Interference Cancellation in Two-Path Successive Relay System with Network Coding

Chunbo Luo, Dr. Yu Gong & Prof. Fuchun Zheng

School of Systems EngineeringUniversity of Reading

United Kingdom

28/09/2010

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Contents

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 rateHigher spectrum efficiencyReliable connectionsLower energy consumptionLonger 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

Source: S Relays: R Destination: D

RELA

Y

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Introduction

Cooperative networks

Large and better coverageLower transmission energyMore reliable connection……

There are loads of benefits. But….

The Limit of half-duplex transmission

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Introduction

Cooperative networks

At the relay:

At the destination:

R1 and R2 alternatively relay the data from S to D.

Solution?

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Introduction

Cooperative networks

But… INTER RELAY INTERFERENCE (IRI)

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IRI Cancellation

Inter relay interference (IRI)

• Interference cancellation schemes• Our scheme: Physical Network Coding (PNC)

What is PNC?Why can PNC solve the problem?How does it work?

Solution

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IRI Cancellation

To clearly show the basic mechanism: we use the following ideal model: Ideal environment: no noise, channels are stable (no fading)

Why and how does PNC work to reduce IRI?

R receives:

At n+1 time slot, R transmits the PNC result.

D receives:

Then R performs PNC.

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IRI Cancellation

Why and how does PNC work to reduce IRI?

IRI is totally removed!!!

At destination, we do another XOR:

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IRI Cancellation

Why and how does PNC work to reduce IRI?

Key:

How does PNC work?

The actual received signal at R is:

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1-0.5*(Magnitude of received signal): 1: A and B are different0: A and B are the same

Physical-layer Network Coding

PNC Example-BPSK

A: -1, 1B: -1, 1

So relay received patterns: -2 0 2, using the following equation:

If BPSK used, we have:

1 Mapping to 10 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….

The system model

The transmissions suffer from channel fading and additive noises.

How about in practical systems?

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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

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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Thank you!

Interference Cancellation in Two-Path Successive Relay System with Network Coding