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80MHz Tone Allocation for VHT Data Mapping: Design Proposal

This presentation by Sudhir Srinivasa et al. discusses the allocation of tones for the 80MHz Very High Throughput (VHT) data in IEEE802.11ac packets. It covers guard tones, pilot subcarriers, pilot positions, and the number of pilot subcarriers. The proposal includes details on how to map data and pilot tones effectively within the 80MHz spectrum. Various aspects such as spectrum mask conformity, pilot positioning, and the impact of pilot subcarrier numbers on performance are explored. The presentation suggests using 8 maximally separated pilots during the VHT-DATA portion of 80MHz packets. References to IEEE802.11 specifications are provided for further details and context.

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80MHz Tone Allocation for VHT Data Mapping: Design Proposal

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  1. 80MHz Tone Allocation Date: 2010-03-17 Authors: Slide 1 Sudhir Srinivasa et al.

  2. Introduction • Functional requirements as per the spec framework document [1]: • R3.1.A (Channelization): The draft specification shall include support for 80 MHz PHY transmission. • Possible preambles for 80MHz OFDM have been discussed in [2, 3]. • This presentation will focus on a possible data and pilot tone mapping for 80MHz VHT data. Sudhir Srinivasa et al.

  3. 6 Guard Tones 121 Data/Pilot Tones 3 DC Tones 121 Data/Pilot Tones 5 Guard Tones Freq -122 Subcarrier Index -2 2 -128 122 127 Tone Allocation • Legacy preamble portion (LLTF/LSIG) needs to be repeated across each of the 20MHz sub-bands • (6+5) guard tones in each 20MHz legacy portion, therefore (6+5) guard tones in 80MHz. • Spectrum mask and filter design will have to conform to (6+5) guard tones anyway • Propose to use (6 + 5) guard tones, 3 DC tones in 80MHz Sudhir Srinivasa et al.

  4. Location of pilot subcarriers • The 802.11n spec mandates that • LSIG of 20MHz packets have pilots at {±7, ±21} and • Repetition of the LSIG sequence across 80MHz • LSIG in an 80MHz 11ac packet will have pilots at location pairs belonging to {±11, ±25, ±39, ±53, ±75, ±89, ±103, ±117}. • Not desirable to change pilot positions between the legacy (11a/n) and VHT parts of the packet. • Some implementers may average pilots across and legacy preamble (SIG fields) and VHT data. • For simple receiver design, better to pick 80MHz pilots among these 16 tones. Sudhir Srinivasa et al.

  5. Number of pilot subcarriers • Simulations show that the performance gap between using 8 and 10 pilots is small. (See backup slides) • Reducing the number of pilots to 6, however, results in a ~1dB loss in performance in some scenarios (See backup slides) • We propose that 11ac packets use 8 pilots during 80MHz VHT-DATA portion. • Can be chosen such that they are maximally separated, with indices {±103, ±75, ±39, ±11} Sudhir Srinivasa et al.

  6. References • IEEE802.11-09/0992r3, R. Stacey et al., Proposed Specification Framework for TGac • IEEE802.11-10/0070r1, H. Zhang et al., 802.11ac Preamble • IEEE802.11-10-0130r0, Y. Tu et. Al., Proposed TGac Preamble Sudhir Srinivasa et al.

  7. Simulation Results 1 Sudhir Srinivasa et al.

  8. Simulation Results 2 Sudhir Srinivasa et al.

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