Decision Feedback Equalization Algorithm Research Articles

Cosine function variable step-size transform domain least mean square algorithm based on matrix rotation

A novel cosine function variable step-size transform domain least mean square (LMS) algorithm based on matrix rotation (COS-ROTDCT-LMS-DFE) was put forward. Based on the discrete cosine transform domain LMS (DCT-LMS) algorithm, it was first processed by matrix rotation in an anticlockwise direction to resolve the problem of self-interference between signals, which effectively sped up the convergence of the algorithm. Subsequently, a cosine function variable step-size algorithm was developed considering that its curve was characterized by a smooth top and fast rising and falling speed so as to further improve the convergence speed of the algorithm. Subsequently, the decision feedback equalizer (DFE) was introduced into the algorithm to compensate signal distortion and noise. The convergence performance of the algorithm was simulated in typical multipath underwater acoustic channels. The simulation results showed that the convergence performance of the new algorithm was equivalent to that of recursive least squares (RLS). The convergence speed of COS-ROTDCT-LMS-DFE was even better than that of the recursive least square decision feedback equalizer (RLS-DFE) algorithm. The new algorithm performed well in terms of both convergence speed and steady-state error and could be easily implemented.

A Decision Feedback Equalization Algorithm Based on Simplified Volterra Structure for PAM4 IM-DD Optical Communication Systems

A novel simplifying Volterra structure algorithm is proposed for an intensity modulation direct detection (IM-DD) optical fiber short distance communication system using the decision feedback equalization algorithm (DFE). Based on this algorithm, the signal damage for the four-level pulse amplitude modulation signal (PAM-4) is compensated, which is caused by device bandwidth limitation and dispersion during transmission. Experiments have been carried out using a 25 GHz Electro-absorption Modulated Laser (EML), showing that PAM-4 signals can transmit over 10 km in standard single-mode fiber (SSMF). The 112 Gbps and 128 Gbps signals can reach the error rate threshold of KP4-FEC (BER = 2 × 10−4) and HD-FEC (BER = 3.8 × 10−3), respectively. The simplified principle and process of the proposed Volterra-based equalization algorithm are presented. Experimental results show that the algorithm complexity is greatly reduced by 75%, which provides effective theoretical support for the commercial application of this algorithm.

An Estimated δ-Based Iterative Block Decision Feedback Equalization in SC-FDE System

We provide a novel nonlinear frequency domain equalization algorithm for the frequency domain equalization of an SC-FDE system by improving the classical iterative block decision feedback equalization (IBDFE) algorithm and applying δ estimation to the improved algorithm. The improvement of the IBDFE algorithm is carried out by replacing the ZF equalization in the feedback branch with the MMSE equalization and eliminating the iteration of the correlation factor, thus reducing the noise error and the computational complexity of the original algorithm. δ estimation can estimate residual inter-symbol interference in the signal after MMSE equalization and reject it, thus further improving the equalization accuracy. The simulation results show that the performance of the novel algorithm is better than that of the IBDFE algorithm with similar complexity, or the complexity of the novel algorithm is lower than that of the IBDFE algorithm with similar performance.

Delay-Doppler domain decision feedback turbo equalization for OTFS modulation

Emerging evidence indicates that orthogonal time–frequency space (OTFS) modulation is a potential candidate modulation scheme for high mobility wireless communications. However, OTFS may experience significant inter-symbol interference (ISI) and inter-Doppler interference (IDI) in the receiver. In this paper, we propose a soft decision feedback turbo equalization for OTFS transmission over delay-Doppler channels to jointly combat both interferences. A novel block decision feedback equalization (BDFE) algorithm is constructed using the band feature of the channels in the delay-Doppler domain. The feedforward and feedback filters are designed by the delay-time channels coefficients. According to the designed filter, an equivalent system model is employed to allow turbo equalization. The posterior probability is established using the soft prior information and feedback filter, and then fed back to the channel decoder as external information. Both theoretical analysis and simulation results demonstrate the effectiveness of the proposed scheme in improving the bit error rate (BER) performance and combat various interference. Numerical simulations are finally provided to justify the validity of the proposed scheme in improving the bit error rate (BER) performance and combating various interference.

Modification in the Range of Information Potentials for Blind Algorithms in Impulsive Noise Environments

In this paper a modification approach to the range of influence for information potentials (IP)of blind decision feedback equalizer (DFE) algorithms is presented to cope better with impulsive noise and severe channel distortion. Analysis of the IP range of influence reveals that the range should be applied separately based on the roles under impulsive noise. A new cost function that can manage ranges of information potentials is proposed, and a related DFE algorithm is derived. Simulation results from the environment of a severe multipath channel obtained from shallow-water communication experiments and impulsive noise show that the proposed DFE algorithm yields more than 10 dB in MSE gain by employing the proposed modification toranges of information potentials.

Burst-Error-Propagation Suppression for Decision-Feedback Equalizer in Field-Trial Submarine Fiber-Optic Communications

In this paper, we present a field-trial C-band 72Gbit/s optical on-off keying (OOK) system over 18.8km dispersion-uncompensated submarine optical cable in the South China Sea. Chromatic dispersion (CD) of 18.8km submarine optical cable causes four spectral nulls on the 36GHz bandwidth of 72Gbit/s OOK signal, which is the main obstacle for achieving an acceptable bit-error-rate (BER) performance. Decision feedback equalizer (DFE) is effective to compensate for the spectral nulls. However, DFE has a serious defect of burst-error propagation when the burst errors emerge due to the unstable submarine environment. Weighted DFE (WDFE) can be used to mitigate the burst-error propagation, but it cannot fully compensate for the spectral nulls because only a part of feedback symbols is directly decided. Fortunately, maximum likelihood sequence estimation (MLSE) can be added after the WDFE to simultaneously eliminate the resisting spectral distortions and implement optimal detection. Compared to the joint DFE and MLSE algorithm, the joint WDFE and MLSE algorithm can effectively suppress the burst-error propagation to obtain a maximum 2.9dB improvement of $\boldsymbol{Q}$ factor and eliminate the phenomenon of BER floor. In conclusion, the joint WDFE and MLSE algorithm can solve the burst-error propagation for the field-trial fiber-optic communications.

Iterative Block Decision Feedback Equalization for IM/DD-Based OCDM to Compensate Chromatic-Dispersion-Induced Power Fading

Orthogonal chirp-division multiplexing (OCDM) has recently been proposed as an attractive modulation technique for high-speed fiber-optic systems in virtue of its resilience against system impairments. In this paper, we propose an iterative block (IB) decision feedback equalization (DFE) algorithm for the intensity-modulation and direct-detection (IM/DD) based OCDM system to effectively mitigate the chromatic-dispersion (CD) induced power fading in the fiber. An efficient algorithm is derived to simplify the IB-DFE at the receiver. Analysis is provided to show that the fading effect is compensated by recovering the noisy signals in the vicinity of frequency notches. Simulations were carried out to study the performance of the proposed system. The results show that the proposed system with IB-DFE is able to compensate severe fading effects and improves the bit error rate (BER) by several orders of magnitude. An experiment was implemented to realize 30.3-Gb/s IM/DD-OCDM signal over 50-km fiber, in which power fading due to CD over 20 dB was observed. The experiment results show that the proposed system further reduced the required optical signal-to-noise ratio by 8 dB to achieve a BER of 3 × 10−5.

Time Domain Precoding for OFDM/OFDMA Systems Without Cyclic Prefix

Cyclic prefix (CP) is used in OFDM/OFDMA systems for data transmission over multipath channels at a dear price of spectral efficiency degradation. This work aims to design a CP-free OFDM/OFDMA system for futuristic high-speed communications, where data block length can be shorter than channel delay spread. In particular, we utilize a time domain precoding scheme working jointly with a multiblock decision feedback equalization algorithm to mitigate intersymbol interference and intercarrier interference caused by multipath propagation. The satisfactory performance of the scheme is validated by simulation results, showing that the proposed CP-free OFDM/OFDMA scheme with known channel state information at transmitter and receiver offers a significantly higher spectral efficiency than traditional CP-based OFDM/OFDMA schemes.

Linear Approximation Signal Detection Scheme in MIMO-OFDM Systems

In this paper, a linearly approximate signal detection scheme is proposed in multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems. The huge MIMO-OFDM system, which uses many transmit antennas and high order modulation, requires a detection scheme at the receiver with very low complexity for practical implementation. In the proposed detection scheme, one N × N MIMO-OFDM system is divided into N / 2 2 × 2 MIMO-OFDM systems for linear increase of complexity. After the partial zero-forcing (ZF), decision feedback equalizer (DFE) and QR decomposition-M algorithm (QRD-M) are applied to each 2 × 2 MIMO-OFDM system. Despite nonlinear detection schemes, the overall complexity of the proposed algorithm increases almost linearly because the DFE and the QRD-M are applied to 2 × 2 MIMO-OFDM systems. Also, the value of M in the QRD-M is fixed according to position of the center point in constellation for efficient signal detection. In simulation results, the proposed detection scheme has higher error performance and lower complexity than the conventional ZF. Also, the proposed detection scheme has very lower complexity than the conventional DFE, with slight loss of error performance.

Improved high gain circuit and DFE algorithm for underwater photoelectric signal recovery

Underwater long-distance optical communications, due to the influence of light scattering and absorption, it will cause severe signal attenuation, in addition, multipath propagation effects and Doppler effect of light will cause serious signal distortion. Based on the problems, an improved amplifier with Direct Current (DC) servo loop is proposed. The amplifier overcomes the shortcoming of conventional amplifiers and has high gain, wide dynamic range. Further, in order to overcome the time varying interference, an improved decision feedback equalizer (DFE) model and algorithm is given, the model can achieve faster convergence and smaller steady-state error. The new algorithms take Marr function as a basic function, and two parameters α and β used to shape the profile of functions. Experiments show that the method can greatly improve the transmission distance of underwater optical communications (UOC).

Optimized Decision Feedback Equalizer Algorithm based on Sparse Underwater Acoustic Channel

Optimized Decision Feedback Equalizer Algorithm based on Sparse Underwater Acoustic Channel

Simplified Parallel Interference Cancelation for Underdetermined MIMO Systems

In this paper, a low-complexity detection scheme is proposed for an underdetermined multiple-input-multiple-output (UD-MIMO) wireless communication system that employs N transmit antennas and M< Nreceive antennas. The proposed scheme combines a simplified parallel interference cancelation (S-PIC) with the block decision feedback equalization (BDFE) algorithm. To account for the extra (N − M )-dimension in the transmitted signal, the UD-MIMO system is partitioned into two subsystems: one with (N − M ) transmit antennas and the other one with M transmit antennas. The interference from the first subsystem to the second one is canceled in parallel, and BDFE is performed over the second subsystem. Unlike conventional PIC methods that exhaustively search all the Q (N −M ) sequences in the first subsystem, with Q being the constellation size, the proposed scheme explores only a small number of candidate sequences in the first subsystem; thus, it achieves significant complexity reduction. Two new candidate sequence selection methods are proposed. In the first iteration, the candidate sequences used for PIC are selected by exploring the statistical properties of the received signals. In the second iteration and beyond, the set containing the candidate sequences is constructed by utilizing the soft informa- tion generated from the previous iteration. The proposed scheme provides a balanced tradeoff between computational complexity and bit error rate (BER) performance. Index Terms—Block decision feedback equalization (BDFE), parallel interference cancelation (PIC), turbo detection, under- determined multiple-input multiple-output (UD-MIMO), wireless communication.

A Modified DFE-MMSE Equalization Algorithm

In wireless communication, inter symbol interference (ISI) and signal distortion are often caused by the frequency deviation and time offset of wireless channel. To eliminate or reduce ISI, people proposed the channel equalization technology. However, traditional decision feedback equalization algorithm based on MMSE criterion equalizer (DFE-MMSE) often introduces the error diffusion which degrades the performance of the equalizer in iterative system. In this paper, we propose an improved DFE-MMSE algorithm to reduce the error diffusion and improve the performance of iterative equalization, with a correction factor. Simulation results show that our algorithm achieves better bit error rate, which makes it competent in more practical cases.

LDPC Coded Combined with Space-Time Codes in Cooperative MIMO System

This paper proposes a method of LDPC coded combined with space-time codes using in the cooperative MIMO system. An algorithm is introduced that the joint iterative detection algorithm based on Fincke-pohst (sphere detecting) maximum a-posteriori (MAP). theoretical analysis and derivation shown that the performance of LDPC cascading space-time codes (STBC) system is slightly better than that of LDPC coded cascading vertical layered space-time codes (VBLAST) in cooperative MIMO systems. And the FP-MAP detection algorithm compares with the detection algorithm----zero forcing sort plus interference cancellation(ZF-OSIC) and the recursive least squares decision feedback equalization(RLS-DFE) algorithm, its performance is improved by about 0. 6dB and 0. 3dB respectively, its performance is closest to the ML detection

Iterative Frequency Domain Equalization for Single-Carrier Space Time Diversity Systems

Single carrier frequency domain equalization (SC-FDE) has been receiving much attention for its advantage of suppressing inter-symbol interference (ISI). We proposed a frequency domain iterative decision feedback equalization (FD-IDFE) algorithm for single carrier space time block coding (STBC) systems. The paper use the multi-antenna transmit and Alamouti signaling scheme to achieve the significant diversity gain. We design the feedback equalization structure by Mean Square Error (MSE) criterion and Lagrange optimization method, and we also consider the parameters estimation. At last, we compare the proposed algorithm with the conventional equalization schemes, the simulation results illustrate that our method has excellent performance.

Self-adjusting decision feedback equalizer for variational underwater acoustic channel environments

Aimed at the abominable influences to blind equalization algorithms caused by complex time-space variability existing in underwater acoustic channels, a new self-adjusting decision feedback equalization (DFE) algorithm adapting to different underwater acoustic channel environments is proposed by changing its central tap position. Besides, this new algorithm behaves faster convergence speed based on the analysis of equalizers' working rules, which is more suitable to implement communications in different unknown channels. Corresponding results and conclusions are validated by simulations and spot experiments.

Single-Carrier Space Time Transmission Diversity with Decision Feedback Equalization

In order to suppress inter-symbol interference (ISI), the Frequency domain decision feedback equalization (FD-DFE) algorithm is proposed in this paper for single carrier frequency domain equalization (SC-FDE) combined with Alamouti space time block coding (STBC) systems over frequency-selective channels. We use the cyclic prefix (CP) and two transmit antennas to achieve the significant diversity gain. The feedback equalization part is designed by Mean Square Error (MSE) criterion and the coefficients of filters are all in the frequency domain for the given channel frequency response. The outage and diversity analysis of system is also made to measure the equalization performance. Finally, the simulation results show that the proposed algorithm has better performance than the conventional liner equalization (LE) and hybrid structure decision feedback equalization (HDFE) schemes, and the computational complexity of our method is acceptable.

Adaptive multichannel decision feedback equalization using subarray processing

The adaptive multichannel Decision Feedback Equalizer (DFE) has been shown to be an effective algorithm for enabling reliable high rate acoustic communications in complex and time-varying underwater environments. The choice of the number of channels used in an equalizer presents a performance trade-off. The minimal achievable error that can be realized by the equalizer decreases as the number of channels increases. However, an increase in the number of channels increases the number of filter weights that need to be adapted. Thus, the computational complexity of least squares and Kalman type adaptation algorithms is proportional to the number of channels squared. In addition, the averaging interval required by an adaptation algorithm in order to achieve good performance grows linearly with the number of parameters. Thus, an increase in the number of M-DFE channels can reduce the rate of channel fluctuation that can successfully tracked by the M-DFE. The partitioning of an array into sub-arrays which are each independently equalized before combining their outputs can both improve performance and reduce complexity in processing real-world signals. The choice of the size and sensor locations for the subarrays is analyzed. The resulting adaptive subarray multichannel DFE algorithm is compared to other multichannel equalization algorithms.

랜덤 심볼열과 결정 궤환을 사용한 자력 등화 알고리듬

Abstract Non-linear equalization techniques using decision feedback structure are highly demanded for cancellation of intersymbol interferences occurred in severe channel environments. In this paper decision feedback structure is applied to the linear blind equalizer algorithm that is based on information theoretic learning and a randomly generated symbol set. At the decision feedback equalizer (DFE) the random symbols are generated to have the same probability density function (PDF) as that of the transmitted symbols. By minimizing difference between the PDF of blind DFE output and that of randomly generated symbols, the proposed DFE algorithm produces equalized output signal. From the simulation results, the proposed method has shown enhanced convergence and error performance compared to its linear counterpart. Key Words : Decision feedback, Blind equalization, PDF, Random symbols, ITL. * 교신저자 : 김남용(namyong@kangwon.ac.kr)접수일 11년 11월 02일 수정일 (1차 11년 12월 26일, 2차 11년 12월 29일) 게재확정일 12년 01월 05일

오류 확률에 근거한 결정 궤환 방식의 통신 등화 알고리듬

For intersymbol interference (ISI) compensation from communication channels with multi-path fading and impulsive noise, a decision feedback equalizer algorithm that minimizes Euclidean distance of error probability is proposed. The Euclidean distance of error probability is defined as the quadratic distance between the probability error signal and Dirac-delta function. By minimizing the distance with respect to equalizer weight based on decision feedback structures, the proposed decision feedback algorithm has shown to have significant effect of residual ISI cancellation on severe multipath channels as well as robustness against impulsive noise.