Papers by ANGELIKI ALEXIOU
Robust linear precoding to compensate for antenna correlation in orthogonal space-time block coded systems
Processing Workshop Proceedings, 2004 Sensor Array and Multichannel Signal
Abstract Antenna correlation has a critical impact on the performance of space-time block coded s... more Abstract Antenna correlation has a critical impact on the performance of space-time block coded systems. In this paper linear precoding, which combats the effects of antenna correlation, is applied to orthogonal space-time block coded systems with two transmit ...
Multi-cell Device-to-Device communication benefits in the presence of densification
2017 IEEE International Conference on Communications Workshops (ICC Workshops), 2017
Device-to-Device (D2D) communication is a promising way to improve spectral, energy and latency p... more Device-to-Device (D2D) communication is a promising way to improve spectral, energy and latency performance in future wireless networks. This paper focuses on the network-controlled approach considering that overlay D2D communications are enabled in a multi-cell system, where legacy users coexist with potential D2D pairs. Two of the most critical problems in the D2D concept, mode selection and user scheduling are jointly addressed. In particular, aiming at maximizing the total system uplink throughput, we present the joint optimization mode selection and scheduling problem in a multi-cell environment with intra-cell and cross-cell D2D communications enabled. Due to the non-linear and non-convex form of the initial problem, we employ a linearization method reformulating it as a 0–1 integer program. In a multi-cell environment, the interference and densification significantly affect the D2D communication gain, as well as the cross-cell D2D concept, which is usual ignored. System-level simulations are executed to evaluate the performance of the proposed scheme and examine the trends of total D2D communication benefit, consisting of direct and offloading gain, for various system parameters.
The road to 5G - visions and challenges
5G Wireless Technologies, 2017
The objective of this book is to present, elaborate and assess, with respect to the impact of cri... more The objective of this book is to present, elaborate and assess, with respect to the impact of critical parameters, the most promising system concepts, architectures, and technology enablers that are expected to play a differentiator's role in the realization and adoption of 5G. To this end, 10 promising advanced technology topics are investigated in the following corresponding book chapters (Chapters 2-11), each describing a 5G innovation that is expected to transform wireless design understanding. A new era is commencing, following “technology-driven,”“user-centric,”and “Everything-as-a-Service”eras: the era of “Connectivity-as-a-Utility.”More specifically, the book chapters are organized into three thematic entities.
Epilogue: wireless beyond 5G
5G Wireless Technologies, 2017
Assuming success, 5G will not just introduce a new way of thinking in wireless networks design an... more Assuming success, 5G will not just introduce a new way of thinking in wireless networks design and optimization, but a new era, where “Wireless Connectivity as a Utility”will completely transform the way people, things, and (any) application devices communicate, store, and process information. As speed (data rate), data volume, distance, agility (latency), security, and reliability become “non-issues,”“infinite”capacity, and unlimited connectivity initiate an ecosystem paradigm shift, according to which network infrastructure as a whole is always available, scalable, and functioning “in the background,”whereas wireless access is ubiquitous and technology agnostic (independent). This new utility-like Quality of Experience clearly shifts the center of gravity from the network (infrastructure) side toward the user end (network edge) and from radio and networking technologies to applications.
Effects of densification and randomness of infrastructure deployment in cellular networks
5G Wireless Technologies, 2017
This chapter examined the effects of densification and randomness of infrastructure in future cel... more This chapter examined the effects of densification and randomness of infrastructure in future cellular networks by employing analytical tools from stochastic geometry. Various operational scenarios were investigated, including uplink and downlink transmissions, multi-tier networks, and variable traffic load, as well as parameters and metrics of interest such as SIR, user rate, degrees of freedom, and multiple access schemes. It was shown that randomness of AP positions introduces an unavoidable but moderate performance degradation compared to a regular placement pattern. Surprisingly enough, densification of randomly placed infrastructure does not (statistically) degrade performance in terms of SIR or user rate, even under the worst case scenario where all nodes are transmitting. Taking into account inactive transmitters (due to having no associated receivers), densification results in performance improvements. Performance gains were explicitly quantified with simple closed-form expressions in most cases.
IEEE Vehicular Technology Magazine, 2009
Impact of Channel Estimation Errors on Various Spatial-Temporal Transmission Schemes
2007 16th IST Mobile and Wireless Communications Summit, 2007
Herein, we investigate the impact of channel estimation errors on different spatial-temporal tran... more Herein, we investigate the impact of channel estimation errors on different spatial-temporal transmission schemes. The channel estimation errors are modeled by an zero mean complex Gaussian matrix. We then study the error floors of several transmission schemes, namely the Alamouti scheme, spatial multiplexing (SM) and the hybrid scheme. Our study reveals that for small estimation error, the Alamouti scheme has lower error floor comparing to the SM, while for 4 transmit antennas, the hybrid scheme is more robust than the pure SM. Moreover, simulation results show that the hybrid scheme with antenna shuffling can lower the error floor even further.
Reconfigurability to antenna correlation: System level performance enhancements in HSDPA
2006 First European Conference on Antennas and Propagation, 2006
In this paper the system level performance of an HSDPA MIMO network, which combats the effects of... more In this paper the system level performance of an HSDPA MIMO network, which combats the effects of antenna correlation by applying novel reconfigurable techniques, is investigated. The impact of antenna correlation on adaptive array techniques has been thoroughly investigated and it has been shown that fading correlations reduce MIMO channel capacity and system performance. Nevertheless, considerable capacity and performance gains
Evolution of packet scheduling for Machine-Type communications over LTE: Algorithmic design and performance analysis
2012 IEEE Globecom Workshops, 2012
ABSTRACT Providing LTE connectivity to emerging Machine-to-Machine (M2M) applications imposes sev... more ABSTRACT Providing LTE connectivity to emerging Machine-to-Machine (M2M) applications imposes several challenges to the operation and optimization of current and future 3GPP mobile broadband standard releases. Scheduling in an efficient way M2M traffic over the existing LTE MAC infrastructure is decisive for the smooth evolution towards an M2M-enabled LTE system. The large number of connecting devices compared to classical LTE terminals, and their vastly diverse quality-of-service requirements, call for the design of new packet scheduling schemes tailored to the M2M paradigm. To this end, we propose low complexity and signaling scheduling policies which period-ically grant access to the M2M devices. In particular, we first propose an analytical model for predicting the QoS performance of M2M services when the fixed periodic scheduling algorithm is employed. Next we propose a modification to this scheme, which exploit queueing-dynamics and finally we examine QoS-differentiation issues when devices are grouped into clusters. Interesting performance-complexity trade-offs are exposed. The results of our study may aid the system designer in tuning and optimizing M2M traffic scheduling.
Hierarchical Quantization and its Application to Multiuser Eigenmode Transmissions for MIMO Broadcast Channels with Limited Feedback
2007 IEEE 18th International Symposium on Personal, Indoor and Mobile Radio Communications, 2007
... In [8] a Fourier codebook construction is proposed which gives good performance with line-of-... more ... In [8] a Fourier codebook construction is proposed which gives good performance with line-of-sight ... Each user shares knowledge of its codebooks with the transmitter, and feeds back the ... Finally, in Section C we give an algorithm for implementing the hierar-chical quantization ...
IET Networks, 2013
In many situations the performance of wireless communication systems decreases especially when th... more In many situations the performance of wireless communication systems decreases especially when they operate over multipath fading channels subject also to shadowing. In this sense, cluster-based networks have been introduced as an efficient solution, offering coverage extension and energy savings. In this paper, we investigate new clusterhead (CH) selection algorithms, where the nodes can select different CHs, according to the corresponding signal strength. Additionally, it is shown that if CHs are equipped with multiple antennas, the negative consequences of the fading/shadowing can be further reduced. The performance of this scheme is theoretically investigated over correlated Nakagami-m fading channels, which are also subject to shadow fading, modelled by the Gamma distribution. The derived statistical metrics are used to obtain numerical evaluated results for the outage and the average bit error probabilities. These results are complemented by computer simulated ones, which validate the accuracy of the proposed analysis.
Green AF Relaying under Error Performance Constraints
In this paper, analytical assessment of overlayinband device-to-device (D2D) communications is in... more In this paper, analytical assessment of overlayinband device-to-device (D2D) communications is investigated, under cellular-network-assisted (coordinated) scheduling. To this end, a simple scheduling scheme is assumed that takes into account only local (per cell) topological information of the D2D links. Stochastic geometry tools are utilized in order to obtain analytical expressions for the interferers density as well as the D2D link signal-to-interference-ratio distribution. The analytical results accuracy is validated by comparison with simulations. In addition, the analytical expressions are employed for efficiently optimizing the parameters of a cellular system with overlay D2D communications. It is shown that coordinated scheduling of D2D transmissions enhances system performance both in terms of average user rate as well as maximum allowable D2D link distance.
Network densification along with universal resources reuse is expected to play a key role in the ... more Network densification along with universal resources reuse is expected to play a key role in the realization of 5G radio access as an enabler for delivering most of the anticipated network capacity improvements. On the one hand, neither the expected additional spectrum allocation nor the forthcoming novel air-interface processing techniques will be sufficient for sustaining the anticipated exponentially-increasing mobile data traffic. On the other hand, enhanced ultra-dense infrastructure deployments are expected to provide remarkable capacity gains, regardless of the evolutionary or revolutionary approach followed towards 5G development. In this work, we thoroughly examine global network coordination as the main enabler for future 5G large dense small-cell deployments. We propose a powerful radio resources coordination framework through which interference management is handled network-wise and jointly over multiple dimensions. In particular, we explore strategies for pairing serving and served access nodes, partitioning the available network resources, as well as dynamically allocating power per pair, towards optimizing system performance and guaranteeing individual minimum performance levels. We develop new optimization formulations, providing network scaling performance upper bounds, along with lower complexity algorithmic solutions tailored to large networks. We apply the proposed solutions to dense network deployments, in order to obtain useful insights on network performance and optimization, such as rate scaling, infrastructure density, optimal bandwidth partitioning and spatial reuse factor optimization.
Evaluating performance of a multiple-input multiple output (MIMO) communications link
Mobile telecommunications network with improved downlink capacity
VTC Spring 2009 - IEEE 69th Vehicular Technology Conference, 2009
In this paper we propose a two-step distributed scheduling algorithm for relay-assisted cellular ... more In this paper we propose a two-step distributed scheduling algorithm for relay-assisted cellular networks where a given user can be either served by the base station or by a relay, in a opportunistic way. Such a distributed approach allows a reduced feedback signaling with respect to the centralized case, especially when a simple scalar feedback is not sufficient for estimating the channel quality. As a result of the reduced feedback signaling requirements the system becomes more scalable, as new relays can be deployed where required without need of a careful network planning. We study the effectiveness of the proposal by means of a multicell simulator.
New Air-interface Technologies and Deployment Concepts
... to have a significant impact on the efficient use of the spectrum, the minimization of the ..... more ... to have a significant impact on the efficient use of the spectrum, the minimization of the ... Thisapproach, called zero-padding [15] requires slightly more com-plex equalization, but has the ... power to each subcarrier, according to its channel gain or Signal-to-Interference and Noise ...
A new antenna shuffling method for hybrid transmission scheme
IET Seminar Digests, 2007
ABSTRACT Herein, we propose a new method on antenna shuffling for hybrid transmission scheme base... more ABSTRACT Herein, we propose a new method on antenna shuffling for hybrid transmission scheme based on capacity metric. The capacity is calculated using the effective channel matrix, and the antenna shuffling pattern associated with the largest capacity is selected. Simulation results show that comparing to the conventional hybrid transmission scheme without antenna shuffling, the system performance is improved with higher capacity and lower BER. Furthermore, when small channel estimation errors exist at the receive side, hybrid scheme with the proposed antenna shuffling achieves lower error floor at high SNR region.
Wireless Personal Communications, 2007
Enormous research, standardization and development efforts continue to be allocated in all areas ... more Enormous research, standardization and development efforts continue to be allocated in all areas related to wireless communications. These efforts result to a powerful, high-speed infrastructure that offers several wireless/mobile connectivity solutions to the digital information society. Currently, the wireless landscape includes several Radio Access Technologies (RATs), e.g., 2.5G/3G/4G mobile infrastructures, the suite of IEEE 802 wireless technologies, Digital Audio/Video Broadcasting (DAB/DVB). Moreover, significant research effort is dedicated to the elaboration of the era of wireless communications, Beyond the 3rd Generation (B3G), in which the available RATs will form an heterogeneous infrastructure that will have to exist in an environment also characterized by the advance of the Internet, the need for broadband everywhere, the convergence of digital industries, the advance of e-commerce, deregulation and globalization, and above all the fact that services and applications are key: the end user is interested in services and applications, and should be served and managed in a way that the underlying infrastructure complexity is abstracted. Moreover, future systems should be sufficiently flexible to match the unpredictable operator and user expectations from a service and economic perspective. In response to the characteristics above, future wireless systems shall respond to versatile requirements, such as the fact that users shall be in control through intuitive interactions with applications, services, and devices. Those services and applications will be personalized, ambient-aware, and adaptive, provided ubiquitously from the user viewpoint. In addition, machines (autonomously communicating devices) shall operate irrespective of place and network, and with agreed quality-of-service (QoS). Those issues allow users, application developers, service and content providers, network operators, and manufactures to efficiently and flexibly create new services and business models based on the component-based architecture of the wireless world. In the light of the aspects above, the goal of this special issue is to present advances in various research areas related to the B3G wireless world, relevant applications, services, and infrastructure technologies. In this respect, a great variety of interesting issues are tackled,
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Papers by ANGELIKI ALEXIOU