In a MIMO system, a transmitter with perfect knowledge of the underlying channel state information (CSI) can achieve a higher channel capacity compared to transmission without CSI. When reciprocity of the wireless channel does not hold, the identification and utilization of partial CSI at the transmitter are important issues. This thesis is focused on partial CSI acquisition and utilization techniques for MIMO channels. We propose a feedback algorithm for tracking the dominant channel subspaces for MIMO systems in a continuously time-varying environment. We exploit the correlation between channel states of adjacent time instants and quantize the variation of channel states. Specifically, we model a subspace as one point in a Grassmann manifold, treat the variations in principal right singular subspaces of the channel matrices as a piecewise-geodesic process in the Grassmann manifold, and quantize the velocity matrix of the geodesic. We design a complexity-constrained MIMO OFDM system where the transmitter has knowledge of channel correlations. The transmitter is constrained to perform at most one inverse Discrete Fourier Transform per OFDM symbol on the average. We show that in the MISO case, time domain beamforming can be used to do two-dimensional eigen-beamforming. For the MIMO case, we derive design criteria for the transmitter beamforming and receiver combining weighting vectors and show some suboptimal solutions. The feedback channel may have uncertainties such as unexpected delay or error. We consider channel mean feedback with an unknown delay and propose a broadcast approach that is able to adapt to the quality of the feedback. Having considered CSI feedback problems where the receiver tries to convey its attained CSI to the transmitter, we turn to noncoherent coding design for fast fading channels, where the receiver does not have reliable CSI. We propose a data-dependent superimposed training scheme to improve the performance of training based codes. The transmitter is equipped with multiple training sequences and dynamically selects a training sequence for each data sequence to minimize channel estimation error. The set of training sequences are optimized to minimize pairwise error probability between codewords.

Previous studies have demonstrated that many existing communication systems can be formulated within a unified multirate filterbank transceiver model. A redundant block transmission system implemented via this unified multirate filterbank transceiver model is usually known as a multiple-input-multiple-output (MIMO) system in literature. This dissertation devises an optimum linear block-based precoder and the corresponding equalizer for MIMO systems over perfect reconstruction (PR) channels by exploiting the proposed oblique projection framework. Particularly, two main criteria of interest in a digital communication link with limited transmission power are investigated, namely, average bit error rate (BER) minimization and mutual information rate maximization. The study framework is developed as follows. For a block-based precoder, a received signal model is formulated for the two redundancy schemes, viz., trailing-zeros (TZ) and cyclic-prefix (CP). By exploiting the property of oblique projection, a cascaded equalizer for block transmission systems (i.e., MIMO systems) is proposed and implemented with a scheme, in which the inter-block interference (IBI) is completely eliminated by the oblique projection and followed by a matrix degree of freedom for inter-symbol interference (ISI) equalization. With the available channel state information at the transmitter side, the matrix for ISI equalization of the cascaded equalizer is utilized to design an optimum linear block-based precoder, such that the BER is minimized (or the mutual information rate is maximized), subject to the ISI-free and the transmission power constraints. Accordingly, the cascaded equalizer with the ISI-free constraint yields a cascaded ZF equalizer. Theoretical derivations and simulation results confirm that the proposed framework not only retains identical BER and information rate performances to previous works for cases with sufficient redundancy, but also allows their results to be extended to the cases of insufficient redundancy.

Thesis (M.B.A. (Rhodes Investec Business School)) - Rhodes University, 2008. / Submitted in partial fulfilment of the requirements for the degree Master of Business Administration in the Rhodes Investec Business School (RIBS)

The need for reliable, high-throughput, mobile wireless communication technologies has never been greater as increases in the demand for on-the-go access to information, entertainment, and other electronic services continues. Two such technologies, which are at the forefront of current research efforts, are orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) systems, their union being known simply as MIMO-OFDM. The successful performance of these technologies depends upon the availability of accurate information concerning the wireless communication channel. In this dissertation, several issues related to quality of this channel state information (CSI) are studied. Specifically, the first part of this dissertation considers the design of optimal pilot signals for OFDM systems. The optimization is addressed via lower bounds on the estimation error variance, which bounds are given by formulations of the Cram'{e}r-Rao bound (CRB). The second part of this dissertation uses the CRB once again, this time as a tool for evaluating the potential performance of MIMO-OFDM channel estimation and prediction. Bounds are found for several parametric time-varying wideband MIMO-OFDM channel models, and numerical evaluations of these bounds are used to illuminate several interesting features regarding the estimation and prediction of MIMO-OFDM channels. The final part of this dissertation considers the problem of MIMO multiplexing using SVD-based methods when only imperfect CSI is available. For this purpose, general per-MIMO-subchannel signal and interference-plus-noise power expressions are derived to quantify the effects of CSI imperfections, and these expressions are then used to find robust MIMO-SVD power and bit allocations which maintain good overall performance in spite of imperfect CSI.

Dans la première partie de la thèse, on se concentre sur la conception d'un système de communication par satellite complet se basant sur la construction de faisceaux adaptatifs aux terminaux mobiles. Comparé à la construction classique de faisceaux fixes, le système à faisceaux adaptatifs peut considérablement améliorer la capacité du système en termes du nombre de STs desservies et de l'efficacité énergétique. Pour la conception du système à faisceaux adaptatifs, les informations sur l'état de canal (CSI) sont essentielles. Vu que le temps de propagation est trop long par rapport au temps de cohérence du canal, le CSI instantané est déjà périmé lorsqu'il est reçu pour la construction des faisceaux. Cependant, une partie de l'information du canal, plus particulièrement, les vecteurs de directivité ont une variation assez lente. On utilise cette connaissance partielle du CSI pour concevoir le système à base de faisceaux adaptatifs. Afin d'estimer les vecteurs de directivité, on propose un algorithme basé sur un critère de minimisation de l'erreur quadratique. Puis, basées sur l'estimation des vecteurs de directivité, on présente deux approches heuristiques pour la conception des faisceaux. En outre, on propose également deux approches qui reposent sur l'estimation de la directivité pour la détection des STs et la résolution possible des collisions sur le canal d'accès aléatoire au satellite. Comme la performance du système SDMA dépend fortement des positions spatiales des STs co-existants, on propose deux algorithmes de faible complexité pour l'attribution des fréquences dans le système de communication par satellite / In the first part of the thesis, we focus on the design of a complete satellite communication system adopting adaptive beamforming with mobile satellite terminals. Compared with conventional fixed beamforming, adaptive beamforming can signi_cantly improve the capacity of a satellite system in terms of served satellite terminals (ST) and power e_ciency. For the design of an adaptive beamforming system, channel state information (CSI) is critical. Since the propagation delay is too long compared to the coherence time of the channel, the instantaneous CSI is already stale when processed for beamforming. However, some parts of the channel, more speci_cally, directivity vectors change quite slowly. We utilize this partial knowledge of CSI to design an adaptive beamforming system. In order to estimate the directivity vectors, we propose an algorithm based on a least square error criterion. Then, based on the estimation of directivity vectors, we propose two heuristics approaches to the design of adaptive beamforming. Additionally, we also propose two approaches, based on directivity estimation for the detection of transmitting terminals and the possible resolution of collisions in the random access channel of the satellite system. Since SDMA system performance depends strongly on the spatial locations of co-existing terminals, we also propose two low complexity algorithms for frequency allocation in a satellite communication system. Finally, we simulate a complete satellite system, including a random access channel and a connection-oriented channel. We analyze the system performance and compare it to conventional fixed beamforming systems

Multi-antenna communication systems are attracting research interest as a means to increase the information capacity, reliability, and spectral efficiency of wireless information transfer. Ray-tracing methods predict the behavior of wireless channels using a model of the propagation environment and are a low-cost alternative to direct measurements. We use ray tracing simulations to validate the statistical time and angle of arrival characteristics of an indoor multipath channel and compare model parameter estimates with estimates derived from channel sounding measurements. Ray tracing predicts the time and angle clustering of multipaths observed in the measurements and provides model parameter estimates which are closely correlated with measured estimates. The ray tracing parameters relating to power characteristics show more deviation from measurements than the time and angle related parameters. Our results also indicate that the description of reflective scatterers in the propagation environment is more important to the quality of the predicted statistical behavior than the description of bulk materials. We use a ray synthesis model to investigate means of efficiently representing the channel for feedback information to the transmitter as a means to increase the information capacity. Several methods of selecting the ray-model feedback information are demonstrated with results from simulated and measured channels. These results indicate that an ESPRIT algorithm coupled with ad hoc transmit/receive pairing can yield better than 90% of the ideal waterfilling capacity when adequate training-based channel estimates are available. Additionally, we investigate a covariance feedback method for providing channel feedback for increased capacity. Both the ray-based and covariance-based feedback methods yield their highest capacity improvements when the signal to noise ratio is low. This results because of the larger benefit of focusing transmit power into the most advantageous eigenmodes of the channel when fewer eigenmodes have power allocated to them by the waterfilling capacity solution. In higher signal to noise ratio cases, more eigenmodes of the channel receive power when waterfilling, and the capacity improvement from feedback information decreases relative to a uniform power allocation. In general, ray model feedback methods are preferable because the covariance feedback quickly requires higher computational effort as the array sizes increase and typically results in lower capacity for a given amount of feedback information.

The history of Software-Defined Radios (SDRs) epitomizes innovation in wireless communication. Initially serving military needs, SDRs swiftly transitioned to civilian applications, revolutionizing communication. This thesis explores SDR applications such as Spectrum Scanning Systems, Contraband Cellphone Detection, and Human Activity Recognition via Wi-Fi signals. SDRs empower Spectrum Scanning Systems to monitor and analyze radio frequencies, optimizing spectrum allocation for seamless wireless communication. In Contraband Cellphone Detection, SDRs identify unauthorized signals in restricted areas, bolstering security efforts by thwarting illicit cellphone usage. Human Activity Recognition utilizes Raspberry Pi 3B+ to track movement patterns via Wi-Fi signals, offering insights across various sectors. Additionally, the thesis conducts a comparative analysis of Wi-Fi-based Human Activity Recognition and Radar for accuracy assessment. SDRs continue to drive innovation, enhancing wireless communication and security in diverse domains, from defense to healthcare and beyond.

'n Onafhanklike, ondersoekende en verantwoordelike media word beskou as een van die belangrikste rolspelers waarvan die behoud van die demokrasie in Suid- Afrika afhanklik is. Die regte en vryhede van die media geniet grondwetlike erkenning en beskerming. As fundamentele regte en onontbeerlike komponente van mediavryheid, waarborg die Grondwet van die Republiek van Suid-Afrika, 1996 aan elkeen die reg op vryheid van uitdrukking (artikel 16) en die reg op toegang tot inligting (artikel 32). Die grondwetlike beskerming van mediavryheid bemagtig die media om (i) openbare aangeleenthede in belang van die publiek aan te spreek, (ii) die staat tot deursigtigheid, openheid en verantwoording op te roep en (iii) as teenwig teen magsmisbruik en wanpraktyke aan regeringskant op te tree. Die reg op mediavryheid is egter nie absoluut afdwingbaar nie en kan gevolglik in die toepassing daarvan beperk word. Die staat beskik oor die gesag om dié reg aan beperkings onderhewig te stel ten einde ander individuele fundamentele regte te beskerm of belangrike openbare belange te dien. Sodanige staatsoptrede is egter slegs moontlik indien dit, weens die oppergesag van die Grondwet (artikel 2), in ooreenstemming met die grondwetlike bepalings geskied. Desnieteenstaande word die media, ondanks die belangrike rol wat hulle ter behoud van die demokrasie in Suid-Afrika vervul en die grondwetlike erkenning en beskerming wat aan mediavryheid verleen word, voortdurend onder groot druk geplaas. Die meeste druk kom van die staat se kant. Die aanname en beoogde implementering van die Protection of State Information Bill, 2010 dien as mees resente voorbeeld hiervan. Staats- en administratiefregtelike beperkings op mediavryheid sal, indien die Wetsontwerp gepromulgeer word, aan die orde van die dag wees. Aangesien die voorgenome beperkings op grond van hulle potensiële ongrondwetlikheid wyd gekritiseer word, is dit die vernaamste doel van hierdie studie om die grondwetlike grense waarbinne die staat mediavryheid mag beperk, te omlyn en ondersoek in te stel na die trefwydte en grondwetlikheid van die staat se gesag om beperkings op mediavryheid te plaas. Deur die omvang van staatsgesag in die algemeen en in besonder rakende die beperking van mediavryheid, aan die hand van die relevante grondwetlike voorskrifte te ondersoek, is bevind dat alle staatsoptrede streng deur die Grondwet gereguleer word. Alhoewel die reg op mediavryheid vatbaar is vir regulering en beperking, is tot die slotsom gekom dat die Grondwet ingevolge artikels 33 en 36 duidelike grense vir die beperking daarvan deur die staat stel. Alle uitvoerende en administratiewe staatsorgane wat kragtens wetgewing en uit hoofde van die diskresionêre bevoegdhede wat aan hulle verleen word, die reg op mediavryheid beperk, moet aan die vereistes vir regverdige administratiewe optrede voldoen. Bygevolg moet alle administratiewe besluite en handelinge wat die reg op mediavryheid beperk, regmatig, redelik en prosedureel billik wees en met die verskaffing van voldoende skriftelike redes gepaard gaan. Sowel staatsregtelike as administratiefregtelike beperkings op mediavryheid moet voldoen aan die vereistes wat die algemene beperkingsklousule vir die grondwetlike beperking van fundamentele regte stel. Enige beperking van die reg op mediavryheid moet dus kragtens 'n algemeen geldende regsvoorskrif geskied en moet, met in agneming van die artikel 36-sleutelfaktore, as redelik en regverdigbaar binne 'n oop en demokratiese samelewing gebaseer op menswaardigheid, gelykheid en vryheid plaasvind. Enige staats- en administratiefregtelike beperkings op mediavryheid wat nie aan hierdie grondwetlike vereistes voldoen nie, is gevolglik ongrondwetlik. Nadat die bepalings ter beperking van mediavryheid deur die Protection of State Information Bill, 2010 krities ontleed is, is bevind dat dit nie daarin sal slaag om die grondwetlike toets te slaag nie. / LLM, North-West University, Potchefstroom Campus, 2015

'n Onafhanklike, ondersoekende en verantwoordelike media word beskou as een van die belangrikste rolspelers waarvan die behoud van die demokrasie in Suid- Afrika afhanklik is. Die regte en vryhede van die media geniet grondwetlike erkenning en beskerming. As fundamentele regte en onontbeerlike komponente van mediavryheid, waarborg die Grondwet van die Republiek van Suid-Afrika, 1996 aan elkeen die reg op vryheid van uitdrukking (artikel 16) en die reg op toegang tot inligting (artikel 32). Die grondwetlike beskerming van mediavryheid bemagtig die media om (i) openbare aangeleenthede in belang van die publiek aan te spreek, (ii) die staat tot deursigtigheid, openheid en verantwoording op te roep en (iii) as teenwig teen magsmisbruik en wanpraktyke aan regeringskant op te tree. Die reg op mediavryheid is egter nie absoluut afdwingbaar nie en kan gevolglik in die toepassing daarvan beperk word. Die staat beskik oor die gesag om dié reg aan beperkings onderhewig te stel ten einde ander individuele fundamentele regte te beskerm of belangrike openbare belange te dien. Sodanige staatsoptrede is egter slegs moontlik indien dit, weens die oppergesag van die Grondwet (artikel 2), in ooreenstemming met die grondwetlike bepalings geskied. Desnieteenstaande word die media, ondanks die belangrike rol wat hulle ter behoud van die demokrasie in Suid-Afrika vervul en die grondwetlike erkenning en beskerming wat aan mediavryheid verleen word, voortdurend onder groot druk geplaas. Die meeste druk kom van die staat se kant. Die aanname en beoogde implementering van die Protection of State Information Bill, 2010 dien as mees resente voorbeeld hiervan. Staats- en administratiefregtelike beperkings op mediavryheid sal, indien die Wetsontwerp gepromulgeer word, aan die orde van die dag wees. Aangesien die voorgenome beperkings op grond van hulle potensiële ongrondwetlikheid wyd gekritiseer word, is dit die vernaamste doel van hierdie studie om die grondwetlike grense waarbinne die staat mediavryheid mag beperk, te omlyn en ondersoek in te stel na die trefwydte en grondwetlikheid van die staat se gesag om beperkings op mediavryheid te plaas. Deur die omvang van staatsgesag in die algemeen en in besonder rakende die beperking van mediavryheid, aan die hand van die relevante grondwetlike voorskrifte te ondersoek, is bevind dat alle staatsoptrede streng deur die Grondwet gereguleer word. Alhoewel die reg op mediavryheid vatbaar is vir regulering en beperking, is tot die slotsom gekom dat die Grondwet ingevolge artikels 33 en 36 duidelike grense vir die beperking daarvan deur die staat stel. Alle uitvoerende en administratiewe staatsorgane wat kragtens wetgewing en uit hoofde van die diskresionêre bevoegdhede wat aan hulle verleen word, die reg op mediavryheid beperk, moet aan die vereistes vir regverdige administratiewe optrede voldoen. Bygevolg moet alle administratiewe besluite en handelinge wat die reg op mediavryheid beperk, regmatig, redelik en prosedureel billik wees en met die verskaffing van voldoende skriftelike redes gepaard gaan. Sowel staatsregtelike as administratiefregtelike beperkings op mediavryheid moet voldoen aan die vereistes wat die algemene beperkingsklousule vir die grondwetlike beperking van fundamentele regte stel. Enige beperking van die reg op mediavryheid moet dus kragtens 'n algemeen geldende regsvoorskrif geskied en moet, met in agneming van die artikel 36-sleutelfaktore, as redelik en regverdigbaar binne 'n oop en demokratiese samelewing gebaseer op menswaardigheid, gelykheid en vryheid plaasvind. Enige staats- en administratiefregtelike beperkings op mediavryheid wat nie aan hierdie grondwetlike vereistes voldoen nie, is gevolglik ongrondwetlik. Nadat die bepalings ter beperking van mediavryheid deur die Protection of State Information Bill, 2010 krities ontleed is, is bevind dat dit nie daarin sal slaag om die grondwetlike toets te slaag nie. / LLM, North-West University, Potchefstroom Campus, 2015

Advanced mobile communication systems are characterized by a dense deployment of different types of wireless access points. Since these systems are primarily limited by interference, multiple-input multiple-output (MIMO) techniques as well as coordinated transmission and detection schemes are necessary to mitigate this limitation. Thus, mobile communication systems become more complex which requires that also the mathematical tools for their theoretical analysis must evolve. These must be able to take the most important system characteristics into account, such as fading, path loss, and interference. The aim of this thesis is to develop such tools based on large random matrix theory and to demonstrate their usefulness with the help of several practical applications, such as the performance analysis of network MIMO and large-scale MIMO systems, the design of low-complexity polynomial expansion detectors, and the study of random beamforming techniques as well as multi-hop relay and double-scattering channels. The methods developed in this work provide deterministic approximations of the system performance which become arbitrarily tight in the large system regime with an unlimited number of transmitting and receiving devices. This leads in many cases to simple and close approximations of the finite-size system performance and allows one to draw relevant conclusions about the most significant parameters. One can think of these methods as a way to provide a deterministic abstraction of the physical layer which substantially reduces the system complexity. Due to this complexity reduction, it is possible to carry out a system optimization which would be otherwise intractable.