Traditional Orthogonal Frequency Division Multiplexing Research Articles

Secure RoF system based on key nested polar code and feedback neural network.

With the development of 6 G network, the issue of information security is becoming more and more significant. In this paper, a secure RoF system based on key nested polar code and feedback neural network (FNN) is proposed. For the nested polar code, the original key is randomly selected from the constructed codebook and the index of key is encoded by inner polar code which is placed at the location with better channel quality bit of the frozen bit of outer polar code, for the other part of outer polar code, information bits are encrypted by chaotic sequence generated by 4-D cellular neural network. The polar coded sequence is mapped to the 16-QAM symbol for orthogonal frequency division multiplexing (OFDM) and then the OFDM signal is modulated to the optical pulse, which is delivered to users through 50 km standard single-mode fiber and 5 m wireless channel. In the receiver, successive cancellation list (SCL) decoder is used for decoding outer polar code and FNN is used for decoding inner polar code to reduce the latency. The experimental results show that, compared with the existing scheme, when the bit err rate is 10-3, the received optical power (ROP) gain of the proposed scheme with SCL2 decoder and SCL4 decoder is ∼1.2 dB and ∼1.6 dB, respectively. And compared with the traditional OFDM signal with polar code, when the bit err rate is 10-3, the ROP gain of the proposed scheme with SCL4 decoder is ∼1 dB. What's more, the randomness of the chaotic key sequence, the ability to resist brute-force attacks and the ability to resist chosen-plaintext attacks are elaborated. Therefore, the proposed scheme can greatly improve the security of the system while ensuring the correct transmission of information.

Filter bank multi-carrier based offset ternary phase shift keying(FBMC/OTPSK)

Filter bank multi-carrier (FBMC) is a popular researched technique for wireless communications that offers several advantages over traditional orthogonal frequency-division multiplexing (OFDM) systems. In this paper, we propose a FBMC system using offset Triangle phase shift keying (TPSK) modulation (FBMC/OTPSK), analyze its bit error rate (BER) performance via additive white Gaussian noise (AWGN) channel, and compare it to that of conventional FBMC using offset quadrature amplitude modulation (FBMC/OQAM) system. Simulation results show that the proposed FBMC/OTPSK system considerably improves BER performance over FBMC/OQAM system. Additionally, we explore the impact of using ternary convolutional coding (TCC) with TPSK and binary convolutional coding (BCC) with QAM. The presented TPSK modulation encoded by TCC offers better error rate performance and minimum amplitude fluctuation compared to QAM encoded by BCC; therefore, TCC-coded OTPSK is proposed to be used with FBMC instead of BCC-coded OQAM to benefit from its lower error rates without bandwidth expansion, as well increase information carried by symbol, hence increases throughput.

An effective technique for increasing capacity and improving bandwidth in 5G narrow-band internet of things

<p>In recent years, the wireless spectrum has become increasingly scarce as demand for wireless services has grown, requiring imaginative approaches to increase capacity within a limited spectral resource. This article proposes a new method that combines modified symbol time compression with orthogonal frequency division multiplexing (MSTC-OFDM), to enhance capacity for the narrow-band internet of things (NB-IoT) system. The suggested method, MSTC-OFDM, is based on the modified symbol time compression (MSTC) technique. The MSTC is a compressed waveform technique that increases capacity by compressing the occupied symbol time without losing bit error rate (BER) performance or data throughput. A comparative analysis is provided between the traditional orthogonal frequency division multiplexing (OFDM) system and the MSTC-OFDM method. The simulation results show that the MSTC-OFDM scheme drastically decreases the symbol time (ST) by 75% compared to a standard OFDM system. As a result, the MSTC-OFDM system offers four times the bit rate of a typical OFDM system using the same bandwidth and modulation but with a little increase in complexity. Moreover, compared to an OFDM system with 16 quadrature amplitude modulation (16QAM-OFDM), the MSTC-OFDM system reduces the signal-to-noise ratio (SNR) by 3.9 dB to transmit the same amount of data.</p>

Block-Wise Index Modulation and Receiver Design for High-Mobility OTFS Communications

As a promising technique for high-mobility wireless communications, orthogonal time frequency space (OTFS) has been proved to enjoy excellent advantages with respect to traditional orthogonal frequency division multiplexing (OFDM). Although multiple studies have considered index modulation (IM) based OTFS (IM-OTFS) schemes to further improve system performance, a challenging and open problem is the development of effective IM schemes and efficient receivers for practical OTFS systems that must operate in the presence of channel delays and Doppler shifts. In this paper, we propose two novel block-wise IM schemes for OTFS systems, named delay-IM with OTFS (DeIM-OTFS) and Doppler-IM with OTFS (DoIM-OTFS), where a block of delay/Doppler resource bins are activated simultaneously. Based on a maximum likelihood (ML) detector, we analyze upper bounds on the average bit error rates for the proposed DeIM-OTFS and DoIM-OTFS schemes, and verify their performance advantages over the existing IM-OTFS systems. We also develop a multi-layer joint symbol and activation pattern detection (MLJSAPD) algorithm and a customized message passing detection (CMPD) algorithm for our proposed DeIM-OTFS and DoIM-OTFS systems with low complexity. Simulation results demonstrate that our proposed MLJSAPD and CMPD algorithms can achieve desired performance with robustness to the imperfect channel state information (CSI).

Coordinated-security based on probabilistic shaping and encryption in MMW-RoF system.

A coordinated-security probabilistic shaping (PS) physical layer encryption scheme is proposed for a W-band millimeter-wave radio-over-fiber (MMW-RoF) system. This scheme mainly includes substituting encryption, coordinated encrypted PS, and unequal length grouping scrambling, which can realize the coordination between PS and chaotic encryption. The key space of the proposed scheme is 10103, which can effectively prevent against brute force cracking and chosen-plaintext attacks. The encrypted orthogonal frequency division multiplexing (OFDM) signal is successfully transmitted over 50-km standard single-mode fiber (SSMF) and a 5-m wireless channel. The results show that the proposed scheme achieves 0.8-dB received optical power gain at a bit error rate (BER) of 10-3 compared with a traditional OFDM signal. The superiority of the proposed scheme in security performance and BER performance has been verified.

Filtered OFDM System Improvement Using Hamming Code

Orthogonal Frequency Division Multiplexing (OFDM) technique is widely adopted for broadband Forth Generation (4G) wireless communication systems at present, owing to its ability to combat multi-path interference. Nevertheless, it suffers from a large Peak to Average Power Ratio (PAPR) and Out Of Band Emission (OOBE), making it unsuitable for a high-speed transmission system. On the other hand, the Filtered-OFDM (f-OFDM) system is suggested to overcome the traditional OFDM system's disadvantages and maintain its advantages. Nowadays, the developments and growing communications systems are rapid, especially on their applications such as wireless networks, internet, satellite communications, mobile telephony, etc. This increases the demand for raising the bit rates with decreasing power consumption and the bit error rates (BER). In this paper, Hamming codes are proposed to improve the f-OFDM system performance, while the presence of the subband filter in system architecture could decrease the values of OOBE than the familiar OFDM system. The outcomes showed that utilizing interleaver with Hamming code considerably improves the proposed system performance, while the OOBE values were lower than the conventional OFDM system.

IRS-Assisted OTFS System: Design and Analysis

Intelligent reflecting surface (IRS) is a recent technology garnering lots of attention amongst the wireless communication research community due to its ability to improve the channel conditions extravagantly. The main feature of IRS technology is its capability to tune the phases of the reflecting elements to trigger a cohesive amalgamation of various multipath. IRS can easily co-exist with almost all technologies, thereby offering flexibility to the designers to come up with attractive systems. Further, orthogonal time frequency space (OTFS) is a recent 2D modulation technique that can mitigate the drawbacks of the traditional orthogonal frequency division multiplexing (OFDM) for fifth generation (5G) and beyond networks, especially in high Doppler wireless environments like vehicle-to-everything (V2X) and millimeter wave (mmWave) communications. This paper presents the system architecture of the IRS-assisted OTFS scheme in the delay-Doppler (DD) domain, including the modulation, demodulation, and detection methods. The selection of the reflection coefficients play the most vital role in the IRS-OTFS system, like any IRS system. IRS reflection optimization cannot perfectly line up all multipath with the same phase in the frequency-selective channels. We adopt an IRS phase optimization method where only the strongest delay-Doppler path is phase-aligned, while the paths with lesser strengths will be out of phase with the direct path. This reconfigurability of IRS elements enhances the OTFS modulation scheme, thereby significantly mitigating the multipath fading effects in high Doppler channels. Additionally, we propose a channel estimation for the IRS-OTFS system where both data and pilots are embedded in the same OTFS frame with minimal guard-band overhead. The paper presents extensive simulation results on the error-rate performance of the proposed system over Rayleigh and Rician fading channels. The effects of the number of IRS elements, the phase selections, and the channel estimation method on the system's performance are investigated. The comprehensive simulation study demonstrates that by exploiting the features of both OTFS and IRS, the proposed approach can provide impressive performance in high Doppler environments.

Multi-antenna GFDM for resilient decentralized communications

Owing to the superior performance of generalized frequency division multiplexing (GFDM), in terms of enhanced spectral efficiency and lower out-of-band radiations, it is considered as a potential replacement of traditional orthogonal frequency division multiplexing (OFDM) for next generation wireless communication systems. However, non-orthogonal pulse shaping in GFDM gives rise to intrinsic self-interference complicating the receiver design. Moreover, its extension to multi-input multi-output (MIMO) designs for spatial diversity and enhanced reliability is also not straightforward as overlapping of transmitted symbols in time and frequency hinders the extension of conventional diversity techniques to MIMO GFDM. In this work, we consider a multi-antenna GFDM decentralized communication system and present a generic framework to achieve spatial transmit diversity along with a low complexity transceiver design. We extend our proposal by presenting a novel multi-antenna preamble that helps not only in acquisition of robust time and frequency synchronization but also in reliable estimation of time-varying frequency selective channels. Performance evaluation over realistic 3GPP simulation scenarios, confirms the attainment of full diversity order along with superior preamble-based time–frequency synchronization and channel estimation performance as compared to state of the art.

Subcarrier Index Modulation for Spectral Efficient Frequency Division Multiplexing in Multi-Input Multi-Output Channels

This work presents spectral efficient frequency division multiplexing with subcarrier index modulation (SEFDM-SIM) for multi-input multi-output (MIMO) wireless networks. SEFDM employs non-orthogonal frequency division multiplexing to enhance the spectral efficiency (SE) at the expense of enhanced inter-carrier interference compared with traditional orthogonal frequency division multiplexing (OFDM). In SEFDM-SIM, the information is conveyed not only by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$M$</tex-math></inline-formula> -ary signal constellations, as in SEFDM, but also by the indices of the subcarriers, which are activated according to the incoming bitstream. SE and bit error rate (BER) are used as the performance measures. Both the analytic and simulation results show that the proposed MIMO-SEFDM-SIM outperforms the conventional MIMO-OFDM and MIMO-OFDM-SIM in SE, while achieving an improved BER than the MIMO-OFDM and MIMO-SEFDM systems.

Low PAPR channel estimation for OTFS with scattered superimposed pilots

Orthogonal time frequency space (OTFS) modulation has been proven to be superior to traditional orthogonal frequency division multiplexing (OFDM) systems in high-speed communication scenarios. However, the existing channel estimation schemes may results in poor peak to average power ratio (PAPR) performance of OTFS system or low spectrum efficiency. Hence, in this paper, we propose a low PAPR channel estimation scheme with high spectrum efficiency. Specifically, we design a multiple scattered pilot pattern, where multiple low power pilot symbols are superimposed with data symbols in delay-Doppler domain. Furthermore, we propose the placement rules for pilot symbols, which can guarantee the low PAPR. Moreover, the data aided iterative channel estimation was invoked, where joint channel estimation is proposed by exploiting multiple independent received signals instead of only one received signal in the existing scheme, which can mitigate the interference imposed by data symbols for channel estimation. Simulation results shows that the proposed multiple scattered pilot aided channel estimation scheme can significantly reduce the PAPR while keeping the high spectrum efficiency.

A TIME-MIRRORING (TM) SCHEME FOR ICI MITIGATION IN TIME-VARYING CHANNEL FOR DIGITAL VIDEO BROADCASTING (DVB) SYSTEMS

High mobility and high data speeds are now highly important requirements. The orthogonal frequency division multiplexing (OFDM) structure, which suffers from inter-carrier interference (ICI) in time-varying channels, is the basic core method in digital video broadcasting (DVB). Hence, the bit error rate (BER) is declined. In this paper, the time mirroring (TM) based on the symbol time compression (STC) technique for entire ICI suppression for DVB systems is proposed. In addition, some missing analysis for STC technique and ICI power analysis is introduced. Finally, the computational complexity of the proposed TM scheme is determined. The simulation results show that the proposed scheme reduces the ICI power by a significant amount when compared to the other traditional schemes. In comparison to traditional systems, the BER performance is greatly enhanced, and the eye diagram is entirely opened. In addition, as compared to traditional schemes, the proposed approach can handle normalized Doppler frequency by up to 40&amp;#37; and it has about the same computational complexity as the STC scheme but it is more efficient in terms of computational complexity than the traditional OFDM system.

Filtered OFDM System Improvement Using Hamming Code

Orthogonal Frequency Division Multiplexing (OFDM) technique is widely adopted for broadband Forth Generation (4G) wireless communication systems at present, owing to its ability to combat multi-path interference. Nevertheless, it suffers from a large Peak to Average Power Ratio (PAPR) and Out Of Band Emission (OOBE), making it unsuitable for a high-speed transmission system. On the other hand, the Filtered-OFDM (f-OFDM) system is suggested to overcome the traditional OFDM system's disadvantages and maintain its advantages. Nowadays, the developments and growing communications systems are rapid, especially on their applications such as wireless networks, internet, satellite communications, mobile telephony, etc. This increases the demand for raising the bit rates with decreasing power consumption and the bit error rates (BER). In this paper, Hamming codes are proposed to improve the f-OFDM system performance, while the presence of the subband filter in system architecture could decrease the values of OOBE than the familiar OFDM system. The outcomes showed that utilizing interleaver with Hamming code considerably improves the proposed system performance, while the OOBE values were lower than the conventional OFDM system.

Capacity and outage performance of multiple AF relays based cooperative OFDM-QIM system

In this paper, we propose a multiple amplify-and-forward (AF) relays based cooperative orthogonal frequency division multiplexing (OFDM) with quadrature index modulation (C-OFDM-QIM) system to enhance the spectral efficiency and the transmission reliability, where two independent subcarrier subsets are activated to convey the real and imaginary symbol vectors, respectively, and the per-subcarrier relay selection (RS) scheme is adopted to select the relay with the maximum end-to-end signal-to-noise ratio (SNR) for each active subcarrier. Both fixed-gain AF and variable-gain AF protocols are investigated at the selected relays. Based on the order statistics and the max-flow min-cut theory, the closed-form average outage probability (AOP) and the average capacity are derived, respectively. Numerical results demonstrate that the theoretical AOP is correct and accurate and the proposed C-OFDM-QIM system outperforms the traditional cooperative OFDM with index modulation (C-OFDM-IM) system in the spectral efficiency, the outage performance, and the average capacity.

Coded-GFDM for Reliable Communication in Underwater Acoustic Channels.

The performance of the coded generalized frequency division multiplexing (GFDM) transceiver has been evaluated in a shallow underwater acoustic channel (UAC). Acoustic transmission is the scheme of choice for communication in UAC since radio waves suffer from absorption and light waves scatter. Although orthogonal frequency division multiplexing (OFDM) has found its ground for multicarrier acoustic underwater communication, it suffers from high peak to average power ratio (PAPR) and out of band (OOB) emissions. We propose a coded-GFDM based multicarrier system since GFDM has a higher spectral efficiency compared to a traditional OFDM system. In doing so, we assess two block codes, namely Bose, Chaudari, and Hocquenghem (BCH) codes, Reed-Solomon (RS) codes, and several convolutional codes. We present the error performances of these codes when used with GFDM. Furthermore, we evaluate the performance of the proposed system using two equalizers: Matched Filter (MF) and Zero-Forcing (ZF). Simulation results show that among the various block coding schemes that we tested, BCH (31,6) and RS (15,3) give the best error performance. Among the convolutional codes that we tested, rate 1/4 convolutional codes give the best performance. However, the performance of BCH and RS codes is much better than the convolutional codes. Moreover, the performance of the ZF equalizer is marginally better than the MF equalizer. In conclusion, using the channel coding schemes with GFDM improves error performance manifolds thereby increasing the reliability of the GFDM system despite slightly higher complexity.

Robust Deep Learning-Based End-to-End Receiver for OFDM System With Non-Linear Distortion

In this letter, we propose a deep learning-based receiver named one-dimensional transmit and recovery net (1D-TRNet), which is robust to non-linear clipping distortion for orthogonal frequency-division multiplexing (OFDM) systems. The proposed scheme uses a 1D U-shape structure with multiple gated recurrent units (GRUs). The 1D-convolution kernel can extract both the low-level (local) and high-level (global) features in the non-linearly distorted OFDM signals. Simulation results show that the proposed 1D-TRNet receiver achieves significant bit-error rate (BER) performance gain over the traditional OFDM receivers. Moreover, the proposed 1D-TRNet receiver outperforms the state-of-the-art generalized approximate message passing (GAMP) receiver under the same computational complexity constraint.

One-time pad scheme based on polar code and OFDM for MMW-RoF system at W-band.

The physical layer security of millimeter-wave radio-over-fiber (MMW-RoF) system at W-band is a promising topic. This paper experimentally demonstrates a one-time pad scheme based on polar code and orthogonal frequency division multiplexing (OFDM) for MMW-RoF system. In the proposed scheme, the initial key is obtained by looking-up table mapping randomly, and chaotic sequence is generated by using 4-D cellular neural network (CNN). The key for next frame is placed in the partial frozen bits of polar code, which can realize the one-time pad mechanism. The encrypted OFDM signal carried by 100GHz millimeter-wave is successfully transmitted over 50 km standard single-mode fiber (SSMF) and 5 m wireless channel in this experiment. The experimental results show that, compared with the traditional OFDM signal, the proposed scheme in SCL8 decoder can achieve ∼4.1 dB gain at the BER of 10-3, which can effectively use the frozen bits of polar code to transmit more information and improve the security and reliability of the whole system.

Partially-Reserved Cyclic Algorithm For OFDM-Based RadCom PAPR Reduction

With the proliferation of internet of vehicles (IoV) applications, the information exchange and anti-collision radar become increasingly important for vehicular safety. The fusion of radar and wireless communication, called RadCom, has been proposed for future intelligent transportation. Traditional orthogonal frequency division multiplexing (OFDM)-based RadCom systems, however, suffer from impractical bandwidth allocation and high peak-to-average power ratio (PAPR), which results in not only severe nonlinear distortion but also low efficiency of high power amplifier (HPA). Motivated by these research problems, we propose a new partially-reserved cyclic algorithm for OFDM-based RadCom fusion systems. Our proposed RadCom algorithm is able to allocate appropriate communication bandwidth on the request of actural transmission by assuming that the entire bandwidth can be used for radar detection. In the frequency-domain, when the spectral sub-band for communication is reserved, we optimize over the remaining spectral sub-band by the proposed algorithm for PAPR reduction. The evaluation of the system with the proposed algorithm shows significantly improved performance over traditional OFDM-based RadCom systems in both the communication and radar functions when HPA is taken into account.

Novel DDS based OFDM transmitter structure without IFFT and interpolation filter

The traditional orthogonal frequency division multiplexing (OFDM) transmitter is implemented by inverse fast Fourier transform (IFFT), up-sampling and low pass shaping filter (LPSF), which occupy a large number of hardware resources and have long latency. To further meet the 5G and future 6G communication requirements, this paper proposes a novel direct digital synthesis (DDS) based OFDM transmitter structure that can replace these modules. Due to the strong parallelism of the system structure, it is very suitable for implementation on field programable gate array (FPGA) platform. After making two special simplifications to the primary structure, the refined structure becomes very simple compared with the traditional structures. Most attractively, the proposed structure has the following three advantages that i) the data transformation from frequency domain to time domain has zero latency, ii) the transformation length does not need to be an integer power of 2 and iii) the structure does not even need to use any multiplier, thus leading to low implementation complexity and high speed. Comparative experiments are carried out on Intel FPGA platform which show that our DDS based structure can save more than half of the resources compared with the traditional structures and can provide the same bit error rate (BER) performance under the condition without using any LPSF.

AI-Aided Online Adaptive OFDM Receiver: Design and Experimental Results

Orthogonal frequency division multiplexing (OFDM) has been widely applied in many wireless communi- cation systems. The artificial intelligence (AI)-aided OFDM receivers are currently brought to the forefront to replace and improve the traditional OFDM receivers. In this paper, we first compare two AI-aided OFDM receivers, namely, data-driven fully connected deep neural network and model-driven ComNet, through extensive simulation and real-time video transmission using a 5G rapid prototyping system for an over-the-air (OTA) test. We find a performance gap between the simulation and the OTA test caused by the discrepancy between the channel model for offline training and the real environment. We develop a novel online training system, which is called SwitchNet receiver, to address this issue. This receiver has a flexible and extendable architecture and can adapt to real channels by training only several parameters online. From the OTA test, the AI-aided OFDM receivers, especially the SwitchNet receiver, are robust to OTA environments and promising for future communication systems. At the end of this paper, we discuss potential challenges and future research inspired by our initial study in this paper.

Cross-phase modulation compensation in multichannel system based on filter bank multicarrier modulation

Futuristic mobile data networks are expected to reach higher data rates per user to accommodate the specifications of emerging services, such as triple play and mobile applications. Researchers are carrying out their works to tackle the drawbacks of traditional orthogonal frequency-division multiplexing by designing new waveforms with high spectral efficiency and low out-of-band emissions. Among many others, filter bank multicarrier (FBMC) is an appealing candidate for beyond 5G that fulfills these constraints. Consequently, it is worth to shed light on the performance of FBMC in multichannel transmission system. The main contribution of our paper is to compensate fiber nonlinearity including self-phase modulation and cross-phase modulation effects using adaptive Volterra equalizer in longhaul FBMC system based on a 6 × 20 Gb / s in wavelength-division multiplexing scheme over 100 km × 30 spans of single-mode fiber (SMF). The impacts of channel spacing, bit rate, and fiber types on system performance are addressed. For a target of bit error rate = 10 − 3, the simulations show that this performance can be reached at −12 dBm of launch power when 5-taps third-order Volterra (TOV) equalizer is used for 12.5 GHz of channel spacing and an improvement of approximately 1 dB is obtained for 7 taps compared with the same equalizer with 3 taps. To further enhance the system performance, standard-SMF is replaced by a new class fiber called pure-silica-core fiber with large effective area, which exhibits a gain of almost 1.3 and 1 dB for 3 and 5 taps, respectively. The complexity burden of the TOV filter is also discussed.