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TGad Common Preamble

TGad Common Preamble. Date: 2010-05-01. Proposal overview. This presentation is part and is in support of the complete proposal described in 802.11-10/432r0 (slides) and 802.11-10/433r0 (text) that: Supports data transmission rates up to 7 Gbps

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TGad Common Preamble

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  1. TGad Common Preamble Date: 2010-05-01 Hongyuan Zhang, Marvell, et. al.

  2. Hongyuan Zhang, Marvell, et. al.

  3. Hongyuan Zhang, Marvell, et. al.

  4. Hongyuan Zhang, Marvell, et. al.

  5. Proposal overview • This presentation is part and is in support of the complete proposal described in 802.11-10/432r0 (slides) and 802.11-10/433r0 (text) that: • Supports data transmission rates up to 7 Gbps • Supplements and extends the 802.11 MAC and is backward compatible with the IEEE 802.11 standard • Enables both the low power and the high performance devices, guaranteeing interoperability and communication at gigabit rates • Supports beamforming, enabling robust communication at distances beyond 10 meters • Supports GCMP security and advanced power management • Supports coexistence with other 60GHz systems • Supports fast session transfer among 2.4GHz, 5GHz and 60GHz Hongyuan Zhang, Marvell, et. al.

  6. Overview 1: SC and OFDM May 2010 • Single Carrier (SC) vs. OFDM • In favor of OFDM • Robustness in higher delay spread environments. • Scalability—higher achievable throughput. • In favor of single carrier • Low PAPR, efficient PA, lower power consumption (at low delay spread) • Lower complexity. • Dual-Mode PHY would be the best solution for TGad: • SC mainly targeted on low power applications with lower achievable throughput. • OFDM mainly targeted on high throughput applications. • SC and OFDM rates are defined in different MCSs in the same MCS table (starting from MCS1). • A low rate common mode is necessary for any device to build up the beamformed links before transmitting regular higher rate SC/OFDM MCSs (refer to [3]). • Named as “Control MCS”, which is MCS0 (see next slide) • SC and OFDM modulation details refer to [1][2]. Slide 6 Hongyuan Zhang, Marvell, et. al.

  7. Overview 2: Control MCS May 2010 • Beamforming is necessary in 60GHz systems, and Control MCS (MCS 0) is required for SC/OFDM/Dual-Mode devices to communicate with each other before setting up beamforming connections. • Main usage of Control MCS: • Beacons • Beamforming training. • Control MCS Design Aspects: • SNR sensitivity (or effective rate) targeted for ~15 dB lower than the sensitivity point of 1Gbps data rate (i.e. the beamforming gain). • Use single carrier with much lower rate. • Refer to [1]. Slide 7 Hongyuan Zhang, Marvell et. al.

  8. Common Preamble Introduction May 2010 • Preamble is the beginning part of a PPDU—used for packet detection, AGC, frequency/timing synchronizations, channel estimation, and signaling of PSDU modulation (SC/OFDM/CtrlMCS). • Regular SC and OFDM MCSs share a common preamble: • Better support of the coexistence between various types of devices • Each device (especially Dual-Mode device) need implement only one packet detection/synchronization/channel estimation mechanism. • Appropriate auto-detection and re-sampling mechanism are required. • Given that OFDM and SC Data portion uses different sampling rates. • PPDU with Control MCS uses a longer preamble with similar design as SC/OFDM MCSs: • Target on lower SNR sensitivity. • Appropriate auto-detection between Control MCS and regular SC/OFDM preambles is needed. Slide 8 Hongyuan Zhang, Marvell, et. al.

  9. I. Common Preamble for SC and OFDM PPDU and Common Preamble general frame formats: May 2010 Preamble Header Payload SC or OFDM Mod Short Training Field (STF) Channel Estimation Field (CEF) • Preamble is composed by STF and CEF: • STF used for packet detection, AGC, frequency/timing synchronizations. • CEF used for channel estimation and SC/OFDM mode auto-detection. • Details see subsequent slides. Slide 9 Hongyuan Zhang, Marvell, et. al.

  10. Preamble Composed by Golay Complementary Sequences Ga128 -Ga128 GV512 Ga128 Ga128 … Ga128 GU512 GV128 Ga128 • Preamble is composed by repeated 128-chip complimentary Golay sequences, denoted as Ga128/Gb128. • GU512/GV512//GV128 are composed by Ga128/Gb128. • Golay sequence is used due to its good auto-correlation property, and simple correlator structure. • Composed by adders and shifters, no complex number multipliers required. • Chip-level π/2-BPSK modulation achieve constant envelope with appropriate filter design. STF, 15 periods (1920 chips) CEF, 1152 chips Slide 10 Hongyuan Zhang, Marvell, et. al.

  11. STF Ga128 -Ga128 GV512 Ga128 Ga128 … Ga128 GU512 GV128 Ga128 • Packet detection, AGC convergence, frequency synchronization and timing synchronization need to be conducted through STF. • Appropriate symbol timing accuracy and frequency offset is required before entering channel estimations. • 15 repetitions of Ga128 is a good tradeoff between PPDU efficiency and preamble detection/synchronization sensitivity. • Preamble det/sync SNR sensitivity matches those for decoding Header, and Payload with MCS1. STF, 15 periods (1920 chips) CEF, 1152 chips Slide 11 Hongyuan Zhang, Marvell, et. al.

  12. CEF SC: STF CEF Ga128 -Ga128 -Ga128 -Gb128 -Gb128 -Ga128 Gb128 -Ga128 -Gb128 Ga128 -Gb128 … Gv128 Postfix of GV512 GU512 GV512 Prefix of GU512 Prefix of GV512 Postfix of GU512 OFDM: STF CEF Ga128 -Ga128 Ga128 -Gb128 -Gb128 Ga128 -Gb128 -Ga128 -Gb128 Ga128 Gb128 … Gv128 Postfix of GV512 GU512 GV512 Prefix of GU512 Prefix of GV512 Postfix of GU512 Slide 12 Hongyuan Zhang, Marvell, et. al.

  13. CEF—Discussions • Frame Delimiter can be realized by either detecting the sign flip at the end of STF, or detecting GU512 in CEF. • GU512/GV512 are a pair of Golay complementary sequences, and are composed by Ga128/Gb128. • GU512/GV512 are with 128-chip cyclic prefix and postfix in an overlapping format. • Interference free time or frequency domain channel estimations can be realized. • Zero side lobe of length 256 around the main tap. • SC/OFDM Auto Detection. • Required for Header/Data processing. • Realized by swapping GU512/GV512 sequences in SC and OFDM PPDUs. Slide 13 Hongyuan Zhang, Marvell, et. al.

  14. Preamble Sampling • The preamble defined above is based on SC chip rate (1760MHz [1]). • OFDM Header and Data are sampled with clock rate 2640MHz (3/2 of SC clock) [2]. • Resampling of 3/2 is required for transmitting the common preamble in a OFDM modulated PPDU. • 3x upsampling  go through a resampling filter hfilt  2x downsampling • The TGad spec needs to define hfilt, so that receiver may recover the appropriate channel estimations. • hfilt with a frequency response satisfying the OFDM transmit mask. Slide 14 Hongyuan Zhang, Marvell, et. al.

  15. II. Preamble for Control MCS • Repeated Gb128 in STF (v.s. Ga128 in SC/OFDM preamble) for reliable auto-detection between Control MCS and regular SC/OFDM MCSs at low SNR. • Control MCS needs to conduct a sync process different from regular SC/OFDM, for lower SNR target and longer delay channels. • Longer STF for lower SNR sensitivity target and longer delay channels. • 40 periods is a good tradeoff between efficiency and preamble detection/synchronization sensitivity. • The preamble detection/sync SNR sensitivity matches that for decoding CP Header and Payload. • CEF with the same format as in regular SC PPDU. May 2010 -Gb128 -Ga128 GV512 Gb128 Gb128 … Gb128 GU512 GV128 Gb128 STF, 40 periods (5120 chips) CEF, 1152 chips Slide 15 Hongyuan Zhang, Marvell, et. al.

  16. III. Golay Complementary Sequences (GCS) • Length-128 GCS and length-512 GCS are chosen for STF and CEF respectively, for the best tradeoff among efficiency, correlation complexity, signal acquisition sensitivity (especially for low rate packets), and channel estimation quality (especially for high rate packets). • Choosing the GCS: • Prefer to choose Golay Code Ga128 with zero-DC after chip level π/2 rotation (i.e. the STF in regular SC/OFDM MCSs). • Prefer to choose GCP Ga128/Gb128 with large zero correlation zone (e.g. 64 taps) around the main tap. • Delay units Dn are chosen to minimize the memory size. • The GCP : • D7 = [64 32 16 1 8 2 4], W7 = [1 1 1 1 -1 -1 1]. Slide 16 Hongyuan Zhang, Marvell, et. al.

  17. Shorter GCS Choices • A Ga64 code is needed for the GI insertions in SC MCSs [1]; and a Ga32 code is needed for data spreading in the Control MCS [1]. • Choosing the shorter GCS: • Use a subset of the delay vector D (reuse correlator hardware), with different coefficient W vectors. • To get Ga64, D6 = [32 16 1 8 2 4], W6 = [-1 1 1 -1 1 -1]. • To get Ga32, D5 = [16 1 8 2 4], W5 = [-1 -1 1 1 1]. • Guarantees good correlation properties between preamble and shorter GCS codes in SC data portion. Slide 17 Hongyuan Zhang, Marvell, et. al.

  18. STF Cross-Correlations (AWGN) Regular SC/OFDM STF Xcorr with Ga128: Ctrl MCS STF Xcorr with Gb128: Hongyuan Zhang, Marvell, et. al.

  19. CEF Cross-Correlations (SC@AWGN) SC CEF Xcorr with Gu512: Example CE Output (256 taps) SC CEF Xcorr with Gv512: Hongyuan Zhang, Marvell, et. al.

  20. Conclusions May 2010 • A Common preamble proposed for different PHY modes. • SC and OFDM MCSs share the same preamble structure. • Control MCS uses a longer preamble with similar STF and CEF structures. • Complementary Golay spreading codes are applied in preamble to simplify receiver processing. • Appropriate auto-detection among different modes are also proposed. Slide 20 Hongyuan Zhang, Marvell, et. al.

  21. References • [1] 11-10-0429-r0 “TGad SC PHY” • [2] 11-10-0440-r0 “TGad OFDM PHY” • [3] 11-10-0430-r0 “TGad Beamforming” Slide 21 Hongyuan Zhang, Marvell, et. al.

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