Multi-Hop on Table-Top： A Scalable Evaluation Workbench for Wireless Ad-Hoc/Sensor Network Systems Gaute Lambertsen, Yu Enokibori, Kazuhiro Takeda, Kiyoto Tani, Koji Shuto, Nobuhiko Nishio Ritsumeikan University / PRESTO, Japan Science and Technology Agency Ad-hoc/Sensor networks seen in Ubiquitous Computing Have you ever seen a real multi-hop network working? Now, you can see it on our table-top. See you at our booth!!! The problem of experimental environment for ad-hoc/sensor network systems IEEE802.11 wireless LAN protocol can transmit data directly to nodes more than 100 meters away outdoors A large physical space and a large number of people is needed in order to create experimental environments How to solve the problem In order for each node to selectively allow communication only with nodes that are located within a specific distance in the workbench: we set a threshold value for the communication link quality, and… do not accept transmissions that do not conform to our settings Implementation of the scale-down network * All nodes are able to communicate physically Spatial Scalability In order to determine whether a neighbor node is connected or disconnected we use signal strength By implementing filtering according to signal strength, we are able to limit the possible transmission distance for a single hop Establishment of threshold value (In Kernel-AODV implementation) Using two types of threshold values LINK_LIMIT Threshold value of signal strength for connection LINK_HYSTERESIS_GAP Gap between connection threshold and disconnection threshold LINK_HYSTERESIS_GAP node LINK_LIMIT Measurement of signal strength Sample data for different signals for two nodes spaced at increasing intervals were used (intervals of about 15cm, max distance 270cm) The signal strength between the nodes were measured for 600 seconds at one-second intervals LINK_HYSTERESIS_GAP=11 LINK_LIMIT=-49 Accumulating of signal strengths (%) １５ｃｍ ３０ｃｍ ４５ｃｍ ６０ｃｍ ７５ｃｍ ９０ｃｍ １０５ｃｍ １２０ｃｍ １３５ｃｍ １５０ｃｍ １６５ｃｍ １８０ｃｍ １９５ｃｍ ２１０ｃｍ ２２５ｃｍ ２４０ｃｍ ２５５ｃｍ ２７０ｃｍ Signal strength (dB) Accumulation of signal strengths for different distances Smoothening the received signal strength In order to avoid the effect of any outliers, we used a smoothing operator on the received signal strength Smoothened signal strength = last signal strength × α + received signal strength (1-α) (※current value α = 0.6) ０．４０ ０．５０ ０．６０ ０．７０ 平滑化処理のグラフ図 Temporal scalability In order to calculate the transmission interval depending on the ratio of status change for the entries in the neighbor table, we adjust the temporally protocol parameters Temporally protocol parameters Hello beacon interval Lifetime of the neighbor node information located in the neighbor table Lifetime of the next-hop route information located in the AODV route table Additional Modules for Sensor Network Implementations Sensor node modules: System modules: Event emulator Sensor emulator Sink Query dispatcher Example application Clustering protocol Our experimental environment PDA SHARP SL-750/760 Wireless LAN Card Linux Kernel 2.4.18 Wireless Extension Version 16 BUFFALO WLI2-CF-S11 Routing Protocol NIST Kernel-AODV_v2.2.1 Implementation of the estimated protocol for sensor network Evaluation of event information clustering mechanism for sensor network Event emulator broadcasting N bytes at a time from a specified file starting from the head of the file, using UDP packets Sensor emulator If the received signal strength from the event is better than the set value from the query, the node senses the event data. Sink processes and displays the received data Query dispatcher floods packet that includes the address of the sink, the type of the event to be sensed and signal strength indicating the sensing range of each node Clustering protocol For nodes in a sensor network with mobility, the nodes surrounding the event forms a cluster in order to improve sensing efficiency, as well as to improve power consumption Sensor Network Data Flow
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