Wireless communications system and method

1. A wireless communications system, comprising:

a base station;

a plurality of relay devices; and

a terminal device configured to:

transmit one or more access request messages of a first type to request uplink resources from the base station, and

transmit an access request message of a second type if no response to the transmitted access request messages of the first type is received from the base station, wherein

the base station is responsive to an access request message of the first type received from the terminal device to transmit an allocation of uplink resources to the terminal device,

the plurality of relay devices are each responsive to an access request message of the second type received from the terminal device to transmit a relayed access request message to the base station to request the base station to allocate uplink resources to the terminal device,

the relayed access request messages include information that triggers the base station to designate a first relay device of the plurality of relay devices to serve the terminal device and to reject any undesignated relay devices of the plurality of relay devices by transmitting a negative acknowledgement message including a NACK indication to the undesignated relay devices; and

the base station is responsive to the relayed access request message from the first relay device to transmit an allocation of uplink resources directly to the terminal device.

2. The wireless communications system according to claim 1 ,

wherein the terminal device is further configured to transmit uplink data to the first relay device on the allocated uplink resources; and

wherein the first relay device is configured to relay to the base station the uplink data received from the terminal device.

3. The wireless communications system according to claim 1 ,

wherein the terminal device is further configured to:

repeatedly transmit access request messages of the first type at successively higher power levels until a response is received from the base station or until a maximum power level is reached; and

transmit the access request message of the second type if no response to the access request message of the first type at the maximum power level is received from the base station.

4. The wireless communications system according to claim 3 ,

wherein the access request message of the second type is transmitted at the maximum power level.

5. The wireless communications system according to claim 3 ,

wherein the maximum power level for transmitting the access request messages of the first type is less than a maximum transmission power of the terminal device.

6. The wireless communications system according to claim 1 ,

wherein the first relay device is configured to determine an identifier for the terminal device from which the access request message of the second type was received and include the identifier in the relayed access request message transmitted to the base station; and

wherein the base station uses the identifier to transmit an allocation of uplink resources to the terminal device.

7. The wireless communications system according to claim 6 ,

wherein the access request messages are transmitted on a random access channel; and

wherein the first relay device is further configured to determine an identifier for the terminal device from the time and/or frequency resource within the random access channel used to transmit the access request message of the second type.

8. The wireless communications system according to claim 1 , wherein the first relay device is further configured to:

measure a received signal power of the access request message of the second type received from the terminal device; and

set power control information in the relayed access request message for controlling a power level of a subsequent transmission from the terminal device to the first relay device on the allocated uplink resources.

9. The wireless communications system according to claim 8 ,

wherein the power control information specifies a power offset from the received signal power of the access request message of the second type.

10. The wireless communications system according to claim 8 , wherein the allocation of uplink resources transmitted from the base station to the terminal device comprises the power control information for controlling the transmission power of the subsequent transmission from the terminal device to the first relay device.

11. The wireless communications system according to claim 1 ,

wherein the first relay device is configured to:

measure a propagation time delay between the terminal device and the first relay device of the access request message of the second type;

determine, based on the propagation time delay, a required timing advance offset for a subsequent transmission from the terminal device to the first relay device so that a receive time of the subsequent transmissions at the first relay device is synchronised with a receive time of transmissions from other terminal devices; and

specify said timing advance offset in the relayed access request message.

12. The wireless communications system according to claim 11 ,

wherein the allocation of uplink resources transmitted from the base station to the terminal device comprises the timing advance offset for controlling the timing of a subsequent transmission from the terminal device to the first relay device.

13. The wireless communications system according to claim 1 ,

wherein the first relay device is responsive to an access request message of the second type received from the terminal device to request the base station to allocate uplink resources to the first relay device to transmit the relayed access request message;

wherein the base station is responsive to the request from the base station to allocate uplink resources to the first relay device; and

wherein the first relay device is configured to transmit the relayed access request message to the base station using the uplink resources allocated to the first relay device by the base station.

14. The wireless communications system according to claim 1 ,

wherein the base station is responsive to receiving relayed access request messages from the plurality of relay devices in relation to the same access request message of the second type to:

select one of the plurality of relay devices to serve the terminal device; and

inform the selected relay device that it is to serve as the first relay device for the terminal device.

15. The wireless communications system according to claim 14 ,

wherein the relayed access request message comprises an indication of the received power level of the access request message of the second type; and

wherein the base station is configured to select as the serving relay device the first relay device having received the access request message of the second type at the highest power level.

16. The wireless communications system according to claim 15 ,

wherein if two or more of the plurality of relay devices received the access request message of the second type at substantially the same power level, the base station is further configured to select as the serving relay device the first relay device, of those having received the access request message of the second type at substantially the same power level, which is currently serving the fewest terminal devices.

17. The wireless communications system according to claim 14 ,

wherein the undesignated relay devices are those of the plurality of relay devices not selected to serve the terminal device.

18. A method of wirelessly communicating data from a terminal device to a base station via a first relay device of a plurality of relay devices, the method comprising:

transmitting one or more access request messages of a first type from the terminal device to request uplink resources from the base station;

transmitting an access request message of a second type from the terminal device, via the plurality of relay devices, to the base station if no response to the transmitted access request messages of the first type is received at the terminal device from the base station;

transmitting from the base station an allocation of uplink resources to the terminal device when an access request message of the first type is received at the base station from the terminal device;

transmitting from each of the plurality of relay devices a relayed access request message to the base station to request the base station to allocate uplink resources to the terminal device when an access request message of the second type is received at each of the plurality of relay devices from the terminal device; and

transmitting from the base station an allocation of uplink resources directly to the terminal device in response to an access request message relayed to the base station from a first relay device of the plurality of relay devices, wherein the access request messaged relayed from the plurality of relay devices include information that triggers the base station to designate the first relay device to serve the terminal device and to reject any undesignated relay devices by transmitting a negative acknowledgement message including a NACK indication to the undesignated relay devices.