Radio Channel Measurement and Modeling

The distortion experienced by radio signals as they propagate through the environment is a complex process that corrupts the digital information they carry. The need for better ways to overcome or exploit this distortion is the essential motivation for research in wireless communications.

Our lab's focus is in developing wireless communication techniques that exploit the radio channel's space, time, and frequency dimensions. This requires that we understand the multidimensional characteristics of channel-induced distortion of digital information carried on radio signals. This understanding begins by measuring radio channel distortion through controlled experiments conducted in realistic usage scenarios. Results from such experiments are analyzed to reveal the underlying mechanisms of the distortion. Mathematical descriptions of these mechanisms then allow us to form channel models that capture the essential characteristics of the radio channel. Realistic channel models with elegant mathematical descriptions are essential for designing improved communication technologies because such models are amenable to analysis and computer simulation.

Our Lab's digital radio systems and measurement equipment allow us to probe the multidimensional characteristics of the radio channel. An example configuration of our narrowband radio system is shown in Figure 1.

Figure 1: Narrowband radio system configured for measuring spatial diversity of the radio channel in a cellular scenario.

A measurements result of the radio channel's spatial diversity in a cellular communications system scenario is shown in Figure 2. In this example, the transmitter broadcasts a radio signal from two antennas separated by 5m on a building rooftop. A radio receiver mounted in a car driving in an urban environment 8km away captures the distorted signals from the two transmit antennas (yellow and red) and displays them in time and frequency. The dissimilar channel distortions experienced by the two transmitted signals are a consequence of the spatial diversity induced in the radio channel by separating the transmit antennas.

Figure 2: Screenshot of received signals from a measurement made with the narrowband radio system.

A mathematical model describes the geometry (Figure 3) of the measurement scenario and captures the spatial characteristics of the channel. The model is used to design and analyze techniques for achieving spatial diversity in cellular communications systems.