72 research outputs found
Fundamental Limits in MIMO Broadcast Channels
This paper studies the fundamental limits of MIMO broadcast channels from a high level, determining the sum-rate capacity of the system as a function of system paramaters, such as the number of transmit antennas, the number of users, the number of receive antennas, and the total transmit power. The crucial role of channel state information at the transmitter is emphasized, as well as the emergence of opportunistic transmission schemes. The effects of channel estimation errors, training, and spatial correlation are studied, as well as issues related to fairness, delay and differentiated rate scheduling
Multiuser Random Beamforming in Millimetre-Waves Channels
This thesis aims to show that in mmWaves channels, schemes based on randomly-directional beamforming allow to harness both the spatial multiplexing and multi-user diversity characterizing the broadcast channel by using only limited feedback and a simple transmitter architecture. The number of necessary users with respect to the number of transmitting antennas for optimal performances is investigated as well as the fairness issue, for which the use of NOMA is shown to be advantageous w.r.t. OMA
Multiuser MAC Schemes for High-Throughput IEEE 802.11n/ac WLANs
In the last decade, the Wireless Local Area Network (WLAN) market has been experiencing
an impressive growth that began with the broad acceptance of the IEEE 802.11 standard [1].
Given the widespread deployment of WLANs and the increasing requirements of multimedia
applications, the need for high capacity and enhanced reliability has become imperative.
Multiple-Input Multiple-Output (MIMO) technology and its single receiving antenna version,
MISO (Multiple-Input Single-Output (MISO), promise a signiÂżcant performance boost and
have been incorporated in the emerging IEEE 802.11n standard.Peer ReviewedPostprint (published version
Radio Communications
In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modiïŹed our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the ïŹeld of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks
Wireless transmission protocols using relays for broadcast and information exchange channels
Relays have been used to overcome existing network performance bottlenecks in meeting the growing
demand for large bandwidth and high quality of service (QoS) in wireless networks. This thesis
proposes several wireless transmission protocols using relays in practical multi-user broadcast and
information exchange channels. The main theme is to demonstrate that efficient use of relays provides
an additional dimension to improve reliability, throughput, power efficiency and secrecy. First,
a spectrally efficient cooperative transmission protocol is proposed for the multiple-input and singleoutput
(MISO) broadcast channel to improve the reliability of wireless transmission. The proposed
protocol mitigates co-channel interference and provides another dimension to improve the diversity
gain. Analytical and simulation results show that outage probability and the diversity and multiplexing
tradeoff of the proposed cooperative protocol outperforms the non-cooperative scheme. Second,
a two-way relaying protocol is proposed for the multi-pair, two-way relaying channel to improve the
throughput and reliability. The proposed protocol enables both the users and the relay to participate
in interference cancellation. Several beamforming schemes are proposed for the multi-antenna
relay. Analytical and simulation results reveal that the proposed protocol delivers significant improvements
in ergodic capacity, outage probability and the diversity and multiplexing tradeoff if compared
to existing schemes. Third, a joint beamforming and power management scheme is proposed for
multiple-input and multiple-output (MIMO) two-way relaying channel to improve the sum-rate. Network
power allocation and power control optimisation problems are formulated and solved using
convex optimisation techniques. Simulation results verify that the proposed scheme delivers better
sum-rate or consumes lower power when compared to existing schemes. Fourth, two-way secrecy
schemes which combine one-time pad and wiretap coding are proposed for the scalar broadcast channel
to improve secrecy rate. The proposed schemes utilise the channel reciprocity and employ relays
to forward secret messages. Analytical and simulation results reveal that the proposed schemes are
able to achieve positive secrecy rates even when the number of users is large. All of these new wireless
transmission protocols help to realise better throughput, reliability, power efficiency and secrecy
for wireless broadcast and information exchange channels through the efficient use of relays
Advanced wireless communications using large numbers of transmit antennas and receive nodes
The concept of deploying a large number of antennas at the base station, often called massive multiple-input multiple-output (MIMO), has drawn considerable interest because of its potential ability to revolutionize current wireless communication systems. Most literature on massive MIMO systems assumes time division duplexing (TDD), although frequency division duplexing (FDD) dominates current cellular systems. Due to the large number of transmit antennas at the base station, currently standardized approaches would require a large percentage of the precious downlink and uplink resources in FDD massive MIMO be used for training signal transmissions and channel state information (CSI) feedback. First, we propose practical open-loop and closed-loop training frameworks to reduce the overhead of the downlink training phase. We then discuss efficient CSI quantization techniques using a trellis search. The proposed CSI quantization techniques can be implemented with a complexity that only grows linearly with the number of transmit antennas while the performance is close to the optimal case. We also analyze distributed reception using a large number of geographically separated nodes, a scenario that may become popular with the emergence of the Internet of Things. For distributed reception, we first propose coded distributed diversity to minimize the symbol error probability at the fusion center when the transmitter is equipped with a single antenna. Then we develop efficient receivers at the fusion center using minimal processing overhead at the receive nodes when the transmitter with multiple transmit antennas sends multiple symbols simultaneously using spatial multiplexing
Quelques Aspects des RĂ©seaux Multi-Cellules Multi-Utilisateurs MIMO : DĂ©lai, Conception d'Emetteur-RĂ©cepteur, SĂ©lection d'Utilisateurs et Topologie
In order to meet ever-growing needs for capacity in wireless networks, transmission techniques and the system models used to study their performances have rapidly evolved. From single-user single-antenna point-to-point communications to modern multi-cell multi-antenna cellular networks there have been large advances in technology. Along the way, several assumptions are made in order to have either more realistic models, but also to allow simpler analysis. We analyze three aspects of actual networks and try to benefit from them when possible or conversely, to mitigate their negative impact. This sometimes corrects overly optimistic results, for instance when delay in the channel state information (CSI) acquisition is no longer neglected. However, this sometimes also corrects overly pessimistic results, for instance when in a broadcast channel (BC) the number of users is no longer limited to be equal to the number of transmit antennas or when partial connectivity is taken into account in cellular networks.We first focus on the delay in the CSI acquisition because it greatly impairs the channel multiplexing gain if nothing is done to use the dead time during which the transmitters are not transmitting and do not yet have the CSI. We review and propose different schemes to use this dead time to improve the multiplexing gain in both the BC and the interference channel (IC). We evaluate the more relevant net multiplexing gain, taking into account the training and feedback overheads. Results are surprising because potential schemes to fight delay reveal to be burdened by impractical overheads in the BC. In the IC, an optimal scheme is proposed. It allows avoiding any loss of multiplexing gain even for significant feedback delay. Concerning the number of users, we propose a new criterion for the greedy user selection in a BC to benefit of the multi-user diversity, and two interference alignment schemes for the IC to benefit of having multiple users in each cell. Finally, partially connected cellular networks are considered and schemes to benefit from said partial connectivity to increase the multiplexing gain are proposed.Afin de rĂ©pondre au besoin sans cesse croissant de capacitĂ© dans les rĂ©seaux sans fil, les techniques de transmission, et les modĂšles utilisĂ©s pour les Ă©tudier, ont Ă©voluĂ©s rapidement. De simples communications point Ă point avec une seuleantenne nous sommes passĂ© aux rĂ©seaux cellulaires de nos jours: de multiples cellules et de multiples antennes Ă lâĂ©mission et Ă la rĂ©ception. Progressivement, plusieurs hypothĂšses ont Ă©tĂ© faites, soit afin dâavoir des modĂšles rĂ©alistes, mais aussi parfois pour permettre une analyse plus simple. Nous examinons et analysons lâimpact de trois aspects des rĂ©seaux rĂ©els. Cela revient parfois Ă corriger des rĂ©sultats trop optimistes, par exemple lorsque le dĂ©lai dans lâacquisition des coefficients des canaux nâest plus nĂ©gligĂ©. Cela revient parfois Ă corriger des rĂ©sultats trop pessimistes, par exemple, lorsque dans un canal de diffusion (BC) le nombre dâutilisateurs nâest plus limitĂ© au nombre dâantennes dâĂ©mission ou lorsque la connectivitĂ© partielle est prise en compte dans les rĂ©seaux cellulaires. Plus prĂ©cisĂ©ment, dans cette thĂšse, nous nous concentrons sur le dĂ©lai dans lâacquisition des coefficients des canaux par lâĂ©metteur puisque sa prise en comptedĂ©tĂ©riore grandement le gain de multiplexage du canal si rien nâest fait pour utiliser efficacement le temps mort au cours duquel les Ă©metteurs ne transmettent pas et nâont pas encore la connaissance du canal. Nous examinons et proposons des schĂ©mas de transmission pour utiliser efficacement ce temps mort afin dâamĂ©liorer le gain de multiplexage. Nous Ă©valuons le gain de multiplexage net, plus pertinent, en tenant compte le temps passĂ© Ă envoyer symboles dâapprentissage et Ă les renvoyer aux transmetteurs. Les rĂ©sultats sont surprenant puisque les schĂ©mas contre le retard de connaissance de canal se rĂ©vĂšle ĂȘtre impraticables Ă cause du cout du partage de la connaissance des canaux. Dans les rĂ©seaux multi-cellulaires, un schĂ©ma de transmission optimal est proposĂ© et permet de nâavoir aucune perte de gain de multiplexage mĂȘme en cas de retard important dans la connaissance de canal. En ce qui concerne le nombre dâutilisateurs, nous proposons un nouveau critĂšre pour la sĂ©lection des utilisateurs de les configurations Ă une seule cellule afin de bĂ©nĂ©ficier de la diversitĂ© multi-utilisateurs, et nous proposons deux schĂ©mas dâalignement dâinterfĂ©rence pour systĂšmes multi-cellulaires afin de bĂ©nĂ©ficier du fait quâil y a gĂ©nĂ©ralement plusieurs utilisateurs dans chaque cellule. Enfin, les rĂ©seaux cellulaires partiellement connectĂ©s sont Ă©tudiĂ©s et des schĂ©mas bĂ©nĂ©ficiant de la connectivitĂ© partielle pour augmenter le gain de multiplexage sont proposĂ©s
Signal design for Multiple-Antenna Systems and Wireless Networks
This dissertation is concerned with the signal design problems for Multiple Input and Multiple Output (MIMO) antenna systems and wireless networks. Three related but distinct problems are considered.The first problem considered is the design of space time codes for MIMO systems in the case when neither the transmitter nor the receiver knows the channel. We present the theoretical concept of communicating over block fading channel using Layered Unitary Space Time Codes (LUSTC), where the input signal is formed as a product of a series of unitary matrices with corresponding dimensionality. We show the channel capacity using isotropically distributed (i.d.) input signaling and optimal decoding can be achieved by layered i.d. signaling scheme along with a low complexity successive decoding. The closed form layered channel capacity is obtained, which serves as a design guideline for practical LUSTC. In the design of LUSTC, a successive design method is applied to leverage the problem of optimizing over lots of parameters.The feedback of channel state information (CSI) to the transmitter in MIMO systems is known to increase the forward channel capacity. A suboptimal power allocation scheme for MIMO systems is then proposed for limited rate feedback of CSI. We find that the capacity loss of this simple scheme is rather small compared to the optimal water-filling solution. This knowledge is applied for the design of the feedback codebook. In the codebook design, a generalized Lloyd algorithm is employed, in which the computation of the centroid is formulated as an optimization problem and solved optimally. Numerical results show that the proposed codebook design outperforms the existing algorithms in the literature.While it is not feasible to deploy multiple antennas in a wireless node due to the space limitation, user cooperation is an alternative to increase performance of the wireless networks. To this end, a coded user cooperation scheme is considered in the dissertation, which is shown to be equivalent to a coding scheme with the encoding done in a distributive manner. Utilizing the coding theoretic bound and simulation results, we show that the coded user cooperation scheme has great advantage over the non-cooperative scheme
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