1,398 research outputs found
Adaptive Importance Sampling for Performance Evaluation and Parameter Optimization of Communication Systems
We present new adaptive importance sampling techniques based on stochastic Newton recursions. Their applicability to the performance evaluation of communication systems is studied. Besides bit-error rate (BER) estimation, the techniques are used for system parameter optimization. Two system models that are analytically tractable are employed to demonstrate the validity of the techniques. As an application to situations that are analytically intractable and numerically intensive, the influence of crosstalk in a wavelength-division multiplexing (WDM) crossconnect is assessed. In order to consider a realistic system model, optimal setting of thresholds in the detector is carried out while estimating error rate performances. Resulting BER estimates indicate that the tolerable crosstalk levels are significantly higher than predicted in the literature. This finding has a strong impact on the design of WDM networks. Power penalties induced by the addition of channels can also be accurately predicted in short run-time
Secure thermal infrared communications using engineered blackbody radiation
The thermal (emitted) infrared frequency bands, from 20–40 THz and 60–100 THz, are best known for applications in thermography. This underused and unregulated part of the spectral range offers opportunities for the development of secure communications. The ‘THz Torch' concept was recently presented by the authors. This technology fundamentally exploits engineered blackbody radiation, by partitioning thermally-generated spectral noise power into pre-defined frequency channels; the energy in each channel is then independently pulsed modulated and multiplexing schemes are introduced to create a robust form of short-range secure communications in the far/mid infrared. To date, octave bandwidth (25–50 THz) single-channel links have been demonstrated with 380 bps speeds. Multi-channel ‘THz Torch' frequency division multiplexing (FDM) and frequency-hopping spread-spectrum (FHSS) schemes have been proposed, but only a slow 40 bps FDM scheme has been demonstrated experimentally. Here, we report a much faster 1,280 bps FDM implementation. In addition, an experimental proof-of-concept FHSS scheme is demonstrated for the first time, having a 320 bps data rate. With both 4-channel multiplexing schemes, measured bit error rates (BERs) of < 10(−6) are achieved over a distance of 2.5 cm. Our approach represents a new paradigm in the way niche secure communications can be established over short links
Design and simulation of 1.28 Tbps dense wavelength division multiplex system suitable for long haul backbone
Wavelength division multiplex (WDM) system with on / off keying (OOK)
modulation and direct detection (DD) is generally simple to implement, less
expensive and energy efficient. The determination of the possible design
capacity limit, in terms of the bit rate-distance product in WDM-OOK-DD systems
is therefore crucial, considering transmitter / receiver simplicity, as well as
energy and cost efficiency. A 32-channel wavelength division multiplex system
is designed and simulated over 1000 km fiber length using Optsim commercial
simulation software. The standard channel spacing of 0.4 nm was used in the
C-band range from 1.5436-1.556 nm. Each channel used the simple non return to
zero - on / off keying (NRZ-OOK) modulation format to modulate a continuous
wave (CW) laser source at 40 Gbps using an external modulator, while the
receiver uses a DD scheme. It is proposed that the design will be suitable for
long haul mobile backbone in a national network, since up to 1.28 Tbps data
rates can be transmitted over 1000 km. A bit rate-length product of 1.28
Pbps.km was obtained as the optimum capacity limit in 32 channel dispersion
managed WDM-OOK-DD system.Comment: Accepted for publication in Journal of Optical Communications - De
Gruyte
Deterministic Raman crosstalk effects in amplified wavelength division multiplexing transmission
We study the deterministic effects of Raman-induced crosstalk in amplified
wavelength division multiplexing (WDM) optical fiber transmission lines. We
show that the dynamics of pulse amplitudes in an N-channel transmission system
is described by an N-dimensional predator-prey model. We find the equilibrium
states with non-zero amplitudes and prove their stability by obtaining the
Lyapunov function. The stability is independent of the exact details of the
approximation for the Raman gain curve. Furthermore, we investigate the impact
of cross phase modulation and Raman self and cross frequency shifts on the
dynamics and establish the stability of the equilibrium state with respect to
these perturbations. Our results provide a quantitative explanation for the
robustness of differential-phase-shift-keyed WDM transmission against Raman
crosstalk effects.Comment: 34 pages and 12 figures. Revised paper. Submitted to Optics
Communication
Forward Error Correction in Memoryless Optical Modulation
The unprecedented growth in demand for digital media has led to an all-time high in society’s demand for information. This demand will in all likelihood continue to grow as technology such as 3D television service, on-demand video and peer-to-peer networking continue to become more common place. The large amount of information required is currently transmitted optically using a wavelength division multiplexing (WDM) network structure. The need to increase the capacity of the existing WDM network infrastructure efficiently is essential to continue to provide new high bandwidth services to end-users, while at the same time minimizing network providers’ costs. In WDM systems the key to reducing the cost per transported information bit is to effectively share all optical components. These components must operate within the same wavelength limited window; therefore it is necessary to place the WDM channels as close together as possible. At the same time, the correct modulation format must be selected in order to create flexible, cost-effective, high-capacity optical networks. This thesis presents a detailed comparison of Differential Quadrature Phase Shift Keying (DQPSK) to other modulation formats. This comparison is implemented through a series of simulations in which the bit error rate of various modulation formats are compared both with and without the presence of forward error correction techniques. Based off of these simulation results, the top performing modulation formats are placed into a multiplexed simulation to assess their overall robustness in the face of multiple filtering impairments
Coherent terabit communications with microresonator Kerr frequency combs
Optical frequency combs enable coherent data transmission on hundreds of
wavelength channels and have the potential to revolutionize terabit
communications. Generation of Kerr combs in nonlinear integrated microcavities
represents a particularly promising option enabling line spacings of tens of
GHz, compliant with wavelength-division multiplexing (WDM) grids. However, Kerr
combs may exhibit strong phase noise and multiplet spectral lines, and this has
made high-speed data transmission impossible up to now. Recent work has shown
that systematic adjustment of pump conditions enables low phase-noise Kerr
combs with singlet spectral lines. Here we demonstrate that Kerr combs are
suited for coherent data transmission with advanced modulation formats that
pose stringent requirements on the spectral purity of the optical source. In a
first experiment, we encode a data stream of 392 Gbit/s on subsequent lines of
a Kerr comb using quadrature phase shift keying (QPSK) and 16-state quadrature
amplitude modulation (16QAM). A second experiment shows feedback-stabilization
of a Kerr comb and transmission of a 1.44 Tbit/s data stream over a distance of
up to 300 km. The results demonstrate that Kerr combs can meet the highly
demanding requirements of multi-terabit/s coherent communications and thus
offer a solution towards chip-scale terabit/s transceivers
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