Design constraint: 3+ External Accelerometers Possible


Basic concept:

We have found in our own research with accelerometers that activity recognition with 3 accelerometers can be quite close to performance with many more (e.g. 7). Intuitively, we can explain this as follows. You optimally want one sensor on the lower body, one sensor on the arms, and one sensor mid-body. With this configuration, very distinctive signals are received for most activities.

When only one sensor is used, such as a single sensor placed at the hip, it often becomes difficult for an algorithm to differentiate certain activities. Cycling, for example, can be tricky to detect. There are papers that report good recognition on a variety of behaviors using a single sensor at the hip, but we believe that these results are strongly dependent on the exact placement/orientation of that single sensor.

Therefore, we want the Wockets to accomodate at least three wireless sensors communicating with the phone at the same time. Even though for many people, not all three may be needed (becuase the sensor in the phone may be used if the phone is kept in the pocket), having the option for three we believe is important, depending on the activities of interest and how someone carries a phone.

Further, for many other applications, we can envision a need for more sensors. A game, for example, might be most fun with a sensor on all four limbs.

Pros:

  • Better activity recognition
  • Creates more opportunity for creative applications
  • May provide more robustness to failure of a single sensor

Cons:

  • Multiple wireless data streams must be either communicated to the phone directly or merged together on some intermediate device and communicated to the phone
  • Creates usability challenge for applications that require wearing more sensors (although not all will)

Inspiration:

Systems that allow multiple wireless accelerometers to communicate with a computer/phone in real-time already...