Communications - November 2010

Lesson #3: Don’t forget about the base station! The base station is a critical component of any sensor network architecture: it is responsible for coordinating the network’s operation, monitoring its activity, and collecting the sensor data itself. Yet it often gets short shrift, perhaps because of the false impression the base station code will be easy to write or that it is uninteresting.

The vast majority of our development efforts focused on the sensor node software, which is fairly complex and uses nonstandard programming languages and tools. The base station, in our case a laptop located at the volcano observatory, was mostly an afterthought: some slapped-together Perl scripts and a monolithic Java program acting as a combined network controller, data log-

figure 3a. original data: bad timing, unnormalized signals.

1.2e+07

1e+07

8e+06

6e+06

4e+06

2e+06

0

ger, monitor, and GUI. The base station code underwent a major overhaul in the first two days after arriving in the field, mostly to add features (such as logging) that we didn’t anticipate needing during our lab testing. We paid for the slapdash nature of the base station software. One race condition in the Java code (for which the author takes full credit) led to an 8-hour outage, while everyone was asleep. (We also assumed that the electricity supply at the observatory would be fairly reliable, which turned out not to be true.)

Our redesign for the 2007 Tungurahua deployment involved modularizing the base station code, so that each component can fail independently. One program communicates with the network; another acts as a GUI; another logs the sensor data; and another runs the algorithm for scheduling downloads. Bugs can be fixed and each of these programs can be restarted at any time without disrupting the other programs.

–2e+06

–4e+06

1.1239e+09

1.1239e+09 1.1239e+

figure 3b. Data after cleanup.

204

213

208

206

209

207

200

201

250

203

202

205

212

210

251

214

conclusion

Scientific discovery is increasingly driven by advances in computing technology, and sensor networks are an important tool to enhance data collection in many scientific domains. Still, there is a gap between the stereotype of a sensor network in the literature and what many scientists need to obtain good field data. Working closely with domain scientists yields tremendous opportunities for furthering a computer science research agenda driven by real-world problems.

03:44: 30

03:44: 40

30:44: 50

03:45:00

03:45: 10

03:45: 30

03:45: 40

03:45: 20

time (utc)

03:45: 50

03:46:00

03:46: 10

03:46: 20

03:46: 30

References

1. Kim, s. et al. Health monitoring of civil infrastructures using wireless sensor networks. In Proceedings of IPSN 2007 (cambridge, ma, apr. 2007).

2. Liu, t. et al. Implementing software on resource-constrained mobile sensors: experiences with Impala and Zebranet. In Proceedings of the Second International Conference on Mobile Systems, Applications, and Services (MobiSYS’04), June 2004.

3. sankarasubramaniam, y., akan, o., and akyildiz, I. esrt: event-to-sink reliable transport in wireless sensor networks. In Proceedings of MobiHoc’03, 2003.

4. tolle, g. et al. a macroscope in the redwoods.

In Proceedings of the Third ACM Conference on Embedded Networked Sensor Systems (sensys 2005).

5. Werner-allen, g., Dawson-Haggerty, s., and Welsh, m. Lance: optimizing high-resolution signal collection in wireless sensor networks. In Proceedings of the 6th ACM Conference on Embedded Networked Sensor Systems (sensys’08), nov. 2008.

6. Werner-allen, g. et al. fidelity and yield in a volcano monitoring sensor network. In Proceedings of the 7th USENIX Symposium on Operating Systems Design and Implementation (osDI 2006), nov. 2006.