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

Preliminary discussion on globally prioritized medium access for multi-channel wireless systems

We discuss the development of a simple globally prioritized multi-channel medium access control (MAC) protocol for wireless networks. This protocol provides “hard” pre-run-time real-time guarantees to sporadic message streams, exploits a very large fraction of the capacity of all channels for “hard” real-time traffic and also makes it possible to fully utilize the channels with non real-time traffic when hard real-time messages do not request to be transmitted. The potential of such protocols for real-time applications is discussed and a schedulability analysis is also presented

A Novel Opportunistic Spectrum Sharing Scheme for Cognitive Ad Hoc Networks

Nowadays, wireless ad hoc networks are using a static spectrum allocation which leads to congestion in this spectrum parts as the number of devices increases. On the contrary, a significant portion of the spectrum in licensed band (e.g. TV band) is not utilized. Cognitive radio (CR) is a promising technology to solve the spectrum inefficiency problem in ad hoc networks. Based on CR, the unlicensed (secondary) users will utilize the unused spectrum of the licensed (primary) users in an opportunistic manner. As a result, the average spectrum usage will be increased. However, the sudden appearance of primary users will have a negative impact on the performance of secondary users, since secondary users must evacuate the occupied channel and handoff to another unutilized one. This process continues till an unlicensed user finishes his transmission. We will name this process consecutive spectrum handoff (CSH). In order to increase the performance of CR, the number of consecutive spectrum handoffs should be reduced. In this paper, a novel opportunistic spectrum sharing scheme under a heterogeneous spectrum environment of licensed and unlicensed bands is introduced. In this scheme, the licensed channels will be used as operating channels and the unlicensed channels will be used as backup channels when the primary user appears. Since the unlicensed channels are not interrupted by primary users, no more spectrum handoff is needed

Multi-channel Utilization Algorithms for IEEE 802.15.4 based Wireless Network: A Survey

In the pass years, IEEE 802.15.4 based Wireless Sensor Networks (WSNs) have received great attention and have been employed in many areas such as inventory checking, local monitoring and alarming etc. One of the key issues affecting WSN's system performance is interference caused by devices operating with the same or different standards on the overlapping frequency within the 2.4 GHz ISM band. This paper addresses the coexistence problem, which is the key motivation for the necessity of flexible channel usage. A review of existing approaches being proposed to date supporting multi-channel utilization in IEEE 802.15.4 based WSNs is categorized and discussed. The paper also presents major functionalities needed in implementing multi-channel utilization

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

A Reservation Protocol Analysis for Multi-Channel Wireless Networks

A synchronous multi-channel multi-access Medium Access Control (MAC) protocol for Wireless Local Area Networks (WLANs) is studied in this paper. The proposed protocol introduces an access control reservation scheme and requires a single radio per station. The receiver collisions phenomenon characterizes the performance of the proposed multi-channel system. A priority scheme is considered in order to primary serve the time-sensitive traffic such as voice, as compared to the delay tolerant data traffic. The innovation of this paper is the extensive and accurate study of the receiver collisions effect on the network performance in multi-traffic environment. An analytic discrete time Markovian model is developed for finite number of stations and channels. The performance measures of throughput, delay, and average rejection probability at destination are analytically estimated. Numerical results are presented for comparison for various numbers of channels and stations. The proposed MAC protocol provides a substantial contribution to the understanding of wireless multi-channel multi-traffic environments

Understanding the Paradoxical Effects of Power Control on the Capacity of Wireless Networks

Recent works show conflicting results: network capacity may increase or decrease with higher transmission power under different scenarios. In this work, we want to understand this paradox. Specifically, we address the following questions: (1)Theoretically, should we increase or decrease transmission power to maximize network capacity? (2) Theoretically, how much network capacity gain can we achieve by power control? (3) Under realistic situations, how do power control, link scheduling and routing interact with each other? Under which scenarios can we expect a large capacity gain by using higher transmission power? To answer these questions, firstly, we prove that the optimal network capacity is a non-decreasing function of transmission power. Secondly, we prove that the optimal network capacity can be increased unlimitedly by higher transmission power in some network configurations. However, when nodes are distributed uniformly, the gain of optimal network capacity by higher transmission power is upper-bounded by a positive constant. Thirdly, we discuss why network capacity in practice may increase or decrease with higher transmission power under different scenarios using carrier sensing and the minimum hop-count routing. Extensive simulations are carried out to verify our analysis.Comment: I refined the previous version in many places, including the title. to appear in IEEE Transactions on Wireless Communication