SYSTEM AND METHOD FOR RANGING AND ROUND TRIP DELAY ADJUSTMENT IN A MULTIPOINT-TO-POINT ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM
Systems and methods for ranging and round trip delay adjustment in a multipoint-to-point orthogonal frequency division multiplexing (OFDM) system are provided. In one embodiment, a multipoint-to-point, OFDM communication system comprises: a host units; a plurality of remote units that access the host using an orthogonal frequency division multiple access scheme; wherein each of the remote units modulates upstream information into an OFDM signal modulated using an inverse Fourier transform; wherein the host receives upstream OFDM signals from a plurality of the remote units, wherein portions of the upstream OFDM signals arrive at the host at the same time; wherein the host detects a round trip delay between the host and each remote unit; and wherein the host transmits at least one timing adjustment signal to at least one of the remote units based at least in part on at least one of the detected round trip delays.
1 . A multipoint-to-point, orthogonal frequency division multiplexed (OFDM) communication system comprising:
a host unit;
a plurality of remote units that access the host unit using an orthogonal frequency division multiple access scheme;
wherein each of the remote units modulates upstream information into an OFDM signal modulated using an inverse Fourier transform;
wherein the host unit receives upstream OFDM signals from a plurality of the remote units, wherein portions of the upstream OFDM signals arrive at the host unit at the same time;
wherein the host unit detects a round trip delay between the host unit and each remote unit; and
wherein the host unit transmits at least one timing adjustment signal to at least one of the remote units based at least in part on at least one of the detected round trip delays.
2 . The system of claim 1 , wherein the timing adjustment signal causes the at least one of the remote units to equalize a round trip delay for the at least one remote unit with a round trip delay for at least one other remote unit of the plurality of remote units.
3 . The communication system of claim 1 wherein the inverse Fourier transform is an inverse fast Fourier transform.
4 . A system comprising:
a host unit;
a plurality of remote units using an orthogonal frequency division multiple access scheme to communicate at the same time with the host unit;
wherein the host unit determines a round trip delay between the host unit and each of the remote units; and
wherein the host unit sends a timing instruction to at least one of the remote units based on a determined round trip delay, the timing instruction calculated so that the round trip delays between the host unit and each of the remote units become closer to equal.
5 . A method for ranging in a multipoint-to-point orthogonal frequency division multiplexed (OFDM) communications system, the method comprising:
sending a first signal from a host unit to a first remote unit;
receiving a second signal transmitted from the first remote unit in response to the first signal;
generating at least one timing adjustment signal based at least in part on a round trip delay between the sending of the first signal and the receiving of the second signal;
transmitting the timing adjustment signal to the first remote unit, the timing adjustment signal instructing the first remote unit to delay upstream OFDM transmission of data.
6 . The method of claim 5 , wherein the timing adjustment signal is generated to improve an alignment of signals at the host unit when such signals are received simultaneously at the host unit from at least two of the plurality of remote units.