1. Pilot Value Definitions
March 2012
Pilot Value Definitions
Date:
Authors:
Seunghee Han, LG Electronics

2. March 2012
Seunghee Han, LG Electronics

3. March 2012
Seunghee Han, LG Electronics

4. March 2012
Motivation
Pilot tones in data OFDM symbols can be used for the purpose of phase tracking and for compensation of residual frequency offset error after initial compensation.
For >= 2MHz mode, it is straightforward to adopt pilot values and tone indices as in 11ac spec [2] applying down-clocking by a factor of 10.
Since the Pilot tone indices and values for 1MHz mode cannot be obtained by down-clocking from 11ac, the specification is needed.
We have pilot tone indices based on [3] stating “Define 1MHz tone allocation as: 24 Data tones, 2 Pilot tones at tone indices +/-7, 3 Guard tones on left and 2 guard tones on right, and 1 DC tone [11/1484r6]”.
However, the pilot values need to be defined.
Seunghee Han, LG Electronics

5. March 2012
Background (1/2)
Design principle on pilot sequence in 11ac [1]
For fast phase tracking, identical pilot sequence values are used for all space-time streams in data symbols in 11ac so that the receiver can track phase without MIMO channel estimation on pilot tones.
For 20 and 40 MHz, the pilot sequence shall be the single spatial stream pilot sequence of 11n copied to the NSTS streams before the per-stream CSDs are applied.
For 80 MHz, the pilot sequence shall be the following sequence (which is the 40 MHz pilot sequence for NSTS = 1 extended with a [1, 1] on the right, resulting in the lowest PAPR on the pilot tones after applying [ ] rotation on the 20 MHz subbands), copied to the NSTS streams before the per-stream CSDs are applied:
Seunghee Han, LG Electronics

6. Background (2/2) Further design principles on pilot sequence in 11ac
March 2012
Background (2/2)
Further design principles on pilot sequence in 11ac
BPSK based (+1 or -1) pilot sequence values to avoid complex multiplication by using sign converter.
Both time and frequency domain varying pilot sequence values by means of
Modulo operation as a function of symbol index n in both time and frequency domains
Pseudo random sequence (ie. pn as defined in [5]) to prevent the generation of spectral line [4]
The worst case would be that all elements have the same signs (eg. All ‘1’ or all ‘-1’).
Seunghee Han, LG Electronics

7. Proposed Design Criteria for Pilot Values
March 2012
Proposed Design Criteria for Pilot Values
For >= 2MHz mode,
Reuse the definitions as in 11ac
For 1 MHz mode,
Succeed the design philosophy of 11ac with;
Minimum impact on specification works
Single table for pilot values with nested property for all bandwidths
BPSK based sequence value for low complexity
Provision of both time and frequency domain varying sign properties with modular operation
It is noted that pseudo random sequence pn is further applied to avoid spectral line [5].  Not part of our proposal
Seunghee Han, LG Electronics

8. Proposal on Pilot Values for 1 MHz Mode
March 2012
Proposal on Pilot Values for 1 MHz Mode
Based on slide 7,
For a 1MHz transmission, two pilot tones shall be inserted in The pilot mapping for subcarrier for symbol shall be as specified in the following equation. where is given in the right table and where n is the DATA symbol index
Table in 11ac D2.0
Seunghee Han, LG Electronics

9. Proposal on Pilot Values for >=2 MHz Modes
March 2012
Proposal on Pilot Values for >=2 MHz Modes
Based on slide 7,
The pilot mapping and values for 2/4/8/16 MHz transmissions, respectively, refer those for 20/40/80/160 MHz transmissions in section (Pilot subcarriers) of IEEE P802.11ac™/D2.0 with the same pilot positions and values.
Seunghee Han, LG Electronics

10. March 2012
Straw Poll 1
Do you support to insert slide 8 at R A of the spec framework as pilot mapping and values for 1MHz mode?
Seunghee Han, LG Electronics

11. March 2012
Straw Poll 2
Do you support to insert slide 9 at the spec framework as pilot mapping and values for 2/4/8/16 MHz modes?
Seunghee Han, LG Electronics

12. March 2012
References
[1] Richard van Nee et al, “Pilot Sequence for VHT-DATA”, IEEE /0811r1
[2] Draft P802.11ac_D2.0
[3] Minyoung Park, “Proposed Specification Framework for TGah”, IEEE /1137r5
[4] Matthew S. Gast, “ Wireless Networks – The Definitive Guide”, O’REILLY
[5] Draft P802.11REVmb_D12.0
Seunghee Han, LG Electronics