Study of the 6 GHz Unlicensed Spectrum
Citing the growing demand for unlicensed spectrum, the FCC in the US and the ECC in Europe have proposed to open large chunks of spectrum in the 6 GHz range for unlicensed access. Abundance of spectrum in these bands (1.2 GHz in the US and 500 MHz in Europe) creates new opportunities for supporting advanced wireless applications, such as AR/VR, which are characterized by tight reliability and latency requirements. However, opening up of this spectrum for unlicensed access also creates new challenges both in terms of coexistence between the bands' incumbents and unlicensed devices and coexistence among unlicensed devices. For the latter issue, the 6 GHz bands are unique in that these bands are greenfield, i.e., no unlicensed devices currently operate in this spectrum. This fact provides a rare opportunity where Wi-Fi and NR-U devices can design mechanisms (including those for coexistence) from the ground up without backward compatibility constraints.
Next Generation Wi-Fi and 5G NR-U in the 6 GHz Bands: Opportunities & Challenges
Standardization advances for cellular and Wi-Fi coexistence in the unlicensed 5 and 6 GHz bands
- We perform a comprehensive survey on technical issues on 6 GHz unlicensed operations.
- We study the coexistence of Wi-Fi 6E and 5G NR-U in the 6 GHz bands and highlight the novel aspects of this coexistence problem.
- We study the impact of additional bandwidth available in the 6 GHz bands on the latency of packets in Wi-Fi 7 systems.
The ever-increasing demand for unlicensed spectrum has prompted regulators in the US and Europe to consider opening up the 6 GHz bands for unlicensed access. These bands will open up 1.2 GHz of additional spectrum for unlicensed radio access technologies (RATs), such as Wi-Fi and 5G New Radio Unlicensed (NR-U), in the US and if permitted, 500 MHz of additional spectrum in Europe. The abundance of spectrum in these bands creates new opportunities for the design of mechanisms and features that can support the emerging bandwidth-intensive and latency-sensitive applications. However, coexistence of unlicensed devices both with the bands’ incumbent users and across different unlicensed RATs present significant challenges. In this paper, we provide a comprehensive survey of the existing literature on various issues surrounding the operations of unlicensed RATs in the 6 GHz bands. In particular, we discuss how key features in next-generation Wi-Fi are being designed to leverage these additional unlicensed bands. We also shed light on the foreseeable challenges that designers of unlicensed RATs might face in the near future. Our survey encompasses key research papers, contributions submitted to standardization bodies and regulatory agencies, and documents presented at various other venues. Finally, we highlight a few key research problems that are likely to arise due to unlicensed operations in the 6 GHz bands. Tackling these research challenges effectively will be critical in ensuring that the new unlicensed bands are efficiently utilized while guaranteeing the interference-free operation of the bands’ incumbent users.
[Download | IEEE Xplore]
Regulators in the US and Europe have stepped up their efforts to open the 6~GHz bands for unlicensed access. The two unlicensed technologies likely to operate and coexist in these bands are Wi-Fi 6E and 5G New Radio Unlicensed (NR-U). The greenfield 6~GHz bands allow us to take a fresh look at the coexistence between Wi-Fi and 3GPP-based unlicensed technologies. In this paper, using tools from stochastic geometry, we study the impact of Multi User Orthogonal Frequency Division Multiple Access, i.e., MU OFDMA---a feature introduced in 802.11ax---on this coexistence issue. Our results reveal that by disabling the use of the legacy contention mechanism (and allowing only MU OFDMA) for uplink access in Wi-Fi 6E, the performance of both NR-U networks and uplink Wi-Fi 6E can be improved. This is indeed feasible in the 6~GHz bands, where there are no operational Wi-Fi or NR-U users. In so doing, we also highlight the importance of accurate channel sensing at the entity that schedules uplink transmissions in Wi-Fi 6E and NR-U. If the channel is incorrectly detected as idle, factors that improve the uplink performance of one technology contribute negatively to the performance of the other technology.
[Download | IEEE Xplore]
Multi Link Aggregation (MLA) is a feature likely to be introduced in Wi-Fi 7, the next-generation of Wi-Fi, which will be based on the IEEE 802.11be specifications. MLA will allow Wi-Fi devices that support multiple bands (such as the 2.4 GHz, 5 GHz, and 6 GHz bands) to operate on them simultaneously. The resulting throughput and latency gains are likely to bring Wi-Fi one step closer to supporting emerging real-time applications like augmented and virtual reality. While throughput gains resulting from the use of MLA are mostly linear, the latency gains exhibit interesting characteristics and are the subject of this paper. We use our in-house simulator to study the latency enhancements resulting from MLA and seek to answer whether Wi-Fi 7 devices can meet the challenging latency requirements demanded by most real-time applications. In this pursuit, we observe that allowing Wi-Fi devices to contend on even a single additional link without changing any physical layer parameters can lead to an order of magnitude improvement in the worst-case latency in many scenarios. In addition, we highlight that even in dense conditions, MLA can help Wi-Fi devices meet the challenging latency requirements of most real-time applications.
[Download | IEEE Xplore]