Apparatus and method for symbol alignment in a multi-point ofdm/dmt digital communications system

Abstract

A multi-point communications system is set forth herein. The communications system comprises a head end unit disposed at a primary site and a plurality of receivers disposed at remote sites. The head end unit includes a transmitter for transmitting OFDM/DMT symbols over a predetermined number of bins across a transmission medium. The OFDM/DMT symbols are transmitted in periodically occurring formatted symbol frames. The cyclic prefix includes a predetermined periodic signal superimposed thereon. The receivers receive the OFDM/DMT symbols over a subset of the predetermined number of bins from the transmission medium and use the superimposed signals to attain symbol alignment. As such, the receivers are designed to process substantially fewer bins than the entire number of bins transmitted by the head end unit.

What is claimed is: 
     
         1 . An apparatus for processing OFDM/DMT data, the apparatus comprising:
 an intermediate frequency (IF) mixer configured to transpose an OFDM/DMT analog signal, output by a head-end unit to a communication path in a first number of data bins, to an IF signal;   a converter configured to band pass filter the IF signal and under-sample the IF signal filtered resulting in OFDM/DMT digital data over a second number of bins, the second number of bins being smaller than the first number of bins;   a processor to process the OFDM/DMT digital data in the second number of bins to extract features including frequency, amplitude, or phase information from the OFDM/DMT digital data; and   a reporter to report the features to a module configured to reconstruct the OFDM/DMT analog data as a function of the features.   
     
     
         2 . The apparatus of  claim 1  further including a recovery module configured to recover the OFDM/DMT analog data as a function of extracted features including the frequency, amplitude, or phase information. 
     
     
         3 . The apparatus of  claim 1 , wherein the processor is arranged to process the OFDM/DMT digital data to extract the features by applying a Fourier Transform to the OFDM/DMT digital data. 
     
     
         4 . The apparatus of  claim 3 , wherein a hardware correlator is arranged to apply the Fourier Transform to the OFDM/DMT digital data. 
     
     
         5 . The apparatus of  claim 1  further including a transmitter configured to transmit OFDM/DMT analog data to the head-end unit across a transmission medium. 
     
     
         6 . The apparatus of  claim 1  further including an analog filter configured to filter the OFDM/DMT analog data, prior to transposing to the IF signal. 
     
     
         7 . A method for processing OFDM/DMT data, the method comprising:
 transposing OFDM/DMT analog data, received from a head-end unit through a communication path in a first number of bins, to an intermediate frequency (IF) signal;   band pass filtering the IF signal and under-sampling the IF signal filtered resulting in OFDM/DMT digital data over a second number of bins, the second number of bins being smaller than the first number of bins;   processing the OFDM/DMT digital data in the second number of bins to extract features including frequency, amplitude, or phase information from the OFDM/DMT digital data; and   reporting the features to a module configured to reconstruct the analog data as a function of the features.   
     
     
         8 . The method of  claim 7  further including recovering the OFDM/DMT analog data as a function of extracted features including the frequency, amplitude, or phase information. 
     
     
         9 . The method of  claim 7  further including processing the OFDM/DMT digital data to extract the features by applying a Fourier Transform to the OFDM/DMT digital data. 
     
     
         10 . The method of  claim 9  further including applying the Fourier Transform to the OFDM/DMT digital data by employing a hardware correlator. 
     
     
         11 . The method of  claim 7  further including transmitting OFDM/DMT analog data to the head-end unit. 
     
     
         12 . The method of  claim 7  further including filtering the OFDM/DMT analog data prior to transposing to the IF signal. 
     
     
         13 . A non-transitory computer readable medium having computer readable program codes embodied therein for processing OFDM/DMT data, the computer readable medium program codes including instructions that, when executed by a processor, cause the processor to:
 transpose OFDM/DMT analog data, received from a head-end unit through a communication path in a first number of bins, to an intermediate frequency (IF) signal;   band pass filter the IF signal and under-sample the IF signal filtered resulting in OFDM/DMT digital data over a second number of bins, the second number of bins being smaller than the first number of bins;   process the OFDM/DMT digital data in the second number of bins to extract features including frequency, amplitude, or phase information from the OFDM/DMT digital data; and   report the features to a module configured to reconstruct the analog data as a function of the features.   
     
     
         14 . The apparatus of  claim 1  wherein the recovery module is arranged to recover the OFDM/DMT analog data as a function rotating the phase information of the OFDM/DMT digital data at a predetermined phase angle during a corresponding symbol period.