後卓越進度報告 蔡育仁老師實驗室 2007/03/19

Distribute Source Coding (DSC) in WSNs Distributed source coding is a data compression technique to reduce the redundancy w/o information exchanges among sensor nodes.  Sensors individually encode their received information.  E.g., Slepian-Wolf method is a widely used distributed source coding algorithm. … … … : received signal : Sensor : Sink Decoding Order

DSC with Slotted ALOHA Random Access Performance of a DSC scheme in a slotted ALOHA WSN has been investigated. Assumptions:  Node i transmit in a slot with a constant probability P i.  The packet of node i can be reconstructed if the packet of node 1 to node i–1 was received successfully. Goal:  Analyze and try to minimize the decoding latency at fusion center Results:  The analytical result and an approx. result were obtained.  Several probability assignment strategies were compared. Prolong decoding latency

DSC with Slotted ALOHA — Adaptive Tx. Probabilities Goal  Design an adaptive criterion for nodes’ transmit probabilities (TxPr) to reduce the decoding latency. Transmission probability adaptation  Initial total traffic load:  Initial TxPr-weighting of node i :  The average reduced traffic in the k -th slot:  Adaptation procedure of i -th node’s Tx. prob. in k -th slot

…… P 1 [0] P 2 [0] …… P N-1 [0] P N [0] TxPr Adaptation with Linear TxPr Weighting For linear TxPr-weighting, we define …… P 1 [0] P 2 [0] …… P N-1 [0] P N [0] Node 3’s packet is received Node 123 …… 4N-1 N 123 …… 4N-1 N

Analytical & Simulation Results — 20 Nodes (Linear TxPr Weighting), ΔP = Time slot Average no. of reconstructed pkts Analytical Simulation Adaptive Transmit Probability Fixed Transmit Probability

Linear Assignment of Nodes ’ Initial TxPr Weighting — with 20 Nodes, Initial Traffic G = Analytical Simulation Time slot Average no. of reconstructed pkts

Future Work Evaluate the average energy consumption for information reconstruction. Take packet lengths into consideration to allocate the optimum P i for packets with different lengths. Take other random access techniques into considerations.