Millimeter-Wave Feasibility in 5G Backhaul: A Cross-Layer Analysis of Blockage Impact

The wireless backhaul has become a key enabler for 5G technology by presenting a cost-effective and scalable alternative to the typical fiber backhaul. WiGig protocols, such as IEEE 802.11ad and later IEEE 802.11ay, have been considered for backhaul connectivity of 5G mobile networks, thanks to the availability of high bandwidths capable of achieving fiber-like data rates. However, this band suffers from high propagation loss that can only be compensated using highly directional antennas, making mmWave links more susceptible to blockage and errors. Thus, to effectively evaluate the viability of WiGig-based technologies in wireless backhaul scenarios, it is crucial to characterize the impact of obstruction across the different network layers. This article presents an extensive measurement campaign and cross-layer analysis of physical (PHY), medium access control (MAC), and transport layers metrics measured for outdoor WiGig-based hardware submitted to short-term and long-term blockage. This study found that maintaining constant and higher modulation and coding schemes (MCSs) in long-term blocked channels may induce packet errors as high as 100%, round-trip-time (RTTs) that can be in the order of a few seconds, and packet losses as high as 90%. Even dynamically adjusting the MCS, the performance can be highly degraded. This effect was exacerbated in short-term links, as they suffered from more extreme MCS changes upon sudden obstructions. Temporary line of sight (LOS) obstruction was shown to cause maximum delays of half a second and a PER of around 20%; in more extreme cases, it has even led to temporary link failures.