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Time-Split Multiple-Access: Interference-Robust Low Data Rate Radio Communication

This paper presents a novel idea to improve interference performance for LPWA networks with little implementation effort on existing systems using Time-Split Multiple-Access (TSMA) scheme.

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Time-Split Multiple-Access: Interference-Robust Low Data Rate Radio Communication

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:Time-Split Multiple-Access for interference robust low data rate radio communication in shared bands. Date Submitted: 17 January, 2018 Source: Johannes Wechsler, Fraunhofer IIS Nordostpark 84, Nuremberg, 90411, Bavaria Voice: +49 911 58061-3227, FAX: +49 911 58061-3299, E-Mail: johannes.wechsler@iis.fraunhofer.de Abstract:Time-Split Multiple-Access is a simple MAC level scheme that allows interference robust transmission for low data rate communication. This robustness makes it an ideal solution for radio communication in unlicensed, shared frequency bands. Purpose: Present a novel idea to improve interference performance for LPWA networks with little implementation effort on existing systems. Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Johannes Wechsler, Fraunhofer IIS

  2. Time-Split Multiple-Access Interference robust low data rate radio communication in shared bands Johannes Wechsler, Fraunhofer IIS

  3. Low Power Wide Area NetworksRecap • Requirements [1] • Wide area coverage requires link budgets of 150 dB and beyond • Suitable for different regions with different regulation requirements for shared, unlicensed frequency bands • Affordable nodes with long battery life and long availability • Results • High link budget and receive strength dynamic of LPWAN result in high interference at the receivers • High link budget attainable by using low data rates • Nodes need to use existing, standard modulation schemes Johannes Wechsler, Fraunhofer IIS

  4. Low Data Rate • Low cost general purpose Sub-GHz transceiver ICs widely support low data rates • Low data rate results in narrow frequency spectrum • Useable in regions that only offer narrow unlicensed channels  Narrow band modulation suited for LPWA Johannes Wechsler, Fraunhofer IIS

  5. Narrow bandChallenge: Interference • More IoT systems get deployed • Othersystems may be spectrally wider • Other systems have considerable less on-air time  Interference of other systems becomes highly problematic • Examples • Current LPWAN/802.15.4 solutions • 125 Hz bandwidth, 2s transmit time • 802.15.4: 12.5 kHz bandwidth and 80ms on-air time, 128 Byte • Other systems in Sub-GHz bands • 802.11ah: 1 MHz Channels, 52µs time slots • Wireless M-Bus: 50 kHz bandwidth, 20ms on-air time, 128 Byte Johannes Wechsler, Fraunhofer IIS

  6. Narrow bandChallenge: Interference • Interference example • Data can be protected by forward error correction • Corrupted pilot sequence results in non-detection and data loss Johannes Wechsler, Fraunhofer IIS

  7. Time-Split Multiple-Access Proposal to overcome interference issues: • Split transmissions into several smaller subpackets • Distribute subpackets over time and frequency • Distribute pilot sequence over all subpackets Johannes Wechsler, Fraunhofer IIS

  8. Time-Split Multiple-Access • Forward error correction allows to tolerate subpacket corruption or loss • Distributed pilot sequence allows detection and synchronization even if multiple subpackets are interfered • The system can tolerate short, wide band interferers by time hopping Johannes Wechsler, Fraunhofer IIS

  9. Time-Split Multiple-Access • The system can tolerate long, narrow band interferers by frequency hopping Johannes Wechsler, Fraunhofer IIS

  10. Time-Split Multiple-Access • TSMA show significant higher interference resilience than non-split transmission [2] • 200 Bits transmission • Rate 1/3 ConvolutionalCode • Random Interleaving • T_interf = 1/5 T_tx • Timeap between sub-packets T_interf • MS = number of subpackets Johannes Wechsler, Fraunhofer IIS

  11. Time-Split Multiple-AccessData Processing Johannes Wechsler, Fraunhofer IIS

  12. Time-Split Multiple-AccessDevice Implementation • TSMA technology can be implemented as a software solution for microcontrollers combined with any existing MAC and PHY Johannes Wechsler, Fraunhofer IIS

  13. Time-Split Multiple-AccessDevice Implementation • Implementation requirement • Timer (Hardware or Software) • TSMA Pattern Table (Simple Lookup Table) • Simple Implementation with all blocks already in place: Transmit, Wait (Sleep), Receive • Current implementation for 802.15.4 • Uplink Tx • Wait • Downlink Rx • TSMA • Uplink: Tx SP1  wait Tx SP2  wait Tx SP3  … • Wait • Downlink: Rx SP1  wait Rx SP2  wait Rx SP3  … Johannes Wechsler, Fraunhofer IIS

  14. Time-Split Multiple-AccessDevice Implementation • Software stack is not hardware or protocol depended • TSMA implemented on various Microcontrollers • ARM Cortex M0, M3, M4 (32bit) • Texas Instruments MSP430 (16bit) • Arduino/ATMega8 (8bit) (ongoing)  One software fits all Johannes Wechsler, Fraunhofer IIS

  15. Time-Split Multiple-AccessDevice Implementation • Time gaps reduce the real-time requirements of the transceiver ICs compared to FHSS • Relaxed timing allows FHSS usage on chips originally not capable to tune frequencies fast enough • Reduce burden on device battery or removes the need for extensive capacitor banks [3] Johannes Wechsler, Fraunhofer IIS

  16. Summary • TSMA is a plug-in extension for existing hardware • TSMA is higher and lower level protocol independent • TSMA reduces the hardware requirements compared to FHSS or non-split low data rate communication • TSMA improves low data rate communication performance in interference channels significantly • TSMA comes as a minimal software update with little to no costs • TSMA is versatile, simple, effective Johannes Wechsler, Fraunhofer IIS

  17. References [1] J. Robert, „Draft IG LPWA Report“ 15-17/528r0, 2017 [2] G. Kilian et al., “Increasing transmission reliability for telemetry systems using telegram splitting,” IEEE Trans. Commun., vol. 63, no. 3, pp. 949–961, Mar. 2015 [3] G. Kilian et al., “Improved coverage for low-power telemetry systems using telegram splitting,” in Proc. Eur. Conf. Smart Objects, Syst. Technol. (SmartSysTech), Jun. 2013, pp. 1–6. Johannes Wechsler, Fraunhofer IIS

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