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 – Experimental Setup – Performance Evaluation 4. Conclusion PNC Prototyping & Application 2

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 PNC Prototyping & Application 3

Simplest Set-up: Two-Hop Relay Network R A B • 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?

PNC Prototyping & Application 4

Traditional Scheduling (TS)

A

P A P B

Time slot 1 Time slot 3 R

P A P B

Time slot 2 Time slot 4 •

Transmissions non-overlapping in time

B PNC Prototyping & Application 5

Straightforward Network Coding (SNC)

P B



P R



P A

A

P A P R



P A



P B

Time slot 1 Time slot 3 R

P B P R



P A



P B P A



P R



P B

B Time slot 2 • •

Transmissions by nodes A and B still non-overlapping Relay R uses one time slot to broadcast

PNC Prototyping & Application 6

Physical-layer Network Coding (PNC)

P B



P R



P A

A

P A P R



P A



P B

Time slot 1 R

P B P R



P A



P B P A



P R



P B

B Time slot 2 •

Transmissions by nodes A and B are simultaneous!

PNC Prototyping & Application 7

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 – Experimental Setup – Performance Evaluation 4. Conclusion and Future Works PNC Prototyping & Application 8

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 API 9 PNC Prototyping & Application

PNC Implementation: Wireless

• Frequency-Domain PNC (FPNC) in GNU Radio testbed R A B PNC Prototyping & Application 10

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 PNC Prototyping & Application 11

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

PNC Prototyping & Application 12

Frame format for RPNC

80 samples Node

A

CP ts A ts A

Node

B

0

80 samples

0 CP ts B ts B CP

2 long training symbols 128 samples

lts lts

Data Totally Overlap

320 samples

0 0 0 CP lts lts data 0 data

Cyclic prefix 16 samples

User Detection Channel Estimation

PNC Prototyping & Application 13

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

PNC Prototyping & Application 14

Single-user Channel Decoder and PNC Channel Decoder in Overall RPNC System  

k

Two Users PNC Soft Demodulator PNC Decoder  1,2,...

User Detector One User 

x



k

 1,2,...

Binary Viterbi Decoder 

A



B



m

 1,2,...

SU Soft Demodulator  or   Single User Decoder

A B



k

 1,2,...



k

 1,2,...



PNC Decoder

Binary Viterbi 

A



m

 1,2,...

Decoder  or 

B



m

 1,2,...

  Soft Information (Log Likelihood Ratio: , k = 1, 2,… )

B B

   PNC Prototyping & Application 15

Reduced Constellation Approach to Computing Soft Information on XOR bit

Received sample with noise

Imag

Mapping four constellation points

y

to two Constellation points for log likelihood computation  

A h B h A h B

0

h B h A



h B h A h A



h B real

• BPSK for both nodes A • and B Between two points of the same XOR, choose the one with the shorter Euclidean distance PNC Prototyping & Application 16

PNC Realization Challenges

• Long Latency between USRP-PC – The turn-around time for USRP-PC may be long and unpredictable –

Solution: Burst Transmission Mode

PNC Prototyping & Application 17

Burst Transmission Mode in RPNC

Uplink Tx End node A Tx End node B Fixed Delay

X

1

A X

1

B

Packet Gap

X

2

A

f 1

X

2

B

… … … …

A X M B X M

Fixed Delay

Y

1

Y

2 … …

Y M

Rx Relay node R M packets for FDD PNC (Burst 1) Downlink Tx Relay node R Bea con

X

1

X

1

X

2 f 2

X

2 … … … …

X M X M

Rx End node A Random Delay

X

1

X

2 … …

X M

Rx End node B Bea con PNC Prototyping & Application 18

Normalized throughput of PNC and TS 2 1.5

PNC TS 1

PNC can double the throughput

0.5

0 5 10 15 SNR (dB) 20 25 PNC Prototyping & Application 19

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 – Network Coding Multiple Access (NCMA) – Performance Evaluation 4. Conclusion and Future Works PNC Prototyping & Application 20

PNC in Non-Relay Setting?

Access Point Access Point Internet C A Wireless LAN A B B • • Access point wants to get both Message A and Message B, not just their XOR.

Does PNC have a role to play?

PNC Prototyping & Application 21 D

PNC In Non-Relay Network: Network Coding Multiple Access (NCMA) A AP B • • • Nodes A and B send to AP simultaneously AP uses three decoders to separately decode packet A,  Eight possible events: – – – – – Packets A and B decoded … None decoded PNC Prototyping & Application 22

PHY-Layer Decoders of NCMA



A



k

 1,2,...

Binary Viterbi Decoder MUD Soft Demodulator 

B



k

 1,2,...

Binary Viterbi Decoder 

x



k

 1,2,...

Two Users PNC Soft Demodulator

C i A C i B

Binary Viterbi Decoder

C i A



C i B

 

k

 1,2,...

User Detector SU Soft Demodulator Single User  or  

A B



k

 1,2,...



k

 1,2,...

 Binary Viterbi Decoder

C i A

 or

C i B

  Soft Information (Log Likelihood Ratio:  PNC Prototyping & Application

B

[ ]

, k =

1, 2,… ) 23

Alternatives for MUD Decoding

RMUD Soft Demodulator  

x A x B



k

 1, 2 ,...

Binary Viterbi Decoder 

k

 1,2 ,...

Binary Viterbi Decoder

C i A C i B C i A

Option 1 Option 2 MUD Decoder RMUD Decoder SIC Decoder

C i B

MUD Decoder

 Two Users PNC Soft Demodulator PNC Decoder 

x A



B



k

 1, 2 ,...

Binary Viterbi Decoder 

k

 1, 2 ,...

User Detector One User SU Soft Demodulator 

x A

 or 

x B

Single User Decoder 

k

 1, 2 ,...



k

 1, 2 ,...

 Binary Viterbi Decoder PNC Prototyping & Application

C i A



C i B C i A

 or

C i B

 24

NCMA: PHY-layer Bridging

C

3

B

PNC Prototyping & Application 25

Are Lone XOR Packets Useful?

• Do lone XOR packets have a role to play?

PNC Prototyping & Application Complementary XOR Lone XOR 26

MAC-Layer Erasure Code + PHY-Layer Channel Code

Message

M A

Message

M B

 Packets {

C C

1

A

, 2

A

,...,

C N A

}  Packets {

C C

1

B

, 2

B

,...,

C N B

} packets {

C

1

A

,

C

2

A

,...,

C N A

}, it can obtain

M A

.

Similarly for

M B

.

Are XOR packets, {

C

1

A



C

1

B

,

C

2

A



C

2

B

, ...,

C N A



C N B

}, useful?

PNC Prototyping & Application 27

NCMA: MAC-Layer Bridging with L = 3

Example: Decoding

M B

, based on

M A

and

M A



M B

, with

L

 3 Packet Index 1 2 3 4 5

Eq A C

1

A Eq C

2

C

4

A C

5

A C

4

Eq B C

3

B C

4

B

Packet Index 1 2 3 4 5

Eq A C

1

A C

2

A C

3

A C

4

A C

5

A Eq C C

2 4

Eq B C

3

B C

4

B

Packet Index 1 2 3 4 5

Eq A C

1

A C

2

A C

3

A C

4

A C

5

A Eq C C

2 4

Eq B C

1

B C

2

B C

3

B C

4

B C

5

B

Packet Index 1 2 3 4 5 PNC Prototyping & Application

Eq A C

1

A C

2

A C

3

A C

4

A C

5

A Eq C C

2 4

Eq B C

2

B C

3

B C

4

B

28

Experiments: Layout of Indoor Environment for 9 USRP N210 Nodes

4 6 3 5 1 9 AP 2 7 8 Institute of Network Coding (INC)

PNC Prototyping & Application 29

PHY-Layer Packet Decoding Statistics (Balanced Power Case)

Solo XOR

100%

packets

80% 60% AB AX|BX A|B X NONE X X 40% AX|BX AX|BX 20% 0% 7 7.5

8 8.5

9 9.5

SNR (dB) 10 10.5

11 AB: Both A and B decoded AX|BX: A and XOR decoded or B and XOR decoded A|B: Either only A or only B decoded X: Only XOR decoded 11.5

PNC Prototyping & Application 30

Overall Throughputs of Different Schemes with RS code parameter LA = 4, 8, 16, 32, and fixed SNR = 9dB.

1.4

1.3

1.2

1.1

1 0.9

0.8

5 10 15 NCMA w. RMUD Upper Bound NCMA w. RMUD, L A =1.5L

B NCMA w. RMUD, L A =L B RMUD L B 20 25 30 PNC Prototyping & Application 31

Overall Throughputs of Different Schemes for Different SNRs L

A

= 1.5

×

L B

= 24.

2 1.5

NCMA MUD SU 1 0.5

0 7.5

8 8.5

9 SNR (dB) 9.5

PNC Prototyping & Application 10 10.5

32

Throughputs of Four User Pairs

2 1.5

1 A, NCMA w. RMUD B, NCMA w. RMUD A, NCMA w. RMUD+SIC B, NCMA w. RMUD+SIC A, SU B, SU

4 6 3 5 1 9 AP 2 7 8

0.5

0 Pair 1 Pair 2 Pair 3 Pair 4 PNC Prototyping & Application 33

Pairing Strategies

4 6 3 5 1 9 AP 2 7 8

3 2.5

NCMA with (RMUD+SIC) Strategy 1 Strategy 2 2 1.5

1 0.5

0 Loc. 2 Loc. 3 Loc. 4 Loc. 5 Sum

Scenario: Four users at locations 2, 3, 4, 5. How to form pairs?

Strategy 1: P2 and P4 Strategy 2: P3 and P5 Pair “strong with weak” rather than “strong with strong and weak with weak”

PNC Prototyping & Application 34

NCMA: Overall Summary

A AP B • • 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 PNC Prototyping & Application 35

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 – Experimental Setup – Performance Evaluation 4. Conclusion PNC Prototyping & Application 36

Conclusions

• • • • • 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 PNC Prototyping & Application 37

PNC Prototyping & Application 38

To Probe Further

• “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

.

PNC Prototyping & Application 39