TERRA: Beam Management for Outdoor mm-Wave Networks

This paper addresses two challenges faced by mm-Wave communication systems in outdoor environments. A temporary blockage of the narrow Line of Sight (LoS) beam between the base station and the mobile, e.g., by an interposed hand, face or a pedestrian, can cause an outage. It has been suggested that a dense deployment of base stations is necessary to combat blockage, which is however a capital expensive proposition. This paper presents a low cost solution. It shows that in outdoor environments with hard surfaces, such as pavements, parking lots, etc., there is generally a ground reflected beam that allows sufficient data rate for a control channel to maintain time synchronization during the blockage of the LoS beam. This makes possible a quick reversion to the LoS beam as soon as the temporary blockage ends. The design of a protocol TERRA is described, and is experimentally shown to avoid outage 84.5 % of the time during pedestrian blockages in outdoor environments. The protocol TERRA also addresses a second problem: when the blockage is permanent, or due to mobility, the user has moved away from the earlier serving base station. In such cases a handover to a neighbor base station is needed. There are several challenges of ensuring a soft handover due to the narrow mmWave beams. Since blockages are sudden, the mobile will need to be always ready to switch to a neighbor base station’s beam. This requires that it always have in hand a suitable neighbor base station, as well as continually realign its beam to that neighbor base station while it is mobile. TERRA shows how this is to be done without the neighbor base station’s active cooperation, since connection with it is not yet established. At the same time, TERRA also needs to and does continually realign the mobile’s beam with its presently serving base station to counteract its mobility. TERRA thereby enables the mobile to perform a soft handover to a neighbor base station in the event of a permanent blockage, without requiring any side information, unlike the existing works. Evaluations show that TERRA maintains received signal strength close to the optimal solution while keeping track of the neighbor base station.