New Radio Beam-Based Access to Unlicensed Spectrum: Design Challenges and Solutions

Abstract

Licensed-Assisted Access (LAA) enabled LTE operators to access unlicensed spectrum while adhering to Listen-Before-Talk (LBT) requirements. LAA is based on enhancements over 4G LTE technology. Differently, 5G New Radio (NR) technology is being designed from the start to support operation in unlicensed bands through a technology referred to as NRbased access to unlicensed spectrum (NR-U). A large amount of unlicensed spectrum has been allocated in millimeter-wave (mmWave) bands, making it an attractive candidate for NR-U. However, the propagation characteristics in mmWave often require beam-based transmissions. Beam-based transmissions enhance spatial reuse, but also complicate interference management due to the dynamic nature of the directional antennas. Therefore, some major design principles need to be revisited in NR-U to address coexistence. This paper elaborates on the design challenges, opportunities, and solutions for NR-U by taking into account beam-based transmissions and the worldwide regulatory requirements. In particular, different problems and the potential solutions related to channel access procedures, frame structure, initial access procedures, HARQ procedures, and scheduling schemes are discussed.

NR-U and IEEE 802.11 Technologies Coexistence in Unlicensed mmWave Spectrum: Models and Evaluation

“…The objective of 3GPP is to define the necessary enhancements to NR to determine a single global solution for NR-U. The key basis for all the enhancements is to be compliant with the regulatory requirements [17], which include LBT, maximum COT, OCB, power limits (in terms of maximum equivalent isotropically radiated power and maximum power spectral density) and specific functionalities (such as dynamic frequency selection and frequency reuse), in case of 5 GHz and 60 GHz bands. Such requirements impose certain redesign of the standard procedures, channels and signals, as well as challenges at the implementation level.…”

“…In December 2019, 3GPP plenary planned to extend NR operation up to 71 GHz, and so also to unlicensed 60 GHz [19], [20]. The key design aspects related to the coexistence of NR-U at 60 GHz unlicensed bands, such as directional LBT and the corresponding beam management impacts [17], are expected to be considered in Release-17 as part of the newly approved study items. [22], and its recent enhancement through 802.11ay amendment in 2019 [23], [36].…”

“…In the rest of the paper, we replicate the same procedure in the 60 GHz band for coexistence between NR-U and WiGig. We extend the indoor and outdoor sub 7 GHz scenarios to indoor mmWave and outdoor mmWave [17], to evaluate 60 GHz coexistence scenarios.…”

“…The results of WiGig coexistence with WiGig, i.e., WiGig only, provide the baseline to compare with, for all the WiGig coexistence with NR-U scenarios. Based on the 3GPP fairness definition, NR-U is expected to operate in a fair and friendly manner to WiGig, by not impacting WiGig's performance more than another WiGig device would do [17].…”

“…One of the key issues to allow cellular networks to operate in the unlicensed spectrum is to ensure a fair coexistence with other unlicensed systems, such as Wi-Fi in the 5 GHz bands (IEEE 802.11a/n/ac/ax) and directional multi-Gigabit Wi-Fi in the 60 GHz bands (IEEE 802.11ad/ay, also known as Wireless Gigabit (WiGig)) [21]- [23]. For a fair coexistence, any RAT that operates in the unlicensed spectrum has to be designed in accordance with the regional regulatory requirements of the corresponding bands [17]. In the case of the 5 GHz and 60 GHz bands, regulations in Europe and Japan mandate the use of Listen-Before-Talk (LBT) [24], among others.…”