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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANS)
Submission Title: [The relationship between DAC and TX LPF to satisfy the transmit PSD mask of MB-OFDM]
Date Submitted: [July 2004]Revised: []
Source: [Sang-sung Choi, Cheol-Ho Shin] Company [Electronics and Telecommunications Research Institute] Address [161 Gajeong-dong, Yuseong-gu, Daejeon, 305-350 Korea] Voice : [+82-42-860-6722], FAX : [+82-42-860-5199], E-mail [sschoi@etri.re.kr]
Re: [Technical contribution]
Abstract: [This presentation presents the performance according to several TX LPF used to satisfy the Transmit PSD mask of MB-OFDM UWB system]
Purpose: [Technical contribution to analyze the relationship between DAC and TX LPF to satisfy the transmit PSD mask proposed for MB-OFDM UWB system]
Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual or organization. The material in this document is subject to change in form and content after further study. The contributor reserves the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
July 2004 doc.: IEEE 802. 15-04-0322-00-003a
July 2004
ETRISlide 2Submission
doc.: IEEE 802.15-04-0322-00-003a
The relationship between DAC and TX LPFto satisfy the transmit PSD mask of MB-
OFDM
Sang-Sung Choi (sschoi@etri.re.kr)
Cheol-Ho Shin (chshin@etri.re.kr)
E T R I
www.etri.re.kr
July 2004
ETRISlide 3Submission
doc.: IEEE 802.15-04-0322-00-003a
Introduction
128IFFT
128FFT
AddZP,
Guardinterval
RemoveZP,
Guardinterval
Time DomainFreq. Domain Freq. Domain
DAC ADC
UWB Channel
TX LO RX LO
TX LPF
The TX LPF is very important to determine the transmit PSD mask of MB-OFDM UWB system.
Two methods are considered to design the TX LPF satisfying the transmit PSD mask. - fix 528MHz sampling rate of DAC , and design high order TX LPF
- increase sampling rate of DAC, and reduce the order of TX LPF
July 2004
ETRISlide 4Submission
doc.: IEEE 802.15-04-0322-00-003a
Transmit PSD mask of MB-OFDM UWB system
A: 260 MHz -> 0 dBr bandwidth not exceeding 260MHz B: 285 MHz -> -12 dBrC: > 330 MHz -> -20dBr
-12 dB
-20 dB
A B C
July 2004
ETRISlide 5Submission
doc.: IEEE 802.15-04-0322-00-003a
Power spectral density at 128 IFFT output
0 dBr
- 12 dBr
- 20 dBr
285MHz 330MHzf
Transmit PSD mask
PSD at IFFT output
The TX LPF design is not easy to satisfy the Transmit PSD mask of MB-OFDM.
July 2004
ETRISlide 6Submission
doc.: IEEE 802.15-04-0322-00-003a
Power spectral density at DAC output
0 dBr
- 12 dBr
- 20 dBr
285MHz 330MHzf
Transmit PSD maskPSD at DAC output
The characteristic of DAC is similar to that of LPF, it can help to design the TX LPF.
July 2004
ETRISlide 7Submission
doc.: IEEE 802.15-04-0322-00-003a
Measurement for DAC Characteristic
The characteristic of DAC as LPF is verified from PSD of OFDM system, the OFDM system used 2 over-sample rate at DAC.
PSD between DAC and TX LPF
PSD after TX LPF
July 2004
ETRISlide 8Submission
doc.: IEEE 802.15-04-0322-00-003a
The PSD characteristics of several TX LPFs
The PSD characteristics of Several 5th order LPFs used to satisfy the Transmit PSD mask.Three types all don’t satisfy the transmit PSD mask by itself
Butterworth 5차
Chebyshev Type I 5 차
Chebyshev Type II 5 차
July 2004
ETRISlide 9Submission
doc.: IEEE 802.15-04-0322-00-003a
5th order Butterworth
Ideal
Before TX LPF
After TX LPF
3dB Bandwidth = 260MHz
July 2004
ETRISlide 10Submission
doc.: IEEE 802.15-04-0322-00-003a
5th order Chebyshev Type I
Ideal
3dB Bandwidth = 260MHzThe passband ripple = 0.5dB
Before TX LPF
After TX LPF
July 2004
ETRISlide 11Submission
doc.: IEEE 802.15-04-0322-00-003a
5th order Chebyshev Type II
Ideal
3dB Bandwidth = 260MHzThe stopband ripple = 10 dB
Before TX LPF
After TX LPF
July 2004
ETRISlide 12Submission
doc.: IEEE 802.15-04-0322-00-003a
Summary of the 9th order TX LPFs
Chebyshev Type I 9 차
Butterworth 9 차
Chebyshev Type II 9 차
Ideal
After TX LPF : 9th order Butterworth
Apply several 9th order TX LPF to satisfy the transmit PSD mask
Before TX LPF
July 2004
ETRISlide 13Submission
doc.: IEEE 802.15-04-0322-00-003a
2 times over-sampling at DAC
Ideal
2 times over sample rate is used at DAC to design TX LPF easily.In this case, the degradation of performance is about 1 dB compared to Ideal condition for BER 10-5.
Before TX LPF
After TX LPF
July 2004
ETRISlide 14Submission
doc.: IEEE 802.15-04-0322-00-003a
Summary of simulations
5th 9th2 times
over-sampling
Butterworth 10.7 dB 8.54 dB
7.6 dB
ChebyShev Type I 8.0 dB 8.05 dB
ChebyShev Type II 8.3 dB 9.8 dB
BER 10-5 기준
The higher order LPF is not always superior to the lower order LPF in the performance of system.In case of Chebyshev Type I , the system performance using 5th TX LPF is almost analogous to that using 9th TX LPF
July 2004
ETRISlide 15Submission
doc.: IEEE 802.15-04-0322-00-003a
Summary• There are two methods to satisfy the Transmit PSD
mask of MB-OFDM 1) Fix the DAC sample rate as 528MHz, then give burden to TX
LPF design.
- the higher order TX LPF is necessary
- but 5th order TX LPF is enough to satisfy the transmit PSD
mask considering the characteristic of DAC.
2) Use 2 times over-sample rate at DAC to design the TX LPF.
- Reduce the order of TX LPF
- It has advantage of the performance compared to method 1).
• There are trade-offs between two methods for considering power consumption and gate size etc.
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