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
More filters
20 Sep 2004
TL;DR: This paper investigates a single carrier system with frequency domain equalization (SC/FDE) which carries out the feed-forward equalization in the frequency domain and allows a better performance as compared to the classical DFE equalizer structures by reducing the effect of error propagation.
Abstract: The wireless radio channel makes powerful equalization structures necessary, where in particular non linear structures such as decision feedback equalizers are promising candidates. Although the theory of these equalizers seems to be well developed, it is pointed out in this paper that it is inevitable to characterize them in an overall system approach which includes processing complexity, channel characteristics, error propagation, modulation schemes, channel coding and others before comparing them to linear equalizer structures. To reduce the signal processing complexity, our investigations are based on a single carrier system with frequency domain equalization (SC/FDE) which carries out the feed-forward equalization in the frequency domain. Furthermore, the specific structure of SC/FDE allows a better performance as compared to the classical DFE equalizer structures by reducing the effect of error propagation.
15 citations
Cites background or methods from "Frequency domain equalization for s..."
...Without going into details (see [ 1 ],[5]) we state that the feed forward equalizer in the frequency domain, responsible for a pre-equalization is given by...
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...While the first structure is based on the classical structure of a cyclic prefix (as it is used for OFDM), the second structure is based on a so called Unique Word (UW) [ 1 ][5][6]....
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...Although OFDM holds an already dominant position in actual and future standards, SC/FDE is gaining more and more momentum, as it combines the advantages of OFDM and classical single carrier transmission [ 1 ],[2],[3]....
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TL;DR: The ROMP-based nonlinear equalizer is found to be the best choice that offers the optimal balance between performance and complexity, which achieves almost the same performance as the conventional Volterra time domain non linear equalizer in OFDM VLC systems with approximately halved number of kernels.
Abstract: The nonlinearity of light emitting diode (LED) in visible light communication (VLC) systems is considered as one major limiting factor that deteriorates the systems’ performance. In this paper, the nonlinear equalization in VLC systems is deemed to be a sparse recovery problem. Three different greedy sparse recovery algorithms, namely matching pursuit (MP), orthogonal MP (OMP), and regularized OMP (ROMP) are employed in constructing the sparsity-aware nonlinear equalizer for LED-based VLC systems. By adopting these greedy algorithms, the number of kernels in the nonlinear equalizer can be significantly reduced with minor performance loss, which enables low-complexity and high-performance nonlinear equalization. The performance of the proposed sparsity-aware nonlinear equalizers is investigated experimentally in orthogonal frequency division multiplexing (OFDM) based VLC systems with commercially available red-green-blue LEDs. The results show that, with the help of greedy sparse recovery algorithms, the number of kernels in nonlinear equalization can be reduced by 32.5%∼62.5% for only 0.5-dB signal-to-noise ratio loss. The compatibility of the proposed sparsity-aware nonlinear equalizer in a ∼1 Gbit/s adaptive bit-power loading OFDM VLC system is also experimentally demonstrated. The ROMP-based nonlinear equalizer is found to be the best choice that offers the optimal balance between performance and complexity, which achieves almost the same performance as the conventional Volterra time domain nonlinear equalizer in OFDM VLC systems with approximately halved number of kernels.
15 citations
Cites background or methods from "Frequency domain equalization for s..."
...For red, green, and blue LED chips, SNR gains of 4.22 dB, 3.68 dB, and 5.65 dB over the linear equalizer FDE are achieved by both the TD-NC and ROMP based nonlinear equalizer....
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...The transmission distance at FEC limit of 3.8× 10−3 can be extended from 0.5 m to 1.7 m when switching the linear equalizer FDE to the nonlinear equalizers....
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...The capacity gap between FDE and nonlinear equalizers are larger than 175 Mbit/s in the whole range of transmission distance of interest (i.e., from 0.5 m to 2 m)....
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...As an extension of our preliminary work on MP/OMP in [24], this paper conducts comprehensive performance comparison of three greedy sparse nonlinear equalizers (i.e., MP, OMP, and ROMP), the conventional non-sparse time domain nonlinear equalizer (TD-NC), and the linear frequency domain equalizer (FDE) in LED based VLC systems....
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...The kernel coefficients of TD-NC and FDE are obtained via training with the LS method....
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IMEC1
TL;DR: This paper introduces WPANs in the 60 GHz band, describing the possible applications, the propagation channel and the standardization context, and shows that beamforming is desirable to boost the link budget, reduce interference and, in some cases, reduce multipath.
Abstract: Thanks to the unprecedented availability of huge bandwidth, the capacity offered by wireless systems in the 60 GHz band can exceed the mythical barrier of 1 Gbps wireless, enabling the deployment of new applications. However, the performance can be limited by the non-ideality of the analog Front-Ends, multipath fading and the difficulty to achieve a reasonable link budget at high data rates. The goal of this paper is to introduce high rate communications in the 60 GHz band and the associated challenges. We will first introduce WPANs in the 60 GHz band, describing the possible applications, the propagation channel and the standardization context.. Furthermore, based on the characteristics of the propagation channel, we will show that beamforming is desirable to boost the link budget, reduce interference and, in some cases, reduce multipath. Next, we will introduce candidate PHY layer solutions that at the same time meet the throughput requirements and relax the analog front-end design. Our solutions rely on the combination of block transmission combined with (nearly) constant envelope modulation: this provides low peak-to-average power ratios, easy equalization, good spectral properties and modest front-end requirements in terms of phase noise and ADC resolution. The receiver signal processing associated with the modulation techniques will be described and link level simulation results will be provided, highlighting the "front-end friendliness" of the modulation technique.
15 citations
Cites background or methods from "Frequency domain equalization for s..."
...The first one uses symbol rate sampling while the second one uses fractional sampling (2 samples per symbol) [7]....
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...Thus, each sub-carrier is equalized individually and independently from the others as in [7]....
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...In this later case, the MMSE equalizer is derived in a similar manner, but uses the polyphase approach to take the fractional sampling into account as in [7]....
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01 Jan 2012
TL;DR: It was observed that the SC-FDE has an overall performance advantage over the OFDM option, especially when employing the iterative block decision feedback equaliser with turbo equalisation and for high code rates.
Abstract: Block transmission techniques, with appropriate cyclic prefixes and employing frequency-domain equalisation techniques, have been shown to be suitable for high data rate transmission over severely time-dispersive channels. The most popular techniques based on this concept are orthogonal frequency division multiplexing (OFDM) and single-carrier with frequency-domain equalisation (SC-FDE).
In this paper, we consider OFDM and SC-FDE transmission schemes and study the impact of the number of multipath components and the diversity order on their performance. It is shown that when we have a high number of separable multipath components, the asymptotic performance of both schemes approaches the matched filter bound, even without diversity. When we have diversity, the performance approaches the matched filter bound faster, with a small number of separable multipath components. It was also observed that the SC-FDE has an overall performance advantage over the OFDM option, especially when employing the iterative block decision feedback equaliser with turbo equalisation and for high code rates. Copyright © 2011 John Wiley & Sons, Ltd.
15 citations
Cites background from "Frequency domain equalization for s..."
...Moreover, the receiver complexity is almost independent of the channel impulse response, making them suitable for severely timedispersive channels [3, 4]....
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...the transmission from the base station to the mobile terminal) because of lower signal processing requirements at the receivers [3, 4]....
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TL;DR: This paper investigates single- and multi-carrier IDMA schemes with cyclic prefixing (CP) and zero padding (ZP) techniques and shows the potential advantages of ZP-based schemes in power efficiency and convergence speed.
Abstract: In this paper, we investigate single-carrier (SC) and multi-carrier IDMA schemes with cyclic prefixing (CP) and zero padding (ZP) techniques. These schemes are called SC-IDMA-CP, SC-IDMA-ZP, orthogonal frequency-division multiplexing (OFDM)-IDMA-CP and OFDM-IDMA-ZP, respectively. By exploiting the circulant property of channel matrices, the multi-user detection of these schemes can be efficiently realised with per-user complexity independent of the number of users and the length of inter-symbol interference (ISI) channels. We show the potential advantages of ZP-based schemes in power efficiency and convergence speed. Simulation results are provided to compare the four schemes. Copyright © 2008 John Wiley & Sons, Ltd.
15 citations
References
More filters
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