Fault Tolerant Sensor Network Routing for

Patient Monitoring

Shanshan Jiang, Annarita Giani, Allen Yang, Yuan Xue, and

Ruzena Bajcsy

Vanderbilt UniversityUniversity of California at Berkeley

TRUST Autumn 2008 ConferenceNovember 11th, 2008

Fault Tolerant Sensor Network Routing for Patient Monitoring

Outline

• Motivation• System and Network Architecture• System Prototype and Implementation

• Network and Routing Model of the Backbone Network

• Optimization-based Routing Restoration of the Backbone Network

• Performance Evaluation

Fault Tolerant Sensor Network Routing for Patient Monitoring

Motivation• Aging population

– According to the U.S. Census Bureau, the number of people over the age of 65 is expected to hit 70 million by 2030, having doubled since 2000.

• Health care expenditures– Health care expenditures in the

United States are projected to rise to 15.9% of the GDP ($2.6 trillion) by 2010.

– The cost of health care for the nation’s aging population has become a national concern.

Fault Tolerant Sensor Network Routing for Patient Monitoring

Motivation• Wireless Sensor Networks

– Deploy wearable sensors on the bodies of patients in a residential setting

– Continuously monitor physiological signals (such as ECG, blood oxygen levels) and other health related information (such as physical activity)

• Advantages– Shift from a clinic-oriented, centralized healthcare system to a patient-

oriented, distributed healthcare system

– Reduce healthcare expenses through more efficient use of clinical resources and earlier detection of medical conditions

• Challenges– Performance, Reliability, Scalability, QoS, Privacy, Security …

– More prone to failures, caused by power exhaustion, software and hardware faults, natural disasters, malicious attacks, and human errors etc.

Provide fault-tolerant wireless communication that can satisfyboth the performance and reliability requirements

Fault Tolerant Sensor Network Routing for Patient Monitoring

Outline

• Motivation• System and Network Architecture• System Prototype and Implementation

• Network and Routing Model of the Backbone Network

• Optimization-based Routing Restoration of the Backbone Network

• Performance Evaluation

Fault Tolerant Sensor Network Routing for Patient Monitoring

System and Network Architecture

Fault Tolerant Sensor Network Routing for Patient Monitoring

System and Network Architecture

Lower Tier: Body Sensor NetworkUpper Tier: Multi-hop Wireless Backbone Network

Fault Tolerant Sensor Network Routing for Patient Monitoring

Outline

• Motivation• System and Network Architecture• System Prototype and Implementation• Network and Routing Model of the Backbone

Network

• Optimization-based Routing Restoration of the Backbone Network

• Performance Evaluation

Fault Tolerant Sensor Network Routing for Patient Monitoring

System Prototype and Implementation

• Hardware Devices

• Software Design

Fault Tolerant Sensor Network Routing for Patient Monitoring

System Prototype Experiment

Fault Tolerant Sensor Network Routing for Patient Monitoring

Outline

• Motivation• System and Network Architecture• System Prototype and Implementation• Network and Routing Model of the Backbone

Network

• Optimization-based Routing Restoration of the Backbone Network

• Performance Evaluation

Fault Tolerant Sensor Network Routing for Patient Monitoring

Network Model of the Backbone Network• Backbone Network Performs Sensor Data

Routing and Forwarding • Network and Interference Model

– Topology: G=(V, E)

– All nodes have a uniform transmission range and interference range

– Two edges interfere with each other if they have two nodes within the interference range of each other

• Traffic Demand Model– df is the traffic demand of flow f, which is an

aggregation amount of all the sensor data received at the sender of flow f

• Be routed over multiple paths

• xf(e) denotes the amount of flow f’s traffic being routed on link e

Backbone Network

Fault Tolerant Sensor Network Routing for Patient Monitoring

Routing Model of the Backbone Network• Metric for routing performance

– Minimum Flow Throughput Scaling Factor• The minimum, over all flows, of the actual flow throughput being routed

divided by its throughput demand

• Optimal Routing Formulation

wireless channel constraint(necessary scheduling condition)

flowconservationconditions

amount of traffic received at the destination node rf

Fault Tolerant Sensor Network Routing for Patient Monitoring

Outline

• Motivation• System and Network Architecture• System Prototype and Implementation

• Network and Routing Model of the Backbone Network

• Optimization-based Routing Restoration of the Backbone Network

• Performance Evaluation

Fault Tolerant Sensor Network Routing for Patient Monitoring

Optimization-based Routing Restoration

• Discover Alternate Paths Bypassing the Failed Nodes• Reactive Restoration

– Not reserve any network resource– Deal with failures only when they occur through network resource

reallocation– Application

• Resource-limited System that allows performance degradation upon failures

• Proactive Restoration– Reserve additional resources a priori– Provide certain performance assurance for the rerouted flows with

a shorter restoration time– Application

• Life-critical System• Admission Control

– Result in a lower network utilization before failure occurs– Need to know the worst-case node failure situations

Fault Tolerant Sensor Network Routing for Patient Monitoring

Optimization-based Routing Restoration

• Global Restoration– All flows will be rerouted in order to get an optimal

utilization of the network– All flows have to be notified with the failure

information

• End-to-end Restoration– The flows from the failed path will be diverted to a

number of paths from its source to the destination– Failure information has to be propagated to the

source nodes of the disrupted flows

• Local Restoration– Uses a set of bypaths to route around the failed

node locally– The restoration is locally activated

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Increase Increase

Fault Tolerant Sensor Network Routing for Patient Monitoring

Optimization-based Routing Restoration• Global Restoration

• End-to-end Restoration: (1) Calculate Unaffected Flow Truncations (2) Optimal Flow Augmentation Restoration Formulation

• Local Restoration: (1) Calculate Bypass Flows (2) Optimal Bypass Restoration Formulation

Fault Tolerant Sensor Network Routing for Patient Monitoring

Outline

• Motivation• System and Network Architecture• System Prototype and Implementation

• Network and Routing Model of the Backbone Network

• Optimization-based Routing Restoration of the Backbone Network

• Performance Evaluation

Fault Tolerant Sensor Network Routing for Patient Monitoring

Performance Evaluation

Simulated Backbone Network

Fault Tolerant Sensor Network Routing for Patient Monitoring

Conclusion

• Three-Phase System Architecture• Two-Tier Data Collection Network

• Routing Restoration of the Backbone Network– Based on optimization theory and linear programming

approach• Reserve network resource or not

– Proactive Restoration– Reactive Restoration

• Restoration scale– Global Restoration– End-to-end Restoration– Local Restoration