Fundamentals of statistical signal processing: Estimation theory: by Steven M. KAY; Prentice Hall signal processing series; Prentice Hall; Englewood Cliffs, NJ, USA; 1993; xii + 595 pp.; $65; ISBN: 0-13-345711-7

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.

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Channel equalization in filter bank based multicarrier modulation for wireless communications

In this paper, the problem of channel equalization in filter bank multicarrier (FBMC) transmission based on the offset quadrature-amplitude modulation (OQAM) subcarrier modulation is addressed. Finite impulse response (FIR) per-subchannel equalizers are derived based on the frequency sampling (FS) approach, both for the single-input multiple-output (SIMO) receive diversity and the multiple-input multiple-output (MIMO) spatially multiplexed FBMC/OQAM systems. The FS design consists of computing the equalizer in the frequency domain at a number of frequency points within a subchannel bandwidth, and based on this, the coefficients of subcarrier-wise equalizers are derived. We evaluate the error rate performance and computational complexity of the proposed scheme for both antenna configurations and compare them with the SIMO/MIMO OFDM equalizers. The results obtained confirm the effectiveness of the proposed technique with channels that exhibit significant frequency selectivity at the subchannel level and show a performance comparable with the optimum minimum mean-square-error equalizer, despite a significantly lower computational complexity. The possibility of tolerating significant subchannel frequency selectivity gives more freedom in the multicarrier system parameterization. For example, it is possible to use significantly wider subcarrier spacing than what is feasible in OFDM, thus relieving various critical design constraints.

Channel Equalization for Multi-Antenna FBMC/OQAM Receivers

This paper investigates the potential of filter bank (FB) processing in the context of uplink multi-user access. First, a FB based scheme, conceptually similar to the single carrier frequency division multiple access (SC-FDMA) developed by 3GPP for uplink in the Long Term Evolution of UMTS, is analyzed. Specifically, a method for synthesizing spectrally well-localized uplink waveforms with low peak-to-average power ratio, using FB based multicarrier (FBMC) modulation in combination with FB spreading, is introduced. Secondly, the superior frequency selectivity of the FB approach, when combined with frequency sampling -designed subchannel/subband processing, is found to enable flexible and bandwidth efficient multi-mode uplink transmission with relaxed constraints on inter-user timing synchronization. The proposed concept allows different mobile terminals to operate in the reverse link simultaneously in multicarrier, SC-FDMA, or conventional single carrier mode according to attributes such as the required transmission power.

Filter bank based multi-mode multiple access scheme for wireless uplink

This paper investigates the use of complex-modulated oversampled filter banks (FBs) for frequency-domain equalization (FDE) in single-carrier systems. The key aspect is mildly frequency-selective subband processing instead of a simple complex gain factor per subband. Two alternative low-complexity linear equalizer structures with MSE criterion are considered for subband-wise equalization: a complex FIR filter structure and a cascade of a linear-phase FIR filter and an allpass filter. The simulation results indicate that in a broadband wireless channel the performance of the studied FB-FDE structures, with modest number of subbands, reaches or exceeds the performance of the widely used FFT-FDE system with cyclic prefix. Furthermore, FB-FDE can perform a significant part of the baseband channel selection filtering. It is thus observed that fractionally spaced processing provides significant performance benefit, with a similar complexity to the symbol-rate system, when the baseband filtering is included. In addition, FB-FDE effectively suppresses narrowband interference present in the signal band.

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Frequency-domain equalization in single-carrier transmission: filter bank approach

Filter bank based frequency domain equalization provides an attractive scheme for single-carrier transmission of broadband wireless communications. With mildly frequency-selective subband processing and a modest number of subbands, it is able to provide better performance than conventional FFT approach with a higher number of subbands. Another benefit of this approach is that the same filter bank can be utilized to implement a significant part of the baseband channel selection filtering task. This paper proposes a technique for tuning the filter bank equalizer to mitigate narrowband interference without additional complexity. Simulation results show that the proposed scheme is effective and can provide better performance than the basic complete subband elimination approach when moderate interference is present.

Mitigation of Narrowband Interference in SC Transmission with Filter Bank Equalization

This paper investigates both transmultiplexer (TMUX) and analysis-synthesis filter banks where the two sides of the filter bank system are of different sizes. Such configurations find applications in filter bank based multicarrier communication systems on one hand and in fractionally-spaced frequency domain equalizers on the other. The errors due to mismatched filter banks are analyzed. Based on this analysis, it is shown how to modify the subband processing to compensate the reconstruction error in the analysis-synthesis configuration, or the inter-carrier and inter-symbol interferences in the multicarrier case. The needed subband processing can be incorporated to the subband-wise channel equalizers with no additional complexity during data processing and minor additional complexity in the equalizer coefficient calculation and their adaptation.

Flexible Filter Bank Dimensioning for Multicarrier Modulation and Frequency Domain Equalization

In earlier studies, we have considered filter bank based frequency domain processing for channel equalization both in multicarrier and single-carrier transmission. With mildly frequency selective subband processing and modest number of subbands, these approaches are able to provide better performance than the conventional FFT-based multicarrier technique OFDM, on one hand, and FFT-based frequency-domain equalizer in single-carrier transmission, on the other. The benefits in transmission link efficiency are due to the lack of guard-interval overhead and, in the multicarrier case, also due to reduced guard- band. Another significant advantage of this approach is that the same filter bank can be utilized to implement significant part of the receiver selectivity, in a very flexible way. In this paper, we extend the filter bank approach to cover also multi- antenna reception schemes. We show that the subband equalizer structure of the basic single-input scheme can be used for the different antennas of a multi-antenna receiver while introducing frequency domain combining of the diversity branches. We also show how to extend the frequency-sampling based techniques for channel equalizer design to the multi-antenna case. Performance evaluation of a simple receiver antenna diversity scheme in single-carrier transmission with maximum ratio combining is included to verify the ideas.

Filter bank based frequency-domain equalizers with diversity combining

Complex modulated filter bank (FB) based frequency-domain equalization (FDE) provides an attractive single-carrier scheme for broadband wireless communications. With mildly frequency selective subband processing and modest number of subbands, it is able to provide better performance than the conventional FDE with FFT due to the lack of guard-interval overhead. Another significant benefit of this approach is that the same filter bank can be utilized to implement significant part of the receiver channel selectivity in a flexible way. This paper studies a hybrid frequency-time domain equalizer, which utilizes FB based equalizer for the feedforward part and a noise predictor (NP) for the feedback. The motivation is that the feedforward and feedback filter can be designed separately, in contrast to a conventional decision-feedback equalizer (DFE). The performance can be adjusted by the order of the NP. A significant advantage of NP based equalizer, over the traditional DFE, is that it is easier to include error control decoding in the equalizer feedback loop. This is able to provide significant performance enhancement over the DFE structure where the decoding is after the feedback loop.

Yuan Yang

Papers

Frequency-domain equalization in single-carrier transmission: filter bank approach

Mitigation of Narrowband Interference in SC Transmission with Filter Bank Equalization

Flexible Filter Bank Dimensioning for Multicarrier Modulation and Frequency Domain Equalization

Filter bank based frequency-domain equalizers with diversity combining

Filter Bank Based Frequency-Domain Equalization with Noise Prediction