1. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Comment resolutions for OFDM Scrambler and HCS]
Date Submitted: [June 24, 2010]
Source: [Tim Schmidl, Texas Instruments]
Re: [TG4g comment resolution]
Abstract: [Comment resolutions related to OFDM Scrambler and HCS]
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
<author>, <company>

2. <month year>
doc.: IEEE <doc#>
Summary
This document describes the proposed resolution on some comments related to OFDM regarding the scrambler, scrambler seeds, and header check sequence.
The following comments are addressed:
Scrambler: CID#1379, 1380, 1434, 1435, 1436, 1437, 1438, 1449
Scrambler seeds: CID#1035, 1037, 1444, 1445, 1446, 1447, 1448
Header check sequence: 1039, 1045, 1055
Page 2
<author>, <company>

3. Comment resolution for OFDM scrambler
Insert section 6.12b.2.10 which details the operation of the scrambler.
The input to the scrambler is the PSDU bits followed by tail bits and then pad bits.
Scrambler uses PN9 sequence (see Figure 65h)
Whitened bitn = input bitn XOR PN9n
Tail bits after scrambling are reset to all zeros.

4. Comment resolution for OFDM scrambler seed
There are 4 possible scrambler seeds specified in the OFDM header.
Seeds are specified in the following table. The leftmost value of the scrambling seed is placed into the leftmost delay element in Figure 65h.
LSB scrambler
(bit 19 of header)
MSB scrambler (bit 20 of header)
Scrambling seed 1

5. Comment resolution for OFDM scrambler (text)
6.12b.2.10 Scrambler and scrambler seeds
The input to the scrambler is the data bits followed by tail bits and then pad bits. The scrambler uses a PN9 sequence which is shown in Figure 65h. The PN9 scrambler is initialized by one of four seeds. The seed to be used for the scrambler is indicated by 2 bits in the header as shown in Table 75-z. The leftmost value of the scrambling seed is placed into the leftmost delay element in Figure 65h.
Table 75n—Initial seeds to be used for PN9 scrambler
The scrambled bits are found by an XOR operation of each bit of the input bits which are the PSDU+tail+pad bits with the PN9 sequence.
bitn = input bitn XOR PN9n
The tail bits after scrambling are reset to all zeros.
LSB scrambler
(bit 19 of header)
MSB scrambler (bit 20 of header)
Scrambling seed 1

6. Comment resolution for OFDM header check sequence
At the end of section 6.3.4a.3 add the description of the header check sequence.
The header check sequence is calculated using the polynomial
G8(x) = x8 + x2 + x + 1

7. Comment resolution for OFDM header check sequence
Insert at end of 6.3.4a.3
The 1-octet HCS shall be computed using the first 22 bits of the header. The header check sequence shall be calculated using the polynomial G8(x) = x8 + x2 + x + 1.
The HCS is the one's complement of the modulo 2 sum of the two remainders in a) and b):
a) The remainder resulting from [x8(x21+x20+x19+x18+x17+x16+x15+x14)] divided (modulo 2) by G8(x).
b) The remainder resulting from the calculation field contents, treated as a polynomial, multiplied by x8 and then divided (modulo 2) by G8(x).
At the transmitter, the initial remainder of the division shall be preset to all ones and then modified via division of the calculation field by the generator polynomial G8(x). The one’s complement of this remainder is the 1-octet HCS field.