Patent ID: 7391714
Filing Date: 2008-06-24
Classification: H04B,H04L

Abstract:
1. System for digital transmission of data, point to multipoint over an electricity network, that comprises a communication in a downstream channel, determined by a link from a head-end to various different users, and a communication in an upstream channel, determined by a link from each of the users to the head-end, where a communication medium is an electricity network and communication is achieved by means of an OFDM modulation (orthogonal frequency division multiplexing) to obtain OFDM symbols, where both the head-end and the users contain a transmitter/receiver that includes a medium access control module (MAC) to provide a master-slave communication, as well as means to add/extract a cyclic prefix in the OFDM symbols and means of converting the OFDM symbols from a frequency domain to a time domain and from the time domain to the frequency domain, and digital-to-analog and analog-to-digital converters; the transmitter/receiver of the head-end and the users comprising: means to adjust a digital signal to the electricity network that provide: where the transmitter includes means of sharing the medium in time TDMA (Time Division Multiple Access), in frequency FDMA (Frequency Division Multiple Access), and/or in Orthogonal Frequency Division Multiple Access (OFDMA), of the data transmitted in both the upstream and downstream channels for multiple users; where the receivers include means to process information corresponding to the data transmitted in the communication in the time and frequency domains, to reach maximum throughput; means to continuously calculate an SNR (signal to noise ratio) for each of the carriers in the OFDM modulation in both the upstream and downstream, so that different users located at differing distances from the head-end use dynamically different carriers in the same OFDM symbol, with a variable number of bits per carrier, maximizing the throughput of the channel in time; where the transmitter includes means to continuously assign the carriers and the number of bits per carrier to each of the carriers in the OFDM modulation from the result of the SNR calculation, and means to associate the number of the bits to be transmitted to each designated carrier to achieve the transmission taking into consideration a degradation of the electricity line response at different distances between the users and the head-end in each frequency, and to adjust transmission speed in function of the SNR calculation and a quality of transmission required for each user; means to translate the frequency to user bandwidths higher than base band, so as to be adjusted to the electricity network and to allow the use of spectral zones superior to base band; wherein the SNR calculation is calculated from a difference of a signal expected and a signal received over a certain time period, and in that the transmission speed is adjusted by comparison of SNR with certain previously fixed thresholds that are a function of different modulation constellations used in the system and a maximum rate of errors allowed at any time, wherein the thresholds previously established contain hysteresis.