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See detailEdge-Caching Wireless Networks: Performance Analysis and Optimization
Vu, Thang Xuan UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2018)

Edge-caching has received much attention as an efficient technique to reduce delivery latency and network congestion during peak-traffic times by bringing data closer to end users. Existing works usually ... [more ▼]

Edge-caching has received much attention as an efficient technique to reduce delivery latency and network congestion during peak-traffic times by bringing data closer to end users. Existing works usually design caching algorithms separately from physical layer design. In this paper, we analyse edge-caching wireless networks by taking into account the caching capability when designing the signal transmission. Particularly, we investigate multi-layer caching where both base station (BS) and users are capable of storing content data in their local cache and analyse the performance of edge-caching wireless networks under two notable uncoded and coded caching strategies. Firstly, we calculate backhaul and access throughputs of the two caching strategies for arbitrary values of cache size. The required backhaul and access throughputs are derived as a function of the BS and user cache sizes. Secondly, closed-form expressions for the system energy efficiency (EE) corresponding to the two caching methods are derived. Based on the derived formulas, the system EE is maximized via precoding vectors design and optimization while satisfying a predefined user request rate. Thirdly, two optimization problems are proposed to minimize the content delivery time for the two caching strategies. Finally, numerical results are presented to verify the effectiveness of the two caching methods. [less ▲]

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See detailAnticipating Suspicious Actions using a Small Dataset of Action Templates
Baptista, Renato UL; Antunes, Michel; Aouada, Djamila UL et al

in 13th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISAPP) (2018, January)

In this paper, we propose to detect an action as soon as possible and ideally before it is fully completed. The objective is to support the monitoring of surveillance videos for preventing criminal or ... [more ▼]

In this paper, we propose to detect an action as soon as possible and ideally before it is fully completed. The objective is to support the monitoring of surveillance videos for preventing criminal or terrorist attacks. For such a scenario, it is of importance to have not only high detection and recognition rates but also low time latency for the detection. Our solution consists in an adaptive sliding window approach in an online manner, which efficiently rejects irrelevant data. Furthermore, we exploit both spatial and temporal information by constructing feature vectors based on temporal blocks. For an added efficiency, only partial template actions are considered for the detection. The relationship between the template size and latency is experimentally evaluated. We show promising preliminary experimental results using Motion Capture data with a skeleton representation of the human body. [less ▲]

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See detailFull 3D Reconstruction of Non-Rigidly Deforming Objects
Afzal, Hassan; Aouada, Djamila UL; Mirbach, Bruno et al

in ACM Transactions on Multimedia Computing, Communications, & Applications (2018)

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See detailDeformation Based 3D Facial Expression Representation
Demisse, Girum UL; Aouada, Djamila UL; Ottersten, Björn UL

in ACM Transactions on Multimedia Computing, Communications, & Applications (2018)

We propose a deformation based representation for analyzing expressions from 3D faces. A point cloud of a 3D face is decomposed into an ordered deformable set of curves that start from a fixed point ... [more ▼]

We propose a deformation based representation for analyzing expressions from 3D faces. A point cloud of a 3D face is decomposed into an ordered deformable set of curves that start from a fixed point. Subsequently, a mapping function is defined to identify the set of curves with an element of a high dimensional matrix Lie group, specifically the direct product of SE(3). Representing 3D faces as an element of a high dimensional Lie group has two main advantages. First, using the group structure, facial expressions can be decoupled from a neutral face. Second, an underlying non-linear facial expression manifold can be captured with the Lie group and mapped to a linear space, Lie algebra of the group. This opens up the possibility of classifying facial expressions with linear models without compromising the underlying manifold. Alternatively, linear combinations of linearised facial expressions can be mapped back from the Lie algebra to the Lie group. The approach is tested on the BU-3DFE and the Bosphorus datasets. The results show that the proposed approach performed comparably, on the BU-3DFE dataset, without using features or extensive landmark points. [less ▲]

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See detailCross-Layer Forward Packet Scheduling for Emerging Precoded Broadband Multibeam Satellite System
Lagunas, Eva UL; Andrenacci, Stefano UL; Chatzinotas, Symeon UL et al

in 9th Advanced Satellite Multimedia Systems Conference (ASMS) and 15th Signal Processing for Space Communications Workshop (SPSC), Berlin, Germany, 10-12 September 2018 (2018)

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See detailHybrid analog-digital transceiver designs for mmwave amplify-and-forward relaying systems
Tsinos, Christos UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in 2018 41st International Conference on Telecommunications and Signal Processing (TSP) (2018)

Hybrid Analog/Digital (A/D) pre-/post-coding solutions aim at the reduction of the hardware complexity and power consumption of a system employed with a large-scale antenna array functioning in the ... [more ▼]

Hybrid Analog/Digital (A/D) pre-/post-coding solutions aim at the reduction of the hardware complexity and power consumption of a system employed with a large-scale antenna array functioning in the millimeter (mmWave) band. This is achieved by enabling the transceiver design with fewer Radio Frequency (RF) chains than antennas. In this work, hybrid A/D transceiver designs are developed for a relay assisted mmWave system that aims at data transmission from a source to a destination node via the well-known amplify-and-forward cooperative protocol. To that end, hybrid solutions are proposed for the joint design of the source and relay nodes precoders and for the destination ones, as well. Contrariwise to existing literature approaches that develop codebook-based solutions and exhibit limitations on the performance, the proposed approaches are codebook-free and present significantly improved spectral efficiency, as it is verified via the presented simulations. [less ▲]

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See detailSequential spatio-temporal symbol-level precoding enabling faster-than-Nyquist signaling for multi-user MISO systems
Spano, Danilo UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in 2018 26th European Signal Processing Conference (EUSIPCO) (2018)

This paper addresses the problem of the interference between multiple co-channel transmissions in the downlink of a multi-antenna wireless system. In this context, symbol-level precoding achieves a ... [more ▼]

This paper addresses the problem of the interference between multiple co-channel transmissions in the downlink of a multi-antenna wireless system. In this context, symbol-level precoding achieves a constructive interference effect which results in SINR gains at the receivers side. Usually the constructive interference is exploited in the spatial dimension (multi-user interference), however in this work we consider a spatio-temporal precoding model which allows to exploit the interference also in the temporal dimension (inter-symbol interference). The proposed method, which optimizes the overs ampled transmit waveforms by minimizing the per-antenna transmit power, allows faster-than-Nyquist signaling over multi-user MISO systems without imposing additional complexity at the user terminals. The optimization is performed in a sequential fashion, by splitting the data streams in blocks and handling the inter-block interference. Numerical results are presented to assess the gains of the scheme in terms of effective rate and energy efficiency. [less ▲]

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See detailUser Selection for symbol-level multigroup multicasting precoding in the downlink of MISO channels
Alodeh, Maha UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in 2018 IEEE International Conference on Communications (ICC) (2018)

We consider the problem of user selection for symbol-level multigroup multicasting in the downlink of multiuser MISO systems. Symbol-level precoding is a new paradigm for multiuser multiple-antenna ... [more ▼]

We consider the problem of user selection for symbol-level multigroup multicasting in the downlink of multiuser MISO systems. Symbol-level precoding is a new paradigm for multiuser multiple-antenna downlink systems which aims at creating constructive interference among the simultaneous 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. This work proposes a user selection algorithm to facilitate serving multiple groups of users, by transmitting a stream of common symbols to each group on symbol-by-symbol basis if we have large number of users. We provide numerical results to validate the proposed algorithm. [less ▲]

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See detail2018 25th International Conference on Telecommunications (ICT)
Lagunas, Eva UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in 2018 25th International Conference on Telecommunications (ICT) (2018)

The anticipated exponential growth in network traffic is posing significant challenges for the implementation of 5G networks. In this context, a major problem is the backhaul network which acts as a ... [more ▼]

The anticipated exponential growth in network traffic is posing significant challenges for the implementation of 5G networks. In this context, a major problem is the backhaul network which acts as a bottleneck preventing the efficient flow of ultra-dense and heavy traffic between the end users and the core network. Spectrum scarcity has emerged as the primary problem encountered when trying to accommodate the traffic upsurge. In this paper, we investigate the carrier allocation problem in the context of Integrated Satellite-Terrestrial Backhaul (ISTB) networks. In particular, we consider the satellite component to be integrated with the conventional terrestrial wireless backhaul network thus providing evident benefits in terms of data-offloading. To enhance the overall spectral efficiency of the proposed network, we consider that both terrestrial and satellite segments operate in the Ka band, where the sharing between terrestrial microwave links and satellite communications is already allowed. A novel carrier allocation algorithm based on fairness is proposed, which ensures that all backhaul links are continuously active to satisfy the operator's coverage needs. The problem is NP-hard by definition. As a consequence, we present a two-step sequential carrier allocation strategy specifically tailored to tackle the interference issues emerging from the spectral co-existence. Supporting results based on numerical simulations show that the proposed carrier allocation can provide a 2x improvement in terms of spectral efficiency when compared to benchmark terrestrial-only backhaul networks. [less ▲]

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See detailSymbol-level precoding with low resolution DACs for large-scale array MU-MIMO systems
Tsinos, Christos UL; Kalantari, Ashkan UL; Chatzinotas, Symeon UL et al

in 2018 IEEE 19th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC) (2018)

While (Multiple Input-Multiple Output) MIMO systems based on large-scale antenna arrays are seen as the solution to the continuously increasing demands in modern wireless systems, they require high ... [more ▼]

While (Multiple Input-Multiple Output) MIMO systems based on large-scale antenna arrays are seen as the solution to the continuously increasing demands in modern wireless systems, they require high hardware complexity and power consumption. To tackle this, solutions based on low resolution Analog-to-Digital Converters (ADCs) / Digital-to-Analog Converters (DACs) have been developed in the literature where they mainly propose quantized versions of typical channel dependent linear precoding solutions. Alternatively, nonlinear Symbol level Precoding techniques have been recently proposed for downlink Multi User (MU)-MIMO systems with low resolution DACs that achieve significantly improved performance in several cases. The existing SLP approaches support only DACs of 1-bit resolution which result in significant performance degradations, especially when constellations with order greater than 4 are employed. To that end, in this work a novel SLP approach is developed that supports systems with DACs of any resolution and it is applicable for any type of constellation. As it is verified by the presented numerical results, the proposed approach exhibits significantly improved performance when constellations with order greater than 4 are employed and require reduced computational complexity, compared to the existing solutions for the 1-bit DAC case. [less ▲]

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See detailCache-aided Simultaneous Wireless Information and Power Transfer (SWIPT) with Relay Selection
Gautam, Sumit UL; Vu, Thang Xuan UL; Chatzinotas, Symeon UL et al

in IEEE Journal on Selected Areas In Communications (2018)

In this paper, we investigate the performance of cache-assisted simultaneous wireless information and power transfer (SWIPT) cooperative systems, in which one source communicates with one destination via ... [more ▼]

In this paper, we investigate the performance of cache-assisted simultaneous wireless information and power transfer (SWIPT) cooperative systems, in which one source communicates with one destination via the aid of multiple relays. In order to prolong the relays’ serving time, the relays are assumed to be equipped with a cache memory and energy harvesting (EH) capability. Based on the time-splitting mechanism, we analyze the effect of caching on the system performance in terms of the serving throughput and the stored energy at the relay. In particular, two optimization problems are formulated to maximize the relay-destination throughput and the energy stored at the relay subject to some quality-of-service (QoS) constraints, respectively. By using the KKT conditions and with the help of the Lambert function, closed-form solutions are obtained for the two formulated problems. In order to further improve the performance, a relay selection policy is introduced to select the best relay based on either the maximum throughput between the relays’ and destination link or maximum stored energy at the relay, for conveying information to the destination. Numerical results reveal significant benefits of incorporating caching capabilities to SWIPT systems, in terms of improved serving time, throughput and energy harvesting performance at the relays. [less ▲]

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See detailConstrained bayesian active learning of linear classifier
Tsakmalis, Anestis UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in 2018 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) (2018)

In this paper, an on-line interactive method is proposed for learning a linear classifier. This problem is studied within the Active Learning (AL) framework where the learning algorithm sequentially ... [more ▼]

In this paper, an on-line interactive method is proposed for learning a linear classifier. This problem is studied within the Active Learning (AL) framework where the learning algorithm sequentially chooses unlabelled training samples and requests their class labels from an oracle in order to learn the classifier with the least queries to the oracle possible. Additionally' a constraint is introduced into this interactive learning process which limits the percentage of the samples from one “unwanted” class under a certain threshold. An optimal AL solution is derived and implemented with a sophisticated, accurate and fast Bayesian Learning method, the Expectation Propagation (EP) and its performance is demonstrated through numerical simulations. [less ▲]

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See detailFaster-than-Nyquist Signaling through Spatio-temporal Symbol-level Precoding for the Multiuser MISO Downlink Channel
Spano, Danilo UL; Alodeh, Maha; Chatzinotas, Symeon UL et al

in IEEE Transactions on Wireless Communications (2018)

This paper deals with the problem of the interference between multiple co-channel transmissions in the downlink of a multi-antenna wireless system. In this framework, symbol-level precoding is a promising ... [more ▼]

This paper deals with the problem of the interference between multiple co-channel transmissions in the downlink of a multi-antenna wireless system. In this framework, symbol-level precoding is a promising technique which is able to constructively exploit the multi-user interference and to transform it into useful power at the receiver side. While previous works on symbol-level precoding were focused on exploiting the multi-user interference, in this paper we extend this concept by jointly handling the interference both in the spatial dimension (multi-user interference) and in the temporal dimension (inter-symbol interference). Accordingly, we propose a novel precoding method, referred to as spatio-temporal symbol-level precoding. In this new precoding paradigm, faster-than-Nyquist signaling can be applied over multi-user MISO systems, and the inter-symbol interference can be tackled at the transmitter side, without additional complexity for the user terminals. While applying faster-than-Nyquist signaling, the proposed optimization strategies perform a sum power minimization with Quality-of-Service constraints. Numerical results are presented in a comparative fashion to show the effectiveness of the proposed techniques, which outperform the state of the art symbol-level precoding schemes in terms of symbol error rate, effective rate, and energy efficiency. [less ▲]

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See detailA Revisit of Action Detection using Improved Trajectories
Papadopoulos, Konstantinos UL; Antunes, Michel; Aouada, Djamila UL et al

in IEEE International Conference on Acoustics, Speech and Signal Processing, Calgary, Alberta, Canada, 15–20 April 2018 (2018)

In this paper, we revisit trajectory-based action detection in a potent and non-uniform way. Improved trajectories have been proven to be an effective model for motion description in action recognition ... [more ▼]

In this paper, we revisit trajectory-based action detection in a potent and non-uniform way. Improved trajectories have been proven to be an effective model for motion description in action recognition. In temporal action localization, however, this approach is not efficiently exploited. Trajectory features extracted from uniform video segments result in significant performance degradation due to two reasons: (a) during uniform segmentation, a significant amount of noise is often added to the main action and (b) partial actions can have negative impact in classifier's performance. Since uniform video segmentation seems to be insufficient for this task, we propose a two-step supervised non-uniform segmentation, performed in an online manner. Action proposals are generated using either 2D or 3D data, therefore action classification can be directly performed on them using the standard improved trajectories approach. We experimentally compare our method with other approaches and we show improved performance on a challenging online action detection dataset. [less ▲]

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See detail2018 IEEE 23rd International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD)
Domouchtsidis, Stavros; Tsinos, Christos UL; Chatzinotas, Symeon UL et al

in 2018 IEEE 23rd International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD) (2018)

Large-Scale Antenna Array Systems may be used to serve multiple users in the same time-frequency resource block which results to harmful multi-user interference (MUI). In the literature precoding ... [more ▼]

Large-Scale Antenna Array Systems may be used to serve multiple users in the same time-frequency resource block which results to harmful multi-user interference (MUI). In the literature precoding techniques have been proposed as a way to mitigate the induced MUI, by designing the transmitted signals using the knowledge of the Channel State Information (CSI), in block-level precoding (BLP) or both the CSI and the information-bearing symbols, in symbol-level precoding (SLP). However, the proposed SLP techniques require fully digital baseband processing which is infeasible in large-scale antenna array systems because of the high cost and power consumption of radio frequency (RF) components. In order to reduce the number of y-RF chains, we address an Antenna Selection Symbol-Level Precoding (AS-SLP) scheme, which minimizes the MUI by activating only a subset of the available antennas. For this scheme we develop an efficient algorithm, based on Coordinate Descent. Simulations provide an insight on the efficiency of the proposed approach and its improvement with respect to the fully digitally approaches. [less ▲]

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See detailOFDM-based automotive joint radar-communication system
Dokhanchi, Sayed Hossein UL; Shankar, Bhavani UL; Stifter, Thomas et al

in 2018 IEEE Radar Conference (RadarConf18) (2018)

We propose a novel automotive joint radar-communication (JRC) system, where the system first transmits OFDM sub-carriers for radar processing followed by sub-carriers enabling radar and communication ... [more ▼]

We propose a novel automotive joint radar-communication (JRC) system, where the system first transmits OFDM sub-carriers for radar processing followed by sub-carriers enabling radar and communication functionalities. The receiver processing includes iterative estimation of parameters to alleviate the shortage of samples to estimate range. The receiver first estimates the target parameters from the sub-carriers dedicated to radar; these parameters then determine the channel for the communication link. The communication data is then extracted, thereby enabling the use of all the carriers for improving the range estimation. It is shown that the range estimation improves significantly after efficient use of all the sub-carriers. Furthermore, for radar parameter estimation, we propose an effective iterative method based on alternating least square (ALS) to recover the angle of arrival (AoA), Doppler and Range. Numerical results demonstrate the feasibility of our proposed system. [less ▲]

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See detailSDR Implementation of a Testbed for Real-Time Interference Detection with Signal Cancellation
Politis, Christos; Maleki, Sina UL; Merlano Duncan, Juan Carlos UL et al

in IEEE Access (2018)

Interference greatly affects the quality of service of wireless and satellite communications, having also a financial impact for the telecommunication operators. Therefore, as the interfering events ... [more ▼]

Interference greatly affects the quality of service of wireless and satellite communications, having also a financial impact for the telecommunication operators. Therefore, as the interfering events increase due to the deployment of new services, there is an increasing demand for the detection and mitigation of interference. There are several interference detectors in the literature, evaluated by using extensive simulations. However, this paper goes one step further, designing, implementing and evaluating the performance of the developed interference detection algorithms experimentally using a software defined radio, and particularly the universal software radio peripheral platform. A realistic communication system is implemented, consisting of a transmitter, a channel emulator and a receiver. Based on this system, we implement all the appropriate communications features such as pulse shaping, synchronization and demodulation. The real-time system implementation is validated and evaluated through signal and interference detection. We observe that the interference detection threshold is critical to the functioning of the system. Several existing interference detection techniques fail in practice due to this fact. In this paper, we propose a robust and practically implementable method the selection of threshold. Finally, we present real-time experimental results for the probabilities of false alarm and detection in order to verify the accuracy of our study and reinforce our theoretical analysis. [less ▲]

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See detailOn-Board Precoding in a Multiple Gateway Multibeam Satellite System
Joroughi, Vahid UL; Shankar, Bhavani UL; Maleki, Sina UL et al

in Proceedings of IEEE VTC Fall 2018 (2018)

This paper present On-Board Precoding (OBP) for a multiple gateway multibeam satellite system where full frequency reuse pattern is employed at both user and feeder links. By reducing the Channel State ... [more ▼]

This paper present On-Board Precoding (OBP) for a multiple gateway multibeam satellite system where full frequency reuse pattern is employed at both user and feeder links. By reducing the Channel State Information (CSI) roundtrip delay to half, OBP offers significant benefits in the emerging multiple gateway scenario in terms of lower gateways coordination. However, two critical issues need to be addressed: (a) interference in both user and feeder links is the bottleneck of the whole system and employing interference mitigation techniques is essential, (b) clear push towards non-adaptive (fixed) payload implementation, leading to low computationally complex satellite architectures. In order to fulfill requirements (a) and (b), this paper studies the impact of employing a fixed OBP technique at the payload which is sufficiently robust to the variations in both user and feeder link channels. In addition to (a) and (b), the provided simulation results depict the performance gain obtained by our proposed OBP with respect to the conventional interference mitigation techniques in multiple gateway multibeam systems. [less ▲]

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See detailLearning-based rainfall estimation via communication satellite links
Gharanjik, Ahmad UL; Mishra, Kumar Vijay; Shankar, Bhavani UL et al

in 2018 IEEE Statistical Signal Processing Workshop (SSP) (2018)

We present a method for estimating rainfall by opportunistic use of Ka-band satellite communication network. Our approach is based on the attenuation of the satellite link signal in the rain medium and ... [more ▼]

We present a method for estimating rainfall by opportunistic use of Ka-band satellite communication network. Our approach is based on the attenuation of the satellite link signal in the rain medium and exploits the nearly linear relation between the rain rate and the specific attenuation at Ka-band frequencies. Although our experimental setup is not intended to achieve high resolutions as millimeter wavelength weather radars, it is instructive because of easy availability of millions of satellite ground terminals throughout the world. The received signal is obtained over a passive link. Therefore, traditional weather radar signal processing to derive parameters for rainfall estimation algorithms is not feasible here. We overcome this disadvantage by employing neural network learning algorithms to extract relevant information. Initial results reveal that rainfall accumulations obtained through our method are 85% closer to the in situ rain gauge estimates than the nearest C-band German weather service Deutscher Wetterdienst (DWD) radar. [less ▲]

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