Chapter 2 Channel Measurements

Radio channel measurements and channel modeling have always been a driving force of the wireless COST actions. These high spirits have been kept up also in COST 2100, where significant advances, particularly in channel measurements, have been made. Channel measurements are indispensable for wireless system design. It is the wireless channel that determines the ultimate performance limits of any communication system. In the beginnings of cellular communications, fading and path loss of the narrowband channel were the key figures of merit. This has changed with wideband multiantenna, multiuser systems. New important features of the radio channel became obvious: the channels’ frequency selectivity, directivity, polarimetric properties, and their relation to channels of the other users. Also for emerging systems, the channel properties need to be identified and modeled: Peer-to-peer systems, which employ distributed nodes indoors or outdoors, show surprising fading characteristics. The propagation channels between vehicles suffer from severe fading under high Doppler shifts. Ultrawideband systems provide an extremely high delay resolution, which needs to be captured. Finally, radio systems using millimeter and submillimeter waves experience strong shadowing by human bodies. All these effects need to be measured and modeled accordingly. Once measurements have been done, and researchers obtained an abundance of data, these measurements need to be analyzed in a sound way. For modeling purposes it is often advantageous to separate the effects of the antenna from the radio channel. This can be achieved by high-resolution parameter estimation, where the channel is characterized as a superposition of multiple wave fronts. Using this data along with maps or photographs of the environment, scattering objects can be automatically located, which provides a deep insight into the processes going on in the radio channel. However, high-resolution parameter estimation methods have several pitfalls, depending on the calibration of the measurement equipment. Only with the knowledge of possible pitfalls, these can be avoided.