FPGA Implementation of Carrier Frequency Offset Estimation in B3G

MIMO OFDM System

Speaker: Yu He

From: Beijing University of Posts and Telecommunications (BUPT),WTI lab

Email:susi104@gmail.com

Outline

1. Background introduction Project background System model

2. My frequency synchronization algorithm

3. My simplified frequency synchronization implementation in MIMO-OFDM system

Background----FuTURE project

Future Technologies for Universal Radio Environment Supported by the national 863 high-tech program China B3G network research and development Members :BUPT/Tsinghua/SJTU/SEU etc,also members of B3G spe

cial group of CCSA. Aims: Meet application requirement around 2010: frequency

efficiency is up to 10b/s/Hz,bandwidth is 20MHz,support IPv6, BER lower than 10e-6 for 100Mbps,vehicular speed 250km/h,flexible air interface can take full advantage of possible radio resources

Two branches: TDD & FDD

B3G-TDD demo system architecture 3 MT、 2 AP、 1control domain

support all IP package transmission， data rate is up to 100Mbps

high vehicular speed :250km/h

high transmission performance， BER<10-6

high spectrum efficiency，5b/s/Hz.

high power efficiency， transmission power: 10dB lower than that of 3GIP Íø

A P 1 A P 2

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Inte r ne t

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Key technologies of B3G-TDD PHY layer(1)

Frame structure:

key technologies of B3G-TDD PHY layer(2)

OFDM: has high spectrum efficiency due to orthogonal subcarrier and low implementation complexity with the help of FFT.

MIMO: taking advantage of spatial resources, can provide spectrum efficiency as high as 20-40b/s/Hz

Others: 64QAM,LDPC,Turbo,etc

B3G-TDD system performance

B3G-TDD MIMO-OFDM system

System model

IF F T

IF F T

T im in gS y n ch ro n izat io n 1 1

S 1 (k )

S Q (k )

R 1 (k )

...

R L(k )

......F F T

freq u en cys y n ch ro n izato n 1 1

T im in gS y n ch ro n izat io n L1

F F T

freq u en cys y n ch ro n izato n L1

T im in gS y n ch ro n izat io n 1 Q

freq u en cys y n ch ro n izato n 1 Q

T im in gS y n ch ro n izat io n LQ

freq u en cys y n ch ro n izato n LQ

Frequency synchronization of MIMO-OFDM B3G-TDD system

What’s synchronization What’s the result if no accurate

synchronization ISI,FFT displacement ICI, carrier waveform distorting

Frequency synchronization algorithm

training sequences for CFO estimation in OFDM frame structure

GP GPDL SYN UL SYN

TimingCodeCP

Coarse frequencyoffet estimation

TimingRecovery

TimingRecovery

T1CP T2 CP2 TI1 TI2

Fine frequencyoffet estimation

Frequency Synchronization

'ˆ( ( ))ˆ angle P d

F

Using the value of coarse frequency estimation to compensate TI1 and TI2

/ 2 1

0

ˆ ˆ ˆ( ) ( ) ( )2

N

n

NP d r d n r d n

Here,

· Fine frequency offset estimation:

2

)(~)(~

ˆ

1

02

"1

N

nTT nrnrangle

F

· Coarse frequency offset estimation:

Two steps Estimation range( 1/ ,1/ )s sT T

Estimation range( 1/ 2 ,1/ 2 )s sT T

Simulation condition:Fig.3: 6-path Rayleigh channel, v=120km/h vs. 250km/h, simulation length is 500 frames,normalized frequency offset is 0.5;

Results of Frequency Synchronization

Fig.3:MSE for frequency offset(120km/h vs. 250km/h)

Implementation of frequency synchronization

R AM( T 1 1 r ea l)

R AM( T 1 1

im ag e)

R AM( T 1 2 r ea l)

R AM( T 1 2

im ag e)

M u ltip le£¨ I 1 * I 2 £©

M u tip le£¨ Q 1 * Q 2

£©

M u ltip le£¨ I 1 * Q 2 £©

M u ltip le£¨ I 2 * Q 1 £©

Ad d£¨ r ea l£©

Ad d£¨ im ag e

£©

+

+

+

-

R AM( r ec ip r o c a l

tab le )M u ltip le£¨ Q /I £©

R AM( ar c tan X

tab le )

d a ta _ re a l

data_ im ag e

M U X

M U XM u ltip le

dN

FN

2

C F O

d

t

N

FNRfff

2

arg

L

ndt NnrnrR

0

* )()(

My simplified scheme for MIMO-OFDM frequency synchronization

IF F T

IF F T

T im in gS y n ch ro n izat io n 1 1

S 1 (k )

S Q (k )

R 1 (k )

...

R L(k )

......

F F T

freq u en cys y n ch ro n izato n 1 1

T im in gS y n ch ro n izat io n L1

F F T

freq u en cys y n ch ro n izato n L1

T im in gS y n ch ro n izat io n 1 Q

freq u en cys y n ch ro n izato n 1 Q

T im in gS y n ch ro n izat io n LQ

freq u en cys y n ch ro n izato n LQ

Q×L×Y

R A M

R A M

R A M

Fin ee s tim a tio n 1

C o a r see s tim a tio n 1

R e c ie v e A n te n n a 1

......

C o a r see s tim a tio n 2

C o a r see s tim a tio n Y

Fin ee s tim a tio n 2

Fin ee s tim a tio n L

R e c ie v e A n te n n a 2

R e c ie v e A n te n n a L

T im esy n c h r o n iza to n

T im esy n c h r o n iza to n

T im esy n c h r o n iza to n

L×Y modulesonly RX 1 calculates the Y users’ coarse frequency offsets ,the other antennas share the result and only need to do their different fine estimation ,so Y course frequency offset estimation modules and L fine frequency offset estimation modules are sufficient

Frequency synchronization implementation result

Services demo

frequency synchronization implementation

Up to 14 channels

case

Xilinx VirtexII Pro50 FPGA

Future work

How to save more resourcesSimplified implementation scheme in

distributed MIMO systems

That’s all!Thank you for your listening!