| 1. |
- Bayley, Todd, et al.
(författare)
-
Call Quality Monitoring for VoIP
- 2011
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 2. |
- Buchinger, Shelley, et al.
(författare)
-
Advances in tools, techniques and practices for multimedia QoE
- 2015
-
Ingår i: Multimedia tools and applications. - : Springer. - 1380-7501 .- 1573-7721.
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Buchinger, Shelley, et al.
(författare)
-
Quality of experience for multimedia content sharing
- 2010
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 4. |
- Buchinger, Shelley, et al.
(författare)
-
Quality of Experience for Multimedia Content Sharing : Ubiquitous QoE assessment and support
- 2011
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Chu, Thi My Chinh, et al.
(författare)
-
Adaptive Modulation and Coding with Queue Awareness in Cognitive Incremental Decode-and-Forward Relay Networks
- 2014
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 6. |
- Chu, Thi My Chinh, et al.
(författare)
-
Amplify-and-Forward Relay Assisting both Primary and Secondary Transmissions in Cognitive Radio Networks over Nakagami-m Fading
- 2012
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 7. |
- Chu, Thi My Chinh, et al.
(författare)
-
Beamforming Transmission in Cognitive AF Relay Networks with Feedback Delay
- 2013
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Chu, Thi My Chinh, et al.
(författare)
-
Cognitive AF Relay Assisting both Primary and Secondary Transmission with Beamforming
- 2014
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 9. |
- Chu, Thi My Chinh, et al.
(författare)
-
Cognitive MIMO AF Relay Network with TAS/MRC Under Peak Interference Power Constraint
- 2013
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 10. |
- Chu, Thi My Chinh, et al.
(författare)
-
Delay Analysis for Cognitive Ad Hoc Networks Using Multi-channel Medium Access Control
- 2014
-
Ingår i: IET Communications. - : IET. - 1751-8628 .- 1751-8636. ; 8:7, s. 1083-1093
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Chu, Thi My Chinh, et al.
(författare)
-
Dynamic Spectrum Access for Cognitive Radio Networks with Prioritized Traffics
- 2014
-
Ingår i: IEEE Communications Letters. - : IEEE. - 1089-7798 .- 1558-2558. ; 18:7, s. 1218-1221
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
- Chu, Thi My Chinh, et al.
(författare)
-
Hybrid Interweave-Underlay Spectrum Access for Cognitive Cooperative Radio Networks
- 2014
-
Ingår i: IEEE Transactions on Communications. - : IEEE. - 0090-6778 .- 1558-0857. ; 62:7, s. 2183-2197
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 13. |
- Chu, Thi My Chinh, et al.
(författare)
-
Hybrid spectrum access with relay assisting both primary and secondary networks under imperfect spectrum sensing
- 2016
-
Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer. - 1687-1472 .- 1687-1499.
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
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| 14. |
- Chu, Thi My Chinh, et al.
(författare)
-
MIMO Incremental AF Relay Networks with TAS/MRC and Adaptive Modulation
- 2013
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 15. |
- Chu, Thi My Chinh, et al.
(författare)
-
MRT/MRC for Cognitive AF Relay Networks under Feedback Delay and Channel Estimation Error
- 2012
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 16. |
- Chu, Thi My Chin, et al.
(författare)
-
On Capacity of Full-Duplex Cognitive Cooperative Radio Networks with Optimal Power Allocation
- 2017
-
Ingår i: 2017 IEEE WIRELESS COMMUNICATIONS AND NETWORKING CONFERENCE (WCNC). - : IEEE. - 9781509041831
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we examine a full-duplex transmission scheme for cognitive cooperative radio networks (CCRNs) to improve capacity. In this network, the secondary transmitter and secondary relay are allowed to utilize the licensed spectrum of the primary user by using underlay spectrum access. We assume that the CCRN is subject to the interference power constraint of the primary receiver and maximum transmit power limit of the secondary transmitter and secondary relay. Under these constraints, we propose an optimal power allocation policy for the secondary transmitter and the secondary relay based on average channel state information (CSI) to optimize capacity. Then, we derive an expression for the corresponding achievable capacity of the secondary network over Nakagami-m fading. Numerical results are provided for several scenarios to study the achievable capacity that can be offered by this full-duplex underlay CCRN using the proposed optimal power allocation scheme.
|
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| 17. |
- Chu, Thi My Chinh, et al.
(författare)
-
On the Performance of Underlay Cognitive Radio Networks Using M/G/1/K Queuing Model
- 2013
-
Ingår i: IEEE Communications Letters. - : IEEE. - 1089-7798 .- 1558-2558. ; 17:5, s. 876-879
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
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| 18. |
- Chu, Thi My Chinh, et al.
(författare)
-
Opportunistic Spectrum Access for Cognitive Amplify-and-Forward Relay Networks
- 2013
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 19. |
- Chu, Thi My Chinh, et al.
(författare)
-
Optimal Secrecy Capacity of Underlay Cognitive Radio Networks with Multiple Relays
- 2016
-
Ingår i: MILCOM 2016 - 2016 IEEE MILITARY COMMUNICATIONS CONFERENCE. - 9781509037810 ; , s. 162-167
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 20. |
- Chu, Thi My Chinh, et al.
(författare)
-
Outage Probability and Ergodic Capacity for MIMO-MRT Systems under Co-Channel Interference and Imperfect CSI
- 2011
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 21. |
- Chu, Thi My Chinh, et al.
(författare)
-
Performance analysis for multiple-input multiple output- maximum ratio transmission systems with channel estimation error, feedback delay and co-channel interference
- 2013
-
Ingår i: IET Communications. - : IET. - 1751-8628 .- 1751-8636. ; 7:4, s. 279-285
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Chu, Thi My Chinh, et al.
(författare)
-
Performance analysis of MIMO cognitive amplify-and-forward relay networks with orthogonal space–time block codes
- 2015
-
Ingår i: Wireless Communications & Mobile Computing. - : John Wiley & Sons. - 1530-8669 .- 1530-8677. ; 15, s. 1659-1679
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Chu, Thi My Chinh, et al.
(författare)
-
Performance Evaluation of Cognitive Multi-Relay Networks with Multi-Receiver Scheduling
- 2014
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 24. |
- Cresp, Gregory, et al.
(författare)
-
Bit Error Rates of Large Area Synchronous Systems
- 2008
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 25. |
- Cresp, Gregory, et al.
(författare)
-
Combination Oppermann Sequences for Spread Spectrum Systems
- 2005
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 26. |
- Cresp, Gregory, et al.
(författare)
-
Design of Modified UCHT Sequences
- 2006
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 27. |
- Cresp, Gregory, et al.
(författare)
-
Design of Sequence Family Subsets Using a Branch and Bound Technique
- 2009
-
Ingår i: IEEE Transactions on Information Theory. - : IEEE. - 0018-9448 .- 1557-9654. ; 55:8, s. 3847-3857
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
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| 28. |
- Cresp, Gregory, et al.
(författare)
-
On the Classification of Large Area Sequences
- 2007
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 29. |
- Cresp, Gregory, et al.
(författare)
-
Periodic Oppermann Sequences for Spread Spectrum Systems
- 2005
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 30. |
- Cresp, Gregory, et al.
(författare)
-
Subset Family Design Using a Branch and Bound Technique
- 2006
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
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| 31. |
- Dahlberg, Anders, et al.
(författare)
-
Multi AP concepts for SCO traffic in a Bluetooth based Radio Infrastructure Network
- 2002
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 32. |
- Dahlberg, Anders, et al.
(författare)
-
Multi AP Strategies for SCO Traffic in a Bluetooth based Wireless LAN
- 2003
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 33. |
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| 34. |
- Dam, Hai Huyen, et al.
(författare)
-
Blind MIMO Equalization in the Frequency Domain
- 2005
-
Konferensbidrag (refereegranskat)abstract
- Broadband wireless systems require low complexity equalizers which can cope with long channel impulse responses and severe intersymbol interference (ISI). In this paper, a frequency domain (FD) approach for adaptive blind equalization for multiple-input multiple-output (MIMO) communication systems is proposed. As an initial step, a time domain (TD) block based updated adaptation is first developed which updates the equalizer coefficients once per each block of data symbols. As such, this algorithm can be equivalently implemented in the FD to reduce computational complexity associated with the symbol by symbol TD update. Simulation results show that the proposed algorithms can successfully separate and equalize the received signals with a significantly lower computational complexity than a corresponding TD approach.
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| 35. |
- Dam, Hai Huyen, et al.
(författare)
-
Complex Spreading Sequence Design
- 2002
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 36. |
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| 37. |
- Dam, Hai Huyen, et al.
(författare)
-
Frequency Domain Blind Equalization for MIMO Systems
- 2005
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 38. |
- Dam, Hai Huyen, et al.
(författare)
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Spreading Code Design Using a Global Optimization Method
- 2005
-
Ingår i: Annals of Operations Research. - : Springer. - 0254-5330 .- 1572-9338. ; 133:1-4, s. 249-264
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 39. |
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| 40. |
- Duong, Quang Trung, et al.
(författare)
-
Adaptive Transmission Scheme for Wireless Cooperative Communications
- 2009
-
Konferensbidrag (refereegranskat)abstract
- An adaptive transmission scheme for cooperative communications is proposed in this paper. Communication protocols with amplify-and-forward relays based on the distributed-Alamouti space-time code (achieving spatial diversity gain) and cooperative spatial multiplexing (C-SM) (pertaining spatial multiplexing gain) are considered. Specifically, under a fix transmission rate, we use adaptively the cooperative diversity (C-DIV) and C-SM according to channel conditions. With this strategy, either C-DIV with higher order modulation or C-SM with lower order modulation can be properly selected to enhance the error rate performance. The proposed adaptive protocol is shown to provide superior performance compared to C-DIV and C-SM.
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| 41. |
- Duong, Quang Trung, et al.
(författare)
-
Amplify-and-Forward MIMO Relaying with OSTBC over Nakagami-m Fading Channels
- 2010
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we analyze the performance of dual-hop channel state information (CSI)-assisted amplify-andforward (AF) cooperative networks using orthogonal space-time block codes (OSTBCs) over independent but not identically distributed Nakagami-m fading channels. Specifically, we present closed-form expressions of the outage probability (OP) and the symbol error probability (SEP). The analytical results are given in tractable forms which readily allow us to assess the performance of AF relay systems using OSTBCs. For sufficiently large signal-to-noise ratio, we obtain the asymptotic results for OP and SEP which reveal insights into the effect of fading factors on the diversity and coding gains. It has been shown that between the two hops the more severe link solely determines the diversity and coding gains. In particular, these two gains strictly depend on the fading severity parameters and the channel mean powers of the more rigorous hop, respectively. Numerical results are provided showing an excellent agreement between our analytical results and those of Monte-Carlo simulations for selected scenarios.
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| 42. |
- Duong, Quang Trung, et al.
(författare)
-
Average Sum-Rate of Distributed Alamouti Space--Time Scheme in Two-Way Amplify-and-Forward Relay Networks
- 2010
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a distributed Alamouti space-time code (DASTC) for two-way relay networks employing a single amplify-and-forward (AF) relay. We first derive closed-form expressions for the approximated average sum-rate of the proposed DASTC scheme. Our analysis is validated by a comparison against the results of Monte-Carlo simulations. Numerical results verify the effectiveness of our proposed scheme over the conventional DASTC with one-way communication.
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| 43. |
- Duong, Quang Trung, et al.
(författare)
-
Beamforming in Two-Way Fixed Gain Amplify-and-Forward Relay Systems with CCI
- 2012
-
Konferensbidrag (refereegranskat)abstract
- We analyze the outage performance of a two-way fixed gain amplify-and-forward (AF) relay system with beamforming, arbitrary antenna correlation, and co-channel interference (CCI). Assuming CCI at the relay, we derive the exact individual user outage probability in closed-form. Additionally, while neglecting CCI, we also investigate the system outage probability of the considered network, which is declared if any of the two users is in transmission outage. Our results indicate that the position of the relay in this system plays an important role in determining the user as well as the system outage probability via such parameters as signal-to-noise imbalance, antenna configuration, spatial correlation, and CCI power. To render further insights into the effect of antenna correlation and CCI on the diversity and array gains, an asymptotic expression which tightly converges to exact results is also derived.
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| 44. |
- Duong, Quang Trung, et al.
(författare)
-
Cooperative spectrum sharing networks with AF relay and selection diversity
- 2011
-
Ingår i: Electronics Letters. - : Institution of Engineering and Technology - IET. - 0013-5194 .- 1350-911X. ; 47:20, s. 1149-1151
-
Tidskriftsartikel (refereegranskat)abstract
- The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.
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| 45. |
- Duong, Quang Trung, et al.
(författare)
-
Cooperative Wireless Communications with Unequal Error Protection and Fixed Decode-And-Forward Relays
- 2010
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we examine an unequal error protection (UEP) scheme for wireless imaging that is based on utilizing the distributed diversity offered by decode-and-forward (DF) networks. Specifically, the data stream after source encoding is divided into high and low priority sub-streams depending on their importance for image reconstruction. A relay-selection combining (R-SC) scheme is exploited for high priority image data to achieve high reliability while cooperative spatial multiplexing is employed to low priority image data to support high spectral efficiency. In this work, we specifically take into account the setting that relays may forward erroneously detected signals to the destination when cooperating with fixed DF. In this context, the analytical and numerical results validate that R-SC outperforms other relaying protocols in terms of average symbol error probability while the considered UEP approach offers the highest spectral efficiency among the examined relaying schemes.
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| 46. |
- Duong, Quang Trung, et al.
(författare)
-
Cross-Layer Design for Integrated Mobile Multimedia Network with Strict Priority Traffic
- 2010
-
Konferensbidrag (refereegranskat)abstract
- In mobile multimedia networks, different traffic classes require various levels of quality of service (QoS). In this paper, we propose a cross-layer design to provide diverse QoS provisions for integrated realtime/non-realtime traffic by jointly taking into account the physical layer, data link layer, and application layer. Specifically, at the physical layer, adaptive modulation and coding (AMC) is employed to cope with the time-varying nature of fading channels whereas impairments due to queuing effects are considered at the data link layer. At the application layer, realtime and non-realtime traffic are classified into high and low priority classes, respectively, with strict priority levels. The cross-layer scheme is characterized as a discrete Markov modulated Poisson process. Solving the steady state probability of this Markov model readily enables us to investigate several important performance metrics such as packet drop rate due to buffer overflow and packet error rate due to transmission errors and network impairments. Our proposed cross-layer design is verified by comparing the analytical results with Monte-Carlo simulations. Furthermore, it has been shown that the proposed cross-layer design can flexibly guarantee QoS requirements for each traffic class.
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| 47. |
- Duong, Quang Trung, et al.
(författare)
-
Cross-Layer Design for MRT Systems with Channel Estimation Error and Feedback Delay
- 2011
-
Ingår i: Wireless personal communications. - : Springer. - 0929-6212 .- 1572-834X. ; 58:4, s. 681-694
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyze the effect of channel estimation error and delayed feedback on the performance of a cross-layer scheme combining adaptive modulation for maximum ratio transmission (MRT) at the physical layer and truncated automatic repeat request (T-ARQ) at the link layer. The cross-layer attempts to maximize the spectral efficiency under predetermined quality of service requirements, namely, delay and packet-loss constraints. In particular, we derive closed-form expressions for the average packet error rate, average achievable spectral efficiency, and the outage probability, hence, enabling to evaluate the performance of the cross-layer scheme in the presence of imperfect channel estimation at the receiver and delayed feedback path between the receiver and transmitter. The final expressions are given in terms of the minimum and maximum number of transceiver antennas as well as the channel estimation error and feedback delay parameters. We further show that with a small amount of channel estimation error and/or feedback delay the system performance is severely degraded. Specifically, numerical results demonstrate that with channel estimation error and feedback delay the performance of the cross-layer scheme is even worse than that of T-ARQ only. We also observe an irreducible outage probability floor appearing in the high signal-to-noise regime.
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| 48. |
- Duong, Quang Trung, et al.
(författare)
-
Cross-Layer Design for Packet Data Transmission in Maximum Ratio Transmission Systems with Imperfect CSI and Co-Channel Interference
- 2012
-
Ingår i: Using Cross-Layer Techniques for Communication Systems. - : IGI. - 9781466609600 ; , s. 376-399
-
Bokkapitel (refereegranskat)abstract
- This chapter will therefore present some new results for the cross-layer design for packet data transmission applied to co-located MIMO with maximum ratio transmission. In this context, closed-form expressions for the average packet error rate, average achievable spectral efficiency, and outage probability are derived. This enables one to evaluate the performance of the cross-layer design under predetermined delay and packet loss constraints. Some important results in the high Signal-to-Noise Ratio (SNR) regime are also provided, revealing insights on how system and channel parameters affect system performance. More importantly, a mathematical analysis is proved to be a powerful tool to investigate the impact of practical issues such as channel estimation error, feedback delay, antenna correlation, and rank-deficient MIMO channel matrix, on the performance of cross-layer design.
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| 49. |
- Duong, Quang Trung, et al.
(författare)
-
Distributed Space-Time Coding in Two-Way Fixed Gain Relay Networks over Nakagami-m Fading
- 2012
-
Ingår i: Proceedings of the IEEE International Conference on Communicatons (ICC). - Ottawa : IEEE. - 9781457720512 - 9781457720529 ; , s. 3521-3525
-
Konferensbidrag (refereegranskat)abstract
- The distributed Alamouti space-time code in two-way fixed gain amplify-and-forward (AF) relay is proposed in this paper. In particular, closed-form expressions for approximated ergodic sum-rate and exact pairwise error probability (PWEP) are derived for Nakagami-m fading channels. To reveal further insights into array and diversity gains, an asymptotic PWEP is also obtained. Finally, numerical results are provided to corroborate the proposed theoretical analysis.
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| 50. |
- Duong, Quang Trung, et al.
(författare)
-
Effect of primary network on performance of spectrum sharing AF relaying
- 2012
-
Ingår i: Electronics Letters. - : IET. - 0013-5194 .- 1350-911X. ; 48:1, s. 25-U95
-
Tidskriftsartikel (refereegranskat)abstract
- Most of the research in spectrum sharing has neglected the effect of interference from primary users. In this reported work, the performance of spectrum sharing amplify-and-forward relay networks under interference-limited environment, where the interference induced by the transmission of primary networks is taken into account, is investigated. In particular, a closed-form expression tight lower bound of outage probability is derived. To reveal additional insights into the effect of primary networks on the diversity and array gains, an asymptotic expression is also obtained.
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