Space-frequency Block Coding Research Articles

Security in Spatially Correlated MIMO OSFBC OFDM Multicast System over Frequency Selective Fading Channel

The system performance can be improved significantly by employing orthogonal space-frequency block coding (OSFBC) and orthogonal frequency division multiplexing (OFDM) because in this combination the receiver suffers lesser complexity. Recently, the wireless systems are deploying by the increasing number of closely spaced antennas. So the assumption of in-dependency among the antenna brunches is not valid. Realizing the advantages of this combination of system and taking account the effect of antenna correlation, this work demonstrates the insight of secured wireless multicasting network consisting multiple antennas both in transmitter and receiver over spatially correlated frequency selective fading channels. The desired signals have been protected from eavesdropping by useful impact of antenna diversity and antenna correlation. The main contribution of this work is the development of mathematical models of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multicasting (SOPM) to secure the system from eavesdropping. The analytical results are verified via Monte-Carlo simulation to ensure the validity of the developed mathematical model. Moreover, the numerical analysis gives a clear indication that security in OSFBC OFDM system with antenna diversity over spatially correlated frequency selective fading channel upgrades due to the effect of transmit antenna correlation and degrades due to receive antenna correlation. But the loss of this security can be significantly reduced employing antenna diversity with OSFBC-OFDM systems.

SFBC Recognition over Orthogonal Frequency Division Multiplexing Schemes in the Presence of Inphase and Quadrature Phase Discrepancies for Cognitive Radio Applications

A radio is adaptive if it can autonomously analyze the communications environment and instantly modify its settings to achieve the best possible efficiency. In orthogonal frequency division multiplexing (OFDM) transmissions, identifying the space frequency block coding (SFBC) category utilized is one of the most important tasks of an adaptive receiver. Previous approaches to this problem did not take into consideration the fact that real systems typically suffer from transmission defects. This study offers a novel maximum likelihood recognizer capable of distinguishing between SFBC OFDM waveforms in the context of inphase and quadrature phase differences (IQDs). The theoretical findings show that IQDs arising from the transmitter and recipient can be combined with channel paths to generate so-called effective channel paths. The conceptual examination demonstrates that the outlined maximum likelihood strategy of the SFBC recognition and effective channel estimation processes is implemented by an expectation maximization tool utilizing the error control decoders’ soft outputs. The simulations results reveal that the suggested strategy delivers a much greater recognition accuracy than the typical approaches outlined in the comparable literature. At a signal-to-noise ratio (SNR) of 14 dB, for example, the proposed approach achieves a bit error rate (BER) of 0.00002, which is very close to the case of perfect estimation and compensation for IQDs, outperforming the previous reported works which achieved BERs of 0.01 and 0.02.

DATA TRANSMISSION IN MIMO-OFDM TECHNOLOGIES FOR CURRENT AND FUTURE WIRELESS COMMUNICATION SYSTEMS: FROM THEORY TO PRACTICE

This paper presents a Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) communication system with space-time and space-Frequency block coded (STBC/SFBC) of present generation downlink channel. Space-time block coding (STBC) and space-frequency block coding are transmit diversity schemes used in a wireless communication system to mitigate the effect of channel fading. The system is aimed to reduce the error rate (BER) by mitigating the effect of multipath fading which increase the quality of the system. In the proposed system, 2 transmit and 2 receive antennas are used, to transmit modulated symbols of block N across an OFDM channel, using SFBC Alamouti’s based encoding algorithm (SFBC-OFDM) derives from the basic criteria for space-time block codes (STBC). The signals from the first and second antennas are encoded and transmitted simultaneously in space and frequency over frequency-selective Rayleigh fading channel using two adjacent carriers. The work examines the SFBC and spatial diversity benefits realized based on the BER performance. The result is simulated effectively using MATLAB application software and the BER performance is compared with the conventional STBC-OFDM. It is shown that both STBC and SFBC techniques achieve similar performance with a diversity gain of four (4) over a slow fading channel with 2 antennas at both ends of the link under simple processing across the transmit and receive antennas.

Massive MIMO Indoor Transmissions at 38 and 65 GHz Applying Novel HBF Techniques for 5G.

The 5G Infrastructure Public Private Partnership (5GPPP) has recently published a white paper about 5G service indoors, since up to now, it had mainly focused on the outdoors. In an indoor environment, the requirements are different since the propagation mechanism differs from other scenarios. Furthermore, previous works have shown that space frequency block code (SFBC) techniques applied to multiple antennas improve performance compared to single-input single-output (SISO) systems. This paper presents an experimental study in an indoor environment regarding the performance of a massive multiple-input multiple-output (mMIMO) millimeter-wave (mmWave) system based on the 5G New Radio (NR) standard in two frequency bands. In a first step, the 38 and 65 GHz bands are compared by applying a low-complexity hybrid beamforming (HBF) algorithm. In a second step, the throughput and the maximum achievable distance are studied using a new algorithm that combines the SFBC technique and HBF. Results show, at 38 GHz with HBF and aggregated bandwidths (4 × 100 MHz), a maximum throughput of 4.30 Gbit/s up to 4.1 m. At 65 GHz, the SFBC + HBF algorithm improves the communication distance by 1.34, 1.61, or 1.75 m for bandwidths of 100, 200, or 400 MHz, respectively.

On SFBC Schemes for Enabling Virtual Array Concept in Monostatic ISAC Scenarios.

The integrated sensing and communication (ISAC) paradigm is being proposed for 6G as a new feature of the physical layer (PHY), for tackling dual-functional applications, i.e., demanding radio-sensing and communication functions, such as the Internet of Things (IoT) and autonomous driving systems. This work considers the integration of sensing and communications functionalities in a unique platform. To achieve this goal, the use of orthogonal space frequency block codes (SFBC) is proposed. SFBC code orthogonality enables both the separation of communications data streams at a user terminal and the estimation of target parameters. The SFBC enhances the communications link diversity without requiring channel state information knowledge at the transmitter and enable the virtual antenna array concept for enhancing the direction-finding resolution. The use of different SFBCs provides a tradeoff between achieved diversity and sensing resolution. For example, an Alamouti code, applicable for the case with two transmitting antennas, duplicates sensing resolution and achieves a diversity order of two while the use of a Tarokh code, applicable for a scenario with four transmitting antennas, provides a fourfold better resolution and diversity order of four. However, the code rate achieved with the Tarokh code is half of the one achieved with the Alamouti code. Furthermore, the unambiguous range is reduced since the bandwidth is divided to multiplex the different antenna signals. For its simplicity, good performance and reduced integration requirements, the method is promising for future ISAC systems.

Power of Error Correcting Codes for SFBC-OFDM Classification Over Unknown Channels

The development of intelligent radios in wireless applications is mainly driven by the growing need for higher data rates, along with constrained spectrum resources. An intelligent radio is one that can autonomously assess the communication environment and automatically update the communication parameters to achieve optimal performance. The problem of determining the type of space-frequency block coding (SFBC) for orthogonal frequency division multiplexing (OFDM) transmissions is one of the main tasks of an intelligent receiver. Previous approaches to this problem are restricted to uncoded communications; nevertheless, existing systems typically utilize error-correcting codes. This study develops a maximum-likelihood (ML) classifier that discriminates among SFBC-OFDM signals using the soft outputs of a channel decoder. The mathematical analysis shows that the maximization of the likelihood function can be carried out by employing an iterative expectation-maximization (EM) procedure. A channel estimator is also included in the proposed classifier as a vital step. The findings show that the classification performance of the proposed algorithm is considerably better than the classical classifiers reported in the literature, at the cost of an acceptable increase in computing complexity.

Security in Multicast Over <i>α</i>-<i>μ</i> Fading Channels with Orthogonal Frequency Division Multiplexing

The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by these advantages of OSFBC-OFDM system, this paper considers a secure wireless multicasting scenario through multiple-input multiple-output (MIMO) OFDM system employing OSFBC over frequency selective α-μ fading channels. The authors are interested to protect the desired signals from eavesdropping considering the impact of the number of multicast users and eavesdroppers, and the fading parameters α and μ. A mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multi-casting (SOPM) to ensure the security in the presence of multiple eaves-droppers. The results show that the security in MIMO OSFBC OFDM system over α-μ fading is more sensitive to the magnitude of α and μ and this effect increases in the high signal-to-noise ratio (SNR) region of the main channel.

Iterative Threshold Channel Estimation in ORGV Convolutional Code MISO-OFDM System

ABSTRACT In the orthogonal frequency division multiplexing (OFDM) transmission system, when the digital symbols are transmitted in the wireless channel, it would be affected by a lot of noise interference due to the unsatisfactory condition characteristics of the wireless channel itself, therefore, the symbol error and bit error would be generated. To achieve a certain bit error rate (BER) under the condition of known signal-to-noise ratio (SNR), convolutional channel coding and block interleaver should be utilized to further reduce the BER. Moreover, convolutional code is almost utilized in all wireless communication systems. This paper proposes a convolutional code channel estimation method in multiple-input single-output (MISO)-based OFDM (MISO-OFDM) system with frequency-shift m-sequence (FSMS) as guard interval (GI) for avoiding inter-symbol interference (ISI). The proposed space-frequency block code (SFBC) MISO-OFDM system achieves higher transmit diversity gains and better BER performance. Simulation results verify that the proposed iterative threshold channel estimation (ITCE) method in octal representation generation vector (ORGV) convolutional code 4 × 1 MISO-OFDM system provides good BER and normalized mean squared error (NMSE) performance with significant coding gains in both static and dynamic multipath channels.

A Comparative Experimental Study of MIMO A&F and D&F Relay Nodes Using a Software-Defined Radio Platform

The relaying technologies in co-operative systems are considered a core element in actual and future wireless communications, assisting the network by enhancing its reliability and improving its capability through exploiting co-operativity. In this paper, a co-operative system testbed based on Software Defined Radio (SDR) through Universal Software Radio Peripherals (USRPs) and the MatlabTM software is presented. The main novelty in this development of the platform is the implementation of 4G signal features, such as Physical Downlink Shared Channel (PDSCH) and Downlink Shared Channel (DL-SCH) for transport channel coding, which is one of the main contribution of the paper. The developed Multi-Input and Multi-Output (MIMO) SDR co-operative platform is capable of developing prototypes for the Relay Nodes. More specifically, the Amplify-&-Forward (A&F)—with or without Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) Pre-Equalization—and Decode-&-Forward (D&F) protocols were implemented. Both Single-Input and Single-Output (SISO) and MIMO modes are supported by our testbed. The developed A&F and D&F MIMO co-operative systems in this paper utilize Orthogonal Space-Frequency Block Codes (OSFBCs) for the transmission of data symbols from the source to the destination. Our results show that relay nodes can substantially improve the Bit Error Rate (BER) and throughput in communications between the eNodeB (eNB) and User Equipment (UE). In particular, the maximum throughput achieved by conventional MIMO A&F is 9.3Mbps at SNR=16dB, which is 4Mbps higher than throughput of MIMO Non-Co-operative. It also shows the capacity improvement when considering the pre-equalization in the A&F schemes, compared to the conventional A&F Relay Node. For example, with MIMO A&F-MMSE pattern, a value of 11.8 Mbps is achieved for SNR=16dB, which is 84.8 % of the maximum system throughput (13.95 Mbps). On the other hand, the obtained results with D&F schemes far exceed those obtained with A&F strategies, achieving the maximum performance with the 2 × 2 MIMO D&F protocol from SNR=8dB. Furthermore, this work constitutes a first stage to the implementation of a 5G New-Radio Co-operative System platform.

Improved Performance of Alamouti Scheme Using Cyclic Delay Diversity and Doppler Diversity for MIMO Systems-Based

This paper addresses a novel Alamouti space frequency block decoding scheme for multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) based systems using diversity techniques over highly frequency selective channels. Unlike the standard Alamouti space-frequency block code (SFBC), that suffer from performance degradation in highly frequency-selective channels, the proposed method combats this problem. Also, this scheme has capability to combine with different methods such as OFDM and some special diversity such as: cyclic delay diversity (CDD) and discontinuous Doppler diversity (DDoD). In addition, a novelty transceiver using CDD is proposed, which performs valuable results. In this paper, this scheme is called “Efficient Δh-Alamouti with CDD”. This efficient Alamouti encoder and decoder allow a high reliability and capacity enhancement. In order to evaluate its capability, we have implemented this scheme for the second generation terrestrial video broadcasting (DVB-T2) system. The properties of the proposed scheme is investigated over different channels. Also, mathematical analyses and simulation results of the bit error performance for the modified encoding method with these diversity techniques, perform mostly better than the other forms of encoding Alamouti over highly frequency-selective channels such as single frequency networks (SFN). The other advantages of the proposed method are simplicity, flexibility and standard compatibility.

Double Focusing: A New Sparse Channel Estimation Algorithm for Doubly Selective SFBC-OFDM-Based Underwater Acoustic Systems

In this letter, a new channel estimation algorithm is proposed for underwater acoustic channels undergoing Rayleigh fading with impulsive noise. For the channel estimation purpose, the algorithm utilizes the path-based channel model characterized by a path delay, a Doppler scaling factor, and an attenuation factor. Assuming antenna diversity coupled with Alamouti’s space-frequency block coding, the proposed estimator first employs matching pursuit algorithm for initialization. Then, the iterative algorithm interchangeably employs delay focusing and Doppler focusing approaches for Doppler shifts and delays estimation, respectively, with their corresponding path gains. The performance of the proposed algorithm is then presented in terms of average mean square error and symbol error rate for 16QAM signaling with different pilot spacings. The simulation results show that the proposed approach with the continuous focusing functions can outperform the compressed sensing-based matching pursuit (MP) algorithm and the projected (PMP), and the basis pursuit-based generalized approximate message passing (GAMP) algorithm.

BER performance evaluation of a non-Hermitian coherent-optical OFDM FSO system with SFBC and polarization diversity

An analytical model is developed for a non-Hermitian coherent-optical OFDM FSO system with space frequency block code (SFBC) and polarization diversity. Analysis is carried out for a non-Hermitian OFDM FSO link with SFBC coding to evaluate the effect of cross polarization induced crosstalk in presence of channel impairments such as atmospheric turbulence. Expressions are developed for signal to noise plus crosstalk ratio for a given amount of polarization misalignment angle. Considering the probability density function of the misalignment angle to be Maxwellian distributed and Gamma–Gamma distribution for strong atmospheric turbulence, the average bit error rate (BER) is determined. Results are evaluated without and with strong atmospheric turbulence. Computed result show that there is significant improvement on receiver sensitivity due to polarization diversity and coding gain due to SFBC. Further, system suffers power penalty due to crosstalk due to cross polarization and as well as turbulence. Results show that, there is 38 dB improvement in receiver sensitivity due to polarization diversity without SFBC in presence of strong turbulence at a BER of 10−12 considering local oscillator power is 5 mW and link distance is 2000 m. At a given BER of 10−12, penalty due to crosstalk is found to be 3.3 dB for mean misalignment angle of 40 when link distance is 2000 m. Finally, it is noticed that, the amount of coding gain due to SFBC is found to be 7.5 dB at a BER of 10−12.

Maximum-Likelihood Integer Frequency Offset Estimator for Alamouti SFBC-OFDM Systems

In this letter, we address the problem of estimating the integer part of carrier frequency offset (CFO) in space frequency block codes (SFBCs) systems with orthogonal frequency division multiplexing (OFDM) modulation schemes. We derive a maximum-likelihood (ML) estimator assuming that the receiver has two receive antenna, and then we extend the analytical analysis to an arbitrary number of receive antennas. The proposed estimator is designed in a way that exploits the additional two-dimensional space-frequency redundancy provided by SFBCs. Because of its popularity, Alamouti code is chosen to be the code of interest. However, a similar analytical treatment could be applied to any other code. The computational complexity analysis and Monte Carlo experiments are carried out to verify effectiveness of the proposed estimator for practical applications.

Space-Frequency Block Coding with Two-Mode Index Modulation OFDM and Increased Stability to Channel Frequency Selectivity

It is considered a technique of mutual application of multi-antenna MIMO systems and multiplexing with orthogonal frequency division of OFDM channels for current-technology systems of wireless communication of special application. There are defined areas of prior application of time and frequency variant of diverse signals transmission according Alamouti principle for wireless channels with limited frequency and energy resources. It is shown that application of fixed precoding matrix of Walsh–Hadamard to outgoing symbols of space-frequency Alamouti coder allows to increase stability of SFBC-OFDM method to frequency selectivity of a channel without system complication. It is analyzed a conception of index modulation of OFDM-IM subcarriers. There are demonstrated advantages of Dual-Mode OFDM-IM with optimized signals ensembles on a basis of BPSK, QPSK and 16-QAM. It is proposed a novel signal-code construction (SCC) with join of dual-mode index modulation of OFDM subcarriers, orthogonal space-frequency block coding with Alamouti kernel and Walsh–Hadamard coder WH-SFBC-DM-OFDM-IM. Such method in contrast to classic SFBC-OFDM method allows to increase simultaneously spectral and energy efficiency of information transmission systems in conditions of frequency-time selectivity of communication channel. Proposed method is completely invariant to frequency selectivity in case of BPSK application and partially invariant in case of application of QPSK and 16-QAM. The simulation results show that noise immunity of such SCC is enough better in compare with the other methods due to providing of identity of space-frequency word at duration of OFDM symbol. The method is advisable to use for provision of high-quality communication with high-dynamic ground objects, pilotless vehicle and the other aircrafts in conditions of critical decrease of channel noise prtection which appears in case of influence of radio countermeasures systems.

Performance analysis of uncoded and SFBC OFDM system over composite fading channels

This paper presents the performance of uncoded and space-frequency block coded (SFBC) orthogonal frequency division multiplexing (OFDM) system for two recently proposed composite fading model i.e. Fisher–Snedecor (F) and κ-μ/gamma. Both models are adequate for wearable communication system. In this paper, we derive the exact and approximate expressions of average bit error rate (ABER) for uncoded and SFBC OFDM system using fast Fourier transform (FFT) and fractional Fourier transform (FrFT). Further, these generalized expressions reduce to special cases of both composite fading models. Particularly, M-ary quadrature amplitude modulation (MQAM) and M-ary phase-shift keying (MPSK) modulation schemes are considered to derive ABER expressions. The numerical results are compared with the previous results of Rayleigh and Nakagami-m distribution. Also, the Monte Carlo simulation results are provided to crosscheck the validity of derived expressions.

Comprehensive Study on Coded Modulation Schemes for Future Communication

In the future communication technology standards, wireless communication in high mobility scenes is extremely important, but the fast fading of the channel and the Doppler frequency shift caused by high-speed mobile will seriously affect the overall performance of the system. The communication performance indicators such as bit error rate (BER), computational complexity and transmission capacity will degrade. This paper introduces several coded modulation schemes of joint coding modulation diversity (JCMD), orthogonal time-frequency space (OTFS) modulation and space-frequency block code (SFBC), and uses bit interleaved coded modulation (BICM) as a reference for comparison. The simulation results show that the JCMD scheme has the best block error rate (BLER) performance under different moving speed and code rate conditions. And JCMD has strong robustness, can achieve large performance gains even under the conditions of high speed and high code rate.

Method of space-frequency block coding with dual-mode index modulation aided OFDM

The technology of combining Multiple Input-Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) for modern Wireless Communication Systems is considered. The areas of priority use of time and frequency variants of Alamouti’s diversity scheme for Wireless Communication Channels with limited frequency and energy resources are determined. The concept of Index Modulation (IM) is analyzed. The method of OFDM subcarriers index modulation is determined as the most promising means of increasing noise immunity and speed of information transmission for real frequency-selective channels of Wireless Communication Systems. The benefits of Dual-Mode OFDM-IM with optimized signal constellations based on BPSK, QPSK and 16-QAM are demonstrated. A novel Signal-Code design combining the Dual-Mode Index Modulation Aided OFDM and the Orthogonal Space-Frequency Block Coding with Alamouti’s core SFBC-DM-OFDM-IM is proposed. Compared to classical SFBC-OFDM the proposed method allows simultaneously to improve spectral and energy efficiency of information transmission systems in frequency and time-varying wireless communication channel. The SFBC-DM-OFDM-IM method is advisable for providing high-quality communications with highly dynamic ground objects, unmanned aerial vehicles and other aircrafts in the conditions of Signal-to-Noise Ratio critical reduction, which takes place under the influence of electronic suppression means. The obtained scientific results can be effectively used for designing new generation Wireless Communication Networks with limited frequency and energy resources.

Low Complexity Transmitter Architecture for SC-FDMA Systems With SFBC Code

In this letter, a novel low complexity transmitter architecture is proposed for a space frequency block coding (SFBC) single carrier frequency division multiple access (SC-FMDA) system, where the transmitted signals for each antenna are generated using a time-domain linear sequence combination (TDLSC) scheme. In the TDLSC method, a specific set of various transmitted signals is designed to reduce the peak-to-average power ratio (PAPR) without destroying the SFBC orthogonality and requiring no side information. Additionally, a low-complexity side information detection method is also presented. Computer simulations show that the PAPR reduction performance of the TDLSC outperforms the existing simplified selective mapping scheme and has a slight performance loss of less than 0.2 dB compared to an ordinary selective mapping scheme. The proposed side information detection method has a significantly lower complexity while achieving the same bit error rate performance compared to the selected mapping-based method with a maximum likelihood decoder.

Investigating the Performance of Various Channel Estimation Techniques for MIMO-OFDM Systems using Matlab

This paper simulates and investigates the performance of four widely-used channel estimation techniques for MIMO-OFDM wireless communication systems; namely, super imposed pilot (SIP), comb-type, spacetime block coding (STBC), and space-frequency block coding (SFBC) techniques. The performance is evaluated through a number of MATLab simulations, where the bit-error rate (BER) and the mean square error (MSE) are estimated and compared for different levels of signal-to-noise ratio (SNR). The simulation results demonstrate that the comb-type channel estimation and the SIP techniques overwhelmed the performance of the STFC and STBC techniques in terms of both bit-error rate (BER) and mean square error (MSE).

MIMO Multicarrier Transmission Over Doubly Selective Channels With Virtual Trajectories Receiver

High mobility and multipath propagation induce Doppler and delay dispersion, respectively. When both phenomena affect the transmitted signal, the communication channel is known as a doubly selective channel (DSC). In multicarrier systems under this scenario, intersymbol interference (ISI) and intercarrier interference (ICI) are ineluctably present, severely degrading the system's performance. Therefore, much effort has been invested in researching convenient waveforms that enable the receiver self-interference cancellation, while making use of the available space, time, and frequency diversity. In this paper, a multicarrier multiple-input multiple-output (MIMO) system for communication in DSCs is presented. By using the virtual trajectory (VT) representation of the MIMO channel, direct conversion of Doppler diversity into additional virtual antennas in the receiver is achieved. This concept is developed for a coherent system with one-tap channel estimation (CE) and equalization algorithms of low complexity as well as for incoherent detection using differential space-frequency block codes (DSFBCs), where pilot signals are not used. For both systems, runtime cancellation and/or inversion of complex interference channel matrices is avoided. Diversity of the doubly selective MIMO channel is exploited without sacrificing compatibility with current multicarrier MIMO systems. The presented system offers robustness in DSCs with minimal extra complexity when compared to conventional approaches. The results demonstrate that MIMO orthogonal frequency division modulation (MIMO-OFDM) can be still implemented in extremely high Doppler scenarios if VT reception is incorporated.