6 research outputs found
Soft MCI cancellation for turbo-coded OFCDM systems
In this paper, the performance of turbo-coded orthogonal frequency and code division multiplexing (OFCDM) systems is investigated with soft multi-code interference (MCI) cancellation. To regenerate the soft interference signal, the conventional turbo decoding algorithm must be modified to provide log likelihood ratio (LLR) values for all coded bits. Based on the LLR outputs of turbo decoder, two soft decision functions are proposed, called LLR-soft-decision and Gaussiansofi-decision functions. By means of computer simulations, the performance of soft MCI cancellation is studied extensively and compared to that of hard ones. It is shown that in a highly frequency selective channel, the proposed soft decision functions outperform the hard decision function with various channel conditions and system parameters. Furthermore, the Gaussian-soft-decision function provides better performance than the LLR-soft-decision function. Š 2006 IEEE.published_or_final_versio
Transmit Power Allocation for Successive Interference Cancellation in Multicode MIMO Systems
Paper approved by X. Wang, the Editor for Multiuser Detection and
Equalization of the IEEE Communications Society. Manuscript received June
10, 2005; revised November 2, 2006 and July 23, 2007. This paper was
presented in part at the IEEE International Conference on Communications,
Seoul, Korea, May 2005.Multiple-input multiple-output (MIMO) system
with multicode transmission can provide high speed data services
by transmitting independent parallel substreams from multiple
antennas and through multicode channelization. In this paper,
we first introduce an iterative two-stage successive interference
cancellation (SIC) detection scheme for a multicode MIMO
system. The proposed technique cancels the interference signals
successively in the space domain followed by the code domain.
Next, we develop various transmit power allocation schemes over
different data substreams for the proposed detection process to
improve error rate performance. The joint transmit power allocation
is derived to make the post-detection signal-to-interferenceplus-
noise ratio (SINR) become the same for all substreams
in both the space and code domains. As a computationally
efficient scheme, we propose a two-stage power allocation scheme,
which allocates the total transmit power to the substreams in
the code domain at the first stage, and allocates this code
domain power to the substreams in the space domain at the
second stage. Furthermore, variable and constant power ratio
(PR) schemes are derived to reduce the feedback overhead. In
particular, the constant PR scheme utilizes the transmit power
ratio determined by the long-term statistical properties of the
fading channel amplitudes, and achieves significantly reduced
feedback rate. Numerical results show that the proposed transmit
power allocation schemes for the two-stage SIC significantly
outperform the equal power allocation scheme
Multicode-Detektion im UMTS [online]
Nach dem Erfolg des bekannten Mobilfunksystems GSM, das als
Vertreter der zweiten Generation auf die Sprachkommunikation
optimiert ist und nachträglich mittels GPRS auf
PaketĂźbermittlung erweitert wurde, bricht nun die dritte
Generation des Mobilfunks mit dem Universal Mobile
Telecommunication System (UMTS) an. Das Konzept von UMTS ist es,
Ăźberall und jederzeit multimediale Daten zur VerfĂźgung zu
stellen. Es steht nicht mehr die
SprachĂźbertragung im Vordergrund, sondern die DatenĂźbertragung.
Der Empfänger muss den Charakter der Daten (Sprache, Video,
Bilder, Texte, ...) entsprechend erfassen. Das Ziel dieser
Arbeit ist es, fĂźr die UTRA-FDD Luftschnittstelle von UMTS
effiziente Detektionsalgorithmen zu finden. Dazu muss zunächst
ein umfassender Ăberblick Ăźber solch ein System gegeben werden.
Daher erfolgt eine allgemeine Darstellung des Direct
Sequence-Code Division Multiple Access (DS-CDMA) Prinzips. Es
wird das fĂźr die MobilfunkĂźbertragung wichtige WSSUS Kanalmodell
erläutert. SchlieĂlich werden die beiden Luftschnittstellen
UTRA-TDD und UTRA-FDD von UMTS beschrieben.
Neue Aspekte in dieser Arbeit sind fĂźr den Single-User Fall die
Anpassung des RAKE-Empfängers an die UTRA-FDD Gegebenheiten und
fĂźr den Multicode (MC) Fall, die Anwendung von linearen
MC-Detektoren (MCD) fĂźr den Multicode Betrieb im UTRA-FDD
uplink. Dabei wird zum einen ein neuer Ansatz verfolgt, der auf
dem bekannten Block Zero Forcing (ZF)-Detektionsprinzip aufbaut,
aber mittels einer Fensterung einen grÜÿeren Bereich in die
Datenschätzung mit einbezieht, als letztlich detektierte Bits
ausgegeben werden. Zum anderen wird der Block-FFT MUD, der
bereits fĂźr das UTRA-TDD System untersucht wurde, an den
UTRA-FDD uplink Multicode Modus angepasst, und mit dem Fenster
MCD verglichen. Es zeigt sich, dass durch Ausnutzung der
Systemstruktur, die Rechenleistung sowohl im RAKE-Empfänger als
auch bei den MC-Detektoren verringert werden kann. Der
RAKE-Empfänger ist natßrlich durch das Prinzip der Single-User
Detektion vom Aufwand klar ßberlegen, kann aber nur sehr mäÿige
Bitfehlerraten erreichen. Wenn man nicht nur in kleinen
geschlossenen Räumen im UTRA-FDD uplink hohe Datenraten
erreichen mĂśchte, muss man auf Verfahren zur MC-Detektion
zurĂźckgreifen.
Der MCD mit Fensterung erreicht bei etwas besseren
Bitfehlerraten als der Block-FFT MCD einen um etwa den Faktor
2;4 geringeren Rechenaufwand
Coded Parity Packet Transmission Method for Two Group Resource Allocation
Gap value control is investigated when the number of source and parity packets
is adjusted in a concatenated coding scheme whilst keeping the overall coding
rate fixed. Packet-based outer codes which are generated from bit-wise XOR
combinations of the source packets are used to adjust the number of both source
packets. Having the source packets, the number of parity packets, which are the
bit-wise XOR combinations of the source packets can be adjusted such that the
gap value, which measures the gap between the theoretical and the required
signal-to-noise ratio (SNR), is controlled without changing the actual coding
rate. Consequently, the required SNR reduces, yielding a lower required energy
to realize the transmission data rate. Integrating this coding technique with
a two-group resource allocation scheme renders efficient utilization of the total
energy to further improve the data rates. With a relatively small-sized set of
discrete data rates, the system throughput achieved by the proposed two-group
loading scheme is observed to be approximately equal to that of the existing
loading scheme, which is operated with a much larger set of discrete data rates.
The gain obtained by the proposed scheme over the existing equal rate and
equal energy loading scheme is approximately 5 dB. Furthermore, a successive
interference cancellation scheme is also integrated with this coding technique,
which can be used to decode and provide consecutive symbols for inter-symbol
interference (ISI) and multiple access interference (MAI) mitigation. With this
integrated scheme, the computational complexity is signi cantly reduced by
eliminating matrix inversions. In the same manner, the proposed coding scheme
is also incorporated into a novel fixed energy loading, which distributes packets
over parallel channels, to control the gap value of the data rates although the
SNR of each code channel varies from each other
Coded Parity Packet Transmission Method for Two Group Resource Allocation
Gap value control is investigated when the number of source and parity packets
is adjusted in a concatenated coding scheme whilst keeping the overall coding
rate fixed. Packet-based outer codes which are generated from bit-wise XOR
combinations of the source packets are used to adjust the number of both source
packets. Having the source packets, the number of parity packets, which are the
bit-wise XOR combinations of the source packets can be adjusted such that the
gap value, which measures the gap between the theoretical and the required
signal-to-noise ratio (SNR), is controlled without changing the actual coding
rate. Consequently, the required SNR reduces, yielding a lower required energy
to realize the transmission data rate. Integrating this coding technique with
a two-group resource allocation scheme renders efficient utilization of the total
energy to further improve the data rates. With a relatively small-sized set of
discrete data rates, the system throughput achieved by the proposed two-group
loading scheme is observed to be approximately equal to that of the existing
loading scheme, which is operated with a much larger set of discrete data rates.
The gain obtained by the proposed scheme over the existing equal rate and
equal energy loading scheme is approximately 5 dB. Furthermore, a successive
interference cancellation scheme is also integrated with this coding technique,
which can be used to decode and provide consecutive symbols for inter-symbol
interference (ISI) and multiple access interference (MAI) mitigation. With this
integrated scheme, the computational complexity is signi cantly reduced by
eliminating matrix inversions. In the same manner, the proposed coding scheme
is also incorporated into a novel fixed energy loading, which distributes packets
over parallel channels, to control the gap value of the data rates although the
SNR of each code channel varies from each other
An optimised QPSK-based receiver structure for possibly sparse data transmission over narrowband and wideband communication systems
In this dissertation an in-depth study was conducted into the design, implementation and evaluation of a QPSK-based receiver structure for application in a UMTS WCDMA environment. The novelty of this work lies with the specific receiver architecture aimed to optimise the BER performance when possibly sparse data streams are transmitted. This scenario is a real possibility according to Verd´u et al [1] and Hagenauer et al [2â6]. A novel receiver structure was conceptualised, developed and evaluated in both narrowband and wideband scenarios, where it was found to outperform conventional receivers when a sparse data stream is transmitted. In order to reach the main conclusions of this study, it was necessary to develop a realistic simulation platform. The developed platform is capable of simulating a communication system meeting the physical layer requirements of the UMTS WCDMA standard. The platform can also perform narrowband simulations. A flexible channel emulator was developed that may be configured to simulate AWGN channel conditions, frequency non-selective fading (either Rayleigh or Rician with a configurable LOS component and Doppler spread), or a full multipath scenario where each path has a configurable LOS component, Doppler spread, path gain and path delay. It is therefore possible to even simulate a complex, yet realistic, COST207-TU channel model. The platform is also capable of simulating MUI. Each interfering user has a unique and independent multipath fading channel, while sharing the same bandwidth. Finally, the entire platform executes all simulations in baseband for improved simulation times. The research outputs of this work are summarised below: A parameter, the sparseness measure, was defined in order to quantify the level by which a data stream differs from an equiprobable data stream. A novel source model was proposed and developed to simulate data streams with a specified amount of sparseness. An introductory investigation was undertaken to determine the effect of simple FEC techniques on the sparseness of an encoded data stream. Novel receiver structures for both narrowband and wideband systems were proposed, developed and evaluated for systems where possibly sparse data streams may be transmitted. Analytic expressions were derived to take the effect of sparseness into account in communication systems, including expressions for the joint PDF of a BPSK branch, the optimal decision region of a detector in AWGN conditions as well as the BER performance of a communication system employing the proposed optimal receiver in both AWGN channel conditions as well as in flat fading channel conditions. Numerous BER performance curves were obtained comparing the proposed receiver structure with conventional receivers in a variety of channel conditions, including AWGN, frequency non-selective fading and a multipath COST207-TU channel environment, as well as the effect of MUI. AFRIKAANS : In hierdie verhandeling word ân in-diepte studie gedoen rakende die ontwerp, implementasie en evaluasie van ân KPSK-gebaseerde ontvanger struktuur wat in ân UMTS WKVVT omgewing gebruik kan word. Die bydrae van hierdie werk lËe in die spesifieke ontvanger argitektuur wat daarop mik om die BFT werksverrigting te optimeer wanneer yl data strome versend word. Hierdie is ân realistiese moontlikheid volgens Verd´u et al [1] en Hagenauer et al [2â6]. ân Nuwe ontvanger struktuur is gekonsepsualiseer, ontwikkel en evalueer vir beide noueband en wyeband stelsels, waar dit gevind is dat dit beter werksverrigting lewer as tradisionele ontvangers wanneer yl data strome versend word. Dit was nodig om ân realistiese simulasie platform te ontwikkel om die belangrikste gevolgtrekkings van hierdie studie te kan maak. Die ontwikkelde platform is in staat om ân kommunikasie stelsel te simuleer wat aan die fisiese laag vereistes van die UMTS WKVVT standaard voldoen. Die platform kan ook noueband stelsels simuleer. ân Aanpasbare kanaal simulator is ontwikkel wat opgestel kan word om SWGR kanaal toestande, plat duining (beide Rayleigh of Ricies met ân verstelbare siglyn komponent en Doppler verspreiding), sowel as ân veelvuldige pad omgewing (waar elke unieke pad ân verstelbare siglyn komponent, Doppler verspreiding, pad wins en pad vertraging het) te emuleer. Dit is selfs moontlik om ân komplekse, maar steeds realistiese COST207-TU kanaal model te simuleer. Die platform het ook die vermo¨e om VGS te simuleer. Elke steurende gebruiker het ân unieke en onafhanklike veelvuldige pad deinende kanaal, terwyl dieselfde bandwydte gedeel word. Laastens, alle simulasies van die platvorm word in basisband uitgevoer wat verkorte simulasie periodes verseker. Die navorsingsuitsette van hierdie werk kan as volg opgesom word: ân Parameter, die ylheidsmaatstaf, is gedefin¨ýeer om dit moontlik te maak om die vlak waarmee die ylheid van ân datastroom verskil van ân ewekansige stroom te versyfer. ân Nuwe bronmodel is voorgestel en ontwikkel om datastrome met ân spesifieke ylheid te emuleer. ân Inleidende ondersoek is onderneem om vas te stel wat die effek van VFK tegnieke op die ylheid van ân enkodeerde datastroom is. Nuwe ontvanger strukture is voorgestel, ontwikkel en evalueer vir beide noueband en wyeband stelsels waar yl datastrome moontlik versend kan word. Analitiese uitdrukkings is afgelei om die effek van ylheid in ag te neem in kommunikasie stelsels. Uitdrukkings vir onder andere die gedeelte WDF van ân BFVK tak, die optimale beslissingspunt van ân detektor in SWGR toestande, sowel as die BFT werksverrigting van ân kommunikasie stelsel wat van die voorgestelde optimale ontvangers gebruik maak, hetsy in SWGR of in plat duinende kanaal toestande. Talryke BFT werksverrigting krommes is verkry wat die voorgestelde ontvanger struktuur vergelyk met die konvensionele ontvangers in ân verskeidenheid kanaal toestande, insluitend SWGR, plat duinende kanale en ân veelvuldige pad COST207-TU kanaal omgewing, sowel as in die teenwoordigheid van VGS.</p CopyrightDissertation (MEng)--University of Pretoria, 2010.Electrical, Electronic and Computer Engineeringunrestricte