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  • 1.
    Advaita, Advaita
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Gali, Mani Meghala
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Chu, Thi My Chinh
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies. Blekinge Inst Technol, SE-37179 Karlskrona, Sweden..
    Outage Probability of MIMO Cognitive Cooperative Radio Networks with Multiple AF Relays Using Orthogonal Space-Time Block Codes2017In: 2017 IEEE 13TH INTERNATIONAL CONFERENCE ON WIRELESS AND MOBILE COMPUTING, NETWORKING AND COMMUNICATIONS (WIMOB), IEEE , 2017, p. 84-89Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze the outage probability of multiple-input multiple-output cognitive cooperative radio networks (CCRNs) with multiple opportunistic amplify-and-forward relays. The CCRN applies underlay spectrum access accounting for the interference power constraint of a primary network and utilizes orthogonal space-time block coding to transmit multiple data streams across a number of antennas over several time slots. As such, the system exploits both time and space diversity to improve the transmission reliability over Nakagami.. fading. The CCRN applies opportunistic relaying in which the relay offering the highest signal-to-noise ratio at the receiver is selected to forward the transmit signal. Furthermore, selection combining is adopted at the secondary receiver to process the signal from the direct and relaying transmissions. To evaluate system performance, we derive an expression for the outage probability which is valid for an arbitrary number of antennas at the source, relays, and receiver of the CCRN. Selected numerical results are provided using Mathematica for analysis and Matlab for simulations, to reveal the effect of network parameters on the outage probability of the system.

  • 2. Bayley, Todd
    et al.
    Rohani, Bijan
    Johansson, Anders
    Caldera, Manora
    Zepernick, Hans-Jürgen
    Call Quality Monitoring for VoIP2011Conference paper (Refereed)
    Abstract [en]

    A method of monitoring the speech quality of a Voice-over-IP call is described in this paper. This method is attractive because it employs the ITU-T standard P.862 for Perceptual Evaluation of Speech Quality which is well-known for its accuracy. In addition, with the proposed method, call quality is monitored without interfering with the call while it is in progress. The results corresponding to an implementation of this method shows call quality can be measured with excellent accuracy under typical network delays.

  • 3. Buchinger, Shelley
    et al.
    Lopes, Rui J.
    Jumisko-Pyykkö, Satu
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Advances in tools, techniques and practices for multimedia QoE2015In: Multimedia tools and applications, ISSN 1380-7501, E-ISSN 1573-7721Article in journal (Refereed)
    Abstract [en]

    It has been realized that the success of multimedia services or applications relies on the analysis of the entire user experience (UX). The relevance of this paradigm ranges from Internet protocol television to video-on-demand systems for distributing and sharing professional television (TV) and user-generated content that is consumed and produced ubiquitously. To obtain a pleasurable user experience, a large amount of aspects have to be taken into account. Major challenges in this context include the identification of relevant UX factors and the quantification of their influence on Quality of Experience (QoE). This special issue is dedicated to advances in, tools, techniques and practices for multimedia QoE that tackle several of the aforementioned challenges.

  • 4. Buchinger, Shelley
    et al.
    Lopez, Rui Jorge
    Jumisko-Pyykkö, Satu
    Zepernick, Hans-Jürgen
    Quality of experience for multimedia content sharing2010Conference paper (Refereed)
    Abstract [en]

    In recent years, it has been realized that the success of multimedia services or applications not only depends on Quality of Service (QoS) parameters but also relies on the analysis of the entire user experience (UX). The relevance of this paradigm ranges from IPTV or video-on-demand systems for distributing and sharing professional TV to user-generated content over the web. To obtain a pleasurable user experience far more aspects than QoS have to be taken into account. Major challenges in this context include the identification of relevant UX factors and the quantification of their influence on Quality of Experience (QoE). In particular, context awareness and assessment of users' expectations play an essential role. This is further justified by the emergence of new multimedia enhancement techniques, notably 3DTV and Free Viewpoint. Future Internet architectures under current research are also promising on the possibility to accommodate protocols and policies that take QoE issues into consideration. Consequently, acquired knowledge on the context and on identified parameters affecting users' experience could be used to improve media delivery.

  • 5. Buchinger, Shelley
    et al.
    Lopez, Rui Jorge
    Jumisko-Pyykkö, Satu
    Zepernick, Hans-Jürgen
    Quality of Experience for Multimedia Content Sharing: Ubiquitous QoE assessment and support2011Conference paper (Refereed)
    Abstract [en]

    In recent years, it has been realized that the success of multimedia services or applications relies on the analysis of the entire user experience (UX). The relevance of this paradigm ranges from IPTV to video-on-demand systems o ering professional TV and user-generated content that is consumed and produced ubiquitously. To obtain a pleasurable and ubiquitous user experience a large amount of aspects have to be taken into account. Major challenges in this context include the identi cation of relevant UX factors and the quanti cation of their inuence on Quality of Experience (QoE). In the particular scenario of ubiquitous production and consumption of content, context awareness and assessment of users' expectations play an essential role. This is further justi ed by the emergence of new multimedia enhancement techniques, notably 3DTV and Free Viewpoint. In the support of ubiquitous QoE the acquired knowledge on the context and on identi ed parameters a ecting users' experience could be used to improve mutimedia applications and their associated content delivery mechanisms.

  • 6.
    Chu, Thi My Chin
    et al.
    Blekinge Institute of Technology, School of Computing.
    Phan, Hoc
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    MIMO Incremental AF Relay Networks with TAS/MRC and Adaptive Modulation2013Conference paper (Other academic)
    Abstract [en]

    In this paper, we study the use of adaptive modulation (AM) for a dual-hop multiple-input multiple-output (MIMO) network with transmit antenna selection (TAS) at the transmitter and maximal ratio combining (MRC) at the receiver. Our system deploys incremental amplify-and-forward (AF) relaying with AM to forward the source signal. A switching policy for selecting between the relaying and the direct communication is utilized to maximize spectrum efficiency. In particular, we derive closed-form expressions for the outage probability, spectrum efficiency, and bit error rate (BER) for the considered system over Nakagami-m fading. The considered network not only takes advantage of TAS transmission such as achieving full diversity order with low transmit complexity but also inherits the beneficial feature of AM such as spectrum efficiency improvement. Reference

  • 7. Chu, Thi My Chinh
    et al.
    Duong, Quang Trung
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    MRT/MRC for Cognitive AF Relay Networks under Feedback Delay and Channel Estimation Error2012Conference paper (Refereed)
    Abstract [en]

    In this paper, we examine the performance of multiple-input multiple-output cognitive amplify-and-forward (AF) relay systems with maximum ratio transmission (MRT). In particular, closed-form expressions in terms of a tight upper bound for outage probability (OP) and symbol error rate (SER) of the system are derived when considering channel estimation error (CEE) and feedback delay (FD) in our analysis. Through our works, one can see the impact of FD and CEE on the system as well as the benefits of deploying multiple antennas at the transceivers utilizing the spatial diversity of an MRT system.

  • 8. Chu, Thi My Chinh
    et al.
    Duong, Quang Trung
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    Outage Probability and Ergodic Capacity for MIMO-MRT Systems under Co-Channel Interference and Imperfect CSI2011Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the performance of multiple-input multiple-output (MIMO) systems deploying maximum ratio transmission (MRT). Our analysis takes into account not only imperfect channel estimation at the receiver and feedback delay at the transmitter, but also includes co-channel interference (CCI). In particular, we first derive the statistical properties of the signal-to-interference-plus-noise ratio (SINR). Next, we obtain a closed-form expression for outage probability and an approximation for capacity. Finally, we show the consistency between analytical results and Monte-Carlo simulations. Our results indicate that the system performance is improved considerably in proportion to the number of transceiver antennas. Conversely, the outage probability increases, and the capacity decreases significantly with the severity of channel estimation error, feedback delay, and CCIs.

  • 9.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, School of Computing.
    Duong, Quang Trung
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    Performance analysis for multiple-input multiple output- maximum ratio transmission systems with channel estimation error, feedback delay and co-channel interference2013In: IET Communications, ISSN 1751-8628, Vol. 7, no 4, p. 279-285Article in journal (Refereed)
    Abstract [en]

    In this study, the authors analyse the impact of channel estimation error (CEE), feedback delay (FD), and co-channel interference (CCI) on the performance of multiple-input multiple-output (MIMO) systems deploying maximum ratio transmission (MRT). In particular, the authors derive closed-form expressions for the ergodic capacity and the symbol error rate (SER) as well as the outage probability (OP). In addition, to reveal the effect of CEE, FD and CCI on the MIMO-MRT system, the authors adopt more simplified and tractable formulas in terms of asymptotic expressions for the ergodic capacity, SER and OP. The analysis shows that the system performance is degraded considerably under imperfect transmission conditions such as CEE, FD and CCI. However, the authors can compensate part of this degradation by deploying MRT transmission with a large number of antennas at the transmitter and receiver. Finally, the selected examples exhibit consistency between analytical results and Monte Carlo simulations.

  • 10.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, School of Computing.
    Phan, Hoc
    Blekinge Institute of Technology, School of Computing.
    Duong, Quang Trung
    Blekinge Institute of Technology, School of Computing.
    Elkashlan, Maged
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    Beamforming Transmission in Cognitive AF Relay Networks with Feedback Delay2013Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the effect of feedback delay on outage probability (OP) and symbol error rate (SER) of cognitive amplify-and-forward (AF) relay networks with beamforming transmission in Rayleigh fading environment. It is assumed that the secondary transmitter and the secondary receiver are equipped with multiple antennas, whereas the relay and the primary user comprise of a single antenna. Furthermore, in this system, the secondary users use the underlay scheme in which the secondary transmitter and the relay can coexist with the primary user as long as their interference caused to the primary receiver is below a predefined threshold. Through our analysis, numerical results are provided to show the level of degradation of cognitive AF relay systems in proportion to the degree of feedback delay. In addition, we also present the effect of the number of antennas at the secondary transceiver on the performance of the considered system.

  • 11.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Adaptive Modulation and Coding with Queue Awareness in Cognitive Incremental Decode-and-Forward Relay Networks2014Conference paper (Refereed)
    Abstract [en]

    This paper studies the performance of adaptive modulation and coding in a cognitive incremental decode-and-forward relaying network where a secondary source can directly communicate with a secondary destination or via an intermediate relay. To maximize transmission efficiency, a policy which flexibly switches between the relaying and direct transmission is proposed. In particular, the transmission, which gives higher average transmission efficiency, will be selected for the communication. Specifically, the direct transmission will be chosen if its instantaneous signal-to-noise ratio (SNR) is higher than one half of that of the relaying transmission. In this case, the appropriate modulation and coding scheme (MCS) of the direct transmission is selected only based on its instantaneous SNR. In the relaying transmission, since the MCS of the transmissions from the source to the relay and from the relay to the destination are implemented independently to each other, buffering of packets at the relay is necessary. To avoid buffer overflow at the relay, the MCS for the relaying transmission is selected by considering both the queue state and the respective instantaneous SNR. Finally, a finite-state Markov chain is modeled to analyze key performance indicators such as outage probability and average transmission efficiency of the cognitive relay network.

  • 12.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, School of Computing.
    Phan, Hoc
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    Amplify-and-Forward Relay Assisting both Primary and Secondary Transmissions in Cognitive Radio Networks over Nakagami-m Fading2012Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the performance for the primary and secondary transmissions in cognitive radio networks where the amplify-and-forward (AF) secondary relay helps to transmit the signals for both the primary and secondary transmitters over independent Nakagami-m fading. First, we derive exact closed-form expressions for outage probability and symbol error rate (SER) of the primary network. Then, we derive an exact closed-form expression for outage probability and a closed-form expression of a tight upper bound for SER of the secondary network. Furthermore, we also make a comparison for the performance of the primary system with and without the help of the secondary relay.

  • 13.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Cognitive AF Relay Assisting both Primary and Secondary Transmission with Beamforming2014Conference paper (Refereed)
    Abstract [en]

    This paper investigates the system performance of a cognitive relay network with underlay spectrum sharing wherein the relay is exploited to assist both the primary and secondary transmitters in forwarding their signals to the respective destinations. To exploit spatial diversity, beamforming transmission is implemented at the transceivers of the primary and secondary networks. Particularly, exact expressions for the outage probability and symbol error rate (SER) of the primary transmission and tight bounded expressions for the outage probability and SER of the secondary transmission are derived. Furthermore, an asymptotic analysis for the primary network, which is utilized to investigate the diversity and coding gain of the network, is developed. Finally, numerical results are presented to show the benefits of the proposed system.

  • 14.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, School of Computing.
    Phan, Hoc
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    Cognitive MIMO AF Relay Network with TAS/MRC Under Peak Interference Power Constraint2013Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the use of transmit antenna selection (TAS) and maximal ratio combining (MRC) for a cognitive multiple-input multiple-output (MIMO) amplify-andforward (AF) relay network. We focus on the scenario that each of the source and relay selects only a single antenna which maximizes the instantaneous signal-to-noise ratio (SNR) to transmit and forward the signal while the receiver combines the signals from all receive antennas. Utilizing TAS, the considered cognitive network not only offers advantages such as achieving full diversity order with low transmit complexity but also reduces the interference induced to the primary transmission as compared to maximum ratio transmission (MRT). This in turn becomes beneficial for the secondary network when this network operates under the interference power constraint of the primary receiver. In particular, we derive expressions for the outage probability and symbol error rate (SER) of the network to evaluate the system performance. We also develop an asymptotic analysis for the outage probability and the SER to obtain diversity and coding gain. With the tractable asymptotic expressions, the effect of network parameters such as the number of antennas, the transmission distances, and the interference power constraint of the primary receiver on the system performance are readily revealed.

  • 15.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Delay Analysis for Cognitive Ad Hoc Networks Using Multi-channel Medium Access Control2014In: IET Communications, ISSN 1751-8628, E-ISSN 1751-8636, Vol. 8, no 7, p. 1083-1093Article in journal (Refereed)
    Abstract [en]

    In this study, the authors analyse the average end-to-end packet delay for a cognitive ad hoc network where multiple secondary nodes randomly contend for accessing the licensed bands of primary users in non-slotted time mode. Before accessing the licensed bands, each node must perform spectrum sensing and collaboratively exchange the sensing results with other nodes of the corresponding communication as a means of improving the accuracy of spectrum sensing. Furthermore, the medium access control with collision avoidance mechanism based distributed coordination function specified by IEEE802.11 is applied to coordinate spectrum access for this cognitive ad hoc network. To evaluate the system performance, the authors model the considered network as an open G/G/1 queuing network and utilise the method of diffusion approximation to analyse the end-to-end packet delay. The authors’ analysis takes into account not only the number of secondary nodes, the arrival rate of primary users and the arrival rate of secondary users but also the effect of the number of licensed bands when assessing the average end-to-end packet delay of the networks.

  • 16.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Dynamic Spectrum Access for Cognitive Radio Networks with Prioritized Traffics2014In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 18, no 7, p. 1218-1221Article in journal (Refereed)
    Abstract [en]

    We develop a dynamic spectrum access (DSA) strategy for cognitive radio networks where prioritized traffic is considered. Assume that there are three classes of traffic, one traffic class of the primary user and two traffic classes of the secondary users, namely, Class 1 and Class 2. The traffic of the primary user has the highest priority, i.e., the primary users can access the spectrum at any time with the largest bandwidth demand. Furthermore, Class 1 has higher access and handoff priority as well as larger bandwidth demand as compared to Class 2. To evaluate the performance of the proposed DSA, we model the state transitions for DSA as a multi-dimensional Markov chain with three-state variables which present the number of packets in the system of the primary users, the secondary Class 1, and secondary Class 2. In particular, the blocking probability and dropping probability of the two secondary traffic classes are assessed.

  • 17.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Hybrid Interweave-Underlay Spectrum Access for Cognitive Cooperative Radio Networks2014In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, no 7, p. 2183-2197Article in journal (Refereed)
    Abstract [en]

    In this paper, we study a hybrid interweave-underlay spectrum access system that integrates amplify-and-forward relaying. In hybrid spectrum access, the secondary users flexibly switch between interweave and underlay schemes based on the state of the primary users. A continuous-time Markov chain is proposed to model and analyze the spectrum access mechanism of this hybrid cognitive cooperative radio network (CCRN). Utilizing the proposed Markov model, steady-state probabilities of spectrum access for the hybrid CCRN are derived. Furthermore, we assess performance in terms of outage probability, symbol error rate (SER), and outage capacity of this CCRN for Nakagami-m fading with integer values of fading severity parameter m. Numerical results are provided showing the effect of network parameters on the secondary network performance such as the primary arrival rate, the distances from the secondary transmitters to the primary receiver, the interference power threshold of the primary receiver in underlay mode, and the average transmit signal-to-noise ratio of the secondary network in interweave mode. To show the performance improvement of the CCRN, comparisons for outage probability, SER, and capacity between the conventional underlay scheme and the hybrid scheme are presented. The numerical results show that the hybrid approach outperforms the conventional underlay spectrum access.

  • 18.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, School of Computing.
    Phan, Hoc
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    MIMO Incremental AF Relay Networks with TAS/MRC and Adaptive Modulation2013Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the use of adaptive modulation (AM) for a dual-hop multiple-input multiple-output (MIMO) network with transmit antenna selection (TAS) at the transmitter and maximal ratio combining (MRC) at the receiver. Our system deploys incremental amplify-and-forward (AF) relaying with AM to forward the source signal. A switching policy for selecting between the relaying and the direct communications is utilized to maximize spectrum efficiency. In particular, we derive expressions for the outage probability, spectrum efficiency, and bit error rate (BER) for the considered system over Nakagamim fading. The considered network not only takes advantage of TAS transmission such as achieving full diversity order with low transmit complexity but also inherits the beneficial feature of AM such as spectrum efficiency improvement.

  • 19.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, School of Computing.
    Phan, Hoc
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    On the Performance of Underlay Cognitive Radio Networks Using M/G/1/K Queuing Model2013In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, no 5, p. 876-879Article in journal (Refereed)
    Abstract [en]

    Motivated by a realistic scenario for cognitive radio systems, we model the underlay cognitive radio network (CRN) under interference power constraint imposed by the primary network as an M/G/1/K queueing system. The respective embedded Markov chain is provided to analyze several key queueing performance measures. In particular, the equilibrium probabilities of all states are derived and utilized to evaluate throughput, blocking probability, mean packet transmission time, mean number of packets in the system, and mean waiting time of an underlay CRN with Nakagami-m fading channels.

  • 20.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, School of Computing.
    Phan, Hoc
    Blekinge Institute of Technology, School of Computing.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, School of Computing.
    Opportunistic Spectrum Access for Cognitive Amplify-and-Forward Relay Networks2013Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the performance of cognitive amplify-and-forward (AF) relay networks where the secondary users opportunistically access M licensed bands of the primary users over Nakagami-m fading channels. In order to enhance the accuracy of spectrum sensing and strongly protect the primary users from being interfered by the secondary transmission, collaborative spectrum sensing is deployed among the secondary transmitter, secondary relay, and secondary receiver. In particular, an analytical expression for the capacity of the considered network is derived. Numerical results are provided to show the influence of the arrival rate of the primary users on the channel utilization of licensed bands. Finally, the impact of the number of the licensed bands, channel utilization of the primary users, false alarm probability, and transmission distances on the capacity of the considered system are investigated.

  • 21.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Performance analysis of MIMO cognitive amplify-and-forward relay networks with orthogonal space–time block codes2015In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 15, p. 1659-1679Article in journal (Refereed)
    Abstract [en]

    In this paper, we study the performance of multiple-input multiple-output cognitive amplify-and-forward relay networks using orthogonal space–time block coding over independent Nakagami-m fading. It is assumed that both the direct transmission and the relaying transmission from the secondary transmitter to the secondary receiver are applicable. In order to process the received signals from these links, selection combining is adopted at the secondary receiver. To evaluate the system performance, an expression for the outage probability valid for an arbitrary number of transceiver antennas is presented. We also derive a tight approximation for the symbol error rate to quantify the error probability. In addition, the asymptotic performance in the high signal-to-noise ratio regime is investigated to render insights into the diversity behavior of the considered networks. To reveal the effect of network parameters on the system performance in terms of outage probability and symbol error rate, selected numerical results are presented. In particular, these results show that the performance of the system is enhanced when increasing the number of antennas at the transceivers of the secondary network. However, increasing the number of antennas at the primary receiver leads to a degradation in the secondary system performance.

  • 22.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies. Blekinge Inst Technol, SE-37179 Karlskrona, Sweden..
    Capacity Analysis of Two-Tier Networks with MIMO Cognitive Small Cells in Nagakami-m Fading2017In: 2017 IEEE 13TH INTERNATIONAL CONFERENCE ON WIRELESS AND MOBILE COMPUTING, NETWORKING AND COMMUNICATIONS (WIMOB), IEEE , 2017, p. 457-463Conference paper (Refereed)
    Abstract [en]

    In this paper, we consider a two-tier cellular network consisting of a primary macro cell base station (PMBS) which is overlaid by cognitive small cell base stations (CSBSs) to achieve efficient spectrum utilization. The deployment of two-tier cellular networks can provide higher capacity for the system but also causes cross-tier, intra-tier, and inter-tier interference within the cellular networks. Thus, we employ transmit and receive beamforming in the considered two-tier cellular network to mitigate interference. We first design the receive beamforming vector for a primary user (PU) such that it cancels all inter-tier interference from other PUs. Then, the transmit beamforming vectors at the secondary users (SUs) are designed to null out the cross-tier interference to the PUs. Further, the receive beamforming vectors at the SUs are designed to mitigate the crosstier interference from the PUs to the SUs. Finally, the transmit beamforming vector at the PMBS is designed to maximize the signal-to-interference-plus-noise ratio at the PUs. To quantify the performance of the system, we derive an expression for the channel capacity in the downlink from the CSBSs to the SUs. Numerical results are provided to reveal the effect of network parameters such as intra-tier interference distances, fading conditions, and number of antennas on the channel capacity of the SUs.

  • 23.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Non-orthogonal multiple access for DF cognitive cooperative radio networks2018In: 2018 IEEE International Conference on Communications Workshops, ICC Workshops 2018 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2018, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper, we study a power domain non-orthogonal multiple access (NOMA) scheme for cognitive cooperative radio networks (CCRNs). In the proposed scheme, a secondary transmitter communicates with two secondary users (SUs) by allocating transmit powers inversely proportional to the channel power gains on the links to the respective SUs. A decode-and-forward (DF) secondary relay is deployed which decodes the superimposed signals associated with the two SUs. Then, power domain NOMA is used to forward the signals from the relay to the two SUs based on the channel power gains on the corresponding two links. Mathematical expressions for the outage probability and ergodic capacity of each SU and the overall power domain NOMA CCRN are derived. Numerical results are provided to reveal the impact of the power allocation coefficients at the secondary transmitter and secondary relay, the interference power threshold at the primary receiver, and the normalized distances of the SUs on the outage probability and ergodic capacity of each SU and the whole NOMA system. © 2018 IEEE.

  • 24.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    On Secrecy Capacity of Full-Duplex Cognitive Cooperative Radio Networks2017In: 2017 IEEE GLOBECOM WORKSHOPS (GC WKSHPS), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze the secrecy capacity of a full-duplex underlay cognitive cooperative radio network (CCRN) in the presence of an eavesdropper and under the interference power constraint of a primary network. The full-duplex mode is used at the secondary relay to improve the spectrum efficiency which in turn leads to an improvement of the secrecy capacity of the full-duplex CCRN. We utilize an approximation-and-fitting method to convert the complicated expression of the signal-to-interference-plus-noise ratio into polynomial form which is then utilized to derive an expression for the secrecy capacity. Numerical results are provided to illustrate the effect of network parameters such as transmit power, interference power limit, self-interference parameters of the full-duplex mode, and distances among links on the secrecy capacity. To reveal the benefits of the full-duplex CCRN, we compare the secrecy capacity obtained when the secondary relay operates in full-duplex and half-duplex mode.

  • 25.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Optimal Power Allocation for Hybrid Cognitive Cooperative Radio Networks with Imperfect Spectrum Sensing2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 10365-10380Article in journal (Refereed)
    Abstract [en]

    In this paper, two optimal power allocation strategies for hybrid interweave-underlay cognitive cooperative radio networks (CCRNs) are proposed to maximize channel capacity and minimize outage probability. The proposed power allocation strategies are derived for the case of Rayleigh fading taking into account the impact of imperfect spectrum sensing on the performance of the hybrid CCRN. Based on the optimal power allocation strategies, the transmit powers of the secondary transmitter and secondary relay are adapted according to the fading conditions, the interference power constraint imposed by the primary network (PN), the interference from the PN to the hybrid CCRN, and the total transmit power limit of the hybrid CCRN. Numerical results are provided to illustrate the effect of the interference power constraint of the PN, arrival rate of the PN, imperfect spectrum sensing, and the transmit power constraint of the hybrid CCRN on channel capacity and outage probability. Finally, comparisons of the channel capacity and outage probability of underlay, overlay, and hybrid interweaveunderlay CCRNs are presented to show the advantages of the hybrid spectrum access. OAPA

  • 26.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies. Blekinge Inst Technol, SE-37179 Karlskrona, Sweden..
    Outage Probability and Secrecy Capacity of a Non-orthogonal Multiple Access System2017In: 11th International Conference on Signal Processing and Communication Systems, ICSPCS, 2017 / [ed] Wysocki, TA Wysocki, BJ, IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze the outage probability and secrecy capacity of a non-orthogonal multiple access (NOMA) system in the presence of an eavesdropper. In order to enhance spectral efficiency, a base station communicates with two users simultaneously in the same frequency band by superpimposing the transmit signals to the users in the power domain. Specifically, the user with the worse channel conditions is allocated higher power such that it is able to directly decode its signal from the received superimposed signal. At the user with the better channel conditions, the interference due to NOMA is processed by successive interference cancelation. Given these system settings and accounting for decoding thresholds, we analyze the outage probability of the NOMA system over Rayleigh fading channels. Furthermore, based on the locations of the users and eavesdropper, the secrecy capacity is analyzed to assess the level of security provided to the legitimate users in the presence of an eavesdropper. Here, the decoding thresholds of legitimate users and eavesdropper are also included in the analysis of the secrecy capacity. Through numerical results, the effects of network parameters on system performance are assessed as well as the the superiority of NOMA in terms of secrecy capacity over traditional orthogonal multiple access.

  • 27.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies. Blekinge Inst Technol, SE-37179 Karlskrona, Sweden..
    Outage Probability of a Hybrid AF-DF Protocol for Two-Way Underlay Cognitive Cooperative Radio Networks2017In: 11th International Conference on Signal Processing and Communication Systems, ICSPCS 2017 / [ed] Wysocki, TA Wysocki, BJ, IEEE , 2017, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper, we study a hybrid amplify-and-forward (AF) and decode-and-forward (DF) scheme for two-way cognitive cooperative radio networks (CCRNs). The proposed scheme applies the AF scheme when the signal-to-interferenceplus-noise ratio (SINR) at the relay is below a predefined threshold such that the relay cannot successfully decode the signal. On the other hand, when the SINR at the relay is greater than the predefined threshold, it decodes the signal and then forwards it to the destination, i.e. avoids noise and interference amplification at the relay. An analytical expression of the outage probability of the hybrid AF-DF two-way CCRN is derived based on the probability density function and cumulative distribution function of the SINR in AF and DF mode. Numerical results are provided to illustrate the influence of network parameters such as transmit power, interference power constraint of the primary network, fading conditions, and link distances on the outage probability. Finally, the numerical results show that the hybrid strategy is able to improve system performance significantly compared to conventional AF or DF relaying.

  • 28.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Performance of a Non-orthogonal Multiple Access System with Full-Duplex Relaying2018In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558Article in journal (Refereed)
    Abstract [en]

    In this paper, we study a power-domain nonorthogonal multiple access (NOMA) system in which a base station (BS) superimposes the transmit signals to the users. To enhance spectral efficiency and link reliability for the far-distance user, a full-duplex (FD) relay assists the BS while the neardistance user is reached over the direct link. For this setting, we analyze outage probability and sum rate of the NOMA system over Nakagami-m fading with integer fading severity parameter m. Numerical results are provided for outage probability and sum rate to show the effect of system parameters on the performance of the FD NOMA system over Nakagami-m fading. IEEE

  • 29.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Creative Technologies.
    Phan, H.
    Duy Tan University, VNM.
    MAC Protocol for Opportunistic Spectrum Access in Multi-Channel Cognitive Relay Networks2017In: IEEE Vehicular Technology Conference, Institute of Electrical and Electronics Engineers Inc. , 2017Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a medium access control (MAC) protocol for multi-channel cognitive cooperative radio networks (CCRNs). In this protocol, each secondary user (SU) senses for spectrum opportunities within M licensed bands of the primary users (PUs). To enhance the accuracy of spectrum sensing, we employ cooperative sequential spectrum sensing where SUs mutually exchange their sensing results. Moreover, the information obtained from cooperative spectrum sensing at the physical layer is integrated into the channel negotiation process at the MAC layer to alleviate the hidden terminal problem. Finally, the performance of the proposed MAC protocol in terms of aggregate throughput of the CCRNs is analyzed. Numerical results are provided to assess the impact of channel utilization by PUs, number of contenting CCRNs, number of licensed bands, and false alarm probability of SUs on the aggregate throughput. © 2017 IEEE.

  • 30.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Juergen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Channel Reservation for Dynamic Spectrum Access of Cognitive Radio Networks with Prioritized Traffic2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOP, IEEE Communications Society, 2015, p. 883-888Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a strategy to coordinate the dynamic spectrum access (DSA) of different types of traffic. It is assumed that the DSA assigns spectrum bands to three kinds of prioritized traffic, the traffic of the primary network, the Class 1 traffic and Class 2 traffic of the secondary network. Possessing the licensed spectrum, the primary traffic has the highest access priority and can access the spectrum bands at anytime. The secondary Class 1 traffic has higher priority compared to secondary Class 2 traffic. In this system, a channel reservation scheme is deployed to control spectrum access of the traffic. Specifically, the optimal number of reservation channels is applied to minimize the forced termination probability of the secondary traffic while satisfying a predefined blocking probability of the primary network. To investigate the system performance, we model state transitions of the DSA as a multi-dimensional Markov chain with three-state variables representing the number of primary, Class 1, and Class 2 packets in the system. Based on this chain, important performance measures, i.e., blocking probability and forced termination probability are derived for the Class 1 and Class 2 secondary traffic.

  • 31.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Univ Reading, GBR.
    Hybrid spectrum access with relay assisting both primary and secondary networks under imperfect spectrum sensing2016In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, article id 244Article in journal (Refereed)
    Abstract [en]

    This paper proposes a novel hybrid interweave-underlay spectrum access for a cognitive amplify-and-forward relay network where the relay forwards the signals of both the primary and secondary networks. In particular, the secondary network (SN) opportunistically operates in interweave spectrum access mode when the primary network (PN) is sensed to be inactive and switches to underlay spectrum access mode if the SN detects that the PN is active. A continuous-time Markov chain approach is utilized to model the state transitions of the system. This enables us to obtain the probability of each state in the Markov chain. Based on these probabilities and taking into account the impact of imperfect spectrum sensing of the SN, the probability of each operation mode of the hybrid scheme is obtained. To assess the performance of the PN and SN, we derive analytical expressions for the outage probability, outage capacity, and symbol error rate over Nakagami-m fading channels. Furthermore, we present comparisons between the performance of underlay cognitive cooperative radio networks (CCRNs) and the performance of the considered hybrid interweave-underlay CCRN in order to reveal the advantages of the proposed hybrid spectrum access scheme. Eventually, with the assistance of the secondary relay, performance improvements for the PN are illustrated by means of selected numerical results.

  • 32.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Duy Tan Univ, VNM.
    Optimal Secrecy Capacity of Underlay Cognitive Radio Networks with Multiple Relays2016In: MILCOM 2016 - 2016 IEEE MILITARY COMMUNICATIONS CONFERENCE, 2016, p. 162-167Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the secrecy capacity of an underlay cooperative cognitive radio network (CCRN) where multiple relays are deployed to assist the secondary transmission. An optimal power allocation algorithm is proposed for the secondary transmitter and secondary relays to obtain the maximum secrecy capacity while satisfy the interference power constraint at the primary receiver and the transmit power budget of the CCRN. Since the optimization problem for the secrecy capacity is non-convex, we utilize an approximation and fitting method to convert the optimization problem into a geometric programming problem which then is solved by applying the Logarithmic barrier function. Numerical results are provided to study the effect of network parameters on the secrecy capacity. Through the numerical results, the advantage of the proposed power allocation algorithm compared to equal power allocation can also be observed.

  • 33.
    Chu, Thi My Chinh
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Zepernick, Hans-Jürgen
    Blekinge Institute of Technology, Faculty of Computing, Department of Communication Systems.
    Phan, Hoc
    Performance Evaluation of Cognitive Multi-Relay Networks with Multi-Receiver Scheduling2014Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the performance of cognitive multiple decode-and-forward relay networks under the interference power constraint of the primary receiver wherein the cognitive downlink channel is shared among multiple secondary relays and secondary receivers. In particular, only one relay and one secondary receiver which offers the highest instantaneous signal-to-noise ratio is scheduled to transmit signals. Accordingly, only one transmission route that offers the best end-to-end quality is selected for communication at a particular time instant. To quantify the system performance, we derive expressions for outage probability and symbol error rate over Nakagami-m fading with integer values of fading severity parameter m. Finally, numerical examples are provided to illustrate the effect of system parameters such as fading conditions, the number of secondary relays and secondary receivers on the secondary system performance.

  • 34. Cresp, Gregory
    et al.
    Dam, Hai Huyen
    Zepernick, Hans-Jürgen
    Design of Modified UCHT Sequences2006Conference paper (Refereed)
    Abstract [en]

    In this paper, we consider the design of a class of unified complex Hadamard transform (UCHT) sequences. An effi- cient modification is imposed to those sequences to better suit applications in asynchronous code-division multiple- access (CDMA) systems. These modified UCHT sequences preserve the orthogonality of the original UCHT sequences and offer increased design options due to an increased number of parameters. The design of UCHT, modified UCHT, and Oppermann sequences is then formulated with reference to optimizing the maximum nontrivial aperiodic correlation value. These optimization problems can then be solved efficiently using a genetic algorithm with the maximum nontrivial aperiodic correlation value serving in the definition of a fitness function. Numerical examples illustrate the benefits of modified UCHT sequences over the original UCHT sequences.

  • 35. Cresp, Gregory
    et al.
    Dam, Hai Huyen
    Zepernick, Hans-Jürgen
    Design of Sequence Family Subsets Using a Branch and Bound Technique2009In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 55, no 8, p. 3847-3857Article in journal (Refereed)
    Abstract [en]

    The number of spreading sequences required for Direct Sequence Code Division Multiple Access (DS-CDMA) systems depends on the number of simultaneous users in the system. Often a sequence family provides more sequences than are required; in many cases the selection of the employed sequences is a computationally intensive task. This selection is a key consideration, as the properties of the sequences assigned affect the error performance in the system. In this paper, a branch and bound algorithm is presented to perform this selection based on two different cost functions. Numerical results are presented to demonstrate the improved performance of this algorithm over previous work.

  • 36. Cresp, Gregory
    et al.
    Dam, Hai Huyen
    Zepernick, Hans-Jürgen
    Subset Family Design Using a Branch and Bound Technique2006Conference paper (Refereed)
    Abstract [en]

    The number of spreading sequences required for Direct Sequence Code Division Multiple Access (DS-CDMA) systems depends on the number of simultaneous users on the channel. The correlation properties of the sequences used affect the bit error rate of the system. Often a sequence family provides more sequences than are required and in many cases the selection of the employed sequences is a computationally intensive task. In this paper, a branch and bound algorithm is presented to optimise the subset of available sequences given the required subset size. In contrast to previous approaches, the resulting subset is guaranteed to be optimal. Numerical results are presented to demonstrate the improved performance of this algorithm over previous work.

  • 37. Cresp, Gregory
    et al.
    Zepernick, Hans-Jürgen
    Dam, Hai Huyen
    Bit Error Rates of Large Area Synchronous Systems2008Conference paper (Refereed)
    Abstract [en]

    Large Area Synchronous (LAS) sequences are a class of ternary interference free window spreading sequences. One of their advantages is the ability to construct permutation LAS families in order to reduce adjacent cell interference (ACI) in cellular systems. There has been little previous numerical work to examine the effect of using permutation families compared to simply reusing the same LAS family across different cells. The bit error rates resulting from two cell systems employing both permutation families and sequence reuse are considered here by simulation.

  • 38. Cresp, Gregory
    et al.
    Zepernick, Hans-Jürgen
    Dam, Hai Huyen
    Combination Oppermann Sequences for Spread Spectrum Systems2005Conference paper (Refereed)
    Abstract [en]

    Numerous spread spectrum applications require families of long spreading sequences, often used at very high chip rates. In this paper, an algebraically simple way of generating long sequences by combining shorter polyphase sequences is presented, aimed at asynchronous spread spectrum systems. The approach is motivated by the fact that polyphase sequences offer increased design options, in terms of the supported range of correlation characteristics, while combination sequences allow for simpler generation of long sequences. It leads to the definition of combination Oppermann sequences, the properties of which are investigated in this paper. Numerical results indicate that the families of these proposed combination sequences provide favourable aperiodic correlations. The presented family of combination Oppermann sequences is therefore suitable for applications that rely on rapid synchronisation and are required to provide multiple access to the system.

  • 39. Cresp, Gregory
    et al.
    Zepernick, Hans-Jürgen
    Dam, Hai Huyen
    On the Classification of Large Area Sequences2007Conference paper (Refereed)
    Abstract [en]

    Large Area (LA) sequences form a class of ternary spreading sequences which exhibit an interference free window. In addition, these sequences have low correlation properties outside this window. Work to date has concentrated on examining the parameters and performance of LA sequences with reference to only a small number of example families. In this paper we develop general conditions which an LA family must satisfy. The development of these conditions allows for the production of computationally efficient tests to determine whether a given family is an LA family. In particular, these tests can form the basis for algorithms to construct LA families, allowing for a larger number of families with the potential for higher energy efficiency than those of previous work.

  • 40. Cresp, Gregory
    et al.
    Zepernick, Hans-Jürgen
    Dam, Hai Huyen
    Periodic Oppermann Sequences for Spread Spectrum Systems2005Conference paper (Refereed)
    Abstract [en]

    In this paper we introduce periodic Oppermann sequences, which constitute a special class of polyphase sequences. The properties of these sequences are presented, and indicate that periodic Oppermann sequences are suitable for combination to generate families of longer sequences. Numerical examples show that periodic Oppermann sequences can be designed for ranging or synchronisation applications or for supporting multiple access spread spectrum communication systems.

  • 41. Dahlberg, Anders
    et al.
    Zepernick, Hans-Jürgen
    Mercankosk, Guven
    Fiedler, Markus
    Multi AP concepts for SCO traffic in a Bluetooth based Radio Infrastructure Network2002Conference paper (Refereed)
    Abstract [en]

    In this paper, we consider a radio infrastructure network (RIN), which consists of Bluetooth Access Points (APs) to provide services to ad hoc users. The RIN inherently supports both voice and data connectivity. Since Bluetooth offers the establishment of Synchronous Circuit-Oriented (SCO) traffic, the concept under study features a low-cost alternative to indoor cellular base stations. However, a single AP can serve a maximum of only three SCO channels and may not be capable of satisfying the voice traffic demands in hot spots. In order to offer more bandwidth in a location with high voice traffic, two or more APs may be placed in the same coverage area. Respective AP clusters will be denoted as Multi APs. Three Multi AP concepts for doing the SCO allocation are presented and discussed. Our findings show that employing Multi APs significantly reduces the blocking probability.

  • 42. Dahlberg, Anders
    et al.
    Zepernick, Hans-Jürgen
    Mercankosk, Guven
    Fiedler, Markus
    Multi AP Strategies for SCO Traffic in a Bluetooth based Wireless LAN2003Conference paper (Refereed)
    Abstract [en]

    We consider a Wireless Local Area Network (WLAN) consisting of Bluetooth Access Points (APs). Thus, it inherently offers both ad-hoc voice and data connectivity. As Bluetooth supports Synchronous Circuit-Oriented (SCO) traffic, the concept under study features a low-cost alternative to indoor cellular base stations. Due to the limitation of only three available SCO channels per AP, several APs can be placed in the same coverage area to satisfy voice traffic demands in hot spots. Such AP clusters will be denoted as Multi AP. Three Multi AP strategies for handling the SCO allocation are presented and discussed in terms of signaling and mean time to connect. Our findings show that employing Multi APs significantly reduces the blocking probability. A simple dimensioning rule for the number of APs is given.

  • 43. Dam, Hai Huyen
    et al.
    Nordberg, Jörgen
    Nordholm, Sven
    Zepernick, Hans-Jürgen
    Stacking Methods for Non-Causal Delayless Subband Addaptive Equalizer2002Conference paper (Refereed)
  • 44. Dam, Hai Huyen
    et al.
    Nordholm, Sven
    Zepernick, Hans-Jürgen
    Frequency Domain Blind Equalization for MIMO Systems2005Conference paper (Refereed)
    Abstract [en]

    This paper presents a new normalized frequency domain approach for adaptive blind equalization for multiple-input multiple-output (MIMO) communication systems. We first develop a time domain block based algorithm that updates the equalizer coefficients once per block of data symbols. As the time domain algorithm involves infinite summations in the separation cost function, an approximation is then proposed to reduce the cost function to finite summations. As a consequence, the block based time domain algorithm can be implemented in the frequency domain to reduce the computational complexity associated with the conventional symbol-by-symbol time domain update. Furthermore, by recognizing that the signals in the frequency domain are orthogonal, it is possible to significantly improve the convergence rate by normalizing the update equations with respect to the signal power in each frequency bin. Simulation results show that the proposed algorithm can successfully equalize the received signals while maintaining low computational complexity. Moreover, the presented normalized frequency domain blind equalization algorithm for MIMO systems significantly improves the convergence rate.

  • 45. Dam, Hai Huyen
    et al.
    Zepernick, Hans-Jürgen
    Nordberg, Jörgen
    Nordholm, Sven
    Application of a Global Optimization Method to the Design of Complex Spreading Sequences2002Conference paper (Refereed)
  • 46. Dam, Hai Huyen
    et al.
    Zepernick, Hans-Jürgen
    Nordberg, Jörgen
    Nordholm, Sven
    Complex Spreading Sequence Design2002Conference paper (Refereed)
    Abstract [en]

    The performance of code division multiple access system depends on the correlation of the employed spreading code. Low cross-correlation values between spreading sequences are desired to suppress multiple access interference. An auto-correlation function with with a distinct peak enables proper synchronization and suppresses intersymbol interference. However, these requirements contradict each other and a trade-off needs to be established. In this paper, a global two dimensional optimization method is proposed to minimize auto-correlation with cross-correlation being allowed to lie within a fixed region. This approach is applied to design a set of complex valued spreading sequences.

  • 47. Dam, Hai Huyen
    et al.
    Zepernick, Hans-Jürgen
    Nordberg, Jörgen
    Nordholm, Sven
    Design of Complex Spreading Sequences2002Conference paper (Refereed)
  • 48. Dam, Hai Huyen
    et al.
    Zepernick, Hans-Jürgen
    Nordholm, Sven
    Nordberg, Jörgen
    Spreading Code Design Using a Global Optimization Method2005In: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 133, no 1-4, p. 249-264Article in journal (Refereed)
    Abstract [en]

    The performance of a code division multiple access system depends on the correlation properties of the employed spreading code. Low cross-correlation values between spreading sequences are desired to suppress multiple access interference and to improve bit error performance. An auto-correlation function with a distinct peak enables proper synchronization and suppresses intersymbol interference. However, these requirements contradict each other and a trade-off needs to be established. In this paper, a global two dimensional optimization method is proposed to minimize the out-of-phase average mean-square aperiodic auto-correlation with average mean-square aperiodic cross-correlation being allowed to lie within a fixed region. This approach is applied to design sets of complex spreading sequences. A design example is presented to illustrate the relation between various correlation characteristics. The correlations of the obtained sets are compared with correlations of other known sequences.

  • 49. Duong, Quang Trung
    et al.
    Alay, Ozgu
    Erkip, Elza
    Zepernick, Hans-Jürgen
    End-to-End Performance of Randomized Distributed Space-Time Codes2010Conference paper (Refereed)
    Abstract [en]

    The exact closed-form expressions for symbol error probability and outage probability of randomized distributed space-time codes (RDSTC) under Rayleigh fading are derived. The diversity gain derived in the literature uses the Chernoff bound which may not be achievable in general. Utilizing the exact expression, the achievable diversity gain of RDSTCs is validated. The closed-form expressions are verified by Monte-Carlo simulations.

  • 50. Duong, Quang Trung
    et al.
    Alexandropoulos, George C.
    Tsiftsis, Theodoros A.
    Zepernick, Hans-Jürgen
    Outage probability of MIMO AF relay networks over Nakagami-m fading channels2010In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 46, no 17Article in journal (Refereed)
    Abstract [en]

    The outage probability (OP) of multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay networks using orthogonal space-time block code is investigated. In particular, a closed-form tight lower bound expression for the OP over independently but not necessarily identically distributed Nakagami-m fading channels is derived. Moreover, an asymptotic approximation for OP which reveals the coding and diversity gains is presented. The analytical expressions are validated by Monte-Carlo simulations.

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