Dynamic Transmission Power Control in Wireless Ad-Hoc Networks EE194 Wireless Sensor Networks Stuart Peloquin & Joe Cerra

Outline Goals Goals Reasons for changing transmit strength Reasons for changing transmit strength Hardware Hardware Distributed algorithms Distributed algorithms Proposed basic algorithm Proposed basic algorithm JiST / SWANS JiST / SWANS

Reduce single node and entire network power consumptionReduce single node and entire network power consumption Define the link metric as a function of transmit power Define the link metric as a function of transmit power Efficiently update link information for use in effective routing Efficiently update link information for use in effective routing Simulate an adaptive transmitter power algorithm using JiST/SWANSSimulate an adaptive transmitter power algorithm using JiST/SWANS Goals

Project considerations Highly mobile environmentHighly mobile environment Distributed algorithms, no central server Distributed algorithms, no central server Distributed routing tables Distributed routing tables Increased loss model Increased loss model Hardware considerationsHardware considerations Crossbow Mica2 Motes Crossbow Mica2 Motes RSSI capableRSSI capable Programmable transmit powerProgrammable transmit power Simulation considerationsSimulation considerations JiST/SWANS JiST/SWANS

Why use dynamic power model? Free space signal attenuation: theoreticalFree space signal attenuation: theoretical Loss ~ d 2 Loss ~ d 2 Loss model ~ d 4 :Loss model ~ d 4 : Mobile nodes Mobile nodes Large d: d > 4πh t h r / λ Large d: d > 4πh t h r / λ Multi-path fading due to: Multi-path fading due to: Urban/congested environmentUrban/congested environment IndoorsIndoors

● Save energy at each node with reduced transmission cost ● Easily accessed and updated accurate link metric for routing ● Can eliminate some channel assignment issues: 4 Channels: Black Red Blue Yellow Able to change power needs All nodes operate at full transmission power. Overlap. This channel cannot be used here. Why use dynamic power model?

Single-hop vs. Multi-hop As seen before: As seen before: Transmitted power ~ d 2 – d 4Transmitted power ~ d 2 – d 4 2 nodes 50m away could drastically decrease the power needed to communicate if relay nodes are used2 nodes 50m away could drastically decrease the power needed to communicate if relay nodes are used 50m 10m 50m Power ~ 50 4 ~ 6.25x10 6 Power ~ 10 4 * 5 ~ 5x10 4

Single-hop vs. Multi-hop When that model fails When that model fails From link metrics shown, B is the obvious choice for routingFrom link metrics shown, B is the obvious choice for routing How to establish these routesHow to establish these routes Polling: Very wasteful Polling: Very wasteful Random inquiries: Can be shown to perform better than constant polling Random inquiries: Can be shown to perform better than constant polling Include link status messages in some/all data packets Include link status messages in some/all data packets A A.B.B.

Information propagation Need for an effective routing protocol Need for an effective routing protocol Must be able to adapt quickly to changing network topology and link statusMust be able to adapt quickly to changing network topology and link status Cannot be over-cumbersomeCannot be over-cumbersome Each node does not have unlimited memory to store this data Each node does not have unlimited memory to store this data Need for an effective method to update link metrics Need for an effective method to update link metrics RSSI is only so good on its ownRSSI is only so good on its own Each node can reduce/increase the cost to send to its neighbor Each node can reduce/increase the cost to send to its neighbor Each node should also forward that information so routing tables can change Each node should also forward that information so routing tables can change

RSSI Received Signal Strength Indicator Received Signal Strength Indicator Available on most Transceivers. RSS can be interrogated from receiver.Available on most Transceivers. RSS can be interrogated from receiver. RSS to dB conversion rates availableRSS to dB conversion rates available How to use RSS? How to use RSS? RSS does not directly translate to distanceRSS does not directly translate to distance Sending node should include the transmitted signal strengthSending node should include the transmitted signal strength Roughly, loss ~ RSS – Transmitted power Roughly, loss ~ RSS – Transmitted power

Hardware Mica2, Mica2 DOT Mica2, Mica2 DOT CPUCPU Active: 8ma Active: 8ma Sleep: <15uA Sleep: <15uA Transceiver – data rate: 38.4 KbaudTransceiver – data rate: 38.4 Kbaud Send: 25 – 27 mA (maximum power) Send: 25 – 27 mA (maximum power) Receive: 8 – 10 mA Receive: 8 – 10 mA Sleep: <1uA Sleep: <1uA RF Power: dB (programmable) RF Power: dB (programmable) Received Sensitivity: dB (RSSI capable) Received Sensitivity: dB (RSSI capable)

Hardware – Mica2 Typical Battery life:Typical Battery life: 1000 milliamp - hours 1000 milliamp - hours CPU:CPU: 1000/8mA ~ 125 hours at full CPU consumption 1000/8mA ~ 125 hours at full CPU consumption Transmitter:Transmitter: 25mA * (38000) -1 sec/bit * (60) -1 hour/sec ~ 1.1x mA – hour /bit 25mA * (38000) -1 sec/bit * (60) -1 hour/sec ~ 1.1x mA – hour /bit 1000/1.1x10 -5 ~ 9.12x10 7 bits 1000/1.1x10 -5 ~ 9.12x10 7 bits Doesn't consider MAC encoding scheme, collision error checkingDoesn't consider MAC encoding scheme, collision error checking Simple 8-bit CDMA: 9.12x10 7 /8 = 1.14x10 7 bits = 1.425x10 6 bytesSimple 8-bit CDMA: 9.12x10 7 /8 = 1.14x10 7 bits = 1.425x10 6 bytes 1.425x10 6 ~ 1.36MB: 1 floppy disk1.425x10 6 ~ 1.36MB: 1 floppy disk

Distributed Algorithms Determine appropriate transmission power levels per node Determine appropriate transmission power levels per node Reduce or increase the amount of neighbors a node has Reduce or increase the amount of neighbors a node has Reduce average RF interference Reduce average RF interference Outline of 5 distributed algorithms…Outline of 5 distributed algorithms…

Fixed Transmission Power Simplest solution Simplest solution Arbitrarily assign a fixed transmission power level to all nodes. Arbitrarily assign a fixed transmission power level to all nodes. Does not adjust transmission power at all.Does not adjust transmission power at all. Distributed Algorithm # 1

Local Mean Algorithm (LMA) 1. All nodes start with same initial transmission power. 2. Every node periodically broadcasts a LifeMsg. 3. These nodes than count the number of responses (LifeAckMsg) they receive. Called NodeResp Called NodeResp 4. If NodeResp < NodeMinThresh, than node increases transmission power 5. If NodeResp > NodeMaxThresh, than node decreases transmission power 6. If NodeResp is between these bounds, than the node does not change its transmission power. Distributed Algorithm # 2

Threshold in Mean Number of Neighbors (LMN) Similar to previous algorithm. Similar to previous algorithm. LifeAckMsg also contains its own number of neighbors.LifeAckMsg also contains its own number of neighbors. Node receiving the LifeAckMsg computes a mean value from this Node receiving the LifeAckMsg computes a mean value from this The new NodeRespThe new NodeResp Distributed Algorithm # 3

Global Solution with Equal Transmission Power Uses the Equal Transmission Power (ETP) Algorithm. Uses the Equal Transmission Power (ETP) Algorithm. Assigns a uniform transmission power to all nodesAssigns a uniform transmission power to all nodes Chooses the minimal value to ensure a fully connected network.Chooses the minimal value to ensure a fully connected network. ETP Algorithm on next page… ETP Algorithm on next page… Distributed Algorithm # 4

Equal Transmission Power (ETP) Algorithm 1. Among the node pairs that are not yet connected, choose the one with the smallest distance. 2. Set transmission power of all nodes to a value sufficient to connect these two nodes. 3. Check connectivity of the resulting network. If not connected, loop. 4. When network is connected, minimum power level is found.

Global Solution with Diverse Transmission Power Uses the Diverse Transmission Power (DTP) Algorithm. Uses the Diverse Transmission Power (DTP) Algorithm. Creates a connected networkCreates a connected network Does not set all transmission ranges to the same value.Does not set all transmission ranges to the same value. Tries to find a minimal power level for every node.Tries to find a minimal power level for every node. DTP Algorithm on next page… DTP Algorithm on next page… Distributed Algorithm # 5

Diverse Transmission Power (DTP) Algorithm 1. Among the node pairs that are not yet connected, choose the one with the smallest distance. 2. Set transmission power of these two nodes to a value sufficient to connect them. 3. Check connectivity of the resulting network. Loop if not connected. 4. When network is fully connected, minimum power level is found.

Proposed Basic Algorithms Before initiating communication with A Before initiating communication with A 1.Make sure there will be no communication interference 2.Put node into FCL if above conditions apply A sends RTS(FCL, L d ) at maximum power A sends RTS(FCL, L d ) at maximum power When B receives RTS When B receives RTS 1.Check whether there is some channel in the FCL 2.Ensure some channel is a free channel after CTS and Data transmission durations, and that it does not interfere with any other channel B replies with CTS(D j, NAV CTS, P CTS ) B replies with CTS(D j, NAV CTS, P CTS ) Each mobile host keeps power[…] array Each mobile host keeps power[…] array For each host Id, power[Id] is the power to transmitFor each host Id, power[Id] is the power to transmit AB

Java Simulation Environment JiST JiST New and rapidly growing simulation environmentNew and rapidly growing simulation environment Simulates using virtual machines Simulates using virtual machines SWANS SWANS Runs on top of JiSTRuns on top of JiST Functionality similar to ns2 and GloMoSimFunctionality similar to ns2 and GloMoSim Component based architecture Component based architecture Parallelized Parallelized

JiST High performance, discrete event simulation engine that runs over standard java virtual machine High performance, discrete event simulation engine that runs over standard java virtual machine Advantages: Advantages: Efficient Efficient Transparent Transparent Standard Standard Java in Simulation Time jist.ece.cornell.edu/docs/ yorku.pdf

SWANS jist.ece.cornell.edu/docs/ swans-dsr.pdf Scalable Wireless Ad hoc Network Simulation Newest technology in wireless sensor networking simulation Simulation program features include: Routing protocol, field dimensions, number of nodes, client/server pairs, transmissions, packet loss probability, node movement rate Control Flow: Route request, route reply Data Structures: Buffers, route cache, route tables – scalable Layers: Routing, network, MAC Routing: DSR, ZRP Detail: Approximate physical level, packet level

Future Plan Simulate a mobile wireless network in JiST/SWANS. Simulate a mobile wireless network in JiST/SWANS. 1.Without power control 2.With power control Develop a refined power control algorithm. Develop a refined power control algorithm.

References ng/documents/kubischtxCtrl.pdf 2.pdf _pdf/ _B_MICA2.pdf /lecture03.ppt na.dankwa.ee.pdf