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

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [ Multi-band OFDM Physical Layer Proposal ] Date Submitted: [ 14 July, 2003 ] Source: [ Presenter: Anuj Batra ] Company [ Texas Instruments ]

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

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Multi-band OFDM Physical Layer Proposal] Date Submitted: [14 July, 2003] Source: [Presenter:Anuj Batra] Company [Texas Instruments] [see page 2,3 for the complete list of company names and authors] Address [12500 TI Blvd, MS 8649, Dallas, TX 75243] Voice:[214-480-4220], FAX: [972-761-6966], E-Mail:[batra@ti.com] Re: [This submission is in response to the IEEE P802.15 Alternate PHY Call for Proposal (doc. 02/372r8) that was issued on January 17, 2003.] Abstract: [This document describes the Multi-band OFDM proposal for IEEE 802.15 TG3a.] Purpose: [For discussion by IEEE 802.15 TG3a.] 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. A. Batra, Texas Instruments et al.

  2. This contribution is a technical merger between*: Texas Instrument [03/141]: Batra \ and femto Devices [03/101]: Cheah FOCUS Enhancements [03/103]: Boehlke General Atomics [03/103]: Ellis Institute for Infocomm Research [03/107]: Chin Intel [03/109]: Brabenac Mitsubishi Electric [03/111]: Molisch Panasonic [03/121]: Mo Philips [03/125]: Kerry Samsung Advanced Institute of Technology [03/135]: Kwon Samsung Electronics [03/133]: Park SONY [03/137]: Fujita Staccato Communications [03/099]: Aiello Time Domain [03/143]: Kelly Wisair [03/151]: Shor * For a complete list of authors, please see page 3. A. Batra, Texas Instruments et al.

  3. Authors femto Devices: J. Cheah FOCUS Enhancements: K. Boehlke General Atomics:J. Ellis, N. Askar, S. Lin, D. Furuno, D. Peters, G. Rogerson, M. Walker Institute for Infocomm Research: F. Chin, Madhukumar, X. Peng, Sivanand Intel:J. Foerster, V. Somayazulu, S. Roy, E. Green, K. Tinsley, C. Brabenac, D. Leeper, M. Ho Mitsubishi Electric:A. F. Molisch, Y.-P. Nakache, P. Orlik, J. Zhang Panasonic: S. Mo Philips: C. Razzell, D. Birru, B. Redman-White, S. Kerry Samsung Advanced Institute of Technology:D. H. Kwon, Y. S. Kim Samsung Electronics: M. Park SONY: E. Fujita, K. Watanabe, K. Tanaka, M. Suzuki, S. Saito, J. Iwasaki, B. Huang Staccato Communications:R. Aiello, T. Larsson, D. Meacham, L. Mucke Texas Instruments: A. Batra, J. Balakrishnan, A. Dabak, R. Gharpurey, J. Lin, P. Fontaine, J.-M. Ho, S. Lee, M. Frechette, S. March, H. Yamaguchi Time Domain: J. Kelly, M. Pendergrass Wisair:G. Shor, Y. Knobel, D. Yaish, S. Goldenberg, A. Krause, E. Wineberger, R. Zack, B. Blumer, Z. Rubin, D. Meshulam, A. Freund A. Batra, Texas Instruments et al.

  4. Overview of OFDM • OFDM was invented more than 40 years ago. • OFDM has been adopted for several technologies: • Asymmetric Digital Subscriber Line (ADSL) services. • IEEE 802.11a/g. • IEEE 802.16a. • Digital Audio Broadcast (DAB). • Digital Terrestrial Television Broadcast: DVD in Europe, ISDB in Japan • OFDM is also being considered for 4G, IEEE 802.11n, IEEE 802.16, and IEEE 802.20. A. Batra, Texas Instruments et al.

  5. Strengths of OFDM • OFDM is spectrally efficient. • IFFT/FFT operation ensures that sub-carriers do not interfere with each other. • OFDM has an inherent robustness against narrowband interference. • Narrowband interference will affect at most a couple of tones. • Information from the affected tones can be erased and recovered via the forward error correction (FEC) codes. • OFDM has excellent robustness in multi-path environments. • Cyclic prefix preserves orthogonality between sub-carriers. • Cyclic prefix allows the receiver to capture multi-path energy more efficiently. A. Batra, Texas Instruments et al.

  6. Worldwide Compliance • Bands and tones can be dynamically turned on and off in order to comply with changing world-wide regulations. • By using OFDM, small and narrow bandwidths can easily be protected by turning off tones near the frequencies of interest. • For example, consider the radio-astronomy bands allocated in Japan. Only need to zero out a few tones in order to protect these services. A. Batra, Texas Instruments et al.

  7. Details of the Multi-band OFDM System *More details about the Multi-band OFDM system can be found in the latest version of 03/268. A. Batra, Texas Instruments et al.

  8. Overview of Multi-band OFDM • Basic idea: divide spectrum into several 528 MHz bands. • Information is transmitted using OFDM modulation on each band. • OFDM carriers are efficiently generated using an 128-point IFFT/FFT. • Internal precision is reduced by limiting the constellation size to QPSK. • Information bits are interleaved across all bands to exploit frequency diversity and provide robustness against multi-path and interference. • 60.6 ns cyclic prefix provides robustness against multi-path even in the worst channel environments. • 9.5 ns guard interval provides sufficient time for switching between bands. A. Batra, Texas Instruments et al.

  9. Multi-band OFDM: TX Architecture • Block diagram of an example TX architecture: • Architecture is similar to that of a conventional and proven OFDM system. Can leverage existing OFDM solutions for the development of the Multi-band OFDM physical layer. • For a given superframe, the time-frequency code is specified in the beacon by the PNC. The time-frequency code is changed from one superframe to another in order to randomize multi-piconet interference. A. Batra, Texas Instruments et al.

  10. Multi-band OFDM System Parameters • System parameters for mandatory and optional data rates: * Mandatory information data rate, ** Optional information data rate A. Batra, Texas Instruments et al.

  11. Simplified TX Analog Section • For rates up to 200 Mb/s, the input to the IFFT is forced to be conjugate symmetric (for spreading gains  2). • Output of the IFFT is REAL. • The analog section of TX can be simplified when the input is real: • Need to only implement the “I” portion of DAC and mixer. • Only requires half the analog die size of a complete “I/Q” transmitter. • For rates > 200 Mb/s, need to implement full “I/Q” transmitter. A. Batra, Texas Instruments et al.

  12. More Details on the OFDM Parameters • By using a contiguous set of orthogonal carriers, the transmit spectrum will always occupy a bandwidth greater than 500 MHz. • Total of 128 tones: • 100 data tones used to transmit information (constellation: QPSK). • 12 pilot tones used for carrier and phase tracking. • 10 user-defined pilot tones. • Remaining 6 tones including DC are NULL tones. • User-defined pilot tones: • Carry no useful information. • Energy is placed on these tones to ensure that the spectrum has a bandwidth greater than 500 MHz. • Can trade the amount of energy placed on tones for relaxing analog filtering specifications. • Ultimately, the amount of energy placed on these tones is left to the implementer. Provides a level of flexibility for the implementer. A. Batra, Texas Instruments et al.

  13. Band Plan (1) • Group the 528 MHz bands into 4 distinct groups. • Group A: Intended for 1st generation devices (3.1 – 4.9 GHz). • Group B: Reserved for future use (4.9 – 6.0 GHz). • Group C: Intended for devices with improved SOP performance (6.0 – 8.1 GHz). • Group D: Reserved for future use (8.1 – 10.6 GHz). A. Batra, Texas Instruments et al.

  14. Band Plan (2) • The relationship between the center frequency fc and the band number nb is: A. Batra, Texas Instruments et al.

  15. Multi-mode Multi-band OFDM Devices (1) • Having multiple groups of bands enables multiple modes of operations for multi-band OFDM devices. • Different modes for multi-band OFDM devices are: • Future expansion into groups B and D will enable an increase in the number of modes. A. Batra, Texas Instruments et al.

  16. Multi-mode Multi-band OFDM Devices (2) • Frequency of operation for a Mode 1 device: • Frequency of operation for a Mode 2 device: A. Batra, Texas Instruments et al.

  17. Frequency Synthesis (1) • Example: frequency synthesis for Mode 1 (3-band) device: • A single PLL can also be used to generate the center frequencies for a Mode 2 (7-band) device. A. Batra, Texas Instruments et al.

  18. Frequency Synthesis (2) • Circuit-level simulation of frequency synthesis: • Nominal switching time = ~2 ns. • Need to use a slightly larger switching time to allow for process and temperature variations. A. Batra, Texas Instruments et al.

  19. Multi-band OFDM: PLCP Frame Format • PLCP frame format: • Rates supported: 55, 80, 110, 160, 200, 320, 480 Mb/s. • Support for 55, 110, and 200 Mb/s is mandatory. • Mode 1 (3-band): • Preamble + Header length = 11.56 ms. Burst preamble + Header length = 4.69 ms. • Mode 2 (7-band): • Preamble + Header length = 14.06 ms. Burst preamble + Header length = 7.19 ms. • Header is sent at an information data rate of 55 Mb/s. • Maximum frame payload supported is 4095 bytes. A. Batra, Texas Instruments et al.

  20. Multiple Access • Multiple piconet performance is governed by the bandwidth expansion factor. • Bandwidth expansion can be achieved using any of the following techniques or combination of techniques: • Spreading, Time-frequency interleaving, Coding • Ex: Multi-band OFDM obtains its BW expansion by using all 3 techniques. • Time Frequency Codes: A. Batra, Texas Instruments et al.

  21. PLCP Preamble (1) • Multi-band OFDM preamble is composed of 3 sections: • Packet sync sequence: used for packet detection. • Frame sync sequence: used for boundary detection. • Channel estimation sequence: used for channel estimation. • Packet and frame sync sequences are constructed from the same hierarchical sequence. • Correlators for hierarchical sequences can be implemented efficiently: • Low gate count. • Extremely low power consumption. • Sequences are designed to be the most robust portion of the packet. A. Batra, Texas Instruments et al.

  22. PLCP Preamble (2) • Preamble needs to be designed to allow both Mode 1 (3-band) and Mode 2 (7-band) devices to operate in the same piconet. • All devices in the same piconet must be able to detect the preamble and demodulate PHY/MAC header. • Preamble structure for Mode 1 (3-band) device: • End of synchronization pattern [p1,p2,p3] is used to indicate that the interleaving sequence remains constant throughout the packet. A. Batra, Texas Instruments et al.

  23. PLCP Preamble (3) • Preamble structure for Mode 2 (7-band) device: • Preamble/header are transmitted on bands 1–3 using length 6 interleaving sequences, so Mode 1 (3-band) devices can correctly decode the header. • End of synchronization pattern [p4,p5,p6] is used to indicate the transition to length 7 interleaving sequence. A. Batra, Texas Instruments et al.

  24. PLCP Preamble (4) • In the multiple overlapping piconet case, it is desirable to use different hierarchical preambles for each of the piconets. • Basic idea: define 4 hierarchical preambles, with low cross-correlation values. • Preambles are generated by spreading a length 16 sequence by a length 8 sequence. A. Batra, Texas Instruments et al.

  25. Link Budget and Receiver Sensitivity • Assumption: Mode 1 DEV (3-band), AWGN, and 0 dBi gain at TX/RX antennas. A. Batra, Texas Instruments et al.

  26. Link Budget and Receiver Sensitivity • Assumption: Mode 2 DEV (7-band), AWGN, and 0 dBi gain at TX/RX antennas. A. Batra, Texas Instruments et al.

  27. System Performance (Mode 1: 3-band) • The distance at which the Multi-band OFDM system can achieve a PER of 8% for a 90% link success probability is tabulated below: * Includes losses due to front-end filtering, clipping at the DAC, ADC degradation, multi-path degradation, channel estimation, carrier tracking, packet acquisition, etc. A. Batra, Texas Instruments et al.

  28. Simultaneously Operating Piconets (1) • Assumptions: • Mode 1 DEV (3-band) operating at a data rate of 110 Mbps. • Simultaneously operating piconet performance as a function of the multipath channel environments: • Results incorporate SIR estimation at the receiver. A. Batra, Texas Instruments et al.

  29. Simultaneously Operating Piconets (2) • Assumptions: • Mode 2 DEV (7-band) operating at a data rate of 110 Mbps. • Simultaneously operating piconet performance as a function of the multipath channel environments: • Results incorporate SIR estimation at the receiver. A. Batra, Texas Instruments et al.

  30. Signal Robustness/Coexistence • Assumption: Received signal is 6 dB above sensitivity. • Value listed below are the required distance or power level needed to obtain a PER  8% for a 1024 byte packet and a Mode 1 DEV (3-band). • Coexistence with 802.11a/b and Bluetooth is relatively straightforward because these bands are completely avoided. * Results can be further improved by erasing all the information from the affected band. A. Batra, Texas Instruments et al.

  31. PHY-SAP Throughput • Assumptions: • MPDU (MAC frame body + FCS) length is 1024 bytes. • SIFS = 10 ms. • MIFS = 2 ms. • Assumptions: • MPDU (MAC frame body + FCS) length is 4024 bytes. A. Batra, Texas Instruments et al.

  32. Complexity (1) • Unit manufacturing cost (selected information): • Process: CMOS 90 nm technology node in 2005. • CMOS 90 nm production will be available from all major SC foundries by early 2004. • Die size for Mode 1 (3-band) device: • Die size for Mode 2 (7-band) device: * Component area. * Component area. A. Batra, Texas Instruments et al.

  33. Complexity (2) • Active CMOS power consumption for Mode 1 (3-band) and Mode 2 (7-band) devices: A. Batra, Texas Instruments et al.

  34. Complexity (3) • Manufacturability: • Leveraging standard CMOS technology results in a straightforward development effort. • OFDM solutions are mature and have been demonstrated in ADSL and 802.11a/g solutions. • Scalability with process: • Digital section complexity/power scales with improvements in technology nodes (Moore’s Law). • Analog section complexity/power scales slowly with technology node. • Time to market: the earliest complete CMOS PHY solutions would be ready for integration is 2005. • Size: Solutions for PC card, compact flash, memory stick, SD memory in 2005. A. Batra, Texas Instruments et al.

  35. Scalability of Multi-band OFDM • Data rate scaling: from 55 Mb/s to 480 Mb/s. • Frequency scaling: • Mode 1 (3-bands) and optional Mode 2 (7-band) devices. • Guaranteed interoperability between different mode devices. • Complexity scaling: • Mandatory data rates ( 200 Mbps) only required a single DAC and mixer for the TX chain  reduced complexity. • Digital section will scale with future CMOS process improvements. • Implementers could always trade-off complexity for performance. • Power scaling: • A half-rate Pulse Repetition Frequency (PRF) approach can increase the off time to enable power saving modes of operation (see back-up slide). • Implementers could always trade-off power consumption for range and information data rate. A. Batra, Texas Instruments et al.

  36. Comparison of OFDM Technologies • Qualitative comparison between Multi-band OFDM and IEEE 802.11a OFDM: 1. Assumes a 256-point FFT for IEEE 802.11a device. 2. Assumes a 128-point FFT for IEEE 802.11a device. 3. Even though the Multi-band OFDM ADC runs faster than the IEEE 802.11a ADC, the bit precision requirements are significantly smaller, therefore the Multi-OFDM ADC will consume much less power. A. Batra, Texas Instruments et al.

  37. Multi-band OFDMAdvantages (1) • Suitable for CMOS implementation (all components). • Only one transmit and one receive chain at all times, even in the presence of multi-path. • Antenna and pre-select filter are easier to design (can possibly use off-the-shelf components). • Early time to market! • Low cost, low power, and CMOS integrated solution leads to: • Early market adoption! A. Batra, Texas Instruments et al.

  38. Multi-band OFDMAdvantages (2) • Inherent robustness in all the expected multipath environments. • Excellent robustness to ISM, U-NII, and other generic narrowband interference. • Ability to comply with world-wide regulations: • Bands and tones can be dynamically turned on/off to comply with changing regulations. • Coexistence with current and future systems: • Bands and tones can be dynamically turned on/off for enhanced coexistence with the other devices. • Scalability with process: • Digital section complexity/power scales with improvements in technology nodes (Moore’s Law). • Analog section complexity/power scales slowly with technology node. A. Batra, Texas Instruments et al.

  39. Summary • The proposed system is specifically designed to be a low power, low complexity all CMOS solution. • Expected range for 110 Mb/s: 20.5 meters in AWGN, and greater than 11 meters in multipath environments. • Expected power consumption for 110 Mb/s: • Mode 1 DEV: 117 mW (TX), 205 mW (RX), 18 mW (deep sleep) for 130 nm. • Mode 2 DEV: 186 mW (TX), 271 mW (RX), 18 mW (deep sleep) for 130 nm. • Multi-band OFDM is coexistence friendly and complies with world-wide regulations. • Multi-band OFDM offers multi-mode devices (scalability). • Multi-band OFDM offers the best trade-off between the various system parameters. A. Batra, Texas Instruments et al.

  40. Backup slides A. Batra, Texas Instruments et al.

  41. Self-evaluation Matrix (1) A. Batra, Texas Instruments et al.

  42. Self-evaluation Matrix (2) A. Batra, Texas Instruments et al.

  43. Convolutional Encoder • Assume a mother convolutional code of R = 1/3, K = 7. Having a single mother code simplifies the implementation. • Generator polynomial: g0 = [1338], g1 = [1458], g2 = [1758]. • Higher rate codes are achieved by puncturing the mother code. Puncturing patterns are specified in latest revision of 03/268. A. Batra, Texas Instruments et al.

  44. Bit Interleaver: Mode 1 (3-band) • Bit interleaving is performed across the bits within an OFDM symbol and across at most three OFDM symbols. • Exploits frequency diversity. • Randomizes any interference  interference looks nearly white. • Latency is less than 1 ms. • Bit interleaving is performed in three stages: • First, 3NCBPS coded bits are grouped together. • Second, the coded bits are interleaved using a NCBPS3 block symbolinterleaver. • Third, the output bits from 2nd stage are interleaved using a (NCBPS/10)10 block tone interleaver. • The end results is that the 3NCBPS coded bits are interleaved across 3 symbols and within each symbol. • If there are less than 3NCBPS coded bits, which can happen at the end of the header or near the end of a packet, then the second stage of the interleaving process is skipped. A. Batra, Texas Instruments et al.

  45. Bit Interleaver: Mode 1 (3-band) • Ex: Second stage (symbol interleaver) for a data rate of 110 Mbps • Ex: Third stage (tone interleaver) for a data rate of 110 Mbps A. Batra, Texas Instruments et al.

  46. Frequency Synthesis • Example: frequency synthesis for a Mode 2 (7-band) device: A. Batra, Texas Instruments et al.

  47. Multi-band OFDM: RX Architecture • Block diagram of an example RX architecture: • Architecture is similar to that of a conventional and proven OFDM system. Can leverage existing OFDM solutions for the development of the Multi-band OFDM physical layer. A. Batra, Texas Instruments et al.

  48. Simulation Parameters • Assumptions: • System as defined in 03/268. • Clipping at the DAC (PAR = 9 dB). • Finite precision ADC (4 bits @ 110/200 Mbps). • Degradations incorporated: • Front-end filtering. • Multi-path degradation. • Clipping at the DAC. • Finite precision ADC. • Crystal frequency mismatch (20 ppm @ TX, 20 ppm @ RX). • Channel estimation. • Carrier/timing offset recovery. • Carrier tracking. • Packet acquisition. A. Batra, Texas Instruments et al.

  49. FFT/IFFT Complexity • Number of complex multipliers and complex adders needed per clock cycle for a 128 point FFT. • OFDM efficiently captures multi-path energy with lower complexity! • 128-point FFT is realizable in current CMOS technology. • A technical contribution (03/213) by Roger Bertschmann (SiWorks, Inc.) shows that they have a 128-point IFFT/FFT core which can be used in a Multi-band OFDM system. • The synthesized core has a gate count of approximately 70K gates in a 130 nm TSMC process. A. Batra, Texas Instruments et al.

  50. System Performance (1) • PER as a function of distance and data rate in an AWGN and CM2 environment for a Mode 1 DEV: 3-band (90% link success probability). A. Batra, Texas Instruments et al.

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