Revisiting LTE LAA: Channel Access, QoS, and Coexistence with WiFi

Abstract

Network operators are looking towards LTE-LAA as a means of extending capacity by offloading traffic to unlicensed bands. However, operation in these bands requires abiding to certain coexistence rules in terms of channel access. The description of these rules in existing literature is not always in line with the latest standards. Therefore, in this paper, we clarify the operation of LAA, focusing on channel access and methods of providing Quality of Service (QoS) support. In terms of coexistence, we evaluate the impact of LAA under its various QoS settings on Wi-Fi performance in an experimental testbed. Finally, we describe the future evolution of LTE-based technologies in unlicensed bands considering the latest developments.

Resolving 5G NR-U Contention for Gap-Based Channel Access in Shared Sub-7 GHz Bands

“…In general, the topic of network coexistence in shared channels (especially the coexistence of Wi-Fi with LAA, the predecessor to NR-U) has gained much attention from the research community. On this topic, we refer the reader to relevant surveys [4], [10]- [14] and tutorials [2], [9], [15]- [23]. In the following, we will look closely at the performance evaluation methods used with respect to their applicability in studying inter-gNB contention under gap-based access.…”

“…If the channel is sensed busy, the gNB freezes the backoff counter and continues to sense the channel. The backoff counter is resumed only after the channel has been again sensed idle for 2 Technically, the general LBT requirements are formally defined in ETSI EN 301 893, while the specific NR-U channel access procedure for shared bands are defined in 3GPP TS 37.213 [56]. 1.…”

“…• defer the transmission by inserting a gap period somewhere during the LBT procedure, e.g., before the backoff, as shown in Figure 3, or • reserve the channel while waiting for the slot boundary using a jamming signal, called the RS, as shown in Figure 4. Use of the latter option was considered normal practice in LAA deployments [2]. This approach, however, has been criticized by the IEEE [58] and the research community [6], [5], [59] as it causes a waste of radio resources.…”

A Comprehensive Survey of Spectrum Sharing Schemes from a Standardization and Implementation Perspective

“…The UE sends an acknowledgment (ACK) or negative acknowledgment (NACK) over the licensed band, and the scheduler assigns a retransmission protocol that is vendor-dependent but typically has a higher scheduling priority. The CW size is also doubled if the NACKs for a given reference subframe surpass a certain threshold; otherwise they are reset [138].…”

Future Is Unlicensed: Private 5G Unlicensed Network for Connecting Industries of Future

“…NR-U is a groundbreaking transformation of LTE in the Unlicensed band (LTE-U) [28]/Licensed Assisted Access (LAA) [29] from 4G LTE to 5G NR and provides an alternative to mitigate the bandwidth scarcity problem by leveraging the unlicensed spectrum in NR operations. Due to its high availability and relatively easy access to the unlicensed spectrum, NR-U is expected to play a crucial role in future cellular networks.…”