Soft-feedback MMSE equalization for non-orthogonal frequency division multiplexing (n-OFDM) signal detection
07 Mar 2012-pp 248-255
TL;DR: It is revealed that the smaller the frequency separation, the larger sum capacity can be achieved compared with the conventional OFDM technique, and the use of soft cancellation- minimum mean-squared error (SCMMSE) turbo equalization is proposed.
Abstract: A frequency division multiplexing technique, nonorthogonal frequency division multiplexing (n-OFDM), is proposed in [1]– [2] to enhance the efficiency of bandwidth utilization. This paper reveals that the smaller the frequency separation, the larger sum capacity can be achieved compared with the conventional OFDM technique. However, n-OFDM system introduces inter-carrier interference (ICI) at the transmitter because the orthogonality between the subcarriers no longer holds. Moreover, since the channel covariance matrix of n-OFDM has high condition number when the overlapping factor, 1 − α, is large, conventional linear detectors suffers from severe noise enhancement. To solve this problem, this paper proposes the use of soft cancellation- minimum mean-squared error (SCMMSE) turbo equalization. Binary constellation constrained mutual information (CCMI) is calculated by utilizing the area property for the EXtrinsic Information Transfer (EXIT) chart of the SC-MMSE equalizer. Results of the EXIT chart analysis and bit-error-rate (BER) simulations in additive white Gaussian noise (AWGN) channel are presented.
Citations
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20 Jul 2018
TL;DR: This survey provides the history of SEFDM development since its inception in 2003, covering fundamentals and concepts, wireless and optical communications applications, circuit design and experimental testbeds, and techniques to improve the performance and practical utility with focus on signal generation, detection and channel estimation.
Abstract: Spectrally efficient frequency division multiplexing (SEFDM) is a multi-carrier signal waveform, which achieves higher spectral efficiency, relative to conventional orthogonal frequency division multiplexing (OFDM), by violating the orthogonality of its sub-carriers. This survey provides the history of SEFDM development since its inception in 2003, covering fundamentals and concepts, wireless and optical communications applications, circuit design and experimental testbeds. We focus on work done at UCL and outline work done other universities and research laboratories worldwide. We outline techniques to improve the performance of SEFDM and its practical utility with focus on signal generation, detection and channel estimation.
64 citations
Cites background from "Soft-feedback MMSE equalization for..."
...2012[66] Soft cancellation MMSE Turbo equalization for n-OFDM Sep....
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18 Dec 2014
TL;DR: Modelling results show the suitability of the detector for use in large size non-orthogonal multicarrier systems and system modelling results show that this coded system with 1024 sub-carriers can save up to 45% of bandwidth compared to an otherwise equivalent OFDM.
Abstract: Spectrally efficient frequency division multiplexing (SEFDM) improves spectral efficiency relative to the well known orthogonal frequency division multiplexing (OFDM) Optimal detection of SEFDM, to recover signals corrupted by inter carrier interference (ICI), has major drawbacks in the exponential growth of detection complexity with the enlargement of system size and modulation level This poses several challenges to SEFDM practical implementations In this work, we present and compare practicable detection algorithms for both uncoded and coded SEFDM systems In the case of the uncoded system, we discuss a multi-band architecture termed block-spectrally efficient frequency division multiplexing (B-SEFDM) which subdivides the signal spectrum into several blocks, allowing each block to be detected separately The other system discussed in the paper utilizes convolutional coding with an appropriate receiver comprising a fast Fourier transform (FFT) based demodulation and detection working alongside a standard Bahl-Cocke-Jelinek-Raviv (BCJR) decoder Mathematical modelling results show the suitability of the detector for use in large size non-orthogonal multicarrier systems In the presence of multipath frequency selective channel, system modelling results show that this coded system with 1024 sub-carriers can save up to 45% of bandwidth compared to an otherwise equivalent OFDM
52 citations
Cites methods from "Soft-feedback MMSE equalization for..."
...Soft detection has been successfully applied to improve detection of non-orthogonal FDM in [10] and iterative detection was implemented and used for FTN in [11]....
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01 Oct 2017
TL;DR: This paper transforms the high-order singular UCA into the low-order concentric UCAs to increase the capacity and proposes the mode-decomposition scheme and the co-mode successive interference cancellation algorithm to mitigate co- mode interference and decode the transmit signals.
Abstract: To meet the rapidly capacity-growing requirements, orbital angular momentum (OAM) based Radio vOrtex Wireless COMMunications (RowComm) has received much attention in recent years. The uniform circular array (UCA) is an efficient and convenient antenna structure to transmit/receive OAM beams with multiple OAM modes simultaneously. However, for high-order OAM modes, the OAM beams are divergent with severe attenuations. Thus, it is difficult to directly utilize high-order OAM modes to achieve high capacity for wireless communications. In this paper, we transform the high-order singular UCA into the low-order concentric UCAs to increase the capacity. In particular, we propose the mode-decomposition scheme and the co-mode successive interference cancellation algorithm to mitigate co-mode interference and decode the transmit signals. Then, we formulate the capacity maximization problem and convert it into an equivalent convex optimization problem. We solve the capacity maximization problem and derive the corresponding optimal power allocation scheme. Numerical simulations are presented to validate and evaluate that our developed low-order concentric UCAs based RowComm can significantly increase the capacity as compared with the high-order singular UCA based RowComm.
19 citations
Cites background from "Soft-feedback MMSE equalization for..."
...In response to the challenges, a great deal of research has been devoted to developing the techniques such as co-frequency co-time full-duplex [2] and non-orthogonal multiplexing [3]....
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Dissertation•
28 Aug 2017
TL;DR: This thesis addresses theoretical and practical challenges of spectrally efficient frequency division multiplexing (SEFDM) systems in both wireless and optical domains and presents solutions for these issues.
Abstract: This thesis addresses theoretical and practical challenges of spectrally efficient frequency division multiplexing (SEFDM) systems in both wireless and optical domains. SEFDM improves spectral efficiency relative to the well-known orthogonal frequency division multiplexing (OFDM) by non-orthogonally multiplexing overlapped sub-carriers. However, the deliberate violation of orthogonality results in inter carrier interference (ICI) and associated detection complexity, thus posing many challenges to practical implementations. This thesis will present solutions for these issues. The thesis commences with the fundamentals by presenting the existing challenges of SEFDM, which are subsequently solved by proposed transceivers. An iterative detection (ID) detector iteratively removes self-created ICI. Following that, a hybrid ID together with fixed sphere decoding (FSD) shows an optimised performance/complexity trade-off. A complexity reduced Block-SEFDM can subdivide the signal detection into several blocks. Finally, a coded Turbo-SEFDM is proved to be an efficient technique that is compatible with the existing mobile standards. The thesis also reports the design and development of wireless and optical practical systems. In the optical domain, given the same spectral efficiency, a low-order modulation scheme is proved to have a better bit error rate (BER) performance when replacing a higher order one. In the wireless domain, an experimental testbed utilizing the LTE-Advanced carrier aggregation (CA) with SEFDM is operated in a realistic radio frequency (RF) environment. Experimental results show that 40% higher data rate can be achieved without extra spectrum occupation. Additionally, a new waveform, termed Nyquist-SEFDM, which compresses bandwidth and suppresses out-of-band power leakage is investigated. A 4th generation (4G) and 5th generation (5G) coexistence experiment is followed to verify its feasibility. Furthermore, a 60 GHz SEFDM testbed is designed and built in a point-to-point indoor fiber wireless experiment showing 67% data rate improvement compared to OFDM. Finally, to meet the requirements of future networks, two simplified SEFDM transceivers are designed together with application scenarios and experimental verifications.
5 citations
Cites background from "Soft-feedback MMSE equalization for..."
...2012[44] Soft cancellation MMSE Turbo equalization for n-OFDM Apr....
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28 Jul 2016
TL;DR: Experimental validations 1 of bandwidth compressed multicarrier waveforms for future 5th generation (5G) applications are comprehensively summarized, aiming to provide high capacity and high mobility, simultaneously while saving spectrum.
Abstract: We comprehensively summarize experimental validations 1 of bandwidth compressed multicarrier waveforms for future 5th generation (5G) applications. The proposed waveforms are derived from an existing non-orthogonal multicarrier concept termed spectrally efficient frequency division multiplexing (SEFDM) where sub-carriers are non-orthogonally packed at frequencies below the symbol rate. This improves the spectral efficiency at the cost of self-created inter carrier interference (ICI). In this work, experiments are reported and testing is carried out in three scenarios including long term evolution (LTE)-like wireless link; millimeter wave radio-over-fiber (RoF) link and optical fiber link. In the first scenario, for a given 25 MHz bandwidth, the SEFDM testbed can provide 70 Mbit/s gross data rate while only 50 Mbit/s can be achieved for an OFDM system occupying the same bandwidth. For the millimeter wave experiment, occupying a 1.125 GHz bandwidth, the gross bit rate for OFDM is 2.25 Gbit/s and with 40% bandwidth compression, 3.75 Gbit/s can be achieved for SEFDM. Two experimental optical fiber links are described in this work; a 10 Gbit/s direct detection optical SEFDM system and a 24 Gbit/s coherent detection SEFDM system. The LTE-like signals and millimeter wave technologies are well suited to provide last mile communications to end users as both can support mobility in wireless environments. The lightwave signals delivered by optical fibers would offer higher data rates and support long-haul communications. The reported techniques, used individually or combined, would be of interest to future wireless system designers, where bandwidth saving is of importance, such as in 5G networks, aiming to provide high capacity and high mobility, simultaneously while saving spectrum.
3 citations
Cites methods from "Soft-feedback MMSE equalization for..."
...To overcome the challenge, some emerging techniques such as massive multiple input multiple output (MIMO) (space domain) [9], millimeter wave (frequency domain) [10] and beamforming (power domain) [11] are combined with OFDM to address this challenge....
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References
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TL;DR: This final installment of the paper considers the case where the signals or the messages or both are continuously variable, in contrast with the discrete nature assumed until now.
Abstract: In this final installment of the paper we consider the case where the signals or the messages or both are continuously variable, in contrast with the discrete nature assumed until now. To a considerable extent the continuous case can be obtained through a limiting process from the discrete case by dividing the continuum of messages and signals into a large but finite number of small regions and calculating the various parameters involved on a discrete basis. As the size of the regions is decreased these parameters in general approach as limits the proper values for the continuous case. There are, however, a few new effects that appear and also a general change of emphasis in the direction of specialization of the general results to particular cases.
65,425 citations
TL;DR: A code search based on the EXIT chart technique has been performed yielding new recursive systematic convolutional constituent codes exhibiting turbo cliffs at lower signal-to-noise ratios than attainable by previously known constituent codes.
Abstract: Mutual information transfer characteristics of soft in/soft out decoders are proposed as a tool to better understand the convergence behavior of iterative decoding schemes. The exchange of extrinsic information is visualized as a decoding trajectory in the extrinsic information transfer chart (EXIT chart). This allows the prediction of turbo cliff position and bit error rate after an arbitrary number of iterations. The influence of code memory, code polynomials as well as different constituent codes on the convergence behavior is studied for parallel concatenated codes. A code search based on the EXIT chart technique has been performed yielding new recursive systematic convolutional constituent codes exhibiting turbo cliffs at lower signal-to-noise ratios than attainable by previously known constituent codes.
2,498 citations
"Soft-feedback MMSE equalization for..." refers background in this paper
...Therefore, a posteriori MI of decoder, Ip,Dec approximately equals to extrinsic MI in the case of high MI which can lead to the expectation of BER [10] as...
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14 Jun 2009
TL;DR: It is shown that it is possible to detect optimally and efficiently FDM signals, with 25% bandwidth gain with respect to analogous OFDM signal parameters, which indicates that the transmission of spectrally efficient non orthogonal F DM signals is tangible.
Abstract: This paper investigates the transmission of Frequency Division Multiplexed (FDM) signals, where carrier orthogonality is intentionally violated in order to increase bandwidth efficiency. In analogy to conventional OFDM, signal generation relies on an Inverse Fractional Fourier Transform (IFRFT) that can be implemented with O(N log2 N) algorithmic complexity. Optimal Maximum Likelihood (ML) detection is overly complex due to the presence of substantial Intercarrier Interference (ICI). Consequently, we investigate an alternative detection mechanism based on the Generalized Sphere Decoding (GSD) algorithm. We examine the bandwidth efficiency and the error performance in Additive White Gaussian Noise (AWGN), for various FDM signal parameters. In particular, we show that it is possible to detect optimally and efficiently FDM signals, with 25% bandwidth gain with respect to analogous OFDM signals. This indicates that the transmission of spectrally efficient non orthogonal FDM signals is tangible.
163 citations
TL;DR: A frequency domain soft-interference canceling minimum mean-square error (MMSE) turbo equalizer and a computationally efficient method for computing extrinsic information transfer (EXIT) function of the equalizer are proposed.
Abstract: A frequency domain soft-interference canceling minimum mean-square error (MMSE) turbo equalizer is studied. A computationally efficient method for computing extrinsic information transfer (EXIT) function of the equalizer is proposed. The method is based on the Gaussian approximation for the equalizer output and it produces an approximate EXIT chart in a fraction of computational load compared to previous numerical methods. The accuracy of the method is verified for both single-input single-output (SISO) and multiple-input multiple output (MIMO) channels
73 citations
"Soft-feedback MMSE equalization for..." refers background in this paper
...The concept of ICI elimination is very similar to turbo equalization for single carrier signalling [6]....
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...SC-MMSE turbo detector has been proven to mitigate the interference efficiently, and achieve excellent performance [6]....
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05 Sep 2004
TL;DR: It is shown that a remarkable improvement in spectral efficiency can be obtained by the HC-MCM as the number of subcarriers increases, and that subcarrier spectra overlapping is sensitive to the minimum Euclidean distance, but large enough in comparison with OFDM under the condition that the transmission rate and the frequency spacing are identical to those in OFDM.
Abstract: A novel multi-carrier transmission system named high compaction multi-carrier modulation (HC-MCM) is proposed to improve the spectral efficiency of OFDM. The HC-MCM can arbitrarily overlap the spectra of its subcarriers with an operation for the transmitting signal, whereby a fast transmission rate can easily be achieved. A DFT-based transmitter and receiver, spectral efficiency, the minimum Euclidean distance, and bit-error rate (BER) characteristics are elaborated. As a result, it is shown that a remarkable improvement in spectral efficiency can be obtained by the HC-MCM as the number of subcarriers increases. It is also shown that subcarrier spectra overlapping is sensitive to the minimum Euclidean distance, but large enough in comparison with OFDM under the condition that the transmission rate and the frequency spacing of subcarriers are identical to those in OFDM.
65 citations
"Soft-feedback MMSE equalization for..." refers methods in this paper
...The problem inherent within the generation of the FDM signal having uniform sub-carrier spacing can be solved by the techniques presented in [3] and [4] where generalized inverse discrete Fourier transform (GIDFT) is used....
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...the output, by which more data can be transmitted compared to the technique in [3] and [4]....
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