Decision Feedback Equalization Technique Research Articles

Single-Mode 850-nm VCSELs for 54-Gb/s ON–OFF Keying Transmission Over 1-km Multi-Mode Fiber

By combing Zn-diffusion and oxide-relief apertures with strong detuning (>20 nm) in our demonstrated short-cavity ( $\lambda $ /2) 850-nm vertical-cavity surface-emitting lasers (VCSELs), wide electrical-to-optical bandwidth (29–24 GHz), low-differential resistance ( $\sim 100~\Omega )$ , and (quasi) single-mode (SM) with reasonable output power ( $\sim 1.4$ mW) performances can be simultaneously achieved. Error-free ON–OFF keying transmission at 54-Gb/s data rate through 1-km OM4 multi-mode fiber can be achieved by using highly SM device with forward error correction and decision feedback equalization techniques. As compared with the reference device with a larger oxide-relief aperture and a multi-mode performance, the SM device exhibits lower bit-error rate ( $1\times {10}^{-5} $ versus $1\times {10}^{-2})$ at 54 Gb/s. This result indicates that modal dispersion plays more important role in transmission than that of output power does. We benchmark these results to an industrial 50-Gb/s SM VCSEL. It shows a higher bit-error-rate value $\sim 3.5\times {10}^{-3}$ versus $\sim 1.4\times {10}^{-4}$ under the same received optical power.

10-Gb/s Pulse-Amplitude Modulated Transmission Over 1-mm Large-Core Polymer Optical Fiber

The authors report on a 10-Gb/s transmission over 1-mm large-core diameter polymer optical fiber (POF) using pulse-amplitude modulation. For the first time, a real-time 10-Gb/s eye-diagram is shown after 5-m standard step-index POF (SI-POF), even with an eye-safe transmitter (0 dBm). With an offline decision feedback equalization technique, a link length of 10-m SI-POF, respectively, 25-m GI-POF was achieved. With a slightly higher optical power of +5 dBm, the maximum link length could even be increased to 30-m SI-POF and 60-m GI-POF.

Eye-Safe Data Transmission of 1.25 Gbit/s Over 100-m SI-POF Using Green Laser Diode

We report on 1.25-Gbit/s transmission over 100-m step-index polymer optical fiber (SI-POF) with 6.5-dB margin. Nonreturn-to-zero modulation with offline decision feedback equalization technique has been applied to an intensity modulated direct-detection optical channel. An edge emitting direct injection laser diode with 515 nm is used, which allows us to improve the system power budget due to a lower attenuation of the POF at this wavelength. The fiber-coupled optical power has been adjusted to 0 dBm which corresponds to eye-safety requirements.

Design Characteristics for a Full-Duplex IM/IM Bidirectional Transmission at 10 Gb/s Using Low Bandwidth RSOA

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, the optimum design characteristics and the transmission performance limits of an intensity modulation full-duplex bidirectional transmission system at 10 Gb/s are experimentally studied and presented for application in next-generation-extended wavelength-division-multiplexed passive optical networks. A low-bandwidth (<formula formulatype="inline"><tex Notation="TeX">${\sim} {\hbox {1.2}}$</tex></formula> GHz) reflective semiconductor optical amplifier (RSOA) is utilized at the optical network unit (ONU) site of the system. Its remodulation properties and performance are examined for both continuous wave and modulated downstream signal, stemming from the optical line terminal (OLT). The techniques adopted to optimize performance are: 1) the use of detuned optical filtering at the OLT receiver that takes advantage of the RSOA chirp and 2) the use of decision feedback equalization (DFE). The extinction ratio of the downstream signal and the driving operation point of the RSOA are examined experimentally in order to find the optimum conditions for the bidirectional transmission. Moreover, the impact of patterning effects in the performance of the system is evaluated. Finally, the additional performance improvement that is achieved with the use of DFE technique is shown. </para>

Power Efficient Gigabit Communication Over Capacitively Driven RC-Limited On-Chip Interconnects

This paper presents a set of circuit techniques to achieve high data rate point-to-point communication over long on-chip RC-limited wire-pairs. The ideal line termination impedances for a flat transfer function with linear phase (pure delay) are derived, using an s-parameter wire-pair model. It is shown that a driver with series capacitance on the one hand and a resistive load on the other, are fair approximations of these ideal terminations in the frequency range of interest. From a perspective of power efficiency, a capacitive driver is preferred, as the series capacitance reduces the voltage swing along the line which reduces dynamic power consumption. To reduce cross-talk and maintain data integrity, parallel differential interconnects with alternatingly one or two twists are used. In combination with a low offset dynamic sense amplifier at the receiver, and a low-power decision feedback equalization technique with analog feedback, gigabit communication is demonstrated at very low power consumption. A point-to-point link on a 90 nm CMOS test chip achieves 2 Gb/s over 10 mm long interconnects, while consuming 0.28 pJ/bit corresponding to 28 fJ/bit/mm, which is much lower than competing designs.

A soft-output bidirectional decision feedback equalization technique for TDMA cellular ratio

Issues encountered in the design of reliable narrowband time-division multiple access (TDMA) digital cellular mobile communication systems are considered. In particular, the problem of compensating for the harsh multipath fading environment in systems whose transmission bandwidth is commensurate with the coherence bandwidth of the fading channel is considered. A TDMA channel characterization parameter, the slot-normalized fade rate, is introduced, and an adaptive bidirectional equalization technique, which estimates the location of a deep fade within a time slot, is proposed. The simulation results show that the carrier-to-noise ratio requirement is only 15.5 dB when this equalization technique is used. This is achieved without diversity, and with low complexity. An equivalent equalized land mobile radio channel model and the analytical solution for the optimal bit likelihood calculation for pi /4-shift quadrature differential phase-shift keying (QDPSK) modulation are also derived under certain channel conditions. The results are used as soft decisions for the convolutional decoder. >

Frequency-selective scintillation effects and decision feedback equalization in high data-rate satellite links

Ionospheric irregularities produce signal amplitude and phase scintillations in transionospheric satellite channels. When the electron-density fluctuation is large, the channel coherence bandwidth is small, causing the scintillations to decorrelate at different frequencies within the bandwidth of a wide-band signal. Frequency-selective scintillation introduces delay spread and intersymbol interference, which can severely limit the usable capacity of the channel. This paper, largely tutorial in nature, relates adaptive equalization techniques, which have been developed previously for other dispersive channels, to the problem of wide-band satellite links operating through a highly disturbed transionospheric channel. Pertinent features of the ionospheric channel and characteristics of signal scintillations are summarized. Effects of frequency-selective scintillation on high data-rate wide-bandwidth digital communication links are described in some detail. Intersymbol interference caused by the loss of channel coherence over the signal bandwidth is shown, via simulations, to severely degrade the performance of a conventional coherent binary PSK receiver. An adaptive decision feedback equalization technique is then shown to be a powerful method of mitigating frequency-selective disturbances in high data-rate satellite links.