Refereed)
    Abstract [en]

    Assume that a multi-user multiple-input multiple-output (MIMO) system is designed from scratch to uniformly cover a given area with maximal energy efficiency (EE). What are the optimal number of antennas, active users, and transmit power? The aim of this paper is to answer this fundamental question. We consider jointly the uplink and downlink with different processing schemes at the base station and propose a new realistic power consumption model that reveals how the above parameters affect the EE. Closed-form expressions for the EE-optimal value of each parameter, when the other two are fixed, are provided for zero-forcing (ZF) processing in single-cell scenarios. These expressions prove how the parameters interact. For example, in sharp contrast to common belief, the transmit power is found to increase (not to decrease) with the number of antennas. This implies that energy-efficient systems can operate in high signal-to-noise ratio regimes in which interference-suppressing signal processing is mandatory. Numerical and analytical results show that the maximal EE is achieved by a massive MIMO setup wherein hundreds of antennas are deployed to serve a relatively large number of users using ZF processing. The numerical results show the same behavior under imperfect channel state information and in symmetric multi-cell scenarios.

  • 12.
    Chang, Peiliang
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Miao, Guowang
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Energy and Spectral Efficiency of Cellular Networks with Discontinuous Transmission2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 5, p. 2991-3002Article in journal (Refereed)
    Abstract [en]

    Cell discontinuous transmission (DTX) has been proposed as a solution to reduce energy consumption of cellular networks. This paper investigates the impact of network traffic load on spectral and energy efficiency of cellular networks with DTX. The SINR distribution as a function of traffic load is derived firstly. Then sufficient condition for ignoring thermal noise and simplifying the SINR distribution is investigated. Based on the simplified SINR distribution, the network spectral and energy efficiency as functions of network traffic load are derived. It is shown that the network spectral efficiency increases monotonically in traffic load, while the optimal network energy efficiency depends on the ratio of the sleep-mode power consumption to the active-mode power consumption of base stations. If the ratio is larger than a certain threshold, the network energy efficiency increases monotonically with network traffic load and is maximized when the network is fully loaded. Otherwise, the network energy efficiency firstly increases and then decreases in network traffic load. The optimal load can be identified with a binary search algorithm. The power ratio threshold depends solely on the path loss exponent α, e.g. 56% for α = 4. All these analytic results are further validated by the numerical simulations.

  • 13. Cho, Jeong-woo
    et al.
    Mo, Jeonghoon
    Yonsei University.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Joint Network-wide Opportunistic Scheduling and Power Control in Multi-cell Networks2009In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 8, no 3, p. 1520-1531Article in journal (Refereed)
    Abstract [en]

    We present a unified analytical framework that maximizes generalized utilities of a wireless network by network-wide opportunistic scheduling and power control. That is, base stations in the network jointly decide mobile stations to be served at the same time as the transmission powers of base stations are coordinated to mitigate the mutually interfering effect. Although the maximization at the first glance appears to be a mixed, twofold and nonlinear optimization requiring excessive computational complexity, we show that the maximization can be transformed into a pure binary optimization with much lower complexity. To be exact, it is proven that binary power control of base stations is necessary and sufficient for maximizing the network-wide utilities under a physical layer regime where the channel capacity is linear in the signal-to-interference-noise ratio. To further reduce the complexity of the problem, a distributed heuristic algorithm is proposed that performs much better than existing opportunistic algorithms. Through extensive simulations, it becomes clear that network-wide opportunistic scheduling and power control is most suitable for fairness-oriented networks and under loaded networks. We believe that our work will serve as a cornerstone for network-wide scheduling approaches from theoretical and practical standpoints.

  • 14.
    Di Marco, Piergiuseppe
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Santucci, Fortunato
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Modeling IEEE 802.15.4 Networks Over Fading Channels2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 10, p. 5366-5381Article in journal (Refereed)
    Abstract [en]

    Although the performance of the medium access control (MAC) of the IEEE 802.15.4 has been investigated under the assumption of ideal wireless channel, the understanding of the cross-layer dynamics between MAC and physical layer is an open problem when the wireless channel exhibits path loss, multi-path fading, and shadowing. The analysis of MAC and wireless channel interaction is essential for consistent performance prediction, correct design and optimization of the protocols. In this paper, a novel approach to analytical modeling of these interactions is proposed. The analysis considers simultaneously a composite channel fading, interference generated by multiple terminals, the effects induced by hidden terminals, and the MAC reduced carrier sensing capabilities. Depending on the MAC parameters and physical layer thresholds, it is shown that the MAC performance indicators over fading channels can be far from those derived under ideal channel assumptions. As novel results, we show to what extent the presence of fading may be beneficial for the overall network performance by reducing the multiple access interference, and how this information can be used for joint selection of MAC and physical layer parameters.

  • 15.
    Do, Tan Tai
    et al.
    KTH, School of Electrical Engineering (EES).
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Kim, Su Min
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Peters, Gunnar
    Uplink Waveform Channel With Imperfect Channel State Information and Finite Constellation Input2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 2, p. 1107-1119Article in journal (Refereed)
    Abstract [en]

    This paper investigates the capacity limit of an uplink waveform channel assuming imperfect channel state information at the receiver (CSIR). Various realistic assumptions are incorporated into the problem, which make the study valuable for performance assessment of real cellular networks to identify potentials for performance improvements in practical receiver designs. We assume that the continuous-time received signal is first discretized by mismatched filtering based on the imperfect CSIR. The resulting discrete-time signals are then decoded considering two different decoding strategies, i.e., an optimal decoding strategy based on specific statistics of channel estimation errors and a sub-optimal decoding strategy treating the estimation error signal as additive Gaussian noise. Motivated by the proposed decoding strategies, we study the performance of the decision feedback equalizer for finite constellation inputs, in which inter-stream interferences are treated either using their true statistics or as Gaussian noise. Numerical results are provided to exemplify the benefit of exploiting the knowledge on the statistics of the channel estimation errors and inter-stream interferences. Simulations also assess the effect of the CSI imperfectness on the achievable rate, which reveal that finite constellation inputs are less sensitive to the estimation accuracy than Gaussian input, especially in the high SNR regime.

  • 16.
    Du, Rong
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Ozcelikkale, Ayca
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Xiao, Ming
    Towards Immortal Wireless Sensor Networks by Optimal Energy Beamforming and Data Routing2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 8, p. 5338-5352Article in journal (Refereed)
    Abstract [en]

    The lifetime of a wireless sensor network (WSN) determines how long the network can be used to monitor the area of interest. Hence, it is one of the most important performance metrics for WSN. The approaches used to prolong the lifetime can be briefly divided into two categories: reducing the energy consumption, such as designing an efficient routing, and providing extra energy, such as using wireless energy transfer (WET) to charge the nodes. Contrary to the previous line of work where only one of those two aspects is considered, we investigate these two together. In particular, we consider a scenario where dedicated wireless chargers transfer energy wirelessly to sensors. The overall goal is to maximize the minimum sampling rate of the nodes while keeping the energy consumption of each node smaller than the energy it receives. This is done by properly designing the routing of the sensors and the WET strategy of the chargers. Although such a joint routing and energy beamforming problem is non-convex, we show that it can be transformed into a semi-definite optimization problem (SDP). We then prove that the strong duality of the SDP problem holds, and hence the optimal solution of the SDP problem is attained. Accordingly, the optimal solution for the original problem is achieved by a simple transformation. We also propose a low-complexity approach based on pre-determined beamforming directions. Moreover, based on the alternating direction method of multipliers (ADMM), the distributed implementations of the proposed approaches are studied. The simulation results illustrate the significant performance improvement achieved by the proposed methods. In particular, the proposed energy beamforming scheme significantly out-performs the schemes where one does not use energy beamforming, or one does not use optimized routing. A thorough investigation of the effect of system parameters, including the number of antennas, the number of nodes, and the number of chargers, on the system performance is provided. The promising convergence behaviour of the proposed distributed approaches is illustrated.

  • 17.
    Du, Rong
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Wirelessly-powered Sensor Networks: Power Allocation for Channel Estimation and Energy beamformingIn: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248Article in journal (Refereed)
    Abstract [en]

    Wirelessly-powered sensor networks (WPSNs) are becoming increasingly important to monitor many internet-of-things systems. We consider a WPSN where a multiple-antenna base station, dedicated for energy transmission, sends pilot signals to estimate the channel state information and consequently shapes the energy beams toward the sensor nodes. Given a fixed energy budget at the base station, in this paper, we investigate the novel problem of optimally allocating the power for the channel estimation and for the energy transmission. We formulate this problem for general channel estimation and beamforming schemes, which turns out to be non-convex. We provide a new solution approach and a performance analysis in terms of optimality and complexity. We also present a closed-form solution for the case where the channels are estimated based on a least square channel estimation and a maximum ratio transmit beamforming scheme. The analysis and simulations indicate a significant gain in terms of the network sensing rate, compared to the fixed power allocation, and the importance of improving the channel estimation efficiency.

  • 18.
    Fallgren, Mikael
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    An Optimization Approach to Joint Cell, Channel and Power Allocation in Multicell Relay Networks2012In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 11, no 8, p. 2868-2875Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider joint resource allocation of a multicell OFDMA-based networks, with fixed two-hop decode-and-forward relay stations. A joint cell, channel and power allocation problem is formulated as an overall optimization problem, where the objective is to maximize the minimum user throughput. Based on previous complexity results for the setting without relays, the overall optimization problem is shown not to be approximable, unless P is equal to NP. We propose a method for solving this challenging problem. First, a feasible cell allocation is obtained, either via greedy allocation or an exhaustive search. Thereafter, the channel and power allocations are alternately updated, either using a heuristic or optimization-based approach while holding the other two allocations fixed. These alternating channel and power allocations are repeated until no further improvement is obtained. The impact of relay stations is investigated by considering a model with relays as well as one without relays. The simulations show that substantial performance improvement can be made by introducing relays. They also indicate, somewhat surprisingly, that the heuristic channel allocation leads to better overall solutions than the corresponding optimization approach in the relay setting. The optimization-based power allocation significantly outperforms the heuristic power approach with as well as without relay stations.

  • 19.
    Fan, Yijia
    et al.
    Department of Electrical Engineering, Princeton University.
    Wang, Chao
    Institute for Digital Communications, The University of Edinburgh.
    Thompson, John
    Institute for Digital Communications, The University of Edinburgh.
    Poor, H. Vincent
    Department of Electrical Engineering, Princeton University.
    Recovering multiplexing loss through successive relaying using repetition coding2007In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 6, no 12, p. 4484-4493Article in journal (Refereed)
    Abstract [en]

    In this paper, a transmission protocol is studied for a two relay wireless network in which simple repetition coding is applied at the relays. Information-theoretic achievable rates for this transmission scheme are given, and a space-time V-BLAST signalling and detection method that can approach them is developed. It is shown through the diversity multiplexing tradeoff analysis that this transmission scheme can recover the multiplexing loss of the half-duple x relay network, while retaining some diversity gain. This scheme is also compared with conventional transmission protocols that exploit only the diversity of the network at the cost of a multiplexing loss. It is shown that the new transmission protocol offers, significant performance advantages over conventional protocols, especially when the interference between the two relays is sufficiently strong.

  • 20.
    Farhadi, Hamed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wang, Chao
    Tongji University.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Transceiver Design and Power Control for Wireless MIMO Interference Networks2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 3, p. 1199-1212, article id 7055983Article in journal (Refereed)
    Abstract [en]

    This paper considers distributed transceiver design and power control for K-user multiple-input-multiple-output interference networks. Each source intends to send multiple independent data streams to its corresponding destination where the number of data streams coincides with the degrees of freedom of the network. Each data stream is encoded at a fixed data rate, whereas different streams can be encoded at possibly different rates. We assume that only local channel side information (i.e., knowledge related to channels directly connected to a terminal) can be acquired by each terminal. We propose iterative algorithms to perform both power control and transceiver design. Transmitter beamforming matrices and receiver filtering matrices are designed to maximize signal-to-interference-plus-noise ratio corresponding to each stream, and a power control scheme is performed to assign the minimum power to each encoded data stream such that successful communication can be guaranteed. The proposed algorithms exhibit a substantial performance improvement compared with the conventional orthogonal transmission schemes.

  • 21.
    Farhadi, Hamed
    et al.
    Chalmers University of Technology, Gothenburg, Sweden.
    Wang, Chao
    Tongji University, Shanghai, China.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ergodic Interference Alignment with Limited Feedback: Power Control and Rate Adaptation2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 4, no 12, p. 6679-6694Article in journal (Refereed)
    Abstract [en]

    Considering the time-varying K-user single-antenna interference channel (IC), it has been shown that, when terminals have perfect global channel state information (CSI) and they can tolerate asymptotically long delay, applying an ergodic interference alignment (EIA) scheme can achieve half of the interference-free achievable rate. However, in practice obtaining such CSI is challenging, and only a limited delay is acceptable. This paper addresses data transmission over the IC by taking these concerns into account. Specifically, we consider the case that each transmitter attains only quantized CSI via limited feedback signals. This causes imperfect interference alignment and a degraded performance. We propose adaptive schemes to compensate the impact of the CSI uncertainties. We first study a power control problem which concerns how to communicate at fixed rates using minimum transmit powers. A power control algorithm is used to reach the solution. Next, we address a throughput maximization problem when the transmit powers are fixed. Through the analysis of system outage probability, we propose a rate adaptation scheme to maximize throughput. Finally, we quantify the throughput loss in delay-limited systems. Our results show that, even with limited feedback, performing the EIA scheme with proper power control or rate adaptation strategies can still outperform conventional orthogonal transmission approaches.

  • 22.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Contractive interference functions and rates of convergence of distributed power control laws2012In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 11, no 12, p. 4494-4502Article in journal (Refereed)
    Abstract [en]

    The standard interference functions introduced by Yates have been very influential on the analysis and design of distributed power control laws. While powerful and versatile, the framework has some drawbacks: the existence of fixed-points has to be established separately, and no guarantees are given on the rate of convergence of the iterates. This paper introduces contractive interference functions, a slight reformulation of the standard interference functions that guarantees the existence and uniqueness of fixed-points along with linear convergence of iterates. We show that many power control laws from the literature are contractive and derive, sometimes for the first time, analytical convergence rate estimates for these algorithms. We also prove that contractive interference functions converge when executed totally asynchronously and, under the assumption that the communication delay is bounded, derive an explicit bound on the convergence time penalty due to increased delay. Finally, we demonstrate that although standard interference functions are, in general, not contractive, they are all para-contractions with respect to a certain metric. Similar results for two-sided scalable interference functions are also derived.

  • 23.
    Fischione, Carlo
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Athanasiou, George
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Santucci, Fortunato
    Dynamic Optimization of Generalized Least Squares Handover Algorithms2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 3, p. 1235-1249Article in journal (Refereed)
    Abstract [en]

    Efficient handover algorithms are essential for highly performing mobile wireless communications. These algorithms depend on numerous parameters, whose settings must be appropriately optimized to offer a seamless connectivity. Nevertheless, such an optimization is difficult in a time varying context, unless adaptive strategies are used. In this paper, a new approach for the handover optimization is proposed. First, a new modeling of the handover process by a hybrid system that takes as input the handover parameters is established. Then, this hybrid system is used to pose some dynamical optimization approaches where the probability of outage and the probability of handover are considered. Since it is shown that these probabilities are difficult to compute, simple approximations of adequate accuracy are developed. Based on these approximations, a new approach to the solution of the handover optimizations is proposed. A distributed optimization algorithm is then developed to maximize handover performance. From an extensive set of results obtained by numerical computations and simulations, it is shown that the proposed algorithm improves performance of the handover considerably when compared to more traditional approaches.

  • 24.
    Fischione, Carlo
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    D'Angelo, M.
    Butussi, M.
    Utility Maximization via Power and Rate Allocation with Outage Constraints in Nakagami-Lognormal Channels2011In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 10, no 4, p. 1108-1120Article in journal (Refereed)
    Abstract [en]

    The problem of maximizing a utility function while limiting the outage probability below an appropriate threshold is investigated. A coded-division multi access wireless network under mixed Nakagami-lognormal fading is considered. Solving such a utility maximization problem is difficult because the problem is non-convex and non-geometric with mixed integer and real decision variables and no explicit functions of the constraints are available. In this paper, three methods for the solution of the utility maximization problem are proposed. By the first method, a simple explicit outage approximation is used and the constraint that rates are integers is relaxed yielding a standard convex programming optimization that can be solved quickly but at the price of a reduced accuracy. The second method uses a more accurate outage approximation, which allows one solving the utility maximization problem by the Lagrange duality for non-convex problems and contraction mapping theory. The third method is a combination of the first and the second one. Numerical results show that the first method performs well for average values of the outage requirements, whereas the second one is always more accurate, but is also more computationally expensive. Finally, the third method gives same accuracy as the second one, but has a lower computational complexity only for a small number of transmitters.

  • 25.
    Flischione, Carlo
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sangiovanni-Vincentelli, A.
    Ares, Benigno Zurita
    KTH.
    Minimum Energy Coding in CDMA Wireless Sensor Networks2009In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 8, no 2, p. 985-994Article in journal (Refereed)
    Abstract [en]

    A theoretical framework is proposed for accurate comparison of minimum energy coding in Coded Division Multiple Access (CDMA) Wireless Sensor Networks (WSNs). Energy consumption and reliability are analyzed for two coding schemes: Minimum Energy coding (ME), and Modified Minimum Energy coding (MME). A detailed model of consumed energy is described as function of the coding, radio transmit power, the characteristics of the transceivers, and the dynamics of the wireless channel. Since CDMA is strongly limited by multi-access interference, the system model includes all the relevant characteristics of wireless propagation. A distributed and asynchronous algorithm, which minimizes the total energy consumption by controlling the radio power, is developed. Numerical results are presented to validate the theoretical analysis and show under which conditions MME outperforms ME with respect to energy consumption and bit error rate. It is concluded that MME is more energy efficient than ME only for short codewords.

  • 26.
    Fu, Liqun
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Energy Efficient Transmissions in Cognitive MIMO Systems With Multiple Data Streams2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 9, p. 5171-5184Article in journal (Refereed)
    Abstract [en]

    We investigate energy-efficient communications for time-division multiple access (TDMA) multiple-input multiple-output (MIMO) cognitive radio (CR) networks operating in underlay mode. In particular, we consider the joint optimization over both the time resource and the transmit precoding matrices to minimize the overall energy consumption of a single cell secondary network with multiple secondary users (SUs), while ensuring their quality of service (QoS). The corresponding mathematical formulations turn out to be non-convex, and thus of high complexity to solve in general. We give a comprehensive treatment of this problem, considering both the cases of perfect channel state information (CSI) and statistical CSI of the channels from the SUs to the primary receiver. We tackle the non-convexity by applying a proper optimization decomposition that allows the overall problem to be efficiently solved. In particular, we show that when the SUs only have statistical CSI, the optimal solution can be found in polynomial time. Moreover, if we consider additional integer constraints on the time variable which is usually a requirement in practical wireless system, the overall problem becomes a mixed-integer non-convex optimization which is more complicated. By exploring the special structure of this particular problem, we show that the optimal integer time solution can be obtained in polynomial time with a simple greedy algorithm. When the SUs have perfect CSI, the decomposition based algorithm is guaranteed to find the optimal solution when the secondary system is under-utilized. Simulation results show that the energy-optimal transmission scheme adapts to the traffic load of the secondary system to create a win-win situation where the SUs are able to decrease the energy consumption and the PUs experience less interference from the secondary system. The effect is particularly pronounced when the secondary system is under-utilized.

  • 27. Furuskar, A.
    et al.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Multiservice allocation for multiaccess wireless systems2005In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 4, no 1, p. 174-184Article in journal (Refereed)
    Abstract [en]

    This paper discusses principles for allocating multiple bearer services onto different subsystems in multiaccess wireless systems. Based on the included subsystem's multiservice capacities, under certain constraints near-optimum subsystem service allocations that maximize combined multiservice capacity are derived through simple optimization procedures. These favorable service allocations are either extreme points where services, as far as possible, are allocated to the subsystems best at supporting them, or they are characterized by the relative efficiency of supporting services being equal in all subsystems. The consequences of this include that services should typically be mixed in subsystems with convex capacity regions and isolated in subsystems with concave capacity regions. Simple user assignment algorithms based on this are also discussed. Additionally, illustrating the main findings of the analysis, some system examples are given, including a case study with combined global system for mobile communications (GSM) and wideband code-division multiple-access (WCDMA) systems. The gain of using the proposed service allocation principles compared to a reference case of maintaining equal service mixes in all subsystems depends on the shape of the subsystem capacity regions; the more different the capacity regions, the larger the gain. In the GSM and WCDMA case study, capacity gains of up to 100% in terms of supported data users for a fixed voice traffic load are achieved.

  • 28.
    Gao, Yulan
    et al.
    Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu 611731, Sichuan, Peoples R China..
    Xiao, Yue
    Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu 611731, Sichuan, Peoples R China..
    Wu, Mingming
    Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu 611731, Sichuan, Peoples R China..
    Xiao, Ming
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Shao, Jinliang
    Univ Elect Sci & Technol China, Sch Math Sci, Chengdu 611731, Sichuan, Peoples R China..
    Game Theory-Based Anti-Jamming Strategies for Frequency Hopping Wireless Communications2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 8, p. 5314-5326Article in journal (Refereed)
    Abstract [en]

    In frequency hopping (FH) wireless communications, finding an effective transmission strategy to properly mitigate jamming has been recently considered as a critical issue, due to the inherent broadcast nature of wireless communications. Recently, game theory has been proposed as a powerful tool for dealing with the jamming problem, which can be considered as a player (jammer) playing against a user (transmitter). Different from existing results, in this paper, a bimatrix game framework is developed for modeling the interaction process between the transmitter and the jammer, and the sufficient and necessary conditions for Nash equilibrium (NE) strategy of the game are obtained under the linear constraints. Furthermore, the relationship between the NE solution and the global optimal solution of the corresponding quadratic programming is presented. In addition, a special analysis case is developed based on the continuous game framework in which each player has a continuum of strategies. Finally, we show that the performance can be improved based on our game theoretic framework, which is verified by numerical investigations.

  • 29.
    Ghauch, Hadi
    et al.
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Dept Informat Sci & Engn, S-11004 Stockholm, Sweden..
    Rahman, Muhammad Mahboob Ur
    KTH Royal Inst Technol, Commun Theory Lab, S-11004 Stockholm, Sweden.;Informat Technol Univ, Dept Elect Engn, Lahore 54000, Pakistan..
    Imtiaz, Sahar
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Dept Informat Sci & Engn, S-11004 Stockholm, Sweden..
    Qvarfordt, Christer
    Huawei Technol, S-16440 Kista, Sweden..
    Skoglund, Mikael
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Dept Informat Sci & Engn, S-11004 Stockholm, Sweden..
    Gross, James
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Dept Informat Sci & Engn, S-11004 Stockholm, Sweden..
    User Assignment in C-RAN Systems: Algorithms and Bounds2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 6, p. 3889-3902Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the problem of mitigating interference between so-called antenna domains of a cloud radio access network (C-RAN). In contrast to previous work, we turn to an approach utilizing primarily the optimal assignment of users to central processors in a C-RAN deployment. We formulate this user assignment problem as an integer optimization problem and propose an iterative algorithm for obtaining a solution. Motivated by the lack of optimality guarantees on such solutions, we opt to find lower bounds on the problem and the resulting interference leakage in the network. We thus derive the corresponding Dantzig-Wolfe decomposition, formulate the dual problem, and show that the former offers a tighter bound than the latter. We highlight the fact that the bounds in question consist of linear problems with an exponential number of variables and adapt the column generation method for solving them. In addition to shedding light on the tightness of the bounds in question, our numerical results show significant sum-rate gains over several comparison schemes. Moreover, the proposed scheme delivers similar performance as weighted minimum mean squared-error (MMSE) with a significantly lower complexity (around 10 times less).

  • 30.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Large-System Analysis of Correlated MIMO Multiple Access Channels with Arbitrary Signaling in the Presence of Interference2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 4, p. 2060-2073Article in journal (Refereed)
    Abstract [en]

    Presence of multiple antennas on both sides of a communication channel promises significant improvements in system throughput and power efficiency. In effect, a new class of large multiple-input multiple-output (MIMO) communication systems has recently emerged and attracted both scientific and industrial attention. To analyze these systems in realistic scenarios one has to include such aspects as co-channel interference, multiple access and spatial correlation. In this paper, we study the properties of correlated MIMO multiple-access channels in the presence of external interference. Using the replica method from statistical physics, we derive the ergodic sum-rate of the communication for arbitrary signal constellations when the numbers of antennas at both ends of the channel grow large. Based on these asymptotic expressions, we also address the problem of sum-rate maximization using statistical channel state information and linear precoding. The numerical results demonstrate that when the interfering terminals use discrete constellations, the resulting interference becomes easier to handle compared to Gaussian signals. Thus, it may be possible to accommodate more interfering transmitter-receiver pairs within the same area as compared to the case of Gaussian signals. In addition, we demonstrate numerically for the Gaussian and QPSK signaling schemes that it is possible to design precoder matrices that significantly improve the achievable rates at low-to-mid range of signal-to-noise ratios when compared to isotropic precoding.

  • 31.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Laganá, Marcello
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Petrioli, Chiara
    Energy Efficient COGnitive MAC for Sensor Networks under WLAN Co-existence2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 7, p. 18p. 4075-4089Article in journal (Refereed)
    Abstract [en]

    Energy efficiency has been the driving force behind the design of communication protocols for battery-constrained wireless sensor networks (WSNs). The energy efficiency and the performance of the proposed protocol stacks, however, degrade dramatically in case the low-powered WSNs are subject to interference from high-power wireless systems such as WLANs. In this paper we propose COG-MAC, a novel cognitive medium access control scheme (MAC) for IEEE 802.15.4-compliant WSNs that minimizes the energy cost for multihop communications, by deriving energy-optimal packet lengths and single-hop transmission distances based on the experienced interference from IEEE 802.11 WLANs. We evaluate COG-MAC by deriving a detailed analytic model for its performance and by comparing it with previous access control schemes. Numerical and simulation results show that a significant decrease in packet transmission energy cost, up to 66%, can be achieved in a wide range of scenarios, particularly under severe WLAN interference. COGMAC is, also, lightweight and shows high robustness against WLAN model estimation errors and is, therefore, an effective, implementable solution to reduce the WSN performance impairment when coexisting with WLANs.

  • 32.
    Grotz, Joel
    et al.
    SES ASTRA, Chateau de Betzdorf, Betzdorf, L-6815 Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Krause, Jens
    SES ASTRA, Chateau de Betzdorf, Betzdorf, L-6815 Luxembourg.
    Joint channel synchronization under interference limited conditions2007In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 6, no 10, p. 3781-3789Article in journal (Refereed)
    Abstract [en]

    Spectral efficiency is of great concern in the return channel of satellite based broadband systems. In [1] the feasibility of increased efficiency by reducing channel spacing below the Symbol Rate was demonstrated using joint detection and decoding for a synchronized system. We extend this work by addressing the critical synchronization problem in the presence of adjacent channel interference (ACI) which limits performance as carrier spacing is reduced. A pilot sequence aided joint synchronization scheme for a multi-frequency time division multiple access (MF-TDMA) system is proposed. Based on a maximum likelihood (ML) criterion, the channel parameters, including frequency, time and phase are jointly estimated for the channel of interest and the adjacent channels. The impact of ACI on the synchronization and detection performance is investigated. It is shown that joint channel parameter estimation outperforms single carrier synchronization with reasonable additional computational complexity in the receiver. Based on the proposed synchronization scheme in conjunction with an appropriate joint detection mechanism, see [1], carrier spacing can be reduced significantly compared to current systems providing a substantial increase in spectral efficiency.

  • 33.
    Grotz, Joel
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Krause, Jens
    SES ASTRA, Luxembourg.
    Signal Detection and Synchronization for Interference Overloaded Satellite Broadcast Reception2010In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 9, no 10, p. 3052-3063Article in journal (Refereed)
    Abstract [en]

    We address fixed satellite broadcast reception with the goal of decreasing the aperture of the receiving antenna. The front-end antenna size is commonly determined by the presence of interference from adjacent satellites. A small antenna aperture leads to interference from neighboring satellites utilizing the same frequency bands. We propose a reception system with. M multiple input elements and with subsequent joint detection of desired and interfering signals that provides reliable communication in the presence of multiple interfering signals. An iterative least squares technique is adopted combining spatial and temporal processing and achieving robustness against pointing errors. Simulation results show how the proposed joint spatial and temporal adapted mechanism outperforms the simple combination of existing techniques under interference overloaded conditions. Also, we demonstrate how to accurately synchronize the signals as part of the detection procedure. The technique is evaluated in a realistic simulation study representing the conditions encountered in a DVB-S2 broadcast scenario.

  • 34.
    Hu, Yulin
    et al.
    RWTH Aachen University.
    Schmeink, Anke
    RWTH Aachen University.
    Gross, James
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Blocklength-Limited Performance of Relaying under Quasi-Static Rayleigh Channels2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 7, p. 4548-4558, article id 7434063Article in journal (Refereed)
    Abstract [en]

    In this paper, the blocklength-limited performance of a relaying system is studied, where channels are assumed to experience quasi-static Rayleigh fading while at the same time only the average channel state information (CSI) is available at the source. Both the physical-layer performance (blocklength-limited throughput) and the link-layer performance (effective capacity) of the relaying system are investigated. We propose a simple system operation by introducing a factor based on which we weight the average CSI and let the source determine the coding rate accordingly. In particular, we show that both the blocklengthlimited throughput and the effective capacity are quasi-concave in the weight factor. Through numerical analysis, we investigate the relaying performance with average CSI while considering perfect CSI scenario and direct transmission as contrasts. We observe that relaying is more efficient than direct transmission in the finite blocklength regime. Moreover, this performance advantage of relaying under the average CSI scenario is more significant than under the perfect CSI scenario. Finally, the speed of convergence (between the blocklength-limited performance and the performance with infinite blocklengths) in relaying system is faster in comparison to the direct transmission under both the average CSI scenario and the perfect CSI scenario.

  • 35.
    Huang, Jinliang
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Signell, Svante
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    On Spectral Efficiency of Low-Complexity Adaptive MIMO Systems in Rayleigh Fading Channel2009In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 8, no 9, p. 4369-4374Article in journal (Refereed)
    Abstract [en]

    Adaptive MQAM modulation is used to maximize spectral efficiency of Multiple-Input Multiple-Output (MIMO) systems while keeping bit error rate (BER) under a target level. Closed-form expressions of the average spectral efficiency, coined as discrete-rate spectral efficiency (DRSE), are derived for adaptive modulation MIMO systems using different algorithms. To further enhance the spectral efficiency, a low complexity adaptation scheme is suggested to switch across different algorithms based on the DRSE. In the current letter, we investigate the adaptation scheme that switches between Orthogonal Space-Time Block Codes (OSTBC) and spatial multiplexing with zero-forcing (ZF) detection for MIMO systems with two transmit antennas. Two types of operating environment are considered: flat Rayleigh fading channel without spatial correlation and spatially correlated Rayleigh fading channel with transmit correlation.

  • 36.
    Huang, Yongming
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zheng, G.
    University of Luxembourg.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wong, Kai-Kit
    University College London.
    Yang, Luxi
    Southeast University, Nanjing, China.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Multicell Beamforming Design Approaching Pareto Boundary with Max-Min Fairness2012In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 11, no 8, p. 2921-2933Article in journal (Refereed)
    Abstract [en]

    This paper addresses coordinated downlink beamforming optimization in multicell time division duplex (TDD) systems where a small number of parameters are exchanged between cells but with no data sharing. With the goal to reach the point on the Pareto boundary with max-min rate fairness, we first develop a two-step centralized optimization algorithm to design the joint beamforming vectors. This algorithm can achieve a further sum-rate improvement over the max-min optimal performance, and is shown to guarantee max-min Pareto optimality for scenarios with two base stations (BSs) each serving a single user. To realize a distributed solution with limited intercell communication, we then propose an iterative algorithm by exploiting an approximate uplink-downlink duality, in which only a small number of positive scalars are shared between cells in each iteration. Simulation results show that the proposed distributed solution achieves a fairness rate performance close to the centralized algorithm while it has a better sum-rate performance, and demonstrates a better tradeoff between sum-rate and fairness than the Nash Bargaining solution especially at high signal-to-noise ratio.

  • 37.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Ronnow, Daniel
    Univ Gavle, Dept Elect Math & Nat Sci, S-80176 Gavle, Sweden..
    Dirty MIMO Transmitters: Does It Matter?2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 8, p. 5425-5436Article in journal (Refereed)
    Abstract [en]

    The radio frequency transmitter is a key component in contemporary multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing systems. A detailed study of a 2 x 2 MIMO transmitter subjected to correlated input data streams, nonlinear distortion, thermal noise, and crosstalk is provided by stochastic modeling. The effects of correlated input streams, crosstalk, and nonlinearities are studied in detail and exemplified both by approximate expressions and numerical simulations. Key results include exact and approximate expressions for the normalized mean-squared error (NMSE) for systems with or without digital predistortion; the relationship between NMSE and the signal-to-noise-and-distortion ratio, the properties of the distortion noise, and a novel design for power amplifier back-off for MIMO transmitters subject to crosstalk. The theoretical derivations are illustrated by numerical examples and simulation results, and their relationships to the state-of-the-art research are discussed.

  • 38. Janssen, G. J. M.
    et al.
    Zander, Jens
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Capacity assessment of a cellular radio system using a narrowband multiuser detector2003In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 2, no 4, p. 703-713Article in journal (Refereed)
    Abstract [en]

    With a narrowband multiuser detector (MUD), multiple users can simultaneously share the same channel without using a bandwidth-expanding signature code when sufficient power differences at the receiver are maintained. In this paper, we assess the capacity gain that can be achieved in a hypothetical cellular system with centralized power control, using a narrowband MUD based on successive cancellation. The power-control algorithm is adapted to multiple users per channel in a cell. Simulation results are presented for two heuristic carrier-to-interference ratio-based channel-assignment schemes. The MUD allows for a substantial capacity gain due to a tighter packing of users in a channel. The observed gain compared with a conventional single user-per-channel system, ranges from 1.4 to 5 for cluster sizes C = 1 and 7, respectively.

  • 39.
    Johansson, Mikael
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Xiao, L.
    Cross-layer optimization of wireless networks using nonlinear column generation2006In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 5, no 2, p. 435-445Article in journal (Refereed)
  • 40.
    Jorswieck, Eduard A.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Boche, Holger
    Delay-limited capacity: Multiple antennas, moment constraints, and fading statistics2007In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 6, no 12, p. 4204-4208Article in journal (Refereed)
    Abstract [en]

    Different performance measures are an important mean in order to analyze and design wireless communications systems. Examples of common performance measures are the ergodic capacity, the outage capacity, and the average mean-square error (MSE). In this work, we study the delay-limited capacity (DLC). The DLC depends on the properties of the fading channel, e.g. on the spatial correlation and on the line-of-sight (LOS) component. In this letter, we derive the DLC for the general class of parallel fading channels, including the multiple antenna channels under moment and long-term power constraint. We prove that the DLC is Schur-concave with respect to the spatial correlation in single-input multiple-output (SIMO), and multiple-input single-output (MISO). Bounds for the DLC of multiple-input multiple-output (MIMO) and parallel fading channels are derived and the impact of the the mean component and spatial correlation on these bounds is characterized.

  • 41.
    Jorswieck, Eduard A.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Svedman, Patrick
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Performance of TDMA and SDMA based Opportunistic Beamforming2008In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, no 11, p. 4058-4063Article in journal (Refereed)
    Abstract [en]

    In this work, we analyze opportunistic beamforming with finite number of single-antenna users under the constraint that the feedback overhead from the mobiles to the base is constant. First, we characterize the impact of the fading variances of the users and the spatial correlation on the sum rate of TDMA based opportunistic beamforming using majorization theory. Further, we describe quantitatively the high-SNR behavior in terms of throughput slope and power offset. Next, the impact of the fading variances of the users on an upper bound of the sum rate for space division multiple access (SDMA) based opportunistic beamforming is derived which is tight for high SNR. We propose to adapt the number of active beams to the SNR and the number of active users in a cell and illustrate the corresponding optimization problem by simulations.

  • 42. Jorswieck, Eduard
    et al.
    Mochaourab, Rami
    Mittelbach, M.
    Effective Capacity Maximization in Multi-Antenna Channels with Covariance Feedback2010In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 9, no 10, p. 2988-2993Article in journal (Refereed)
    Abstract [en]

    The tradeoff between average transmission rate and average delay is important for the system design of future wireless communication systems. In double-correlated multiple antenna channels, the spatial degrees of freedom allow to optimize the transmit strategy under throughput/delay priority. In this work, we maximize the effective capacity of a MIMO system with covariance feedback. Interestingly, the larger the delay requirement is, the more spatial degrees of freedom are used to avoid low instantaneous transmission rates. This fact is shown analytically by deriving a closed-form expression for the beamforming optimality range as a function of the spatial correlation, the SNR, and the QoS exponent. Numerical simulations illustrate the average effective capacity optimization and confirm the theoretical results.

  • 43.
    Kim, Su Min
    et al.
    KTH, School of Electrical Engineering (EES). Korea Polytechnic University, South Korea.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Virtual Full-Duplex Buffer-Aided Relaying in the Presence of Inter-Relay Interference2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 4, p. 2966-2980Article in journal (Refereed)
    Abstract [en]

    In this paper, we study virtual full-duplex (FD) buffer-aided relaying to recover the loss of multiplexing gain caused by half-duplex (HD) relaying in a multiple relay network, where each relay is equipped with a buffer and multiple antennas, through joint opportunistic relay selection (RS) and beamforming (BF) design. The main idea behind virtual FD buffer-aided relaying is that the source and one of the relays simultaneously transmit their own information to another relay and the destination, respectively. In such networks, interrelay interference (IRI) is a crucial problem, which has to be resolved like self-interference in the FD relaying. In contrast to previous work that neglected IRI, we propose joint RS and BF schemes taking IRI into consideration by using multiple antennas at the relays. To maximize average end-to-end rate, we propose a weighted sum-rate maximization strategy assuming that adaptive rate transmission is employed in both the source to relay and relay to destination links. Then, we propose several BF schemes cancelling or suppressing IRI in order to maximize the weighted sum-rate. Numerical results show that our proposed optimal, zero-forcing, and minimum mean square error BF-based RS schemes asymptotically approach the ideal FD relaying upper bound when increasing the number of antennas and/or the number of relays.

  • 44. Kim, Taejoon
    et al.
    Love, David J.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Jin, Zhong-Yi
    An Approach to Sensor Network Throughput Enhancement by PHY-Aided MAC2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 2, p. 670-684Article in journal (Refereed)
    Abstract [en]

    Low power sensor networks with communication enabled by WiFi are expected to be widely deployed. A major challenge is collecting event-driven uplink data from a large number of low-power sensors with low latency. In WiFi, the access point (AP) typically polls nodes individually to schedule uplink transmission times, resulting in a large latency. In this paper, we present a physical (PHY) layer-aided medium access control (MAC) framework to enhance the uplink throughput of sensor data traffic. In the approach, the acknowledgements from the sensor nodes to the poll message are parallelized. By detecting the parallel acknowledgement, the AP knows which nodes have data to send and allocates channel resources by sending a pull message. This approach is referred to as the probe and pull MAC (PPMAC) mechanism. Our scheme is based on maximizing the achievable throughput of PPMAC by optimizing the PHY layer components. More precisely, we investigate the parallel acknowledgement detector design problem and develop a non-convex optimization framework that maximizes the PPMAC throughput by optimizing the parallel acknowledgement detection statistics. Numerical examples illustrate that PPMAC outperforms the point coordination function (PCF) and distributed coordination function (DCF) mechanisms, standardized in IEEE 802.11, in terms of the achievable throughput and the overhead.

  • 45.
    Kim, Thanh Tung
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Combining long-term and low-rate short-term channel state information over correlated MIMO channels2008In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, no 7, p. 2409-2414Article in journal (Refereed)
    Abstract [en]

    A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is combined with a unitary transformation based on the long-term channel statistics. The heavily quantized feedback link is directly optimized to maximize the expected achievable rate under different power constraints, using vector quantization and convex optimization techniques on a sample channel distribution. Robustness against errors in the feedback link is also pursued with tools in channel optimized vector quantization. Simulations indicate the benefits of the proposed scheme.

  • 46.
    Kim, Yunesung
    et al.
    Yonsei University.
    Miao, Guowang
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Hwang, Taewon
    Yonsei University.
    Energy Efficient Pilot and Link Adaptation for Mobile Users in TDD Multi-User MIMO Systems2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 1, p. 382-393Article in journal (Refereed)
    Abstract [en]

    In this paper, we develop an uplink pilot and downlink link adaptation approach to improve the energy efficiency (EE) of mobile users in time division duplexing (TDD) multi-user multiple input and multiple output (MU-MIMO) systems. Assuming reciprocity between uplink and downlink channels, the downlink transmission is based on uplink channel estimation. While more uplink pilot power ensures more accurate channel estimation and better downlink performance, it incurs higher energy consumption of mobile users. This paper reveals the relationship and tradeoff among pilot power, channel estimation, and downlink link adaptation that achieves the highest energy efficiency for mobile users. We show that the energy efficiency of different users can be decoupled because the downlink average throughput of each user is independent of the pilot powers of other users and energy-efficient design can be done on a per-user basis. Based on the analysis, we propose an uplink pilot and downlink link adaptation algorithm to improve the EE of mobile users. Simulation results are finally provided to demonstrate the significant gain in energy efficiency for mobile users.

  • 47.
    Kliewer, J.
    et al.
    University of Kiel.
    Thobaben, Ragnar
    University of Kiel.
    Iterative joint source-channel decoding of variable-length codes using residual source redundancy2005In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 4, no 3, p. 919-929Article in journal (Refereed)
    Abstract [en]

    We present a novel symbol-based soft-input a posteriori probability (APP) decoder for packetized variable-length encoded source indexes transmitted over wireless channels where the residual redundancy after source encoding is exploited for error protection. In combination with a mean-square or maximum APP estimation of the reconstructed source data, the whole decoding process is close to optimal. Furthermore, solutions for the proposed APP decoder with reduced complexity are discussed and compared to the near-optimal solution. When, in addition, channel codes are employed for protecting the variable-length encoded data, an iterative source-channel decoder can be obtained in the same way as for serially concatenated codes, where the proposed APP source decoder then represents one of the two constituent decoders. The simulation results show that this iterative decoding technique leads to substantial error protection for variable-length encoded correlated source signals, especially, when they are transmitted over highly corrupted channels.

  • 48. Krikidis, Ioannis
    et al.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Thompson, John S.
    Buffer-Aided Relay Selection for Cooperative Diversity Systems without Delay Constraints2012In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 11, no 5, p. 1957-1967Article in journal (Refereed)
    Abstract [en]

    In this paper, we study the relay selection problem for a finite buffer-aided decode-and-forward cooperative wireless network. A relay selection policy that fully exploits the flexibility offered by the buffering ability of the relay nodes in order to maximize the achieved diversity gain is investigated. This new scheme incorporates the instantaneous strength of the wireless links as well as the status of the finite relay buffers and adapts the relay selection decision on the strongest available link by dynamically switching between relay reception and transmission. In order to analyse the new relay selection policy in terms of outage probability and diversity gain, a theoretical framework that models the evolution of the relay buffers as a Markov chain (MC) is introduced. The construction of the state transition matrix and the related steady state of the MC are studied and their impact on the derivation of the outage probability is investigated. We show that the proposed relay selection scheme significantly outperforms conventional relay selection policies for all cases and ensures a diversity gain equal to two times the number of relays for large buffer sizes.

  • 49.
    Kwon, Younggap
    et al.
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea.;Agcy Def Dev, Daejeon 305600, South Korea..
    Park, Hyunsung
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea..
    Oh, Jintaek
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea..
    Miao, Guowang
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Hwang, Taewon
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea..
    Energy-Efficient Routing and Link Adaptation for 2D Wireless Relay Networks in the Wideband Regime2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 11, p. 7325-7339Article in journal (Refereed)
    Abstract [en]

    We discuss the globally optimal energy-efficient design of a 2D relay network. Different from the existing routing protocols on energy saving, which finds the minimal energy route for a given data rate, the proposed algorithm jointly optimizes routing and data rate to maximize energy efficiency (EE) defined as the achievable data rate per power consumption. We propose a low-complexity algorithm to circumvent the huge complexity of the exhaustive search for the network EE maximization and prove its global optimality. Moreover, the proposed algorithm is implemented in a distributed fashion because each relay needs to send its routing information only to the relays in its adjacent tiers, which significantly reduces the signaling overhead of the centralized implementation. Our analysis on the worst-case complexity in a fading channel shows that the complexity of the proposed algorithm increases linearly while that of the exhaustive search increases exponentially as the tier index increases. Simulation results confirm that the proposed algorithm outperforms the existing routing protocols on energy saving and achieves the globally optimal network EE at a significantly lower complexity than the exhaustive search.

  • 50.
    Larsson, Erik G.
    et al.
    Linköping University, Dept. of Electrical Engineering (ISY), Division of Communication Systems.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cognitive Radio in a Frequency-Planned Environment: Some Basic Limits2008In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, no 12, p. 4800-4806Article in journal (Refereed)
    Abstract [en]

    The objective of this work is to assess some fundamental limits for opportunistic spectrum reuse via cognitive radio in a frequency-planned environment. We present a first-order analysis of the signal-to-noise-and-interference situation in a wireless cellular network, and analyze the impact of cognitive users starting to transmit. Two main conclusions emerge from our study. First, obtaining any substantial benefits from opportunistic spatial spectrum reuse in a frequency-planned network without causing substantial interference is going to be very challenging. Second, the cognitive users need to be more sensitive, by orders of magnitude, than the receivers in the primary system, especially if there is significant shadow fading. This latter problem can be alleviated by having cognitive users cooperate, but only if they are separated far apart so that they experience independent shadowing.

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