Orthogonal Frequency Division Multiplexing Communication Research Articles

A hybrid OFDM–CDMA-based robust image watermarking technique

Digital watermarking is a process of embedding hidden information called watermark into different kinds of media objects. It uses basic modulation, multiplexing and transform techniques of communication for hiding information. Traditional techniques used are least significant bit (LSB) modification, discrete cosine transform (DCT), discrete wavelet transform (DWT), discrete Fourier transform (DFT), code division multiple access (CDMA) or a combination of these. Among these, CDMA is the most robust against different attacks except geometric attacks. This paper proposes a blind and highly robust watermarking technique by utilizing the basis of orthogonal frequency division multiplexing (OFDM) and CDMA communication system. In this scheme, the insertion process starts by taking DFT of host images, permuting the watermark bits in randomized manner and recording them in a seed as a key. Then PSK modulation follows inverse DFT (IDFT) that gives watermark information as OFDM symbols. These symbols are spread using spreading codes and then arithmetically added to the host image. Finally, scheme applies inverse DCT (IDCT) to get watermarked host images. The simulation results of the proposed scheme are compared with CDMA-based scheme in DCT domain. The results show that the robustness of the proposed scheme is higher than the existing scheme for non-geometric attacks.

Characterization of Orthogonal Frequency Division Multiplexing (OFDM) Communication Links

The demand for high data rate transmission is rapidly increasing in the area of wireless communications and Orthogonal Frequency Division Multiplexing (OFDM) is known to be a promising technique for high-rate transmission that can overcome the inter symbol interference (ISI) which results from the time dispersive nature of wireless channels. The idea is to utilize a number of carriers, spread regularly over a frequency band, in such a way so that the available bandwidth is utilized to maximal efficiency. This study presents the comparison of the performance of different modulation schemes: M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) over Additive White Gaussian Noise (AWGN), Rayleigh and Rician multipath fading channels in OFDM system. Bit error rate (BER) was used to evaluate the performance of the system; the number of fast Fourier transform (FFT) points used during the transmission was also examined. The results showed that for all the channels, lower order modulation schemes perform better than the higher order schemes. This comes at the detriment of the data rate, as lower order schemes have lower data rates compared with their higher order counterparts. In addition, it was observed that the system performed better in AWGN channel than Rayleigh and Rician fading channels for all the modulation schemes used. It was observed that the number of FFT points used during the transmission do not have much effects on the performance of the system.

An Efficient Implementation and Analysis of Tail-Biting Convolution Coding Algorithm for OFDM Based System in Terms of Speed, Memory and Peak-to-Average Power Ratio Using DSP

Fourth Generation (4G) mobile communication system uses Orthogonal Frequency Division Multiplexing (OFDM). With this technique, high data rate demands are achieved. Tail biting Convolution Coding (TBCC) avoids the data rate loss, hence it is widely used error control coding algorithm in OFDM and other various wireless communication technologies. But, OFDM has increased Peak to Average Power Ratio (PAPR). High PAPR signal consumes more power and makes system power inefficient. To gain supercomputing performance in terms of Speed, Memory and Power on mobile devices, an efficient implementation of algorithms on Digital Signal Processing (DSP) processor is an essential requirement. This requirement becomes more stringent for Fifth Generation (5G) mobile devices. For this, wide scope of knowledge as well as skills are required to understand the algorithm, DSP architecture, instruction set, optimization and performance measurement. In this article, we have implemented TBCC algorithm using Bit by Bit (BYB) and Look Up Table (LUT) approaches on Freescale StarCore SC140 based DSP platform and proposed an efficient algorithm implementation methodology by comparing the machine cycles and memory requirement. We have used coding rate (R) = 1/2, 1/3, 1/4 and constraint length (K) = 5 and K = 9 for implementation of TBCC. Using our proposed LUT approach, we have achieved average 45.82% Computational Complexity Reduction Ratio (CCRR) in machine cycles compared to BYB approach. Proposed LUT approach increases the TBCC execution speed. Our developed fixed point routines can be used for any K ≤ 9. TBCC is also analyzed for PAPR to get an overall profiling results and three dimensional optimization of TBCC algorithm in terms of Speed, Memory and Power.

Design and implementation of reconfigurable DCT based adaptive PST techniques in OFDM communication system using interleaver encoder

Objectives: To propose Reconfigurable Discrete Cosine Transform (RDCT) in Orthogonal Frequency Division Multiplexing (OFDM) high speed communication system to improve efficient spectrum utilization and mitigation of jitter,selective fading effects. The adaptive PTS method reduces Inter-Carrier-Interference (ICI), Inter-Symbol-Interference (ISI), PAPR and the computational intricacy of the communication system. To analyse and compare the performance of proposed Reconfigurable method with existing conventional OFDM communication system. Methods: This proposed technique employs interleaver encoder with both PTS and adaptive PTS with the Reconfigurable Discrete Cosine Transform (RDCT) in OFDM Communication system. Finding: A case study has been carried out and the proposed method is found to be better in CCDF performance, reliability, flexibility and accuracy. To reduce the autocorrelation between every modulated data bit, Forward error Correction in comparison with the conventional OFDM communication system. Novelty: The recent high-speed communication system most commonly using Orthogonal Frequency division multiplexing (OFDM) to enhance the quality of service(QoS) and Bandwidth on demand. Even though the OFDM scheme offers many advantages the signal of OFDM consists of a noise that causes variation in the amplitude resulting in high peak to average power ratio (PAPR) and since OFDM is a multi-carrier system, it is more susceptible to signal drifts. Various methods to reduce the PAPR in OFDM signal are already proposed, in this paper, a technique called interleaver encoder-based Partial Transmit sequence (IEPTS) is reviewed and the new proposed technique employs interleaving encoder utilizing in both PTS and A-PTS with reconfigurable discrete cosine transform (RDCT) in OFDM high-speed communication system. Keywords: Interleaver encoder; adaptive partial transmit sequence (A-PTS);orthogonal frequency-division multiplexing (OFDM); reconfigurable discrete cosine transform (RDCT); partial transmit sequence (PTS)

Doppler Compensation of Orthogonal Frequency Division Multiplexing for Ocean Intelligent Multimodal Information Technology

The era of intelligence has arrived. Intelligent multimodal information is essential for underwater engineering. Sound is an indispensable medium in underwater multi-modal information technology. Orthogonal frequency division multiplexing underwater acoustic communication technology can achieve high bit rate communication. However, the time-varying Doppler of the underwater acoustic channel will cause inter carrier interference in the OFDM system, destroy the orthogonality between subcarriers, and affect system performance. In this paper, we propose a method based on wavelet function to compensate for the Doppler distortions of the underwater acoustic channel for OFDM data. This method uses a set of orthogonal polynomials to perform channel estimation in both the time and frequency domains and uses the matched filtering for channel equalization. Compared with the traditional polynomials, the smoothly varying polynomials in Wavelet FFT greatly reduces the correlation of the processed data, enable more accurate channel estimation and equalization. Finally, this paper verifies the feasibility of the algorithm through the Songhua Lake underwater experiment.

Time-Varying Channel Equalization in Underwater Acoustic OFDM Communication System

In this paper, three time-varying channel equalization schemes are studied in the underwater acoustic (UWA) Orthogonal Frequency Division Multiplexing (OFDM) communication system. The equalization algorithms are the zero-forcing (ZF) equalization algorithm, and the minimum mean square error equalization (MMSE) algorithm and the serial interference cancellation (SIC) equalization algorithm. Among the schemes, there is a problem of needing a large amount of operation when obtaining the inversion of the channel matrix. Then, to reduce the computation complexity of channel matrix inversion, the band approximation of the channel matrix, the serial equalization and the LDLH decomposition are also studied. To evaluate the efficacy of the algorithms studied in this paper, numerical simulation and the field experiment are both conducted. The simulation results proof that each equalization algorithm can work appropriately under different time-varying conditions, and valid the reliability of each simplified algorithm under the same Doppler factor. The results of two sets of field experiment also prove that the simplified algorithm eliminates the influence of the residual narrow band Doppler to a certain extent, and a better effect is obtained while a channel estimation algorithm with higher accuracy is combined.

Differential orthogonal frequency division multiplexing communication in water pipeline channels.

The problem of information transmission through water pipelines is addressed and a class of methods based on differentially encoded orthogonal frequency division multiplexing (OFDM) is proposed. Specifically, two methods are investigated; one based on conventional differential encoding with an estimation of the average time of arrival and another based on double encoding. Results show that the first approach improves performance in the low signal to noise ratio (SNR) region, while the second is better suited at high SNR. Adopting these techniques closes the performance gap between differential OFDM systems and coherent OFDM systems while retaining the benefits of computational simplicity.

Physical Layer Encryption for Wireless OFDM Communication Systems

Our everyday lives are impacted by the widespread adoption of wireless communication systems integral to residential, industrial, and commercial settings. Devices must be secure and reliable to support the emergence of large scale heterogeneous networks. Higher layer encryption techniques such as Wi-Fi Protected Access (WPA/WPA2) are vulnerable to threats, including even the latest WPA3 release. Physical layer security leverages existing components of the physical or PHY layer to provide a low-complexity solution appropriate for wireless devices. This work presents a PHY layer encryption technique based on frequency induction for Orthogonal Frequency Division Multiplexing (OFDM) signals to increase security against eavesdroppers. The secure transceiver consists of a key to frequency shift mapper, encryption module, and modified synchronizer for decryption. The system has been implemented on a Virtex-7 FPGA. The additional hardware overhead incurred on the Virtex-7 for both the transmitter and the receiver is low. Both simulation and hardware evaluation results demonstrate that the proposed system is capable of providing secure communication from an eavesdropper with no decrease in performance as compared with the baseline case of a standard OFDM transceiver. The techniques developed in this paper provide greater security to OFDM-based wireless communication systems.

Sparse DFT Based Channel Estimation In OFDM Systems

Channel estimation is an essential part of Orthogonal Frequency Division Multiplexing (OFDM) communication systems. In this paper, two Discrete Fourier Transform (DFT) improvement algorithms are proposed and compared where the 1st one exploits channel sparsity concept while the other considers significant channel coefficients only. In the proposed algorithms; Enhanced and Sparse DFT (E-DFT and S-DFT), different number of significant channel components is selected either by a threshold determining procedure such as in E-DFT, or through determining channel sparsity level such as in S-DFT. In the presence of Doppler frequency shifts, the Inter Symbol Interference (ISI) effect on channel coefficients is successfully reduced using the proposed estimation algorithms. Vehicular A-ITU channel model is considered with a relatively high vehicle speed up to 68 Km/h in order to test the suitability of the proposed algorithms for mobile systems. E-DFT and S-DFT improves conventional as well as previous DFT improvement methods (I-DFT) suggested by [7], [8], [9], [15]. For 64 subcarriers, S-DFT outperforms E-DFT and I-DFT by about 3dB at a BER of 0.01 with a mobility reaches 45 Km/h, and by about 0.4dB and 2.5dB at a BER of 0.02 with a mobility reaches 68Km/h.

Performance Investigations and PAPR Reduction Analysis Using Very Efficient and Optimized Amended SLM Algorithm for Wireless Communication OFDM System

The orthogonal frequency division multiplexing (OFDM) is the most encouraging multi-carrier modulation system chosen for the high data rates but the objective is to resolve intrinsic common issue of peak to average power ratio (PAPR). The projected algorithm is illustrated in this research study which is established upon selected mapping (SLM) with pseudo-random sequence under time domain μ law companding of signal. Besides the significant competitive characteristics of conventional SLM algorithm (ConvenSLM-Algo) (Mestdagh et al. in Electron Lett 32(22):2056–2057, 1996. https://doi.org/10.1049/el:19961384 ), it undergoes the tedious complexity in generation of phase sequence and for the recovery of sequence, side information is mandatory. The key concern, thus, to eliminate the tedious problem of designing of phase sequence along with the aim of reducing the fluctuation of signal with high PAPR. Henceforth, in the projected algorithm (Projected-Algo) a noteworthy strategy has been investigated and followed for the designing of phase sequence which is very easy and for the recovery of information at receiver, side information of index of column of phase sequences can be used because of straightforwardness in its establishment. Hence, we demonstrate the effective overall excellent performance of Projected-Algo along with analysis and also comparative study of Projected-Algo outperforms the conventional OFDM system (unchanged), ConvenSLM-Algo [16], SLM with new pseudo random phase sequences (ModSLM-Algo) given in literature (Ali et al. in Canadian conference on electrical and computer engineering, 2018. https://doi.org/10.1109/CCECE.2018.8447835 ).

Joint low‐complexity nonlinear equalization and carrier frequency offset compensation for multiple‐input multiple‐output orthogonal frequency division multiplexing communication systems

AbstractThe conventional zero forcing (ZF) equalizer suffers from the noise enhancement problem and the increasing complexity with the increase of the number of subcarriers. On the other hand, the minimum mean square error (MMSE) equalizer mitigates the noise enhancement, but it needs estimation of the signal‐to‐noise ratio (SNR) to work properly. In addition, the Joint Low‐complexity Regularized ZF (JLRZF) equalization and carrier frequency offset compensation scheme mitigates the noise enhancement using a constant parameter called the regularization parameter without SNR estimation. In this paper, we present a JLRZF with successive iInterference cancelation (JLRZF‐SIC) scheme for multiple‐input multiple‐output (MIMO) discrete Fourier transform orthogonal frequency division multiplexing (DFT‐OFDM) system to cope with the above‐mentioned problems. The proposed JLRZF‐SIC scheme jointly performs the equalization and the carrier frequency offset (CFO) compensation processes in two steps. The coupling nature of the MIMO channel is canceled in the first step. A regularization term is added in the second step to avoid the inter‐symbol‐interference (ISI). Simulation results show that the proposed JLRZF‐SIC scheme improves the system performance with low complexity, especially in the presence of estimation errors.

Modified OFDM configurations with equalization and CFO compensation for performance enhancement of OFDM communication systems using symmetry of the Fourier transform

The Orthogonal Frequency Division Multiplexing (OFDM) systems allow efficient spectrum usage and simple Frequency Domain Equalization (FDE). However, a large number of sub-carriers increases the computational complexity of the equalization process. In this paper, the conventional OFDM system is modified to enhance the Bit-Error-Rate (BER) performance or reduce the computational complexity. Also, the banded-matrix approximation is taken into account to reduce the equalization complexity. Simulation results show that the 1st proposed OFDM system based on Binary Phase Shift Keying (BPSK) can reduce the computational complexity to O(N/2) instead of O(N) compared to the conventional OFDM configuration based on the banded-matrix approximation concept. The 2nd proposed OFDM system based on BPSK requires approximately the same computational complexity of the conventional OFDM configuration and gives a Signal-to-Noise Ratio (SNR) gain of about 7.05 dB at BER = 10−3 compared to the corresponding conventional OFDM configuration. The 3rd proposed OFDM system based on Quadrature Phase Shift Keying (QPSK) gives an SNR gain of about 4.51 dB at a BER = 10−3 compared to the corresponding conventional OFDM configuration. The 2nd proposed OFDM system based on BPSK outperforms the different schemes in the presence of estimation errors.

EVALUATION OF BER PERFORMANCE OF FFT-OFDM FOR WIRELESS COMMUNICATION NETWORKS

Orthogonal Frequency Division Multiplexing (OFDM) is used to enhance Bit Error Rates (BER) performance for error free transmission in free space in free pace. OFDM-based systems operate in the hostile multipath radio environment, which allows efficient sharing of limited resources. This research work was designed, developed and simulated an FFT-OFDM based System using the basic blocks of Simulink in MATLAB/Simulink software, to enhance BER for error free transmission. The system was design using Fast Fourier transform (FFT) and Inverse Fast Fourier transform (IFFT). This was achieved in backing of collection and review of high-quality research papers, which reported the latest research developments in OFDM communications networks, and its applications in future wireless systems. The research mitigated the noise enhancement effect. And many critical problems associated with the error transmission in wireless communication networks in the future. An error transmission in wireless systems is global issues and challenges that are still looking for efficient solutions. This research work would overcome the global issues and challenges facing the wireless communication network.

AoA-based channel estimation for massive MIMO OFDM communication systems on high speed rails

Channel estimation is a well-known challenge for wireless orthogonal frequency division multiplexing (OFDM) communication systems with massive antennas on high speed rails (HSRs). This paper investigates this problem and design two practicable uplink and downlink channel estimators for orthogonal frequency division multiplexing (OFDM) communication systems with massive antenna arrays at base station on HSRs. Specifically, we first use pilots to estimate the initial angle of arrival (AoA) and channel gain information of each uplink path through discrete Fourier transform (DFT), and then refine the estimates via the angle rotation technique and suggested pilot design. Based on the uplink angel estimation, we design a new downlink channel estimator for frequency division duplexing (FDD) systems. Additionally, we derive the Cramer-Rao lower bounds (CRLBs) of the AoA and channel gain estimates. Finally, numerical results are provided to corroborate our proposed studies.

Equalization and blind CFO estimation for performance enhancement of OFDM communication systems using discrete cosine transform

SummaryIn wireless communication systems, equalization is one of the most important schemes to improve the system performance. This paper consists of two main parts. The first part presents a blind carrier frequency offset (CFO) estimation scheme based on discrete cosine transform (DCT). The second part presents a joint low‐complexity equalization, and CFO compensation in orthogonal frequency division multiplexing (OFDM) systems. Moreover, in the second part, we present a joint low‐complexity regularized zero‐forcing (JLRZF) equalizer based on the proposed CFO estimation scheme. Simulation results show that the proposed configuration has the ability to perform blind CFO estimation and enhance the system performance in the presence of estimation errors.

A Novel Low-Complexity Estimation of Sampling and Carrier Frequency Offsets in OFDM Communications

This paper presents a novel low-complexity sequential, blind, pilot-assisted estimator for the sampling frequency offset (SFO) and the carrier frequency offset (CFO), for orthogonal frequency-division multiplexing (OFDM) communications. The proposed algorithm processes the received subcarriers to obtain a cost function which depends only on a single unknown parameter at a time, either the SFO or the CFO, as well as on a specifically designed auxiliary parameter, while ignoring the noise. Then, by computing the cost function at a few selected values of the auxiliary parameter, an explicit estimator for each unknown parameter is derived, thereby avoiding the need for a search. To the best of our knowledge, this is the first time such a deterministic approach is applied to the joint estimation of the SFO and the CFO. Moreover, the proposed estimator does not require knowledge of the channel coefficients at the pilot subcarriers, and achieves good performance with a relatively small number of pilot symbols, which results in a low computational complexity. Simulation results show that at low computational complexity, there are many scenarios in which the new estimator achieves smaller estimation errors compared to other existing methods.

A Carrier Frequency Offset Estimation for OFDM System via Local Searching Capon Algorithm

Orthogonal frequency division multiplexing (OFDM) technology is an important modulation technology in wireless communication. One of the main disadvantages of OFDM system is that it is very sensitive to carrier frequency deviation. Therefore, estimation of carrier frequency deviation is one of the key technologies of OFDM system. In this paper, the global search Capon algorithm is improved, and a local search Capon algorithm is proposed. Simulation results show that the algorithm has low complexity and high performance. In the local search, P spectral peaks are superimposed, which can effectively overcome the problem that the estimation performance of traditional Capon algorithm is seriously reduced due to the unapparent spectral peaks or the missing spectral peaks in the case of low SNR., and it has a good application prospect in power wireless OFDM communication system. Since contemporary information-retrieval systems rely heavily on the content of titles and abstracts to identify relevant articles in literature searches, great care should be taken in constructing both.

MIMO–OFDM communication systems for traffic data transmission in 5G drone small cells

A compressed sensing-based channel estimation (CE) method is proposed for doubly selective channels whilst multiple-input multiple-output (MIMO)–orthogonal frequency-division multiplexing (OFDM) system is employed. According to the simulation results, the proposed CE method, which is dubbed as the MIMO-linearising scheme performs better than the basic expansion model (BEM), which is a state-of-the-art CE method and applies frequency domain scattered pilots. Furthermore, MIMO-linearising can be utilised as an accurate procedure for estimating only the positions of non-zero channel taps in the scenarios where those positions change with a slower rate than amplitudes and phases of the channel taps. Based on that priori estimated positions (PEPs), modified versions of the linearising scheme and the BEM methods, called MIMO-linearising-PEP and BEM-PEP, respectively, are described, showing improvement on performance and spectral efficiency. In addition, by considering the physical characteristic of the vehicular channels, an alternative version of the MIMO-linearising-PEP, called MIMO-linearising-efficient, is described to reduce the computational complexity and increase the spectral efficiency further. Simulation results indicate that the proposed CE methods can measure the channel more accurately and enhance the car detection accuracy in the frames which have been used as the inputs of the communication systems.

Receiver Algorithms for Single-Carrier OSM Based High-Rate Indoor Visible Light Communications

In intensity-modulation and direct-detection (IM/DD) multiple-input and multiple-output (MIMO) visible light communication (VLC) systems, spatial subchannels are usually correlated, and spatial modulation is a good choice to achieve the advantages of MIMO technology. Peak-to-average power ratio (PAPR) is a key issue in VLCs due to the limited linear dynamic range of light emitting diodes (LEDs). Single-carrier communication systems have a lower PAPR than orthogonal frequency division multiplexing (OFDM) communication systems. However, it is challenging to design a single-carrier spatial modulation for high-rate transmissions because of the time domain intersymbol interference. This paper develops an optical spatial modulation (OSM) scheme based on bipolar pulse amplitude modulation (PAM) and spatial elements for high-rate indoor VLC systems. Multiple data streams can be transmitted simultaneously in the proposed scheme. Based on the transmit strategy, we develop a low-complexity receiver algorithm that achieves better bit-error rate performance than reference schemes, and the proposed OSM scheme has a much lower PAPR than OFDM based OSM schemes. When the spatial subchannels are highly correlated, a spatial area division strategy is applied, and the receiver algorithm is investigated. The symbol-error rate expression of the proposed OSM scheme is derived, and the computational complexity is analyzed.

Chaotic-precoder based PAPR reduction in MIMO SFBC-OFDM

ABSTRACT This letter demonstrates the chaotic precoding approach in multiple-input multiple-output space frequency block coded orthogonal frequency division multiplexing (MIMO SFBC-OFDM) communication systems as an appropriate solution for peak-to-average power ratio (PAPR) reduction. Firstly, we have proposed four cascades chaotic generators (CCGs) by using at each time two conventional one dimension (1D) chaotic maps in series. We further proposed a hybrid chaotic system (HCS) based on combination of three 1D maps. Simulation results show that HCS-based precoded MIMO SFBC-OFDM system can achieve better PAPR reduction performance and lower bit error rate (BER) compared to conventional MIMO SFBC-OFDM systems, with less computational complexity and without side information requirement.