A UBIQUITOUS PUBLISH/SUBSCRIBE
PLATFORM FOR WIRELESS SENSOR
NETWORKS WITH MOBILE MULES
Xiaoyu Tong and Edith C.-H. Ngai
Dept. of Information Technology, Uppsala University, Sweden
Problems of Ubiquitous Sensing
• Stationary sensors are more
likely to be sparsely deployed
in most scenarios.
• But it is cost prohibitive to
connect each of them to the
Internet at every site.
• As a result, their deployments
and usages are heavily limited.
Sparsely Deployed Temperature Sensors in a Forest
Problems of Ubiquitous Sensing
• On the other hand, applications of
mobile sensors become incredibly
popular.
• But they are constrained by sensor
types and abilities.
• Our goal:
– Easier and more flexible
deployments of stationary sensors.
– Enable ubiquitous sensing services
from both stationary sensors and
mobile sensors.
System Model
• Publish/subscribe paradigm is employed to
support asynchronous communications.
• Smart phones are utilized as both mobile
sensors and data mules.
– Built-in sensors: GPS, Camera, etc.
– Short range communication with wireless sensors,
IEEE802.15.4, Bluetooth, or ANT.
– Encounter and communicate with wireless sensors
opportunistically.
• Stationary sensors are sparsely deployed.
Key Challenges
• Deployments of both stationary sensors and
mobile sensors are dynamic.
• Communication overhead will draw power
quickly from both mobile phones and
stationary sensors.
• Mobile users who carry the smart phones have
individual and uncontrollable mobility.
Related Work
• MQTT-S has been proposed to enable topic-based publish/subscribe in
WSNs.
• Huang et al. described how to distribute the system across multiple
computers or mobile devices to distribute load and cope with failures,
message loss and disconnections.
• The above works focus on adoption of publish/subscribe in WSNs and
publish/subscribe system with mobile environments, while the sensing
context, heterogeneity of sensing devices, mobility of nodes and limited
connectivity of wireless sensors remain to be further explored.
Network Model
•
•
•
•
•
Stationary Sensor:
SSensor.
Mobile Sensor:
MSensor.
Platform Server:
Broker.
Mobile Phone:
Mobile Broker.
Sparse Sensor Networks: SSNs.
Publish/Subscribe Platform Design
• Area-based Subscriptions
Publish/Subscribe Platform Design
• Adaptive Location
Updates
– How often should a MB
update its locations?
– Default: periodically with
constant time interval
– Reduce unnecessary
location updates
–
Publish/Subscribe Platform Design
• Full Installation
• Best-effort Subscription
Delivery
– Number of MSensors in a
target area is higher dynamic.
– Installations of subscriptions
to SSensors are opportunistic.
– Keep deployments of sensors
transparent to platform.
Publish/Subscribe Platform Design
• Event Data Collection
– ECF: flag avoiding
unnecessary collection.
– Push-based event collection
for MSensors.
– Pull-based event collection
for Ssensors.
Implementation
• Broker:
– Restful Http Server.
• Mobile Broker:
– Android + Usb cable + IEEE 802.15.4.
– ANT or Bluetooth 4 in the future
• Stationary Sensor:
– Contiki + Rime + Coffee + IEEE802.15.4.
Experimentation
• Scenario and Settings
Experimentation
• Installation of Stationary Sensors along Hiking Trail.
Experimentation
• Sensing Data from Stationary Sensors
Experimentation
• Sensing Data from Mobile Sensors
Experimentation
• Sensing Data from Mobile Sensors
Experimentation
• Data Delivery Delay
Experimentation
• Number of Received Data
Experimentation
• Communication Overhead
Summary
• We proposed and implemented a novel publish/subscribe platform for
ubiquitous data access from both wireless sensors and mobile phones
without relying on any network infrastructure.
• Mobile phones are utilized as mobile mules to relay subscriptions and
published data between the Internet users and the remote sensors.
• We implemented our platform on real hardwares and experimented it in a
hiking trail application.
• In the future, we plan to study the coordination among heterogeneous
mobile and sensing devices to further reduce the energy consumption and
communication overhead.