Decision Feedback Research Articles

A 12-Gb/s 10-ns Turn-On Time Rapid ON/OFF Baud-Rate DFE Receiver in 65-nm CMOS

Rapid ON/OFF (ROO) operation helps scale power in accordance with link utilization. In this article, we present a baud-rate ROO receiver that can turn on in just 10 ns (~120 UI). Baud-rate clock and data recovery (CDR) is implemented using a new timing function that is amenable to operation with a loop un-rolled decision feedback equalizer (DFE). The receiver is turned on rapidly by sweeping the recovered clock phase across the received data bit by offsetting the digitally controlled oscillator (DCO) frequency at each power-ON event. This first ROO DFE receiver also includes a continuous-time linear equalizer (CTLE) and three-tap DFE to compensate up to 20-dB channel loss at Nyquist. Fabricated in a 65-nm CMOS process, the prototype receiver recovers 12 Gb/s with BER 30-MHz JTOL corner, 377 $fs_{\text {rms}}$ recovered clock jitter, and 3.8-pJ/bit energy efficiency.

The effect of odor enrichment on olfactory acuity: Olfactometric testing in mice using two mirror-molecular pairs.

Intelligent systems in nature like the mammalian nervous system benefit from adaptable inputs that can tailor response profiles to their environment that varies in time and space. Study of such plasticity, in all its manifestations, forms a pillar of classical and modern neuroscience. This study is concerned with a novel form of plasticity in the olfactory system referred to as induction. In this process, subjects unable to smell a particular odor, or unable to differentiate similar odors, gain these abilities through mere exposure to the odor(s) over time without the need for attention or feedback (reward or punishment). However, few studies of induction have rigorously documented changes in olfactory threshold for the odor(s) used for "enrichment." We trained 36 CD-1 mice in an operant-olfactometer (go/no go task) to discriminate a mixture of stereoisomers from a lone stereoisomer using two enantiomeric pairs: limonene and carvone. We also measured each subject's ability to detect one of the stereoisomers of each odor. In order to assess the effect of odor enrichment on enantiomer discrimination and detection, mice were exposed to both stereoisomers of limonene or carvone for 2 to 12 weeks. Enrichment was effected by adulterating a subject's food (passive enrichment) with one pair of enantiomers or by exposing a subject to the enantiomers in daily operant discrimination testing (active enrichment). We found that neither form of enrichment altered discrimination nor detection. And this result pertained using either within-subject or between-subject experimental designs. Unexpectedly, our threshold measurements were among the lowest ever recorded for any species, which we attributed to the relatively greater amount of practice (task replication) we allowed our mice compared to other reports. Interestingly, discrimination thresholds were no greater (limonene) or only modestly greater (carvone) from detection thresholds suggesting chiral-specific olfactory receptors determine thresholds for these compounds. The super-sensitivity of mice, shown in this study, to the limonene and carvone enantiomers, compared to the much lesser acuity of humans for these compounds, reported elsewhere, may resolve the mystery of why the former group with four-fold more olfactory receptors have tended, in previous studies, to have similar thresholds to the latter group. Finally, our results are consistent with the conclusion that supervised-perceptual learning i.e. that involving repeated feedback for correct and incorrect decisions, rather than induction, is the form of plasticity that allows animals to fully realize the capabilities of their olfactory system.

56-m/3.31-Gbps underwater wireless optical communication employing Nyquist single carrier frequency domain equalization with noise prediction.

We propose and experimentally demonstrate an underwater wireless optical communication (UWOC) system using a 520-nm laser diode (LD) and 32-quadrature amplitude modulation (32-QAM) single carrier signals. To mitigate the inter-symbol interference (ISI), a frequency domain equalizer combined with a time-domain decision feedback noise predictor is employed at the receiver. However, this structure cannot apply channel coding conjunctively. Therefore, an interleaver/deinterleaver pair is applied to handle the decoding delay, and thus systematic Reed-Solomon (RS) code can provide reliable feedback signals. With a 3-dB bandwidth of 200 MHz, the proposed system with the frequency domain equalization and noise prediction (FDE-NP) scheme can achieve a maximal net data rate of 3.48 Gbps, which is 17.2% higher than that of orthogonal frequency division multiplexing (OFDM) scheme. At a net data rate of 3.31 Gbps, we have successfully achieved a transmission distance up to 56 m. To the best of our knowledge, this is the first time to employ FDE-NP in UWOC where OFDM conventionally plays a prevailing role for high-speed transmission.

Frequency-Domain Decision Feedback Equalization for Single-Carrier Transmissions in Fast Time-Varying Underwater Acoustic Channels

Frequency-domain equalization (FDE) is a computationally efficient method to recover underwater acoustic single-carrier transmissions in a multipath environment. The FDE receivers often operate in a block-by-block manner, assuming that the channel is time invariant during a block duration. This assumption implies that traditional block-based FDE receivers experience performance degradation in fast time-varying channel conditions, since the interfrequency interference (IFI) is often not considered. Here, we focus on the IFI cancelation (IFIC) in single-carrier transmissions. The IFI formulations are developed for a blockwise FDE receiver, where the time reversal (TR) processing is incorporated to alleviate the interblock interference. Based on the formulations, the IFI is estimated by the time-varying impulse responses, which are obtained from an adaptive basis expansion model. A soft two-step IFIC strategy is then employed to address the IFI. In the first step, the main IFI is removed by the time-varying TR processing and explicit IFI cancelation. The residual IFI is suppressed by the frequency-domain decision feedback equalization (FD-DFE) in the second step. To further enhance the communication performance, we develop a soft-symbol-based iterative receiver, referred to as IFIC-FD-DFE. The impulse responses, explicit IFI, and residual IFI are updated in an iterative fashion, based on the soft symbol estimates. The proposed receiver has been tested using the at-sea measurements collected at the Gulf of Mexico in August 2017. Communication packets at four ranges at the carrier frequency of 160 kHz with a symbol rate of 32 kHz have been decoded. The effectiveness of the IFIC-FD-DFE receiver has been demonstrated via comparisons with several FDE schemes in the current literature.

A Nonlinear Distortion Removal Based on Deep Neural Network for Underwater Acoustic OFDM Communication with the Mitigation of Peak to Average Power Ratio

Machine learning and deep learning algorithms have proved to be a powerful tool for developing data-driven signal processing algorithms for challenging engineering problems. This paper studies the modern machine learning algorithm for modeling nonlinear devices like power amplifiers (PAs) for underwater acoustic (UWA) orthogonal frequency divisional multiplexing (OFDM) communication. The OFDM system has a high peak to average power ratio (PAPR) in the time domain because the subcarriers are added coherently via inverse fast Fourier transform (IFFT). This causes a higher bit error rate (BER) and degrades the performance of the PAs; hence, it reduces the power efficiency. For long-range underwater acoustic applications such as the long-term monitoring of the sea, the PA works in full consumption mode. Thus, it becomes a challenging task to minimize power consumption and unnecessary distortion. To mitigate this problem, a receiver-based nonlinearity distortion mitigation method is proposed, assuming that the transmitting side has enough computation power. We propose a novel approach to identify the nonlinear power model using a modern deep learning algorithm named frequentative decision feedback (FFB); PAPR performance is verified by the clipping method. The simulation results prove the better performance of the PA model with a BER with the shortest learning time.

30-Gb/s 1.11-pJ/bit Single-Ended PAM-3 Transceiver for High-Speed Memory Links

A 30-Gb/s three-level pulse amplitude modulation (PAM-3) transceiver is designed with a one-tap tri-level decision feedback equalizer (DFE) to realize a high-speed dynamic random access memory (DRAM) interface via the 28-nm CMOS process. A 1.5-bit/pin bit efficiency is achieved by encoding and decoding 3-bit data in two unit intervals (UIs). The half-rate PAM-3 transmitter modulates single-ended pseudorandom binary sequence (PRBS) 7/15 data using a low-power encoding logic and an output driver. The receiver achieves a bit error rate (BER) of less than 1E-12 over an 80-mm FR-4 printed circuit board (PCB) channel. At the maximum data rate, the bit efficiency of the transceiver is 1.11 pJ/bit, consuming 33.4 mW. In the receiver, the attenuated PAM-3 data are equalized by a continuous-time linear equalizer (CTLE) and a one-tap tri-level DFE, which has the same complexity as that of non-return-to-zero (NRZ) signaling. The tri-state buffers, which have a floating PMOS switch, convert the output of the comparator into NRZ data, resulting in reduced delay and power dissipation. Four channels of the transceivers operate at data rates of up to 30 $\times $ 4 Gb/s, and the horizontal eye margin of the measured PAM-3 data is achieved at a UI of 0.14 for the PRBS-7 pattern at the maximum data rate.

Nonlinear Kalman Filter-Based Robust Channel Estimation for High Mobility OFDM Systems

High-speed train (HST) and vehicle-to-vehicle (V2V), as typical scenes of 5G communication, have attracted extensive attention from academia and industry in recent years. Aiming at the channel characteristics of frequency-selective fading, fast time-varying and time-domain non-stationary in high mobility scenarios, a nonlinear Kalman filter-based high-speed channel estimation algorithm for orthogonal frequency-division multiplexing (OFDM) systems is proposed. We adopt basis expansion model (BEM) to eliminate the inter-subcarrier interference (ICI) caused by the fast time-varying characteristics. For the non-stationary characteristics of high mobility channel, a channel interpolation algorithm based on extended Kalman filter (EKF) is introduced to jointly estimate the channel impulse response (CIR) and time correlation coefficients. However, the EKF channel estimation uses structure of decision feedback to construct the observation matrix, which would lead to error propagation. This paper analyzes the generation of error propagation through theoretical derivation. Furthermore, for the error propagation of EKF, we introduce unscented Kalman filter (UKF) algorithm to perform Gaussian approximation of non-Gaussian observing system, and eliminate the influence by Kalman filter (KF). Simulation results demonstrate that the channel estimation accuracy of BEM-UKF is further improved compared with BEM-EKF, and the influence of pilot distance (PD) is smaller, which further improves the robustness of the algorithm.

How do we use electronic clinical decision support and feedback to promote good transfusion practice.

This report describes the evolution of the electronic clinical decision support system (CDSS) and feedback methods at our center and the challenges and lessons learned. The electronic blood product order with integrated CDSS ensures collection of data regarding the patient's clinical condition and the justification for the blood product order. An alert is generated in real time if the order is placed outside agreed guidelines. We have provided feedback in several ways. We began with monthly review meetings with the junior hematology clinicians responsible for ordering blood. This was successful in reducing unjustified transfusions in this setting. We expanded the feedback to the rest of our hospitals in two ways. First, a dashboard was developed allowing visualization of ordering data by clinicians. Second, these data were summarized on a quarterly basis into a report circulated to the senior clinical staff by e-mail. Finally, a daily report collates all orders placed for blood products that have triggered a CDSS alert from the previous day. A multidisciplinary team reviews these daily. If an order appears unjustified the specialist transfusion clinician contacts the prescribing clinician to ask for further information and, if necessary, provides education. The CDSS and feedback, allied with other patient blood management measures, have reduced total blood product costs for our hospitals by 26% over 6 years. The description of how we have developed and implemented CDSS and feedback to influence transfusion practice may be of particular value to others developing their own systems.

Time-frequency Analysis of Electroencephalogram Signals in a Cognitive Decision-making Task.

Choices and decisions involve a series of complex cognitive processes, and the time-frequency analysis of electroencephalogram (EEG) signals can help understand the brain activities in different cognitive tasks. In this study, a decision-making cognitive task of rock-paper-scissors was designed, and the complex decision-making task was divided into three stages (decision planning, confirmation, and feedback). 64 channels of EEG signals were simultaneously recorded using the Neuroscan QuikCap system during the whole task. The average spectral power and phase synchronization values of each frequency band (delta, theta, alpha and beta band) were extracted and compared within and across different stages. The results showed the desire to win or not to lose within the first stage might be accompanied by the increase of alpha and theta components. In the second stage, the spectral power inhibition of alpha wave and phase synchronization increase of delta wave indicated that subjects would improve their attentions when they confirmed their choice. In the third stage, the theta increased effect and alpha decreased effect were related to different feedback. This pilot study suggests that the time-frequency analysis of EEG signals could be a great tool to visualize the brain activities in response to different cognitive tasks.

SDP-IGD: An Iterative Power Allocation Technique for Cluster-Based Multihop Vehicular Communications

This paper addresses the formulation of power allocation for cluster based multihop vehicular relaying communications in order to improve the network quality-of-services (QoS). The cluster-to-cluster (C2C) channel is completely depend on the power gain of vehicle-to-vehicle (V2V) channel that increases the difficulties of the power allocation problem. To meet this goal, we have derived a global channel obtained by joint V2V and C2C cooperation. The most challenging aspect is however the joint V2V and C2C power allocation of the global channel due to the association of its multi-variables objective function. To solve this problem, we apply an alternative optimization technique to make the global problem into a series of sub-problems. We then apply a semi-definite programming (SDP)-based iterative gradient descent (SDP-IGD) power allocation to assign power in each relay. The SDP-IGD power allocation algorithm has been extended from Lagrange Multiplier (LM) that provides better performance than separate LM technique. The minimum mean-square error (MMSE)-decision feedback equalizer (MMSE-DFE) is designed at the receiver to improve the signal detection capability under exact channel state information (CSI) in all forward-and-backward links. Finally, simulation results confirm that our proposed solution performs significantly superior compared to other solutions found in the literature.

Performance improvement of space diversity technique using space time block coding for time varying channels in wireless environment

Performance improvement of space diversity technique using space time block coding for time varying channels in wireless environment

A 7.8 Gb/s/pin, 1.96 pJ/b Transceiver With Phase-Difference-Modulation Signaling for Highly Reflective Interconnects

This paper presents a phase-difference-modulation transceiver with simple clock recovery for highly-reflective interconnects. By greatly suppressing reflective intersymbol interferences with two new enabling mechanisms, phase–difference modulation enables high-speed data communication through highly-reflective multi-drop channels without utilizing decision feedback equalization. A systematic analytical approach is presented, and provides guidelines on how to determine channel and signaling parameters to exploit the two enabling mechanisms based on a newly derived formula of a single bit response of a channel. In addition, we propose a phase-difference amplifier that relieves the timing constraint of the bit decision at the receiver. By deserializing the received signals using the clock embedded in the received signals, the phase-difference amplifier can greatly reduce the design complexity of the clock recovery circuit. The proposed transceiver was fabricated in 65-nm CMOS technology. In single-ended mode, the transceiver achieved a maximum speed of 7.8 Gb/s/pin at energy cost of only 1.96 pJ/b while overcoming 10 in-band notches without decision feedback equalization. Also, the phase-difference amplifier enables clock recovery at power and area costs of only 0.12 pJ/b and 550 $\mu \text{m}^{2}$ , respectively, in single-ended 6-Gb/s/pin operation.

Adaptive Channel-Matched Detection for C-Band 64-Gbit/s Optical OOK System Over 100-km Dispersion-Uncompensated Link

In this paper, we propose adaptive channel-matched detection (ACMD) for C-band 64-Gbit/s intensity-modulation and direct-detection (IM/DD) optical on-off keying (OOK) system over a 100-km dispersion-uncompensated link. The proposed ACMD can adaptively compensate most of the link distortions based on channel and noise characteristics, which includes a polynomial nonlinear equalizer (PNLE), a decision feedback equalizer (DFE) and maximum likelihood sequence estimation (MLSE). Based on the channel characteristics, PNLE eliminates the linear and nonlinear distortions, while the followed DFE compensates the spectral nulls caused by chromatic dispersion. Finally, based on the noise characteristics, a post filter can whiten the noise for implementing optimal signal detection using MLSE. To the best of our knowledge, we present a record C-band 64-Gbit/s IM/DD optical OOK system over a 100 km dispersion-uncompensated link achieving 7\% hard-decision forward error correction limit using only the proposed ACMD at the receiver side. In conclusion, ACMD-based C-band 64-Gbit/s optical OOK system shows great potential for future optical interconnects.

A 64-Gb/s PAM-4 Optical Receiver With Amplitude/Phase Correction and Threshold Voltage/Data Level Calibration

We present a 64-Gb/s four-level pulse amplitude modulation (PAM-4) optical receiver with the amplitude/phase correction and the threshold voltage/data level calibration, utilizing an inverter-based transimpedance amplifier (TIA). A variable gain amplifier (VGA) with the amplitude/phase correction is also presented. The threshold voltage of the data slicers and the data levels for the error slicers are calibrated. A three-tap decision feedback equalizer is utilized to compensate for the intersymbol interference. The tap coefficients are calibrated by using the sign-sign least-mean-square algorithm. This PAM-4 optical receiver is fabricated in a 40-nm CMOS process. For the TIA with five VGAs, the measured maximum amplitude imbalance is less than 0.4 dB and the phase imbalance is less than ±1°. Its power is 420 mW from a supply of 1.1 V excluding the output buffers. Its core area is 2.2 mm2.

Digital Pre- and Post-Equalization for C-Band 112-Gb/s PAM4 Short-Reach Transport Systems

Insufficient system bandwidth and chromatic dispersion (CD) of fiber are major limitations for high-speed four-level pulse amplitude modulation (PAM4) direct detection systems. In this article, we investigate C-band 112-Gb/s PAM4 optical transport systems over 10-km and 20-km standard single-mode fiber (SSMF) transmission, which suffers from both bandwidth limitation and CD-induced power fading. Advanced digital signal processing techniques are proposed to handle those channel distortions. At the transmitter, a low-complexity $1+\alpha Z^{-1}$ finite impulse response (FIR) filter coarsely pre-compensates system bandwidth without a preliminary channel estimation. At the receiver, a modified feed-forward equalizer and decision feedback equalizer (FFE-DFE) is employed to compensate residual insufficient bandwidth and CD-induced power fading. Moreover, a novel multi-symbols joint decision is proposed for receiver-side FFE-DFE to mitigate symbol error propagation and correct possible previous error symbols. Experimental results show that the proposed pre-equalization technique exhibits a better transmission performance, which reduces bit error ratio (BER) from $3.3\times 10^{-3}$ to $5.5\times 10^{-4}$ for optical back to back transmission. As for 10-km transmission case, FFE-DFE with 5-symbols joint decision achieves a BER of $7.3\times 10^{-5}$ , which is better than the BER of $1.6\times 10^{-4}$ with ideal error-propagation-free FFE-DFE (EPF-FFE-DFE). Furthermore, for 20-km transmission scenario, FFE-DFE with 8-symbols joint decision achieves a BER of $6.0\times 10^{-4}$ , which is also a superior result than the BER of $9.1\times 10^{-4}$ with EPF-FFE-DFE.

Signal Detection in Multi Carrier–Code Division Multiple Access System using Iterative Block Decision Feedback Equalizer

Signal Detection in Multi Carrier–Code Division Multiple Access System using Iterative Block Decision Feedback Equalizer

A 0.1-pJ/b/dB 1.62-to-10.8-Gb/s Video Interface Receiver With Jointly Adaptive CTLE and DFE Using Biased Data-Level Reference

In this article, a 1.62-to-10.8-Gb/s video interface receiver with jointly adaptive equalization is presented. Sign–sign least-mean-squares (SSLMS) algorithm is applied to adaptation for not only a decision feedback equalizer (DFE) but also a continuous-time linear equalizer (CTLE) to unify the adaptation methods. This approach facilitates concurrent adaptation that results in short adaptation time and also reduces the extra hardware and power consumption. An average value of fourth- and fifth-post-cursors is used as an indicator for CTLE adaptation, and the validity is substantiated by numerical analysis and simulation. Furthermore, the concept of a biased data-level reference (dLev) is proposed and analyzed to alleviate insufficient adaptation of the SSLMS algorithm in the presence of pre-cursor inter-symbol interference (ISI). The proposed dLev is acquired by simply adjusting up and down ratios of the dLev update equation. The prototype test chip is implemented in 65-nm CMOS technology and occupies an active area of 0.174 mm2. The proposed adaptive equalizers compensate for the channel loss of up to 34 dB at 10.8 Gb/s. Total power consumption of the receiver is 37.2 mW at 10.8 Gb/s, and the figure of merit (energy efficiency per channel loss at Nyquist frequency) of 0.1 pJ/b/dB is achieved.

ANALYSIS OF DATA TRANSMISSION SCHEME FOR WIDE BAND CODE DIVISION MULTIPLE ACCESS WITH RAKE RECEIVER

Fifth generation systems are required to fulfill the objectives like compatibility, flexibility, high speed data rate and low cost. Universal Mobile Telecommunication System (UMTS) use WCDMA as the air interface for 4th generation mobile system. The performance of wireless communication system is often limited by the radio channel models. In urban areas, channel is modeled as Rayleigh fading channel. This channel causes multipath channels and other problems resulting degraded performance. Hence, channel estimation before receiver helps to receive the transmitted signal using rake receiver. Rake receiver is a conventional receiver for DS-CDMA system. In this, channel is estimated adaptively using LMS algorithm and performance of this algorithm is studied for various multipath channels and step sizes. Moreover, the channel introduces Inter Symbol Interference (ISI) and channel equalizers are used to compensate for the ISI. In this work, BER vs. SNR performance of Zero Forcing Equalizer (ZFE), Minimum Mean Square Error (MMSE) and MMSE- Decision Feedback Equalizer (MMSE-DFE) in WCDMA downlink system are compared with conventional rake receiver for various spread factors in Rayleigh multipath fading channel with Additive White Gaussian Noise.

A 6-Gb/s Wireline Receiver With Intrapair Skew Compensation and Three-Tap Decision-Feedback Equalizer in 28-nm CMOS

A receiver for a three-lane 6-Gb/s/lane serial link has been developed in 28-nm CMOS technology. It incorporates an intrapair skew compensator (IPSC) and a three-tap decision feedback equalizer (DFE). The IPSC removes the IPS in analog front end by adding differential and common-mode signals of a differential pair. The three-tap DFE is realized with clock and data recovery (CDR) circuit with minimum hardware complexity. The receiver consumes 31.0 mW/lane at 6 Gb/s/lane and occupies an active area of 0.08 mm2.

Reduction of Time Complexity for CLS-DFE MIMO-OFDMA System

OFDMA is a multiuser of digital modulation technique used to increase wireless transmission rate. As a one of promising technique, OFDMA still suffer from a few types of interference especially ISI. ISI is an interference that occurs due to the multipath propagation and can distort signal efficiency. Upgraded Cascaded Least Square (CLS) with Decision Feedback Equalizer (DFE) had been used in this research in order to mitigate ISI in OFDMA system. CLS is combination of two adaptive algorithms which are Least Mean Square (LMS) and Recursive Least Square (RLS). Although RLS is one of the best adaptive algorithm but it still suffer from high complexity. Wireless system should use algorithm that ran quickly and used available computing resources efficiently. Running time of an algorithm need to be considered in order to reduce cost when being implemented to hardware. Due to that reason, inverse matrix method is implemented for RLS instead of using basic RLS in order to overcome disadvantage of time complexity in RLS. For equalization technique, DFE as a nonlinear equalizer is used because of its performance which is not enhancing noise during simulation. The combination of CLS with DFE can minimize ISI better compare to conventional LMS and RLS alone. This research also justified that combination of CLS-DFE OFDMA with MIMO antenna enable to mitigate ISI too.