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See detailAsymptotic Analysis of Max-Min Weighted SINR for IRS-Assisted MISO Systems with Hardware Impairments
Papazafeiropoulo, Anastasios; Pan, Cunhua; Elbir, Ahmet et al

in IEEE Wireless Communications Letters (in press)

We focus on the realistic maximization of the up-link minimum-signal-to-interference-plus-noise ratio (SINR) of a general multiple-input-single-output (MISO) system assisted by an intelligent reflecting ... [more ▼]

We focus on the realistic maximization of the up-link minimum-signal-to-interference-plus-noise ratio (SINR) of a general multiple-input-single-output (MISO) system assisted by an intelligent reflecting surface (IRS) in the large system limit accounting for HIs. In particular, we introduce the HIs at both the IRS (IRS-HIs) and the transceiver HIs (AT-HIs), usually neglected despite their inevitable impact. Specifically, the deterministic equivalent analysis enables the derivation of the asymptotic weighted maximum-minimum SINR with HIs by jointly optimizing the HIs-aware receiver, the transmit power, and the reflect beamforming matrix (RBM). Notably, we obtain the optimal power allocation and reflect beamforming matrix with low overhead instead of their frequent necessary computation in conventional MIMO systems based on the instantaneous channel information. Monte Carlo simulations verify the analytical results which show the insightful interplay among the key parameters and the degradation of the performance due to HIs. [less ▲]

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See detailOptimal Detection of Multiple Symbol-Slotted Random Access based Packet Transmissions
Kisseleff, Steven UL; Gerstacker, Wolfgang H.

in IEEE Wireless Communications Letters (2021)

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See detailRobust Probabilistic-Constrained Optimization for IRS-Aided MISO Communication Systems
Le, Anh Tuan; Trinh, van Chien UL; Di Renzo, Marco

in IEEE Wireless Communications Letters (2020)

Taking into account imperfect channel state information, this letter formulates and solves a joint active/passive beamforming optimization problem in multiple-input single-output systems with the support ... [more ▼]

Taking into account imperfect channel state information, this letter formulates and solves a joint active/passive beamforming optimization problem in multiple-input single-output systems with the support of an intelligent reflecting surface. In particular, we introduce an optimization problem to minimize the total transmit power subject to maintaining the users' signal-to-interference-plus-noise-ratio coverage probability above a predefined target. Due to the presence of probabilistic constraints, the proposed optimization problem is non-convex. To circumvent this issue, we first recast the proposed problem in a convex form by adopting the Bernstein-type inequality, and we then introduce a converging alternating optimization approach to iteratively find the active/passive beamforming vectors. In particular, the transformed robust optimization problem can be effectively solved by using standard interior-point methods. Numerical results demonstrate the effectiveness of jointly optimizing the active/passive beamforming vectors. [less ▲]

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See detailResource Allocation for Energy Efficiency in OFDMA-Enabled WPCN
Nguyen, Tien-Tung; Pham, Quoc-Viet; Nguyen, van Dinh UL et al

in IEEE Wireless Communications Letters (2020), 9(12), 2049-2053

This letter considers a wireless powered communication network (WPCN), where an energy-constrained device directly uses harvested energy from a power transfer source to transmit independent signals to ... [more ▼]

This letter considers a wireless powered communication network (WPCN), where an energy-constrained device directly uses harvested energy from a power transfer source to transmit independent signals to multiple Internet of Things (IoT) users using orthogonal frequency division multiple access (OFDMA). Our goal is to maximize the system energy efficiency (EE) by jointly optimizing the duration of energy harvesting (EH), subcarrier and power allocation. The formulated problem is a mixed integer nonlinear programming (MINLP) problem due to the presence of binary assignment variables, and thus it is very challenging to solve it directly. By leveraging Dinkelbach method, a very efficient iterative algorithm with closed-form solutions in each iteration is developed, where its convergence is guaranteed. Numerical results show that the proposed algorithm obtains a fast convergence and outperforms baseline algorithms. Notably, they also reveal that the power source should transmit its maximum allowable power to obtain the optimal EE performance. [less ▲]

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See detailUnified Framework for Secrecy Characteristics with Mixture of Gaussian (MoG) Distribution
Kong, Long UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Wireless Communications Letters (2020)

The mixture of Gaussian (MoG) distribution was proposed to model the wireless channels by implementing the completely unsupervised expectation-maximization (EM) learning algorithm. With the high ... [more ▼]

The mixture of Gaussian (MoG) distribution was proposed to model the wireless channels by implementing the completely unsupervised expectation-maximization (EM) learning algorithm. With the high convenience for density estimation applications, the focus of this letter is supposed to investigate the secrecy metrics, including secrecy outage probability (SOP), the lower bound of SOP, the probability of non-zero secrecy capacity (PNZ), and the average secrecy capacity (ASC) from the information-theoretic perspective. The above-mentioned metrics are derived with simple and unified closed-form expressions. The effectiveness of our obtained analytical expressions are successfully examined and compared with Monte-Carlo simulations. One can conclude that this letter provides a simple but effective closed-form secrecy analysis solution exploiting the MoG distribution. [less ▲]

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See detailDeep Channel Learning For Large Intelligent Surfaces Aided mm-Wave Massive MIMO Systems
Elbir, Ahmet M.; Papazafeiropoulos, Anastasios; Kourtessis, Pandelis et al

in IEEE Wireless Communications Letters (2020), 9(Sept. 2020), 1447-1451

This letter presents the first work introducing a deep learning (DL) framework for channel estimation in large intelligent surface (LIS) assisted massive MIMO (multiple-input multiple-output) systems. A ... [more ▼]

This letter presents the first work introducing a deep learning (DL) framework for channel estimation in large intelligent surface (LIS) assisted massive MIMO (multiple-input multiple-output) systems. A twin convolutional neural network (CNN) architecture is designed and it is fed with the received pilot signals to estimate both direct and cascaded channels. In a multi-user scenario, each user has access to the CNN to estimate its own channel. The performance of the proposed DL approach is evaluated and compared with state-of-the-art DL-based techniques and its superior performance is demonstrated. [less ▲]

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See detailEnergy Minimization for Cache-Assisted Content Delivery Networks With Wireless Backhaul
Vu, Thang Xuan UL; Chatzinotas, Symeon UL; Ottersten, Björn UL et al

in IEEE Wireless Communications Letters (2018), 7(3), 332-335

Content caching is an efficient technique to reduce delivery latency and system congestion during peak-traffic time by bringing data closer to end users. In this letter, we investigate energy-efficiency ... [more ▼]

Content caching is an efficient technique to reduce delivery latency and system congestion during peak-traffic time by bringing data closer to end users. In this letter, we investigate energy-efficiency performance of cache-assisted content delivery networks with wireless backhaul by taking into account cache capability when designing the signal transmission. We consider multi-layer caching and the performance in cases when both base station and users are capable of storing content data in their local cache. Specifically, we analyze energy consumption in both backhaul and access links under two uncoded and coded caching strategies. Then two optimization problems are formulated to minimize total energy cost for the two caching strategies while satisfying some given quality of service constraint. We demonstrate via numerical results that the uncoded caching achieves higher energy efficiency than the coded caching in the small user cache size regime. [less ▲]

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See detailEnergy Minimization for Cache-assisted Content Delivery Networks with Wireless Backhaul
Vu, Thang Xuan UL; Chatzinotas, Symeon UL; Ottersten, Björn UL et al

in IEEE Wireless Communications Letters (2017)

Content caching is an efficient technique to reduce delivery latency and system congestion during peak-traffic time by bringing data closer to end users. In this paper, we investigate energy-efficiency ... [more ▼]

Content caching is an efficient technique to reduce delivery latency and system congestion during peak-traffic time by bringing data closer to end users. In this paper, we investigate energy-efficiency performance of cache-assisted content delivery networks with wireless backhaul by taking into account cache capability when designing the signal transmission. We consider multi-layer caching and the performance in cases when both base station (BS) and users are capable of storing content data in their local cache. Specifically, we analyse energy consumption in both backhaul and access links under two uncoded and coded caching strategies. Then two optimization problems are formulated to minimize total energy cost for the two caching strategies while satisfying some given quality of service constraint. We demonstrate via numerical results that the uncoded caching achieves higher energy efficiency than the coded caching in the small user cache size regime. [less ▲]

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See detailPrecoding in Multibeam Satellite Communications: Present and Future Challenges
Vazquez, MA; Perez-Neira, A; Christopoulos, D et al

in IEEE Wireless Communications Letters (2016), 23(6), 88-95

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See detailHow many bits should be reported in quantized cooperative spectrum sensing?
Nguyen-Thanh, Nhan; Ciblat, Philippe; Maleki, Sina UL et al

in IEEE Wireless Communications Letters (2015)

We introduce an algorithm for optimizing sensing parameters including the number of sensing samples and the number of reporting bits of a quantization-based cooperative spectrum sensing scheme in ... [more ▼]

We introduce an algorithm for optimizing sensing parameters including the number of sensing samples and the number of reporting bits of a quantization-based cooperative spectrum sensing scheme in cognitive radio networks. This is obtained by maximizing the network throughput subject to a target detection probability. With Rayleigh fading and energy detector, the proposed algorithm simultaneously optimizes the number of sensing samples at a local node, the number of bits for quantizing local sensing data and the global threshold at a fusion center. [less ▲]

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See detailCognitive Zone for Broadband Satellite Communication in 17.3-17.7 GHz Band
Maleki, Sina UL; Chatzinotas, Symeon UL; Krause, Jens et al

in IEEE Wireless Communications Letters (2015)

Deploying high throughput satellite systems in Ka band to accommodate the ever increasing demand for high data rates hits a spectrum barrier. Cognitive spectrum utilization of the allocated frequency ... [more ▼]

Deploying high throughput satellite systems in Ka band to accommodate the ever increasing demand for high data rates hits a spectrum barrier. Cognitive spectrum utilization of the allocated frequency bands to other services is a potential solution. Designing a cognitive zone around incumbent broadcasting satellite service (BSS) feeder links beyond which the cognitive fixed satellite service (FSS) terminals can freely utilize the same frequency band is considered in this paper. In addition, we show that there is a rain rate called rain wall, above which cognitive downlink communications becomes infeasible. [less ▲]

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See detailSuccessive Pilot Contamination Elimination in Multiantenna Multicell Networks
Vu, Thang Xuan UL; Vu, T. A.; Quek, Tony Q. S.

in IEEE Wireless Communications Letters (2014), 3(6), 617-620

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See detailMMSE Performance Analysis of Generalized Multibeam Satellite Channels
Christopoulos, Dimitrios UL; Arnau, Jesus; Chatzinotas, Symeon UL et al

in IEEE Wireless Communications Letters (2013), 17(7), 1332-1335

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See detailMaximizing Minimum Throughput Guarantees: The Small Violation Probability Region
Butt, Majid UL; Kapetanovic, Dzevdan UL; Ottersten, Björn UL

in IEEE Wireless Communications Letters (2013)

Providing minimum throughput guarantees is one of the goals for radio resource allocation schemes. It is difficult to provide these guarantees without defining violation probability due to limited power ... [more ▼]

Providing minimum throughput guarantees is one of the goals for radio resource allocation schemes. It is difficult to provide these guarantees without defining violation probability due to limited power budget and rapidly changing conditions of the wireless channel. For every practical scheduling scheme, there is a feasibility region defined by the minimum guaranteed throughput and the corresponding probability that the users fail to get the guaranteed throughput (violation probability). In this work, we focus on minimizing the violation probability specifically in the small probability region. We compare our results with major schedulers available in literature and show that our scheme outperforms them in the small violation probability region. [less ▲]

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See detailEnergy-Performance Trade-offs in Multiuser Scheduling: Large System Analysis
Butt, Majid UL

in IEEE Wireless Communications Letters (2012), 1(3), 217-220

This work addresses the problem of data scheduling over fading channels in a deadline (strict delay) constrained multiuser system where a certain amount of data loss can be tolerated. We propose a scheme ... [more ▼]

This work addresses the problem of data scheduling over fading channels in a deadline (strict delay) constrained multiuser system where a certain amount of data loss can be tolerated. We propose a scheme which schedules the users based on their instantaneous channel conditions and backlog of the packets stored in the buffer. The scheme is analyzed in large user limit. Numerical results demonstrate the energy-performance trade-offs and quantify the gain in energy efficiency for the proposed scheme. [less ▲]

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