Millimeter-wave blind spots: Mitigating deafness collisions using frame aggregation

Multi-gigabit-per-second data rates in millimeter-wave networks can result in an excessive amount of channel accesses. Transmitting a single packet at such rates often only requires a few microseconds. In contrast, the medium access control (MAC) overhead is about 20× larger. This is particularly harmful if one or more nodes are deaf due to the use of directional antennas. Deaf nodes cannot overhear ongoing transmissions, and thus cause a high number of collisions, exacerbating MAC overhead even more. In addition, the contention window of deaf nodes becomes very large since their transmissions often fail, resulting in unfairness. To mitigate this issue, we suggest increasing traffic burstiness deliberately to allow for higher frame aggregation at the physical layer. This reduces the number of medium accesses, and thus decreases the probability of collision in case of deafness. We adapt existing theoretical models to our scenario to show the effectiveness of this strategy. Moreover, we validate our scheme in a practical testbed operating in the 60 GHz band. In particular, our evaluation shows that our strategy improves fairness by 20% and throughput by 66% compared to a system that does not exploit deliberate burstiness.