Multicarrier Technique Research Articles

Frequency Diverse Array Beampattern Synthesis Using Symmetrical Logarithmic Frequency Offsets for Target Indication

Although phased arrays have been widely used in various applications, their beams can only be steered to an angle for all range bins. In contrast, the frequency diverse array (FDA) introduces a tiny frequency offset across its array elements to form a range-angle-dependent beampattern. Nevertheless, the standard linear FDA can only provide an S-shaped beampattern, which is a disadvantage for target indication. In this communication, we propose a new FDA framework, which adopts symmetrical and logarithmic frequency offsets together with multicarrier technique, to produce a dot-shaped beampattern for target indication. The superiority of the proposed scheme is verified by both numerical results and comparisons with existing FDA frameworks.

Enhanced DCT-OFDM System With Index Modulation

Discrete cosine transform (DCT) based orthogonal frequency-division multiplexing (OFDM), which has double the number of subcarriers compared to the classic discrete Fourier transform (DFT) based OFDM (DFT-OFDM) at the same bandwidth, is a promising high spectral efficiency multicarrier technique for future wireless communications. In this paper, an enhanced DCT-OFDM with index modulation (IM) (EDCT-OFDM-IM) is proposed to further exploit the benefits of the DCT-OFDM and IM techniques. To be more specific, a pre-filtering method based DCT-OFDM-IM transmitter is first designed and non-linear maximum likelihood (ML) is developed for the proposed EDCT-OFDM-IM system. Moreover, the average bit error probability of the proposed EDCT-OFDM-IM system is derived, which is confirmed by simulation results. Both simulation and theoretical results show that the proposed EDCT-OFDM-IM system exhibits better bit error rate performance over the conventional DFT-OFDM-IM and DCT-OFDM-IM counterparts.

An Enhanced Peak to Average Power Ratio Reduction Scheme for Interleaved and Sub-Band Orthogonal Frequency-Division Multiple Access Frameworks with Low Complexity

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique which has the major drawback namely Peak to Average Power Ratio (PAPR). The high PAPR influences the efficiency of the power amplifier. The Selected Level Mapping (SLM) gives reduced PAPR contrasted with different strategies but the complexity is high due to the necessity of various Inverse Fast Fourier Transform (IFFTs). With the end goal to reduce the complexity, the proposed design requires only one IFFT, the candidate signals are produced by cyclic shifting the original time domain signal then multiplying with the distinctive genuine positive numbers. At that point the candidate with most minimal PAPR is chosen for transmission.

Dual-Polarization FBMC for Improved Performance in Wireless Communication Systems

Filter bank multi-carrier (FBMC) offers superior spectral properties compared to cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM), at the cost of an inherent shortcoming in dispersive channels called intrinsic imaginary interference. In this paper we propose a new FBMC based communication system using two orthogonal polarizations for wireless communication systems: dual-polarization FBMC (DP-FBMC). Using this system we can significantly suppress the FBMC intrinsic interference. Therefore in DP-FBMC all the multicarrier techniques used in CP-OFDM systems such as channel equalization, etc., should be applicable without using the complex processing methods required for conventional FBMC. DP-FBMC also has other interesting advantages over CP-OFDM and FBMC: it is more robust in highly dispersive channels, and also to receiver carrier frequency offset (CFO) and timing offset (TO). In our DP-FBMC system we propose three different structures based on different multiplexing techniques. We show that compared to conventional FBMC, one of these DP-FBMC structures has equivalent complexity and equipment requirements. We compare DP-FBMC with other systems through simulations. According to our results DP-FBMC has potential as a promising candidate for future wireless communication networks.

Performance Analysis of Hybrid Peak to Average Power Ratio Reduction Techniques in 5G UFMC Systems

The universal filtered multi-carrier (UFMC) technique has been proposed as a prominent waveform candidate for fifth generation (5G) communication techniques. However, UFMC systems exhibit a high peak-to-average power ratio (PAPR), which causes serious degradation in the performance of the system. Therefore, this paper puts forward an effective hybrid PAPR reduction method to reduce the high PAPR of the UFMC system. The proposed hybrid scheme consists of a combination of precoding and non-linear companding techniques (NLCTs). A comparative analysis of the performance of different precoding methods, NLCTs, and hybrid methods are investigated in terms of the cumulative distribution function of the PAPR and the bit error rate (BER). The simulation results show that the proposed hybrid UFMC system has better PAPR reduction performance compared to conventional NLC and precoded UFMC systems. Moreover, the BER analysis of the UFMC system verifies that the proposed hybrid technique shows better BER performance compared to conventional companding techniques.

Emerging 5G Multicarrier Chaotic Sequence Spread Spectrum Technology for Underwater Acoustic Communication

Generalized frequency division multiplexing (GFDM) is a newly introduced technique for the wireless fifth-generation (5G) standard based on multicarrier filter bank theory, which has the advantage of flexibility in setting the number of subcarriers and subblocks. The application of GFDM in underwater acoustic (UWA) communication can take full advantage of the limited spectral resources, which is a prime limitation in UWA communication and will promote the development of UWA network technology. However, the multicarrier communication technique utilized in radio 5G communication offers difficulty in channel estimation, and the influence of a channel cannot be ignored especially in the UWA communication field. Therefore, GFDM cannot be implemented directly in UWA communication; to solve this problem, a system combining chaotic sequence spread spectrum technology with GFDM is proposed, which is a novel technique with high spectrum efficiency. Simulation and experimental results verified the effectiveness of the proposed system.

Novel hybrid PAPR reduction schemes for the MGFDM system

Fifth generation wireless communications are expected to serve future wireless needs such as machine-to-machine communications, tactile internet, be highly reliable, have low latency and perform satisfactorily in high speed communication links. Generalized Frequency Division Multiplexing (GFDM) is one of the promising and leading candidates proposed for the 5G physical layer waveform, to fulfill the above applications. Due to the non-orthogonal pulse shaping of individual subcarriers, GFDM suffers from self interference and also increased peak amplitude. The benefit of prolate windows can be exploited to convert a non-orthogonal GFDM system to an improved orthogonal Multi-taper GFDM (MGFDM) one. Similarly to other multicarrier (MC) techniques, MGFDM also suffers from high peak-to-average-power ratio (PAPR). In this article, we first explore some of the standard PAPR reduction approaches such as, Selective Mapping (SLM), Partial Transmit Sequence (PTS) and Zadoff–Chu Transform (ZCT) and a comparative performance is carried out in terms of the cumulative distribution function (CCDF). In addition, we propose in this article a novel hybrid Walsh–Hadamard precoding with both SLM and PTS PAPR reduction techniques to further reduce the PAPR level at the transmitter side. The Walsh–Hadamard kernel which is a square wave with values ±1 helps to reduce the PAPR without introducing distortion, compared to clipping based methods. Using these proposed schemes the results show a superior PAPR reduction improvement when compared to the conventional SLM and PTS techniques. Mathematical equations of the proposed systems were derived and the corresponding complexity analysis was carried out.

Single-Carrier and Multi-Carrier 400 Gbps Transmission With Multi-Rate Multi-Format Real-Time Transceiver Prototypes

New customer usages such as on-demand high-definition videos, business analytics, and cloud services stress more and more optical transport networks. While 100 Gbps WDM systems have been widely adopted by operators to cope with the capacity growth of the past 6–7 years, a new generation of the optical transmission system is required to respond to the exponential traffic demands coming from mobile, fixed, and data center networks. Equipment manufacturers recently planned to enhance to 400 Gbps the data rate carried by WDM channels to meet this ever-increasing traffic requirement. Various trends are in competition to achieve this objective. Single-carrier and multi-carrier techniques operating at different symbol rates (i.e., 32, 45, > 60 Gbaud) and with diverse modulation formats (DP-QPSK, DP-8QAM, DP-16QAM) are proposed depending on whether transmission distance, spectral efficiency, or cost is the predominant driver. In this paper, we investigate the potential of these various 400 Gbps solutions by using real-time transceiver prototypes generating 32/64 Gbaud DP-QPSK, 45 Gbaud DP-8QAM, 32/61 Gbaud DP-16QAM formats over various fiber types (i.e., G.652, G.654, G.655 fibers). In particular, we demonstrate 400 Gbps WDM transmission with 61 Gbaud DP-16QAM channels using bandwidth-limited DAC/ADC (i.e., A NL parameter and quantify non-linear interference affecting optical channels after fiber propagation.

Low-Complexity Blind Selected Mapping Scheme for Peak-to-Average Power Ratio Reduction in Orthogonal Frequency-Division Multiplexing Systems

Orthogonal frequency-division multiplexing (OFDM) is an attractive multicarrier technique for the simplicity of equalization and high data throughput. However, the transmitted OFDM signal has a very high peak-to-average power ratio (PAPR), which severely degrades the performance of practical OFDM systems and reduces the efficiency of high-power amplifiers (HPA). The selected mapping (SLM) scheme is an effective PAPR reduction method of OFDM signals. However, this approach usually requires side information (SI) transmission, which increases the difficulty of the hardware implementation with high complexity and reduces the data transmission rate. In this paper, based on designing phase rotation vectors in the time domain, a novel blind SLM method with low complexity is proposed to reduce the PAPR of OFDM signals. At the transmitter, the proposed method properly designs the phase rotation vectors in the time domain, which can be considered as an equivalent wireless channel without SI transmission. At the receiver, the effect of phase rotation vectors can be removed by the conventional channel estimation method, and the data demodulation processing can be easily performed by the frequency domain equalization. Simulation results show that the proposed scheme can achieve low complexity in PAPR reduction and has great robustness in bit error rate (BER) performance compared to the other low-complexity SLM PAPR schemes.

Power Spectral Analysis of UW-OFDM Systems

Unique word- (UW-) orthogonal frequency division multiplexing (OFDM) is a new multicarrier technique that is shown to be superior to the cyclic prefix- (CP-) OFDM system in terms of bit-error-rate performance in fading channels. Furthermore, in the literature, it is shown by simulations that UW-OFDM has a considerably lower out-of-band (OOB) radiation compared with CP-OFDM. In this paper, we derive an analytical expression to investigate the spectral characteristics of UW-OFDM to be able to determine the effect of the different system parameters on the OOB radiation. In addition, we include in our analysis the effects of the interpolation filter and the unique word. We show that the OOB radiation in UW-OFDM is mainly determined by the number of non-modulated subcarriers reserved as the guard band, and the ratio of the UW sequence length to the number of subcarriers. By increasing either of these two parameters, we show that we can suppress the OOB radiation to any amount. This is an important advantage of UW-OFDM over classic CP-OFDM systems, and shows that UW-OFDM is an excellent candidate for cognitive radio systems.

Novel Adaptive Filter Design for Filter Bank Multicarrier System Under Doubly Dispersive Channel Conditions

ABSTRACTFilter bank multicarrier (FBMC) has emerged as the favourite multicarrier communication technique since it meets the demands of the next-generation standards, especially for communication under doubly dispersive channels. In order to combat the undesirable channel effects like inter symbol interference and inter carrier interference, the prototype filters used in FBMC systems must satisfy orthogonality conditions and be well localized simultaneously in both time and frequency domains. Even though conventional doubly localized filters are optimum in the absence of channel, they fail to satisfy orthogonality and localization criteria under doubly dispersive channels. In the present study, an adaptive filter design method is proposed in which the prototype filter is designed as the weighted sum of a time-limited Nyquist filter, a band-limited Nyquist filter, and doubly localized Gaussian filter based on the analysis of discrete ambiguity function (DAF). The filter is designed to vary its characteristics according to the maximum time and frequency domain dispersions of the channel, so that signal-to-interference ratio is maximized. In order to ensure distortion-less transmission, the perfect reconstruction criterion for distortion-less transmission is mapped to specific conditions for DAF according to two-dimensional channel scattering function. The superiority in performance of the proposed adaptive filter is analysed in terms of signal-to-interference ratio and bit error rate, and is compared with the conventional filters for various channel scattering conditions.

Coded downlink MIMO MC-CDMA system for cognitive radio network: performance results

In this letter, the error-rate (ER) performance of multiple input and multiple output multi-carrier code-division-multiple-access (MIMO MC-CDMA) is evaluated with the aid of cognitive radio network (CRN). MIMO is proven to be useful for high data rate application. MC-CDMA is used to accommodate higher number of user by eliminating channel impairments. CRN is suggested for 5G network to offer higher bandwidth by exposing idle spectrum. Multi-carrier modulation is processed inverse fast-Fourier transform at transmitter and demodulation at each receiver using fast-Fourier transform. Multi-carrier technique is introduced to obtain bandwidth efficiency and overcome the problem of frequency selectivity. At each mobile station, we estimate user’s information using MMSE based iterative algorithm. Further; the system performance is tested using channel encoder. We structure channel encoder using turbo code which is designed with the help of two convolutional encoder. The input information is interleaved using random interleaver and is fed to second convolutional encoder. We create puncturing matrix using input information and output of two convolutional encoders. Then we puncture parity bit information to obtain necessary code rate. Further, we decode and estimate information using iterative decoder which ensure higher performance with lower signal-to-noise ratio. It is vindicated from simulations that CRN based MIMO MC-CDMA system with iterative decoder swell better ER while ensuring higher data rate for downlink signal transmission.

Asynchronous Detection and Identification of Multiple Users by Multi-Carrier Modulated Complementary Set of Sequences

The correct detection of arrivals is a crucial step in any communication system, in order to achieve frame synchronization. This step is even more relevant in underwater acoustic communications, as the medium is characterized by hazardous phenomena such as long multipath delays and non-uniform Doppler shifts, which hinder the detection process. All these phenomena make the detection of arrivals and identification of multiple users in underwater communication systems a challenging task. In this paper, a multi-user detector is presented. The detection is based on the direct-sequence code-division multiple access technique, by using a combination of two sequences as a preamble: a Zadoff-Chu sequence that provides candidate peaks and frame synchronization, and a complementary set of sequences (CSS) that validates the true Zadoff-Chu arrival while at the same time identifies the user. Both sequences are modulated using multi-carrier techniques, and the users can transmit asynchronously to the channel. In the case of CSS, multi-carrier modulation techniques allow performing channel equalization and demodulation at the receiver in a simple manner, enabling the correlation of the CSS at bit level, thus keeping its ideal correlation properties. Sea trials were conducted in February 2017 at Suruga Bay, Japan, in which the reception of two different users was analyzed under different noise and multipath conditions, as well as uniform and non-uniform Doppler shifts. The results show that, even under strong multipath and non-uniform Doppler shifts caused by roll and pitch motions, the receiver is able to detect and identify the user in 98% of the transmitted packets.

QAM Signal Transmission Based on Matrix Model in Filter-Bank Multicarrier Systems

In the upcoming fifth-generation (5G) mobile network, the filter bank multi-carrier (FBMC) technique provides an alternative to cyclic prefix-orthogonal frequency-division multiplexing (CP-OFDM). The most fascinating features of FBMC are high spectral efficiency and extremely low out-of-band emissions by removing the CP and using well-localized pulse shapes. FBMC exhibits intrinsic inter-carrier/inter-symbol interference which can be mitigated by techniques such as offset quadrature amplitude modulation (OQAM). However, OQAM does not work well in multi-path fading channels. Consequently, conventional channel estimation methods and MIMO based upon space–time/frequency block coding are not straightforward applicable to the FBMC system. This paper presents two new transceiver architectures for the FBMC/QAM matrix. First of all, the matrix models of the FBMC/QAM scheme are derived. Second, based on the matrix models, three receiver methods are then described. Then, the scheme of combining FBMC/QAM with channel estimation and MIMO is proposed. Finally, two simplified receiver algorithms based on the matrix models are proposed. Simulation results indicate that the proposed transceivers of the FBMC/QAM matrix scheme can directly combine with the channel estimation and MIMO techniques used in conventional OFDM systems. Furthermore, the proposed transceivers of the FBMC/QAM matrix scheme have almost the same BER performance compared with the conventional OFDM systems.

Pseudo-Noise Sequence Based Synchronization for Generalized Frequency Division Multiplexing in 5G Communication System

As one of the candidate waveforms for 5G, generalized frequency division multiplexing (GFDM) is a flexible non-orthogonal multicarrier technique. Similar to orthogonal frequency division multiplexing, GFDM communication system suffers from symbol timing offset (STO) and carrier frequency offset (CFO) caused by multipath effect and Doppler shift. In this paper, we design a pseudo noise (PN) based preamble and propose an approach for signal synchronization. The preamble is composed of two identical PN sequences whose autocorrelation and cross-correlation are better than cyclic prefix (CP). STO can be detected by calculating the correlation coefficient between the local PN sequence of receiver and the corresponding preamble part of sliding window. These two adjacent PN sequences can be used to calculate phase offset value by Fourier transform, and then obtain CFO value. Simulation results demonstrate that, compared with conventional CP-based synchronization, the proposed approach has the lower mean square error and symbol error rate at the cost of just a little bit more bandwidth.

Throughput Analysis of Wavelet OFDM in Broadband Power Line Communications

Windowed orthogonal frequency-division multiplexing (OFDM) and wavelet OFDM have been proposed as multicarrier techniques for broadband communications over the power line network by the standard IEEE 1901. The windowed OFDM has been extensively researched and employed in different fields of communication, while the wavelet OFDM has been recently recommended for the first time in a standard. This paper is aimed to show that the wavelet OFDM, which basically is an extended lapped transform-based multicarrier modulation (ELT-MCM), is a viable and attractive alternative for data transmission in hostile scenarios, such as in-home power line communications (PLC). To this end, we obtain theoretical expressions for ELT-MCM of: 1) the desired signal power; 2) the inter-symbol interference power; 3) the inter-carrier interference power; and 4) the noise power at the receiver side. These expressions are used to derive the throughput. This paper includes several computer simulations that show that ELT-MCM is an efficient alternative to improve data rates in the PLC systems.

Combined Influence of Channel and Amplifier on Multicarrier Modulated RADAR Signals

In recent times, the domain of high speed information transfer has seen a quantum jump in performance with the advent of novel RADAR techniques. The spectrum available for programmable, pulsed radar systems is limited; hence, devising different multicarrier techniques to meet the demands for high data throughput becomes imperative. At a radar base station the amplifiers placed in the RF front end are devices that consume most of the power. It creates distortions in the transmitted signal due to its non-linear characteristics. Here, the performance of OFDM and FBMC multicarrier signals transmitted over additive white Gaussian noise (AWGN), Rayleigh fading and Rician fading channels along with the influence of the high power amplifier (HPA) are analyzed. The different types of amplifier models used for comparison are of the solid state power amplifier (SSPA) and traveling wave tube amplifier (TWTA) type. The results are compared for evident degradation in the quality metrics such as spectral efficiency and PAPR.

Automatic Multicarrier Waveform Classification via PCA and Convolutional Neural Networks

To make up the disadvantages of OFDM-QAM applied in 4G systems, some new non-orthogonal asynchronous PHY multicarrier techniques have been proposed for multiple 5G application scenarios, such as universal-filtered multicarrier (UFMC) and filterbank-based multicarrier (FBMC). Accurate classification of multiple multicarrier waveforms is indispensable in the future wireless communication systems. Here, we propose a new multicarrier waveforms classification system, which utilizes deep convolutional neural networks to classify OFDM-QAM, UFMC, and FBMC-OQAM. Since the classification accuracy is greatly reduced in AWGN environment, principal component analysis (PCA)-based processing method is proposed in this paper to suppress the AWGN and reduce the dimensions of inputs of convolutional neural networks. Amplitude data is used in this paper as input for CNN and shows promise when compared to which uses raw I/Q data as input. The dense channel environment effects including timing errors, carrier frequency offsets, and multi-fading channels are also considered in this paper and our proposed system can obtain the high classification accuracy in noisy channels.

Interference analysis for asynchrounous OFDM/FBMC based cognitive radio networks over Rayleigh fading channel

In the future fifth generation networked society, devices will suffer from the asynchronous multi-carrier effect which impacts the user’s quality of experience. This paper investigates the timing misalignment effect on interference level in the context of a cognitive radio (CR) network. Our study considers both multicarrier techniques orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC). The originality of our paper consists in proposing a simple but accurate analytical model to evaluate our system’s performance in terms of interference level, signal-to-interference-plus-noise ratio and bit error rate. Specifically, two case studies are considered, a single-user case (one primary user and one secondary user) and a multi-user case with exact theoretical expressions of interference level. We had also made a comparison between OFDM and FBMC techniques. The most striking observation to emerge from our results is that the asynchronous interference is inversely propositional to timing offset even for the multi-user case, and that differences in the normalized interference level between the single/multi-user cases is barely perceived for the FBMC technique, proving its efficiency. Our simulations’ results had further strengthened our confidence in the suggested model. It shows that FBMC is best suited for CR networks since it provides BER improvements compared to OFDM.

On MIMO‐UFMC in the Presence of Phase Noise and Antenna Mutual Coupling

AbstractThe universal filtered multicarrier (UFMC) technique has been proposed as a waveform candidate for the fifth generation (5G) communications and beyond 5G. Compared with conventional orthogonal frequency division multiplexing (OFDM), UFMC has lower out‐of‐band emission and is also compatible with the multiple‐input multiple‐output (MIMO) technique. However, like other multicarrier waveforms, it suffers from phase noise of imperfect oscillator. In contrast to the rich literature on phase noise effect on MIMO‐OFDM (where the antenna mutual coupling effect is usually omitted though), there is little work investigating the phase noise effect on MIMO‐UFMC. In this paper, we study the MIMO‐UFMC systems in the presence of phase noise and with/without mutual coupling effect. A phase noise mitigation scheme for MIMO‐UFMC systems is presented. The scheme does not require detailed knowledge of the phase noise statistics and can effectively mitigate the phase noise within each UFMC symbol. Moreover, it is shown that at small antenna separations, the performance of the MIMO‐UFMC system taking the mutual coupling effect into account is better than that when the mutual coupling effect is overlooked.