67 research outputs found
Symbol-by-symbol APP decoding of the Golay code and iterative decoding of concatenated Golay codes
An efficient coset based symbol-by-symbol soft-in/soft-out a posteriori probability (APP) decoding algorithm is presented for the Golay code. Its application in the iterative decoding of concatenated Golay codes is analyzed.published_or_final_versio
Iterative decoding for error resilient wireless data transmission
Both turbo codes and LDPC codes form two new classes of codes that offer energy
efficiencies close to theoretical limit predicted by Claude Shannon. The features of turbo
codes include parallel code catenation, recursive convolutional encoders, punctured
convolutional codes and an associated decoding algorithm. The features of LDPC codes
include code construction, encoding algorithm, and an associated decoding algorithm.
This dissertation specifically describes the process of encoding and decoding for both turbo
and LDPC codes and demonstrates the performance comparison between theses two codes
in terms of some performance factors. In addition, a more general discussion of iterative
decoding is presented.
One significant contribution of this dissertation is a study of some major performance
factors that intensely contribute in the performance of both turbo codes and LDPC codes.
These include Bit Error Rate, latency, code rate and computational resources. Simulation
results show the performance of turbo codes and LDPC codes under different performance
factors
FPGA based Design and Simulation of Extended Golay Codec with Hardware Optimization for high speed Applications
In wireless communication systems the ability of the receiver to detect and correct the error from the received information is become one of the most important issue, so as to provide the processor the correct information data. To achieve this there are numbers of such methods are available to implement the hardware and software. But, length of the communication link plays an important role because the distance of the transmitter and the receiver depends on the length as length increases the distance between the transmitter and the receiver, and multiple bits of the transmitted information may change due to the effect of noise on the transmitted signal. This can cause extreme loss in many cases. This paper presents a brief of Field Programmable Gate Array (FPGA) based design and simulation of Golay Code (G23) and Extended Golay Code (G24) Encoding scheme. This paper using the Golay Encoder to work on the optimization of the time delay of the operational circuit to encode a data packet
Heuristics for optimizing in complexity SISO trellis-based decoding of linear block codes
- Un problÚme important qui se pose lors du décodage des codes linéaires en blocs par l'algorithme Forward-Backward (FB) est de trouver une permutation des coordonnées qui minimise la complexité de branches des treillis associés aux codes. Dans cet article, des heuristiques sont proposées. Nous fournissons une table récapitulative des résultats obtenus pour de nombreux codes et les comparons à ceux publiés dans la littérature. L'optimisation en complexité des treillis et donc de l'algorithme FB permet d'envisager de nouveaux schémas de concaténation parallÚle de codes en blocs, basés sur des codes composants plus puissants que de simples codes de Hamming (étendus) et de comparer leurs performances à celles des turbo-codes
802.11 Payload Iterative decoding between multiple transmission attempts
Abstract. The institute of electrical and electronics engineers (IEEE) 802.11 standard specifies widely used technology for wireless local area networks (WLAN). Standard specifies high-performance physical and media access control (MAC) layers for a distributed network but lacks an effective hybrid automatic repeat request (HARQ). Currently, the standard specifies forward error correction (FEC), error detection (ED), and automatic repeat request (ARQ), but in case of decoding errors, the previously transmitted information is not used when decoding the retransmitted packet. This is called Type 1 HARQ. Type 1 HARQ uses received energy inefficiently, but the simple implementation makes it an attractive solution. Unfortunately, research applying more sophisticated HARQ schemes on top of IEEE 802.11 is limited.
In this Masterâs Thesis, a novel HARQ technology based on packet retransmissions that can be decoded in a turbo-like manner, keeping as much as possible compatibility with vanilla 802.11, is proposed. The proposed technology is simulated with both the IEEE 802.11 code and with the robust, efficient and smart communication in unpredictable environments (RESCUE) code. An additional interleaver is added before the convolutional encoder in the proposed technology, interleaving either the whole frame or only the payload to enable effective iterative decoding. For received frames, turbo-like iterations are done between initially transmitted packet copy and retransmissions. Results are compared against the non-iterative combining method maximizing signal-to-noise ratio (SNR), maximum ratio combining (MRC). The main design goal for this technology is to maintain compatibility with the 802.11 standard while allowing efficient HARQ. Other design goals are range extension, higher throughput, and better performance in terms of bit error rate (BER) and frame error rate (FER).
This technology can be used for range extension at low SNR range and may provide up to 4 dB gain at medium SNR range compared to MRC. At high SNR, technology can reduce the penalty from retransmission allowing higher average modulation and coding scheme (MCS). However, these gains come with the cost of computational complexity from the iterative decoding. The main limiting factors of the proposed technology are decoding errors in the header and the scrambler area, and resource-hungry-processing. In simulations, perfect synchronization and packet detection is assumed, but in reality, especially at low SNR, packet detection and synchronization would be challenging. 802.11 pakettien iteratiivinen dekoodaus lÀhetysten vÀlillÀ. TiivistelmÀ. IEEE 802.11-standardi mÀÀrittelee yleisesti kÀytetyn teknologian langattomille lÀhiverkoille. Standardissa mÀÀritellÀÀn tehokas fyysinen- ja verkkoliityntÀkerros hajautetuille verkoille, mutta siitÀ puuttuu tehokas yhdistetty automaattinen uudelleenlÀhetys. NykyisellÀÀn standardi mÀÀrittelee virheenkorjaavan koodin, virheellisen paketin tunnistuksen sekÀ automaattisen uudelleenlÀhetyksen, mutta aikaisemmin lÀhetetyn paketin informaatiota ei kÀytetÀ hyvÀksi uudelleenlÀhetystilanteessa. TÀmÀ menetelmÀ tunnetaan tyypin yksi yhdistettynÀ automaattisena uudelleenlÀhetyksenÀ. Tyypin yksi yhdistetty automaattinen uudelleenlÀhetys kÀyttÀÀ vastaanotettua signaalia tehottomasti, mutta yksinkertaisuus tekee siitÀ houkuttelevan vaihtoehdon. Valitettavasti edistyneempien uudelleenlÀhetysvaihtoehtojen tutkimusta 802.11-standardiin on rajoitetusti.
TÀssÀ diplomityössÀ esitellÀÀn uusi yhdistetty uudelleenlÀhetysteknologia, joka pohjautuu pakettien uudelleenlÀhetykseen, sallien turbo-tyylisen dekoodaamisen sÀilyttÀen mahdollisimman hyvÀn taaksepÀin yhteensopivuutta alkuperÀisen 802.11-standardin kanssa. TÀmÀ teknologia on simuloitu kÀyttÀen sekÀ 802.11- ettÀ nk. RESCUE-virheenkorjauskoodia. Teknologiassa uusi lomittaja on lisÀtty konvoluutio-enkoodaajan eteen, sallien tehokkaan iteratiivisen dekoodaamisen, lomittaen joko koko paketin tai ainoastaan hyötykuorman. Vastaanotetuille paketeille tehdÀÀn turbo-tyyppinen iteraatio alkuperÀisen vastaanotetun kopion ja uudelleenlÀhetyksien vÀlillÀ. Tuloksia vertaillaan eiiteratiiviseen yhdistÀmismenetelmÀÀn, maksimisuhdeyhdistelyyn, joka maksimoi yhdistetyn signaali-kohinasuhteen. TÀrkeimpÀnÀ suunnittelutavoitteena tÀssÀ työssÀ on tehokas uudelleenlÀhetysmenetelmÀ, joka yllÀpitÀÀ taaksepÀin yhteensopivuutta IEEE 802.11-standardin kanssa. Muita tavoitteita ovat kantaman lisÀys, nopeampi yhteys ja matalampi bitti- ja pakettivirhesuhde.
KehitettyÀ teknologiaa voidaan kÀyttÀÀ kantaman lisÀykseen matalan signaalikohinasuhteen vallitessa ja se on jopa 4 dB parempi kohtuullisella signaalikohinasuhteella kuin maksimisuhdeyhdistely. Korkealla signaali-kohinasuhteella teknologiaa voidaan kÀyttÀÀ pienentÀmÀÀn hÀviötÀ epÀonnistuneesta paketinlÀhetyksestÀ ja tÀten sallien korkeamman modulaatio-koodiasteen kÀyttÀmisen. Valitettavasti nÀmÀ parannukset tulevat kasvaneen laskennallisen monimutkaisuuden kustannuksella, johtuen iteratiivisesta dekoodaamisesta. Isoimmat rajoittavat tekijÀt teknologian kÀytössÀ ovat dekoodausvirheet otsikossa ja datamuokkaimen siemenessÀ. TÀmÀn lisÀksi kÀyttöÀ rajoittaa resurssisyöppö prosessointi. Simulaatioissa oletetaan tÀydellinen synkronisointi, mutta todellisuudessa, erityisesti matalalla signaali-kohinasuhteella, paketin tunnistus ja synkronointi voivat olla haasteellisia
Replacing the Soft FEC Limit Paradigm in the Design of Optical Communication Systems
The FEC limit paradigm is the prevalent practice for designing optical
communication systems to attain a certain bit-error rate (BER) without forward
error correction (FEC). This practice assumes that there is an FEC code that
will reduce the BER after decoding to the desired level. In this paper, we
challenge this practice and show that the concept of a channel-independent FEC
limit is invalid for soft-decision bit-wise decoding. It is shown that for low
code rates and high order modulation formats, the use of the soft FEC limit
paradigm can underestimate the spectral efficiencies by up to 20%. A better
predictor for the BER after decoding is the generalized mutual information,
which is shown to give consistent post-FEC BER predictions across different
channel conditions and modulation formats. Extensive optical full-field
simulations and experiments are carried out in both the linear and nonlinear
transmission regimes to confirm the theoretical analysis
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