A Deterministic Backoff Approach for Wi-Fi and NR-U Coexistence in Shared Bands

In unlicensed (shared) bands, wireless technologies typically operate without central coordination, which can lead to unwanted transmission interruptions, collisions, and resource wastage. We focus on Wi-Fi and NR-U coexistence in shared bands and solve the aforementioned problem with a deterministic backoff approach. The proposed scheme allows active transmitters to learn the number of nearby interferers in a distributed manner and, as a result, implement an ordered round-robin transmission schedule to minimize collisions. We show analytically that the scheme converges not only in equilibrium (when collisions are negligible), but also in a general case (when collisions are frequent at the beginning or in the middle of the proposed scheme's operation). Furthermore, extensive simulations prove that the proposed scheme guarantees fairness between contenting cells and technologies (both in terms of throughput and delay) as well as optimizes channel efficiency. We also study the impact of imperfect readings of the number of contending nodes (which may be the result of, e.g., asymmetric channel conditions) on the performance of the proposed scheme. In most cases, the deterministic backoff approach outperforms legacy channel access schemes. Additionally, our proposal does not add additional signaling overhead and is backward compatible with standard Wi-Fi and NR-U operation.