Multicarrier Transmission Research Articles

An Enhanced Peak to Average Power Ratio Reduction Scheme for Interleaved and Sub-Band Orthogonal Frequency-Division Multiple Access Frameworks with Low Complexity

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique which has the major drawback namely Peak to Average Power Ratio (PAPR). The high PAPR influences the efficiency of the power amplifier. The Selected Level Mapping (SLM) gives reduced PAPR contrasted with different strategies but the complexity is high due to the necessity of various Inverse Fast Fourier Transform (IFFTs). With the end goal to reduce the complexity, the proposed design requires only one IFFT, the candidate signals are produced by cyclic shifting the original time domain signal then multiplying with the distinctive genuine positive numbers. At that point the candidate with most minimal PAPR is chosen for transmission.

An Overview of Physical Layer Security With Finite-Alphabet Signaling

Providing secure communications over the physical layer with the objective of achieving 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 toward a practical implementation of physical layer security. With this motivation, this paper 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 discuss some open problems and directions for future research.

Precoded GFDM system for self-interference mitigation

Generalised frequency division multiplexing (GFDM) is a multicarrier transmission scheme that offers a flexible framework to address diverse requirements of fifth generation of cellular networks. Compared to orthogonal frequency division multiplexing (OFDM), the application of pulse shaping in GFDM can control the out of band (OOB) radiation and enables relaxed synchronisation requirements. However, the sub-carriers in GFDM are no longer orthogonal and there is inherent interference. Since this interference is known at the transmitter, it can be mitigated by means of precoding techniques. In this paper, Tomlinson-Harashima precoding (THP) scheme is applied to GFDM transceiver and its performances is compared to previous methods in terms of bit error rate (BER) and peak to average power ratio (PAPR). The results show that the proposed precoder outperforms previous methods in both BER and PAPR.

GFDM Based Wireless Powered Communication for Cooperative Relay System

Green and sustainable communications are crucial for cellular devices and the Internet of Things (IoT) devices in the fifth generation (5G) mobile communication system. Wireless-powered communication (WPC) provides a successful technical paradigm to support wireless information transmission for mobile devices by using harvested radio-frequency (RF) energy. In the meantime, non-orthogonal multicarrier transmission techniques, typically represented by the generalized frequency-division multiplexing (GFDM), can not only enhance spectrum efficiency but also improve the flexibility of resource allocation due to its fine-granularity sub-block. In this paper, a GFDM-based cooperative relay system model is proposed to improve the quality of experience of the cell-edge user. Specifically, the system is composed of one source node, one destination node (cell-edge user), and one relay node. The source node transmits a signal to the destination node and the relay node. The relay node performs information transmission and power transfer to the destination node by using different GFDM sub-block sets. The destination node combines the signals from the source node and relay node. In order to maximize the information rate at the destination node subject to the minimum harvested energy, a joint sub-block, sub-block power, and subslot allocation-based WPC scheme is proposed. To solve the non-convex optimization problem, an iterative algorithm is proposed and its effectiveness is validated by simulations. The simulation results demonstrate that the GFDM-based WPC scheme outperforms the orthogonal frequency-division multiplexing (OFDM), and the subslot optimization can significantly increase the information rate at the destination node.

Precoded GFDM system for self-interference mitigation

Generalised frequency division multiplexing (GFDM) is a multicarrier transmission scheme that offers a flexible framework to address diverse requirements of fifth generation of cellular networks. Compared to orthogonal frequency division multiplexing (OFDM), the application of pulse shaping in GFDM can control the out of band (OOB) radiation and enables relaxed synchronisation requirements. However, the sub-carriers in GFDM are no longer orthogonal and there is inherent interference. Since this interference is known at the transmitter, it can be mitigated by means of precoding techniques. In this paper, Tomlinson-Harashima precoding (THP) scheme is applied to GFDM transceiver and its performances is compared to previous methods in terms of bit error rate (BER) and peak to average power ratio (PAPR). The results show that the proposed precoder outperforms previous methods in both BER and PAPR.

Joint channel estimation and turbo equalisation for MIMO-OFDM-IM systems

ABSTRACTMultiple-Input Multiple-Output (MIMO) communications are frequently employed to improve the transmitted data rate and the link quality. Index modulated orthogonal frequency division multiplexing (OFDM-IM) improves the error rate performance and the peak-to-average power ratio (PAPR) compared with those of the conventional OFDM system due to the activation of partial subcarriers. The MIMO OFDM-IM can transmit additional information bits via the indices of active subcarriers. Also, in order to reduce the transmission power of the OFDM system, the MIMO OFDM-IM scheme can be employed to approach the demanded data transmission rate and the error rate performance. Multiple-input multiple-output orthogonal frequency division multiplexing index modulation (MIMO-OFDM-IM) is an effective multicarrier transmission scheme and can be proposed as an alternative to conventional MIMO-OFDM system. In this scheme, OFDM-IM is combined with MIMO transmission to take the benefits of these two techniques. In this paper, we propose a joint channel estimation and turbo equalisation receiver for MIMO-OFDM-IM system. Some simulation examples are given to demonstrate the effectiveness of the proposed receiver.

SINR‐based adaptive MIMO FBMC/OQAM transmission with automatic modulation classification

The performance of filter bank multicarrier offset quadrature-amplitude modulation systems is known to be limited by intrinsic interference in highly frequency-selective radio propagation conditions. In this article, a novel adaptive multiple-input–multiple-output (MIMO) filter bank multicarrier transmission system in time-division duplex mode is analyzed in which filter bank-based interference power is considered in the bit loading (BL) and automatic modulation classification (AMC) algorithm. In order to reduce the amount of intrinsic interference, a filter design for a general multitap MIMO channel equalization is elaborated. For this linear MIMO receiver technique, an analytical expression of the signal-to-interference-and-noise power ratio after equalization is described. Since BL and AMC rely on the information about the subcarrier link quality, the influence of residual interference on its performance in a MIMO setup is quantified. For a wireless local area network similar propagation scenario, incorporating the information about the interference power in the BL and AMC method results in a significant system performance improvement at high signal-to-noise power ratios.

Maximizing physical layer security in relay‐assisted multicarrier nonorthogonal multiple access transmission

This letter investigates the physical layer security of dual‐hop nonorthogonal multiple access (NOMA) networks. We consider a multicarrier transmission scenario which consists of a single source, a relay, an eavesdropper, and multiple users. Our objective is to maximize the sum secure rate of the system with optimal power allocation over different sub‐carriers at the source. Because of the rate expression and binary variable, the optimization problem is formulated as a nonconvex and mixed integer programming problem. Thus, the optimal solution is obtained through duality theory which is considered to be an efficient method for solving nonconvex optimization problems. We compare the performance of the proposed NOMA scheme with orthogonal frequency multiple access (OFDMA) scheme. Our simulation results show that the proposed NOMA scheme has good performance in convergence and significantly outperforms the traditional OFDMA scheme.

A Review: Analysis of PAPR Reduction Techniques of OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is an efficient multicarrier modulation scheme in wireless communication. It is used in applications like 4G (fourth generation) mobile Communications, wireless networks, digital television, power line networks and audio Broadcasting. It offers both advantages and disadvantages for multicarrier transmission. The main advantages are the elimination of Inter Carrier Interference (ICI) and Inter Symbol Interference (ISI) in the signal. But OFDM’s one of the main detrimental aspects are high Peak-to-Average Power Ratio (PAPR) value of the transmitted signal which highly affects the power amplifiers complexity.

SS‐OFDM: an enhanced multicarrier transmission scheme based on variable granularity spectrum allocation for 5G

When oriented to the needs of the future fifth generation (5G) networks, orthogonal frequency division multiplexing (OFDM), as a modulation scheme, has some drawbacks: high out-of-band emission (OOBE) of power, relatively low spectrum efficiency, and poor flexibility for allocating resources. In this study, a subband superposed OFDM (OFDM) scheme, based on a variable granularity spectrum allocation, is proposed to divide the transmission channel into several subbands considering the compromises between single-carrier and multicarrier spectrum utilisation. For accommodating the diverse 5G scenarios, appropriate signalling parameters can be independently configured among the subbands. A multistage polyphase interpolator is developed in the transmitter to reduce the implementation cost of time-domain filter depressing the OOBE. Extremely narrow frequency guard intervals between subbands are realised by filtering to maximise the spectrum utilisation. At the receiver, a subband decision feedback and feedforward equaliser, relying on the subband's oversampling architecture, is designed to utilise the diversity gains in both the Doppler and the multipath delay domains. Simulation results indicate that the spectral efficiency, in terms of the spectrum utilisation rate, is increased up to 98.5 % and that the bit-error-rate performance is significantly improved for the subbands experiencing high-speed mobile channels while preserving a relatively low computational complexity.

CO-OFDM and DP-QPSK Based DWDM Optical Wireless Communication System

Abstract The 5 G technology provides a promising solution for future broadband networks. It requires access to high-speed wireless services for systems at anytime and anywhere. For adapting the 5 G services, this paper proposes an optical wireless system with hybrid scheme of dual polarized Gbps dense wavelength division multiplexed (DWDM) system. The multi-carrier transmission technique such as coherent optical orthogonal frequency division multiplexing (CO-OFDM) has also been incorporated into the system. The frequency spacing for the DWDM system is taken 25, 50 and 100 GHz according to the ITU-T standard. Here the subcarriers of each channel are modulated with the dual polarized-quadrature phase shift keying (DP-QPSK) sequence. The information is transmitted with an overall data rate of 0.32 Tbps. The system is successfully demonstrated at different turbulence regime from clear weather to severe turbulence weather under Gamma-Gamma atmospheric turbulence channel model. Due to the high optical signal-to-noise ratio (OSNR) tolerance and high spectrum efficiency of the dual polarized multi-channel and multicarrier transmission technique, the link distance achieved is 2.9 km in clear weather, 2.6 km in moderate turbulence regime, 2.3 km in high turbulence regime and 0.9 km in severe turbulence regime. A comparison study with related works has been carried out. Mathematical modeling is also incorporated for detail analysis of the proposed system.

Downlink Design for Spectrum Efficient IoT Network

The Internet of Things (IoT) is a new network that connects massive devices which have the communication ability. With the requirement of various services and the wireless spectrums becoming increasingly scarce, we consider a nonorthogonal multicarrier transmission scheme that is spectrum efficient frequency division multiplexing (SEFDM) as the downlink transmission scheme for IoT network. SEFDM has the merit of improved bandwidth usage efficiency, but the serious inter carrier interference (ICI) will be introduced by multiplexing overlapped carriers. Thus, the signal detection is challenged for recovering the signal which is suffered from ICI due to the loss of the orthogonality. In this paper, a low complexity detector based on quasi-orthogonality compensation (QOC) is proposed in the downlink receiver. And the complexity of the QOC detector is also analyzed. Moreover, a novel detector which joint QOC and fixed sphere decoding (FSD) algorithm is proposed. The bit error rate performances of QOC and QOC-FSD detectors are evaluated by numerical simulations. Numerical results show that the QOC and QOC-FSD detectors can achieve better performance than conventional iterative detection (ID) and ID-FSD, respectively. Furthermore, QOC-FSD detector performs a lower complexity than ID-FSD detector.

Equalization of Frequency Selective Channels Using Multirate Signal Processing

Multirate signal processing techniques for the equalization of frequency selective communications channels are proposed. It is shown that a multirate equalizer (MRE) is substantially less complex compared to the conventional channel equalizers. This feature makes single-carrier transmission feasible in channels having much longer delay-spreads or wider bandwidths than it was possible earlier. The proposed algorithms do not require transmission of a cyclic prefix. They have both linear and nonlinear versions, wherein the latter employs successive interference cancellation similar to the decision-feedback equalizer (DFE). It is possible to perform decoding prior to interference cancellation. Thus, successive interference canceling (SIC) MRE does not suffer from error propagation if operating on an achievable rate. The SIC-MRE can provably achieve the independent identically distributed information rate of the channel if a Gaussian input alphabet is used. For finite input alphabets, numerical results demonstrate that the single-carrier transmission with the SIC-MRE outperforms multicarrier transmission in terms of throughput. This result holds not only for low-order modulations and relatively narrow bandwidths but also for high-order modulations and wide bandwidths.

Suitable Spreading Sequences for Asynchronous MC-CDMA Systems

In order to meet the demand of high data rate transmission with good quality maintained, the multi-carrier code division multiple access (MC-CDMA) technology is considered for the next generation wireless communication systems. However, their high crest factor (CF) is one of the major drawbacks of multi-carrier transmission systems. Thus, CF reduction is one of the most important research areas in MC-CDMA systems. In addition, asynchronous MC-CDMA suffers from the effect of multiple access interference (MAI), caused by all users active in the system. Degradation of the system’s bit error rate (BER) caused by MAI must be taken into consideration as well. The aim of this paper is to provide a comparative study on the enhancement of performance of an MC-CDMA system. The spreading sequences used in CDMA play an important role in CF and interference reduction. Hence, spreading sequences should be selected to simultaneously ensure low CF and low BER values. Therefore, the effect that correlation properties of sequences exert on CF values is investigated in this study. Furthermore, a numerical BER evaluation, as a function of the signal-to-noise ratio (SNR) and the number of users, is provided. The results obtained indicate that a trade-off between the two criteria is necessary to ensure good performance. It was concluded that zero correlation zone (ZCZ) sequences are the most suitable spreading sequences as far as the satisfaction of the above criteria is concerned.

Desempeño de Controladores Inalámbricos Codificados Aplicados en Turbinas Eólicas Conectadas a una Smart Grid

<p>Actualmente, con el avance de las tecnologías de smart grid, la participación de las fuentes renovables en los sistemas energéticos está cambiando para atender las nuevas necesidades y aumentar la eficiencia de los sistemas. Con una visión del contexto de smart grid, este trabajo propone la revisión del moderno sistema de control inalámbrico propuesto basado en los generadores de inducción de jaula de ardilla conectados a la red eléctrica. El sistema de comunicación inalámbrico aplicado transmite las señales de potencia de referencia al controlador SCIG con la confiabilidad necesaria para asegurar la calidad de energía proporcionada por el generador eólico con codificación LDPC y OFDM. Los resultados de esta investigación respaldan la operatividad y las ventajas de la aplicación del sistema de control inalámbrico para plantas eólicas cuando son empleados requisitos y técnicas basados en la modulación digital y las técnicas de codificación.</p>

Performance Assessment of OFDM System using Reed-Solomon Codes over Fading Channels

This paper study the performance of Orthogonal Frequency Division Multiplexing (OFDM) system over AWGN and Rayleigh fading channels. OFDM performs multi-carrier transmission where all the subcarriers are orthogonal to each other. The channel coding was applied to improve the OFDM system performance. Reed Solomon (RS) codes was chosen that an efficient channel coding algorithm and has intense error correction ability. Adding the benefits of multicarrier OFDM system and Reed Solomon codes to achieve the expected system performance. The coded OFDM system was modeled over and simulated using Matlab. The bit error rate (BER) and energy bit (Eb) per noise power density (No) was performed during system simulations. QPSK modulation was used to modulate the random bits. From the simulation results It can be seen that BER vs. EB/No parameter for Coded OFDM system lower than uncoded OFDM. This was because RS codes succeed to correcting the error generated along data transmission.

Linearized Electro-Optical Modulation for Analog Radio over Fiber

ABSTRACTIntermodulation distortion (IMD) in Analog Radio-over-Fiber (a-RoF) poses a severe limitation to achievable error-free transmission. In this work, an optical feed-forward linearization scheme is presented and compared to an electrical pre-distortion solution. Both techniques show identical performance for intermodulation compensation of neighboring frequencies. The former suits wideband multi-carrier transmission better because it does not present limited operational bandwidth. Proof-of-concept experiments for reducing intermodulation and distortions are offered. A 5-dB improvement in the Error Vector Magnitude (EVM) distortion floor level is achieved. Trade-off between compensating for second and third harmonics was verified. Results indicate the solution allows maximal exploitation in a-RoF capacity.

Lower Order Modulation Aided BER Reduction in OFDM With Index Modulation

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a multi-carrier transmission scheme in which a set of sub-carriers is chosen and modulated according to the incoming bit-stream. It is already established that for the same average bits per channel use, OFDM-IM can provide a better error rate performance when compared to conventional OFDM. In this letter, we propose a novel method to further improve the error rate performance of OFDM-IM with the aid of lower order signal constellations, by using fewer bits for symbol selection and using the remaining bits to select the index combinations. As the increased number of indexing bits demand more index combinations for mapping them, certain index combinations are reused, with the reuse made unambiguous by rotating lower order constellation. This approach provides significant signal-to-noise ratio gains without compromising spectral efficiency when compared to existing OFDM-IM schemes.

Low-Complexity LLR Calculation for OFDM With Index Modulation

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a promising multicarrier transmission technique. In OFDM-IM, only a subset of subcarriers are activated to transmit modulated symbols and the indices of the activated subcarriers are used to convey information bits implicitly. In the coded OFDM-IM system, we need to calculate the log likelihood ratio (LLR) value of each bit, whose computational complexity is extremely high due to the dependence between the subcarriers caused by the subcarrier-index modulation. In this letter, we propose a novel simplified LLR calculation algorithm for OFDM-IM. Simulation results show that the proposed algorithm achieves near-optimal coded bit error rate performance with considerably low computational complexity.

Diversity Enhancing Multiple-Mode OFDM With Index Modulation

As an emerging multi-carrier transmission scheme, multiple-mode orthogonal frequency division multiplexing with index modulation (MM-OFDM-IM) conveys information through multiple distinguishable constellations (or modes, alternatively) and their full permutations, increasing the spectral efficiency of OFDM-IM and classical OFDM. However, both MM-OFDM-IM and its extension, that is, MM-OFDM with in-phase/quadrature index modulation (MM-OFDM-IM-IQ), cannot provide any transmit diversity gain, which may be critical for ultra-reliable communications. In this paper, aiming at enhancing the diversity gain of MM-OFDM-IM(-IQ) schemes, coordinate interleaved (CI-)MM-OFDM-IM and linear constellation precoded (LCP-) MM-OFDM-IM-IQ are proposed, both of which achieve a diversity order of two without loss of spectral efficiency. The optimal rotation angle for CI-MM-OFDM-IM and the optimal precoding matrix for LCP-MM-OFDM-IM-IQ, in the sense of maximizing their coding gains, are derived in closed form. Computer simulations corroborate the advantages of the proposed schemes in terms of diversity and bit error rate performance toward next-generation wireless networks.