4 research outputs found
Exploiting Interference Alignment in Multi-Cell Cooperative OFDMA Resource Allocation
This paper studies interference alignment (IA) based multi-cell cooperative
resource allocation for the downlink OFDMA with universal frequency reuse.
Unlike the traditional scheme that treats subcarriers as separate dimensions
for resource allocation, the IA technique is utilized to enable
frequency-domain precoding over parallel subcarriers. In this paper, the joint
optimization of frequency-domain precoding via IA, subcarrier user selection
and power allocation is investigated for a cooperative three-cell OFDMA system
to maximize the downlink throughput. Numerical results for a simplified
symmetric channel setup reveal that the IA-based scheme achieves notable
throughput gains over the traditional scheme only when the inter-cell
interference link has a comparable strength as the direct link, and the
receiver SNR is sufficiently large. Motivated by this observation, a practical
hybrid scheme is proposed for cellular systems with heterogenous channel
conditions, where the total spectrum is divided into two subbands, over which
the IAbased scheme and the traditional scheme are applied for resource
allocation to users located in the cell-intersection region and cellnon-
intersection region, respectively. It is shown that this hybrid resource
allocation scheme flexibly exploits the downlink IA gains for OFDMA-based
cellular systems.Comment: 5 pages, 5 figures, GC2011 conferenc
Fairness Evaluation in Cooperative Hybrid Cellular Systems
Many method has been applied previously to improve the fairness of a wireless communication system. In this paper, we propose using hybrid schemes, where more than one transmission scheme are used in one system, to achieve this objective. These schemes consist of cooperative transmission schemes, maximal ratio transmission and interference alignment, and non-cooperative schemes, orthogonal and non-orthogonal schemes used alongside and in combinations in the same system to improve the fairness. We provide different weight calculation methods to vary the output of the fairness problem. We show the solution of the radio resource allocation problem for the transmission schemes used. Finally, simulation results is provided to show fairness achieved, in terms of Jain's fairness index, by applying the hybrid schemes proposed and the different weight calculation methods at different inter-site distances
Cognitive Orthogonal Precoder for Two-tiered Networks Deployment
In this work, the problem of cross-tier interference in a two-tiered
(macro-cell and cognitive small-cells) network, under the complete spectrum
sharing paradigm, is studied. A new orthogonal precoder transmit scheme for the
small base stations, called multi-user Vandermonde-subspace frequency division
multiplexing (MU-VFDM), is proposed. MU-VFDM allows several cognitive small
base stations to coexist with legacy macro-cell receivers, by nulling the
small- to macro-cell cross-tier interference, without any cooperation between
the two tiers. This cleverly designed cascaded precoder structure, not only
cancels the cross-tier interference, but avoids the co-tier interference for
the small-cell network. The achievable sum-rate of the small-cell network,
satisfying the interference cancelation requirements, is evaluated for perfect
and imperfect channel state information at the transmitter. Simulation results
for the cascaded MU-VFDM precoder show a comparable performance to that of
state-of-the-art dirty paper coding technique, for the case of a dense cellular
layout. Finally, a comparison between MU-VFDM and a standard complete spectrum
separation strategy is proposed. Promising gains in terms of achievable
sum-rate are shown for the two-tiered network w.r.t. the traditional bandwidth
management approach.Comment: 11 pages, 9 figures, accepted and to appear in IEEE Journal on
Selected Areas in Communications: Cognitive Radio Series, 2013. Copyright
transferred to IEE
Downlink Cellular Interference Alignment
Cellular networks have been notoriously interference-limited systems in dense urban areas, where base stations are deployed in close proximity to one-another. Recently, a signal processing method called Interference Alignment has emerged, making use of the increasing signal dimensions available in the system through multiple-input multiple output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) technologies. In this report, we review the state of the art of interference alignment since its foundation, and we detail algorithms and baseline comparisons to make when applying interference alignment schemes to downlink cellular networks. We also propose a number of research directions of interest which are not yet answered in the current literature.Les réseaux cellulaires ont été l'exemple typique de réseaux dont les performances sont limités par les interférences, particulièrement dans les régions urbaines. Récemment, une nouvelle technique de traitement du signal appelée "alignement d'interférences" a été dévelopée, et permet d'utiliser les dimensions du signal reçu à travers les technologies MIMO (multiple input multiple output) et OFDM (orthogonal frequency division multiplexing) pour annuler tout ou partie de l'interférence reçue par les mobiles. Dans ce rapport, nous évaluons la littérature liée à l'alignement d'interférence et nous détaillons les algorithmes existants et leur application aux réseaux cellulaires en voie descendante. Nous proposons ensuite un ensemble de directions de recherche d'intérêt par rapport à l'état de l'art actuel