Orthogonal Frequency Division Multiplexing Technique Research Articles

A multilayers adaptive ALACO-OFDM for spectral efficiency improvement using PSO algorithm in visible light communication systems

Abstract In this paper, we propose a new adaptive layered asymmetrically-clipped optical orthogonal frequency division multiplexing (ALACO-OFDM) technique as a method to improve the spectral efficiency of optical system, especially visible light communication (VLC). Particle swarm optimisation (PSO)-based LACO-OFDM method is used for this purpose and the channel capacities are studied. Simulations using variable layers are carried out to validate the theoretical steps. The simulation results indicate that the ALACO-OFDM technique has significantly improve the spectral efficiency compared to previous techniques such as ACO-OFDM. Moreover, it is shown that channel capacities of different layers are significantly improved when electrical power is increased.

PAPR reduction scheme for optical OFDM techniques

Abstract In both optical wireless and optical fiber communication, orthogonal frequency division multiplexing (OFDM) plays an important role in data transmission. In the similar context, DC-coupled optical (DCO) OFDM and asymmetrically clipped optical (ACO) OFDM are discussed. DCO-OFDM has better peak to average power ratio (PAPR) but bit error rate (BER) performance is poor; however, in case of ACO-OFDM, PAPR is poor but BER performance is good. Moreover, DCO-OFDM is more power hungry; therefore, ACO-OFDM is considered as a preferred choice. Recently, asymmetrically clipped DC-biased optical (ADO)-OFDM is proposed, which shows good PAPR and BER performance. Clipping and µ-law companding techniques are discussed for PAPR reduction. The mathematical model is developed for all the three methods for received signal while considering clipping and companding noises along with channel noise. It is found that ADO-OFDM is better choice in comparison to DCO and ACO-OFDM. However, in case of ADO-OFDM, receiver structure is more complex.

Performance analysis of hybrid SAC-OCDMA-OFDM model over free space optical communication

Recently, free space optical (FSO) communication network has gained popularity because of its unlicensed spectrum, high data rate, low power consumption and ease of installation. Spectral amplitude coded optical code division multiple access (SAC-OCDMA) technique has become significant because of enhanced network capacity, privacy, and simultaneous use of multiple asynchronous users. However, the climatic turbulence causes signal fluctuations and degrades the quality of the received signal. Therefore, to improve the quality of the received signal in this work, SAC-OCDMA technique is integrated with orthogonal frequency division multiplexing (OFDM) technique and performance of such hybrid model is investigated. Two SAC-OCDMA codes are proposed in this work referred as triangular matrix-zero cross correlation (TM-ZCC) and pulse shifting substitution-zero cross correlation (PSS-ZCC) codes. The hybrid model uses the novel one dimensional (1D) SAC-OCDMA codes with two different types of receivers such as modified AND (M-AND), and single photodiode detection (SPD) receivers over Gamma-Gamma fading channel to evaluate the bit error rate (BER) performance of the proposed hybrid model. It is observed from the simulation results that the hybrid SAC-OCDMA-OFDM model with SPD detection receiver performs better in terms of bit error rate (BER) than that of M-AND detection receiver. Furthermore, it is also observed from the simulation results that the hybrid model based on the proposed TM-ZCC code performs better than the proposed PSS-ZCC code in terms of BER and higher FSO distance coverage. The performance of the proposed model is estimated for 20 and 30 active users simultaneously at various data rates. The TM-ZCC and PSS-ZCC codes are generated using MATLAB platform and the proposed hybrid SAC-OCDMA-OFDM model is validated using optisystem version 15 over the Gamma-Gamma fading channel.

The intrapulse beamsteering radar based on OFDM Chirp signals

The OFDM (Orthogonal Frequency Division Multiplexing) technique is widely used in communication field due to the great waveform diversity and anti-fading ability of OFDM signals. Because of the similarity of radar system and communication system, The OFDM radar has gradually emerged as a new system radar in recent years. At the same time, Intrapulse beamsteering system is a kind of multi-dimensional waveform encoding, which can improve the transmitting efficiency and multi-mission performance of radar. So, this paper proposes a new radar operating mode with the combination of the OFDM chirp signals and the intrapulse beamsteering in elevation, that is the combination of waveform orthogonality and beam orthogonality, we can also call it “double insurance”, which can greatly improve the emission efficiency and the system performance. Especially the interference suppression and the robustness to terrain undulation. The simulation results at the end of the paper prove the feasibility and advantages of the proposed operating mode.

Analysis of DCO-OFDM for Indoor Visible Light Communications

A novel orthogonal frequency division multiplexing (OFDM) technique called DC-biased optical OFDM (DCO-OFDM) as-applied to indoor visible light communication (VLC) systems was analysed in this study. Line-of-sight (LOS) and non-LOS (NLOS) models were assumed and the luminance intensity and multipath dispersion of a single reflection were measured for indoor LOS and NLOS models; 1-dB and 3-dB DC biases were applied to DCO-OFDM with 4-, 64-, or 128-QAMs for BER analysis, respectively. The quantity of lighting equipment appropriates for communication based on the model room was determined, as well as the optimal number of sources dependent on illuminance, mean density of pedestrians, room model. The results showed that as M and DC bias values increase, SNR grows excessively (about 2.5 dB) in the LOS model. Reflection, additionally, has a severe impact on BER in NLOS conditions (nearly 10−3) regardless of M or DCdB value. Compared to the LOS model, the NLOS model requires a loss of about 12 dB of DCO-OFDM SNR.

Overlap-Save FBMC Receivers

Future communication systems are foreseen to support several services with different requirements. Waveform designs based on filter-bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) can offer interesting advantages in this context, such as low out-of-band power leakage and high spectral efficiency due to the lack of guard intervals. However, downsides of FBMC/OQAM with respect to a typical orthogonal frequency-division multiplexing (OFDM) solution include higher latency, higher complexity and difficulties in adapting some existing OFDM techniques such as MIMO Alamouti. To address these issues, novel FBMC receivers suitable for short prototype filters are proposed. Based on the Overlap-Save algorithm, the proposed receivers improve error-rate performance on multipath channels and support asynchronous communication. We show that complexity can be further reduced by efficiently processing blocks of FBMC symbols jointly, and that user mobility support can be traded off for additional complexity reductions in a flexible way through polynomial decomposition of the equalizer stage. Finally, we show that a block-Alamouti scheme can be applied, and we propose a MIMO equalizer with improved error-rate performance on time-varying channels, compared to the typical FBMC block-Alamouti equalizer.

LDPCC and OFDM based cooperative communication for wireless sensor networks

This paper investigates the low-density parity-check codes and orthogonal frequency division multiplexing technique effects on the relay assisted sensor networks. The investigation utilizes Rician and Rayleigh fading environments for the performance analysis. The investigation also considers two different types of information exchange processes, which are direct and relay assisted cases. In the relay assisted case, the relay terminal operates in amplify-and-forward and decode-and-forward modes. Monte-Carlo based computer simulations reveal that 10-5 bit error rate value is reached at 16.50 dB for low density parity check coded orthogonal frequency division multiplexing over Rician fading environment in decode-and-forward relay protocol. Similarly, 10-5 bit error rate value is reached at 0.36 dB for the low density parity check coded orthogonal frequency division multiplexing over Rician fading environment in amplify-and-forward relay protocol and finally 10-5 bit error rate value is reached at -5.30 dB for low density parity check coded orthogonal frequency division multiplexing over Rician fading environment without relay protocols.

Non-Contact Sensing Testbed for Post-Surgery Monitoring by Exploiting Artificial-Intelligence

Non-contact health care monitoring is a unique feature in the emerging 5G networks that is achieved by exploiting artificial intelligence (AI). The ratio of the number of health care problems and patients is increasing exponentially and creating burgeoning data. The integration of AI and Internet of things (IoT) systems enables us to increase the huge volume of data to be generated. The approach by which AI is applied to the IoT systems enhances the intelligence of the health care system. In post-surgery monitoring of the patient, timely consultation is essential before further loss. Unfortunately, even after the advice of the doctor to the patient, he/she may forget to perform the activity in the correct way, which may lead to complications in recovery. In this research, the idea is to design a non-contact sensing testbed using AI for the classification of post-surgery activities. Universal software-defined radio peripheral (USRP) is utilized to collect the data of spinal cord operated patients during weight lifting activity. The wireless channel state information (WCSI) is extracted by using orthogonal frequency division multiplexing (OFDM) technique. AI applies machine learning to classify the correct and wrong way of weight lifting activity that was considered for experimental analysis. The accuracy achieved by the proposed testbed by using a fine K-nearest neighbor (FKNN) algorithm is 99.6%.

Compensation of Non-linear Distortion Effects in MIMO-OFDM Systems Using Constant Envelope OFDM for 5G Applications

Orthogonal frequency division multiplexing (OFDM) is a multicarrier transmission system that can achieve high data rate over wireless channels. At the same time, multiple input multiple output OFDM (MIMO-OFDM) in wireless communication systems has been exposed to offer significant improvement over wireless technology by providing transmit diversity. It has become a promising technique for high-performance 5G broadband wireless communications. However, the main problem associated with MIMO-OFDM is that its signal exhibits high peak-to-average power ratio (PAPR), which causes nonlinear distortion and consequently performance degradation. Besides, PAPR carries weaknesses such as an increase in power consumption of high power amplifier (HPA) and analog to digital converter (ADC). Thus, 5G base stations will push up power requirements because energy consumption grows with the number of transceiver elements. So, mobile operators must find the right compromise that, on the one hand, guarantees a certain level of performance to a data flow, and, on the other hand, the energy cost generated for the deployment of the network. For this, as part of the management of power consumption, we propose MIMO constant envelope OFDM (MIMO-CE-OFDM) technique. In this work, we used MIMO-CE-OFDM to mitigate the nonlinear effect of HPA and ADC. To perform practical simulations, we have used COST 2100 MIMO channel model. In this paper, a MIMO-CE-OFDM system has been presented and analyzed under COST 2100 channel model conditions. Simulation results are given to illustrate the performance of [Formula: see text] MIMO-CE-OFDM in the presence of both HPA and ADC nonlinearity. This work shows that the effect of nonlinearity is shown to be negligible on MIMO-CE-OFDM signal.

MDW and EDW/DDW codes with AND subtraction/single photodiode detection for high performance hybrid SAC-OCDMA/OFDM system

In this paper, a hybrid system is introduced using orthogonal frequency division multiplexing (OFDM) technique with spectral amplitude coding optical code division multiple access (SAC-OCDMA). In this system, the AND subtraction detection is used with the modified double weight (MDW) and enhanced double weight (EDW) codes, in addition to the single photodiode detection with the diagonal double weight (DDW) code. The proposed system achieves performance enhancement in the performance enhancement concerning the maximum allowable number of users, signal to noise ratio and (minimum) bit error rate (BER) $${\Re}$$. The proposed codes that used with AND subtraction detection techniques are: MDW and EDW, while the DDW codes are used with single photodiode detection (SPD). Detection techniques are investigated to reduce the effect of both the multiple access interference and phase induced intensity noise. A comparison is performed between the conventional SAC-OCDMA systems and OFDM with SAC-OCDMA. The obtained results reveal that OFDM with SAC-OCDMA gives better performance than conventional SAC-OCDMA. OFDM with SAC-OCDMA using DDW code with SPD detection can support a high bit rate up to 10 Gbps for 70 users with a BER of 10–9.

FSO-Based Analysis of LTE-A MAC Protocols to Achieve Improved QoS

Abstract Fiber wireless (Fi-Wi) communication network is the amalgamation of optical and wireless access networks, which provides better bandwidth for achieving efficient data transmission. Medium access control (MAC) protocols are used in the wireless network for controlling the data flow from the transmitter to the receiver end. The delay produced by these protocols tells about the system efficiency. This paper shows a Fi-Wi system in the long-term evaluation-advanced (LTE-A) environment, which incorporates the dependency of delay generated by the specific MAC protocols during the transmission process. This paper aimed to scrutinize the effects of Carrier Sense Multiplexing Access with Collision Detection (CSMA/CD), Carrier Sense Multiplexing Access with Collision Avoidance (CSMA/CA) and Slotted ALOHA on the performance of the Fi-Wi system. Free space optical (FSO) channel is incorporated to forward the data to user end. In such system, the optical signal is multiplexed using the Orthogonal Frequency Division Multiplexing (OFDM) technique and finally the data are fetched at the receiver end and different criterions such eye-height, Q-factor and bit error rate are evaluated. Simulation results are performed using MATLAB software. The comparative analysis is also performed in terms of data transmission efficiency, delay and throughput of MAC protocols. This shows the effective results of the proposed system according to the delay produced by MAC protocols.

20Gbit/s-40 GHz OFDM based LEO-GEO Radio over Inter-satellite optical wireless communication (Ro-IsOWC) system using 4-QAM modulation

This work discusses the modeling and the numerical investigation of Ro-IsOWC link between a low earth orbit LEO and geosynchronous earth orbit GEO satellite. 4-level quadrature amplitude modulation 4-QAM signal with orthogonal frequency division multiplexing OFDM technique has been used to transmit high-speed data between two satellites separated at 35,000 km link distance in outer space. The proposed link performance has been numerically evaluated under the impact of operating wavelength, transmission distance, input power, pointing errors, additional losses, and receiver aperture diameter. Signal-to-noise ratio SNR and received electrical power of the information signal are considered as the performance metrics to evaluate the link performance. Through numerical simulations, we report a successful transportation of 20Gbit/s-40GHz information between two satellites over a transmission distance of 35,000 km using the proposed Ro-IsOWC system. Also, an improved link performance has been investigated in this work by using a Square root module SRm technique at the receiver terminal for non-linearity compensation.

Very High-Performance Echo Canceller for Digital Terrestrial Television in Single Frequency Network

The principal aim of this paper is to cancel out the natural and man-made echoes in single-frequency networks (SFN). The challenge is to detect and remove feedback echoes and enhance the intelligibility of the essential parameters in SFN of digital terrestrial television broadcasting (DTTB) transmitter systems, especially the Modulation Error Ratio (MER), with optimizing coverage areas. We suggest a Digital Video Broadcasting (DVB) gap filler (GF) with two types of echo cancelling: Digital Adaptive Equalizer (DAE) and Doppler Enhanced Echo Canceller (DEEC). The proposed GF outperforms standard GF (SGF), finite impulse response filter (FIR GF), and adaptive GF (AGF) techniques by 33%, 17%, and 13%, respectively. Furthermore, the obtained MER makes the proposed GF (PGF) ideal for operating in SFN using Coded Orthogonal Frequency Division Multiplex (COFDM) technique.

Underwater Acoustic Communication Using OFDM Technique in Simulink Environment

The paper contains modeling and simulation of Orthogonal Frequency Division Multiplexing (OFDM) technique for under water acoustic communication. Speed of sound inside water is 1500 m/s which causes large delay spread due to multipath propagation and also fading effect can be observed which gives birth to interference. Orthogonal frequency division multiplexing reduces long delay spread due to low data rate of subcarriers and hence Inter Symbol Interference (ISI) can be eliminated. Also the orthogonality of subcarriers reduces Inter Carrier Interference (ICI). The objective of the paper is to improve the performance of OFDM in underwater environment by the use of interleaver. Also the effect of coding is observed. The model was simulated in MATLAB Simulink and the results are presented.

Symbol Level Precoding With Low Resolution DACs for Constant Envelope OFDM MU-MIMO Systems

In Constant Envelope Symbol Level Precoding (CESLP), the transmitted signals by the antennas have constant amplitude regardless of the channel realization and the conveyed information symbols. Such solutions enable the use of power-efficient components, i.e. non-linear power amplifiers and thus, are suitable for systems based on large-scale antenna arrays. In the latter systems, the hardware complexity and power consumption can be limiting factors since each antenna element requires dedicated hardware components. These components include the Digital-to-Analog Converters (DACs) that have exponential complexity and power consumption with the number of the supported resolution. To that end, in this paper, a CESLP precoding technique is presented for Multi-User Multiple Input-Multiple Output (MU-MIMO) systems with low resolution DACs. The case of a multi-carrier system employing the well-known Orthogonal Frequency Division Multiplexing (OFDM) technique is considered. The precoding design problem is formulated as a mixed discrete-continuous least-squares optimization one which is NP-hard. An efficient low complexity solution is developed based on the Cyclic Coordinate Descent (CCD) optimization framework. Simulations show that the proposed solution is able to achieve very close performance to the one of the infinite resolution CESLP precoding counterpart even though, it is based on DACs that have resolution of only a few bits.

Performance Improvement of OFDM Systems by Reducing Papr using SLM-Grasshopper Optimization

Orthogonal Frequency Division Multiplexing (OFDM) is an emerging technology which is been most commonly used for transmission of data in wireless based systems. The OFDM technique is capable of achieving more speed i.e it has higher data rate transmission which is reliable and efficient. Peak power is the major drawback while transmitting the signal which is termed as PAPR. The signals achieves high peak value while transmitting due to the presence of large subcarriers which are independent in nature. The amplitude of the signal need to be reduced. Many PAPR reductions schemes have been presented in past and the reduction is done to some extents. In this paper , a new optimisation technique i.e grasshopper optimization (GOA) is proposed. The optimization technique is combined with one of the efficient PAPR reduction technique i.e selective mapping technique. The combination of SLM-Grasshopper help in reducing the PAPR as low as possible and is also compared with other techniques like SLM-GA, SLM-FA and SLM-GWO. The experimental results are performed using matlab.

Autocorrelation Method for Cyclic Prefix OFDM Estimation

A radio system design providing various data service needs becomes one of the Software Defined Radio (SDR) system advantages. SDR technology applies software functions further to be run in hardware platforms. The need for services with greater data rates can be resolved by using multi-carrier transmission techniques, one of which is the Orthogonal Frequency Division Multiplexing (OFDM) technique. This paper discusses the detection of OFDM signals and their parameters. Multi-carrier transmission can prevent Inter-Symbol Interference (ISI) occurrence due to multi-path fading effect. The recognition can classify the correctly received signals, including the signal conditions mixed with AWGN noise. The autocorrelation method was used to estimate the OFDM parameters, namely the one symbol duration and the cyclic prefix duration. The detected cyclic prefix durations were 1/2, 1/4, 1/8, and 1/16. This method is very simple, because with the cyclic prefix presence, a different signal peak will be detected to further estimate the cyclic prefix duration. The results show the correlation method performance can detect one symbol duration with 100%, accuracy, starting at SNR 0 dB, whereas the cyclic prefix duration accuracy rate is getting more accurate by using a less cyclic prefix duration, which is 1/16 of the total symbol duration.

An Underwater Acoustic OFDM System Based on NI CompactDAQ and LabVIEW

Recently the orthogonal frequency division multiplexing (OFDM) technique has attracted increasing interests in underwater acoustic (UA) communications. In this paper, we present an OFDM-based UA communication system, which is designed based on the National Instruments LabVIEW software and the CompactDAQ device. Details on both the transmitter and receiver system design are discussed. The performance of this UA OFDM system is verified through recent UA communication experiments performed in a tank, in the Canning River, and in the estuary of the Swan River, Western Australia. Experimental results show that the system achieves a reliable bit error rate performance even with high-order modulation schemes. Compared with conventional field-programmable gate array and digital signal processor based designs, the proposed implementation simplifies the prototype design process and reduces the software development time. The proposed system provides a flexible and reconfigurable prototype for researchers to test and validate the performance of UA communication algorithms in real UA channels.

Implementation of Polar Codes in 5G Systems with Different Waveform Modulations by Using USRP

Long Term Evolution (LTE) is an access technique that is used in radio networks. LTE provides high data bandwidth in transmitting data by providing flexibility against noise and interference. Orthogonal Frequency Division Multiplexing (OFDM) technique uses the FDM (Frequency Division Multiplexer) modulation technique to increase the amount of carried information over the wireless network. The OFDM signal is transmitted to the receiver at different frequencies which they are orthogonal to each other by dividing the bandwidth of a signal into smaller sub-carriers. Recently, the use of polar codes as a coding scheme in the new generation 5G systems has come to the communications markets. Polar codes as a channel coding scheme are a promising technique for the future because it is the first codes that reach Shannon capacity limit. The cyclical prefix – OFDM (CP-OFDM), which is used in 4G systems, performs well in many aspects, however, it has much weakness that make the researches look for a new modulation technique to be used in 5G systems. Filtered–OFDM (F-OFDM) is considered one solution to the problems appeared in CP–OFDM. In this paper, the differences between CP-OFDM and F-OFDM regarding advantages and disadvantages of each type are studied in details. The comparison between the two modulations waveforms are done by studying their Error Vector Magnitude (EVM) that deals with measuring the accuracy of the received signals. Furthermore, the comparison between the two modulations waveforms with polar codes in the USRP B210 radio are applied to make our work more practical.

Simple 2D chaotic remapping scheme for securing optical communication networks

In this work, a simple and new method is proposed to simultaneously improve the physical layer security and the transmission performance of the optical orthogonal frequency division multiplexing system, by combining orthogonal frequency division multiplexing technique with chaotic theory principles. In the system, a 2-D chaotic map is employed. The introduced system replaces complex operations such as matrix multiplication with simple operations such as multiplexing and inverting. The system performance in terms of bit error rate (BER) and peak to average ratio (PAPR) is enhanced. The system is simulated using Optisystem15 with a MATLAB2016 and for different constellations. The simulation results showed that the BER of an unauthorized receiver reaches 0.5. Furthermore, the peak-to-average-power-ratio (PAPR) of the transmitted OFDM signal can be decreased by about 0.8 dB at BER equal to 10^-4.