Contention window adjustment in unlicensed cellular radio network

1. A method carried out in a base station of a cellular radio communications network configured to transmit data to a terminal in an unlicensed radio band, comprising the steps of:

determining a contention window, within which to transmit data between the base station and a terminal;

receiving a signal from the terminal, comprising an indication of occupancy of a radio channel, as detected by the terminal;

establishing a metric on a number of Not Acknowledged (NACK) feedback values received on the radio channel in respect to a predetermined period of time;

comparing the indication of occupancy to a first threshold value

determining that the indication of occupancy meets or exceeds the first threshold value;

comparing the metric with a second threshold value;

determining that the metric meets or exceeds the second threshold;

in response to the determining that the indication of occupancy meets or exceeds the first threshold value and the determining that the metric meets or exceeds the second threshold, increasing the contention window size; and

transmitting data to the terminal within the increased contention window.

2. The method of claim 1 , wherein the indication of occupancy represents measured signal strength on the radio channel in the terminal within a measurement period.

3. The method of claim 1 , further comprising:

establishing a second metric on a degree of operation by the base station on the radio channel;

comparing the second metric with a third threshold value; and

in response to determining that the second metric meets or exceeds the second threshold, further increasing the contention window size.

4. The method of claim 1 , wherein the step of establishing a metric on a number of NACK feedback values received on the radio channel in respect to a predetermined period of time includes measuring a number of busy slots or periods on the radio channel within an observation window.

5. A base station of a cellular radio communications network configured to operate in an unlicensed radio band, the base station comprising:

a radio transceiver connected to an antenna;

a memory holding a computer program code; and

a controller including a processor, wherein the computer program code controls the processor to:

determine a size for a contention window, within which the base station may transmit data from the transceiver to a radio terminal operating in the network;

receive a signal from the terminal, comprising an indication of occupancy of a radio channel, as detected by the terminal;

establish a metric on a number of Not Acknowledged (NACK) feedback values received on the radio channel in respect to a predetermined period of time;

compare the indication of occupancy to a first threshold value;

determine that the indication of occupancy meets or exceeds the first threshold value;

compare the metric with a second threshold value;

determine that the metric meets or exceeds the second threshold;

in response to the determination that the indication of occupancy meets or exceeds the first threshold value and the determination that the metric meets or exceeds the second threshold, increase the contention window size; and

transmit data to the terminal within the increased contention window.

6. The base station of claim 5 , wherein the indication of occupancy represents measured signal strength on the radio channel in the terminal within a measurement period.

7. The base station of claim 5 , wherein the computer program code controls the processor to:

establish a second metric on a degree of operation by the base station on the radio channel;

compare the second metric with a third threshold value; and

in response to the determination that the second metric meets or exceeds the second threshold, further increase the contention window size.

8. The base station of claim 5 , wherein the establishing a metric on a number of NACK feedback values received on the radio channel in respect to a predetermined period of time includes measuring a number of busy slots or periods on the radio channel within an observation window.

9. A non-transitory machine-readable storage medium having instructions stored thereon, that, when executed by a base station of a cellular radio communications network, cause the base station to perform steps comprising:

determining a contention window, within which to transmit data between the base station and a terminal;

receiving a signal from the terminal, comprising an indication of occupancy of a radio channel, as detected by the terminal;

establishing a metric on a number of Not Acknowledged (MACK) feedback values received on the radio channel in respect to a predetermined period of time;

comparing the indication of occupancy to a first threshold value

determining that the indication of occupancy meets or exceeds the first threshold value;

comparing the metric with a second threshold value;

determining that the metric meets or exceeds the second threshold;

in response to the determining that the indication of occupancy meets or exceeds the first threshold value and the determining that the metric meets or exceeds the second threshold, increasing the contention window size; and

transmitting data to the terminal within the increased contention window.

10. The non-transitory machine-readable storage medium of claim 9 , wherein the indication of occupancy represents measured signal strength on the radio channel in the terminal within a measurement period.

11. The non-transitory machine-readable storage medium of claim 9 , further comprising:

establishing a second metric on a degree of operation by the base station on the radio channel;

comparing the second metric with a third threshold value; and

in response to the determination that the second metric meets or exceeds the second threshold, further increasing the contention window size.

12. The non-transitory machine-readable storage medium of claim 9 , wherein the establishing a metric on a number of HACK feedback values received on the radio channel in respect to a predetermined period of time includes measuring a number of busy slots or periods on the radio channel within an observation window.