464 research outputs found
Strictly Bandlimited ISI-Free Transmission Over Intensity-Modulated Channels
In this paper, the design and analysis of a new bandwidth-efficient signalling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is pro- posed. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise. Due to the nonnegativity constraint, the methods previously proposed for conventional bandlimited channels cannot be applied here. We propose a method to transmit without intersymbol interference in a narrower bandwidth compared to previous works, by combining Nyquist pulses with a constant bias. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. At low bandwidths, the most power- efficient transmission is obtained by either the parametric linear pulse or the so-called “better than Nyquist” pulse, depending on the exact bandwidth
Bandlimited Intensity Modulation
In this paper, the design and analysis of a new bandwidth-efficient signaling
method over the bandlimited intensity-modulated direct-detection (IM/DD)
channel is presented. The channel can be modeled as a bandlimited channel with
nonnegative input and additive white Gaussian noise (AWGN). Due to the
nonnegativity constraint, standard methods for coherent bandlimited channels
cannot be applied here. Previously established techniques for the IM/DD channel
require bandwidth twice the required bandwidth over the conventional coherent
channel. We propose a method to transmit without intersymbol interference in a
bandwidth no larger than the bit rate. This is done by combining Nyquist or
root-Nyquist pulses with a constant bias and using higher-order modulation
formats. In fact, we can transmit with a bandwidth equal to that of coherent
transmission. A trade-off between the required average optical power and the
bandwidth is investigated. Depending on the bandwidth required, the most
power-efficient transmission is obtained by the parametric linear pulse, the
so-called "better than Nyquist" pulse, or the root-raised cosine pulse.Comment: 28 pages 10 Figure
Nonlinear limits to the information capacity of optical fiber communications
The exponential growth in the rate at which information can be communicated
through an optical fiber is a key element in the so called information
revolution. However, like all exponential growth laws, there are physical
limits to be considered. The nonlinear nature of the propagation of light in
optical fiber has made these limits difficult to elucidate. Here we obtain
basic insights into the limits to the information capacity of an optical fiber
arising from these nonlinearities. The key simplification lies in relating the
nonlinear channel to a linear channel with multiplicative noise, for which we
are able to obtain analytical results. In fundamental distinction to the linear
additive noise case, the capacity does not grow indefinitely with increasing
signal power, but has a maximal value. The ideas presented here have broader
implications for other nonlinear information channels, such as those involved
in sensory transduction in neurobiology. These have been often examined using
additive noise linear channel models, and as we show here, nonlinearities can
change the picture qualitatively.Comment: 1 figure, 7 pages, submitted to Natur
Information capacity of optical fiber channels with zero average dispersion
We study the statistics of optical data transmission in a noisy nonlinear
fiber channel with a weak dispersion management and zero average dispersion.
Applying path integral methods we have found exactly the probability density
functions of channel output both for a non-linear noisy channel and for a
linear channel with additive and multiplicative noise. We have obtained
analytically a lower bound estimate for the Shannon capacity of considered
nonlinear fiber channel.Comment: 4 pages, subbmited to Phys. Rev. Let
When to Use Optical Amplification in Noncoherent Transmission: An Information-Theoretic Approach
The standard solution for short-haul fiber-optic communications is to deploy noncoherent systems, i.e., to modulate and detect only the light intensity. In such systems, the signal is corrupted with optical noise from amplifiers and with thermal (electrical) noise. The capacity of noncoherent optical links has been studied extensively in the presence of either optical noise or thermal noise. In this paper, for the first time, we characterize the capacity under an average power constraint with both noise sources by establishing upper and lower bounds. In the two extreme cases of zero optical noise or zero thermal noise, we assess our bounds against some well-known results in the literature; improvements in both cases are observed. Next, for amplified fiber-optic systems, we study the trade-off between boosting signal energy (mitigating the effects of thermal noise) and adding optical noise. For a wide spectrum of system parameters and received power levels, we determine the optimal amplification gain. While mostly either no amplification or high-gain amplification is optimal, the best performance is for some parameter intervals achieved at finite gains
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