IEEE C802.16m-09/1842
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Proposed changes to MIMO midamble (15.3.5.4.2)
Date
Submitted
2009-08-31
Source(s)
Seunghyun Kang, Jinyoung Chun, Bin-Chul Ihm
and Wookbong Lee
sh_kang@lge.com
LG Electronics
Re:
IEEE 802.16 Working Group Letter Ballot #30
P802.16m/D1 : MIMO midamble (15.3.5.4.2)
Abstract
This contribution provides the proposed text for MIMO Midamble.
Purpose
To be discussed and adopted by TGm for the 802.16m amendment.
Notice
Release
Patent
Policy
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represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion.
It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein.
The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution,
and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any
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acknowledges and accepts that this contribution may be made public by IEEE 802.16.
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<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and
<http://standards.ieee.org/guides/opman/sect6.html#6.3>.
Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and
<http://standards.ieee.org/board/pat>.
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IEEE C802.16m-09/1842
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Proposed changes to MIMO midamble (15.3.5.4.2)
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Seunghyun Kang, Jinyoung Chun, Bin-Chul Ihm and Wookbong Lee
LG Electronics
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1. Introduction
In session #62, the details of MIMO midamble such as MIMO midamble sequence, subcarrier mapping rule
and MIMO midamble symbol location in the DL frame has been proposed and adopted in [1]. In this
contribution, we provide analysis of the current MIMO midamble and propose modified MIMO midamble
design.
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2. Analysis of the current AWD MIMO midamble
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According to the equation (197) in [1], the current MIMO midamble subcarrier mapping rule has its
periodicity depending on a number of ABS transmit antennas Nt. Furthermore, the midamble subcarriers are
shifted by considering frequency reuse of 3 in order to avoid midamble collision between neighboring cells.
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Therefore, the period of the midamble subcarriers is 3×Nt and a midamble subcarrier for each antenna is
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regularly mapped every 3×Nt subcarriers.
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When there exist ABSs having different cell deployment or exist both Femtocell BS and Macro BS
simultaneously, the neighboring cells may be assumed to have different number of transmit antennas. In these
cases, there is no way to avoid midamble collision even though the current MIMO midamble subcarrier
mapping rule has considered frequency reuse of 3. Figure 1 shows an example of midamble collision between
two cells assuming two transmit antennas and four transmit antennas for each. In the figure, there exist
midamble collisions in the subcarrier index 6 and 7. Moreover, there exist midamble collisions every 12
subcarriers because of their periodicity.
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Figure 1. Midamble collision between neighboring cells
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IEEE C802.16m-09/1842
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In the figure 2, the average Mean Square Error (MSE) of channel estimation are derived for MIMO midamble
employing 4 cases of transmit antenna configurations. The transmit antenna configurations are as follows.
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Transmit antenna configurations:
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Case-1: # transmit antennas of Serving cell = 2 & # transmit antennas of two neighboring cells = 2
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Case-2: # transmit antennas of Serving cell = 2 & # transmit antennas of two neighboring cells = 4
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Case-3: # transmit antennas of Serving cell = 4 & # transmit antennas of two neighboring cells = 4
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Case-4: # transmit antennas of Serving cell = 4 & # transmit antennas of two neighboring cells = 2
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Also, the average MSE has been performed by considering SIR of 0, 3 and 6 dB where SIR is a term for
midamble power ratio between a serving cell midamble power and a sum of two neighboring cells midamble powers
which are interference to the serving cell. In the figure, the average MSE of Case-1 and Case-3 configurations is
getting smaller while increasing SNR. Also, there is no impact of the interference from the neighboring cells
since there is no midamble collision. However, for Case-2 and Case-4 configurations, the average MSE are
converging to some values depending on SIR. Also, for all the SNR ranges, their average MSE is always
larger than that of Case-1 and Case-3 configurations due to the midamble collision.
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AWD Midamble, SIR=6[dB]
AWD Midamble, SIR=3[dB]
1.000
Average MSE
Average MSE
1.000
0.100
0.010
0.100
0.010
0.001
0
4
8
12
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0.001
0
SNR [dB]
4
8
12
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SNR [dB]
AWD,Case-1
AWD,Case-2
AWD,Case-3
AWD,Case-4
AWD,Case-1
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AWD,Case-2
AWD,Case-3
AWD,Case-4
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AWD Midamble, SIR= 0[dB]
Average MSE
1.000
0.100
0.010
0.001
0
4
8
12
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SNR [dB]
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AWD,Case-1
AWD,Case-2
AWD,Case-3
AWD,Case-4
Figure 2. Average MSE performance of the current AWD midamble design (SIR=0, 3 and 6[dB])
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3. Modified MIMO midamble
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The subcarrier mapping rule of the current MIMO midamble design causes midamble collisions when the neighboring
cells are assumed to have different number of transmit antennas. In order to avoid midamble collision with
minimal change, we have modified the current MIMO midamble equation as follows.
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 24  10 0.2

 k  s 
N 1
 1  2  G ([ k  u  offsetD ( fft)] mod fft), k  used
, k mod 24   g  

  mod N t  8 * ( BSID mod 3)
bk  
Nt
2
 N1 * N sc  


0, otherwise
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First of all, the period of the subcarrier mapping rule is fixed to the period of the eight transmit antennas
regardless a number of transmit antennas. By using this modification on the subcarrier mapping rule, a
midamble subcarrier for each antenna is regularly mapped every 24 subcarriers. Also, the shift values for
frequency reuse of 3 is fixed to the period of the eight transmit antennas. As a result of this modification, the
number of midamble subcarriers is proportionally reduced. In order to compensate the midamble subcarrier
density, we have increased the midamble signal power depending on Nt. Since the period of the subcarrier
mapping rule and the shift values for frequency reuse have been fixed, there is no midamble collision between
neighboring cells having a different number of transmit antennas.
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In the figure 3, the average MSE performance of the modified midamble design has been evaluated and
compared with that of the current AWD midamble design. The modified midamble design shows almost same
performance for the Case-1 and Case-3 configurations and shows good enhancement for the Case-2 and
Case-4 configurations.
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Midamble comparison Case-1, SIR= 0[dB]
Midamble comparison Case-2, SIR= 0[dB]
1.000
Average MSE
Average MSE
1.000
0.100
0.010
0.001
0.100
0.010
0.001
0
4
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12
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0
4
8
SNR [dB]
AWD
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SNR [dB]
Modified
AWD
Modified
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Midamble comparison Case-3, SIR= 0[dB]
Midamble comparison Case-4, SIR= 0[dB]
1.000
Average MSE
Average MSE
1.000
0.100
0.010
0.100
0.010
0
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12
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0
4
8
SNR [dB]
AWD
Modified
AWD
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SNR [dB]
Figure 3. Average MSE comparison (SIR= 0[dB])
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Modified
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IEEE C802.16m-09/1842
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4. References
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[1] IEEE P802.16m/D1, “Draft Amendment to IEEE Standard for Local and Metropolitan Area Networks- Part 16: Air
Interface for Broadband Wireless Access Systems”
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[2] IEEE 80216m-09/0037, “Call for Contributions on Project 802.16m Amendment Content”
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[3] IEEE C802.16m-09/1313r3, “MIMO midamble sequence proposal”
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[4] IEEE C802.16m-09/1700, “Proposed Changes to MIMO Midamble (15.3.5.4.2) for the IEEE 802.16m/D1”
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5. Text proposal for inclusion in the 802.16m AWD
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Proposed text has been underlined in blue and deleted text has been struck through in red. Existing AWD text
is shown in black.
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Text Start -----------------------------------------------------------------
<Modify subsection 15.3.5.4.2 as follows :>
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15.3.5.4.2 MIMO midamble
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MIMO midamble is used for PMI selection in closed loop MIMO. For OL MIMO, midamble can be
used to calculate CQI. MIMO midamble shall be transmitted every frame on the second last DL
subframe. The midamble signal occupies the first OFDMA symbol in a DL type-1 or type-2
sub-frame. For the type-1 6 symbol DL subframe case, the remaining 5 consecutive symbols form a
type-3 subframe. For the type-2 subframe case, the remaining 6 consecutive symbols form a type-1
subframe.
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The MIMO midamble signal transmitted by the ABS antenna is defined by Equation (196):
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

N used 1


k  N used 1
j 2 ( k 
) f t Tg  
 j 2f ct
2
s t   Re e
bk  e


k 0


N
1
k  used


2
(196)
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where bk is a complex coefficients modulating subcarriers in the midamble symbol defined from
Equation (197)
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

 k  s 
N 1
1  2  G ([ k  u  offsetD ( fft)] mod fft), k  used , k mod( 3 * N t )   g  
  mod N t  N t * ( BSID mod 3)
bk  
2
 N1 * N sc  


0, otherwise
 24  10 0.2

 k  s 
N 1
 1  2  G ([ k  u  offsetD ( fft)] mod fft), k  used
, k mod 24   g  

  mod N t  8 * ( BSID mod 3)
bk  
Nt
2
 N1 * N sc  


0, otherwise
where k is the subcarrier index (0 ≤k ≤ Nused -1), Nused is the number of used subcarriers, Nt is a
number of transmit antennas, G(x) is the Golay sequence defined in Table 658 (0 ≤ x ≤ 2047), fft is
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IEEE C802.16m-09/1842
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the FFT size used, u is a shift value (0 ≤ u ≤ 127), where the actual value of u is derived from u =
mod(BSID, 128), offsetD(fft) is an FFT size specific offset as defined in Table 659, g is a ABS
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transmit antenna index, Nt is a number of ABS transmit antennas, parameter s = 0, for k≤(Nused - 1)/2
and s = 1, for k>(Nused - 1)/2.
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Example of physical structure of MIMO midamble is shown in Figure 447 423 for 4TX antenna and
BSID = 0.
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1st subband
2nd subband
Nth subband
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1st TX antenna
3rd TX antenna
2nd TX antenna
4th TX antenna
Null subcarrier
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1st subband
2nd subband
Nth subband
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1st TX antenna
3rd TX antenna
2nd TX antenna
4th TX antenna
Null subcarrier
Figure 423. MIMO midamble physical structure for 4TX antennas and BSID = 0
MIMO midamble shall be transmitted with boosting of 2dB.
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Table 658 – Golay sequence of length 2048 bits
0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2
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IEEE C802.16m-09/1842
0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D
0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2
0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2
0x121D 0x12E2 0x121D 0xED1D 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2
0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D
0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2
0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D
0x121D 0x12E2 0x121D 0xED1D 0x121D 0x12E2 0xEDE2 0x12E2 0x121D 0x12E2 0x121D 0xED1D
0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D
0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D
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Table 659 – Offsets in the Golay sequence
FFT size
2048
1024
512
Offset
30
60
40
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Text End -------------------------------------------------------------------
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