Offset Quadrature Amplitude Modulation Research Articles

IRCI-free OQAM-OFDM radar pulse compression

In this paper, a pulse compression method is proposed with the offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OQAM-OFDM) signal. By establishing the received OQAM-OFDM signal as a linear model form and without inserting any cyclic prefix (CP), we propose a concise and easily implemented pulse compression method. The proposed method realizes the inter-range-cell interference (IRCI) free pulse compression perfectly, which improves the power efficiency, and the scope of observation will not be restrained by the number of subcarriers. Besides, the signal-to-noise ratio (SNR) after the pulse compression is derived. It is proved that the SNR gain for the proposed pulse compression method can reach the same as that of the method using the matched filter. Finally, numerical simulation results are provided and discussed.

Pairs of Pilots Design for Preamble-Based Channel Estimation in OQAM/FBMC Systems

In this letter, we propose an improved pairs of pilots (POP) design method for channel estimation in offset quadrature amplitude modulation based filter bank multicarrier (OQAM/FBMC) systems. Based on an error analysis of the conventional POP channel estimation method, we first develop a heuristic pilot design in which each pilot pair is inserted at two consecutive subcarriers. Besides, we further propose to build a preamble by quartet of subcarriers and conduct a pilot optimization subject to a pilot power constraint, aiming to suppress the noise effect as much as possible. To obtain its optimal solution, we convert the original non-convex pilot optimization problem into a convex semidefinite programming problem, which is shown to be computationally efficient and readily solvable. Numerical simulations validate the effectiveness and superiority of the proposed pilot design method compared to the conventional POP and interference approximation methods.

P.648 Pre-weaning maternal rat antibiotic exposure leads to long-term neurobehavioral and neurochemical outcome in rat offspring

On the basis of coherent optical orthogonal frequency-division-multiplexing (CO-OFDM), CO-OFDM/ offset quadrature amplitude modulation (CO-OFDM/OQAM) improves the spectrum efficiency by utilizing specially designed filter banks to eliminate the cyclic prefix (CP) inserted between consecutive OFDM blocks and decreases the demanding of guard band between two channels, being a promising candidate for the next generation optical transmission link. Due to the relaxation of the orthogonal condition from the complex field to the real field, chromatic Dispersion (CD) and polarization mode dispersion (PMD) bring serious intrinsic imaginary interference (IMI) to an optical OFDM/OQAM system. Channel estimation schemes based on the interference approximation method (IAM) have been proved to be effective in suppressing the IMI with low complexity. For the IAMs, increasing the power of the pseudo pilot could decrease the effects of amplified spontaneous emission (ASE) noise and other frequency domain residual error on the channel estimation accuracy. In most of the previous reported IAM works, pilot blocks were designed according to the structure of the center pilot block loaded, while the two side pilots nulled for simplicity. However, the power of the pseudo pilot under this method did not reach the maximum, resulting in non-optimal channel estimation accuracy. In this paper, channel estimation method based on the combined phase offset (CMPO) is proposed and systematically discussed. For the proposed method, three consecutive full loaded blocks are treated as the pilot blocks and the optimal pilot structure have been obtained by utilizing the maximum likelihood algorithm. As validated by numerous Montel Carlo simulations results, system robustness against IMI, phase noised induced interference, and nonlinear effect have been improved significantly, thanks to CMPO.

Preamble Power Optimization Based on Intrinsic Interference Utilization for OQAM/FBMC Channel Estimation

Benefiting from high spectral efficiency, agility of carrier aggregation and support for asynchronous transmissions, offset quadrature amplitude modulation based filter bank multicarrier (OQAM/FBMC) is being developed as an attractive alternative to cyclic-prefix based orthogonal frequency division multiplexing (CP-OFDM) as the air interface technology for future communications. However, its non-orthogonal nature results in intrinsic interference among symbols and subcarriers, which makes channel estimation in OQAM/FBMC significantly more difficult than that in CP-OFDM. In this paper, we propose a novel preamble design method based on intrinsic interference utilization for OQAM/FBMC channel estimation. Specifically, we build a preamble by triplets of subcarriers, each of which is determined by a preamble power optimization problem that minimizes the channel estimation mean square error (MSE) at the central subcarrier. We derive the optimal closed-form solution by exploiting the linearly dependent relationship between preamble symbols and intrinsic interference weights. Moreover, extensions to multiple-input multiple-output (MIMO) setup capable of improving both spectral efficiency and channel estimation performance are investigated. Theoretical analysis and simulation results show the superiority of the proposed preamble design method over the conventional methods in terms of channel estimation MSE, bit error ratio (BER) and peak-to-average power ratio (PAPR).

Bayesian Learning-Based Doubly-Selective Sparse Channel Estimation for Millimeter Wave Hybrid MIMO-FBMC-OQAM Systems

We design and analyse filter bank multicarrier (FBMC) offset quadrature amplitude modulation (OQAM)-based millimeter wave (mmWave) hybrid multiple-input multiple-output (MIMO) systems. Furthermore, a novel channel estimation model is conceived for quasi-static mmWave hybrid MIMO-FBMC-OQAM (mmH-MFO) systems that reconfigures the radio-frequency (RF) circuitry during the transmission of zero symbols. Subsequently, a Bayesian learning (BL) technique is proposed for sparse channel estimation, which relies on multiple measurement vectors combined with selective subcarrier grouping for enhanced estimation. Additionally, an online BL based Kalman filter (OBL-KF) is designed for sparse channel tracking in doubly-selective mmH-MFO systems. Then the Bayesian Cramér-Rao lower bounds (BCRLBs) are derived for characterizing the performance of the proposed frequency-selective and doubly-selective channel estimation techniques. Finally, a limited feedback based algorithm relying on beamspace channel estimates is proposed for hybrid precoder/combiner design. The accuracy of our analytical results is confirmed by our simulation results.

A novel PTS-based PAPR reduction scheme for FBMC-OQAM system without extra bit transmission of SI

ABSTRACT In this paper, a Novel Partial Transmit Sequence-based scheme is proposed, namely (N-PTS). The aim is to solve the major hindrance of high Peak to Average Power Ratio (PAPR); as well as to combat the overlapping structure issue affecting Filter Bank Multicarrier system based on the Offset Quadrature Amplitude Modulation (FBMC-OQAM). On that note, computational complexity is also reduced. The proposed scheme uses FBMC-OQAM signal in the frequency domain. To this end, the lowest PAPR value is calculated from data located in a Storage Device (SD). Accordingly, it is properly identified through its location referred to as ’Row’ which consists of the Side Information (SI) to recover the original signal at the receiver. As a result, a substantial reduction in PAPR and computational complexity are achieved. Finally, it is found necessary to mention that SI is claimed not to require extra bits to be transmitted, using phase offset with Minimum Euclidian Distance (MED) criterion, while the Bit Error Rate (BER) performance remains very satisfactory.

Efficient Time Synchronization Method With Adaptive Resource Configuration for FBMC Systems

We propose a time synchronization method which is applicable to both offset quadrature amplitude modulation based filter-bank multicarrier (FBMC-OQAM) system and quadrature amplitude modulation based filter-bank multicarrier (FBMC-QAM) system. Based on the relation between the transmitted data symbols and FBMC signal, we design the scattered symbols to make a specific time domain region empty. Then, we insert the preamble in that region so as to transmit it perfectly. The performance of the proposed synchronization method is compared with the conventional time synchronization methods for the FBMC systems in terms of root mean square error (RMSE) of symbol timing offset (STO), bit error ratio (BER) and correctly detected data bit ratio per frame. Since the proposed method can reduce the resource usage for the synchronization, the resources for data transmission can be increased, thereby improving the spectral efficiency of the FBMC systems.

OQAM-OFDM Radar Approximated IRCI-Free Pulse Compression

This paper proposes a pulse compression method by using the offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OQAM-OFDM) signal without inserting any cyclic prefix (CP). A modified interference approximation-based pulse compression method (MIA-based PCM) is proposed, by exploiting the demodulated real weights of the OQAM-OFDM signal, the inter-symbol and inter-subcarrier interferences to enhance the performance. The MIA-based PCM achieves approximated inter-range-cell interference (IRCI)-free pulse compression and perfect Doppler estimation, which has both the benefits of power efficiency and good Doppler tolerance. Finally, numerical simulation results are provided and discussed.

Estimation of carrier frequency offset for FBMC/OQAM by using modified Kalman filtering

SummaryFilter bank multicarrier (FBMC) based on offset quadrature amplitude modulation (OQAM) is regarded as the prospective system for mobile communication. To utilize the potential of the system, the issues like carrier frequency offset have to be investigated extensively. The modulations in the multicarrier system draw a great interest among researchers and engineers in the telecommunication field. Despite the OFDM advantages, significant disadvantages in the system enable researches to approach into efficiently evolved FBMC system. In this paper, the detrimental effects caused by carrier frequency offset on the received signal is considered. Carrier Frequency Offset (CFO) compensation has been effectively undertaken by modified Kalman filtering. The compensation technique not only depends on the specific FBMC modification but also influenced by the selected receiver. A comprehensive analysis of the frequency offset response under three conditions (without offset, with offset, and the compensated samples) has been performed in the proposed system with performance measures as bit error rate (BER) and signal‐to‐noise ratio. 9 CFO compensation is analyzed by varying the channel characteristics (additive white Gaussian noise [AWGN] and Rayleigh Fading) and subcarrier filtering (prototype filter, Gaussian filter, and root‐raised coefficients). From the overall analysis, it is observed that the BER varies from 0.1 to 0.001.

Overlap-Save FBMC Receivers

Future communication systems are foreseen to support several services with different requirements. Waveform designs based on filter-bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) can offer interesting advantages in this context, such as low out-of-band power leakage and high spectral efficiency due to the lack of guard intervals. However, downsides of FBMC/OQAM with respect to a typical orthogonal frequency-division multiplexing (OFDM) solution include higher latency, higher complexity and difficulties in adapting some existing OFDM techniques such as MIMO Alamouti. To address these issues, novel FBMC receivers suitable for short prototype filters are proposed. Based on the Overlap-Save algorithm, the proposed receivers improve error-rate performance on multipath channels and support asynchronous communication. We show that complexity can be further reduced by efficiently processing blocks of FBMC symbols jointly, and that user mobility support can be traded off for additional complexity reductions in a flexible way through polynomial decomposition of the equalizer stage. Finally, we show that a block-Alamouti scheme can be applied, and we propose a MIMO equalizer with improved error-rate performance on time-varying channels, compared to the typical FBMC block-Alamouti equalizer.

Short Prototype Filter Design for OQAM-FBMC Modulation

Offset Quadrature Amplitude Modulation based Filter-Bank Multicarrier (OQAM-FBMC) has gained research interest for future wireless communication. Conventional OQAM-FBMC systems are mainly designed with long filters that offer better spectral shape. However, latency is also another key parameter when considering low response systems. Therefore, in this context, short prototype filters should be applied for OQAM-FBMC. In this letter, we propose to design short filters with low undesirable spectral emission by using an optimization method. In this approach, we propose a novel objective function to be minimized. Simulation results show that the proposed filters exhibit better behavior in comparison with the existing short filters.

Joint synchronization estimation based on genetic algorithm for OFDM/OQAM systems

This paper investigates the problem of synchronization for offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OFDM/OQAM) systems based on the genetic algorithm. In order to increase the spectrum efficiency, an improved preamble structure without guard symbols is derived at first. On this basis, instead of deriving the log likelihood function of power spectral density, joint estimation of the symbol timing offset and carrier frequency offset based on the preamble proposed is formulated into a bivariate optimization problem. After that, an improved genetic algorithm is used to find its global optimum solution. Conclusions can be drawn from simulation results that the proposed method has advantages in the joint estimation of synchronization.

Receiver design for CDMA‐FBMC/ OQAM systems

This Letter documents BER performance analysis of orthogonal affine precoder (OAP)-based CDMA filter bank multi-carrier offset QAM (CDMA-FBMC/OQAM) systems. The use of OAP cancels the interference introduced by simultaneous transmission of data and training sequence during channel estimation and data detection. This makes the channel estimation and data detection more accurate and hence, BER performance is improved. BER is calculated for different power coefficients of the superimposed training sequence and is compared with that of other FBMC systems. It is observed that the proposed system outperforms the state-of-art FBMC systems from BER perspective.

Joint Iterative filtering and companding parameter optimization for PAPR reduction of OFDM/OQAM signal

An efficient companding transform combined with iterative filtering is proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) signals. The proposed method can jointly optimize PAPR and BER performance, and effectively eliminate out-of-band radiation caused by signal amplitude distortion in the iterative process. Moreover, by adaptively adjusting transform parameters in the iterative process, more design flexibility in companding and lower out-of-band radiation are given to satisfy various system requirements. The proposed method had a simple functional form and less computational complexity, the theoretical PAPR reduction gain and the impact of companding distortion were derived. Simulation results show that this scheme can substantially offer better overall performances in terms of PAPR reduction, BER performance and bandwidth efficiency.

Preamble-Based Channel Estimation for OQAM/FBMC Systems With Delay Diversity

Delay diversity (DD) is a low-complexity and flexible transmit diversity technology for coded offset quadrature amplitude modulation based filter bank multicarrier (OQAM/FBMC) transmission systems. However, the introduction of delay parameters in DD-OQAM/FBMC systems leads to increased channel frequency selectivity, which makes the channel estimation problem more complicated. In this paper, we analyze and develop preamble-based channel estimation methods in DD-OQAM/FBMC systems from the perspective of frequency-domain, transform-domain, and time-domain aspects. Besides, channel estimators that can obtain the minimum channel estimation mean square error under least squares (LS) and linear minimum mean square error (LMMSE) criteria are derived according to different levels of channel knowledge. Specifically, the proposed frequency-domain method estimates each channel frequency response individually based on a simplified frequency-domain channel model. The transform-domain method first estimates the equivalent single-input-single-output channel observed at the receiver assuming subchannel flatness, and then uses a window function in the time domain to separate the channels of different transmit antennas. The time-domain method is constructed based on an accurate time-domain channel model to directly estimate the channel impulse response without making any assumption about the subchannel flatness. A series of simulation experiments is conducted to verify the effectivity of these channel estimation methods for DD-OQAM/FBMC systems.

Uplink sum rate analysis of multi‐user massive MIMO–OFDM/OQAM systems in Ricean fading

This study investigates the uplink performance of offset quadrature amplitude modulation (OQAM)-based orthogonal frequency division multiplexing (OFDM) waveform in single-cell multi-user massive multiple-input multiple-output (MIMO) systems over Ricean fading. An uplink training-based minimum mean square error (MMSE) channel estimation by exploiting the inherent characteristics of OFDM/OQAM waveform is briefly presented. By leveraging the second-order statistical characteristics of the intrinsic interference, the achievable uplink sum rates and corresponding closed-form approximations are derived in the presence of MMSE channel estimate at the base station with zero-forcing (ZF) and maximum-ratio combining (MRC) receivers. Based on the above analytical results for the uplink rates, power scaling laws are also investigated. The effect of Ricean-K factor on the achievable uplink sum rate is also examined analytically for both the MRC and ZF receivers. Numerical results compare the performance of OFDM/OQAM and classic cyclic-prefix OFDM-based massive MIMO systems and also validate the various analytical expressions derived in this work.

Comparison of Linear, Widely Linear and Fresh Equalizers for FBMC-OQAM Systems with Different Numerologies

This paper deals with the equalization of rectilinear and quasi-rectilinear modulated signals over frequency selective channels. This study is motivated by the fact that offset quadrature amplitude modulation based filter bank multi-carrier, one of the most prominent post orthogonal frequency division multiplexing contenders for beyond 5G wireless communication systems, employs offset quadrature modulation. This modulation is known to be cyclo-stationary and non-second order circular. Three minimum mean squared error based equalizing structures have been developed, referred to as linear (LE), widely linear (WLE) and widely linear Fresh (WL Fresh) equalizers. For the proposed equalizers, both symbol spaced and fractionally spaced processing have been evaluated, in synchronous DL/UL and asynchronous UL scenarios, with mixed numerologies transmissions. The simulation results show the ability of WL Fresh equalizer to suppress inter-numerology and inter-symbol interferences over frequency selective channels, outperforming the WLE and LE equalization schemes.

Channel Estimation Performance Analysis of FBMC/OQAM Systems with Bayesian Approach for 5G-Enabled IoT Applications

A filter bank multicarrier (FBMC) with offset quadrature amplitude modulation (OQAM) (FBMC/OQAM) is considered to be one of the physical layer technologies in future communication systems, and it is also a wireless transmission technology that supports the applications of Internet of Things (IoT). However, efficient channel parameter estimation is one of the difficulties in realization of highly available FBMC systems. In this paper, the Bayesian compressive sensing (BCS) channel estimation approach for FBMC/OQAM systems is investigated and the performance in a multiple-input multiple-output (MIMO) scenario is also analyzed. An iterative fast Bayesian matching pursuit algorithm is proposed for high channel estimation. Bayesian channel estimation is first presented by exploring the prior statistical information of a sparse channel model. It is indicated that the BCS channel estimation scheme can effectively estimate the channel impulse response. Then, a modified FBMP algorithm is proposed by optimizing the iterative termination conditions. The simulation results indicate that the proposed method provides better mean square error (MSE) and bit error rate (BER) performance than conventional compressive sensing methods.

Low Complexity Maximum Likelihood FBMC QAM for Improved Performance in Longer Delay Channels

Filter bank multi-carrier (FBMC) is an emerging 5G technology due to its finer spectral characteristics than its counterpart orthogonal frequency-division multiplexing (OFDM). In most cases, FBMC is united with an Offset Quadrature Amplitude modulation (OQAM) for individual sub-carrier to maximize the spectrum efficiency and Nyquist rate. But it is achieved at the cost of an inherent accumulative imaginary interference called intrinsic interference. When a channel is highly selective, the FBMC system undergoes inter-symbol-interference (ISI) and co-channel interference (CCI). In this research, we consider FBMC QAM as a solution to intrinsic interference and mitigates both ISI and CCI by incorporating ML equivalent signal detection. In this paper, some of the prominent issues related to the existing FBMC–OQAM are explored and its potential integrity constraints with existing MIMO and signal detection techniques are studied. In addition to that, a lightweight optimized ML which constitutes parallel sub-detectors with the least hardware complexity overhead is proposed. It also achieved a near-optimal performance that matches the CP-OFDM system. In this research, the experimental results proved that the proposed suboptimal ML detector offered significant complexity reduction with improved quality of services. Thus evidently shows the proposed system is attractive from both BER performance and hardware complexity reduction perspectives for 5G communications.

SSB Pruned DFT-Spread FBMC Signal With Low PAPR in Direct-Detection PONs

Filter bank multi-carrier (FBMC) using offset quadrature amplitude modulation (OQAM) has recently attracted increasing interests for the next-generation high-speed optical transmission systems, due to the salient FBMC modulation advantages in terms of high spectrum efficiency by completely removing the cyclic prefix. However, high peak-to-average power ratio (PAPR) still plays a key role of constraining the performance of FBMC systems. In this paper, we investigate a single sideband (SSB) pruned discrete Fourier transform (DFT)-spread FBMC for direct-detection (DD) passive optical network systems (PONs). It is demonstrated that the PAPR of the SSB pruned DFT-spread FBMC signal with the overlapping factor of 1.56 outperforms the conventional FBMC signal and the simple DFT-spread FBMC signal by ∼2 dB and 1 dB at the complementary cumulative distribution function (CCDF) of 1 × 10−3, respectively. Finally, by using the pruned DFT-spread FBMC with low PAPR, the aggregate data rate of 50-Gbit/s can be achieved after 50-km single mode fiber (SMF) transmission below the 7% hard decision forward-error correction (HD-FEC) threshold in the DD PONs.