Abstract
New Radio Unlicensed (NR-U) enables 5G networks to operate in unlicensed channels, including the sub-7 GHz bands where transmitters are required to adhere to a set of contention resolution rules known as listen before talk (LBT). NR-U derives from a scheduled radio access technology where transmissions are expected to begin at fixed slot boundaries. The end of an LBT procedure, however, may not coincide with such a boundary. One solution to this problem is to have the NR-U base station wait a gap period to align with the slot boundary. We design, implement, and validate a simulator of NR-U channel access and conduct a performance analysis to assess several important issues: slot boundary synchronization between NR-U base stations, gap placement methods, impact of transmission settings, and performance under dense deployments. We also propose a method for improving the fairness of contending NR-U base stations and conclude our research with guidelines for configuring NR-U networks operating under gap-based channel access.
Highlights
Shared bands are an attractive resource for cellular radio access technologies to increase their capacity beyond licensed bands
Using shared bands was first considered in the form of periodic transmissions in LTE Unlicensed (LTE-U) [1] and with improved coexistence through channel sensing in LTE Licensed-Assisted Access (LAA) [2]
In this paper, we addressed the problem of contending NR Unlicensed (NR-U) base stations in sub-7 GHz bands, where gNBs are required to conform to listen before talk (LBT) and initiate transmissions at slot boundaries
Summary
Shared bands are an attractive resource for cellular radio access technologies to increase their capacity beyond licensed bands. Using shared bands was first considered in the form of periodic transmissions in LTE Unlicensed (LTE-U) [1] and with improved coexistence through channel sensing in LTE Licensed-Assisted Access (LAA) [2]. The scheduled approach of NR, as well as its predecessor, requires that transmissions are synchronized to slot boundaries, which correspond to subframe starting positions [5] This is trivial in licensed channels, where the NR base station (the generation Node B, gNB) supervises all transmissions. In shared channels, this becomes a problem due to other. We analyze the synchronization of gNB slot boundaries, gap placement methods, the impact of partial subframes and NR-U numerology on obtaining channel access, as well as performance in dense deployments.
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