1. January 2018
Project: IEEE P 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
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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 P 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 P
Johannes Wechsler, Fraunhofer IIS

2. Time-Split Multiple-Access
January 2018
Time-Split Multiple-Access
Interference robust low data rate radio communication in shared bands
Johannes Wechsler, Fraunhofer IIS

3. Low Power Wide Area Networks Recap
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Low Power Wide Area Networks Recap
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
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4. doc.: IEEE 802.15-<doc#>
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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
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5. Narrow band Challenge: Interference
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Narrow band Challenge: Interference
More IoT systems get deployed
Other systems may be spectrally wider
Other systems have considerable less on-air time
 Interference of other systems becomes highly problematic
Examples
Current LPWAN/ solutions
125 Hz bandwidth, 2s transmit time
: 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
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6. Narrow band Challenge: Interference
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Narrow band Challenge: 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
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7. Time-Split Multiple-Access
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January 2018
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
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8. Time-Split Multiple-Access
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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
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9. Time-Split Multiple-Access
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Time-Split Multiple-Access
The system can tolerate long, narrow band interferers by frequency hopping
Johannes Wechsler, Fraunhofer IIS
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10. Time-Split Multiple-Access
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Time-Split Multiple-Access
TSMA show significant higher interference resilience than non-split transmission [2]
200 Bits transmission
Rate 1/3 Convolutional Code
Random Interleaving
T_interf = 1/5 T_tx
Timeap between sub- packets T_interf
MS = number of subpackets
Johannes Wechsler, Fraunhofer IIS
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11. Time-Split Multiple-Access Data Processing
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Time-Split Multiple-Access Data Processing
Johannes Wechsler, Fraunhofer IIS
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12. Time-Split Multiple-Access Device Implementation
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Time-Split Multiple-Access Device Implementation
TSMA technology can be implemented as a software solution for microcontrollers combined with any existing MAC and PHY
Johannes Wechsler, Fraunhofer IIS
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13. Time-Split Multiple-Access Device Implementation
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Time-Split Multiple-Access Device 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
Uplink Tx
Wait
Downlink Rx
TSMA
Uplink: Tx SP1  wait Tx SP2  wait Tx SP3  …
Downlink: Rx SP1  wait Rx SP2  wait Rx SP3  …
Johannes Wechsler, Fraunhofer IIS
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14. Time-Split Multiple-Access Device Implementation
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Time-Split Multiple-Access Device 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
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15. Time-Split Multiple-Access Device Implementation
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Time-Split Multiple-Access Device 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]
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16. doc.: IEEE 802.15-<doc#>
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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
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17. doc.: IEEE 802.15-<doc#>
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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 , pp. 1–6.
Johannes Wechsler, Fraunhofer IIS
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