Domain Decision Feedback Equalizer Research Articles

An Improved Iterative Frequency Domain Decision Feedback Equalization for STBC-SC-FDE

This article proposes an improved iterative frequency domain decision feedback equalization(IBDFE) for the unique word(UW) based system of space-time block coded-single carrier frequency domain equalization(STBC-SC-FDE). Compared with the conventional IBDFE, this algorithm uses minimum mean square error(MMSE) equalization and a noise prediction module based on UW instead of the feedback equalization part, while maintain the feedforward equalization. It is shown from the simulation results that the improved IBDFE can achieve satisfactory performance without iterations.

An Energy Efficient VLSI Architecture of Decision Feedback Equalizer for 5G Communication System

Decision feedback equalizer (DFE) is widely used to mitigate the inter-symbol interference. In gigabit applications, the complexity of time domain DFE grows exponentially with feedback filter (FBF) order. In this paper, we have derived low complexity, high throughput architectural designs for time domain DFEs, which meets the requirements of 5G communication systems. These designs are based on the concept of pre-speedup the conventional DFE architecture. The number of FBF coefficient combinations to be stored in the lookup table (LUT) and the hardware complexity of proposed designs are reduced by almost $(M/2)^{-1}$ with $M$ being the number of levels in quadrature-amplitude modulation (QAM). The proposed design achieves the throughput nearly 2.15 Gb/s for 16-QAM. A new strategy for updating the FBF coefficients is proposed to improve the convergence rate and steady state error performances without extra hardware overhead. This is based on storing the past decisions in separate LUT, whose contents are updated time to time using parallel error multiplexor. In addition, the bit-error-rate performance of proposed designs is evaluated for different speedup factors in AWGN and Rayleigh fading channels. From the implementation results, it is found that the area, power, and logic utilization of the proposed designs are significantly reduced. For example, an $8^{\mathrm{ th}}$ -order FBF of proposed adaptive DFE for 16-QAM occupies times 1.19 less area, 1.04 times less area-time product, with nearly consumes 2.48 times less power and; utilizes 1.93 times less slice LUTs and 2.04 times less flip-flops as compared with the best existing scheme.

Combined Hybrid DFE and CCK Remodulator for Medium-Range Single-Carrier Underwater Acoustic Communications

Advanced modulation and channel equalization techniques are essential for improving the performance of medium-range single-carrier underwater acoustic communications. In this paper, an enhanced detection scheme, hybrid time-frequency domain decision feedback equalizer (DFE) combined with complementary code keying (CCK) remodulator, is presented. CCK modulation technique provides strong tolerance to intersymbol interference caused by multipath propagation in underwater acoustic channels. The conventional hybrid DFE, using a frequency domain feedforward filter and a time domain feedback filter, provides good performance along with low computational complexity. The error propagation in the feedback filter, caused by feedbacking wrong decisions prior to CCK demodulation, may lead to great performance degradation. In our proposed scheme, with the help of CCK coding gain, more accurate remodulated CCK chips can be used as feedback. The proposed detection scheme is tested by the practical ocean experiments. The experimental results show that the proposed detection scheme ensures robust communications over 10-kilometre underwater acoustic channels with the data rate at 5 Kbits/s in 3 kHz of channel bandwidth.

High spectral efficient W-band optical/wireless system employing Single-Sideband Single-Carrier Modulation

With broader available bandwidth, W-band wireless transmission has attracted a lot of interests for future Giga-bit communication. In this article, we experimentally demonstrate W-band radio-over-fiber (RoF) system employing single-sideband single-carrier (SSB-SC) modulation with lower peak-to-average-power ratio (PAPR) than orthogonal frequency division multiplex (OFDM). To overcome the inter-symbol interference (ISI) of the penalty from uneven frequency response and SSB-SC modulation, frequency domain equalizer (FDE) and decision feedback equalizer (DFE) are implemented. We discuss the maximum available bandwidth of different modulation formats between SSB-SC and OFDM signals at the BER below forward error correction (FEC) threshold (3.8 × 10(-3)). Up to 50-Gbps 32-QAM SSB-SC signals with spectral efficiency of 5 bit/s/Hz can be achieved.

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.

Frequency Domain DFE for Single-Carrier STBC Block Transmission

Space-time block coding (STBC) is a novel transmit diversity technique that can substantially improve the reliability of wireless communication channel. In this letter, we investigate single-carrier STBC block transmission over frequency-selective fading channel. Based on the minimum mean square error (MMSE) criterion, by exploiting the reliability of tentative decision symbols, we propose a novel suboptimal, low complexity frequency domain decision feedback equalization (FD-DFE) scheme for SC STBC. Simulation results show that the proposed scheme provides better performance than the conventional scheme.

Iterative Frequency Domain Decision Feedback Equalization and Decoding for Underwater Acoustic Communications

Iterative Frequency Domain Decision Feedback Equalization and Decoding for Underwater Acoustic Communications

Iterative Frequency Domain Decision Feedback Equalization and Decoding for Underwater Acoustic Communications

Single-carrier (SC) transmission with frequency-domain equalization (FDE) is today recognized as an attractive alternative to orthogonal frequency-division multiplexing (OFDM) for communication application with the inter-symbol interference (ISI) caused by multi-path propagation, especially in shallow water channel. In this paper, we investigate an iterative receiver based on minimum mean square error (MMSE) decision feedback equalizer (DFE) with symbol rate and fractional rate samplings in the frequency domain (FD) and serially concatenated trellis coded modulation (SCTCM) decoder. Based on sound speed profiles (SSP) measured in the lake and finite-element ray tracking (Bellhop) method, the shallow water channel is constructed to evaluate the performance of the proposed iterative receiver. Performance results show that the proposed iterative receiver can significantly improve the performance and obtain better data transmission than FD linear and adaptive decision feedback equalizers, especially in adopting fractional rate sampling.

Frequency domain decision feedback equalizer for time-reversal space-time block coding

In this paper, a frequency domain decision feedback equalizer is proposed for single carrier transmission with time-reversal space-time block coding (TR-STBC). It is shown that the diagonal decision feedback equalizer matrix can be calculated from the frequency domain channel response. Under the perfect feedback assumption, the proposed equalizer can approach matched filter bound (MFB). Compared with the existing time domain decision feedback equalizer, the proposed equalizer exhibits better performance with the same equalization complexity.

Partial PIC-MRC Receiver Design for Single Carrier Block Transmission System over Multipath Fading Channels

Single carrier block transmission (SCBT) system has become one of the most popular modulation systems due to its low peak-to-average power ratio (PAPR), and it is gradually considered to be used for uplink wireless communication systems. In this paper, a low complexity partial parallel interference cancellation (PIC) with maximum ratio combining (MRC) technology is proposed to use for receiver to combat the intersymbol interference (ISI) problem over multipath fading channel. With the aid of MRC scheme, the proposed partial PIC technique can effectively perform the interference cancellation and acquire the benefit of time diversity gain. Finally, the proposed system can be extended to use for multiple antenna systems to provide excellent performance. Simulation results reveal that the proposed low complexity partial PIC-MRC SIMO system can provide robust performance and outperform the conventional PIC and the iterative frequency domain decision feedback equalizer (FD-DFE) systems over multipath fading channel environment.

Low-Complexity Iterative Frequency Domain Decision Feedback Equalization

Single-carrier transmission with frequency-domain equalization (SC-FDE) offers a viable design alternative to the classic orthogonal frequency-division multiplexing (OFDM) technique. However, SC-FDE using a linear equalizer may suffer from serious performance deterioration for transmission over severely frequency-selective fading channels. An effective method of solving this problem is to introduce nonlinear decision feedback equalization (DFE) to SC-FDE. In this paper, a low-complexity iterative DFE operating in the frequency domain of single-carrier systems is proposed. Based on the minimum-mean-square-error (MMSE) criterion, a simplified parameter estimation method is introduced to calculate the coefficients of the feedforward and feedback filters, which significantly reduces the implementation complexity of the equalizer. Simulation results show that the performance of the proposed simplified design is similar to the traditional iterative block DFE under various multipath fading channels, but it imposes a much lower complexity than the latter.

Frequency-domain precoding for single carrier frequency-division multiple access

At present there is considerable interest in the use of single carrier frequency-division multiple access. This interest is justified by the inherent single carrier structure of the SC-FDMA scheme, which is more robust against phase noise and has a lower peak-to-average power ratio than orthogonal frequency-division multiple access. This consequently makes it more attractive for uplink transmission from low-cost devices with limited transmit power. SC-FDMA commonly makes use of frequency domain linear equalization in order to combat the frequency selectivity of the transmission channel. Frequency domain decision feedback equalization, composed of a frequency domain feed forward filter and a time domain feedback filter, outperforms LE due to its ability to cancel precursor echoes. Although these solutions suffer from error propagation, results show that DFE still offers a significant performance gain over conventional LE for uncoded SC-FDMA. In this article we show how precoding can be used on the uplink of the LTE standard to overcome the frequency selective nature of the radio channel. We propose a frequency domain implementation of Tomlinson- Harashima precoding and investigate the bit error rate and the PAPR performance for SCFDMA using ZF and MMSE THP.

Iterative decision feedback equalizer with cyclic detection for DFT-S OFDM system

One of the most challenging problems in high-data-rate wireless transmission is to reduce inter-symbol interference (ISI) resulted from the time dispersion caused by multi-path propagation. To solve this problem, equalization is introduced. Generally, efficient decision feedback equalizer (DFE) holds better performance than linear equalizer for the cancellation of ISI without noise enhancement. However, its inherent error propagation has some limitation for further improvement. In fact, as shown later in simulation results, conventional frequency domain DFE (FD-DFE) almost cannot be used in Discrete Fourier Transform-Spread Orthogonal Frequency Division Multiplex (DFT-S OFDM) system in Evolved-UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (E-UTRA) uplink transmission [3GPP, TR 25.814 V1.2.3. Physical layer aspects for evolved UTRA. May 2006 [release 7]]. Unique word (UW) is proposed in the literatures, as a known symbol sequence, can make error propagation beyond one FFT-block impossible since the last symbols of every block are always decided correctly. But the UW-based scheme is not appropriate for DFT-S OFDM, so it must be modified. This paper proposes a simple DFE-based equalization algorithm for DFT-S OFDM. Through cyclic detection and iteration, the new algorithm obtains a noticeable gain than conventional DFE, and is almost as effective as the modified UW-based methods but with much higher bandwidth efficiency. Furthermore, it does not need to change the frame structure of existing protocol.