Richard C. Younce

Impulse response shortening for discrete multitone transceivers

In discrete multitone (DMT) transceivers an intelligent guard time sequence, called a cyclic prefix (CP), is inserted between symbols to ensure that samples from one symbol do not interfere with the samples of another symbol. The length of the CP is determined by the length of the impulse response of the effective physical channel. Using a long CP reduces the throughput of the transceiver, To avoid using a long CP, a short time-domain finite impulse response (FIR) filter is used to shorten the effective channels impulse response. This paper explores various methods of determining the coefficients for this time-domain filter. An optimal shortening and a least-squares (LS) approach are developed for shortening the channels impulse response. To provide a computationally efficient algorithm a variation of the LS approach is explored. In full-duplex transceivers the length of the effective echo path impacts the computational requirements of the transceiver. A new paradigm of joint shortening is introduced and three methods are developed to jointly shorten the channel and the echo impulse responses in order to reduce the length of the CP and reduce computational requirements for the echo canceller.

Identification with non-parametric uncertainty

An identification technique that is robust to nonparametric uncertainty (i.e. model mismatch) is presented. The identifier produces both a parameter set estimate and a frequency response set estimate. The estimates result from the inclusion of a model of the nonparametric uncertainty in that plant model. The frequency response set estimate is shown to always contain the frequency response of the plant, as long as certain design conditions are met.<<ETX>>

Engineering 400G for colorless-directionless-contentionless architecture in metro/regional networks [invited]

Metro/regional networks are beginning the transition from 10 to 100 Gb/s on dispersion unmanaged optical links. Long-haul networks have a head start in the move to all-coherent networking and have popularized route-and-select-based node designs and colorless, directionless, and contentionless add/drop structures. Both metro and long-haul coherent networks are expected to support future 400 Gb/s transmission. This paper examines the node architecture and 400G transmission options for coherent metro networks with the distinctive characteristics of short spans and high optical filtering penalties. Reach results are derived for signals based on 100, 200, and 400 Gb/s superchannels. Additionally, blocking probabilities are reported for two approaches to nodal add/drop architecture. The results provide a clear direction for metro/regional node and network architecture decisions.

Identification with nonparametric uncertainty

The authors present an identification technique that is robust to nonparametric uncertainty (i.e., model mismatch). The identifier produces both a parameter set estimate and a frequency response set estimate. The estimates result from the inclusion of a model of the nonparametric uncertainty in the plant model. The frequency response set estimate is shown to always contain the frequency response of the plant as long as certain modeling conditions are met. This type of identifier would be useful in applications such as control where a property such as stability or performance level must be achieved in the face of low-order modeling and its associated nonparametric uncertainty.<<ETX>>

Experimental demonstration of adaptive digital monitoring and compensation of chromatic dispersion for coherent DP-QPSK receiver

We experimentally demonstrate a digital signal processing (DSP)-based optical performance monitoring (OPM) algorithm for in-service monitoring of chromatic dispersion (CD) in coherent transport networks. Dispersion accumulated in 40 Gbit/s QPSK signal after 80 km of fiber transmission is successfully monitored and automatically compensated without prior knowledge of fiber dispersion coefficient. Four different metrics for assessing CD mitigation are implemented and simultaneously verified proving to have high estimation accuracy. No observable penalty is measured when the monitoring module drives an adaptive digital CD equalizer.

Echo cancellation for asymmetrical digital subscriber lines

Discrete multitone modulation has been chosen to provide the high speed link for asymmetrical digital subscriber lines (ADSL). Modulating bidirectional digital traffic over the existing twisted pair loop plant necessitates the used of a high performance echo canceller. This paper investigates an echo canceller structure for ADSL. A combination frequency domain echo canceller and a time domain echo synthesizer are detailed along with timing and fixed point effects. Detailed simulation results show the canceller performance is more than adequate and does not limit the transceivers performance. Complexity issues are addressed and show that an effective canceller can be implemented with only modest computational requirements. Hence, there exists an effective and efficient echo canceller for ADSL.<<ETX>>

High phase noise tolerant pilot-tone-aided DP-QPSK optical communication systems.

In this paper we experimentally demonstrate a novel, high phase-noise tolerant, optical dual polarization (DP) quadrature phase-shift keying (QPSK) communication system based on pilot-tone-aided phase noise cancellation (PNC) algorithm. Vertical cavity surface emitting lasers (VCSELs) with approximate 300 MHz linewidth are used as transmitters and local oscillators for coherent detection of optical DP-QPSK signals. The proposed system, with central wavelength at 1540.68 nm, operates at 40 Gb/s over 80 km single mode fiber (SMF) as part of a passive optical network (PON). The deployment of pilot-tone-aided PNC algorithm guarantees a bit error rate (BER) performance below the forward error correction (FEC) threshold. Moreover, we also evaluate a novel digital signal processing (DSP) algorithm for adaptive pilot tone detection.

Joint optimal impulse response shortening

In discrete multitone a cyclic prefix (CP) is inserted between symbols to ensure that samples from one symbol do not interfere with the samples of another symbol. The CP length is determined by the impulse response length of the effective physical channel. The cyclic prefix reduces the throughput of the transceiver. When the transceiver is used in a full-duplex environment the portion of the receive signal arising from echo must be reduced through the use of echo cancellation, the complexity of which is directly related to the length of the echo path impulse response. To alleviate both problems a short time-domain FIR filter can be used to shorten both the effective channel and echo impulse responses. This paper explores a joint optimal algorithm for determining the coefficients of this time-domain filter, resulting in reduced ISI and echo canceller complexity. For the simulations a configuration is chosen which is representative of that encountered by the remote terminal in the asymmetrical digital subscriber lines (ADSL) environment.

Next generation 100Gb/s ethernet technologies

We have designed and experimentally demonstrated optical networking technologies for generating, transmitting and switching 100Gbit/s packet signals in optical networks. The performance of 100Gb/s packet transmission over cascaded ROADM nodes with WSSs and over label switched metro networks are discussed.

Contentionless and near contentionless blocking performance and economics for all coherent metro/regional networks

Architectural alternatives are considered for networks carrying all coherent transmission. Blocking and network economics are modeled for four high potential add/drop structures and the results provide clear direction for nodal architectural decisions.