Browsing by Author "Sun, Yanjun"

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    Efficient duty cycle MAC protocols for dynamic traffic loads in wireless sensor networks
    (2009) Sun, Yanjun; Johnson, David B.
    Idle listening is one of the most significant causes of energy consumption in wireless sensor networks (WSNs), and many protocols have been proposed based on duty cycling to reduce this cost. These protocols, either synchronous or asynchronous, are mainly optimized for light traffic loads. A WSN, however, could often experience bursty and high traffic loads, as may happen for example with broadcast or convergecast traffic. In this thesis, I design and evaluate a new synchronous protocol, DW-MAC (Demand Wakeup MAC), and a new asynchronous protocol, RI-MAC (Receiver Initiated MAC), that are both efficient under dynamic traffic loads, including light or heavy loads. I also design and evaluate ADB (Asynchronous Duty-cycle Broadcasting), a new protocol for efficient multihop broadcasting in WSNs using asynchronous duty cycling. DW-MAC introduces a new low-overhead scheduling algorithm that allows nodes to wake up on demand during the Sleep period of an operational cycle and ensures that data transmissions do not collide at their intended receivers; this demand wakeup adaptively increases effective channel capacity as traffic load increases. RI-MAC, instead, uses receiver-initiated transmissions, in which each transmitter passively waits until its intended receiver wakes up and transmits a beacon frame; this technique minimizes the time a sender and its intended receiver occupy the wireless medium to find a rendezvous time for exchanging data. ADB is integrated with RI-MAC to exploit information only available at this layer; rather than treating the data transmission from a node to all of its neighbors as the basic unit of progress for the multihop broadcast. ADB dynamically optimizes the broadcast at the level of transmission to each individual neighbor of a node as the neighbors asynchronously wakeup, avoiding redundant transmissions and transmissions over poor links, and allowing a transmitter to go to sleep as early as possible. In detailed simulation of all three protocols using ns-2, they each substantially outperform earlier competing protocols in terms of reduced energy and latency and increased packet delivery ratio. I also implemented RI-MAC and ADB in a testbed of MICAz motes using TinyOS and further demonstrate the significant performance improvements made over prior protocols.
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    Interference-aware protocol enhancements for ad hoc wireless networks
    (2006) Sun, Yanjun; Johnson, David B.
    An ad hoc network is an autonomous system of wireless mobile nodes, in which each node forwards packets for other nodes so that nodes out of direct wireless transmission range can communicate. In on-demand routing protocols for ad hoc networks, we find that existing schemes mistakenly may decide that a link is broken when it is not, especially when either endpoint node of the link experiences heavy interference. Moreover, a route claimed to be available may contain broken links due to the presence of stale routing information. We develop interference-aware enhancements both at the MAC layer and at the routing layer to address these problems. Simulation results show that our proposed enhancements reduce the problem dramatically and in turn increase the performance and efficiency of the routing protocol. In our simulations, total network throughput improved by up to 38% with DSR and by up to 13% with AODV.