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Practical experiences in implementing an LC-optimized PHY proposed for TGbb

This submission discusses practical experiences in implementing the ITU G.9991 PHY for TGbb, which is proposed as an LC-optimized PHY for Intensity Modulated Light Communication. It explores the system architecture, medium access, and the need for adaptive bit and power loading strategies in LC channels.

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Practical experiences in implementing an LC-optimized PHY proposed for TGbb

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  1. Practical experiences in implementing an LC-optimized PHY proposed for TGbb Date: 2019-07-11 Author: Linnartz, Wendt (Signify)

  2. Abstract The submission reports experiences with the practical implementation of the ITU G.9991 PHY 1, which is proposed as an LC-optimized PHY for TGbb based [1]. Linnartz, Wendt (Signify)

  3. ITU G.9991 as a PHY for OWC • PHY: G.vlc (G.9991) was derived from PHY’s for base band communication (PLC, Coax, POF, ADSL), and thereby particularly suited for Intensity Modulated Light Communication • Existing IC’s have now been used successfully by various system integrators, first experiments confirm their suitability. Linnartz, Wendt (Signify)

  4. ITU G.9991 Medium Access • Light does not go through the wall, OWC signals are confined to the room • That allows OWC to offer unique QoS, unaffected by traffic in other rooms, • G.9991 exploits this by a TDMA structure that reserves bandwidth. • In contrast, RF communication in ISM bands, in practice suffers from interference travelling through the wall. • The OWC QoS is well appreciated in demanding environments. • Having a contention-free MAC, appropriate for OWC, is important for QoS uses cases. G.9991 designed for guided communication over wires offers this naturally Linnartz, Wendt (Signify)

  5. System architecture at Signify Linnartz, Wendt (Signify)

  6. Installer view Linnartz, Wendt (Signify)

  7. Dongle (Client Device) Linnartz, Wendt (Signify)

  8. Modulating transmission LEDs Linnartz, Wendt (Signify)

  9. Series Transistor Modulator LED DC drivers are Switched Mode Power Supplies (SMPSs), thus current drivers in essence. We use a special trick to cascade two CURRENT source [2]. Linnartz, Wendt (Signify)

  10. What channel does the PHY have to handle? Our considerations • The LED channel is not a narrowband carrier modulated radio channel, as a radio channel would be. • Ample scientific literature confirms that even the Line-of-Sight channel it is a low pass channel with a gentle roll off • That is, we do not recognize claims in [Proposed way forward on TGbb PHY, and Proposed Front End models] that the LED channel is flat to 200 MHz • Is not verified for a wide enough variety of LED and a drivers, at least we do not see fit with products that we plan to use • It is not in agreement with the majority of scientific literature • Of course, with electronics, this low-pass channel can be inverted electronically, to make the response flat artificially, but this comes at a severe performance penalty • A proper, adaptive bit and power loading strategy is essential to achieve a decent bit/rate over a low-pass LED channel Linnartz, Wendt (Signify)

  11. Why an optimized PHY is needed for LC? • In RF NLOS channels, bit-interleaved coded modulation (BICM) works well. BICM is the concept behind all existing 802.11 OFDM PHYs. • BICM first creates redundancy and then permutes the bits in a code-word randomly over all subcarriers. In a rare fading event, lost bits can be repaired by the FEC using the redundant bits. • LC NLOS channels are 1st order low-pass in general [1], therefore the concept of BICM is likely to fail. Assuming 100 MHz bandwidth and 20 MHz cut-off frequency, 80% of bits are lost. RF Yet we also see a low-pass roll of for LOS LC Source: [4] Slide 7 doc.: IEEE 802.11-19/0388r0 Linnartz, Wendt (Signify)

  12. Impedance Small-Signal Measurements Source: [5] https://doi.org/10.1117/12.2511099 Linnartz, Wendt (Signify)

  13. Conclusions • G.9991 is deployed in the market to offer bit rates above 150 Mbit/s, with just baseband analog front-ends • QoS and coordinated transmissions, re-using the full bandwidth in every with QoS-guaranteed throughput appeared to be a key differentiator • Adaptive bit loading is needed to handle the LED channel, even more so in multipath and multi-emitter “single frequency network”. • Adaptive power loading may not have to be used, but switching off unused subcarrier is recommended. Linnartz, Wendt (Signify)

  14. References [1] LC-optimized PHY proposal for TGbb, doc.: IEEE 802.11-19/1053r0 [2] ITU-T G.9991 - https://www.itu.int/rec/T-REC-G.9991-201903-P [3] Arulandu, K., Linnartz, J. P. M. G., & Deng, X. (2019). Efficient amplitude modulator and ripple canceller for visible light communication. In 2018 IEEE Globecom Workshops, GC Wkshps 2018 - Proceedings [8644210] Piscataway: IEEE. https://doi.org/10.1109/GLOCOMW.2018.8644210 [4] Proposed way forward on TGbb PHY, doc.: IEEE 802.11-19/0388r0 [5] Mardani, S., Alexeev, A., & Linnartz, J. P. (2019). Modeling and compensating dynamic nonlinearities in LED photon-emission rates to enhance OWC. In J. K. Kim, M. R. Krames, & M. Strassburg (Eds.), Light-Emitting Devices, Materials, and Applications [109400U] (Proceedings of SPIE; Vol. 10940). Bellingham: SPIE. https://doi.org/10.1117/12.2511099 [6] Mardanikorani, S., Deng, X., & Linnartz, J. P. M. G. (2019). Efficiency of power loading strategies for visible light communication. In 2018 IEEE Globecom Workshops, GC Wkshps 2018 - Proceedings [8644083] Piscataway: IEEE. https://doi.org/10.1109/GLOCOMW.2018.8644083 Linnartz, Wendt (Signify)

  15. Spare slides Slide 16: Signal routing in product Linnartz, Wendt (Signify)

  16. Ceiling Units (Modem and Optical Frontends) Linnartz, Wendt (Signify)

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