OFDM Simulation Tutorial

OFDM Simulation Tutorial

연세대학교전기전자공학과

황규호 [email protected]

2/23

Contents

LAB 1 기본적인 OFDM subcarrier signalingLAB 2 Subcarrier signaling과 FFT block을사용한시스템LAB 3 FFT block 을사용한 OFDM

LAB 4 GI 의영향LAB 5 ISI channel 의영향

LAB 6 Van De BeekLAB 7 Minn A & SchmidlLAB 8 Minn BLAB 9 Park Hong

LAB 10 PAPRLAB 11 LS LMMSE channel estimation 비교

3/23

LAB 1 기본적인 OFDM subcarrier signaling

OFDM 신호의생성과복원

– Data가 N개의부반송파에의해변조되어하나의 OFDM 심볼로전송

– Orthogonal principle 에의해각부반송파의신호가복원됨

4/23

LAB 1 기본적인 OFDM subcarrier signaling

0 0.5 1-1

0

1Subcar. #1

-1 0 1-1

0

1Tx ang. #1

0 0.5 1-1

0

1Sub sig. #1

0 0.5 1-1

0

1MF #1

-1 0 1-1

0

1Rx ang. #1

0 0.5 1-1

0

1Subcar. #2

-1 0 1-1

0

1Tx ang. #2

0 0.5 1-1

0

1Sub sig. #2

0 0.5 1-1

0

1MF #2

-1 0 1-1

0

1Rx ang. #2

0 0.5 1-1

0

1Subcar. #3

-1 0 1-1

0

1Tx ang. #3

0 0.5 1-1

0

1Sub sig. #3

0 0.5 1-1

0

1MF #3

-1 0 1-1

0

1Rx ang. #3

0 0.5 1-1

0

1Subcar. #4

-1 0 1-1

0

1Tx ang. #4

0 0.5 1-1

0

1Sub sig. #4

0 0.5 1-1

0

1MF #4

-1 0 1-1

0

1Rx ang. #4

0 0.5 1-5

0

5Tx signal

5/23

효율적인 OFDM 변복조시스템

– OFDM 복조과정에는각반송파에대한 Oscillator 와적분기가필요

– N 이커졌을경우, 구현이매우복잡함

– IFFT/FFT 쌍을이용하면효율적임

LAB 2 Subcarrier signaling과 FFT block을사용한시스템

6/23

LAB 2 Subcarrier signaling과 FFT block을사용한시스템

-1 0 1-1

0

1Tx ang. #1

0 0.5 1-1

0

1Sub sig. #1

-1 0 1-1

0

1Sub sig. #1

-1 0 1-1

0

1Tx ang. #2

0 0.5 1-1

0

1Sub sig. #2

-1 0 1-1

0

1Sub sig. #2

-1 0 1-1

0

1Tx ang. #3

0 0.5 1-1

0

1Sub sig. #3

-1 0 1-1

0

1Sub sig. #3

-1 0 1-1

0

1Tx ang. #4

0 0.5 1-1

0

1Sub sig. #4

-1 0 1-1

0

1Sub sig. #4

-1 0 1-1

0

1Tx ang. #5

0 0.5 1-1

0

1Sub sig. #5

-1 0 1-1

0

1Sub sig. #5

-1 0 1-1

0

1Tx ang. #6

0 0.5 1-1

0

1Sub sig. #6

-1 0 1-1

0

1Sub sig. #6

-1 0 1-1

0

1Tx ang. #7

0 0.5 1-1

0

1Sub sig. #7

-1 0 1-1

0

1Sub sig. #7

0 0.5 1-5

0

5Sum(real)

0 0.5 1-5

0

5Sum(image)

0 5 10-5

0

5IFFT(real)

0 5 10-5

0

5IFFT(image)

0 0.2 0.4 0.6 0.8 1-5

0

5Comparison(real)

0 0.2 0.4 0.6 0.8 1-5

0

5Comparison(image)

0 5 10-10

0

10Real sig.

0 5 10-10

0

10Image sig

7/23

LAB 3 FFT block 을사용한 OFDM

0 5 10 15 20 25 30-1

0

1TX information

0 2 4 6 8 10 12 14 16-1

0

1Freq domain(real)

0 2 4 6 8 10 12 14 16-1

0

1Freq domain(imag)

0 2 4 6 8 10 12 14 16

-1

0

1

Time domain(real)

0 2 4 6 8 10 12 14 16

-1

0

1

Time domain(imag)

0 2 4 6 8 10 12 14 16-2

0

2radio signal

0 2 4 6 8 10 12 14 16

-1

0

1

Freq domain(real)

0 2 4 6 8 10 12 14 16

-1

0

1

Freq domain(imag)

0 5 10 15 20 25 30-1

0

1RX information

8/23

LAB 4 GI 의영향

보호구간이없는 OFDM 시스템의문제

– 채널이이상적이지않은경우 or 시간동기가틀린경우• 인접심볼로인해직교성상실→ ICI 발생

보호구간 (Guard Interval)

– Null 보호구간• 시간동기오차에의한신호왜곡현상

– 순환보호구간 (Cyclic Prefix)• 보호구간보다짧은시간응답을갖는채널에서 ICI 의발생이없음

• 시간동기오차에의해발생되는 ICI 가없음• 위상및크기의왜곡은등화기를이용하여보상가능

9/23

LAB 4 GI 의영향CP OFF CP ON

compensate OFF compensate ON

-1 0 1-1

-0.5

0

0.5

1Tx constellation

140 160 180 200 220 240 260 280 300 320 3400

1

2

3Timing

IFFT signal

GIFFT timing

-1 0 1-1

-0.5

0

0.5

1Rx constellation

-1 0 1-1

-0.5

0

0.5

1Tx constellation

140 160 180 200 220 240 260 280 300 320 3400

1

2

3Timing

IFFT signal

GIFFT timing

-1 0 1-1

-0.5

0

0.5

1Rx constellation

-1 0 1-1

-0.5

0

0.5

1Tx constellation

140 160 180 200 220 240 260 280 300 320 3400

1

2

3Timing

IFFT signal

GIFFT timing

-1 0 1-1

-0.5

0

0.5

1Rx constellation

-1 0 1-1

-0.5

0

0.5

1Tx constellation

140 160 180 200 220 240 260 280 300 320 3400

1

2

3Timing

IFFT signal

GIFFT timing

-1 0 1-1

-0.5

0

0.5

1Rx constellation

10/23

LAB 5 ISI channel 의영향

Offset = -10, CP_on = 1, compensate = 0

-1 0 1-1

-0.5

0

0.5

1Tx constellation

0 2 4 60

0.2

0.4

0.6

0.8

1

ISI channel

140 160 180 200 220 240 260 280 300 320 3400

1

2

3Timing

IFFT signal

GIFFT timing

-2 0 2-2

-1

0

1

2Rx constellation

11/23

LAB 6 Van De Beek

Correlation property - Cyclic prefix

– 연속된 2N+L 개의샘플속에는 N+L 개의샘플로구성된완전한하나의 OFDM 심볼이포함됨

– I 와 I’ 에포함되는시간영역의신호들은서로상관관계를가짐

– 나머지신호들은서로상관관계가없음

12/23

LAB 6 Van De Beek

freqoff = 0.2, Noise_dB = -100

100 200 300 400 500 600 700 800 900 1000 11000

0.5

1

1.5

2

2.5

3Signals

IFFT signal

GI

100 200 300 400 500 600 700 800 900 1000 11000

0.2

0.4

0.6

0.8

1

Timing estimation

interval sum

estimated start point

100 200 300 400 500 600 700 800 900 1000 1100-1

-0.5

0

0.5

1Frequency estimation

frequency

estimated frequency

13/23

LAB 7 Minn A & Schmidl

Schmidl의동기방법

– Preamble 설계를통한적용

– 한심볼내에반복되는패턴을갖게함

– 보호구간내에서는상관값이일정구간에서평평해짐

N/2

14/23


Minn method A 동기방법

– 새로운 preable설계를통한동기방법

– Schmidl동기방법에서의문제점해결

– Schmidl의동기알고리즘에서평균을취하는방법을바꿈

15/23



100 200 300 400 500 600 700 800 900 1000 11000

0.5

1

1.5

2

2.5

3Signals

IFFT signal

GI

100 200 300 400 500 600 700 800 900 1000 11000

0.2

0.4

0.6

0.8

1

Timing estimation

Schmidl

Minn Aestimated start point

100 200 300 400 500 600 700 800 900 1000 1100-1

-0.5

0

0.5

1Frequency estimation

frequency

estimated frequency

16/23

LAB 8 Minn B

Training symbol method

– 새로운 preamble 구조제안

– A 는 N/4 의길이로 PN 신호를 IFFT 한결과

17/23

LAB 8 Minn B


100 200 300 400 500 600 700 800 900 1000 11000

0.5

1

1.5

2

2.5

3Signals

IFFT signal

GI

100 200 300 400 500 600 700 800 900 1000 11000

0.2

0.4

0.6

0.8

1

Timing estimation

interval sum


18/23

LAB 9 Park Hong

Park 의동기방법

– 새로운 preamble 설계를통한동기방법

– Preamble 에 symmetric, complex-conjugate sample 을이용함

GI A B B* A* GI

19/23

LAB 9 Park Hong


100 200 300 400 500 600 700 800 900 10000

0.5

1

1.5

2

2.5

3Signals

IFFT signal

GI

100 200 300 400 500 600 700 800 900 10000

0.2

0.4

0.6

0.8

1

Timing estimation

interval sum


20/23

LAB 10 PAPR

Peak power problem

– OFDM 시스템의단점중하나는기저대역신호의무작위성

– 변/복조기내의모든회로들이랜덤한신호를처리해야하는어려움

– 무작위성의측정 : PAPR (peak power to average power ratio)

– OFDM 신호의전력이증폭기의선형영역을넘어서면, 그 amplitude 를 Clipping 하여전송함

– Clipping 은신호 power 를감소시키므로, BER 성능열화발생

21/23

LAB 10 PAPR

PAPR = 2dB PAPR = 5dB

0 2 4 6 8 1010

-4

10-3

10-2

10-1

100

OFDM symbol

SNR

BE

R

Uncliped

PAPR=2dB

0 500 10000

2

4

6

8OFDM symbol

0 500 10000

2

4

6

8After clipping

0 2 4 6 8 1010

-4

10-3

10-2

10-1

100

OFDM symbol

SNRB

ER

Uncliped

PAPR=5dB

0 500 10000

2

4

6

8OFDM symbol

0 500 10000

2

4

6

8After clipping

22/23

LAB 11 LS LMMSE channel estimation 비교

LS estimation

– 간단한추정방법

LMMSE estimation

– 잡음의통계적특성을파악할수있을때,최적의 estimator

– LS estimator 를이용하는방법

23/23

LAB 11 LS LMMSE channel estimation 비교

SNR = 0 dB SNR = 15 dB

errorls = 1.0098errormmse = 0.9635

errorls = 0.8994errormmse = 0.8967

0 5 10 1510

-5

10-4

10-3

10-2

10-1

100

Channel Estimation

SNR

BE

R

LS

LMMSE

0 2 4 60

1

2Channel

0 2 4 60

1

2LS estimation

0 2 4 60

1

2MMSE estimation

0 5 10 1510

-4

10-3

10-2

10-1

100

Channel Estimation

SNR

BE

R

LS

LMMSE

0 2 4 60

1

2Channel

0 2 4 60

1

2LS estimation

0 2 4 60

1

2MMSE estimation

Documents

OFDM Simulation Tutorial