Patent ID: 7545733

Claim:
Automatic gain control system for a digital OFDM multiuser transmission system over the electricity network, comprising a number of user kits ( 2 ) and a head-end kit ( 1 ) in two-way communication over the electricity network, with independent control for both an upstream channel which runs from the user kits ( 2 ) to the head-end kit ( 1 ), and a downstream channel which runs from the head-end ( 1 ) to the user kits ( 2 ), where a division of the electricity network for both the upstream and the downstream channels is accomplished with frequency division duplexing (FDD) means and/or time division duplexing (TDD) means, where a signal is transmitted with OFDM (orthogonal frequency division multiplexing) modulation means resulting in a signal with non-constant envelope; and comprising amplifiers acting on transmission and reception gains, enabling to use various combinations of head-end ( 1 ) and user kits ( 2 ), that reuse same frequencies and times, where access to the upstream and downstream channels is accomplished with OFDMA/TDMA (orthogonal frequency division/time division) multiplexing means wherein said Automatic Gain Control System comprises: carrier by carrier treatment means for emission signals, which attenuate to a greater extent carriers that less attenuated by the channel, and which attenuate to a lesser extent carriers more attenuated by the channel; in order to compensate in advance an effect that a frequency selective channel, as the electricity network, has on the signal before being transformed to a time domain where average power of the signal is fixed, carrier by carrier treatment means for received signals in the frequency domain, where a block that compensates an attenuation caused by the channel carries out a scaling in frequency of the received signal and of elements that correct the signal, representing the compensated signal by a floating point and fixing a number of bits of a mantissa to obtain a determined maximum precision, or signal/noise ratio defined by carrier, transmission power control means that control the transmission power from various kits ( 2 ) with means that increase the power in the carriers that suffer more attenuation on being transmitted by the channel, and decreasing the power in the carriers that are transmitted by the channel with less attenuation; in order to achieve that the power for various users ( 2 ) is received with a same level and to enable to use analog/digital converters of few bits, transmission power (S) control means that control the transmission gains in the head-end and user kits; in order to ensure that the signals sent by the users ( 2 ) to the head-end ( 18 ) do not interfere in a functioning of other groups of head-end ( 18 ) and users ( 2 ) that may be using the same frequencies and times.