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Medium Access Protocol for the EYES sensor nodes. Lodewijk van Hoesel hoesel@cs.utwente.nl. Contents. Current EYES sensor node design Network structure MAC protocol Future work. Current sensor node design. Processor: TI MSP-430F149 560 μ A for 1 Mips 16 bit 2 Kb RAM 60 Kb ROM - PowerPoint PPT Presentation
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Medium Access Protocol for the EYES Medium Access Protocol for the EYES sensor nodessensor nodes
Lodewijk van Hoesel
hoesel@cs.utwente.nl
2 energy efficient sensor networks
ContentsContents
Current EYES sensor node design
Network structure
MAC protocol
Future work
3 energy efficient sensor networks
Current sensor node designCurrent sensor node design
Processor: TI MSP-430F149560 μA for 1 Mips16 bit2 Kb RAM60 Kb ROMBuilt-in AD converterSupports power save modes
Transceiver: RFM TR1001115.2 Kbps data rateAmplitude Shift Keying (ASK)No mixers are used; SAW filtersVery low standby power consumption Analog RSSI (AD converter necessary)
4 energy efficient sensor networks
RF power consumption in the RF power consumption in the current sensor node designcurrent sensor node design
RFM TR1001 worst case power consumption:
Transmit 20.0 mJ/s
Receive 14.4 mJ/s
Dormant 15.0 µJ/s
Battery capacity
3.6 V @ 1Ah 12.96 kJ
180 h
250 h
27 y
5 energy efficient sensor networks
Network structureNetwork structure Wireless network nodes are capable of:
Measuring physical conditions Relaying messages from other nodes
Routing decides main function:Sensor node (mainly measuring; passive or event driven)Relay node (mainly relaying messages; passive)
Source
To sink
Source
To sink
6 energy efficient sensor networks
Communication typesCommunication types
Sensor node Sensor nodeRoute discovery, clustering, neighborhood discovery, localizationUnicast or Multicast
Relay node Sensor node Requests for data, signaling messages Unicast or Multicast
Sensor node Relay node Sensor data Unicast
Relay node Relay node Backbone traffic Unicast
OFTENOFTEN
RARELYRARELY
7 energy efficient sensor networks
MAC protocol: CSMA, CDMA, MAC protocol: CSMA, CDMA, FDMA, TDMA,... ?? FDMA, TDMA,... ??
Carrier Sense Multiple AccessCarrier Sense Multiple Access (CSMA)High collision rate
Transmissions of sensor data occurs in groups due to physical event horizonRequires constant channel monitoring
Code Division Multiple AccessCode Division Multiple Access (CDMA)Requires signal processing of analog received signal
Not supported by current hardware designRequires constant channel monitoring
Frequency Division Multiple AccessFrequency Division Multiple Access (FDMA)Requires multi-channel receiver
Not supported by current hardware designRequires constant channel monitoring
Time Division Multiple AccessTime Division Multiple Access (TDMA)Does not require constant channel monitoringRequires synchronization between nodes
8 energy efficient sensor networks
Overview of the proposed MAC Overview of the proposed MAC protocol for the EYES sensor protocol for the EYES sensor
nodesnodes
Communication Request (CR) Claim a timeslot (for nodes that join the network)Notify the need for data communication to the owner of the timeslot
Traffic Control (TC) Owner of the timeslot transmits its schedule
DataContains a data packet
1 s
Frames:
t
n n+1
t1/16 s
Time slots:
s s+1 s+2
Channels:
t
CR DataTC
9 energy efficient sensor networks
Communication Request SectionCommunication Request Section Contains requests to timeslot owner
Node Announcement (NA)Request to listen to TC in specified timeslot
Request to Receive (RTR)Useful to ask data from passive sensor nodes
Request to Send (RTS)Useful for event driven nodes and relay nodes
Collisions can occurTimeslot owner should detect collisionsRetry in data section (CSMA/cd based)
Direct transmission of (abbreviated) request +dataOnly useful for RTS
DATACR TC
SD DATACollision detected
10 energy efficient sensor networks
Traffic Control SectionTraffic Control SectionTC Schedule
Indicates to which TCs this node is listeningNew nodes in the network: “AND” all schedules, a timeslot is free at “zero”
Acks/Nacks of request in CRContains a “collision detected” flag
Timeslot owner listens to data section for retries NA is acknowledged implicitly in TC schedule
Multicast flag Gives the node the option for multicast transmissions
Request for Any (RFA)Gives the node the option to request for a reply of any node that has the specified information availableRandom node respond in data section (CSMA/cd)
11 energy efficient sensor networks
Data SectionData Section
TC indicates whether Data Section is:Used
Data transmission as indicated in TC
FreeMay be used for transmissions agreed on higher protocol layers“Slotted” CSMA/cd usagei.e. 8 possible start times for transmissions
Priority of the data section usage:1. Multicast transmissions (discards any requests in CR
except NA)2. Request to Send (RTS)3. Request to Receive (RTR)4. Requests for any (RFA) data type5. Higher protocol layers (CSMA/cd)
12 energy efficient sensor networks
Energy consumption (transceiver Energy consumption (transceiver only) with current MAC design: only) with current MAC design:
OverheadOverhead
Receive CR (18 bytes) in own timeslot: 1.25 ms 18 µJ/frame
TC of 4 other nodes: 5.00 ms 72 µJ/frame
Transmit Own TC (18 bytes): 1.25 ms 25 µJ/frame
Sleep Remainder of the frame: 992.50 ms 15 µJ/frame
130 µJ/frame
Lifetime of a sensor node:Lifetime of a sensor node: 3 y 60 d3 y 60 d
+
13 energy efficient sensor networks
Conclusion: MAC protocol power Conclusion: MAC protocol power consumptionconsumption
Minimize the number of transmissions Do useful transmissions
Each transmission should reach its sink Do not discard packets Add own sensor readings to relayed data
Group transmissions to a neighbor Compress data Minimize the number of transmitted TCs
Minimize the number of receptions Minimize the number of received TCs Use wakeup schemes
14 energy efficient sensor networks
Timeslot OwnershipTimeslot Ownership
Not all nodes need to own a timeslot Event driven nodes may redeem their right to own a timeslot
Saves energy
Eases scalability of the network
Can participate in: Do RTS/RTRs in CR sections
Listen to omnicast messages
Receive data on higher layers negotiated times
15 energy efficient sensor networks
Current state of MAC Current state of MAC implementationimplementation
Finalizing OS radio control functions
MAC implementation Work in progress
No higher layer negotiated communication No CSMA/cd retries of collisions in CR
To do: physical layer Measurements to determine:
Best DC balancing schemePreamble usage for UART synchronizationTransmission power control“Raw” bit error rate
16 energy efficient sensor networks
Ideas for MAC protocol Ideas for MAC protocol communication demonstrationcommunication demonstration
Coffee status Measure weight of coffee can Determine coffee machine status; coffee ready??
Mobility test Node controls an electric car Determine direction of a beacon and drive to it
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