Method and apparatus for efficient data transmissions in half-duplex communication systems with large propagation delays
Methods and apparatus for efficient transmission of data by half-duplex transceivers in satellite communication systems are provided. Time reference for the return link is skewed or time-lagged relative to the time reference for the forward link to reduce the amount of guard time required to separate return link transmission from forward link reception by the half-duplex transceiver of a user terminal. The guard time is determined based on a maximum differential round-trip propagation delay and transition times of the half-duplexer transceiver to switch between transmit and receive modes. In a satellite communication system in which a large number of active user terminals are present in a beam coverage, random time offsets are applied to spread approximately equal traffic loads across the time offsets.
1. A method of determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system, the method comprising:
determining a minimum round-trip propagation delay of signals between a ground station and a satellite;
determining a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode;
determining a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode;
determining the time lag of the return link time reference relative to the forward link time reference by offsetting the system parameter from the minimum round-trip propagation delay; and
scheduling at least one of one or more transmission operations by the satellite or one or more reception operations by the satellite in accordance with the determined time lag,
wherein the scheduling schedules the one or more transmission operations by the satellite on a first of n+k frames and the scheduling schedules the one or more reception operations by the satellite on a second set of n+k frames, where n is greater than or equal to zero,
wherein a leading edge of a frame k in the second set of n+k frames is skewed by the determined time lag at the satellite from a leading edge of a frame k in the first set of n+k frames,
wherein the return link time reference is a return link receiver time reference of the satellite, and
wherein the forward link time reference is a forward link transmitter time reference of the satellite.
2. The method of claim 1 , further comprising determining a guard time between reception and transmission in the half-duplex transceiver.
3. The method of claim 2 , wherein determining the guard time between reception and transmission in the half-duplex transceiver comprises:
determining a maximum round-trip propagation delay of signals between the ground station and the satellite;
determining a maximum differential round-trip propagation delay based on the maximum round-trip propagation delay and the minimum round-trip propagation delay; and
determining the guard time based on the maximum differential round-trip propagation delay and the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode.
4. The method of claim 1 , wherein the ground station comprises a user terminal.
5. The method of claim 1 , wherein the satellite comprises a non-geosynchronous satellite.
6. An apparatus configured to determine a time lag of a return link time reference relative to a forward link time reference in a satellite communication system, the apparatus comprising:
at least one processor; and
at least one memory coupled to the at least one processor, the at least one processor and the at least one memory being configured to:
determine a minimum round-trip propagation delay of signals between a ground station and a satellite;
determine a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode;
determine a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode;
determine the time lag of the return link time reference relative to the forward link time reference by offsetting the system parameter from the minimum round-trip propagation delay; and
schedule at least one of one or more transmission operations by the satellite or one or more reception operations by the satellite in accordance with the determined time lag,
wherein the at least one processor schedules the one or more transmission operations by the satellite on a first of n+k frames and the at least one processor schedules the one or more reception operations by the satellite on a second set of n+k frames, where n is greater than or equal to zero,
wherein a leading edge of a frame k in the second set of n+k frames is skewed by the determined time lag at the satellite from a leading edge of a frame k in the first set of n+k frames,
wherein the return link time reference is a return link receiver time reference of the satellite, and
wherein the forward link time reference is a forward link transmitter time reference of the satellite.
7. An apparatus for determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system, the apparatus comprising:
means for determining a minimum round-trip propagation delay of signals between a ground station and a satellite;
means for determining a transition time for a half-duplex transceiver at the ground station to switch between a transmit mode and a receive mode;
means for determining a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode;
means for determining the time lag of the return link time reference relative to the forward link time reference by offsetting the system parameter from the minimum round-trip propagation delay; and
means for scheduling at least one of one or more transmission operations by the satellite or one or more reception operations by the satellite in accordance with the determined time lag,
wherein the means for scheduling schedules the one or more transmission operations by the satellite on a first of n+k frames and the means for scheduling schedules the one or more reception operations by the satellite on a second set of n+k frames, where n is greater than or equal to zero,
wherein a leading edge of a frame k in the second set of n+k frames is skewed by the determined time lag at the satellite from a leading edge of a frame k in the first set of n+k frames,
wherein the return link time reference is a return link receiver time reference of the satellite, and
wherein the forward link time reference is a forward link transmitter time reference of the satellite.
8. A non-transitory computer-readable medium comprising at least one instruction for causing a computer or processor to perform a method to determine a time lag of a return link time reference relative to a forward link time reference in a satellite communication system, the at least one instruction comprising instructions to:
determine a minimum round-trip propagation delay of signals between a ground station and a satellite;
determine a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode;
determine a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode;
determine the time lag of the return link time reference relative to the forward link time reference by offsetting the system parameter from the minimum round-trip propagation delay; and
schedule at least one of one or more transmission operations by the satellite or one or more reception operations by the satellite in accordance with the determined time lag,
wherein the one or more transmission operations by the satellite are scheduled on a first of n+k frames and the one or more reception operations by the satellite are scheduled on a second set of n+k frames, where n is greater than or equal to zero,
wherein a leading edge of a frame k in the second set of n+k frames is skewed by the determined time lag at the satellite from a leading edge of a frame k in the first set of n+k frames,
wherein the return link time reference is a return link receiver time reference of the satellite, and
wherein the forward link time reference is a forward link transmitter time reference of the satellite.
9. A method of determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system, the method comprising:
determining a minimum round-trip propagation delay of signals between a ground station and a satellite;
determining a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode;
determining a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode;
determining the time lag of the return link time reference relative to the forward link time reference by offsetting the system parameter from the minimum round-trip propagation delay; and
scheduling at least one of one or more transmission operations by the satellite or one or more reception operations by the satellite in accordance with the determined time lag,
wherein the scheduling schedules the one or more transmission operations by the satellite on a first of n+k frames and the scheduling schedules the one or more reception operations by the satellite on a second set of n+k frames, where n is greater than or equal to zero,
wherein a leading edge of a frame k in the second set of n+k frames is skewed by the determined time lag at the satellite from a leading edge of a frame k in the first set of n+k frames,
wherein the return link time reference is a return link receiver time reference of the satellite, and
wherein the forward link time reference is a forward link transmitter time reference of the satellite.