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  • 1.
    Gabry, Frédéric
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Li, Nan
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Schrammar, Nicolas
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karipidis, Eleftherios
    Thobaben, Ragnar
    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.
    Larsson, Erik G.
    Skoglund, Mikeal
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Secure Broadcasting in Cooperative Cognitive Radio Networks2012In: 2012 Future Network and Mobile Summit, FutureNetw 2012, IIMC , 2012Conference paper (Refereed)
    Abstract [en]

    This paper explores the trade-off between cooperation and secrecy in cognitive radio networks. We consider a scenario consisting of a primary and a secondary system. In the simplest case, each system is represented by a pair of transmitter and receiver. We assume a secrecy constraint on the transmission in the sense that the message of the primary transmitter has to be concealed from the secondary user. Both situations where the secondary transmitter is aware and unaware of the primary message are investigated and compared. Furthermore, we extend our results to the scenario where the secondary system comprises multiple users. For each case we sketch the derivation of the rates that are achievable from an information theoretic perspective. We then investigate the findings by numerical simulations. Our main result is that, in spite of the secrecy constraint, cooperation is beneficial in terms of the achievable rates. The secondary transmitter has the two contradicting tasks of helping the primary system and transmitting its own message. Our results show that both tasks can be accomplished simultaneously, improving both systems' performance. In particular, the secondary system can achieve a significant rate without decreasing the primary rate below the benchmark rate achievable without the help of the secondary transmitter. In the case of multiple secondary users, the rate region reduces, which results in a lower individual rate. However, the linear increase in sumrate counterbalances this effect.

  • 2.
    Gabry, Frédéric
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Li, Nan
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Schrammar, Nicolas
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Girnyk, Maksym
    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.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the Optimization of the Secondary Transmitter's Strategy in Cognitive Radio Channels with Secrecy2014In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 32, no 3, p. 451-463Article in journal (Refereed)
    Abstract [en]

    This paper investigates cooperation for secrecy in cognitive radio networks. In particular, we consider a four-node cognitive scenario where the secondary receiver is treated as a potential eavesdropper with respect to the primary transmission. The cognitive transmitter can help the primary transmission, and it should also ensure that the primary message is not leaked to the secondary user. We consider two cognitive scenarios depending on whether the secondary transmitter knows the primary message or not. In the first case, the secondary transmitter is unaware of the primary transmitter's message and acts as a helping interferer to enhance the secrecy of the primary transmission, whereas in the second case, relaying of the primary message is also within its capabilities. First, we find achievable rate regions for these two scenarios in the case of AWGN channels. We then investigate three different optimization problems: the maximization of the primary rate, the maximization of the secondary rate and the minimization of the secondary transmit power. For these optimization problems, we find closed-form expressions in important special cases. Furthermore, we analyze the cooperation between the primary and secondary transmitters from a game-theoretic perspective. We model their interaction as a Stackelberg game, for which we define and find the Stackelberg equilibrium. Finally, we use numerical examples to illustrate the rate regions, the three optimizations, and the impact of the Stackelberg game on the achievable rates and on the transmission strategies of the secondary transmitter.

  • 3.
    Gabry, Frédéric
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Schrammar, Nicolas
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Li, Nan
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Thobaben, Ragnar
    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.
    Cooperation for Secure Broadcasting in Cognitive Radio Networks2012In: Communications (ICC), 2012 IEEE International Conference on, IEEE , 2012, p. 5613-5618Conference paper (Refereed)
    Abstract [en]

    This paper explores the trade-off between cooperation and secrecy in cognitive radio networks. We consider a scenario consisting of a primary and a secondary system. In the simplest case, each system is represented by a pair of transmitter and receiver. We assume a secrecy constraint on the transmission in the sense that the message of the primary transmitter has to be concealed from the secondary receiver. Both situations where the secondary transmitter is aware and unaware of the primary message are investigated and compared. In the first case, the secondary transmitter helps by allocating power for jamming, which increases the secrecy of the first message. In the latter case, it can also act as a relay for the primary message, thus improving the reliability of the primary transmission. Furthermore, we extend our results to the scenario where the secondary system comprises multiple receivers. For each case we present achievable rate regions. We then provide numerical illustrations for these rate regions. Our main result is that, in spite of the secrecy constraint, cooperation is beneficial in terms of the achievable rates. In particular, the secondary system can achieve a significant rate without decreasing the primary rate below the benchmark rate achievable without the help of the secondary transmitter. Finally, we investigate the influence of the distances between users on the system's performance.

  • 4.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Statistical-Physics Approach to the Analysisof Wireless Communication Systems2014Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Multiple antennas at each side of the communication channel seem to be vital for future wireless communication systems. Multi-antenna communication provides throughput gains roughly proportional to the smallest number of antennas at the communicating terminals. On the other hand, multiple antennas at a terminal inevitably increase the hardware complexity of the latter. For efficient design of such systems relevant mathematical tools, capable of capturing the most significant features of the wireless multi-antenna channel - such as fading, spatial correlation, interference - are essential.

    This thesis, based on the asymptotic methods from statistical physics and random matrix theory, develops a series of asymptotic approximations for various metrics characterizing the performance of multi-antenna systems in different settings. The approximations become increasingly precise as the number of antennas at each terminal grows large and are shown to significantly simplify the performance analysis. This, in turn, enables efficient performance optimization, which would otherwise be intractable.

    After a general introduction, provided in Chapter 2, this thesis provides four different applications of large-system analysis. Thus, Chapter 3 analyzes multi-antenna multiple-access channel in the presence of non-Gaussian interference. The obtained large-system approximation of the sum rate is further used to carry out the precoder optimization routine for both Gaussian and finite-alphabet types of inputs. Meanwhile, Chapter 4 carries out the large-system analysis for a multi-hop relay channel with an arbitrary number of hops. Suboptimality of some conventional detectors has been captured through the concept of generalized posterior mean estimate. The obtained decoupling principle allows performance evaluation for a number of conventional detection schemes in terms of achievable rates and bit error rate. Chapter 5, in turn, studies achievable secrecy rates of multi-antenna wiretap channels in three different scenarios. In the quasi-static scenario, an alternating-optimization algorithm for the non-convex precoder optimization problem is proposed. The algorithm is shown to outperform the existing solutions, and it is conjectured to provide a secrecy capacity-achieving precoder. In the uncorrelated ergodic scenario, a large-system analysis is carried out for the ergodic secrecy capacity yielding a closed-form expression. In the correlated ergodic scenario, the obtained large-system approximation is used to address the corresponding problem of precoder optimization. Finally, Chapter6 addresses a practical case of random network topology for two scenarios: i) cellular mobile networks with randomly placed mobile users and ii) wiretap channel with randomly located eavesdroppers. Large-system approximations for the achievable sum rates are derived for each scenario, yielding simplified precoder optimization procedures for various system parameters.

  • 5.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Cooperative communication for multi-user cognitive radio networks2012Licentiate thesis, monograph (Other academic)
    Abstract [en]

    In recent years, the main trend in wireless communications has been shifted from voice transmission to data-centric communication. This shift has caused an increase in the data rate requirements for future wireless communication systems. These requirements result in need for large bandwidth. Being a limited and thus expensive resource, wireless spectrum needs to be used efficiently. For higher spectral efficiency, new transmission techniques as well as new dynamic spectrum-allocationpolicies are needed. Cognitive radio is a promising approach for increasing spectral efficiency of wireless systems. By exploiting advanced signal processing techniques and sophisticated transmission schemes, cognitive radio devices allow to serve new wireless users within the existing crowded spectrum. Typically, a cognitive radio network is installed in parallel to an existing primary network, a legacy owner of the spectrum. The cognitive radio network adapts to its electro-magnetic environment in order to limit or even avoid the disturbance to the primary network. This thesis focuses on the underlay cognitive radio paradigm, which assumes that both the primary network and the ad hoc cognitive radio network operate within the same time and frequency band, as well as at the same geographic location. The cognitive network is able to estimate the interference caused to the primary network by means of channel training and possible feedback. This knowledge is then used to adjust the cognitive network’s transmissions in such a way that the disturbance to the primary network is below some acceptable threshold. In the first part of the thesis, we discuss the multi-hop line cognitive networks, in which the information content before reaching its destination passes through several hops from node to node within the cognitive network. In this way, transmission power at the source terminal may be decreased, thus producing less interference to the primary network. Moreover, the powers at each terminal within the cognitive network may be optimally allocated so that the interference constraint at the primary network is satisfied. This power allocation can be realized in both centralized and decentralized ways, depending on the available information about the channel state. We discuss both of these allocations subject to different interference constraints employed at the primary network. In the second part of the thesis, we discuss the reliability of transmission within the line cognitive ad hoc networks in terms of outage probability and diversity. We also illustrate the benefit of network coding for such networks and provide a heuristic algorithm for optimal scheduling. In the final part of the thesis, we study the uplink relay-assisted cellular cognitive radio scenario. Both, the cognitive network and the primary network, contain a set of multi-antenna users that communicate with a corresponding base station. The users create mutual interference and hence limit each other’s performance. Using certain mathematical tools originally developed within the field of statistical physics, we are able derive a closed-form expression for the ergodic mutual information for arbitrary channels inputs, which enables characterization of the achievable rate region of such scenario.

  • 6.
    Girnyk, Maksym A.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Muller, A.
    Vehkapera, M.
    Kildehøj Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Debbah, M.
    On the asymptotic sum rate of downlink cellular systems with random user locations2015In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 4, no 3, p. 333-336, article id 7065231Article in journal (Refereed)
    Abstract [en]

    We consider a downlink cellular communication system with a multi-antenna base station (BS). A regularized zero forcing precoder is employed at the BS to manage the inter-user interference within the cell. Using methods from random matrix theory, we derive a deterministic approximation for the achievable ergodic sum rate, taking into account the randomness from both fading and random user locations. The obtained approximation describes well the behavior of finite-sized systems and enables efficient optimization of the precoder matrix.

  • 7.
    Girnyk, Maksym A.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkapera, M.
    Yuan, J.
    Rasmussen, Lars Kildehøj
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the ergodic secrecy capacity of MIMO wiretap channels with statistical CSI2014In: Proceedings of 2014 International Symposium on Information Theory and Its Applications, ISITA 2014, 2014, p. 398-402Conference paper (Refereed)
    Abstract [en]

    Wireless security has become an important issue for modern wireless networks. Due to the broadcast nature of wireless channels possibility of eavesdropping the transmission is provided for non-legitimate receivers. In the present paper, we consider a multi-antenna wiretap channel in a fast-fading environment with only statistical channel state information available at the receiver. The overall performance of such channel is characterized by the ergodic secrecy capacity, which, in general, cannot be characterized explicitly. Nevertheless, based on the assumption that the numbers of antennas at legitimate terminals and the number of eavesdroppers grow large without bound, we derive a deterministic approximation for the achievable ergodic secrecy rate under arbitrary channel inputs. The obtained large-system approximation matches well with the actual simulated secrecy rates, revealing some interesting behavior of the secrecy rates in the given scenario.

  • 8.
    Girnyk, Maksym A.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Vehkapera, Mikko
    Rasmussen, Lars Kildehoj
    Christakou, Athanasia
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Wiklund, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Onfelt, Bjorn
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Orange, Jordan
    Lytic granule convergence is essential for NK cells to promote targeted killing while preventing collateral damage2016In: Journal of Immunology, ISSN 0022-1767, E-ISSN 1550-6606, Vol. 196Article in journal (Other academic)
  • 9.
    Girnyk, Maksym A.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehoj
    Asymptotic Performance Analysis of a K-Hop Amplify-and-Forward Relay MIMO Channel2016In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 62, no 6, p. 3532-3546Article in journal (Refereed)
    Abstract [en]

    This paper studies the asymptotic performance of multi-hop amplify-and-forward relay multiple-antenna communication channels. Each multi-antenna relay terminal in the considered network amplifies the received signal, sent by a source, and retransmits it upstream toward a destination. Achievable ergodic rates of the relay channel with both jointly optimal detection and decoding and practical separate-decoding receiver architectures for arbitrary signaling schemes, along with average bit error rates for various types of detectors are derived in the regime where the number of antennas at each terminal grows large without a bound. To overcome the difficulty of averaging over channel realizations, we apply a large-system analysis based on the replica method from statistical physics. The validity of the large-system analysis is further verified through Monte Carlo simulations of realistic finite-sized systems.

  • 10.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gabry, Fredric
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    Rasmussen, Lars Kildehöj
    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.
    MIMO wiretap channels with randomly located eavesdroppers: Large-system analysis2015In: 2015 IEEE International Conference on Communication Workshop, ICCW 2015, IEEE conference proceedings, 2015, p. 480-484Conference paper (Refereed)
    Abstract [en]

    Security issues in wireless networks have become a subject of growing interest in recent years due to the broadcast nature of wireless channels. In this paper, we investigate secure communication over a multi-antenna wiretap channel in the presence of randomly distributed eavesdroppers. In the fast fading environment, the overall performance of this channel is traditionally characterized by the ergodic secrecy capacity, which, in general, cannot be derived explicitly. Nevertheless, based on the assumption that the numbers of antennas at legitimate terminals and the number of eavesdroppers grow large without bound, we derive a deterministic approximation of an achievable ergodic secrecy rate for arbitrary inputs. In addition, we characterize the secrecy rates for practically relevant separate-decoding scheme at the receiver. We validate the proposed large-system approximation through numerical simulations and observe a good match with the actual secrecy rates. Finally, we also analyze some interesting behavior of the secrecy rates in the given scenario depending on the geometry of the nodes.

  • 11.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gabry, Frédéric
    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.
    Lars, Rasmussen
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mikael, Skoglund
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the transmit beamforming for MIMO wiretap channels: Large-system analysis2013In: Information Theoretic Security: 7th International Conference, ICITS 2013, Singapore, November 28-30, 2013, Proceedings, Springer Publishing Company, 2013, p. 90-102Conference paper (Refereed)
    Abstract [en]

    With the growth of wireless networks, security has become a fundamental issue in wireless communications due to the broadcast nature of these networks. In this work, we consider MIMO wiretap channels in a fast fading environment, for which the overall performance is characterized by the ergodic MIMO secrecy rate. Unfortunately, the direct solution to finding ergodic secrecy rates is prohibitive due to the expectations in the rates expressions in this setting. To overcome this difficulty, we invoke the large-system assumption, which allows a deterministic approximation to the ergodic mutual information. Leveraging results from random matrix theory, we are able to characterize the achievable ergodic secrecy rates. Based on this characterization, we address the problem of covariance optimization at the transmitter. Our numerical results demonstrate a good match between the large-system approximation and the actual simulated secrecy rates, as well as some interesting features of the precoder optimization.

  • 12.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gabry, Frédéric
    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.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Large-System Analysis of MIMO Wire-Tap Channels with Randomly Located Eavesdroppers2013In: Proceedings of the Tenth International Symposium on Wireless Communication Systems (ISWCS 2013), VDE Verlag GmbH, 2013, p. 380-384Conference paper (Refereed)
    Abstract [en]

    Wireless security has become a subject of growinginterest in wireless communications due to the broadcast natureof wireless channels. In the present paper, we consider a multiantennawire-tap channel with randomly distributed eavesdroppers.In the fast fading environment, the overall performance ofsuch channel is characterized by the ergodic secrecy capacity,which, in general, cannot be characterized explicitly. Nevertheless,based on the assumption that the numbers of antennasat legitimate terminals and the number of eavesdroppers growlarge without bound, we derive a deterministic approximation forthe achievable ergodic secrecy rate. The obtained large-systemapproximation matches well with the actual simulated secrecyrates, revealing some interesting behavior of the secrecy rates inthe given scenario.

  • 13.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Myopic Multi-Hop Transmission Strategies in Layered Wireless Networks2011In: 2011 IEEE 22nd International Symposium On Personal Indoor And Mobile Radio Communications (PIMRC), New York: IEEE , 2011, p. 1763-1767Conference paper (Refereed)
    Abstract [en]

    A layered wireless network is considered, where information is transmitted in a multi-hop MIMO-like fashion from the source node layer through several intermediate layers of nodes before reaching the sink node layer. Analog network coding is investigated as the network transmission strategy, exploiting the inherent superposition features of the wireless channel. A general myopic transmission protocol is proposed, allowing overhearing across several layers. Special cases are investigated in terms of diversity and bit error rate when using different types of linear detectors. Conditions for successful decoding of all source node messages at each sink node are derived.

  • 14.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Vehkapera, M.
    Vorobyov, S.A.
    On the optimal relay design for multi-antenna cognitive two-way AF relay networks2015In: Conference Record: Asilomar Conference on Signals, Systems and Computers, 2015, Vol. 2015-April, p. 1579-1583Conference paper (Refereed)
    Abstract [en]

    Cognitive relaying is an efficient method for tackling the problem of spectrum scarcity by serving new (secondary) users, while keeping the existing (primary) users satisfied with their service. Moreover, additional gains can be attained from employment of the two-way relaying with multiple-antenna relays within the secondary network. In this paper, we consider an underlay two-way cognitive network and propose an efficient algorithm for computing a (nearly) optimal relay precoder matrix subject to the interference constraint towards the primary network. The efficiency of the proposed solution is highlighted by means of numerical simulations.

  • 15.
    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
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the asymptotic sum-rate of the relay-assisted amplify-and-forward cognitive MIMO channel2012In: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on, IEEE , 2012, p. 709-714Conference paper (Refereed)
    Abstract [en]

    This paper studies the asymptotic sum-rate of the primary network within the relay-assisted multi-antenna cognitive radio system performing amplify-and-forward relaying. The achievable sum-rates are derived in the large-system limit by means of the replica method. A closed-form expression for the sum-rate of the primary network is obtained for large antenna arrays as a function of parameters obtained by solving a set of fixed-point equations. Numerical simulations confirm the validity of the results even for systems with only a few antennas at each terminal.

  • 16.
    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
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the Asymptotic Sum-Rate of Uplink MIMO Cellular Systems in the Presence of Non-Gaussian Inter-Cell Interference2012In: 2012 IEEE Global Communications Conference (GLOBECOM 2012), New York: IEEE , 2012, p. 2475-2480Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a scenario, where several mobile multi-antenna terminals communicate with the multi- antenna base station within a cellular communication system over the flat Rayleigh fading channel. In addition, several terminals from the neighboring cell cause interference. For such a scenario, we derive, using the replica method, the asymptotic sum-rate of the communication in the large-system limit for arbitrary signal constellations. Moreover, we show via numerical results that when the interfering terminals use a QPSK constellation, the resulting interference becomes easier to handle. In effect, we may be able to accumulate more interfering transmitter-receiver pairs within the same area as compared to the case of Gaussian signals. Monte- Carlo simulations show that the derived asymptotic expression matches well with the simulated values even for small numbers of antennas.

  • 17.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    Aalto University.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Asymptotic properties of dual-hop AF relay MIMO communication systems2014In: 2014 IEEE International Symposium on Information Theory (ISIT), IEEE conference proceedings, 2014, p. 476-480Conference paper (Refereed)
    Abstract [en]

    The present paper studies the asymptotic performance of dual-hop amplify-and-forward multiple-input multiple-output relay communication systems. In the corresponding setup, a relay amplifies the signal received from a source, retransmitting it towards a destination, while the direct source-destination link is absent. Ergodic achievable rates under separate decoding, along with the average bit error rate under various detection schemes are derived in the regime where the number of antennas at each terminal grows without bound. To overcome the mathematical difficulty of averaging over both channel realizations and input signals we apply large-system analysis based on the replica method from statistical physics. The validity of the large-system analysis is further verified through Monte Carlo simulations, providing particularly good accuracy at low SNR.

  • 18.
    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.

  • 19.
    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 the K-Hop AF MIMO Relay Channel with Arbitrary Inputs2013In: IEEE International Symposium on Information Theory: Proceedings, IEEE conference proceedings, 2013, p. 439-443Conference paper (Refereed)
    Abstract [en]

    The present paper investigates the achievable data rates of multi-hop amplify-and-forward multi-antenna relay channels with arbitrary number of hops K. Each multi-antenna terminal in the system amplifies the received signal and retransmits it upstream. To analyze the ergodic end-to-end mutual information of the system, one has to perform averaging over the fading coefficients. To overcome this difficulty we apply large-system analysis, based on the assumption that the number of antennas grows without bound at every terminal. Using the replica method, we derive an explicit asymptotic expression for the ergodic mutual information between the input and output of the K-hop channel with no restrictions on the channel inputs. Numerical results support the validity of the replica analysis and show that the result is tight even for small antenna arrays.

  • 20.
    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.
    Multi-Cell Cooperation with Random User Locations under Arbitrary Signaling2013In: 2013 IEEE Information Theory Workshop (ITW), IEEE , 2013, p. 6691326-Conference paper (Refereed)
    Abstract [en]

    Base station cooperation in cellular networks has been recently recognized as a key technology for mitigating interference, providing thus significant improvements in the system performance. In this paper, we consider a simple scenario consisting of two one-dimensional cells, where the base stations have fixed locations, while the user terminals are randomly distributed on a line. Exploiting the replica method from statistical physics, we derive the ergodic sum-rate under arbitrary signaling for both cooperative and non-cooperative scenarios, when the system size grows large. The obtained results are analytically tractable and can be used to optimize the system parameters in a simple manner. The numerical examples show that the analysis provides good approximations for finite-sized systems.

  • 21.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kildehöj Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cooperative communication in multi-source line networks2012In: 2012 IEEE Wireless Communications and Networking Conference, WCNC, IEEE Communications Society, 2012, p. 2379-2383Conference paper (Refereed)
    Abstract [en]

    Cooperative communication is shown to be an efficient method of combating fading in wireless networks. By "sharing" their antennas cooperating single-antenna nodes create a virtual multi-antenna system and therefore, benefit from spatial diversity. Network coding being a particular cooperative communication technique provides substantial gains in data rate, especially in networks with many sink nodes. By allowing intermediate nodes of a network to mix the incoming data streams, one can achieve the multicast capacity. Recently, Xiao and Skoglund showed that binary network coding (BNC) is not optimal for multi-user multi-relay networks in terms of diversity and proposed diversity network coding (DNC) scheme that outperforms BNC approach. Following this approach we examine potential diversity gains of using the DNC scheme for multi-source line networks. We show that the DNC technique outperforms both conventional time-orthogonal transmission and the BNC scheme. Further, the problem of optimal scheduling of the transmission is explored. We formulate the optimization problem and propose efficient solutions. Numerical results are presented to support theoretical findings.

  • 22.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Power Allocation for Multi-Hop Decode-and-Forward Cognitive Radio Networks with Line Topology2012In: 2012 Swedish Communication Technologies Workshop, Swe-CTW 2012, Lund, 2012, p. 7-12Conference paper (Refereed)
    Abstract [en]

    In the present paper we study the power allocation for multi-hop underlay cognitive radio networks (CRNs) with line topology. That is, we consider a scenario, where a CRN operates in parallel to the primary network provided that the interference created to the primary network is limited by an acceptable threshold. The CNR is assumed to be a multi-hop relay network and hence before reaching the destination information from the source node may pass several hops from node to node. At each hop, the information is decoded and forwarded to the following node. It is further assumed that transmissions can be overheard by neighboring nodes, thereby creating interference. The power at each node can be optimally adjusted so that the end-to-end throughput of the CRN is maximized, while the constraint on interference towards the primary network is satisfied. In this paper, we show that for line CRNs the optimal power allocation is achieved when capacities of all intermediate links are equal and the interference constraint of the most disturbed primary user is fulfilled with equality. To simplify the computation of the optimal power allocation we derive two approximate solutions as well as several distributed power allocation schemes. The numerical results illustrate the interplay between the proposed solutions and the optimal power allocation.

  • 23.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehöj
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal Power Allocation in Multi-Hop Cognitive Radio Networks2011In: 2011 IEEE 22nd International Symposium On Personal Indoor And Mobile Radio Communications (PIMRC), New York: IEEE conference proceedings, 2011, p. 472-476Conference paper (Refereed)
    Abstract [en]

    Optimal power allocation in a multi-hop cognitive radio network is investigated. Information transmitted from the source passes through several wireless relay nodes before reaching the destination. At each hop, the received signal is decoded, re-encoded and retransmitted to the following node. Transmissions at every hop are overheard by nearby nodes and therefore cause interference. We study optimal power allocation strategies that maximize the end-to-end throughput of the network under the constraint of strictly limited interference to external users. We show that for networks that can be modeled as a line topology the optimal solution is achieved when the capacities of every intermediate link are equal and the interference power constraint is satisfied with equality. High-and low-SNR approximations that simplify the problem of finding the optimal power allocation are presented as well. The numerical results show good performance compared to schemes with equal power allocation.

  • 24.
    Khabbazibasmenj, Arash
    et al.
    University of Alberta.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vorobyov, Sergiy
    Aalto Univeristy.
    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.
    On the Optimal Precoding for MIMO Gaussian Wire-Tap Channels2013In: Proc. Int. Symp. Wireless Commun. (ISWCS) 2013, VDE Verlag GmbH, 2013, p. 356-359Conference paper (Refereed)
    Abstract [en]

    We consider the problem of finding secrecy rate ofa multiple-input multiple-output (MIMO) wire-tap channel. Atransmitter, a legitimate receiver, and an eavesdropper are allequipped with multiple antennas. The channel states from thetransmitter to the legitimate user and to the eavesdropper areassumed to be known at the transmitter. In this contribution,we address the problem of finding the optimal precoder/transmitcovariance matrix maximizing the secrecy rate of the given wiretapchannel. The problem formulation is shown to be equivalentto a difference of convex functions programming problem andan efficient algorithm for addressing this problem is developed.

  • 25. Vehkapera, M.
    et al.
    Riihonen, T.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Björnson, E.
    Debbah, M.
    Kildehøj Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wichman, R.
    Asymptotic analysis of asymmetric MIMO links: EVM limits for joint decoding of PSK and QAM2015In: 2015 IEEE International Conference on Communications (ICC), IEEE conference proceedings, 2015, Vol. 2015, p. 1869-1873Conference paper (Refereed)
    Abstract [en]

    Hardware non-idealities in wireless transmitter electronics cause distortion that is not captured by conventional linear channel models; in fact, error-vector magnitude (EVM) measurements in conformance testing conceptually reduce their collective effect to an additive noise component at each subcarrier. Motivated by the EVM, the present paper considers a 'binoisy' multiple-input multiple-output (MIMO) channel model where the additional non-idealities manifest themselves as an additive distortion noise term at the transmit side. Through this extended MIMO relation, the effects of hardware impairments on the achievable rates of different digital modulation schemes are studied via large system analysis. The numerical results illustrate how tolerable EVM levels depend non-trivially on various factors, including the signal-to-noise ratio, modulation order and the level of asymmetry in antenna array configurations.

  • 26. Vehkapera, Mikko
    et al.
    Riihonen, Taneli
    Girnyk, Maksym A.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bjornson, Emil
    Debbah, Merouane
    Kildehøj, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wichman, Risto
    Asymptotic Analysis of SU-MIMO Channels With Transmitter Noise and Mismatched Joint Decoding2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 3, p. 749-765Article in journal (Refereed)
    Abstract [en]

    Hardware impairments in radio-frequency components of a wireless system cause unavoidable distortions to transmission that are not captured by the conventional linear channel model. In this paper, a "binoisy" single-user multiple-input multiple-output (SU-MIMO) relation is considered where the additional distortions are modeled via an additive noise term at the transmit side. Through this extended SU-MIMO channel model, the effects of transceiver hardware impairments on the achievable rate of multi-antenna point-to-point systems are studied. Channel input distributions encompassing practical discrete modulation schemes, such as, QAM and PSK, as well as Gaussian signaling are covered. In addition, the impact of mismatched detection and decoding when the receiver has insufficient information about the non-idealities is investigated. The numerical results show that for realistic system parameters, the effects of transmit-side noise and mismatched decoding become significant only at high modulation orders.

  • 27.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Riihonen, Taneli
    Aalto University, Department of Signal Processing and Acoustics.
    Wichman, Risto
    Aalto University, Department of Signal Processing and Acoustics.
    Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On Achievable Rate Regions at Large-System Limit in Full-Duplex Wireless Local Access2013In: International Black Sea Conference on Communications and Networking, 2013Conference paper (Refereed)
    Abstract [en]

    High capacity requirements in wireless systems can be met, at the network level, by using dense small cell deployments and, at the link level, by improving spectral efficiency via spectrum reuse. In this context, we consider a small-area radio system, e.g. a pico- or femtocell, where a full-duplex access point serves simultaneously two half-duplex devices, one in downlink and one in uplink direction. All transceivers are equipped with multiple antennas exploited for spatial multiplexing. Instead of limiting the study to the total sum rate, we analyze the complete achievable rate regions of the two directions. We also take into account the effects of mismatched decoding at the receivers due to imperfect knowledge of the transceiver impairments. The analysis is conducted in the large-system limit using the replica method from statistical physics, which allows to encompass arbitrary channel input distributions. The analytical results characterize the effect of self-interference at the access point and inter-device interference on the achievable rate regions. Numerical examples for particular signaling schemes are also given.

1 - 27 of 27
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