Li-Hsing Yen | National University of Kaohsiung (original) (raw)
Papers by Li-Hsing Yen
Journal of Parallel and Distributed Computing, 2004
In a mobile ad hoc (multi-hop) wireless network, the logical structure of a ring is likely to bec... more In a mobile ad hoc (multi-hop) wireless network, the logical structure of a ring is likely to become volatile or expensive to maintain over time due to changeable network topology. Additional adverse effects take place when a process joins or leaves the computation in the presence of mobility. This paper presents a distributed algorithm that adapts a ring among mobile nodes to the network dynamics to reflect overall communication efficiency. This is achieved by modifying the ring structure in a localized, mutual exclusive fashion, thereby allowing for concurrent segment-wise modifications to proceed. Remarkably our proposal operates without global knowledge of the logical structure and can be embodied as an underlying protocol stratum that supports transparent deployments of conventional algorithms in mobile environment. Subsequent to correctness proof, simulation results show that our proposal is promising in several regards.
Bluetooth is a short-range TDD (Time Division Duplex) wireless network that supports both circuit... more Bluetooth is a short-range TDD (Time Division Duplex) wireless network that supports both circuit-and packetoriented applications. A piconet is composed of a device configured as master and at most seven other devices acting as slaves. At Medium Access Control (MAC) layer, the master can select a slave to send a data packet and until then, the slave is not allowed to transmit. Round-Robin (RR) and Exhaustive Round-Robin (ERR) are two elementary MAC scheduling schemes that are both simple and efficient. This paper proposes RR-FCFS, a simple MAC scheduling scheme that has the same advantages as RR and ERR. RR-FCFS acts as RR if the master's queue is empty and starts transmitting packets in first-come-first-serve order otherwise. The simulation results show that RR-FCFS's performance in terms of packet delay and queue length is comparable with those of RR and ERR.
Causal message ordering (CMO) demands that messages directed to the same destinations must be del... more Causal message ordering (CMO) demands that messages directed to the same destinations must be delivered in an order consistent with their potential causality. In this paper, we present a modular decomposition of CMO, and evaluate the probability of breaking CMO by assuming two probabilistic models on message delays: exponential distribution and uniform distribution. These models represent the contexts where message delays are unpredictable and, respectively, unbounded and bounded. Our analysis result helps understanding the necessity of CMO schemes, and suggests a probabilistic approach to CMO: deferredsending. The effect of deferred-sending is analyzed.
This paper has analyzed link probability, expected node degree, expected number of links, and exp... more This paper has analyzed link probability, expected node degree, expected number of links, and expected area collectively covered by a finite number of nodes in wireless ad hoc networks. Apart from the formulation of exact mathematical expressions for these properties, we have disclosed two fundamental results: (1) Every possible link has an equal probability of occurrence.
Ad Hoc Networks, 2006
We are concerned with wireless sensor networks where n sensors are independently and uniformly di... more We are concerned with wireless sensor networks where n sensors are independently and uniformly distributed at random in a finite plane. Events that are within a fixed distance from some sensor are assumed to be detectable and the sensor is said to cover that point. In this paper, we have formulated an exact mathematical expression for the expected area that can be covered by at least k out of n sensors. Our results are important in predicting the degree of coverage a sensor network may provide and in determining related parameters (sensory range, number of sensors, etc.) for a desired level of coverage. We demonstrate the utility of our results by presenting a node scheduling scheme that conserves energy while retaining network coverage. Additional simulation results have confirmed the accuracy of our analysis.
Density control in a wireless sensor network refers to the process of deciding which node is elig... more Density control in a wireless sensor network refers to the process of deciding which node is eligible to sleep (enter power-saving mode) after random deployment to conserve energy while retaining network coverage. Most existing approaches toward this problem require sensor's location information, which may be impractical considering costly locating overheads. This paper proposes a new density control protocol that needs sensor-to-sensor distance but no location information. It attempts to approach an optimal sensor selection pattern that demands the least number of working (awake) sensors. Simulation results indicate that the proposed protocol is comparable to its location-based counterpart in terms of coverage quality and the reduction of working sensors.
A k-connected wireless sensor network (WSN) allows messages to be routed via one (or more) of at ... more A k-connected wireless sensor network (WSN) allows messages to be routed via one (or more) of at least k nodedisjoint paths, so that even if some nodes along one of the paths fail, or are compromised, the other paths can still be used. This is a much desired feature in fault tolerance and security. k-connectivity in this context is largely a well-studied subject. When we apply the random key predistribution scheme to secure a WSN however, and only consider the paths consisting entirely of secure (encrypted and/or authenticated) links, we are concerned with the secure k-connectivity of the WSN. This notion of secure kconnectivity is relatively new and no results are yet available. The random key pre-distribution scheme has two important parameters: the key ring size and the key pool size. While it has been determined before the relation between these parameters and 1-connectivity, our work in kconnectivity is new. Using a recently introduced random graph model called kryptograph, we derive mathematical formulae to estimate the asymptotic probability of a WSN being securely k-connected, and the expected secure kconnectivity, as a function of the key ring size and the key pool size. Finally, our theoretical findings are supported by simulation results.
Wireless Personal Communications, 2009
Sleep scheduling in a wireless sensor network is the process of deciding which nodes are eligible... more Sleep scheduling in a wireless sensor network is the process of deciding which nodes are eligible to sleep (enter power-saving mode) after random deployment to conserve energy while retaining network coverage. Most existing approaches toward this problem require sensor’s location information, which may be impractical considering costly locating overheads. This paper proposes range-based sleep scheduling (RBSS) protocol which needs sensor-to-sensor distance but no location information. RBSS attempts to approach an optimal sensor selection pattern that demands the fewest working (awake) sensors. Simulation results indicate that RBSS is comparable to its location-based counterpart in terms of coverage quality and the reduction of working sensors.
Density control in a wireless sensor network refers to the process of deciding which node is elig... more Density control in a wireless sensor network refers to the process of deciding which node is eligible to sleep (enter power-saving mode) after random deployment to conserve energy while retaining network coverage. Most existing approaches toward this problem require sensor's location information, which may be impractical considering costly locating overheads. This paper proposes a new density control protocol that needs sensor-to-sensor distance but no location information. It attempts to approach an optimal sensor selection pattern that demands the least number of working (awake) sensors. Simulation results indicate that the proposed protocol is comparable to its location-based counterpart in terms of coverage quality and the reduction of working sensors.
IEEE Communications Letters, 2005
Clustering coefficient has been proposed to characterize complex networks. Hidden terminals may d... more Clustering coefficient has been proposed to characterize complex networks. Hidden terminals may degrade the performance of CSMA (carrier sense multiple access) protocol. This letter computes analytically the clustering coefficient and the quantity of hidden terminals for ad hoc networks. The former turns out to be a constant and the latter is proportional to n 3 p 2 , where n is the number of nodes and p is the link probability. The connection between them has been established, and simulation results confirm our analytic work.
International Journal of Communication Systems, 2007
This paper aims to minimize energy expense for chain-based data gathering schemes, which is essen... more This paper aims to minimize energy expense for chain-based data gathering schemes, which is essential to prolong the operation lifetime of wireless sensor networks. Energy expense in chain-based data gathering schemes consists of two parts. One corresponds to inter-sensor communications and depends on chain structure. The other corresponds to leader-BS (base station) communications and depends on leader scheduling policy. To optimize inter-sensor communications, the notion of virtual chain is utilized, where an edge may correspond to a multi-hop data propagation path to conserve power. In contrast, an edge in previous work can only be a costly direct communication link. To optimize leader-BS communications, a leader scheduling rule is presented, where the node with the maximum residual power will be selected to be the leader of the chain. In contrast, nodes in previous work act as leaders by turns, resulting in non-uniform energy consumption among sensors. Simulation results show that our strategies are nearly optimal in terms of power conservation. Copyright © 2006 John Wiley & Sons, Ltd.
Crossover nodes have been utilized to achieve smooth handoffs for micro mobility management schem... more Crossover nodes have been utilized to achieve smooth handoffs for micro mobility management schemes. IEEE 802.11s supports proxy-based frame delivery services for mobile hosts roaming within a wireless mesh network (WMN). Discovering crossover node for mobile hosts in 802.11s WMNs, however, faces several challenges due to intrinsic properties of mesh networks. This paper identifies these challenges and proposes a scheme suitable for crossover node discovery under 802.11s WMNs. This scheme is characterized by source-oriented, MAPcentric, and per-source. It can be performed off-line with the derived results cached for on-line retrievals during handoffs. Simulation results show that the proposed scheme can reduce packet losses due to handoffs, and confirm the necessity of the source-oriented principle.
Journal of Parallel and Distributed Computing, 2004
In a mobile ad hoc (multi-hop) wireless network, the logical structure of a ring is likely to bec... more In a mobile ad hoc (multi-hop) wireless network, the logical structure of a ring is likely to become volatile or expensive to maintain over time due to changeable network topology. Additional adverse effects take place when a process joins or leaves the computation in the presence of mobility. This paper presents a distributed algorithm that adapts a ring among mobile nodes to the network dynamics to reflect overall communication efficiency. This is achieved by modifying the ring structure in a localized, mutual exclusive fashion, thereby allowing for concurrent segment-wise modifications to proceed. Remarkably our proposal operates without global knowledge of the logical structure and can be embodied as an underlying protocol stratum that supports transparent deployments of conventional algorithms in mobile environment. Subsequent to correctness proof, simulation results show that our proposal is promising in several regards.
Bluetooth is a short-range TDD (Time Division Duplex) wireless network that supports both circuit... more Bluetooth is a short-range TDD (Time Division Duplex) wireless network that supports both circuit-and packetoriented applications. A piconet is composed of a device configured as master and at most seven other devices acting as slaves. At Medium Access Control (MAC) layer, the master can select a slave to send a data packet and until then, the slave is not allowed to transmit. Round-Robin (RR) and Exhaustive Round-Robin (ERR) are two elementary MAC scheduling schemes that are both simple and efficient. This paper proposes RR-FCFS, a simple MAC scheduling scheme that has the same advantages as RR and ERR. RR-FCFS acts as RR if the master's queue is empty and starts transmitting packets in first-come-first-serve order otherwise. The simulation results show that RR-FCFS's performance in terms of packet delay and queue length is comparable with those of RR and ERR.
Causal message ordering (CMO) demands that messages directed to the same destinations must be del... more Causal message ordering (CMO) demands that messages directed to the same destinations must be delivered in an order consistent with their potential causality. In this paper, we present a modular decomposition of CMO, and evaluate the probability of breaking CMO by assuming two probabilistic models on message delays: exponential distribution and uniform distribution. These models represent the contexts where message delays are unpredictable and, respectively, unbounded and bounded. Our analysis result helps understanding the necessity of CMO schemes, and suggests a probabilistic approach to CMO: deferredsending. The effect of deferred-sending is analyzed.
This paper has analyzed link probability, expected node degree, expected number of links, and exp... more This paper has analyzed link probability, expected node degree, expected number of links, and expected area collectively covered by a finite number of nodes in wireless ad hoc networks. Apart from the formulation of exact mathematical expressions for these properties, we have disclosed two fundamental results: (1) Every possible link has an equal probability of occurrence.
Ad Hoc Networks, 2006
We are concerned with wireless sensor networks where n sensors are independently and uniformly di... more We are concerned with wireless sensor networks where n sensors are independently and uniformly distributed at random in a finite plane. Events that are within a fixed distance from some sensor are assumed to be detectable and the sensor is said to cover that point. In this paper, we have formulated an exact mathematical expression for the expected area that can be covered by at least k out of n sensors. Our results are important in predicting the degree of coverage a sensor network may provide and in determining related parameters (sensory range, number of sensors, etc.) for a desired level of coverage. We demonstrate the utility of our results by presenting a node scheduling scheme that conserves energy while retaining network coverage. Additional simulation results have confirmed the accuracy of our analysis.
Density control in a wireless sensor network refers to the process of deciding which node is elig... more Density control in a wireless sensor network refers to the process of deciding which node is eligible to sleep (enter power-saving mode) after random deployment to conserve energy while retaining network coverage. Most existing approaches toward this problem require sensor's location information, which may be impractical considering costly locating overheads. This paper proposes a new density control protocol that needs sensor-to-sensor distance but no location information. It attempts to approach an optimal sensor selection pattern that demands the least number of working (awake) sensors. Simulation results indicate that the proposed protocol is comparable to its location-based counterpart in terms of coverage quality and the reduction of working sensors.
A k-connected wireless sensor network (WSN) allows messages to be routed via one (or more) of at ... more A k-connected wireless sensor network (WSN) allows messages to be routed via one (or more) of at least k nodedisjoint paths, so that even if some nodes along one of the paths fail, or are compromised, the other paths can still be used. This is a much desired feature in fault tolerance and security. k-connectivity in this context is largely a well-studied subject. When we apply the random key predistribution scheme to secure a WSN however, and only consider the paths consisting entirely of secure (encrypted and/or authenticated) links, we are concerned with the secure k-connectivity of the WSN. This notion of secure kconnectivity is relatively new and no results are yet available. The random key pre-distribution scheme has two important parameters: the key ring size and the key pool size. While it has been determined before the relation between these parameters and 1-connectivity, our work in kconnectivity is new. Using a recently introduced random graph model called kryptograph, we derive mathematical formulae to estimate the asymptotic probability of a WSN being securely k-connected, and the expected secure kconnectivity, as a function of the key ring size and the key pool size. Finally, our theoretical findings are supported by simulation results.
Wireless Personal Communications, 2009
Sleep scheduling in a wireless sensor network is the process of deciding which nodes are eligible... more Sleep scheduling in a wireless sensor network is the process of deciding which nodes are eligible to sleep (enter power-saving mode) after random deployment to conserve energy while retaining network coverage. Most existing approaches toward this problem require sensor’s location information, which may be impractical considering costly locating overheads. This paper proposes range-based sleep scheduling (RBSS) protocol which needs sensor-to-sensor distance but no location information. RBSS attempts to approach an optimal sensor selection pattern that demands the fewest working (awake) sensors. Simulation results indicate that RBSS is comparable to its location-based counterpart in terms of coverage quality and the reduction of working sensors.
Density control in a wireless sensor network refers to the process of deciding which node is elig... more Density control in a wireless sensor network refers to the process of deciding which node is eligible to sleep (enter power-saving mode) after random deployment to conserve energy while retaining network coverage. Most existing approaches toward this problem require sensor's location information, which may be impractical considering costly locating overheads. This paper proposes a new density control protocol that needs sensor-to-sensor distance but no location information. It attempts to approach an optimal sensor selection pattern that demands the least number of working (awake) sensors. Simulation results indicate that the proposed protocol is comparable to its location-based counterpart in terms of coverage quality and the reduction of working sensors.
IEEE Communications Letters, 2005
Clustering coefficient has been proposed to characterize complex networks. Hidden terminals may d... more Clustering coefficient has been proposed to characterize complex networks. Hidden terminals may degrade the performance of CSMA (carrier sense multiple access) protocol. This letter computes analytically the clustering coefficient and the quantity of hidden terminals for ad hoc networks. The former turns out to be a constant and the latter is proportional to n 3 p 2 , where n is the number of nodes and p is the link probability. The connection between them has been established, and simulation results confirm our analytic work.
International Journal of Communication Systems, 2007
This paper aims to minimize energy expense for chain-based data gathering schemes, which is essen... more This paper aims to minimize energy expense for chain-based data gathering schemes, which is essential to prolong the operation lifetime of wireless sensor networks. Energy expense in chain-based data gathering schemes consists of two parts. One corresponds to inter-sensor communications and depends on chain structure. The other corresponds to leader-BS (base station) communications and depends on leader scheduling policy. To optimize inter-sensor communications, the notion of virtual chain is utilized, where an edge may correspond to a multi-hop data propagation path to conserve power. In contrast, an edge in previous work can only be a costly direct communication link. To optimize leader-BS communications, a leader scheduling rule is presented, where the node with the maximum residual power will be selected to be the leader of the chain. In contrast, nodes in previous work act as leaders by turns, resulting in non-uniform energy consumption among sensors. Simulation results show that our strategies are nearly optimal in terms of power conservation. Copyright © 2006 John Wiley & Sons, Ltd.
Crossover nodes have been utilized to achieve smooth handoffs for micro mobility management schem... more Crossover nodes have been utilized to achieve smooth handoffs for micro mobility management schemes. IEEE 802.11s supports proxy-based frame delivery services for mobile hosts roaming within a wireless mesh network (WMN). Discovering crossover node for mobile hosts in 802.11s WMNs, however, faces several challenges due to intrinsic properties of mesh networks. This paper identifies these challenges and proposes a scheme suitable for crossover node discovery under 802.11s WMNs. This scheme is characterized by source-oriented, MAPcentric, and per-source. It can be performed off-line with the derived results cached for on-line retrievals during handoffs. Simulation results show that the proposed scheme can reduce packet losses due to handoffs, and confirm the necessity of the source-oriented principle.