301 research outputs found
Wireless MIMO Switching: Weighted Sum Mean Square Error and Sum Rate Optimization
This paper addresses joint transceiver and relay design for a wireless
multiple-input-multiple-output (MIMO) switching scheme that enables data
exchange among multiple users. Here, a multi-antenna relay linearly precodes
the received (uplink) signals from multiple users before forwarding the signal
in the downlink, where the purpose of precoding is to let each user receive its
desired signal with interference from other users suppressed. The problem of
optimizing the precoder based on various design criteria is typically
non-convex and difficult to solve. The main contribution of this paper is a
unified approach to solve the weighted sum mean square error (MSE) minimization
and weighted sum rate maximization problems in MIMO switching. Specifically, an
iterative algorithm is proposed for jointly optimizing the relay's precoder and
the users' receive filters to minimize the weighted sum MSE. It is also shown
that the weighted sum rate maximization problem can be reformulated as an
iterated weighted sum MSE minimization problem and can therefore be solved
similarly to the case of weighted sum MSE minimization. With properly chosen
initial values, the proposed iterative algorithms are asymptotically optimal in
both high and low signal-to-noise ratio (SNR) regimes for MIMO switching,
either with or without self-interference cancellation (a.k.a., physical-layer
network coding). Numerical results show that the optimized MIMO switching
scheme based on the proposed algorithms significantly outperforms existing
approaches in the literature.Comment: This manuscript is under 2nd review of IEEE Transactions on
Information Theor
Capacity Bounds for Two-Hop Interference Networks
This paper considers a two-hop interference network, where two users transmit
independent messages to their respective receivers with the help of two relay
nodes. The transmitters do not have direct links to the receivers; instead, two
relay nodes serve as intermediaries between the transmitters and receivers.
Each hop, one from the transmitters to the relays and the other from the relays
to the receivers, is modeled as a Gaussian interference channel, thus the
network is essentially a cascade of two interference channels. For this
network, achievable symmetric rates for different parameter regimes under
decode-and- forward relaying and amplify-and-forward relaying are proposed and
the corresponding coding schemes are carefully studied. Numerical results are
also provided.Comment: 8 pages, 5 figures, presented in Allerton Conference'0
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
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
Joint transceiver design and power optimization for wireless sensor networks in underground mines
Avec les grands dĂ©veloppements des technologies de communication sans fil, les rĂ©seaux de capteurs sans fil (WSN) ont attirĂ© beaucoup dâattention dans le monde entier au cours de la derniĂšre dĂ©cennie. Les rĂ©seaux de capteurs sans fil sont maintenant utilisĂ©s pour a surveillance sanitaire, la gestion des catastrophes, la dĂ©fense, les tĂ©lĂ©communications, etc. De tels rĂ©seaux sont utilisĂ©s dans de nombreuses applications industrielles et commerciales comme la surveillance des processus industriels et de lâenvironnement, etc. Un rĂ©seau WSN est une collection de transducteurs spĂ©cialisĂ©s connus sous le nom de noeuds de capteurs avec une liaison de communication distribuĂ©e de maniĂšre alĂ©atoire dans tous les emplacements pour surveiller les paramĂštres. Chaque noeud de capteur est Ă©quipĂ© dâun transducteur, dâun processeur de signal, dâune unitĂ© dâalimentation et dâun Ă©metteur-rĂ©cepteur. Les WSN sont maintenant largement utilisĂ©s dans lâindustrie miniĂšre souterraine pour surveiller certains paramĂštres environnementaux, comme la quantitĂ© de gaz, dâeau, la tempĂ©rature, lâhumiditĂ©, le niveau dâoxygĂšne, de poussiĂšre, etc. Dans le cas de la surveillance de lâenvironnement, un WSN peut ĂȘtre remplacĂ© de maniĂšre Ă©quivalente par un rĂ©seau Ă relais Ă entrĂ©es et sorties multiples (MIMO). Les rĂ©seaux de relais multisauts ont attirĂ© un intĂ©rĂȘt de recherche important ces derniers temps grĂące Ă leur capacitĂ© Ă augmenter la portĂ©e de la couverture. La liaison de communication rĂ©seau dâune source vers une destination est mise en oeuvre en utilisant un schĂ©ma dâamplification/transmission (AF) ou de dĂ©codage/transfert (DF). Le relais AF reçoit des informations du relais prĂ©cĂ©dent et amplifie simplement le signal reçu, puis il le transmet au relais suivant. Dâautre part, le relais DF dĂ©code dâabord le signal reçu, puis il le transmet au relais suivant au deuxiĂšme Ă©tage sâil peut parfaitement dĂ©coder le signal entrant. En raison de la simplicitĂ© analytique, dans cette thĂšse, nous considĂ©rons le schĂ©ma de relais AF et les rĂ©sultats de ce travail peuvent Ă©galement ĂȘtre dĂ©veloppĂ©s pour le relais DF. La conception dâun Ă©metteur/rĂ©cepteur pour le relais MIMO multisauts est trĂšs difficile. Car Ă lâĂ©tape de relais L, il y a 2L canaux possibles. Donc, pour un rĂ©seau Ă grande Ă©chelle, il nâest pas Ă©conomique dâenvoyer un signal par tous les liens possibles. Au lieu de cela, nous pouvons trouver le meilleur chemin de la source Ă la destination qui donne le rapport signal sur bruit (SNR) de bout en bout le plus Ă©levĂ©. Nous pouvons minimiser la fonction objectif dâerreur quadratique moyenne (MSE) ou de taux dâerreur binaire (BER) en envoyant le signal utilisant le chemin sĂ©lectionnĂ©. Lâensemble de relais dans le chemin reste actif et le reste des relais sâĂ©teint, ce qui permet dâĂ©conomiser de lâĂ©nergie afin dâamĂ©liorer la durĂ©e de vie du rĂ©seau. Le meilleur chemin de transmission de signal a Ă©tĂ© Ă©tudiĂ© dans la littĂ©rature pour un relais MIMO Ă deux bonds mais est plus complexe pour un ...With the great developments in wireless communication technologies, Wireless Sensor Networks (WSNs) have gained attention worldwide in the past decade and are now being used in health monitoring, disaster management, defense, telecommunications, etc. Such networks are used in many industrial and consumer applications such as industrial process and environment monitoring, among others. A WSN network is a collection of specialized transducers known as sensor nodes with a communication link distributed randomly in any locations to monitor environmental parameters such as water level, and temperature. Each sensor node is equipped with a transducer, a signal processor, a power unit, and a transceiver. WSNs are now being widely used in the underground mining industry to monitor environmental parameters, including the amount of gas, water, temperature, humidity, oxygen level, dust, etc. The WSN for environment monitoring can be equivalently replaced by a multiple-input multiple-output (MIMO) relay network. Multi-hop relay networks have attracted significant research interest in recent years for their capability in increasing the coverage range. The network communication link from a source to a destination is implemented using the amplify-and-forward (AF) or decode-and-forward (DF) schemes. The AF relay receives information from the previous relay and simply amplifies the received signal and then forwards it to the next relay. On the other hand, the DF relay first decodes the received signal and then forwards it to the next relay in the second stage if it can perfectly decode the incoming signal. For analytical simplicity, in this thesis, we consider the AF relaying scheme and the results of this work can also be developed for the DF relay. The transceiver design for multi-hop MIMO relay is very challenging. This is because at the L-th relay stage, there are 2L possible channels. So, for a large scale network, it is not economical to send the signal through all possible links. Instead, we can find the best path from source-to-destination that gives the highest end-to-end signal-to-noise ratio (SNR). We can minimize the mean square error (MSE) or bit error rate (BER) objective function by sending the signal using the selected path. The set of relay in the path remains active and the rest of the relays are turned off which can save power to enhance network life-time. The best path signal transmission has been carried out in the literature for 2-hop MIMO relay and for multiple relaying it becomes very complex. In the first part of this thesis, we propose an optimal best path finding algorithm at perfect channel state information (CSI). We consider a parallel multi-hop multiple-input multiple-output (MIMO) AF relay system where a linear minimum mean-squared error (MMSE) receiver is used at the destination. We simplify the parallel network into equivalent series multi-hop MIMO relay link using best relaying, where the best relay ..
Data mixing at the source, relay, and in the air in multiple-access relay networks
The concept of cooperative relay is an essential technique for future cellular networks such as wireless mesh networking or wireless ad-hoc networking. In a practical relay network, channel coding, network coding, and antenna arrays, will coexist and yet the joint optimization of these conventional coding schemes and cooperative relay is not well understood. To build a design guideline for relay network, this dissertation develop a joint optimization methodology for multiple coding schemes in multiple access relay network.
There are four major contributions in this thesis: First, we jointly optimize conventional coding schemes and radio resources of multiple access relay network with multiple antennas. The combined design of MIMO transmission modes, channel coding at the source, network coding at the relay have been investigated. We develop optimal design rule that minimize the end-to-end error probability. Second, we derive the fundamental tradeoff between achievable rate and reliability of multiple access relay network with multiple antennas. We consider three MIMO transmission modes, spatial multiplexing (SM), Alamouti coding as transmit diversity (TD), and Golden Coding, and random linear network coding at the relay. We compare the average decoding error probability of each transmission mode. Third, we present an interference cancellation scheme for multi-user MIMO. The proposed Log-likelihood-ratio (LLR) ordered successive interference cancellation (SIC) scheme provides 1 ~ 3 dB gain over the conventional SNR-ordered SIC and the gain increases with increasing number of users. Finally, we present a new architecture for MIMO receivers that cancel the co-channel interference (CCI) using a single radio frequency (RF) and baseband (BB) chain, while still achieving nearly the same bit error rate that can be provided by the conventional receiver requiring multiple RF/BB chains
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