1. 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 FRANCE ]
Voice:[ ], FAX: [ ],
Re: [.]
Abstract: [This document give preliminary information on the proposal that we submit]
Purpose: [Description of what the author wants P to do with the information in the document]
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
J. Schwoerer (France Telecom) – N. Dejean (Elster))

2. Orange - France Telecom / ELSTER Preliminary Technical Proposal

3. Agenda LECIM devices needs : Proposed network capabilities
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, MHz
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 : 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 ( MHz)
x50 channels or less to comply with FCC part (915 MHz)
SHR + PHR
PSDU
Frame
Chan. #1
Chan. #2
Chan. #N
Data block #1
Data block #2
Data block #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 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
Channel Model Parameters
Notes
Frequency (MHz)
915
Valid Range MHz
Collector Antenna Height (m) 30
Valid Range m, including terrain.
Endpoint Antenna Height (m) 1
Valid Range 1-10 m
Distance (km) 2
Valid Range 1-20 km
Downlink Path Loss Calculation
Collector Tx Power (dBm)
Subject to Tx Power Regulations
Collector Tx Antenna Gain (dBi) 6
Hata Path Loss (dB)
-128,53
Must reference the right path loss from the next worksheet
Shadowing Margin (dB)
-16
To buffer against variable shadowing loss
Penetration Loss (dB)
-10
For underground vaults, etc.
Endpoint Rx Antenna Gain (dBi)
If using same antenna for Tx, must be same as in Uplink Table
Endpoint Interference (dB)
Rise over Thermal Interference
Rx Power at Endpoint (dBm)
-115,53
Compare against Rx sensitivity
Uplink Path Loss Calculation
Endpoint Tx Power (dBm) 27
Subject to Tx Power Regulations. Can be different from Collector
Endpoint Tx Antenna Gain (dBi)
Same as Downlink
Collector Rx Antenna Gain (dBi)
If using same antenna for Tx, must be same as in Downlink Table
Collector Interference (dB) 10
Rx Power at Collector (dBm)
-109,53
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
Channel Model Parameters
Notes
Frequency (MHz)
868
Valid Range MHz
Collector Antenna Height (m) 30
Valid Range m, including terrain.
Endpoint Antenna Height (m) 1
Valid Range 1-10 m
Distance (km)
Valid Range 1-20 km
Downlink Path Loss Calculation
Collector Tx Power (dBm) 14
Subject to Tx Power Regulations
Collector Tx Antenna Gain (dBi)
Hata Path Loss (dB)
-117,47
Must reference the right path loss from the next worksheet
Shadowing Margin (dB)
-16
To buffer against variable shadowing loss
Penetration Loss (dB)
For underground vaults, etc.
Endpoint Rx Antenna Gain (dBi) 2
If using same antenna for Tx, must be same as in Uplink Table
Endpoint Interference (dB)
Rise over Thermal Interference
Rx Power at Endpoint (dBm)
-116,47
Compare against Rx sensitivity
Uplink Path Loss Calculation
Endpoint Tx Power (dBm) 12
Subject to Tx Power Regulations. Can be different from Collector
Endpoint Tx Antenna Gain (dBi)
Same as Downlink
Collector Rx Antenna Gain (dBi) 6
If using same antenna for Tx, must be same as in Downlink Table
Collector Interference (dB) 10
Rx Power at Collector (dBm)
-103,47
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)
Channel Model Parameters
Notes
Frequency (MHz)
868
Valid Range MHz
Collector Antenna Height (m) 20
Valid Range m, including terrain.
Endpoint Antenna Height (m) 1
Valid Range 1-10 m
Distance (km)
0,1
Valid Range 1-20 km
Downlink Path Loss Calculation
Collector Tx Power (dBm) 12
Subject to Tx Power Regulations
Collector Tx Antenna Gain (dBi) 2
Wallfish Ikegami Path Loss (dB)
-99,57
Must reference the right path loss from the next worksheet
Shadowing Margin (dB)
-10
To buffer against variable shadowing loss
Penetration Loss (dB)
-20
For underground vaults, etc.
Endpoint Rx Antenna Gain (dBi)
If using same antenna for Tx, must be same as in Uplink Table
Endpoint Interference (dB)
Rise over Thermal Interference
Rx Power at Endpoint (dBm)
-112,57
Compare against Rx sensitivity
Uplink Path Loss Calculation
Endpoint Tx Power (dBm)
Subject to Tx Power Regulations. Can be different from Collector
Endpoint Tx Antenna Gain (dBi)
Hata Path Loss (dB)
Same as Downlink
Collector Rx Antenna Gain (dBi)
If using same antenna for Tx, must be same as in Downlink Table
Collector Interference (dB) 5
Rx Power at Collector (dBm)
-108,57
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
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. 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. Will be happy to discuss exchange with everybody interested
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