The Communication Technology Laboratory of the Swiss Federal Institute of Technology has developed a way to reduce both complexity and power consumption of MIMO systems by using nonlinear detection methods. There method is known as low-cost approaches to receiver design, since they can be implemented with much simpler and more energy-efficient circuitry. According to the report, phase detectors are not prone to system nonlinearities, since amplitude carries no information, while amplitude detection can be simply implemented using an envelope detector, thus avoiding the power consuming down-conversion.
Conventional MIMO systems studied so far by the group strictly employ linear receivers, meaning that an I/Q demodulator yields a complex baseband received signal. Their linearity property is attractive since it enables mathematical tracking. Their work considers the combination of nonlinear receivers and MIMO systems, whereas the nonlinear nature of such systems introduces certain idiosyncrasies, apart from the aforementioned advantages. Mathematical tractability according to them is not straight-forward anymore, while most known results/observations for linear MIMO systems are no more valid.
This technology by the communication group is especially lucrative for systems that require high numbers of very low-cost and low-power devices with Sensor networks as a typical example of their application. The very low cost and long lifetime of sensor nodes is very critical in such systems. Another, example is RFID tagging systems. As technology advances, it is possible to build more complicated tags, while at the same time the demand for higher data rates increases. Furthermore, as carrier frequencies continue to increase up to and beyond 60 GHz, practical implementation of receivers becomes very cumbersome, while nonlinear reception offers a means to circumvent such problems. In general, nonlinear MIMO systems are relevant in a future environment where wireless access is enabled by an ubiquitous network of sensors and nodes. Their work on nonlinear MIMO systems has led to the implementation of the sMILE test bed. This is the first MIMO test bed that employs envelope detectors at the receiver.
Source
MIMO enveLope dEtection (sMILE) Testbed