Cyclic Prefix OFDM Research Articles

FBMC as 5G candidate for high speed mobility

Beyond 4G, communication systems will be highly flexible and more congested. This is because of the increased demand for wireless applications, such as machine type communications (MTC) aside from the cellular mobile communications. Hence the need for the next generation, 5G, becomes essential. In the 4G systems, the cyclic-prefix orthogonal frequency division multiplexing (CP-OFDM) has been adopted as a modulation technique. However, CP-OFDM suffers from the spectrum waste problem, because of the high out of band (OOB) emission. Thus, not all frequency spectrums will be useful. On the other hand, the required, increased demand, for high data rate motivated the industry to find another candidate as a modulation technique to be adopted in the next generation. Different candidates have been introduced; the Filter Bank Multi-Carrier (FBMC) is one of the promising candidates for that job. In this paper, we will show that the FBMC can be employed in 5G communication systems and can exploit almost, all, the advantages of the previous, CP-OFDM, system with little increment in the complexity, such as the implementation of multiple input-multiple output (MIMO) antenna diversity, and the high throughput with noteworthy mobility speeds.

Study of OFDM Precoded Filter-Bank Waveforms

Forthcoming wireless systems will have to cope with heterogeneous and dense traffic. High demands in terms of bandwidth use efficiency and increased flexibility are therefore required for the related air-interface technology. In this context, Filter-Bank MultiCarrier with Offset QAM (FBMC/OQAM) waveform has been recognized as an enabling technology providing strong assets with a well-confined spectrum and enhanced spectral efficiency with respect to cyclic prefix orthogonal frequency-division multiplexing (OFDM). Nonetheless, FBMC-OQAM presents a few challenges to overcome: the intrinsic interference must be taken into consideration in the channel estimation processes and multiple antenna schemes’ design. Those challenges are induced by the reduction of the orthogonality property to the real field. In this paper, OFDM precoding/decoding is proposed as an alternative to the OQAM signaling for filter-bank-based waveforms. The OFDM precoding makes the waveforms near-complex orthogonal, which enables a straightforward adaptation to channel estimation techniques and MIMO scheme design. Two waveforms based on this precoding, namely fast Fourier transform FBMC and block-filtered OFDM, have been proposed. A common framework is proposed to study the two waveforms. This paper also investigates changing the time structure of the transmitted signal by introducing the rate factor parameter. It is shown that intrinsic interference can be greatly reduced at the price of a slight side-lobe increase.

Advanced Low-Complexity Multicarrier Schemes Using Fast-Convolution Processing and Circular Convolution Decomposition

Filter-bank-based waveform processing has been suggested as an alternative for the plain cyclic-prefix (CP) orthogonal frequency-division multiplexing (OFDM) based schemes in fifth-generation and future wireless communication systems. This is because of the new requirements, such as asynchronous and mixed numerology scenarios supporting multi-service operation in a common framework, including enhanced mobile broadband, low-latency high-reliability communications, and low-rate machine-type communications (MTC). Nevertheless, advanced multicarrier waveforms impose significantly increased computational complexity compared to the CP-OFDM scheme. Multirate fast-convolution (FC) processing has recently been proposed as an effective implementation for advanced waveforms, such as filtered OFDM (F-OFDM) and filter-bank multicarrier (FBMC) schemes, providing extreme flexibility in the subband spectral control. In this paper, we investigate the computational complexity of FC-based waveform processing and propose two computationally efficient schemes using the idea of circular convolution decomposition. The first scheme targets at narrow bandwidth scenarios, such as MTC. The second scheme considers dense spectral use of non-overlapping subbands. Both schemes achieve significant reduction in the computational complexity compared to direct FC and polyphase filter-bank-based implementations. This reduction in the complexity is achieved without performance loss with respect to direct FC processing. Mathematical analyses are provided for both schemes, along with evaluation and comparison of the computational complexities considering F-OFDM and FBMC waveforms in long-term-evolution-like scenarios.

A Reliable OFDM-Based MMW Mobile Fronthaul With DSP-Aided Sub-Band Spreading and Time-Confined Windowing

Performance of digital signal processing (DSP) aided sub-band spreading orthogonal frequency division multiplexing (S-OFDM) implemented with the well-defined, time-located window is evaluated and compared with the cyclic prefix (CP) OFDM signal under severe interference circumstances. A four-quadrature amplitude modulation (QAM) mobile fronthaul over 20 km fiber link and 1 m millimeter wave 60-GHz wireless channel is demonstrated experimentally. The bit-error rate performance of applying time windowing on OFDM and S-OFDM are measured in the single channel scenario. In such simplified system, CP-OFDM is found to be a widely adopted waveform. While, as it suffers from the unexpected external interference, the received error vector magnitude (EVM) would be degraded dramatically for typical OFDM signals. By applying the Hanning window, the impact on the EVM performance can be alleviated as the interference is at the edge of the desired signal band and resulting a 2.5% EVM enhancement. However, an irrecoverable 20% data loss is obtained if the interference is totally immersed in the victim signal. In contrast, S-OFDM exhibits a frequency diversity property by grouping OFDM subcarriers into several sub-bands and spreading them into whole available bandwidth. Thus, as S-OFDM suffers from strong interference inside the signal band, about 12.61% and 43.53% EVM improvements of the average and the worst subcarrier performance with respect to the ordinary OFDM can be achieved via applying the spreading codes orthogonality restoring equalizer. All subcarriers in the S-OFDM are generated to meet the forward error correction threshold with reasonably flat performance. Therefore, the S-OFDM shows its superiority in an MMW mobile fronthaul for better reliability in data transmission.

Generalized Fast-Convolution-Based Filtered-OFDM: Techniques and Application to 5G New Radio

This paper proposes a generalized model and methods for fast-convolution (FC)-based waveform generation and processing with specific applications to fifth generation new radio (5G-NR). Following the progress of 5G-NR standardization in 3rd generation partnership project (3GPP), the main focus is on subband-filtered cyclic prefix (CP) orthogonal frequency-division multiplexing (OFDM) processing with specific emphasis on spectrally well localized transmitter processing. Subband filtering is able to suppress the interference leakage between adjacent subbands, thus supporting different numerologies for so-called bandwidth parts as well as asynchronous multiple access. The proposed generalized FC scheme effectively combines overlapped block processing with time- and frequency-domain windowing to provide highly selective subband filtering with very low intrinsic interference level. Jointly optimized multi-window designs with different allocation sizes and design parameters are compared in terms of interference levels and implementation complexity. The proposed methods are shown to clearly outperform the existing state-of-the-art windowing and filtering-based methods.

The impact of out of band emissions: A measurement based performance comparison of UF-OFDM and CP-OFDM

Long Term Evolution (LTE) networks, along with their recent releases, rely on the cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) waveform as the foundation. However, high side lobes, synchronization problems and spectral efficiency constraints of CP-OFDM cannot meet future requirements of cellular network design targets. At this point, universal filtered orthogonal frequency division multiplexing (UF-OFDM) emerges as a strong candidate. Equipped with the advantages of using filters, UF-OFDM provides additional design flexibility to address the fundamental problems of CP-OFDM. In this study, the effect of adjacent channels that causes interference between different frequency channels because of out-of-band (OoB) emissions on UF-OFDM performance is investigated by performing real-time tests on software defined radio (SDR) nodes with multiple reception paths. Frequency domain carrier frequency offset (CFO) and symbol timing offset (STO) correction techniques are used. By the application of the same correction approaches to CP-OFDM, these two waveforms are evaluated in terms of signal to noise ratio (SNR), bit/symbol error rate (BER/SER) and error vector magnitude (EVM). Test results indicate that, based on lower OoB emissions, UF-OFDM uses the spectrum more efficiently and provides better results than CP-OFDM in congested environments.

Enhanced 5G Throughput using UFMC Multiplexing

The next era of communication, fifth generation (5G), substituted the fourth generation (4G) in different aspects. For instance, 5G should support massive machine communications (MMC), which uses very small message signals. The cyclic prefix orthogonal frequency division multiplexing (CP-OFDM), which is adopted in 4G systems, requires a huge number of bits as an overhead along with the cyclic prefix.Moreover, the sinc-shape of the subcarriers in the frequency domain makes the rectangular pulse in the time domain have long tails; therefore, it is not conceivable to transmit short message signals, which requires no synchronization, while CP-OFDM requires tight synchronization both in time and frequency domain. Accordingly, a new air-interface has to be introduced to overcome the CP-OFDM shortcomings. Various candidates have been suggested such as the universal filtered multicarrier (UFMC). UFMC divides the allocated band into several sub-bands and filter them individually, rather than filtering completely the band. Thus, enabling low tails, this gives more flexibility for MMC signals. In this paper, a comparison and design parameters have been set up, the simulation results show that the UFMC outperforms the CP-OFDM with respect to power spectral density efficiency and the throughput with different signal-to-noise ratios with low and high user equipment velocities.

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.

A Comparison of CP-OFDM, PCC-OFDM and UFMC for 5G Uplink Communications

Polynomial-cancellation-coded orthogonal frequency division multiplexing (PCC-OFDM) is a form of OFDM that has waveforms which are very well localized in both the time and frequency domains and so it is ideally suited for use in the 5G network. This paper analyzes the performance of PCC-OFDM in the uplink of a multiuser system using orthogonal frequency division multiple access (OFDMA) and compares it with conventional cyclic prefix OFDM (CP-OFDM), and universal filtered multicarrier (UFMC). PCC-OFDM is shown to be very much less sensitive to time and frequency offsets than either CP-OFDM or UFMC. For a given constellation size, PCC-OFDM in additive white Gaussian noise (AWGN) requires 3 dB lower signal-to-noise ratio (SNR) for a given bit-error-rate, and the SNR advantage of PCC-OFDM increases rapidly when there are timing and/or frequency offsets. For PCC-OFDM no frequency guard-band is required between different OFDMA users. PCC-OFDM is completely compatible with CP-OFDM and adds negligible complexity and latency, because it uses a simple mapping of data onto pairs of subcarriers at the transmitter, and a simple weighting-and-adding of pairs of subcarriers at the receiver. The weighting-and-adding step, which has been omitted in some of the literature, is shown to contribute substantially to the SNR advantage of PCC-OFDM. A disadvantage of PCC-OFDM (without overlapping) is the potential reduction in spectral efficiency because subcarriers are modulated in pairs, but this reduction is more than regained because no guard band is required and because, for a given channel, larger constellations can be used.

Cyclostationarity‐based joint sensing and equalisation of fast convolution‐based DWPT block‐filtered orthogonal frequency division multiplexing for fifth‐generation wireless systems

Traditional cyclic prefix-orthogonal frequency division multiplexing is a popular multicarrier modulation (MCM) scheme, which provides advantages of good bandwidth utilisation and simplicity in transceiver design. However, the waveform suffers from poor spectral utilisation due to the utilisation of rectangular window and lack of flexibility. Hence, an alternative MCM scheme based on wavelet filter-bank architecture is considered in this study for fifth-generation wireless access systems. Cyclostationarity-based joint sensing and channel equalisation is applied at the receiver side, which demonstrates improved signal detection performance. Adaptive line enhancement adaptive line enhancement (ALE)-based noise cancellation is explored to improve the sensing performance. The combined noise cancellation and sensing scheme improve the cyclostationarity-based equalisation and demodulation performance.

Time Spread-Windowed OFDM for Spectral Efficiency Improvement

This letter proposes a new orthogonal frequency division multiplexing (OFDM)-based waveform, called time spread-windowed OFDM (TS-W-OFDM). TS-W-OFDM applies a windowing procedure to improve spectral efficiency and a time spreading method to create a block signal structure. Numerical results show that TS-W-OFDM has higher spectral efficiency and nearly same error rate compared to the conventional cyclic prefix-OFDM, windowed-OFDM (W-OFDM), weighted overlap and add-based OFDM (WOLA-OFDM), and filtered-OFDM (F-OFDM). In addition, they also show that TS-W-OFDM has lower complexity than W-OFDM, WOLA-OFDM, and F-OFDM.

Universal-Filtered Multi-Carrier

The emerging Internet of Things will make the next generation 5G systems to support a broad range of diverse needs with greater efficiency requirements. The new class of services will need a higher data rates, to handle these demands, the lowest layer of the 5G systems must be flexible. Therefore, the waveform will have an important role in offering these new requirements. These waveforms should enable efficient multiple access to handle the requirements of the future wireless communication system. This means that the corresponding required waveforms should be able to handle as much different type of traffic as possible in the same band. In this paper we compare three candidate multicarrier waveforms for the air interface of 5G: the original cyclic prefix OFDM applied in the 4G systems today, the Filter Bank Multicarrier (FBMC) heavily discussed in previous papers, and Universal Filtered Multi-Carrier (UFMC) a new contender making its appearance recently. These new waveforms will be more robust against the time frequency synchronization problem, it has the potential for mixing different traffic specifications, and supports the scenarios of spectrum fragmentation, due to the improvement in the localization of spectrum. In the same time, they support all multiple input and multiple output (MIMO) scenarios and applications. The simulation results shown that there is a good difference in the time frequency efficiency for transmitting very small bursts where the response time is required (like car-to-car communications). Due to the cyclic prefix the FBMC and CP-OFDM suffer when transmitting short bursts, the UFMC outperforms CP-OFDM by 10% for any case and FBMC for the very short packets and it is similar to FBMC for long sequences. Other simulation results are shown, which demonstrate the potential of this waveform.

Waveform comparison and PA nonlinearity effects on CP‐OFDM and 5G FBMC wireless systems

AbstractIn this article, a waveform comparison and power amplifier nonlinearity effects on cyclic prefix orthogonal frequency‐division multiplexing (CP‐OFDM) and 5G filter bank multicarrier (FBMC) wireless systems are presented. The 5 MHz CP‐OFDM and 5G FBMC signals are used in Matlab simulations, while 1.4 and 3 MHz of both signals are used in experiment. It is noted that 1.4 and 3 MHz CP‐OFDM signals have larger side‐lobes in comparison with 5G FBMC signals. The 5G FBMC signals have stepper slope at the edges and very low out‐of‐band leakage.

Low-Complexity Iterative MMSE-PIC Detection for MIMO-GFDM

Driven by 5G requirements, research on alternatives to the popular cyclic-prefix orthogonal frequency division multiplexing (CP-OFDM) waveform recently arose. In particular, non-orthogonal circularly filtered waveforms such as generalized frequency division multiplexing (GFDM) were proposed due to flexibility and robustness. Applying multiple-input multiple-output (MIMO) techniques for future wireless networks are unquestionable and thereby compulsory for any alternative waveform. Despite advancements in accurate MIMO detection algorithms for GFDM, compared with CP-OFDM their complexity still exhibited a higher order of magnitude, impeding an energy-efficient implementation. In this paper, we propose a low-complexity formulation for iterative minimum mean squared error with parallel interference cancellation (MMSE-PIC) detection for non-orthogonal waveforms with localized inter-carrier interference, where we focus on the application to MIMO-GFDM. The proposal achieves complexity similar to CP-OFDM and we evaluate its performance under realistic channel conditions with imperfect channel state information, where we obtain up to 2-dB gain of GFDM compared with OFDM. We confirm our findings by analyzing the measured extrinsic information transfer charts and show that the proposal achieves the performance of optimal maximum likelihood detection. The results point out the MMSE-PIC algorithm as a viable technique for iterative MIMO receiver implementations for non-orthogonal waveforms.

Performance Analysis of Linear Receivers for Uplink Massive MIMO FBMC-OQAM Systems

Offset-quadratic-amplitude-modulation-based filterbank multicarrier (FBMC-OQAM) has been shown to be a promising alternative to cyclic prefix-orthogonal frequency division multiplexing. More recently, the use of FBMC-OQAM has been proposed in combination with massive MIMO communications. In this context, it is interesting to study the overall effect of massive MIMO on the FBMC-OQAM intrinsic interference and its interaction with channel frequency selectivity. In this paper, the performance of an FBMC-OQAM uplink massive MIMO system is theoretically characterized in terms of the output mean squared error (MSE) of the estimated transmitted symbols and for three types of linear receivers, namely, zero forcer, linear minimum mean squared error, and matched filter. Using random matrix theory, the output MSE of these receivers is asymptotically characterized as the number of base station antennas $N$ and the number of users $K$ grow large, while keeping a finite ratio $N/K$ . The obtained expressions allow to draw many conclusions, some of which were already noticed in the literature but not yet theoretically proven. First, the MSE becomes uniform across the frequency band as a result of the channel hardening effect. Second, it is shown that a good synchronization of the users is crucial in a massive MIMO scenario. Finally, if the users are well synchronized, the different terms that compose the MSE, such as noise, interuser interference, and the distortion caused by the channel frequency selectivity, become negligible for large values of the ratio $N/K$ . This effect was previously referred to as “self-equalization” in the literature.

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.

Efficient Fast-Convolution-Based Waveform Processing for 5G Physical Layer

This paper investigates the application of fast-convolution (FC) filtering schemes for flexible and effective waveform generation and processing in the fifth generation (5G) systems. FC-based filtering is presented as a generic multimode waveform processing engine while, following the progress of 5G new radio standardization in the Third-Generation Partnership Project, the main focus is on efficient generation and processing of subband-filtered cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM) signals. First, a matrix model for analyzing FC filter processing responses is presented and used for designing optimized multiplexing of filtered groups of CP-OFDM physical resource blocks (PRBs) in a spectrally well-localized manner, i.e., with narrow guardbands. Subband filtering is able to suppress interference leakage between adjacent subbands, thus supporting independent waveform parametrization and different numerologies for different groups of PRBs, as well as asynchronous multiuser operation in uplink. These are central ingredients in the 5G waveform developments, particularly at sub-6-GHz bands. The FC filter optimization criterion is passband error vector magnitude minimization subject to a given subband band-limitation constraint. Optimized designs with different guardband widths, PRB group sizes, and essential design parameters are compared in terms of interference levels and implementation complexity. Finally, extensive coded 5G radio link simulation results are presented to compare the proposed approach with other subband-filtered CP-OFDM schemes and time-domain windowing methods, considering cases with different numerologies or asynchronous transmissions in adjacent subbands. Also the feasibility of using independent transmitter and receiver processing for CP-OFDM spectrum control is demonstrated.

Chi-Square Distribution-Based Confidence Measure Channel Estimation Method in OFDM Systems

ABSTRACTThere are many channel estimation algorithms for orthogonal frequency division multiplexing (OFDM) system. However, most algorithms cannot suppress the noise effectively, which affects the quality of the final received signal. During wireless channel estimation, the noise has negative impact on channel estimation result. To reduce channel estimation errors, it is necessary to suppress the noise of the channel. In confidence measure (CM) channel estimation, the sampling points are distinguished into multipath and noise, and then the noise is suppressed based on the confidence. However, the performance of CM channel estimation method is not better than that of conventional methods in dynamic channels. Furthermore, to reduce the false alarms effectively, this paper proposes Chi-square distribution-based CM channel estimation method in cyclic prefix OFDM (CP-OFDM) system. Performance comparison is shown to verify the effectiveness of the proposed Chi-square distribution-based CM channel estimation method in multipath propagation conditions.

UFMC 시스템에서 모바일 장치의 이동속도에 대한 성능평가

UFMC(Universal Filtered Multi Carrier)는 새로운 종류의 다중 반송파 전송 기술로 OFDM을 대체하는 것을 목표로 하고 있는 5세대 무선 통신 시스템의 하나이다. 이것은 OFDM(Orthogonal Frequency Division Modulation)과 FBMC(Filter Bank Multi Carrier)의 장점을 결합하고 주요한 단점은 피한 두 시스템의 일반화된 모델이라 할 수 있다. UFMC는 기존의 CP-OFDM(Cyclic Prefix-OFDM)에 비해 시간-주파수 불일치와 같은 동기화 조건에 대하여 비교적 강인한 특징을 갖는다. 또한 5G 시스템 M2M(Machine to Machine) 전송과 같이 burst uplink 전송에 적합하다. 이 논문에서 우리는 다양한 채널 상황과 이동속도의 변화에 따른 UFMC의 BER(Bit Error Rate)성능 변화에 대하여 분석 하였다. 시뮬레이션 결과 모바일 장치의 이동 속도가 높을수록 낮은 BER성능을 확인 할 수 있었고 채널 상황이 좋을수록 속도에 대하여 민감하였다. UFMC is known as the one among novel multi-carrier modulation techniques which are designed for replacing OFDM for 5G wireless communication systems. It is the generalized model of OFDM and FBMC, which combines the advantages of OFDM and FBMC and avoids their weak points. UFMC is more robust in synchronization condition like Time-frequency misalignment compared to CP-OFDM. Moreover UFMC is more proper to burst uplink transmission like M2M 5G Communications. In this paper we analyze the BER performance in various channels and speeds. The simulation result shows that the BER performance is lowered when mobile devices are moving fast and the BER performance is so sensitive for the good channel environment.

Analysis of a FTN Multicarrier System: Interference Mitigation Based on Tight Gabor Frames

Cognitive radio applications require flexible waveforms to overcome several challenges such as opportunistic spectrum allocation and white spaces utilization. In this context, multicarrier modulations generalizing traditional cyclic-prefix orthogonal frequency-division multiplexing are particularly justified to fit time-frequency characteristics of the channel while improving spectral efficiency.In our theoretical framework, a multicarrier signal is described as a Gabor family the coefficients of which are the symbols to be transmitted and the generators are the time-frequency shifted pulse shapes to be used. In this article, we consider the case where non-rectangular pulse shapes are used with a signaling density increased such that inter-pulse interference is unavoidable. Such an interference is minimized when the Gabor family used is a tight frame. We show that, in this case, interference can be approximated as an additive Gaussian noise. This allows us to compute theoretical and simulated bit-error-probability for a non-coded system using a quadrature phase-shift keying constellation. Such a characterization is then used in order to predict the convergence of a coded system using low-density parity check codes. We also study the robustness of such a system to errors on the received bits in an interference cancellation context.