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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: [ TI Physical Layer Proposal ] Date Submitted: [ 03 March, 2003 ] Source: [ Anuj Batra, Jaiganesh Balakrishnan, Anand Dabak, et al. ] 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: [TI Physical Layer Proposal] Date Submitted: [03 March, 2003] Source: [Anuj Batra, Jaiganesh Balakrishnan, Anand Dabak, et al.] Company [Texas Instruments] 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 TI physical layer 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. Anuj Batra et al., Texas Instruments

  2. TI Physical Layer Proposal:Time-Frequency Interleaved OFDM Anuj Batra, Jaiganesh Balakrishnan, Anand Dabak Ranjit Gharpurey, Paul Fontaine, Jerry LinJin-Meng Ho, Simon Lee, Michel FrechetteSteven March, Hirohisa Yamaguchi Texas Instruments12500 TI Blvd, MS 8649Dallas, TXMarch 3, 2003 Anuj Batra et al., Texas Instruments

  3. Outline • Examine the trade-offs in the design of a UWB system: • Choice of operating bandwidth • Spreading gain vs. Pulse repetition frequency (PRF) • Overview of Time-Frequency Interleaved OFDM (TFI-OFDM) • Performance results for the TFI-OFDM system • Selected responses to the selection criteria • Advantages of the TFI-OFDM system • Summary Anuj Batra et al., Texas Instruments

  4. Trade-offs in Designing a UWB system: - Choice of Operating Bandwidth- Spreading Gain vs. PRF Anuj Batra et al., Texas Instruments

  5. What Operating BW to Use? • Goals to keep in mind when selecting the operating BW: • Early time to market: want to enable UWB technology ASAP. • CMOS friendly solutions: want solutions that can be integrated. • Low cost: enable adoption of technology in portable CE devices. • U-NII interference robustness: 802.11a is the incumbent device. • World-wide compliance: one solution for the world. • Antenna/filter design: want to be able to use off-the-shelf components. • We now examine the various trade-offs in choosing the operating BW. We want to select the operating BW in such a way as to achieve all of these goals. Anuj Batra et al., Texas Instruments

  6. Small Gains by Increasing BW (1) • Assume that the TX signal occupies the BW from fL to fU. • Assume that fL is fixed at 3.1 GHz. • Vary upper frequency fU between 4.8 GHz and 10.6 GHz. • Assume that the transmit spectrum is flat over entire BW. • TX power = -41.25 dBm + 10log10(fU – fL). • 802.15.3a has specified a free-space propagation model: • fg is the Geometric mean of lower/upper frequencies (10-dB points) • d is the UWB transmitter-receiver separation distance (assume d = 10 m) • c is the speed of light • Look at Received Power = TX Power - Path Loss, as a function of upper frequency. Anuj Batra et al., Texas Instruments

  7. Small Gains From Increasing BW (2) • Increasing the upper frequency to 7.0 GHz (10.5 GHz) gives at most a 2.0 dB (3.0 dB) advantage in total received power. • On the other hand, increasing the upper frequency, results in an increased noise figure: • For fu = 7.0 GHz, by at least 1.0 dB. • For fu = 10.5 GHz, by at least 2.0 dB. • Result: using frequencies larger than 4.8 GHz increases the overall link margin by at most 1.0 dB with the current RF technology, but at the cost of higher complexity and higher power consumption. • Conclusion: only incremental gains in the link budget can be realized by using frequencies above 4.8 GHz. Anuj Batra et al., Texas Instruments

  8. U-NII band: 802.11a Start with this band Use this band in the future as technology improves 3.1 GHz 4.8 GHz 5.9 GHz 10.6 GHz Optimal Operating Bandwidth • Start with the frequency band from 3.1 to 4.8 GHz: • Simplifies the front-end design: LNA and mixers (CMOS friendly). • Can use higher precision, lower sampling rate ADCs. • Rake implementation, needed to collect multi-path, is easier. • U-NII rejection is simplified.  Quicker time to market! • As the RF technology improves, start using the higher band as well. Anuj Batra et al., Texas Instruments

  9. TFI-OFDM Sub-band Full-band Coding Coding Coding UWB system parameters Low PRF Spreading (High PRF) Low PRF Spreading Lower rate ADC, low transmit power, single receive chain, relaxed timing Higher transmit power, multiple receiver chains Higher A/D speed, accurate timing Spreading vs. PRF • A full-band system obtains its processing gain by spreading (high PRF) the signal across the entire UWB bandwidth. • A sub-band system obtains its processing gain by using a lower pulse repetition frequency (PRF) in each of the sub-bands. Anuj Batra et al., Texas Instruments

  10. Proposed System: TFI-OFDM Anuj Batra et al., Texas Instruments

  11. Time-Frequency Interleaved OFDM • Basic idea is to use OFDM over the entire BW: • Start with frequencies from 3168 MHz to 5280 MHz. • Total of 512 tones, where each tone has a bandwidth of 4.125 MHz. • Use different subsets of frequency tones from one OFDM symbol to the next. • Equivalent to interleaving OFDM symbols across time and across frequency. Anuj Batra et al., Texas Instruments

  12. Simplified TFI-OFDM • The implementation of TFI-OFDM can be simplified by introducing a small guard interval (9.5 ns) between the OFDM symbols. • The simplified TFI-OFDM system can now be implemented using a single TX/RX chain, 128-point IFFT/FFT, and low rate DACs/ADCs. Anuj Batra et al., Texas Instruments

  13. Alternative Views of TFI-OFDM • TFI-OFDM can be looked upon as a full-band OFDM system using a 512-point IFFT/FFT. • TFI-OFDM can also be interpreted as a sub-band OFDM system using a 128-point IFFT/FFT on each of the sub-channels. • Because TFI-OFDM can be viewed as both a full-band and a sub-band approach, it inherits strengths from both types of systems. • We choose to view TFI-OFDM in terms of the second approach, because it leads to a much lower complexity solution and can be realized in today’s CMOS technology. Anuj Batra et al., Texas Instruments

  14. Details of the TFI-OFDM System *More details about the TFI-OFDM system can be found in the latest version of 03/142. Anuj Batra et al., Texas Instruments

  15. TFI-OFDM: Example 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 TFI-OFDM physical layer. • For a given superframe, the interleaving pattern is specified in the beacon by the PNC. The interleaving pattern is rotated across multiple superframes to mitigate multi-piconet interference. Anuj Batra et al., Texas Instruments

  16. TFI-OFDM System Parameters • System parameters for rates specifically mentioned in selection criteria document: Anuj Batra et al., Texas Instruments

  17. 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. Anuj Batra et al., Texas Instruments

  18. OFDM Parameters • Transmit information using orthogonal carriers: • Carriers are efficiently generated using a 128-point IFFT. • Use 100 tones for data (QPSK modulation). • Use 12 tones for standard pilots. • Use 10 tones for user-defined pilots (used to meet 500 MHz BW requirement). • Remaining 6 orthogonal tones are NULL (zero). • Sub-carrier frequency spacing = 4.125 MHz. • Cyclic prefix length = 32 samples (60.6 ns). • Guard interval length = 5 samples (9.5) – time used for switching. • Total OFDM symbol length = 165 samples (312.5 ns). Anuj Batra et al., Texas Instruments

  19. Convolutional Encoder and Bit Interleaver • 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. • Bit interleaving is performed across bits within an OFDM symbol and across at most three OFDM symbols. • Exploits frequency diversity and randomizes any interference. Anuj Batra et al., Texas Instruments

  20. Channelization • The relationship between fc and channel number nch is • Initially, only the first 3 channels will be defined. • More channels can be added as RF technology improves. Anuj Batra et al., Texas Instruments

  21. TFI-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. • Preamble length = 9.38 ms. Burst preamble length = 4.69 ms. • For the sake of robustness, the PLCP header, MAC header, HCS, and tail bits are always sent at the information data rate of 55 Mb/s. • PLCP header + MAC header + HCS + tail bits = 2.19 ms. • Maximum frame payload supported is 4095 bytes. Anuj Batra et al., Texas Instruments

  22. Link Budget and Receiver Sensitivity • Assumption: AWGN and 0 dBi gain at TX and RX antennas. Anuj Batra et al., Texas Instruments

  23. System Performance (1) • PER as a function of distance and information data rate in an AWGN and CM2 environment*. * Results obtained using old channel model. Anuj Batra et al., Texas Instruments

  24. System Performance (2) • PER as a function of distance and information data rate in an CM3 and CM4 environment*. * Results obtained using old channel model. Anuj Batra et al., Texas Instruments

  25. System Performance (3) • The distance at which the TFI-OFDM system can achieve a PER of 8 % for a 90% link success probability is tabulated below**: * Includes losses due to front-end filtering, ADC degradation, multi-path degradation, channel estimation, carrier tracking, packet acquisition, etc. ** Results obtained using old channel model. Anuj Batra et al., Texas Instruments

  26. Simultaneously Operating Piconets • Assumptions: • Received signal is 6 dB above sensitivity  dref = 9.55 meters • Single co-channel interferer separation distance as a function of the reference and interfering multipath channel environments. Anuj Batra et al., Texas Instruments

  27. 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. • Coexistence with 802.11a/b and Bluetooth is relatively straightforward because these bands are completely avoided. Anuj Batra et al., Texas Instruments

  28. 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. Anuj Batra et al., Texas Instruments

  29. Complexity • Unit manufacturing cost (selected information): • Process: CMOS 90 nm technology node in 2005. • Analog section: die size of 2.7 mm2. Digital section: 295K gates, die size of 1.5 mm2. • Power consumption: • Manufacturability: Leveraging standard CMOS technology results in a straightforward development effort. OFDM solutions are mature and have been demonstrated in 802.11a and 802.11g solutions. • Time to market: the earliest a complete CMOS PHY solution would be ready for integration is 2005. • Size: Solutions for PC card, compact flash, memory stick, SD memory in 2005. Anuj Batra et al., Texas Instruments

  30. MAC Enhancements • Add a time-frequency interleaving information element (TFI IE) to the beacon: • TFI IE contains parameters for synchronizing DEVs using TFI-OFDM PHY. • IE payload contains Interleaving Sequence (IS) and Rotation Sequence (RS) parameters. • IS field specifies the current pattern for interleaving over the channels. • RS field specifies the current rotation pattern for the interleaving sequences. • PNC updates the IS parameter in the beacon for each superframe according to the RS parameter. • DEVs that miss the beacon can determine the IS based on the definition of the RS in the last beacon received. • PNC may change the RS parameter by applying the piconet parameter change procedure specified in the IEEE 802.15.3 draft standard. • Reuse “New Channel Index” as “New Channel Index/RS Number”. Anuj Batra et al., Texas Instruments

  31. MAC Controlled Rules for Interleaving • Piconet #1: • Ex: RS_2 = {IS_2, IS_3, IS_1, IS_3, IS_2, IS_1, Repeat} • Ex: IS_1 = {Chan_2, Chan_1, Chan_3, Chan_1, Chan_2, Chan_3, Repeat} • Piconet #2: • Ex: RS_2 = {IS_1, IS_3, IS_2, IS_1, IS_2, IS_3, Repeat} Anuj Batra et al., Texas Instruments

  32. TFI-OFDMAdvantages (1) • Suitable for CMOS implementation. • Only one transmit and one receive chain. • 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! Anuj Batra et al., Texas Instruments

  33. TFI-OFDMAdvantages (2) • Excellent robustness to ISM and U-NII interference. • Excellent robustness to narrowband interference. • Ability to comply with world-wide regulations: • Channels and tones can be dynamically turned on/off to comply with changing regulations. • Coexistence with current and future systems: • Channels and tones can be dynamically turned on/off for enhanced coexistence with the other devices. • Scalability: • More channels can be added as the RF technology improves. • Digital section complexity/power scales with improvements in technology nodes (Moore’s Law). Anuj Batra et al., Texas Instruments

  34. Summary • The proposed system is specifically designed to be a low power, low complexity CMOS solution. • Expected range for 110 Mb/s: 19.1 meters in AWGN, and nearly 10 meters in multipath environments. • Expected power consumption for 110 Mb/s: 93 mW (TX), 142 mW (RX), 15 mW (deep sleep) • TFI-OFDM is coexistence friendly and complies with world-wide regulations. • PHY solution are expected to be ready for integration in 2005. • TFI-OFDM offers the best trade-off between the various system parameters. Anuj Batra et al., Texas Instruments

  35. Backup slides Anuj Batra et al., Texas Instruments

  36. Signal Acquisition • Preamble was designed to be robust and work at 3 dB below sensitivity for 55 Mbps. • The start of a valid OFDM transmission at a receiver sensitivity level  -83 dBm shall cause CCA to indicate busy with a prob. > 90% in 4.69 ms. Anuj Batra et al., Texas Instruments

  37. Is Cyclic Prefix (CP) Sufficient? • For a data rate of 110 Mb/s, studied effect of CP length on performance. • Curves were averaged over 100 realizations of CM3. • For a CP length of 60 ns, the average loss in collected multi-path energy is approx. 0.1 dB. • Inter-carrier interference (ICI) due to multi-path outside the CP is approximately 18.5 dB below the signal. Anuj Batra et al., Texas Instruments

  38. Peak-to-Average Ratio (PAR) for TFI-OFDM • Average TX Power = –9.5 dBm (this value includes pilot tones) • PAR of 9 dB results in: • 0.04 % packets being clipped at TX DAC. • Loss of less than 0.1 dB in AWGN. • Loss of less than 0.1 dB in multipath. • Peak TX power  0 dBm. • Implication: TX can be built completely in CMOS. Anuj Batra et al., Texas Instruments

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