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Merged FSK Proposal TG4g - Update

This document describes the updates to the Merged FSK Proposal for consideration of inclusion into the 802.15.4 PHY draft amendment. It includes new technical details, updates to band plan and channelization, and support for higher data rates.

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Merged FSK Proposal TG4g - Update

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  1. Project: IEEE P802.15 WG for Wireless Personal Area Networks (WPANs) Submission Title: [Merged FSK Proposal TG4g - Update] Date Submitted: [September, 2009] Source: [Kuor-Hsin Chang1, Rodney Hemminger1, Bob Mason1, John Buffington2, Daniel Popa2, Hartman VanWyk2, Fumihide Kojima3, Hiroshi Harada3, Henk de Ruijter4, Ross Sabolcik4, Ping Xiong4, Péter Onódy4, Khanh Tuan Le5, Tim Schmidl5, Anuj Batra5, Srinath Hosur5, Per Roine5, Stephen P. Pope] Company [1Elster Electricity, 2Itron, 3NICT, 4Silicon Laboratories, 5Texas Instruments] Address:[ ] Voice: [ ]E-Mail: [ ]Re: [Response to CFP issued January 22nd 2009, document 15-09-077-00-004g ]Abstract: [This document describes the updates to the Merged FSK Proposal since the July 2009 meeting.]Purpose: [Proposal for consideration of inclusion into 802.15.4 PHY draft amendment ] 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. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  2. Merged Proposal This is a MERGED PROPOSAL from the following authors, representing a combination of equipment suppliers and Silicon vendors. This merged proposal is supported by: <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  3. Overview • Review key philosophies of this merged proposal • Explanation of data rates • Present new technical details since the July 2009 meeting • Updates to band plan and channelization • Simplified frame format • Support for interoperability with non-standardized devices • Details added for FEC correction of payload and PHY header • Support for higher data rates using OFDM • Summary and conclusions <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  4. Key Philosophies of Merged Proposal <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • A PHY that provides a foundation for interoperability is of utmost importance • For each frequency band, one definition • Common starting point for all communications • Based on technical merit without bias to any legacy system • Proposal is not any of the vendor’s legacy systems • Provide a robust platform with future proof data rates • Common starting point for all communications uses most robust communication scheme and data rate (i.e. lowest data rate) • From common starting point, provide mechanisms to shift to higher data rates and different modulation schemes • Core proposal based on technologies that can be implemented today, but provides a roadmap for higher data rate options without compromising interoperability • GFSK low, medium and high data rates can be implemented today • Higher data rates with OFDM can be implemented with support from silicon vendors

  5. Data Rate Selection Criteria <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Each frequency band is optimized per regulatory requirements to provide a high data rate option based on the allowed channel bandwidth • Make each band as future proof as possible • The low data rate is the common starting point for all communications • For example, for 902-928 and 2400 MHz bands, the low data rate is defined as: 40 kbps, GFSK, Modulation index = 1.0, BT = 0.5 • 40 kbps provides a robust common starting point: • 4 dB improvement in link budget as compared to equivalent modulation scheme at 100 kbps • Can be supported by simple, battery powered devices • Legacy devices can be modified to support this data rate • Better performance with respect to multipath fading

  6. Advantages of a low data rate for common starting point <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Multipath fading varies per environment, but 40 kbps is a good fit for the typical urban environment with a delay spread of 3 sec • To minimize ISI, the symbol rate should be less than 10% of the mean delay spread • Fs = 0.1 / 3 sec = 33 kbaud • The urban mean spreading delay is used, but mean spreading delays are typically higher for hilly terrain, common in many rural settings • Mesh networks can typically optimize performance by choosing different communication links, BUT utility networks must also work reliably in rural areas where long communication links with limited alternate paths are required

  7. Importance of a Common Starting Point for All Communications <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • For a mesh network, one device may need to listen for messages initiated by a variety of devices. For example, a given device may need to listen for messages from: • Full function, high data rate devices with good communication links • Simple devices that only support a low data rate • Legacy devices that only support a low data rate • Long communication hop devices that need a more robust communication link • For interoperability, all devices should initiate communications using a common starting point • Emphasis from NIST and others is to provide standards so that products from multiple vendors can interoperate • 802.15.4g by itself will not provide vendor interoperability, but it must provide a good foundation so that future standard efforts (higher layer protocols) can be added to provide the desired interoperability • Without interoperability at the PHY layer, overall interoperability will not be achieved

  8. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Frequency Band Plans

  9. Updated Frequency Band Plans <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> * Data rates and channel width vary per frequency band to optimize per regulatory requirements

  10. 863-870 MHz ISM Band in Europe (1) • Frequency Band: 863-870 MHz • Unit Channel Spacing: 200 kHz • Channel Spacing: N x 200 kHz , N=1,2,3,6 • Number of channels: • 31 x 200 kHz • 14 x 400 kHz • 9 x 600 kHz • 4 x 1200 kHz • Adaptive Frequency Agility (AFA) with Listen-Before-Talk (LBT) <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  11. 863-870 MHz ISM Band in Europe (2) • Modulation format: • BT=0.5 • 2-GFSK modulation index h=1.0 • 4-GFSK modulation index h=1/3 • N-GFSK Data rates: • (R1) 40 kbps • (R2) 80 kbps • (R3) 160 kbps • (R4) 320 kbps <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  12. 470-510 MHz ISM Band in China (1) This proposal is presented as a possible technical solution. The suitability of this frequency band for SUN applications needs to be confirmed and aligned with the appropriate Chinese standardization bodies. • Frequency band: 470-510 MHz • Max output power: 50 mW (+17 dBm) • Channel spacing: 200 kHz • Transmission time: Less than 5 seconds • Frequency Hopping Spread Spectrum across the whole 40 MHz band • Dynamic power control <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  13. 470-510 MHz ISM Band in China (2) • Multiple sets of (offset) channels could be defined to support several co-existing networks in the same area • The main coexistence mechanism would still be the use of different hopping sequences • Although networks share the same frequency range, coexistence is improved by good far-away selectivity, as the networks have a high probability of large frequency spacing at any given moment in time • Multipath fading mitigation and coexistence with other networks are maximized utilizing the entire frequency band <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  14. Band Plan Methodology • To accommodate potential frequency band changes and possible relaxation in radio regulation, we adopt the band adaptation method proposed in doc. 15-09-0453/r1 and doc. 15-09-0503/r0. Assume the start of the frequency band is S, the channel spacing is C, the low side and the high side of the guard band is GL and GH, and the channel index is N; then the carrier frequency as a function of the channel index can be expressed as: where <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  15. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Simplified Frame Format

  16. Simplified Frame Format <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Based on input from silicon vendors, the frame structure and mechanisms to control data rate changes has been simplified • Two types of PHY frames: • Type #1 – Normal frame (no data rate or modulation change) • Type #2 – Format Change frame (indicates change of data rate and/or modulation) • A Format Change frame is a simple frame followed by a Normal frame • All frames have a simple FEC algorithm to protect the PHY header

  17. Normal Frame • Header FEC1: 5-bit wide extended Hamming code (single error correct, double error detect) covering the following 11 bits of information • Legacy: Indicates if the frame is from or to a legacy device. If Legacy = 1, the remainder of the frame is defined by the legacy vendor, but are still protected by Header FEC1 • Format Change: A value of zero indicates a normal frame • PSDU FEC: Indicates if FEC is used for the payload. Options are provided for a simple (i.e. block) or more complex (convolutional) algorithms 0 = no FEC 1 = option #1 (RS xx,yy) 2 = option #2 (convolutional) 3 = reserved <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Normal frame

  18. Normal Frame • Data Whitening: Indicates if data whitening is used on the PSDU field. If used, the seed value is based on the channel number • RFU: Reserved for future use • Network Id: An indication of the utility network • Header FEC2: 5-bit wide extended Hamming code (single error correct, double error detect) covering the following 11 bit length field • Length: The length of the PSDU. The length does not include the PHY header or the CRC fields. Length is the payload size before payload FEC. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Normal frame

  19. Format Change Frame • Header FEC1: 5-bit wide extended Hamming code (single error correct, double error detect) covering the following 11 bits of information • Legacy: Indicates if the frame is from or to a legacy device. If Legacy = 1, the remainder of the frame is defined by the legacy vendor, but are still protected by Header FEC1 • Format Change: A value of one indicates a format change frame • Setting Delay: Indicates if following normal frame (transmitted at the new data rate, modulatino scheme, etc) is transmitted after a default (0) or extended (1) settling delay. Settling delay values are functions of the Modulation/Data Rate/Channel field. • Modulation/Channel/Data Rate: Indicates the modulation, channel, and data rate to be used for the following normal frame. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Format Change frame

  20. Example Frame with Data Rate Change Example Frame without Data Rate Change <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  21. Example of modulation, rate and bandwidth coding for the 902-928 MHz band <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  22. Comparison of Data Rate Options <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Evaluate impact of common starting mode of 40 kbps as compared to other proposed data rates

  23. Comparison of Various Common Starting Point Data Rates <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Compare MAC payload size vs total frame time • Analysis based on the following PHY and MAC overhead:

  24. Frame Time Evaluation <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • The chart compares a medium data rate that starts at 40 kbps and switches to 160 kbps to a constant 100 kbps • Interoperability achieved with a common starting point is not expensive!

  25. Frame Time Evaluation • The chart compares a high data rate that starts at 40 kbps and switches to 320 kbps to a high data rate that starts at 100 kbps and switches to 200 kbps <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  26. 32-bit CRC Slide 26 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Propose use of CRC-32K (Koopman) due to technical advantages • Polynomial x32+x30+x29+x28+x26+x20+x19+x17+x16+x15+x11+x10+x7+x6+x4+x2+x+1 (0xBA0DC66B) • Advantages • Hamming distance >= 6 up to 16Kbit message length • Traditional CRC-32 only offers HD >=6 up to 268 bits, HD = 5 up to 2974 bits and HD = 4 up to 91607 bits. • CRC-32K yields two additional bits of error detection for 1500 octet message lengths [1] • CRC-32K advantage in the 269-16360 bit (34 to 2045 octet) length range aligns with PAR requirement for minimum 1500 octet payloads [1] Koopman, P. "32-Bit Cyclic Redundancy Codes for Internet Applications," Int'l Conf. on Dependable Systems and Networks, 2002.

  27. Best data rate for common starting point Criteria Must be selected for most robust option Best link margin Highest immunity against interference Best option against Multipath and ISI Must cater for all use case scenarios Interference immunity September 2009 Slide 27 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Interference is mitigated by • Time diversity • Frequency diversity • Improving signal to interference ratio • Coding and FEC • Success of mitigation is depending on the nature of interference A very simple model could be: • Uniform random density distribution of time, frequency and power • Increasing data rates • Improves time diversity (shorter packets) • Reduce frequency diversity (larger bandwidth) • Reduce signal to interference ratio (less energy per bit thus will be less probable to over shout interferers)

  28. PHY vs. MAC change management Change management Is required for Data rate changes Modulation type changes Supporting legacy devices Ensuring interoperability Needs to be done At startup and discovery Each time network changes (communication path change, network optimization, takeout point changes, addition/change out of units….) For networks containing devices supporting multi physical layer capabilities Performing at September 2009 Slide 28 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • MAC • Requires a method to multiplex between PHYs (Polling , TDM….) • Will reduce system capacity and increase latency (reduced system bandwidth to 25% with TDM for 2 PHY implementation) • PHY • Offers ultimate flexibility for management • Have very little overhead • Proposal outperforms single PHY implementation from CPP

  29. Support for Legacy Devices • Propose a method for supporting any legacy device • existing and ongoing deployments will not become obsolete • simultaneous (and parallel) operation of any system based on legacy and standard devices, respectively • Propose a method that opens up for multi-vendor interoperability • Minimize the impact of legacy device support on the standard and not encumber the choice of the “best” technology Slide 29 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  30. Support for legacy devices (cont’d) Slide 30 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Upgrade over-the-air the legacy devices affected by 802.15.4g support • only legacy devices that can accommodate radio parameter changes, while keeping (transmission link) communication performance at an acceptable level • Let system implementations decide if standard devices support legacy devices • standard devices can support legacy devices by dual-stacking (proprietary layers and 802.15.4(e)g layers) rather than bridging • BUT • Make standard PHY able to recognize if legacy devices are present in the field by using standard information for legacy device identification (i.e., format frame change) • modulated with the common starting point : 2-GFSK, 40 kbps • respects all PHY parameters as defined in this proposal • Give PHY Layer tools to support a cross-layer efficient interoperability

  31. Support for legacy devices (cont’d) Legacy Device (LD) 802.15.4(e)g standard device (SD) with dual-stack Upper Layers Upper Layers upgraded legacy MAC upgraded (legacy) MAC** 802.15.4 MAC 802.15.4(e)g SD 802.15.4 PHY* (upgraded) PHY** Upper Layers 802.14.5 MAC 802.15.4 PHY (*) From the perspective of 802.15.4g, standardize only the transmission of some PHY fields required for legacy device identification purpose; however, vendors can accommodate multiple PHYs (other than 15.4g) on such devices, based on their legacy system parameters; for flexibility, this should be a vendor prerogative (**) over-the-air upgrade the legacy MAC that will further (re-)configure legacy PHY to deal with radio parameter changes for supporting legacy device identification Slide 31 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  32. Support for legacy devices (cont’d) PPDU format supporting legacy devices, modulation, data rate, PHY parameters,… User case A: “Shim” legacy PHY upgrade Settling delay Legacy frame format Format Change Frame • data sent with respect to some specific (legacy) PHY parameters • legacy PHY (and its parameters) to be defined by each vendor but not standardized • most common modulation: 2-GFSK • lowest acceptable and robust data rate : 40 Kbps • respect all (PHY+MAC) parameters as defined by 802.15.4(e)g, e.g., channel spacing, channel bandwidth User case B: Full legacy PHY upgrade Legacy frame format Format Change Frame Slide 32 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  33. Support legacy devices with 802.15.4g PHY802.15.4g devices receiving frames from legacy device Format Change Frame processing @ “std” PHY parameters 1 Process frame following Format Change Frame as defined by each vendor Legacy device No YES Idle Supportlegacy devices ? 2 YES No 1 “Discard” frame 2 Frameprocessing @ standard PHY parameters Idle Slide 33 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Idle

  34. Advantages Slide 34 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Minimum impact on standard development • minimum on-air cost, minimum complexity and can be ignored where not necessary • Does not require “bridging everywhere” to support legacy devices • where possible just over-the-air upgrade the legacy devices • Opens up for multi-vendor interoperability • open platform by stacking up multi-vendor protocols on top of a common PHY (and MAC) • Provides extensibility • further versions of the 802.15.4g PHY standard (different modulation) can be supported

  35. Payload FEC Design for Merged FSK Proposal Stephen P. Pope spp@rahul.net <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  36. Forward Error Correction Algorithms Slide 36 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • Standard PHY header requires simple FEC • Optional FEC for PHY payload • Will present Reed Solomon option for PHY payload FEC

  37. Payload FEC Design -- Goals • Provide significant normalized coding gain in AWGN • Low gate-count / low-power • Reasonable latency (to meet turnaround time) • Not too esoteric -- well known coding preferred • Systematic code more desirable • Must allow for payload sizes from 1-2048 octets • Burst-error capability not a specific requirement(but may add to robustness) • Variable code rate not a requirement (selectable data rates already available in modem) <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  38. Overview of Code Design Tradeoffs • Some popular codes are too complex for this application: • Near-channel capacity codes (e.. LDPC, Turbo) • Concatenated codes (e.g RS over convolutional) • Convolutional codes are workable • Good performance at low SNR but soft-decisions needed • Performance less interesting at higher SNR or for longer payloads • High gate-count • Algebraic codes • Many low gate-count possibilities: BCH, Golay, Reed-Solomon • Reed-Solomon codes meet all requirements and can be low gate-count <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  39. Properties of Reed-Solomon Codes • Many choices of RS parameters m, n, k m = symbol size n = total symbols per codeword k = information symbols per codeword t = (n-k)/2 = correction ability n < 2 m for non-extended codes n = 2 m extended code n = 2 m + 1 doubly-extended code n > 2 m + 1 Algebraic Geometry Codethese are increasingly esoteric • Tend to perform best when payload size (in bits) is roughly the same order as the maximum codeword size n * mFor our range of packet sizes this suggests m = 6 to m = 8 • Approach: evaluate RS code parameter possibilities and find an economical, effective set of parameters <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  40. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  41. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  42. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  43. Performance Comparison: PER vs. Eb/No for 6- and 8-bit RS Codes Assumptions: BER vs. SNR derived for 2-FSK modulation AWGN Channel Errors-only decoding (no erasures) <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  44. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  45. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  46. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  47. Summary of Performance Comparisons • (6-bit vs. 8-bit RS in AWGN) • Coding Gain – payload length 28 • The 6-bit, RS(52,38) code has a normalized coding gain of 3.4 dB, compared to 2.9 dB for the 8-bit RS(38,28) code. • Coding Gain – payload length 180 • A long, 8-bit RS(240,180) code has 4.7 dB of normalized coding gain, compared to 4.1 dB for the 6 bit code, or 3.5 dB for the short, 8-bit (38,28) code. • Coding Gain – payload length 1500 • The 6-bit, RS(52,38) code has a normalized coding gain of 4.7 dB, whereas various 8-bit RS codes • range from 4.9 to 5.3 dB normalized coding gain. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

  48. <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> Support for Higher Data Rates Using OFDM Tim Schmidl – Texas Instruments

  49. Support for Higher Data Rates Using OFDM Slide 49 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope> • OFDM can be deployed in a network to increase data rates • Can be a secondary deployment when the installed base is FSK • Channelization for OFDM should be compatible with FSK • Should be the same channel bandwidth as FSK or integer multiple of the bandwidth • Higher data rates provided by OFDM • How to transmit OFDM when FSK is frequency hopping

  50. Channelization for OFDM and FSK Slide 50 <Elster>,<Itron>,<NICT>,<Silicon Labs>, <Texas Instruments>,<Stephen P. Pope>

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