Frequency domain equalization for single-carrier broadband wireless systems
TL;DR: This article surveys frequency domain equalization (FDE) applied to single-carrier (SC) modulation solutions and discusses similarities and differences of SC and OFDM systems and coexistence possibilities, and presents examples of SC-FDE performance capabilities.
Abstract: Broadband wireless access systems deployed in residential and business environments are likely to face hostile radio propagation environments, with multipath delay spread extending over tens or hundreds of bit intervals. Orthogonal frequency-division multiplex (OFDM) is a recognized multicarrier solution to combat the effects of such multipath conditions. This article surveys frequency domain equalization (FDE) applied to single-carrier (SC) modulation solutions. SC radio modems with frequency domain equalization have similar performance, efficiency, and low signal processing complexity advantages as OFDM, and in addition are less sensitive than OFDM to RF impairments such as power amplifier nonlinearities. We discuss similarities and differences of SC and OFDM systems and coexistence possibilities, and present examples of SC-FDE performance capabilities.
Citations
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19 Oct 2007
TL;DR: The main objective of this thesis is to establish a novel single-carrier frequency-domain equalization model utilizing perfect reconstruction, orthogonal, complex modulated filter banks, and two low-complexity solutions for the equalization/decoding loop.
Abstract: Channel equalization is a very important anti-multipath technique in broadband communication systems and it has received much attention during the era of digital communications. Frequency selective fading arises whenever the bandwidth of the transmitted signals is comparable to, or larger than the channel delay spread. In the absence of any suitable signal processing in the receiver, this leads to significant distortion of the signal due to intersymbol interference, which is a major barrier to high-speed digital transmission over wireless channels. This thesis considers frequency-domain signal processing techniques to combat intersymbol interference effects in the context of single-carrier broadband wireless transmission. Meanwhile, it has been recognized that filter bank transforms with high frequency selectivity can offer many advantages over the current discrete Fourier transform based approaches for frequency-domain processing. The main objective of this thesis is to establish a novel single-carrier frequency-domain equalization model utilizing perfect reconstruction, orthogonal, complex modulated filter banks. An introduction to modulated filter banks and common channel equalization techniques is first given. The main research work presented in this thesis can be separated into two topic areas: frequency-domain channel equalization and combined equalization/decoding schemes for coded transmission. First, compared to the discrete Fourier transform approach, the important property of filter bank based equalization is that the channel subband response is not flat anymore. The subband equalizer responses are designed to cope with the channel response within each subband, by utilizing a low-complexity frequency sampling based approach. This is in contrast with the discrete Fourier transform approaches where channel equalization is done with a single complex multiplier per subband. One merit of using the filter bank approach is the absence of cyclic prefix preceding the data block, improving the data rate accordingly. Furthermore, this scheme can be used for any communications waveform and it exhibits improved tolerance against narrowband interference. The same filter banks can be used to provide a significant part of the channel filtering, thus relieving the receiver front-end complexity and leading to a very flexible receiver structure. Second, in the case of coded transmission, the optimal way for equalization/decoding is to use the maximum a posteriori probability equalizer. The problematic issue of such an optimal method would be the high calculation complexity involved, especially when highorder modulation is applied and long channel delay spread may be encountered. This motivates to develop low-complexity solutions for the equalization/decoding loop. A brief introduction of well-known turbo equalization is given in this thesis and two low-complexity
1 citations
01 Oct 2017
TL;DR: A noise-eliminated minimum-mean-square-error channel estimation (MMSE-CE) algorithm that utilizes a novel polynomial interpolation method to obtain the interpolation vectors for channel estimation over fast time-varying multipath channels.
Abstract: This paper considers a novel pilot-assisted channel estimation algorithm for multiple-input-multiple-output with single-carrier frequency-domain-equalization (MIMO-SCFDE) systems over fast time-varying multipath channels. Given that the fast time-varying channels can no longer support the assumption that the channel frequency-domain response remains invariant for the duration of one block, most of the channel estimation methods cannot be applied directly in it. We put forward a noise-eliminated minimum-mean-square-error channel estimation (MMSE-CE) algorithm for the channel estimation. The proposed pilot-assisted MMSE-CE method utilizes a novel polynomial interpolation method to obtain the interpolation vectors. Analysis and simulation results validate the improved performance of the proposed method in fast time-varying frequency-selective MIMO channel for both dense and sparse multipath channel environments.
1 citations
Cites background from "Frequency domain equalization for s..."
...The multipath channel causes a time dispersion of the transmitted signal, resulting in the overlap of the various transmitted symbols at the receiver [1], [2]....
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01 Jun 2019
TL;DR: The set of results presented here show the good tolerance against misalignments of these transmission structures, which is crucial to assess the impact of misaligned beams associated to each user.
Abstract: Massive multiple-input multiple-output (mMIMO) with perfect channel state information (CSI) can lead array power gain increments proportional to the number of antennas. Despite this fact constrains on power amplification still exist due to envelope variations of high order constellation signals. These constrains can be overpassed by a transmitter with several amplification branches, with each one associated to a component signal that results from the decomposition of a multilevel constellation as a sum of several quasi constant envelope signals that are sent independently. When combined with antenna arrays at the end of each amplification branch the security improves due to the energy separation achieved by beamforming. However, to avoid distortion on the signal resulting from the combination of all components at channel level all the beams of signal components should be directed in same direction. In such conditions it is crucial to assess the impact of misalignments between beams associated to each user, which is the purpose of this work. The set of results presented here show the good tolerance against misalignments of these transmission structures.
1 citations
Cites methods from "Frequency domain equalization for s..."
...Having in mind this impairment it is adopted a single-carrier with frequency domain equalization (SC-FDE) scheme [6, 7]....
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01 Nov 2014
TL;DR: Various equalization algorithms are proposed with the aim of exploiting the prefix redundancy for data detection and channel estimation based on the linear minimum mean square error (LMMSE) principle.
Abstract: In communication systems, the transmitted signals often experience various forms of corruption, and a very destructive one is the inter-symbol interference (ISI), resulting from the signals travelling through multiple paths and arriving with different delays. To compensate for the multipath propagation effect, equalization is often required at the receiver and as a very powerful candidate, the turbo equalization technique iteratively exchanges soft information between the equalizer and the decoder, offering excellent performance. Meantime, single-carrier frequency domain equalization (SC-FDE) and orthogonal frequency division multiplexing (OFDM) have become two of the most important modulation schemes in communications. Both schemes are based on guard interval assisted block transmissions and both can be implemented by fast Fourier transform/inverse fast Fourier transform (FFT/IFFT) operations, featuring very low complexity. Cyclic prefix (CP), as a commonly used guard interval, is typically discarded at the receiver. However, the fact that it is a repetition of part of the data suggests that it contains useful information and can be exploited for enhancing the system performance. This thesis considers the application of turbo equalization in SC-FDE and OFDM systems and based on the linear minimum mean square error (LMMSE) principle, various equalization algorithms are proposed with the aim of exploiting the prefix redundancy for data detection and channel estimation. To facilitate the description
1 citations
TL;DR: This paper proposes a new estimation method of the correlation matrices that guarantees that the non-constant-modulus FDE-FDDF scheme is numerically stable and that the relationship between these two FDTE schemes holds for both constant-Modulus and non- constant- modulus modulations.
Abstract: This paper investigates two typical frequency-domain turbo equalization (FDTE) schemes, i.e., frequency-domain equalization (FDE) with parallel interference cancelation (FDE-PIC) and FDE with frequency-domain decision feedback (FDE-FDDF) in single-carrier (SC) multiple-input–multiple-output (MIMO) systems. These two FDTE schemes are proven to be equivalent under the condition that we derived. We discover that the covariance matrix of the low-complexity FDE-PIC scheme and the correlation matrix of the FDE-FDDF scheme satisfy a unique relationship for constant-modulus modulations, and the original FDE-FDDF scheme suffers numerical instability for non-constant-modulus modulations because the estimation of the correlation matrices leads to the inversion of ill-conditioned matrices. By proposing a new estimation method of the correlation matrices, we guarantee that the non-constant-modulus FDE-FDDF scheme is numerically stable and that the relationship between these two FDTE schemes holds for both constant-modulus and non-constant-modulus modulations. Furthermore, we prove that the FDE-PIC and FDE-FDDF schemes are equivalent under this relationship. The equivalence of these two FDTE schemes is also verified through numerical simulations in terms of bit error rate (BER) at each turbo iteration and the estimation of the correlation matrices.
1 citations
Cites background from "Frequency domain equalization for s..."
...While OFDM also suffers from the high peakto-average power ratio, single-carrier (SC) transmission leads to more efficient use of power amplifiers [2], [3]....
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References
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Book•
01 Jan 1986
TL;DR: In this paper, the authors propose a recursive least square adaptive filter (RLF) based on the Kalman filter, which is used as the unifying base for RLS Filters.
Abstract: Background and Overview. 1. Stochastic Processes and Models. 2. Wiener Filters. 3. Linear Prediction. 4. Method of Steepest Descent. 5. Least-Mean-Square Adaptive Filters. 6. Normalized Least-Mean-Square Adaptive Filters. 7. Transform-Domain and Sub-Band Adaptive Filters. 8. Method of Least Squares. 9. Recursive Least-Square Adaptive Filters. 10. Kalman Filters as the Unifying Bases for RLS Filters. 11. Square-Root Adaptive Filters. 12. Order-Recursive Adaptive Filters. 13. Finite-Precision Effects. 14. Tracking of Time-Varying Systems. 15. Adaptive Filters Using Infinite-Duration Impulse Response Structures. 16. Blind Deconvolution. 17. Back-Propagation Learning. Epilogue. Appendix A. Complex Variables. Appendix B. Differentiation with Respect to a Vector. Appendix C. Method of Lagrange Multipliers. Appendix D. Estimation Theory. Appendix E. Eigenanalysis. Appendix F. Rotations and Reflections. Appendix G. Complex Wishart Distribution. Glossary. Abbreviations. Principal Symbols. Bibliography. Index.
16,062 citations
"Frequency domain equalization for s..." refers methods in this paper
...Adaptation can be done with LMS (least mean square), RLS, or least squares minimization (LS) techniques, analogous to adaptation of time domain equalizers [Hay96], [Cla98]....
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...Overlap-save or overlap-add signal processing techniques could also be used to avoid the extra overhead of the cyclic prefix [Fer85], [Hay96]....
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TL;DR: The analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel using the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel is discussed.
Abstract: This paper discusses the analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel. This system uses the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel. When this technique is used with pilot-based correction, the effects of flat Rayleigh fading can be reduced significantly. An improvement in signal-to-interference ratio of 6 dB can be obtained over the bursty Rayleigh channel. In addition, with each subchannel signaling at a low rate, this technique can provide added protection against delay spread. To enhance the behavior of the technique in a heavily frequency-selective environment, interpolated pilots are used. A frequency offset reference scheme is employed for the pilots to improve protection against cochannel interference.
2,627 citations
"Frequency domain equalization for s..." refers background in this paper
...OFDM transmits multiple modulated subcarriers in parallel [ 1 ]....
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...Several variations of orthogonal frequency-division multiplexing (OFDM) have been proposed as effective anti-multipath techniques, primarily because of the favorable trade-off they offer between performance in severe multipath and signal processing complexity [ 1 ]....
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TL;DR: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered and the degradation of the bit error rate is evaluated.
Abstract: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate. >
1,816 citations
TL;DR: This correspondence describes the construction of complex codes of the form exp i \alpha_k whose discrete circular autocorrelations are zero for all nonzero lags.
Abstract: This correspondence describes the construction of complex codes of the form exp i \alpha_k whose discrete circular autocorrelations are zero for all nonzero lags. There is no restriction on code lengths.
1,624 citations