Baseband modem implementing communication protocol stack

1. A baseband modem comprising:

a first subsystem configured to operate when the baseband modem is in a high-power mode and to not operate when the baseband modem is in a low-power mode, the first subsystem comprising:

a first processor;

a first memory, configured to store instructions for implementing a communication protocol stack; and

first baseband processing circuitry;

a second subsystem configured to operate when the baseband modem is in the low-power mode and to not operate when the baseband modem is in the high-power mode, the second subsystem comprising:

a second processor, different from the first processor;

a second memory, different from the first memory, configured to store instructions for implementing a partial version of the communication protocol stack; and

second baseband processing circuitry, different from the first baseband processing circuitry; and

third baseband processing circuitry configured to operate when the baseband modem is in the high-power mode and when the baseband modem is in the low-power mode;

wherein the baseband modem is configured to transition from a sleep mode to the low-power mode in response to expiration of a timer.

2. The baseband modem of claim 1 , further comprising a third memory configured to operate when the baseband modem is in the high-power mode and when the baseband modem is in the low-power mode.

3. The baseband modem of claim 1 , wherein the first subsystem and the second subsystem are configured to not operate when the baseband modem is in the sleep mode.

4. The baseband modem of claim 3 , wherein the baseband modem is configured to utilize discontinuous reception (DRX), wherein the baseband modem is configured to enter the sleep mode during a DRX off period, wherein the baseband modem is configured to enter the low-power mode during a DRX on period, and wherein the baseband modem is configured to enter the high-power mode during an active session.

5. The baseband modem of claim 3 ,

wherein the first processor is configured to cause the baseband modem to transition from the high-power mode to the sleep mode in response to a period of communication inactivity; and

wherein the second processor is configured to:

monitor a control channel for an indication that a payload channel will contain communication traffic directed to the baseband modem;

cause the baseband modem to transition from the low-power mode to the high-power mode in response to detecting the indication; and

cause the baseband modem to transition from the low-power mode to the sleep mode in response to not detecting the indication within a predetermined period of time.

6. The baseband modem of claim 5 , wherein the baseband modem communicates according to a cellular radio access technology that includes the control channel and the payload channel, wherein the control channel is a physical downlink control channel (PDCCH) and the payload channel is a physical downlink shared channel (PDSCH).

7. The baseband modem of claim 1 , wherein the first subsystem operates at a first clock rate and the second subsystem operates at a second clock rate, wherein the first clock rate is higher than the second clock rate.

8. A method for conserving power in a baseband modem, the baseband modem configured to use a cellular radio access technology having a control channel and a payload channel, the method comprising:

at the baseband modem:

operating in a high-power mode using a first set of circuitry, wherein the high-power mode supports full communication traffic by implementing a protocol stack of the cellular radio access technology, the protocol stack being stored in a first memory of the first set of circuitry;

transitioning from operating in the high-power mode to operating in a sleep mode in response to determining a period of communication inactivity, wherein the sleep mode does not support communication traffic;

transitioning from operating in the sleep mode to operating in a low-power mode using a second set of circuitry, in response to expiration of a timer, wherein the second set of circuitry uses less power than the first set of circuitry, wherein the low-power mode supports reception of the control channel by implementing a partial version of the protocol stack stored in a second memory of the second set of circuitry, and wherein the partial version of the protocol stack does not support reception of the payload channel;

disabling the first set of circuitry when transitioning to one of the low-power mode and the sleep mode; and

disabling the second set of circuitry when transitioning to one of the high-power mode and the sleep mode, wherein a third set of circuitry remains enabled in both the low-power mode and the high-power mode.

9. The method of claim 8 , further comprising:

determining, while in the low-power mode, whether the control channel includes an indication that the payload channel will contain communication traffic directed to the baseband modem;

if the control channel includes the indication:

transitioning from the low-power mode to the high-power mode; and

if the control channel does not include the indication:

transitioning from the low-power mode to the sleep mode.

10. The method of claim 9 , wherein the control channel is a physical downlink control channel (PDCCH) and the payload channel is a physical downlink shared channel (PDSCH).

11. The method of claim 9 , wherein the first set of circuitry operates at a higher clock rate than the second set of circuitry.

12. A non-transitory computer-readable memory medium storing instructions executable by a baseband modem to cause the baseband modem to:

operate in a high-power mode utilizing a first set of circuitry, wherein the high-power mode supports full communication traffic by implementing a communication protocol stack stored in a first memory of the first set of circuitry;

transition from operating in the high-power mode to operating in a sleep mode in response to determining a period of communication inactivity, wherein the sleep mode does not support communication traffic; and

transition from operating in the sleep mode to operating in a low-power mode utilizing a second set of circuitry, in response to expiration of a timer, wherein the low-power mode supports reception of a control channel by implementing a partial version of the communication protocol stack stored in a second memory of the second set of circuitry, and wherein the partial version of the protocol stack does not support full communication traffic;

wherein the first set of circuitry is disabled while the baseband modem is in the low-power mode and while the baseband modem is in the sleep mode; and

wherein the second set of circuitry is disabled while the baseband modem is in the high-power mode and while the baseband modem is in the sleep mode, wherein a third set of circuitry remains enabled in both the low-power mode and the high-power mode.

13. The non-transitory computer-readable memory medium of claim 12 , wherein the instructions are further executable to cause the baseband modem to:

determine, while in the low-power mode, whether the control channel includes an indication that a payload channel will contain communication traffic directed to the baseband modem, wherein the low-power mode does not support reception of the payload channel;

if the control channel includes the indication:

transition from the low-power mode to the high-power mode; and

if the control channel does not include the indication:

transition from the low-power mode to the sleep mode.

14. The non-transitory computer-readable memory medium of claim 13 , wherein the baseband modem communicates according to a cellular radio access technology that includes the control channel and the payload channel, wherein the control channel is a physical downlink control channel (PDCCH) and the payload channel is a physical downlink shared channel (PDSCH).

15. The non-transitory computer-readable memory medium of claim 12 , wherein the first set of circuitry operates at a higher clock rate than the second set of circuitry.