Modified quasi-orthogonal space-time block coding in distributed wireless networks

Cooperative networks have developed as a useful technique that can achieve the same advantage as multi-input and multi-output (MIMO) wireless systems such as spatial diversity, whilst resolving the difficulties of co-located multiple antennas at individual nodes and avoiding the effect of path-loss and shadowing. Spatial diversity in cooperative networks is known as cooperative diversity, and can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission and outage. In this thesis, therefore, firstly, a modified distributed quasi-orthogonal space-time block coding (M-D-QO-STBC) scheme with increased code gain distance (CGD) for one-way and two-way amplify-and-forward wireless relay networks is proposed. This modified code is designed from set partitioning a larger codebook formed from two quasi-orthogonal space time block codes with different signal rotations then the subcodes are combined and pruned to arrive at the modified codebook with the desired rate in order to increase the CGD. Moreover, for higher rate codes the code distance is maximized by using a genetic algorithm to search for the optimum rotation matrix. This scheme has very good performance and significant coding gain over existing codes such as the open-loop and closed-loop QO-STBC schemes. In addition, the topic of outage probability analysis in the context of multi-relay selection from $N$ available relay nodes for one-way amplify-and-forward cooperative relay networks is considered together with the best relay selection, the $N^{th}$ relay selection and best four relay selection in two-way amplify-and-forward cooperative relay networks. The relay selection is performed either on the basis of a max-min strategy or one based on maximizing exact end-to-end signal-to-noise ratio. Furthermore, in this thesis, robust schemes for cooperative relays based on the M-D-QO-STBC scheme for both one-way and two-way asynchronous cooperative relay networks are considered to overcome the issue of a synchronism in wireless cooperative relay networks. In particular, an orthogonal frequency division multiplexing (OFDM) data structure is employed with cyclic prefix (CP) insertion at the source in the one-way cooperative relay network and at the two terminal nodes in the two-way cooperative network to combat the effects of time asynchronism. As such, this technique can effectively cope with the effects of timing errors. Finally, outage probability performance of a proposed amplify-and-forward cooperative cognitive relay network is evaluated and the cognitive relays are assumed to exploit an overlay approach. A closed form expression for the outage probability for multi-relay selection cooperation over Rayleigh frequency flat fading channels is derived for perfect and imperfect spectrum acquisitions. Furthermore, the M-QO-STBC scheme is also proposed for use in wireless cognitive relay networks. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of new algorithms and methods

Novel transmission schemes for application in two-way cooperative relay wireless communication networks

Recently, cooperative relay networks have emerged as an attractive communications technique that can generate a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. To achieve cooperative diversity single-antenna terminals in a wireless relay network typically share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission, interference and outage. Therefore, the focus of this thesis is to exploit cooperative relay networks within two-way transmission schemes. Such schemes have the potential to double the data rate as compared to one-way transmission schemes. Firstly, a new approach to two-way cooperative communications via extended distributed orthogonal space-time block coding (E-DOSTBC) based on phase rotation feedback is proposed with four relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain. Then, distributed orthogonal space-time block coding (DOSTBC) is applied within an asynchronous two-way cooperative wireless relay network using two relay nodes. A parallel interference cancelation (PIC) detection scheme with low structural and computational complexity is applied at the terminal nodes in order to overcome the effect of imperfect synchronization among the cooperative relay nodes. Next, a DOSTBC scheme based on cooperative orthogonal frequency division multiplexing (OFDM) type transmission is proposed for flat fading channels which can overcome imperfect synchronization in the network. As such, this technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, a closed-loop EDOSTBC approach using through a three-time slot framework is proposed. A full interference cancelation scheme with OFDM and cyclic prefix type transmission is used in a two-hop cooperative four relay network with asynchronism in the both hops to achieve full data rate and completely cancel the timing error. The topic of outage probability analysis in the context of multi-relay selection for one-way cooperative amplify and forward networks is then considered. Local measurements of the instantaneous channel conditions are used to select the best single and best two relays from a number of available relays. Asymptotical conventional polices are provided to select the best single and two relays from a number of available relays. Finally, the outage probability of a two-way amplify and forward relay network with best and Mth relay selection is analyzed. The relay selection is performed either on the basis of a max-min strategy or one based on maximizing exact end-to-end signal-to-noise ratio. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of new algorithms and methods

Exploiting spatial modulation and analog network coding for the design of energy-efficient wireless networks

As the data rate demands of the cellular users increase, together with their number, it is expected that unprecedented capacity demands should be met in wireless networks in the forthcoming years. However, the energy consumption to meet these rates is expected to increase exponentially, according to trends. This can become a serious issue for both the environment, due to CO2 emissions, and the operators, which will have to pay more for electricity. Hence, several energy-efficient solutions have been proposed, such as multiple antenna systems, dynamic spectrum allocation, heterogeneous networks, and Network Coding, to name a few. Based on the above, the aim of this thesis to propose low-complexity and energy-efficient physical layer-based solutions compared to the already existing approaches, without sacrificing the quality of performance. More specifically, the focus is on the technologies of Spatial Modulation and Analog Network Coding. Both schemes offer the so-called multiplexing gain, which means that multiple streams can be transmitted without sacrificing resources, such as bandwidth. As far as Spatial Modulation is concerned, Spatial Modulation-based schemes are proposed that are more energy efficient than state-of-the-art technologies. Regarding Analog Network Coding, we study its implementation in relay-based scenarios and how it compares in terms of energy efficiency with conventional protocols, such as the time-division multiple access protocol. From the obtained results, the conclusion that can be drawn is that depending on the scenario both Spatial Modulation and Analog Network Coding can provide significant energy gains compared to existing technologies without sacrificing performance.A medida que las demandas de velocidad de datos de los usuarios de redes celulares aumentan, así como su número, se espera que las demandas de capacidad sin precedentes se deban cumplir en las redes inalámbricas en los próximos años. Sin embargo, se espera que aumente de forma exponencial el consumo de energía para satisfacer estas tasas, de acuerdo a las tendencias. Esto puede convertirse en un grave problema ambos para el medio ambiente, debido a las emisiones de CO2, y los operadores, que tendrán que pagar más por la electricidad. Por lo tanto, se han propuesto varias soluciones de eficiencia energética, tales como sistemas de múltiples antenas, la asignación de espectro dinámico, redes heterogéneas, y Network Coding, para nombrar unos pocos. Con base en lo anterior, el objetivo de esta tesis es proponer soluciones de baja complejidad y de eficiencia energética basadas en la capa física, en comparación con los enfoques ya existentes, sin sacrificar la calidad del funcionamiento. Más específicamente, la atención se centra en las tecnologías de Spatial Modulation y Analog Network Coding. Ambos esquemas ofrecen la llamada ganancia de multiplexación, lo que significa que múltiples flujos pueden ser transmitidos sin sacrificar recursos, tales como el ancho de banda. En lo que se refiere a Spatial Modulation, se proponen esquemas basados en Spatial Modulation que son más energéticamente que tecnologías ya existentes. En cuanto a Analog Network Coding, se estudia su aplicación en escenarios inalámbricos basados en relays y cómo se compara en términos de eficiencia energética con los protocolos convencionales, tales como el protocolo de acceso mútiple por división de tiempo. De los resultados obtenidos, la conclusión que se puede extraer es que dependiendo del escenario, ambos Spatial Modulation y Analog Network Coding pueden proporcionar beneficios significativos de energía en comparación con las tecnologías existentes sin sacrificar el funcionamiento