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.
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TL;DR: It is shown that the use of frequency-domain equalization based on minimum mean square error criterion (MMSE-FDE) can significantly improve the BER performance, compared to the conventional OFDM, by exploiting the channel frequency-selectivity while reducing the PAPR or improving the robustness against long time delays.
Abstract: Orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (TDM), in this paper called OFDM/TDM, can overcome the high peak-to-average-power ratio (PAPR) problem of the conventional OFDM and improve the robustness against long time delays. In this paper, the bit error rate (BER) performance of OFDM/TDM in a frequency-selective Rayleigh fading channel is evaluated by computer simulation. It is shown that the use of frequency-domain equalization based on minimum mean square error criterion (MMSE-FDE) can significantly improve the BER performance, compared to the conventional OFDM, by exploiting the channel frequency-selectivity while reducing the PAPR or improving the robustness against long time delays. It is also shown that the performance of OFDM/TDM de- signed to reduce the PAPR can bridge the conventional OFDM and single-carrier (SC) transmission by changing the design parameter.
16 citations
Cites methods from "Frequency domain equalization for s..."
...We consider FDE techniques based on ZF, maximal ratio combining (MRC), and minimum mean square error (MMSE) criteria used for equalization in SC transmission [14], multicarrier code division multiple access (MCCDMA) [15]–[17], and quite recently in direct sequence CDMA (DS-CDMA) [18], [19]....
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05 Sep 2004
TL;DR: An iterative space-time equalizer employing soft cancellation followed by frequency-domain linear filtering is explored, and the error-rate performance in LDPC-coded MIMO transmissions over time-varying frequency-selective fading channels is evaluated.
Abstract: Multiple-input multiple-output (MIMO) transmission systems, exploiting multiple antennas at both Tx and Rx sides, have potential to dramatically increase the spectral efficiency in rich-scattering wireless links. At the receiver, the so-called space-time equalizer can adaptively deal with dispersive channels and jointly decode multiplexed signals. Recently, low-density parity-check (LDPC) codes have drawn lots of attention for achieving excellent error-correction performance by means of the low-complexity belief propagation (BP) algorithm. This paper explores an iterative space-time equalizer employing soft cancellation followed by frequency-domain linear filtering, and evaluates the error-rate performance in LDPC-coded MIMO transmissions over time-varying frequency-selective fading channels.
16 citations
01 Nov 2011
TL;DR: The approach is based on two ideas: Depending upon the satellite orbit position, distinctly displaced ground antennas grant access to a MIMO channel with maximum spatial multiplexing gain, and nearly optimal data rates are achieved through maximum likelihood equalization with a low-effort single carrier frequency domain equalizer and a zero-forcing filter.
Abstract: The Multiple Input - Multiple Output (MIMO) technology is applied to military satellite communication (SATCOM) systems. Superior system performance with respect to channel capacity and data rate is proven utilizing an exemplary communication setup with two antennas at both the ground stations and the geostationary satellite. Contrary to widespread discussed polarization multiplexing SATCOM systems, the approach is suited to fully exploit the multiplexing gain in the spatial domain. This goes along with a linear increase of the channel capacity and the throughput in net data rate depending upon the number of antennas used. Hence, the data rate is almost doubled for the exemplary setup in this paper without the need of higher transmit power or channel bandwidth. Moreover, the system offers improved link availability through antenna diversity. Our approach is based on two ideas: Depending upon the satellite orbit position, distinctly displaced ground antennas grant access to a MIMO channel with maximum spatial multiplexing gain. Nearly optimal data rates are then achieved through maximum likelihood equalization with a low-effort single carrier frequency domain equalizer and a zero-forcing filter. A summary on the robustness of the architecture in respect of capacity degrading influences completes the paper.
16 citations
Cites methods from "Frequency domain equalization for s..."
...This SC-FDE based system concept is presented in section V....
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...To overcome this problem we suggest a block-based transmission and the insertion of a guard-interval as known from single-carrier systems with frequency domain equalization (SC-FDE) [2]....
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...In figure 5 uncoded bit-error-rates (BERs) for QPSK, 8- PSK, 16-APSK and 32-APSK are shown as derived by simulation applying the proposed SC-FDE concept....
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...With respect to this problem, a further advantage of orthogonal MIMO channels becomes striking: Besides the superior channel capacity, the orthogonality enables a low-effort SC-FDE channel equalization....
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...SC-FDE overcomes this drawback....
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01 Mar 2021
TL;DR: A physical layer based on high-bandwidth on-off keying modulation allows for highly efficient transmitter frontend designs that avoid operation of amplifier stages in a resistive mode, which has the potential of reducing their energy usage by an order of magnitude.
Abstract: Energy consumption is one of the critical issues in optical wireless communications transmitter design and a limiting factor to miniaturization and deployment in mobile devices. In order to reduce energy requirements, we assess a physical layer based on high-bandwidth on-off keying modulation. The use of on-off keying allows for highly efficient transmitter frontend designs that avoid operation of amplifier stages in a resistive mode, which has the potential of reducing their energy usage by an order of magnitude. Link-level simulations show that this physical layer can deal with typical frontend limitations and can operate in challenging non-line-of-sight channels. For these reasons, we believe that the solution evaluated here can deliver a significant contribution to optical wireless communications technology in a wide range of use cases.
16 citations
Cites background from "Frequency domain equalization for s..."
...As shown in [17], the SNR level needed for a reliable transmission does not vary significantly between single-carrier and multi-carrier modulation if an adequate equalizer is used, but is rather determined by its spectral efficiency....
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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