Dynamic control of PRACH format based on RRC-connection-establishment-failure history

1. A method for dynamically controlling random-access-request transmission in a cell of a wireless communication system, the method comprising:

determining an extent to which the cell has experienced access blocks due to connection-request communication failure; and

using the determined extent as a basis to dynamically set a physical random access channel (PRACH) format of the cell, wherein the PRACH format defines one or more configuration settings for random-access-request transmission by user equipment devices (UEs) in the cell and correlates with an effective radius of the cell, and wherein using the determined extent as a basis to dynamically set the PRACH format of the cell comprises (i) determining, by referring to mapping data that maps various extents of access blocks respectively to associated PRACH formats, a PRACH format corresponding with the determined extent and (ii) based on the determining of the PRACH format, setting the PRACH format of the cell to be the determined PRACH format,

wherein the mapping data maps progressively higher extents of access blocks respectively to PRACH formats that correlate with progressively shorter effective cell radii.

2. The method of claim 1 , wherein the cell is provided by an access node, wherein the access node supports access attempts by UEs, each access attempt by a UE respectively including (i) the UE engaging in random access signaling with the access node and (ii) the UE then engaging in up to a maximum allowed number of connection-request transmissions to the access node in an effort to ensure successful receipt by the access node of a connection request from the UE, wherein an access block occurs when the access node does not successfully receive connection-request transmission from the UE through the maximum allowed number connection-request transmissions by the UE.

3. The method of claim 1 , wherein the one or more configuration settings comprise at least one configuration setting selected from the group consisting of:

(i) cyclic-shift interval to be used for establishing a set of preamble sequences from which to randomly select a preamble sequence to be transmitted,

(ii) cyclic-prefix length to be used for transmission of the randomly selected preamble sequence,

(iii) number of repetitions of the randomly selected preamble sequence to include in the random-access-request transmission, and

(iv) guard period to follow the number of repetitions of the randomly selected preamble sequence.

4. The method of claim 1 , wherein the mapping data maps a first extent of access blocks to PRACH format B4 that correlates with a first effective cell radius, and the mapping data maps a second extent of access blocks to PRACH format B3 that correlates with a second effective cell radius, the second extent being greater than the first extent, and the second effective cell radius being shorter than the first effective cell radius.

5. The method of claim 1 , wherein the cell is set with default PRACH format that correlates with a first effective cell radius, and wherein using the determined extent as a basis to dynamically set the PRACH format of the cell comprises:

determining that the determined extent is at least as high as a predefined threshold extent; and

responsive to at least the determining that the determined extent is at least as high as the predefined threshold extent, adjusting the PRACH format of the cell from the default PRACH format to a modified PRACH format that correlates with a second effective cell radius that is shorter than the first effective cell radius.

6. The method of claim 1 , wherein the determined extent to which the cell has experienced the access blocks is a rate of access blocks experienced in the cell.

7. The method of claim 1 , wherein determining the extent to which the cell has experienced the access blocks comprises an action selected from the group consisting of (i) tracking occurrences of the access blocks in the cell over time and determining the extent as a most recent extent and (ii) tracking occurrences of the access blocks in the cell on a per time of day basis to facilitate a prediction of an extent of access blocks in the cell.

8. The method of claim 1 , wherein the cell is provided by an access node, and wherein the method is carried out by the access node.

9. The method of claim 1 , wherein the cell is provided by an access node, and wherein the method is carried out by a computing system external to the access node,

wherein using the determined extent as a basis to dynamically set the PRACH format of the cell comprises the computing system using the determined extent as a basis to determine the PRACH format, and the computing system transmitting to the access node a control signal specifying the determined PRACH format, the control signal being interpretable by the access node to cause the access node to set the PRACH format.

10. The method of claim 1 , wherein the cell is provided by an access node, and wherein setting the PRACH format of the cell comprises setting the PRACH format at the access node, wherein the access node broadcasts a control signal that specifies the set PRACH format.

11. The method of claim 10 , wherein the control signal specifies the set PRACH format as a prach-ConfigIndex parameter value.

12. A method for dynamically controlling random-access-request transmission in a cell of a wireless communication system, the method comprising:

determining a rate at which the cell has experienced access blocks due to connection-request communication failure; and

using the determined rate as a basis to dynamically configure a set of one or more operational settings for random-access-request transmission in the cell, wherein the set of one or more operational settings correlates with an effective radius of the cell, and wherein using the determined rate as a basis to dynamically set a physical random access channel (PRACH) format of the cell comprises (i) determining, by referring to mapping data that maps various rates of access blocks respectively to associated PRACH formats, a PRACH format corresponding with the determined rate and (ii) based on the determining of the PRACH format, setting the PRACH format of the cell to be the determined PRACH format,

wherein the mapping data maps progressively higher rates of access blocks respectively to PRACH formats that correlate with progressively shorter effective cell radii.

13. A computing system operable to control random-access-request transmission in a cell of a wireless communication system, the computing system comprising:

a processing unit;

non-transitory data storage; and

program instructions stored in the non-transitory data storage and executable by the processing unit to carry out operations including:

determining an extent to which the cell has experienced access blocks due to connection-request communication failure; and

using the determined extent as a basis to dynamically set a physical random access channel (PRACH) format of the cell, wherein the PRACH format defines one or more configuration settings for random-access-request transmission by user equipment devices (UEs) in the cell and correlates with an effective radius of the cell, and wherein using the determined extent as a basis to dynamically set the PRACH format of the cell comprises (i) determining, by referring to mapping data that maps various extents of access blocks respectively to associated PRACH formats, a PRACH format corresponding with the determined extent and (ii) based on the determining of the PRACH format, setting the PRACH format of the cell to be the determined PRACH format,

wherein the mapping data maps progressively higher extents of access blocks respectively to PRACH formats that correlate with progressively shorter effective cell radii.

14. The computing system of claim 13 , wherein the cell is provided by an access node, wherein the access node supports access attempts by user equipment devices (UEs), each access attempt by a UE respectively including (i) the UE engaging in random access signaling with the access node and (ii) the UE then engaging in up to a maximum allowed number of connection-request transmissions to the access node in an effort to ensure successful receipt by the access node of a connection request from the UE, wherein an access block occurs if the access node does not successfully receive connection-request transmission from the UE through the maximum allowed number connection-request transmissions by the UE.

15. The computing system of claim 14 , wherein the computing system is provided at the access node.

16. The computing system of claim 13 , wherein the cell is set with default PRACH format that correlates with a first effective cell radius, and wherein using the determined extent as a basis to dynamically set the PRACH format of the cell comprises:

determining that the determined extent is at least as high as a predefined threshold extent; and

responsive to at least the determining that the determined extent is at least as high as the predefined threshold extent, adjusting the PRACH format of the cell from the default PRACH format to a modified PRACH format that correlates with a second effective cell radius that is shorter than the first effective cell radius.