Long term evolution (LTE) system operating in an unlicensed spectral band with active network discovery and optimization of the unlicensed channels

1. A method for assigning a percentage of time to each radio node (RN) in a plurality of RNs that belong to a first small cell radio access network (RAN) having a central controller operatively coupled to each of the RNs the percentage of time being a percentage of time during which each of the RNs are able to occupy a channel shared by nodes employing a different radio access technology (RAT) from a RAT employed by the first small cell RAN, comprising:

(i) for each repetitive period defined by a time-division multiplexing access (TDMA) technique during which the RNs share a channel with one or more nodes that employ the different RAT, assigning, with the central controller, a default occupancy percentage of time periods to each of the RNs during which the RNs are able to occupy the channel;

(ii) determining, with the central controller, if the default occupancy percentage for a first RN of the RNs is able to be increased without violating one or more co-existence principles pre-established for the RAT employed by the RNs in the first small cell RAN and the different RAT employed by the one or more nodes;

(iii) assigning, with the central controller, an increased occupancy percentage to the first RN if it is determined that the default occupancy percentage for the first RN is able to be increased without violating the one or more co-existence principles; and

(iv) sequentially repeating (ii)-(iii) for each remaining one of the RNs in the first small cell RAN.

2. The method of claim 1 , wherein the default occupancy percentage that is assigned to at least one of the RNs is determined by using a channel occupancy decision rule that would be employed if each of the RNs were to employ the different RAT.

3. The method of claim 1 , wherein the one or more co-existence principles ensure that the RNs should not interfere with the one or more nodes employing the different RAT any more than would another node employing the different RAT.

4. The method of claim 1 , wherein the TDMA technique employs a Carrier Sensing Adaptive Transmission (CSAT) algorithm.

5. The method of claim 1 , wherein the first small cell RAN operates in accordance with Long Term Evolution—Unlicensed (LTE-U) and the shared channel is an unlicensed channel.

6. The method of claim 1 , further comprising detecting an external network topology of the one or more nodes that employ the different RAT.

7. The method of claim 6 , wherein the external network topology is detected using radio environment monitoring (REM) scans.

8. The method of claim 6 , wherein the channel is also shared by a second RAN that operates in accordance with the RAT employed by the first small cell RAN, the second RAN being controlled by a different network operator than the first small cell RAN, and further comprising using the central controller to determine an external network topology of external RNs in the second RAN and which are able to interfere with one or more of the RNs in the first small cell RAN.

9. The method of claim 8 , wherein determining the default occupancy percentage and any increases in the default occupancy percentage are based at least in part on the external network topology that is determined for the one or more nodes that employ the different RAT and on the external network topology that is determined for the external RNs in the second RAN.

10. The method of claim 8 , wherein determining the external network topology of the external RNs in the second RAN includes using the central controller to sequentially cause each of the RNs in the first small cell RAN to be OFF during a normally ON portion of the time periods so that the RNs are able to detect transmissions from the external RNs in the second RAN while the RNs in the first small cell RAN are OFF.

11. The method of claim 9 , further comprising determining if a link exists between one of the one or more nodes that employ the different RAT and the external RNs in the second RAN such that they are able to interfere with one another.

12. The method of claim 11 , wherein determining if the link exists includes using the central controller to select at least one pair of the RNs that are each able to detect transmissions from at least one common one of the external RNs and at least one common one of the one or more nodes that employs the different RAT and using one of the RNs in the at least one pair to transmit while varying its transmission start time and using the other of the RNs in the at least one pair to detect signals from the one or more nodes that employs the different RAT, wherein the determining if the link exists is based on whether a transmission duration of the one or more nodes that employs the different RAT varies when the transmission start time of the RN in the at least one pair that transmits is varied.

13. The method of claim 1 , further comprising adjusting, without changing the occupancy percentages that are assigned, a transmission start time for the first RN during the time periods so that an overlapping period of a transmission time for the first RN with any transmissions from the one or more nodes that employ the different RAT and that are able to interfere with the first RN is reduced.

14. The method of claim 1 , wherein the one or more nodes employing the different RAT are Wi-Fi Access Points.

15. A centralized controller operable in a cell in a first small cell radio access network (RAN), comprising:

one or more processors;

a network interface operatively coupled to the one or more processors and arranged for bidirectional communications with a plurality of radio nodes (RNs) in the first small cell RAN; and

memory operatively coupled to the one or more processors, the memory storing computer-readable instructions which, when executed by the one or more processors, implement a method for assigning a percentage of time to each of the RNs in the plurality of RNs, the percentage of time being a percentage of time during which each of the RNs are able to occupy a channel shared by nodes employing a different radio access technology (RAT) from a RAT employed by the first small cell RAN, comprising:

(i) for each repetitive period defined by a time-division multiplexing access (TDMA) technique during which the RNs share a channel with one or more nodes that employ the different RAT, assigning a default occupancy percentage of time periods to each of the RNs during which the RNs are able to occupy the channel;

(ii) determining if the default occupancy percentage for a first RN of the RNs is able to be increased without violating one or more co-existence principles pre-established for the RAT employed by the RNs in the first small cell RAN and the different RAT employed by the one or more nodes;

(iii) assigning an increased occupancy percentage to the first RN if it is determined that the default occupancy percentage for the first RN is able to be increased without violating the one or more co-existence principles; and

(iv) sequentially repeating (ii)-(iii) for each remaining one of the RNs in the first small cell RAN.

16. The centralized controller of claim 15 , wherein the computer-readable instructions comprise instructions that, when executed by the one or more processors, cause the centralized controller to assign the default occupancy percentage to at least one of the RNs that is determined by using a channel occupancy decision rule that would be employed if each of the RNs were to employ the different RAT.

17. The centralized controller of claim 15 , wherein the computer-readable instructions comprise instructions that, when executed by the one or more processors, cause the centralized controller to apply the one or more co-existence principles that ensure that the RNs should not interfere with the one or more nodes employing the different RAT any more than would another node employing the different RAT.

18. The centralized controller of claim 15 , wherein the channel is also shared by a second small cell RAN that operates in accordance with the RAT employed by the first small cell RAN, the second small cell RAN being controlled by a different network operator than the first small cell RAN, and wherein the computer-readable instructions comprise instructions that, when executed by the one or more processors, cause the centralized controller to:

detect an external network topology of the one or more nodes that employ the different RAT; and

determine an external network topology of external RNs in the second small cell RAN and which are able to interfere with one or more of the RNs in the first small cell RAN.

19. The centralized controller of claim 18 , wherein the computer-readable instructions comprise instructions that, when executed by the one or more processors, cause the centralized controller to determine the default occupancy percentage and any increases in the default occupancy percentage based at least in part on the external network topology that is determined for the one or more nodes that employ the different RAT and on the external network topology that is determined for the external RNs in the second small cell RAN.

20. The centralized controller of claim 18 , wherein the computer-readable instructions comprise instructions that, when executed by the one or more processors, cause the centralized controller to determine the external network topology of the external RNs in the second small cell RAN by sequentially causing each of the RNs in the first small cell RAN to be OFF during a normally ON portion of the time periods so that the RNs are able to detect transmissions from the external RNs in the second small cell RAN while the RNs in the first small cell RAN are OFF.