Design Of Orthogonal Frequency Division Multiplexing Research Articles

Waveform Design with Constellation Extension for OFDM Dual-Functional Radar-Communications

Orthogonal frequency division multiplexing (OFDM) is widely used and works efficiently for the communication, but emerging applications requires OFDM to be flexible to meet sensing requirements. The time-frequency waveform design of OFDM for dual-functional radar-communications (DFRC) is critical to achieve the future communication and sensing requirements. Therefore, we propose a novel method to minimize Cramér-Rao bounds (CRBs) of the delay and Doppler estimation to improve radar performance of an OFDM DFRC system. Although some methods are proposed in the literature to improve the CRBs, these methods either require feedforward signaling or subcarrier reservation. However, it is possible to exploit the constellation extension of quadrature amplitude modulation (QAM) to achieve lower CRBs without these requirements. Therefore, the proposed method provides a transparent communication along with the CRB minimization for conventional OFDM systems. For the evaluation of the proposed method, CRB and symbol error rate (SER) are considered in the simulation results. Furthermore, the theoretical SER analysis of the proposed method is derived to understand the effects of CRB minimization on the communication performance.

Design of Offset Spatial Modulation OFDM

In this paper, the idea of offset spatial modulation (OSM) is integrated with orthogonal frequency division multiplexing (OFDM), toward an efficient design to bridge their advantages. Compared to its conventional counterpart as spatial modulation (SM)-OFDM, the proposed OSM-OFDM scheme aims at providing a simplified implementation structure with less number of radio frequency (RF) chains, by introducing an offset between the RF chain and the index of the activated transmit antenna on each subcarrier. Specifically, three types of offset antenna selection (OAS) methods are developed to meet different scene requirements for different number of available RF chains. Furthermore, through theoretical analysis, we quantify the bit error rate upper bounds of OSM-OFDM with different types of OAS methods. Finally, extensive computer simulations demonstrate that OSM-OFDM provides a flexible tradeoff among implementation cost, computation complexity and error performance.

Hybrid beamforming design for mmWave OFDM distributed antenna systems

This paper presents a hybrid beamforming design for millimeter-wave (mmWave) orthogonal frequency division multiplexing (OFDM) distributed antenna systems (DASs). First, we derive a downlink signal transmission model that considers the delay spread differences (DSDs) caused by the distributed nature of the network. We then propose a cooperative wideband hybrid beamforming method under the transmitting power constraints of each remote access unit. In a simulation study, the proposed method performed comparably to fully-digital beamforming, even when operated with practical finite-resolution phase shifters. We further confirm that the DSDs are the dominant cause of performance degradation in mmWave OFDM DASs.

Information theoretic waveform design for OFDM radar‐communication coexistence in Gaussian mixture interference

In this study, mutual information (MI)-based waveform design methods for the coexistence between orthogonal frequency division multiplexing (OFDM) radar system and communication system corrupted by Gaussian mixture interference are investigated for the first time. Firstly, the received signal is formulated as a Bayesian linear model. Subsequently, from a statistical perspective, the approximate differential entropy of received signal is derived, followed by three different approximate MIs and corresponding theoretic upper bounds. After that, two adaptive waveform design methods are proposed by maximising MI and minimising radar transmitted power, respectively. The numerical results show that exploiting the reflected communication signals helps to obtain higher MI value and reduce radar transmitted power. Besides, by maximising the MIs, the optimised radar waveforms remarkably outperform the fixed ones, which benefits the estimation performance.

Enhancing Performance of Orthogonal Frequency Division Multiplexing (OFDM) Based On Fast Fourier Transform (FFT) In Wireless Communication System

Orthogonal Frequency Division Multiplexing (OFDM) is one of the multicarrier transmission techniques used in wireless communication system. It has many benefits such as robust in channel fading and has high spectral density. The main objective of OFDM implementation in wireless communication system is to achieve less or zero Bit Error Rate (BER). However, OFDM design complexity, requirement and selection of the suitable modulation method are among the current issues. Thus, this paper aims to investigate the performance of OFDM in wireless communication by developing two OFDM based system designs. The transmitter, channel and receiver are designed based on OFDM system principles. Forward Error Correction (FEC) method is applied to reduce the BER. Both OFDM designs produce less BER with zero BER for the second OFDM design. The investigation study shows that the performance of OFDM can be enhanced by applying Fast Fourier Transform (FFT) technique. Zero BER can be achieved if the suitable modulation scheme is applied in the system. The developed designs are not complex, suitable to be applied for IEEE 802.11 standard. The BER performance can be influenced by the types of channels, signal to noise ratio (SNR) and various modulation schemes. Thus, this study can be used as a guidance to implement the OFDM in the current or future wireless communication system.

Design and Simulation of OFDM for BPSK, QPSK and QAM with Peak Power Reduction Using Clipping Technique

Abstract Due to the increase in demand for high data rates in mobile communication, orthogonal frequency division multiplexing (OFDM) system is employed in many applications. It efficiently overcomes the effect of Inter-symbol Interference caused due to the fading of the channel, but Peak to Average Power Ratio (PAPR) is unitary of the disadvantages in OFDM System. In the stage-I, the OFDM system is designed with different modulation schemes like QAM-16, BPSK, and QPSK. In the latter stage, we work on the reduction of PAPR by using a clipping technique and we establish a significant reduction in PAPR as compared to the conventional clipping technique.

Design and Performance Analysis of OFDM and FBMC Modulation Techniques

Abstract Researchers have already proved that data consumption in coming years will increase by leaps and bounds, so the present technologies like 3G, OFDM (Orthogonal Frequency Division Multiplexing) cannot hold the addition of huge capacitance, data use and demand of high data-rate. Hence, on that point is a necessity of fifth generation mobile communication system (5G). Presently the rollout for 5G is going virtually everywhere in the world and among several issues; selection of better modulation techniques is seen as unitary of the significant issues in the implementation of the 5G. In this work, we designed and analyse the performance of OFDM and FBMC (Filter Band Multi Carrier) multicarrier modulation schemes on the basis of Bit Error rate (BER) and Signal to Noise Ratio (SNR). Simulation results and mathematical analysis have confirmed that the performance and spectrum utilization of FBMC is better or equivalent as compared to OFDM, which can be very useful in next generation mobile communication and Internet of Things (IOT).

Multiobjective optimal waveform design for OFDM integrated radar and communication systems

To improve the availability of limited spectral resources and construct a cost-efficient platform simultaneously performing both radar and communication functions, the orthogonal frequency division multiplexing (OFDM) integrated radar and communication system (IRCS), which is referred to as OFDM-IRCS, is provided. For the frequency sensitive target and frequency selective fading channel, it is able to improve the radar and communication performance by efficiently employing the limited transmit power in the OFDM-IRCS. To this end, we propose two optimal waveform design methods that meet different users’ demands. First, the Cramér-Rao bounds (CRBs) for estimating range, velocity and target scattering coefficients with integrated OFDM waveform are derived. And the channel capacity in communication is formulated. Then, the multiobjective optimization problem is devised, and the adaptive weighted-optimal and Pareto-optimal waveform design approaches are proposed to simultaneously improve the estimation accuracy of range and velocity in radar and the channel capacity in communication. Finally, several numerical examples are presented to demonstrate the effectiveness of the proposed design methods.

Analysis of Timing and Frequency Offset Estimation of OFDM System using Scaled Precision Model

Orthogonal Frequency-Division Multiplexing (OFDM) is a robust multi carrier modulation system most commonly used in many wireless communication standards. The overall OFDM system performance is stable over signal distortions caused by multipath fading channels but synchronization problems caused significant quality degradation at receiver side. In recent years many papers have been published to mitigate this synchronization problem still the overall system performance is getting worsened due error caused by fixed point model. In this paper we analyzed the limitations of the fixed point computations in timing and frequency offset estimation and its performance in terms of error rate. Here we carry out both analytical approach and statistical results obtained through extensive numerical simulations and the bit length of floating point IEEE 754 standard single precision formats is optimized with the required degree for an accurate offset estimation to reduce OFDM design complexity. Also, a unique floating point precision model for error less FFT computations for all mapping levels used in OFDM system. The proposed scaled floating point precision model is compared over full precision model and its efficiency against fixed point model in OFDM synchronization process is proved through MATLAB simulations. Finally through FPGA hardware synthesis the complexity reduction of proposed scaled precision model is proved in basic arithmetic models such as adder and multiplier against single precision format. Here we proved the resource utilization rate is reduced by half as compared to standard full precision models without compromising any quality degradations. The computational error free nature of proposed scaled precision model in both timing and frequency offset estimation process and its overall OFDM system performance in terms of BER rate is proved.

A Wavelet Multiplexing to Reduce Phase Noise Effects in OFDM based DVB-t

Orthogonal Frequency Division Multiplexing (OFDM) is a highly recommended multiplexing/modulation scheme for high data rate communications due to its high spectrum efficiency and robustness against Inter Symbol Interference (ISI). The OFDM is based on dividing the available spectrum into narrow band orthogonal subcarriers and modulating data on each subcarrier. Due to long symbol period, OFDM system is more sensitive to phase noise of the oscillator compared to single carrier systems. The Phase noise of oscillators used in the transmitters & receivers results in two effects, Common Phase Error (CPE) & Inter Carrier Interference (ICI). These effects results in increasing SNR requirement at the receiver to achieve certain BER. The design & simulation of OFDM based DVB-t system with wavelet multiplexing & demultiplexing and analysis of phase noise effects on BER is presented in this paper. The performance of simulated DVB-t system is analysed by considering SNR requirement to achieve certain BER in the presence of oscillator instabilities on AWGN & mobile radio channels. The modelled Wiener phase noise is generated for different 3dB bandwidths of noise spectrum. The simulation results shows that, the SNR required to achieve a bit rate of 10-2 in wavelet multiplexing is around 6dB lower as compared to FFT counterpart. The result also reveal that PAPR is also less, however wavelet multiplexing computational intensive.

Filter-and-Forward Transparent Relay Design for OFDM Systems

In this paper, the filter-and-forward (FF) relay design for orthogonal frequency-division multiplexing (OFDM) transmission systems is considered for improving system performance over simple amplify-and-forward (AF) relaying. Unlike conventional OFDM relays performing OFDM demodulation and remodulation, to reduce processing complexity, the proposed FF relay directly filters the incoming signal in the time domain with a finite impulse response (FIR) and forwards the filtered signal to the destination. Three design criteria are considered for optimizing the relay filter. The first criterion is the minimization of the relay transmit power subject to per-subcarrier signal-to-noise ratio (SNR) constraints, the second criterion is the maximization of the worst subcarrier channel SNR subject to source and relay transmit power constraints, and the third criterion is the maximization of the data rate subject to source and relay transmit power constraints. It is shown that the first problem reduces to a semi-definite programming (SDP) problem by semi-definite relaxation (SDR), and the solution to the relaxed SDP problem has rank one under a mild condition. For the latter two problems, the problem of joint source power allocation and relay filter design is considered, and an efficient algorithm is proposed for each problem based on alternating optimization and the projected gradient method (PGM). Numerical results show that the proposed FF relay significantly outperforms simple AF relays with an insignificant increase in complexity. Thus, the proposed FF relay provides a practical alternative to the AF relaying scheme for OFDM transmission.

Power Allocation and Time-Domain Artificial Noise Design for Wiretap OFDM with Discrete Inputs

Optimal power allocation for orthogonal frequency division multiplexing (OFDM) wiretap channels with Gaussian channel inputs has already been studied in some previous works from an information theoretical viewpoint. However, these results are not sufficient for practical system designs. One reason is that discrete channel inputs, such as quadrature amplitude modulation (QAM) signals, instead of Gaussian channel inputs, are deployed in current practical wireless systems to maintain moderate peak transmission power and receiver complexity. In this paper, we investigate the power allocation and artificial noise design for OFDM wiretap channels with discrete channel inputs. We first prove that the secrecy rate function for discrete channel inputs is nonconcave with respect to the transmission power. To resolve the corresponding nonconvex secrecy rate maximization problem, we develop a low-complexity power allocation algorithm, which yields a duality gap diminishing in the order of O(1/√N), where N is the number of subcarriers of OFDM. We then show that independent frequency-domain artificial noise cannot improve the secrecy rate of single-antenna wiretap channels. Towards this end, we propose a novel time-domain artificial noise design which exploits temporal degrees of freedom provided by the cyclic prefix of OFDM systems to jam the eavesdropper and boost the secrecy rate even with a single antenna at the transmitter. Numerical results are provided to illustrate the performance of the proposed design schemes.

A Radon-Multiwavelet Based OFDM System Design and Simulation Under Different Channel Conditions

Finite Radon transform (FRAT) mapper has the ability to increase orthogonality of sub-carriers, it is non sensitive to channel parameters variations, and has a small constellation energy compared with conventional fast Fourier transform (FFT) based orthogonal frequency division multiplexing (OFDM). It is also able to work as a good interleaver which significantly reduces the bit error rate (BER). Due to its good orthogonality, discrete Multiwavelet transform (DMWT) is attractive for implementation in OFDM systems which reduces inter-symbol interference (ISI) and inter-carrier interference (ICI) and eliminates the need for cyclic prefix and increases the spectral efficiency of the design. In this paper both FRAT and DMWT are implemented in a new design for OFDM. The new structure was tested and compared with conventional FFT-based OFDM, Radon-based OFDM, and DMWT-based OFDM for additive white Gaussian noise channel, flat fading channel, and multi-path selective fading channel. Simulation tests were generated for different channels parameters values. The obtained results showed that proposed system has increased spectral efficiency, reduced ISI and ICI, and improved BER performance compared with other systems.

Design of Multicarrier OFDM Modulator/Demodulator Based on Discrete Hartley Transform

In this paper, a novel orthogonal frequency-division multiplexing (OFDM) modulator/demodulator based on real-valued discrete Hartley transform (DHT) is presented and implemented for the IEEE 802.11a/g wireless local area network (LAN). Instead of the conventional complex-valued fast Fourier transform (FFT) for OFDM systems, the proposed architecture employs two real-valued fast DHT (FHT) kernels and one post processing unit. By taking advantage of the real-valued operation of FHT, this approach reduces the number of multiplications compared with the radix-2 FFT. The proposed DHT-based modulator/demodulator was designed and fabricated in 0.18-µm CMOS technology with a core area of 928 × 935µm2. The average power consumption is about 20.16mW at 20MHz and 1.8V supply voltage. Measurement results of the integrated circuit illustrate its superior chip area and power consumption.

Pilot design for OFDM with null edge subcarriers

Pilot symbol assisted modulation (PSAM) orthogonal frequency division multiplexing (OFDM) has proven to be a popular technique for high-speed communication through multipath fading channels. In this paper we examine PSAM pilot design optimization in OFDM systems that employ edge null subcarriers for spectral shaping. Specifically, we show that the commonly used even pilot spacing design is suboptimal in terms of symbol estimate mean squared error (MSE) performance when a sufficient number of null subcarriers are present. We pursue a parametric design of the pilot spacings and use convex optimization techniques in order to find a pilot design that results in near-optimal symbol estimate MSE performance. Finally, we present several example PSAM OFDM pilot designs including one example based on the IEEE 802.16 standard to demonstrate performance improvements over the conventional even-spacing pilot design when null edge subcarriers are present.

Training Signal and Precoder Designs for OFDM Under Colored Noise

Based on convex programming, this paper presents a new training signal design for orthogonal frequency-division multiplexing (OFDM) under colored Gaussian noise. An effective method for OFDM symbol detection with the use of precoding is also described. Both analytical and simulation results show that the proposed training design and detection method can effectively estimate the frequency-selective fading channel and reliably recover the OFDM symbols. The superiority of the proposed design over the previously known design under the colored Gaussian noise is also demonstrated.

Preamble Design for Multiple-Antenna OFDM

In this paper, we pursue the preamble design for multiple-antenna orthogonal frequency division multiplexing (OFDM) communications over frequency-selective channels. To reduce the overhead and minimize the peak-to-average power ratio, we propose a preamble consisting of a single constant- modulus training sequence per transmit-antenna. This proposed design is shown capable of not only achieving reliable frequency and time synchronization but also facilitating low-complexity channel estimation. Furthermore, when synchronization is perfect, it is optimal in the sense of minimizing the mean squared error of least-squares channel estimation. The performance of the proposed design is investigated via simulations and compared with a competing alternative.

Frequency Offset Estimation and Training Sequence Design for MIMO OFDM

This paper addresses carrier frequency offset (CFO) estimation and training sequence design for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems over frequency selective fading channels. By exploiting the orthogonality of the training sequences in the frequency domain, integer. CFO (ICFO) is estimated. With the uniformly spaced non-zero pilots in the training sequences and the corresponding geometric mapping, fractional CFO (FCFO) is estimated through the roots of a real polynomial. Furthermore, the condition for the training sequences to guarantee estimation identifiability is developed. Through the analysis of the correlation property of the training sequences, two types of sub-optimal training sequences generated from the Chu sequence are constructed. Simulation results verify the good performance of the CFO estimator assisted by the proposed training sequences.

Optimum training symbol design for MIMO OFDM in correlated fading channels

Multiple transmit and receive antennas (MIMO) have been used with orthogonal frequency division multiplexing (OFDM) for capacity improvement in frequency-selective channels. In certain propagation environments, there exists spatial correlation among channels corresponding to different pairs of transmit and receive antennas. In this paper, we investigate training sequence design for channel estimation in MIMO-OFDM systems. We develop necessary conditions for a training sequence to minimize the mean-square error (MSE) of channel estimation when spatial correlation of MIMO channel is known to the transmitter and discuss training sequence design for some special cases. The performance improvement of the designed training sequences is confirmed by simulation examples

Low-Complexity Block Double-Differential Design for OFDM With Carrier Frequency Offset

Carrier frequency offset (CFO) estimation for orthogonal frequency-division multiplexing (OFDM) has caught attention as OFDM systems have become widely adopted in recent years. In this paper, we design a novel double-differential (DD) codec with low computational complexity. Our design bypasses CFO and channel estimation, and is easy to implement at both transmitter and receiver. It also guarantees full multipath diversity, and reduces the peak-to-average power ratio from the number of subcarriers to the channel order. In addition, it is robust to CFO drifting. The closed form of the performance for our design is derived for OFDM transmissions over frequency-selective channels with CFO. Thorough simulation results corroborate our claims.