Poster Abstract: Towards a Framework for a Versatile Wireless Multimedia Sensor Network Platform Damien O’Rourke1 , Junbin Liu1,2 , Tim Wark1 , Wen Hu1 , Darren Moore1 , Leslie Overs1 , Raja Jurdak1 1
2
1.
Autonomous Systems Laboratory, CSIRO ICT Centre, Brisbane, Australia School of Engineering Systems, Queensland University of Technology, Brisbane, Australia
[email protected]
INTRODUCTION
Our second generation Wireless Multimedia Sensor Network (WMSN) platform (figures 1(a) and 1(b)) has increased image resolution, in-built audio sensors, Passive Infra-Red (PIR) sensors, and servo-mechanisms (cf. figure 2). These devices have a wide disparity in their energy consumption and in the information quality they return. As a result, we are developing a framework that establishes a hierarchy of devices (sensors and actuators) within the node and uses frequent sampling of cheaper devices to trigger the activation of more energyhungry devices. Within this framework, we consider the suitability of servos for WMSNs by examining their functional characteristics and by measuring the energy consumption of a number of analog and digital servos.
TWI OV9655 1.3 Mp CMOS Sensor
microSD card (16GB)
Bluetechnix BF537E
PPI
Fleck Atmega 1281 NRF 905
• Blackfin BF537 (600MHz)
SPI
PWM Signal
Servo
• 132 kB L1 memory • 32 MB SDRAM GPIO
• Ethernet Port
PIR
2 x LED Enable
Serial
SPI
TLV320AIC3254 Audio Codec 8kS/s - 192 kS/s miniDSP ADC/DAC
GPIO
• • • •
TWI - Two Wire Interface PPI - Parallel Peripheral Interface SPI - Serial Peripheral Interface PWM - Pulse Width Modulated
Figure 2: Block Diagram.
Figure 1: Our new multimedia node. It is shown in [1] how a multi-tier network can achieve significant improvements over a single-tier approach. However, another possible option is to use a homogeneous network of moderately powerful devices and to operate them in such a way that they act as a multi-tiered
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network. This idea is becoming increasingly feasible as single-chip devices have the ability to operate in multiple operating modes of varying powers and complexity. In a heterogeneous hierarchical network inter-tier interactions can increase the complexity of application design significantly [1]. For example, inter-tier wakeup is not only a challenging problem (as it is required that no wasteful wake-ups are attempted) but can also consume a significant amount of energy at upper tiers. Also, the separation of detection and recognition across multiple tiers introduces large amounts of latency which may be undesirable in a rare species detection application, for example. Moreover, the number of tiers is inherently quite small in this type of design, reducing system flexibility. A homogeneous design where the hierarchy is contained within each node reduces many of these problems. Figures 3(a) and 3(b) illustrate the ideas of moving from an inter-tier to an intra-tier approach [2]. In the latter figure the size of each device reflects its relative power consumption (not to scale).
were calculated as a percentage of the total number of times the node was on. Front Node (F) Side Node (S) Servo Node Two Nodes (F and S combined)
(a) External Tiers
Tp (%) 57.9 39.5 88.2 97.4
Fp (%) 24.1 11.8 21.2 19.6
Table 1: Number of resulting true-positives Tp and false-positives Fp for each setup.
100
% of two node energy
80 60 40 20 0Side Node
(b) Internal Tiers
Figure 3: Combining multiple tiers into one device.
2.
Front Node
Two Nodes
Servo Node
Figure 4: The energy of each setup relative to the two node case (i.e. the combination of the front node and side node).
RESULTS
To assist in our development of the framework just described and to help us understand our new multimedia platform more thoroughly we carried out a number of preliminary outdoor car detection experiments. Each setup consisted of two static nodes placed at right angles to each other along with a servo-mounted node for comparison with the static setup. The purpose was to help compare the effectiveness of implementing a preliminary triggering strategy (using the PIR sensors) on a servo-based system with a static setup of two nodes. The experiment was performed at a cross section of two roads near the front gate of our workplace. It was carried out during the busy periods of the day, such as morning when people were coming into work and evening when they were leaving. The combined results produced a number of true-positives (Tp ) and falsepositives (Fp )1 . Ground-truth information was also obtained during the experiments for analysis. The results are shown in table 1 and figure 4 and show promising benefits when using a servo based system along with an efficient triggering mechanism. The number of truepositives were calculated as a percentage of the actual number of events whereas the number of false-positives 1 True-negatives and false-negatives are also ultimately of interest but are not considered in this preliminary analysis.
3.
FUTURE WORK
Although the system considered here is rather specific we intend to fully generalize this framework to any system with multiple sensors. Future sensor nodes may consist of a combination of temperature, humidity, PIR, audio, and image - to mention but a few. Combining the outputs of these sensors effectively would extend the nodes capabilities to allow, for example, images to assist in weather monitoring (e.g. fog estimation/detection). As more components are integrated, a coherent, energy efficient collaboration is a necessity.
4.
REFERENCES
[1] P. Kulkarni, D. Ganesan, P. Shenoy, and Q. Lu. Senseye: a multi-tier camera sensor network. In MULTIMEDIA ’05: Proceedings of the 13th annual ACM international conference on Multimedia, pages 229–238, 2005. [2] D. O’Rourke, R. Jurdak, J. liu, D. Moore, and T. Wark. On the feasibility of using servo-mechanisms in wireless multimedia sensor network deployments. In SenseApp ’09, held in conjunction with the 34th IEEE Conference on Local Computer Networks (LCN), to appear, 2009.
