Etablissement Public De Diffusion Dit 'telediffusion De France'

Guy P Dublet

Jacques P Palicot

Echo cancellation is carried out on a received demodulated analog signal. The apparatus comprises an analog transversal filter, a computing circuit for generating the direct coefficients a1 to ar and, eventually, feedback coefficients b2 to bm of an analog transversal filter. The input of a computing circuit is connected to the input of an analog transversal filter. The computing circuit is comprised of an analog-to-digital converter, whose output is connected to a self-adaptive digital transversal filter. The values of the digital transversal filter multiplication coefficients are applied, as coefficients, to the multipliers of the analog transversal filter. The optimization criterion is that of the mean quadratic error. The convergence algorithm is that of the gradient. The iterative correction may be carried out at each step on the digital transversal filter's group of coefficients. Or, it can be carried out cyclically of each of the digital transversal filter's coefficients. Variations of the self-adaptive digital transversal filter are described.

Echo correction especially for television broadcast systems

The structure of an access point to a data packet broadcasting network comprises a plurality of couplers (Cx), a buffer memory (MTP) and a central control unit (MPC) interconnected by a main bus (MB). Each coupler (Cx) is connected to a plurality of data sources. The buffer memory (MTP) is connected to a transmission equipment of the data packet broadcasting network. Each coupler (Cx) includes a dual access (MCx), a microprocessor (MUPx), a read only memory (ROMx), a plurality of access circuits (CAS1-CAS4 and CAP1-CAP4) each connected to a data source, a local bus (Bx). In each coupler there is stored, in addition to the coupler control software, a set of subroutines for exchanging information with the buffer memory (MTP). The memory of the central control unit (MPC) stores the connection table relating to the established time-division switched connections between the couplers (Cx) and the buffer memory (MTP) as well as the subroutines of the interconnections established between every coupler and the data sources connected thereto. Each coupler (Cx) still includes a local access circuit (CALx) between the dual access memory (MCx) and the local bus (Bx), and a general access circuit (CAGx) between the dual access memory (MCx) and the main bus (MB), the local access circuit (CALx) and the general access circuit (CAGx) being controlled by a control circuit (CGMx) connected to the main bus (MB).

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Rennes, France

Guy P Dublet