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AuthorAlouini, Mohamed-Slim (2)Wonka, Peter (2)Al Farhan, Mohammed (1)Al-Naffouri, Tareq Y. (1)Alqerm, Ismail (1)View MoreDepartmentComputer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division (8)Computer Science Program (3)Electrical Engineering Program (3)Visual Computing Center (VCC) (2)Advanced Semiconductor Laboratory (1)View MoreJournalACM Transactions on Graphics (TOG) (1)IEEE Access (1)IEEE Transactions on Mobile Computing (1)IEEE Transactions on Parallel and Distributed Systems (1)IEEE Transactions on Pattern Analysis and Machine Intelligence (1)View MorePublisherInstitute of Electrical and Electronics Engineers (IEEE) (7)Association for Computing Machinery (ACM) (1)Subject

Optimization (8)

Decoding (2)Energy efficiency (2)Quality of service (2)Wireless communication (2)View MoreTypeArticle (8)Year (Issue Date)
2018 (8)

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Open Access (8)

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Delay Reduction in Multi-Hop Device-to-Device Communication using Network Coding

Douik, Ahmed; Sorour, Sameh; Al-Naffouri, Tareq Y.; Yang, Hong Chuan; Alouini, Mohamed-Slim (IEEE Transactions on Wireless Communications, Institute of Electrical and Electronics Engineers (IEEE), 2018-08-22) [Article]

This paper considers the problem of reducing the broadcast decoding delay of wireless networks using instantly decodable network coding (IDNC) based device-to-device (D2D) communications. In contrast with previous works that assume a fully connected network, this paper investigates a partially connected configuration in which multiple devices are allowed to transmit simultaneously. To that end, the different events occurring at each device are identified so as to derive an expression for the probability distribution of the decoding delay. Afterward, the joint optimization problem over the set of transmitting devices and packet combination of each is formulated. The optimal solution of the joint optimization problem is derived using a graph theoretic approach by introducing the cooperation graph in which each vertex represents a transmitting device with a weight translating its contribution to the network. The paper solves the problem by reformulating it as a maximum weight clique problem which can efficiently be solved. Numerical results suggest that the proposed solution outperforms state-of-the-art schemes and provides significant gain, especially for poorly connected networks.

Space-time Tomography for Continuously Deforming Objects

Zang, Guangming; Idoughi, Ramzi; Tao, Ran; Lubineau, Gilles; Wonka, Peter; Heidrich, Wolfgang (ACM Transactions on Graphics (TOG), Association for Computing Machinery (ACM), 2018-07-31) [Article]

X-ray computed tomography (CT) is a valuable tool for analyzing objects with interesting internal structure or complex geometries that are not accessible with optical means. Unfortunately, tomographic reconstruction of complex shapes requires a multitude (often hundreds or thousands) of projections from different viewpoints. Such a large number of projections can only be acquired in a time-sequential fashion. This significantly limits the ability to use x-ray tomography for either objects that undergo uncontrolled shape change at the time scale of a scan, or else for analyzing dynamic phenomena, where the motion itself is under investigation.
In this work, we present a non-parametric space-time tomographic method for tackling such dynamic settings. Through a combination of a new CT image acquisition strategy, a space-time tomographic image formation model, and an alternating, multi-scale solver, we achieve a general approach that can be used to analyze a wide range of dynamic phenomena. We demonstrate our method with extensive experiments on both real and simulated data.

Exploiting Smallest Error to Calibrate Non-linearity in SAR ADCs

Fan, Hua; Li, Jingtao; Feng, Quanyuan; Diao, Xiaopeng; Lin, Lishuang; Zhang, Kelin; Sun, Haiding; Heidari, Hadi (IEEE Access, Institute of Electrical and Electronics Engineers (IEEE), 2018-07-03) [Article]

This paper presents a statistics-optimised organisation technique to achieve better element matching in Successive Approximation Register (SAR) Analog-to-Digital Converter (ADC) in smart sensor systems. We demonstrate the proposed technique ability to achieve a significant improvement of around 23 dB on Spurious Free Dynamic Range (SFDR) of the ADC than the conventional, testing with a capacitor mismatch σu = 0.2% in a 14 bit SAR ADC system. For the static performance, the max root mean square (rms) value of differential nonlinearity (DNL) reduces from 1.63 to 0.20 LSB and the max rms value of integral nonlinearity (INL) reduces from 2.10 to 0.21 LSB. In addition, it is demonstrated that by applying grouping optimisation and strategy optimisation, the performance boosting on SFDR can be effectively achieved. Such great improvement on the resolution of the ADC only requires an off-line pre-processing digital part.

lp-Box ADMM: A Versatile Framework for Integer Programming

Wu, Baoyuan; Ghanem, Bernard (IEEE Transactions on Pattern Analysis and Machine Intelligence, Institute of Electrical and Electronics Engineers (IEEE), 2018-06-11) [Article]

This paper revisits the integer programming (IP) problem, which plays a fundamental role in many computer vision and machine learning applications. The literature abounds with many seminal works that address this problem, some focusing on continuous approaches (e.g., linear program relaxation), while others on discrete ones (e.g., min-cut). However, since many of these methods are designed to solve specific IP forms, they cannot adequately satisfy the simultaneous requirements of accuracy, feasibility, and scalability. To this end, we propose a novel and versatile framework called <formula><tex>$l_p$</tex></formula>-box ADMM, which is based on two main ideas. (1) The discrete constraint is equivalently replaced by the intersection of a box and an <formula><tex>$l_p$</tex></formula>-norm sphere. (2) We infuse this equivalence into the ADMM (Alternating Direction Method of Multipliers) framework to handle the continuous constraints separately and to harness its attractive properties. More importantly, the ADMM update steps can lead to manageable sub-problems in the continuous domain. To demonstrate its efficacy, we apply it to an optimization form that occurs often in computer vision and machine learning, namely binary quadratic programming (BQP). In this case, the ADMM steps are simple, computationally efficient. Moreover, we present the theoretic analysis about the global convergence of the <formula><tex>$l_p$</tex></formula>-box ADMM through adding a perturbation with the sufficiently small factor <formula><tex>$\epsilon$</tex></formula> to the original IP problem. Specifically, the globally converged solution generated by <formula><tex>$l_p$</tex></formula>-box ADMM for the perturbed IP problem will be close to the stationary and feasible point of the original IP problem within <formula><tex>$O(\epsilon)$</tex></formula>. We demonstrate the applicability of <formula><tex>$l_p$</tex></formula>-box ADMM on three important applications: MRF energy minimization, graph matching, and clustering. Results clearly show that it significantly outperforms existing generic IP solvers both in runtime and objective. It also achieves very competitive performance to state-of-the-art methods designed specifically for these applications

Isotropic Surface Remeshing without Large and Small Angles

Wang, Yiqun; Yan, Dong-Ming; Liu, Xiaohan; Tang, Chengcheng; Guo, Jianwei; Zhang, Xiaopeng; Wonka, Peter (IEEE Transactions on Visualization and Computer Graphics, Institute of Electrical and Electronics Engineers (IEEE), 2018-05-18) [Article]

We introduce a novel algorithm for isotropic surface remeshing which progressively eliminates obtuse triangles and improves small angles. The main novelty of the proposed approach is a simple vertex insertion scheme that facilitates the removal of large angles, and a vertex removal operation that improves the distribution of small angles. In combination with other standard local mesh operators, e.g., connectivity optimization and local tangential smoothing, our algorithm is able to remesh efficiently a low-quality mesh surface. Our approach can be applied directly or used as a post-processing step following other remeshing approaches. Our method has a similar computational efficiency to the fastest approach available, i.e., real-time adaptive remeshing [1]. In comparison with state-of-the-art approaches, our method consistently generates better results based on evaluations using different metrics.

Optimizations of Unstructured Aerodynamics Computations for Many-core Architectures

Al Farhan, Mohammed; Keyes, David E. (IEEE Transactions on Parallel and Distributed Systems, Institute of Electrical and Electronics Engineers (IEEE), 2018-04-13) [Article]

We investigate several state-of-the-practice shared-memory optimization techniques applied to key routines of an unstructured computational aerodynamics application with irregular memory accesses. We illustrate for the Intel KNL processor, as a representative of the processors in contemporary leading supercomputers, identifying and addressing performance challenges without compromising the floating point numerics of the original code. We employ low and high-level architecture-specific code optimizations involving thread and data-level parallelism. Our approach is based upon a multi-level hierarchical distribution of work and data across both the threads and the SIMD units within every hardware core. On a 64-core KNL chip, we achieve nearly 2.9x speedup of the dominant routines relative to the baseline. These exhibit almost linear strong scalability up to 64 threads, and thereafter some improvement with hyperthreading. At substantially fewer Watts, we achieve up to 1.7x speedup relative to the performance of 72 threads of a 36-core Haswell CPU and roughly equivalent performance to 112 threads of a 56-core Skylake scalable processor. These optimizations are expected to be of value for many other unstructured mesh PDE-based scientific applications as multi and many-core architecture evolves.

Energy-Efficient Optimization for HARQ Schemes over Time-Correlated Fading Channels

Shi, Zheng; Ma, Shaodan; Yang, Guanghua; Alouini, Mohamed-Slim (IEEE Transactions on Vehicular Technology, Institute of Electrical and Electronics Engineers (IEEE), 2018-03-19) [Article]

Energy efficiency of three common hybrid automatic repeat request (HARQ) schemes including Type I HARQ, HARQ with chase combining (HARQ-CC) and HARQ with incremental redundancy (HARQ-IR), is analyzed and joint power allocation and rate selection to maximize the energy efficiency is investigated in this paper. Unlike prior literature, time-correlated fading channels is considered and two widely concerned quality of service (QoS) constraints, i.e., outage and goodput constraints, are also considered in the optimization, which further differentiates this work from prior ones. Using a unified expression of asymptotic outage probabilities, optimal transmission powers and optimal rate are derived in closed-forms to maximize the energy efficiency while satisfying the QoS constraints. These closed-form solutions then enable a thorough analysis of the maximal energy efficiencies of various HARQ schemes. It is revealed that with low outage constraint, the maximal energy efficiency achieved by Type I HARQ is <formula><tex>$\frac{1}{4\ln2}$</tex></formula> bits/J, while HARQ-CC and HARQ-IR can achieve the same maximal energy efficiency as <formula><tex>$\frac{\kappa_\infty}{4\ln2}$</tex></formula> bits/J where <formula><tex>$\kappa_\infty = 1.6617$</tex></formula>. Moreover, time correlation in the fading channels has a negative impact on the energy efficiency, while large maximal allowable number of transmissions is favorable for the improvement of energy efficiency. The effectiveness of the energy-efficient optimization is verified by extensive simulations and the results also show that HARQ-CC can achieve the best tradeoff between energy efficiency and spectral efficiency among the three HARQ schemes.

Sophisticated Online Learning Scheme for Green Resource Allocation in 5G Heterogeneous Cloud Radio Access Networks

Alqerm, Ismail; Shihada, Basem (IEEE Transactions on Mobile Computing, Institute of Electrical and Electronics Engineers (IEEE), 2018-01-23) [Article]

5G is the upcoming evolution for the current cellular networks that aims at satisfying the future demand for data services. Heterogeneous cloud radio access networks (H-CRANs) are envisioned as a new trend of 5G that exploits the advantages of heterogeneous and cloud radio access networks to enhance spectral and energy efficiency. Remote radio heads (RRHs) are small cells utilized to provide high data rates for users with high quality of service (QoS) requirements, while high power macro base station (BS) is deployed for coverage maintenance and low QoS users service. Inter-tier interference between macro BSs and RRHs and energy efficiency are critical challenges that accompany resource allocation in H-CRANs. Therefore, we propose an efficient resource allocation scheme using online learning, which mitigates interference and maximizes energy efficiency while maintaining QoS requirements for all users. The resource allocation includes resource blocks (RBs) and power. The proposed scheme is implemented using two approaches: centralized, where the resource allocation is processed at a controller integrated with the baseband processing unit and decentralized, where macro BSs cooperate to achieve optimal resource allocation strategy. To foster the performance of such sophisticated scheme with a model free learning, we consider users' priority in RB allocation and compact state representation learning methodology to improve the speed of convergence and account for the curse of dimensionality during the learning process. The proposed scheme including both approaches is implemented using software defined radios testbed. The obtained results and simulation results confirm that the proposed resource allocation solution in H-CRANs increases the energy efficiency significantly and maintains users' QoS.

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