Various applications of wireless sensor networks require multihop data transmission over error-prone wireless links, hence multipath routing can be used to meet the application's reliability requirement. On the other hand, wireless sensors are usually battery powered, and thus it is very important to save energy in order to prolong the network lifetime. In this article, we propose (1) Sleeping Multipath Routing, which can trade off reliability and network lifetime by dynamically activating an optimal number of paths to support the application's reliability requirement and putting the rest of the sensors to sleep, and (2) an adaptive sensor sleeping solution, which includes Sleeping Multipath Routing, a duty-cycled MAC protocol, and cross-layer coordination to further prolong the network lifetime by putting sensors to sleep at both the routing and the MAC layers. Our proposed Sleeping Multipath Routing and adaptive sensor sleeping solution can be implemented on any multipath routing protocol that discovers multiple disjoint paths between two nodes, and any duty-cycled MAC protocol that has fixed cycle length. We show an example of implementing our adaptive sensor sleeping solution using Directed Diffusion and S-MAC. Simulation results show that our proposed adaptive sensor sleeping solution outperforms single-layer sensor sleeping with a longer network lifetime with required reliability support. Moreover, our proposed adaptive sensor sleeping solution can significantly prolong the network lifetime when the application's reliability requirement varies over time, or when the number of alive nodes in the network changes over time.

Wireless sensor networks are often battery-powered, and hence extending the network lifetime is one of the primary concerns in the ubiquitous deployment of wireless sensor networks. One approach to efficiently utilize the limited energy supplies of the sensors is to have the medium access control (MAC) protocol duty-cycle the sensors, periodically putting the sensors to sleep and waking them up to reduce idle listening, which is energy intensive. Among duty-cycled MAC protocols, some protocols are synchronized so that nodes wake up at the same time in each cycle, and other protocols are asynchronous, where nodes have arbitrary offsets to start their cycles. For protocol designers, it is important to understand which type of duty-cycled MAC protocol should be chosen (synchronized or asynchronous), as well as what values should be assigned to the protocol parameters under a given network scenario in order to achieve a desirable performance for throughput, delay, or energy consumption. However, previous work to analyze the performance of different duty-cycled MAC protocols is either protocol-specific, or limited to one aspect of the performance metric. In this paper, we propose a Markov queuing model to analyze the throughput, delay, and energy consumption of both synchronized and asynchronous duty-cycled MAC protocols with applications to S-MAC and X-MAC. Our contributions include: 1) proposing a Markov queuing model to describe the queuing behavior of both synchronous and asynchronous duty-cycled nodes, 2) modeling the queue dynamics and the stationary probability of packet transmissions for S-MAC, a synchronized duty-cycled MAC protocol, to analyze its performance, 3) modeling the queue dynamics and the stationary probability of packet transmissions for X-MAC, an asynchronous duty-cycled MAC protocol, to analyze its performance, 4) providing comprehensive performance estimation and comparison for different duty-cycled MAC protocols, and 5) providing flexibility to tradeoff different performance metrics by optimizing the protocol parameters. Our model results are validated by comparing with NS-2 and Matlab simulations.

In wireless sensor networks, multipath routing is used to alleviate reliability degradation due to multihop transmissions over error-prone wireless channels. However, multipath routing is not energy-efficient, as it requires all the nodes in the network to always be awake. To prolong the network lifetime while maintaining a certain reliability performance, we propose Sleeping Multipath Routing, which selects the minimum number of disjoint paths to achieve a given reliability requirement and puts the rest of the network to sleep. Simulation results show that Sleeping Multipath Routing can significantly extend the network lifetime, and it can trade off reliability for lifetime.

MAC layer duty-cycling is widely used to reduce idling listening, which is energy-intensive in wireless sensor networks. Among duty-cycling MAC protocols, asynchronous protocols generally have higher energy-efficiency and lower packet latency than synchronized ones. In this paper, we propose a Markov model to analyze the throughput of X-MAC, an asynchronous duty-cycled MAC protocol for wireless sensor networks. Simulations show that our analytical model provides throughput values that closely match the simulation results under various network conditions. Using our model to estimate the throughput of X-MAC is computationally efficient, providing accurate results quickly compared with simulations, which take a long time to run and require many iterations due to the large standard deviations in throughput. More importantly, our model enables designers to obtain a better understanding of the effect of different numbers of nodes and data arrival rates on the performance of X-MAC.

Single-hop centralized wireless sensor networks are widely used for applications ranging from security and surveillance to medical monitoring. Often the goal of these networks is to provide satisfactory quality of service (QoS) to the application under different system states, but it is difficult to determine how the appropriate sensor sets should be selected over time, given the knowledge of all possible sensor sets to support the application QoS requirements. To address this problem, in this paper we propose a novel cost function called SUI (Sensor Usage Index) that is based on a sensor's relative ideal lifetime (SRIL) and can be used to select sensor sets so as to meet application QoS requirements for extended periods of time. Simulation results show that utilizing the proposed cost function for sensor set selection enables the network to meet application QoS requirements for longer than using other standard sensor selection schemes. In fact, our scheme approaches the optimal network lifetime, which can be found using global knowledge of the sensors and the system dynamics.

IEEE fixed 802.16 network aims at providing broadband wireless access with quality of service (QoS) guarantee. In all its services, real-time video traffic plays an impeditive role because of its varying bit-rate. In this paper, by taking advantage of traffic characteristics, a new scheduling and call admission control (CAC) scheme for real-time video traffic in IEEE fixed 802.16 networks is proposed. Simulations using real life video traces show that the proposed scheme provides significant improvement in throughput while maintaining QoS performance at an acceptable level.