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Scalable SCMA
Jianglei Ma Sept. 24., 2017
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2
5G-NR Air-Interface
f-OFDM
New
Technologies for
Future Releases
eMBB
SoftAI: Programmable Air-Interface Adaptive numerology Adaptive transmission
duration Adaptive multiple access
scheme Adaptive HARQ
eMBB
mMTC URLLC
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From Orthogonal Multiple Access to Non-orthogonal Multiple Access
time
Dual-layer non-orthogonality for SoftAI Inter-subband non-orthogonality:
Subband based numerology optimization enabled by
spectrum localized waveform from filtering/windowing
Intra-subband non-orthogonality
Non-orthogonal multiple access
UE1
UE2
UE3
UEn
f-OFDM
UE1
Numerology-1
UE1 Numerology-2
Intra-band
Non-Orthgonality
-NOMA
Inter-band
Non-Orthgonality
-f/w-OFDM
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Multiple Access Scheme Evolution s
ing
le d
imen
sio
nal m
ult
i-U
E m
ult
iple
xin
g
Two dimensional multi-UE
multiplexing
Three dimensional multi-UE
multiplexing (NoMA)
Power domain and spatial domain
separation can be further exploited
frequency
time User 3
User 3
Code
User 3
Use
r 2
Use
r 3
Use
r 4
Use
r 2
time
frequency
time
frequency
Code
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NoMA Application Scenarios
Scenarios Motivations
eMBB • Enhance spectrum efficiency
• Improve edge UE experience
• Enable seamless mobility
• Support more UEs
mMTC • Support massive connectivity
• Reduce signaling overhead
• Reduce UE energy consumption
URLLC • Reduce latency
• Improve reliability
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Non-orthogonal Multiple Access for UE Experience
Enhancement
Multi-TRP Cooperation for guaranteed data rate
everywhere
Transparent TRP HO for seamless mobility
Cloud
Processor
C-RAN
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Non-orthogonal Multiple Access for Latency/Signaling
Overhead/Energy Consumption Reduction
Grant-free for sporadic small packet transmission
Low latency
Low signaling overhead
Low energy consumption
However potential UE collision
UE gNB UE gNB Scheduling request
Scheduling grant
Data
Data
Non-orthogonal Multiple Access
Robust to UE collision
Better SE
More delay and overhead for grant based TDD transmission
SR Grant Data
DL UL
SR/Grant Grant-free
t
f
Collision
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Grant-free for Different UE States
Grant Free
NR Cell
UE State
UE-ID
mMBB
URLLC
mMTC
Active-State Echo State
(Inactive-State) Idle-State
eMBB
mMTC URLLC
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Non-orthogonal Multiple Access for Hyper Connectivity
f-OFDM
t
f
UE group-1
UE group-2
UE1
UE2 UE3
UEn
Superposed transmission to support more concurrent users Enhanced connectivity
Synchronous transmission is maintained within UE group without TA. Close proximity based local time synchronization
Asynchronous transmission is allowed between UE groups. Time synchronization is not required between different groups.
Sub-band filter is applied to eliminate int.er-group interference
Asynchronous
Group-2
Group-1
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Bit level
Sequence Generator Symbol to RE Mapping
Bit level operations Symbol level operations
Non-orthogonal Multiple Access Construction
• Non-orthogonal multiple access components: Symbol level operation:
Without spreading or with spreading (linear or non-liner)
Resource mapping Sparse or on-sparse
Non-orthogonal multiple access has been studied in Rel-14 NR study item phase.
All proposed non-orthogonal MA schemes follow the following basic representation
Modulated Symbol
Bit-Level
Interleaver/Scrambler
FEC
Resource
Mapping
Generate Non-zero
Modulated
Components
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FEC Symbol Level
Operation
Non-orthogonal Multiple Access - Symbol Level Operation
Without spreading Power domain superposition Rely on advanced Rx to separate users
With spreading Additional code domain separation Better inter-user interference suppression
Linear spreading Symbol level repetition Spreading code optimization to allow
more UE collision
Non-linear spreading Symbol level non-repetitive spreading Additional code gain/diversity gain
Linear spreading
[ y ] = [ S ] [ x (b) ]
Non-linear spreading:
[ y ] = [ S(x) ] [ x (b) ]
b0 b1b32…… y0 y1 y2 …
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Resource Mapping: Partial Collision With Sparse Spreading
Non-sparse Resource
Mapping
t
f
Sparse Resource
Mapping
t
f
Sparse RE mapping: Partial collision reduces inter-UE collision
Partial collision reduces multi-user detection complexity
UE1
UE2
Full Collision
UE1
UE2
Partial Collision
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SCMA (Sparse Coded Multiple Access) NoMA with Sparse Non-linear Spreading
Example 1: SCMA 4-point
codebook
Bit stream-0 b0
b1 Bit stream-2
x0
x1
y
y
Example 2: SCMA 8-point
codebook
Bit stream-0
Bit Stream-1
Bit Stream -2
b0
b1
b2
x0
x1
x2
j02
1
0j2
1
000
100 001
101
010
110
011
111
000
010 001
011
100
110
101
111
Non-zero component-1 Non-zero component-2
11
01 10
00
00 11
01 10
Non-zero component-1 Non-zero component-2
1 2
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Scalable SCMA
SCMA codebook Adaptation to meet different system requirements
System requirements
SCMA Parameters
SCMA
Configuration
SCMA Codebook
Spectrum Efficiency Coverage Connectivity
Codebook Number of codewords of an SCMA codebook: M Spreading factor: K Max number of layers (or codebooks/signatures) : J Number of nonzero elements of each codeword: N
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Flexible SCMA codebook Design for Different Application Scenarios
Med
inactive
RE
Muted
RE
Active
RE
For coverage enhancement Long codeword
Non-sparse RE mapping
Active
RE
Inactive
RE
Inactive
RE Active
RE Active
RE
Muted
RE
For connectivity enhancement Short codeword
Sparse RE mapping
For PAPR reduction Short codeword
Only one RE is active at each
time
Inactive
RE Active
RE
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Benefits of Non-linear Spreading
Scheme Receiver
OFDMA MMSE & Turbo-ML
MC-CDMA (linear non-sparse spreading) MMSE-SIC
LDS (linear sparse spreading) Turbo-MPA
SCMA (non-linear sparse spreading) Turbo-MPA
Parameter Value
Transmission mode UL
Antenna configuration 1x2 uncorrelated
Channel model TDLC-1000
Channel estimation perfect
Resource allocation 12 RBs for NoMA, 1RB for OFDMA
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Conclusions Non-orthogonal multiple access can be applied to enhance the
performance of different applications:
eMBB
mMTC
URLL
Scalable SCMA can be configured to meet different requirements of
different services.
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Thank you
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