Symbol alignment in multipoint-to-point orthogonal frequency division multiplexing communication

Abstract

A system is provided. The system includes a host and a plurality of remote units. Upstream bandwidth capacity is shared among a plurality of remote units in a manner that permits at least two of the remote units to transmit to the host at any one time using the upstream bandwidth capacity. The upstream bandwidth capacity includes a plurality of orthogonal tones generated using inverse fast Fourier transforms. The host causes at least one remote unit to adjust the manner in which symbols are transmitted therefrom on at least one of the plurality of orthogonal tones in order to improve the alignment of symbols received at the host.

1 . A system comprising: 
 a host; and    a plurality of remote units, wherein upstream bandwidth capacity is shared among a plurality of remote units in a manner that permits at least two of the remote units to transmit to the host at any one time using the upstream bandwidth capacity, the upstream bandwidth capacity comprising a plurality of orthogonal tones generated using inverse fast Fourier transforms; and    wherein the host causes at least one remote unit to adjust the manner in which symbols are transmitted therefrom on at least one of the plurality of orthogonal tones in order to improve the alignment of symbols received at the host.    
     
     
         2 . The system of  claim 1 , wherein the symbols are transmitted from the at least one remote unit as frames, each frame comprising at least one symbol.  
     
     
         3 . The system of  claim 2 , wherein the host causes the at least one remote unit to adjust the manner in which symbols are transmitted therefrom on the at least one of the plurality of orthogonal tones in order to improve the alignment of frames received at the host.  
     
     
         4 . The system of  claim 1 , further comprising generating information indicative of a transmission adjustment for the at least one remote unit and communicating the information to the at least one remote unit for use by the at least one remote unit in making the transmission adjustment based at least in part on the information in order to improve the alignment of the predetermined groupings of frames when received at the host.  
     
     
         5 . The system of  claim 1 , wherein the host: 
 determines a phase shift associated with the receipt at the host of a first symbol transmitted from one of the plurality of remote units; and    causes the at least one remote unit to add a delay to the transmission of a second symbol therefrom, wherein the delay is related to the phase shift.    
     
     
         6 . The system of  claim 1 , wherein the host communicates a command to the at least one remote unit, wherein the at least one remote unit adjusts the manner in which symbols are transmitted therefrom in response to the command.  
     
     
         7 . The system of  claim 1 , wherein the host causes the at least one remote unit to adjust the manner in which symbols are transmitted therefrom on the at least one of the plurality of orthogonal tones by doing at least one of adjusting a carrier amplitude and a carrier frequency.  
     
     
         8 . The system of  claim 1 , wherein the system is used in a wireless network.  
     
     
         9 . A system comprising: 
 a host; and    a plurality of remote units;    wherein the host receives a plurality of upstream symbols transmitted from the remote units on a plurality of orthogonal tones using orthogonal frequency division multiplexing;    wherein a symbol timing error for at least one remote unit is determined; and    wherein at least one remote unit adjusts the manner in which symbols are transmitted therefrom based on the symbol timing error.    
     
     
         10 . The system of  claim 9 , wherein the at least one remote adjusts the manner in which symbols are transmitted therefrom in response to a symbol timing adjustment command transmitted thereto, wherein the symbol timing adjustment command is related to the symbol timing error.  
     
     
         11 . A remote unit for a multi-point to point communication system, the remote unit comprising: 
 a multi-carrier transceiver coupled to a multipoint-to-point host unit, wherein the transceiver is configured to transmit upstream information to the multipoint-to-point host unit using one or more tones within an orthogonal frequency division multiplexing waveform;    a modem coupled to the multi-carrier transceiver, the modem configured to process the upstream information for transmission as symbols via the one or more tones based on an inverse Fourier transform algorithm; and    a logic circuit coupled to the modem, the logic circuit configured to adjust a manner in which symbols are transmitted by the modem and the multi-carrier transceiver based on a symbol timing error received from the multipoint-to-point host unit.    
     
     
         12 . The remote unit of  claim 11 , the multi-carrier transceiver coupled to the multipoint-to-point host unit by a distribution network coupled between the multipoint-to-point host unit and a plurality of remote units.  
     
     
         13 . The remote unit of  claim 12 , wherein the distribution network comprises one of a wireless system and a hybrid fiber/coax network.  
     
     
         14 . A host unit for a multi-point to point communication system, the host unit comprising: 
 a multi-carrier transceiver communicatively coupled to a plurality of remote units through an orthogonal frequency division multiplexing waveform;    a modem that decodes upstream information from the orthogonal frequency division multiplexing waveform based on a Fourier transform algorithm; and    a logic circuit configured to estimate a phase shift error associated with a first symbol received from a first remote unit of the plurality of remote units;    wherein the modem and the multi-carrier transceiver transmit a signal directing the first remote unit to adjust transmission of symbols based on the symbol timing error.    
     
     
         15 . The host unit of  claim 14 , wherein the multi-carrier transceiver transmits a signal directing the first remote unit to adjust transmission of symbols so that when a plurality of tones are transmitted from the first remote unit and at least one other remote unit of the plurality of remote units, the plurality of tones are substantially orthogonal when received at the host unit.  
     
     
         16 . The host unit of  claim 15 , the multi-carrier transceiver communicatively coupled to the plurality of remote units by a distribution network coupled between the multipoint-to-point host unit and the plurality of remote units.  
     
     
         17 . The host unit of  claim 16 , wherein the distribution network comprises one of a wireless system and a hybrid fiber/coax network.