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Network Coding Innovation Technology Workshop. Physical-layer Network Coding: Prototyping and Application. Lu Lu 30 th August 2013. Outlines. 1. Background of Physical-layer Network Coding (PNC) 2. Real-time PNC Prototype Demo Video PNC Realization Challenges 3. PNC in Non-relay Setting - PowerPoint PPT Presentation
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Physical-layer Network Coding: Prototyping and Application
Lu Lu30th August 2013
Network Coding Innovation Technology Workshop
• 1. Background of Physical-layer Network Coding (PNC)
• 2. Real-time PNC Prototype– Demo Video– PNC Realization Challenges
• 3. PNC in Non-relay Setting– Experimental Setup– Performance Evaluation
• 4. Conclusion
Outlines
2PNC Prototyping & Application
What is PNC?
• Traditional view in wireless networking: interference is bad.
• PNC turns things around by exploiting network coding (NC) performed by nature.
• When electromagnetic waves superimpose, they add, a form of NC.
• Benefits of PNC: – boost throughput
3PNC Prototyping & Application
Simplest Set-up: Two-Hop Relay Network
• System Model: 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 node R?
A B
R
4PNC Prototyping & Application
Traditional Scheduling (TS)
• Transmissions non-overlapping in time
A R BPA PA
PB PB
Time slot 1
Time slot 3
Time slot 2
Time slot 4
5PNC Prototyping & Application
Straightforward Network Coding (SNC)
• Transmissions by nodes A and B still non-overlapping• Relay R uses one time slot to broadcast
RB AP P P RA BP P P
R A BP P P A R B
PA PB
Time slot 1
Time slot 3
Time slot 2
R A BP P P
6PNC Prototyping & Application
Physical-layer Network Coding (PNC)
• Transmissions by nodes A and B are simultaneous!
RB AP P P RA BP P P
R A BP P P A R B
PA PB
Time slot 1 Time slot 2
R A BP P P
7PNC Prototyping & Application
• 1. Background of Physical-layer Network Coding (PNC)
• 2. Real-time PNC Prototype– Demo Video– PNC Realization Challenges
• 3. PNC in Non-relay Setting– Experimental Setup– Performance Evaluation
• 4. Conclusion and Future Works
Outlines
8PNC Prototyping & Application
Specifics
• Frequency-domain PNC (FPNC) for TWRC
–Build on OFDM technology as used in Wi-Fi
–First PNC implementation in 2012
–First real-time PNC implementation in 2013 • Support “real” application in real-time through
API9PNC Prototyping & Application
PNC Implementation: Wireless• Frequency-Domain PNC (FPNC) in GNU Radio testbed
A
BR
10PNC Prototyping & Application
Demo Video: Real-Time File Exchange with PNC
• A short video followed by a demo
See demo video in http://www.youtube.com/watch?v=HmRBm_IIBQQ
11PNC Prototyping & Application
PNC Realization Challenges• Asynchrony
– Signals from nodes A and B may arrive at the relay R with symbol and carrier-phase misalignments
– Solution: PNC with OFDM (FPNC)
• Channel Estimation– Relay needs to estimate two channels based on
simultaneous signals– Solution: FPNC Frame Format Design
12PNC Prototyping & Application
Frame format for RPNC
lts lts data0
0 data
Node A
Node B
80 samples 128 samples
320 samples
Cyclic prefix16 samples
2 long training symbols
0
lts lts 0
CP
CP
0CP tsAtsA
CP tsBtsB0
80 samples
User Detection Channel Estimation
Data Totally Overlap
13PNC Prototyping & Application
PNC Realization Challenges• Channel-decoding and Network Coding (CNC)
– Tradeoff between optimality and simplicity – Solution: Opt for simplicity; adopt 802.11
convolutional code and XOR-CD CNC. Reduced constellation approach
• ARQ for Retransmission– End-to-end ARQ or Relay-assisted ARQ– Solution: Opt for simplicity; adopt end-to-end
ARQ
14PNC Prototyping & Application
Single-user Channel Decoder and PNC Channel Decoder in Overall RPNC System
1,2,...[ ]
ky k
Two Users
Single User Decoder
Binary Viterbi Decoder
User Detector
SU Soft Demodulator
PNC SoftDemodulator
Binary Viterbi Decoder
1,2,...[ ]A B k
x k 1,2,...
[ ] [ ]A B ms m s m
1,2,...or [ ]B m
s m 1,2,...
or [ ]B kx k
1,2,...[ ]A m
s m
1,2,...[ ]A k
x k
PNC Decoder
One User
PNC Decoder
Soft Information (Log Likelihood Ratio: , k = 1, 2,… )( [ ] | [ ] 1)
log( [ ] | [ ] 1)
B
B
P y k x k
P y k x k
15PNC Prototyping & Application
Reduced Constellation Approach to Computing Soft Information on XOR bit
real
Imag
A Bh h
A Bh h
A Bh h
A Bh h
y
0Ah
Bh
Mapping four constellation points to two Constellation points for log
likelihood computation
• BPSK for both nodes A and B• Between two points of the same XOR, choose the one with the shorter Euclidean distance
Received sample with noise
16PNC Prototyping & Application
PNC Realization Challenges• Long Latency between USRP-PC
– The turn-around time for USRP-PC may be long and unpredictable
– Solution: Burst Transmission Mode
17PNC Prototyping & Application
Burst Transmission Mode in RPNC
f2
f1 Tx End node B
Tx End node A
1AX
1BX 2
BX
2AX
BMX
AMX… …
… …
Rx End node B
Rx End node A
A BMX … …
1A BX … …
Tx Relay node R
Beacon
M packets for FDD PNC (Burst 1)
Beacon
Packet Gap
Rx Relay node R
1A BX A B
MX … …
1A BY … …2
A BY A BMY
RandomDelay
2A BX
A BMX
2A BX
2A BX
1A BX
FixedDelay
FixedDelay
Uplink
Downlink
18PNC Prototyping & Application
Normalized throughput of PNC and TS
5 10 15 20 250
0.5
1
1.5
2
SNR (dB)
Nor
mal
ized
Thr
oug
hpu
t
PNCTS
PNC can double the throughput
19PNC Prototyping & Application
• 1. Background of Physical-layer Network Coding (PNC)
• 2. Real-time PNC Prototype– Demo Video– PNC Realization Challenges
• 3. PNC in Non-relay Setting– Network Coding Multiple Access (NCMA)– Performance Evaluation
• 4. Conclusion and Future Works
Outlines
20PNC Prototyping & Application
PNC in Non-Relay Setting?
• Access point wants to get both Message A and Message B, not just their XOR.
• Does PNC have a role to play?
A B
Wireless LAN
Access Point Access Point Internet
A B
C
D
21PNC Prototyping & Application
PNC In Non-Relay Network: Network Coding Multiple Access (NCMA)
• Nodes A and B send to AP simultaneously• AP uses three decoders to separately decode packet A,
packet B, and packet A B• Eight possible events:
– Packets A, B, and A B decoded– Packets A and B decoded– …– Packet A B decoded– None decoded
A AP B
22PNC Prototyping & Application
PHY-Layer Decoders of NCMA
Soft Information (Log Likelihood Ratio: , k = 1, 2,… )( [ ] | [ ] 1)
log( [ ] | [ ] 1)
B
B
P y k x k
P y k x k
23PNC Prototyping & Application
1,2,...[ ]
ky k
Two Users
Single User
User Detector
SU Soft Demodulator
PNC SoftDemodulator
MUD SoftDemodulator
Binary Viterbi Decoder or B
iC 1,2,...or [ ]B k
x k
AiC 1,2,...
[ ]A kx k
Binary Viterbi Decoder
1,2,...[ ]A B k
x k A B
i iC C
Binary Viterbi Decoder
1,2,...[ ]A k
x k
Binary Viterbi Decoder
1,2,...[ ]B k
x k
AiC
BiC
Alternatives for MUD Decoding
1,2,...[ ]
ky k
Two Users
Single User Decoder
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
RMUD 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
PNC Decoder
MUD Decoder
RMUD Decoder
SIC Decoder
Option 1
Option 2
AiC
BiC
One User
24PNC Prototyping & Application
MUD Decoder
NCMA: PHY-layer Bridging
3BC
25PNC Prototyping & Application
Are Lone XOR Packets Useful?
Complementary XOR
Lone XOR
• Do lone XOR packets have a role to play?
26PNC Prototyping & Application
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
1 1 2 2Are XOR packets, { , , ..., }, useful?A B A B A BN NC C C C C C
27PNC Prototyping & Application
NCMA: MAC-Layer Bridging with L = 3Example: Decoding , based on and , with 3B A A BM M M M L
1
2
3
4
5
1AC
2A BC
3BC
4AC
5AC
2AC
3AC
PacketIndex
A BEq AEq BEq
4BC4
A BC
1
2
3
4
5
1AC
2A BC
3BC
4AC 4
BC
5AC
PacketIndex
A BEq AEq BEq
4A BC
PacketIndex
A BEq
1
2
3
4
5
AEq BEq
1AC
2A BC
3BC
4AC
5AC
2AC
3AC
2BC
4BC4
A BC
PacketIndex
A BEq
1
2
3
4
5
AEq BEq
1AC
2A BC
3BC
4AC
5AC
2AC
3AC
2BC
1BC
4BC
5BC
4A BC
28PNC Prototyping & Application
Experiments: Layout of Indoor Environment for 9 USRP N210 Nodes
9
14
5
3
26
7
8
AP
Institute of Network Coding (INC)
29PNC Prototyping & Application
PHY-Layer Packet Decoding Statistics(Balanced Power Case)
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
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
30PNC Prototyping & Application
Solo XOR packets
Overall Throughputs of Different Schemes with RS code parameter LA = 4, 8, 16, 32, and fixed SNR = 9dB.
31PNC Prototyping & Application
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
Overall Throughputs of Different Schemes for Different SNRs LA = 1.5×LB = 24.
32PNC Prototyping & Application
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
Throughputs of Four User Pairs
33PNC Prototyping & Application
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
9
14
5
3
26
7
8
AP
Pairing Strategies
34PNC Prototyping & Application
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?
Strategy 1: P2 and P4Strategy 2: P3 and P5
9
14
5
3
26
7
8
AP
Pair “strong with weak” rather than “strong with strong and weak with weak”
NCMA: Overall Summary
• First venture into non-relay setting for PNC• PNC may have a role to play in the multiple access
scenario– for simplification of decoder design– for jumbo messages
A AP B
35PNC Prototyping & Application
• 1. Background of Physical-layer Network Coding (PNC)
• 2. Real-time PNC Prototype– Demo Video– PNC Realization Challenges
• 3. PNC in Non-relay Setting– Experimental Setup– Performance Evaluation
• 4. Conclusion
Outlines
36PNC Prototyping & Application
• There has been a lot of theoretical work on PNC• Relatively few experimental investigations• RPNC: The first real-time PNC prototype• NCMA: PNC can be applied in a non-relay
setting to boost system throughput• Future: apply PNC and NCMA to commercial
wireless networks: cellular (e.g., LTE-A) and WLAN
Conclusions
37PNC Prototyping & Application
38PNC Prototyping & Application
• “Implementation of Physical-layer Network Coding,” in ICC ’12 and Phycom, Mar. 2013.
• “Real-time Implementation of Physical-layer Network Coding,” in SRIF ’13, an ACM SIGCOMM Workshop.
• “Network-coded Multiple Access,” Technical Report, http://arxiv.org/abs/1307.1514.
To Probe Further
39PNC Prototyping & Application