This paper investigates the performance of IEEE 802.11 in multi-hop scenarios and shows how its aggressive behavior can throttle the spatial reuse and reduce bandwidth efficiency. An adaptive, layer-2, distributed coordination scheme for 802.11 using explicit medium access control (MAC) feedback is then proposed to pace the transmissions on adjacent nodes, thereby assisting the MAC protocol to operate around its saturation state while minimizing resource contention. Simulation results show that the proposed scheme outperforms the original 802.11 MAC.

This paper addresses the problem of data acquisition in ad hoc and sensor networks with mobile sinks and proposes a protocol based on swarm intelligence, SIMPLE, to route data in such environments. The proposed protocol is based on a swarm agent that integrates the residual energy of nodes into the route selection mechanism and maximizes the network's lifetime by evenly balancing the residual energy across nodes and minimizing the protocol overhead. The protocol is robust and scales well with both the network size and in the presence of multiple sinks. An information theoretic lower bound on the protocol overhead associated with the swarm agent advertisement is also obtained. SIMPLE is also shown to have a lower message complexity compared to similar algorithms previously proposed in literature. Simulation results are used to verify SIMPLE's performance and robustness and also to demonstrate its superior performance over existing algorithms.

In this paper, we investigate the spatial reuse and saturation throughput of static ad-hoc networks with unbiased medium access control (MAC) protocols. Under the stochastic assumptions of our model, we obtain the upper bound on the equivalent saturation throughput of such MAC protocols as a function of node density. We also obtain the scaling properties of the spatial reuse and saturation throughput.

In this paper we propose a distributed, mobility transparent broadcast (DMTB) protocol to achieve efficient and effective broadcast in mobile ad-hoc networks. The protocol is fully distributed and highly adaptive to node mobility. It does not demand any neighborhood information and incurs little overhead. On one hand, the cross-layer design approach helps achieve effective broadcast with higher efficiency and alleviated interference; on the other hand, the proposed protocol achieves network energy balance by randomly rotating the set of relay nodes in different broadcast events even when the network topology stays unchanged. The protocol's performance is proved to be within a constant of the optimum. Detailed analysis regarding the broadcast interference, node density and protocol overhead is presented. DMTB is not only efficient, but also robust against node failures and scalable with the node density or the network area size.

In a wireless ad hoc network where multi-hop traffic dominates the network, spatial reuse has an enormous impact on the network performance in terms of end-to-end throughput and delay characteristics. In this paper, we investigate the MAC coordination of persistent flows in 802.11 ad hoc networks and point out that the aggressive behavior of 802.11 MAC can throttle the spatial reuse and reduce bandwidth efficiency. We thus propose an adaptive layer-2 pacing scheme fully compatible with 802.11 MAC using explicit MAC feedback to balance the transmissions on adjacent nodes. By promoting MAC coordination, our scheme can assist the MAC to operate around its saturation state while minimizing resource contention. Experiment results demonstrate that our scheme significantly outperforms the original 802.11 MAC by boosting the throughput while still maintaining latency at a low level.

Abstract — This paper addresses the data acquisition problem in sensor networks using mobile sinks. Sensor nodes ’ low computational capabilities and limited energy motivate our design of a swarm intelligence based, energy aware protocol, SIMPLE, to route data to the mobile destination via the shortest paths. Using a swarm agent technique to integrate nodes ’ residual energy as a metric for the shortest path selection, SIMPLE maximizes the network’s lifetime by evenly balancing residual energy across the network and minimizing the protocol overhead. The protocol’s resilience against node failures is guaranteed by the multiple path technique. It scales well with both the network size and multiple sinks. Simulation results are presented to observe and verify SIMPLE’s performance and robustness. Compared with existing algorithms, SIMPLE is shown to have superior performance. A general tradeoff model is presented to evaluate the performance tradeoffs associated with different protocol parameters. Index Terms — Swarm intelligence, data acquisition, mobilesink, sensor network, energy awareness

In this paper we address the issue of improving the spatial reuse in virtual carrier sensing (VCS) mechanisms for wireless networks. The paper examines in detail the channel reservation mechanisms of IEEE 802.11 VCS and shows that its spatial reuse is sub-optimal in a number of scenarios. We also show that the area that should be reserved by the VCS depends on the distance between the transmitter and receiver. We then present a novel VCS scheme that optimizes spatial reuse by incorporating this distance information in the decision making process for the channel reservation. Unlike existing proposals for improving spatial reuse, our scheme does not rely on special hardware design such as directional antennas, power adaptable or dual-channel devices etc., and is thus easily implementable. Simulation results quantify and demonstrate the substantial performance improvements obtained by the proposed scheme.

Static broadcast tree protocols have been proposed in literature to optimize the querying procedure in sensor networks. In this paper we address the issue of how to mitigate the unevenness of energy distribution and its undesirable effects like reduced network lifetime and loss of connectivity in a sensor network that are caused by static broadcast trees. We propose a "dynamic query-tree energy balancing" (DQEB) protocol to dynamically adjust the tree structure and minimize the overall broadcast cost. The proposed algorithm scales well, is distributed and does not need any global information. Locally, the broadcast power consumption is minimized while globally, the broadcast load and power distribution are balanced across the whole sensor network. Our simulation results verify that the DQEB protocol achieves significantly better balance in the battery power distribution and extends the network's lifetime considerably.

In this paper, we evaluate and suggest methods to improve the performance of IEEE 802.11 based ad hoc networks from the perspective of spatial reuse. Since 802.11 employs virtual carrier sensing to reserve the medium prior to a packet transmission, the relative size of the spatial region it reserves for the impending traffic significantly affects the overall network performance. We show that the space reserved by 802.11 for a successful transmission is far from optimal and depending on the one hop distances between the sender and the receiver. We study three scenarios with very different spatial reuse characteristics. We also introduce a new quantitative measure, the spatial reuse index, to evaluate the efficiency of the medium reservation accomplished by 802.11 virtual carrier sensing. We also propose an improved virtual carrier sensing mechanism for wireless LAN scenarios and using analysis and simulation results, show that it can significantly increase the spatial reuse and network throughput.