Upstream pilot structures in point-to-multipoint orthogonal frequency-division multiplexing (ofdm) communication systems

Abstract

A central access network unit comprising a processor configured to assign a plurality of upstream training blocks from an upstream OFDM symbol to a plurality of downstream network units, wherein the OFDM symbol comprises a plurality of pilot subcarriers equally spaced across an upstream RF spectrum in a pre-determined time interval, and wherein each upstream training block comprises a different subset of the pilot subcarriers that are non-consecutive and situated across the upstream RF spectrum, and generate one or more messages comprising assignments of the upstream training blocks, and a transmitter coupled to the processor and configured to transmit the messages to the plurality of downstream network units via a network, wherein the messages instruct at least one of the plurality of downstream network units to transmit a modulated pre-determined sequence at the pilot subcarriers corresponding to the upstream training block assigned to the downstream network unit.

What is claimed is: 
     
         1 . A method implemented by a cable modem termination system (CMTS), the method comprising:
 assigning, to a cable modem, a set of scattered subcarriers from a set of first equally-spaced subcarriers of an orthogonal frequency-division multiplexing (OFDM) symbol, with the set of scattered subcarriers starting from a certain subcarrier of the set of first equally-spaced subcarriers and with the set of scattered subcarriers being equally spaced by a fixed number of the first equally-subcarriers; and   transmitting, to the cable modem, location information that indicates a location of the set of scattered subcarriers in the OFDM symbol, with the location information indicating that the set of scattered subcarriers starts from the certain subcarrier and indicating the fixed number.   
     
     
         2 . The method of  claim 1 , wherein the set of scattered subcarriers spans a radio frequency (RF) spectrum of the OFDM symbol. 
     
     
         3 . The method of  claim 1 , further comprising assigning all first equally-spaced subcarriers of a second OFDM symbol to either the cable modem or a second cable modem. 
     
     
         4 . The method of  claim 1 , further comprising assigning a second set of scattered subcarriers of the OFDM symbol to either the cable modem or a second cable modem, with the second set of scattered subcarriers starting from a second subcarrier of the OFDM symbol and being equally spaced by the fixed number of the first equally-spaced subcarriers. 
     
     
         5 . An apparatus in a cable modem termination system (CMTS) network, the apparatus comprising:
 a memory storing instructions; and   a processor coupled to the memory, with the processor executing the instructions to:
 assign, to a cable modem, a set of scattered subcarriers from a set of first equally-spaced subcarriers of an orthogonal frequency-division multiplexing (OFDM) symbol, with the set of scattered subcarriers starting from a certain subcarrier of the set of first equally-spaced subcarriers and with the set of scattered subcarriers being equally-spaced by a fixed number of the first equally-subcarriers; and 
 transmit, to the cable modem, location information that indicates a location of the set of scattered subcarriers in the OFDM symbol, with the location information indicating that the set of scattered subcarriers starts from the certain subcarrier and indicating the fixed number. 
   
     
     
         6 . The apparatus of  claim 5 , wherein the set of scattered subcarriers spans a radio frequency (RF) spectrum of the OFDM symbol. 
     
     
         7 . The apparatus of  claim 5 , wherein the processor is further configured to assign all first equally-spaced subcarriers of a second OFDM symbol to either the cable modem or a second cable modem. 
     
     
         8 . The apparatus of  claim 5 , wherein the processor is further configured to assign a second set of scattered subcarriers of the OFDM symbol to either the cable modem or a second cable modem, with the second set of scattered subcarriers starting from a second subcarrier of the OFDM symbol and being equally spaced by the fixed number of the first equally-spaced subcarriers. 
     
     
         9 . A method implemented in a cable modem termination system (CMTS) network that supports orthogonal frequency-division multiplexing (OFDM) symbol transmission, the method comprising:
 receiving, by a cable modem from a CMTS coupled to the cable modem via the CMTS network, location information indicating a location of a set of scattered subcarriers in an OFDM symbol, wherein the OFDM symbol comprises a set of first equally-spaced subcarriers;   determining, by the cable modem and based on the location information, that the set of scattered subcarriers starts from a certain subcarrier of the set of first equally-spaced subcarriers and is equally spaced by a fixed number of the first equally-spaced subcarriers; and   transmitting, to the CMTS and in response to the location information, a pilot sequence on the set of scattered subcarriers.   
     
     
         10 . The method of  claim 9 , wherein the set of scattered subcarriers spans a radio frequency (RF) spectrum of the OFDM symbol. 
     
     
         11 . The method of  claim 9 , further comprising assigning all first equally-spaced subcarriers of a second OFDM symbol to either the cable modem or a second cable modem. 
     
     
         12 . The method of  claim 9 , further comprising assigning a second set of scattered subcarriers of the OFDM symbol to either the cable modem or a second cable modem, with the second set of scattered subcarriers starting from a second subcarrier of the OFDM symbol and being equally spaced by the fixed number of the first equally-spaced subcarriers. 
     
     
         13 . A cable modem in a cable modem termination system (CMTS) network, the cable modem comprising:
 a memory comprising instructions; and   a processor coupled to the memory, with the processor executing the instructions to:
 receive, by a cable modem from a CMTS coupled to the cable modem via the CMTS network, location information indicating a location of a set of scattered subcarriers in an OFDM symbol, wherein the OFDM symbol comprises a set of first equally-spaced subcarriers; 
 determine, by the cable modem and based on the location information, that the set of scattered subcarriers starts from a certain subcarrier of the set of first equally-spaced subcarriers and is equally spaced by a fixed number of the first equally-spaced subcarriers; and 
 transmit, to the CMTS and in response to the location information, a pilot sequence on the set of scattered subcarriers. 
   
     
     
         14 . The cable modem of  claim 13 , wherein the set of scattered subcarriers spans a radio frequency (RF) spectrum of the OFDM symbol. 
     
     
         15 . The cable modem of  claim 13 , wherein the processor is further configured to assign all first equally-spaced subcarriers of a second OFDM symbol to either the cable modem or a second cable modem. 
     
     
         16 . The cable modem of  claim 13 , wherein the processor is further configured to assign a second set of scattered subcarriers of the OFDM symbol to either the cable modem or a second cable modem, with the second set of scattered subcarriers starting from a second subcarrier of the OFDM symbol and being equally spaced by the fixed number of the first equally-spaced subcarriers.