Compression of IMU data for transmission of AP
A method, controller and system in accordance with various aspects of the present disclosure facilitate reduced energy consumption in a motion sensing device having an inertial measurement unit (IMU), with a strap down integration unit, and an application processing unit (AP). The system and method include rounding velocity increments and orientation increments at the inertial measurement unit, thereby producing a remainder values. The remainder values are added to subsequent velocity increments and orientation increments prior to rounding of those values, and so on. In this way, while motion granularity is slightly decreased, there is no drift of integration errors over time.
1. A method for data compression in a motion sensing device having an inertial measurement unit with a strap down integration unit and an application processing unit, the method comprising:
generating a first velocity increment and a first orientation increment at the inertial measurement unit;
rounding the first velocity increment and first orientation increment at the inertial measurement unit, thereby producing a first remainder velocity value and a first remainder orientation value, wherein the step of rounding each velocity increment and orientation increment reduces its bit count from a first bit count to a second lower bit count;
combining the first remainder velocity value and the first remainder orientation value with a second velocity increment and a second orientation increment respectively at the inertial measurement unit; and
repeating the rounding and combining steps for subsequent velocity and orientation increments at the inertial measurement unit.
2. The method for data compression in accordance with claim 1 , wherein each velocity increment and orientation increment is produced by digitizing and integrating accelerometer and gyroscope signals respectively.
3. The method for data compression in accordance with claim 1 , further comprising delaying the remainder values by one output sample period prior to the step of combining.
4. The method for data compression in accordance with claim 1 , wherein the first bit count is in the range of between 16 and 32 bits and the second lower bit count is in the range of between 4 and 16 bits.
5. The method for data compression in accordance with claim 1 , further comprising applying a signal pre-conditioning transformation to motion increments, the signal pre-conditioning transformation applying a transformation curve such that the values of the motion increments are variably compressed according to the curve.
6. The method for data compression in accordance with claim 1 , further comprising applying a mapping of rounded increments using variable length coding at the inertial measurement unit.
7. The method for data compression in accordance with claim 1 , further comprising applying a predicative algorithm to the rounded values at the inertial measurement unit.
8. The method for data compression in accordance with claim 1 , wherein the step of rounding includes a variable quantization step.
9. The method for data compression in accordance with claim 8 , wherein the variable quantization step rounds smaller increments with a finer resolution than larger increments.