It has recently been shown that the oxygen content of a three-way catalyst can be observed directly by a microwave-assisted technique. In this contribution, several control strategies based on this microwave measurement approach are proposed. In the first step, the lambda probe downstream of the catalyst is replaced by the microwave-based state observer. In the second step, the microwave-based state observer replaces both lambda probes, upstream and downstream of the catalyst. A model-based rapid control prototyping approach is used to test the selected control schemes and to compare their performance to the conventional air-fuel ratio control. This comparison is completed using a complex catalyst model and measured data for a realistic driving cycle. It is shown that under idealized conditions the new microwave-based control strategies can outperform the conventional lambda control based on two lambda probes. One important result is that improving the time resolution of the current microwave measurement system is essential to use the full potential of the new approach.