np complete – An unknown combinatorial optimization problem

I have $N$ available sensors and $M$ devices. Each device needs $a$ sensors. One sensor cannot be used on multiple devices. Each sensor has two properties defined by $H$ and $R$.

Let $sigma_{i_H}$ be the standard deviation of property $H$ for sensors on device $i$. Similarly, $sigma_{i_R}$ is the standard deviation of property $R$ for sensors on device $i$.

Now let $s_{H}=sqrt{sum_{i=1}^{M} sigma_{i_H}^2 }$ of all devices for the $H$ property. And $s_{R}=sqrt{sum_{i=1}^{M} sigma_{i_R}^2 }$ of all devices for the $R$ property.

The goal is to minimize $mu=frac{s_H + s_R}{2}$ .

Looking for guidance on which type of optimization problem this might be and for inspiration for different search algorithms.