Wake-up radio system

1. A radio system comprising:

a slave comprising a short-range transmitter and a wake-up radio receiver,

wherein the slave is configured to have a sniff sub-rating with a master, the master being configured to wake up the slave via the wake-up radio receiver, wherein the master and slave define a sniff period (T sniff ) comprising a period between successive sniff event times, wherein the slave is scheduled to wake-up once every predetermined number of sniff periods, the predetermined number being greater than one;

wherein when the master initiates communication with the slave prior to the slave's scheduled wake-up time by transmitting a wakeup message to the slave, a latency associated with the slave's response to the wakeup message does not exceed the sniff period (T sniff ), and

wherein when the slave initiates communication with the master prior to the slave's scheduled wake-up time, a latency associated with the slave's communication with the master does not exceed the sniff period (T sniff ).

2. The radio system of claim 1 , wherein the sniff sub-rating allows the slave and master to establish a latency period of about 1.28 s.

3. The radio system of claim 1 , wherein when the slave wakes-up once every predetermined number of sniff periods, the slave resynchronizes a clock associated with the slave with a clock associated with the master.

4. The radio system of claim 1 , wherein the master is configured to wake up the slave via the wake-up radio receiver so that during the next sniff period the slave wakes up and communicates with the master.

5. The radio system of claim 1 , wherein the predetermined number of sniff periods comprise a subrating period (T subrate ).

6. The radio system of claim 1 , further comprising the master, the master comprising a short-range transmitter to communicate with the the slave after the slave has been woken up via the wake up radio receiver.

7. The radio system of claim 1 , wherein the master further comprises a wake-up transmitter to send the wake-up receiver a wake up message to alert the slave to respond at a next sniff period.

8. The radio system of claim 1 , wherein the master comprises a mobile telecommunications device.

9. The radio system of claim 1 , wherein the slave comprises a Bluetooth accessory.

10. The radio system of claim 9 , wherein the slave comprises one of a headset or a watch.

11. The radio system of claim 1 , wherein the slave connects to the master over a Bluetooth network.

12. The radio system of claim 1 , wherein the slave is configured to achieve a standby current of about 1 μA with a latency of about 1 s.

13. A mobile device comprising:

a wake-up transmitter to initiate communication with slave device by sending a wake-up message to the slave device to wake-up the slave device prior to the slave device's scheduled wake-up time such that the slave device responds to the mobile device during the next sniff interval, wherein the slave device has a sniff sub-rating with the mobile device such that the slave device is scheduled to wake-up once every predetermined number of sniff intervals, the predetermined number being greater than one, wherein when the slave device initiates communication with the master prior to the slave device's scheduled wake-up time, the slave device communicates with the master during the next sniff interval; and

a short-range transmitter to communicate with the slave device during the next sniff interval once the slave device has been woken up.

14. The radio system of claim 13 , wherein the mobile device is configured to communicate with the slave device and to send the wake-up message to the slave device over a Bluetooth network.

15. The radio system of claim 13 , wherein the wake up transmitter is a uni-directional radio device.

16. The radio system of claim 13 , wherein the wake-up transmitter and the short-range transmitter comprise common hardware components to form a unitary transmitter.

17. A method of establishing communication between a master device and a slave device over a short-range network, the method comprising:

establishing a sniff period between the master device and the slave device; and

establishing a subrating period between the master device and the slave device, wherein the subrating period is greater than the sniff period, the slave device being scheduled to wake-up once every subrating period;

wherein when the master device initiates communication with the slave device by sending a wakeup message to the slave device causing the slave device to wake up prior to the slave device's scheduled wake-up time, the slave device communicates with the master device during the next sniff period, and

wherein when the slave device initiates communication with the master device prior to the slave's scheduled wake-up time, the slave device communicates with the master device during the next sniff period.

18. The method of claim 17 , wherein the sending a wakeup message comprises a wake-up transmitter associated with the master device sending a wake-up message to a wake-up receiver associated with the slave device so that when the wake-up receiver receives the wake-up message, the slave device communicates with the master during the next sniff period.

19. The method of claim 17 , wherein when the slave device wakes-up once every subrating period, the slave device resynchronizes a clock associated with the slave device with a clock associated with the master device.

20. The method of claim 17 , wherein the sending a wakeup message comprises causing the master device to wake-up the slave device using a wake-up sequence that is unique to the slave device.