Abstract
Trellis decoding is a popular method to recover encoded information corrupted during transmission over a noisy channel. Prominent members of this class of decoding algorithms are the Viterbi algorithm, which provides maximum likelihood estimates, and the BCJR algorithm, which is a maximum a posteriori estimator commonly used in iterative decoding. In this thesis, the Viterbi algorithm is chosen since it provides a good tradeoff between achievable coding gain and implementation complexity. This is the basis for considerations on simplified, hybrid, and, most importantly, flexible VLSI architectures.
Algorithm simplifications are necessary to reduce the computational burden laid
on an implementation platform. In our work on trellis decoding blocks, a simplification that lowers the number of arithmetic operations is derived and evaluated. By using a complementary code property, the arithmetic complexity of the main part on the Viterbi algorithm is reduced by 17%. Synthesized blocks show varying savings for cell area and estimated power consumption. A comparison to a competing simplification shows the advantage in a hardware implementation of our work for the important class of rate 1/2 convolutional codes.
Hybrid architectures try to combine benefits of several approaches to lower the drawbacks of the individual contributors. For survivor path processing in Viterbi decoders, a new hybrid approach is proposed. A lowlatency algorithm, whose implementation complexity quickly increases with the number of trellis states, is combined with a scalable RAMbased method. As a result, the developed hybrid architecture exhibits a better latencycomplexity behavior compared to other hybrid approaches.
Flexible VLSI architectures to cover several communication standards become increasingly important as fabrication costs for microchips rise rapidly with every new process generation. In the context of flexible trellis decoding, earlier work mostly concentrated on varying encoder memory and thus the number of trellis states. This work studies the effects on hardware size and throughput introduced by flexibility if the code rate is varied. The investigation of a decoder for bandwidthefficient codes, which was fabricated in a 0.13 um digital CMOS process and verified for functionality, distinguishes between task and rateflexibility. A comparison is carried out between flexible designs, which decode both convolutional and TCM codes and provide two or three transmission rates. It is concluded that the larger number of rates is more beneficial from a costflexibility viewpoint.
Algorithm simplifications are necessary to reduce the computational burden laid
on an implementation platform. In our work on trellis decoding blocks, a simplification that lowers the number of arithmetic operations is derived and evaluated. By using a complementary code property, the arithmetic complexity of the main part on the Viterbi algorithm is reduced by 17%. Synthesized blocks show varying savings for cell area and estimated power consumption. A comparison to a competing simplification shows the advantage in a hardware implementation of our work for the important class of rate 1/2 convolutional codes.
Hybrid architectures try to combine benefits of several approaches to lower the drawbacks of the individual contributors. For survivor path processing in Viterbi decoders, a new hybrid approach is proposed. A lowlatency algorithm, whose implementation complexity quickly increases with the number of trellis states, is combined with a scalable RAMbased method. As a result, the developed hybrid architecture exhibits a better latencycomplexity behavior compared to other hybrid approaches.
Flexible VLSI architectures to cover several communication standards become increasingly important as fabrication costs for microchips rise rapidly with every new process generation. In the context of flexible trellis decoding, earlier work mostly concentrated on varying encoder memory and thus the number of trellis states. This work studies the effects on hardware size and throughput introduced by flexibility if the code rate is varied. The investigation of a decoder for bandwidthefficient codes, which was fabricated in a 0.13 um digital CMOS process and verified for functionality, distinguishes between task and rateflexibility. A comparison is carried out between flexible designs, which decode both convolutional and TCM codes and provide two or three transmission rates. It is concluded that the larger number of rates is more beneficial from a costflexibility viewpoint.
Original language  English 

Qualification  Doctor 
Awarding Institution 

Supervisors/Advisors 

Award date  2007 Mar 23 
Publisher  
Publication status  Published  2007 
Bibliographical note
Defence detailsDate: 20070323
Time: 10:15
Place: E:1406, Ehuset, Ole Römers väg 3, Lunds Tekniska Högskola, Lund
External reviewer(s)
Name: Fettweis, Gerhard
Title: Professor
Affiliation: Technische Universität Dresden, Dresden, Tyskland

Subject classification (UKÄ)
 Electrical Engineering, Electronic Engineering, Information Engineering
Free keywords
 Electronics
 Signalbehandling
 Signal processing
 VLSI
 Viterbi algorithm
 trellis decoding
 TCM
 survivor path
 flexibility
 convolutional codes
 ACS
 ASIC
 Elektronik
 Telecommunication engineering
 Telekommunikationsteknik