Adaptive generalized space shift keying

In this article, we propose a closed-loop precoding method for the Generalized Space Shift Keying (GSSK) modulation scheme, suitable for Multiple-Input-Single-Output (MISO) systems and denoted as adaptive GSSK (AGSSK), which achieves transmit-diversity gains in contrast to GSSK. For the case of a perfect feedback channel, we analytically show that for three and four antennas at the transmitter and rates 1 and 2 bits per channel use (bpcu), respectively, a full transmit-diversity can be achieved without reducing the achievable rate. For higher number of transmit antennas and rates, the performance of the proposed scheme degrades due to the smaller average minimum Euclidean distance as the rate increases. Due to this, we, furthermore, propose an enhancing method for AGSSK which relies on the use of time-orthogonal shaping filters for the different constellation points. For the enhanced method, named as AGSSK with time-orthogonal signal design (AGSSK-TOSD), we analytically prove that it offers transmit-diversity gains which are greater than the number of active transmit antennas for any number of transmit antennas and supported rate. This is attained without any antenna subset selection technique, which alleviates the processing burden on the terminal side. Monte Carlo simulations show that AGSSK significantly outperforms GSSK in terms of average bit error probability (ABEP) and, moreover, for medium to high rates and practical signal-to-noise ratio (SNR) regions AGSSK-TOSD outperforms well-known feedback-based multiple-antenna schemes. This advantage of AGSSK-TOSD is further substantiated with an energy effficiency comparison over the conventional schemes for a target (uncoded) ABEP.Peer ReviewedPostprint (published version

Interference driven antenna selection for Massive Multi-User MIMO

Low-complexity linear precoders are known to be close-to-optimal for massive multi-input multi-output (M-MIMO) systems. However, the large number of antennas at the transmitter imposes high computational burdens and high hardware overloads. In line with the above, in this paper we propose a low complexity antenna selection (AS) scheme which selects the antennas that maximize constructive interference between the users. Our analyses show that the proposed AS algorithm, in combination with a simple matched filter (MF) precoder at the transmitter, is able to achieve better performances than systems equipped with a more complex channel inversion (CI) precoder and computationally expensive AS techniques. First, we give an analytical definition of constructive and destructive interference, based on the phase of the received signals from phase-shifted-keying (PSK) modulated transmissions. Then, we introduce the proposed antenna selection algorithm, which identifies the antenna subset with the highest constructive interference, maximizing the power received by the user. In our studies, we derive the computational burden of the proposed technique with a rigorous and thorough analysis and we identify a closed form expression of the upper bound received power at the user side. In addition, we evaluate in detail the power benefits of the proposed transmission scheme by defining an efficiency metric based on the achieved throughput. The results presented in this paper prove that antenna selection and green radio concepts can be jointly used for power efficient M-MIMO, as they lead to significant power savings and complexity reductions

Spatial Modulation for Multiple-Antenna Wireless Systems : A Survey

International audienceMultiple-antenna techniques constitute a key technology for modern wireless communications, which trade-off superior error performance and higher data rates for increased system complexity and cost. Among the many transmission principles that exploit multiple-antenna at either the transmitter, the receiver, or both, Spatial Modulation (SM) is a novel and recently proposed multiple- uniqueness and randomness properties of the wireless channel for communication. This is achieved by adopting a simple but effective coding mechanism that establishes a one-to-one mapping between blocks of information bits to be transmitted and the spatial positions of the transmit-antenna in the antenna-array. In this article, we summarize the latest research achievements and outline some relevant open research issues of this recently proposed transmission technique

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

An Overview of Physical Layer Security with Finite-Alphabet Signaling

Providing secure communications over the physical layer with the objective of achieving perfect secrecy without requiring a secret key has been receiving growing attention within the past decade. The vast majority of the existing studies in the area of physical layer security focus exclusively on the scenarios where the channel inputs are Gaussian distributed. However, in practice, the signals employed for transmission are drawn from discrete signal constellations such as phase shift keying and quadrature amplitude modulation. Hence, understanding the impact of the finite-alphabet input constraints and designing secure transmission schemes under this assumption is a mandatory step towards a practical implementation of physical layer security. With this motivation, this article reviews recent developments on physical layer security with finite-alphabet inputs. We explore transmit signal design algorithms for single-antenna as well as multi-antenna wiretap channels under different assumptions on the channel state information at the transmitter. Moreover, we present a review of the recent results on secure transmission with discrete signaling for various scenarios including multi-carrier transmission systems, broadcast channels with confidential messages, cognitive multiple access and relay networks. Throughout the article, we stress the important behavioral differences of discrete versus Gaussian inputs in the context of the physical layer security. We also present an overview of practical code construction over Gaussian and fading wiretap channels, and we discuss some open problems and directions for future research.Comment: Submitted to IEEE Communications Surveys & Tutorials (1st Revision

Multidimensional Index Modulation for 5G and Beyond Wireless Networks

This study examines the flexible utilization of existing IM techniques in a comprehensive manner to satisfy the challenging and diverse requirements of 5G and beyond services. After spatial modulation (SM), which transmits information bits through antenna indices, application of IM to orthogonal frequency division multiplexing (OFDM) subcarriers has opened the door for the extension of IM into different dimensions, such as radio frequency (RF) mirrors, time slots, codes, and dispersion matrices. Recent studies have introduced the concept of multidimensional IM by various combinations of one-dimensional IM techniques to provide higher spectral efficiency (SE) and better bit error rate (BER) performance at the expense of higher transmitter (Tx) and receiver (Rx) complexity. Despite the ongoing research on the design of new IM techniques and their implementation challenges, proper use of the available IM techniques to address different requirements of 5G and beyond networks is an open research area in the literature. For this reason, we first provide the dimensional-based categorization of available IM domains and review the existing IM types regarding this categorization. Then, we develop a framework that investigates the efficient utilization of these techniques and establishes a link between the IM schemes and 5G services, namely enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communication (URLLC). Additionally, this work defines key performance indicators (KPIs) to quantify the advantages and disadvantages of IM techniques in time, frequency, space, and code dimensions. Finally, future recommendations are given regarding the design of flexible IM-based communication systems for 5G and beyond wireless networks.Comment: This work has been submitted to Proceedings of the IEEE for possible publicatio

Energy-Efficient System Design for Future Wireless Communications

The exponential growth of wireless data traffic has caused a significant increase in the power consumption of wireless communications systems due to the higher complexity of the transceiver structures required to establish the communication links. For this reason, in this Thesis we propose and characterize technologies for improving the energy efficiency of multiple-antenna wireless communications. This Thesis firstly focuses on energy-efficient transmission schemes and commences by introducing a scheme for alleviating the power loss experienced by the Tomlinson-Harashima precoder, by aligning the interference of a number of users with the symbols to transmit. Subsequently, a strategy for improving the performance of space shift keying transmission via symbol pre-scaling is presented. This scheme re-formulates complex optimization problems via semidefinite relaxation to yield problem formulations that can be efficiently solved. In a similar line, this Thesis designs a signal detection scheme based on compressive sensing to improve the energy efficiency of spatial modulation systems in multiple access channels. The proposed technique relies on exploiting the particular structure and sparsity that spatial modulation systems inherently possess to enhance performance. This Thesis also presents research carried out with the aim of reducing the hardware complexity and associated power consumption of large scale multiple-antenna base stations. In this context, the employment of incomplete channel state information is proposed to achieve the above-mentioned objective in correlated communication channels. The candidate’s work developed in Bell Labs is also presented, where the feasibility of simplified hardware architectures for massive antenna systems is assessed with real channel measurements. Moreover, a strategy for reducing the hardware complexity of antenna selection schemes by simplifying the design of the switching procedure is also analyzed. Overall, extensive theoretical and simulation results support the improved energy efficiency and complexity of the proposed schemes, towards green wireless communications systems