Ändra sökning
Avgränsa sökresultatet
12345 51 - 100 av 249
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 51. Dam, Hai Huyen
    et al.
    Zepernick, Hans-Jürgen
    Nordberg, Jörgen
    Nordholm, Sven
    Design of Complex Spreading Sequences2002Konferensbidrag (Refereegranskat)
  • 52. Dam, Hai Huyen
    et al.
    Zepernick, Hans-Jürgen
    Nordholm, Sven
    Nordberg, Jörgen
    Spreading Code Design Using a Global Optimization Method2005Ingår i: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 133, nr 1-4, s. 249-264Artikel i tidskrift (Refereegranskat)
    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.

  • 53. Duong, Quang Trung
    et al.
    Alay, Ozgu
    Erkip, Elza
    Zepernick, Hans-Jürgen
    End-to-End Performance of Randomized Distributed Space-Time Codes2010Konferensbidrag (Refereegranskat)
    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.

  • 54. 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 channels2010Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 46, nr 17Artikel i tidskrift (Refereegranskat)
    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.

  • 55. Duong, Quang Trung
    et al.
    Alexandropoulos, George C.
    Zepernick, Hans-Jürgen
    Tsiftsis, Theodoros A.
    Orthogonal Space-Time Block Codes with CSI-Assisted Amplify-and-Forward Relaying in Correlated Nakagami-m Fading Channels2011Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 60, nr 3, s. 882-889Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the performance of multiple-input multiple-output (MIMO) dual-hop amplify-and-forward (AF) relay systems using orthogonal space-time block codes (OSTBCs) over arbitrarily correlated Nakagami-m fading channels is analyzed. In particular, closed-form expressions for the end-to-end outage probability (OP) and the symbol error probability (SEP) with arbitrary number of transceiver antennas and general correlation matrices are derived. Their mathematically tractable forms readily enable us to evaluate the performance of MIMO AF relay systems that utilize OSTBCs. For sufficiently high signal-to-noise ratios, asymptotically tight approximations for the OP and SEP are also attained which reveal insights into the effects of fading parameters and antenna correlation on the system’s performance. Furthermore, we prove that the correlation has no impact on the achievable diversity gain which is equal to the minimum of the sum of fading parameters between the two hops. Selected numerically evaluated results are presented showing an excellent agreement between the proposed analysis and equivalent Monte-Carlo simulations.

  • 56. Duong, Quang Trung
    et al.
    Bao, Vo Nguyen Quoc
    Alexandropoulos, George C.
    Zepernick, Hans-Jürgen
    Cooperative spectrum sharing networks with AF relay and selection diversity2011Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 47, nr 20, s. 1149-1151Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 57.
    Duong, Quang Trung
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Bao, Vo Nguyen Quoc
    Tran, Hung
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Alexandropoulos, George C.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Effect of primary network on performance of spectrum sharing AF relaying2012Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 48, nr 1, s. 25-U95Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

    Ladda ner fulltext (pdf)
    fulltext
  • 58. Duong, Quang Trung
    et al.
    Bao, Vo Nguyen Quoc
    Zepernick, Hans-Jürgen
    Exact outage probability of cognitive AF relaying with underlay spectrum sharing2011Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 47, nr 17, s. 1001-1002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The exact closed-form expression for the outage probability (OP) of cognitive radio dual-hop amplify-and-forward (AF) relay networks is derived. The tractable expression of the OP, given in the form of elementary functions, readily enables evaluating the effect of primary users on the secondary system performance. It has been shown that the use of AF relaying significantly improves the performance of cognitive radio networks compared to its direct transmission counterpart.

  • 59. Duong, Quang Trung
    et al.
    Bao, Vo Nguyen Quoc
    Zepernick, Hans-Jürgen
    On the Performance of Selection Decode-and-Forward Relay Networks over Nakagami-m Fading Channels2009Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 13, nr 3, s. 172-174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we present the performance of fixed decode-and-forward cooperative networks with relay selection over independent but not identically distributed Nakagamim fading channels, with integer values of the fading severity parameter m. Specifically, closed-form expressions for the symbol error probability and the outage probability are derived using the statistical characteristic of the signal-to-noise ratio. We also perform Monte-Carlo simulations to verify the analytical results

  • 60. Duong, Quang Trung
    et al.
    Engelke, Ulrich
    Zepernick, Hans-Jürgen
    Cooperative Wireless Communications with Unequal Error Protection and Fixed Decode-And-Forward Relays2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 61. Duong, Quang Trung
    et al.
    Engelke, Ulrich
    Zepernick, Hans-Jürgen
    Unequal Error Protection for Wireless Multimedia Transmission in Decode-and-Forward Relay Networks2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we propose an unequal error protection (UEP) scheme for multimedia transmission over wireless decode-and-forward (DF) relay networks. We prove that relay selection combining (R-SC) mode yields a better error rate performance than all-participate relays, i.e., distributed spacetime codes (DSTC) and orthogonal transmission with maximum ratio combining (OT-MRC) at the destination. Hence, we apply the R-SC scheme for transmitting bit sequence with high priority while the cooperative spatial multiplexing scheme is employed for the bit-stream with low priority. With this strategy, we achieve the maximum spatial diversity gain for high priority data and a high spatial multiplexing gain for low priority data. Monte- Carlo simulations and analytical results are shown to validate the proposed UEP scheme.

  • 62.
    Duong, Quang Trung
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Kim, Kyeongjin
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Tellambura, Chintha
    Opportunistic relaying for cognitive network with multiple primary users over Nakagami-m fading2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    The performance of cognitive spectrum sharing systems with opportunistic relay selection over Nakagami-m fading is analyzed in the presence of multiple primary users (PUs). In particular, we derive an exact closed-form expression for the outage probability (OP) of the considered cognitive relay systems under the joint impact of maximal transmit power Pt at secondary transmitter and peak interference power Ip at the primary user. Our general formulas cover several specific practical scenarios, e.g., where the maximal transmit power can be neglected compared to the peak interference power. In addition, a tractable expression for the asymptotic OP is also derived and reveals important insights into the system performance. We show that the number of PUs only affects the coding gain but not the diversity gain.

  • 63. Duong, Quang Trung
    et al.
    Le, Thanh-Tan
    Zepernick, Hans-Jürgen
    Performance of Cognitive Radio Networks with Maximal Ratio Combining over Correlated Rayleigh Fading2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we apply the maximal ratio combining (MRC) technique to achieve higher detection probability in cognitive radio networks over correlated Rayleigh fading channels. We present a simple approach to derive the probability of detection in closed-form expression. The numerical results reveal that the detection performance is a monotonically increasing function with respect to the number of antennas. Moreover, we provide sets of complementary receiver operating characteristic (ROC) curves to illustrate the effect of antenna correlation on the sensing performance of cognitive radio networks employing MRC schemes in some respective scenarios.

  • 64.
    Duong, Quang Trung
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Ngo, Hien Quoc
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Nallanathan, Arumugam
    Distributed Space-Time Coding in Two-Way Fixed Gain Relay Networks over Nakagami-m Fading2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 65.
    Duong, Quang Trung
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Suraweera, Himal A.
    Tsiftsis, Theodoros A.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Nallanathan, Arumugam
    Keyhole Effect in Dual-Hop MIMO AF Relay Transmission with Space-Time Block Codes2012Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 60, nr 12, s. 1-11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the effect of keyhole on the performance of multiple-input multiple-output (MIMO) amplifyand-forward (AF) relay networks with orthogonal space-time block codes (OSTBCs) transmission is investigated. In particular, we analyze the asymptotic symbol error probability (SEP) performance of a downlink communication system where the amplifying processing at the relay can be implemented by either the linear or squaring approach. Our tractable asymptotic SEP expressions enable us to obtain both diversity and array gains. Our finding reveals that with condition nS > min(nR, nD), the linear approach can provide the full achievable diversity gain of min(nR, nD) when only the second hop suffers from the keyhole effect, i.e., single keyhole effect (SKE), where nS, nR, and nD are the number of antennas at source, relay, and destination, respectively. However, for the case that both the source-relay and relay-destination links experience the keyhole effect, i.e., double keyhole effect (DKE), the achievable diversity order is only one regardless of the number of antennas. In contrast, utilizing the squaring approach, the overall diversity gain can be achieved as min(nR, nD) for both SKE and DKE. An important observation corroborated by our studies is that for satisfying the tradeoff between performance and complexity, we should use the linear approach for SKE and the squaring approach for DKE.

  • 66. Duong, Quang Trung
    et al.
    Suraweera, Himal A.
    Tsiftsis, Theodoros A.
    Zepernick, Hans-Jürgen
    Nallanathan, Arumugam
    OSTBC Transmission in MIMO AF Relay Systems with Keyhole and Spatial Correlation Effects2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we investigate the degenerative effects of antenna correlation and keyhole on the performance of multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay networks. In particular, we considered a downlink MIMO AF relay system consisting of an nS-antenna base station S, an nR-antenna relay station R, and an nD-antenna mobile station D, in which the signal propagation originated from the mobile station suffers from keyhole and spatial correlation effects. We have derived an exact expression for the moment generation function of the instantaneous signal-to-noise ratio which enables us to analyze the symbol error probability and outage probability of the considered system.We have shown that although the mobile station is in a poor scattering environment, i.e., keyhole, the relay channel (S → R → D link) still achieves a cooperative diversity order of min(nR, nD) provided that the channel from the source (S → R link) is keyhole-free. This result is important to radio system designers since under such a severe scenario it is unnecessary to deploy a large number of antennas on the relay station (nR) but only requires nR = nD to obtain the maximum achievable diversity gain.

  • 67. Duong, Quang Trung
    et al.
    Suraweera, Himal A.
    Yuen, Chau
    Zepernick, Hans-Jürgen
    Multi-Keyhole Effect in MIMO AF Relay Downlink Transmission with Space-Time Block Codes2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Multi-keyhole bridges the gap between single keyhole and full-scattering multiple-input multiple-output (MIMO) channels. In this paper, we therefore investigate the multi-keyhole effect on the MIMO amplify-and-forward (AF) relay downlink transmission with orthogonal space-time block codes. In particular, we derive the analytical symbol error rate (SER) expression for the considered system with arbitrary number of keyholes. Moreover, SER approximations in the high SNR regime for several important special scenarios of multi-keyhole channels are further derived. These asymptotic results provide important insights into the impact of system's parameters on the SER performance. Our analysis is confirmed by comparing with Monte-Carlo simulations.

  • 68.
    Duong, Quang Trung
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Suraweera, Himal A.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Yuen, Chau
    Beamforming in Two-Way Fixed Gain Amplify-and-Forward Relay Systems with CCI2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 69.
    Duong, Quang Trung
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Vo, Nguyen-Son
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Shu, Lei
    Du, Xu
    Cheng, Wenping
    Replication Strategies for Video On-Demand over Wireless Mesh Networks: A Cross-Layer Optimization Approach2012Ingår i: Using Cross-Layer Techniques for Communication Systems / [ed] Rashvand, Habib F.; Kavian, Yousef S., IGI , 2012, s. 349-375Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    In this chapter, dependencies between the different protocol layers and across the hops through WMNs will be exploited to deliver video streaming with high QoE. Specifically, a cross-layer optimization approach is applied to a replication strategy for video on-demand over WMNs. Additionally, the authors consider a distributed implementation algorithm, namely Mod&Timer, to handle the placement of replicas for saving storage resources of the network. Simulation results are shown to demonstrate that the proposed cross-layer design outperforms many existing schemes in terms of QoE. More importantly, compared to other strategies without cross-layer interaction, the proposed cross-layer design satisfies the heterogeneous bandwidth constraint of end users.

  • 70. Duong, Quang Trung
    et al.
    Yuen, Chau
    Zepernick, Hans-Jürgen
    Lei, Xianfu
    Average Sum-Rate of Distributed Alamouti Space--Time Scheme in Two-Way Amplify-and-Forward Relay Networks2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 71. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Adaptive Transmission Scheme for Wireless Cooperative Communications2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 72. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Cross-Layer Design for MRT Systems with Channel Estimation Error and Feedback Delay2011Ingår i: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 58, nr 4, s. 681-694Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 73.
    Duong, Quang Trung
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Cross-Layer Design for Packet Data Transmission in Maximum Ratio Transmission Systems with Imperfect CSI and Co-Channel Interference2012Ingår i: Using Cross-Layer Techniques for Communication Systems / [ed] Rashvand, Habib F.; Kavian, Yousef S., IGI , 2012, s. 376-399Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    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.

  • 74. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Exact Average Symbol Error Rate of Cooperative Spatial Multiplexing in Composite Channels2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Performance of cooperative spatial multiplexing systems over composite channels is presented. In particular, we derive the exact closed-form average symbol error rate (SER) expressions for cooperative spatial multiplexing systems with linear equalization receiver (e.g., Zero-Forcing) and M-ary modulation scheme in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the average SER is expressed in the forms of Appell hypergeometric function. Applying the series representation of Appell hypergeometric function, we derive a very tight approximation for the average SER. We also perform Monte-Carlo simulations to validate our analysis.

  • 75. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Hybrid Decode-Amplify-Forward Cooperative Communications with Multiple Relays2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we investigate the performance gain of hybrid decode-amplify-forward (HDAF) relay protocol over the two conventional ones: the adaptive decode-forward (ADF) and amplify-forward (AF) in dual-hop multiple-relay networks. We analyze the performance gain in terms of the symbol error probability (SEP) in the high signal-to-noise ratio (SNR) regime. Similarly as in the single relay case [1], under a specific modulation scheme, these gains only depend on the ratio of channel mean power between the first-hop and second-hop transmission. In particular, we show that the HDAF protocol obtains a large gain, medium gain, and small gain over ADF, AF as the relays are placed close to the destination, half-way between the source and destination (symmetric case), and nearby the source, respectively. In contrast to the single-relay case in which the HDAF scheme has no benefit compared to ADF and AF as the relay is located close to the source [1], HDAF still achieves a small gain with multiple relays. Interestingly, we further show that for all cases the performance gains are saturated as the number of relays is large.

  • 76. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    On the Ergodic Capacity of Cooperative Spatial Multiplexing Systems in Composite Channels2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    The ergodic capacity of cooperative spatial multiplexing systems over composite channels is presented. Specifically, we derive the exact closed-form expressions for ergodic capacity of cooperative spatial multiplexing systems with linear receiver in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the final analytical result of ergodic capacity is described in a closed-form expression. We also perform Monte-Carlo simulations to validate our analysis. Subsequently, we apply the obtained analytical expression to evaluate some representative scenarios regarding to spatial multiplexing gain in relay composite channels

  • 77. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    On the Performance Gain of Hybrid Decode-Amplify-Forward Cooperative Communications2009Ingår i: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we investigate the performance of adaptive decode-forward (ADF), amplify-forward (AF), and hybrid decode-amplify-forward (HDAF) relaying protocol. In particular, we derive the closedform expression of symbol error probability (SEP) for these three relaying protocols. For the AF protocol, we derive a simpler and more tractable final result than previously published work [1]. Furthermore, analyzing the high signal-to-noise ratio (SNR) regime, we derive an asymptotically tight approximation for SEP. Especially, for the AF protocol, our SEP approximation is tighter than the result in [2]. The SEP approximation is used to assess an important aspect between the three different relaying protocols, i.e., the SEP performance gain of HADF over the two conventional relaying schemes ADF and AF. It is shown that the performance gain of HDAF over ADF and AF significantly depends on the relative value of channel conditions between source-to-relay and relay-to- estination link (relay channels). Interestingly, it is shown that the HDAF protocol has no benefit compare to the two others if the relay is located close to the source. In contrast, the performance gains of HDAF over the ADF and AF scheme are remarkably large as the relay moves nearby the destination. Specifically, the numerical results given as well as our analysis indicate that for QPSK modulation, HDAF outperforms ADF and AF with a performance improvement by 5 dB and 6 dB, respectively.

  • 78. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    On the Performance of ROI-Based Image Transmission Using Cooperative Diversity2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we examine the spatial diversity of cooperative communications for image transmission without deploying multiple antennas at the transmitter. We propose a novel region of interest (ROI)-based scheme for image transmission over wireless cooperative/relay fading channels. By having the relay terminal assist the direct communications, we can increase the resilience for ROI against the error-prone fading channels. Our proposed scheme significantly improves the performance of ROI compared to the direct communications (no-cooperation) and conventional relay networks without performing any forward error correction. Although we focus on the adaptive decode-forward (ADF) relay protocol, our proposed scheme can be easily adopted to any other relaying protocol such as fixed decode-forward (FDF), amplify-forward (AF), hybrid decode-amplify-forward (HDAF), and distributed-Alamouti space--time coding. Simulation results show that under the the same total transmit power constraint our proposed scheme significant outperforms the conventional ones in terms of bit error rate (BER) and peak signal-to-noise ratio (PSNR).

  • 79. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Performance Analysis of Cooperative Spatial Multiplexing with Amplify-and-Forward Relays2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cooperative spatial multiplexing (CSM) systems can achieve high spatial multiplexing gain in wireless relay networks since each single-antenna relay forwards simultaneously a different subset of source messages to the destination. In this paper, the performance of CSM with amplify-and-forward (AF) relays are presented. Specifically, we derive exact closed-form expressions for symbol error probability (SEP) and achievable spectral efficiency of CSM with linear receiver in dissimilar Rayleigh fading channels. Assessing the SEP performance in the high signal-to-noise regime, we further show that CSM with AF relays obtains the first order of diversity gain. Furthermore, it has been observed that CSM outperforms two well-known cooperative diversity systems, e.g., selection combining and maximal ratio combining, in term of spectral efficiency. We also perform Monte-Carlo simulations to validate our analysis.

  • 80. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Robust EZW Image Transmission Scheme Using Distributed-Alamouti Codes in Relay Networks2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    A robust image transmission scheme deploying distributed-Alamouti space-time code (STC) over wireless relay networks is proposed. Specifically, we propose a cross-layer design combining application, networking, and physical layer to enhance the quality of multimedia data over error-prone wireless channels. At the application layer, a coded image sequence based on the wavelet transform is divided into two priorities. The higher priority contains the most significant information of image and the lower priority conveys less important information. At the physical layer, two pre-assigned relays cooperate to form a distributed-Alamouti code which help the source to transmit the low priority sequence of the image over error-prone wireless channels. At the networking layer, among the whole relay nodes in the networks we select two relay nodes which provides the maximum signal-to-noise ratio to convey the higher priority. With this strategy, we implicitly achieve unequal error protection for image transmission without controlling power or varying modulation and coding at the transmitter at the expense of increasing network's overhead (i.e. feedback information). The selection of relays needs limited feedback, hence, enabling our proposed scheme feasible in practical applications. Analytical and simulation results are provided to verify our proposal. It has been shown that the image quality is remarkably enhanced in terms of objective quality using the proposed scheme compared to the conventional transmission schemes.

  • 81. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Bao, Vo Nguyen Quoc
    Symbol error probability of hop-by-hop beamforming in Nakagami-m fading2009Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 45, nr 20, s. 1042-1044Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The symbol error probability (SEP) of amplify-and-forward(AF) multiple-input multiple-output (MIMO) cooperative networks where beamforming is adopted at both the source and destination is investigated. In particular, the tight lower bound for SEP of AF MIMO relay systems is presented with hop-by-hop beamforming over independent, but not necessarily identically distributed, Nakagami-m fading channels. Furthermore, assessing the high SNR, an asymptotic SEP expression is derived which reveals the array and diversity gain. Numerical results are shown to verify the analysis in some representative scenarios.

  • 82. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Fiedler, Markus
    Cross-Layer Design for Integrated Mobile Multimedia Network with Strict Priority Traffic2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 83. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Tsiftsis, Theodoros A.
    Bao, Vo Nguyen Quoc
    Amplify-and-Forward MIMO Relaying with OSTBC over Nakagami-m Fading Channels2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 84. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Tsiftsis, Theodoros A.
    Bao, Vo Nguyen Quoc
    Performance Analysis of Amplify-and-Forward MIMO Relay Networks with Transmit Antenna Selection over Nakagami-m Channels2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    We analyze the performance of amplify-and-forward (AF) multiple-input multiple-output (MIMO) cooperative networks over independent but not identically distributed Nakagami-$m$ fading channels. Specifically, we consider an AF MIMO relay network where the source deploys the transmit antenna selection scheme to communicate with the destination through the help of a relay. We derive closed-form approximations for outage probability (OP) and symbol error probability (SEP). Moreover, asymptotically tight approximations for OP and SEP have been obtained to facilitate insights on how fading parameters affect the performance. Our analytical results are verified by Monte-Carlo simulations for respective scenarios.

  • 85. Duong, Trung Quang
    et al.
    Lei, Xianfu
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för kommunikationssystem.
    MIMO Amplify-and-Forward Relay Systems with Dissimilar Channel Characteristics2014Ingår i: 2014 INTERNATIONAL CONFERENCE ON COMPUTING, MANAGEMENT AND TELECOMMUNICATIONS (COMMANTEL), IEEE , 2014, s. 67-69Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we investigate the asymmetric property of multiple-input multiple-output (MIMO) dual-hop amplify-and- forward (AF) relay networks. We consider the difference of the two hops in terms of both fading channels and scattering environment. In particular, we analyze the symbol error probability (SEP) of a MIMO orthogonal space-time block code (OSTBC) AF relay network in which the first and second hop undergo Rayleigh fading with a rich-scattering environment and Nakagami-m fading with a poor-scattering environment, respectively. Moreover, an asymptotic SEP expression yielding insights on the diversity gain is also obtained.

    Ladda ner fulltext (pdf)
    fulltext
  • 86.
    Elwardy, Majed
    et al.
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Zepernick, Hans-Juergen
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Chu, Thi My Chinh
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Sundstedt, Veronica
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Objective Perceptual Video Quality Prediction Using Spatial and Temporal Information Differences2019Ingår i: Proceedings - 2019 19th International Symposium on Communications and Information Technologies, ISCIT 2019, Institute of Electrical and Electronics Engineers Inc. , 2019, s. 436-441Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, objective perceptual video quality models are proposed that use spatial and temporal perceptual information differences for predicting video quality as perceived by human observers. Spatial perceptual information characterizes the complexity and temporal perceptual information quantifies the motion contained in a video. As such, differences in the spatial and temporal perceptual information of a reference video (original) and test video (processed) may be used to predict quality of videos that have undergone encoding, transmission, or other processing. In particular, several video quality prediction functions are derived using curve fitting along with training and validation on data from a publicly available annotated database. The obtained functions provide predicted mean opinion scores as a measure of perceptual quality subject to spatial and temporal perceptual information differences. The analysis of the video quality prediction performance of the proposed models shows that differences in spatial and temporal perceptual information can be used for objective video quality prediction. © 2019 IEEE.

  • 87.
    Elwardy, Majed
    et al.
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Zepernick, Hans-Juergen
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Sundstedt, Veronica
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Annotated 360-Degree Image and Video Databases: A Comprehensive Survey2019Ingår i: 13th International Conference on Signal Processing and Communication Systems, ICSPCS 2019 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The advances in 5G mobile networks are expected to enable immersive interconnected mobile multimedia systems. As humans are the final judges of the quality of immersive multimedia, it is essential to engage a suitable ground truth in the design of such systems. Databases annotated with results from subjective tests constitute such ground truth given as opinion scores, head movements, eye tracking data, psychophysiological data, and other data related to the viewers' behavior. On this basis, perception-based quality assessment of algorithms, systems, and services can be performed, and objective perceptual quality models can be developed. In this paper, a comprehensive survey of publicly available annotated 360-degree image and video databases is provided. The survey may guide the selection of ground truth on 360-degree images and videos to support quality assessment and modeling research. Further, the survey reveals the need for establishing new annotated databases that address the full range of subjective aspects of immersive multimedia. © 2019 IEEE.

  • 88.
    Elwardy, Majed
    et al.
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Zepernick, Hans-Juergen
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Sundstedt, Veronica
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Hu, Yan
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Impact of Participants' Experiences with Immersive Multimedia on 360° Video Quality Assessment2019Ingår i: 13th International Conference on Signal Processing and Communication Systems, ICSPCS 2019 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we study the impact that the level of experience of participants with immersive multimedia has on 360° video quality assessment. An extensive subjective experiment using the modified absolute category rating with hidden reference (M-ACR-HR) method was conducted. The opinion scores obtained from the participants in this experiment along with other sensor data support this study. The statistical analysis is performed in terms of screening participants' distribution of opinion scores for consistency, average rating time, box plots related to mean opinion scores (MOSs) and differential MOS (DMOS). Detailed results for MOS and DMOS are also provided for reference and test sequences covering a wide range of qualities. Major findings include: (1) Screening detects many outliers for participants with no experience, (2) Average rating times show that experts learn the quality assessment task fast, (3) Participants with no experience provide lower opinion scores in average, (4) DMOS may alleviate the bias in quality rating caused by different levels of experience. © 2019 IEEE.

  • 89. Engelke, Ulrich
    et al.
    Barkowsky, Marcus
    Callet, Patrick Le
    Zepernick, Hans-Jürgen
    Modelling Saliency Awareness for Objective Video Quality Assessment2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Existing video quality metrics do usually not take into consideration that spatial regions in video frames are of varying saliency and thus, differently attract the viewer's attention. This paper proposes a model of saliency awareness to complement existing video quality metrics, with the aim to improve the agreement of objectively predicted quality with subjectively rated quality. For this purpose, we conducted a subjective experiment in which human observers rated the annoyance of videos with transmission distortions appearing either in a salient region or in a non-salient region. The mean opinion scores confirm that distortions in salient regions are perceived much more annoying. It is shown that application of the saliency awareness model to two video quality metrics considerably improves their quality prediction performance.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 90. Engelke, Ulrich
    et al.
    Kaprykowsky, Hagen
    Zepernick, Hans-Jürgen
    Ndjiki-Nya, Patrik
    Visual Attention in Quality Assessment2011Ingår i: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 28, nr 6, s. 50-59Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Perceptual quality metrics are widely deployed in image and video processing systems. These metrics aim to emulate the integral mechanisms of the human visual system (HVS) to correlate well with visual perception of quality. One integral property of the HVS is, however, often neglected: visual attention (VA) [1]. The essential mechanisms associated with VA consist mainly of higher cognitive processing, deployed to reduce the complexity of scene analysis. For this purpose, a subset of the visual information is selected by shifting the focus of attention across the visual scene to the most relevant objects. By neglecting VA, perceptual quality models inherently assume that all objects draw the attention of the viewer to the same degree.

  • 91. Engelke, Ulrich
    et al.
    Kusuma, Tubagus Maulana
    Zepernick, Hans-Jürgen
    Perceptual Quality Assessment of Wireless Video Applications2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    The rapid evolution of wireless networks is driven by the growth of wireless packet data applications such as interactive mobile multimedia applications, wireless streaming services, and video-on-demand. The largely heterogeneous network structures, severe channel impairments, and complex traffic patterns make the wireless networks much more unpredictable compared to their wired counterparts. One of the major challenges with the roll-out of these services is therefore the design of wireless networks that fulfill the stringent quality of service requirements of wireless video applications. In this paper, the applicability of perceptual image quality metrics for real-time quality assessment of Motion JPEG2000 (MJ2) video streams over wireless channels is investigated. In particular, a reduced-reference hybrid image quality metric (HIQM) is identified as suitable for an extension to video applications. It outperforms other known metrics in terms of required overhead and prediction performance.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 92. Engelke, Ulrich
    et al.
    Kusuma, Tubagus Maulana
    Zepernick, Hans-Jürgen
    Caldera, Manora
    Reduced-reference metric design for objective perceptual quality assessment in wireless imaging2009Ingår i: Signal Processing-Image Communication, ISSN 0923-5965 , Vol. 24, nr 7, s. 525-547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rapid growth of third and development of future generation mobile systems has led to an increase in the demand for image and video services. However, the hostile nature of the wireless channel makes the deployment of such services much more challenging, as in the case of a wireline system. In this context, the importance of taking care of user satisfaction with service provisioning as a whole has been recognized. The related user-oriented quality concepts cover end-to-end quality of service and subjective factors such as experiences with the service. To monitor quality and adapt system resources, performance indicators that represent service integrity have to be selected and related to objective measures that correlate well with the quality as perceived by humans. Such objective perceptual quality metrics can then be utilized to optimize quality perception associated with applications in technical systems. In this paper, we focus on the design of reduced-reference objective perceptual image quality metrics for use in wireless imaging. Specifically, the Normalized Hybrid Image Quality Metric (NHIQM) and a perceptual relevance weighted L_p-norm are designed. The main idea behind both feature-based metrics relates to the fact that the human visual system (HVS) is trained to extract structural information from the viewing area. Accordingly, NHIQM and L_p-norm are designed to account for different structural artifacts that have been observed in our distortion model of a wireless link. The extent by which individual artifacts are present in a given image is obtained by measuring related image features. The overall quality measure is then computed as a weighting sum of the features with the respective perceptual relevance weight obtained from subjective experiments. The proposed metrics differ mainly in the pooling of the features and amount of reduced-reference produced. While NHIQM performs the pooling at the transmitter of the system to produce a single value as reduced-reference, the L_p-norm requires all involved feature values from the transmitted and received image to perform the pooling on the feature differences at the receiver. In addition, non-linear mapping functions are developed that relate the metric values to predicted mean opinion scores (MOS) and account for saturations in the HVS. The evaluation of prediction performance of NHIQM and the L_p-norm reveals their excellent correlation with human perception in terms of accuracy, monotonicity, and consistency. This holds not only for the prediction performance on images taken for the training of the metrics but also for the generalization to unknown images. In addition, it is shown that the NHIQM approach and the perceptual relevance weighted L_p-norm outperform other prominent objective quality metrics in prediction performance.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 93. Engelke, Ulrich
    et al.
    Liu, Hantao
    Wang, Junle
    Le Callet, Patrick
    Heynderickx, Ingrid E J
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Maeder, Anthony J.
    Comparative Study of Fixation Density Maps2013Ingår i: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 22, nr 3, s. 1121-1133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fixation density maps (FDM) created from eye tracking experiments are widely used in image processing applications. The FDM are assumed to be reliable ground truths of human visual attention and as such, one expects a high similarity between FDM created in different laboratories. So far, no studies have analyzed the degree of similarity between FDM from independent laboratories and the related impact on the applications. In this paper, we perform a thorough comparison of FDM from three independently conducted eye tracking experiments. We focus on the effect of presentation time and image content and evaluate the impact of the FDM differences on three applications: visual saliency modeling, image quality assessment, and image retargeting. It is shown that the FDM are very similar and that their impact on the applications is low. The individual experiment comparisons, however, are found to be significantly different, showing that inter-laboratory differences strongly depend on the experimental conditions of the laboratories. The FDM are publicly available to the research community.

  • 94. Engelke, Ulrich
    et al.
    Liu, Hantao
    Zepernick, Hans-Jürgen
    Heynderickx, Ingrid
    Maeder, Anthony
    Comparing Two Eye-Tracking Databases: The Effect Of Experimental Setup And Image Presentation Time On The Creation Of Saliency Maps2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Visual attention models are typically designed based on human gaze patterns recorded through eye tracking. In this paper, two similar eye tracking experiments from independent laboratories are presented, in which humans observed natural images under task-free condition. The resulting saliency maps are analysedwith respect to two criteria; the consistency between the experiments and the impact of the image presentation time. It is shown, that the saliency maps between the experiments are strongly correlated independent of presentation time. It is further revealed that the presentation time can be reduced without substantially sacrificing the accuracy of the convergent saliency map. The results provide valuable insight into the similarity of saliency maps from independent laboratories and are highly beneficial for the creation of converging saliency maps at reduced experimental time and cost.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 95. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    Analysing Inter-Observer Saliency Variations in Task-Free Viewing of Natural Images2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    We analyse variations of saliency between human observers when viewing natural image content. For this purpose, we conducted an eye tracking experiment to record gaze patterns of humans when viewing natural images. The resulting gaze patterns were used to create saliency maps for each observer and image. A correlation analysis is then conducted with the aim to quantify the variability of saliency between the observers and the different images. The results are considered to be a first step towards gaining a better understanding regarding the reliability of saliency maps for natural images.

  • 96. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Human Observer Confidence in Image Quality Assessment2012Ingår i: Signal processing. Image communication, ISSN 0923-5965, E-ISSN 1879-2677, Vol. 27, nr 9, s. 935-947Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mean opinion scores obtained from subjective quality assessment are widely used as a ground truth for the development of predictive quality models. The underlying variance between observer ratings is typically quantified using confidence intervals, which do not provide any direct insight into the underlying causes of the disagreement. For better understanding of human visual quality perception and to develop more accurate models, it is important to identify the factors that impact on the variations in quality ratings. This work considers one such factor: observer confidence. This consideration is motivated by the view that quality assessment is a difficult task and hence quality ratings are provided with varying levels of confidence. The first goal of this paper is to analyse the results of an experiment to determine association between observer confidence and image quality judgement. Secondly, models are developed that aim to predict mean observer confidence as a complementary measure to the widely used mean opinion scores. It is shown that there is indeed a strong interrelation between quality perception and confidence, resulting in predictive models of high accuracy.

  • 97. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    On Confidence and Response Times of Human Observers in Subjective Image Quality Assessment2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Mean opinion scores obtained in subjective image quality experiments are widely accepted as measures of perceived visual quality. They have, however, a strong limitation regarding the reliability of the rated quality, since there is no explicit information as to whether the human observer experienced difficulties when judging image quality. We thus suggest that additional information about the observers confidence should be provided along with the actual quality measure. In this paper, we analyse two ways of obtaining this confidence measure; firstly as a confidence score given by the human observer and secondly as an indirect measure of the observers response time to provide the quality score. We reveal strong relationships of confidence scores and response times to the quality scores. We further propose a model to predict observer confidence based on the quality scores and response times.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 98. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    The Effect of Spatial Distortion Distributions on Human Viewing Behaviour when Judging Image Quality2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    In wireless communication, distortions are induced into an image through both lossy source coding and an error prone channel. The combination thereof causes complex distortion patterns in the visual content which vary strongly in their spatial distribution, some being uniformly spread and others being locally clustered. In the context of image quality, it is of interest to identify as to how the distribution of the distortions impact on the visual attention of human observers and thus on the perceived quality. For this reason, we conducted an experiment in which fifteen participants were asked to rate the quality of eighty distorted images and their corresponding reference images, while we recorded their gaze patterns using an eye tracker. The test images contained a wide range of artifact magnitudes, both locally and globally distributed, and were created using a wireless channel simulation model. We then correlate the visual gaze patterns of the human observers with local energy measures of the distortions in order to identify the effect of distortion distributions on the viewing behaviour of human observers when judging image quality. The outcomes serve to improve the prediction performance of objective image quality metrics that we previously proposed.

  • 99. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    Visual Attention Modelling for Subjective Image Quality Databases2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    The modelling of perceptual image quality metrics has experienced increased effort in recent years. In order to allow for model design, validation, and comparison, a number of subjective image quality databases has been made available to the research community. Most metrics that were designed using these databases assess the quality uniformly over the whole image, not taking into account stronger attention to salient regions of an image. In order to facilitate incorporation of visual attention (VA) into objective metric design we have conducted an eye tracking experiment. The experiment and its outcomes will be explained in detail in this paper. The actual gaze data recorded in the experiment is publicly available in order to facilitate and encourage VA modelling for image quality metrics.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 100. Engelke, Ulrich
    et al.
    Pepion, Romuald
    Callet, Patrick Le
    Zepernick, Hans-Jürgen
    Linking Distortion Perception and Visual Saliency in H.264/AVC Coded Video Containing Packet Loss2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, distortions caused by packet loss during video transmission are evaluated with respect to their perceived annoyance. In this respect, the impact of visual saliency on the level of annoyance is of particular interest, as regions and objects in a video frame are typically not of equal importance to the viewer. For this purpose, gaze patterns from a task free eye tracking experiment were utilised to identify salient regions in a number of videos. Packet loss was then introduced into the bit stream such as that the corresponding distortions appear either in a salient region or in a non-salient region. A subjective experiment was then conducted in which human observers rated the annoyance of the distortions in the videos. The outcomes show a strong tendency that distortions in a salient region are indeed perceived as much more annoying as compared to distortions in the non-salient region. The saliency of the distorted image content was further found to have a larger impact on the perceived annoyance as compared to the distortion duration. The findings of this work are considered to be of great use to improve prediction performance of video quality metrics in the context of transmission errors.

    Ladda ner fulltext (pdf)
    FULLTEXT01
12345 51 - 100 av 249
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf