Soft-feedback MMSE equalization for non-orthogonal frequency division multiplexing (n-OFDM) signal detection

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 (SC-MMSE) 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.

Signal modulation techniques in Non-orthogonal waveform for future wireless communication system

“…Therefore, a few combination techniques are proposed to achieve a better spectral enhancement and reduce the complexity of the system implementation. For instance, in [25] has proposed a turbo equalizer namely soft-cancellation minimum mean square error (SC-MMSE). The technique is functioned as severe ICI mitigation for the non-orthogonal system.…”

“…In [25] and [27], the author has proposed a non-orthogonal system known as Generalized Inverse Discrete Fourier Transform (GIDFT-nOFDM) which has higher subcarrier compare to a total number of sampling. The system block diagram is shown in Figure 1, and its transmitted signal is represented as:…”

“…Virtual MIMO Channel Figure 1. GIDFT-nOFDM system [25] The GIDFT matrix is being multiplexed with the modulated signal that will produce the received signal as.…”

“…As mentioned in [25], the author represents an EXtrinsic Information Transfer (EXIT) chart [28] to analyze the matching between the BCJR decoder and equalizer for a recursive system. However, the results showed that the ending point is not exactly reached (1.0, 1.0) point which makes the system unable to eliminate the error floor.…”

Spectrally Efficient FDM: Spectrum Saving Technique for 5G?

“…The requirement of orthogonality is reduced and signals can be properly recovered by using appropriate detectors. 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]. In [12], an efficient iterative soft detector was introduced and this allowed SEFDM to save 45% of bandwidth compared to OFDM.…”