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
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
 Efficient
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
TinyOS
 Moteiv
 Ember Corp
 Dust Networks – TDMA-FDMA based
MAC

WSN MAC protocols

Random access schemes
 LPL,
B-MAC, X-MAC
 802.15.4 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
– routing protocol
 BMA (utilizes LEACH for clustering)
 LEACH
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 (DLab 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
Refine Concept
Simulate
(Arvora)
Unsatisfactory
Results
Satisfactory
Results
Unsatisfactory
Results
Process
End
Satisfactory
Results
Completed
Analyze Results
In progress
Analyze Results
Execute on
MICA2 motes
To be done
TDMA MAC
mote #2
mote #3
Transmission
Group
Radio range
of BS
Base station
(Gateway)
mote #1
(Data Mule)
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
Slot
0
1
2
3
4
5
1
2
3
1
2
3
…
Time
tx start packet
Uplink
tx end packet
Downlink
Also serves as ack
packet
…
Time
tx start packet
Uplink
tx end packet
Downlink
Guard period
Contention Period
Tb,max
Tp
Tb,max
Tp
Tb
Tb
…
RTS
Time
con start
packet
Uplink
con end
packet + CTS
Downlink
- Max back-off
- Packet time
- 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
11000
Throughput (bps)
10000
9000
32 PPC
8000
64 PPC
128 PPC
7000
inf PPC
6000
BMAC
5000
4000
0
2
4
6
8
10
Number of Nodes
12
14
16
Delay vs Number of Nodes
8
7
Delay (s)
6
5
32 PPC
64 PPC
4
128
3
2
1
0
0
2
4
6
8
10
Number of Nodes
12
14
16
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