Core Concepts
The authors propose two solutions that allow a mobile network operator to dynamically multiplex unlicensed radio resources between a Wi-Fi network and a scheduled cellular network, such as LTE LAA or 5G NR-U, with different levels of resource sharing granularity.
Abstract
The content discusses the need for wireless connectivity in industrial environments and the increasing use of both Wi-Fi and cellular technologies in unlicensed spectrum bands. It highlights the challenges of direct coexistence between these technologies, which can lead to performance degradation.
The key points are:
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The authors propose two solutions for dynamic sharing of unlicensed radio resources between Wi-Fi and scheduled cellular networks:
- Dynamic Time Multiplexing (DTM): The channel is alternately allocated to Wi-Fi and cellular transmitters at separate intervals of variable durations. The Wi-Fi access point uses the CTS-to-self mechanism to notify Wi-Fi stations to remain silent during the cellular transmission windows.
- Dynamic Frequency Multiplexing (DFM): The channel bandwidth is dynamically divided between Wi-Fi and cellular carriers. The Wi-Fi access point uses the Channel Switch Announcement (CSA) mechanism to notify Wi-Fi stations about the channel bandwidth changes.
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These solutions do not require modifications to current commercial off-the-shelf (COTS) end devices and can be easily extended to 5G NR-U or any other scheduled wireless technology.
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The authors analyze the sharing granularity, overhead, and capacity of the proposed solutions, and compare them to direct coexistence of the technologies. They demonstrate that the dynamic sharing proposals outperform direct coexistence in most scenarios.
Stats
The maximum transmission duration of a Wi-Fi device is constrained by both the maximum PHY transmission duration of 5.484 ms and the maximum A-MPDU length, which depends on the A-MPDU capabilities of the station, the physical transmission data rate, and the length of the encapsulated data.
LTE LAA transmissions are composed of 1 ms subframes, each consisting of two 0.5 ms slots. LAA data bursts may end with a partial subframe of length k ∈ {0, 214.29, 428.57, 500, 642.86, 714.29, 785.71, 857.14, 1000} μs.
Quotes
"The licensed spectrum is a scarce resource that is seldom available for the deployment of private 5G networks in factories or other environments."
"Static allocation of separate frequencies to different technologies would be far from optimal in most situations, because none of the technologies can take advantage of the others' surplus resources."