1. IEEE P802.22 Wireless RANs Date: 2006-06-20
June 2006
doc.: IEEE xxx
June 2006
ETRI OFDMA Parameters
IEEE P Wireless RANs Date:
Authors:
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Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

2. June 2006
doc.: IEEE xxx
June 2006
Abstract
This presentation describes the OFDMA parameters for IEEE WRAN systems. It includes the system parameters and OFDMA parameters for single channel of 6, 7, and 8 MHz. Moreover, this presentation describes the preamble pattern, pilot pattern, and details of subchannelization.
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

3. System Parameters/Single Channel (6MHz)
June 2006
doc.: IEEE xxx
June 2006
System Parameters/Single Channel (6MHz)
Mode 1K 2K 4K 6K
FFT Size
1024
2048
4096
6144
Bandwidth
(k = 1, 2, …, 6)
k MHz
Sampling Factor
8/7
No. of Used Subcarriers
(including pilot, but not DC)
140 * k
280 * k
560 * k
840 * k
Sampling Frequency
48/7 MHz
Subcarrier Spacing
6.696 kHz(***)
3.348 kHz
1.674 kHz
1.116 kHz
Occupied Bandwidth
6.696 kHz*140*k
3.348 kHz*280*k
1.674 kHz*560*k
1.116 kHz*840*k
Bandwidth Efficiency(*)
93~94 %
FFT Time us us us
896 us
Cyclic Prefix Time(**)
37.33 us
74.66 us
224 us
OFDMA Symbol Time us us us
1120 us
(*) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW
(**) It is assumed that cyclic prefix mode is 1/4.
(***) Italics indicate an approximated value.
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

4. System Parameters/Single Channel (7MHz)
June 2006
doc.: IEEE xxx
June 2006
System Parameters/Single Channel (7MHz)
Mode 1K 2K 4K 6K
FFT Size
1024
2048
4096
6144
Bandwidth
(k = 1, 2, …, 7)
k MHz
Sampling Factor
8/7
No. of Used Subcarriers
(including pilot, but not DC)
120 * k
240 * k
480 * k
720 * k
Sampling Frequency
8 MHz
Subcarrier Spacing
7.812 kHz(***)
3.906 kHz
1.953 kHz
1.302 kHz
Occupied Bandwidth
7.812 kHz*120*k
3.906 kHz*240*k
1.953 kHz*480*k
1.302 kHz*720*k
Bandwidth Efficiency(*)
93~94 %
FFT Time
128 us
256 us
512 us
768 us
Cyclic Prefix Time(**)
32 us
64 us
192 us
OFDMA Symbol Time
160 us
320 us
640 us
960 us
(*) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW
(**) It is assumed that cyclic prefix mode is 1/4.
(***) Italics indicate an approximated value.
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

5. System Parameters/Single Channel (8MHz)
June 2006
doc.: IEEE xxx
June 2006
System Parameters/Single Channel (8MHz)
Mode 1K 2K 4K 6K
FFT Size
1024
2048
4096
6144
Bandwidth
(k = 1, 2, …, 8)
k MHz
Sampling Factor
8/7
No. of Used Subcarriers
(including pilot, but not DC)
105 * k
210 * k
420 * k
630 * k
Sampling Frequency
64/7 MHz
Subcarrier Spacing
8.928 kHz(***)
4.464 kHz
2.232 kHz
1.488 kHz
Occupied Bandwidth
8.928 kHz*105*k
4.464 kHz*210*k
2.232 kHz*420*k
1.488 kHz*630*k
Bandwidth Efficiency(*)
93~94 %
FFT Time
112 us
224 us
448 us
672 us
Cyclic Prefix Time(**)
28 us
56 us
168 us
OFDMA Symbol Time
140 us
280 us
560 us
840 us
(*) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW
(**) It is assumed that cyclic prefix mode is 1/4.
(***) Italics indicate an approximated value.
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

6. Preamble Pattern June 2006 June 2006 doc.: IEEE 802.22-06-0xxx-00-0000
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

7. Preamble Pattern Two repetitions within one OFDMA symbol
June 2006
doc.: IEEE xxx
June 2006
Preamble Pattern
Two repetitions within one OFDMA symbol
GI=1/4 (fixed)
Preamble pattern should support the fractional BW usage
Preamble shall be modulated using BPSK modulation
Used in channel estimation and synchronization GI
NFFT/2
NFFT/2
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

8. Pilot Pattern June 2006 June 2006 doc.: IEEE 802.22-06-0xxx-00-0000
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

9. Pilot Subcarrier Interval
June 2006
doc.: IEEE xxx
June 2006
Pilot Subcarrier Interval
RMS delay spread of WRAN profile (Approximated)
Pilot subcarrier interval can be determined as follows
Pilot subcarrier interval*subcarrier spacing < coherent bandwidth
Multipath Profile A B C D
RMS Delay Spread (us)
2.772
1.956
5.692
16.527(*)
(*) We assume that the 6-th path has the excess delay of 60 us and relative amplitude of -10 dB
Multipath Profile
Parameters A B C D
Coherent
Bandwidth
(kHz)
90%
7.21
10.22
3.51
1.21
50%
72.15
102.25
35.13
12.10
Maximum
Pilot Subcarrier
Interval
2.15
3.05
1.04
0.36
21.53
30.52
10.48
3.61
1) We assume that the BW is 6 MHz and FFT mode is 2K.
2) 90% coherent BW=1/(50*rms delay spread), 50% coherent BW=1/(5*rms delay spread)
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

10. Maximum Doppler Shift (Hz)
June 2006
doc.: IEEE xxx
June 2006
Pilot Symbol Interval
Coherent Time
1/fm, where, fm is the maximum doppler shift
Pilot symbol interval can be determined as follows
Pilot symbol interval*OFDMA symbol time < coherent time
Multipath Profile
Parameters A B C D
Maximum Doppler Shift (Hz)
2.5
Coherent Time (sec)
0.4
Pilot Symbol Interval
1071.4
Here, we assume that the BW is 6 MHz, FFT mode is 2K, and GI mode is 1/4.
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

11. OFDMA Parameters (2K FFT Mode)
June 2006
doc.: IEEE xxx
June 2006
OFDMA Parameters (2K FFT Mode)
Parameter
1 TV bands 6 7 8
Inter-carrier spacing, DF (Hz) (*)
3348
3906
4464
FFT period, TFFT (ms) (*)
298.66
256.00
224.00
Total no. of sub-carriers, NFFT
2048
No. of guard sub-carriers, NG (L, DC, R)
368 (184,1,183)
No. of used sub-carriers, NT = ND + NP
1680
No. of data sub-carriers, ND
1440
No. of pilot sub-carriers, NP
240
No. of sub-carriers per BIN
14 (12 datas + 2 pilots)
No. of BIN per subchannel 4
No. of sub-carriers per subchannel
56 (48 datas + 8 pilots)
Occupied bandwidth (MHz) (*)
5.628
6.566
7.504
Bandwidth Efficiency (%) (**)
93.8
(*) Italics indicate an approximated value.
(**) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

12. Proposed Pilot Pattern (Common to DL & UL)
June 2006
doc.: IEEE xxx
June 2006
Proposed Pilot Pattern (Common to DL & UL)
OFDMA Symbol
time
Pilot Structure for Extendable Channel Estimation
Available Pilot Pattern for Channel Estimation
BIN
Repetition
Unit
frequency
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

13. Comparisons with 16e DL PUSC
June 2006
doc.: IEEE xxx
June 2006
Comparisons with 16e DL PUSC
The pilot subcarrier interval is always fixed as 3
OFDMA Symbol
time
BIN
Fixed as 3
frequency
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

14. Comparisons with 16e UL PUSC
June 2006
doc.: IEEE xxx
June 2006
Comparisons with 16e UL PUSC
The maximum pilot subcarrier interval is 2
It has to be verified that the performance is not severely degraded by intermittent (non-uniform) pilot transmission
OFDMA Symbol
time
Tile
Maximum
pilot
subcarrier
interval is 2
frequency
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

15. Subchannelization June 2006 June 2006
doc.: IEEE xxx
June 2006
Subchannelization
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

16. Why We Need Two Types of Subchannel?
June 2006
doc.: IEEE xxx
June 2006
Why We Need Two Types of Subchannel?
Subcarrier Allocation
Diversity Subchannel
AMC Subchannel
In general, distributed subcarrier permutations perform very well in mobile applications or severe frequency selective environments,
While adjacent subcarrier permutations can be properly used for fixed applications or flat fading environments.
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

17. Symbol Structure For Diversity Subchannel
June 2006
doc.: IEEE xxx
June 2006
Symbol Structure For Diversity Subchannel
Diversity subchannel (common to DL and UL)
All the pilot subcarriers are allocated first
And then the remaining subcarriers are used exclusively for data transmission
The Diversity subchannel consists of 4 contiguous BINs
The BIN structure is a set of 12 distributed data subcarriers and 2 pilot subcarriers within an OFDMA symbol
To allocate data subchannels, the remaining subcarriers are grouped into the number of data subcarriers per BIN, Nsubcarrier
The number of the subcarriers in a group is equal to the number of BINs, Nbin
Thus, the number of data subcarriers is equal to Nsubcarrier*Nbin
The subcarrier index of subcarrier k in BIN b is according to following equation
subcarrier(k,b)=Nbin*k+Nsubchannel*(b%4)+int(b/4)
where,
b is the index of BIN, from 0 to Nbin-1
k is the index of subcarrier in BIN, from 0 to Nsubcarrier-1
Nsubchannel is the number of subchannel in one OFDMA symbol
int(x) is the integer value of x
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

18. Symbol Structure For AMC Subchannel
June 2006
doc.: IEEE xxx
June 2006
Symbol Structure For AMC Subchannel
AMC subchannel
The AMC subchannel consists of 4 contiguous BINs
The BIN structure is a set of 14 contiguous subcarriers within an OFDMA symbol
The BIN has a 12 data subcarriers and 2 pilot subcarriers
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

19. Mixed Resource Composition
June 2006
doc.: IEEE xxx
June 2006
Mixed Resource Composition
Resource composition based on BIN unit
time
AMC 0
AMC 1
AMC 2
Diversity 0
Diversity 1
Diversity 2
BIN
frequency
OFDMA Symbol
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

20. Simulations for Mixed Resource Composition (1)
June 2006
doc.: IEEE xxx
June 2006
Simulations for Mixed Resource Composition (1)
Different Resource Composition in DL
Subcarrier-unit mixture
with frequency hopping
BIN-unit mixture
with frequency hopping
Subcarrier-unit mixture
without frequency hopping
BIN-unit mixture
without frequency hopping
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

21. Simulations for Mixed Resource Composition (2)
June 2006
doc.: IEEE xxx
June 2006
Simulations for Mixed Resource Composition (2)
Simulation Conditions
IEEE WRAN multipath profile A
2K FFT
Number of subcarriers per BIN = 8
One subchannel consists of 48 subcarriers
Perfect channel estimation
Convolutional turbo code (CTC) is used for channel coding
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI

22. Simulations for Mixed Resource Composition (3)
June 2006
doc.: IEEE xxx
June 2006
Simulations for Mixed Resource Composition (3) 
 BIN-unit,
w/o freq. hopping
 BIN-unit,
w/ freq. hopping
 Subcarrier-unit,
 Subcarrier-unit,               
Sunghyun Hwang, ETRI
Sunghyun Hwang, ETRI