60 GHz range boost: Exploiting frequency selectivity in millimeter-wave networks

The directional nature of communication in millimeter-wave bands suggests that the frequency selectivity of the channel may be limited due to the absence of reflected paths. However, our measurement studies show that reflections often cause significant frequency selectivity in practical scenarios, which we can exploit to increase the otherwise limited range of 60 GHz networks. Specifically, we measure real-world indoor 60 GHz channels with a bandwidth of 2 GHz, and study their behavior with respect to techniques such as bitloading, subcarrier switch-off, and waterfilling. To this end, we consider Orthogonal Frequency-Division Multiplexing (OFDM) as defined in the IEEE 802.11ad standard and show that in contrast to common belief, these techniques are highly beneficial in millimeter-wave networks. We analyze this in practice for both horn antennas as well as an electronically-steerable phased antenna array. Most importantly, our practical results demonstrate that for the specific case of the 60 GHz band, this selectivity allows for a range extension of up to 50%. Hence, our approach enables us to alleviate one of the main limitations of millimeter-wave networks.