1 / 66

WWiSE IEEE 802.11n Proposal

This proposal by WWiSE group aims to develop a specification for worldwide deployment of next-generation WLAN technology. It emphasizes compatibility with existing installed bases and offers high performance and throughput.

jewella
Download Presentation

WWiSE IEEE 802.11n Proposal

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. WWiSE IEEE 802.11n Proposal November 16, 2004 Airgo, Broadcom, Buffalo, Conexant, ETRI, Realtek, STMicroelectronics, Texas Instruments, Winbond S. Coffey, et al., WWiSE group

  2. Contributors and contact information • Airgo Networks: VK Jones, vkjones@airgonetworks.com • Broadcom: Jason Trachewsky, jat@broadcom.com • Buffalo: Takashi Ishidoshiro, doshir@melcoinc.co.jp • Conexant: Michael Seals, michael.seals@conexant.com • ETRI: Taehyun Jeon, thjeon@etri.re.kr • Realtek: Stephan ten Brink, stenbrink@realtek-us.com • STMicroelectronics: George Vlantis, George.Vlantis@st.com • Texas Instruments: Sean Coffey, coffey@ti.com • Winbond: Jeng-Hong Chen, JHChen2@winbond.com S. Coffey, et al., WWiSE group

  3. Contents • WWiSE approach • Overview of key features & updates • Proposal description • Physical layer design • MAC features • Discussion • Summary S. Coffey, et al., WWiSE group

  4. The WWiSE approach • WWiSE = World Wide Spectrum Efficiency • The partnership was formed to develop a specification for next generation WLAN technology suitable for worldwide deployment • Mandatory modes of the WWiSE proposal comply with current requirements in all major regulatory domains: Europe, Asia, Americas • Proposal design emphasizes compatibility with existing installed base, building on experience with interoperability in 802.11g and previous 802.11 amendments • All modes are compatible with QoS and 802.11e • Maximal spectral efficiency translates to highest performance and throughput in all modes S. Coffey, et al., WWiSE group

  5. WWiSE proposal development process • Approximately 150 documents submitted • Many contributions per topic: short sequence, pilots, laboratory testing results, etc. • Many contributions per company • Collaborative process • Technical selection • Modeled after the IEEE process, with supermajority voting • Proposal drafting • Detailed technical specification in 802.11 draft format prepared S. Coffey, et al., WWiSE group

  6. Recap • WWiSE proposes 2 transmitters in 20 MHz mandatory • Rates 54, 81, 108, 121.5, 135 Mbps • Optional extensions to 3 and 4 transmit antennas • Optional space-time block codes for longer range • Optional 40 MHz counterparts of all 20 MHz modes • Optional LDPC code • MAC: HTP burst, aggregation, extended Block Ack • See 11-04-0935r3 for a full description S. Coffey, et al., WWiSE group

  7. Update • 20/40 MHz coexistence language strengthened • Devices must perform CCA on secondary channel • All space-time block codes are now optional • Modifications to rate tables for 2x1-20 MHz, 1x1-40 MHz, and 2x1-40 MHz • See 11-04-0886r5 S. Coffey, et al., WWiSE group

  8. 2x1, 20 MHz: 1x1, 40 MHz; 2x1, 40 MHz Old rate plan S. Coffey, et al., WWiSE group

  9. 2x1, 20 MHz: (optional) 1x1, 40 MHz; 2x1, 40 MHz New rate plan S. Coffey, et al., WWiSE group

  10. Unified format All combinations of 2, 3, 4 transmit antennas and 20/40 MHz offer exactly these 5 modes All 20 MHz modes have 54 data subcarriers, 2 pilots. All 40 MHz modes have 108 data subcarriers, 4 pilots S. Coffey, et al., WWiSE group

  11. WWiSE and TGnSync each use 108 data tones at 40 MHz Extra tones via filling gap between 20 MHz channels However WWiSE also uses extra tones in 20 MHz, filling tones out to existing spectral mask 108 Data tones WWiSE 54 48 TGnSync 40 MHz 20 MHz Bandwidth Tone usage in 20 MHz and 40 MHz 48 S. Coffey, et al., WWiSE group

  12. 2 transmitter SDM, 20 MHz (mandatory) S. Coffey, et al., WWiSE group

  13. Optional data modes • 20 MHz: • 3 Tx space-division multiplexing • 4 Tx space division multiplexing • 40 MHz: (all 40 MHz modes optional) • 1 Tx antenna • 2 Tx space division multiplexing • 3 Tx space division multiplexing • 4 Tx space division multiplexing • Space-time block codes: (all STBCs optional) • 2x1, 3x2, 4x2, 4x3 in 20 MHz and 40 MHz • LDPC code option • An option in all proposed MIMO configurations and channel bandwidths S. Coffey, et al., WWiSE group

  14. Optional mode data rates 20 MHz: 40 MHz: S. Coffey, et al., WWiSE group

  15. Proposal performance S. Coffey, et al., WWiSE group

  16. For 2x2 operation with 64-QAM, rate 5/6 is feasible This rate marks the limit of feasibility ML gains 5 dB over MMSE (1% PER) LDPC gains 2 dB over BCC Similar results for 40 MHz at 2x data rate Curves slightly to left due to frquency diversity Robustness, 135 Mbps, multipath S. Coffey, et al., WWiSE group

  17. Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) S. Coffey, et al., WWiSE group

  18. Parameterized 802.11a-style interleaver 5 subcarrier shift, same interleaver Bit-cycling across NTX transmitters . . . MIMO interleaving TX 0 interleaved bits Coded bits TX 1 interleaved bits Shift of 5 additional subcarriers for each additional antenna S. Coffey, et al., WWiSE group

  19. Both schemes have 2x2, 64-QAM, rate 3/4 WWiSE: 121.5 Mbps TGnSync: 108 Mbps WWiSE interleaver has an advantage of 1.25 dB at 2% PER Interleaver comparison with TGnSync S. Coffey, et al., WWiSE group

  20. Both schemes are 108 Mbps WWiSE: rate 2/3 TGnSync: rate 3/4 WWiSE interleaver has an advantage of 3.75 dB at 2% PER 108 Mbps modes comparison with TGnSync S. Coffey, et al., WWiSE group

  21. Pending comparisons, modes & interleavers • WWiSE 135 Mbps vs. TGnSync 126 Mbps • 2x2 rate 5/6 with WWiSE interleaver vs. 2x2 rate 7/8 with TGnSync interleaver • WWiSE 135 Mbps vs. TGnSync 144 Mbps • 2x2 rate 5/6 64-QAM vs. 2x2 rate 3/4 256-QAM • WWiSE 243 Mbps vs. TGnSync 243 Mbps, @ 40 MHz • Different interleavers S. Coffey, et al., WWiSE group

  22. Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) S. Coffey, et al., WWiSE group

  23. AP STA Space-time block codes and asymmetry • Simple space-time block codes (STBCs) are used to handle asymmetric antenna configurations • STBC rate always is an integer - No new PHY rates result from STBC encoding of streams • Block size is always two OFDM symbols • STBC encoding follows the stream encoding S. Coffey, et al., WWiSE group

  24. 4x2 gains 4.6 dB over 2x2 (121.5 Mbps); 6.2 dB (135 Mbps) These results for MMSE receiver, BCC 4x2 space-time block code S. Coffey, et al., WWiSE group

  25. Insert training Add pilots FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) WWiSE 20 MHz OFDM format Much of the robustness advantage comes from the WWiSE 20 MHz OFDM format of 56 tones: 54 data, 2 pilots S. Coffey, et al., WWiSE group

  26. 52 tones, 3 dB backoff • This is the same 52-tone signal • The PA is operated 3 dB backed off from PO-1 dB compression point • The signal is now contained within the spectral mask. - S. Coffey, et al., WWiSE group

  27. 56-tone OFDM signals • This is a 56 tone OFDM signal with a short trapezoidal window • The signal meets spectral mask, with an extra 0.5 dB of PA backoff compared to 52 tone OFDM signal • 58 tones fails spectral mask even with an 8 dB backoff • 56 tones works well, and is also the feasible limit • More details in separate spectral mask presentation - S. Coffey, et al., WWiSE group

  28. Pilots in a frequency selective channel SISO Rx 1 MIMO Rx 2 S. Coffey, et al., WWiSE group

  29. Pilots in frequency selective channels • Optimal performance depends on total pilot SINR • Figure of merit is nr x np • Two systems that have same nr x np and correlations will have the same performance • In the WWiSE format, correlation in frequency is less than in legacy mode, due to increased pilot separation • Correlation in space depends on antenna separation • For half-l separation in channel models D and B the net effect is that the WWiSE format has the same distribution function as legacy SISO S. Coffey, et al., WWiSE group

  30. Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) S. Coffey, et al., WWiSE group

  31. Preambles • Mixed mode: • Basic preamble, used when there is on-the-air mixing of legacy 11a/g traffic with 11n traffic • “Green field/patch/timeslot”: • Used (even in a mixed BSS) in time intervals where there is no legacy on-air traffic • For example: • Within protection mechanisms • Within a burst, with initial preamble mixed mode • Within a HCCA poll S. Coffey, et al., WWiSE group

  32. Short Long SIG Long - N SIG-N SIG-N Short-N Long-N Long-N Preambles: 2 Tx, mixed mode 20 MHz Legacy WWiSE: 32 msec 8 4 or 44.8 msec TGnSync: 20 8 7.2 7.2 2.4 S. Coffey, et al., WWiSE group

  33. SIG-N Short-N Long-N Long-N Preambles: 2 Tx, “green time” 20 MHz Short Long - N SIG-N WWiSE: 20 msec 8 8 4 or 44.8 msec TGnSync: 20 8 7.2 7.2 2.4 S. Coffey, et al., WWiSE group

  34. The frequency division preamble is double the length of the WWiSE preamble The loss due to lack of smoothing offsets the gain due to doubling the length In this case the two effects balance each other out Channel estimation performance S. Coffey, et al., WWiSE group

  35. STS vs. LTS Rx power CDF:Cyclic shift on STS and not LTS 25 nsec RMS DS: 50, 100, 200, 400 nsec CDD Large power discontinuity observed S. Coffey, et al., WWiSE group

  36. STS vs. LTS Rx power CDF:Cyclic shift on both STS and LTS 25 nsec RMS DS: 50, 100, 200, 400 nsec CDD Looks well behaved S. Coffey, et al., WWiSE group

  37. Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) S. Coffey, et al., WWiSE group

  38. BCC encoder, puncturer To MIMO interleaver BCC encoder, puncturer Multiplexing across two encoders (round robin) Parallel encoders • For 40 MHz modes with more than two spatial streams, two parallel BCC encoders are used: Data payload S. Coffey, et al., WWiSE group

  39. Advanced coding option • Rate-compatible LDPC code with the following parameters: • Transmitter block diagram as for BCC modes, except symbol interleaver, rate-compatible puncturing, and tail bits are not used Rate Information bits Block length 1/2 972 1944 2/3 1296 1944 3/4 1458 1944 5/6 1620 1944 S. Coffey, et al., WWiSE group

  40. LDPC code, contd. • There is no change required to SIFS or to any other system timing parameters when the advanced coding option is used • The block size of 1944 reduces or eliminates the need for pad bits at the end of a packet • Pad bits are eliminated for 2 transmitter operation in 20 MHz channels, and 2x1 and 1x1 in 40 MHz channels • The four parity check matrices are derived from the rate-1/2 matrix via row combining • The parity check matrices are structured and based on square-shaped building blocks of size 27x27 • The parity check matrices are structured to enable efficient encoding S. Coffey, et al., WWiSE group

  41. MAC features S. Coffey, et al., WWiSE group

  42. MAC features • The WWiSE proposal builds on 802.11e functionality as much as possible, in particular EDCA, HCCA, and Block Ack • Block Ack mandatory • WWiSE proposal ensures backwards compatibility • Targeted effectiveness - ROI • Eliminate the big bottlenecks • Avoid schemes which yield relatively small improvement in performance in return for large complexity changes • Benefits of simplicity • Shorter time to standardization • Shorter time to productization • Shorter time to interoperability S. Coffey, et al., WWiSE group

  43. WWiSE TGn MAC features • WWiSE proposal introduces: • Only ONEnew frame subtype • not actually a new subtype – uses QOS field reserved bit • No new MAC access control functions • Re-uses existing DCF/EDCA/HCCA • TGE => QOS + Efficiency enhancements • EDCA: reduce DCF overhead with continuation TXOP • HCCA: reduce EDCA overhead with controlled access • WWiSE brings forth three simple efficiency enhancements • These achieve high performance, even compared to other proposed enhancements S. Coffey, et al., WWiSE group

  44. The three WWiSE MAC enhancements • MSDU (MAC Layer) Aggregation • Removes significant MAC overhead • HTP Burst • Eliminates major remaining components of MAC / PHY overhead • Enhanced Block Ack • Allow No-ACK policy • Removes significant ACK overhead • Block Ack eliminates MAC transmitter turnaround overhead S. Coffey, et al., WWiSE group

  45. The Ideal Protocol No IFS • All MSDU data bits, all the time • 100% MAC Efficiency MSDU = PSDU No MAC Header t0 = - ∞ t1 = + ∞ S. Coffey, et al., WWiSE group

  46. MSDU aggregation @ Ideal No IFS • Requires minor change to MAC protocol • Need new aggregation subtype • Efficiency increases as n increases • Efficiency approaches 100% for very large n • Flexibility in choice of n allows for per-installation tradeoff of latency vs throughput vs fairness Np Ns MH nMSDU xIFS MAC Header t0≠ - ∞ t1≠ + ∞ S. Coffey, et al., WWiSE group

  47. WWiSE MSDU aggregation • “New frame subtype” • Uses reserved bit of QOS subfield • Increased maximum PSDU length, to 8191 octets • Impressive improvements in MAC throughput • WWiSE simulations use n=8 (with overriding max MPDU size limitation of 8191 Bytes) S. Coffey, et al., WWiSE group

  48. MSDU aggregation shortcomings • Upper limit on n (number of MSDU per aggregate) • PHY limitations • QOS latency limitations affect aggregate assembly process • IFS between aggregates • PHY overhead between aggregates • Single RA per aggregate • Single Rate per aggregate • Single TX power value per aggregate • Good stuff, but not so ideal due to practical constraints S. Coffey, et al., WWiSE group

  49. HTP Burst more ideal No idle gap Optional normal ACK policy • Multiple RA allowed within the burst • Block Ack Request and Block Ack frames allowed within burst • More IFS eliminated • RIFS and ZIFS allowed within burst • PHY overhead reduced • “Last PSDU” bit indicates receiver should revert to preamble search Ns PSDU Ns PSDU Ns PSDU xIFS Np PSDU can be an aggregate MSDU! Non-normal ACK = N-Preamble Np Last PSDU bit set = N-Signal field @ robust encoding rate Ns S. Coffey, et al., WWiSE group

  50. HTP Burst • HTP Burst • Sequence of MPDUs from same transmitter • IFS between MPDUs not necessary, since same transmitter is used for all MPDUs in the HTP Burst • 0 usec IFS if at same Tx power level and PHY configuration • 2 usec IFS otherwise (with preamble) • IFS value not dependent on RA • Preamble also not necessary • Optional with ZIFS, required with RIFS • PPDUs may be “aggregated” • i.e. ZIFS with no preamble between PPDU • MPDUs may be of the aggregated-MSDU type • MPDUs may have different RAs and Rates S. Coffey, et al., WWiSE group

More Related