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IEEE 802.11ad Overview for CWPAN

IEEE 802.11ad Overview for CWPAN

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IEEE 802.11ad Overview for CWPAN

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  1. IEEE 802.11ad Overview for CWPAN Authors: Date: 2011-03-19 Eldad Perahia, Intel Corporation

  2. Motivation for 60 GHz Eldad Perahia, Intel Corporation

  3. Outline • 802.11ad task group background • Summary of 802.11ad Enhancements • PHY • MAC • Beamforming • Coexistence with other 60 GHz systems Eldad Perahia, Intel Corporation

  4. History Very High Throughput Study Group 802.11ad Task group started Jan 2009 Task group documents Functional Requirements Evaluation Methodology Channel Models Usage Models Complete proposal approved May 2010 to create draft 0.1 D1.0 approved by WG in Sept 2010 D2.0 completed by TG in March 2011 • Started in May 2007 initially to address Very High Throughput for < 5GHz IMT-Advanced operation • Initial discussions on 60 GHz started in Nov 2007 • 60 GHz PAR approved Dec 2008 Eldad Perahia, Intel Corporation

  5. Project Authorization Request (PAR) • The 60 GHz ISM band provides the opportunity for much wider band channels than in <6 GHz enabling single link throughputs greater than 1 Gbps • Two aspects of the PAR ensure distinct identity from 802.15.3c • Enable fast session transfer between PHYs • Maintain the 802.11 user experience • Fast session transfer provides seamless rate fall back between VHT and 802.11n for multi-band devices • Provides expected WLAN coverage from combo 60 + 2.4/5 GHz devices • Does not mandate multi-band devices • As an amendment to 802.11, VHT maintains the 802.11 user experience • maintaining the network architecture of the 802.11 system • E.g. infrastructure basic service set, extended service set, access point, station • Reuse and maintain backward compatibility to 802.11 management plane • E.g. association, authentication, security, measurement, capability exchange, MIB • Coexistence • Coexistence with 802.15.3c in the 60 GHz band is an important issue to VHT demonstrated by being explicitly called out in the PAR scope • Furthermore, the task group will produce a coexistence assurance document Eldad Perahia, Intel Corporation

  6. 802.11ad Official Timeline • PAR approved: Dec 09, 2009 • Initial Working Group Letter Ballot: September 2010 • Recirculation Working Group Letter Ballot: March 2011 • Initial Sponsor Ballot: planned for December 2011 • Recirculation Sponsor Ballot: planned for March 2012 • Final Working Group Approval: planned for July 2012 • RevCom & Standards Board Final Approval: planned for December 2012 Eldad Perahia, Intel Corporation

  7. Summary of 802.11ad Enhancements Eldad Perahia, Intel Corporation

  8. PHY Eldad Perahia, Intel Corporation

  9. Channelization Same channelization as 802.15.3c, compatible mask requirement for coexistence Eldad Perahia, Intel Corporation

  10. PHY Overview (1/2) • Different PHY types for different usages: • Control PHY • Designed for low SNR operation prior to beamforming • Single Carrier PHY • SC enables low power/low complexity transceivers • Low Power SC • Additional support for further reduction in implementation processing power with simpler coding and shorter symbol structure • OFDM PHY • High performance in frequency selective channels • Maximum data rates using up to 64 QAM Eldad Perahia, Intel Corporation

  11. PHY Overview (2/2) • Interoperable devices • Control PHY and SC PHY mandatory for all devices • PHY design simplified with common properties between Control, SC and OFDM PHYs • Common packet structure • Same Golay sequences used for preamble training fields • Common LDPC structure for coding • Embedded support for BF Eldad Perahia, Intel Corporation

  12. Short Training Field (STF) STF=38xGb128, -Gb, -Ga (2.91 us) CEF Control PHY: … -Gb128 -Ga128 Gb128 Gb128 -Gb128 … STF=16xGa128,-Ga (1.09 us) CEF SC/OFDM: … -Ga128 Ga128 Ga128 -Gb128 … • STF used for packet detection, AGC, frequency offset estimation, synchronization • Ga, Gb composed of 128 sample Golay sequence, transmitted using π/2-BPSK at SC symbol rate • Complementary sequences are used to differentiate control MCS and high rate MCSs Slide 12 Eldad Perahia, Intel Corporation

  13. Channel Estimation Field (CEF) • CEF is used for channel estimation and an indication of modulation type • Ga, Gb composed of 128 sample Golay sequence, transmitted using π/2-BPSK at SC symbol rate STF CEF (655 ns) SC/ Control: Ga128 -Ga128 -Ga128 -Gb128 -Gb128 -Ga128 Gb128 -Ga128 -Gb128 Ga128 -Gb128 … v128 u512 v512 OFDM: STF CEF (655 ns) Ga128 -Ga128 -Ga128 -Gb128 -Gb128 Ga128 -Gb128 -Gb128 -Ga128 Gb128 -Ga128 … v128 v512 u512 Eldad Perahia, Intel Corporation

  14. Header and Data Field Transmission Scrambler Encoder Modulator Spreading Symbol Blocking GI Insertion Control: Symbol Blocking GI Insertion SC: Pilot Insertion IDFT GI Insertion OFDM: Eldad Perahia, Intel Corporation

  15. Control PHY • Designed for very low SNR operation to close link prior to beamforming • Mandatory single carrier mode with data rate ~27.5 Mbps (MCS 0) • 32 sample Golay spreading sequence, also mitigates against longer delay spread channels • π/2 - Differential BPSK modulation: more robust in the presence of phase noise allowing for shorter training fields • Rate ½ coding used, shortened from the common 3/4 LDPC code • Effective shorter block size: 336 bits • Short LDPC code is more efficient for short packets • Bits are evenly divided between codewords to allow equal protection • Packet length limitations • A-MPDU aggregation is not allowed using Control MCS • Maximum length is limited to 1024 bytes Eldad Perahia, Intel Corporation

  16. Single Carrier PHY • Block size – 512 symbols • 448 data symbols • 64 GI symbols; fixed sequence (Ga64) • Tracking purposes • Can be used for equalization • Symbol Rate = 1760 MHz • π/2rotation applied to all modulations • To reduce PAPR for BPSK • To enable GMSK equivalent modulation Mandatory Eldad Perahia, Intel Corporation

  17. Low Power Single Carrier PHY • The FEC is one of the major contributor to the relatively high power consumption of the SC mode • Simple FEC: • Reed Solomon (224, 208) for high data rate • Outer Reed Solomon (224, 208) + Inner block code (N,8) Eldad Perahia, Intel Corporation

  18. OFDM PHY • Sampling Rate = 2640 MHz • Exactly 1.5x the SC symbol rate • 512 point FFT (193.9 ns) • 336 data subcarriers • 16 pilot subcarriers • 3 null subcarriers at DC • GI length of 128 samples (48.5 ns) • Spread QPSK (SQPSK) used for two lowest rates • Symbol interleaver for 16 QAM and 64 QAM embedded in modulator • 16 QAM – 2 code words per symbol • 64 QAM – 3 code words per symbol Eldad Perahia, Intel Corporation

  19. MAC Eldad Perahia, Intel Corporation

  20. MAC Challenges • The primary challenge for the MAC is how to deal with directional communication, which is used to combat the high propagation loss in 60 GHz • Device discovery becomes a non-trivial problem • Devices need to find the direction for communication, which necessitates the support for beamforming • 802.11 CSMA/CA has limitations in the presence of directionality • How to exploit spatial frequency reuse in face of directional communication Eldad Perahia, Intel Corporation

  21. New MAC features • A new network architecture named Personal Basic Service Set (PBSS), while retaining the existent 802.11 network architectures • Channel access that support directionality and spatial frequency reuse, including both random access and scheduled access • A unified and flexible beamforming scheme that can be tuned to simple, low power devices as well as complex devices • Enhanced security (GCMP), link adaptation and power saving • Multi-band support (fast session transfer) Eldad Perahia, Intel Corporation

  22. Personal BSS (PBSS) • New network architecture in addition to infrastructure BSS and IBSS, which are also supported • PBSS is defined to address some unique usages and challenges of 60GHz communication • Usages: Rapid sync-n-go file transfer, projection to TV/projector, etc. • Challenges: directional channel access, power saving, etc. • Ad hoc network similar to the IBSS, but: • A STA assumes the role of the PBSS Central Point (PCP) • Only the PCP transmits beacon frames Eldad Perahia, Intel Corporation

  23. Beacon Interval (BI) structure • Beacon transmission interval (BTI): AP/PCP performs one or more beacon transmissions potentially in different directions • Association beamforming training (A-BFT): BF for BSS joining, BF link re-establishment, etc. Efficient by using beacon to bootstrap BF • Announcement time (AT): used to convey control/management between AP/PCP and STA • Data transfer time (DTT): prescribed STAs access the channel during SP, negotiated between AP/PCP and STA or dynamically allocated. Any STA can access the channel during CBAP; access is based on 802.11 EDCA Eldad Perahia, Intel Corporation

  24. Channel Access • Channel access is coordinated using a schedule, which is delivered by the PCP/AP to non-PCP/non-AP STAs • STAs are permitted to transmit data frames during contention-based periods (CBPs) and service periods (SPs) • Access during CBPs is based on EDCA fine-tuned for directionalaccess • Access during SPs is reserved to specific STAs as announced in the schedule or granted by the PCP/AP MAC efficiency is above (or very close to) 90% of the PHY rate for payload sizes larger than 8Kbytes Eldad Perahia, Intel Corporation

  25. Fast session transfer (FST) for multi-band operation Common Upper MAC (management) • Enables seamless integration of 60GHz with 802.11a/b/g/n/ac • Allows transition of communication from any band/channel to any other band/channel • Supports both simultaneous and non-simultaneous operation • Supports both transparent and non-transparent FST • Transparent: the MAC address is the same in both bands/channels • Non-transparent: the MAC addresses are different Fast Session Transfer (802.11ad) BB & Lower MAC (802.11b/a/g/n/ac) BB & Lower MAC for 60G (802.11ad) 2.4 GHz (ant, FEM, RFIC) 5 GHz (ant, FEM, RFIC) 60 GHz (ant, FEM, RFIC) Eldad Perahia, Intel Corporation

  26. Beamforming Eldad Perahia, Intel Corporation

  27. Beamforming • High antenna gains require mechanisms to point the antennas, since beamwidths will be narrow (e.g. ~13 dB gain corresponds to ~45 degree beamwidth) • Pointing must automatically find the best path to potentially avoid obstructions • Beamforming encompasses different techniques – switched beams, phased/weighted arrays, multiple arrays • Beamforming protocol must support interoperable devices with different technologies Eldad Perahia, Intel Corporation

  28. Beamforming Protocol Overview • Specification employs: • Directional TX / low gain (quasi-omni) RX for acquisition in sector level sweep (SLS) phase • Beam refinement phase (BRP) adds RX gain and final adjustment for combined TX and RX • Tracking during data transmission to adjust for channel changes Eldad Perahia, Intel Corporation

  29. Overview of TX Sector Level Sweeps STA 2 1 3 4 • For the initial connection between two devices (STA and AP/PCP), one will receive with a quasi-omni-directional antenna while the other sends a sequence of frames covering different TX sectors • For direct connections between two STAs in a PBSS PCP (PBSS Control Point) Eldad Perahia, Intel Corporation

  30. Overview of RX Sector Level Sweeps • A device with a simple antenna may not have enough TX gain to reach a distant receiver that is using an omni-directional receiving antenna • RX Sector Sweep may be employed by the device with the higher performance antenna system • Allows a simple antenna device, like a handset, to connect at greater range 1 2 RX Sector Sweep is used to initiate beamforming on this link 4 3 Simple Antenna Device Eldad Perahia, Intel Corporation

  31. Sector Level Sweep Packet Sequence • Each packet in the transmit sector sweep includes countdown indication (CDOWN), a Sector ID, and an Antenna ID • The best Sector ID and Antenna ID information are fed back with the Sector Sweep Feedback and Sector Sweep ACK packets Eldad Perahia, Intel Corporation

  32. Coexistence Eldad Perahia, Intel Corporation

  33. Coexistence with other 60 GHz systems • The same channelization as other 60 GHz systems is used, and the same SC chip rate as that of 802.15.3c CMS is adopted • AP should not start a BSS where the signal level is above a threshold or upon detecting a 802.15.3c CMS preamble at >= -60 dBm • In 802.11a/n, MCS 0 (BPSK, R=1/2) receive sensitivity is -82 dBm and non-802.11 detection level is -62 dBm → 20 dB difference • In 802.11ad, SC MCS 1 receive sensitivity is -68 dBm → 8 dB difference with respect to required 802.15.3c CMS preamble detection threshold • Requirement of detection of 802.15.3c CMS preamble is 12dB more stringent than 802.11a/n and non-802.11 detection! • STAs can perform channel measurements and report results to AP/PCP • Several mechanisms can be used to mitigate interference with other 60 GHz systems, including: • Change operating channel, beamforming, reduce transmit power, move the BT (and thus the BI) in case of an AP or PCP, change or request the change of scheduled SPs and CBPs in the BI, defer transmission for a later time Eldad Perahia, Intel Corporation

  34. Acronyms (1/3) • A-BFT - Association beamforming training • ACK - acknowledgment • AP – access point • AT - Announcement time • BB - baseband • BF - beamforming • BPSK - binary phase shift keying • BRP - beam refinement protocol • BTI - beacon transmission interval • CBAP – contention-based access period • CE, CEF – channel estimation field • CMS – common mode signaling • CSMA/CA - carrier sense multiple access with collision avoidance • DTT - Data transfer time • FFT - Fast Fourier Transform • FEM – front-end module • FST – fast session transfer • GCMP - Galois/Counter mode protocol • GMSK - Gaussian minimum shift keying • GI – guard interval • IBSS – independent basic service set • ID - identification • Infra-BSS – infrastructure basic service set Eldad Perahia, Intel Corporation

  35. Acronyms (2/3) • ISM - industrial, scientific, and medical • LDPC - low-density parity check • MCS – modulation, coding scheme • MAC - medium access control • MIB - management information base • OFDM - orthogonal frequency division multiplexing • PAR - Project Authorization Request • PAPR - Peak-to-Average Power Ratio • PBSS - personal basic service set • PCP - PBSS control point • PHY - physical layer • QAM - quadrature amplitude modulation • QPSK - quadrature phase shift keying • RFIC – radio frequency integrated circuit • RX – receive or receiver • SC – single carrier • SLS - sector level sweep • SNR – signal to noise ratio • SP – service period • SQPSK – spread QPSK • STA – station • STF – short training field • TG – task group • TX – transmit or transmitter Eldad Perahia, Intel Corporation

  36. Acronyms (3/3) • VHT – very high throughput • WG – working group • WPAN – wireless personal area networking Eldad Perahia, Intel Corporation

  37. References • P802.11ad Draft 1.2 • Cordeiro, Carlos, “PHY/MAC Complete Proposal to TGad”, May 16, 2010, 11-10/0432r2 • Hansen, Christopher, “Beamforming Introduction”, May 16, 2010, 11-10/0430r1 • Cordeiro, Carlos and Shankar, Sai, “Next Generation Multi-Gbps Wireless LANs and PANs”, IEEE Globecom 2010, Dec 2010 Eldad Perahia, Intel Corporation