Low power receiver for wireless communication

A power saving station integrates a low power consumption wake-up receiver with wideband wireless of main radio. The low power wake-up receiver of power saving station receives a wake-up request signal sent from the wireless network and wakes up the main radio of the station to communicate with the wireless network over wideband frequency channel. The wake-up request signal is transmitted over a narrow band frequency channel and can be addressed to a single station or multiple of stations via OFDMA in wideband channel.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document claims the benefit of priority under 35 U.S.C. § 119(a) and the Paris Convention of International Patent Application No. PCT/CN2016/081548, filed on May 10, 2016. The entire content of the before-mentioned patent application is incorporated by reference as part of the disclosure of this patent document.

BACKGROUND

This patent document relates to wireless communications.

Wireless communication systems can include a network of one or more access points (AP) to communicate with one or more wireless stations (STA). An AP can emit radio signals that carry management information, control information or users' data to one or more wireless stations, and a station can also transmit radio signals to the access point in the same frequency channel via time division duplexing (TDD) or in a different frequency channel via frequency division duplexing (FDD).

IEEE 802.11 is an asynchronous time division duplexing technology for operation of a wireless local area network (WLAN). The basic unit of WLAN is a basic service set (BSS). An infrastructure BSS is the BSS with stations that communicate through associating with an Access Point (AP) to connect to the wired network or Internet. In a BSS, both access point and stations share the same frequency channel via using Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) technology, a kind of TDD mechanism, for multiple access and data transmission.

SUMMARY

This patent document describes technologies for, among other things, a new power saving mechanism for reducing both power consumption of wireless devices and access latency.

In one example aspect, a method of wireless communication is disclosed. The method includes transmission of wake-up request signal over a narrow band frequency channel to a low power wake-up receiver to wake-up the main wireless communication module in the sleep mode of power saving station.

In another example aspect, an apparatus for wireless communication is disclosed. The apparatus includes a low power consumption wake-up receiver in the power saving device that is used to wake up the main wireless communication module from its sleep mode. The low power consumption wake-up receiver can receive the wake-up request signal from the wireless network over the narrow band frequency channel to wake-up the main radio.

In yet another example aspect, a method of a power saving mechanism is disclosed. The method includes a mechanism to embed multiple wake-up request messages in multiple narrow band sub-channels and transmit them simultaneously over wideband channel to wake up multiple power saving stations for multi-user transmissions.

In another example aspect, a method of power saving mechanism is disclosed. The method includes the mechanism to configure the low power consumption wake-up receiver to operate on specified narrow band channel for detecting the wake-up request signal associating with a BSS. Once the wake-up signal with the unique sequence to the BSS is detected, the wake-up receiver should detect and decode the following signal fields.

In another example aspect, a method of power saving mechanism is disclosed. The method includes the mechanism that the wireless network can use the wake-up request signal with a broadcast address to wake-up all the power saving stations in the sleep mode in the BSS.

In yet another example aspect, a method of wireless communication, implemented at a wireless network controller device in a wireless network that includes a wireless device is disclosed. The method includes setting up a wideband communication channel with the wireless device for data communication, determining, during operation of the wideband communication channel that the wireless device is in a power saving mode and is to be woken up, and transmitting, upon the determining, over a narrowband communication channel having a narrowband communication bandwidth lower than that of the wideband communication channel, a wake-up request signal to the wireless device to wake-up the wireless device for communication over the wideband communication channel. The wake-up request signal includes a preamble sequence which uniquely identifies the wake-up request signal as being for the wideband communication network, an identifier of the wireless device for whom the wake-up request signal is intended, and an error correction sequence facilitating error-free reception of the wake-up request signal.

In another example aspect, a wireless controller apparatus operable in a wireless network that includes a wireless device is disclosed. The apparatus includes a memory for storing instructions, a processor, a wideband air interface for communication over a wideband communication channel, and a narrowband air interface for communication over a narrowband communication channel. The processor reads instructions from the memory and performs the operations of determining, during operation of the wideband communication channel that the wireless device is in a power saving mode and is to be woken up, and performing transmission, upon the determining, over the narrowband air interface, a wake-up request signal to the wireless device to wake-up the wireless device for communication over the wideband air interface. The wake-up request signal includes a preamble sequence which uniquely identifies the wake-up request signal as being for the wideband communication network, an identifier of the wireless device for whom the wake-up request signal is intended, and an error correction sequence facilitating error-free reception of the wake-up request signal.

In yet another aspect, a method of wireless communication, implemented by a wireless device for operation in a wireless network, includes operating a wideband interface for data communication, wherein the wideband interface is operated in at least two states, including an awake state in which data transfer occurs over the wideband interface and a sleep state in which data transfer is disabled on the wideband interface, operating a narrowband interface in a receive-only mode for receiving control message communication, wherein the narrowband interface operates at a bandwidth substantially lower than that of the wideband interface, and transitioning, selectively based on a wake-up request message received on the narrowband interface, the wireless device from the sleep state to the awake state.

Details of the above aspects and their implementations, and other features, are set forth in the accompanying drawings, the description and the claims.

DETAILED DESCRIPTION

This document describes techniques, mechanisms, devices, and systems for improving the power saving performance of wireless devices and reducing the access latency of power saving devices from the sleep mode in contention based wireless communications.

In one example aspect, a method of wireless communication is disclosed, including transmission of wake-up request signal over a narrow band frequency channel to a low power consumption wake-up receiver to wake-up the main wireless communication module in the sleep mode.

In another example aspect, an apparatus for wireless communication is disclosed. The apparatus includes a low power consumption wake-up receiver in the power saving device that is used to wake up the main wireless communication module from its sleep. The low power consumption wake-up receiver can receive the wake-up request signal from the wireless network over the narrow band frequency channel and wake-up the main radio once such request is received.

In yet another example aspect, a method of power saving mechanism is disclosed. The method includes mechanism to embed multiple wake-up request messages in multiple narrow band sub-channels and transmit them simultaneously over wideband channel to wake up multiple power saving stations for multi-user transmissions.

In another example aspect, a method of power saving is disclosed. The method includes a mechanism to configure the low power consumption wake-up receiver to operate on specified narrow band channel for detecting the wake-up request signal associating with a BSS. Once the wake-up signal with the unique sequence to the BSS is detected, the wake-up receiver should detect and decode the following signal fields.

In IEEE 802.11, the basic service set (BSS) is the building block of a Wireless Local Area Network (WLAN). Wireless stations (also called stations) associated in the radio coverage area establish a BSS and provide basic service of WLAN.

FIG. 1illustrates an example of a wireless communication system100. BSS1and BSS2are infrastructure BSSes. BSS1contains one access point (AP1) and several non-AP stations, STA11, STA12, and STA13. The AP1maintains associations with, e.g., maintains a wireless connectivity or reserves wireless communication resources for, stations STA11, STA12, and STA13. BSS2contains one access point (AP2) and two non-AP stations, STA21and STA22. The AP2maintains associations with stations STA21and STA22. Infrastructure BSS1and BSS2may be interconnected via the AP1and AP2or connected to a switch/gateway through a distribution system (DS). In 802.11 terminology, a central station being associated with other stations and performing management of the BSS is referred to an Access Point (AP). A BSS built around an AP is called an infrastructure BSS. Two or more BSSes could be inter-connected via DS and form as Enhanced Service Set (ESS). An ESS may be managed and controlled by an access controller (AC).

IEEE 802.11 is a TDM based asynchronous technology. The AP, however, does not allocate dedicated time slots for the transmissions between AP and STAs. All the transmissions no matter management frames, control signaling or data frames have to go through medium contention prior to sending their transmissions.

IEEE 802.11 is usually said to consume more power on the mobile devices. It is not only because of IEEE 802.11 has weak power saving mechanism, but also of its ultra wide bandwidth and implementation. As WiFi technology could be used in many different IoT types of devices for wireless access, it is beneficial to use a new mechanism to reduce the power consumption in systematic and network levels.

The current IEEE 802.11 power saving is similar to the power saving mechanism used in cellular (paging cycle). In order to save power consumption, IEEE 802.11 network implements a power saving (PS) mechanism, which includes the sleep period and the wake-up period. In the sleep period, the power saving station is allowed to go to deep sleep so as to save the power consumption. In the wake-up period, the power saving station is active listening to the transmission from the network.

FIG. 2shows an example of the power saving mechanism used in the IEEE 802.11 network or other wireless networks. A power saving station is designed to have two states:

In the awake state (204), the power saving station could be in listening mode, transmit mode or receiving mode.The transmit mode is the sub-state that the power saving station is sending a PPDU.The receiving mode is the sub-state that the power saving station is receiving a PPDU from other station.The listening mode is the sub-state that the power saving station only enables the carrier sensing module to detect the Wi-Fi preamble signal via CCA mechanism.

the power saving station will go to sleep in the state (206) which consists of two sub-states (or modes):the shallow sleep mode: the power saving station will turn off transmitter and receiver circuit and leave baseband modem and main processor on for fast switching to the listening mode.the deep sleep mode: the power saving station will turn off all the circuitry except for the slow clock for further reducing power consumption.

As shown along the timeline202, a power saving station is configured to periodically switch between sleep period and wake-up period for listening to the transmission from the AP. If a power saving station receives detect a preamble and/or decode the message from the AP in the wake-up period that indicates there is scheduled DL data, it will remain wake-up to receive the following DL data frames. Otherwise, the power saving station will go back to sleep until the next wake-up period.

As the power station only monitors the wireless channel on the wake-up period, the AP of the BSS shall only transmit the control or user data frames to the power saving station in its wake-up period.

To avoid congestion on particular period, the wake-up period of a power saving station should be evenly distributed in time domain especially for dense deployment of WLANs. The power saving station can negotiate with the AP the target wakeup time (TWT) individually during the association and/or at any time so that different power saving station could be able to wake up at different TWT serving period.

On the other hand, in order to make transmission efficiently, the AP could group a couple of power saving stations together and set their TWT to the same time. Therefore the AP could schedule and transmit the multiple paging (or power saving polling) messages to the group of power saving stations together at the same time.

This power saving mechanism could save the power consumption of stations but it encounters other issues.

The power saving performance highly depends on the ratio of sleep period in the total duty cycle (i.e. sleep period+wake-up period). The longer sleep period, the more power saving could be achieved. However the longer sleep period would cause the access delay as the power saving station would not listen to any paging message during its sleep period even the AP wants to reach the power saving station immediately for high priority message or buffered data. Therefore, to balance the power saving performance and access latency, the duty cycle of wake-up should not be set too long.

The second issue causing more power consumption in IEEE 802.11 is the operating channel bandwidth. To reduce the implementation cost, the IEEE 802.11 only supports single carrier with wide bandwidth such as 20 MHz, 40 MHz or 80 MHz. The minimum channel bandwidth is 20 MHz for the primary channel. When the IEEE 802.11 station is powered on, its transmitter and receiver have to operate on the entire channel bandwidth. Such operation could fully use the channel for data transmission but might not be good for the power saving. When the power saving station enters the wake-up period to check whether there is scheduled DL data from AP, the receiver has to operate on the entire bandwidth, and its wideband radio circuit would consume a lot of power especially when frequent wake-ups.

This document discloses some embodiments which introduce a separate low power wake-up receiver module in the wireless device to control the operation of main IEEE 802.11 module.

FIG. 3Ashows an example of wireless device302which consists of:

a) a main wireless communication module308, such as 802.11 air interface component. The main wireless communication module is responsible to transmit or receive the regular control, or user data over the wide bandwidth wireless interface;

b) a low power wake-up receiver (WUR) module310that is operating on the narrow band channel to receive the wake-up request signal (WUS) from the network and to wake-up the main wireless communication module in the sleep mode. The modules308,310may share antenna or may have separate antennas304,306.

FIG. 3Bshows an example of functional blocks of low power consumption wake-up receiver310. The matching filter312operates on radio frequency channel specified for the lower power consumption WUR to filter out the out-band interference from the received signal on the narrow band of WUR. The RF amplifier module314boosts the received radio signal in the narrow band for the energy detection. The energy detector316and digitizer318modules are used to convert the received analog signal to digital signal for digital signal processor320. If the digital signal processor detects the received signal is the wake-up request signal, it will generate the wake-up indication to wake-up the main wireless communication module from the sleep mode.

The WUR module can operate in one of two modes:

A) always-on mode. In this mode, the WUR module is always-on to monitor the WUS over a narrow band operation channel and ready for decoding the WUS all the time;

B) period-on mode. In this mode, WUR module is periodically turned on at particular time to monitor and receive the WUS on the narrow band operation channel, while at other time, the WUR would go to sleep. Comparing to the “always-on” mode, the period-on mode would be able to reduce more power consumption for the device, but would cause more complex of implementation and increase the latency of wake-up control signal transmission.

FIG. 4shows an example of wireless device (STA) with WUR module communicating with the wireless network (AP) to receive the WUS.

InFIG. 4(A), the wireless device AP contains a main wireless communication module based on the wireless technology such as 802.11 operating on wide bandwidth channel and the module of Wakeup Transmitter (WUT) operating on a narrow band channel. The WUT could be a logic entity in the AP. When the main wireless communication module wants to send the data or signal to the power saving device (STA) in the sleep state, the main wireless communication module will send the wake-up request command to the WUT first to ask WUT to send the WUS to the WUR of the power saving device. When the STA receives the WUS addressing to it, it will send a wakeup indication to the main wireless communication module for wake-up from the sleep mode. Once the main wireless communication module of STA is awake, it will start communication with the AP over wide bandwidth channel.

The WUS could be transmitted at the same frequency channel of the main wireless communication module (i.e. in-band operation), or different frequency channel from the operation channel of the main wireless communication module (i.e. out-band). If the WUS shares the same radio frequency channel with the main wireless communication module, the main wireless communication module may be used to send the WUS over the multiple narrow band channels (e.g., OFDM), shared with regular wideband signals in the time division.

FIGS. 5A-5Bshow an example of WUS signal format used for the communication between WUT and WUR modules.

FIG. 5Ashows an example of a wireless WUS format502for communication between WUT and WUR modules over a single narrow band frequency channel. The WUS signal contains:

(a) WUS-Preamble field504: this field contains a unique sequence which is to identify the WUS signal. It indicates the commencing of the WUS signal, and may be used for simple timing synchronization between WUR and WUT modules. When the WUR monitors the WUS on narrow band frequency channel and detects the WUS preamble, it can start to receive the following field of the signal. The WUS-Preamble could be set to a unique sequence within the BSS. Different BSS may have different sequence so that the WUR could distinguish WUS from its BSS or other BSS.

(b) WUR ID field506: this field is used to identify the WUR module which is associated with the power saving device (STA). This field could be set to the AID directly or hashed AID of the power saving STA. When the WUR ID of received WUS matches with the AID of the power saving STA, the STA sends the wake-up indication to the main wireless communication module in the sleep mode.

(c) FCS field508: this field is to provide error correction in decoding WUR ID field to reduce the probability of mis-detection of WUS.

The WUS transmissions over the narrow band frequency channel could be sequentially in inter frame space, WUS-IFS, which is the idle time between two consecutive WUS signals. The WUR uses the WUS-IFS time to separate WUS signals, and determine the starting point of WUS.

In order to reduce the implementation complexity and reduce the bandwidth requirement, the WUS could be modulated via On-Off-Key (OOK) over single carrier.

FIG. 5Bshows another example of format510of WUS signal which is embedded within the 802.11 frame transmitted over wideband such as 20 Mhz channel bandwidth.

(a) The embedded WUS signal starts with the 802.11 preamble which includes L-STF, L-LTF and L-SIG fields. The 802.11 preamble is used for coexistence with 802.11 networks and identified by other 802.11 stations when WUS and other 802.11 signal are transmitted over the same channel (in-band).

(b) The wideband channel is divided into multiple sub-channels, each of which is a narrow band channel such as one sub-carrier of OFDM to carry WUS signal as shown in the format (A). Therefore, a single frame of WUS format (B) could be able to carry multiple WUS signals simultaneously to wake-up multiple power saving stations at the same time to enable multi-user communications.

FIG. 6Ashows an example of transmission procedure of the wake-up request signal over the narrow band frequency channel. The timeline602shows operation of AP. The timeline604shows, along the same time, operation of an STA.

The main radio of power saving STA is in sleep mode when there is no data communication between the STA and AP after a certain time. Once the STA enters the sleep mode, the main wireless communication module is turned off to reduce the power consumption. The STA should inform or synchronize its state to the AP before entering the sleep mode. Meanwhile the WUR of the STA remains on and continues monitoring the transmission over WUS channel. The WUR could operate in the always-on mode or periodic-on mode to monitor WUS channel.

If the AP with WUT module has some buffered data for the power saving STA, it will send the wake-up request signal to the WUR over the WUS channel if the STA is in the sleep mode. Then the AP will enter the receiving mode to wait for the wake-up response sent from the main wireless communication module of STA over the main wireless channel within the wake-up window.

When the WUR of STA receives the WUS from the AP, it will send a wake-up indication to wake-up the main wireless communication module of STA from the sleep state to the wake-up state for transmitting the wake-up response signal over wideband wireless channel. Then STA and AP could start the normal wireless communications over the main radios.

The similar procedure could be used to wake-up multiple power saving STAs at same time via the embedded WUS in 802.11 frame over wideband carrier.

FIG. 6Bshows an example of procedure of transmitting embedded wake-up request signals over OFDMA subchannels. The timeline606shows operation of AP. The timelines608,610show, along the same time, operation of two different STAs. The AP with WUT sends an embedded WUS to multiple STAs in the sleep mode (i.e. STA1and STA2in the example) over wideband channel using OFDMA mechanism. When WURs of STAs receive the WUS embedded in IEEE802.11 frame, they will wake-up the main radio in the sleep mode and send the wake-up response within the wake-up window. As multiple wake-up responses from different STAs are mixed over the air, the AP may not be able to distinguish them. Therefore, the AP shall send a trigger frame (like MU-RTS) after wake-up window to the STAs in the wake-up state for further identifying them. Once the STAs in wake-up state receive the trigger frame addressing to them, they shall send the trigger response (like MU-CTS) frame back to the AP over the OFDMA sub-channel allocated in trigger frame. Then STAs and AP can proceed the normal communications over the main radio. After finishing communications over the main radio, the power saving STAs need to inform the AP about entering the sleep mode which it only remains WUR on. Therefore, if the AP would like further communicate with those STAs, the AP sends WUS to wake-up their main radio first.

FIG. 7shows the procedure of power saving STA702and AP704to negotiate with the wake-up capability. The STA702has two air interfaces, a wideband interface, e.g., 802.11708, and a narrowband interface706, as described herein. Similarly, the AP704may have corresponding wideband air interface712and a narrowband air interface710. During the association, the WUR capable station transmits the association request message714with the WUR information to the WUT capable AP. The WUR capable information may include the WUR capability indication and supported operating channel for the WUS signal.

When the WUT capable AP receives the association request message with the WUR capability information and supports the WUR capability, the AP should respond in the association response message716with the WUR setup information, including:

(a) WUS operating channel that the WUR should operate on;

(b) WUS-preamble sequence unique to the BSS;

(c) WUR ID for the WUR of the power saving STA. The WUR ID may be same as AID or mapped to AID.

Otherwise, the AP shall send the association response with the indication of WUR un-supported.

Once the WUR capable STA receives the association response with WUR configuration, it enables WUR module to monitor WUS when the main wireless communication module (such as 802.11) is in the sleep mode. The main wireless communication module of the power saving STA may include the sleep state indication in the last message to the AP and automatically enter the sleep mode after a given period.

FIG. 8shows an example of unicast wakeup signal to control the main wireless communication module of the power saving station.

The AP with WUT capability needs to send the buffered data to the WUR capable power saving STA. The main wireless communication module of the AP (i.e. 802.11) sends the internal signal of wakeup request801to the WUT to request sending the Wakeup Request signal802addressing to the power saving STA over the specified WUS channel. Then the AP will monitor the main wireless channel for the wake-up response806from the power saving STA.

After the WUR of STA receives the Wakeup Request, it then sends the wake-up indication804to turn on the main wireless communication module to respond with the Wakeup Response806or other message such as RTS over the main wireless channel, so that the power saving STA and AP could start normal communications. Then, the AP continues normal 802.11 operation by sending a clear to send signal808and a protocol data unit810that includes data to be communicated to the STA702.

FIG. 9shows an example of AP sending a broadcast WUS to wake-up power saving STAs at same time.

When the AP with WUT capable wants to send a broadcast message to the power saving STAs in the BSS, it could send the Wake-up Request904to the WUT to request sending the broadcast WUS to WURs of power saving stations in the BSS. WUT of AP could set the WUR ID field of WUS to the broadcast address so that the WUS could be reached to WUR of power saving STAs in the BSS.

After AP sends out the broadcast WUS904, it could send 802.11 beacon, trigger frame or other broadcast messages912to power saving stations after wake-up window. The AP may wait to receive wake-up responses908,910from the STAs before broadcasting the broadcast message.

FIG. 10is a flowchart depiction of an example method1000of wireless communication implemented by a network controller such as the above-discussed AP in the 802.11 networks.

The method1000includes, at1002, setting up a wideband communication channel with the wireless device for data communication. The wideband communication channel may use a well-known technology such as 802.11, and various ways to setting up such wireless networks is well-known in the art.

The method1000includes, at1004, determining, during operation of the wideband communication channel that the wireless device is in a power saving mode and is to be woken up. The determination may be performed by the network controller maintaining a status table in its memory of all the wireless devices in the network, and which of these wireless devices are in sleep mode or are actively communicating in the network. For example, for each wireless device, the table may include an entry that may have a value of either “active” or “sleeping”. The transition between these two values may be based on, e.g., receiving previously discussed wake-up response messages and/or direct or indirect (e.g., capabilities setting) indication from wireless device that they are entering sleep mode.

The method1000includes, at1006, transmitting, upon the determining, over a narrowband communication channel having a narrowband communication bandwidth lower than that of the wideband communication channel, a wake-up request signal to the wireless device to wake-up the wireless device for communication over the wideband communication channel. The network controller, in general, not mind if a wireless device goes into an extended sleep period. Only when there is data that needs to go to the wireless device, and the data is either about to exceed either a buffering time budget or a buffering amount budget, the network controller may want to determine whether the device is awake, and if not, wake up the device so the data can be sent to the device without exceeding delay or buffer that stores the data.

As described in the present document, the wake-up request signal includes a preamble sequence which uniquely identifies the wake-up request signal as being for the wideband communication network, an identifier of the wireless device for whom the wake-up request signal is intended, and an error correction sequence facilitating error-free reception of the wake-up request signal.

In some embodiments, the network controller device may, after sending the wake-up request, wait for an amount of time to receive a confirmation on the wideband communication channel that the requested device has woken up. In some embodiments, the network controller may assume, even without an explicit message from the wireless device, that the wireless device is awake after a predetermined time period after the wake-up request was transmitted.

To achieve significant power savings, bandwidth of the narrowband channel may be selected to be much smaller than that of the wideband channel. For example, in some embodiments, the wideband channel may have approximately 20, 40 or 80 MHz bandwidth, while the narrowband channel may be at least an order of magnitude smaller, e.g., 1/10th or 1/20th or 1/40th of the wideband channel. Even at such narrowband transmission rates, using a simple modulation scheme such as on-off keying, about 1 bit per Hz per second can be transmitted, and therefore 100 bits could be transmitted in 1 millisecond on the narrowband channel (assuming 1 MHz bandwidth), which may be sufficient to carry the entire wake-up request message. Furthermore, additional complexity and power reduction can be obtained knowing that the narrowband channel is a unidirectional channel—that is, in some embodiments, the network controller is transmit-only and the wireless device is a receive-only device of the narrowband channel.

FIG. 11is a flowchart depiction of a method1100of wireless communication implemented by a wireless device that is not acting as a network controller.

The method1100includes, at1102, operating a wideband interface for data communication, wherein the wideband interface is operated in at least two states, including an awake state in which data transfer occurs over the wideband interface and a sleep state in which data transfer is disabled on the wideband interface.

The method1100includes, at1104, operating a narrowband interface in a receive-only mode for receiving control message communication, wherein the narrowband interface operates at a bandwidth substantially lower than that of the wideband interface.

The method1100includes, at1106, transitioning, selectively based on a wake-up request message received on the narrowband interface, the wireless device from the sleep state to the awake state.