![]() Arora, Aakash ![]() ![]() ![]() in Proc. 7th IEEE Global Conference on Signal and Information Processing (GlobalSIP) 2019 (2019) Beamforming with large-scale antenna arrays (LSAA) is one of the predominant operations in designing wireless communication systems. However, the implementation of a fully digital system significantly ... [more ▼] Beamforming with large-scale antenna arrays (LSAA) is one of the predominant operations in designing wireless communication systems. However, the implementation of a fully digital system significantly increases the number of required radio-frequency (RF) chains, which may be prohibitive. Thus, analog beamforming based on a phase-shifting network driven by a variable gain amplifier (VGA) is a potential alternative technology. In this paper, we cast the beamforming vector design problem as a beampattern matching problem, with an unknown power gain. This is formulated as a unit-modulus least-squares (ULS) problem where the optimal gain of the VGA is also designed in addition to the beamforming vector. We also consider a scenario where the receivers have the additional processing capability to adjust the phases of the incoming signals to mitigate specular multipath components. We propose efficient majorization-minimization (MM) based algorithms with convergence guarantees to a stationary point for solving both variants of the proposed ULS problem. Numerical results verify the effectiveness of the proposed solution in comparison with the existing state-of-the-art techniques. [less ▲] Detailed reference viewed: 337 (59 UL)![]() Arora, Aakash ![]() ![]() ![]() in Proc. 37th International Communications Satellite Systems Conference (ICSSC'19) (2019) The work investigates the feasibility of massive MIMO in SatCom. Towards this, the necessary channel models, system parameters and scenarios are identified and a basic simulator developed. The work then ... [more ▼] The work investigates the feasibility of massive MIMO in SatCom. Towards this, the necessary channel models, system parameters and scenarios are identified and a basic simulator developed. The work then considers an efficient implementation of the massive MIMO transmission through the use of hybrid analog/digital precoder. Efficient algorithmic solutions are proposed for the partially connected precoder architecture which enables efficiency in power/ hardware complexity and its performance evaluated. [less ▲] Detailed reference viewed: 184 (42 UL)![]() Domouchtsidis, Stavros ![]() ![]() ![]() in IEEE Transactions on Wireless Communications (2019) In this paper, we consider three transmitter designs for symbol-level-precoding (SLP), a technique that mitigates multiuser interference (MUI) in multiuser systems by designing the transmitted signals ... [more ▼] In this paper, we consider three transmitter designs for symbol-level-precoding (SLP), a technique that mitigates multiuser interference (MUI) in multiuser systems by designing the transmitted signals using the channel state information and the information-bearing symbols. The considered systems tackle the high hardware complexity and power consumption of existing SLP techniques by reducing or completely eliminating fully digital radio frequency (RF) chains. The first proposed architecture referred to as, Antenna Selection SLP, minimizes the MUI by activating a subset of the available antennas and thus, reducing the number of required RF chains to the number of active antennas. In the other two architectures, which we refer to as RF domain SLP, the processing happens entirely in the RF domain, thus eliminating the need for multiple fully digital RF chains altogether. Instead, the analog phase shifters directly modulate the signals on the transmit antennas. The precoding design for all the considered cases is formulated as a constrained least squares problem and efficient algorithmic solutions are developed via the Coordinate Descent method. Simulations provide insights into the power efficiency of the proposed schemes and the improvements over the fully digital counterparts. [less ▲] Detailed reference viewed: 44 (1 UL)![]() Arora, Aakash ![]() ![]() ![]() in Proc. 2019 IEEE Global Communications Conference (GLOBECOM) (2019) In a mmWave multiple-input multiple-output (MIMO) communication system employing a large-scale antenna array (LSAA), the hybrid transceivers are used to reduce the power consumption and the hardware cost ... [more ▼] In a mmWave multiple-input multiple-output (MIMO) communication system employing a large-scale antenna array (LSAA), the hybrid transceivers are used to reduce the power consumption and the hardware cost. In a hybrid analog-digital (A/D) transceiver, the pre/post-processing operation splits into a lower-dimensional baseband (BB) pre/postcoder, followed by a network of analog phase shifters. Primarily two kinds of hybrid architectures are proposed in the literature to implement hybrid transceivers namely, the fully-connected and the partially-connected. Implementation of fully-connected architecture has higher hardware complexity, cost and power consumption in comparison with partially-connected. In this paper, we focus on partially-connected hybrid architecture and develop a low-complexity algorithm for transceiver design for a single user point-to-point mmWave MIMO system. The proposed algorithm utilizes the variable elimination (projection) and the minorization-maximization (MM) frameworks and has convergence guarantees to a stationary point. Simulation results demonstrate that the proposed algorithm is easily scalable for LSAA systems and achieves significantly improved performance in terms of the spectral efficiency (SE) of the system compared to the state-of-the-art solution. [less ▲] Detailed reference viewed: 141 (32 UL)![]() ; Tsinos, Christos ![]() ![]() in IEEE Transactions on Wireless Communications (2018) In this paper we consider three transmitter designs for symbol-level-precoding (SLP), a technique that mitigates multiuser interference (MUI) in multiuser systems by designing the transmitted signals ... [more ▼] In this paper we consider three transmitter designs for symbol-level-precoding (SLP), a technique that mitigates multiuser interference (MUI) in multiuser systems by designing the transmitted signals using the Channel State Information and the information-bearing symbols. The considered systems tackle the high hardware complexity and power consumption of existing SLP techniques by reducing or completely eliminating fully digital Radio Frequency (RF) chains. The first proposed architecture referred as, Antenna Selection SLP, minimizes the MUI by activating a subset of the available antennas and thus, reducing the number of required RF chains to the number of active antennas. In the other two architectures, which we refer to as RF domain SLP, the processing happens entirely in the RF domain, thus eliminating the need for multiple fully digital RF chains altogether. Instead, analog phase shifters directly modulate the signals on the transmit antennas. The precoding design for all the considered cases is formulated as a constrained least squares problem and efficient algorithmic solutions are developed via the Coordinate Descent method. Simulations provide insights on the power efficiency of the proposed schemes and the improvements over the fully digital counterparts. [less ▲] Detailed reference viewed: 143 (19 UL)![]() ; Spano, Danilo ![]() in IEEE Communications Surveys and Tutorials (2018) Precoding has been conventionally considered as an effective means of mitigating or exploiting the interference in the multiantenna downlink channel, where multiple users are simultaneously served with ... [more ▼] Precoding has been conventionally considered as an effective means of mitigating or exploiting the interference in the multiantenna downlink channel, where multiple users are simultaneously served with independent information over the same channel resources. The early works in this area were focused on transmitting an individual information stream to each user by constructing weighted linear combinations of symbol blocks (codewords). However, more recent works have moved beyond this traditional view by: i) transmitting distinct data streams to groups of users and ii) applying precoding on a symbol-per-symbol basis. In this context, the current survey presents a unified view and classification of precoding techniques with respect to two main axes: i) the switching rate of the precoding weights, leading to the classes of block-level and symbol-level precoding, ii) the number of users that each stream is addressed to, hence unicast, multicast, and broadcast precoding. Furthermore, the classified techniques are compared through representative numerical results to demonstrate their relative performance and uncover fundamental insights. Finally, a list of open theoretical problems and practical challenges are presented to inspire further research in this area. [less ▲] Detailed reference viewed: 232 (23 UL)![]() Tsinos, Christos ![]() ![]() ![]() 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 ▲] Detailed reference viewed: 129 (2 UL)![]() Tsinos, Christos ![]() ![]() ![]() 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 ▲] Detailed reference viewed: 142 (8 UL)![]() ; Tsinos, Christos ![]() ![]() 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 ▲] Detailed reference viewed: 128 (1 UL)![]() Tsinos, Christos ![]() ![]() in IEEE Signal Processing Letters (2018) Detailed reference viewed: 175 (10 UL)![]() ; ; et al in European Conference on Networks and Communications (EuCNC), June 2017 (2017, June) Detailed reference viewed: 183 (10 UL)![]() Lagunas, Eva ![]() ![]() ![]() in ICC Workshop on Satellite Communications: Challenges and Integration in the 5G ecosystem, Paris, France, May 2017 (2017, May) Detailed reference viewed: 258 (23 UL)![]() Politis, Christos ![]() ![]() ![]() in The 42nd IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP 2017 (2017) Interference is identified as a critical issue for satellite communication (SATCOM) systems and services. There is a growing concern in the satellite industry to manage and mitigate interference ... [more ▼] Interference is identified as a critical issue for satellite communication (SATCOM) systems and services. There is a growing concern in the satellite industry to manage and mitigate interference efficiently. While there are efficient techniques to monitor strong interference in SATCOM, weak interference is not so easily detected because of its low interference to signal and noise ratio (ISNR). To address this issue, this paper proposes and develops a technique which takes place on-board the satellite by decoding the desired signal, removing it from the total received signal and applying an Energy Detector (ED) in the remaining signal for the detection of interference. Different from the existing literature, this paper considers imperfect signal cancellation, examining how the decoding errors affect the sensing performance, derives the expressions for the probability of false alarm and provides a set of simulations results, verifying the efficiency of the technique. [less ▲] Detailed reference viewed: 356 (39 UL)![]() Politis, Christos ![]() ![]() ![]() in IEEE Transactions on Wireless Communications (2017) In conventional cognitive radio systems, the secondary user employs a “listen-before-talk” paradigm, where it senses if the primary user is active or idle, before it decides to access the licensed ... [more ▼] In conventional cognitive radio systems, the secondary user employs a “listen-before-talk” paradigm, where it senses if the primary user is active or idle, before it decides to access the licensed spectrum. However, this method faces challenges with the most important being the reduction of the secondary user’s throughput, as no data transmission takes place during the sensing period. In this context, the idea of simultaneous spectrum sensing and data transmission is proposed. The present work studies a system model where this concept is obtained through the collaboration of the secondary transmitter with the secondary receiver. First, the secondary receiver decodes the signal from the secondary transmitter, subsequently, removes it from the total received signal and then, carries out spectrum sensing in the remaining signal in order to decide about the presence/absence of the primary user. Different from the existing literature, this paper takes into account the imperfect signal cancellation, evaluating how the decoding errors affect the sensing reliability and derives the analytical expressions for the probability of false alarm. Finally, numerical results are presented illustrating the accuracy of the proposed analysis. [less ▲] Detailed reference viewed: 298 (31 UL)![]() ; ; et al in International Journal of Satellite Communications and Networking (2017) SANSA (Shared Access terrestrial-satellite backhaul Network enabled by Smart Antennas) is a project funded by the EU under the H2020 program. The main aim of SANSA is to boost the performance of mobile ... [more ▼] SANSA (Shared Access terrestrial-satellite backhaul Network enabled by Smart Antennas) is a project funded by the EU under the H2020 program. The main aim of SANSA is to boost the performance of mobile wireless backhaul networks in terms of capacity, energy efficiency and resilience against link failure or congestion while easing the deployment in both rural and urban areas and assuring at the same time an efficient use of the spectrum. This paper provides an overview and the first results of the project and, more specifically, it describes the regulatory environment, the State of The Art of mobile backhauling technologies regarding Ka band, the scenarios, the use cases, and the KPIs along with the SANSA architecture, network (NET), and physical (PHY) layer techniques used to enhance wireless backhauling capabilities. [less ▲] Detailed reference viewed: 381 (40 UL)![]() Kalantari, Ashkan ![]() ![]() ![]() in MIMO directional modulation M-QAM precoding for transceivers performance enhancement. (2017) Detailed reference viewed: 161 (1 UL)![]() Kalantari, Ashkan ![]() ![]() ![]() in Spatial peak power minimization for relaxed phase M-PSK MIMO directional modulation transmitter (2017) Detailed reference viewed: 121 (0 UL)![]() Tsinos, Christos ![]() ![]() ![]() in IEEE Journal on Selected Areas In Communications (2017) Hybrid Analog-Digital transceivers are employed with the view to reduce the hardware complexity and the energy consumption in millimeter wave/large antenna array systems by reducing the number of their ... [more ▼] Hybrid Analog-Digital transceivers are employed with the view to reduce the hardware complexity and the energy consumption in millimeter wave/large antenna array systems by reducing the number of their Radio Frequency (RF) chains. However, the analog processing network requires power for its operation and it further introduces power losses, dependent on the number of the transceiver antennas and RF chains, that have to be compensated. Thus, the reduction in the power consumption is usually much less than it is expected and given that the hybrid solutions present in general inferior spectral efficiency than a fully digital one, it is possible for the former to be less energy efficient than the latter in several cases. Existing approaches propose hybrid solutions that maximize the spectral efficiency of the system without providing any insight on their energy requirements/efficiency. To that end, in this paper, a novel algorithmic framework is developed based on which energy efficient hybrid transceiver designs are derived and their performance is examined with respect to the number of RF chains and antennas. Solutions are proposed for fully and partially connected hybrid architectures and for both single- and multi-carrier systems under the Orthogonal Frequency Division Multiplexing (OFDM) modulation. Simulations and theoretical results provide insight on the cases where a hybrid transceiver is the most energy efficient solution or not. [less ▲] Detailed reference viewed: 332 (31 UL)![]() ![]() ; Lagunas, Eva ![]() ![]() in Access, Fronthaul and Backhaul Networks for 5G and Beyond (2017) Detailed reference viewed: 162 (3 UL)![]() Tsinos, Christos ![]() ![]() ![]() in On the energy-efficiency of hybrid analog-digital transceivers for large antenna array systems (2017) Detailed reference viewed: 149 (2 UL) |
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