Mark Taylor Core

Cross polarization interference cancellation for fiber optic systems

One method of improving the bandwidth efficiency of a fiber optic communication system is to use polarization multiplexing, where independent signals are transmitted with orthogonal polarizations. A receiver can reconstruct both signals without interference by tracking their polarizations as long as they remain orthogonal. Since orthogonality is lost to some extent during propagation through an optical fiber, a polarization tracking system will incur a signal crosstalk penalty. A new and practical method using cross polarization interference cancellation (XPIC) is proposed to correct for the loss of orthogonality incurred during propagation through an optical fiber. The system optimally reconstructs both signals at the receiver and eliminates the need for conventional polarization tracking. XPI cancellation uses fewer lasers than conventional polarization interleave multiplexing and can also mitigate effects that currently limit link performance such as chromatic and polarization mode dispersion (PMD).

BER for optical heterodyne DPSK receivers using delay demodulation and integration detection

Previous work on the bit error rate (BER) performance of differential phase-shift keying (DPSK) including the effects of additive white Gaussian noise (AWGN) and phase noise has concentrated on the delay demodulator with narrow-band intermediate frequency (IF) bandpass filtering (BPF) and sampling detection. No similar analysis has yet been performed for the delay demodulator with wideband IF bandpass filtering and integration detection. Phase noise is an important consideration in coherent optical communication systems and the most widely accepted model is a Brownian motion process. A closed-form BER expression along with detailed Monte Carlo simulation results are presented for the DPSK delay demodulator with wideband IF bandpass filtering and integration detection filtering including phase noise effects using the Brownian motion model. Analytic expressions are also obtained for the moments of the phase noise component of the decision variable. Using these moments, estimates of the phase noise BER floor are produced. It is found that this receiver has noise performance comparable to receivers with narrowband IF bandpass filtering and sampling detectors for signal-to-noise ratio (SNR) and phase noise in the range of practical interest, but with potentially less degradation due to intersymbol interference (ISI).

26.3 An 800MS/S 10b/13b receiver for 10GBASE-T Ethernet in 28nm CMOS

The IEEE 802.3an standard describes full-duplex 10Gb/s Ethernet transmission over four pairs of up to 100m UTP cable. The performance required from the analog front end (AFE) of a 10GBASE-T Ethernet transceiver strongly depends on the length of the cable connected to it. Maximum-length cables require the highest performance, and hence, determine the worst-case power dissipation of the transceiver. In practice, however, the vast majority of cable lengths used are below 30m. For these shorter cables, the standard specifies the transmitted power level to be lowered, inherently leading to a reduction in power consumption of the transmitter (TX). In most designs, the power consumption of the receiver (RX), unfortunately, does not benefit from the shorter cable lengths [1,2]. This paper presents a power-efficient 13b RX, implemented in 28nm CMOS. By switching to a 10b mode for short cables, 143mW is saved in the AFE for one complete Ethernet port, comprising four receivers. In addition, to further reduce power, the RX heavily relies on calibrations.

Semianalytic BER for PSK

Semianalytic bit error rate (BER) estimation is a well-known method for evaluating the BER of a digital communication system. The main utility of the method is the significant time savings in computation relative to Monte Carlo simulation. Despite this advantage, no known reference defines the procedure for computing exact BER for M-ary phase shift keying (PSK) with ISI and AWGN using the semianalytic method. This letter defines an efficient procedure for computing exact semianalytic BER for modulation formats with circular constellations when the noise component of the decision variable has a circularly symmetric Gaussian distribution. The technique is demonstrated for 8PSK over the Digital Video Broadcasting-Satellite-Second Generation (DVB-S2) channel.