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Reduced Receivers for Faster-than-Nyquist Signaling and General Linear Channels

Prlja, Adnan LU (2013) In Series of licentiate and doctoral theses no. 48.
Abstract (Swedish)
Popular Abstract in Swedish

Dagens samhälle är allt mer beroende av elektroniska hjälpmedel så som smarta telefoner, läsplattor, datorer osv. Prestandakraven ökar i en allt högre takt och därför måste även den bakomliggande teknologin följa samma trend. De flesta av oss vill att den nya mobiltelefonen ska ha så hög kameraupplösning som möjligt men få av oss tänker

på att detta medför en större mängd data. Den nya 4G telefonen förväntas också kunna ladda upp dessa högupplösta foton och videoklipp på Internet snabbare än den gamla slitna GSM telefonen. Den ska dessutom vara lika billig i inköp. Man inser snabbt att detta

ställer stora krav på den bakomliggande kommunikationsteknologin. I denna avhandling... (More)
Popular Abstract in Swedish

Dagens samhälle är allt mer beroende av elektroniska hjälpmedel så som smarta telefoner, läsplattor, datorer osv. Prestandakraven ökar i en allt högre takt och därför måste även den bakomliggande teknologin följa samma trend. De flesta av oss vill att den nya mobiltelefonen ska ha så hög kameraupplösning som möjligt men få av oss tänker

på att detta medför en större mängd data. Den nya 4G telefonen förväntas också kunna ladda upp dessa högupplösta foton och videoklipp på Internet snabbare än den gamla slitna GSM telefonen. Den ska dessutom vara lika billig i inköp. Man inser snabbt att detta

ställer stora krav på den bakomliggande kommunikationsteknologin. I denna avhandling analyseras därför de praktiska utmaningarna hos en potentiell lösning.



Snabb och tillförlitlig dataöverföring tillsammans med hög bandbreddseffektivitet är viktiga designaspekter i ett modernt kommunikationssystem som t.ex. 3G, WiFi och LTE. Bandbreddseffektivitet är i grova drag ett mått på hur mycket data ett kommunikationssystem kan överföra per tidsenhet och hertz (Hz). Idag baseras all konventionell teknologi på att de olika informationsbitarna, ettorna och nollorna, ska kunna behandlas oberoende av varandra på mottagarsidan. Denna avhandling undersöker en väsentligt annorlunda metod, nämligen att interferens mellan bitarna införs avsiktligt på sändarsidan med hjälp av den så kallade faster-than-Nyquist (FTN) tekniken. Detta medför i sin tur att bitarna stör varandra vilket resulterar i att mottagaren inte kan behandla dem var för sig. Denna signaleringsteknik introducerades redan 1975 av James Mazo, forskare på Bell Laboratories i USA, och har sedan dess utökats i många riktningar. Tidigare arbete inom området har påvisat signifikanta vinster i bandbreddseffektivitet men också påpekat att mottagaren blir alltför komplex för praktisk realisering. I denna avhandling föreslår vi ett antal lågkomplexitetslösningar för mottagning av denna typ av självstörande signaler. Vår slutsats är att de teoretiska vinsterna i bandbreddseffektivitet, som tidigare påvisats, är fullt möjliga att uppnå i praktiken då våra lågkomplexitetsmottagare har mycket god prestanda för praktiska komplexitetsnivåer.



Den första delen av avhandlingen behandlar lågkomplexitetsmottagare och relaterade stabilitetsproblem. Nya algoritmer presenteras tillsammans med en rad viktiga förbättringar vilka tillsammans radikalt reducerar mottagarens komplexitet utan att nämnvärt öka antalet felaktigt mottagna bitar.



Den andra delen analyserar effekten av de mottagarinterna beräkningarna på prestandan, kvoten mellan antalet felaktigt mottagna bitar och det totala antalet bitar, hos två i grunden olika mottagarmodeller. En av dessa två standarmodeller är välundersökt i litteraturen. Även om deras slutresultat är identiska vid optimal mottagning, så är de interna beräkningarna i allmänhet annorlunda för de två modellerna. Icke optimala mottagare, dvs. mottagare som utför ett mindre antal beräkningar, behöver därför inte generera samma slutresultat. Färre beräkningar medför i regel viktiga energibesparingar hos batteridrivna enheter samt billigare produktionskostnader. Utöver detta så föreslås och utvärderas nya typer av mottagarmodeller som arbetar emellan de två standardmodellerna.



Den sista delen av avhandlingen ägnas åt ett annat tillvägagångssätt

för att reducera antalet beräkningar. Så kallade kanalkortningsmottagare optimeras ur ett icke konventionellt perspektiv. Istället för att reducera antalet beräkningar genom en förbättrad inre mottagarstruktur, så försöker en kanalkortningsmottagare att neutralisera effekterna av omgivningen(kanalen) och därefter arbeta med en förenklad kanalmodell. Ramverket som används för kanalkortning i denna avhandling är mer generell än vad som tidigare använts inom området. (Less)
Abstract
Fast and reliable data transmission together with high bandwidth efficiency are important design aspects in a modern digital communication system. Many different approaches exist but in this thesis bandwidth efficiency is obtained by increasing the data transmission rate with the faster-than-Nyquist (FTN) framework while keeping a fixed power spectral density (PSD). In FTN consecutive information carrying symbols can overlap in time and in that way

introduce a controlled amount of intentional intersymbol interference (ISI). This technique was introduced already in 1975 by Mazo and has since then been extended in many directions.



Since the ISI stemming from practical FTN signaling can be of significant duration,... (More)
Fast and reliable data transmission together with high bandwidth efficiency are important design aspects in a modern digital communication system. Many different approaches exist but in this thesis bandwidth efficiency is obtained by increasing the data transmission rate with the faster-than-Nyquist (FTN) framework while keeping a fixed power spectral density (PSD). In FTN consecutive information carrying symbols can overlap in time and in that way

introduce a controlled amount of intentional intersymbol interference (ISI). This technique was introduced already in 1975 by Mazo and has since then been extended in many directions.



Since the ISI stemming from practical FTN signaling can be of significant duration, optimum detection with traditional methods is often prohibitively complex, and alternative equalization methods with acceptable complexity-performance tradeoffs are needed. The key objective of this thesis is therefore to design reduced-complexity receivers for FTN and general linear channels that achieve optimal or near-optimal performance. Although the performance of a detector can be measured by several means, this thesis is restricted to bit error rate (BER) and mutual information results. FTN signaling is applied in two ways: As a separate uncoded narrowband communication system or in a coded scenario consisting of a convolutional encoder, interleaver and the inner ISI mechanism in serial concatenation. Turbo equalization where soft information in the form of log likelihood ratios (LLRs) is exchanged between the equalizer and the decoder is a commonly used decoding technique for coded FTN signals.



The first part of the thesis considers receivers and arising stability problems when working within the white noise constraint. New M-BCJR algorithms for turbo equalization are proposed and compared to reduced-trellis VA and BCJR benchmarks based on an offset label idea. By adding a third low-complexity M-BCJR recursion, LLR quality is improved for practical values of M. M here measures the reduced number of BCJR computations for each data symbol. An improvement of the minimum phase conversion that sharpens the focus of the ISI model energy is proposed. When combined with a delayed and slightly mismatched receiver, the decoding allows a smaller M without significant loss in BER.



The second part analyzes the effect of the internal metric calculations on the performance of Forney- and Ungerboeck-based reduced-complexity equalizers of the M-algorithm type for both ISI and multiple-input multiple-output (MIMO) channels. Even though the final output of a full-complexity equalizer is identical for both models, the internal metric calculations are in general different. Hence, suboptimum methods need not produce the same final output. Additionally, new models working in between the two extremes are proposed and evaluated. Note that the choice of observation model does not impact the detection complexity as the underlying algorithm is unaltered.



The last part of the thesis is devoted to a different complexity reducing approach. Optimal channel shortening detectors for linear channels are optimized from an information theoretical perspective. The achievable information rates of the shortened models as well as closed form expressions for all components of the optimal detector of the class are derived. The framework used in this thesis is more general than what has been previously used within the area. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Hagenauer, Joachim, Technical University of Munich (TUM), Germany
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Digital data transmission, receivers, decoders, channel modeling, intersymbol interference, ISI, MIMO, Faster-than-Nyquist signaling, complexity reduction, observation models, BCJR algorithm, turbo equalization, iterative detection, channel shortening
in
Series of licentiate and doctoral theses
volume
no. 48
pages
209 pages
publisher
Tryckeriet i E-huset, Lunds universitet
defense location
Lecture hall E:1406, E-building, John Ericssons väg 4, Lund University Faculty of Engineering
defense date
2013-02-28 10:15
ISSN
1654-790X
ISBN
978-91-7473-427-0
language
English
LU publication?
yes
id
c910cdd9-6836-4b06-b254-1f540a35f6d4 (old id 3441332)
date added to LUP
2013-02-06 09:29:47
date last changed
2019-05-24 08:45:44
@phdthesis{c910cdd9-6836-4b06-b254-1f540a35f6d4,
  abstract     = {Fast and reliable data transmission together with high bandwidth efficiency are important design aspects in a modern digital communication system. Many different approaches exist but in this thesis bandwidth efficiency is obtained by increasing the data transmission rate with the faster-than-Nyquist (FTN) framework while keeping a fixed power spectral density (PSD). In FTN consecutive information carrying symbols can overlap in time and in that way <br/><br>
introduce a controlled amount of intentional intersymbol interference (ISI). This technique was introduced already in 1975 by Mazo and has since then been extended in many directions.<br/><br>
<br/><br>
Since the ISI stemming from practical FTN signaling can be of significant duration, optimum detection with traditional methods is often prohibitively complex, and alternative equalization methods with acceptable complexity-performance tradeoffs are needed. The key objective of this thesis is therefore to design reduced-complexity receivers for FTN and general linear channels that achieve optimal or near-optimal performance. Although the performance of a detector can be measured by several means, this thesis is restricted to bit error rate (BER) and mutual information results. FTN signaling is applied in two ways: As a separate uncoded narrowband communication system or in a coded scenario consisting of a convolutional encoder, interleaver and the inner ISI mechanism in serial concatenation. Turbo equalization where soft information in the form of log likelihood ratios (LLRs) is exchanged between the equalizer and the decoder is a commonly used decoding technique for coded FTN signals.<br/><br>
<br/><br>
The first part of the thesis considers receivers and arising stability problems when working within the white noise constraint. New M-BCJR algorithms for turbo equalization are proposed and compared to reduced-trellis VA and BCJR benchmarks based on an offset label idea. By adding a third low-complexity M-BCJR recursion, LLR quality is improved for practical values of M. M here measures the reduced number of BCJR computations for each data symbol. An improvement of the minimum phase conversion that sharpens the focus of the ISI model energy is proposed. When combined with a delayed and slightly mismatched receiver, the decoding allows a smaller M without significant loss in BER.<br/><br>
<br/><br>
The second part analyzes the effect of the internal metric calculations on the performance of Forney- and Ungerboeck-based reduced-complexity equalizers of the M-algorithm type for both ISI and multiple-input multiple-output (MIMO) channels. Even though the final output of a full-complexity equalizer is identical for both models, the internal metric calculations are in general different. Hence, suboptimum methods need not produce the same final output. Additionally, new models working in between the two extremes are proposed and evaluated. Note that the choice of observation model does not impact the detection complexity as the underlying algorithm is unaltered.<br/><br>
<br/><br>
The last part of the thesis is devoted to a different complexity reducing approach. Optimal channel shortening detectors for linear channels are optimized from an information theoretical perspective. The achievable information rates of the shortened models as well as closed form expressions for all components of the optimal detector of the class are derived. The framework used in this thesis is more general than what has been previously used within the area.},
  author       = {Prlja, Adnan},
  isbn         = {978-91-7473-427-0},
  issn         = {1654-790X},
  keyword      = {Digital data transmission,receivers,decoders,channel modeling,intersymbol interference,ISI,MIMO,Faster-than-Nyquist signaling,complexity reduction,observation models,BCJR algorithm,turbo equalization,iterative detection,channel shortening},
  language     = {eng},
  pages        = {209},
  publisher    = {Tryckeriet i E-huset, Lunds universitet},
  school       = {Lund University},
  series       = {Series of licentiate and doctoral theses},
  title        = {Reduced Receivers for Faster-than-Nyquist Signaling and General Linear Channels},
  volume       = {no. 48},
  year         = {2013},
}