IEEE C802.16m-10/0316r1
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Proposed text to disambiguate the interpretation of burst CRC encoding (16.3.11)
Date
Submitted
2010-3-14
Source(s)
Minh-Anh Q. Vuong and
Yi Hsuan
Intel Corporation
Yu-Chuan Fang, Zheng Yan-Xiu, Chang-Lan
Tsai, Chung-Lien Ho
ITRI
Re:
Category: AWD comments / Area: Chapter 16.3.11.1.1
“Comments on AWD 16.3.11.1.1 Burst CRC encoding”
Abstract
This contribution proposes editorial change to disambiguate the burst CRC encoding procedure
Purpose
To be discussed and adopted by TGm for the 802.16m amendment
Notice
This document does not represent the agreed views of the IEEE 802.16 Working Group or any
of its subgroups. It represents only the views of the participants listed in the “Source(s)” field
above. It is offered as a basis for discussion. It is not binding on the contributor(s), who
reserve(s) the right to add, amend or withdraw material contained herein.
Release
The contributor grant a free, irrevocable license to the IEEE to incorporate material contained in
this contribution, and any modifications thereof, in the creation of an IEEE Standards
publication; to copyright in the IEEE’s name any IEEE Standards publication even though it
may include portions of this contribution; and at the IEEE’s sole discretion to permit others to
reproduce in whole or in part the resulting IEEE Standards publication. The contributor also
acknowledges and accepts that this contribution may be made public by IEEE 802.16
Patent
Policy
The contributor is familiar with the IEEE-SA Patent Policy and Procedures:
<http://standards.ieee.org/guides/bylaws/sect6-7.html#6>
<http://standards.ieee.org/guides/opman/sect6.html#6.3>.
and
Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and
<http://standards.ieee.org/board/pat>.
1
IEEE C802.16m-10/0316r1
Proposed text to disambiguate the interpretation of burst CRC
encoding (16.3.11)
Minh-Anh Q. Vuong and Yi Hsuan
Intel Corporation
1. Statement of Problem
The first three paragraphs of 802.16m-D4 Section 16.3.11.1.1 are as below:
Paragraph 1
Cyclic Redundancy Code (CRC) bits are used to detect errors in the received packets. A 16-bit burst
CRC, for which CRC16-CCITT as defined in ITU-T recommendation X.25 is used, shall be appended to
the data burst using the cyclic generator polynomial in Equation (298) if the number of FEC block
partitions KFB is larger than 1:
(Equation 298 – Defining gDB-CRC(D))
Paragraph 2
Denote the bits of the input data burst by d1 d 2 ... d N PL where d1 is the MSB and NPL is the size of
the input data burst. Denote the parity bits produced by the burst CRC generator by p1 p2 … p16. The
burst CRC encoding is performed in a systematic form, which means that in GF(2), the polynomial in
Equation (299):
(Equation 299 – Describing the input data with appended 16-bit checksum)
yields a remainder equal to 0 when divided by gDB-CRC(D).
Paragraph 3
As an example, if the input data of 4 bytes in hexadecimal is 0x1234ABCD, the burst CRC encoding
above yields 16-bit burst CRC of 0x5DF0. Note that this is just for the purpose of giving an example for
the burst CRC encoding itself and the burst CRC shall be appended only when the data burst is
partitioned into multiple FEC blocks (or KFB > 1).
The first paragraph specifies for burst CRC the CRC16-CCITT polynomial to be used and the encoding
procedure as per ITU-T recommendation X.25. The X.25 recommendation consists of:
1. Preset the CRC calculation register to 0xFFFF; that is equivalent to replacing the first 16 bits of the
payload with their one’s complements.
2
IEEE C802.16m-10/0316r1
2. Augment the thus obtained message by appending 16 zeros.
3. Compute the GF(2) remainder by gDB-CRC.
4. The checksum is the one’s complement of the remainder obtained in step 3.
The second paragraph, while intended to illustrate the encoding procedure, fails to include the steps 1 and 4 as
described above.
The third paragraph provides an example that matches the X.25 recommendation and disagrees with the
elaboration in second paragraph.
To resolve the ambiguity, the second paragraph should look like the following:
Denote the bits of the input data burst by d1 d 2 ... d N PL where d1 is the MSB and NPL is the size of
the input data burst. Denote the parity bits produced by the burst CRC generator by p1 p2 … p16. The
burst CRC encoding is performed in a systematic form, which means that in GF(2), the polynomial in
Equation (299):
~
~
d1 D N PL 15  ...  d16 D N PL  d17 D N PL 1  ...  d N PL D16  ~
p1 D15  ...  ~
p15 D  ~
p16
yields a remainder equal to 0 when divided by gDB-CRC(D) and where ~
x denotes the one’s complement
of x.
However because P802.16 Rev 2 has already used the same CRC in several places with a simple reference to
CRC16-CCITT as defined in ITU-T Recommendation X.25, there is no need to change the CRC or add more
description on how it’s generated. We therefore propose to remove paragraph 2 from P802.16m/D4 to eliminate
the ambiguity.
-------------------------------
Start Text Proposal ---------------------------------------------------
[ Recommended AWD Text Proposal (16.3.11.1.1, page 676, line 33) ]
Denote the bits of the input data burst by d1 d 2 ... d N PL where d1 is the MSB and NPL is the size of
the input data burst. Denote the parity bits produced by the burst CRC generator by p1 p2 … p16. The
burst CRC encoding is performed in a systematic form, which means that in GF(2), the polynomial in
Equation (299):
d1 D N PL 15  d 2 D N PL 14  ...  d n D16  p1 D15  p 2 D14  ...  p15 D  p16
yields a remainder equal to 0 when divided by gDB-CRC(D).
-------------------------------------- End of Text Proposal -------------------------------------------
3
(299)