System and method providing various pilot sub-carrier densities in OFDMA communications

1. A method for varying pilot sub-carrier density in OFDMA communications comprising;

calculating channel quality from sub-carriers;

determining whether the channel quality is outside a threshold range;

selecting a different pilot sub-carrier density for a sub-zone of an existing zone based on the value of the channel quality when the channel quality is outside the threshold range, a single type of sub-channel assignment protocol being used within the zone; and

setting the sub-zone to the different pilot sub-carrier density.

2. The method of claim 1 , wherein the different pilot subcarrier density is lower than a pilot sub-carrier density in use by the sub-zone.

3. The method of claim 1 , wherein the pilot sub-carrier locations maximize|PSInew-PSIe, where PSInew is a Pilot Sub-carrier Index for new pilot sub-carrier locations and PSIe is a Pilot Sub-Carrier Index for existing pilot sub-carrier locations.

4. The method of claim 1 , wherein the selecting comprises selecting the minimal different pilot sub-carrier density resulting in the mean-squared error of a predicted channel estimation error being between a desired range.

5. The method of claim 1 , wherein the OFDMA communications are performed by a multiple-input and multiple-output (MIMO) station.

6. The method of claim 1 , wherein one or more steps of the method are implemented by a mobile station.

7. The method of claim 1 , wherein one or more steps of the method are implemented by a base station.

8. The method of claim 1 , further comprising determining that two or more mobile stations are substantially co-located.

9. The method of claim 1 , wherein the channel quality comprises using one or more of channel condition, standard deviation of the channel condition, ACK/NACK, channel correlation, channel rank, or a combination thereof.

10. The method of claim 1 , wherein the setting comprises instructing a base station and a mobile station to implement the sub-zone to the different pilot sub-carrier density.

11. The method of claim 1 , wherein the OFDMA communications are LTE, fixed WiMAX, or mobile WiMAX compliant.

12. The method of claim 11 , wherein the setting comprising:

establishing a sub-carrier specification structure with the different pilot sub-carrier density, wherein the sub-carrier specification structure includes a cluster structure, a tile structure, or a zone structure; and using a sub-zone information element (IE) to implement the sub-carrier specification structure for the sub-zone.

13. The method of claim 11 , wherein the sub-carrier specification structure with a different pilot sub-carrier density is implemented in one or more of Full Usage of SubChannels (FUSC), optional FUSC, Partial Usage of Sub-channels (PUSC), optional PUSC, Tile Usage of Sub-Channel 1 (TUSC 1 ), Tile Usage of Sub-Channel 1 (Tusc 2 ), and Adaptive Modulation and Coding (AMC) subzones.

14. The method of claim 1 , wherein the setting comprises checking whether setting the sub-zone to the different pilot sub-carrier density is permitted.

15. The method of claim 14 , wherein the checking comprises determining whether a system has sufficient resources to permit setting the sub-zone to the different pilot sub-carrier density.

16. The method of claim 14 , wherein the checking comprises determining that a base station and a mobile station are adapted to implement the sub-zone to the different pilot subcarrier density.

17. The method of claim 1 , further comprising provisioning an OFDMA station with a plurality of sub-carrier specification structures with different pilot sub-carrier densities.

18. The method of claim 17 , wherein the setting comprises using a pre-provisioned sub-zone having the different pilot density for the OFDMA communications.

19. A system for varying pilot sub-carrier density in OFDMA communications comprising:

a channel quality calculator configured to calculate channel quality based on sub-carriers;

a determiner configured to determine whether the channel quality is outside a threshold range;

a selector configured to select a different pilot sub-carrier density for a sub-zone of an existing zone based on the value of the channel quality when the channel quality is outside the threshold range, a single type of sub-channel assignment protocol being used within the zone, and

a scheduler configured to set the sub-zone to the different pilot subcarrier density.

20. The system of claim 19 , wherein the different pilot sub-carrier density is lower than a pilot sub-carrier density in use by the sub-zone.

21. The system of claim 19 , wherein the selector selects the minimal different pilot sub-carrier density resulting in the mean-squared error of a predicted channel estimation error being between a desired range.

22. The system of claim 19 , wherein the system is implemented by a base station.

23. The system of claim 19 , wherein the scheduler instructs a base station and a mobile station to implement the sub-zone to the different pilot sub-carrier density.

24. The system of claim 19 , wherein the OFDMA communications are LTE, fixed WiMAX, or mobile WiMAX compliant.

25. The system of claim 19 , further comprising a storage provisioned with a plurality of sub-carrier specification structures with different pilot sub-carrier densities.

26. The system of claim 25 , wherein the scheduler establishes a sub-carrier specification structure with the different pilot sub-carrier density and transmits a sub-zone information.

27. The system of claim 19 , wherein the selector determines whether a system has sufficient resources to permit setting the sub-zone to the different pilot sub-carrier density.

28. The system of claim 19 , wherein the sub-carriers are pilot sub-carriers.

29. A machine-readable storage device in which software is recorded, wherein the software is configured to implement a method for varying pilot sub-carrier density in OFDMA communications comprising:

calculating channel quality from sub-carriers;

determining whether the channel quality is outside a threshold;

selecting a different pilot sub-carrier density for a sub-zone of an existing zone based on the value of the channel quality when the channel quality is outside the threshold, a single type of sub-channel assignment protocol being used within the zone; and

setting the sub-zone to the different pilot sub-carrier density.