Multicarrier Communication Systems Research Articles

Multicarrier Acoustic Communications in Multiuser and Interference-Limited Regimes

In this article, we address the design of a multicarrier communication system based on orthogonal frequency-division multiplexing and direct sequence spread spectrum. The design targets operation in the low-signal-to-noise-ratio regimes and multiuser settings. Specifically, coding is employed across carriers such that channel estimation and signal detection are coupled. We consider both coherent and differentially coherent detection and extend the principles to multichannel reception. A custom-designed frequency synchronization technique is proposed to counteract the motion-induced Doppler frequency shifting effect. Using the recordings from the 2010 Mobile Acoustic Communication Experiment, where signals were transmitted in the 10.5–15.5-kHz acoustic band in shallow water, with relative motion up to 1.5 m/s, we demonstrate the system performance in terms of the mean squared error and bit error rate in data detection. Further employing Polar and low-density parity-check coding, we show that the proposed methods provide excellent performance while maintaining low computational complexity, making them suitable for a practical implementation.

On the Exposure Dose Minimization of Multi-Antenna Multi-Carrier System Users

From the fourth generation (4G) of cellular systems onward, wireless personal devices (WPDs) support multi-input multi-output (MIMO) communication. However, the impact of MIMO communication on the electromagnetic field (EMF) of WPD users has yet to be fully understood and analyzed at the system level. In this paper, we first provide a generic model for assessing the individual exposure dose of multi-antenna WPD users in a multi-user multi-carrier communication system. An optimization framework for minimizing this exposure dose is then developed based on our exposure model. This framework helps us to identify a new criterion, i.e., the ratio between the normalized exposure dose and the channel to noise ratio (CNR), as the main system level criterion for minimizing the individual exposure dose of multi-antenna WPD users. This criterion is further integrated in the design of two novel centralized resource allocation schemes that take advantage of the multiple antennas at the WPD to minimize the per-user exposure dose, when full or limited knowledge of each user channel is available. Our new schemes can significantly reduce the individual exposure dose of WPD users (by approximately 80%) in comparison with the most relevant existing resource allocation schemes. Our results also provide insights into the logarithmic relationship between the per-user exposure dose and the number of receive antennas (or the number of time slots), and how such a parameter can be exploited to further reduce the exposure and/or provide a higher SE while maintaining a low exposure dose.

OTFS vs. OFDM in the Presence of Sparsity: A Fair Comparison

Many recent works in the literature declare that Orthogonal Time-Frequency-Space (OTFS) modulation is a promising candidate technology for high mobility communication scenarios. However, a truly fair comparison with its direct concurrent and widely used Orthogonal Frequency-Division Multiplexing (OFDM) modulation has not yet been provided. In this paper, we present such a fair comparison between the two digital modulation formats in terms of achievable communication rate. In this context, we explicitly address the problem of channel estimation by considering, for each modulation, a pilot scheme and the associated channel estimation algorithm specifically adapted to sparse channels in the Doppler-delay domain, targeting the optimization of the pilot overhead to maximize the overall achievable rate. In our achievable rate analysis we consider also the presence of a guard interval or cyclic prefix. The results are supported by numerical simulations, for different time-frequency selective channels including multiple scattering components and under non-perfect channel state information resulting from the considered pilot schemes. This work does not claim to establish in a fully definitive way which is the best modulation format, since such choice depends on many other features which are outside the scope of this work (e.g., legacy, intellectual property, ease and know-how for implementation, and many other criteria). Nevertheless, we provide the foundations to properly compare multi-carrier communication systems in terms of their information theoretic achievable rate potential, within meaningful and sensible assumptions on the channel models and on the receiver complexity (both in terms of channel estimation and in terms of soft-output symbol detection).

Precoder and Decoder Co-Designs for Radar and Communication Spectrum Sharing.

The coexistence of radar and communication systems is necessary to facilitate new wireless systems and services due to the shortage of the useful radio spectrum. Moreover, changes in spectrum regulation will be introduced in which the spectrum is allocated in larger chunks and different radio systems need to share the spectrum. For example, 5G NR, LTE and Wi-Fi systems have to share the spectrum with S-band radars. Managing interference is a key task in coexistence scenarios. Cognitive radio and radar technologies facilitate using the spectrum in a flexible manner and sharing channel awareness between the two subsystems. In this paper, we propose a nullspace-based joint precoder–decoder design for coexisting multicarrier radar and multiuser multicarrier communication systems. The maximizing signal interference noise ratio (max-SINR) criterion and interference alignment (IA) constraints are employed in finding the precoder and decoder. By taking advantage of IA theory, a maximum degree of freedom upper bound for the -radar-communication-user interference channel can be achieved. Our simulation studies demonstrate that interference can be practically fully canceled in both communication and radar systems. This leads to improved detection performance in radar and a higher rate in communication subsystems. A significant performance gain over a nullspace-based precoder-only design is also obtained.

A Fair SINR Performance Comparison of FBMC/OQAM and FBMC/QAM Multicarrier Communication Systems in the Discrete-Time Framework

In the last couple of decades, multicarrier modulations have witnessed a considerable interest in wireless communication networks due to their ability to fight against multipath fading and offer multiple access with flexible resource sharing. One of the well known multicarrier modulation systems is filter-bank multi-carrier with an offset quadrature amplitude modulation (FBMC/OQAM), which was proposed as a powerful solution during the standardization of 5G. In this paper, we derive a closed-form expression of the signal to interference plus noise ratio (SINR) for FBMC/OQAM systems in the discrete-time context, for arbitrary wide sense stationary uncorrelated scattering (WSSUS) channels as well as transmitter (Tx) and receiver (Rx) waveforms. We quantify the potential gains in SINR brought by FBMC/OQAM, which exclusively operates on critical lattice density, with respect to FBMC/QAM, which have the flexibility to operate on critical or non-critical lattice densities. For completeness, we compare the performance of FBMC/OQAM in the discrete-time context, sweeping the discrete space of waveforms supports, with that of FBMC/OQAM in the continuous-time context, using the Hermite functions, and show how they perform similarly. Simulation results prove that FBMC/OQAM optimization algorithm, performing with the ping-pong optimized pulse shaping (POPS) paradigm, converges rapidly to excellent SINR values, even with small supports durations, in discrete-time context, which is equivalent to a reduced number of Hermite functions, in the continuous-time context.

Iterative Interference Cancellation for Multi-Carrier Modulation in MIMO-DWT Downlink Transmission

The Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) scheme represents the dominant radio interface for broadband multicarrier communication systems. However, with insufficient Cyclic Prefixes (CP), Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) occur due to the time-varying multipath channel. This means that the performance of the system will be degraded. In this paper, we investigate the interference problem for a MIMO Discrete Wavelet Transform (MIMO-DWT) system under the effect of the downlink LTE channel. A Low-Density Parity-Check (LDPC) decoder is used to estimate the decoded signal. The proposed iterative algorithm uses the estimated decoded signal to compute the components required for ICI/ISI interference reduction. In this paper, Iterative Interference Cancellation (IIC) is employed to mitigate the effects of interference that contaminates the received signal due to multiple antenna transmission and a multipath channel. An equalizer with minimum mean square error is considered. We compare the performance of our proposed algorithm with the traditional MIMO-OFDM scheme in terms of bit error probability under insufficient CP. Simulation results verify that significant improvements are achieved by using IIC and MIMO-IIC for both systems.

A novel efficient time and frequency waveform design for filter bank multicarrier communication systems by using Hybrid gray wolf optimization algorithm

To realize reliable high data rate transmission in multicarrier communication systems, the orthogonality of prototype filters in time and frequency is required. However, the time and frequency dispersion of the mobile radio channel leads to the loss of orthogonality which produces intersymbol interference (ISI) and interchannel interference (ICI). Therefore, the prototype filter design plays a critical role in the performance of multicarrier systems. In this paper, we address this issue as an optimization problem. To the best of our knowledge, in all previous prototype filter optimization algorithms, a solution is obtained by working on the samples of filter only in time or frequency domains to satisfy both time and frequency domain characteristics. In this study, the proposed algorithm jointly works on the filter samples both in time and frequency domains. To do this, the hybrid of gray wolf optimization (GWO), Levenberg Marquardt (LM) and pattern search (PS) algorithms is introduced. The GWO algorithm used for exploring space, the LM and PS algorithms exploit the solution, locally. While the PS algorithm nondeterministically changes the samples, the LM algorithm moves all samples by considering gradient descent direction. Furthermore, a smoothing approach is used to achieve better characteristics of designed filter by applying a moving average filter. By using the proposed algorithm, prototype filters can be designed with any possible characteristics based on the user preferences, while in other studies, usually filters are designed with some limited special characteristics. Simulation results show that the prototype filter which is obtained by our proposed algorithm, achieves better characteristics in comparison with the other conventional filters.

Performance analysis of OFDM-IM scheme under STO and CFO

In this letter, performance analysis of orthogonal frequency division multiplexing with index modulation (OFDM-IM) is presented in term of bit error rate (BERs). The analysis considers its performance under two impairments, symbol time offset (STO) and carrier frequency offset (CFO) in frequency-selective fading channel. As orthogonal multicarrier system, OFDM-IM is subject to both inter-symbol interference (ISI) and inter-carrier interference (ICI) in a frequency-selective fading channel. OFDM-IM is a new multicarrier communication system, where the active subcarriers indices are used to carry additional bits of information. In general, in the previous existing works, OFDM-IM are evaluated only for near-ideal communication scenarios by only incorporating the CFO factor. In this work, the OFDM-IM performance is investigated and compared with conventional OFDM in the presence of two impairments, STO and CFO. Simulation results show that OFDM-IM outperforms the conventional OFDM with the presence of STO and CFO, especially at high SNR areas.

Performance comparison of multicarrier communication systems over doubly-selective channels

To mitigate the effect of 5G wireless channel, new multicarrier with robust features and waveform needs to replace the conventional OFDM system. In this study, three adopted multicarrier systems are employed and compared with OFDM including FBMC, FOFDM and UFMC over 5G channel. The BER performance, PAPR and PSD are compared with OFDM system. One tap frequency domain equalizer is used with all multicarrier systems and test the performance over 5G channel. The consequences show that, FBM has the best BER at high Doppler spread and has lowest PSD. In the other side, FBMC has highest PAPR comparing with other multicarrier system.

Flexible OFDM Transceiver for Underwater Acoustic Channel: Modeling, Implementation and Parameter Tuning

Acoustic signals are a first choice in underwater communication since sound waves face very low attenuation in water compared to radio frequency (RF). However, the tendency of receiver to detect multipath signals (due to signals bouncing off surface or the bottom) induces large delay spreads and thus strong channel frequency selectivity. Additionally, rapid spatial and temporal variations in underwater acoustic (UWA) channel makes it hostile for communication systems based on single carrier modulation. Multicarrier modulation techniques, on the other hand, can greatly improve bandwidth utilization and help deal with time dispersal effects. Orthogonal frequency division multiplexing (OFDM) is a proven multicarrier communication system having capabilities to cope with frequency selectivity and delay spreads effectively. OFDM has started to get attention for being a simpler alternative to high complexity and high maintenance single carrier systems in UWA communication systems. This work proposes a Matlab model of an OFDM transceiver along with UWA channel characterization based on Rician shadowed fading model as it perfectly characterizes the way in which a shallow UWA channel behaves. Eventually, the proposed design allows implementation of various OFDM modulation methods and to perform Monte Carlo simulations for bit error rate comparisons together with the ability to tune multiple UWA channel parameters.

Intelligent Indoor Positioning Based on Artificial Neural Networks

LBS has become an integral part of people's life nowadays. However, the GPS restricted by the shielding effect is unavailable for indoor environments. Therefore, accurately locating an electronic device indoors has become a challenging issue in recent years. This work employs the CSi combined with neural networks to achieve an accurate indoor positioning. The CSi refers to known channel properties of a communication link in wireless communications. This information describes how a signal propagates from the transmitter to the receiver and represents the combined effects of, for example, scattering, fading, and power decay with distance. This work will evaluate several neural networks for the positioning, including the FCNN, CNN, and GCNN. in multi-carrier communication systems, the CSi of adjacent subcarriers has a high correlation, and hence, the CNN is promising to learn and extract the features of this input information corresponding to the location of radio devices. Beyond that, we also investigate an improved CNN, that is, the GCNN, which has more talent to locate in indoor environments than traditional CNNs. Experimental results show that the proposed GCNN can achieve a root-mean-square error (RMSE) of less than 0.08m and 0.3m for 16 and two antennas, respectively. in addition, the computational complexities and required numbers of parameters of compared deep neural networks have been analyzed as well.

Full spark of even discrete cosine transforms

In this paper, we investigate the spark of a family of transforms that are frequently used in signal processing applications such as Multicarrier Communication systems: we consider the even Discrete Cosine Transform matrices (DCTs). On one hand, we provide several theorems that prove that the submatrices obtained from its first rows present maximum spark; on the other hand, we give counterexamples of other sets of rows that do not present this good property. Besides the mathematical interest of our contributions, we also show that our results have important novel applications in compressed sensing problems such as sparse signal reconstruction and compressed channel estimation. We also demonstrate that a channel filter can be perfectly estimated by means of a small amount of its DCT coefficients, which can be furthermore arbitrarily selected. Thus, random compressive sampling schemes are valid for solving channel estimation problems when using even DCTs. Finally, numerical simulations show the good performance of the DCT transforms for practical sparse signal recovery in both noisy and noise-free scenarios.

Frequency synchronization for FBMC-based massive MIMO system uplink

Frequency synchronization and channel equalization are of a great importance in any multicarrier communication system. Hence, in this paper, a joint carrier frequency offset (CFO) and channel estimation approach is proposed for multiuser filter bank multicarrier (FBMC) in the uplink of massive multiple input multiple output (MIMO) systems. Our proposed solution jointly estimates the CFO and channel responses based on the maximum likelihood (ML) criterion. The computational complexity of the estimator is high due to a large number of antennas at the base station (BS). To address this issue, a low-complexity CFO estimation technique is investigated after combining the received signals at the BS antennas. It is worth mentioning that our proposed method estimates both integer and fractional part of CFO values. Also, to characterize the accuracy of our estimation techniques, the asymptotic Cramér–Rao bounds (CRBs) are derived. Furthermore, the CFO correction and channel equalization techniques are performed for FBMC systems. Finally, we show the efficacy of our proposed algorithms through numerical results.

Mitigation Techniques for Impulsive Noise With Memory Modeled by a Two State Markov-Gaussian Process

Impulsive noise, a common impediment preventing the system from achieving error-free transmission, is significant in many wireless and power line communication environments. Although the performance of several mitigation techniques for orthogonal frequency division multiplexing (OFDM)-based multicarrier communication systems impaired by memoryless impulsive noise are widely acknowledged, we note that OFDM is outperformed by its single-carrier counterpart when the impulses are very strong and/or they occur frequently, which is likely to exist in contemporary communication systems including smart grid communications. On the other hand, many communication technologies used in the smart grid do not employ OFDM and likewise, the assumption of memoryless noise is not valid for such communication scenarios. Memoryless noise models cannot take into account one of the main features of the actual noise, i.e., the time-correlation among the noise samples. The aim of this article is to compare and analyze several mitigation techniques such as clipping, blanking, and combined clipping-blanking to mitigate the noxious effects of bursty impulsive noise for low-density parity-check coded single-carrier communication systems. Moreover, we propose a log-likelihood ratio (LLR)-based impulsive noise mitigation for the considered scenario. In this context, provided simulation results highlight the superiority of the LLR-based mitigation scheme over the clipping/blanking schemes.

The research on 220GHz multicarrier high-speed communication system

This paper presents our investigation into a 220 GHz multicarrier high-speed communication system based on solid state transceivers. The proposed system has eased the demand of high sampling rate analog-to-digital converter (ADC) by providing several signal carriers in microwave band and converting them to 220 GHz channel. The system consists of a set of 220 GHz solid-state transceiver with 2 signal carriers, two base-bands for 4 GSPS ADCs. It has achieved 12.8 Gbps rate real-time signal transmission using 16QAM modulation over a distance of 20 m without any other auxiliary equipment or test instruments. The baseband algorithm overcomes the problem of frequency difference generates by non-coherent structure, which guarantees the feasibility of long-distance transmission application. Most importantly, the proposed system has already carried out multi-channel 8K video parallel transmission through switch equipment, which shows the multicarrier high-speed communication system in submillimeter wave has great application prospects. To the best of the authors' knowledge, this is the first all-solid-state electronics multicarrier communication system in submillimeter and terahertz band.

A Novel Design and Implementation of FBMC Transceiver for Low Power Applications

The complex structure of the Filter Bank Multicarrier (FBMC) communication system is the main drawback affecting the performance of the system and causes a high-power consumption. The complexity arises from using a polyphase filter bank, which consists of fast Fourier Transform/ Inverse Fast Fourier Transform (FFT/IFFT) processors and a filter bank of Finite Impulse Response (FIR) filters. This paper presents the analysis and the implementation of a new design model for FBMC transceiver in which the polyphase filter is removed completely in both transmitter and receiver and uses instead of it, a multi-level cascaded structure of FIR subfilters. The coefficients of each subfilter selected using an optimization algorithm to minimize the amplitude of sidelobes compared to the amplitude of the main lobe in the frequency response of the subfilter. The proposed design reduces the number of multiplications compared to the conventional design by 65%. The field-programmable gate array (FPGA) implementation results indicate that the proposed architecture saves 24% of resources of the FPGA board, works faster, and saves 27% of power consumption compared to conventional FBMC transceiver.

A Novel Design and Implementation of FBMC Transceiver for Low Power Applications

The complex structure of the Filter Bank Multicarrier (FBMC) communication system is the main drawback affecting the performance of the system and causes a high-power consumption. The complexity arises from using a polyphase filter bank, which consists of fast Fourier Transform/ Inverse Fast Fourier Transform (FFT/IFFT) processors and a filter bank of Finite Impulse Response (FIR) filters. This paper presents the analysis and the implementation of a new design model for FBMC transceiver in which the polyphase filter is removed completely in both transmitter and receiver and uses instead of it, a multi-level cascaded structure of FIR subfilters. The coefficients of each subfilter selected using an optimization algorithm to minimize the amplitude of sidelobes compared to the amplitude of the main lobe in the frequency response of the subfilter. The proposed design reduces the number of multiplications compared to the conventional design by 65%. The field-programmable gate array (FPGA) implementation results indicate that the proposed architecture saves 24% of resources of the FPGA board, works faster, and saves 27% of power consumption compared to conventional FBMC transceiver.

FBMC + Security – A New Candidate for 5G

Recent researches and discussions stress the need for waveforms with better spectral efficiency which could be obtained by Orthogonal Frequency Division Multiplexing (OFDM). OFDM supports multicarrier communication and is capable of mitigating Inter Symbol Interference. Hence there is no need of equalizer at the receiving side. Human life has become easy and comfortable due to the rapid of wireless technology. At the same time there is an increase in the number of malicious users and the threat created by them for secure data transmission is noteworthy. Hence this work aims at to provide a solution which could solve the above discussed issues. Filter banks with multicarrier communication systems has gained popularity because of its capability to overcome the spectral leakage. Hence filter banks are placed instead of cyclic prefix. Near perfect reconstruction filter has been utilized to reduce the leakage. Further, Secure data transmission is accomplished by means of authentication tag. Pseudo Noise (PN) sequence named XOROSHIRO has been generated and appended with the information to be transmitted. At the receiving end only the information with authentication tag is accepted and the rest are omitted. FBMC system together with the authentication tag improves the spectral efficiency and also ensures safe and successful communication.

A Construction of Binary Golay Complementary Sets Based on Even-Shift Complementary Pairs

Orthogonal frequency division multiplexing (OFDM) has been widely used in multi-carrier communication systems. However, high the peak-to-average power ratio (PAPR) is a very troublesome problem in OFDM system. In the paper, we propose a construction of Golay complementary sets (GCSs) with size 4 of flexible lengths using even-shift complementary pairs (ESCPs). Based on computer search, we find that there exist a large number of even-shift complementary pairs of various lengths, and we also propose some constructions of ESCPs, which are very useful for the construction of GCSs.

웨이블릿패킷변환 방식의 다중반송파 통신시스템의 설계와 스펙트럼 특성

웨이블릿패킷변환 방식의 다중반송파 통신시스템의 설계와 스펙트럼 특성