Multiple-Input Multiple-Output Channel Models: Theory and Practice

5

CHANNEL SOUNDING

5.1 INTRODUCTION

The ultimate goal of any channel model is to simulate the behavior of real-life channels. At some point, this implies that the channel itself must be measured and the channel model performance compared using real-life data. Channel modeling is thus closely coupled with channel sounding. We measure the channel using a channel sounder and a variety of techniques. The technique depends on the type of channel we wish to measure.

This chapter covers some theoretical and practical aspects of channel sounding. We begin by describing an example of a 4 × 4 MIMO channel sounder, McMaster's wideband MIMO software defined radio (WMSDR). The WMSDR was designed to be used to gather real-life channel estimation data. The data can, in turn, be used to develop communication algorithms or channel models.

Here, we discuss the theory behind various channel sounding techniques, leading from periodic pulse sounding, probably the simplest form of channel sounding, to wideband MIMO channel sounding techniques. Two channel sounding techniques are of particular importance, as they are popular in the literature today; these are the digital matched filtering and sampled spectrum techniques. Digital matched filtering is a technique that can be used to obtain calibrated estimates of the wideband MIMO channel. We discuss correlative channel sounding and receiver calibration. We then move on to discuss sampled spectrum channel sounding and switched-array architectures, which ...