Uplink sounding transmission with carrier aggregation

1. A method comprising:

a) receiving, by a wireless device, at least one control message from a base station, said at least one control message causing in said wireless device:

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

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; and

(2) a secondary cell group comprising a second subset of said at least one secondary cell; and

iii) configuration of transmissions of sounding reference signals on a secondary cell in said secondary cell group;

b) receiving, by said wireless device, an activation command to activate said secondary cell in said wireless device;

c) receiving, by said wireless device, a control command configured to cause transmission of a random access preamble on random access resources of one of said at least one secondary cell in said second subset;

d) receiving, by said wireless device, a random access response, said random access response comprising a timing advance command for said secondary cell group;

e) transmitting, by said wireless device, one or more of said sounding reference signals on said secondary cell after applying said timing advance command to said secondary cell group, said wireless device configured to not transmit any of said sounding reference signals on said secondary cell during a period between receiving said at least one control message and applying said timing advance command to said secondary cell group; and

f) dropping, by said wireless device, transmission of a sounding reference signal in said sounding reference signals in a subframe of said secondary cell when said wireless device is power limited in said subframe.

2. The method of claim 1 , wherein said sounding reference signals are type zero sounding reference signals.

3. The method of claim 1 , wherein said sounding reference signals are configured to be transmitted during a time period.

4. The method of claim 1 , wherein said one or more of said sounding reference signals are transmitted on the last symbol of a plurality of subframes.

5. The method of claim 1 , further comprising dropping transmission of a second sounding reference signal in said sounding reference signals in a second subframe of said secondary cell if said wireless device transmits data in said second subframe of said secondary cell.

6. The method of claim 1 , wherein applying said timing advance command causes alignment of reception timing of uplink signals in frames and subframes of said secondary cell group at said base station.

7. The method of claim 1 , wherein said wireless device drops at least one sounding reference signal if one or more pre-defined conditions are met.

8. The method of claim 1 , wherein said random access response comprises a preamble identifier, said preamble identifier identifying said random access preamble.

9. The method of claim 1 , wherein said at least one control message further causes configuration of said random access resources.

10. A method comprising:

a) receiving, by a wireless device, at least one control message from a base station, said at least one control message causing in said wireless device:

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

(2) a secondary cell group comprising a second subset of said at least one secondary cell;

b) receiving, by said wireless device, a control command configured to cause transmission of a random access preamble on random access resources of one of said at least one secondary cell in said second subset;

c) receiving, by said wireless device, a random access response, said random access response comprising a timing advance command for said secondary cell group;

d) receiving, by said wireless device, a second control message from said base station, said second control message causing in said wireless device configuration of transmissions of sounding reference signals on a secondary cell in said secondary cell group;

e) transmitting, by said wireless device, one or more of said sounding reference signals on said secondary cell after applying said timing advance command to said secondary cell group, said wireless device configured to not transmit any of said sounding reference signals on said secondary cell during a period between receiving said at least one control message and applying said timing advance command to said secondary cell group; and

f) dropping, by said wireless device, transmission of a sounding reference signal in said sounding reference signals in a subframe of said secondary cell when said wireless device is power limited in said subframe.

11. The method of claim 10 , wherein said at least one control message is configured to further cause in said wireless device configuration of a time alignment timer for each of said plurality of cell groups, said time alignment timer starting or restarting in response to said wireless device receiving a timing advance command to adjust uplink transmission timing of a commanded cell group in said plurality of cell groups.

12. The method of claim 10 , wherein applying said timing advance command causes alignment of reception timing of uplink signals in frames and subframes of said secondary cell group at said base station.

13. The method of claim 10 , wherein said wireless device drops at least one sounding reference signal if one or more pre-defined conditions are met.

14. The method of claim 10 , wherein said random access response comprises a preamble identifier, said preamble identifier identifying said random access preamble.

15. 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 causing in said wireless device:

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

(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; and

(b) a secondary cell group comprising a second subset of said at least one secondary cell; and

(3) transmissions of sounding reference signals on a secondary cell in said secondary cell group; and

ii) receive a control command configured to cause transmission of a random access preamble on random access resources of one of said at least one secondary cell in said second subset;

iii) receive a random access response, said random access response comprising a timing advance command for said secondary cell group;

iv) transmit one or more of said sounding reference signals on said secondary cell after applying said timing advance command to said secondary cell group, said wireless device configured to not transmit any of said sounding reference signals on said secondary cell during a period between receiving said at least one control message and applying said timing advance command to said secondary cell group; and

v) drop transmission of a sounding reference signal in said sounding reference signals in a subframe of said secondary cell when said wireless device is power limited in said subframe.

16. The wireless device of claim 15 , wherein said sounding reference signals are type zero sounding reference signals.

17. The wireless device of claim 15 , wherein said sounding reference signals are configured to be transmitted during a period.

18. The wireless device of claim 15 , wherein said one or more of said sounding reference signals are transmitted on the last symbol of a plurality of subframes.