Terminal device, method and system for coordinating relay node access in a wireless telecommunications system

1. A terminal device for use with a wireless telecommunications system comprising a base station and a plurality of relay nodes, the terminal device comprising:

a transmitter;

a receiver; and

circuitry configured to

select a first relay node from the plurality of relay nodes and control the transmitter and receiver to exchange signals with the base station via the first relay node;

measure a signal characteristic associated with the first relay node and compare the measured signal characteristic with a predetermined threshold value;

control the transmitter and receiver to continue to exchange signals with the base station via the first relay node in a case that the measured signal characteristic is greater than the predetermined threshold value; and

perform a procedure for selecting a second relay node from the plurality of relay nodes via which the transmitter and receiver may exchange signals with the base station in a case that the measured signal characteristic is less than the predetermined threshold value, wherein

the procedure for selecting the second relay node includes performing measurements of a characteristic of a discovery signal received from each of the plurality of relay nodes at the receiver, and

the circuitry is configured to control the transmitter to transmit a discovery signal initiation message to each of the plurality of relay nodes instructing each of the plurality of relay nodes to transmit the discovery signal in the case that the measured signal characteristic associated with the first relay node is determined to be less than the predetermined threshold value.

2. The terminal device of claim 1 , wherein

the discovery signal is transmitted periodically by each of the plurality of relay nodes.

3. The terminal device of claim 1 , wherein

the circuitry is configured to select a second relay node and control the transmitter and receiver to exchange signals with the base station via the selected second relay node based on the measurements.

4. The terminal device of claim 1 , wherein

the predetermined threshold value is greater than a first value of a signal characteristic associated with the first relay node below which the circuitry determines that at least one of the transmitter and receiver cannot exchange signals with the first relay node.

5. The terminal device of claim 4 , wherein

the predetermined threshold value is greater than the first value by a predetermined amount.

6. The terminal device of claim 4 , wherein

the receiver is configured to receive the predetermined amount by which the predetermined threshold value is greater than the first threshold value from one of the base station or first relay node.

7. The terminal device of claim 1 , wherein

the receiver is configured to receive the predetermined threshold value from one of the base station or first relay node.

8. The terminal device of claim 1 , wherein

the measured signal characteristic associated with the first relay node is a ProSe Communication 5 (PC5) Device-to-Device (D2D) Reference Signal Received Power (RSRP).

9. The terminal device of claim 1 , wherein

the measured signal characteristic of the discovery signal transmitted by each of the plurality of relay nodes is a ProSe Communication 5 (PC5) Device-to-Device (D2D) Reference Signal Received Power (RSRP).

10. The terminal device of claim 1 , wherein

at least one of the plurality of relay nodes is another terminal device.

11. A method of operating a terminal device for use with a wireless telecommunications system comprising a base station and a plurality of relay nodes, the terminal device comprising a transmitter and a receiver, the method comprising:

selecting a first relay node from the plurality of relay nodes and controlling the transmitter and receiver to exchange signals with the base station via the first relay node;

measuring a signal characteristic associated with the first relay node and comparing the measured signal characteristic with a predetermined threshold value;

controlling the transmitter and receiver to continue to exchange signals with the base station via the first relay node in a case that the measured signal characteristic is greater than the predetermined threshold value;

performing a procedure to select a second relay node from the plurality of relay nodes via which the transmitter and receiver may exchange signals with the base station in a case that the measured signal characteristic is less than the predetermined threshold value, wherein performing the procedure to select the second relay node includes performing measurements of a characteristic of a discovery signal received from each of the plurality of relay nodes at the receiver, and

controlling the transmitter to transmit a discovery signal initiation message to each of the plurality of relay nodes in the case that the measured signal characteristic associated with the first relay node is determined to be less than the predetermined threshold value, the discovery signal initiation message instructing each of the plurality of relay nodes to transmit the discovery signal.

12. The method of claim 11 , wherein

the discovery signal is transmitted periodically by each of the plurality of relay nodes.

13. The method of claim 11 , wherein

the measured signal characteristic associated with the first relay node is a ProSe Communication 5 (PC5) Device-to-Device (D2D) Reference Signal Received Power (RSRP).

14. The method of claim 11 , wherein

the measured signal characteristic of the discovery signal transmitted by each of the plurality of relay nodes is a ProSe Communication 5 (PC5) Device-to-Device (D2D) Reference Signal Received Power (RSRP).

15. A user equipment (UE) for use with a wireless telecommunications system comprising a base station and a plurality of other UEs, the terminal device comprising:

a transmitter;

a receiver; and

circuitry configured to

select a first UE from the plurality of other UEs and control the transmitter and receiver to exchange signals with the base station via the first UE;

measure a ProSe Communication 5 (PC5) Device-to-Device (D2D) Reference Signal Received Power (RSRP) associated with the first UE and compare the measured PC5 D2D RSPS with a predetermined threshold value;

control the transmitter and receiver to continue to exchange signals with the base station via the first UE in a case that the measured PC5 D2D RSPS is greater than the predetermined threshold value; and

perform a procedure for selecting a second UE from the plurality of other UEs via which the transmitter and receiver may exchange signals with the base station in a case that the measured PC5 D2D RSPS is less than the predetermined threshold value, wherein

the procedure for selecting the second UE includes performing measurements of PC5 D2D RSPS of a discovery signal received from each of the plurality of other UEs at the receiver, and

the circuitry is configured to control the transmitter to transmit a discovery signal initiation message to each of the plurality of other UEs instructing each of the plurality of other UEs to transmit the discovery signal in the case that the measured PC5 D2D RSPS associated with the first UE is determined to be less than the predetermined threshold value.