Transmit Antenna Selection

MIMO wireless downlinks using transmit zero-forcing beamforming (TZFBF) with M T transmit antennas can serve up to K = M T users, each equipped with one antenna. To maximize the channel sum rate, it has been shown that user selection, which is akin to receive antenna selection (RAS) in this case, is required along with waterfilling to find the optimal subset of active receivers S a , where |S a | = 1,…,M T . To implement TZFBF, channel state information is required at the transmitter (CSIT). When CSIT is available, it is known that additional constraints imposed on the transmitter will reduce the system sum rate. Despite this, transmit antenna selection (TAS) provides a means of increasing the sum rate in some cases when sub-optimal RAS algorithms are used. The mechanism works by assisting the RAS search path to get out of a local maximum. The proposed method requires further RAS to follow any prior TAS process and the restoration of any transmit antennas that were removed. An analysis is provided to give insight to the proposed method. The analysis and scheme are applicable to any sub-optimal RAS algorithm and guidelines on decoupled search strategies are given. The analysis also affirms the statement that given CSIT, TAS does not help improve the sum rate of TZFBF, regardless of the channel condition and signal-to-noise ratio when optimal RAS is already done. This means that joint exhaustive RAS-TAS searches are not needed to achieve the optimal sum rate and instead, only exhaustive RAS or user selection search is needed.

Recent advancements in self-interference (SI) cancellation capability of low-power wireless devices motivate inband full-duplex (FD) wireless backhauling in small cell networks (SCNs). In-band FD wireless backhauling allows the use of same frequency spectrum for the backhaul as well as access links of the small cells concurrently. In this paper, using tools from stochastic geometry, we develop a framework to model the downlink rate coverage probability of a user in a given SCN with massive MIMO-enabled wireless backhauls. The considered SCN is composed of a mixture of small cells that are configured in either in-band or out-of-band backhaul modes with a certain probability. The performance of the user in the considered hierarchical network is limited by several sources of interference such as the backhaul interference, small cell base station (SBS)-to-SBS interference and the SI. Moreover, due to the channel hardening effect in massive MIMO, the backhaul links experience long term channel effects only, whereas the access links experience both the long term and short term channel effects. Consequently, the developed framework is flexible to characterize different sources of interference while capturing the heterogeneity of the access and backhaul channels. In specific scenarios, the framework enables deriving closed-form coverage probability expressions. Under perfect backhaul coverage, the simplified expressions are utilized to optimize the proportion of in-band and out-of-band small cells in the SCN in closed-form. Finally, few remedial solutions are proposed that can potentially mitigate the backhaul interference and in turn improve the performance of in-band FD wireless backhauling. Numerical results investigate the scenarios in which in-band wireless backhauling is useful and demonstrate that maintaining a correct proportion of in-band and out-of-band FD small cells is crucial in wireless backhauled SCNs.

Em primeiro lugar, agradeço ao Prof. Dr. Vyacheslav Futorny, pela dedicação e paciência na orientação da tese, e pelos ensinamentos ao longo desses anos de trabalho juntos. Minha gratidão também ao Prof. Dr. Luis Enrique Ramirez, pelas significativas considerações para o encaminhamento da pesquisa e pela presença constante nas dificuldades. Agradeço à Capes pela bolsa de estudos concedida para a realização da pesquisa. Aos amigos do IME-USP, que de várias maneiras me apoiaram na realização do trabalho, deixo registrado meu agradecimento. Pela generosa ajuda nos momentos de dúvida e dificuldades durante a elaboração desse trabalho, um agradecimento especial aos amigos André Silva de Oliveira, Marcela Guerrini Alves e Felipe Rocha Félix. Um agradecimento especial dedico a minha família que, mesmo distante, sempre buscou me ajudar da melhor maneira possível para que tudo desse certo comigo neste país. Ao Henrique e à Zósia, pelos momentos agradáveis na companhia de boa comida, meu muito obrigado. Agradeço também ao Orlando, pelos churrascos nas festas de Natal, e à Izabel, pela comida farta. Agradeço à Flávia pelo convívio nos momentos de alegria e pela compreensão e carinho nos momentos difíceis. Ainda, agradeço a ela por ter me "abrasileirado". iii iv HERNÁNDEZ MORALES, O. A. Representações de Gelfand-Tsetlin de álgebras de Vertex. 2021. 159 f. Tese (Doutorado) -

In this paper, we propose a rateless codes-based communication protocol to provide security for wireless systems. In the proposed protocol, a source uses the transmit antenna selection (TAS) technique to transmit Fountain-encoded packets to a destination in presence of an eavesdropper. Moreover, a cooperative jammer node harvests energy from radio frequency (RF) signals of the source and the interference sources to generate jamming noises on the eavesdropper. The data transmission terminates as soon as the destination can receive a sufficient number of the encoded packets for decoding the original data of the source. To obtain secure communication, the destination must receive sufficient encoded packets before the eavesdropper. The combination of the TAS and harvest-to-jam techniques obtains the security and efficient energy via reducing the number of the data transmission, increasing the quality of the data channel, decreasing the quality of the eavesdropping channel, and supportin...

The use of multiple-input multiple-output (MIMO) configurations in wireless systems is becoming increasingly popular, due to the potential capacity enhancing properties. The use of such configurations, requires deployment of multiple RF chains and results in an increase in cost and complexity. This paper focuses on transmitter design, where cost is often dominated by the need to utilise linearized power amplifiers. Thus, the effect of reducing the number of active transmit antennae through selection can yield a significant cost advantage. Three criteria for transmit antenna selection are evaluated and characterised through the use of real channel data in the UHF band. The criteria are based only on the channel gains and have relatively low complexity; thus are suitable for practical purposes. This study examines the performance of the tested selection algorithms under a variety of operating conditions. The paper also considers the issue of delayed switch time due to reverse-link communication latency.

The use of multiple-input multiple-output (MIMO) configurations in wireless systems is becoming increasingly popular, due to the potential capacity enhancing properties. The use of such configurations, requires deployment of multiple RF chains and results in an increase in cost and complexity. This paper focuses on transmitter design, where cost is often dominated by the need to utilise linearized power amplifiers. Thus, the effect of reducing the number of active transmit antennae through selection can yield a significant cost advantage. Three criteria for transmit antenna selection are evaluated and characterised through the use of real channel data in the UHF band. The criteria are based only on the channel gains and have relatively low complexity; thus are suitable for practical purposes. This study examines the performance of the tested selection algorithms under a variety of operating conditions. The paper also considers the issue of delayed switch time due to reverse-link communication latency.

This paper considers the error performance of an uncoded multiple-input-multiple-output (MIMO) wireless system with antenna selection at the transmitter and maximal ratio combining (MRC) at the receiver end. Exact closed-form expressions are derived for symbol error probability of the aforementioned scheme in independent and identically distributed (i.i.d) Nakagami-m fading channels.

Walingo and co-supervisor, Prof. Fambirai Takawira. Your fatherly role, tireless personal commitments and continuous impetus made this work possible. I am most grateful. My parents and siblings quickly come to mind as I put together this acknowledgement. You guys are the best in the whole wide world! Though very far away, yet you kept so near. We went through the hurdles and the challenges together. I am forever indebted to you all. Special appreciation goes to the following sweethearts: Dr Oluwafemi Ilesanmi and family (who God used not only to make my coming to SA a possibility but who also stood as great mentors and builders of destiny!); Dr Oyerinde Olutayo and family (who were not just spiritual guides but also encouraged, motivated and challenged me towards great achievements); My colleagues (Olugbenga Imole, Sithembiso Gama, Abdulrahman Mogbonjubola and Maria Sefuba) who helped me in all capacities than I could ever imagine. We kept moving on through the hard and difficult times, yes, together! Thanks a bunch guys; Fellow brethren in the Deeper Life Campus Fellowship house (lovely brothers and sisters who are making my stay in SA enjoyable). Thank you all for showing me much love. To the staff and students (both post grads and under grads) of the School of Electrical, Electronic and Computer Engineering, UKZN Howard College who through their constant love and many sacrifices keep challenging me to keep going forward. I appreciate you all! And the utmost gratitude goes to the Almighty God who indeed makes all things beautiful in His time. Thank you Lord.

Abstract- Mobile ad hoc networks (MANETs) are more vulnerable to security attacks compared to the wired networks mainly because they are wireless and dynamic in topology. So security has become a primary requirement for successful operation. Achievement of key goals like confidentiality, access control, authentication, availability, integrity, and non-repudiation is very crucial. Cryptographic techniques using cryptographic keys are widely used for secure communications. It becomes very crucial to provide secured and efficient key management scheme as well as all the messages should also be secured. A number of key management schemes are proposed in MANET. The computational load and complexity for key management are strongly subject to restriction by the node’s available resources and the dynamic nature of network topology. We hereby present a comprehensive study of various key management techniques available for MANET.

A two-input multiple-output (TIMO) system represents an important special case of multiple-input multipleoutput (MIMO) systems and occurs in practical scenarios where there are limitations on cost and/or space to install more antennas, in MIMO with transmit antenna selection which selects two out of multiple transmit antennas and turns MIMO into TIMO, or in cooperative communications with two singleantenna mobiles sharing their antennas. In this paper, minimum bit error rate (MBER) transmit optimization for TIMO spatial multiplexing systems is investigated. Approximate MBER transmit power allocation for a variety of receiver structures is proposed. Transmit beamforming schemes using 4-ary Pulse-Amplitude-Modulation (4-PAM) and Quaternary Phase-Shift-Keying (QPSK) pre-mixing are also proposed, which eliminate error floors in ill-conditioned TIMO channels. It is shown both analytically and by numerical simulations that the proposed schemes offer superior performance over existing schemes. Essentially, the proposed transmit optimization provides a simple and efficient means to utilize partial channel state information at the transmitter.

Cooperative communication describes strategies to transfer the data from a source to a destination by employing relay nodes between them. It is considered as one of the most efficient techniques to overcome fading in wireless networks since it can achieve spatial diversity. Employing all the relays in the network to transfer the data, consumes high power and cost. Selection of one or more relays reduces the complexity, decreases the power consumption and reduces the interference. In this paper, with these goals in mind, a relay selection algorithm is proposed in a slow flat fading channel. The algorithm is based on evaluating the log-likelihood ratio of all relays and the relay which has the largest magnitude of log-likelihood ratio (LLR) is selected to help the source to transmit the data to the destination. The performance of the algorithm is evaluated by simulation and compared with other relay selection algorithms. The performance is measured in terms of bit error rate (BER) and outage probability. Both decode and forward and amplify and forward protocols are investigated. The performance is evaluated for known and estimated channel. The channel is estimated using least square algorithm. The performance of channel estimation algorithm is measured in terms of the mean square error. The results show that the LLR algorithm minimizes bit error probability (BEP) and BEP provided by LLR-based selection combining algorithm is lower than BEP provided by the conventional SNR-based selection combining schemes.

With the use of power domain non-orthogonal multiple access (NOMA) and backscatter communication (BAC), future sixth-generation ultra massive machine-type communications networks are expected to connect large-scale internet of things (IoT) devices. However, due to NOMA co-channel interference, the power allocation to large-scale IoT devices becomes critical. The existing convex optimization-based solutions are highly complex, and therefore it is difficult to find the optimal solution to the resource allocation problem in a highly dynamic environment. To alleviate this problem, this work develops an efficient model-free BAC approach with a NOMA system to assist the base station with complex resource scheduling tasks in a dynamic BAC-NOMA IoT network. The objective is to increase the sum rate of uplink backscatter devices. More specifically, we jointly optimize the transmit power of downlink IoT users and the reflection coefficient of uplink backscatter devices using a reinforcement learning algorithm, namely, the soft-actor critic (SAC) algorithm. With the advantage of entropy regularization, the SAC agent learns to explore and exploit the dynamic BAC-NOMA network efficiently. The proposed algorithm ensures the quality of service (QoS) requirements of downlink users while enhancing the sum rate of uplink backscatter devices. Numerical results reveal the superiority of the proposed algorithm over the conventional optimization (benchmark) approach in terms of the average sum rate of uplink backscatter devices. We show that the network with multiple downlink users obtained a higher reward with respect to a large number of iterations compared to episodes with a lower number of iterations. Moreover, the proposed algorithm outperforms the benchmark scheme and BAC with orthogonal multiple access in terms of the average sum rate with the different number of backscatter devices. Additionally, we show that our proposed algorithm enhances sum rate efficiency with respect to different self-interference coefficients and different noise levels. Finally, we evaluate and show the sum rate efficiency of the proposed algorithm with different QoS requirements and cell radii.

With the use of power domain non-orthogonal multiple access (NOMA) and backscatter communication (BAC), future sixth-generation ultra massive machine-type communications networks are expected to connect large-scale internet of things (IoT) devices. However, due to NOMA co-channel interference, the power allocation to large-scale IoT devices becomes critical. The existing convex optimization-based solutions are highly complex, and therefore it is difficult to find the optimal solution to the resource allocation problem in a highly dynamic environment. To alleviate this problem, this work develops an efficient model-free BAC approach with a NOMA system to assist the base station with complex resource scheduling tasks in a dynamic BAC-NOMA IoT network. The objective is to increase the sum rate of uplink backscatter devices. More specifically, we jointly optimize the transmit power of downlink IoT users and the reflection coefficient of uplink backscatter devices using a reinforcement learning algorithm, namely, the soft-actor critic (SAC) algorithm. With the advantage of entropy regularization, the SAC agent learns to explore and exploit the dynamic BAC-NOMA network efficiently. The proposed algorithm ensures the quality of service (QoS) requirements of downlink users while enhancing the sum rate of uplink backscatter devices. Numerical results reveal the superiority of the proposed algorithm over the conventional optimization (benchmark) approach in terms of the average sum rate of uplink backscatter devices. We show that the network with multiple downlink users obtained a higher reward with respect to a large number of iterations compared to episodes with a lower number of iterations. Moreover, the proposed algorithm outperforms the benchmark scheme and BAC with orthogonal multiple access in terms of the average sum rate with the different number of backscatter devices. Additionally, we show that our proposed algorithm enhances sum rate efficiency with respect to different self-interference coefficients and different noise levels. Finally, we evaluate and show the sum rate efficiency of the proposed algorithm with different QoS requirements and cell radii.

In this paper, a new lifetime model called Kumaraswamy exponentiated U-quadratic (KwEUq) distribution is proposed. Several mathematical and statistical properties are derived and studied such as the explicit form of the quantile function, moments, moment generating function, order statistics, probability weighted moments, Shannon entropy and Renyi entropy. We also found that the usual maximum likelihood estimates (MLEs) fail to hold for the KwEUq distribution. Two alternative methods are suggested for the parameter estimation of the KwEUq, the alternative maximum likelihood estimation (AMLE) and modified maximum likelihood estimation (MMLE). Simulation studies were conducted to assess the finite sample behavior of the AMLEs and MMLEs. Finally, we provide application of the KwEUq for illustration purposes.

List of Tables xii List of Figures xiii Chapter 1. Introduction 157 Vita 175 xi xv 4.4 Effective harvested power vs. energy splitting parameter ξ for M = 500. A user can maximize the effective harvested power by allocating the right amount of harvested energy for uplink pilot transmission.

Em primeiro lugar, agradeço ao Prof. Dr. Vyacheslav Futorny, pela dedicação e paciência na orientação da tese, e pelos ensinamentos ao longo desses anos de trabalho juntos. Minha gratidão também ao Prof. Dr. Luis Enrique Ramirez, pelas significativas considerações para o encaminhamento da pesquisa e pela presença constante nas dificuldades. Agradeço à Capes pela bolsa de estudos concedida para a realização da pesquisa. Aos amigos do IME-USP, que de várias maneiras me apoiaram na realização do trabalho, deixo registrado meu agradecimento. Pela generosa ajuda nos momentos de dúvida e dificuldades durante a elaboração desse trabalho, um agradecimento especial aos amigos André Silva de Oliveira, Marcela Guerrini Alves e Felipe Rocha Félix. Um agradecimento especial dedico a minha família que, mesmo distante, sempre buscou me ajudar da melhor maneira possível para que tudo desse certo comigo neste país. Ao Henrique e à Zósia, pelos momentos agradáveis na companhia de boa comida, meu muito obrigado. Agradeço também ao Orlando, pelos churrascos nas festas de Natal, e à Izabel, pela comida farta. Agradeço à Flávia pelo convívio nos momentos de alegria e pela compreensão e carinho nos momentos difíceis. Ainda, agradeço a ela por ter me "abrasileirado". iii iv Resumo HERNÁNDEZ MORALES, O. A. Representações de Gelfand-Tsetlin de álgebras de Vertex. 2021. 159 f. Tese

Now-a-days, intense research is going on two-hop wireless link under different fading conditions with its remedial measures. In this paper work, a two-hop link under three different conditions is considered: (i) MIMO on both hops, (ii) MISO in first hop and SIMO in second hop and finally (iii) SIMO in first hop and MISO in second hop. The three models used here give the flexibility of using STBC (Space Time Block Coding) and combining scheme on any of the source to relay (S-R) and relay to destination (R-D) link. Even incorporation of Transmitting Antenna Selection (TAS) is possible on any link. Here, the variation of SER (Symbol Error Rate) is determined against mean SNR (Signal-to-Noise Ratio) of R-D link for three different modulation schemes: BPSK, 8-PSK and 16-PSK, taking the number of antennas and SNR of S-R link as parameters under Nakagami-m fading condition.

In this paper, we research the performance of a bi-directional three-node cooperative relaying network that aids simultaneous wireless information and power transfer (SWIPT) in a direct connection region that is inuenced by the Nakagami-m fading environment. The information transfer between source nodes can be completed in three equal time phases if we consider two source nodes with direct links and a battery-enabled node.[1] . The maximum-ratio combining (MRC) approach was used at the destination node to use both the direct and relay links. In the rst two stages, the harvested energy at the relay node was used for power splitting (PS), and in the third phase, the harvested energy was used for information processing (IP) and broadcasting. We extract simple and detailed generalized average bit error rate (ABER) expressions for BFSK, BPSK, QPSK, and 4-PAM for the Consider scheme. The derived expressions are applicable to any coherent modulation scheme.