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Static Multipoint Networks in Software Implement qrcode in Software Static Multipoint Networks

Static Multipoint Networks use none none generating toattach none on none QR Code Overview repetition rate i none for none s used, which generates phase-locked frequency components at a 5-GHz separation, giving 16 frequencies in a selected 80-GHz bandwidth. By tuning to different portions of the spectrum (using a bandpass lter in the laser cavity), different bands can be assigned to different users, resulting in a relatively narrowband tunable coherent source. The periodic pulse stream can then be modulated to produce a stream of data pulses.

Phase coding of the data pulses is implemented in an optical system that demultiplexes the 16 frequency components, impresses binary phase shifts (0 or ) on them according to codes selected for desired CDMA performance, and remultiplexes them for transmission. A matched decoder employing a conjugate phase mask at the receiver completes the system. An additional consideration in this system is the width of the spectral lines being phase encoded.

When the periodic pulse stream is modulated, it is transformed into a random data bit stream. Because it is no longer periodic, the spectral lines widen into bands. The widths of these bands must be controlled for proper operation of the phase modulator, and this is accomplished by using a data-modulation format that induces correlation among the data pulses, thereby narrowing the bands.

Single-user operation was demonstrated experimentally with satisfactory results, with simulations used to study MAI.. Optical CDMA Using Superstructure Fiber Gratings A superstructure none for none ber Bragg grating (SSFBG) is a standard FBG with rapidly varying spatial refractive index of uniform amplitude and pitch, on which is superimposed a slow spatial refractive index modulation. A property of a weakly re ecting SSFBG is that a prescribed optical impulse response can be written into it by the superimposed slow spatial modulation [Eggleton+94]. As a result, when excited by an optical pulse, the re ective output of the SSFBG is the convolution of the pulse waveform and the SSFBG impulse response.

This is a true coherent CDMA encoder, and the corresponding decoder is just the spatially reversed image of the encoder, so they are conjugate lters. This corresponds to the coherent system described in Figure 5.18.

In [Lee+02, The+01], a DS-CDMA system is described based on SSFBGs. The basic transmitter and receiver structures use circulators and re ecting FBGs as in the noncoherent systems (see Figure 5.20).

In this case, the desired impulse response consists of a series of chips for a DS-CDMA code, each one containing a spread and phase-shifted version of the narrow data pulse. When multiple users are active in any CDMA system, the output of the decoder is a relatively sharp pulse that must be distinguished from a background noise and interference level consisting of MAI from other users, as well as many other effects. These include imperfections in the encoder/decoder, ber impairments, intersymbol interference, OBI, and random noise.

The result is a reduction in the contrast between the decoded pulse and the aggregate background effects. A novel nonlinear processing approach is used in the proposed system to improve contrast. It consists of a NOLM acting as a saturable absorber, inserted in front of the photodetector to sharpen the decoded pulse before detection and thresholding (see Section 4.

11.2). Experiments at data rates up to 2.

5 Gbps over 25 km of dispersion compensated ber were run with narrow (2.5 ps) data pulses and a 63-chip bipolar code. The encoder.

Multiwavelength Optical Networks spread the data p none none ulse width to chip pulse widths of 6.4 ps and impressed a binary DS code onto the chips using phase reversals; i.e.

, a binary DPSK modulation format. BER measurements were taken with a single user and with one interferer. The NOLM signi cantly improved system performance, permitting higher bit rates and reducing power penalties as compared to linear processing alone.

More ambitious experiments were reported involving a 511-chip SSFBG using DPSK modulation [Wang+06]. Acceptable BER12 was reported with MAI from eight interferers, and its performance was shown to be superior to optical CDMA using OOK in terms of tolerance to MAI and OBI, as well as in simplifying threshold settings. A variant of the basic scheme [Hamanaka+06] was designed to operate with compound data rates running from 622 Mbps to 2.

488 Gbps for demand provisioning of multiple services..
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