Reliable transmissions in large scale sensor networks for medical monitoring applications
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Reliable Transmissions in Large Scale Sensor Networks for Medical Monitoring Applications. 曾俊元 C. Henry Tseng. Academia Experience. Degree University of California, Davis, PhD in Computer Science, 2006 Current position NTPU CSIE, Assistant Professor, 2009~

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Reliable Transmissions in Large Scale Sensor Networks for Medical Monitoring Applications

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Reliable transmissions in large scale sensor networks for medical monitoring applications

Reliable Transmissions in Large Scale Sensor Networks for Medical Monitoring Applications

曾俊元

C. Henry Tseng


Academia experience

Academia Experience

  • Degree

    • University of California, Davis, PhD in Computer Science, 2006

  • Current position

    • NTPU CSIE, Assistant Professor, 2009~

    • NTPU Information Center, Section Chief of System, 2012~

  • Experience

    • NTPU MIS, Joint Appointment Asst. Prof., 2010~2011

    • NTPU Office of R&D, Section Chief of Planning, 2010~2011


Industrial experience

Industrial Experience

  • Telcordia Taiwan Research Center, 2009

    • Senior Research Scientist

    • Telmatics projects with III & ITRI

  • Cisco Systems Inc., 2006~2008

    • Software Engineer III, IOS OSPF Developer

    • Core Campus, San Jose, CA, USA

  • McAFee Software Engineer, 2001

    • IntruShield IDS prototype development


Security research topics

Security research topics

  • Past

    • Intrusion detection for MANET Routing

    • Malicious Domain name detection

  • Current

    • Rootkit detection & prevention

    • Malware sample collection, analysis & evaluation

    • Automation for web logs of intrusions

    • HoneyPod of SQL injection attacks

  • Future

    • Online game anti-bot detection & prevention at server side


Outline of zigbee research

Outline of Zigbee research

  • Zigbeestack

  • Issues of Zigbee stack

  • Solutions

  • New monitoring applications


1 zigbee stack

1. Zigbee Stack

  • 1.1 Introduction

  • 1.2 Applications


Overview

Overview

  • Zigbeenetwork

    • Nodes:Coordinator, Router, End device

    • PAN: Personal Area Network

    • End devices send sensor data to Coordinator

    • Coordinator forwards data to sink node (backend data server)


Zigbee sample network

Zigbee Sample network

S

Sink

C

Coordinator

R

S

R

End devices

R

C

R

R

Router

Data


Pan address

PAN address

  • Join PAN

    • Coordinator broadcasts joining messages with its PAN ID

    • Routers join PAN and forward the joining messages

    • End devices join PAN by forwarded messages

  • PAN address assignment

    • Network address of Zigbee stack

    • Coordinator’s PAN address is always “0”

    • Coordinator assigns others’ PAN addresses in random


Sensor data delivery

Sensor data delivery

  • Zigbee stack layers

    • MAC: IEEE 802.15.4

    • Network: Mesh routing, a modified version of AODV

    • APS: application sub-layer, management of application data transmission

  • Data delivery

    • End devices(EDs) transfer data to Coordinator periodically

    • Each ED builds a “binding” for data transmission session

    • ED can support multiple sensors by “End Point”, which is similar with port in TCP


Reliable transferring

Reliable transferring

  • Acknowledgement

    • MAC ACK

    • APS ACK

  • MAC ACK

    • Each link transmission requires a MAC ACK

    • Ensure reliability of each wireless link transmission

  • APS

    • Each remote transmission of a binding requires a APS ACK

    • Ensure reliability of each remote transferring

    • Independent from MAC ACK


Example data delivery

Example data delivery

Coordinator

End Device

Router

[3] Send the data

[1] Send the data

[2] MAC ACK

[4] MAC ACK

[7] APS ACK

[5] APS ACK

[8] MAC ACK

[6] MAC ACK


1 zigbee stack1

1. Zigbee Stack

  • 1.1 Introduction

  • 1.2 Applications


1 2 capabilities for applications

1.2 Capabilities for applications

  • Light weight sensor data collection

    • Usually < 1 k bps

    • Transmission radio power: 0 dbm

    • Theoretical speed 250 k bps

    • Realistic max speed without lost in one hop: 20 k bps

  • Support wide range of data collection

    • Each PAN can support a large Mesh topology with several hops of network dialog

    • Transmission reliability reduces a lot while forwarding 2 or more hop away: max speed becomes < 15 k bps for 2 hop

    • Indoor obstacles effect the performance a lot


Implementation

Implementation

  • TI CC2530 embedded system

    • Enhanced 8051, 256k flash memory

    • 8 bit CPU with 32 M Hz speed

    • Support RS232 UR connection to PC/NB

    • Modified version for USB & Bluetooth connections

    • Very small, low power consumption, low ratio power

  • Software development environment

    • IAR for firmware development

    • Sample development codes for applications

    • Codes of APS and NWK layers can be modified


Current applications

Current applications

  • Temperature

    • Green house, Fish farm

  • Light control

    • Digital home

  • Medical data monitoring

    • Temperature

    • Pulse of human blood system

    • Wearable medical device

    • Body sensor network


2 issues of zigbee stack

2. Issues of Zigbee stack

  • 2.1 Limitation of Coordinator

  • 2.2 Transport Layer

  • 2.3 Load balance

  • 2.4 Scalability


Role of coordinator

Role of Coordinator

  • PAN management

    • Coordinator (CO) must be unique in a PAN

    • Node joining relies on CO

    • IEEE802.15.4 can hardly be modified

  • Data transmission

    • EDs send data to CO by default

    • Manual binding setting is costly

  • Failure of CO


Failure of co

Failure of CO

  • PAN network services collapse

    • PAN management fails

    • Data transmission may completely stop

  • No solution for CO failure

    • A PAN cannot have 2 COs

    • No automatic solution


2 issues of zigbee stack1

2. Issues of Zigbee stack

  • 2.1 Limitation of Coordinator

  • 2.2 Transport Layer

  • 2.3 Load balance

  • 2.4 Scalability


Transport layer

Transport Layer

  • Included functions in APS

    • ACK service

    • Binding

    • End port

    • ID of data packet

  • Between UDP & TCP

    • UDP is too simple

    • TCP is too heavy for Zigbee

    • Sufficient but limited functions


New demands

New demands

  • Issues

    • Cannot send a large data message

    • No flow control

    • Resent times is fixed (3 times)

    • RTT is fixed

  • Desirable functions

    • Data fragmentation & re-assembling

    • Receive window

    • Enhanced timeout & resending strategy

    • Sequence number


2 issues of zigbee stack2

2. Issues of Zigbee stack

  • 2.1 Limitation of Coordinator

  • 2.2 Transport Layer

  • 2.3 Load balance

  • 2.4 Scalability


Load balance

Load Balance

  • First ring nodes

    • Nodes directly connected to Sink or Coordinator

    • Can directly forward data to Sink or Coordinator

    • Usually accumulate large amount of data traffic

    • Can be network bottleneck or die out easily

  • Balancing traffic of whole PAN

    • Local balance vs. global balance


Flow control

Flow control

  • Sending rate control

    • Queuing delay grows exponentially

    • Signal interference also grows exponentially

    • Limit the sending rate to avoid traffic jamming

    • Find out the upper bound dynamically

  • Top down vs. bottom up

    • Data sending behavior is bottom up approach

    • PAN management is top down approach

    • Both approaches should be used in different aspects


2 issues of zigbee stack3

2. Issues of Zigbee stack

  • 2.1 Limitation of Coordinator

  • 2.2 Transport Layer

  • 2.3 Load balance

  • 2.4 Scalability


Scalability

Scalability

  • Old Tree based approach

    • Can support limited global routing optimization

    • Support only several dozens of node

  • New mesh topology

    • Same as MANET routing

    • Can support up to 200 nodes

    • Still need a new hierarchical routing control for large networks


Measure metrics

Measure metrics

  • Number of nodes

    • Tree level

    • Topology dialog

  • Node density

    • Number of neighbors

    • Routing load

    • Signal interference


3 solutions

3. Solutions

  • 3.1 CDTS

  • 3.2 Backup Coordinator


Coordinator data traffic shunt cdts

Coordinator Data Traffic Shunt (CDTS)

  • CDTS Router

    • Helper node of Coordinator traffic forwarding

    • Connect sink node with Direct Communication Link (DCL)

      • RS232, Bluetooth, USB

  • CDTS Group

    • CDTS routers nearby the sink node

    • Absorb traffic toward the sink node without going through Coordinator


Example topology

Example Topology


Cdts layer

CDTS Layer

  • Low cost design

    • Insert a layer between NWK & MAC layer

    • Require modification in CDTS router only

  • Maximize compatibility

    • No modification of Coordinator, applications, end devices, routers

    • No modification of MAC layer, IEEE 802.15.4

    • Slight medication of NWK layer


Address modification

Address modification

CDTS layer in Zigbeestack

Address Modification


Reuse aps functions

CDTSrouter

Reuse APS functions

End-device

[1] Send the data

[2] APS ACK

CDTS


Experiments

Experiments

  • Embedded system

    • TI CC2530 development board

    • Simple topology:

      • ED->R->C->Sink

      • ED->R->CDTS Router->Sink

    • Use real ECG medical sample data as testing network traffic

  • Ns2

    • Testing in large scale node topology

    • Tests of several ED traffic flows


Deliver ratio vs sending rate

Deliver ratio vs. Sending rate

threshold

80%

Embedded system


Coordinator loading vs sending rate

Coordinator loading vs. Sending rate

60%

Embedded system


Deliver ratio vs number of nodes

Deliver ratio vs. number of nodes

80%


Achievement

Achievement

  • TBME

    • ChinyangHenry Tseng, "Coordinator Traffic Diffusion for Data-Intensive Zigbee Transmission in Real-time Electrocardiography Monitoring", IEEE Transactions on Biomedical Engineering, to appear.

  • ICS 2012

    • Chinyang Henry Tseng, ShiauHuey Wang, Bor-Shing Lin, Tong-Ying Junag, Xiao-RuJi, "CDTS: Coordinator Data Traffic Shunt model for Zigbee networks", International Computer Symposium (ICS 2012)


3 solutions1

3. Solutions

  • 3.1 CDTS

  • 3.2 Backup Coordinator


Back coordinator

Back Coordinator

  • Back Coordinator group

    • BC1, BC2, …

    • Compatible with CDTS group

  • Automatic Coordinator recovery

    • Monitoring Coordinator network status

    • Detection of Coordinator failure

    • Replace Coordinator automatically


Problem statement

Problem statement

R

Bc2

Bc1

sink node

E

E

E

E

E

E

coordinator

Bc

E

E

S

other Bc

Backup Coordinator Group

C

Bc1

R

Bc2

BC router

Backup Coordinator 2

Backup Coordinator 1


Coordinator recovery

Coordinator recovery

E

E

E

E

E

E

E

E

S

Backup Coordinator Group

R

Bc1

Bc1

Bc2

R

C

Bc2

Bc1


3 2 coordinator monitoring

3.2 Coordinator monitoring

  • Binding

    • BC1 actively build a binding with Coordinator

    • Once the binding is close, Coordinator malfunctions

  • Listen

    • BC1 passively listen to beacons sent by Coordinator

    • If Coordinator does not send beacons, Coordinator fails to operate


Coordinator recovery steps

Coordinator recovery steps

  • BC1 -> C

    • Change its setting as Coordinator

    • Execute Coordinator mechanisms

    • No need of rebooting the firmware

  • Modification requirements

    • Only in BC

    • APS for Coordinator monitoring

    • NWK for Coordinator mechanism re-establishment


Sensor data sending issue

Sensor data sending issue

  • Bindings of sensor data sending

    • End devices send sensor data to Coordinator by default

    • Coordinator has lots of bindings with end devices for sensor data retrieving

  • If Coordinator fails to operate

    • Bindings are broken

    • No more sensor data retrieving

    • End devices have to re-build new bindings manually by default


Automatic data traffic recovery

Automatic data traffic recovery

  • Re-connect with new Coordinator

    • End devices require updating Coordinator info

    • Automatically maintenance of bindings with the Coordinator

  • Recovery steps

    • New Coordinator floods its new info to entire PAN

    • End devices receive flooding messages from new Coordinator

    • End devices update its Coordinator info, including the bindings


Recovery time of data binding

Recovery time of data binding

Recovery of Data binding

Binding : 669 ms

Failure of Coordinator

  • Listen-15(sec) :15400 (ms)


Recovery time binding vs listen

Recovery time (Binding vs. Listen)


Achievement1

Achievement

  • Advantech Co.

    • They are highly interested in this work

  • Patent

    • Should be done soon

  • Paper

    • Journal paper submission will be done this year


4 new monitoring applications

4. New monitoring applications

  • 4.1 Remote ECG monitoring

  • 4.2 Ongoing works


4 1 remote ecg monitoring

4.1 Remote ECG monitoring

  • Current ECG

    • Local ECG measurement

    • Bluetooth transmission

      • Short range, high radio power transmission

  • New deign by Zigbee

    • Large network topology coverage

    • Sufficient data rate

    • Low radio power transmission

    • Low cost deployment

    • Automatic self-configured system


4 2 ongoing works

4.2 Ongoing works

  • New sensor devices

    • Remote power switch

    • SPO2

    • Blood pulse

  • New works

    • Load balance for entire PAN

    • Transport layer for Zigbee stack


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