doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Joint Coding and Modulation Diversity for 802.11ah

Date: 2011-11-05

Name Affiliations Address Phone Zhanji Wu Beijing

University of Post and Telecommunication (BUPT)

Xitucheng Road 10, Haidian district, Beijing, China

+86 13126589948

Zhendong Luo China Academy of Telecommunication Research (CATR)

No.52 Hua Yuan Bei Rd., Beijing, China

+86 10 62300171

Yunzhou Li Tsinghua University

Tsinghua Rd. Beijng, China

+86 10 62773363

Authors:

Slide1

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

• 802.11ah shall include support for 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz PHY transmissions. [1]

• An 802.11ah STA shall support reception of 1 MHz and 2 MHz PHY transmissions. [1]

• The 2 MHz PHY transmission shall be an OFDM based waveform consisting of a total of 64 tones (including tones allocated as pilot, guard and DC). This implies a tone spacing of 31.25 kHz. The tone spacing for all other bandwidths PHY transmissions shall be same as the tone spacing in the 2 MHz PHY transmission.

• Compared with 802.11ac, Tgah has smaller bandwidth and tone spacing .

Background

Slide2

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

• Based on IEEE 802.11-11/0883r1[2]

• TGah outdoor channel model

3GPP/3GPP2 SCM (spatial channel model) shall be used to evaluate 11ah outdoor MIMO link and system performance.

• TGah indoor channel model

The proposed indoor channel model for TGah is based on the 802.11n channel models, which have been widely used in the 802.11 Standard development.

802.11ah Channel Model

Slide3

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Abstract• Doc.IEEE802.11-11/0069r0[3] proposed to use TGac

features as a basis for Tgah.

• Doc. IEEE 802.11-10/0336r0 [4] has demonstrated the performance advantages of Joint Coding and Modulation Diversity technique in 802.11 ac system.

• Based on our recent research, Joint Coding and Modulation Diversity technique can also improve the overall performance of 802.11ah system, especially in MIMO-OFDM scenario. Therefore, we recommend to introduce this technique to 802.11ah system.

Slide 4

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Proposed Transmitter/Receiver Block Diagram

NOTES— Red blocks are our proposed amendment.—The number of transmit chains can be not equal to the number of space-time streams— SVD-precoding, codebook-percoding and non-precoding are all supported.

Slide 5

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

• In the amendment, we use rotational modulation method to combine with time diversity of channel coding, spatial diversity of MIMO and frequency diversity of OFDM, which is named joint coding and modulation diversity (JCMD) .

• As compared with JCMD, the processing scheme in IEEE 802.11n/ac Standard is named bit interleaved coded modulation (BICM) for simplicity.

• Amendment and simulation are based on the document IEEE 802.11n-2009 ,IEEE 802.11-09/0992r18 and Draft 802.11ac D1.1.

Slide 6

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

• According to rotational matrix ， rotate the conventional modulated symbol.

• The relationship between conventional modulated complex symbol A + j*B and the rotational modulated complex symbol X + j*Y is shown in equation:

• where A and B are the I (in-phase) and Q (quadrature) component of the normal QAM, respectively; X and Y are the I and Q component of rotated QAM, respectively

Basic principle of the rotational modulation

iu

cos sin

sin cos

X A

Y B

Slide 7

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

It is already used in IEEE 802.11ad.

An example of rotated QPSK

14

00

10

11

01

I

Q

Slide8

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Our Proposed Rotation Matrix to 802.11ah system

Modulation Proposed Rotation Matrix

QPSK

16QAM

64QAM

256QAM

3 11

1 310Q

4 11

1 417Q

2 11

1 25Q

7 11

1 750Q

Slide 9

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Basic principle of the Spatial Interleaving• In this process , denotes rotated symbol on the stream at

time sample. So the interleaving is usual spiral layer interleaving process among all streams at the same time. The method is as follow:

• Where is the number of spatial streams.• For example, consider the case, =4:

• Corresponding, uses the inverse algorithm at the receiver as follow:

itx

Nss

' , ' [( ) mod ]i it t ssy i i t N y

' ', ' [( ) mod ] , 0,1... 1i it t ss ssi i t N i i N x x

thi tht

1 1 1 11 2 3 42 2 2 21 2 3 43 3 3 31 2 3 44 4 4 41 2 3 4

(a)

x x x x

x x x x

x x x x

x x x x

1 4 3 21 2 3 42 1 4 31 2 3 43 2 1 41 2 3 44 3 2 11 2 3 4

(b)

x x x x

x x x x

x x x x

x x x x

Nss

Slide 10

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Basic principle of the Spatial Q-Interleaving

• In the spatial Q-interleaving process, I components of the complex signals are unchanged, while Q components of signals are changed as follows:

• That is to say, Q component on stream i will be moved to the stream (Nss-i-1).

• So, it is just a simple reverse interleaver, and the interleaver length is the number of the spatial streams.

k

k 1k i

k i

I I i

Q Q Nss i

Stream

0Q 1SSNQ 1Q

1SSNQ 0Q2SSN

Q

Stream

2SSNQ

1Q

Slide 11

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Basic principle of the Frequency domain Q-interleaveing

• In the frequency domain Q-interleaving process, the I components of the complex signals are unchanged, while Q components of signals are changed as follows:

• is the number of subcarriers for data.• That is to say, Q component on subcarrier i will be moved to the subcarrier• .

• So, it is just a simple cyclic-shift interleaver, and the linterleaver length is the number of data subcarriers .

SDN

k

k ( / 2 ) modk i

k i SD SD

I I i

Q Q N i N

F

0Q / 2 1SDNQ 1SDN

Q / 2SDNQ

F

/ 2SDNQ / 2 1SDN

Q 0Q1SDN

Q

( / 2 ) modSD SDN i N

Slide 12

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Basic principle of demodulation

• Due to spatial Q-interleaving and frequency Q-interleaving, fading coefficient of I component is usually different from that of Q component .

Q

Received Point

H1

H2

d2

d3

d4

d1

10

11

01

00

I

2H

1H

Slide 13

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Basic principle of demodulation

• For example, consider the R-QPSK （ rotational quadrature phase-shift keying ） :

• The procedure for demodulation is shown as follows:

1) Compute the distance between the received point and each reference constellation point. The relationship between the reference constellation point and the rotational constellation point is shown as follows:

so

' '( , )I QS S( , )I QS S

' '2 1( , ) ( , ) (1)I Q I QS S H S H S

( , )I QR R

2 ' 2 ' 2( ) ( ) (2)I I Q Qd R S R S

1 4d ~ d

Slide 14

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Basic principle of demodulation• 2) Compute the Likelihood ratio (LLR) for every bit. The LLR is the

input of the decoder.• For the first bit :

• For the second bit:

• There is also a simplified algorithm to compute the LLRs:

• Similarly, for M-ary QAM(Quadrature amplitude modulation), we should compute LLRs for bits.

2 21 4

2 2

2 23 2

2 2

exp exp2 2

( ) log (1)

exp exp2 2

d d

LLR ad d

2 2

1 22 2

2 23 4

2 2

exp exp2 2

( ) log (2)

exp exp2 2

d d

LLR bd d

2Log M

2 2 2 22 3 1 4

2

min( , ) min( , )( ) (3)

2

d d d dLLR a

2 2 2 23 4 1 2

2

min( , ) min( , )( ) (4)

2

d d d dLLR b

2Log M

Slide 15

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Simulation Parameters

Parameters Values

PHY scheme OFDM

Antenna scheme 2*2

Length of FFT 64

Number of subcarriers 56

Number of data subcarriers

52

Code Type BCC

Channel Model802.11n channel models (Indoor)

3GPP SCM channel model (Outdoor)

Code Rate 3/4, 5/6

Modulation Type QPSK 16QAM 64QAM

Bandwidth 2 MHz

Sub-carrier spacing 31.25 kHZ

Channel estimation Ideal channel estimation

Slide 16

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

MCS (modulation and coding scheme)（ 2*2）

MCS MODULATION CODE RATE

Number of OFDM

symbols per frame

Block Size

2 QPSK 3/4 6 1248

4 16-QAM 3/4 4 1668

7 64-QAM 5/6 2 1248

Slide 17

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Indoor Channel Model LOS case E [2],BCC

Parameters Value222

Carrier Frequency 0.8 GHzCode Rate 3/4, 5/6

Modulation Type QPSK,16QAM,64QAMBandwidth 2.0 MHz

Sample Time 500 nsFFT 64

Subcarrier Bandwidth 31.25 kHz

CP 16Speed 1.2 km/h

TXN

STSNRXN

Gain dB (FER=0.1)

QPSK 6

16QAM 5.6

64QAM 5

Slide 18

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Outdoor Channel Model 3GPP SCM[3],BCC

Parameters Value222

Carrier Frequency 0.8 GHzCode Rate 3/4, 5/6

Modulation Type QPSK,16QAM,64QAMBandwidth 2.0 MHz

Sample Time 500 nsFFT 64

Subcarrier Bandwidth 31.25 kHz

CP 16Speed 1.2 km/h

Gain dB (FER=0.1)

QPSK 8

16QAM 7

64QAM 6

TXN

STSNRXN

Slide 19

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Hardware Platform

The platform •Rohde&Schwarz AMU (fading simulator)• 2*FSV(signal analyzer)• 2*SMBV(vector signal generator)•2*PicoChip PC203 Baseband Unit • 2*RRU

Slide 20

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Hardware Simulation Results

• SISO: JCMD obtains 2 dB SNR gain at FER=0.1 as compared with BICM.

6 8 10 12 14 16 1810

-5

10-4

10-3

10-2

10-1

100

LS-QPSK-TU 3 paths | SMBV:-55dBm

S/N

BE

R

BICM-pico

JCMD-picoBICM-C-fixed

JCMD-C-fixed

Parameters Value

Code Turbp

Modulation Type QPSK

Code Rate 3/4

Code Length 768

Channel Model TU 3Path

Speed 0km/h

Channel Estimation LS

Slide 21

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Hardware Simulation Results

2*2 MIMO: JCMD obtains 3.3dB SNR gain at FER=0.1 as compared with BICM.

Parameters Value

Channel Model VA_MIMO_60km/h

Code 3GPP LTE Turbo

Code Rate 3/4

Modulation Type QPSK

Scheme BICM/JCMD

Precoding No-Precoding

Channel Estimation LS, LMMSE

MIMO detection MMSE

Slide 22

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Conclusions

• It is proved that the proposed scheme has the obvious SNR gains over the current scheme, which implies– Larger coverage area

– Lower transmit power

• The proposed scheme is easy to be implemented– Rotated QAM modulation– Q-components Interleaver within one OFDM symbol

• In a word, the proposed scheme is very suitable for TGah to meet the requirement of PAR.

Slide 23

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

References

[1] 11-11-1294-00-00ah-spec-framework-text-of-11ah-bw-modes.pptx

[2] 11-11-0883-01-00ah-Channel-Model-Text.docx

[3] 3GPP TR 25.996 - Technical Specification Group Radio Access Network; Spatial channel model for Multiple Input Multiple Output (MIMO) simulations

[4] 11-11-0069-01-00ah-tgah-Introductory-proposal.ppt

[5] 11-11-0336-00-00ac-joint-coding-and-modulation-diversity-to-802-11ac.ppt

[6]11-11-1137-02-00ah-specification-framework-for-tgah.docx

Slide 24

doc.: IEEE 802.11-11/1536r1

Zhanji Wu, et. Al.

November 2011

Submission

Strawpoll

• Do you accept JCMD as an enhanced coded modulation scheme to be considered for 802.11ah?

-Yes

-No

-Abstain

Slide 25