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LAA / Wi-Fi Coexistence evaluations with commercial hardware

LAA / Wi-Fi Coexistence evaluations with commercial hardware. Kyu -Han Kim, Liang Li, Eldad Perahia , Dorothy Stanley, Stuart Strickland, and Christina Vlachou. 17 July 2019. Coexistence testbed. LAA eNodeB Commercially available LAA base station controlled using OpenEPC

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LAA / Wi-Fi Coexistence evaluations with commercial hardware

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  1. LAA / Wi-Fi Coexistence evaluationswith commercial hardware Kyu-Han Kim, Liang Li, Eldad Perahia, Dorothy Stanley, Stuart Strickland, and Christina Vlachou 17 July 2019

  2. Coexistence testbed LAA eNodeB • Commercially available LAA base station controlled using OpenEPC • Dual radio: one licensed primary and one unlicensed secondary cell • Compliant with 3GPP Release 13 with primary cell carrying uplink and control plane traffic in a single 20MHz channel of licensed spectrum and secondary cell carrying downlink traffic in a single 20MHz channel of Band 46 (5GHz) • Secondary cell implements listen-before-talk (LBT) per 3GPP specification with Energy Detect (ED) threshold of -72dBm and maximum Transmit Opportunity (TXOP) duration of 8ms Wi-Fi Access Point • 802.11ac access point configured to operate in a single 20MHz channel of unlicensed 5GHz spectrum • Implements Clear Channel Assessment (CCA) per IEEE 802.11 specification with ED threshold of -62dBm, Preamble Detect (PD) threshold of -82dBm, and TXOP duration of < 2.528ms as specified for “best effort” traffic Client Devices • Samsung Galaxy Note8 supporting 802.11ac and LAA in a single 20MHz channel of Band 46 as specified in 3GPP Release 13 • Separate client devices dedicated to LAA and Wi-Fi Traffic Models & Procedure • Full-buffer UDP traffic generated by iPerf for both Wi-Fi and LAA. Youtube video traffic for LAA in “real traffic” scenario • Throughput measured across several scenarios in which the LAA and Wi-Fi system were audible to each other above and below their respective LBT thresholds and maximum TXOP times were varied

  3. Wi-Fi Clear Channel Assessment Interferer Signal Strength Wi-Fi systems base assessment of channel availability using a two-tiered method, detecting energy from any source and detecting preambles specific to Wi-Fi • Both LAA and other Wi-Fi transmissions are detected and deferred to by a Wi-Fi system if energy is detected at levels greater than -62dBm* • Other Wi-Fi transmissions are detected and deferred to if their preambles are detected at levels greater than -82dBm* • LAA transmissions received at levels below -62dBm and Wi-Fi transmissions received at levels below -82dBm are effectively hidden nodes creating unmitigated interference with a Wi-Fi system No hidden terminals -62dBm (ED) LAA hidden terminals -82dBm (PD) LAA and Wi-Fi hidden terminals *20MHz bandwidth

  4. SCENARIO 1: LAA Above Wi-Fi ED Threshold Interferer Signal Strength • LAA eNB and Wi-Fi AP in close proximity to each other and their respective clients • Results collected for LAA TXOP of 8ms and 4ms and Wi-Fi TXOP of ~2.5ms • Wi-Fi throughput reduced by 63% when LAA TXOP = 8ms and by 34% when LAA TXOP = 4ms • Wi-Fi MCS and SFER were not affected by collisions, suggesting that reduction in throughput is due to TXOP differences -62dBm (ED) -82dBm (PD) *20MHz bandwidth LAA TXOP: 8ms LAA TXOP: 4ms

  5. SCENARIO 2: LAA & Wi-Fi BELOW ED ThresholdS Interferer Signal Strength • eNB and all APs set to 13dBm Tx power and separated by 38ft such that all nodes were visible to each other at levels below their ED thresholds and above the Wi-Fi PD threshold of -82dBm • Wi-Fi SFER raised significantly by collisions with LAA and throughput impacted more severely by LAA than by Wi-Fi due to interference from hidden LAA nodes -72dBm (ED) -82dBm (PD) Impact of Wi-Fi on Wi-Fi Impact of LAA on Wi-Fi *20MHz bandwidth

  6. SCENARIO 3: REAL Traffic ABOVE and BELOW Wi-Fi ED Interferer Signal Strength • Question: How does LAA affect Wi-Fi during actual use? • LAA client continuously streaming YouTube video at 1440p throughout a 180s test session • Wi-Fi system loaded with full buffer UDP traffic • Results: Wi-Fi performance suffers more when LAA is below its ED threshold, with frequent disconnects and points at which throughput drops below 1Mbps -62dBm (ED) -82dBm (PD) LAA Above Wi-Fi ED LAA Below Wi-Fi ED *20MHz bandwidth

  7. CONCLUSIONS & RECOMMENDATIONS OBSERVATIONS • Under common deployment scenarios, LAA can significantly degrade Wi-Fi performance • Above Wi-Fi ED, LAA can degrade Wi-Fi more than would another Wi-Fi system due to differences in TXOP duration • Below Wi-Fi ED, interference from hidden LAA nodes significantly degrades Wi-Fi performance • In the presence of streaming LAA connections below Wi-Fi ED, Wi-Fi suffers from continuous performance degradation and frequent disconnections RECOMMENDATIONS • 802.11 systems should adopt TXOP limits aligned with those of 3GPP systems operating in unlicensed spectrum to avoid unfairly disadvantaging Wi-Fi • 802.11 and and 3GPP systems operating in unlicensed spectrum should establish a common preamble to interference from hidden nodes

  8. THANK YOU

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