  With vast amounts of spectrum available in the millimeter wave (mmWave) band,
small cells at mmWave frequencies densely deployed underlying the conventional
homogeneous macrocell network have gained considerable interest from academia,
industry, and standards bodies. Due to high propagation loss at higher
frequencies, mmWave communications are inherently directional, and concurrent
transmissions (spatial reuse) under low inter-link interference can be enabled
to significantly improve network capacity. On the other hand, mmWave links are
easily blocked by obstacles such as human body and furniture. In this paper, we
develop a Multi-Hop Relaying Transmission scheme, termed as MHRT, to steer
blocked flows around obstacles by establishing multi-hop relay paths. InMHRT, a
relay path selection algorithmis proposed to establish relay paths for blocked
flows for better use of concurrent transmissions. After relay path selection,
we use a multi-hop transmission scheduling algorithm to compute near-optimal
schedules by fully exploiting the spatial reuse. Through extensive simulations
under various traffic patterns and channel conditions, we demonstrate MHRT
achieves superior performance in terms of network throughput and connection
robustness compared with other existing protocols, especially under serious
blockage conditions. The performance of MHRT with different hop limitations is
also simulated and analyzed for a better choice of themaximum hop number in
practice.
