Frequency Division Multiplexing Systems Research Articles

Joint estimation and compensation of transceiver IQ imbalance for PDM CO-OFDM system

In this paper, a frequency-domain mathematical model is deduced for polarization-division multiplexing (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) system with transceiver in-phase and quadrature (IQ) imbalances. A novel training symbol structure is designed in which the mirror-subcarriers of pilot subcarriers were modulated with zero signal so that the channel distortion with transceiver IQ imbalances can be estimated. It proves that the channel distortion and transmitter IQ imbalances cannot be separated using the training symbols; therefore, the channel equalization method was used to recover the signals. Simulation results show that at 2 dB transmitter amplitude imbalances, 15° transmitter phase imbalances, 100 Gbit/s transmission rate, 1 040 km standard signal-mode fiber link, and 1×10−3 bit error rate, 23.5 dB optical signal-to-noise ratio (OSNR) is necessary for the proposed method. However, the compared schemes cannot achieve effective transmission.

Relay Selection Scheme Enhancing Reliability Based on MIMO-OFDM System

In this paper, a relay selection scheme is proposed in the Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. The conventional relay selection schemes in the wireless cooperative communication system have high implementation complexity and overhead. The proposed scheme is an adaptive relay selection scheme using Singular Value Decomposition (SVD) to select a relay with channel coefficients that maximize channel capacity. Proposed scheme uses combining factor with singular value in order to combine received signal. Simulation result shows that the proposed scheme improves the Bit Error Rate (BER) performance, compared with the conventional schemes. The proposed scheme with combining factors has enhanced BER performance than the conventional schemes.

Quantized Polar Transmitters for Power Efficient Massive MIMO Systems

This letter investigates the feasibility of the quantized digital polar transmitter architecture in a downlink multi-user massive multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system, where a low amplitude resolution and a moderate phase resolution are utilized. We derive a lower bound on the average sum-rate achievable with Gaussian signaling inputs and linear precoding by a simple diagonal approximation for the quantization distortion. The analysis and simulations demonstrate that the quantized polar transmitter can enable excellent performance in terms of average sum-rate throughput, symbol error rate (SER), and out-of-band (OOB) emission level, thus providing an attractive option for the traditional Cartesian architecture.

Maximum likelihood-based adaptive iteration algorithm design for joint CFO and channel estimation in MIMO-OFDM systems

In this paper, we present a joint time-variant carrier frequency offset (CFO) and frequency-selective channel response estimation scheme for multiple input-multiple output-orthogonal frequency-division multiplexing (MIMO-OFDM) systems for mobile users. The signal model of the MIMO-OFDM system is introduced, and the joint estimator is derived according to the maximum likelihood criterion. The proposed algorithm can be separated into three major parts. In the first part of the proposed algorithm, an initial CFO is estimated using derotation, and the result is used to apply a frequency-domain equalizer. In the second part, an iterative method is employed to locate the fine frequency peak for better CFO estimation. An adaptive process is used in the third part of the proposed algorithm to obtain the updated CFO estimation and track parameter time variations, including the time-varying CFOs and time-varying channels. The computational complexity of the proposed algorithm is considerably lower than that of the maximum likelihood-based grid search method. In a simulation, the mean squared error performance of the proposed algorithm was close to the Cramer-Rao lower bound. The simulation results indicate that the proposed novel joint estimation algorithm provides a bit error rate performance close to that in the perfect channel estimation condition. The results also suggest that the proposed method has reliable tracking performance in Jakes’ channel models.

Electrical cross talk of a frequency division multiplexing readout for a transition edge sensor bolometer array

We have characterized and mapped the electrical cross talk (ECT) of a frequency division multiplexing (FDM) system with a transition edge sensor (TES) bolometer array, which is intended for space applications. By adding a small modulation at 120Hz to the AC bias voltage of one bolometer and measuring the cross talk response in the current noise spectra of the others simultaneously, we have for the first time mapped the ECT level of 61 pixels with a nominal frequency spacing of 32 kHz in a 61 × 61 matrix and a carrier frequency ranging from 1MHz to 4MHz. We find that about 94% of the pixels show an ECT level of less than 0.4%. Only the adjacent pixels reach this level, and the ECT for the rest of the pixels is less than 0.1%. We also observe higher ECT levels, up to 10%, between some of the pixels, which have bundled long, parallel coplanar wires connecting TES bolometers to inductor-capacitor filters. In this case, the high mutual inductances dominate. To mitigate this source of ECT, the coplanar wires should be replaced by microstrip wires in the array. Our study suggests that an FDM system can have a relatively low ECT level, e.g., around 0.4% if the frequency spacing is 30 kHz. Our results successfully demonstrate a low electrical cross talk for a space FDM technology.

Polarization Multiplexed Optical OFDM System With a Beat Interference Cancellation Receiver

A novel beat interference cancellation receiver (BICR) is proposed to cancel the signal-signal beat interference (SSBI) for polarization division multiplexed (PDM) optical orthogonal frequency division multiplexing (OOFDM) system, where two single sideband (SSB) OOFDM signals are polarization multiplexed along with their offset optical carriers (OCs) located at opposite sides. At receiver, the PDM SSB-OOFDM signal is equally power split into four beams with one or two OCs filtered out, and then fed into two balanced photodiode pairs for recovering the RF-OFDM signals with SSBI cancellation. The PDM SSB-OOFDM system is insensitive to fiber polarization mode dispersion since the proposed BICR is implemented without polarization-sensitive devices. Moreover, the spectral efficiency is greatly improved because of PDM and the small guard band since the SSBIs are eliminated. The proposed BICR scheme is validated with a simulation link of 112 Gbps 16-QAM PDM SSB-OOFDM signals. After 120km SSMF transmission, the EVM keeps below forward error correction limit of 16.3%.

Adaptive Blind Channel Estimation for MIMO-OFDM Systems Based on PARAFAC

In order to track the changing channel in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, it is prior to estimate channel impulse response adaptively. In this paper, we proposed an adaptive blind channel estimation method based on parallel factor analysis (PARAFAC). We used an exponential window to weight the past observations; thus, the cost function can be constructed via a weighted least squares criterion. The minimization of the cost function is equivalent to the decomposition of third-order tensor which consists of the weighted OFDM data symbols. To reduce the computational load, we adopt a recursive singular value decomposition method for tensor decomposition; then, the channel parameters can be estimated adaptively. Simulation results validate the effectiveness of the proposed algorithm under diverse signalling conditions.

Sub-Sampled Time Domain Sparse Information in Wired OFDM and STBC-OFDM Systems

A sub-sampling method developed for wired or wireless Orthogonal Frequency Division Multiplexing (OFDM) systems is presented. The proposed technique can be activated during the exchange of sparse data. The sub-sampling method is implemented with low cost and complexity hardware since it requires the customization of a few specific OFDM stages like channel interleaving, sampling control, etc, and does not require any iterative optimization procedure. Employing special Inverse-Fast Fourier Transform (I-FFT) input structures, the recovery of the original data from fewer samples than those required by the receiver FFT is possible without any other cost for general OFDM applications. A special detector initiates the sub-sampling mode when sparse information is exchanged like sensor data or uncompressed real-time video with stationary views like night surveillance cameras. Up to ¾ of the time, the system can operate in sub-sampling mode reducing the power consumed by the Analogue/Digital Converter (ADC), the FFT and the IFFT. Memory needed for sample storage, intermediate results and FFT/IFFT coefficients can be released in real time if the proposed architecture is adopted. A Bit Error Rate (BER) below 10−3 or full information recovery is achieved in most of the cases. An image reconstruction example is also tested in a wireless environment with Normalised Mean Square Error (NMSE) ranging from 10−5 to less than 0.1.

Message authentication algorithm for OFDM communication systems

With the huge expansion in the telecommunications industry, the need for robust information security is becoming more critical than ever. Physical Layer Security has, recently, emerged as a promising candidate to secure emerging communication systems in a lightweight manner. This approach has proven to be superior to existing schemes, which has motivated many researchers to shift their work towards studying, understanding and exploiting the randomness of the physical layer. In this context, this paper presents a novel keyed-hash function for Orthogonal Frequency Division Multiplexing (OFDM) systems based on the physical characteristics and properties of wireless channels. More specifically, communicating entities sharing the same channel, extract common properties and mix them with a pre-shared secret key to produce a channel-based dynamic key. This key will later be used to generate the cipher primitives needed for performing source authentication and message integrity of the transmitted OFDM symbols. Since OFDM symbols, in the frequency-domain and time-domain, have different properties, the proposed keyed-hash function is modified and adapted to suit each case leading to two variants of the solution. To the best of our knowledge, this is the first work that proposes a keyed-hash function for complex OFDM symbols, based on physical layer conditions. Finally, different security and performance tests are conducted to prove the robustness and efficiency of this technique, in comparison to currently employed message authentication schemes.

Compressive sensing for PAPR reduction of DC-biased optical OFDM signals with exploiting joint sparsity for signal reconstruction

Compressive sensing (CS) is an attractive technique to mitigate the high peak-to-average power ratio (PAPR) in optical orthogonal frequency division multiplexing (OFDM) systems. The lower computational complexity, easy implementation, and lack of side information requirement make signal compression an appropriate approach for PAPR reduction in both original and optical OFDM systems. We propose the CS approach for compressing the time-domain DC-biased optical OFDM (DCO-OFDM) signals at the transmitter side and multiple measurement vectors (MMV) based on orthogonal matching pursuit (OMP) algorithm to reconstruct the original signals at the receiver end. Simulations are conducted for QPSK and 16-QAM modulated symbols, and the results indicate that the PAPR of compressed signals is significantly reduced compared with the PAPR of the original DCO-OFDM signals. Furthermore, using the MMV-OMP algorithm and only about 1 dB additional signal-to-noise ratio, the original symbols are reconstructed at the receiver end without deteriorating the bit error rate performance.

16QAM spectral efficiency frequency division multiplexing transmission with Tomlinson–Harashima precoding for intensity modulation and direct detection optical links

In the spectral efficient frequency division multiplexing (SEFDM) system, in order to minimize mutual interference between subcarriers, a detector should be introduced at the receiver to handle the interference, but increases the complexity of system. In this paper, we propose a simplified precoding algorithm at transmitter instead of receiver, which can first implement higher 16QAM SEFDM transmission over standard single mode fiber (SSMF). The technique is based on interference information from non-orthogonality between subcarriers and uses nonlinear matrix operations to improve system performance with low complexity. The numerical results show that the precoding scheme achieves SSMF transmission of intensity modulation and direct detection (IM/DD) 16QAM SEFDM system under the premise of achieving higher spectral efficiency, and obtains good bit error rate performance.

Non-linear equalisation and CFO compensation for MIMO-OFDM communication systems based on DWT

ABSTRACT Equalisation is one of the most important algorithms to improve the Bit-Error-Rate (BER) performance in communication systems. In general, equalisation can be classified into two categories: linear and non-linear equalisation. The linear equalisers include Zero Forcing (ZF), and Minimum Mean Square Error (MMSE) equalisers. The non-linear equalisers include ZF and MMSE equalisers that are based on Successive Interference Cancellation (SIC). The ZF equaliser suffers from noise enhancement. The MMSE equaliser can mitigate the noise enhancement using the estimated Signal-to-Noise Ratio (SNR). The ZF-SIC and MMSE-SIC equalisers suffer from error propagation, and high computational complexity, respectively. In this paper, the Orthogonal Frequency Division Multiplexing (OFDM) system is modulated and demodulated using Inverse Discrete Wavelet Transform (IDWT), and DWT instead of Inverse Discrete Fourier Transform (IDFT) and DFT, respectively. Also, we propose a Joint Low-complexity Regularised ZF-SIC (JLRZF-SIC) equaliser that jointly performs the equalisation, and Carrier Frequency Offset (CFO) compensation with lower complexity using banded matrix approximation. The proposed JLRZF-SIC equaliser can accomplish the equalisation, and CFO compensation processes with low-complexity compared to the corresponding MMSE-SIC equaliser. Simulation results show that the proposed JLRZF-SIC equaliser outperforms different linearand non-linear equalisers.

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.

A novel phase noise compensation algorithm combining the DF algorithm with LCSC algorithm in CO-OFDM systems

A novel phase noise (PN) compensation algorithm based on the decision feedback (DF) algorithm and the linear combination self cancellation (LCSC) algorithm is proposed to improve the system performance degradation caused by laser linewidth in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. In this proposed LCSC-DF algorithm, the LCSC algorithm is used to precode the subcarrier information at the transmitter and decode the demodulation information and inter-carrier interference (ICI) related information at the receiver. And then the pilot information is used to obtain the final compensation signal by the improved DF algorithm. The simulation results show that the PN compensation performance of the proposed LCSC-DF algorithm is better than that of the DF algorithm. Furthermore, with the increase of the signal to noise ratio (SNR), its bit error rate (BER) performance approaches to that of the SC-DF algorithm at the larger PN linewidth. The subcarriers utilization ratio of the proposed algorithm is higher than that of the SC-DF algorithm. As a result, the proposed algorithm can effectively improve the performance of the system.

Unitary Matrix Method for PAPR Reduction of IDFT-VFDM Signals

To enable the frequency reuse between the new radio (NR) and the long-term evolution (LTE) systems, inverse discrete Fourier transform-based Vandermonde-subspace frequency division multiplexing (IDFT-VFDM) has been proposed to exploit the guard intervals of the conventional orthogonal frequency division multiplexing (OFDM) system. One important issue of the IDFT-VFDM system is the high peak-to-average power ratio (PAPR), which distorts the transmitted signal and causes severe performance degradation. Compared to OFDM, the method to reduce the PAPR in IDFT-VFDM requires unique design to guarantee zero interference to the legacy LTE system. To deal with this problem, a unitary matrix based method is proposed to design the precoder at the NR users to reduce the PAPR, which can also guarantee the minimum residual interference to the LTE system. Simulation results are demonstrated to verify the effectiveness of the proposed scheme.

Joint Adaptive Blind Channel Estimation and Data Detection for MIMO-OFDM Systems

In order to track a changing channel in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, it is a priority to estimate channel impulse response adaptively. In this paper, we propose an adaptive blind channel estimation method based on parallel factor analysis (PARAFAC). We used an exponential window to weigh the past observations; thus, the cost function can be constructed via a weighted least squares criterion. The minimization of the cost function is equivalent to the decomposition of a third-order tensor, which consists of the weighted OFDM data symbols. By preserving the Khatri-Rao product, we used a recursive least squares solution to update the estimated subspace at each time instant, then the channel parameters can be estimated adaptively, and the algorithm achieves superior convergence performance. Simulation results validate the effectiveness of the proposed algorithm.

A Combined Approach of DPD and CFR in F-OFDM System

The nonlinear distortion of the power amplifier (PA) is studied for Filtered Orthogonal Frequency Division Multiplexing (F-OFDM) systems, which will be adopted in the fifth generation (5G) mobile communication systems. The peak to average power ratio (PAPR) of F-OFDM signal may make the PAs work in the saturation region and result into extremely serious nonlinear saturation distortion, and the nonlinear saturation distortion is usually compensated by predistortion technology. A digital predistortion (DPD) structure is designed to compensate the nonlinear characteristics of the PA in the article. Firstly, repeated iterative clipping revision (RICR) algorithm is used to reduce the PAPR, which makes the working region of PA infinitely close to the saturation region, and as a result, the efficiency is improved. Furthermore, an integrated structure combining crest factor reduction (CFR) and DPD is employed. The experimental results show that the performance of the proposed CFR joint adaptive DPD lowers the PAPR of the predistorted signal by 2dB. The combined CFR & DPD reduces the ACPR of the transmitter by 3dB compared with the unlinearized PA.

Pilot Based Channel Estimation and Synchronization in OFDM System

Channel estimation and synchronization are considered the most challenging issues in Orthogonal Frequency Division Multiplexing (OFDM) system. OFDM is highly affected by synchronization errors that cause reduction in subcarriers orthogonality, leading to significant performance degradation. The synchronization errors cause two issues: Symbol Time Offset (STO), which produces inter symbol interference (ISI) and Carrier Frequency Offset (CFO), which results in inter carrier interference (ICI). The aim of the research is to simulate Comb type pilot based channel estimation for OFDM system showing the effect of pilot numbers on the channel estimation performance and propose a modified estimation method for STO with less number of pilot to mitigate ISI effect. Channel estimation is simulated for different pilot number with 16QAM modulation in Ped-A Rayleigh channel. The STO effect assumed less than the cyclic prefix length to minimize ISI and maintain the orthogonality between subcarriers. The simulation results show that the high number of pilots are needed to achieve good channel estimation in case no synchronization used while similar results are achieved with smaller number of pilots if the propose modification on the synchronization method are used aligned with the channel estimation. The proposed system is evaluated in terms of BER and SNR.

Experimental Investigation of Intensity Modulator/Direct Detection (IM/DD) Optical OFDM System with Fiber Bragg Grating (FBG)

AbstractTo improve the performance of optical fiber transmission and to compensate the fiber chromatic dispersion (CD), we propose to use fiber Bragg grating (FBG) in intensity modulator/direct detection IM/DD optical orthogonal frequency division multiplexing (OOFDM) system, and experimentally demonstrate 2.5-Gbit/s QPSK-OFDM transmission over 200 km SMF-28. FBG used before the detection as a chromatic dispersion compensation module, reducing the beating noise between ASE noise and OFDM signal. By using the FBG in IM/DD OOFDM system, our experimental results show that the receiver sensitivity was improved about 2 dB at a bit error rate (BER) of $1 \times {10^{ - 3}}$ for 2.5 Gbit/s QPSK-OFDM signals after 200 km SMF-transmission compared to regular system without FBG.

An Efficient DWT DAPM Technique for PAPR Reduction in OFDM System

In this paper, Discrete Wavelet Transform (DWT) Orthogonal Frequency Division Multiplexing (OFDM) system is compared with Discrete Cosine Transform (DCT) and Discrete Fourier Transform (DFT) OFDM systems. The channel noise is modelled with A white Gaussian Model (AWGN), the fading is the impairment in the channel and modelled by Rayleigh fading which is frequency selective fading channel and flat fading channel. The comparisons of Peak to Average Power Ratio (PAPR) and Bit Error Rate (BER) are made using modulation techniques such as Differential Amplitude and Phase Modulation (DAPM), Quadrature Amplitude Modulation (QAM) and Pulse Amplitude Modulation (PAM). Simulation results shows that PAPR is 4.497 dB for DWT-DAPM combination, 4.684 dB for DWT-QAM combination and 6.211 dB for DWT- PAM combination at 10-3 Complementary Cumulative Distributive Function (CCDF).The performance Analysis with the combination of DFT, DCT with DAPM, QAM and PAM are also compared. The BER is 0.01816, 0.01806 at 20 dB SNR in frequency selective channel, flat fading channel for DWT-DAPM and for DWT- QAM, AWGN channel BER is 0.01765 at 20dB SNR.