89 research outputs found
Optimization of Efficiency and Energy Consumption in p-persistent CSMA-based Wireless LANs
Wireless technologies in the LAN environment are becoming increasingly important. The IEEE 802.11 is the most mature technology for Wireless Local Area Networks (WLANs). The limited bandwidth and the finite battery power of mobile computers represent one of the greatest limitations of current WLANs. In this paper we deeply investigate the efficiency and the energy consumption of MAC protocols that can be described with a p-persistent CSMA model. As already shown in the literature, the IEEE 802.11 protocol performance can be studied using a p-persistent CSMA model [Cal00]. For this class of protocols, in the paper we define an analytical framework to study the theoretical performance bounds from the throughput and the energy consumption standpoint. Specifically, we derive the p values (i.e., the average size of the contention window in the IEEE 802.11 protocol) that maximizes the throughput, , and minimizes the energy consumption, . By providing analytical closed formulas for the optimal values, we discuss the trade-off between efficiency and energy consumption. Specifically, we show that power saving and throughput maximization can be jointly achieved. Our analytical formulas indicate that the optimal values depend on the network configuration, i.e., number of active stations and length of the messages transmitted on the channel
Unsaturated Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects
In this paper, we provide a throughput analysis of the IEEE 802.11 protocol
at the data link layer in non-saturated traffic conditions taking into account
the impact of both transmission channel and capture effects in Rayleigh fading
environment. The impact of both non-ideal channel and capture become important
in terms of the actual observed throughput in typical network conditions
whereby traffic is mainly unsaturated, especially in an environment of high
interference.
We extend the multi-dimensional Markovian state transition model
characterizing the behavior at the MAC layer by including transmission states
that account for packet transmission failures due to errors caused by
propagation through the channel, along with a state characterizing the system
when there are no packets to be transmitted in the buffer of a station.
Finally, we derive a linear model of the throughput along with its interval of
validity.
Simulation results closely match the theoretical derivations confirming the
effectiveness of the proposed model.Comment: To appear on IEEE Transactions on Wireless Communications, 200
A Model of the IEEE 802.11 DCF in Presence of Non Ideal Transmission Channel and Capture Effects
In this paper, we provide a throughput analysis of the IEEE 802.11 protocol
at the data link layer in non-saturated traffic conditions taking into account
the impact of both transmission channel and capture effects in Rayleigh fading
environment. Impacts of both non-ideal channel and capture become important in
terms of the actual observed throughput in typical network conditions whereby
traffic is mainly unsaturated, specially in an environment of high
interference.
We extend the multi-dimensional Markovian state transition model
characterizing the behavior at the MAC layer by including transmission states
that account for packet transmission failures due to errors caused by
propagation through the channel, along with a state characterizing the system
when there are no packets to be transmitted in the buffer of a station.Comment: Accepted for oral presentation to IEEE Globecom 2007, Washington
D.C., November 200
Supporting Real-Time Communication in CSMA-Based Networks : the VTP-CSMA Virtual Token Passing Approach
Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200
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 versiĂł de lâestĂ ndard deWLAN, anomenada IEEE 802.11n, ha augmentat la seva capacitat notablement en relaciĂł als sistemes anteriors grĂ cies a la incorporaciĂł de la tecnologia de mĂșltiples antenes en transmissiĂł i recepciĂł (MIMO). No obstant aixĂČ, la nova proposta, al igual que les anteriors, segueix sense especificar com sâhan dâimplementar elsmecanismes de configuraciĂłmĂ©s crucials, un dels quals Ă©s lâalgoritme de codificaciĂł imodulaciĂł adaptativa (AMC). Aquests algoritmes ja han demostrat la seva importĂ ncia a lâhora demaximitzar el rendiment del sistema tenint en compte les condicions canviants del canal. En aquesta tesis sâha proposat un algoritme AMC de llaç tancat, anomenat adaptaciĂł rĂ pida de lâenllaç (FLA), que selecciona eficientment lâesquema demodulaciĂł i codificaciĂł adaptativa per xarxes WLAN basades en arquitectures multiportadora multiantena. Lâalgoritme FLA determina el mode de transmissiĂł capaç de maximitzar el throughput per les condicions de canal actuals, mentre satisfĂ un requisit de qualitat de servei en forma de taxa dâerror per paquet (PER). FLA utilitza una metodologia de predicciĂł de PER basada en lâestimaciĂł de la relaciĂł senyal renou (SNR) efectiva exponencial (EESM). El rendiment de lâalgoritme FLA ha estat avaluat en sistemes IEEE 802.11n, ja que aquests, grĂ cies a la incorporaciĂł dâunmecanisme de realimentaciĂł demodes de transmissiĂł, poden adoptar solucions AMC de llaç tancat. En una primera part, lâestudi sâha centrat a la capa fĂsica i desprĂ©s sâha estĂšs a la subcapa MAC. A la capa fĂsica sâha demostrat lâefectivitat de lâalgoritme FLA aconseguint un rendiment molt proper al que ens proporcionaria un esquema AMC ĂČptim en termes de throughput, alhora que es satisfan els requisits de PER objectiu. Lâalgoritme FLA tambĂ© ha estat avaluat utilitzant informaciĂł imperfecte del canal. Sâha vist que lâalgoritme FLA proposat Ă©s robust en front dels efectes dâestimaciĂł imperfecte del canal, i nomĂ©s en canals altament selectius en freqĂŒĂšncia, la informaciĂł imperfecte del canal provoca una davallada en el rendiment en termes de throughput. A la subcapa MAC, lâalgoritme FLA ha estat complementat amb una estratĂšgia de temps dâespera que disminueix la dependĂšncia amb la informaciĂł de canal disponible a mesura que aquesta va quedant desfassada respecte de lâestat actual. Aquesta informaciĂł de canal desfassada Ă©s conseqĂŒĂšncia de la subcapa MAC que degut a la multiplexaciĂł dâusuaris introdueix grans retards entre que es determina el mode de transmissiĂł mĂ©s adequat i la seva utilitzaciĂł per a lâaccĂ©s al canal. Els resultats obtinguts han demostrat la superioritat de FLA respecte dâaltres algoritmes de llaç obert en condicions de saturaciĂł i de no saturaciĂł, i independentment de la longitud de paquet, nombre dâusuaris, protocol (CSMA/CA i CSMA/E2CA) i esquema dâaccĂ©s (Basic Access i RTS/CTS). AmĂ©s, sâhan desenvolupat diversosmodels analĂtics per tal dâestimar 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, lâslot anĂČmal o els errors introduĂŻts pel canal. Inicialment sâha proposat unmodel semi-analĂtic que determina el throughtput en condicions de saturaciĂł, considerant el rendiment dels algoritmes AMC. DesprĂ©s sâha presentat un model analĂtic que estima el rendiment del sistema per condicions de no saturaciĂł, mitjançat elmodelat de cues finites a cada estaciĂł. Aquestmodel consideramodes de transmissiĂł fixes i Ă©s capaç de determinar de manera molt precisa mĂštriques de rendimentmolt importants comsĂłn la probabilitat de bloqueig de cada estaciĂł, el retard mitjĂ del paquets, la probabilitat de descart o la mesura del goodput. Finalment, el model analĂtic de no saturaciĂł sâha utilitzat per definir un model semi-analĂtic per tal dâestimar el rendiment del sistema quan es considera lâĂșs dâalgoritmes AMC
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Position-based routing and MAC protocols for wireless ad-hoc networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis presents the Forecasting Routing Technique (FORTEL), a routing protocol for Mobile Ad-Hoc Networks (MANETs) based on the nodesâ Location Information. FORTEL stores the nodesâ location information in the Location Table (LT) in order to construct routes between the source and the destination nodes. FORTEL follows the source routing strategy, which has rarely been applied in position-based routing. According to the source routing strategy, the end-to-end route is attached to the packet, therefore, the processing cost, in regards to the intermediate nodes that simply relay the packet according to route, is minimized. FORTELâs key mechanisms include: first, the location update scheme, employed to keep the LT entries up-to-date with the network topology. Besides the mobility variation and the constant rate location update schemes applied, a window location update scheme is presented to increase the LTâs information accuracy. Second, the switching mechanism, between âHelloâ message and location update employed, to reduce the protocolâs routing overhead. Third and most important is the route computation mechanism, which is integrated with a topology forecasting technique to construct up-to-date routes between the communication peers, aiming to achieve high delivery rate and increase the protocol robustness against the nodesâ movement. FORTEL demonstrates higher performance as compared to other MANETâs routing protocols, and it delivers up to 20% more packets than AODV and up to 60 % more than DSR and OLSR, while maintaining low levels of routing overhead and network delay at the same time. The effectiveness of the window update scheme is also discussed, and it proves to increase FORTELâs delivery rate by up to 30% as compared to the other update schemes.
A common and frequently occurring phenomenon, in wireless networks, is the Hidden Terminal problem that significantly impacts the communication performance and the efficiency of the routing and MAC protocols. Beaconless routing approach in MANETs, which delivers data packets without prior knowledge of any sort `of information, suffers from packet duplication caused by the hidden nodes during the contention process. Moreover, the throughput of the IEEE MAC protocol decreases dramatically when the hidden terminal problem occurs. RTS/CTS mechanism fails to eliminate the problem and can further degrade the networkâs performance by introducing additional overhead. To tackle these challenges, this thesis presents two techniques, the Sender Suppression Algorithm and the Location-Aided MAC, where both rely on the nodesâ position to eliminate packet duplication in the beaconless routing and improve the performance of the 802.11 MAC respectively. Both schemes are based on the concept of grouping the nodes into zones and assign different time delay to each one. According to the Sender Suppression Algorithm, the senderâs forwarding area is divided into three zones, therefore, the local timer, set to define the time that the receiver has to wait before responding to the senderâs transmission, is added to the assigned zone delay. Following the first response, the sender interferes and suppresses the receivers with active timer of. On the other hand, the Location-Aided MAC, essentially a hybrid MAC, combines the concepts of time division and carrier sensing. The radio range of the wireless receiver is partitioned into four zones with different zone delays assigned to each zone. Channel access within the zone is purely controlled by CSMA/CA protocol, while it is time-based amongst zones. The effectiveness of the proposed techniques is demonstrated through simulation tests. Location-Aided MAC considerably improves the networkâs throughput compared to CSMA/CA and RTS/CTS. However, remarkable results come when the proposed technique and the RTS/CTS are combined, which achieves up to 20% more throughput as compared to the standalone RTS/CTS. Finally, the thesis presents a novel link lifetime estimation method for greedy forwarding to compute the link duration between two nodes. Based on a newly introduced Stability-Aware Greedy (SAG) scheme, the proposed method incorporates the destination node in the computation process and thus has a significant advantage over the conventional method, which only considers the information of the nodes composing the link
Improving Performance for CSMA/CA Based Wireless Networks
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) based wireless networks are becoming increasingly ubiquitous. With the aim of supporting rich multimedia
applications such as high-definition television (HDTV, 20Mbps) and DVD (9.8Mbps), one of the technology trends is towards increasingly higher bandwidth. Some recent IEEE 802.11n proposals seek to provide PHY rates of up to 600 Mbps. In addition to increasing bandwidth, there is also strong interest in extending the coverage of CSMA/CA based wireless networks. One solution is to relay traffic via multiple intermediate stations if the sender and the receiver are far apart. The so called âmeshâ networks based on this relay-based approach, if properly designed, may feature both âhigh speedâ and âlarge coverageâ at the
same time. This thesis focusses on MAC layer performance enhancements in CSMA/CA based networks in this context.
Firstly, we observe that higher PHY rates do not necessarily translate into corresponding increases in MAC layer throughput due to the overhead of the CSMA/CA based MAC/PHY layers. To mitigate the overhead, we propose a novel MAC scheme whereby transported information is partially acknowledged and retransmitted. Theoretical analysis and extensive simulations show that the proposed MAC approach can achieve high efficiency (low MAC
overhead) for a wide range of channel variations and realistic traffic types.
Secondly, we investigate the close interaction between the MAC layer and the buffer above it to improve performance for real world traffic such as TCP. Surprisingly, the issue
of buffer sizing in 802.11 wireless networks has received little attention in the literature yet it poses fundamentally new challenges compared to buffer sizing in wired networks. We propose a new adaptive buffer sizing approach for 802.11e WLANs that maintains a high
level of link utilisation, while minimising queueing delay.
Thirdly, we highlight that gross unfairness can exist between competing flows in multihop mesh networks even if we assume that orthogonal channels are used in neighbouring
hops. That is, even without inter-channel interference and hidden terminals, multi-hop mesh networks which aim to offer a both âhigh speedâ and âlarge coverageâ are not achieved. We propose the use of 802.11eâs TXOP mechanism to restore/enfore fairness. The proposed approach is implementable using off-the-shelf devices and fully decentralised (requires no message passing)
Final report on the evaluation of RRM/CRRM algorithms
Deliverable public del projecte EVERESTThis deliverable provides a definition and a complete evaluation of the RRM/CRRM algorithms selected in D11 and D15, and evolved and refined on an iterative process. The evaluation will be carried out by means of simulations using the simulators provided at D07, and D14.Preprin
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