950 research outputs found
Turbo Decoding and Detection for Wireless Applications
A historical perspective of turbo coding and turbo transceivers inspired by the generic turbo principles is provided, as it evolved from Shannonâs visionary predictions. More specifically, we commence by discussing the turbo principles, which have been shown to be capable of performing close to Shannonâs capacity limit. We continue by reviewing the classic maximum a posteriori probability decoder. These discussions are followed by studying the effect of a range of system parameters in a systematic fashion, in order to gauge their performance ramifications. In the second part of this treatise, we focus our attention on the family of iterative receivers designed for wireless communication systems, which were partly inspired by the invention of turbo codes. More specifically, the family of iteratively detected joint coding and modulation schemes, turbo equalization, concatenated spacetime and channel coding arrangements, as well as multi-user detection and three-stage multimedia systems are highlighted
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
Hybrid ARQ with parallel and serial concatenated convolutional codes for next generation wireless communications
This research focuses on evaluating the currently used FEC encoding-decoding schemes and improving the performance of error control systems by incorporating these schemes in a hybrid FEC-ARQ environment. Beginning with an overview of wireless communications and the various ARQ protocols, the thesis provides an in-depth explanation of convolutional encoding and Viterbi decoding, turbo (PCCC) and serial concatenated convolutional (SCCC) encoding with their respective MAP decoding strategies.;A type-II hybrid ARQ scheme with SCCCs is proposed for the first time and is a major contribution of this thesis. A vast improvement is seen in the BER performance of the successive individual FEC schemes discussed above. Also, very high throughputs can be achieved when these schemes are incorporated in an adaptive type-II hybrid ARQ system.;Finally, the thesis discusses the equivalence of the PCCCs and the SCCCs and proposes a technique to generate a hybrid code using both schemes
Turbo codes and turbo algorithms
In the first part of this paper, several basic ideas that prompted the coming of turbo codes are commented on. We then present some personal points of view on the main advances obtained in past years on turbo coding and decoding such as the circular trellis termination of recursive systematic convolutional codes and double-binary turbo codes associated with Max-Log-MAP decoding. A novel evaluation method, called genieinitialised iterative processing (GIIP), is introduced to assess the error performance of iterative processing. We show that using GIIP produces a result that can be viewed as a lower bound of the maximum likelihood iterative decoding and detection performance. Finally, two wireless communication systems are presented to illustrate recent applications of the turbo principle, the first one being multiple-input/multiple-output channel iterative detection and the second one multi-carrier modulation with linear precoding
Investigation of non-binary trellis codes designed for impulsive noise environments
PhD ThesisIt is well known that binary codes with iterative decoders can achieve
near Shannon limit performance on the additive white Gaussian noise
(AWGN) channel, but their performance on more realistic wired or wireless
channels can become degraded due to the presence of burst errors
or impulsive noise. In such extreme environments, error correction alone
cannot combat the serious e ect of the channel and must be combined
with the signal processing techniques such as channel estimation, channel
equalisation and orthogonal frequency division multiplexing (OFDM).
However, even after the received signal has been processed, it can still
contain burst errors, or the noise present in the signal maybe non Gaussian.
In these cases, popular binary coding schemes such as Low-Density
Parity-Check (LDPC) or turbo codes may not perform optimally, resulting
in the degradation of performance. Nevertheless, there is still scope
for the design of new non-binary codes that are more suitable for these
environments, allowing us to achieve further gains in performance. In
this thesis, an investigation into good non-binary trellis error-correcting
codes and advanced noise reduction techniques has been carried out with
the aim of enhancing the performance of wired and wireless communication
networks in di erent extreme environments. These environments
include, urban, indoor, pedestrian, underwater, and powerline communication
(PLC). This work includes an examination of the performance
of non-binary trellis codes in harsh scenarios such as underwater communications
when the noise channel is additive S S noise. Similar work
was also conducted for single input single output (SISO) power line communication
systems for single carrier (SC) and multi carrier (MC) over
realistic multi-path frequency selective channels. A further examination
of multi-input multi-output (MIMO) wired and wireless systems on
Middleton class A noise channel was carried out. The main focus of the
project was non-binary coding schemes as it is well-known that they outperform
their binary counterparts when the channel is bursty. However,
few studies have investigated non-binary codes for other environments.
The major novelty of this work is the comparison of the performance
of non-binary trellis codes with binary trellis codes in various scenarios,
leading to the conclusion that non-binary codes are, in most cases,
superior in performance to binary codes. Furthermore, the theoretical
bounds of SISO and MIMO binary and non-binary convolutional coded
OFDM-PLC systems have been investigated for the rst time. In order
to validate our results, the implementation of simulated and theoretical
results have been obtained for di erent values of noise parameters and
on di erent PLC channels. The results show a strong agreement between
the simulated and theoretical analysis for all cases.University of
Thi-Qar for choosing me for their PhD scholarship and the Iraqi Ministry
of Higher Education and Scienti c Research (MOHESR) for granting me
the funds to study in UK. In addition, there was ample support towards
my stay in the UK from the Iraqi Cultural Attach e in Londo
New VLSI design of a MAP/BCJR decoder.
Any communication channel suffers from different kinds of noises. By employing forward error correction (FEC) techniques, the reliability of the communication channel can be increased. One of the emerging FEC methods is turbo coding (iterative coding), which employs soft input soft output (SISO) decoding algorithms like maximum a posteriori (MAP) algorithm in its constituent decoders. In this thesis we introduce a design with lower complexity and less than 0.1dB performance loss compare to the best performance observed in Max-Log-MAP algorithm. A parallel and pipeline design of a MAP decoder suitable for ASIC (Application Specific Integrated Circuits) is used to increase the throughput of the chip. The branch metric calculation unit is studied in detail and a new design with lower complexity is proposed. The design is also flexible to communication block sizes, which makes it ideal for variable frame length communication systems. A new even-spaced quantization technique for the proposed MAP decoder is utilized. Normalization techniques are studied and a suitable technique for the Max-Log-MAP decoder is explained. The decoder chip is synthesized and implemented in a 0.18 mum six-layer metal CMOS technology. (Abstract shortened by UMI.)Dept. of Electrical and Computer Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2004 .S23. Source: Masters Abstracts International, Volume: 43-05, page: 1783. Adviser: Majid Ahmadi. Thesis (M.A.Sc.)--University of Windsor (Canada), 2004
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
Serial turbo trellis coded modulation using a serially concatenated coder
Serial concatenated trellis coded modulation (SCTCM) includes an outer coder, an interleaver, a recursive inner coder and a mapping element. The outer coder receives data to be coded and produces outer coded data. The interleaver permutes the outer coded data to produce interleaved data. The recursive inner coder codes the interleaved data to produce inner coded data. The mapping element maps the inner coded data to a symbol. The recursive inner coder has a structure which facilitates iterative decoding of the symbols at a decoder system. The recursive inner coder and the mapping element are selected to maximize the effective free Euclidean distance of a trellis coded modulator formed from the recursive inner coder and the mapping element. The decoder system includes a demodulation unit, an inner SISO (soft-input soft-output) decoder, a deinterleaver, an outer SISO decoder, and an interleaver
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