Transcript IEEE C802.16m-08/1164

MIMO Supports for IEEE 802.16m Synchronization Channel
IEEE 802.16 Presentation Submission Template (Rev. 9)
Document Number:
IEEE C802.16m-08/1164
Date Submitted:
2008-09-05
Source:
Seunghee Han, Sungho Moon, Jin Sam Kwak
Voice: +82-31-450-1935
e-mail : {dondai; msungho; samji}@lge.com
LG Electronics
LG R&D Complex, 533 Hogye-1dong, Dongan-gu, Anyang, 431-749, Korea
Venue:
IEEE 802.16m-08/033, Call for Detailed Physical Layer Comments
Purpose:
This contribution proposes SDD text for SCH based on ToC in IEEE 802.16m-08/003r4.
Notice:
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It 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.
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1
MIMO Supports for IEEE 802.16m
Synchronization Channel
2
Contents
 MIMO Support Options
 Comparisons of MIMO Options (CDD and FSTD)





Simulation environments
Cell ID detection error (AWGN, TU6 120km/h)
Beamforming effect in CDD
Convergence time
Frequency reuse
 Summary
 Text Proposals for 16m SDD
 Annexes
3
MIMO Supports
 Description in the SDD
 MIMO support is achieved by transmitting SCH subcarriers from known
antennas. Antennas are:
 Cyclic delay diversity (with antenna specific delay values)  CDD
 Interleaved either within a symbol (multiple antennas can transmit within a single
symbol but on distinct subcarriers)  FSTD
 Across frames (only one antenna transmits in each symbol)  TSTD
 Or some combination – Actual approach is FFS.
 Considerations
 TSTD has problems in the convergence time with low mobility MSs and in
power transition time from antenna on/off.
 TSTD requires multiple time instances to get diversity gain while CDD/FSTD
can achieve the diversity in single time instance.
 CDD and FSTD are promising candidates for 16m SCH in multi-antenna
transmissions.
4
Comparisons of MIMO Options (CDD and FSTD)
 Commonalities
 Multi-antenna transmission schemes for 16m SCH
 Distinguishable channel responses for each antenna  Possible for CE
 Support of various channel conditions
 High mobility, Large delay spread, etc
 CDD
 Spatial diversity with MS-transparent TxD on the number of antennas can be
achievable.
 Larger spreading gain with longer preamble sequence
 FSTD
 Complete separation between antennas
 Limited frequency diversity can be achievable.
 Worse correlation property with shorter sequence length
5
Cell Search Procedure and Simulation Environments
 Major Parameters (Detailed in Annex A)
 Search duration : 5 ms (coarse timing
synchronization only for one SCH)
 Multi-antenna transmission: CDD (1/4*Tu shifts for
2Tx, 1/8*Tu shifts for 4Tx), FSTD (Localized type)
 System bandwidth: 5MHz
 Carrier frequency offset: random within ±3ppm @
2.5GHz carrier frequency
 Number of cell IDs: 256
 Sequence length: 212/(frequency reuse) for CDD,
212/(frequency reuse)/(# of Tx antennas) for FSTD
 Randomly generated BPSK signals (not optimized
about PAPR and x-correlation)
 Cell ID detection: ML hypotheses by non-coherent
detection
 # of cells: 1, 2, 3 <cellA(desired cell): 0dB, cellB: 6dB, cellC: -6dB>
START
Coarse Symbol Timing Acquisition
(Auto-correlation based, Moving averaging)
Frequency Offset Estimation & Compensation
Cell ID Detection
Fine Symbol Timing Acquisition
 Correct Detection Probability
 Probability to choose a BS which received power is
within 3 dB of the BS with the highest received
power
6
END
Skipped in the simulation
Cell ID Detector
 Full Correlator in Frequency Domain
 The correlation profiles are calculated coherently for entire sequence length.
 Since there always exists timing error (particularly large error after coarse
timing sync step) and frequency selectivity in practical situation, it doesn’t
work.
 Partial Correlator in Frequency Domain
 The block-wise correlation profiles are calculated in order to reduce timing
error and frequency selectivity.
 For intra-blocks, coherent summation
 For inter-blocks, non-coherent summation
 Differential Correlator in Frequency Domain
 To reduce timing error and frequency selectivity.
 In taking differential operations for CDD, a proper interval selection would be
needed. (refer to Annex A)
 Energy Detector using FFT (IFFT) Operation
 The energies of channel impulse response are aggregated using FFT operation
 Unfeasible due to large complexity. For example, the ML complexity could be
256*512*log2(512) [=1179648] multiplications even in ignoring energy
aggregation operations.  Not considered in the simulation
7
Cell ID Detector (cont’d)
 Observations
 Full correlator is not feasible.
 The performance for partial
correlator depends on the
size of blocks.
 Different correlator
works well.
 The differential correlator
is deployed for evaluations.
Prob. of detection error
 It needs to optimize the
parameters.
TU6 120km/h, 3ppm FO, Practical time/freq sync, # of cells=1, 2Tx/1Rx antennas
0
10
CDD, Full corr
CDD, Partial corr
CDD, Diff corr
FSTD, Full corr
FSTD, Partial corr
FSTD, Diff corr
-1
10
-2
10
-3
10
-18
8
-16
-14
-12
-10
-8
SNR[dB]
-6
-4
-2
0
Cell ID Detection Error (AWGN)
 3ppm FO, Practical timing/freq sync, # of cells=1
 Both CDD and FSTD work well.
AWGN, 3ppm, Practical time/freq sync,# of cells=1
0
10
Prob. of detection error
CDD (2Tx-1Rx)
FSTD (2Tx-1Rx)
CDD (4Tx-1Rx)
FSTD (4Tx-1Rx)
-1
10
-2
10
-3
10
-18
-16
-14
-12
-10
-8
SNR[dB]
9
-6
-4
-2
0
Cell ID Detection Error (AWGN) (cont’d)
 3ppm FO, Practical timing/freq sync, # of cells=3
 CDD is better than FSTD due to interference randomization.
 For CDD,
 Good interference randomization
between cells
 For FSTD,
AWGN, 3ppm FO, Practical time/freq sync, # of cells=3
CDD (2Tx-1Rx)
FSTD (2Tx-1Rx)
CDD (4Tx-1Rx)
FSTD (4Tx-1Rx)
Prob. of detection error
 ~0.6dB SNR loss to CDD
for 2Tx @1% error rate
 Severe degradation by
~2.9dB SNR to CDD for
4Tx @ 1% error rate
0
10
-1
10
-2
10
-3
10
-18
10
-16
-14
-12
-10
-8
SNR[dB]
-6
-4
-2
0
Beamforming effect in CDD
 3ppm FO, Practical
timing/freq sync, # of cells=1
 No Coverage Hole
 The overall energies can be
maintained. (Annex C)
 No coverage hole has been
found for both CDD and FSTD.
0
AWGN, Practical time/freq sync, 3ppm FO, SNR=-13dB, # of cells=1
10
CDD (2Tx-1Rx)
FSTD (2Tx-1Rx)
CDD (4Tx-1Rx)
FSTD (4Tx-1Rx)
-1
10
Prob. of detection error
 Not significant impact of
frequency selectivity due to the
beam-forming in different
subcarriers
 Constructive subcarriers can
be used to maintain the cellID detection performance
 Impact of beamforming steerlike CDD in a certain DoA
varies in different subcarriers
-2
10
-3
10
-4
10
11
-80
-60
-40
-20
0
20
DOA [degrees]
40
60
80
Cell ID Detection Error (TU6, 120km/h)
 3ppm FO, Practical timing/freq sync
 4Tx is better than 2Tx due to spatial diversity gain.
 CDD is better than FSTD due to frequency diversity gain @ 1% error
rate.
 by ~0.5dB for 2Tx
 by ~0.6dB for 4Tx
0
TU6 120km/h, 3ppm, Practical time/freq sync, # of cells=1
10
Prob. of detection error
CDD (2Tx-1Rx)
FSTD (2Tx-1Rx)
CDD (4Tx-1Rx)
FSTD (4Tx-1Rx)
-1
10
-2
10
-3
10
-18
-16
-14
12
-12
-10
-8
SNR[dB]
-6
-4
-2
0
Convergence Time
TU6, 120km/h, CDD, FO=3ppm, Practical time/freq sync, # of cells=2
40
1Tx-1Rx
2Tx-1Rx
4Tx-1Rx
35
 Definition
 Time interval for cell ID detection error
to be less than 1%
 Observation
 # of cells
Convergence time [ms]
30
25
20
15
10
 The inter-cell interference increases a
convergence time.
5
0
 # of transmission antennas
 Multi-antenna transmission is
necessary to reduce the convergence
time.
-10
-9
-8
-7
-6
SNR [dB]
-5
-4
-3
TU6, 120km/h, CDD, FO=3ppm, Practical time/freq sync, # of cells=3
40
1Tx-1Rx
2Tx-1Rx
4Tx-1Rx
35
 Periodicity of 16m SCH
 If the periodicity of a complete SCH
instance is 20 ms, the convergence time
will become four times.
 In case of FSTD
 Similar trend to the above statements
Convergence time [ms]
30
25
20
15
10
5
0
13
-10
-9
-8
-7
-6
SNR [dB]
-5
-4
-3
Frequency Reuse in SCH
 Pros and Cons
 Decease in interference from other cells
 Reduced sequence length (Poor x-correlation property)
 Single-Cell Environment
 Reuse 1 is always better than Reuse 3 regardless of CDD and FSTD due to
reduced sequence lengths.
0
TU6,120km/h, CDD, FO=3ppm, Practical time/freq sync,# of cells=1
0
1Tx-1Rx
1Tx-1Rx
2Tx-1Rx
2Tx-1Rx
4Tx-1Rx
4Tx-1Rx
-1
(Reuse1)
(Reuse3)
(Reuse1)
(Reuse3)
(Reuse1)
(Reuse3)
10
-2
10
-3
10
TU6,120km/h, LFSTD, FO=3ppm, Practical time/freq sync,# of cells=1
10
Prob. of detection error
Prob. of detection error
10
-18
1Tx-1Rx
1Tx-1Rx
2Tx-1Rx
2Tx-1Rx
4Tx-1Rx
4Tx-1Rx
-1
(Reuse1)
(Reuse3)
(Reuse1)
(Reuse3)
(Reuse1)
(Reuse3)
10
-2
10
-3
-16
-14
-12
-10
-8
SNR[dB]
-6
-4
-2
10
0
14
-18
-16
-14
-12
-10
-8
SNR[dB]
-6
-4
-2
0
Frequency Reuse in SCH (cont’d)
0
TU6,120km/h, CDD, FO=3ppm, Practical time/freq sync,# of cells=3
10
 Multi-Cell Environment
1Tx-1Rx
1Tx-1Rx
2Tx-1Rx
2Tx-1Rx
4Tx-1Rx
4Tx-1Rx
 Reuse 1 is better than reuse 3 due to the
sequence lengths.
 No gain in finding a sector ID due to absence of
frequency reuse information
 Low SNR region (< -10 dB)
Prob. of detection error
 High SNR region (> -10 dB)
-1
(Reuse1)
(Reuse3)
(Reuse1)
(Reuse3)
(Reuse1)
(Reuse3)
10
-2
10
 Reuse 3 is better than reuse 1 due to the
reduced interference.
 Multiple SCH combining is needed for the
reliable performance.
-3
10
 # of combined symbols = 5
 Reuse 1 is better than reuse 3 even in the low
SNR region.
 With the symbol combining, the x-correlation
property is more dominant than interference.
 FSTD has the same trend regarding frequency
reuse.
Prob. of detection error
 Multiple SCH Combining
-18
-16
-14
-12
-10
-8
SNR[dB]
-6
-4
-2
0
TU6, 120km/h, CDD, FO=3ppm, Practical time/freq sync, # of cells=3, # of symbols=5
0
10
1Tx-1Rx (Reuse1)
1Tx-1Rx (Reuse3)
2Tx-1Rx (Reuse1)
2Tx-1Rx (Reuse3)
4Tx-1Rx (Reuse1)
-1
4Tx-1Rx (Reuse3)
10
-2
10
-3
10
15
-18
-16
-14
-12
-10
-8
SNR [dB]
-6
-4
-2
0
Summary
 The CDD transmission of SCH has better performance in terms of
the cell ID detection error than FSTD.
 The proposed CDD transmission shows reasonable convergence
times even in multi-cell scenarios.
 With the symbol combining, a SCH transmission with reuse 1 is
better than that with reuse 3 due to the larger sequence length.
16
Text Proposal for IEEE802.16m SDD
============= Start of text proposal for C80216m-08/003r4================
[Replace the whole section 11.7.2.1.2.5 with the following texts]
11.7.2.1.2.5 MIMO support and channel estimation
Figure xx shows the MIMO support in IEEE 802.16m synchronization channel (SCH).
Each antenna transmits a cyclic delayed symbol with antenna-specific delay values for
IEEE 802.16m MSs to perform full-band channel estimation for each antenna in the whole
SCH bandwidth. The number of BS antennas supported for MIMO channel
measurements is FFS, depending on the requirements of other 16m SDD content, such as
IFFT / FFT
DL MIMO and interference mitigation.
Time
1 OFDM Symbol
CP
Tx. Ant 0
a
Frequency
5 MHz
-a
CP
...
A
-A
...
f
...
...
Circular
Shift
-5 -3 -1 1 3 5
Sector/Cell-Common
Allocation
From Other Sectors
CP
Tx. Ant Ntx-1
a'
...
-a'
...
-5 -3 -1 1 3 5
f
5 MHz
Figure xx. Multi-antenna transmission for IEEE 802.16m synchronization channel
================== End of text proposal =============================
17
Annex A : Simulation Environments
 Simulation Parameters













Carrier frequency: 2.5GHz
System bandwidth: 5MHz
Sampling factor: 28/25
Sampling frequency: 5.6MHz
Subcarrier spacing: 10.9375kHz
FFT size: 512
CP length: 1/8*Tu, where Tu is effective OFDM symbol duration
Number of used subcarriers: 424
Number of guard subcarriers: 88
Carrier frequency offset: random within 0ppm and ±3ppm
Frame configuration: All DL signals, 5ms periodicity for Sync channel
Number of antennas: 2Tx-1Rx, 4Tx-1Rx
Multi-antenna transmission: CDD (1/4*Tu shifts for 2Tx, 1/8*Tu shifts for
4Tx), FSTD (Localized type)
 Sync channel repetition: 2 (every even subcarrier is nulled)
 Power boosting to other data channel per antenna on Sync channel: 12.04dB
(=16) for CDD, 12.04dB+10*log10(# of Tx antennas)dB (=16*(# of Tx antennas))
FSTD  same total transmit power in SCH
18
Annex A : Simulation Environments (cont’d)
 Simulation Descriptions
 Number of cell IDs: 256
 Other data channel modeling: Randomly generated QPSK signals
 Sequence length for Sync channel: 212 for CDD, 212/(# of Tx antennas) for
FSTD  All antennas transmit the same sequences.
 Sequence type for Sync channel: Randomly generated BPSK signals (not
optimized about PAPR and x-correlation)
 # of cells: 1, 2, 3 <cellA(desired cell): 0dB, cellB: -6dB, cellC: -6dB>
 All signals from each cell are arrived with same absolute times at MS side.
 Channel model: AWGN, TU6 (120km/h)
 Search duration for coarse timing synchronization: 5ms (one sync channel
used)
 Algorithms
 for coarse timing synchronization: auto-correlation based and further moving
averaging to make smooth correlation profile
 for frequency offset estimation: differential based (auto-correlation based)
 Cell ID detection: ML hypotheses by non-coherent detection
19
Annex B : Differential Detector
 Received signal at k-th subcarrier (assuming non-repeated signals)
yk 
Ntx 1

a 0
H k ,a e j 2 k d kuc
 kH H k d kuc
 In AWGN,
H k  a    [a0 a1
an  e
j
2

]T
d sin  
 λ: wavelength, d: antenna spacing
 The value d is set to d= λ/2 for evaluation.
 Differential detector
 Differential operation at Rx
zk  y
*
k  Ntx
yk   H k H
H
k
H
k  Ntx
 Correlation for differential signal
RZ B
H
where B  [b0 b1

H
k  Ntx
d
uc
k
d
uc
k  Ntx

u
l  Ntx
] , bl  d
T
20

*
d
*
u
l
Annex C : Beamforming Effect in CDD
 The overall energies can be maintained.
CDD diff, 2Tx
CDD diff, 4Tx
Correlation output [R]
1
0.8
0.6
0.4
0.2
0
-100
-80
-60
-40
20
0
-20
DoA [degress]
21
40
60
80
100