Experimental study of the effects of Transmission Power Control and Blacklisting in Wireless Sensor Networks Dongjin Son, Bhaskar Krishnamachari and John Heidemann Presented by Anandha Gopalan Nov. 3, 2004

Outline Introduction Experiments Transmission Power Control (TPC) with blacklisting Conclusion and Future work

Introduction Zikes !!! Yet another paper on power- management This one has a slightly different take about it  Thank goodness for that So, what’s different ???  Simulations usually assume idealized link conditions Experimentally evaluate the effect of transmission power on link conditions Sometimes, increasing TP may help  Aha !!! that’s a bit different

Experiments Effects of unreliable wireless links Effects of TPC Experimental study of varying TP on a single wireless link  One receiver and multiple transmitters  One transmitter and multiple receivers  Wireless link distance  Node location (Multi-Path and Interference)  Time (Environment change)

Experiments Testbed  PC104 testbed with mica2 motes  Directed diffusion routing  S-MAC MAC protocol Weak link  Packet Reception Rate (PRR) < Threshold Asymmetric link  PRR > Threshold in only one direction

Experiments Effect of unreliable wireless links  Having unreliable links is worse than having any links at all They tend to be utilized  Convert unreliable links to good links or prevent them from being used

Experiments Effects of TPC  Increased TP leads to more good links Unreliable links can be converted to good links  New communication links can be discovered and used for packet delivery  Problem: May lead to new unreliable links Taken care of by blacklisting  Problem: May use up more network capacity

Experiments New definitions:  Weak link Packet Reception Rate (PRR) < Threshold, even after TPC  Asymmetric link PRR > Threshold in only one direction, even after TPC

Experiments One receiver and multiple transmitters  Difference is not obvious at close distances  Difference b/w node 27 and nodes (30,20) noticed after a distance of 17m  Difference b/w nodes 30 and 20 noticed after a distance of 23m

Experiments One transmitter and multiple receivers  In the TP range b/w -3 and 6 dBm, the link quality is different at the same TP level, while different TP is required for each link to reach the same PRR level Range of TP that generates this kind of variation is called unreliable transmission power range (UTPR)  UTPR can be avoided in two ways: Assign a TP high enough for every link to be outside UTPR Assign a distinct TP for each link

Experiments Effect of wireless link distance  Clear line of sight b/w transmitter and receiver  Distance b/w transmitter and receiver is varied  Experiments show that new reliable, communication links that are not available at default TP can be generated with TPC

Experiments Effect of node location  No clear line of sight b/w the sender and receiver  Receiver is placed in six different locations in the same indoor environment  Results: Multi-path interference effect are severe indoors, where signal is weak Severe link quality variation can be expected with small movement of sensor nodes

Experiments Effect of surrounding environment change  Variation in link quality is observed at different times of the day and night  Results: Variation in link quality observed during the day due to change in surrounding environment The difference in link quality is only b/w the TP of -7 to 2 dBm

TPC with blacklisting (PCBL) - Characteristics TPC for link quality control  Convert unreliable links to reliable links Packet-based TPC  TP is assigned to each packet based on its destination and type of packet, considering link quality requirement Metric-based link quality estimation  Link quality is measured based on PRR

PCBL - Characteristics Blacklisting at adjusted TP level  Not all links can be converted to a good link with TPC  New weak or asymmetric links can be generated at adjusted TP level  Blacklisting is used with TPC to remove remaining unreliable links after TPC

PCBL - Algorithm 1. Collect link statistics in PRR metric 2. Select a unicast power for each link 3. Blacklist unreliable links 4. Select a broadcast power for each node

PCBL - Algorithm 1. Collect link statistics  PRRs at pre-selected transmission power levels are collected 2. Select a unicast power for each link  Select a link quality control threshold (TH LQ )  Unicast power for each link is assigned such as: U i->j = P where PRR pi > TH LQ and P = min p i, otherwise U i->j is set to maximum TP (P max )

PCBL - Algorithm 3. Blacklist unreliable links  Links that cannot be converted to good links based on the blacklist threshold (TH BL ) are blacklisted and not used for any packet transmission or reception 4. Select a broadcast power for each node  Broadcast transmission power of node i (B i ) is selected to be max (U i->j ) Ensures that broadcast packets reach every node with a good wireless link

PCBL Algorithm – On-demand optimization for Long-lived Routing 1. Collect link statistics only at the maximum transmission power level 2. Blacklist unreliable links before using a routing protocol 3. Find a delivery path with a routing protocol 4. Identify unicast transmission powers to use only for links in the delivery path

PCBL – Analysis for Single Data Flows Packet Delivery Rates  PCBL is better than TPP-P0, TPP-P5 and TPP- P10, but worse than M-BL Energy Consumption  PCBL consumes more than TPP-P0 Energy consumption per packet  PCBL consumes less than TPP-P0

PCBL – Analysis for Multiple Data Flows Packet Delivery Rates  PCBL is better than M-BL for flows 1&2, but is slightly worse for flow 3  Improvement in flows 1&2 due to the saturation of the wireless link around node 11 for M-BL

Conclusion and Future work Presented an experimental study of the effects of TPC on wireless link quality A TPC scheme with blacklisting for link quality control was proposed Analysis of the proposed scheme was carried out using experiments Optimizations for the proposed algorithm is to be studied for future work

Issues with the paper Overhead of collecting link statistics ??? How are the statistics collected ??? Comparing PCBL with TPP-P0, TPP-P5 and TPP-P10 for multiple flows How do you get the threshold values ??? Mistakes in the paper ?????