Double-directional Radio Channel Measurements – What We Can Derive from Them

Double-directional is the feature of propagation that is utilized in multiple-input multiple-output (MIMO) systems with antenna arrays at both ends of the radio link. This contribution discusses which information can be derived from measured/estimated directions of arrival (DOAs) and directions of departure (DODs), and establishes a new parameter describing the multipath spread from both linkends. We find that the ”multipath component separation” combines delay, Doppler, and (double-) angular dispersion. Evaluation of indoor and outdoor environments show the usefulness and the limits of the multipath component separation concept. We also show statistics of the number of multipath components in these environments. In many instances, we observe more than a single reflection/scattering point that a wave passes before reaching the receiver. Introduction The investigation of smart antennas has lead to better understanding of the radio channel, and to more accurate and realistic spatial channel models [1], [2]. To identify useful multipath components and to suppress undesired co-channel interference has great potential in smart antennas. Multi-element antennas at both link ends establish a spatial MIMO channel. We call this the doubledirectional radio channel, in contrast to the ordinary directional channel (Fig.1). A most exciting reason for investigating the MIMO channel is the huge potential for transmission capacity [3]. In recent simulations of this capacity [4], it turned out that the channel model chosen for such simulations bears great impact on the resulting capacity. The ”multipath richness” of an environment [5] is an important parameter for capacity assessment. φ τ R h(t, , ) φR φT τ h(t, , , ) h(t, ) τ TX-Site RX-Site Propagation Channel Radio Channel