TDMA based MAC protocol to assist in Wide - Electronic ...

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 stationEfficient use of radio resources – i.e. minimize

packet collisionsFair bandwidth allocation to all data mulesCollect maximum data volume from data mule

in given time

Objectives

Develop suitable MAC protocolSingle hop networkTraffic pattern: data flows from data mule to

base stationMaximize throughputMinimize delay

Develop storage engineData 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 schemesLPL, B-MAC, X-MAC802.15.4 MAC

Slotted schemesS-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

PACTEMACLEACH – routing protocolBMA (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 onMICA2 motes

SatisfactoryResults

UnsatisfactoryResults

Analyze Results

UnsatisfactoryResults

Process End

SatisfactoryResults

Completed In progress To be done

TDMA MAC

Base station(Gateway)

Radio rangeof BS

mote #1(Data Mule)

mote #2

mote #3

TransmissionGroup

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

…

Uplink Downlink

tx start packet tx end packet

Guard period

Time

1 …

Uplink Downlink

2 3 1 2 3

0 1 2 3 4 5Slot

tx start packet tx end packet

Also serves as ack packet

Contention Period

Time

…

Uplink Downlink

RTS

con start packet

con end packet + CTS

Tb

Tb,maxTp Tb,max - Max back-off

Tp - Packet timeTb - 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

Throughput vs Number of Nodes

4000

5000

6000

7000

8000

9000

10000

11000

0 2 4 6 8 10 12 14 16

Number of Nodes

Th

rou

gh

pu

t (b

ps) 32 PPC

64 PPC

128 PPC

inf PPC

BMAC

Delay vs Number of Nodes

0

1

2

3

4

5

6

7

8

0 2 4 6 8 10 12 14 16

Number of Nodes

De

lay

(s

)

32 PPC

64 PPC

128

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