61 research outputs found
Centralized random backoff for collision free wireless local area networks
Over the past few decades, wireless local area networks (WLANs) have been
widely deployed for data communication in indoor environments such as offices,
houses, and airports. In order to fairly and efficiently use the unlicensed frequency
band that Wi-Fi devices share, the devices follow a set of channel access rules,
which is called a wireless medium access control (MAC) protocol. It is known that
wireless devices following the 802.11 standard MAC protocol, i.e. the distributed
coordination function (DCF), suffer from packet collisions when multiple nodes
simultaneously transmit. This significantly degrades the throughput performance.
Recently, several studies have reported access techniques to reduce the number
of packet collisions and to achieve a collision free WLAN. Although these studies
have shown that the number of collisions can be reduced to zero in a simple
way, there have been a couple of remaining issues to solve, such as dynamic
parameter adjustment and fairness to legacy DCF nodes in terms of channel
access opportunity.
Recently, In-Band Full Duplex (IBFD) communication has received much
attention, because it has significant potential to improve the communication
capacity of a radio band. IBFD means that a node can simultaneously transmit
one signal and receive another signal in the same band at the same time. In
order to maximize the performance of IBFD communication capability and to
fairly share access to the wireless medium among distributed devices in WLANs,
a number of IBFD MAC protocols have been proposed. However, little attention
has been paid to fairness issues between half duplex nodes (i.e. nodes that can
either transmit or receive but not both simultaneously in one time-frequency
resource block) and IBFD capable nodes in the presence of the hidden node
problem
Novel Medium Access Control (MAC) Protocols for Wireless Sensor and Ad Hoc Networks (WSANs) and Vehicular Ad Hoc Networks (VANETs)
Efficient medium access control (MAC) is a key part of any wireless network communication architecture. MAC protocols are needed for nodes to access the shared wireless medium efficiently. Providing high throughput is one of the primary goals of the MAC protocols designed for wireless networks. MAC protocols for Wireless Sensor and Ad hoc networks (WSANs) must also conserve energy as sensor nodes have limited battery power. On the other hand, MAC protocols for Vehicular Ad hoc networks (VANETs) must also adapt to the highly dynamic nature of the network. As communication link failure is very common in VANETs because of the fast movement of vehicles so quick reservation of packet transmission slots by vehicles is important.
In this thesis we propose two new distributed MAC algorithms. One is for WSANs and the other one is for VANETs. We demonstrate using simulations that our algorithms outperform the state-of-the-art algorithms
On the Design of MAC Protocols for Multi-Packet Communication in IEEE 802.11 Heterogeneous Networks Using Adaptive Antenna Arrays
This paper discusses the design requirements for enabling multiple simultaneous peer-to-peer communications in IEEE 802.11 asynchronous networks in the presence of adaptive antenna arrays, and proposes two novel access schemes to realize multipacket communication (MPC). Both presented solutions, which rely on the information acquired by each node during the monitoring of the network activity, are suitable for distributed and heterogeneous scenarios, where nodes equipped with different antenna systems can coexist. The first designed scheme, called threshold access MPC (TAMPC), is based on a threshold on the load sustainable by the single-node, while the second protocol, called signal-to-interference ratio (SIR) access MPC (SAMPC), is based on an accurate estimation of the SIR and on the adoption of low density parity check codes. Both protocols, which are designed to be backward compatible with the 802.11 standard, are numerically tested in realistic scenarios. Furthermore, the performance of the two schemes is compared to the theoretical one and to that of the 802.11n extension in a mobile environment
An analytical model of IEEE 80211 DCF for multi-hop wireless networks and its application to goodput and energy analysis
Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010.Thesis (Ph. D.) -- Bilkent University, 2010.Includes bibliographical references leaves 168-181.In this thesis, we present an analytical model for the IEEE 802.11 DCF in multihop
networks that considers hidden terminals and works for a large range of
traffic loads. A goodput model which considers rate reduction due to collisions,
retransmissions and hidden terminals, and an energy model, which considers
energy consumption due to collisions, retransmissions, exponential backoff and
freezing mechanisms, and overhearing of nodes, are proposed and used to analyze
the goodput and energy performance of various routing strategies in IEEE
802.11 DCF based multi-hop wireless networks. Moreover, an adaptive routing
algorithm which determines the optimum routing strategy adaptively according
to the network and traffic conditions is suggested.
Viewed from goodput aspect the results are as follows: Under light traf-
fic, arrival rate of packets is dominant, making any routing strategy equivalently
optimum. Under moderate traffic, concurrent transmissions dominate and multihop
transmissions become more advantageous. At heavy traffic, multi-hoppingbecomes unstable due to increased packet collisions and excessive traffic congestion,
and direct transmission increases goodput. From a throughput aspect, it is
shown that throughput is topology dependent rather than traffic load dependent,
and multi-hopping is optimum for large networks whereas direct transmissions
may increase the throughput for small networks.
Viewed from energy aspect similar results are obtained: Under light traf-
fic, energy spent during idle mode dominates in the energy model, making any
routing strategy nearly optimum. Under moderate traffic, energy spent during
idle and receive modes dominates and multi-hop transmissions become more advantageous
as the optimum hop number varies with processing power consumed
at intermediate nodes. At the very heavy traffic conditions, multi-hopping becomes
unstable due to increased collisions and direct transmission becomes more
energy-efficient.The choice of hop-count in routing strategy is observed to affect energyefficiency
and goodput more for large and homogeneous networks where it is
possible to use shorter hops each covering similar distances. The results indicate
that a cross-layer routing approach, which takes energy expenditure due to MAC
contentions into account and dynamically changes the routing strategy according
to the network traffic load, can increase goodput by at least 18% and save energy
by at least 21% in a realistic wireless network where the network traffic load
changes in time. The goodput gain increases up to 222% and energy saving up
to 68% for denser networks where multi-hopping with much shorter hops becomes
possible.AydoÄdu, CananPh.D
Recommended from our members
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
Cross-layer optimizations in multi-hop ad hoc networks
Unlike traditional wireless networks, characterized by the presence of last-mile, static and
reliable infrastructures, Mobile ad Hoc Networks (MANETs) are dynamically formed by
collections of mobile and static terminals that exchange data by enabling each other's
communication. Supporting multi-hop communication in a MANET is a challenging
research area because it requires cooperation between different protocol layers (MAC,
routing, transport). In particular, MAC and routing protocols could be considered
mutually cooperative protocol layers. When a route is established, the exposed and
hidden terminal problems at MAC layer may decrease the end-to-end performance
proportionally with the length of each route. Conversely, the contention at MAC layer
may cause a routing protocol to respond by initiating new routes queries and routing table
updates.
Multi-hop communication may also benefit the presence of pseudo-centralized virtual
infrastructures obtained by grouping nodes into clusters. Clustering structures may
facilitate the spatial reuse of resources by increasing the system capacity: at the same
time, the clustering hierarchy may be used to coordinate transmissions events inside the
network and to support intra-cluster routing schemes. Again, MAC and clustering
protocols could be considered mutually cooperative protocol layers: the clustering
scheme could support MAC layer coordination among nodes, by shifting the distributed
MAC paradigm towards a pseudo-centralized MAC paradigm. On the other hand, the
system benefits of the clustering scheme could be emphasized by the pseudo-centralized
MAC layer with the support for differentiated access priorities and controlled contention.
In this thesis, we propose cross-layer solutions involving joint design of MAC, clustering
and routing protocols in MANETs.
As main contribution, we study and analyze the integration of MAC and clustering
schemes to support multi-hop communication in large-scale ad hoc networks. A novel
clustering protocol, named Availability Clustering (AC), is defined under general nodes'
heterogeneity assumptions in terms of connectivity, available energy and relative
mobility. On this basis, we design and analyze a distributed and adaptive MAC protocol,
named Differentiated Distributed Coordination Function (DDCF), whose focus is to
implement adaptive access differentiation based on the node roles, which have been
assigned by the upper-layer's clustering scheme. We extensively simulate the proposed
clustering scheme by showing its effectiveness in dominating the network dynamics,
under some stressing mobility models and different mobility rates. Based on these results,
we propose a possible application of the cross-layer MAC+Clustering scheme to support
the fast propagation of alert messages in a vehicular environment.
At the same time, we investigate the integration of MAC and routing protocols in large
scale multi-hop ad-hoc networks. A novel multipath routing scheme is proposed, by
extending the AOMDV protocol with a novel load-balancing approach to concurrently
distribute the traffic among the multiple paths. We also study the composition effect of a
IEEE 802.11-based enhanced MAC forwarding mechanism called Fast Forward (FF),
used to reduce the effects of self-contention among frames at the MAC layer. The
protocol framework is modelled and extensively simulated for a large set of metrics and
scenarios.
For both the schemes, the simulation results reveal the benefits of the cross-layer
MAC+routing and MAC+clustering approaches over single-layer solutions
Power saving and energy optimization techniques for Wireless Sensor Networks
Wireless sensor networks have become
increasingly popular due to their wide range of applications.
Energy consumption is one of the biggest constraints of the
wireless sensor node and this limitation combined with a
typical deployment of large number of nodes have added
many challenges to the design and management of wireless
sensor networks. They are typically used for remote
environment monitoring in areas where providing electrical
power is difficult. Therefore, the devices need to be powered
by batteries and alternative energy sources. Because battery
energy is limited, the use of different techniques for energy
saving is one of the hottest topics in WSNs. In this work, we
present a survey of power saving and energy optimization
techniques for wireless sensor networks, which enhances the
ones in existence and introduces the reader to the most well
known available methods that can be used to save energy.
They are analyzed from several points of view: Device
hardware, transmission, MAC and routing protocols.Sendra Compte, S.; Lloret, J.; GarcĂa Pineda, M.; Toledo AlarcĂłn, JF. (2011). Power saving and energy optimization techniques for Wireless Sensor Networks. Journal of Communications. 6(6):439-459. doi:10.4304/jcm.6.6.439-459S4394596
The improvements in ad hoc routing and network performance with directional antennas
The ad hoc network has typically been applied in military and emergency environments. In the past decade, a tremendous amount of MAC protocols and routing protocols have been developed, but most of these protocols are designed for networks where devices equipped with omni-directional antennas. With fast development of the antenna technology, directional antennas have been proposed to improve routing and network performance in ad hoc networks. However, several challenges and design issues (like new hidden terminal problem, deafness problem, neighbor discovery problem and routing overhead problem) arise when applying directional antennas to ad hoc networks, consequently a great number of directional MAC and routing protocols have been proposed.
In this thesis the implementation of directional antennas in ad hoc networks is studied from technical point of view. This thesis discusses the problems of utilizing directional antenna in ad hoc networks and reviews several recent proposed MAC algorithms and routing algorithms. The improvement of ad hoc routing and network performance with directional antennas compared with omni-directional antennas are evaluated based on simulations which are done with the QualNet simulator.
The main finding of this study is that directional antennas always outperform omni-directional antennas in both static and mobility scenarios, and the advantage of directional antennas is more obvious when channel condition becomes worse or mobility level is larger.
This thesis provides a survey of directional MAC and routing protocols in ad hoc networks. The result and principles obtained in this thesis are quite valuable for researchers working in this field. They can use it as reference for further researches. The theory parts of smart antenna technology and IEEE 802.11 MAC protocol can be considered as a technical introduction for beginners
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