Synthetic Aperture Radar Algorithms on Transport Triggered Architecture Processors using OpenCL

Live SAR imaging from small UAVs is an emerging field. On-board processing of the radar data requires high-performance and energy-efficient platforms. One candidate for this are Transport Triggered Architecture (TTA) processors. We implement Backprojection and Backprojection Autofocus on a TTA processor specially adapted for this task using OpenCL. The resulting implementation is compared to other platforms in terms of energy efficiency. We find that the TTA is on-par with embedded GPUs and surpasses other OpenCL-based platforms. It is outperformed only by a dedicated FPGA implementation. © 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Décodage de codes polaires sur des architectures programmables

RÉSUMÉ Les codes polaires constituent une classe de codes correcteurs d’erreurs inventés récemment qui suscite l’intérêt des chercheurs et des industriels, comme en atteste leur sélection pour le codage des canaux de contrôle dans la prochaine génération de téléphonie mobile (5G). Un des enjeux des futurs réseaux mobiles est la virtualisation des traitements numériques du signal, et en particulier les algorithmes de codage et de décodage. Afin d’améliorer la flexibilité du réseau, ces algorithmes doivent être décrits de manière logicielle et être déployés sur des architectures programmables. Une telle infrastructure de réseau permet de mieux répartir l’effort de calcul sur l’ensemble des noeuds et d’améliorer la coopération entre cellules. Ces techniques ont pour but de réduire la consommation d’énergie, d’augmenter le débit et de diminuer la latence des communications. Les travaux présentés dans ce manuscrit portent sur l’implémentation logicielle des algorithmes de décodage de codes polaires et la conception d’architectures programmables spécialisées pour leur exécution. Une des caractéristiques principales d’une chaîne de communication mobile est l’instabilité du canal de communication. Afin de remédier à cette instabilité, des techniques de modulations et de codages adaptatifs sont utilisées dans les normes de communication. Ces techniques impliquent que les décodeurs supportent une vaste gamme de codes : ils doivent être génériques. La première contribution de ces travaux est l’implémentation logicielle de décodeurs génériques des algorithmes de décodage "à Liste" sur des processeurs à usage général. En plus d’être génériques, les décodeurs proposés sont également flexibles. Ils permettent en effet des compromis entre pouvoir de correction, débit et latence de décodage par la paramétrisation fine des algorithmes. En outre, les débits des décodeurs proposés atteignent les performances de l’état de l’art et, dans certains cas, les dépassent. La deuxième contribution de ces travaux est la proposition d’une nouvelle architecture programmable performante spécialisée dans le décodage de codes polaires. Elle fait partie de la famille des processeurs à jeu d’instructions dédiés à l’application. Un processeur de type RISC à faible consommation en constitue la base. Cette base est ensuite configurée, son jeu d’instructions est étendu et des unités matérielles dédiées lui sont ajoutées. Les simulations montrent que cette architecture atteint des débits et des latences proches des implémentations logicielles de l’état de l’art sur des processeurs à usage général. La consommation énergétique est réduite d’un ordre de grandeur.----------ABSTRACT Polar codes are a recently invented class of error-correcting codes that are of interest to both researchers and industry, as evidenced by their selection for the coding of control channels in the next generation of cellular mobile communications (5G). One of the challenges of future mobile networks is the virtualization of digital signal processing, including channel encoding and decoding algorithms. In order to improve network flexibility, these algorithms must be written in software and deployed on programmable architectures. Such a network infrastructure allow dynamic balancing of the computational effort across the network, as well as inter-cell cooperation. These techniques are designed to reduce energy consumption, increase throughput and reduce communication latency. The work presented in this manuscript focuses on the software implementation of polar codes decoding algorithms and the design of programmable architectures specialized in their execution. One of the main characteristics of a mobile communication chain is that the state of communication channel changes over time. In order to address issue, adaptive modulation and coding techniques are used in communication standards. These techniques require the decoders to support a wide range of codes : they must be generic. The first contribution of this work is the software implementation of generic decoders for "List" polar decoding algorithms on general purpose processors. In addition to their genericity, the proposed decoders are also flexible. Trade-offs between correction power, throughput and decoding latency are enabled by fine-tuning the algorithms. In addition, the throughputs of the proposed decoders achieve state-of-the-art performance and, in some cases, exceed it. The second contribution of this work is the proposal of a new high-performance programmable architecture specialized in polar code decoding. It is part of the family of Application Specific Instruction-set Processors (ASIP). The base architecture is a RISC processor. This base architecture is then configured, its instruction set is extended and dedicated hardware units are added. Simulations show that this architecture achieves throughputs and latencies close to state-of-the-art software implementations on general purpose processors. Energy consumption is reduced by an order of magnitude. The energy required per decoded bit is about 10 nJ on general purpose processors compared to 1 nJ on proposed processors when considering the Successive Cancellation (SC) decoding algorithm of a polar code (1024,512). The third contribution of this work is also the design of an ASIP architecture

Transport Triggered Polar Decoders

In this paper, the first transport triggered architecture (TTA) customized for the decoding of polar codes is proposed. A first version of this programmable processor is optimized for the successive cancellation (SC) decoding of polar codes while a second architecture is further specialized to also support Soft CANcellation (SCAN) decoding. Both architectures were fully validated on FPGA device by prototyping. The first architecture was also synthesized in 28nm ASIC technology. It runs at a frequency of 800 MHz and reaches a throughput of 352 Mbps for a (1024, 512) polar code decoded with the SC algorithm. Compared to previous work, the energy consumption is reduced by one order of magnitude (0.14 nJ / bit) and the throughput is increased fivefold. Compared to an optimized software implementation on a general purpose processor (x86 architecture), the throughput is 37 % higher and the energy consumption is two orders of magnitude lower. TTA can be seen as a way to reduce the gap between programmable and dedicated polar decoders.acceptedVersionPeer reviewe