Power saving in soft access point devices

A method and apparatus to save power in a soft access point for a network. If no network traffic is detected for an integral number of TBTT (Target Beacon Transmission Time) intervals immediately prior to a current TBTT interval, and if no network traffic is detected for a first time slot in the current TBTT interval, then the soft access point sends a CTS (Clear-to-Send) packet addressed to itself to quiet the network for a second time slot and enters a low power mode for the second time slot. At the beginning of a third time slot, the soft access point puts itself into an active mode and monitors network traffic.

FIELD OF DISCLOSURE

The present invention relates to wireless communication systems, and more particularly to soft access point devices.

BACKGROUND

Many types of cell phones and mobile devices can be configured to serve as access points for wireless local area networks. For example, if a landline Internet connection is not available, one may configure a cell phone as a hot spot for other devices, such as a laptop, so that the laptop may connect with the Internet. In such situations, it is desirable to efficiently use the battery power of the cell phone so that the wireless local area network may be up and running as long as possible.

SUMMARY

Embodiments of the invention are directed to systems and methods for power saving in soft access point devices.

In one embodiment, a method of operating a soft access point in a wireless network includes monitoring with the soft access point the network for network activity in a first time slot of a current TBTT (Target Beacon Transmission Time) interval; sending with the soft access point a CTS (Clear-To-Send) packet addressed to itself and entering a low power state for a second time slot in the current TBTT interval provided the soft access point detects no network activity for N consecutive TBTT intervals immediately prior to the current TBTT interval, where N is an integer greater than one, and provided the soft access point detects no network activity during the first time slot; and entering an active state of the soft access point at the beginning of a third time slot in the current TBTT interval

In another embodiment, a method of operating a soft access point in a wireless network includes transmitting by the soft access point a frame at the beginning of a current TBTT interval to at least one device in the wireless network to silence transmissions from the at least device during a portion of the current TBTT interval provided the soft access point detects no network activity for N consecutive TBTT intervals immediately prior to the current TBTT interval, where N is an integer greater than one.

In another embodiment, a soft access point in a wireless network includes an antenna; a modem coupled to the antenna; and a processor coupled to the modem. The processor to monitors for network activity detected by the modem in a first time slot of a current TBTT (Target Beacon Transmission Time interval); causes the modem to send a CTS (Clear-To-Send) packet addressed to the soft access point and put itself into a low power state for a second time slot in the current TBTT interval provided the modem detects no network activity for N consecutive TBTT intervals immediately prior to the current TBTT interval, where N is an integer greater than one, and provided the modem detects no network activity during the first time slot; and puts itself into an active state at the beginning of a third time slot in the current TBTT interval.

In another embodiment, instructions stored on a computer readable storage medium cause a processor in a soft access point to perform a procedure comprising monitoring with the soft access point the network for network activity in a first time slot of a current TBTT (Target Beacon Transmission Time interval); sending with the soft access point a CTS (Clear-To-Send) packet addressed to itself and entering a low power state for a second time slot in the current TBTT interval provided the soft access point detects no network activity for N consecutive TBTT intervals immediately prior to the current TBTT interval, where N is an integer greater than one, and provided the soft access point detects no network during the first time slot; and entering an active state of the soft access point at the beginning of a third time slot in the current TBTT interval.

In another embodiment, a soft access point in a wireless network includes means for monitoring, wherein the means for monitoring monitors the network for network activity in a first time slot of a current TBTT (Target Beacon Transmission Time interval); means for transmitting, wherein the means for transmitting transmits a CTS (Clear-To-Send) packet addressed to the soft access point provided the means for monitoring detects no network activity for N consecutive TBTT intervals immediately prior to the current TBTT interval, where N is an integer greater than one, and provided the means for monitoring detects no network activity during the first time slot; and means for changing power mode, wherein the means for changing power mode puts the soft access point into a low power state for a second time slot in the current TBTT interval provided the means for monitoring detects no network activity for N consecutive TBTT intervals immediately prior to the current TBTT interval, and provided the means for monitoring detects no network activity during the first time slot; wherein the means for changing power mode puts the soft access point into an active state at the beginning of a third time slot in the current TBTT interval.

DETAILED DESCRIPTION

The term “embodiments of the invention” does not require that all embodiments of the invention include the discussed feature, advantage or mode of operation.

Embodiments may find widespread application in numerous systems, such as a wireless communication system, and more particularly a cellular phone network. For example,FIG. 1illustrates Wireless Communication System102comprising Base Stations104A,104B, and104C.FIG. 1shows a communication device, labeled106, which may be a mobile cellular communication device such as a so-called smart phone, a tablet, or some other kind of communication device suitable for a wireless communication system. Communication Device106need not be mobile. In the particular example ofFIG. 1, Communication Device106is located within the cell associated with Base Station104C. Arrows108and110pictorially represent the uplink channel and the downlink channel, respectively, by which Communication Device106communicates with Base Station104C.

Communication Device106may serve as an access point to provide an Internet connection for other wireless devices. For example, Communication Device106, Laptop112, and Tablet114form a WLAN (Wireless Local Access Network), with Communication Device106serving as the access point (i.e., hotspot). In this instance, communication device106serves as a soft access point, where it's mode of operation is configured by software. The WLAN may, for example, conform to the IEEE (Institute of Electrical and Electronics Engineers) 802.11g WLAN standard.

FIG. 2illustrates a simplified abstraction of a mobile platform that may find application in Communication Device106. Shown inFIG. 2are Application Processor202, Modem204, Radio Frequency Integrated Circuit (RFIC)206, Power Amplifier208, Radio Frequency (RF) Antenna210, Wireless Local Area Network (WLAN) Module212, Display214, and Memory216. For simplicity, not all components typically found in a mobile platform are illustrated inFIG. 2. The modules illustrated inFIG. 2may comprise one or more discrete integrated circuits. Software stored in Memory216when executed by Application Processor202configures the mobile platform (e.g., Communication Device106) so that it may operate as a soft access point for a WLAN.

When Communication Device106serves as an access point, it periodically transmits Beacon frames at Target Beacon Transmission Time (TBTT) intervals. In an embodiment, Communication Device106saves power when operating as a soft access point by putting itself into a power saving mode (e.g., sleep state) at various time intervals, depending upon the state of the WLAN. Software stored in Memory216configures Application Processor202such that when the WLAN is inactive for a time interval spanning N TBTT intervals, Application Processor202sends a CTS (Clear-To-Send) packet addressed to itself over the WLAN for a period of X milliseconds, and then goes into a power saving mode. Here, N is an integer and X is some positive number, which may be stored in Memory216. By sending itself a CTS packet, Communication Device106takes advantage of the CTS-to-self protection method described in the IEEE 802.11g standard to prevent other clients on the WLAN from transmitting over the medium for some period of time.

Some embodiments may help insure the availability of Communication Device106to other devices on the WLAN as follows. A TBTT interval may be viewed as being divided into four slots, with each time slot equal to 25 milliseconds. When Communication Device106detects inactivity for N consecutive TBTT intervals, at the next TBTT interval it will be available to other stations and will listen during the first time slot to check whether any associated station begins a transmission. If there is no activity detected in the first time slot, Communication Device106sends itself a CTS packet at the beginning of the second slot time and puts itself into a power saving mode for the duration of the second slot time. It will then wake up at the end of the second time slot so that it will be in an active mode for the third time slot. If there is no activity detected for the third time slot, then again it sends a self-CTS packet at the beginning of the fourth time slot and goes into the power saving mode for the duration of the fourth time slot. The Communication Device106will wake itself up at the end of the fourth time slot so as to be available to other stations for the next TBTT interval.

Embodiments are not limited to dividing a TBTT interval into four time slots. More generally, a TBTT interval may be divided into n time slots, where n is an integer, not necessarily equal to four.

FIG. 3illustrates a flow diagram for the above-described embodiment, generalized to where a TBTT interval is divided into an arbitrary number of n time slots. The flow diagram begins with Communication Device106determining if there is any activity for N consecutive TBTT intervals (302). Once N consecutive TBTT intervals have elapsed for which no activity has been detected, an index i for counting time slots is initialized to one (304), and Communication Device106determines whether there is any activity in time slot i for the TBTT interval immediately following the N consecutive TBTT intervals for which no activity was detected (304).

If activity is detected at any time during time slot i (306), then control is brought back to302and the process of detecting whether there is any activity for N consecutive TBTT intervals begins anew; but if no such activity is detected, then the counter index i is tested against n (308). If i=n, then the end of the current TBTT interval has been reached, in which case control is brought to302. But if i<n, then the end of the current TBTT interval has not yet been reached, in which case the counter index i is incremented by one (310), and Communication Device106sends a self CTS packet and enters into a power saving mode for the duration of time slot i (312).

A determination is again made as to whether i=n to determine if the end of the current TBTT interval has been reached (314). If i=n, then control is brought back to302, otherwise, the counter index i is incremented by one (316), Communication Device106exits out of the power saving mode (318), and control is brought back to306.

As a specific example, for a TBTT interval of 100 ms, if n=4 then a TBTT interval is divided into 4 slots of 25 ms duration each. After N consecutive TBTT intervals of no activity, Communication Device106listens during the first 25 ms slot in the N+1 TBTT interval. If there is no activity, then Communication Device106puts itself into a power saving mode for the second 25 ms slot, and causes the WLAN to be quiet during the second 25 ms slot by sending a self-CTS packet. Communication Device106then wakes up and listens during the third 25 ms slot. If no activity is detected during the third 25 ms slot, then Communication Device106puts itself into a power saving mode for the fourth 25 ms slot, and causes the WLAN to be quiet by sending a self-CTS packet. As a result, if no activity is detected during the first and third 25 ms slots, Communication Device106will be in a power saving mode during the second and fourth 25 ms slots.

FIG. 4illustrates a flow diagram for the above-described embodiment. Network activity is monitored during a first time slot of a current TBTT (402). Provided the soft access point detects no network during the first time slot and no network activity for N consecutive TBTT intervals immediately prior to the current TBTT interval (404), the soft access point sends a CTS packet addressed to itself and enters a low power state for a second time slot in the current TBTT interval (406). Otherwise, the soft access point stays in an active state for the second time slot of the current TBTT (408). The soft access point then enters the active state for the third time slot in the current TBTT (410). The network is monitored for activity during the third time slot, and if no network activity is detected during third time slot (412), then the soft access point sends a CTS packet addressed to itself and enters the low power state for a fourth time slot in the current TBTT interval (414). Otherwise, the soft access point stays in the active state during the fourth time slot of the current TBTT (416).

In another embodiment, for the 5 GHz band, a Quiet Information element in Beacon frames or Probe Response frames may be utilized by Communication Device106to put itself into a power saving mode instead of sending a self-CTS packet. The Quiet Information element defines an interval during which no transmission shall occur in the current channel in a BSS (Basic Service Set) or IBSS (Independent Basic Service Set). To ensure that not all quiet intervals have the same timing relationship to TBTT intervals, multiple independent quiet intervals may be scheduled by including multiple Quiet Information elements in Beacon frames or Probe Response frames. That is, more than one quiet interval may be scheduled between two successive Beacon frames.

For the 802.11g specification, a Quiet Information element comprises a number of fields, each an octet in length: an Element ID field, a Length field, a Quiet Count field, a Quiet Period field, a Quiet Duration field, and a Quiet Offset field. An example embodiment may include two Quiet Information elements in a Beacon frame: a first Quiet Information element with a Quiet Offset field set to 25 ms and a second Quiet Information element with a Quiet Offset field set to 75 ms. Each Quiet Information element has a Length field set to 6, a Quiet Count field set to 1 so that a quiet interval will start during the Beacon frame interval starting at the next TBTT interval, a Quiet Period field set to 0 so that there is no periodic quiet intervals, and a Quiet Duration field set to 25 ms.

With the above parameters, the WLAN will be quiet during the second and fourth 25 ms slots, and Communication Device106can put itself into a power saving mode during these time slots.

Accordingly, an embodiment of the invention can include a computer readable media embodying a method for power saving in soft access point devices. Accordingly, the invention is not limited to illustrated examples and any means for performing the functionality described herein are included in embodiments of the invention.