Adaptable measurement testbed for wireless systems applied to mimo channel modeling

Abstract

A new experimental way of testing MIMO systems is proposed by means of two reverberation chambers coupled through a waveguide. The modularity of this experimental setup is emphasized and some theoretical and experimental results are presented. The effect of the waveguide on the propagation channel is pointed out. I. INTRODUCTION MIMO systems have gained a lot of attention since they promise an increase of the capacity with a very high spectral efficiency. The knowledge of the propagation mechanisms is crucial in order to define reliable, precise and adaptive channel models. Theoretical researches have been carried out in order to obtain such a channel model (1). However, a model must be supported by measurements campaigns. Those measurements are highly environment dependent and it is difficult to reproduce or to control the environment. In this paper, a new measurement system is proposed which allows to control and to reproduce different specific environments. This measurement testbed is composed of two reverberation chambers coupled through a waveguide. First, the theoretical modeling of the chambers is presented. To model accurately the channel we have to deepen the understanding of the propagation in the waveguide. The basics of waveguide modal analysis are presented. Then, the power weight of each mode is computed. From this result, we are able to understand intu- itively the propagation mechanism in waveguide like systems and the notion of independent paths with different amount of power. To fulfill the understanding of the waveguide, the radiation of each mode in the receiving chamber is deduced. Some numerical results are provided. A channel model is then presented in order to take into account all the parameters of our system. Measurement results are finally provided, pointing out the ability to obtain different propagation conditions. A discussion about the benefits and the drawbacks of this system concludes the paper. II. THE COUPLED REVERBERATION CHAMBERS The proposed testbed is composed of two mode stirred reverberation chambers (MSRC) of about 16m 3 each. MSRC have first been developed for susceptibility testing of electronic devices. Since they allow to produce a dense and isotropic multipath environment, they are now also used for testing antenna characteristics (such as correlation between antennas, mutual coupling or embedded element pattern) and wireless communications systems (2), (3). By means of the movement of the mechanical stirrer, the boundary conditions are changed and a new distribution of the propagating plane waves in the chamber is obtained. The originality in this paper is the use of two chambers to model separate environments for the emitter and the receiver. Those chambers are coupled through a waveguide (cf. Fig. 1) whose transverse dimensions can be changed in order to modify the channel characteristics between the emitter and the receiver. The waveguide allows to obtain independent propagation paths, and to control the degrees of freedom of the channel.