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Adaptive Throughput/Link-Budget Mode in 802.15.4 PHY Proposal

This proposal suggests implementing an adaptive throughput/link-budget mode in the 802.15.4 PHY to accommodate extreme reliability requirements for safety and security sensors in IoT applications.

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Adaptive Throughput/Link-Budget Mode in 802.15.4 PHY Proposal

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Proposal for an adaptive throughput/link-budget mode in the 802.15.4 PHY] Date Submitted: [March 15, 2016] Source: [Willem Mulder] Company [Dialog Semiconductor] Address [Het Zuiderkruis 52, 5215MV, Den Bosch, Netherlands] Voice:[+31 6 45232890], Fax: [+31 736408823], E-Mail:[willem.mulder@diasemi.com] Abstract: [Proposal for an adaptive throughput/link-budget mode in the 802.15.4 PHY] Purpose: [Initiate discussion] 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 or organization. The material in this document is subject to change in form and content after further study. The contributor reserves 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. Willem Mulder, Dialog Semiconductor.

  2. Proposal for an adaptive throughput/link-budget mode in the 802.15.4 PHY Willem Mulder, Dialog Semiconductor

  3. IoT in the Smart Home Smart Home connectivity in the ISM band. “Best Effort” connectivity. Proven technology, it works great. For some use cases, “Best Effort” is not enough • Safety sensors (Fire/CarbonMonoxide) • => single bit messages, extreme reliability requirements • Security sensors • => single bit messages, extreme reliability requirements • Door-locks • => single bit messages, extreme reliability requirements Can we ignore these use cases ? We think not.. Why don’t we use adaptive throughput/link-budget allocation like WiFi ,UMTS, LTE ? Willem Mulder, Dialog Semiconductor

  4. 802.15.4 Sensor Network Topology A global IPv6-enabled mesh network example Shannon: Fixed 250 kbps throughput, fixed link-budget What holds us from trading throughput for link-budget ? FFD Coordinator (Router) FFD Coordinator (Border Router) FFD PAN Coordinator (Leader) Router–Router link Network Device (Sleepy End Device) SED link Network Device (Powered End Device) Wifi link Willem Mulder, Dialog Semiconductor

  5. The 802.15.4 PHY • PHY Packet Fields • Preamble (32 bits) – synchronization • Start of Packet Delimiter (8 bits) • PHY Header (8 bits) – PSDU length • PSDU (0 to 1016 bits) – Data field PHY Payload: max 127 bytes 0 – 1016 bits (127 bytes) 32 bits 8 bits 8 bits Preamble SPD PHDR PSDU 128 us 32 us 32 us 0 – 4.064 ms 12 symbols 0 – 254 symbols PHY packet duration: max 4.256 ms 1 symbol = 16us = 0.5 byte (octet) Willem Mulder, Dialog Semiconductor

  6. How do we use the payload ? What holds us from scaling down the throughput ? • Authentication • Security • Routing • Medium Access 768 us (24 bytes), native 802.15.4 MAC packet 802.15.4 Data-poll packet 1 .. 4 ms (64/63 bytes overhead/payload with DTLS, 35/92 bytes overhead/payload without DTLS) 6LoWPAN enabled Data-transfer packet Willem Mulder, Dialog Semiconductor

  7. 802.15.4 Authentication and Security Receive Side Step 1: Message Authentication Message Integrity Hash AES-CCM32 Step 2: Encryption Encrypt Decrypt AES-CCM32 AES-CCM32 Transmit Side 16 Message Integrity Hash Compare AES-CCM32 16 MAC Security Key MAC Security Key Willem Mulder, Dialog Semiconductor

  8. The 802.15.4 PHY Trading throughput for link-budget: we already do it Each new symbol is created by a 4-chip right-shift (first 8 symbols), or by taking the complex conjugate (last 8 symbols), reducing correlator complexity (cost) … Excellent Autocorrelation • Good Hamming Distance • mean = 17 • min = 12 • max = 21 I Tchip= 0.5 us, 32 chips/symbol Tsymbol= 16 us, 4 bits/symbol => 2.5 dB coding gain => 9 dB processing gain => 250 kbps throughput Q Willem Mulder, Dialog Semiconductor

  9. The 802.15.4 PHY What when we don’t need 127 bytes ? How scalable are we ? 32 chips 0 – 8128 chips 256 chips 32 chips Preamble SPD PHDR PSDU 128 us 32 us 32 us 0 – 4.064 ms 12 symbols 0 – 254 symbols • Boundary conditions / Design considerations: • 802.15.4 RF compatible (channel BW, chiprate, O-QPSK-sensitivity) • 802.15.4 Receiver-conditioning compatible (Preamble, AGC, ..) • Flexible packet size/pn-code-length, max pn-code-length is 8128 chips • Processing gain upper bound: 39.1 dB for a 1-bit message • Coding gain: dependent on the chosen pn-code-bundle (Hamming distance) • Security/Authentication: use pn-code-selection and pn-code-rotation Processing gain: energy-per-bit to energy-per-chip ratio in zero-mean AWGN channels Coding gain / Hamming distance: how many chips can go wrong before our detector chooses the wrong code Willem Mulder, Dialog Semiconductor

  10. Corner Case: 1-bit Extreme Reliability • Robustness: • Mesh Diversity: Multiple ER receivers (Routers) • Extended link budget (Processing Gain) • Multiple IPv6 routes - to any IPv6 destination on Earth Extreme Reliability Node 1 ER-Node commissioning using the regular protocol 2 ER-Node subscribes at multiple ER-capable Routers 3 ER-Node receives the security parameters 4 ER-Node sends the alert-action table to the Router 5 pn-code-bundle and pn-code-rotation agreed (security/authentication by code-selection) 6 ER-node switches to ER-mode-operation: send regular heartbeat-messages send alert-messages when needed Router Border Router Leader role Router–Router link Sleepy End Device SED link Powered End Device Wifi link Willem Mulder, Dialog Semiconductor

  11. Trading throughput for Link Budget Some reference numbers pn-codes shall have a regular/repeating stucture (correlator complexity) Willem Mulder, Dialog Semiconductor

  12. The proposal: To develop an optional adaptive throughput/link-budget allocation mode for the 802.15.4 PHY The 5 IEEE 802 LMSC PAR review criteria : • Broad Market Potential • Broad sets of applicability. • Multiple vendors and numerous users. • Compatibility • Compliance with IEEE Std 802 • Compliance with IEEE Std 802.1D • Compliance with IEEE Std 802.1Q • Distinct Identity • Substantially different from other IEEE 802 standards. • One unique solution per problem (not two solutions to a problem) • Technical Feasibility • Demonstrated system feasibility • Proven technology, reasonable testing • Confidence in reliability • Economic Feasibility • Known cost factors, reliable data • Reasonable cost for performance • Consideration of installation costs Willem Mulder, Dialog Semiconductor

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