RCFD: A Novel Channel Access Scheme for Full-Duplex Wireless Networks Based on Contention in Time and Frequency Domains

In the last years, the advancements in signal processing and integrated circuits technology allowed several research groups to develop working prototypes of in-band full-duplex wireless systems. The introduction of such a revolutionary concept is promising in terms of increasing network performance, but at the same time poses several new challenges, especially at the MAC layer. Consequently, innovative channel access strategies are needed to exploit the opportunities provided by full-duplex while dealing with the increased complexity derived from its adoption. In this direction, this paper proposes RTS/CTS in the Frequency Domain (RCFD), a MAC layer scheme for full-duplex ad hoc wireless networks, based on the idea of time-frequency channel contention. According to this approach, different OFDM subcarriers are used to coordinate how nodes access the shared medium. The proposed scheme leads to efficient transmission scheduling with the result of avoiding collisions and exploiting full-duplex opportunities. The considerable performance improvements with respect to standard and state-of-the-art MAC protocols for wireless networks are highlighted through both theoretical analysis and network simulations.Comment: Submitted at IEEE Transactions on Mobile Computing. arXiv admin note: text overlap with arXiv:1605.0971

Decentralised Learning MACs for Collision-free Access in WLANs

By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then design two \changed{schemes} that are practically realisable, decentralised approximations of this optimal scheme and operate with different amounts of sensing information. We achieve this by (1) introducing learning algorithms that can substantially speed up convergence to collision free operation; (2) developing a decentralised schedule length adaptation scheme that provides long-run fair (uniform) access to the medium while maintaining collision-free access for arbitrary numbers of stations

State-of-the-art in Power Line Communications: from the Applications to the Medium

In recent decades, power line communication has attracted considerable attention from the research community and industry, as well as from regulatory and standardization bodies. In this article we provide an overview of both narrowband and broadband systems, covering potential applications, regulatory and standardization efforts and recent research advancements in channel characterization, physical layer performance, medium access and higher layer specifications and evaluations. We also identify areas of current and further study that will enable the continued success of power line communication technology.Comment: 19 pages, 12 figures. Accepted for publication, IEEE Journal on Selected Areas in Communications. Special Issue on Power Line Communications and its Integration with the Networking Ecosystem. 201

Characterising the interactions between unicast and broadcast in IEEE 802.11 ad hoc networks

This paper investigates the relative performance of unicast and broadcast traffic traversing a one-hop ad hoc network utilising the 802.11 DCF. An extended Markov model has been developed and validated through computer simulation, which successfully predicts the respective performance of unicast and broadcast in a variety of mixed traffic scenarios. Under heavy network traffic conditions, a significant divergence is seen to develop between the performance of the two traffic classes - in particular, when network becomes saturated, unicast traffic is effectively given higher precedence over broadcast. As a result, the network becomes dominated by unicast frames, leading to poor rates of broadcast frame delivery

Mac-Phy Cross-Layer analysis and design of Mimo-Ofdm Wlans based on fast link adaptation

The latestWLAN standard, known as IEEE 802.11n, has notably increased the network capacity with respect to its predecessors thanks to the incorporation of the multipleinput multiple-output (MIMO) technology. Nonetheless, the new amendment, as its previous ones, does not specify how crucial configuration mechanisms, most notably the adaptive modulation and coding (AMC) algorithm should be implemented. The AMC process has proved essential to fully exploit the system resources in light of varying channel conditions. In this dissertation, a closed-loop AMC technique, referred to as fast link adaption (FLA) algorithm, that effectively selects themodulation and coding scheme (MCS) for multicarriermultiantennaWLAN networks is proposed. The FLA algorithm determines the MCS that maximizes the throughput while satisfying a quality of service (QoS) constraint, usually defined in the form of an objective packet error rate (PER). To this end, FLA uses a packet/bit error rate prediction methodology based on the exponential effective SNRmetric (EESM). The FLA algorithm performance has been evaluated under IEEE 802.11n systems that thanks to the incorporation of a feedbackmechanismare able to implement closed- loop AMC mechanisms. Initially, this AMC technique relies only on physical layer information but it is subsequently extended to also take into account themediumaccess control (MAC) sublayer performance. At the physical layer, the FLA algorithm has demonstrated its effectivity by performing very close to optimality in terms of throughput, while satisfying a prescribed PER constraint. The FLA algorithm has also been evaluated using imperfect channel information. It has been observed that the proposed FLA technique is rather robust against imperfect channel information, and only in highly-frequency selective channels, imperfect channel knowledge causes a noticeable degradation in throughput. At the MAC sublayer, the FLA algorithm has been complemented with a timeout strategy that weighs down the influence of the available channel information as this becomes outdated. This channel information outdate is caused by the MAC sublayer whose user multiplexing policy potentially results in large delays between acquiring the instant in which the channel state information is acquired and that in which the channel is accessed. Results demonstrate the superiority of FLA when compared to open-loop algorithms under saturated and non-saturated conditions and irrespective of the packet length, number of users, protocol (CSMA/CA or CDMA/E2CA) and access scheme (Basic Access or RTS/CTS). Additionally, several analytical models have been developed to estimate the system performance at the MAC sublayer. These models account for all operational details of the IEEE 802.11n MAC sublayer, such as finite number of retries, anomalous slot or channel errors. In particular, a semi-analytical model that assesses the MAC layer throughput under saturated conditions, considering the AMC performance is first introduced. Then, an analytical model that allows the evaluation of the QoS performance under non-saturated conditions is presented. This model focuses on single MCS and it is able to accurately predict very important system performance metrics such as blocking probability, delay, probability of discard or goodput thanks to the consideration of the finite queues on each station. Finally, the previous non-saturated analytical approach is used to define a semi-analytical model in order to estimate the system performance when considering AMC algorithms (i.e. whenmultiple MCSs are available)La darrera versió de l’estàndard deWLAN, anomenada IEEE 802.11n, ha augmentat la seva capacitat notablement en relació als sistemes anteriors gràcies a la incorporació de la tecnologia de múltiples antenes en transmissió i recepció (MIMO). No obstant això, la nova proposta, al igual que les anteriors, segueix sense especificar com s’han d’implementar elsmecanismes de configuraciómés crucials, un dels quals és l’algoritme de codificació imodulació adaptativa (AMC). Aquests algoritmes ja han demostrat la seva importància a l’hora demaximitzar el rendiment del sistema tenint en compte les condicions canviants del canal. En aquesta tesis s’ha proposat un algoritme AMC de llaç tancat, anomenat adaptació ràpida de l’enllaç (FLA), que selecciona eficientment l’esquema demodulació i codificació adaptativa per xarxes WLAN basades en arquitectures multiportadora multiantena. L’algoritme FLA determina el mode de transmissió capaç de maximitzar el throughput per les condicions de canal actuals, mentre satisfà un requisit de qualitat de servei en forma de taxa d’error per paquet (PER). FLA utilitza una metodologia de predicció de PER basada en l’estimació de la relació senyal renou (SNR) efectiva exponencial (EESM). El rendiment de l’algoritme FLA ha estat avaluat en sistemes IEEE 802.11n, ja que aquests, gràcies a la incorporació d’unmecanisme de realimentació demodes de transmissió, poden adoptar solucions AMC de llaç tancat. En una primera part, l’estudi s’ha centrat a la capa física i després s’ha estès a la subcapa MAC. A la capa física s’ha demostrat l’efectivitat de l’algoritme FLA aconseguint un rendiment molt proper al que ens proporcionaria un esquema AMC òptim en termes de throughput, alhora que es satisfan els requisits de PER objectiu. L’algoritme FLA també ha estat avaluat utilitzant informació imperfecte del canal. S’ha vist que l’algoritme FLA proposat és robust en front dels efectes d’estimació imperfecte del canal, i només en canals altament selectius en freqüència, la informació imperfecte del canal provoca una davallada en el rendiment en termes de throughput. A la subcapa MAC, l’algoritme FLA ha estat complementat amb una estratègia de temps d’espera que disminueix la dependència amb la informació de canal disponible a mesura que aquesta va quedant desfassada respecte de l’estat actual. Aquesta informació de canal desfassada és conseqüència de la subcapa MAC que degut a la multiplexació d’usuaris introdueix grans retards entre que es determina el mode de transmissió més adequat i la seva utilització per a l’accés al canal. Els resultats obtinguts han demostrat la superioritat de FLA respecte d’altres algoritmes de llaç obert en condicions de saturació i de no saturació, i independentment de la longitud de paquet, nombre d’usuaris, protocol (CSMA/CA i CSMA/E2CA) i esquema d’accés (Basic Access i RTS/CTS). Amés, s’han desenvolupat diversosmodels analítics per tal d’estimar el rendiment del sistema a la subcapa MAC. Aquests models consideren tots els detalls de funcionament de la subcapaMAC del 802.11n, comper exemple un nombre finit de retransmissions de cada paquet, l’slot anòmal o els errors introduïts pel canal. Inicialment s’ha proposat unmodel semi-analític que determina el throughtput en condicions de saturació, considerant el rendiment dels algoritmes AMC. Després s’ha presentat un model analític que estima el rendiment del sistema per condicions de no saturació, mitjançat elmodelat de cues finites a cada estació. Aquestmodel consideramodes de transmissió fixes i és capaç de determinar de manera molt precisa mètriques de rendimentmolt importants comsón la probabilitat de bloqueig de cada estació, el retard mitjà del paquets, la probabilitat de descart o la mesura del goodput. Finalment, el model analític de no saturació s’ha utilitzat per definir un model semi-analític per tal d’estimar el rendiment del sistema quan es considera l’ús d’algoritmes AMC

Verification of Common 802.11 MAC Model Assumptions

There has been considerable success in analytic modeling of the 802.11 MAC layer. These models are based on a number of fundamental assumptions. In this paper we attempt to verify these assumptions by taking careful measurements using an 802.11e testbed with commodity hardware. We show that the assumptions do not always hold but our measurements offer insight as to why the models may still produce good predictions. To our knowledge, this is the first in-detail attempt to compare 802.11 models and their assumptions with experimental measurements from an 802.11 testbed. The measurements collect also allow us to test if the basic MAC operation adhere to the 802.11 standards

Verification of Common 802.11 MAC Model Assumptions

There has been considerable success in analytic modeling of the 802.11 MAC layer. These models are based on a number of fundamental assumptions. In this paper we attempt to verify these assumptions by taking careful measurements using an 802.11e testbed with commodity hardware. We show that the assumptions do not always hold but our measurements offer insight as to why the models may still produce good predictions. To our knowledge, this is the first in-detail attempt to compare 802.11 models and their assumptions with experimental measurements from an 802.11 testbed. The measurements collect also allow us to test if the basic MAC operation adhere to the 802.11 standards

Modelling IEEE 802.11 CSMA/CA RTS/CTS with stochastic bigraphs with sharing

Stochastic bigraphical reactive systems (SBRS) is a recent formalism for modelling systems that evolve in time and space. However, the underlying spatial model is based on sets of trees and thus cannot represent spatial locations that are shared among several entities in a simple or intuitive way. We adopt an extension of the formalism, SBRS with sharing, in which the topology is modelled by a directed acyclic graph structure. We give an overview of SBRS with sharing, we extend it with rule priorities, and then use it to develop a model of the 802.11 CSMA/CA RTS/CTS protocol with exponential backoff, for an arbitrary network topology with possibly overlapping signals. The model uses sharing to model overlapping connectedness areas, instantaneous prioritised rules for deterministic computations, and stochastic rules with exponential reaction rates to model constant and uniformly distributed timeouts and constant transmission times. Equivalence classes of model states modulo instantaneous reactions yield states in a CTMC that can be analysed using the model checker PRISM. We illustrate the model on a simple example wireless network with three overlapping signals and we present some example quantitative properties