Low-power Remote Monitoring
The micromole system consists of several ring devices that are placed in the sewage. In order to ease mounting and dismounting of the ring devices, the communication between these rings is made wirelessly.
Law Enforcement Agencies would like our system to be autonomous and self-suficient system. In order to achieve this, we need to
- Increase the range of wireless communication in the sewage environment
- Reduce at a minimum the consumed energy for wireless transmissions
- Reduce the amount of data that is transmitted
- Provide protocols for autonomous and also remote control of the system
Range of wireless communication in the sewage
Wireless transmission in the sewage environment can be attenuated rapidly due to water steam, sediments in the water and the surrounding materials (pipe and earth metals). The challenge is to find proper means of radio communications in such situations.
We have tested radio communications in the sewage achieving no more than nine meters of communications using a commercial radio, where in normal conditions it can achieve a range of 200 meters above ground.
Since it is not possible to increase radio power, we focus on designing different customized radio modulations and evaluate radio transmission at different radio frequencies, in order to provide more robust radio channels, increase radio sensitivity and the transmission range.
Consumed energy for wireless transmissions
Traditional mechanisms for reducing energy consumption due to wireless transmission imply scheduling of time-slots transmissions. A radio transmitter and received agree on a precise time-slot where a transmission will take place. Outside of this time-slot, both transmitter and receiver are in sleep modes.
In order to keep synchronization, it is desirable to have a clock which does not drift, and mechanism to detect and compensate for clock drifts across several devices. Detection of clock drifts is usually achieved thanks to the transmission of beacon frames.
In micromole, we analyse mechanisms that will reduce the amount of beacons that are needed in order to synchronize clocks in the network.
The amount of data that could be generated by all the sensors of one ring device after certain period of time is expected to be significantly large. The transmission of all generated data from all rings nearby using only one GSM modem could deplete the stored energy quickly of the ring device with the active GSM modem
The μMole devices will be equipped with a special communication stack that will allow the devices to prioritize generated information to be sent to the final user and also with mechanisms that will allow summarizing data that could be less relevant to the final user (for example, collected sensors data without suspicious chemicals in the sewage). Such mechanisms are context-dependent. The protocol will be flexible enough as to allow the central station to send details about previously transmitted summarized data, if requested. The level in which data will be summarized will be self-adjusted by the system depending on the provided energy for transmission in the network.
We will implement more reliable and meaningful statistics methods for summarizing data, and also provide a more flexible set of data query operations for retrieving spread data among different rings scheme, while reducing the amount of information.
Autonomous and also remote control
Given the low data-rate needed for the application and the need of preserving energy, we design our solution based on 6LoWPAN. Remote management of resources can be achieved using the CoAP protocol, which can work on top of 6LoWPAN/UDP.
By the end of the first period, BTEC and WUT have already a prototype of the communication subsystem (based on CoAP/6LoWPAN) working on the low-power microcontrollers of the ring devices. In addition, parts of this software implementation have already been tested by other partners.