First, consider the following standard sampling case: A sensor measures a vector-valued signal at a fixed sampling rate and transmits it with a fixed sampling rate to a receiver, which then processes the data. In contrast to this standard case, we introduce an event-based sampling protocol that defines under which conditions the sensor sends the current measurement sample to the receiver. At every sampling instant *t*, the sensor evaluates a transmission criterion based on current and old measurements. If the criterion is fulfilled, the current sample is sent. If a sample is sent, it is used directly for data processing. If no sample is sent, the receiver reuses the last received sample instead^{3}, such that the reconstructed data exhibits the same constant sampling rate as the original data. The following two approaches are considered:

**Send-on-delta (SOD):** In analogy to [3], the sample is sent if the Euclidean norm of the difference between the current measurement and the last sent measurement exceeds a certain threshold.

**Send-on-area (SOA):** In analogy to [4], the Euclidean norm of the aforementioned difference is added up. If this sum exceeds a certain threshold, the current sample is sent and the sum is reset to zero.^{4}

**Decreasing threshold:** In their current form, both approaches can result in very long communication gaps. This might be undesirable from an application point of view. Therefore, we propose the following extension that can be combined with both send-on-delta and send-on-area: For each series of consecutively skipped samples, the threshold *c* is linearly decreased in $n\in {\mathbb{N}}_{\ge 0}$ steps, assuring that at most *n* consecutive samples are skipped. For example, with *n* = 3 the actual thresholds are *c*, $\frac{2}{3}$*c*, $\frac{1}{3}$*c* and 0.

For the present application, consider two or more Inertial Measurement Units (IMUs), which wirelessly transmit their acceleration **a**(*t*) ∈ *ℝ*^{3} and angular rate **g**(*t*) ∈ *ℝ*^{3} readings to a receiver, which then uses a realtime algorithm to estimate motion parameters from the reconstructed data. Each IMU applies either send-on-delta or send-on-area with either constant or decreasing threshold to the current measurements **a**(*t*) and **g**(*t*) separately. If one or both criteria are fulfilled, the IMU sends a combined data sample consisting of both **a**(*t*) and **g**(*t*) to the receiver.^{5}

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