Applications
Learning outcomes
Understand
- the different parts that make up a typical IoT application
- ethical issues that may arise
- key constraints on what IoT can do
Parts of an IoT Application
The mote or node
- Generally, all motes receive the same software
The border router
- Also known as sink, gateway, or root node
- Generally consists of a mote connected to the USB port of a PC
- Can also be a Raspberry PI and mote
- Converts protocols between mote network (e.g., RPL or 6LowPAN) and ordinary IP network
- May require special software that is different from all other motes
Message Queue
- The Message Queue (e.g., MQTT) provides a connector between the source (motes) and sink (back-end database)
- Publish / subscribe architecture is used
- Security may be an issue and consider configuring passwords early in the design
Web-server (CoAP)
- CoAP is the Constrained Application Protocol (RFC7252)
- It can be thought of as a REST web server approach
- The CoAP server provides a HTTP style service and sits on a PC
- Motes make CoAP requests using GET, PUT, POST, DELETE verbs
- The server responds with responses
- See IoT in 5 days for more info.
Rule-based systems (Node-RED, IFTTT)
- Systems like Node-RED can subscribe to messages from MQTT
- They can then transform and act on those messages
- Node-RED is good for wiring systems together
Ethical issues
Considering privacy
- If you are performing an `experiment’, then standard ethical tests apply
- participants must have informed consent
- they must be able to opt out at any time
- Information can often be derived indirectly:
- Bathroom humidity might indicate when shower is in use
- Bedroom CO2 sensors might identify sleep patterns or sexual activity
- Participants should be anonymised
Consider GDPR issues
- Data protection provides guidance about what data should be stored and processed
- Reprocessing data for a different purpose than the originally stated purpose is not allowed
- Further reading is available
Who owns the data?
- Data ownership is often overlooked
- Your contract may state that the data is owned by the company who employed you
- When considering ownership, keep in mind GDPR reprocessing issues
It shouldn’t be up to the individual to decide
- As a researcher or an employee, neither you nor your superior should decide what is ethical
- There must always be a higher, independent authority
- This might be a professional association, such as the IEEE, or a university ethics board
Constraints
Radio limitations
- Maximal transmission / reception distances are a factor of:
- transmitter power
- receiver power / sensitivity
- radio frequency
- building materials for any structures
- interference
- Overall, expect typical IoT devices to have a range of around 20m indoors and about 100m outdoors
Transmission power
- IoT devices tend to operate with much less power than laptop WiFi and thus will have a smaller range
- Transmission power can be adjusted to help reduce power consumption
Radio frequency
- As with all electromagnetic waves, higher frequencies are blocked by solid objects whereas lower frequencies tend to pass through
- WiFi, BlueTooth, ZigBee and other IEEE 802.15.4 use the 2.4GHz ISM band
Building materials and shape
- Electrically conductive materials (water or metal) tend to absorb RF better than non-conductive materials (wood or air)
- In some cases, structures may help to extend the range slightly (e.g., in a long corridor)
Interference
- Many systems use the same ISM bands and interference is common
- Channel hopping approaches may help to bypass interference - particularly when operating near heavy machinery
Network lifetime
- How long a network lasts for without changing the batteries is an important factor for many applications
- Power consumption is an important consideration and has been discussed in another lecture.
- Energy harvesting may allow indefinite extension of the network life
- Specialist batteries can improve lifetime also
- Software approaches are another avenue for improving lifetime
Battery technology
- Specialist batteries may help extend the life of a system
- Main consideration for the battery is volume / weight and mAh rating
- For energy harvesting consider lead-acid batteries (although these can be dangerous in some situations)
- Rechargeable batteries will tend to have shorter lifetimes per charge cycle but last longer overall
Energy harvesting
- Solar panels are inexpensive and reliable but you must also have a battery that you can charge to continue to operate overnight
- Wind is less reliable
- Supercapacitors can be used to smooth out small fluctuations
Memory
- Most motes have very limited memory and thus will restrict
- code size
- stored data
- It may be possible to store more data in non-volatile flash memory
- e.g., Telos mote has 1Mb flash
Time accuracy
- Motes generally have inaccurate clocks
- Protocols such as TSCH (Time Synchronized Channel Hopping) may help
- Assume that your mote clock is several seconds out