436 research outputs found
A Cascadable Pragmatic Block Decoding Algorithm Exploiting Channel Measurement Information
The complexity of algorithms to perform soft decision decoding on block codes has impeded their inclusion in practical systems. A well-known class of algorithms for decoding block codes utilizing channel measurement information along with the algebraic properties of the code are the Chase algorithms.1 In this paper a decoding method similar to Chase\u27s third algorithm is presented. However, in this method, a single test pattern or alternate codeword makes up one stage of the decoder. The method uses information from the previous decoding(s) to assist in generating a test pattern. This single stage âSecond Chance Algorithmâ can then be extended to a âThird Chance Algorithmâ (and beyond) to enhance performance. The method does not invoke the hard decision decoder as often as the Chase algorithms
Determinate-state convolutional codes
A determinate state convolutional code is formed from a conventional convolutional code by pruning away some of the possible state transitions in the decoding trellis. The type of staged power transfer used in determinate state convolutional codes proves to be an extremely efficient way of enhancing the performance of a concatenated coding system. The decoder complexity is analyzed along with free distances of these new codes and extensive simulation results is provided of their performance at the low signal to noise ratios where a real communication system would operate. Concise, practical examples are provided
Peak-to-Mean Power Control in OFDM, Golay Complementary Sequences, and ReedâMuller Codes
We present a range of coding schemes for OFDM transmission using binary, quaternary, octary, and higher order modulation that give high code rates for moderate numbers of carriers. These schemes have tightly bounded peak-to-mean envelope power ratio (PMEPR) and simultaneously have good error correction capability. The key theoretical result is a previously unrecognized connection between Golay complementary sequences and second-order ReedâMuller codes over alphabets â€2h. We obtain additional flexibility in trading off code rate, PMEPR, and error correction capability by partitioning the second-order ReedâMuller code into cosets such that codewords with large values of PMEPR are isolated. For all the proposed schemes we show that encoding is straightforward and give an efficient decoding algorithm involving multiple fast Hadamard transforms. Since the coding schemes are all based on the same formal generator matrix we can deal adaptively with varying channel constraints and evolving system requirements
Performance of binary block codes at low signal-to-noise ratios
The performance of general binary block codes on an unquantized additive white Gaussian noise (AWGN) channel at low signal-to-noise ratios is considered. Expressions are derived for both the block error and the bit error probabilities near the point where the bit signal-to-noise ratio is zero. These expressions depend on the global geometric structure of the code, although the minimum distance still seems to play a crucial role. Examples of codes such as orthogonal codes, biorthogonal codes, the (24,12) extended Golay code, and the (15,6) expurgated BCH code are discussed. The asymptotic coding gain at low signal-to-noise ratios is also studied
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
Sparse Graph Codes for Quantum Error-Correction
We present sparse graph codes appropriate for use in quantum
error-correction. Quantum error-correcting codes based on sparse graphs are of
interest for three reasons. First, the best codes currently known for classical
channels are based on sparse graphs. Second, sparse graph codes keep the number
of quantum interactions associated with the quantum error correction process
small: a constant number per quantum bit, independent of the blocklength.
Third, sparse graph codes often offer great flexibility with respect to
blocklength and rate. We believe some of the codes we present are unsurpassed
by previously published quantum error-correcting codes.Comment: Version 7.3e: 42 pages. Extended version, Feb 2004. A shortened
version was resubmitted to IEEE Transactions on Information Theory Jan 20,
200
Self-Dual Codes
Self-dual codes are important because many of the best codes known are of
this type and they have a rich mathematical theory. Topics covered in this
survey include codes over F_2, F_3, F_4, F_q, Z_4, Z_m, shadow codes, weight
enumerators, Gleason-Pierce theorem, invariant theory, Gleason theorems,
bounds, mass formulae, enumeration, extremal codes, open problems. There is a
comprehensive bibliography.Comment: 136 page
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
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