Turbo Codes

kt.agh.edu.pl

Turbo Codes

Turbo Codes

Mateusz Wielgosz

1


Introduction

History

Turbo Codes

Performance

Practical issues

Applications

Trends

Conclusion

References

2


History

Standard convolutional codes offered 3dB gap between Shannon’s limit and

practical implementation.

Newly proposed “turbo codes” in 1993 offered performance at 0,7dB from that

theoretical limit.

Early versions presented variety of problems:

o Computational complexity

o High latency

o Error floors

o Memory requirements

First practical applications came around 1998 with 3G standards.

3


Turbo Codes

Composite structure – multiple

low-complexity codes.

Interleaving – reordering of

information bits.

Soft iterative decoding – repetitive

decoding, estimates of values.

4


Why “Turbo”?

Maximum Likehood (ML) – optimal, impractical

Iterative

Soft-in, soft out

5


Performance

Rates different that 1/3 can

be obtained by “puncturing”.

“waterfall” – interleaver

performance.

“error floor” – decoder

performance.

6


Interleaver designs

7


Practical Issues

Error Rate Performance and Power Savings

Computational Complexity

Memory Requirements

Latency

Flexibility

Intellectual Property

8


Applications

3G and 4G Wireless

o Wideband-CDMA

o cdma2000

o Time-division, synchronous CDMA

Satellite Communications

o NASA missions

o Digital Video Broadcasting - Return Channel via Satellite (DVB-RCS)

o Digital Video Broadcasting via Satellite, Second Generation (DVB-S2)

o Broadband Satellite Systems

Wireless Networking

o Wi-MAX (IEEE 802.16)

o Wi-Fi (IEEE 802.11)

Other

9


Future Trends

Further specialization and new classes of turbo codes

Additional performance improvements, including closing on capacity limit

Improvements in computational efficiency are still possible

Tailoring turbo codes for channel conditions and system desings

New ranges of applications (storage media)

10


Conclusion

Few concluding remarks:

Unprecedented performance

Composition of codes

Iterative decoding with soft decisions

Flexibility

Widespread use

11


References

1. Ken Gracie, Marie-Helene Hamon – “Turbo and Turbo-Like Codes: Principles and

Applications in Telecommunications”

2. Emilia Kasper – “Turbo Codes

3. Bernard Sklar – “Fundamentals of Turbo Codes

4. D. Divsalar, F. Pollara – “Turbo Codes for Deep-Space Communications”

5. Johan Briffa – “Interleavers for Turbo Codes

6. Jakob Dahl Anderson – “A Turbo Tutorial”

7. Anum Ali – “Soft In Soft Out Reed Solomon Decoding”

12

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