Modulation-based Filter Bank Multicarrier Research Articles

BER performance analysis of polar-coded FBMC/OQAM in the presence of AWGN and Nakagami-m fading channel

<abstract> <p>Offset quadrature amplitude modulation–based filter bank multicarrier (FBMC-OQAM) method is a promising technology for future wireless communication systems. It offers several advantages over traditional orthogonal frequency-division multiplexing (OFDM) modulation, including higher spectral efficiency, lower out-of-band emission, and improved robustness to time-frequency selective channels. Polar codes, a new class of error-correcting codes, have received much attention recently due to their ability to achieve the Shannon limit with practical decoding complexity. This paper analyzed and investigated the error rate performance of polar-coded FBMC-OQAM systems. Our results show that applying polar codes to FBMC-OQAM systems significantly improves the error rate. In addition, we found that employing random code interleavers can yield additional coding gains of up to 0.75 dB in additive white Gaussian noise (AWGN) and 2 dB in Nakagami-m fading channels. Our findings suggest that polar-coded FBMC-OQAM is a promising combination for future wireless communication systems. We also compared turbo-coded FBMC-OQAM for short code lengths, and our simulations showed that polar codes exhibit comparable error-correcting capabilities. These results will be of interest to researchers and engineers working on the advancement of future wireless communication systems.</p> </abstract>

Symbol Encryption and Placement Design for OQAM/FBMC Systems

In this paper, we propose a symbol encryption method based on the complex-valued symbol multiplication and design the encryption symbol placement for offset quadrature amplitude modulation based filter bank multicarrier (OQAM/FBMC) systems. Specifically, we firstly analyze the encryption and decryption effects of complex-valued symbol multiplication on the original OQAM symbols. Then, by utilizing the intrinsic interference characteristics of prototype filters, a symbol encryption method and the placement design are proposed to simultaneously achieve the encryption of all OQAM symbols and low complexity decryption. Finally, the symbol error rate (SER), average signal transmit power, computational overhead and power spectral density (PSD) are analyzed. Simulation results are consistent with the theoretical analysis and demonstrate that the proposed method outperforms the traditional method based on imaginary-valued encryption symbol insertion in terms of the SERs of both legitimate and illegitimate receivers.

Block-Wise Preamble Design in OQAM/FBMC Systems With Interference Cancellation

In this letter, we propose a novel complex-valued offset quadrature amplitude modulation based filter bank multicarrier (OQAM/FBMC) system with interference cancellation. Specifically, we construct the frame structure of OQAM/FBMC in a frequency-reversal form, where complex-valued symbols are transmitted repeatedly at paired symmetric subcarriers, with appropriate sign changes being inserted to achieve a complete self-cancellation of the intrinsic interference. Besides, we further present a block-wise preamble design method with frequency reversal to reduce the pilot overhead. The whole preamble is divided into multiple subblocks of equal size, each of which is optimally designed to provide a virtual boost of the pseudo-pilot power. Simulation results validate the effectiveness of the proposed complex-valued OQAM/FBMC and significant performance gains are demonstrated against conventional methods with the block-wise preamble design method.

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.

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).

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.

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.

Receivers for VBLAST FBMC-OQAM Systems

We consider vertical Bell laboratories layered space-time architecture for offset quadrature amplitude modulation based filter bank multicarrier (FBMC) systems, and propose two different receivers. We first investigate a low-complexity QR decomposition (QRD) based conventional minimum mean square error (MMSE) successive interference cancellation (C-MMSE-SIC) receiver. The intrinsic interference in FBMC systems severely degrades the symbol error rate (SER) of the C-MMSE-SIC receiver. By exploiting the overlapping nature of neighboring symbols in an FBMC system, and the fact that the desired symbol in an FBMC system interferes with the symbols in a small neighborhood, we propose novel low-complexity intrinsic interference estimation (IIE) based sequential MMSE-SIC (IIE-SMMSE-SIC) receivers with QRD and its sorted version. We show that the IIE-SMMSE-SIC receivers, with similar complexity order as that of the C-MMSE-SIC, have lower SER.

Prototype Filter Design to Minimize Stopband Energy With Constraint on Channel Estimation Performance for OQAM/FBMC Systems

In this paper, we propose a prototype filter design method to minimize the stopband energy of the filter with guaranteed time-domain channel estimation performance for offset quadrature amplitude modulation based filter bank multicarrier (OQAM/FBMC) systems. First, we analytically derive the total mean squared error (MSE) of estimated channel impulse response with two channel estimation schemes, i.e., the linear minimum mean square error and weighted least square, where the impact of intrinsic interference from data symbols is taken into account. Then, we formulate an optimization problem of filter coefficients to minimize the stopband energy with constraint on the total MSE. By exploiting the Heisenberg–Gabor uncertainty principle, the original optimization problem is transformed into an equality-constrained one. Finally, we employ the Lagrange multiplier method to solve the transformed problem and obtain the filter coefficients with the Newton’s method. Simulation results demonstrate that the proposed filter outperforms the isotropic orthogonal transform algorithm and extended Gaussian function filters considering both the MSE and stopband energy performances.

Pilot-Aided Channel Estimation Utilizing Intrinsic Interference for FBMC/OQAM Systems

This paper proposes a novel channel estimation technique for the offset quadrature amplitude modulation based filter bank multi-carrier (FBMC/OQAM) systems. Unlike the conventional approaches, the proposed pilot signals utilize their intrinsic interference for the channel estimation, and provide an improved power efficiency compared to the conventional auxiliary pilot method. However, due to the non-whiteness of the noise components at the output of the analysis filter banks, the power gain obtained by the proposed scheme cannot be maximized. To overcome this difficulty, we propose a semiblind channel estimation by grouping the pilot signals and imposing sign ambiguities to them. Theoretical analysis shows that the proposed semiblind channel estimation remarkably improves the power efficiency of its non-semiblind version. Finally, it is demonstrated that the near optimum detection performance is achieved by the proposed scheme at a reduced complexity.

Adaptive filterbank-based multi-carrier waveform design for flexible data rates

Filterbank-based multicarrier (FBMC) scheme is one of the candidate waveforms to handle possible problems in next-generation communication systems, such as high out-of-band (OOB) emission and large peak-to-average power ratio (PAPR). In LTE (Long Term Evaluation), the frequency spectrum is shared by users with pre-defined bandwidths (i.e., 1,4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz), which is not a flexible solution for users having different data rate demands. Similarly, in conventional FBMC systems, bandwidth is divided into equal subbands. Recent studies on FBMC modulation have not provided an effective remedy for such users. Motivated by this requirement, we propose a novel FBMC waveform design that allows an adaptive bandwidth allocation scheme. Accordingly, users will not be restricted to the specified bandwidth schedules. In the paper, subband-based and subcarrier based filtering models are constructed with polyphase filter structures. The proposed structures are realized analytically and tested through computer simulations for different scenarios.

A Fair Radio Resource Allocation Algorithm for Uplink of FBMC Based CR Systems

Spectrum scarcity seems to be the most challenging issue to be solved in new wireless telecommunication services. It is shown that spectrum unavailability is mainly due to spectrum inefficient utilization and inappropriate physical layer execution rather than spectrum shortage. Daily increasing demand for new wireless services with higher data rate and QoS level makes the upgrade of the physical layer modulation techniques inevitable. Orthogonal Frequency Division Multiple Access (OFDMA) which utilizes multicarrier modulation to provide higher data rates with the capability of flexible resource allocation, although has widely been used in current wireless systems and standards, seems not to be the best candidate for cognitive radio systems. Filter Bank based Multi-Carrier (FBMC) is an evolutionary scheme with some advantages over the widely-used OFDM multicarrier technique. In this paper, we focus on the total throughput improvement of a cognitive radio network using FBMC modulation. Along with this modulation scheme, we propose a novel uplink radio resource allocation algorithm in which fairness issue is also considered. Moreover, the average throughput of the proposed FBMC based cognitive radio is compared to a conventional OFDM system in order to illustrate the efficiency of using FBMC in future cognitive radio systems. Simulation results show that in comparison with the state of the art two algorithms (namely, Shaat and Wang) our proposed algorithm achieves higher throughputs and a better fairness for cognitive radio applications.

Channel Equalization in Filter Bank Based Multicarrier Modulation for Wireless Communications

Channel equalization in filter bank based multicarrier (FBMC) modulation is addressed. We utilize an efficient oversampled filter bank concept with 2x-oversampled subcarrier signals that can be equalized independently of each other. Due to Nyquist pulse shaping, consecutive symbol waveforms overlap in time, which calls for special means for equalization. Two alternative linear low-complexity subcarrier equalizer structures are developed together with straightforward channel estimation-based methods to calculate the equalizer coefficients using pointwise equalization within each subband (in a frequency-sampled manner). A novel structure, consisting of a linear-phase FIR amplitude equalizer and an allpass filter as phase equalizer, is found to provide enhanced robustness to timing estimation errors. This allows the receiver to be operated without time synchronization before the filter bank. The coded error-rate performance of FBMC with the studied equalization scheme is compared to a cyclic prefix OFDM reference in wireless mobile channel conditions, taking into account issues like spectral regrowth with practical nonlinear transmitters and sensitivity to frequency offsets. It is further emphasized that FBMC provides flexible means for high-quality frequency selective filtering in the receiver to suppress strong interfering spectral components within or close to the used frequency band.