Alcatel N.v.

Denis J Mestdagh

Gert Van Der Plas

Christiaan H Sierens

Willem J Verbiest

Ingrid Zulma Van De Voorde

Bart J Pauwels

Martin L De Prycker

Robertus J Van Engelshoven

The demodulation of data modulated on a set of carriers with equidistant frequencies by a plurality of transmitters (T1 . . . Tn) is executed in the present transmission system (TS) by a discrete multitone receiver (DMT-R). The transmitters (T1 . . . Tn) in the transmission system (TS) modulate their data on subsets of carriers which form part of the set of carriers with equidistant frequencies. These transmitters (T1 . . . Tn) are possibly additionally equipped with a cyclic prefix adder (CPA); synchronization between them is guaranteed if a predefined condition is fulfilled.

Frequency division multiple access (FDMA) dedicated transmission system,

The present invention discloses a so called Discrete Multi Tone or DMT signal processor which is coupled to a transmitting end of a communication line and which reduces the need for the clipping of the amplitude of the output signal OS'. The signal processor includes the cascade connection of a vector transformation circuit VTC, a modulator MOD and a peak detection circuit PDC. The VTC circuit is provided with a plurality of input vectors IN whereon a vector transformation is performed according to a signal at a control terminal (CT) of the peak detection circuit PDC which is indicative of the fact that the amplitude of the output signal OS provided by the modulator MOD exceeds a predetermined threshold value.

Signal processor

The system includes two transmitters (T1, T2) and two receivers (R1, R2). One transmitter (T1) may include a wavelength tunable laser, sending an FSK optical signal (OS1) which has a constant intensity. In a first receiver (R1) this FSK optical signal (OS1) is transformed into an IM signal (OS1') by an optical pass band filter. This IM signal (OS1') is then detected by a first direct detection receiver (DM). In a second direct detection receiver (R2) the FSK optical signal (OS1) is not detected, since it has constant intensity. A second transmitter (T2) includes a Fabry Perot laser or a LED with a broad linewidth, sending an IM optical signal (OS2). This IM optical signal (OS2) is detected by the second direct detection receiver (R2). It is not detected by the first direct detection receiver (DM), because it is strongly attenuated when passing through the narrow bandpass optical filter (TM) before being applied to the first direct detection receiver. This system is especially advantageous in bidirectional optical transmission systems, due to its inherent insensitivity to reflections.

Optical transmission system

The time slot management system is included in a digital time division multiple access system includes a main station MS and a plurality of substations U1/16 connected to each other via a tree network. The substations U1/16 send to the main station MS upstream information packets in time slots assigned to each of the former stations by the main station. Part of the time slots are reserved for management information and used by the substation to inform the main station about the bandwidth needed for the further transfer of the upstream information, According to this information the time slot management system allocates the time slots and informs the substations thereof. In this way a flexible and dynamic time slot allocation is provided.

Time slot management system

Communication system including allocating free signalling channels to

To determine the equalisation delay of a substation (S3), the main station (C) of a transmission system measures, during an initial coarse measurement, the time interval between the sending of a first ranging signal to the substation and the receipt of a reply signal. This reply signal has a frequency and amplitude substantially lower than the information signals sent by other substations (S1, S2) of the system to avoid interference therewith. During a subsequent fine measurement the main station measures the time interval between the sending of a second ranging signal and the receipt of a second reply signal having the same characteristics as the information signals. The other substations have to stop transmission of signals during an interval equal to the uncertainty time interval with which the equalisation delay was measured during the coarse measurement. To be able to apply this method, the receiver at the main station includes a device (A2) used to isolate the first reply signal from the information signals and to recognize (COR) them, and a processing unit (PU) to determine the equalisation delay.

Method and apparatus for determining equalization delays in a

Optical transceiver arrangement to transmit information signals (S1, . , Sn) from a transmitter arrangement (T) to a receiver arrangement (R) over an optical waveguide (L). This is achieved by modulating electrical subcarrier waveforms with these information signals (S1, . , Sn) using modulation means (M1, . , Mn), converting them to optical signals using electrical/optical convertors (E/01, . , E/01n), and by transmitting these optical signals, by means of time division multiplexing means (TDM1, . , TDMn), in different time slots if the subcarrier waveforms have the same frequency. The modulation- and time division multiplexing means are controlled by corresponding individual control modules (C1, . , Cn) under control of a central control module (CC) included in the receiver arrangement.

Transceiver arrangement using TDM to transmit assigned subcarrier

A protection arrangement protects an optical transmitter device with n optical transmit circuits or an optical receiver device with n optical receive circuits. It includes fault evaluating circuitry to detect a defective transmit/receive circuit, a spare transmit/receive circuit, and switching circuitry. Upon detection of a defective transmit/receive circuit by the fault evaluating circuitry, the fault evaluation circuitry controls the spare transmit/receive circuit and the switching circuitry to bypass the defective transmit/receive circuit with the spare transmit/receive circuit.

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Brussels, Belgium

Denis J Mestdagh