Cell timing in a wireless device and base station

1. A method comprising:

a) receiving, by a wireless device to communicate employing a plurality of cells, at least one control message from a base station, said at least one control message to cause in said wireless device:

i) configuration of a primary cell and at least one secondary cell in said plurality of cells; and

ii) assignment of each of said at least one secondary cell to a cell group in a plurality of cell groups, said plurality of cell groups comprising:

(1) a primary cell group comprising a first subset of said plurality of cells, said first subset comprising said primary cell, uplink transmissions by said wireless device in said primary cell group employing a first synchronization signal transmitted on said primary cell as a primary timing reference; and

(2) a secondary cell group comprising a second subset of said at least one secondary cell, uplink transmissions in said secondary cell group employing a second synchronization signal on an activated secondary cell in said secondary cell group as a secondary timing reference;

b) receiving, by said wireless device, at least one timing advance command from said base station, said timing advance command comprising:

i) a time adjustment value; and

ii) an index identifying said secondary cell group;

c) applying, by said wireless device, said time adjustment value to uplink transmission timing of said secondary cell group;

d) determining, by said wireless device, a timing difference between primary cell group timing and secondary cell group timing; and

e) triggering an action, by said wireless device, in response to said wireless device detecting that said timing difference is greater than a threshold.

2. The method of claim 1 , wherein:

a) said primary cell group timing is a primary cell group uplink signal timing; and

b) said secondary cell group timing is a secondary cell group uplink signal timing.

3. The method of claim 1 , wherein:

a) said primary cell group timing is a primary cell group downlink signal timing; and

b) said secondary cell group timing is a secondary cell group downlink signal timing.

4. The method of claim 1 , wherein transmission of downlink signals in said primary cell group and said secondary cell group are time aligned within a predetermined value.

5. The method of claim 1 , wherein said action is an action in a radio resource control layer or an action in a medium access control layer.

6. The method of claim 1 , wherein said action comprises at least one of the following:

a) transmitting a radio resource control message to said base station;

b) transmitting a medium access control message to said base station;

c) changing the synchronization state of a cell from an in-sync state to an out-of-sync state; and

d) changing the synchronization state of a cell group from an in-sync state to an out-of-sync state.

7. The method of claim 1 , wherein detecting said difference employs, at least in part, said first synchronization signal and said second synchronization signal.

8. A wireless device comprising:

a) one or more communication interfaces;

b) one or more processors; and

c) memory storing instructions that, when executed, cause said wireless device to:

i) receive at least one control message from a base station, said at least one control message to cause in said wireless device:

(1) configuration of a primary cell and at least one secondary cell in a plurality of cells; and

(2) assignment of each of said at least one secondary cell to a cell group in a plurality of cell groups, said plurality of cell groups comprising:

(a) a primary cell group comprising a first subset of said plurality of cells, said first subset comprising said primary cell, uplink transmissions by said wireless device in said primary cell group employing a first synchronization signal transmitted on said primary cell as a primary timing reference; and

(b) a secondary cell group comprising a second subset of said at least one secondary cell, uplink transmissions in said secondary cell group employing a second synchronization signal on an activated secondary cell in said secondary cell group as a secondary timing reference;

ii) receive at least one timing advance command from said base station, said timing advance command comprising:

(1) a time adjustment value; and

(2) an index identifying said secondary cell group;

iii) apply said time adjustment value to uplink transmission timing of said secondary cell group;

iv) determine a timing difference between primary cell group timing and secondary cell group timing; and

v) trigger an action in response to said wireless device detecting that said timing difference is greater than a threshold.

9. The wireless device of claim 8 , wherein:

a) said primary cell group timing is a primary cell group uplink signal timing; and

b) said secondary cell group timing is a secondary cell group uplink signal timing.

10. The wireless device of claim 8 , wherein:

a) said primary cell group timing is a primary cell group downlink signal timing; and

b) said secondary cell group timing is a secondary cell group downlink signal timing.

11. The wireless device of claim 8 , wherein said action comprises at least one of the following:

a) suspending uplink transmission on a cell;

b) suspending uplink transmission on a cell group; and

c) ignoring a received timing advance command resulting in an increase in said difference.

12. The wireless device of claim 8 , wherein detecting said difference employs, at least in part, primary cell group uplink signal timing and secondary cell group uplink signal timing.

13. The wireless device of claim 8 , wherein said action is an action in a radio resource control layer or an action in a medium access control layer.