Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. J. Schwoerer (France Telecom) – N. Dejean (Elster)) Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Elster & France Telecom proposal] Date Submitted: [13 July, 2011] Source: [Jean Schwoerer, Nicolas Dejean] Company [France Telecom R&D, Elster] Address [28 chemin du vieux chênes 38240 FRANCE ] Voice:[+33 4 76 76 44 83], FAX: [+33 4 76 76 44 50], E-Mail:[jean.schwoerer@orange-ftgroup.com] Re: [.] Abstract: [This document give preliminary information on the proposal that we submit] Purpose: [Description of what the author wants P802.15 to do with the information in the document] 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.

2. Orange - France Telecom / ELSTERPreliminary Technical Proposal

3. Agenda • LECIM devices needs : • Long ranges • Low power • Proposed network capabilities • Proposed PHY features • RF characteristic • FEC and interleaving • MAC • Coexistence • Conclusion

4. Sub-GHz wireless connectivity platform • Large scale wireless sensor network needs : • Typical network structure (star and tree) at reasonable cost • Mesh / relaying for hard to reach endpoints or to recover wireless connectivity after major events • Efficient power management to save endpoint battery life • “allmost” allways on and limited latency for application involving IP or human interaction • Battery powered LECIM devices will provides : • Long range (high link budget) for cost effective network infrastructure and long operating range • Ultra-low power management to reach multi-year operation • Ability to peacefully coexist with other devices • permanent reachability with human acceptable turn-around time (a few 10’s of sec)

5. Sub-GHz wireless connectivity platform • How to get long range ? there is two way • Go wide band thanks to spread spectrum, and get benefit from diversity and de-spreading gain • Go narrow band and take benefit from • Increased sensivity (less noise) • Limited cost and complexity • Reduced spectrum use (better coexistence) • In addition, Frequency Hopping and efficient FEC and interleaving can bring diversity and reduce system margin, even for narrow band system

6. Sub-GHz wireless connectivity platform • Ultra-low power design to reach multi-year operation : • The best way to save power : just do nothing ! • But we also need to save bidirectionnality and limited latency • Network synchronization : • Allow endpoint sto sleep as soon as no activity is planned for them • Minimize unwanted wake up and coordinate RX windows : each endpoint stay reachable in acceptable time (always-on illusion) • Very short media probing at regular interval • Keep network probing duration as short as possible (direct impact on the duty cycle!) and as low level as possible : Full wake up occurs only if some activity is detected on the channel • Probing period can be in the order of one to a few second (low latency)

7. Fundamentals – RF features • Sub-GHz ISM license free bands 915MHz, 868MHz, 316-433MHz • better propagation properties and less interferences than 2.4 Ghz • Simple to implement modulation : GFSK / FSK • Simple and low power : very power efficient implementation are allready available for endpoint • Concentrator can offer more complex receiver (coherent, soft decision..) • Low data rate and narrow bandwidth : 15 Kbps GFSK modulation • 40 KHz bandwidth and 50 kHz channelization • Limited noise bandwitdh : - 127 dBm thermal noise • RX sensivity up to – 115 dBm (endpoint) • Low spectrum occupancy : better coexistence properties

8. Fundamentals – Reliable Comms • Intra Frame Frequency Hopping : Provide channel diversity • Frame is sliced into several data blocks • Data block length is user configurable • Hopping occurs between each data block over a N-hopping sequence • Short training symbol at the beginning of each data block • up to 63 channels in EU (863-870 MHz) • x50 channels or less to comply with FCC part.15-247 (915 MHz) Frame SHR + PHR PSDU Data block #N Data block #1 Data block #2 Chan. #1 SHR + PHR PSDU Chan. #2 PSDU Chan. #N

9. Fundamentals – Reliable Comms • FEC: several options under study • Block code (255,131) - optimal length yet to be defined • Convolutional codes K=7 (171,133) – allready included in 802.15.4 PHY • Data interleaving + LSFR data scrambling (whitenning) • Spread data and code bit among data blocks • Each blocks carry data bits and uncorrelated code bits • Thanks to FH : code bits and data bits are sent over a different channel • Ultimate goal : be able to recover loss of a full data block (won’t be possible at all time….)

10. Link Budget – 915 MHz Scenario 1 : 2 km range in a Sub-urban area, between pole and indoor meter Indoor endpoint

11. Link Budget – 868 MHz 25 mW Scenario 2 : 1 km range in a Sub-urban area, between pole and typical outdoor gaz meter Outdoor endpoint Help to save endpoint power

12. Link Budget – 868 MHz 25 mW Scenario 3 : 100m range in a Sub-urban area, between a rooftop device and underground water meter (typical relaying scenarios) Wallfish Ikegami model as valid range down to 20m. Underground endpoint

13. Frame Fragmentation • Transmitting long frame at a low date rate can be problematic : • Channel coherence time is estimated to 20 ms (300bits@15kbit/S) • Frame error rate increased when frame length increase • But Fast FH provide a «de-facto» PHY fragmentation : • A frame is sliced in several “data blocks” • Data block duration is shorter than channel coherence time • Only ACK need to be modified to allows signaling of damaged data block

14. MAC Layer compatibility • 15.4e TSCH resources management • Time Slot Channel Hopping defines the automatic repetition of a slotframe based on a shared notion of time • TSCH Allows the devices hopping over the entire channel space in a slotted way thus minimizing the negative effects of multipath fading and interference while avoiding collisions • Slotframe is configurable through the definition of the channels used, the number of slots and the duration of the slots • TSCH parameters will define data block duration

15. MAC Layer compatibility • Packet fragmentation in a slotframe • Fast FH provide a PHY level fragmentation • An adaptation layer between PHY and MAC needs to be defined for hopping on PHY fragments instead of MAC frames • This adaptation layer will also define a group ACK mechanism allowing the retransmission of the corrupted fragments only

16. Example • As an example, with a 15kbps data rate and ½ FEC, 16 data bytes can be transmitted in a ~20ms slot • Data block duration is shortest than channel coherence time • 128 slots are required for transmitting 2047 bytes (longuest possible frame) • Average 100 bytes frames will requires 7 data blocks

17. Coexistence • Several mean to help coexistence • Narrow channel (50 kHz) : limited spectrum usage • Frequency hopping : • Adequate sequences management mitigate interference between independent networks • Short data block minimize interference on a single channel as individual channel occupancy time remain low

18. Conclusions • FSK/GFSK are proven solutions : • To address very low power wireless devices • To allow flexible implementations • Narrow band, FH, efficient FEC and interleaving allow supporting path loss larger than 140 dB. • Frequency Hopping bring channel diversity and frame fragmentation “built-in” : improved robustness • Relaying allows yet improved network coverage and network resilience against major channel changes • but handling yet higher path loss requires other technology • Limited latency and always-on behaviour can be provided at an acceptable cost • Will be happy to discuss exchange with everybody interested

19. Thank You

20. FSK Receiver implementation • Comparison between : • Low cost non coherent FSK receiver using hard decision and viterbi decoder • Coherent FSK receiver using soft decision and viterbi decoder • Performance increase by 4 dB at BER = 1.10e-3