logo EDITE Paul DE KERRET
Identité
Paul DE KERRET
État académique
Thèse soutenue le 2013-12-17
Sujet: Coopération distribuée dans les réseaux sans-fil avec interférences
Direction de thèse:
Laboratoire: personnel permanent
Encadrement de thèses (depuis 2007)
0.5
Voisinage
Ellipse bleue: doctorant, ellipse jaune: docteur, rectangle vert: permanent, rectangle jaune: HDR. Trait vert: encadrant de thèse, trait bleu: directeur de thèse, pointillé: jury d'évaluation à mi-parcours ou jury de thèse.
Productions scientifiques
oai:hal.archives-ouvertes.fr:hal-00807323
MIMO interference alignment algorithms with hierarchical CSIT
This work1 deals with interference alignment (IA) in a K-users MIMO interference channel with only incomplete Channel State Information at the Transmitters (CSIT). Incompleteness of CSIT is defined by the perfect knowledge of only a sub-matrix of the global channel matrix. Additionally, each Transmitter (TX) may have different incomplete CSIT. Most IA techniques are developed under a full (complete) CSIT assumption -either explicitly or implicitly when the CSI is progressively acquired in the form of RX-to-TX feedback iterations. In contrast, we are interested here in the feasibility of IA based only on incomplete CSIT. We show that even in antenna settings where no extra-antenna is available in terms of feasibility of IA, which we denote as tightly-feasible, IA can be achieved on some cases with some TXs having incomplete CSIT. Especially, for each antenna setting, we provide an incomplete CSIT sharing preserving feasibility and we adapt IA algorithms from the literature to achieve perfect IA under this condition of incomplete CSIT. We confirm by simulations that the proposed IA algorithm based on incomplete CSIT achieves no significant losses compared to the algorithm based on perfect CSIT sharing.
2012 International Symposium on Wireless Communication Systems (ISWCS) 2012 International Symposium on Wireless Communication Systems (ISWCS)conference proceeding 2013-08-28
oai:hal.archives-ouvertes.fr:hal-00807320
The asymptotic limits of interference in multicell networks with channel aware scheduling
Interference is emerging as a fundamental bottleneck in many important wireless communication scenarios, including dense cellular networks and cognitive networks with spectrum sharing by multiple service providers. Although multiple-antenna signal processing is known to offer useful degrees of freedom to cancel interference, extreme-value theoretic analysis recently showed that, even in the absence of multiple-antenna processing, the scaling law of the capacity in the number of users for a multi-cell network with and without inter-cell interference was asymptotically identical provided a simple signal to noise and interference ratio (SINR) maximizing scheduler is exploited. This suggests that scheduling can help reduce inter-cell interference substantially, thus possibly limiting the need for multiple-antenna processing. However, the convergence limits of interference after scheduling in a multi-cell setting are not yet identified. In this paper1 we analyze such limits theoretically. We consider channel statistics under Rayleigh fading with equal path loss for all users or with unequal path loss. We uncover two surprisingly different behaviors for such systems. For the equal path loss case, we show that scheduling alone can cause the residual interference to converge to zero for large number of users. With unequal path loss however, the interference power is shown to converge in average to a nonzero constant. Simulations back our findings.
2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2011 IEEE 12th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC),conference proceeding 2012-06-10
oai:hal.archives-ouvertes.fr:hal-00807318
Optimized data symbol allocation in multicell MIMO channels
In this work, we consider the joint precoding across K distant transmitters (TXs) towards K single-antenna receivers (RXs). In practical networks, cooperation between TXs is limited by the constraints on the backhaul network and the common approach to limit the backhaul overhead is to form small disjoint clusters of cooperating TXs. Yet, this limits the performance due to interference at the cluster edge. We overcome this problem by directly optimizing the allocation of the user's data symbol without clustering but solely subject to a constraint on the total number of symbols allocated. Since the problem of optimal data symbol allocation is of combinatorial nature, we use a greedy approach and develop greedy algorithms having low complexity while incuring only small losses compared to the optimal data symbol allocation. Moreover, the algorithms are shown to be Multiplexing Gain (MG) optimal in many settings. Simulations results confirm that our approach outperforms dynamic clustering methods from the literature.
2011 Conference Record of the Forty Fifth Asilomar Conference on Signals, Systems and Computers (ASILOMAR), 2011 Conference Record of the Forty Fifth Asilomar Conference on Signals, Systems and Computers (ASILOMAR),conference proceeding 2011-11-06
oai:hal.archives-ouvertes.fr:hal-00807312
A practical precoding scheme for multicell MIMO channels with partial user's data sharing
In this work, we consider the joint precoding across K distant transmitters (TXs) towards K single-antenna receivers (RXs) and we let the TXs have access to perfect Channel State Information (CSI). Instead of considering the conventional method of clustering to allocate the user's data symbols, we focus on determining the most efficient symbol sharing patterns. Consequently, we optimize directly the user's data symbol allocation subject to a constraint on the total number of user's data bits transmitted through the core network. We develop a novel approach whereby sparse precoders approximating the true precoders are computed. These precoders require only a fraction of the overall symbol sharing overhead while introducing only limited losses. Thereby, allocating the symbols only to their nonzero coefficients leads to very efficient symbol sharing (or routing) algorithms. Furthermore, these algorithms have a much lower complexity that conventional approaches. By simulations, we show that our approach outperforms clustering-based multicell MIMO methods from the literature and that the routing obtained is mainly dependent on the pathloss structure and can be applied using only long term CSI with reduced losses.
2012 IEEE Wireless Communications and Networking Conference Workshops (WCNCW) 2012 IEEE Wireless Communications and Networking Conference Workshops (WCNCW)conference proceeding 2012-04-01
oai:hal.archives-ouvertes.fr:hal-00807310
CSI feedback allocation in multicell MIMO channels
In this work1, we consider the joint precoding across K transmitters (TXs), sharing the knowledge of the user's data symbols being transmitted to K single-antenna receivers (RXs). We consider a distributed channel state information (DCSI) configuration where each TX has its own local estimate of the overall multiuser MIMO channel. Our focus is on the optimization of the allocation of the CSI feedback subject to a constraint on the total amount of feedback. As a starting point, we consider the Wyner model where we derive a distance-based CSI allocation achieving close to the optimal performance using only a small percentage of the total feedback. The approach relies on the exploitation of the attenuation to restrict the cooperation at a local scale. Indeed, the CSI and the user's data symbols are then shared to only a finite number of neighbors such that our approach appears as an improved alternative to clustering.
IEEE International Conference on Communications (ICC), 2012 IEEE International Conference on Communications (ICC), 2012conference proceeding 2012-06-10
oai:hal.archives-ouvertes.fr:hal-00807325
The multiplexing gain of a two-cell MIMO channel with unequal CSI
In this work, the joint precoding across two distant transmitters (TXs), sharing the knowledge of the data symbols to be transmitted, to two receivers (RXs), each equipped with one antenna, is discussed. We consider a distributed channel state information (CSI) configuration where each TX has its own local estimate of the channel and no communication is possible between the TXs. Based on the distributed CSI configuration, we introduce a concept of distributed MIMO precoding. We focus on the high signal-to-noise ratio (SNR) regime such that the two TXs aim at designing a precoding matrix to cancel the interference. Building on the study of the multiple antenna broadcast channel, we obtain the following key results: We derive the multiplexing gain (MG) as a function of the scaling in the SNR of the number of bits quantizing at each TX the channel to a given RX. Particularly, we show that the conventional Zero Forcing precoder is not MG maximizing, and we provide a precoding scheme optimal in terms of MG. Beyond the established MG optimality, simulations show that the proposed precoding schemes achieve better performances at intermediate SNR than known linear precoders.
2011 IEEE International Symposium on Information Theory Proceedings (ISIT) 2011 IEEE International Symposium on Information Theory Proceedings (ISIT)conference proceeding 2012-07-31
oai:hal.archives-ouvertes.fr:hal-00807327
Degrees of Freedom of the Network MIMO Channel With Distributed CSI
In this paper, we discuss the joint precoding with finite rate feedback in the so-called network multiple-input multiple-output (MIMO) where the TXs share the knowledge of the data symbols to be transmitted. We introduce a distributed channel state information (DCSI) model where each TX has its own local estimate of the overall multiuser MIMO channel and must make a precoding decision solely based on the available local CSI. We refer to this channel as the DCSI-MIMO channel and the precoding problem as distributed precoding. We extend to the DCSI setting the work from Jindal in 2006 for the conventional MIMO broadcast channel (BC) in which the number of degrees of freedom (DoFs) achieved by zero forcing (ZF) was derived as a function of the scaling in the logarithm of the signal-to-noise ratio of the number of quantizing bits. Particularly, we show the seemingly pessimistic result that the number of DoFs at each user is limited by the worst CSI across all users and across all TXs. This is in contrast to the conventional MIMO BC where the number of DoFs at one user is solely dependent on the quality of the estimation of his own feedback. Consequently, we provide precoding schemes improving on the achieved number of DoFs. For the two-user case, the derived novel precoder achieves a number of DoFs limited by the best CSI accuracy across the TXs instead of the worst with conventional ZF. We also advocate the use of hierarchical quantization of the CSI, for which we show that considerable gains are possible. Finally, we use the previous analysis to derive the DoFs optimal allocation of the feedback bits to the various TXs under a constraint on the size of the aggregate feedback in the network, in the case where conventional ZF is used.
IEEE Transactions on Information Theoryarticle in peer-reviewed journal 2012-11-01
oai:hal.archives-ouvertes.fr:hal-00807328
CSI sharing strategies for transmitter cooperation in wireless networks
Multiple-antenna "based" transmitter cooperation has been established as a promising tool toward avoiding, aligning, or shaping the interference resulting from aggressive spectral reuse. The price paid in the form of feedback and exchanging channel state information between cooperating devices in most existing methods is often underestimated, though. In reality, feedback and information overhead threatens the practicality and scalability of TX cooperation approaches in dense networks. Hereby we addresses a "Who needs to know what?" problem when it comes to CSI at cooperating transmitters. A comprehensive answer to this question remains beyond our reach and the scope of this article. Nevertheless, recent results in this area suggest that CSI overhead can be contained for even large networks provided the allocation of feedback to TXs is made non-uniform and to properly depend on the network's topology. This article provides a few hints toward solving the problem.
IEEE Wireless Communicationsarticle in peer-reviewed journal 2013-02-01
oai:hal.archives-ouvertes.fr:hal-00807307
Sparse precoding in multicell MIMO systems
In this work, we consider the joint precoding across K distant transmitters (TXs) towards K single-antenna receivers (RXs) and we let the TXs have access to perfect Channel State Information (CSI). Instead of considering the conventional method of clustering to allocate the user's data symbols, we focus on determining the most efficient symbol sharing patterns. Consequently, we optimize directly the user's data symbol allocation subject to a constraint on the total number of user's data bits transmitted through the core network. We develop a novel approach whereby sparse precoders approximating the true precoders are computed. These precoders require only a fraction of the overall symbol sharing overhead while introducing only limited losses. Thereby, allocating the symbols only to their nonzero coefficients leads to very efficient symbol sharing (or routing) algorithms. Furthermore, these algorithms have a much lower complexity that conventional approaches. By simulations, we show that our approach outperforms clustering-based multicell MIMO methods from the literature and that the routing obtained is mainly dependent on the pathloss structure and can be applied using only long term CSI with reduced losses.
Wireless Communications and Networking Conference (WCNC), 2012 IEEE Wireless Communications and Networking Conference (WCNC), 2012 IEEEconference proceeding 2012-04-01
oai:hal.archives-ouvertes.fr:hal-00868390
Rate loss analysis of transmitter cooperation with distributed CSIT
We consider in this work the problem of determining the number of feedback bits which should be used to quantize the channel state information (CSI) in a broadcast channel (BC) with K transmit antennas (or equivalently K single-antenna transmitters (TXs)) and K single-antenna receivers (RXs). We focus on an extension of the conventional centralized CSI at the TX (CSIT) model, where instead of having a single channel estimate, or quantized version, perfectly shared by all the TX antennas, each TX receives its own estimate of the global multiuser channel. This CSIT configuration, denoted as distributed CSIT, is particularly suited to model the joint transmission from TXs which are not colocated. With centralized CSIT, a very important design guideline for the feedback link was provided by Jindal [Trans. Inf. Theory 2006] by providing a sufficient feedback rate to ensure that the rate loss stays below a maximum value. In the distributed CSIT setting, additional errors occur and the design guidelines for the centralized case are no longer valid. Consequently, we obtain a new relation between the rate loss and the number of feedback bits. Interestingly, the feedback rate derived in the distributed CSIT setting is roughly K log2(K) bits larger than its counterpart in the centralized case. This highlights the critical impact of the CSIT distributedness over the performance.
Proc. IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2013conference proceeding 2013-06-17
oai:hal.archives-ouvertes.fr:hal-00868389
Degrees of freedom of certain interference alignment schemes with distributed CSI
Print Request Permissions Save to Project In this work, we consider the use of interference alignment (IA) in a MIMO interference channel (IC) under the assumption that each transmitter (TX) has access to channel state information (CSI) that generally differs from that available to other TXs. This setting is referred to as distributed CSIT. In a setting where CSI accuracy is controlled by a set of power exponents, we show that in the static 3-user MIMO square IC, the number of degrees-of-freedom (DoF) that can be achieved with distributed CSIT is at least equal to the DoF achieved with the worst accuracy taken across the TXs and across the interfering links. We conjecture further that this represents exactly the DoF achieved. This result is in strong contrast with the centralized CSIT configuration usually studied (where all the TXs share the same, possibly imperfect, channel estimate) for which it was shown that the DoF achieved at receiver (RX) i is solely limited by the quality of its own feedback. This shows the critical impact of CSI discrepancies between the TXs, and highlights the price paid by distributed precoding.
Proc. IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2013conference proceeding 2013-06-17
Soutenance
Thèse: Transmission coopérative dans les réseeaux sans-fil avec feedback distribué.
Soutenance: 2013-12-17