Method and system for diversity using orthogonal frequency/division multiplexing
A method and system for achieving a link budget improvement in a diverse OFDM radio system by addressing the timing misalignment issue that can occur due to the differences in propagation time in signals between mobile stations and Radio Access Nodes. Timing misalignment is shared or split between the primary path to a primary Radio Access Node and a diverse path to a diverse Radio Access Node. The relative timing offsets between mobile stations are adjusted, the mobile stations are grouped into zones using a variety of different grouping techniques, and the transmission for each mobile station is scheduled, using one or more of a variety of scheduling techniques.
1. A method of transmitting OFDM signals between a plurality of spatially separated transmit antennas and at least one receive antenna, the method comprising:
determining relative timing differential values for the plurality of transmit antennas when the transmit antennas transmit OFDM signals to the at least one receive antenna via at least one diverse path, wherein the relative timing differential values result in a timing misalignment; and
resolving the timing misalignment by allocating the relative timing differential values among the one or more diverse paths; and
grouping the spatially separated transmit antennas into zones based at least in part on timing characteristics.
2. The method of claim 1 , wherein the at least one receive antenna is mounted to a satellite.
3. The method of claim 1 , wherein the timing characteristics include relative timing differential values such that a maximum timing differential value within a zone is not more than a predetermined limit.
4. The method of claim 3 , wherein the limit is based on a length of a cyclic prefix of the OFDM signals.
5. The method of claim 4 , further comprising increasing the length of the cyclic prefix to decrease a likelihood of timing misalignment.
6. The method of claim 3 , further comprising inserting guard carriers between transmit antenna transmissions for each zone.
7. The method of claim 3 , further comprising scheduling transmission of signals to respective receive antennas associated with the transmit antennas, wherein signals for receive antennas associated with transmit antennas in at least one zone are scheduled together.
8. The method of claim 3 , further comprising sizing each zone into one or more subchannel blocks, wherein transmit antennas within each subchannel block are scheduled to transmit signals together.
9. The method of claim 1 , wherein the zones are geographic zones, the timing characteristics associated with the transmit antennas within each geographic zone satisfy timing requirements.
10. The method of claim 9 , wherein transmit antennas within each geographic zone schedule their transmissions together.
11. An OFDM transceiver comprising:
a timing differential component configured to determine relative timing differential values for a plurality of spatially separated transmit antennas when the transmit antennas transmit OFDM signals to the OFDM transceiver via at least one diverse path; and
a timing misalignment resolution component configured to:
allocate the relative timing differential values among the at least one diverse path; and
group the spatially separated transmit antennas into zones based at least in part on timing characteristics.
12. The transceiver of claim 11 , wherein the transceiver is mounted to a satellite.
13. The transceiver of claim 11 , wherein the timing characteristics include relative timing differential values such that a maximum timing differential value within a zone is not more than a predetermined limit.
14. The transceiver of claim 13 , wherein the limit is based on a length of a cyclic prefix of the OFDM signals.
15. The transceiver of claim 14 , wherein the timing misalignment resolution component operates to increase the length of the cyclic prefix to decrease a likelihood of timing misalignment.
16. The transceiver of claim 13 , wherein the timing misalignment resolution component operates to insert guard carriers between transmit antenna transmissions for each zone.
17. The transceiver of claim 13 , the timing misalignment resolution component is further configured to schedule transmission of signals to respective receive antennas associated with the transmit antennas, such that signals for receive antennas associated with transmit antennas in at least one zone are scheduled together.
18. The transceiver of claim 13 , wherein the timing misalignment resolution component is further configured to size each zone into one or more subchannel blocks, wherein transmit antennas within each subchannel block are scheduled to transmit signals together.
19. The transceiver of claim 11 , wherein the zones are geographic zones, the timing characteristics associated with the transmit antennas within each geographic zone satisfy timing requirements.
20. The transceiver of claim 19 , wherein the timing misalignment resolution component is further configured to schedule transmissions for transmit antennas within each geographic zone schedule together.