| 1. |
- Ahlberg, Jörgen, 1971-, et al.
(författare)
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Representing and Compressing MPEG-4 Facial Animation Parameters using Facial Action Basis Functions
- 1999
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Ingår i: IEEE Transactions on Circuits and Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 0098-4094 .- 1558-1276 .- 1051-8215. ; 9:3, s. 405-410
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Tidskriftsartikel (refereegranskat)abstract
- In model-based, or semantic, coding, parameters describing the nonrigid motion of objects, e.g., the mimics of a face, are of crucial interest. The facial animation parameters (FAPs) specified in MPEG-4 compose a very rich set of such parameters, allowing a wide range of facial motion. However, the FAPs are typically correlated and also constrained in their motion due to the physiology of the human face. We seek here to utilize this spatial correlation to achieve efficient compression. As it does not introduce any interframe delay, the method is suitable for interactive applications, e.g., videophone and interactive video, where low delay is a vital issue.
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| 2. |
- Kjellström, Gregor, et al.
(författare)
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Stochastic optimization in system design
- 1981
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Ingår i: IEEE Transactions on Circuits and Systems. - : IEEE. - 0098-4094 .- 1558-1276. ; 28:7, s. 702-715
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear optimization problem and statistical design problem can both be formulated as a region search problem. In this paper, we present a stochastic optimization process, suitable for optimizing functions of a certain measure over generalized regions in R". Conditions for an optimal process are discussed, and examples of a wide range of different optimization problems are given. These include the optimization of constrained, discontinuous and random functions in both discrete and continuous variable space. Design centering and tolerancing of large size system subject to environmental disturbances are also treated.
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| 3. |
- Taxén, Lars, et al.
(författare)
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Discrete optimization of digital filters using Gaussian adaptation and quadratic function minimization
- 1987
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Ingår i: IEEE Transactions on Circuits and Systems. - : IEEE. - 0098-4094 .- 1558-1276. ; 34:10, s. 1238-1242
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a new strategy for discrete optimization of a function F(x) is presented. Let A be the region in the n-dimensional parameter space, where F{x) is less than some constant. First, A is located and characterized by a Gaussian search process, called Gaussian adaptation. This makes it possible to approximate the behavior of F(x) over A by a quadratic function Q(x). Q(x) is then optimized for the N best discrete solutions using a branch and bound technique. Finally, these points are evaluated for the best F(x) points. By various digital filter examples it win be demonstrated that the new method is more e capable of finding good solutions than methods presented so far
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| 4. |
- A. Mouris, Boules, et al.
(författare)
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Multi-tone Signal Optimization for Wireless Power Transfer in the Presence of Wireless Communication Links
- 2020
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Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1536-1276 .- 1558-2248. ; 19:5, s. 3575-3590
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study optimization of multi-tone signals for wireless power transfer (WPT) systems. We investigate different non-linear energy harvesting models. Two of them are adopted to optimize the multi-tone signal according to the channel state information available at the transmitter. We show that a second-order polynomial curve-fitting model can be utilized to optimize the multi-tone signal for any RF energy harvester design. We consider both single-antenna and multi-antenna WPT systems. In-band co-existing communication links are also considered in this work by imposing a constraint on the received power at the nearby information receiver to prevent its RF front end from saturation. We emphasize the importance of imposing such constraint by explaining how inter-modulation products, due to saturation, can cause high interference at the information receiver in the case of multi-tone signals. The multi-tone optimization problem is formulated as a non-convex linearly constrained quadratic program. Two globally optimal solution approaches using mixed-integer linear programming and finite branch-and-bound techniques are proposed to solve the problem. The achieved improvement resulting from applying both solution methods to the multi-tone optimization problem is highlighted through simulations and comparisons with other solutions existing in the literature.
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| 5. |
- Abu-Shaban, Z., et al.
(författare)
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Error Bounds for Uplink and Downlink 3D Localization in 5G Millimeter Wave Systems
- 2018
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Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 17:8, s. 4939-4954
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Tidskriftsartikel (refereegranskat)abstract
- Location-aware communication systems are expected to play a pivotal part in the next generation of mobile communication networks. Therefore, there is a need to understand the localization limits in these networks, particularly, using millimeter-wave technology (mm-wave). Towards that, we address the uplink and downlink localization limits in terms of 3D position and orientation error bounds for mm-wave multipath channels. We also carry out a detailed analysis of the dependence of the bounds on different system parameters. Our key findings indicate that the uplink and downlink behave differently in two distinct ways. First of all, the error bounds have different scaling factors with respect to the number of antennas in the uplink and downlink. Secondly, uplink localization is sensitive to the orientation angle of the user equipment (UE), whereas downlink is not. Moreover, in the considered outdoor scenarios, the non-line-of-sight paths generally improve localization when a line-of-sight path exists. Finally, our numerical results show that mm-wave systems are capable of localizing a UE with sub-meter position error, and sub-degree orientation error.
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| 6. |
- Alabbasi, Abdulrahman, et al.
(författare)
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Optimal Cross-Layer Design for Energy Efficient D2D Sharing Systems
- 2017
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE Press. - 1536-1276 .- 1558-2248. ; 16:2, s. 839-855
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we propose a cross-layer design, which optimizes the energy efficiency of a potential future 5G spectrum-sharing environment, in two sharing scenarios. In the first scenario, underlying sharing is considered. We propose and minimize a modified energy per good bit (MEPG) metric, with respect to the spectrum sharing user's transmission power and media access frame length. The cellular users, legacy users, are protected by an outage probability constraint. To optimize the non-convex targeted problem, we utilize the generalized convexity theory and verify the problem's strictly pseudoconvex structure. We also derive analytical expressions of the optimal resources. In the second scenario, we minimize a generalized MEPG function while considering a probabilistic activity of cellular users and its impact on the MEPG performance of the spectrum sharing users. Finally, we derive the associated optimal resource allocation of this problem. Selected numerical results show the improvement of the proposed system compared with other systems.
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| 7. |
- Alodeh, M., et al.
(författare)
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Energy-Efficient Symbol-Level Precoding in Multiuser MISO Based on Relaxed Detection Region
- 2016
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 15:5, s. 3755-3767
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the problem of exploiting interference among simultaneous multiuser transmissions in the downlink of multiple-antenna systems. Using symbol-level precoding, a new approach toward addressing the multiuser interference is discussed through jointly utilizing the channel state information (CSI) and data information (DI). The interference among the data streams is transformed under certain conditions to a useful signal that can improve the signal-to-interference noise ratio (SINR) of the downlink transmissions and as a result the system's energy efficiency. In this context, new constructive interference precoding techniques that tackle the transmit power minimization (min power) with individual SINR constraints at each user's receiver have been proposed. In this paper, we generalize the constructive interference (CI) precoding design under the assumption that the received MPSK symbol can reside in a relaxed region in order to be correctly detected. Moreover, a weighted maximization of the minimum SNR among all users is studied taking into account the relaxed detection region. Symbol error rate analysis (SER) for the proposed precoding is discussed to characterize the tradeoff between transmit power reduction and SER increase due to the relaxation. Based on this tradeoff, the energy efficiency performance of the proposed technique is analyzed. Finally, extensive numerical results show that the proposed schemes outperform other state-of-the-art techniques.
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| 8. |
- Alodeh, M., et al.
(författare)
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Symbol-Level Multiuser MISO Precoding for Multi-Level Adaptive Modulation
- 2017
-
Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 16:8, s. 5511-5524
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Tidskriftsartikel (refereegranskat)abstract
- Symbol-level precoding is a new paradigm for multiuser multiple-antenna downlink systems aimed at creating constructive interference among transmitted data streams. This can be enabled by designing the precoded signal of the multiantenna transmitter on a symbol level, taking into account both channel state information and data symbols. Previous literature has studied this paradigm for Mary phase shift keying modulations by addressing various performance metrics, such as power minimization and maximization of the minimum rate. In this paper, we extend this to generic multi-level modulations, i.e., Mary quadrature amplitude modulation by establishing connection to PHY layer multicasting with phase constraints. Furthermore, we address the adaptive modulation schemes which are crucial in enabling the throughput scaling of symbol-level precoded systems. In this direction, we design the signal processing algorithms for minimizing the required power under per-user signal to interference noise ratio or goodput constraints. Extensive numerical results show that the proposed algorithm provides considerable power and energy efficiency gains, while adapting the employed modulation scheme to match the requested data rate.
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| 9. |
- Amarasuriya, Gayan, et al.
(författare)
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Wireless Information and Power Transfer in Multiway Massive MIMO Relay Networks
- 2016
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1276 .- 1558-2248. ; 15:6, s. 3837-3855
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous wireless information and power transfer techniques for multiway massive multiple-input multiple-output (MIMO) relay networks are investigated. By using two practically viable relay receiver designs, namely 1) the power splitting receiver and 2) the time switching receiver, asymptotic signal-to-interference-plus-noise ratio (SINR) expressions are derived for an unlimited number of antennas at the relay. These asymptotic SINRs are then used to derive asymptotic symmetric sum rate expressions in closed form. Notably, these asymptotic SINRs and sum rates become independent of radio frequency-to-direct current (RF-to-DC) conversion efficiency in the limit of infinitely many relay antennas. Moreover, tight average sum rate approximations are derived in closed form for finitely many relay antennas. The fundamental tradeoff between the harvested energy and the sum rate is quantified for both relay receiver structures. Notably, the detrimental impact of imperfect channel state information (CSI) on the MIMO detector/precoder is investigated, and thereby, the performance degradation caused by pilot contamination, which is the residual interference due to nonorthogonal pilot sequence usage in adjacent/cochannel systems, is quantified. The presence of cochannel interference (CCI) can be exploited to be beneficial for energy harvesting at the relay, and consequently, the asymptotic harvested energy is an increasing function of the number of cochannel interferers. Notably, in the genie-aided perfect CSI case, the detrimental impact of CCI for signal decoding can be cancelled completely whenever the number of relay antennas grows without bound. Nevertheless, the pilot contamination severely degrades the sum rate performance even for infinitely many relay antennas.
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| 10. |
- Antonioli, Roberto Pinto, et al.
(författare)
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On the Energy Efficiency of Cell-Free Systems With Limited Fronthauls : Is Coherent Transmission Always the Best Alternative?
- 2022
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Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1536-1276 .- 1558-2248. ; 21:10, s. 8729-8743
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Tidskriftsartikel (refereegranskat)abstract
- Existing works concluded that coherent transmission outperforms non-coherent transmission in the downlink of cell-free systems when the fronthaul links have unlimited capacity. Since the capacity of the fronthaul links of cell-free networks is typically limited, in this paper we ask the question whether this conclusion holds under more realistic assumptions on the fronthaul capacity. To answer this question, we study and compare the performance of these transmission strategies by formulating novel energy efficiency (EE) maximization problems for both strategies, where we explicitly consider realistic fronthaul capacity and power consumption constraints. Despite the non-convexity of these problems, we derive closed-form equations to find suboptimal solutions of both problems using a unified framework that combines successive convex approximation and the Dinkelbach algorithm. Numerical results show that the performance of coherent transmission is severely impacted by limited fronthaul capacities, power consumption on the fronthaul links, user-centric cluster size and the number of antennas at the access points, such that in many cases non-coherent transmission achieves higher EE than coherent transmission. Based on these results, we provide deployment guidelines on when to use coherent or non-coherent transmission to maximize the EE of cell-free systems with limited fronthauls.
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