TDMA based MAC protocol to assist in Wide area Sensor Network Deployment Nuwan Gajaweera

Outline Wireless Sensor Networks Background & Objectives Literature Survey Technology Choices TDMA MAC protocol Remaining Work

Wireless Sensor Network Collection of low power computer With integrated sensors Networked via short range radio transceivers Application Areas  Environmental Monitoring  Defense & security  Health  etc

Outline Wireless Sensor Networks Background & Objectives Literature Survey Technology Choices TDMA MAC protocol Remaining Work

Background Monitoring of a large area  WSN deployment over a large area  Large number of repeater nodes needed Alternative  Use a Data Mule Data Mule – Mobile mote that traverse the area of the sensor network  Random Path: Motes mounted on people, livestock or vehicles  Deterministic Path: Robots

Background Area to be monitored Gateway Data Mule

Issue Multiple Data Mules at the Base station  Efficient use of radio resources – i.e. minimize packet collisions  Fair bandwidth allocation to all data mules  Collect maximum data volume from data mule in given time

Objectives Develop suitable MAC protocol  Single hop network  Traffic pattern: data flows from data mule to base station  Maximize throughput  Minimize delay Develop storage engine  Data collected from leaf nodes should stored so that fast retrieval is possible

Outline Wireless Sensor Networks Background & Objectives Literature Survey Technology Choices TDMA MAC protocol Remaining Work

Literature Survey Wireless sensor network platforms Different MAC protocols in existence

Wireless sensor network platforms - Research TinyOS  Popular event driven OS for deeply embedded systems SOS Mantis Contiki

Wireless sensor network platforms - Commercial Crossbow Moteiv Ember Corp Dust Networks – TDMA-FDMA based MAC TinyOS

WSN MAC protocols Random access schemes  LPL, B-MAC, X-MAC  MAC Slotted schemes  S-MAC, S-MAC/AI, T-MAC TDMA based schemes Hybrids protocols

TDMA MAC protocols Pros  High channel utilization due to absence of packet collisions Cons  Complexity in building a scheduling  Need for node synchronization  Inability to handle mobile nodes, due the frequent need to reschedule

TDMA MAC protocols PEDMACS LMACS Cluster Based  PACT  EMAC  LEACH – routing protocol  BMA (utilizes LEACH for clustering)

Outline Wireless Sensor Networks Background & Objectives Literature Survey Technology Choices TDMA MAC protocol Remaining Work

Technology Choices Wireless Sensor Network Platform  TinyOS Mote  MICA2 MAC Protocol  TDMA MAC Storage engine  Under review

Why TDMA? CSMA  Channel capacity wasted due to packet collisions TDMA  Channel capacity wasted due to control traffic  Maximize throughput  Energy conservation is a not a priority “Develop demand assigned TDMA MAC Minimizes control traffic”

D-Lab Mote MICA2 Clone Developed at Dialog UoM Lab (D- Lab Mote)  Exact copy of MICA2 Currently working on developing D-Lab Mote V2  Small modifications to original MICA2  GPS, GSM Modules  RTC  Flash Memory (MMC card)

Outline Wireless Sensor Networks Background & Objectives Literature Survey Technology Choices TDMA MAC protocol Remaining Work

MAC protocol development process Concept Development Write TinyOS Code Simulate (Arvora) Analyze ResultsRefine Concept Execute on MICA2 motes Satisfactory Results Unsatisfactory Results Analyze Results Unsatisfactory Results Process End Satisfactory Results Completed In progressTo be done

TDMA MAC Base station (Gateway) Radio range of BS mote #1 (Data Mule) mote #2 mote #3 Transmission Group

TDMA MAC Contention Periods  Motes contend for membership of the tx group Transmission Periods  Motes in the tx group transmit data in allocated slot Time … Transmission period Contention Period

Transmission Period Time … UplinkDownlink tx start packet tx end packet Guard period Time 1 … UplinkDownlink Slot tx start packet tx end packet Also serves as ack packet

Contention Period Time … UplinkDownlink RTS con start packet con end packet + CTS TbTb T b,max TpTp T b,max - Max back-off T p - Packet time T b - Actual b-off

Contention Period Motes are only told if they were added to the tx group or not The time slot is only advertised during the tx start packet When the membership of the tx group changes, the following tx start packet will carry a uplink map that gives the time slot allocation.

TDMA MAC Simulation Base station wakes up at simulation start motes wake up after random delay The motes that are awake contend for membership of the transmission group After transmitting ‘N’ packets, the mote removes itself from the tx group.  (N = 32, 64, 128, ∞ ) The said mote again starts to contend for tx group membership

Outline Wireless Sensor Networks Background & Objectives Literature Survey Technology Choices TDMA MAC protocol Remaining Work

Storage Engine Mote will contain  SRAM  Flash Memory (MMC Card) Mote (Data mule) will collect data from leaf nodes and store data in flash memory When in range of the base station the mote will read data from the (slow) flash into the SRAM in fixed size blocks The mote will then attempt to become a member of the tx group and upload this block of data to the base station Once the block is transferred to the BS, the mote will remove itself from the group and repeat the process

Remaining Work Select/Develop storage engine Build MICA2 Clone (V2) Integration of storage engine & TDMA MAC Uploading base station data to a server

Conclusion