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.

In IEEE 802.16e networks, with the popularisation of multimedia services, multicast and unicast services can coexist in one mobile subscriber station (MSS). The mobile devices are generally powered by battery, which is limited in energy. Thus, power saving is an important issue to be considered for extending the lifetime of the MSSs. The authors have proposed a multicast services‐based scheduling (MSBS) algorithm that improves the energy efficiency of both unicast and multicast services, while satisfying the quality of service requirements of the MSSs in 802.16e wireless networks. MSBS schedules the packets in such a way that each packet is transmitted before its deadline and the energy consumed by the MSSs is reduced by minimising the number of state transitions by the MSSs. The simulation results show that MSBS can produce significant overall energy‐saving and prolonged lifetime as compared to other scheduling schemes in 802.16e wireless networks.

In IEEE 802.16m networks, each frame is divided into eight advanced air interface (AAI) subframes, composed of Logical Resource Units (LRUs). According to stations' requirements, advanced base stations (ABSs) allocate bursts constructed by contiguous LRUs to stations. If ABSs can not efficiently schedule and allocate bursts, bandwidth resource will be wasted in or among bursts. Such these problems are called internal fragmentation and external fragmentation in this paper. In this study, this paper formulates a downlink burst allocation problem, considering both internal fragmentation (IF) and external fragmentation (EF), and then proposes a variable-length burst scheduling algorithm, called VLBS, to determine the position and the number of required LRUs of each burst in the downlink (DL) AAI subframe, subject to minimizing the bandwidth wastage. Moreover, VLBS also tries to allocate bursts across several AAI subframes so that the bandwidth wastage can further be decreased. Simulation results show that VLBS outperforms other related approaches in the network throughput, service ratio, and the bandwidth utilization ratio.

The paper investigates the downlink burst scheduling problem (BSP) in IEEE 802.16 OFDMA systems. To solve the problem, a subchannel-aware burst fragmentation, packing and scheduling (BFPS) algorithm is proposed to schedule the position of each burst with high subchannel utilization and low DL-MAP overhead. BFPS is composed of the burst allocation scheme, burst fragmentation and packing scheme, and the burst swapping scheme. The burst allocation scheme and the burst fragmentation and packing scheme are to reduce the wasted and unused slots in and among bursts, and the DL-MAP control overhead. Moreover, in order for the channel compensation, the burst swapping scheme is used to adjust the positions of bursts. The simulation results highlight that BFPS outperforms other related approaches in the network throughput, DL-MAP IE efficiency, service ratio, and the bandwidth utilization ratio.

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 paper proposed a distributed algorithm, namely CoBRA (Cone-based Barrier coveRage Algorithm), to achieve barrier coverage in wireless camera sensor networks (WCSNs). To the best understanding, CoBRA is the first algorithm which try to deal with the barrier coverage issue in WCSNs. Based on some observations, the basic concept of CoBRA is that each camera sensor can determine the local possible barrier lines according to the geographical relations with their neighbors. A sink in a WCSN initiates Barrier Request (BREQ) messages to form the possible barrier lines. Afterward, a barrier line is constructed by the Barrier Reply (BREQ) message initiated by another sink. CoBRA mainly includes three phases: Initial Phase, Candidate Selection Phase, and Decision Phase. In the Initial Phase, each camera sensor collects the local information of its neighbors and estimates the possible barrier lines. In the Candidate Selection Phase, a sink initiates the BREQ packets and forwards the BREQ packets to camera sensors. Camera sensors receiving the BREQ then reforward the BREQ packets to its neighbors who are capable of forming a barrier line. All camera sensors receiving the BREQ will forward the BREQ to their neighbors again in the same manner. Finally, in the decision phase, after the BREQ message is transmitted through the whole monitoring area, a BREP message is used by the sink to select a barrier line in a WCSN. The barrier coverage is achieved by finding the barrier line in the monitoring area. Experiment results show that CoBRA can efficiently achieve barrier coverage in WCSNs. Comparing to the ideal results, CoBRA can use fewer nodes to accomplish barrier coverage in random deployment scenarios.

In IEEE 802.11 standard, the use of multi-channel is one of the most important characteristic features contributing to the improvement of the overall network throughput. However, the channel utilization based on the use of multi-channel is relatively low because most medium access control (MAC) protocols were designed based primarily on the application of non-overlapping channels. This paper analyzes the channel utilization for the schemes using both non-overlapping and overlapping channels. Based on the analysis, we propose a scheme to exploit overlapping channels with collision avoidance mechanism. The proposed scheme makes use of the non-overlapping channels to increase the network throughput and it also takes into account the transmissions on different channels in order to maximize the throughput. Simulation results verify the effectiveness of the proposed scheme.

In IEEE 802.16e WiMAX networks, burst is the system resource allocated by BS for users to receive or transmit data. Due to the limitation in system resource, designing an efficient way for BS to allocate the burst to MS becomes important. In general, burst allocation is regarded as the determination of the shape, location, and the modulation scheme of each burst, and it has been proved an NP problem. In this paper, we propose an efficient downlink bandwidth allocation scheme, namely EDBA, to allocate downlink bursts in a heuristic way. EDBA mainly considers the subchannel quality and selects a better modulation scheme for burst transmission to improve the subchannel utilization. Moreover, EDBA adjusts the shape and determines the location of the burst to reduce the numbers of unused slots (i.e., internal bandwidth wastage) and unallocated slots (external bandwidth wastage) resulted from the restriction of rectangular burst. The simulation results reveal that the proposed EDBA can achieve significant improvement in subchannel utilization and better network throughput than other mechanisms.

This paper investigates the downlink burst allocation problem in IEEE 802.16 OFDMA system. In order to increase the subchannel utilization and to improve the network throughput, a channel-aware renumbering (CSR) scheme and a channel-aware downlink burst allocation (CDBA) scheme are proposed in this paper. CSR considers the difference among subchannel qualities of MSs and logically renumbers the subchannels so that each MS can have a group of subchannels supported the same and more efficient modulation and coding (MC) scheme. CDBA is to decide the size, shape and the position of each burst. Because of the rectangular burst allocation constraint, some slots in or among rectangular bursts will be wasted. These two kinds of slot wastage problems are defined as internal and external fragmentation problems in the paper. Therefore, in order to comply with the rectangular burst allocation constraint, to overcome the fragmentation problems and to increase the network throughput, CDBA is to determine the size and the position of each MS's burst based on the subchannel qualities of MSs and the bandwidth requirements. The simulation results show that CDBA with CSR outperforms other related approaches with or without CSR in terms of the throughput, the service ratio, the subchannel utilization and the DL-MAP overhead.

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.

In the IEEE 802.16j multi-hop relay (MR) network, the design of an effective path selection scheme is an important issue for throughput gain and overhead reduction. This paper proposes a new metric, called SEL, to evaluate the possible relay paths and thereby determine the appropriate one among these paths. SEL mainly considers both link spectral efficiency and link load, and based on SEL, a comprising function is developed to formulate the path cost to select the appropriate relay path. As confirmed by the performance evaluation, the proposed path selection scheme with SEL consideration significantly outperforms the existing path selection schemes in network throughput and map overhead.

This paper aims to investigate the minislot scheduling problem in IEEE 802.16 mesh networks, where a minislot is the atomic unit for bandwidth allocation. Inappropriate minislot selection will cause minislot insufficient problems and the data collision problems. These problems will degrade the network throughput and the minislot utilization. Therefore, a Decentralized Minislot Scheduling Protocol (DMSP) is proposed for throughput gains in IEEE 802.16 mesh networks. DMSP contains Minislot Usage Constraints (MUCs) and Minislot Decision Strategies (MDSs) for Subscriber Stations (SSs) to determine the validity of each minislot and to select minislots from valid minislots for the data transmission, respectively. Simulation results show that DMSP can achieve better performance than related work in terms of the transmission delay, control overhead, minislot utilization, and the network throughput.

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.

This study proposes a novel multi-channel medium access control protocol for mobile ad hoc networks that enables nodes to transmit packets in distributed channels. In our protocol, the ad hoc traffic indication message window is divided into two windows. The first window is called the deciding channel window (DCW). Source and destination nodes can negotiate with each other in deciding a channel that can be used to compete for the final data channel in the DCW. The second window is called the exchanging packet window (EPW). Pair source and destination nodes can compete to obtain a channel to transfer packets in the EPW. This mechanism can distribute pair source and destination nodes to compete for a data channel. Hence, because of this, collisions can be avoided greatly and throughput can be increased. The simulation results show that our protocol successfully exploits the use of the bandwidth of multiple channels effectively.

The paper presents a cross-layer energy-efficient and reliable routing (named CLE2aR2) protocol to construct an energy efficient and reliable route and resist the variation of wireless channels for wireless ad hoc networks. CLE2aR2not only considers how to construct a route from the source to the destination, but also takes some important lower-layer factors, such as power strength, data transfer rate, and interference, into account to reflect the real situation of a wireless channel dynamically and instantly. Based on these factors, a reliable route can be constructed such that the retransmission cost can be reduced and the energy consumption can be saved. Simulation results also show that CLE2aR2can indeed construct an energy efficient and reliable route in comparison with the related work.

The paper proposes a fragment and rate matching (FaRM) MAC protocol for wireless local area networks (LANs) to resist the frequent changing of channel quality and increase the network throughput. In wireless environments, channel quality varies with time. FaRM dynamically detects the current SNR to estimate the channel quality through the control frame exchanges. A Finite State Markov Chain (FSMC) is adopted to predict the variation of the channel condition. According to the results generated from FSMC, FaRM enables a station to select an appropriate transmission rate as well as an acceptable fragment length dynamically to transmit in order to both increase the reliability and shorten the channel access time of the transmission. The simulation results show FaRM has better performance, higher transmission reliability, and lower transmission delay time by fragment and rate matching.

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 proposes a self-regulatory-learning- cycle-based system to not only provide a pleasant learning environment, but also effectively enhance the performance of self-regulated learning (SRL) of learners. Learners utilizing the proposed system can repeatedly experience SRL processes and establish their patterns of SRL gradually. Experiment results show that the proposed system can help learners possess SRL skills, especially for unskillful learners.

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 considers the target coverage problem in wireless heterogeneous sensor networks (WHSNs) with multiple sensing units. The paper reduces the problem to a set cover problem and further formulates it as integer programming (IP) constraints. Moreover, two heuristic but distributed schemes, remaining energy first scheme (REFS) and energy efficient first scheme (EEFS), are proposed to solve the target coverage problem. Simulation results show that REFS and EEFS effectively prolong the network lifetime. In addition, EEFS outperforms REFS in network lifetime.

The paper proposes a distributed partition avoidance lazy movement (PALM) protocol for mobile sensor networks (MSNs). In general, connectivity and coverage are two major factors to the success of a sensor network. Therefore, PALM takes both connectivity and coverage into account to avoid network partition and keep high sensing quality. Since sensor movement is the major source of energy consumption, thus, in order not to cause frequent movement, PALM triggers sensor movement only when the network has a risk of partition, but not when coverage holes appear. The paper proposes a sufficient condition of keeping a network connected. Based on the condition, PALM adopts the lazy movement policy for a sensor to determine when to move and uses the principles of an effective movement for a sensor to decide where to move. Accordingly, PALM can keep the network connected and can make the effective coverage as large as possible to maintain high sensing quality. In comparison with the related work, PALM can reduce the energy consumption and further extend the network lifetime due to the lazy movement policy and the principles of an effective movement. Simulation results also verify the advantages of the proposed protocol.

The paper proposes an RCA MAC protocol to reduce RTS collisions. The protocol utilizes a narrow band, called the tone channel, to announce the RTS transmission in advance to preclude the RTS transmissions of two-hop neighbors. To reduce the channel and hardware overhead, an improvement to the RCA protocol is also devised, which only uses a single channel and one transceiver to reduce RTS collisions. The RCA protocol provides a type of fast collision detection and decreases the probability of RTS collisions. Meanwhile, the RCA protocol can reduce the retransmission cost and has lower control overhead than that of IEEE 802.11 DCF. In addition, simulation results verify the advantages of the RCA protocol in comparison with IEEE 802.11 DCF.

In wireless sensor networks (WSNs), nodes closer to the sink node have heavier traffic load for packet forwarding. The unbalanced power consumption among sensor nodes may cause network partition. This paper proposes efficient node placement and topology control protocols to balance the power consumption of sensor nodes. Firstly, a virtual tree topology is constructed based on Grid-based WSNs. Then two node placement techniques, namely Distance-based and Density-based deployment schemes are proposed to balance the power consumption of sensor nodes. Finally, extension of the proposed protocols are made from a Grid-based WSN to a randomly deployed WSN, making the developed energy-balanced schemes can be generally applied to randomly deployed WSNs. Simulation results reveal that the developed protocols can efficiently balance each sensor node's power consumption and prolong the network lifetime in both Grid-based and randomly deployed WSNs.

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.

Event detection and tracking are attractive research issues in the wireless sensor network (WSN). The paper proposes a fully distributed protocol, CollECT, to event detection and tracking in a Wireless Heterogeneous Sensor Network (WHSN), composed of many kinds of sensors. In CollECT, three major procedures, vicinity triangulation, event determination, and border sensor selection are used to construct the logical triangle in the vicinity of a sensor, to determine the event, and to select the border sensor to identify the event boundary, respectively. The procedures perform repeatedly to both detect and track events. Simulation results demonstrate that CollECT is promising for event detection and tracking due to satisfactory event accuracy and reasonable fitness of border sensors.

In wireless sensor networks, a geographic region without functionality of sensing and communication can be generally treated as an obstacle, which significantly impacts the performance of existing location-based routing. In a WSN, an obstacle can be dynamically formed due to unbalanced deployment, failure or power exhaustion of sensors, animus interference, or physical obstacles such as mountains or buildings. This paper proposes a novel algorithm, namely RGP, to enable the existing location-based routing protocols resisting obstacles. Applying the proposed RGP, border nodes that surround the obstacles will actively establish a forbidden region for concave obstacles and make the obstacle information transparent. Then packets will be guided to overcome the obstacle and move along the shortest path from the encountered border node to the sink node. Simulation results show that RGP creates low overhead and significantly reduces the average route length and therefore improves the energy consumption and end-to-end delay for a wireless sensor network with obstacles

Bluetooth is a low cost, low power, short-range radio technology used for wireless personal area networks (PANS). Bluetooth scatternet is a set of piconets interconnected via bridge devices. Good interpiconet schedulings are necessary for bridge devices to switch among piconets they participate in. This paper proposes an interpiconet scheduling algorithm named "Traffic-Aware Scatternet Scheduling" (TASS), for bridges in Bluetooth scatternets. According to masters' traffic information, TASS can adaptively switch the bridge to high traffic load masters, and increase the usage of the bridge. In addition, TASS can reduce the number of failed "unsniffs" and the overhead of "bridge switch wastes" to further increase overall system performance. Simulation results show that TASS outperforms existing interpiconet scheduling in both network throughput and adaptability for various traffic loads.

Scarce resources of wireless medium (e.g., bandwidth, battery power, and so on) significantly restrict the progress of wireless local area networks (WLANs). Heavy traffic load and high station density are most likely to incur collisions, and further consume bandwidth and energy. In this paper, a distributed power-saving protocol, power-efficient MAC protocol (PEM), to avoid collisions and to save energy is proposed. PEM takes advantage of power control technique to reduce the interferences among transmission pairs and increase the spatial reuse of WLANs. Based on the concept of maximum independent set (MIS), a novel heuristic scheme with the aid of interference relationship is proposed to provide as many simultaneous transmission pairs as possible. In PEM, all stations know when to wake up and when they can enter doze state. Thus, stations need not waste power to idle listen and can save much power. The network bandwidth can be efficiently utilized as well. To verify the performance of PEM, a lot of simulations are performed. The experimental results show that with the property of spatial reuse, PEM not only reduces power consumption, but also leads to higher network throughput in comparison with the existing work, such as DCF, DCS, and DPSM.

The paper proposes a distributed spatial reuse (DSR) MAC protocol for IEEE 802.11 ad-hoc wireless LANs (WLANs) to increase bandwidth utilization and reduce power consumption. Through power control, the communications that do not interfere with each other can transmit simultaneously. Therefore, the overall efficiency and effectiveness of IEEE 802.11 ad-hoc WLANs can be enhanced. DSR allows the maximum number of interference-free communication pairs to transmit in parallel without collisions. According to the experiment results, DSR is much better than traditional WLAN protocol, IEEE 802.11 DCF, and the related work. The protocol indeed can effectively enhance the overall WLANs efficiency.

Localization is an important issue in wireless sensor networks (WSNs). Several applications in WSNs can tolerate the diverse levels of accuracy in geographic information such as physical location. Besides, direction information is sufficient for numerous applications in WSNs. Thus, the paper develops a direction-based localization scheme, DLS, in which a node can be aware of its relative direction to a sink rather than its physical absolute location without requiring additional equipments. DLS not only takes the spatial locality property into account, but also exploits the anchor deployment strategy to benefit sensor direction learning. Additionally, DLS can more precisely position sensors around the boundaries with the aid of the dual-direction coordinate system. Experimental results validate the practicability of DLS and show that DLS is able to achieve well accurate direction estimates.

Wireless sensor networks (WSNs) have been widely used in monitoring and collecting information. Packet flooding or broadcasting is an essential function for establishing a communication path from the sink node to a region of sensor nodes. However, flooding operation consumes power and bandwidth resources and raises the packet collision and contention problems, which reduce the success rate of packet transmissions and consume energy. This article proposes an efficient broadcasting protocol to reduce the number of sensor nodes that forward the query request, hence improving the packet delivery rate and saving bandwidth and power consumptions. The sensor node that received the query request dynamically transfers the coordinate system according to the zone-ID of the source node and determines whether it would forward the request or not in a distributed manner. Compared with a traditional flooding operation, experimental results show that the proposed zone-based broadcasting protocol decreases the bandwidth and power consumptions, reduces the packet collisions, and achieves a high success rate of packet broadcasting.

We devote to provide teachers and students with short-range wireless learning environment. The wireless learning platform consists of wireless handheld devices (PDA, notebook, etc.) carried by the guide and learners. A content-based image retrieval system (CBIR) is constructed to provide learner with required information using image recognition and wireless transmission technologies, such that the objective of outdoor ecology learning can be achieved. A firefly database is used as an instance to illustrate the operations of CBIR system. Instead of learning from textbook, a real firefly in natural environment can be observed and learned through digital camera and image recognition system. During the learning activity, the teacher can use this CBIR system to control the learning progress, evaluate the learning effects and provide necessary assistances to students in order to have a flourish learning environment.

Bluetooth is a low-power, low-cost, and short-range wireless technology. A well structured scatternet, with the appropriate number of piconets and bridges for a specific traffic pattern, increases the performance of a Bluetooth network. However, the structure of a scatternet is difficult to control or predefine because the scatternet is formed using a distributed procedure, with the master and slaves of each piconet connected at random. The participation of mobile Bluetooth devices in a scatternet at different times also increases the difficulty of maintaining a good structure. A badly structured scatternet exhibits the following characteristics: too many bridges in the scatternet creates a guard slot overhead associated with bridge switching among the participating piconets, increasing the probability that a packet is lost; too many piconets in a communicative range causes packet collision and thus degrades the performance; unnecessary piconets also lengthen the routing path, delaying the transmission of packets from source to destination. The paper proposes a distributed scatternet reconstruction protocol for dynamically reorganizing the scatternet. Unnecessary bridges and piconets can be dynamically removed by applying a role switching operation, improving the packet error rate, saving guard slots, and reducing the average routing length. By experiment, it is shown that the proposed protocol improves the data transmission performance of a Bluetooth scatternet.

This paper considers the bandwidth reservation problem in a mobile ad hoc network (MANET) to support QoS (quality-of-service) routing. We approach this problem by assuming a common channel shared by all hosts under a TDMA (time division multiple access) channel model. Existing solutions have addressed this problem by assuming a stronger multi-antenna model, where the bandwidth of a link is independent of the transmitting/receiving activities of its neighboring links, or a less strong CDMA-over-TDMA channel model, where the use of a time slot on a link is only dependent on the status of its one-hop neighboring links. While more practical and less costly, using a TDMA model needs to face the challenge of radio interference problems. In this paper, we propose a new protocol that can reserve routes by addressing both the hidden-terminal and exposed-terminal problems. The protocol can conduct accurate bandwidth calculation while performing route discovery. Simulation results are presented to verify how this new protocol performs.

This paper presents an efficient compilation technique to generate the local memory access sequences for block-cyclically distributed array references with affine subscripts in data-parallel programs. For the memory accesses of an array reference with affine subscript within a two-nested loop, there exist repetitive patterns both at the outer and inner loops. We use tables to record the memory accesses of repetitive patterns. According to these tables, a new start-computation algorithm is proposed to compute the starting elements on a processor for each outer loop iteration. The complexities of the table constructions are O(k+s/sub 2/), where k is the distribution block size and s/sub 2/ is the access stride for the inner loop. After tables are constructed, generating each starting element for each outer loop iteration can run in O(1) time. Moreover, we also show that the repetitive iterations for outer loop are Pk/gcd(Pk,s/sub 1/), where P is the number of processors and s/sub 1/ is the access stride for the outer loop. Therefore, the total complexity to generate the local memory access sequences for a block-cyclically distributed array with affine subscript in a two-nested loop is O(Pk/gcd/(Pk,s/sub 1/)+k+s/sub 2/).