Interference Cancellation in Two-Path
Successive Relay System with Network
Coding
Chunbo Luo, Dr. Yu Gong & Prof. Fuchun Zheng
School of Systems Engineering
University of Reading
United Kingdom
28/09/2010
Contents
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Introduction and System Model
Physical-layer Network Coding
Interference Cancellation
Simulation Results
Conclusion and Future Work
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Introduction
Cooperative networks
•Demands in wireless communications:
Higher data rate
Higher spectrum efficiency
Reliable connections
Lower energy consumption
Longer battery life
…
•Dilemma: Limited resource <-> Unlimited requirements
•Solutions? Cooperative networks
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Introduction
Cooperative networks
WHY and HOW?
Please see one of the cooperative models: two- Path cooperative model
RELAY
Source: S
Relays: R
Destination: D
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Introduction
Cooperative networks
Large and better coverage
Lower transmission energy
More reliable connection
……
There are loads of benefits. But….
The Limit of half-duplex transmission
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Introduction
Cooperative networks
Solution?
R1 and R2 alternatively relay the data from S to D.
At the relay:
At the destination:
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Introduction
Cooperative networks
But…
INTER RELAY INTERFERENCE (IRI)
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IRI Cancellation
Inter relay interference (IRI)
Solution
• Interference cancellation schemes
• Our scheme: Physical Network Coding (PNC)
What is PNC?
Why can PNC solve the problem?
How does it work?
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IRI Cancellation
Why and how does PNC work to reduce IRI?
To clearly show the basic mechanism: we use the following ideal model:
Ideal environment: no noise, channels are stable (no fading)
R receives:
Then R performs PNC.
At n+1 time slot, R
transmits the PNC result.
D receives:
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IRI Cancellation
Why and how does PNC work to reduce IRI?
At destination, we do another XOR:
IRI is totally removed!!!
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IRI Cancellation
Why and how does PNC work to reduce IRI?
The actual received signal at R is:
How does PNC work?
Key:
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Physical-layer Network Coding
PNC Example-BPSK
If BPSK used, we have:
A: -1, 1
B: -1, 1
So relay received patterns: -2 0 2, using the following equation:
1-0.5*(Magnitude of received signal):
1: A and B are different
0: A and B are the same
1 Mapping to 1
0 Mapping to -1
XOR!
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Physical-layer Network Coding
XOR in Physical layer:
By using certain equations, we have:
Y=A
B
XOR in Physical layer
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Physical-layer Network Coding
XOR in Physical layer: But….
How about other modulation schemes? e.g. QPSK
See the table below (It can be found in the paper)
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IRI Cancellation
XOR in Physical layer: But….
How about in practical systems?
The transmissions suffer from channel fading and additive noises.
The system model
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IRI Cancellation
In practical system
1) MAP Detection at relays:
2) Joint detection and PNC:
3) Relay transmission
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IRI Cancellation
In practical situation:
4) MAP Detection at destination:
5) PNC decoding:
where
is the result we want!
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Simulation results
Gaussian model:
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Simulation results
Rayleigh model:
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Conclusion and future work
 The proposed PNC interference cancellation
scheme can effectively reduce IRI
 Its performance depends on the accuracy of
channel estimation (MAP detection)
 PNC can be used in signal processing areas to
deal with interference problems
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Conclusion and future work
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The scenario with direct link available
The joint coding and detection
Multi-source multi relay scenario
The complexity of MAP detection
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Interference Cancellation in Two-Path
Successive Relay System with Network Coding
Thank you!
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