3,360 research outputs found
Cooperative and fair MAC protocols for cognitive radio ad-hoc networks
A secondary user (SU) in multichannel cognitive
radio ad hoc network (CRAHN) has a limited transmission
range, which may raise a hidden multichannel sensing
problem. In addition, CRAHNs can be deployed ubiquitously,
and SUs from any CRAHNs could co-exist utilizing
the spectrum. This situation leads to the fairness issue of
spectrum resource sharing between the SUs. Both cooperative
and fairness issues are important to CRAHN performance.
In this paper, a cooperative and a non-cooperative
multichannel (MC)-MAC protocol is proposed. In order to
address the fairness issue, a fair multichannel (FMC)-MAC
protocol for CRAHN is proposed, which orientates to the
fairness in resource sharing. In this FMC-MAC, the SU
keeps the current backoff (CB) counter when a PU appears
to claim the intended channel. These proposed MAC protocols
are simulated using NS2 and compared with other
protocols. In addition, a mathematical model using Markov
chain is constructed for FMC-MAC and the performance
measures are derived. From results, the MC-MAC protocol
has enhanced the network utilization and the cooperative
scheme has signiďŹcantly enhanced the packet delivery ratio
and decreased the end-to-end delay of SUs in high trafďŹc.
The cooperative protocol enhances packet delivery ratio up
to 15 % and decreases end-to-end delay down to 32 %,
compared to the non-cooperative one. The FMC-MAC
protocol with other two existing protocols. From the
comparison results, a higher fairness has been shown by
FMC-MAC CB while still maintaining a high throughput
A New Exposed-terminal-free MAC Protocol for Multi-hop Wireless Networks
AbstractThis article presents a new multichannel medium access control (MAC) protocol to solve the exposed-terminal (ET) problem for efficient channel sharing in multi-hop wireless networks. It uses request-to-send and clear-to-send (RTS/CTS) dialogue on a common channel and flexibly opts for conflict-free traffic channels to carry out the data packet transmission on the basis of a new channel selection scheme. The acknowledgment (ACK) packet for the data packet transmission is sent back to the sender over another common channel thus completely eliminating the exposed-terminal effects. Any adjacent communication pair can take full advantage of multiple traffic channels without collision and the spatial reuse of the same channel is extended to other communication pairs which are even within 2 hops from them. In addition, the hidden-terminal effect is also considerably reduced because most of possible packet collisions on a single channel are avoided due to traffic load balance on multichannels. Finally, a performance comparison is made between the proposed protocol and other typical MAC protocols. Simulation results evidence its obvious superiority to the MAC protocols associated with other channel selection schemes and traditional ACK transmission scheme as well as cooperative asynchronous multichannel MAC (CAM-MAC) protocol in terms of four performance indices: total channel utilization, average channel utilization, average packet delay, and packet dropping rate
When Channel Bonding is Beneficial for Opportunistic Spectrum Access Networks
Transmission over multiple frequency bands combined into one logical channel
speeds up data transfer for wireless networks. On the other hand, the
allocation of multiple channels to a single user decreases the probability of
finding a free logical channel for new connections, which may result in a
network-wide throughput loss. While this relationship has been studied
experimentally, especially in the WLAN configuration, little is known on how to
analytically model such phenomena. With the advent of Opportunistic Spectrum
Access (OSA) networks, it is even more important to understand the
circumstances in which it is beneficial to bond channels occupied by primary
users with dynamic duty cycle patterns. In this paper we propose an analytical
framework which allows the investigation of the average channel throughput at
the medium access control layer for OSA networks with channel bonding enabled.
We show that channel bonding is generally beneficial, though the extent of the
benefits depend on the features of the OSA network, including OSA network size
and the total number of channels available for bonding. In addition, we show
that performance benefits can be realized by adaptively changing the number of
bonded channels depending on network conditions. Finally, we evaluate channel
bonding considering physical layer constraints, i.e. throughput reduction
compared to the theoretical throughput of a single virtual channel due to a
transmission power limit for any bonding size.Comment: accepted to IEEE Transactions on Wireless Communication
An efficient multichannel wireless sensor networks MAC protocol based on IEEE 802.11 distributed co-ordinated function.
This research aimed to create new knowledge and pioneer a path in the area relating to future trends in the WSN, by resolving some of the issues at the MAC layer in Wireless Sensor Networks. This work introduced a Multi-channel Distributed Coordinated Function (MC-DCF) which takes advantage of multi-channel assignment. The backoff algorithm of the IEEE 802.11 distributed coordination function (DCF) was modified to invoke channel switching, based on threshold criteria in order to improve the overall throughput for wireless sensor networks.
This work commenced by surveying different protocols: contention-based MAC protocols, transport layer protocols, cross-layered design and multichannel multi-radio assignments. A number of existing protocols were analysed, each attempting to resolve one or more problems faced by the current layers.
The 802.15.4 performed very poorly at high data rate and at long range. Therefore 802.15.4 is not suitable for sensor multimedia or surveillance system with streaming data for future multichannel multi-radio systems.
A survey on 802.11 DCF - which was designed mainly for wireless networks âsupports and confirm that it has a power saving mechanism which is used to synchronise nodes. However it uses a random back-off mechanism that cannot provide deterministic upper bounds on channel access delay and as such cannot support real-time traffic. The weaknesses identified by surveying this protocol form the backbone of this thesis
The overall aim for this thesis was to introduce multichannel with single radio as a new paradigm for IEEE 802.11 Distributed Coordinated Function (DCF) in wireless sensor networks (WSNs) that is used in a wide range of applications, from military application, environmental monitoring, medical care, smart buildings and other industry and to extend WSNs with multimedia capability which sense for instance sounds or motion, video sensor which capture video events of interest.
Traditionally WSNs do not need high data rate and throughput, since events are normally captured periodically. With the paradigm shift in technology, multimedia streaming has become more demanding than data sensing applications as such the need for high data rate protocol for WSN which is an emerging technology in this area. The IEEE 802.11 can support data rates up to 54Mbps and 802.11 DCF was designed specifically for use in wireless networks.
This thesis focused on designing an algorithm that applied multichannel to IEEE 802.11 DCF back-off algorithm to reduce the waiting time of a node and increase throughput when attempting to access the medium. Data collection in WSN tends to suffer from heavy congestion especially nodes nearer to the sink node. Therefore, this thesis proposes a contention based MAC protocol to address this problem from the inspiration of the 802.11 DCF backoff algorithm resulting from a comparison of IEEE 802.11 and IEEE 802.15.4 for Future Green Multichannel Multi-radio Wireless Sensor Networks
Adaptive multi-channel MAC protocol for dense VANET with directional antennas
Directional antennas in Ad hoc networks offer more benefits than the traditional antennas with omni-directional mode. With directional antennas, it can increase the spatial reuse of the wireless channel. A higher gain of directional antennas makes terminals a further transmission range and fewer hops to the destination. This paper presents the design, implementation and simulation results of a multi-channel Medium Access Control (MAC) protocols for dense Vehicular Ad hoc Networks using directional antennas with local beam tables. Numeric results show that our protocol performs better than the existing multichannel protocols in vehicular environment
A novel multi-fold security framework for cognitive radio wireless ad-hoc networks
Cognitive Radio (CR) Technology has emerged as a smart and intelligent technology to address the problem of spectrum scarcity and its under-utilization. CR nodes sense the environment for vacant channels, exchange control information, and agree upon free channels list (FCL) to use for data transmission and conclusion. CR technology is heavily dependent on the control channel to dialogue on the exchanged control information which is usually in the Industrial-Scientific-Medical (ISM) band. As the ISM band is publically available this makes the CR network more prone to security vulnerabilities and flaws. In this paper a novel multi-fold security framework for cognitive radio wireless ad-hoc networks has been proposed. Multiple security levels, such as, encryption of beacon frame and privately exchanging the FCL, and the dynamic and adaptive behaviour of the framework makes the proposed protocol more resilient and secure against the traditional security attacks when compared with existing protocols
MAC-Oriented Programmable Terahertz PHY via Graphene-based Yagi-Uda Antennas
Graphene is enabling a plethora of applications in a wide range of fields due
to its unique electrical, mechanical, and optical properties. In the realm of
wireless communications, graphene shows great promise for the implementation of
miniaturized and tunable antennas in the terahertz band. These unique
advantages open the door to new reconfigurable antenna structures which, in
turn, enable novel communication protocols at different levels of the stack.
This paper explores both aspects by, first, presenting a terahertz
Yagi-Uda-like antenna concept that achieves reconfiguration both in frequency
and beam direction simultaneously. Then, a programmable antenna controller
design is proposed to expose the reconfigurability to the PHY and MAC layers,
and several examples of its applicability are given. The performance and cost
of the proposed scheme is evaluated through full-wave simulations and
comparative analysis, demonstrating reconfigurability at nanosecond granularity
with overheads below 0.02 mm and 0.2 mW.Comment: Accepted for presentation in IEEE WCNC '1
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