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Mobile broadband [MBB] power management for modern standby platforms

• Article
• 08/24/2021
• 11 minutes to read

In this article

A mobile broadband [MBB] device provides a mobile computer with a wireless data connection to a cellular service. An MBB device supports one or more cellular radio technologies, such as GSM, 3G, CDMA, or LTE. MBB devices in modern standby platforms are all required to provide the same set of power management capabilities and to implement the same general hardware configuration, regardless of the specific cellular technologies supported.

The MBB device is expected to use Universal Serial Bus [USB] to connect to the modern standby platform, and to use software provided by Microsoft for all connectivity and power management operations. Windows includes an inbox Mobile Broadband Class Driver, which provides a standardized interface for mobile broadband data transfer, connection management, and power management for MBB radios. The following guidance focuses on power management for MBB devices that are integrated inside the mobile computer chassis. MBB devices that connect to an external USB port are not discussed.

During modern standby [when the screen is off], the MBB device is expected to be in a low-power state. How much power the MBB device consumes in this low-power state depends on whether the user has provisioned the MBB device on the cellular network. If the MBB device is provisioned and the radio in the device is currently enabled by the user for a data connection, the device should be in a low-power connected-sleep mode in which the device's USB function is in the D2 [suspend] device power state. However, if the MBB device has not been provisioned on the network or the user has disabled the radio for a data connection, the device should be in a low-power radio-off mode. In radio-off mode, the MBB device has only enough power applied to respond to host commands over the USB interface.

The implementation of MBB device power management for a modern standby platform is based on the following:

• The user-controlled radio power state of the MBB device.
• The USB bus suspend and resume transitions.

The MBB device must be able to enter a low-power D2 [suspend] state after the MBB radio is turned off and the USB bus interface enters the suspend state. All sleep and wake power transitions must be signaled over the USB bus. There is no support for out-of-band GPIO signaling to initiate MBB device power transitions or to interrupt the main processor on the System on a Chip [SoC] or core silicon.

If the radio in the MBB device is currently enabled by the user for a data connection, the device must be able to use in-band, USB resume signaling to wake the SoC or core silicon from modern standby. The SoC or core silicon must be able to wake from its lowest power state in response to in-band, USB resume signaling from the MBB device.

Power management modes

The MBB device is expected to support five power-management modes. These modes are a combination of provisioned, connectivity, and radio power states. A transition from one mode to another is communicated to the device directly over the USB bus through commands from the Mobile Broadband Class Driver or USB device state transitions. Transitions between power management modes must not use external GPIO signaling.

The five power-management modes are:

Active

The radio is actively transmitting data or is actively connected to the cellular network.

Connected-sleep

The radio is provisioned on the network and a user account is enabled. The platform is in modern standby. The MBB device is waiting for data from the network to wake up the SoC, and also for events from the SoC. Average across 2G, 3G, LTE, and various DRX modes.

Radio-off

The radio is provisioned on the network, but Windows or the user has turned off the radio in the MBB device.

No-subscription

The user does not have an active subscription.

No-SIM

The device has no SIM.

The following table compares the five power-management modes.