Methods and apparatus to allocate reference signals in wireless communication systems

1. A method comprising:

applying a first cyclic shift to a first reference sequence during a first time interval of a signal;

applying a second cyclic shift to a second reference sequence during a second time interval of the signal, wherein the first cyclic shift differs from the second cyclic shift; and

the first and second cyclic shifts are members of a set of cyclic shifts assigned to devices of a wireless region.

2. A method as defined in claim 1 , wherein the set of cyclic shifts defines an order in which devices of the wireless region are to apply cyclic shifts.

3. A method as defined in claim 1 , wherein the first reference sequence is substantially randomly selected.

4. A method as defined in claim 1 , further comprising selecting the first and second reference sequence from a set of reference sequences assigned to devices of a wireless region.

5. A method as defined in claim 4 , wherein the set of reference sequences defines an order in which devices of the wireless region are to select a reference sequence.

6. A method as defined in claim 1 , wherein the first wireless device is at least one of a user endpoint, a mobile station, a mobile terminal, an access point, a nodeB, a fixed station, wireless communication cell or wireless communication cell sector.

7. A method as defined in claim 1 , wherein the first wireless device is at least one of an access point, a nodeB, a fixed station, or a cell tower, and wherein the second wireless device is at least one of a user endpoint, a mobile station, or a mobile terminal.

8. A method as defined in claim 1 , wherein the first reference sequence and the second reference sequence are transmitted to the same wireless device during different time intervals.

9. A method as defined in claim 1 , wherein the first reference sequence and the second reference sequence are the same.

10. An apparatus comprising:

a reference signal generator comprising:

a sequence selector to select a first reference sequence from a group of reference sequences assigned to a first wireless region and

a second reference sequence from a group of reference sequences assigned to a second wireless region;

a cyclic shift selector to select a first cyclic shift for a first time interval from a group of cyclic shifts assigned to a first wireless region;

a cyclic shifter to cyclically shift solely the first reference sequence based on the selected first cyclic shift to form a first reference signal; and

a transmit adapter to transmit the first reference signal during the first time interval via the wireless channel.

11. An apparatus as defined in claim 10 , wherein the cyclic shift selector is to select a second cyclic shift for a second time interval from a group of cyclic shifts assigned to a second wireless region; and

wherein the cyclic shifter is to cyclically shift solely the reference sequence based on the second selected cyclic shift during a second time interval.

12. An apparatus as defined in claim 10 , wherein the selection is based upon at least one of a frame number, a sub-frame offset, a slot offset, a transmitted symbol offset, a wireless region identifier, a NodeB identifier, a user endpoint identifier or a group identifier.

13. An apparatus as defined in claim 10 , further comprising a modulator to modulate the first reference sequence, the modulator comprising:

a Fourier transform module to perform a Fourier transform of the first reference sequence;

an inverse Fourier transform module to perform an Inverse Fourier transform; and

an interface to map outputs of the Fourier transform to selected inputs of the Inverse Fourier transform.