TDD FDD communication interface

Abstract

TDD access equipment modified by introducing a frequency change at the normal TDD guard point, with respective downlink or uplink periods for individual subscriber stations offset to form overlapping frames. Cyclo-stationary processing, block equalization, and burst timing coordination allow the boundary between downlink and uplink portions of both frames to be set dynamically, improving spectral efficiency. Fast frequency switching within an allotted physical slot enables synchronization of time-sharing the dedicated frequencies to be maintained among subscriber stations. Duplex spacing between downlink and uplink frequencies for individual subscriber stations, combined with in-depth filtering of received signals, prevents spurious out-of-band transmission signal strength from reaching an interference level.

1 - 24 . (canceled) 
   
   
       25 . A method of TDD operation in a first subscriber unit having a cable modem, the method comprising:
 receiving in the first subscriber unit a first signal from a first base station on a downlink frequency during a first time period; and   transmitting from the first subscriber unit a second signal to the first base station on an uplink frequency during a second time period following the first time period, wherein the downlink frequency and the uplink frequency are separated by a predefined duplex spacing.   
   
   
       26 . A cable modem configured to use TDD in a first subscriber station, the cable modem comprising:
 a receiver circuit configured to receive a first signal on a first frequency designated for downlink transmission during a first time period; and   a transmitter circuit configured to transmit a second signal on a second frequency different from the first frequency and designated for uplink transmission during a second time period following the first time period,   wherein the first frequency is employed for downlink transmission to a second subscriber station during the second time period and the second frequency is employed for uplink transmission from the second subscriber station during the first time period.   
   
   
       27 . For use in conjunction with a cable modem, a method of time sharing frequencies reserved for FDD operation, the method comprising:
 receiving in the cable modem a first signal from a first base station on a downlink frequency during a first time period; and   transmitting from the cable modem a second signal to the first base station on an uplink frequency during a second time period following the first time period, wherein the downlink frequency and the uplink frequency are separated by a predefined duplex spacing.   
   
   
       28 . A cable modem configured to use TDD, the modem comprising:
 a transmitter circuit configured to
 transmit a first signal on a first frequency to a first subscriber station during a first time period, and 
 transmit a second signal on a second frequency, different from the first frequency, to a second subscriber station during a second time period following the first time period; and 
   a receiver circuit configured to
 receive a third signal on the second frequency from the second subscriber station during the first time period, and 
 receive a fourth signal on the first frequency from the first subscriber during the second time period.