Since Release 8 Long-Term Evolution (LTE) by the 3rd Generation Partnership Project (3GPP), the uplink control channel called the physical uplink control channel (PUCCH) is specified. In this paper, we propose a new multi-user joint receiver processing for LTE PUCCH that counteracts the intra-cell interference (ICI). Using the fact that the received signal in PUCCH signaling follows a constrained tensor model, a multi-user receiver based on an iterative joint channel/code estimation and symbol detection is proposed. The interest in such a challenging setting relies on the overhead reduction synchronization errors defined by time offset and inaccuracies of timing align. Simulation results show remarkable performance gains of the proposed receiver compared to the conventional time-frequency decorrelator based receiver under the same conditions.
1. TELFOR-2013
November 26-28, 2013
Tensor-Based Multiuser Detection
and
Intra-Cell Interference Mitigation
in LTE PUCCH
www.huawei.com
Vladimir Lyashev | Ivan Oseledets | Delai Zheng
Huawei Technologies
Russian Research Center, Moscow
(vladimir.lyashev@huawei.com)
Huawei Technologies Co., Ltd.
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Slide 1
2. Why does PUCCH important?
“40% Of YouTube Traffic Now Mobile,
Up From 25% In 2012, 6% In 2011.”
“PUCCH occupies too much bandwidth and
is used not in the most efficient way.”
Field-test scenario:
• eRAN7, 10 MHz
• 60 connected UEs
• 30 UEs constantly downloading
large files (i.e. video streaming)
eNodB allocates
• 10RB for PUCCH,
• 3 UE per RB in average
“VoLTE dramatically
increases PUCCH usage.”
•
•
•
•
8 million VoLTE users worldwide
VoLTE will take off in 2015-2016 worldwide
over 10-20 MHz spectrum - hundreds users
46% MBB providers required VoLTE during 1 year
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AMR calls/1MHz
GSM
8
UMTS
12
HSPA
24
VoLTE
50
Slide 2
4. PUCCH Allocation and SRS Signal
SRS bandwidth is multiplied
by 4RB: 4, 8, 12, …
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Slide 4
5. Intra-cell Interference in LTE PUCCH
Up to:
• 36UE per 1RB in Format 1x
• 12UE per 1RB in Format 2x
Separation by CAZAC sequence
In practice, time-alignment of the
signals at the eNodeB receiver is
not perfect.
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Slide 5
6. Timing Error: Main Reasons
limited resolution and measurement errors
propagation time change due to UE movement
oscillator drift
abrupt change of the multipath channel
misdetection of the Timing Advance
(Initial or Update) command
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Slide 6
7. Abrupt changes in channel delay profile
can’t be compensated by TA commands alone!
200ms-1s
200ms-1s
200ms-1s
TA
command
abs(timing
error)
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Timing
correction at
UE
Timing
correction at
UE
Path birthdeath
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Timing
correction at
UE
Path birthdeath
Slide 7
8. Field-test measurements: scenario
20 km/h speed
600 m length difference
720kHz (6RB) SRS signal
generation
// blue line
1
14.4 MHz measurement signal
// red line
2
2
1
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Slide 8
10. Mathematical Model
1,
𝐏𝑗 𝐏 𝑞 =
0,
𝐻
CAZAC property for ideal sync.:
𝑗 = 𝑞;
𝑗 ≠ 𝑞.
Q
Y j P H j T j P j X j P H q Tq Pq X q P I
q 1
power loss
q j
H
j
H
j
Measurement #
Measurement results
NUE = 6, TAerror = 0 μs
Desired user
Interference
23.7
0.11
12.52
0.67
13.37
0.95
9.83
0.65
7.5
0.26
10.6
0.51
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2
H
j
intra cell interference
SIR
23 dB
22 dB
11 dB
12 dB
15 dB
13 dB
NUE = 6, TAerror = 1.56 μs
Desired user
Interference
14.41
4.12
11.23
2.63
16.91
1.01
2.42
3.15
7.97
2.71
5.11
4.21
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Slide 10
SIR
5.5 dB
6.5 dB
12 dB
-1.2 dB
4.5 dB
0.8 dB
11. Mathematical Model and Its Approximation
Q
Y (n, l , k ) P(q, k , l ) H (q, n, k , l ) X (q, l )T (q, k ) E (n, l , k )
q 1
B-rank channel approximation:
B
H ( q , n, k , l ) W ( , q , n ) S ( , k )
1
Rank-2 model basically gives a very good fit to the
experimental channel H(q, n, l, k), usually of a fit of order 95%.
The rank-1 model also look promising, and can approximate
70% of the energy.
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Slide 11
12. Rank-1 (B=1) Model Approximation
Mathematical Notation in
Slice Form
Yl (n, k ) Y (n, l , k )
l th slice for 3D tensor (received signal)
Pl (q, k ) P(q, l , k )
T (k ) T (k ) S (k )
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Yl WX l Pl T El
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Slide 12
Joint
Algorithm
ALS-1
l th slice for 3D tensor (reference sequence)
13. Joint Detection
^
Update T
Update W
ˆ
WX l Pl T IT Yl
Update X
ˆ
W X I Xl Pl Yl
ˆ
W X l W I Yl
Iteration++
Receive Signal
Y
Simple Channel
Estimation & MRC
with equalizing
H0
W0
QPSK-symbols
demapping &
decoding
XMRC
X0
Set as initial guess
for ALS iterations
X
ALS-1 iterations
^
T0= I12x12
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Slide 13
Output CQI bits
14. Quality decoding
Joint Detection with Quality Control
TErr = 3 TErr = 0
Pilots
FER in MRC:
FER in ALS-1:
MRC & ALS-1 have the same error frames:
ALS-1 males mistake (MRC not):
FER in MRC:
FER in ALS-1:
MRC & ALS-1 have the same error frames:
ALS-1 males mistake (MRC not):
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128 / 12 000
225 / 12 000
114 / 12 000
111 / 12 000
407 / 12 000
180 / 12 000
107 / 12 000
73 / 12 000
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Slide 14
15. Simulation Parameters
Parameter
LTE PUCCH format
Bandwidth
CQI
Modulation type
Number of Rx antennas
Number of Tx antennas per user
Number of users
Cyclic shift (CS) interval for RS
Value
format 2
1.4 MHz
7 bits
QPSK
4
1
6
π/3
Power of desired user (CS=0)
Power for UE with CS=1,3,5
Power for UE with CS=2,4
Timing error (uniform distribution)
Propagation channel
Number of simulated sub-frames
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0 dB
3 dB
0 dB
-1.56 … 1.56 us
ETU70
20 000
Slide 15
17. Simulation Results
without Quality Decoding Control
Gap: 0.8 dB
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with Quality Decoding Control
Gap: 0.4 dB
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Slide 17
18. Outlook
Non-Orthogonal Access
MU-MIMO and Massive-MIMO
Algorithm Diversity for Cloud RAN (cRAN)
Dimension Reduction in Non-Linear Signal
Processing
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Slide 18