Acquiring cipher keys for positioning system information blocks

1 . A method for transmitting a cipher key request, performed by a user equipment, comprising:

receiving first cipher key information including a first cipher key and an indication of a first validity time duration during which the first cipher key is valid;

receiving an indication of an advance time duration, that is a portion of the first validity time duration, during which the cipher key request is transmitted in order to receive second cipher key information, including a second cipher key, before a second validity time during which the second cipher key is valid;

transmitting a first cipher key request prior to the advance time duration;

receiving, in response to transmitting the first cipher key request prior to the advance time duration, a response that includes the first cipher key information without including the second cipher key information;

transmitting a second cipher key request within the advance time duration; and

receiving, in response to transmitting the second cipher key request within the advance time duration, a response that includes the second cipher key information.

2 . The method of claim 1 further comprising determining a random time within the advance time duration and transmitting the cipher key request based at least in part on the random time.

3 . The method of claim 1 wherein the cipher key information is received via one or more non-access stratum (NAS) messages.

4 . The method of claim 1 wherein the advance time duration is equal to a pre-established timer value in a communication system.

5 . The method of claim 4 wherein the pre-established timer value is based on a T3512 timer.

6 . The method of claim 1 further comprising receiving additional cipher key information in response to transmitting the cipher key request within the advance time duration.

7 . The method of claim 6 further comprising:

receiving an encrypted positioning system information block; and

decrypting the encrypted positioning system information block based at least in part on the additional cipher key information.

8 . The method of claim 6 further comprising:

storing the cipher key information in a data structure; and

storing the additional cipher key information in the data structure.

9 . The method of claim 1 wherein the cipher key information is associated with a tracking area.

10 . A method for receiving positioning information from a plurality of base stations, comprising:

requesting, receiving, and storing, by a mobile device, a first cipher key associated with a first location as a stored first cipher key;

determining that the mobile device has left a first location and entered a second location that is different from the first location;

requesting, receiving, and storing, by the mobile device, a second cipher key associated with the second location based on the mobile device determining that the mobile device has left the first location and entered the second location;

determining that the mobile device has re-entered the first location;

receiving, at the mobile device, encrypted positioning information from a base station;

decrypting, by the mobile device and based on the mobile device determining that the mobile device has re-entered the first location, the encrypted positioning information with the stored first cipher key to determine decrypted positioning information without the mobile device re-requesting the first cipher key;

measuring, by the mobile device, positioning signals using the decrypted positioning information; and

determining a position of the mobile device based on measurements of the positioning signals.

11 . The method of claim 10 wherein the first location is a first tracking area and the second location is a second tracking area.

12 . The method of claim 10 wherein the first cipher key is associated with a first tracking area identity (TAI) and the second cipher key is associated with a second tracking area identity (TAI).

13 . The method of claim 10 wherein storing the first cipher key includes storing a first valid start time, a first duration time, a first TAI list, and a first time stamp based on when the first cipher key is received in a data structure, and storing the second cipher key includes storing a second valid start time, a second duration time, a second TAI list, and a second time stamp based on when the second cipher key is received in the data structure.

14 . The method of claim 13 further comprising removing the first cipher key from the data structure based at least in part on the first time stamp, or removing the second cipher key from the data structure based at least in part on the second time stamp.

15 . An apparatus, comprising:

a memory;

at least one transceiver;

at least one processor communicatively coupled to the memory and the at least one transceiver, and configured to:

receive first cipher key information including a first cipher key and an indication of a first validity time duration during which the first cipher key is valid;

receive, via the at least one transceiver, an indication of an advance time duration, that is a portion of the first validity time duration, during which a cipher key request is transmitted in order to receive second cipher key information, including a second cipher key, before a second validity time during which the second cipher key is valid;

transmit a first cipher key request prior to the advance time duration;

receive, in response to transmitting the first cipher key request prior to the advance time duration, a response that includes the first cipher key information without including the second cipher key information;

transmit a second cipher key request within the advance time duration; and

receive, in response to transmitting the second cipher key request within the advance time duration, a response that includes the second cipher key information.

16 . The apparatus of claim 15 wherein the at least one processor is further configured to determine a random time within the advance time duration and to transmit the cipher key request based at least in part on the random time.

17 . The apparatus of claim 15 wherein the at least one processor is further configured to receive the cipher key information via one or more non-access stratum (NAS) messages.

18 . The apparatus of claim 15 wherein the advance time duration is equal to a pre-established timer value in a communication system.

19 . The apparatus of claim 18 wherein the pre-established timer value is based on a T3512 timer.

20 . The apparatus of claim 15 wherein the at least one processor is further configured to receive additional cipher key information in response to transmitting the cipher key request within the advance time duration.

21 . The apparatus of claim 20 wherein the at least one processor is further configured to:

receive an encrypted positioning system information block; and

decrypt the encrypted positioning system information block based at least in part on the additional cipher key information.

22 . The apparatus of claim 20 wherein the at least one processor is further configured to:

store the cipher key information in a data structure; and

store the additional cipher key information in the data structure.

23 . The apparatus of claim 15 wherein the cipher key information is associated with a tracking area.

24 . An apparatus, comprising:

a memory;

at least one transceiver;

at least one processor communicatively coupled to the memory and the at least one transceiver, and configured to:

request, receive, and store a first cipher key associated with a first location as a stored first cipher key;

determine that the mobile device has left a first location and entered a second location that is different from the first location;

request, receive, and store a second cipher key associated with the second location based on the mobile device determining that the mobile device has left the first location and entered the second location;

determine that the mobile device has re-entered the first location;

receive encrypted positioning information from a base station;

decrypt, based on the mobile device determining that the mobile device has re-entered the first location, the encrypted positioning information with the stored first cipher key to determine decrypted positioning information without re-requesting the first cipher key;

measure positioning signals, received via the at least one transceiver, using the decrypted positioning information; and

determine a position of the apparatus based on measurements of the positioning signals.

25 . The apparatus of claim 24 wherein the first location is a first tracking area and the second location is a second tracking area.

26 . The apparatus of claim 24 wherein the first cipher key is associated with a first tracking area identity (TAI) and the second cipher key is associated with a second tracking area identity (TAI).

27 . The apparatus of claim 24 wherein the at least one processor is further configured to store a first valid start time, a first duration time, a first TAI list, and a first time stamp based on when the first cipher key is received in a data structure, and store a second valid start time, a second duration time, a second TAI list, and a second time stamp based on when the second cipher key is received in the data structure.

28 . The apparatus of claim 27 wherein the at least one processor is further configured to remove the first cipher key from the data structure based at least in part on the first time stamp, or remove the second cipher key from the data structure based at least in part on the second time stamp.