WO2018098622A1

WO2018098622A1 - Adaptive frequency calibration

Info

Publication number: WO2018098622A1
Application number: PCT/CN2016/107685
Authority: WO
Inventors: Liyuan Liu; Jian Li
Original assignee: Microsoft Technology Licensing, Llc.
Priority date: 2016-11-29
Filing date: 2016-11-29
Publication date: 2018-06-07

Abstract

According to implementations of the subject matter described herein, a new approach for adaptively calibrating frequency is proposed herein. Generally speaking, a device determines, upon receipt of a signal from another device, a quality of the received signal. Then, the device obtains a frequency offset based on the quality of the signal, and calibrates a local frequency generator of the device based on the frequency offset. In this way, an error between the local frequency generator and a frequency generator of the further device can be reduced. As a result, high-qualified radio synchronization and connection can be guaranteed, even when the device is under poor radio coverage.

Description

ADAPTIVE FREQUENCY CALIBRATION

BACKGROUND

When a device receives a signal from another device， a frequency error between a local frequency generator of the device and a frequency generator of the other device always exists due to a variety of factors， such as temperature wave， shock， and so on. As used herein， the frequency error means the difference between the frequency generators of transmitting and receiving devices. The frequency error would have a negative impact on radio synchronization and/or connection and result in an undesired communication effect， such as discontinuous voice quality. To reduce the frequency error， Automatic Frequency Control (AFC) has been proposed to automatically keep the frequencies of the frequency generators to be consistent. However， for those devices under poor radio coverage， the frequency errors would be very large even ifthe AFC feature is enabled.

SUMMARY

Generally speaking， a new approach for adaptively calibrating frequency is proposed herein. In accordance with implementations of the subject matter described herein， a device determines， upon receipt of a signal from another device， a quality of the received signal. Then， the device obtains a frequency offset based on the quality of the signal， and calibrates a local frequency generator of the device based on the frequency offset. In this way， an error between the local frequency generator and a frequency generator of the further device can be reduced. As a result， high-qualified radio synchronization and connection can be guaranteed， even when the device is under poor radio coverage.

It is to be understood that the Summary is not intended to identify key or essential features of implementations of the subject matter described herein， nor is it intended to be used to limit the scope of the subject matter described herein. Other features of the subject matter described herein will become easily comprehensible through the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more implementations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features， aspects， and advantages of the disclosure will become apparent from the description， the drawings， and the claims， wherein：

Fig. 1 is a flowchart illustrating a method for performing adaptive frequency calibration in accordance with an example implementation of the subject matter described herein；

Fig. 2 is a flowchart illustrating another method for performing adaptive frequency calibration in accordance with another example implementation of the subject matter described herein；

Fig. 3 is a graph illustrating an original error and an updated error obtained after the calibration in accordance with an example implementation of the subject matter described herein； and

Fig. 4 is a block diagram of a device suitable for implementing one or more implementations of the subject matter described herein.

Throughout the figures， same or similar reference numbers will always indicate same or similar elements.

DETAILED DESCRIPTION

Principle of the subject matter described herein will now be described with reference to some example implementations. It is to be understood that these implementations are described only for the purpose of illustration and help those skilled in the art to understand and implement the subject matter described herein， without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones describe below.

As used herein， the term “include” and its variants are to be read as open terms that mean “include， but is not limited to” . The term “based on” is to be read as “based at least in part on” . The term “a” is to be read as “one or more” unless otherwise specified. The term “one implementation” and “an implementation” are to be read as “at least one implementation” . The term “another implementation” is to be read as “at least one other implementation” . Moreover， it is to be understood that in the context of the subject matter described herein， the terms “first” ， “second” and the like are used to indicate individual elements or components， without suggesting any limitation as to the order of these elements. Further， a first element may or may not be the same as a second element. Other definitions， explicit and implicit， may be included below.

Usually a device with the AFC feature is able to calibrate frequency error of the local frequency generator caused by temperature wave， shock， and so on. However， in some cases， if the device is under poor radio coverage， such as， impacted by radio signal fluctuation， common channel interferences， blind areas and barriers， the traditional AFC feature cannot calibrate the local frequency generator in an accurate way. As such， the device would have to use long time to synchronize radio signal services with poor signal quality. As a result， radio functions such as radio connection， call generation， and so on， would not work well， and audio loss or distortion would occur.

In order to at least partially solve the above and other potential problems， a new method and device for adaptive frequency calibration are provided herein. According to implementations of the subject matter described herein， upon receiving a signal from a second device， a first device determines a quality of the received signal， obtains a frequency offset based on the quality and calibrates the local frequency generator of the first device based on the frequency offset. As such， a dynamic frequency offset associated with the signal quality is applied to the calibration.

Through the process， the device may calibrate the local frequency generator in consideration of the signal quality. In this way， an error between the local frequency generator of the first device and a frequency generator of the second device can be reduced. As a result， high-qualified radio synchronization and connection can be guaranteed， even when the device is under poor radio coverage.

Some example implementations of the subject matter described herein will be described with reference to a device (referred to as “afirst device” hereafter) to synchronize with a further device (referred to as “asecond device” hereafter) . The first device may have a local frequency generator (referred to as “a first frequency generator” hereafter) ， such as a clock source， for generating frequency. The second device may have its own local frequency generator (referred to as “a second frequency generator” hereafter) .

In accordance with implementations of the subject matter described herein， the devices may be implemented in a variety of ways. In some implementations， either the first device or the second device may be a network device or a terminal device.

As used herein， a network device refers to a device in a communication network， from which a terminal device may receive services. The network device may be a base station (BS) ， an access point (AP) ， a server or any other suitable device in the communication network. The BS may be， for example， a node B (NodeB or NB) ， an evolved NodeB (eNodeB or eNB) ， a Remote Radio Unit (RRU) ， a radio header (RH) ， a remote radio head (RRH) ， a relay， a low power node such as a femto， a pico， and so forth.

A terminal device refers to any end device that can communicate with the network device and receive services from communication a network. By way of example and not limitation， the terminal device refers to a mobile terminal， user equipment (UE) ， or other suitable device. The UE may be， for example， a Subscriber Station (SS) ， a Portable Subscriber Station， a Mobile Station (MS) ， or an Access Terminal (AT) . The terminal device may include， but not limited to， a mobile phone， a cellular phone， a smart phone， a laptop computer， a tablet， a personal digital assistant (PDA) ， a vehicle， and the like.

The first and second device may operate in a communication network. As used herein， the term “communication network” refers to a network following any suitable communication standards， such as Long Term Evolution (LTE) ， LTE-Advanced (LTE-A) ， Wideband Code Division Multiple Access (WCDMA) ， High-Speed Packet Access (HSPA) ， and so on. Furthermore， the communications between devices in the communication network may be performed according to any suitable generation communication protocols， including， but not limited to， the first generation (1G) ， the second generation (2G) ， 2.5G， 2.75G， the third generation (3G) ， the fourth generation (4G) ， 4.5G， the future fifth generation (5G) communication protocols， and/or any other protocols either currently known or to be developed in the future.

The functionalities and operations of the first device will be described with reference to Fig. 1， which is a flowchart illustrating a method 100 for performing adaptive frequency calibration in accordance with an example implementation of the subject matter described herein. In other word， the method 100 is implemented at the first device， for example a terminal device， a network device， or other suitable device.

As shown， at 110， the first device determines a quality of a signal received from a further device (for example， the second device) at a first time point. The quality of the signal may be affected by， for example， proximity to a tower， obstructions such as buildings or trees， etc.， and some other kinds of interference or noise. Note that the phrases “quality of signal” and “signal quality” can be used interchangeably in the context.

The first device may determine the signal quality based on a variety of factors associated with the signal. These factors includes， for example， but not limited to， a signal strength， a power level， a ratio of the power level to the signal strength， a Signal to Noise Ratio (SNR) ， a Signal to Interference plus Noise Ratio (SINR) ， a Signal to Interference Ratio (SIR) ， a Carrier to Noise Ratio (CNR) ， a Carrier to Interference plus Noise Ratio (CINR) ， a Channel Quality Indicator (CQI) ， a carrier frequency， a time duration for synchronization between devices， and so on.

By way of example， in some implementations， the first device may determine the signal quality based on the signal strength. The signal strength may be indicated by， for instance， Received Signal Strength Indication (RSSI) . If the RSSI value is high， the first device may determine that the signal quality is good. Otherwise， the first device may determine that the signal quality is poor.

Alternatively， or in addition， in some implementations， the first device may determine the signal quality based on the power level of the signal. The power level may be indicated by， for example， Reference Signal Receiving Power (RSRP) . If the RSRP value is high， the first device may determine that the signal quality is good. Otherwise， the first device may determine that the signal quality is poor.

As another example， in some implementations， the first device may determine the signal quality based on the ratio of the power level to the signal strength. The ratio may be indicated by， for example， Reference Signal Receiving Quality (RSRQ) ， which may be calculated based on RSRP and RSSI. If the RSRQ value is high， the first device may determine that the signal quality is good. Otherwise， the first device may determine that the signal quality is poor.

In some implementations， the CQI may be sent to provide channel quality information including， for example， but not limited in， RSSI， bit error rate (BER) ， and so on， to represent a measure of channel quality for transmitting the signal. In the implementations， the first device may determine the quality of the channel based on the CQI.

In some implementations， the carrier frequency may indicate a frequency band of the carrier for carrying the signal. If the first device determines that the carrier frequency belongs to a predefined range， for example， an edge of the allocated frequency band， it may determine that the signal may have poor quality since interference at the edge of the allocated frequency band is usually large.

It is also possible for the first device to determine the signal quality based on the time duration for synchronization between the first device and the second device. This time duration may indicate a time interval from Frequency Correction Channel (FCCH) searching to registration on the second device. In some implementations， if it is detected that the time duration is too long (that is， length of the time duration exceeds a predefined threshold) ， the first device may determine that the signal quality is not so good.

In some implementations， the first device may determine the signal quality based on SNR， SINR， SIR， CINR， and CNR， alone or in combination. Actually， according to implementations of the subject matter described herein， the first device may determine one of the above factors or any combination thereof as the signal quality， and then may obtain the frequency offset according to the determined signal quality. It is to be understood that the above examples factors are only described for purpose of discussion， rather than limitation. Those skilled in the art would appreciate that the first device can determine the signal quality in other suitable ways.

Still in reference to Fig. 1， at 120， the first device obtains a frequency offset based on the quality of the signal. In some implementations， the frequency offset may be obtained from a predetermined set of candidate offsets based on the quality of the signal. The predetermined set of candidate offsets may include frequency offsets associated with different signal quality levels， and may be predetermined in several ways.

In an implementation， the candidate offsets may be obtained based on testing data before selling of the first device. For example， in a testing process made by a device manufacturer， different signal quality levels may be simulated and applied to the first device. Thus， the corresponding frequency errors may be obtained and corresponding frequency offsets may be calculated based on these frequency errors and original frequency errors. The original frequency errors may be obtained in an environment where the signal quality level is good and unchanged， and can reflect intrinsic frequency errors caused by components of the first device to some extent.

Alternatively， in another implementation， the candidate offsets may be obtained by the first device itself when the first device is idle， or in an initialization phase predefined for obtaining the candidate offsets.

Then candidate offsets may be stored in a variety of ways. For example， the candidate offsets (e.g.， in Hz) and their corresponding signal quality levels (e.g.， in dB) may be recorded in a table， a file or any other suitable forms. Thus， the first device may compare the quality of the signal (for example， 3.1dB) determined at 110 with the signal quality levels (for example， 3dB， 4dB... ) ， determine a signal quality level associated with the quality of the signal based on the comparing result， for example， as 3dB， and obtain from the table the frequency offset corresponding to 3dB. Table 1 illustrates an example of correspondence between candidate offsets and signal quality levels. In this example， the frequency offset determined based on the quality of the signal (for example， 3.1 dB) is 10 Hz.

Table 1

Signal Quality Levels (dB)	Candidate Offsets (Hz)
3	10
4	15
5	20
6	-15
7	20
8	20

9

30

It is to be understood that the above example is discussed for illustration， rather than limitation. Those skilled in the art would appreciate that there are other suitable forms for storing the candidate offsets and corresponding signal quality levels. For example， the signal quality levels may be non-integers， such as 3dB， 3.5dB， 4dB， 4.5dB ... 10dB， ... and each of them may have a corresponding candidate offset.

In some implementations， the frequency calibration is triggered by a predefined event， for example， when the signal quality is too poor. In this case， the first device obtains the frequency offset at 120 only ifthe signal quality is less than a threshold quality. The threshold quality may be predefined in several ways， for example， according to testing results， system requirements， manufacture settings， and the like. If the signal quality is good enough， for example， exceeding the threshold quality， the first device would not obtain the frequency offset. As such， power of the first device can be saved.

At 130， the first device calibrates a first frequency generator of the device based on the frequency offset. The calibration may be performed in a variety of ways. For example， in some implementations， the first device may directly apply the frequency offset to the first frequency generator， namely， the local frequency generator or time source of the first device. In this way， an error between the first frequency generator and a second frequency generator of the second device can be reduced.

Alternatively， or in addition， in some implementations， an inherent frequency variation of the first frequency generator may be considered in the calibration as well. In this case， the first device may obtain the inherent frequency variation and adjust the frequency offset with the inherent frequency variation. Then， the first device may calibrate the first frequency generator based on the adjusted frequency offset. In this way， more factors that possibly affect accuracy of the calibration can be considered and thus the effect of the calibration can be improved.

In some implementations， optionally， the first device may further adjust the periodicity of the forthcoming calibrations based on a result of the current calibration. In some implementations， the first device may determine an updated error between the first frequency generator and the second frequency generator after the current calibration. If the updated error is still quite large， which means that the result of the current calibration is not very good， the first device may carry out the next calibration more eagerly.

More particularly， the first device may determine whether the updated error exceeds an error threshold. If so， the time interval between the first time point and a second time point when a next calibration begins may be reduced. In an implementation， if the time interval is reduced to a burst， the first device may perform burst-aligned calibrations. In this way， the calibration can be performed adaptively and the accuracy of the calibration can be improved.

Alternatively， or in addition， in some implementations， if the updated error is small enough， which means that the result of the current calibration is good， the first device may slow down the calibrations. In such a case， if the updated error is less than the error threshold， the first device may determine to increase the time interval between the first time point and the second time point. In this way， the calibration can be performed adaptively and the power of the first device can be saved.

It is to be understood that this is just an example for discussion and is optional， and those skilled in the art would implement in many other ways. For example， if the result of the current calibration is good enough， the first device may not adjust the occurrence of the next calibration.

Now some example implementations of the method 200 will be described with reference to Fig. 2. Fig. 2 is a flowchart illustrating another method 200 for performing adaptive frequency calibration in accordance with an example implementation of the subject matter described herein. It is to be understood that the method 200， which may be performed by the first device， for example， a terminal device or a network device， can be considered as an example implementation of the method 100.

At 210， the first device receives a signal from a further device， namely， the second device. The signal may be received at a signal burst at the first time point.

At 220， the first device determines quality of the received signal.

At 230， the first device compares the quality with a threshold quality， and determines whether the quality is less than the threshold quality. If so， the first device may know the quality of the signal is not so good and the calibration can be triggered. Otherwise， the first device may determine that the signal quality is good enough and there is no need to perform the calibration. In this case， at 290， the first device increases the time interval between the current and the next calibrations. As such， the power of the first device can be reduced.

When the calibration is triggered， at 240， the first device obtains the frequency offset based on the signal quality， as discussed at 120. Then， at 250， the first device calibrates the first frequency generator based on the obtained frequency offset.

At 260， the first device determines the updated error between the first frequency generator and the second frequency generator after the current calibration. At 270， the first device compares the updated error with an error threshold and determines whether the updated error exceeds the error threshold. If so， at 280， the first device understands that the effect of the current calibration is not so good and thus reduces the time interval between the current calibration and the next calibration. In this way， the next calibration can occur shortly to avoid significant deterioration on synchronization or connection between the first and second devices.

On the other side， if the updated error is less than the error threshold， at 290， the first device may understand that the effect of the current calibration is good enough and thus increases the time interval between the current calibration and the next calibration to save power.

In this way， the first device may adaptively perform the frequency calibration based on the signal quality of the current communication environment. As such， the accuracy of the calibration can be improved. Furthermore， by adjusting the time interval between the current and next calibrations， power consumption of the first device can be controlled efficiently.

Fig. 3 is a graph illustrating an original error and an updated error obtained after the calibration in accordance with an example implementation of the subject matter described herein. The curve 330 represents an original error between the first frequency generator and the second frequency generator before performing the calibration according to implementations of the subject matter described herein. The curve 320 represents the frequency offset obtained by the first device， and the curve 330 represents the updated error between the first frequency generator and the second frequency generator after the calibration.

In the example shown by the diagram 300， at a time point 301， the original error is -20dB. The signal quality determined at the time point 301 is 2dB， which triggers the first device to obtain the frequency offset based on the signal quality and perform the calibration accordingly. At a time point 302， assuming that the quality of the signal received by the first device is 5dB， the first device may obtain the frequency offset associated with the quality， 5dB， is 20Hz. Then， the first device may calibrate the local frequency generator by applying the frequency offset， 20Hz. After the calibration， the updated error is -20Hz which is better than the original error， -55Hz. In this way， the updated error can be reduced effectively.

It is to be understood that implementations described above， such as the

methods

100 and 200， are only example implementations. Various modifications and/or variations can be made within the scope of the subject matter described herein. As an example， in the method 200 as shown in Fig. 2， after determining the quality of the received signal is good or the updated error is small， it is possible to not adjust the starting time point of the next calibration at 290.

Fig. 4 is a block diagram of a device 400 suitable for implementing one or more implementations of the subject matter described herein. For example， the device 400 may function as the first device as discussed above with reference to Figs. 1-3. Description of the device 400 is not intended to suggest any limitation as to scope of use or functionality of the subject matter described herein， as various implementations may be implemented in diverse general-purpose or special-purpose environments.

As shown， the device 400 includes a controller 420 and a memory 430. The controller 420 may be a real or a virtual processor that is capable of executing a program or computer-executable instructions 440 stored in the memory 430. The memory 430 may be volatile memory (e.g.， registers， cache， RAM) ， non-volatile memory (e.g.， ROM， EEPROM， flash memory) ， or some combination thereof.

In the example shown in Fig. 4， the device 400 further includes a transceiver 410. The transceiver 410 may be configured by the controller 420 to perform communications with other one or more devices， for example， via an antenna (s) or an antenna array (s) 450. In some implementations， the controller 420 may be configured by the program 440 stored in the memory 430 to work with the transceiver 410 to carry out the methods 100 and/or 200 as described above.

Additionally， the device 400 further includes a frequency generator 460 adjusted by the controller 420. The frequency generator 460 may be implemented in a variety of forms of clock sources， for example， a digitally-controlled crystal oscillator (DCXO) ， a voltage controlled crystal oscillator (VCXO) ， an oven-controlled crystal oscillator (OCXO) ， a voltage-controlled temperature-compensated oscillator (VCTCXO) ， a voltage controlled oven-controlled crystal oscillator (VCOCXO) ， a microprocessor compensated crystal oscillator (MCXO) ， and the like.

Additionally， functionality of the components of the device 400 may be implemented in a single computing machine， for example， a single mobile phone， or in multiple computing machines that are able to communicate over communication connections， for example， a cloud system.

For the purpose of illustrating spirit and principle of the subject matter described herein， some specific implementations thereof have been described above. Through the process， the device may calibrate the local frequency generator in consideration of the signal quality. In this way， an error between the local frequency generator of the first device and a frequency generator of the second device can be reduced. As a result， high-qualified radio synchronization and connection can be guaranteed， even when the device is under poor radio coverage.

Now only for the purpose of illustration， some example implemented will be listed below.

The subject matter described herein may be embodied as a method implemented at a device， for example， the device 400. The method comprises determining a quality of a signal received from a further device at a first time point； obtaining a frequency offset based on the quality of the signal； and calibrating a first frequency generator of the device based on the frequency offset to reduce an error between the first frequency generator and a second frequency generator of the further device.

In some implementations， the obtaining a frequency offset comprises： in response to the quality being less than a threshold quality， obtaining the frequency offset.

In some implementations， the obtaining a frequency offset comprises： obtaining the frequency offset from a predetermined set of candidate offsets based on the quality of the signal， the predetermined set of candidate offsets including frequency offsets associated with different signal quality levels.

In some implementations， the determining a quality of a signal comprises： determining the quality of the signal based on at least one of the following associated with the signal： a signal strength， a power level， a ratio of the power level to the signal strength， a SNR， a SINR， a SIR， a CNR， a CINR， a CQI， a carrier frequency， and a time duration for synchronization between the device and the further device.

In some implementations， the calibrating a first frequency generator of the device comprises： obtaining an inherent frequency variation of the first frequency generator； adjusting the frequency offset with the inherent frequency variation； and calibrating the first frequency generator of the device based on the adjusted frequency offset.

In some implementations， the method further comprises： determining an updated error between the first frequency generator and the second frequency generator after the calibration； determining whether the updated error exceeds an error threshold； and in response to determining that the updated error exceeds the error threshold， reducing a time interval between the first time point and a second time point when a next calibration begins.

In some implementations， the method further comprises： in response to determining that the updated error being less than the error threshold， increasing the time interval between the first time point and the second time point.

The subject matter described herein can be also embodied as a device. The device comprises： a controller； and a memory coupled to the controller and storing instructions for execution by the controller， the instructions， when executed by the controller， causing the device to perform acts including： determining a quality of a signal received from a further device at a first time point； obtaining a frequency offset based on the quality of the signal； and calibrating a first frequency generator of the device based on the frequency offset to reduce an error between the first frequency generator and a second frequency generator of the further device.

In some implementations， the controller is further configured to， in response to the quality being less than a threshold quality， obtain the frequency offset.

In some implementations， the controller is further configured to， obtain the frequency offset from a predetermined set of candidate offsets based on the quality of the signal， the predetermined set of candidate offsets including frequency offsets associated with different signal quality levels.

In some implementations， the controller is further configured to， determine the quality of the signal based on at least one of the following associated with the signal： a signal strength， a power level， a ratio of the power level to the signal strength， a SNR， a SINR， a SIR， a CNR， a CINR， a CQI， a carrier frequency， and a time duration for synchronization between the device and the further device.

In some implementations， the controller is further configured to， obtain an inherent frequency variation of the first frequency generator； adjust the frequency offset with the inherent frequency variation； and calibrate the first frequency generator of the device based on the adjusted frequency offset.

In some implementations， the controller is further configured to， determine an updated error between the first frequency generator and the second frequency generator after the calibration； determine whether the updated error exceeds an error threshold； and in response to determining that the updated error exceeds the error threshold， reduce a time interval between the first time point and a second time point when a next calibration begins.

In some implementations， the controller is further configured to， in response to determining that the updated error being less than the error threshold， increase the time interval between the first time point and the second time point.

The subject matter described herein may be embodied as a computer program product being tangibly stored on a non-transient machine-readable medium and comprising machine-executable instructions. The instructions， when executed by a device， cause the device to： determine a quality of a signal received from a further device at a first time point； obtain a frequency offset based on the quality of the signal； and calibrate a first frequency generator of the device based on the frequency offset to reduce an error between the first frequency generator and a second frequency generator of the further device.

In some implementations， the instructions， when executed by the device， further cause the device to： in response to the quality being less than a threshold quality， obtain the frequency offset.

In some implementations， the instructions， when executed by the device， further cause the device to： obtain the frequency offset from a predetermined set of candidate offsets based on the quality of the signal， the predetermined set of candidate offsets including frequency offsets associated with different signal quality levels.

In some implementations， the instructions， when executed by the device， further cause the device to： determine the quality of the signal based on at least one of the following associated with the signal： a signal strength， a power level， a ratio of the power level to the signal strength， a SNR， a SINR， a SIR， a CNR， a CINR， a CQI， a carrier frequency， and a time duration for synchronization between the device and the further device.

In some implementations， the instructions， when executed by the device， further cause the device to： obtain an inherent frequency variation of the first frequency generator； adjust the frequency offset with the inherent frequency variation； and calibrate the first frequency generator of the device based on the adjusted frequency offset.

In some implementations， the instructions， when executed by the device， further cause the device to： determine an updated error between the first frequency generator and the second frequency generator after the calibration； determine whether the updated error exceeds an error threshold； and in response to determining that the updated error exceeds the error threshold， reduce a time interval between the first time point and a second time point when a next calibration begins.

In some implementations， the instructions， when executed by the device， further cause the device to： in response to determining that the updated error being less than the error threshold， increase the time interval between the first time point and the second time point.

Implementations of the subject matter described herein may further include one or more computer program products being tangibly stored on a non-transient machine-readable medium and comprising machine-executable instructions. The instructions， when executed on a device， causing the device to carry out one or more processes as described above.

Example implementations may be implemented in hardware or special purpose circuits， software， logic or any combination thereof. Some aspects may be implemented in hardware， while other aspects may be implemented in firmware or software which may be executed by a controller， microprocessor or other computing device. While various aspects of the example implementations of the subject matter described herein are illustrated and described as block diagrams， flowcharts， or using some other pictorial representation， it will be appreciated that the blocks， apparatus， systems， techniques or methods described herein may be implemented in， as non-limiting examples， hardware， software， firmware， special purpose circuits or logic， general purpose hardware or controller or other computing devices， or some combination thereof.

In the context of the subject matter described herein， a machine readable medium may be any tangible medium that can contain， or store a program for use by or in connection with an instruction execution system， apparatus， or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic， magnetic， optical， electromagnetic， infrared， or semiconductor system， apparatus， or device， or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires， a portable computer diskette， a hard disk， a random access memory (RAM) ， a read-only memory (ROM) ， an erasable programmable read-only memory (EPROM or Flash memory) ， an optical fiber， a portable compact disc read-only memory (CD-ROM) ， an optical storage device， a magnetic storage device， or any suitable combination of the foregoing.

Computer program code for carrying out methods of the subject matter described herein may be written in any combination of one or more programming languages. These computer program codes may be provided to a processor of a general purpose computer， special purpose computer， or other programmable data processing apparatus， such that the program codes， when executed by the processor of the computer or other programmable data processing apparatus， cause the functions or operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a computer， partly on the computer， as a stand-alone software package， partly on the computer and partly on a remote computer or entirely on the remote computer or server.

Further， while operations are depicted in a particular order， this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order， or that all illustrated operations be performed， to achieve desirable results. In certain circumstances， multitasking and parallel processing may be advantageous. Likewise， while several specific implementation details are contained in the above discussions， these should not be construed as limitations on the scope of any disclosure or of what may be claimed， but rather as descriptions of features that may be specific to particular implementations of particular disclosures. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely， various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable sub-combination.

Various modifications， adaptations to the foregoing example implementations of this disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description， when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and example implementations of this disclosure. Furthermore， other implementations of the disclosures set forth herein will come to mind to one skilled in the art to which these implementations of the disclosure pertain having the benefit of the teachings presented in the foregoing descriptions and the drawings.

Therefore， it will be appreciated that the implementations of the disclosure are not to be limited to the specific implementations disclosed and that modifications and other implementations are intended to be included within the scope of the appended claims. Although specific terms are used herein， they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

A device comprising：

a controller； and

a memory coupled to the controller and storing instructions for execution by the controller， the instructions， when executed by the controller， causing the device to perform acts including：

determining a quality of a signal received from a further device at a first time point；

obtaining a frequency offset based on the quality of the signal； and

calibrating a first frequency generator of the device based on the frequency offset to reduce an error between the first frequency generator and a second frequency generator of the further device.
The device of claim 1， wherein the obtaining a frequency offset comprises：

in response to the quality being less than a threshold quality， obtaining the frequency offset.
The device of claim 1， wherein the obtaining a frequency offset comprises：

obtaining the frequency offset from a predetermined set of candidate offsets based on the quality of the signal， the predetermined set of candidate offsets including frequency offsets associated with different signal quality levels.
The device of claim 1， wherein the determining a quality of a signal comprises：

determining the quality of the signal based on at least one of the following associated with the signal：

a signal strength，

a power level，

a ratio of the power level to the signal strength，

a Signal to Noise Ratio (SNR) ，

a Signal to Interference plus Noise Ratio (SINR) ，

a Signal to Interference Ratio (SIR) ，

a Carrier to Noise Ratio (CNR) ，

a Carrier to Interference plus Noise Ratio (CINR) ，

a Channel Quality Indicator (CQI) ，

a carrier frequency， and

a time duration for synchronization between the device and the further device.
The device of claim 1， wherein the calibrating a first frequency generator of the device comprises：

obtaining an inherent frequency variation of the first frequency generator；

adjusting the frequency offset with the inherent frequency variation； and

calibrating the first frequency generator of the device based on the adjusted frequency offset.
The device of claim 1， the acts further comprising：

determining an updated error between the first frequency generator and the second frequency generator after the calibration；

determining whether the updated error exceeds an error threshold； and

in response to determining that the updated error exceeds the error threshold， reducing a time interval between the first time point and a second time point when a next calibration begins.
The device of claim 6， the acts further comprising：

in response to determining that the updated error being less than the error threshold， increasing the time interval between the first time point and the second time point.
A method comprising：

determining， at a device， a quality of a signal received from a further device at a first time point；

obtaining a frequency offset based on the quality of the signal； and

calibrating a first frequency generator of the device based on the frequency offset to reduce an error between the first frequency generator and a second frequency generator of the further device.
The method of claim 8， wherein the obtaining a frequency offset comprises：

in response to the quality being less than a threshold quality， obtaining the frequency offset.
The method of claim 8， wherein the obtaining a frequency offset comprises：

obtaining the frequency offset from a predetermined set of candidate offsets based on the quality of the signal， the predetermined set of candidate offsets including frequency offsets associated with different signal quality levels.
The method of claim 8， wherein the determining a quality of a signal comprises：

determining the quality of the signal based on at least one of the following associated with the signal：

a signal strength，

a power level，

a ratio of the power level to the signal strength，

a Signal to Noise Ratio (SNR) ，

a Signal to Interference plus Noise Ratio (SINR) ，

a Signal to Interference Ratio (SIR) ，

a Carrier to Noise Ratio (CNR) ，

a Carrier to Interference plus Noise Ratio (CINR) ，

a Channel Quality Indicator (CQI) ，

a carrier frequency， and

a time duration for synchronization between the device and the further device.
The method of claim 8， wherein the calibrating a first frequency generator of the device comprises：

obtaining an inherent frequency variation of the first frequency generator；

adjusting the frequency offset with the inherent frequency variation； and

calibrating the first frequency generator of the device based on the adjusted frequency offset.
The method of claim 8， further comprising：

determining an updated error between the first frequency generator and the second frequency generator after the calibration；

determining whether the updated error exceeds an error threshold； and

in response to determining that the updated error exceeds the error threshold， reducing a time interval between the first time point and a second time point when a next calibration begins.
The method of claim 13， further comprising：

in response to determining that the updated error being less than the error threshold， increasing the time interval between the first time point and the second time point.
A computer program product being tangibly stored on a non-transient machine-readable medium and comprising machine-executable instructions， the instructions， when executed by a device， causing the device to perform acts including：

determining a quality of a signal received from a further device at a first time point；

obtaining a frequency offset based on the quality of the signal； and

calibrating a first frequency generator of the device based on the frequency offset to reduce an error between the first frequency generator and a second frequency generator of the further device.
The computer program product of claim 15， wherein the instructions， when executed by the device， further cause the device to perform acts including：

in response to the quality being less than a threshold quality， obtaining the frequency offset.
The computer program product of claim 15， wherein the instructions， when executed by the device， further cause the device to perform acts including：

obtaining the frequency offset from a predetermined set of candidate offsets based on the quality of the signal， the predetermined set of candidate offsets including frequency offsets associated with different signal quality levels.
The computer program product of claim 15， wherein the instructions， when executed by the device， further cause the device to perform acts including：

obtaining an inherent frequency variation of the first frequency generator；

adjusting the frequency offset with the inherent frequency variation； and

calibrating the first frequency generator of the device based on the adjusted frequency offset.
The computer program product of claim 15， wherein the instructions， when executed by the device， further cause the device to perform acts including：

determining an updated error between the first frequency generator and the second frequency generator after the calibration；

determining whether the updated error exceeds an error threshold； and

in response to determining that the updated error exceeds the error threshold， reducing a time interval between the first time point and a second time point when a next calibration begins.
The computer program product of claim 19， wherein the instructions， when executed by the device， further cause the device to perform acts including：

in response to determining that the updated error being less than the error threshold， increasing the time interval between the first time point and the second time point.