3,400 research outputs found
Adaptive Multicell 3D Beamforming in Multi-Antenna Cellular Networks
We consider a cellular network with multi-antenna base stations (BSs) and
single-antenna users, multicell cooperation, imperfect channel state
information, and directional antennas each with a vertically adjustable beam.
We investigate the impact of the elevation angle of the BS antenna pattern,
denoted as tilt, on the performance of the considered network when employing
either a conventional single-cell transmission or a fully cooperative multicell
transmission. Using the results of this investigation, we propose a novel
hybrid multicell cooperation technique in which the intercell interference is
controlled via either cooperative beamforming in the horizontal plane or
coordinated beamfroming in the vertical plane of the wireless channel, denoted
as adaptive multicell 3D beamforming. The main idea is to divide the coverage
area into two disjoint vertical regions and adapt the multicell cooperation
strategy at the BSs when serving each region. A fair scheduler is used to share
the time-slots between the vertical regions. It is shown that the proposed
technique can achieve performance comparable to that of a fully cooperative
transmission but with a significantly lower complexity and signaling
requirements. To make the performance analysis computationally efficient,
analytical expressions for the user ergodic rates under different beamforming
strategies are also derived.Comment: Accepted for publication in IEEE Transaction on Vehicular Technolog
Resource Allocation for Next Generation Radio Access Networks
Driven by data hungry applications, the architecture of mobile networks is
moving towards that of densely deployed cells where each cell may use a different
access technology as well as a different frequency band. Next generation
networks (NGNs) are essentially identified by their dramatically increased data
rates and their sustainable deployment. Motivated by these requirements, in
this thesis we focus on (i) capacity maximisation, (ii) energy efficient configuration
of different classes of radio access networks (RANs). To fairly allocate
the available resources, we consider proportional fair rate allocations. We
first consider capacity maximisation in co-channel 4G (LTE) networks, then
we proceed to capacity maximisation in mixed LTE (including licensed LTE
small cells) and 802.11 (WiFi) networks. And finally we study energy efficient
capacity maximisation of dense 3G/4G co-channel small cell networks.
In each chapter we provide a network model and a scalable resource allocation
approach which may be implemented in a centralised or distributed manner
depending on the objective and network constraints
A survey of self organisation in future cellular networks
This article surveys the literature over the period of the last decade on the emerging field of self organisation as applied to wireless cellular communication networks. Self organisation has been extensively studied and applied in adhoc networks, wireless sensor networks and autonomic computer networks; however in the context of wireless cellular networks, this is the first attempt to put in perspective the various efforts in form of a tutorial/survey. We provide a comprehensive survey of the existing literature, projects and standards in self organising cellular networks. Additionally, we also aim to present a clear understanding of this active research area, identifying a clear taxonomy and guidelines for design of self organising mechanisms. We compare strength and weakness of existing solutions and highlight the key research areas for further development. This paper serves as a guide and a starting point for anyone willing to delve into research on self organisation in wireless cellular communication networks
Large-Scale MIMO versus Network MIMO for Multicell Interference Mitigation
This paper compares two important downlink multicell interference mitigation
techniques, namely, large-scale (LS) multiple-input multiple-output (MIMO) and
network MIMO. We consider a cooperative wireless cellular system operating in
time-division duplex (TDD) mode, wherein each cooperating cluster includes
base-stations (BSs), each equipped with multiple antennas and scheduling
single-antenna users. In an LS-MIMO system, each BS employs antennas not
only to serve its scheduled users, but also to null out interference caused to
the other users within the cooperating cluster using zero-forcing (ZF)
beamforming. In a network MIMO system, each BS is equipped with only
antennas, but interference cancellation is realized by data and channel state
information exchange over the backhaul links and joint downlink transmission
using ZF beamforming. Both systems are able to completely eliminate
intra-cluster interference and to provide the same number of spatial degrees of
freedom per user. Assuming the uplink-downlink channel reciprocity provided by
TDD, both systems are subject to identical channel acquisition overhead during
the uplink pilot transmission stage. Further, the available sum power at each
cluster is fixed and assumed to be equally distributed across the downlink
beams in both systems. Building upon the channel distribution functions and
using tools from stochastic ordering, this paper shows, however, that from a
performance point of view, users experience better quality of service, averaged
over small-scale fading, under an LS-MIMO system than a network MIMO system.
Numerical simulations for a multicell network reveal that this conclusion also
holds true with regularized ZF beamforming scheme. Hence, given the likely
lower cost of adding excess number of antennas at each BS, LS-MIMO could be the
preferred route toward interference mitigation in cellular networks.Comment: 13 pages, 7 figures; IEEE Journal of Selected Topics in Signal
Processing, Special Issue on Signal Processing for Large-Scale MIMO
Communication
Assessing 3GPP LTE-Advanced as IMT-Advanced Technology: The WINNER+ Evaluation Group Approach
[EN] This article describes the WINNER+ approach to performance evaluation of the 3GPP LTE-Advanced proposal as an IMT-Advanced technology candidate. The official registered WINNER+ Independent Evaluation Group evaluated this proposal against ITU-R requirements. The first part of the article gives an overview of the ITU-R evaluation process, criteria, and scenarios. The second part is focused on the working method of the evaluation group, emphasizing the simulator calibration approach. Finally, the article contains exemplary evaluation results based on analytical and simulation approaches. The obtained results allow WINNER+ to confirm that the 3GPP LTE Release 10 & Beyond (LTE-Advanced) proposal satisfies all the IMT-Advanced requirements, and thus qualifies as an IMT-advanced system.This work has been performed in the framework of the CELTIC project CP5-026 WINNER+. The authors would like to acknowledge the contributions of their colleagues in the WINNER+ consortium. The authors wish to thank colleagues from Ericsson, Per Skillermark and Johnan Nystrom, for their effort in leading the simulations part of the WINNER+ evaluation group. The work of David Martin-Sacristan was supported by an FPU grant of the Spanish Ministry of Education.Safjan, K.; D'amico, V.; Bültmann, D.; MartÃn-Sacristán, D.; Saadani, A.; Schöneich, H. (2011). Assessing 3GPP LTE-Advanced as IMT-Advanced Technology: The WINNER+ Evaluation Group Approach. IEEE Communications Magazine. 49(2):92-100. doi:10.1109/MCOM.2011.5706316S9210049
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