Full-Diversity QO-STBC Technique for Large-Antenna MIMO Systems

YesThe need to achieve high data rates in modern telecommunication systems, such as 5G standard, motivates the study and development of large antenna and multiple-input multiple-output (MIMO) systems. This study introduces a large antenna-order design of MIMO quasi-orthogonal space-time block code (QO-STBC) system that achieves better signal-to-noise ratio (SNR) and bit-error ratio (BER) performances than the conventional QO-STBCs with the potential for massive MIMO (mMIMO) configurations. Although some earlier MIMO standards were built on orthogonal space-time block codes (O-STBCs), which are limited to two transmit antennas and data rates, the need for higher data rates motivates the exploration of higher antenna configurations using different QO-STBC schemes. The standard QO-STBC offers a higher number of antennas than the O-STBC with the full spatial rate. Unfortunately, also, the standard QO-STBCs are not able to achieve full diversity due to self-interference within their detection matrices; this diminishes the BER performance of the QO-STBC scheme. The detection also involves nonlinear processing, which further complicates the system. To solve these problems, we propose a linear processing design technique (which eliminates the system complexity) for constructing interference-free QO-STBCs and that also achieves full diversity using Hadamard modal matrices with the potential for mMIMO design. Since the modal matrices that orthogonalize QO-STBC are not sparse, our proposal also supports O-STBCs with a well-behaved peak-to-average power ratio (PAPR) and better BER. The results of the proposed QO-STBC outperform other full diversity techniques including Givens-rotation and the eigenvalue decomposition (EVD) techniques by 15 dB for both MIMO and multiple-input single-output (MISO) antenna configurations at 10−3 BER. The proposed interference-free QO-STBC is also implemented for 16×NR and 32×NR MIMO systems, where NR≤2. We demonstrate 8 x 16 and 32 transmit antenna-enabled MIMO systems with the potential for mMIMO design applications with attractive BER and PAPR performance characteristics

Multiuser non coherent massive MIMO schemes based on DPSK for future communication systems

The explosive usage of rich multimedia content in wireless devices has overloaded the communication networks. Moreover, the fifth generation (5G) of wireless communications involves new requirements in the radio access network (RAN) which require higher network capacities and new capabilities such as ultra-reliable and low-latency communication (URLLC), vehicular communications or augmented reality. All this has encouraged a remarkable spectrum crisis in the RF bands. A need for searching alternative techniques with more spectral efficiency to accommodate the needs of future emerging wireless communications is emerging. In this context, massive MIMO (m-MIMO) systems have been proposed as a promising solution for providing a substantial increase in the network capacity, becoming one of the key enabling technologies for 5G and beyond. m-MIMO provides high spectral- and energy-efficiency thanks to the deployment of a large number of antennas at the BS. However, we have to take into account that the current communication technologies are based on coherent transmission techniques so far, which require the transmission of a huge amount of signaling. This drawback is escalating with the excessive available number of antennas in m-MIMO. Therefore, the differential encoding and non coherent (NC) detection are an alternative solution to circumvent the drawbacks of m-MIMO in coherent systems. This Ph.D. Thesis is focused on signal processing techniques for NC detection in conjunction with m-MIMO, proposing new constellation designs and NC detection algorithms, where the information is transmitted in the signal differential phase. First, we design new constellation schemes for an uplink multiuser NC m-MIMO system in Rayleigh fading channels. These designs allow us to separate the users' signals at the receiver thanks to a one-to-one correspondence between the constellation for each user and the received joint constellation. Two approaches are considered in terms of BER: each user achieves a different performance and, on the other hand, the same performance is provided for all users. We analyze the number of antennas needed for those designs and compare to the required number by other designs in the literature. It is shown that our designs based on DPSK require a lower number of antennas than that required by their counterpart schemes based on energy. In addition, we compare the performance to their coherent counterpart systems, resulting NC-m-MIMO based on DPSK capable of outperforming the coherent systems with the suitable designs. Second, in order to reduce the number of antennas required for a target performance we propose a multi-user bit interleaved coded modulation - iterative decoding (BICM-ID) scheme as channel coding for a NC-m-MIMO system based on DPSK. We propose a novel NC approach for calculating EXIT curves based on the number of antennas. Then using the EXIT chart we find the best channel coding scheme for our NC-m-MIMO proposal. We show that the number of users served by the BS can be increased with a 70% reduction in the number of antennas with respect to the case without channel coding. In particular, we show that with 100 antennas for error protection equal design for all users and a coding rate of 1/2 we achieve the minimum probability of error. Third, we consider that current scenarios such as backhaul wireless systems, rural or suburban environments, and even new device-to-device (D2D) communications or the communications in higher frequencies (millimeter and the emerging ones in terahertz frequencies) can have a predominant line-of-sight (LOS) component, modeled by Rician fading. For all these new possible scenarios in 5G, we analyze the behavior of the NC m-MIMO systems when we have a Rician fading. We present a new constellation design to overcome the problem of the LOS channel component, as well as an associated detection algorithm to separate each user in reception taking into account the characterization of the constellation. In addition, for contemplating a more realistic scenario, we propose grouping users which experience a Rayleigh fading with those with Rician fading, analyzing the SINR and the performance of such combination in a multi-user NC m-MIMO system based on M-DPSK. The adequate user grouping allows unifying the constellation for both groups of users and the detection algorithm, reducing the complexity of the receiver. Also, the number of users that may be multiplexed may be further increased thanks to the improved performance. In the fourth part of this Thesis, we analyse the performance of multi-user NC m- MIMO based on DPSK in real environments and practical channels defined for the current standards such as LTE, the future technologies such as 5G and even for communications in the terahertz band. For this purpose, we use a metric to model the time-varying characteristics of the practical channels. We employ again the EXIT charts tool for analyzing and designing iteratively decoded systems. This analysis allows us to obtain an estimate of the degradation of the system's performance imposed by realistic channels. Hence, we show that our proposed system is robust to temporal variations, thus it is more recommendable the employment of NC-m-MIMO-DPSK in the future communication standards such as 5G. In order to reduce he number of hardware resources required in terms of RF chains, facilitating its implementation in a real system, we propose incorporating differential spatial modulation (DSM). We present and analyze a novel multiuser scheme for NC-m-MIMO combined with DSM with which we can see that the number of antennas is not a affected by the incorporation of DSM, even we have an improvement on the performance with respect to the coherent case. Finally, we study the viability of multiplexing users by constellation schemes against classical multiplexing techniques such as time division multiple access (TDMA). In order to fully characterize the system performance we analyze the block error rate (BLER) and the throughput of a NC-m-MIMO system. The results show a significant advantage regarding the number of antennas for multiplexing in the constellation against TDMA. However, in some cases, the demodulation of multiple users in constellation could require an excessively large number of antennas compared to TDMA. Therefore, it is necessary to properly manage the tradeoff between throughout and the number of antennas, to reach an optimal operational point, as shown in this Thesis.El inmenso uso de contenido multimedia en los dispositivos inalámbricos ha sobrecargado las redes de comunicaciones. Además, la quinta generación (5G) de sistemas de comunicaciones demanda nuevos requisitos para la red de acceso radio, la cual requiere ofrecer capacidades de red mayores y nuevas funcionalidades como comunicaciones ultra fiables y con muy poca letancia (URLLC), comunicaciones vehiculares o aplicaciones como la realidad aumentada. Todo esto ha propiciado una crisis notable en el espectro electromagnético, lo que ha llevado a una necesidad por buscar técnicas alternativas con más eficiencia espectral para acomodar todos los requisitos de las tecnologías de comunicaciones emergentes y futuras. En este contexto, los sistemas multi antena masivos, conocidos como massive MIMO, m-MIMO, han sido propuestos como una solución prometedora que proporciona un incremento substancial de la capacidad de red, convirtiéndose en una de las tecnologías claves para el 5G. Los sistemas m-MIMO elevan enormemente el número de antenas en la estación base, lo que les permite ofrecer alta eficiencia espectral y energética. No obstante, tenemos que tener en cuenta que las actuales tecnologías de comunicaciones emplean técnicas coherentes, las cuales requieren de información del estado del canal y por ello la transmisión de una enorme cantidad de información de señalización. Este inconveniente se ve agravado en el caso del m-MIMO debido al enorme número de antenas. Por ello, la codificación diferencial y la detección no coherente (NC) son una solución alternativa para solventar el problema de m-MIMO en los sistemas coherentes. Esta Tesis se centra en las técnicas de procesado de señal para detección NC junto con m-MIMO, proponiendo nuevos esquemas de constelación y algoritmos de detección NC, donde la información sea transmitida en la diferencia de fase de la señal. Primero, diseñamos nuevas constelaciones para un sistema multi usuario NC en m- MIMO en enlace ascendente (uplink) en canales con desvanecimiento tipo Rayleigh. Estos diseños nos permiten separar las señales de los usuarios en el receptor gracias a la correspondencia unívoca entre la constelación de cada usuario individual y la constelación conjunta recibida en la estación base. Hemos considerado dos enfoques para el diseño en términos de probabilidad de error: cada usuario consigue un rendimiento distinto, mientras que por otro lado, todos los usuarios son capaces de recibir las mismas prestaciones de probabilidad de error. Analizamos el número de antenas necesario para estos diseños y comparamos con el número requerido por otros diseños propuestos en la literatura. Nuestro diseño basado en DPSK requiere un número menor de antenas comparado con los sistemas basados en detección de energía. También comparamos con su homólogo coherente, resultando que NC-m-MIMO basado en DPSK es capaz de superar a los sistemas coherentes con los diseños adecuados. En segundo lugar, para reducir el número de antenas requerido para un rendimiento dado, proponemos incluir un esquema de codificación de canal. Hemos optado por un esquema de modulación codificado por bit entrelazado y decodificación iterativa (BICMID). Hemos empleado la herramienta EXIT chart para el diseño de la codificación de canal, proponiendo un nuevo enfoque para calcular las curvas EXIT de forma NC y basadas en el número de antenas. Los resultados muestran que el número de usuarios servidos por la estación base puede ser incrementado reduciendo un 70% el número de antenas con respecto al caso sin codificación de canal. En particular, para un array de 100 antenas y un diseño que ofrezca iguales prestaciones a todos los usuarios, con un código de tasa 1=2, podemos conseguir la mínima probabilidad de error. En tercer lugar, consideramos escenarios donde el canal tenga una componente predominante de visión directa (LOS) con la estación base modelada mediante un desvanecimiento tipo Rician. Por ejemplo, sistemas inalámbricos de backhaul, entornos rurales o sub urbanos, comunicaciones entre dispositivos (D2D), también cuando nos movemos hacia frecuencias superiores como son en la banda de milimétricas o más recientemente, la banda de terahercios para buscar mayores anchos de banda. Todos estos escenarios están contemplados en el futuro 5G. Los diseños presentados para canales Rayleigh ya no son válidos debido a la componente LOS del canal, por ello presentamos un nuevo diseño de constelación que resuelve el problema de la componente LOS, así como una guía para diseñar nuevas constelaciones. También proponemos un algoritmo asociado al diseñno de la constelación para poder separar a los usuarios en recepción. Además, para contemplar un escenario más realista donde podamos encontrar tanto desvanecimiento Rayleigh como Rice, proponemos agrupar usuarios de ambos grupos, analizando su rendimiento y relación señal a interferencia en la combinación. El adecuado agrupamiento permite unificar el diseño de la constelación para ambos desvanecimientos y por tanto reducir la complejidad en el receptor. También, el número de usuarios multiplicados en la constelación podría ser incrementado, gracias a la mejora en el rendimiento. El cuarto módulo de esta tesis es dedicado a analizar el rendimiento de los diseños propuestos en presencia de canales reales, donde disponemos de variabilidad temporal y en frecuencia. Proponemos usar una métrica que modela las características de la variabilidad temporal y, usando de nuevo la herramienta EXIT, analizamos los sistemas decodificados iterativamente considerando ahora los parámetros prácticos del canal. Este análisis nos permite obtener una estimación de la degradación que sufre el rendimiento del sistema impuesto por canales reales. Los resultados muestran que los sistemas NC-m-MIMO basados en DPSK son muy robustos a la variabilidad temporal por lo que son recomendables para los nuevos escenarios propuestos por el 5G, donde el canal cambia rápidamente. Otra consideración para introducir los sistemas NC con m-MIMO es la problemática de necesitar muchas cadenas de radio frecuencia que llevarían a tamaños de dispositivos enormes. Para reducir este número se propone la modulación espacial. En esta Tesis, estudiamos su uso con los sistemas NC, proponiendo una solución de modulación espacial diferencial para esquemas con múltiples usuarios combinado con NC-m-MIMO. Finalmente, estudiamos la viabilidad de multiplexar usuarios en la constelación frente a usar técnicas clásicas de multiplexación como TDMA. Para caracterizar completamente el rendimiento del sistema, analizamos la tasa de error de bloque (BLER) y el throughput de un sistema NC-m-MIMO. Los resultados muestran una ventaja significativa en cuanto al número de antennas para multiplexar usuarios en la constelación frente al requerido por TDMA. No obstante, en algunos casos, la demodulación de múltiples usuarios en la constelación podría requerir un número de antennas excesivamente grande comparado con la multiplexación en el tiempo. Por ello, es necesario gestionar adecuadamente un balance entre el throughput y el número de antenas para alcanzar un punto operacional óptimo, como se muestra en esta Tesis.Programa Oficial de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Ana Isabel Pérez Neira.- Secretario: Máximo Morales Céspedes.- Vocal: María del Carmen Aguayo Torre

Interference-free Spectrum Sharing In Cognitive Radio Based On Space Time Coding

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2016Thesis (M.Sc.) -- İstanbul Technical University, Instıtute of Science and Technology, 2016Yeni nesil telsiz iletişim sistemleri ve gezgin sistemler daha yüksek veri hızlarının yanında, maksimum bant genişliği kullanımına da gereksinim duyarlar. Son yıllarda, literatürde bazı teknikler telsiz sistemlerin yüksek veri hızlarını destekleyeceği çeşitli şekillerde ortaya konulmuştur. Ancak, yüksek veri hızlarını destekleme gereksinimini karşılamada, spektrumun çoğunun lisanslı kullanıcılara ait olduğu spektrum tahsis tablosunda olduğu gibi spektrum yetersizliği problemiyle karşılaşılır. Bununla birlikte, spektrum ölçümleri frekansa, coğrafi konuma ve zamana bağlı olarak spektrumun büyük bir kısmının sürekli olarak kullanılmadığını göstermektedir. Sonuç olarak, yüksek veri hızlarını desteklemek için spektrum dağılımını kabul edilebilir servis kalitesine göre yöneterek kaynakların verimli bir şekilde kullanılması gerekmektedir. Bu nedenle, telsiz iletişimde mevcut spektrumu paylaşarak spektrum yetersizliği problemini ortadan kaldırmak için pek çok yaklaşım ortaya atılmıştır. İki farklı telsiz sistemin önceliklerine göre aynı frekans bandında çalıştığı bilişsel radio (CR) spektrum kullanımını arttırmak ve spektrum yetersizliğini çözmek için potansiyel bir yol olarak kabul edilmiştir. CR ilerideki yeni nesil kablosuz sistemler için yenilikçi bir teknik ve gelişen bir araştırma alanıdır. CR’da lisanslı bandlara erişmek için ikincil kullanıcılar (SU) tarafından araya yerleştirme, altına serme ve üstüne serme teknikleri kullanılabilir. Araya yerleştirme tekniğinde, SU’lar birincil kullanıcılara (PU) girişim yaratmadan spektrum boşluklarını kullanmak için PU’ların varlığını ya da yokluğunu sezerler. Altına serme tekniğinde, eğer PU’lardaki girişim önceden belirlenmiş bir girişim seviyesinin altındaysa, SU’lara lisanslı spektrumu kullanma hakkı verilir. Üstüne serme tekniğinde ise, lisanssız kullanıcılar genellikle lisanslı spektrumu paylaşmak için spektrum sahiplerinin yararına işbirliği yaparak bir bedel öderler. Literatürde karma ve toplamsal kodlama teknikleri gibi farklı spektrum paylaşım türleri önerilmiştir. Toplamsal kodlamada SU, PU’nun ve kendi işaretini birleştirir, sonra birincil alıcıya (PR) ve ikincil alıcıya (SR) yayın yapar. Ancak bu teknik her iki kullanıcının alıcılarında önemli girişime neden olur. Sistemin, spektrumdan yarar sağlamak ve PU ile işbirliği yapmak için farklı teknikleri bir araya getirdiği karma yöntemlerden de yaralanılabilir. İletilen işarete kanalların sönümleme etkisini azaltabilen, modülasyon çeşitlemesi olarak da bilinen bir çeşitleme tekniği işaret uzayı çeşitlemesidir (SSD). SSD fazladan band genişliği ya da güç kullanmadan sönümlemeli kanallarda başarımı artırır. SSD işleminde veri iletiminin öncesinde modülasyonlu işaret kümeleri belli bir açı ile döndürülür ve döndürülen işaretler arasındaki minimum çarpımsal uzaklık maksimize edilir. Döndürülmüş işaret kümesine koordinat serpiştirmeli dik tasarım (CIOD) uygulandıktan sonra düzensiz bir modülasyonlu işaret kümesi elde edilir. Normalde işbirlikli haberleşmede verinin alıcıya iletilmesi birden fazla zaman aralığı aldığı için tüm sistemin band verimliliği düşer. Ancak, SSD ve CIOD tekniklerini sistem yapısında kullanmak sistemin karmaşıklığını artırmadan işbirlikli sistemlerde band verimliliğini kolaylıkla artırabilir. Bu tezde, üstüne serme yöntemiyle çalışan bilişsel radyo için iki farklı spektrum paylaşım protokolü önerilmiştir. İlk protokolde, birincil sistem her biri bir antenle donatılmış bir birincil verici (PT) ve bir birincil alıcı (PR) ile ikincil sistem ise her biri bir antenle donatılmış bir ikincil verici (ST) ve bir ikincil alıcı (SR) dan oluşmaktadır. Birincil sistem ile işbirliği çerçevesinde, SU’nun PU ya ait spektrum bandını kullanmasına izin verilmektedir. Bu çalışmada hem spektral verimliliği ve çeşitlemeyi artırmak hem de iki kullanıcının karşılıklı girişimini ortadan kaldırmak amacıyla üç zaman aralığında iki kullanıcının iletimini sağlayan CIOD uzay zaman kodlaması kullanan bir iletim protokolu önerilmektedir. İlk zaman aralığında, PT kendi işaretini PR ve ST’ye iletir ve ST iletilen işareti çözmeye çalışır. ST, PU nun işaretini doğru çözerse, serpiştirilmiş birincil işaret koordinat çiftini PR’ye ikinci zaman aralığında iletilmektir ve PR, PT ve ST’den aldığı işaretler yardımıyla işareti çözmeye çalışır. Ancak, ST’nin PT’den aldığı işareti doğru çözemediği durumda, PR sadece ilk zaman aralığında PT den gelen işarete dayanarak iletilen işareti çözmeye çalışır. Son olarak, ST üçüncü zaman aralığında kendi (ikincil) işaretini SR’ye iletir. Önerilen protokolde ikincil kullanıcıya ayrı bir zaman aralığı ayrılması iki kullanıcı arasındaki girişimi kaldırırken iki birincil işaretin CIOD yardımıyla iki zaman aralığında iletilmesi üç kanal kullanımı başına iki birincil işaretin iletilmesini sağlamakta, böylece iki kanal kullanımı başına bir birincil işaretin iletildiği referans sistemlere göre kanalın daha verimli kullanılmasını sağlamaktadır. PT ile ST arasında bir kritik uzaklık tanımlanmakta, ST, PT ye bu uzaklıktan daha yakın olduğu sürece PU nun servis kesilme olasılığı spektrum paylaşımı olmadığı durumdakine eşit veya daha düşük olmaktadır. Rayleigh sönümlemeli kanalda, PU ve SU nun servis kesilme olasılıkları için kapalı biçimde kuramsal ifadeler türetilmekte, hedeflenen farklı hızlar için protokolun başarımı değerlendirilmektedir. Kuramsal sonuçların bilgisayar benzetimleriyle bütünüyle uyum içerisinde olduğu görülmektedir. Önerilen protokol için hem PU nun hem de SU nun başarımında ST de toplamsal kodlamanın kullanıldığı literatürde verilen referans protokole göre önemli kazançlar elde edilmektedir. Diğer yandan birincil kullanıcının bit hata olasılığı için kuramsal bir üst sınır elde edilmekte, sonuçlar bilgisayar benzetimleriyle desteklenmektedir. Beklendiği gibi bilgisayar benzetim sonuçları artan işaret-gürültü oranı ile kuramsal üst sınıra yaklaşmaktadır. Son olarak, ikincil kullanıcının BER başarımı klasik doğrudan iletime eşdeğerdir. 4QAM ve 16QAM modülasyonları ve ST ile SR arasındaki uzaklığın farklı değerleri için elde edilen BER başarım eğrileri önerilen protokolun toplamsal kodlamalı referans protokole üstünlüğünü ortaya koymaktadır. İkincil protokolde birincil kullanıcı, birer antenli PT ve PR den oluşurken ikincil kullanıcı için ST iki antenli olup SR bir antenlidir. ST bir önceki protokolden farklı olarak en büyük oran birleştirme (MRC) ve Alamouti uzay-zaman kodlama tekniklerinden yararlanmaktadır. Protokol yine üstüne serme tekniğine dayalı olup spektral verimliliği artırma, çeşitleme sağlama ve alıcılarda girişimi önleme amacıyla CIOD ve Alamouti uzay zaman kodlama teknikleri bir arada kullanılmaktadır. Protokol PU nun iki, SU nun bir işaretini üç zaman aralığında iletmektedir. Birinci zaman aralığında PT iki birincil işaretin yalnız gerçel ve sanal kısımlarını PR ve ST ye iletmekte, ST iki anteni yardımıyla MRC uygulayarak bu iki birincil işareti yalnız gerçel ve sanal bileşenlerinden çözmekte, ikinci zaman aralığında ilişkin sanal ve gerçel bileşenleri bir araya getirerek birinci anteninden PR ye iletmektedir. Kendi ikincil işaretini ise aynı anda ikinci anteninden SR ye iletmektedir. Üçüncü zaman aralığında ise ikinci zaman aralığında ilettiği işaretlere Alamouti uzay zaman blok kodlaması uygulayarak her iki anteninde iletmektedir. ST, PT den gelen işareti çözemezse ikinci ve üçüncü zaman aralıklarında Alamouti koduna uygun biçimde kendi işaretini iletmektedir. Protokol hem PR hem de SR de Alamouti kodlamanın getirdiği tek simge çözme özelliğiyle girişimi ortadan kaldırmakta ayrıca her iki kullanıcı için uzay çeşitlemesi sağlamaktadır. Tezde birincil kullanıcının bit hata olasılığı için kuramsal bir üst sınır türetilmekte, üst sınırın geçerliliği bilgisayar benzetim sonuçlarıyla desteklenmektedir. PT, ST ve PR arasındaki farklı uzaklık değerleri için sonuçlar irdelenmekte, protokolun sağladığı BER başarım kazancı referans protokolle karşılaştırılarak ortaya konmaktadır. Diğer yandan, ikincil kullanıcının BER başarımı klasik Alamouti kodununkine eşdeğer olmakta, ST ile SR arasındaki uzaklığın çeşitli değerleri ve 16QAM modülasyonu için irdelenmekte, doğrudan iletim durumu ve toplamsal kodlamanın kullanıldığı referans protokolle karşılaştırılarak üstünlüğü ortaya konmaktadır.Next generation wireless communications and mobile systems demand higher data rates with maximum bandwidth utilization. Over the past years, some techniques in the literature are provided in various ways where wireless systems should support high data rates. However, this requirement is faced with spectrum scarcity accommodation problem as in spectrum allocation chart where majority of the spectrum is under license. Nevertheless, spectrum measurements show that most of the spectrum is not continuously used based on the frequency, geographical location and time. As a result, this requirement necessitates the efficient use of the available resources by managing spectrum distribution to provide acceptable service quality. Therefore, several approaches in wireless systems are introduced in literature for sharing the available spectrum to overcome the spectrum scarcity problem. Cognitive Radio (CR) is considered as a potential solution to boost the spectrum utilization and solve the spectrum scarcity in which two different wireless systems could operate in the same frequency band with respect to their priority. CR is an innovative technique and developing area of research for the next wireless generation systems. In CR, to access the licensed bands interweave, underlay and overlay patterns can be used by the Secondary Users (SUs). In the interweave protocol, SUs sense the existence or nonexistence of Primary Users (PUs) to use spectrum holes without causing interference to PUs. In the underlay protocol, SUs are certified to use the licensed spectrum if the interference caused at PUs is below a predetermined interference level. In the overlay protocol, unlicensed users generally pay a price to share a licensed spectrum by cooperating for the benefit of spectrum owners. Different kinds of spectrum sharing model such as hybrid and superposition coding techniques are proposed in the literature. In superposition coding SU combines the PU's and its own signal and then broadcast to both Primary Receiver (PR) and Secondary Receiver (SR). However, this technique causes severe interference in both receivers. Two CR patterns can be combined to approach the hybrid mode where in this case the system has flexibility to operate in different protocols to obtain benefits from the spectrum and cooperate with PU. One diversity technique that could mitigate the fading channels effect on the transmitted signal is Signal Space Diversity (SSD) also known as modulation diversity. SSD provides performance improvement over fading channels without using extra bandwidth or power. In SSD, constellation points of the modulation are rotated by an angle before the transmission which maximize the minimum product distance of the rotated constellation, and after applying Coordinate Interleaved Orthogonal Design (CIOD) on the rotated constellation an irregular modulation points are acquired. Normally, in cooperative communications overall system spectral efficiency and rate are decreased due to the fact that data takes more than one time slot to be transmitted to the receiver. However, using SSD and CIOD technique in the system configuration, one can easily enhance the overall spectral efficiency and rate in cooperative systems without adding any complexity to the system. In this thesis, two different spectrum sharing protocols for cognitive radio operating in overlay mode are proposed. In the first protocol, the primary and secondary system is comprised of PT, PR, ST and SR equipped all with one antenna. SU is allowed to use the shared spectrum band in accordance to cooperate with primary system. We take advantages of the SSD and CIOD concepts in this three-phase overlay protocol to enhance the spectral efficiency, rate and diversity as well as to provide single symbol decoding. In the first transmission time slot, PT broadcasts its signal to PR and ST where ST tries to decode the transmitted signal from PT. If ST correctly decodes the PU's signal, ST forwards the coordinate interleaved signal pair to PR in the second time slot and PR tries to estimate the symbol by received signals from PT and ST. However, in the case that ST could not correctly decode the signal received from PT, PR decodes the symbol only from PT. Finally, SU's signal is transmitted to SR by ST at the third time slot. Due to the fact that a specific time slot is dedicated to SU data transmission, this protocol avoids interference. A critical distance between PT and ST is obtained such that as long as ST is located within that distance the outage probability of PU will be equal or lower than the case that of without spectrum sharing and ST will benefit from the band. The outage probabilities for PU and SU over Rayleigh fading channels are derived in a closed-form expressions and depicted for different target rates. Note that, the theoretic outcomes match perfectly with simulation results. It is shown that a significant performance improvement in the proposed scheme is notable both for PU and SU in comparison to the reference protocol where superposition coding is used at ST. Furthermore, an upper bound on the Bit Error Probability (BEP) of primary system is obtained and supported via simulation results. The simulation results agree well with the theoretical upper bound in the high Signal to Noise Ratio (SNR), respectively. Finally, for the secondary system, BEP performance is the same as classical direct transmission. The BEP performance for 16-QAM and 4-QPSK modulation for different values of the distance between ST and SR are depicted where in both cases simulation. The results confirm the efficiency of the proposed spectrum sharing compared to the reference protocol. In the second protocol, PU consists of a pair of PT and PR with one antenna and for SU, ST is equipped with two antennas to use the benefits of Maximum Ratio Combining (MRC) and Alamouti techniques and SR has only one antenna. A CR protocol which is configured on overlay mode to share the spectrum of the primary system is presented. SSD, CIOD and Alamouti concepts are used together to benefit from the single symbol decoding, diversity gain and to increase the overall system rate and spectral efficiency. The protocol comprises of three time slots to transmit PU's and SU's data. In the first time slot, PT transmits the primary signal to PR and to both antennas of ST. Then, ST uses the MRC technique to decode the transmitted signal. If ST correctly decodes the transmitted signal from PT, it applies Alamouti coding to transmit the primary and its own symbols to PR and SR in the second and third time slots. Nevertheless, if ST could not correctly decode the signal pair received from PT, PR will estimate the symbol from the direct link PT$\to$PR. Meanwhile, secondary signal is transmitted in the second and third time slots which provides diversity which enhances SU system performance. This protocol guarantees an interference-free communication for both users by considering the fact that PR and SR could extract their own signal based on the single symbol decoding technique provided by Alamouti coding. An upper bound for the BEP of the primary system is derived and it is shown that computer simulation results are in perfectly match with the theoretical upper bound in high SNR which validates the theoretical derivations. Results for different values of the distance between PT, ST and PR are obtained where in all cases, they validate the significant improvement in the Bit Error Rate (BER) performance for the proposed protocol. For the secondary system, BEP performance is the same as classical Alamouti code and is depicted for various values of the distance between ST and SR for classical 16-QAM and is compared with the straightforward transmission scheme and with the reference scheme where SU uses nearly all of its power to transmit the PU's signal and SU is in outage in most cases and operates a relay.Yüksek LisansM.Sc

Unified Framework for Multicarrier and Multiple Access based on Generalized Frequency Division Multiplexing

The advancements in wireless communications are the key-enablers of new applications with stringent requirements in low-latency, ultra-reliability, high data rate, high mobility, and massive connectivity. Diverse types of devices, ranging from tiny sensors to vehicles, with different capabilities need to be connected under various channel conditions. Thus, modern connectivity and network techniques at all layers are essential to overcome these challenges. In particular, the physical layer (PHY) transmission is required to achieve certain link reliability, data rate, and latency. In modern digital communications systems, the transmission is performed by means of a digital signal processing module that derives analog hardware. The performance of the analog part is influenced by the quality of the hardware and the baseband signal denoted as waveform. In most of the modern systems such as fifth generation (5G) and WiFi, orthogonal frequency division multiplexing (OFDM) is adopted as a favorite waveform due to its low-complexity advantages in terms of signal processing. However, OFDM requires strict requirements on hardware quality. Many devices are equipped with simplified analog hardware to reduce the cost. In this case, OFDM does not work properly as a result of its high peak-to-average power ratio (PAPR) and sensitivity to synchronization errors. To tackle these problems, many waveforms design have been recently proposed in the literature. Some of these designs are modified versions of OFDM or based on conventional single subcarrier. Moreover, multicarrier frameworks, such as generalized frequency division multiplexing (GFDM), have been proposed to realize varieties of conventional waveforms. Furthermore, recent studies show the potential of using non-conventional waveforms for increasing the link reliability with affordable complexity. Based on that, flexible waveforms and transmission techniques are necessary to adapt the system for different hardware and channel constraints in order to fulfill the applications requirements while optimizing the resources. The objective of this thesis is to provide a holistic view of waveforms and the related multiple access (MA) techniques to enable efficient study and evaluation of different approaches. First, the wireless communications system is reviewed with specific focus on the impact of hardware impairments and the wireless channel on the waveform design. Then, generalized model of waveforms and MA are presented highlighting various special cases. Finally, this work introduces low-complexity architectures for hardware implementation of flexible waveforms. Integrating such designs with software-defined radio (SDR) contributes to the development of practical real-time flexible PHY.:1 Introduction 1.1 Baseband transmission model 1.2 History of multicarrier systems 1.3 The state-of-the-art waveforms 1.4 Prior works related to GFDM 1.5 Objective and contributions 2 Fundamentals of Wireless Communications 2.1 Wireless communications system 2.2 RF transceiver 2.2.1 Digital-analogue conversion 2.2.2 QAM modulation 2.2.3 Effective channel 2.2.4 Hardware impairments 2.3 Waveform aspects 2.3.1 Single-carrier waveform 2.3.2 Multicarrier waveform 2.3.3 MIMO-Waveforms 2.3.4 Waveform performance metrics 2.4 Wireless Channel 2.4.1 Line-of-sight propagation 2.4.2 Multi path and fading process 2.4.3 General baseband statistical channel model 2.4.4 MIMO channel 2.5 Summary 3 Generic Block-based Waveforms 3.1 Block-based waveform formulation 3.1.1 Variable-rate multicarrier 3.1.2 General block-based multicarrier model 3.2 Waveform processing techniques 3.2.1 Linear and circular filtering 3.2.2 Windowing 3.3 Structured representation 3.3.1 Modulator 3.3.2 Demodulator 3.3.3 MIMO Waveform processing 3.4 Detection 3.4.1 Maximum-likelihood detection 3.4.2 Linear detection 3.4.3 Iterative Detection 3.4.4 Numerical example and insights 3.5 Summary 4 Generic Multiple Access Schemes 57 4.1 Basic multiple access and multiplexing schemes 4.1.1 Infrastructure network system model 4.1.2 Duplex schemes 4.1.3 Common multiplexing and multiple access schemes 4.2 General multicarrier-based multiple access 4.2.1 Design with fixed set of pulses 4.2.2 Computational model 4.2.3 Asynchronous multiple access 4.3 Summary 5 Time-Frequency Analyses of Multicarrier 5.1 General time-frequency representation 5.1.1 Block representation 5.1.2 Relation to Zak transform 5.2 Time-frequency spreading 5.3 Time-frequency block in LTV channel 5.3.1 Subcarrier and subsymbol numerology 5.3.2 Processing based on the time-domain signal 5.3.3 Processing based on the frequency-domain signal 5.3.4 Unified signal model 5.4 summary 6 Generalized waveforms based on time-frequency shifts 6.1 General time-frequency shift 6.1.1 Time-frequency shift design 6.1.2 Relation between the shifted pulses 6.2 Time-frequency shift in Gabor frame 6.2.1 Conventional GFDM 6.3 GFDM modulation 6.3.1 Filter bank representation 6.3.2 Block representation 6.3.3 GFDM matrix structure 6.3.4 GFDM demodulator 6.3.5 Alternative interpretation of GFDM 6.3.6 Orthogonal modulation and GFDM spreading 6.4 Summary 7 Modulation Framework: Architectures and Applications 7.1 Modem architectures 7.1.1 General modulation matrix structure 7.1.2 Run-time flexibility 7.1.3 Generic GFDM-based architecture 7.1.4 Flexible parallel multiplications architecture 7.1.5 MIMO waveform architecture 7.2 Extended GFDM framework 7.2.1 Architectures complexity and flexibility analysis 7.2.2 Number of multiplications 7.2.3 Hardware analysis 7.3 Applications of the extended GFDM framework 7.3.1 Generalized FDMA 7.3.2 Enchantment of OFDM system 7.4 Summary 7 Conclusions and Future work

Joint signal detection and channel estimation in rank-deficient MIMO systems

L'évolution de la prospère famille des standards 802.11 a encouragé le développement des technologies appliquées aux réseaux locaux sans fil (WLANs). Pour faire face à la toujours croissante nécessité de rendre possible les communications à très haut débit, les systèmes à antennes multiples (MIMO) sont une solution viable. Ils ont l'avantage d'accroître le débit de transmission sans avoir recours à plus de puissance ou de largeur de bande. Cependant, l'industrie hésite encore à augmenter le nombre d'antennes des portables et des accésoires sans fil. De plus, à l'intérieur des bâtiments, la déficience de rang de la matrice de canal peut se produire dû à la nature de la dispersion des parcours de propagation, ce phénomène est aussi occasionné à l'extérieur par de longues distances de transmission. Ce projet est motivé par les raisons décrites antérieurement, il se veut un étude sur la viabilité des transcepteurs sans fil à large bande capables de régulariser la déficience de rang du canal sans fil. On vise le développement des techniques capables de séparer M signaux co-canal, même avec une seule antenne et à faire une estimation précise du canal. Les solutions décrites dans ce document cherchent à surmonter les difficultés posées par le medium aux transcepteurs sans fil à large bande. Le résultat de cette étude est un algorithme transcepteur approprié aux systèmes MIMO à rang déficient

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

Signal space cooperative communication with partial relay selection.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.Exploiting the available diversity from various sources in wireless networks is an easy way to improve performance at the expense of additional hardware, space, complexity and/or bandwidth. Signal space diversity (SSD) and cooperative communication are two promising techniques that exploit the available signal space and space diversity respectively. This study first presents symbol error rate (SER) analysis of an SSD system containing a single transmit antenna and N receive antennas with maximal-ratio combining (MRC) reception; thereafter it presents a simplified maximum-likelihood (ML) detection scheme for SSD systems, and finally presents the incorporation of SSD into a distributed switch and stay combining with partial relay selection (DSSC-PRS) system. Performance analysis of an SSD system containing a single transmit antenna and multiple receive antennas with MRC reception has been presented previously in the literature using the nearest neighbour (NN) approximation to the union bound, however results were not presented in closed form. Hence, closed form expressions are presented in this work. A new lower bound for the SER of an SSD system is also presented which is simpler to evaluate than the union bound/NN approximation and also simpler to use with other systems. The new lower bound is based on the minimum Euclidean distance of a rotated constellation and is termed the minimum distance lower bound (MDLB); it is also presented here in closed form. The presented bounds have been validated with simulation and found to be tight under certain conditions. The SSD scheme offers error performance and diversity benefits with the only penalty being an increase in detector complexity. Detection is performed in the ML sense and conventionally, all points in an M-ary quadrature amplitude modulation (M-QAM) constellation are searched to find the transmitted symbol. Hence, a simplified detection scheme is proposed that only searches m symbols from M after performing initial signal conditioning. The simplified detection scheme is able to provide SER performance close to that of optimal ML detection in systems with multiple receive antennas. Cooperative communication systems can benefit from the error performance and diversity gains of the spectrally efficient SSD scheme since it requires no additional hardware, bandwidth or transmit power. Integrating SSD into a DSSC-PRS system has shown an improvement of approximately 5dB at an SER of 10-4 with a slight decrease in spectral efficiency at low SNR. Analysis has been performed using the newly derived MDLB and confirmed with simulation

Transmission strategies for broadband wireless systems with MMSE turbo equalization

This monograph details efficient transmission strategies for single-carrier wireless broadband communication systems employing iterative (turbo) equalization. In particular, the first part focuses on the design and analysis of low complexity and robust MMSE-based turbo equalizers operating in the frequency domain. Accordingly, several novel receiver schemes are presented which improve the convergence properties and error performance over the existing turbo equalizers. The second part discusses concepts and algorithms that aim to increase the power and spectral efficiency of the communication system by efficiently exploiting the available resources at the transmitter side based upon the channel conditions. The challenging issue encountered in this context is how the transmission rate and power can be optimized, while a specific convergence constraint of the turbo equalizer is guaranteed.Die vorliegende Arbeit beschäftigt sich mit dem Entwurf und der Analyse von effizienten Übertragungs-konzepten für drahtlose, breitbandige Einträger-Kommunikationssysteme mit iterativer (Turbo-) Entzerrung und Kanaldekodierung. Dies beinhaltet einerseits die Entwicklung von empfängerseitigen Frequenzbereichs-entzerrern mit geringer Komplexität basierend auf dem Prinzip der Soft Interference Cancellation Minimum-Mean Squared-Error (SC-MMSE) Filterung und andererseits den Entwurf von senderseitigen Algorithmen, die durch Ausnutzung von Kanalzustandsinformationen die Bandbreiten- und Leistungseffizienz in Ein- und Mehrnutzersystemen mit Mehrfachantennen (sog. Multiple-Input Multiple-Output (MIMO)) verbessern. Im ersten Teil dieser Arbeit wird ein allgemeiner Ansatz für Verfahren zur Turbo-Entzerrung nach dem Prinzip der linearen MMSE-Schätzung, der nichtlinearen MMSE-Schätzung sowie der kombinierten MMSE- und Maximum-a-Posteriori (MAP)-Schätzung vorgestellt. In diesem Zusammenhang werden zwei neue Empfängerkonzepte, die eine Steigerung der Leistungsfähigkeit und Verbesserung der Konvergenz in Bezug auf existierende SC-MMSE Turbo-Entzerrer in verschiedenen Kanalumgebungen erzielen, eingeführt. Der erste Empfänger - PDA SC-MMSE - stellt eine Kombination aus dem Probabilistic-Data-Association (PDA) Ansatz und dem bekannten SC-MMSE Entzerrer dar. Im Gegensatz zum SC-MMSE nutzt der PDA SC-MMSE eine interne Entscheidungsrückführung, so dass zur Unterdrückung von Interferenzen neben den a priori Informationen der Kanaldekodierung auch weiche Entscheidungen der vorherigen Detektions-schritte berücksichtigt werden. Durch die zusätzlich interne Entscheidungsrückführung erzielt der PDA SC-MMSE einen wesentlichen Gewinn an Performance in räumlich unkorrelierten MIMO-Kanälen gegenüber dem SC-MMSE, ohne dabei die Komplexität des Entzerrers wesentlich zu erhöhen. Der zweite Empfänger - hybrid SC-MMSE - bildet eine Verknüpfung von gruppenbasierter SC-MMSE Frequenzbereichsfilterung und MAP-Detektion. Dieser Empfänger besitzt eine skalierbare Berechnungskomplexität und weist eine hohe Robustheit gegenüber räumlichen Korrelationen in MIMO-Kanälen auf. Die numerischen Ergebnisse von Simulationen basierend auf Messungen mit einem Channel-Sounder in Mehrnutzerkanälen mit starken räumlichen Korrelationen zeigen eindrucksvoll die Überlegenheit des hybriden SC-MMSE-Ansatzes gegenüber dem konventionellen SC-MMSE-basiertem Empfänger. Im zweiten Teil wird der Einfluss von System- und Kanalmodellparametern auf die Konvergenzeigenschaften der vorgestellten iterativen Empfänger mit Hilfe sogenannter Korrelationsdiagramme untersucht. Durch semi-analytische Berechnungen der Entzerrer- und Kanaldecoder-Korrelationsfunktionen wird eine einfache Berechnungsvorschrift zur Vorhersage der Bitfehlerwahrscheinlichkeit von SC-MMSE und PDA SC-MMSE Turbo Entzerrern für MIMO-Fadingkanäle entwickelt. Des Weiteren werden zwei Fehlerschranken für die Ausfallwahrscheinlichkeit der Empfänger vorgestellt. Die semi-analytische Methode und die abgeleiteten Fehlerschranken ermöglichen eine aufwandsgeringe Abschätzung sowie Optimierung der Leistungsfähigkeit des iterativen Systems. Im dritten und abschließenden Teil werden Strategien zur Raten- und Leistungszuweisung in Kommunikationssystemen mit konventionellen iterativen SC-MMSE Empfängern untersucht. Zunächst wird das Problem der Maximierung der instantanen Summendatenrate unter der Berücksichtigung der Konvergenz des iterativen Empfängers für einen Zweinutzerkanal mit fester Leistungsallokation betrachtet. Mit Hilfe des Flächentheorems von Extrinsic-Information-Transfer (EXIT)-Funktionen wird eine obere Schranke für die erreichbare Ratenregion hergeleitet. Auf Grundlage dieser Schranke wird ein einfacher Algorithmus entwickelt, der für jeden Nutzer aus einer Menge von vorgegebenen Kanalcodes mit verschiedenen Codierraten denjenigen auswählt, der den instantanen Datendurchsatz des Mehrnutzersystems verbessert. Neben der instantanen Ratenzuweisung wird auch ein ausfallbasierter Ansatz zur Ratenzuweisung entwickelt. Hierbei erfolgt die Auswahl der Kanalcodes für die Nutzer unter Berücksichtigung der Einhaltung einer bestimmten Ausfallwahrscheinlichkeit (outage probability) des iterativen Empfängers. Des Weiteren wird ein neues Entwurfskriterium für irreguläre Faltungscodes hergeleitet, das die Ausfallwahrscheinlichkeit von Turbo SC-MMSE Systemen verringert und somit die Zuverlässigkeit der Datenübertragung erhöht. Eine Reihe von Simulationsergebnissen von Kapazitäts- und Durchsatzberechnungen werden vorgestellt, die die Wirksamkeit der vorgeschlagenen Algorithmen und Optimierungsverfahren in Mehrnutzerkanälen belegen. Abschließend werden außerdem verschiedene Maßnahmen zur Minimierung der Sendeleistung in Einnutzersystemen mit senderseitiger Singular-Value-Decomposition (SVD)-basierter Vorcodierung untersucht. Es wird gezeigt, dass eine Methode, welche die Leistungspegel des Senders hinsichtlich der Bitfehlerrate des iterativen Empfängers optimiert, den konventionellen Verfahren zur Leistungszuweisung überlegen ist