Towards Software-Centric Listen-Before-Talk on Software-Defined Radios
Sebastian Brauer, Anatolij Zubow, Falko Dressler · 2021
Listen-Before-Talk (LBT) is an essential function of many MAC protocols and a key mechanism of sharing spectrum in an uncoordinated manner. However, this simple but effective concept remains a major challenge for Software-Defined Radios (SDRs). If performing the protocol stack on a host PC, due to their structure, SDRs have inherent latencies built in. These latencies increase their reaction time, the so-called turnaround time, significantly, compared to their conventional radio counterparts. Unfortunately, this means that they cannot comply with the LBT channel access procedures used in modern protocols like IEEE 802.11 or LTE Licensed-Assisted Access (LTE-LAA). Given the flexibility and rapid-prototyping capabilities of SDRs, these protocols could clearly benefit from such SDR-based implementations. In this paper, we fill this gap and present a design approach for SDRs supporting LBT. We particularly focus on the rather complicated timing issues. As a proof-of-concept, we showcase our LBT-enabled implementation of the srsLTE software stack for LTE.