16 QAM Modulation for High Capacity Digital Radio System

A computational method allowing the calculation of bit error rate in the presence of filtering and some other impairments is described for 16 QAM modulation; a breadboard working at a bit rate of 140 Mbits/s has been implemented and experimental results are compared with calculated values. The possible use of this modulation type for a high capacity digital radio-relay system is considered. Some parameters are introduced for this purpose, especially the net fade margin parameter. In the case of the 140 Mbit/s system in the 10.7-11.7 GHz frequency band, 4 PSK and 8 PSK modulation types are compared with 16 QAM. System gain, frequency arrangement, nodal capacity and outage performances are evaluated.     

La réception hétérodyne en microondes et en optique: analogies et différences

The introduction of the heterodyne reception in radio technique many years ago, allows a better sensitivity of the receiver and then an increase of the range of the transmission system, when compared to the direct detection. The same improvement can be expected for optical systems and this is the reason why this technique is now being investigated in several laboratories and could be applied to transmission over single mode fibres. This paper tries to exhibit the analogies which can exist between the microwaves and optical techniques and are sometimes not very evident because the words are different, although describing identical or at least comparable concepts. Some key functions of a system are compared (amplification mixing, oscillation).     

Conception et réalisation d’un égaliseur auto-adaptatif pour lutter contre les évanouissements sélectifs sur les liaisons hertziennes numériques

Selective fading drastically affects the high capacity digital radiolinks. Baseband equalization, which has been applied for several years to data transmission over telephone lines, appears to be very efficient for compensating for these fadings. The paper presents a very simplified fade model, the different equalizer structures that could be used and gives experimental results achieved with an equalizer breadboard built in CNETlaboratories in Lannion. The modulation sheme is 16 QAM,the bit rate 140 Mbit/s, and the fades are simulated, using a tworay model.     

Performances asymptotiques des égaliseurs fractionnés

The analytical method for deriving the mean square error at the output of a linear fractional tap-spacing equalizer with an infinite number of taps is presented. The mean square error is expressed as a function of the spectral characteristics of the transmission channel, and for equalizer tap-spacings which are a rational part of the system symbol period. Moreover, for particular tap-spacing values, the equalizer equivalent structure is detailed. This method is applied to a particular case related to radiolink transmission system. It is shown that the mean square error sensitivity to the timing phase, though important for synchronous equalizers, is a fast decaying function of the fractional tap-spacing.     

Noise Tolerance Assessment and System Design Discussion of a Saturable-Absorption-Based All-Optical 2R Regenerator

This letter presents the cascadability assessment and the noise tolerance characterization of an all-optical 2R regenerator based on saturable absorption and nonlinear effects in fiber. The impact of optical signal-to-noise ratio on the 2R regenerator performance is shown, and a regenerator characterization technique that can be used for system design and engineering is discussed.     

Forward error correction in WDM PON using spectrum slicing

This paper presents experimental results of the introduction of FEC (forward error correction) in optical access network architectures operating at 625 Mb/s. We have first tested a Reed Solomon code on a point to point architecture to confirm the theoretical 3 dB gain in link budget. The innovative architecture is a wavelength division multiplexed passive optical network (WDM PON) using spectrum slicing and a reflective semiconductor optical amplifier (RSOA) to generate upstream signals. Optical carrier supply by spectrum slicing and modulation and amplification by RSOA is a way of reducing costs in WDM PON but it gives a noisy transmission due to excess intensity noise of broadband sources, Amplified Spontaneous emission of the SOA and beat noise at detection. In this case, adding FEC has more effect and it results in an increased link budget of 5.5 dB. FEC are a simple and efficient solution to compensate for penalties introduced by low cost components in innovative architectures like WDM PON.