The paper addresses a bandwidth selection problem while channel bonding scheme is used in IEEE 802.11ac wireless local area networks (WLANs) such that a channel with appropriate bandwidth can be utilized by STAs to transmit without collision. The goal of IEEE 802.11ac is to provide very high throughput (VHT) WLANs over 5 GHz band. Among the new technologies specified in IEEE 802.11ac, channel bonding is regarded as a quite useful scheme to accommodate growing traffic demands in WLANs. However, to effectively exploit the efficiency of channel bonding scheme, a well-designed MAC protocol is of crucial importance. As a result, the transmission in a wider bandwidth is analyzed first. Based on the results, two problems, Carrier Sensing Decreasing Problem (CSDP) and Outside Warning Range Problem (OWRP), are conducted in this paper. Moreover, the paper analyzes the relationships among the transmission range, carrier-sensing range, and interference range in case that channel bonding is adopted. Consequently, a dynamic bandwidth selection (DBS) MAC protocol for IEEE 802.11ac WLANs is proposed to avoid collisions. DBS can not only prevent CSDP and OWRP problems but also can increase network performance. Simulation results show that DBS outperforms against other protocols in packet successful rate and network throughput.

The paper addresses an area coverage problem by using rotatable cameras in wireless camera sensor networks. It has been recognized as an important issue not only to effectively cover an area of interest without holes but also to identify the object invaded the area by cameras in wireless camera sensor networks. Therefore, this paper presents a Full-View Area Coverage (FVAC) scheme to effectively deploy rotatable camera sensors and tune their directions such that not only the area can be covered completely but also the object can be identified. In FVAC, the sizes of safe and unsafe regions with effective angle are derived. Moreover, a grid deployment model is investigated to deploy and rotate the camera sensors in accordance with the safe and unsafe regions in order not only to cover the area but also to identify the object. The grid size, that is, the distance among camera sensors, is also derived according to the effective angle and the sensing radius of camera sensors. Performance results show that the proposed scheme can reduce the number of deployed camera sensors and successfully identify objects against the related work in cases of a small effective angle or a short sensing radius.

Effectively broadcasting emergency messages in vehicular ad hoc networks (VANETs) is an important issue in VANETs. This paper proposes a Dynamic Search-Assisted Broadcast (DSAB) protocol to effectively broadcast emergency messages in VANETs. Dynamically adjusting the transmission power of control messages to estimate the vehicle density and appropriately adopting n-way search to find the farthest vehicle are the major techniques in DSAB protocol. To do so can not only find the best vehicle in the farthest segment to relay the emergency messages in the network, but also can reduce the interference among vehicles to save the network resource and increase the packet delivery ratio. Some mathematical analyses about time slot overhead in n-way search are done to support DSAB protocol in different vehicle densities. Based on the network simulations, the proposed protocol, DSAB, has a significant performance against the related work in one hop delay and packet delivery ratio.

Distributed Coordination Function (DCF) is a well-known MAC protocol for single channel wireless ad-hoc networks. However, hidden terminal and false blocking problems may happen if DCF is directly applied to multi-channel environments. As a result, the paper proposes a Multi-group Multipipeline Multi-channel MAC protocol (3M MAC) for wireless multi-channel ad-hoc networks to avoid multi-channel hidden terminal and false blocking problems. 3M MAC divides a transmission into several subtransmissions. Each subtransmission is transmitted sequentially on all channels. Under this pipelinelike scheme, we further analyze the impact of the channel switch time and DATA packet size on network performance. Based on the analyzed results, a channel leak problem will happen to decrease the performance in case that the number of channels is large. The main concept of 3M MAC is to classify channels into groups to alleviate the channel leak problem. Finally, we compare 3M MAC with three well-known multi-channel MAC protocols and IEEE 802.11 DCF. Simulation results show that 3M MAC has the best performance in network throughput and transmission delay.

This study proposes a link quality aware routing protocol for low-power and lossy networks. The proposed protocol primarily considers the quality of links to determine the node rank for constructing a proper destination-oriented directed acyclic graph, on which a node may have many parents. In the proposed protocol, a node selects the node with the maximum remaining energy from all of its neighbors as the next hop to guarantee that the packet has a high probability of being forwarded toward the destination. Simulation results confirm that, compared with the routing protocol based on the hop count, the proposed protocol improves the packet delivery ratio, especially for environments with a high bit error rate. Results also show that the proposed protocol can balance the energy consumption of nodes in the network.

A kind of hidden terminal problem, called the POINT problem, which is caused by the expansion of the interference range of the receiver due to the controlled transmission power of the sender, is deemed a notorious problem in wireless ad hoc networks. This paper utilizes physical and virtual carrier-sensing schemes to avoid the POINT problem. We analyze the relationships among the transmission range, the carrier-sensing range, and the interference range in case power control is adopted, and based on the analyzed results, we propose four mechanisms to prevent the POINT problem from occurring in wireless ad hoc networks. This paper further analyzes the superiority of each mechanism under certain situations and proposes an adaptive range-based power control (ARPC) MAC protocol to make use of the advantages of the four mechanisms to avoid the POINT problem from happening. The proposed protocol cannot only prevent collisions caused by the POINT problem, but it can also reduce the energy consumption of STAs. Simulation results also verify the advantages of the proposed protocol.

The activity scheduling of sensors to alternately wake up for sensing obligation such that the network lifetime can be efficiently prolonged is a very important issue in wireless sensor networks (WSNs). Target area coverage is a new coverage problem in wireless sensor networks. The paper addresses the target area coverage problem and schedules sensors to alternatively wake up to collaboratively cover and sense the target area. A geometric-based activity scheduling scheme, named GAS scheme, for WSNs to fully cover a target area is proposed. By means of computational geometry, the sensors can self-determine when to sleep or wake up while preserving the sensing coverage. GAS is able to find as few sensors as possible to cover the target area, which is termed a cover set. In addition, GAS can find as many number of cover sets as possible to be alternately in charge of the sensing task. Simulation results show that GAS can efficiently schedule the sensor when to switch between active and sleep modes. Furthermore, the network lifetime can be prolonged significantly in comparison with the state-of-the-art schemes.

The paper proposes a multi-rate supported power control, named MRPC, MAC protocol to avoid the LIRC (Large Interference Range Collision) problem for wireless ad hoc networks. The main concept of the MRPC protocol is to protect the current reception by means of the carrier-sensing range of the previous transmission to cover the induced interference range of the current reception. Based on the concept, MRPC formulates the requirements of a successful transmission and figures out the appropriate power strength for transmissions. Furthermore, since the threshold values of SNR and receiver sensitivity values are changed with the data transfer rates, MRPC also takes the different threshold values in multi-rate environments into consideration in formulating these requirements. MRPC can reduce the energy consumption and increase the spatial reuse due to the controlled transmission power. It is further shown that MRPC can also work correctly in multi-rate environments. Simulation results show that MRPC performs much better than the related work in terms of network throughput as well as the energy efficiency.

Resolving hidden terminal problem is one of the major responsibilities in designing MAC protocols for wireless ad hoc networks. The paper proposes a fragmentation-based MAC protocol with power control, named F-RCRC MAC protocol, to avoid the LIRC (large interference range collision) problem, a kind of hidden terminal problem, for wireless ad hoc networks. F-RCRC designs a new interframe space, named FIFS, to reduce the overhead caused by the fragmentation scheme. With the fragmentation, the design of FIFS can effectively avoid the hidden STAs interfering with the receivers' receiving. Moreover, a dynamic transmission power scheme is devised to actively and timely warn the hidden STAs such that the possible collision is avoided. Thus, the LIRC problem can be solved and the network throughput is increased accordingly. In addition, F-RCRC can reduce the energy consumption and increase the spatial reuse due to the controlled transmission power. Simulation results show that F-RCRC performs much better than the related work in terms of network throughput as well as the power throughput.

The paper analyzes the relationships among the transmission range, carrier sensing range, and interference range in case that power control is adopted and proposes an adaptive range-based power control (ARPC) MAC protocol for wireless ad hoc networks to avoid collisions. Based on the analysis results, four mechanisms, STRC, RTRC, SCRC, and RCRC are proposed to prevent from collisions. The paper further analyzes the superiority of each mechanism under certain situations and proposes the ARPC MAC protocol to make use of the advantages of the four mechanisms to avoid collisions. The proposed protocol can not only reduce energy consumption of STAs, but also prevent from collisions. Simulation results also verify the advantages of the proposed protocol.

The paper proposes a distributed active sensor selection scheme, named DASS, for WSNs, under the requirement of complete coverage of a sensing field. By means of Voronoi diagram, the sensor can find appropriate sensors to work together for the sensing tasks. DASS can find as few number of sensors as possible to be in charge of the sensing task. Simulation results show that DASS can efficiently select few sensors to cover the whole sensing field. Furthermore, the network lifetime can be protracted significantly in comparison with the state-of-the-art schemes.

Increasing the capacity of wireless communication is an open and interesting research area which has attracted much attention. The familiar solution is dividing the radio spectrum into several independent radio channels, which can be operated and accessed simultaneously by all nodes within its radio transmitting power. All solutions of researches adopt multiple transceivers to fulfil this goal. Nevertheless, these schemes will be short of implementation and may increase the prime cost since most wireless devices only equip one transceiver. Moreover, with a few exceptions, most researchers have emphasized centralized resource allocation algorithms for cellular systems where the base station keeps track of the requirements of the various users and is thus responsible for the management of network resources. However, on the other hand, multihop mobile ad hoc networks (MANETs) are generally configured as peer-to-peer networks with no centralized hubs or controllers. Therefore, in this paper, we proposed a multichannel medium access control (MAC) protocol, named ad hoc multichannel negotiation protocol (AMNP), for multichannel transmission in distribution fashion. We address the issue of distributed resource allocation for multihop MANETs by presenting an AMNP that builds on the multichannel request-to-send/clear-to-send (MRTS/MCTS) bandwidth reservation mechanism under the constraint of single transceiver. We show via simulations that AMNP provides a higher throughput compared to its single channel counterpart by promoting simultaneous transmissions in different channels. Simulation results also show that the performance of proposed AMNP derives well than other multichannel approaches with multiple transceivers.