Download - Network-Coded Multiple Access
Network-Coded Multiple Access
Presented by Soung Liew (Joint Work with Lu Lu, Lizhao You, Shenghao Yang)
Institute of Network Coding
The Chinese University of Hong Kong
March 2014 Soung Liew, CUHK 1
March 2014 2
Background on PNC
First proposed in Mobicom 06 [1]
A subfield of Network Coding building up momentum in recent years:
- Google scholar citations: 1000+ (annual growth ~300)- A main topic in special journal issues and numerous conferences.- A main topic in an upcoming IEEE JSAC issue on wireless network
coding- Half-day workshop in IEEE WNCN 2013: New Advances for PNC- Invited talks
[1] S. Zhang, S. C. Liew, P. P. Lam, “Physical-Layer Network Coding,” ACM Mobicom 2006 .Similar idea in [2] P. Popovski and H. Yomo, “The anti-packets can increase the achievable throughput of a wireless multi-hop
network,” ICC 2006.
Soung Liew, CUHK
March 2014
Simplest Set-up: Two-Hop Linear Network
Two-way Relay Channel (TWRC) No direct channel between nodes A and B.Half duplex: nodes cannot transmit and receive at the
same time.What is the minimum number of time slots needed
for nodes A and B to exchange one packet via relay R?
A R B
SA SB
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PNC
March 2014
B R AS S S A R BS S S
R A BS S S A R B
SA SB
Time slot 1 Time slot 2
R A BS S S
Transmissions by nodes A and B are simultaneous!
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March 2014
PNC for Multiple Access (Non-Relay Setting)?
Access Point InternetRelay
(a) (b)
A B A B
C
D
Access point wants to get both Message A and Message B, not just their XOR
Does PNC have a role to play?
Relay Network
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Wireless LAN
Access Point
PNC In Non-Relay Network: Network Coding Multiple Access (NCMA)
Nodes A and B send CA and CB to AP simultaneously AP tries to decode packets CA , CB, and
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A AP B
AC
A BC C
BC
1,2,...[ ]
ky k
Two Users
Single User
Binary Viterbi Decoder
User Detector
SU Soft Demodulator
PNC SoftDemodulator
Binary Viterbi Decoder
1,2,...[ ]A B k
x k A B
i iC C
MUD SoftDemodulator
Binary Viterbi Decoder
1,2,...[ ]A k
x k
Binary Viterbi Decoder
1,2,...[ ]B k
x k
AiC
BiC
or BiC 1,2,...
or [ ]B kx k
AiC 1,2,...
[ ]A kx k
PHY-Layer Decoders of NCMA
March 2014
Soft Information (Log Likelihood Ratio: , k=1,2,… )
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( [ ] | [ ] 1)log
( [ ] | [ ] 1)B
B
P y k x k
P y k x k
PHY-layer Bridging
March 2014
3BC
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Are Lone XOR Packets Useful?
March 2014
Complementary XOR
Lone XOR
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• Do lone XOR packets have a role to play?
March 2014
MAC-Layer Erasure Code + PHY-Layer Channel Code
1 2
1 2
Message Packets { , ,..., }
Message Packets { , ,..., }
A A A AN
B B B BN
M C C C
M C C C
1 2
If RS code is used, as soon as AP decodes any of
packets { , ,..., }, it can obtain .
Similarly for .
A A A AN
B
L
C C C M
M
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MAC-Layer Bridging with L = 3
1
2
3
4
5
Erasuredecoding andreconstruct A
Network decoding B using XOR information
Erasuredecoding andreconstruct B
Example: Decoding , based on and , with 3B A A BM M M M L
1AC
2A BC
3BC
4AC 4
BC
5AC
1
2
3
4
5
1AC
2A BC
3BC
4AC
5AC
2AC
3AC
PacketIndex
A BEq
1
2
3
4
5
AEq BEq
1AC
2A BC
3BC
4AC
5AC
2AC
3AC
2BC
PacketIndex
A BEq AEq BEq PacketIndex
A BEq AEq BEq
PacketIndex
A BEq
1
2
3
4
5
AEq BEq
1AC
2A BC
3BC
4AC
5AC
2AC
3AC
2BC
1BC
4BC
4BC 4
BC
5BC
4A BC
4A BC
4A BC
4A BC
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Experiments: Layout of Indoor Environment for 9 USRP N210 Nodes
9
14
5
3
26
7
8
AP
Institute of Network Coding (INC)
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PHY-Layer Packet Decoding Statistics(Balanced Power Case)
AB: Both A and B decodedAX|BX: A and XOR decoded or B and XOR decodedA|B: Either only A or only B decodedX: Only XOR decoded
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7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 0%
20%
40%
60%
80%
100%
SNR (dB)
Per
cent
age
ABAX|BXA|BXNONE
X
AX|BX
X
AX|BX
PNC decoding works but MUD does not when phases are aligned
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-2 -1 0 1 2-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5Constellation Map
XA
XB
XA+X
B
5 6 7 8 90%
20%
40%
60%
80%
100%
SNR (dB)P
erc
enta
ge
ABXABAXBXABXNONE
A BY X X Received Signal Decode Outcomes
PNC does add value when phases are severely misaligned
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Decode Outcomes2j
A BY X X e
Received
Signal
5 6 7 8 90%
20%
40%
60%
80%
100%
SNR (dB)P
erc
enta
ge
ABXABAXBXABXNONE
-2 -1 0 1 2-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5Constellation Map
XA
XBej/2
XA+X
Bej/2
Combination of PNC and MUD is effective when phases are moderately misaligned
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4j
A BY X X e
Received Signal Decode Outcomes
5 6 7 8 90%
20%
40%
60%
80%
100%
SNR (dB)P
erc
enta
ge
ABXABAXBXABXNONE
-2 -1 0 1 2-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5Constellation Map
XA
XBej/4
XA+X
Bej/4
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7.5 8 8.5 9 9.5 10 10.50
0.5
1
1.5
2
SNR (dB)
Thro
ughp
ut (p
acke
ts p
er s
lot)
NCMAMUDSU
Overall Throughputs of Different Schemes for Different SNRs LA = 1.5×LB = 24.
Pairing Strategies
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Loc. 2 Loc. 3 Loc. 4 Loc. 5 Sum0
0.5
1
1.5
2
2.5
3
Th
roug
hpu
t
NCMA with (RMUD+SIC)
Strategy 1Strategy 2
Scenario: Four users at locations 2, 3, 4, 5. How to form pairs?
Pair “strong with weak” rather than “strong with strong and weak with weak”
Strategy 1: pair 2 with 3; 4 with 5
Strategy 2: pair 3 with 4; 2 with 5
9
14
5
3
26
7
8
AP
12.3dB 9dB 7dB 7.4dB
Linearly Coupled Codes at MAC Layer
Single-equation System:
March 2014 Soung Liew, CUHK 19
0
0
, : Generator matrices of Node A and Node B.
: corresponds to subset of A packets received,
: corresponds t
A AAA AX X A BA BB B
B BB
A B
A AA A
BB B
G CM M
G G G CM M
G C
G G
G G C
G G
o the subset of B packets received,
, : correspond to the subset of lone XOR packets received,
Suppose that and are not full-rank; however, there are 2 rows in .
The
B
X X A BA A B B
A BA B
C
G G G G C
G G L G
8
n the probability of the matrix being full-rank is more than 99.5% if elements of
, are randomly drawn from (2 )A B
G
G G GF
Linearly Coupled Raptor Codes
Near optimal and availability of fast decoding
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Channel-coded symbols of user A Channel-coded symbols of user B
Linearly-Coupled Channel-coded symbols from users A and B
Dynamic Equation
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Degree Optimization Problem
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For some positive integer
Use SIC at low SNR Regime
Suppose an (N,3) RS code
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Slot Index
AEq A BEq BEq
1A BC
1AC 1
BC PHY-layer SIC
2AC
3BC
5BC
4BC4
ACCross-layer SIC
Message decoding
1
2
3
4
5
Overall Throughputs of Different Schemes for Different SNRs LA = 1.5×LB = 24.
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NCMA: Conclusion
First venture into non-relay (multiple-access) setting for PNC
PNC may have a role to play in the multiple access scenario: To simplify decoder design For delivering jumbo messages
Ongoing NCMA Investigations: Better performance for high and low SNR regime Investigation of linearly-coupled code for MAC layer
of NCMA
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The End
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Throughputs of Four User Pairs
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Pair 1 Pair 2 Pair 3 Pair 40
0.5
1
1.5
2
Th
roug
hpu
t
A, NCMA w. RMUDB, NCMA w. RMUDA, NCMA w. RMUD+SICB, NCMA w. RMUD+SICA, SUB, SU
Overall Throughputs of Different Schemes with RS code parameter LA = 4, 8, 16, 32, and fixed SNR = 9dB.
March 2014 Soung Liew, CUHK 28
5 10 15 20 25 300.8
0.9
1
1.1
1.2
1.3
1.4
LB
Thr
ough
put (
pac
kets
per
slo
t)
NCMA w. RMUD Upper BoundNCMA w. RMUD, L
A=1.5L
B
NCMA w. RMUD, LA=L
B
RMUD
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Frequency-Domain PNC (FPNC) in GNU Radio testbed,
PNC Implementation: Wireless
Soung Liew, CUHK
A
BR