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Future-Proofing Wireless Metering with Narrow Band OFDM

This proposal presents a protocol based on narrow band OFDM with slow frequency hopping for future-proofing wireless smart metering systems. It addresses the need for low-cost, efficient, and reliable communication in AMI implementations.

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Future-Proofing Wireless Metering with Narrow Band OFDM

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: It’s all about future proofing Date Submitted: 1 May, 2009 Source: Emmanuel Monnerie Company: Landis+Gyr Address: 30000 Mill Creek Avenue, Alpharetta, GA 30022 USA Voice: +1 678 258 1695, E-Mail: emmanuel . monnerie [at] landisgyr.com Re: IEEE 802.15 Task Group 4g Call for Proposals (CFP) on 22 January, 2009 Abstract: This presentation describes a protocol based on narrow band OFDM, combined with slow frequency hopping Purpose: Proposal for consideration by the TG4g 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. Emmanuel Monnerie, Landis+Gyr

  2. It’s all about future proofing • “Smart meters can run from $100 to $250 apiece by the time you factor in installation costs” Business Week, March 31, 2009 • “Regulators, vendors, utility executives, and ratepayers have a vested interest in future-proofing AMI implementations to avoid stranded costs of the old meter assets, additional costs for new assets, and costly, time-consuming, and difficult system reengineering and integration.” Assessment of Demand Response and Advanced Metering, Federal Energy Regulatory Commission, December 2008 Emmanuel Monnerie, Landis+Gyr

  3. Narrow Band OFDM Proposition • Operation in all license free bands defined in 802.15-4 (780MHz, 868MHz, 915 MHz, 950MHz, 2.4GHz,…) • 64 orthogonal tones (48 effective + 4 pilots + 12 guard tones) separated by 1.5kHz • Total signal bandwidth <100KHz • Slow frequency hopping controlled by MAC layer • Channel map covering the whole band, with 100kHz spacing (up to 260 channels in the US 915MHz ISM band) • Data Modulation: BPSK, QPSK,16-QAM, 64-QAM • Reed Solomon [15,9] option. • Data Rates: (without coding) 67kbps, 136kbps, 272kbps, 408kbps, (with coding) 40kbps, 82kbps, 163 kbps, 245kbps • 42us cyclic prefix (1/16 of FFT cycle time) Emmanuel Monnerie, Landis+Gyr

  4. Channel Characteristics • Field measurements in urban environment have shown that the signal from a meter to a near by pole top radio can easily reach over 1us, even in line of sight and short distance conditions (<150m) TG4g Document # 15-09-0279-00-004g • “Urban areas typically have rms delay spreads on the order of 2-3 us and continuous multipath power out to excess delays of 5 us. In hilly residential areas and in open areas within a city, root mean square (rms) delay spreads are slightly larger, typically having values of 5-7 us.” 900 MHz multipath propagation measurements for US digital cellular radiotelephone (Rappaport, T.S.; Seidel, S.Y.; Singh, R.). Global Telecommunications Conference, 1989, and Exhibition. Communications Technology for the 1990s and Beyond. GLOBECOM’89., IEEE Emmanuel Monnerie, Landis+Gyr

  5. A simple modulation scheme without channel equalization is strongly affected by multipath fading 100kbps FSK in different multipath channels Emmanuel Monnerie, Landis+Gyr

  6. OFDM systems are robust against most delay spreads • 100kbps OFDM in Multipath Channel • Channel equalization is simple with OFDM • The performance loss caused by the cyclic prefix is largely compensated by the removal of the Inter Symbol Interference Emmanuel Monnerie, Landis+Gyr

  7. Multi-path mitigation at different levels • Long Cyclic Prefix before each OFDM symbol The ISI is removed and the signal is coherent during the remaining symbol duration. • Frequency Hopping, providing channel diversity • Combined with mesh networking, providing alternate paths for the worst cases 42us 667us Emmanuel Monnerie, Landis+Gyr

  8. Interference mitigation • Data spread among multiple narrow tones, combined with Reed Solomon: narrow jammers can be tolerated, even within the signal bandwidth. • Frequency Hopping among a large number of channels, improving jamming immunity. Emmanuel Monnerie, Landis+Gyr

  9. Packet Success Rate and System Latency In a mesh network, it is important to maximize the link performance because it impacts directly the system latency and the amount of energy spent. Emmanuel Monnerie, Landis+Gyr

  10. Link Margin versus Data Rate Typically: • low data rate OFDM (<100 kbps) addresses long range, rural applications. • Medium data rate OFDM (around 100kbps) address most of utilities deployments in suburban and urban areas. • Higher data rate (100 kbps to 400kbps) for the network devices with pole top antennas. Practically: • each radio decides automatically which link margin is required, and thus the appropriate data rate Emmanuel Monnerie, Landis+Gyr

  11. More channels for the SUN The total OFDM signal bandwidth remain the same at 100kHz regardless of data rate. Emmanuel Monnerie, Landis+Gyr

  12. Channel Count and Collision Rate • Systems with higher channel count outperform the other systems • Links involving a Network Device are affected more heavily by collisions than meter-to-meter links Emmanuel Monnerie, Landis+Gyr

  13. An OFDM modem… in a meter? • OFDM modems are already widely implemented in PLC-based Smart Meters • EDF is currently rolling out 35 millions residential meters with an OFDM modem inside • An FFT 64 channels at 100k samples per seconds can be implemented in a small silicon space or in a low cost DSP • ADC/DAC operating a few 100’s of kSamples/sec are low cost and low power. Emmanuel Monnerie, Landis+Gyr

  14. How about power consumption? • Low energy radio • The SUN radio is a low-duty cycle device. • Smart Meters spend 99% of the time listening. • The power consumption of a receiver is roughly proportional to its bandwidth. A radio with a 100kHz bandwidth consumes roughly 3 time less energy than a radio with a 300kHz bandwidth. • During transmit mode, Crest Factor Reduction techniques can be applied to reduce the PAPR of the OFDM signal. Signal Clipping is a simple and valid CFR technique for BPSK. • Low energy system • Robust and reliable PHY lowers the need for network devices in the system (repeaters or routers) • Robust and reliable PHY lowers the need to re-transmit or re-route packets Emmanuel Monnerie, Landis+Gyr

  15. OFDM preambles Emmanuel Monnerie, Landis+Gyr

  16. Example of OFDM Preamble detector Rx Samples If 1, then Packet Found! where, C = A = • Low energy design using a small logic and running at a few 100’s of kHz • The bigger DSP functions (FFT, decoder) are remaining inactive during the preamble detection C >? Z-8 A /2 Emmanuel Monnerie, Landis+Gyr

  17. So, again, what are the benefits of a narrow band OFDM protocol? • More robust communication protocol. • Spectrally efficient modulation • Proven and widely used technology • Better fit for most international regulations • Broader range of applications for the Utilities • Scalability and flexibility • Not more costly than comparable solutions • Not more power hungry than comparable solutions Emmanuel Monnerie, Landis+Gyr

  18. Benefits for the Utilities • More reliable communication network • System with low energy footprint • Improved network orthogonality thanks to a high number of channels • Lower system latency • More frequent and more accurate metering data • Increased HAN traffic through the SUN. • More room for security overhead • Future proof and flexible solution: most of the radio design can be implemented in firmware, allowing PHY upgrade “over the air”. Emmanuel Monnerie, Landis+Gyr

  19. Worldwide Compatibility • A 100kHz bandwidth makes the solution compatible for most regions (USA, Europe, Japan, South Korea, New Zealand,…). • When required, the MAC layer can skip channels to meet some specific requirements. • Most regions have a very limited license free space. 100 kHz channels are allowing a higher number of channels for improved network collocation and network coexistence. Emmanuel Monnerie, Landis+Gyr

  20. Conclusion Narrow band OFDM excels in meeting the goals of the TG4g PAR, more particularly: • “Achieve the optimal energy efficient link margin given the environmental conditions encountered in Smart Metering deployments.” • “Data rate of at least 40 kbits per second but not more than 1000 kbits per second” • “The Wireless Smart Metering Utility Network requirement is thus for the largest number of orthogonal traffic carrying channels allowed per local regulations consistent with the simultaneous requirement to provide at least 40kbps” • “the requirements of the Wireless Smart Metering Utility Network further intensify the need for maximum range as many devices are located sub-optimally. An example is electricity meters located in highly obstructed, high multipath locations with inflexible antenna orientation” Emmanuel Monnerie, Landis+Gyr

  21. Q & A Emmanuel Monnerie, Landis+Gyr

  22. Thank you! Emmanuel Monnerie, Landis+Gyr

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