OFDM packing and LDPC framing for constellation shaping in NG WLANs
An apparatus for a station (STA) configured for operating in a next-generation (NG) wireless local area network (WLAN) comprises the processing circuitry configured to modify probabilities of constellation points to generate a more Gaussian distribution. In these embodiments, for LDPC framing and OFDM packing, the transmitter circuitry may be configured to compute a number of output bits (b out ) to be transmitted based on a number of payload bits (b in ) at an output of a shaping encoder, a shaping rate (r shaping ), and an overhead percent (B overhead ). A shaping gain of up to 1.53 dB may be achieved. A new shaping encoder is provided to address the issue that the number of bits is not fixed.
1. An apparatus for a station (STA) configured for operating in a next-generation (NG) wireless local area network (WLAN), the apparatus comprising:
transmitter circuitry, including processing circuitry; and memory,
wherein for LDPC framing and OFDM packing, the transmitter circuitry is configured to divide payload bits into LDPC codewords, add shortening bits, and map a coded bit stream into QAM symbols and into OFDM tones for transmission,
wherein for the LDPC framing and OFDM packing, the transmitter circuitry is configured to:
compute a number of output bits (b out ) to be transmitted based on a number of payload bits (b in ) at an output of a shaping encoder, a shaping rate (r shaping ), and an overhead percent (B overhead );
calculate a number of OFDM symbols (N sym ) based on the number of output bits (b out ) to be transmitted and a number of data bits per OFDM symbol (N dbps );
calculate a number of LDPC codewords (N CW ) based on a number of codebits per LDPC codeword (N LDPC ), the code rate (R ldpc ), and the number of output bits (b out );
calculate a number of shortening bits (N shrt ) to be appended to a LDPC codeword based on the number of output bits (b out ), a number of shorting bits per codeword (N SPCW ) and a number of codewords with additional shorting bits (N SPCW1 );
append a number of repetition bits (N rep ) after LDPC encoding based on whether an LDPC code rate matches a ratio between amplitude bits and sign bits of a target QAM level; and
perform OFDM packing by adding the number of repetition bits (N rep ) after interleaving to fill the number of OFDM symbols (N sym ) including adding an additional OFDM symbol when a number of total coded bits (N TCB ) does not be fit into the number of OFDM symbols (N sym ).
2. The apparatus of claim 1 , wherein the number of OFDM symbols (N sym ) is calculated using the following equation:
N
sym
=
⌈
b
out
N
dbps
⌉
,
and
wherein the number of LDPC codewords (N CW ) is calculated using the following equation:
N
CW
=
⌈
b
out
N
LDPC
R
Idpc
⌉
.
3. The apparatus of claim 2 , wherein the number of shortening bits (N shrt ) to be appended to a LDPC codeword and the number of shorting bits per codeword (N SPCW ) are calculated using the following equations:
N
shrt
=
max
(
0
,
(
N
CW
·
N
LDPC
·
R
ldpc
)
-
b
out
)
N
spcw
=
⌊
N
shrt
N
CW
·
(
M
pam
-
1
)
⌋
(
M
pam
-
1
)
,
and
the number of codewords with additional shorting bits (N SPCW1 ) is calculated using the following equation:
N spcw1 =rem( N shrt ,N CW ·( M pam −1)).
4. The apparatus of claim 3 , wherein the number of repetition bits to be appended after LDPC encoding is equal to the number of shortening bits when the LDPC code rate matches the ratio between amplitude bits and sign bits of the target QAM level, and
when the LDPC code rate does not match the ratio between amplitude bits and sign bits of the target QAM level, repetition bits are appended, or puncturing is applied so that the ratio between the amplitude bits and sign bits meets the target QAM level.
5. The apparatus of claim 4 , wherein padding bits are added to the number of payload bits (b in ) to calculate the number of OFDM symbols (N sym ) based on the shaping rate (r shaping ) using the following equation:
b in =b out ·r shaping .
6. The apparatus of claim 5 , wherein the number of repetition bits (N rep ) to completely fill up the number of OFDM symbols (N sym ) is calculated using the following equation:
N rep =N sym ·N CBPS −N TCB .
7. The apparatus of claim 1 , wherein the transmitted circuitry is configured to compute the number of output bits (b out ) using the following equation:
b
out
=
⌈
le
4
·
(
4
3
+
0.01
)
⌉
=
⌈
le
4
r
shaping
⌉
,
where
r
shaping
=
(
4
3
+
0.01
)
-
1
.
8. The apparatus of claim 7 , wherein the processing circuitry comprises a baseband processor.
9. The apparatus of claim 8 wherein the transceiver circuitry is configured to be coupled to two or more antennas for a MIMO transmission of the number of OFDM symbols (N sym ).
10. The apparatus of claim 9 , wherein the memory is configured to store the number of OFDM symbols (N sym ).
11. A non-transitory computer-readable storage medium that stores instructions for execution by processing circuitry a station (STA) for operating in a next-generation wireless local area network (WLAN), the instructions to configure the STA for LDPC framing and OFDM packing, wherein transmitter circuitry is configured by the processing circuitry to divide payload bits into LDPC codewords, add shortening bits, and map a coded bit stream into QAM symbols and into OFDM tones for transmission,
wherein for the LDPC framing and OFDM packing, the transmitter circuitry is configured to:
compute a number of output bits (b out ) to be transmitted based on a number of payload bits (b in ) at an output of a shaping encoder, a shaping rate (r shaping ), and an overhead percent (B overhead );
calculate a number of OFDM symbols (N sym ) based on the number of output bits (b out ) to be transmitted and a number of data bits per OFDM symbol (N dbps );
calculate a number of LDPC codewords (N CW ) based on a number of codebits per LDPC codeword (N LDPC ), the code rate (R ldpc ), and the number of output bits (b out );
calculate a number of shortening bits (N shrt ) to be appended to a LDPC codeword based on the number of output bits (b out ), a number of shorting bits per codeword (N SPCW ) and a number of codewords with additional shorting bits (N SPCW1 );
append a number of repetition bits (N rep ) after LDPC encoding based on whether an LDPC code rate matches a ratio between amplitude bits and sign bits of a target QAM level; and
perform OFDM packing by adding the number of repetition bits (N rep ) after interleaving to fill the number of OFDM symbols (N sym ) including adding an additional OFDM symbol when a number of total coded bits (N TCB ) does not be fit into the number of OFDM symbols (N sym ).
12. The non-transitory computer-readable storage medium of claim 11 , wherein the number of OFDM symbols (N sym ) is calculated using the following equation:
N
sym
=
⌈
b
out
N
dbps
⌉
,
and
wherein the number of LDPC codewords (N CW ) is calculated using the following equation:
N
CW
=
⌈
b
out
N
LDPC
R
ldpc
⌉
.
13. The non-transitory computer-readable storage medium of claim 12 , wherein the number of shortening bits (N shrt ) to be appended to a LDPC codeword and the number of shorting bits per codeword (N SPCW ) are calculated using the following equations:
N
shrt
=
max
(
0
,
(
N
CW
·
N
LDPC
·
R
ldpc
)
-
b
out
)
N
spcw
=
⌊
N
shrt
N
CW
·
(
M
pam
-
1
)
⌋
(
M
pam
-
1
)
,
and
the number of codewords with additional shorting bits (N SPCW1 ) is calculated using the following equation:
N spcw1 =rem( N shrt ,N CW ·( M pam −1)).
14. The non-transitory computer-readable storage medium of claim 13 , wherein the number of repetition bits to be appended after LDPC encoding is equal to the number of shortening bits when the LDPC code rate matches the ratio between amplitude bits and sign bits of the target QAM level, and
when the LDPC code rate does not match the ratio between amplitude bits and sign bits of the target QAM level, repetition bits are appended, or puncturing is applied so that the ratio between the amplitude hits and sign bits meets the target QAM level.
15. The non-transitory computer-readable storage medium of claim 14 , wherein padding bits are added to the number of payload bits (b in ) to calculate the number of OFDM symbols (N sym ) based on the shaping rate (r shaping ) using the following equation:
b in =b out ·r shaping .
16. The non-transitory computer-readable storage medium of claim 15 , wherein the number of repetition bits (N rep ) to completely fill up the number of OFDM symbols (N sym ) is calculated using the following equation:
N rep =N sym ·N CBPS −N TCB .
17. The non-transitory computer-readable storage medium of claim 11 , wherein the transmitted circuitry is configured to compute the number of output bits (b out ) using the following equation:
b
out
=
⌈
le
4
·
(
4
3
+
0.01
)
⌉
=
⌈
le
4
r
shaping
⌉
,
where
r
shaping
=
(
4
3
+
0.01
)
-
1
.