Constructive interference as an information carrier by dual-layered MIMO transmission

We propose a bandwidth efficient (BE) transmission scheme for multiple-input-multiple-output (MIMO) point-to-point (P2P) and downlink (DL) channels. The BE of spatial multiplexing (SMX) is improved by implicitly encoding information in the spatial domain based on the existence of constructive interference in the received symbols, that creates a differentiation in the symbol power. Explicitly, the combination of symbols received at a higher power level carries implicit information in the spatial domain in the same manner as the combination of non-zero elements in the receive symbol vector carries information for receive-antenna based spatial modulation (RSM). The non-zero power throughout the received symbol vector for the proposed technique, allows a full SMX underlying transmission, with the BE enhancement brought by the spatial symbol. Our simulation results demonstrate both significant BE gains and error probability reduction for our approach over the conventional SMX and RSM schemes

Constructive interference as an information carrier by dual-layered MIMO transmission

We propose a bandwidth-efficient transmission scheme for multiple-input-multiple-output point-to-point and downlink channels. The bandwidth efficiency (BE) of spatial multiplexing (SMX) is improved by implicitly encoding information in the spatial domain based on the existence of constructive interference in the received symbols, which creates a differentiation in the symbol power. Explicitly, the combination of symbols received at a higher power level carries implicit information in the spatial domain in the same manner as that the combination of nonzero elements in the received symbol vector carries information for receive-antenna-based spatial modulation (RSM). The nonzero power throughout the received symbol vector for the proposed technique allows a full SMX underlying transmission, with the BE enhancement brought by the spatial symbol. Our simulation results demonstrate both significant BE gains and error probability reduction for our approach over the conventional SMX and RSM schemes

Applications of Lattice Codes in Communication Systems

In the last decade, there has been an explosive growth in different applications of wireless technology, due to users' increasing expectations for multi-media services. With the current trend, the present systems will not be able to handle the required data traffic. Lattice codes have attracted considerable attention in recent years, because they provide high data rate constellations. In this thesis, the applications of implementing lattice codes in different communication systems are investigated. The thesis is divided into two major parts. Focus of the first part is on constellation shaping and the problem of lattice labeling. The second part is devoted to the lattice decoding problem. In constellation shaping technique, conventional constellations are replaced by lattice codes that satisfy some geometrical properties. However, a simple algorithm, called lattice labeling, is required to map the input data to the lattice code points. In the first part of this thesis, the application of lattice codes for constellation shaping in Orthogonal Frequency Division Multiplexing (OFDM) and Multi-Input Multi-Output (MIMO) broadcast systems are considered. In an OFDM system a lattice code with low Peak to Average Power Ratio (PAPR) is desired. Here, a new lattice code with considerable PAPR reduction for OFDM systems is proposed. Due to the recursive structure of this lattice code, a simple lattice labeling method based on Smith normal decomposition of an integer matrix is obtained. A selective mapping method in conjunction with the proposed lattice code is also presented to further reduce the PAPR. MIMO broadcast systems are also considered in the thesis. In a multiple antenna broadcast system, the lattice labeling algorithm should be such that different users can decode their data independently. Moreover, the implemented lattice code should result in a low average transmit energy. Here, a selective mapping technique provides such a lattice code. Lattice decoding is the focus of the second part of the thesis, which concerns the operation of finding the closest point of the lattice code to any point in N-dimensional real space. In digital communication applications, this problem is known as the integer least-square problem, which can be seen in many areas, e.g. the detection of symbols transmitted over the multiple antenna wireless channel, the multiuser detection problem in Code Division Multiple Access (CDMA) systems, and the simultaneous detection of multiple users in a Digital Subscriber Line (DSL) system affected by crosstalk. Here, an efficient lattice decoding algorithm based on using Semi-Definite Programming (SDP) is introduced. The proposed algorithm is capable of handling any form of lattice constellation for an arbitrary labeling of points. In the proposed methods, the distance minimization problem is expressed in terms of a binary quadratic minimization problem, which is solved by introducing several matrix and vector lifting SDP relaxation models. The new SDP models provide a wealth of trade-off between the complexity and the performance of the decoding problem

A Tutorial on Interference Exploitation via Symbol-Level Precoding: Overview, State-of-the-Art and Future Directions

IEEE Interference is traditionally viewed as a performance limiting factor in wireless communication systems, which is to be minimized or mitigated. Nevertheless, a recent line of work has shown that by manipulating the interfering signals such that they add up constructively at the receiver side, known interference can be made beneficial and further improve the system performance in a variety of wireless scenarios, achieved by symbol-level precoding (SLP). This paper aims to provide a tutorial on interference exploitation techniques from the perspective of precoding design in a multi-antenna wireless communication system, by beginning with the classification of constructive interference (CI) and destructive interference (DI). The definition for CI is presented and the corresponding mathematical characterization is formulated for popular modulation types, based on which optimization-based precoding techniques are discussed. In addition, the extension of CI precoding to other application scenarios as well as for hardware efficiency is also described. Proof-of-concept testbeds are demonstrated for the potential practical implementation of CI precoding, and finally a list of open problems and practical challenges are presented to inspire and motivate further research directions in this area

The First 15 Years of SEFDM: A Brief Survey

Spectrally efficient frequency division multiplexing (SEFDM) is a multi-carrier signal waveform, which achieves higher spectral efficiency, relative to conventional orthogonal frequency division multiplexing (OFDM), by violating the orthogonality of its sub-carriers. This survey provides the history of SEFDM development since its inception in 2003, covering fundamentals and concepts, wireless and optical communications applications, circuit design and experimental testbeds. We focus on work done at UCL and outline work done other universities and research laboratories worldwide. We outline techniques to improve the performance of SEFDM and its practical utility with focus on signal generation, detection and channel estimation