PATENT DOCUMENT

Publication Number: US-9860095-B1
Application Number: US-201615196275-A
Country: US
Kind Code: B1

Title: Drift robust non-coherent demodulation scheme

Abstract:
This document describes techniques for performing non-coherent demodulation of a differentially modulated signal in a drift robust manner. A differentially modulated signal, including a plurality of symbols, may be received. Non-coherent domodulation of the differentially modulated signal may be performed. The non-coherent demodulation may include performing noise prediction using a high-pass filtered estimated error signal associated with the differentially modulated signal. In some embodiments, frequency offset estimation to reduce frequency offset of the differentially modulated signal may also be performed as part of the non-coherent demodulation.

Claims:
I claim: 
     
       1. A wireless device, comprising:
 an antenna; 
 a radio operatively coupled to the antenna; and 
 a processing element operatively coupled to the radio; 
 wherein the wireless device is configured to:
 wirelessly receive a differentially modulated signal comprising a plurality of symbols; and 
 demodulate the differentially modulated signal, 
 
 wherein the wireless device comprises a noise prediction loop configured to reduce noise characteristics of the differentially modulated signal, wherein the noise prediction loop performs noise prediction for a next symbol of the differentially modulated signal based at least in part on a high-pass filtered error signal associated with a current symbol of the differentially modulated signal and modifies the next symbol based at least in part on a result of the noise prediction, wherein the noise prediction is based at least in part upon a difference between an ideal angular domain result and an angular domain result of subtraction of a previous symbol from the current symbol. 
 
     
     
       2. The wireless device of  claim 1 ,
 wherein the wireless device further comprises a frequency offset estimation loop configured to reduce a constant frequency offset and/or a frequency offset drift of the differentially modulated signal. 
 
     
     
       3. The wireless device of  claim 2 ,
 wherein the frequency offset estimation loop performs frequency offset estimation for the next symbol of the differentially modulated signal based at least in part on a non-high-pass filtered error signal associated with the current symbol of the differentially modulated signal and modifies the next symbol based at least in part on a result of the frequency offset estimation. 
 
     
     
       4. The wireless device of  claim 3 ,
 wherein the frequency offset estimation loop is further configured to wait a predetermined amount of time prior to modifying the next symbol based at least in part on the result of the frequency offset estimation to allow the result of the frequency offset estimation to converge. 
 
     
     
       5. The wireless device of  claim 1 ,
 wherein the noise prediction loop is further configured to wait a predetermined amount of time prior to modifying the next symbol based at least in part on the result of the noise prediction to allow the result of the noise prediction to converge. 
 
     
     
       6. The wireless device of  claim 1 ,
 wherein the differentially modulated signal comprises a Bluetooth signal. 
 
     
     
       7. A method, comprising:
 at a wireless device: 
 receiving a differentially modulated signal; and 
 performing non-coherent demodulation of the differentially modulated signal, 
 wherein the non-coherent demodulation comprises performing noise prediction using a high pass filtered estimated error signal associated with the differentially modulated signal, 
 wherein the noise prediction is based at least in part upon a difference between an ideal angular domain result and an angular domain result of subtraction of a previous symbol from the current symbol. 
 
     
     
       8. The method of  claim 7 , wherein performing non-coherent demodulation of the differentially modulated signal further comprises:
 determining a symbol value for each symbol of the differentially modulated signal using an angular domain result of a subtraction of a previous symbol from a current symbol of the differentially modulated signal, and further using a constellation diagram associating possible angular domain results with possible symbol values. 
 
     
     
       9. The method of  claim 8 , wherein performing non-coherent demodulation of the differentially modulated signal further comprises:
 calculating an estimated error signal for each symbol of the differentially modulated signal based at least in part on a difference between the angular domain result of the subtraction of the previous symbol from the current symbol and an ideal angular domain result associated with the determined symbol value of the current symbol; 
 high-pass filtering the estimated error signal for the current symbol; 
 performing noise prediction using the high pass filtered error signal for the current symbol; and 
 modifying a next symbol of the differentially modulated signal based at least in part on a result of the noise prediction for the current symbol. 
 
     
     
       10. The method of  claim 9 ,
 wherein performing noise prediction for the current symbol is performed for at least a predetermined period of time prior to modifying the next symbol based at least in part on the result of the noise prediction for the current symbol. 
 
     
     
       11. The method of  claim 9 ,
 wherein modifying the next symbol based at least in part on the result of the noise prediction for the current symbol whitens noise characteristics of the next symbol. 
 
     
     
       12. The method of  claim 9 , wherein performing non-coherent demodulation of the differentially modulated signal further comprises:
 estimating frequency offset for the current symbol of the differentially modulated signal using the estimated error signal; and 
 modifying the next symbol of the differentially modulated signal based at least in part on the estimated frequency offset for the current symbol. 
 
     
     
       13. The method of  claim 12 ,
 wherein estimating frequency offset for the current symbol is performed for at least a predetermined period of time prior to modifying the next symbol based at least in part on the estimated frequency offset for the current symbol. 
 
     
     
       14. The method of  claim 7 ,
 wherein the differentially modulated signal comprises a 4 differential quadrature phase shift keying (4DQPSK) signal or an 8 differential phase shift keying (8DPSK) signal. 
 
     
     
       15. An integrated circuit, comprising:
 a symbol value selection circuit portion configured to determine symbol values for symbols of a differentially modulated signal; 
 an error estimation circuit portion configured to calculate an estimated error signal for symbols of the differentially modulated signal; 
 a high pass filtering circuit portion configured to perform high pass filtering of the estimated error signal; and 
 a noise prediction circuit portion configured to perform noise prediction based on the estimated error signal after the high pass filtering, 
 wherein the noise prediction is based at least in part upon a difference between an ideal angular domain result and an angular domain result of subtraction of a previous symbol from the current symbol, and 
 wherein the noise prediction circuit portion is further configured to feed back a result of the noise prediction into the differentially modulated signal to whiten noise effects in the differentially modulated signal. 
 
     
     
       16. The integrated circuit of  claim 15 , wherein the integrated circuit further comprises:
 a frequency offset estimation circuit portion configured to estimate frequency offset in the differentially modulated signal; 
 wherein the frequency offset estimation circuit portion is further configured to feed back a result of the frequency offset estimation into the differentially modulated signal to reduce frequency offset effects in the differentially modulated signal. 
 
     
     
       17. The integrated circuit of  claim 16 ,
 wherein the frequency offset estimation circuit portion is further configured to implement a convergence condition on the frequency offset estimation prior to feeding back the result of the frequency offset estimation into the differentially modulated signal. 
 
     
     
       18. The integrated circuit of  claim 16 ,
 wherein the frequency offset estimation circuit portion is configured to estimate both constant frequency offset and frequency offset drift in the differentially modulated signal. 
 
     
     
       19. The integrated circuit of  claim 15 ,
 wherein to determine symbol values for symbols of the differentially modulated signal, the symbol value selection circuit portion is configured to, for each respective symbol of the differentially modulated signal: 
 compare an angular domain result of subtracting a previous symbol from the respective symbol with possible ideal angular domain results; and 
 select a symbol value associated with an ideal angular domain result most similar to the angular domain result of subtracting the previous symbol from the respective symbol as the determined symbol value of the respective symbol based on comparing the angular domain result of subtracting the previous symbol from the respective symbol with possible ideal angular domain results. 
 
     
     
       20. The integrated circuit of  claim 19 ,
 wherein to calculate the estimated error signal for symbols of the differentially modulated signal, the error estimation circuit portion is configured to, for each respective symbol of the differentially modulated signal: 
 determine a difference between the angular domain result of subtracting the previous symbol from the respective symbol and the ideal angular domain result associated with the determined symbol value of the respective symbol.

Description:
FIELD 
     The present disclosure relates to wireless devices, including to techniques for wireless devices to perform drift robust non-coherent demodulation, e.g., for differential phase shift keying, such as for enhanced data rate Bluetooth communications. 
     DESCRIPTION OF THE RELATED ART 
     Wireless communication systems are rapidly growing in usage. Additionally, there exist numerous different wireless communication technologies and standards. Some examples of wireless communication standards include GSM, UMTS (WCDMA), LTE, LTE Advanced (LTE-A), 3GPP2 CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), IEEE 802.11 (WLAN or Wi-Fi), IEEE 802.16 (WiMAX), Bluetooth, and others. Bluetooth is a family of wireless communication technologies typically used for short-range communication. The Bluetooth family encompasses ‘Classic Bluetooth’ (also referred to herein as “Classic BT” or simply “BT”) as well as ‘Bluetooth Low Energy’ (referred to herein as “BLE”). 
     Differential modulation techniques, including certain differential phase shift keying techniques that can be used when performing BT communication, may make use of the difference between successive symbols transmitted in a signal to convey information. Because the data in such modulation techniques underlies the difference between symbols, it is generally possible to utilize non-coherent demodulation techniques to decode differentially modulated signals. Non-coherent demodulation may be relatively simple to implement, but can suffer from lower effective signal strength relative to coherent demodulation. 
     SUMMARY 
     Embodiments are presented herein of systems, apparatuses, and methods for wireless devices to perform drift robust non-coherent demodulation of a differentially modulated signal. 
     According to the techniques described herein, a noise prediction scheme may be used in conjunction with non-coherent demodulation of a differentially modulated signal. The noise prediction scheme may result in an effective signal strength gain that may (at least partially) offset the relative loss when compared with performing coherent demodulation. The noise prediction scheme may be performed in the high frequency domain. For example, an error signal (e.g., associated with the differentially modulated signal) used by the noise prediction process may be high-pass filtered prior to being provided to the noise prediction module. 
     While noise prediction may have the potential to increase the sensitivity of the non-coherent demodulation of the differentially modulated signal to constant frequency offset and frequency offset drift, since such effects may (e.g., at least in some instances, such as certain Bluetooth implementations) characteristically be predominantly in the low frequency domain, performing the noise prediction in the high frequency domain may substantially reduce or avoid increasing the sensitivity to frequency offset effects. Additionally, as noise in the differentially modulated signal may (e.g., at least in some instances, such as certain Bluetooth implementations) characteristically be predominantly in the high frequency domain, this may not substantially negatively affect the effectiveness of the noise prediction scheme. 
     According to some embodiments, an additional loop may be added to further increase the robustness of the non-coherent demodulation techniques described herein to frequency offset of the differentially modulated signal. For example, a frequency offset estimation loop may be employed to estimate constant frequency offset and/or frequency offset drift, and to adjust the differentially modulated signal to reduce the frequency offset according to the estimated constant frequency offset and/or frequency offset drift. 
     Additionally, if desired, one or more convergence conditions may be used to increase the stability of the estimation results from the frequency offset estimation and/or the noise prediction scheme. 
     The techniques described herein may be implemented in and/or used with a number of different types of devices, including but not limited to cellular phones, tablet computers, portable computers, desktop computers, accessory and/or wearable computing devices, portable media players, remote controls, wireless speakers, set top box devices, television and/or media systems, and any of various other computing devices. 
     This Summary is intended to provide a brief overview of some of the subject matter described in this document. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present subject matter can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which: 
         FIGS. 1-3  illustrate exemplary wireless communication systems; 
         FIGS. 4-5  illustrate exemplary block diagrams of wireless devices; 
         FIG. 6  is a flowchart diagram illustrating an exemplary method for performing non-coherent demodulation in a drift robust manner; 
         FIGS. 7-8  illustrate exemplary possible differential modulation constellations; and 
         FIGS. 9-11  are circuit diagrams illustrating exemplary demodulation arrangements with various possible noise prediction schemes. 
     
    
    
     While the features described herein are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to be limiting to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the subject matter as defined by the appended claims. 
     The term “configured to” is used herein to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry) that performs the task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke interpretation under 35 U.S.C. §112(f) for that unit/circuit/component. 
     DETAILED DESCRIPTION 
     Terms 
     The following is a glossary of terms used in the present disclosure: 
     Memory Medium—Any of various types of memory devices or storage devices. The term “memory medium” is intended to include an installation medium, e.g., a CD-ROM, floppy disks, or tape device; a computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash, magnetic media, e.g., a hard drive, or optical storage; registers, or other similar types of memory elements, etc. The memory medium may include other types of memory as well or combinations thereof. In addition, the memory medium may be located in a first computer system in which the programs are executed, or may be located in a second different computer system which connects to the first computer system over a network, such as the Internet. In the latter instance, the second computer system may provide program instructions to the first computer for execution. The term “memory medium” may include two or more memory mediums which may reside in different locations, e.g., in different computer systems that are connected over a network. The memory medium may store program instructions (e.g., embodied as computer programs) that may be executed by one or more processors. 
     Carrier Medium—a memory medium as described above, as well as a physical transmission medium, such as a bus, network, and/or other physical transmission medium that conveys signals such as electrical, electromagnetic, or digital signals. 
     Programmable Hardware Element—includes various hardware devices comprising multiple programmable function blocks connected via a programmable interconnect. Examples include FPGAs (Field Programmable Gate Arrays), PLDs (Programmable Logic Devices), FPOAs (Field Programmable Object Arrays), and CPLDs (Complex PLDs). The programmable function blocks may range from fine grained (combinatorial logic or look up tables) to coarse grained (arithmetic logic units or processor cores). A programmable hardware element may also be referred to as “reconfigurable logic”. 
     Computer System—any of various types of computing or processing systems, including a personal computer system (PC), mainframe computer system, workstation, network appliance, Internet appliance, personal digital assistant (PDA), personal communication device, smart phone, television system, grid computing system, or other device or combinations of devices. In general, the term “computer system” can be broadly defined to encompass any device (or combination of devices) having at least one processor that executes instructions from a memory medium. 
     User Equipment (UE) (or “UE Device”)—any of various types of computer systems devices which are mobile or portable and which performs wireless communications. Examples of UE devices include mobile telephones or smart phones (e.g., iPhone™, Android™-based phones), portable gaming devices (e.g., Nintendo DS™, Play Station Portable™, Gameboy Advance™, iPhone™), laptops, wearable devices (e.g. smart watch, smart glasses), PDAs, portable Internet devices, music players, data storage devices, or other handheld devices, etc. In general, the term “UE” or “UE device” can be broadly defined to encompass any electronic, computing, and/or telecommunications device (or combination of devices) which is easily transported by a user and capable of wireless communication. 
     Wireless Device—any of various types of computer system devices which performs wireless communications. A wireless device can be portable (or mobile) or may be stationary or fixed at a certain location. A UE is an example of a wireless device. 
     Communication Device—any of various types of computer systems or devices that perform communications, where the communications can be wired or wireless. A communication device can be portable (or mobile) or may be stationary or fixed at a certain location. A wireless device is an example of a communication device. A UE is another example of a communication device. 
     Base Station—The term “Base Station” has the full breadth of its ordinary meaning, and at least includes a wireless communication station installed at a fixed location and used to communicate as part of a wireless telephone system or radio system. 
     Processing Element—refers to various elements or combinations of elements. Processing elements include, for example, circuits such as an ASIC (Application Specific Integrated Circuit), portions or circuits of individual processor cores, entire processor cores, individual processors, programmable hardware devices such as a field programmable gate array (FPGA), and/or larger portions of systems that include multiple processors. 
     Automatically—refers to an action or operation performed by a computer system (e.g., software executed by the computer system) or device (e.g., circuitry, programmable hardware elements, ASICs, etc.), without user input directly specifying or performing the action or operation. Thus the term “automatically” is in contrast to an operation being manually performed or specified by the user, where the user provides input to directly perform the operation. An automatic procedure may be initiated by input provided by the user, but the subsequent actions that are performed “automatically” are not specified by the user, i.e., are not performed “manually”, where the user specifies each action to perform. For example, a user filling out an electronic form by selecting each field and providing input specifying information (e.g., by typing information, selecting check boxes, radio selections, etc.) is filling out the form manually, even though the computer system must update the form in response to the user actions. The form may be automatically filled out by the computer system where the computer system (e.g., software executing on the computer system) analyzes the fields of the form and fills in the form without any user input specifying the answers to the fields. As indicated above, the user may invoke the automatic filling of the form, but is not involved in the actual filling of the form (e.g., the user is not manually specifying answers to fields but rather they are being automatically completed). The present specification provides various examples of operations being automatically performed in response to actions the user has taken. 
       FIGS. 1-3 —Communication System 
       FIG. 1  illustrates an exemplary (and simplified) wireless communication system  100  in which aspects of this disclosure may be implemented. It is noted that the system of  FIG. 1  is merely one example of a possible system, and embodiments of this disclosure may be implemented in any of various systems, as desired. 
     As shown, the exemplary wireless communication system includes a (“first”) wireless device  102  in communication with another (“second”) wireless device  104 . The first wireless device  102  and the second wireless device  104  may communicate wirelessly using at least one wireless communication technique that utilizes differential modulation. 
     As one possibility, the first wireless device  102  and the second wireless device  104  may communicate using Bluetooth (BT) wireless communication and/or techniques based on BT wireless communication. In such a context, the first wireless device  102  may be referred to as the master (or “central”) device  102  while the second wireless device  104  may be referred to as the slave (or “peripheral”) device  104  (e.g., the ‘master’ and ‘slave’ designations may be specific to the roles of the devices  102 ,  104  with respect to BT communication). One or both of the master device  102  and the slave device  104  may also be capable of communicating via one or more additional wireless communication protocols, such as any of Bluetooth Low Energy (also referred to as “BLE”), IEEE 802.11 (Wi-Fi), near field communication (NFC), GSM, UMTS (WCDMA, TDSCDMA), LTE, LTE-Advanced (LTE-A), 3GPP2 CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), Wi-MAX, GPS, etc. 
     As shown, as one possibility a single master (e.g., primary) device  102  may communicate with a single slave (e.g., secondary) device  104  at a particular time. Note that it may also be possible for a master device  102  to communicate with multiple slave devices  104 . The master device  102  may be any of a variety of types of devices. As one possibility, the master device  102  may be a substantially portable wireless user equipment (UE) device, such as a smart phone, hand-held device, a wearable device, a tablet, or virtually any type of wireless device. As another possibility, the master device  102  may be a substantially stationary device, such as a set top box, media player (e.g., an audio or audiovisual device), gaming console, or any of a variety of other types of device. 
     The slave device  104  may also be any of various types of devices. In some cases, the slave device  104  may be a device with a relatively low power usage profile, e.g., which is designed to operate for relatively long periods of time before replacing or recharging its power source. Some examples might include hearing aids, speakers, remote control devices, microphones, headsets, various types of sensors, watches and other wearable computing devices, etc. Note that some devices may be configured to act as either a master device or a slave device, while others may be configured to act only as a master device, or only as a slave device. 
     Each of the master device  102  and the slave device  104  may include wireless communication circuitry configured to facilitate the performance of wireless communication, which may include various digital and/or analog radio frequency (RF) components, a processor that is configured to execute program instructions stored in memory, a programmable hardware element such as a field-programmable gate array (FPGA), and/or any of various other components. The master device  102  and/or the slave device  104  may perform any of the method embodiments described herein, or any portion of any of the method embodiments described herein, using any or all of such components. 
     Each of the master device  102  and the slave device  104  may include one or more antennas for communicating using one or more wireless communication protocols. In some cases, one or more parts of a receive and/or transmit chain may be shared between multiple wireless communication standards; for example, a device might be configured to communicate using either of Bluetooth or Wi-Fi using partially or entirely shared wireless communication circuitry (e.g., using a shared radio or at least shared radio components). The shared communication circuitry may include a single antenna, or may include multiple antennas (e.g., for MIMO) for performing wireless communications. Alternatively, a device may include separate transmit and/or receive chains (e.g., including separate antennas and other radio components) for each wireless communication protocol with which it is configured to communicate. As a further possibility, a device may include one or more radios or radio components which are shared between multiple wireless communication protocols, and one or more radios or radio components which are used exclusively by a single wireless communication protocol. For example, a device might include a shared radio for communicating using either of LTE or CDMA2000 1×RTT, and separate radios for communicating using each of Wi-Fi and Bluetooth. Other configurations are also possible. 
     The slave device  104  may include one or more microphones and/or one or more speakers, e.g., in order to receive and/or render audio. For example, the slave device  104  might include one or more microphones for picking up audio in order to provide audio input to the master device  102 , one or more speakers for rendering audio received as audio output from the master device  102 , or may include both microphone and speaker for use in conjunction with any of input, output, or bi-directional communication with the master device  102 . The master device  102  may similarly include one or more microphones and/or one or more speakers. Note additionally that aspects of the present disclosure may also be implemented in scenarios in which one or both of the master device  102  and the slave device  104  do not include speakers and/or microphones; for example, while audio data may commonly be communicated using BT communication, any of various other types of data may also or alternatively be communicated using BT and other wireless communication technologies. 
     As previously noted, aspects of this disclosure may be implemented in conjunction with the wireless communication system of  FIG. 1 . For example, since the wireless devices  102 ,  104  may communicate using at least one wireless communication technique that utilizes differential modulation, one or both of the wireless devices  102 ,  104  may implement some or all of those features described subsequently herein with respect to  FIGS. 6-11 , such as performing high frequency domain noise prediction in conjunction with non-coherent demodulation of a differentially modulated signal. By utilizing such techniques (and/or other techniques described herein), the wireless device(s) may (at least according to some embodiments) be able to advantageously obtain the gain benefits of noise prediction without (or with less) susceptibility to frequency offset effects when performing non-coherent demodulation of a differentially modulated signal. 
     As a further example of a possible wireless communication system in which aspects of this disclosure may be implemented,  FIG. 2  illustrates a system  200  in which a wireless user equipment (UE) device  202  (e.g., a smart phone, acting as a central or master device) is in communication with a smart watch  204  (acting as a peripheral or slave device). In such an example implementation, the UE  202  may provide data (e.g., audio data, video data, configuration data, synchronization data, and/or any of various other types of data) to the smart watch  204 , and/or may receive data from the smart watch  204 , via BT communication as described herein. 
     The wireless devices of the communication system of  FIG. 2  may also be configured to communicate using at least one wireless communication technique that utilizes differential modulation. Accordingly (e.g., to obtain the gain benefits of noise prediction with reduced susceptibility to frequency offset effects when performing non-coherent demodulation), one or both of the wireless devices  202 ,  204  may implement some or all of those features described subsequently herein with respect to  FIGS. 6-11 , such as performing high frequency domain noise prediction in conjunction with non-coherent demodulation of a differentially modulated signal. 
     As another example of a possible wireless communication system in which aspects of this disclosure may be implemented,  FIG. 3  illustrates a system  300  in which a remote control device  304  (acting as a peripheral or slave device) is in communication with a set top box  306  (acting as a master or central device). In such an exemplary implementation, the remote control  304  may receive audio signals (e.g., voice commands for controlling the set top box  306 ) from a user  302  via a microphone, and may provide audio data corresponding to those audio signals as an input audio stream to the set top box  306  via BT communication as described herein. In some instances, once the audio data is received at the set top box  306 , the following may be performed: the set top box  306  may communicate the audio data to a server (not depicted in  FIG. 3 ) via the Internet for processing; the server may analyze the received audio data and determine that the audio data corresponds to a command that can be executed by the set top box  306 ; the server may transmit one or more messages back to the set top box  306  that indicate the command; and then the set top box  306  may execute the command. 
     Alternatively or additionally, the set top box  306  of  FIG. 3  may execute a videoconferencing application. In such a scenario, the remote control  304  may receive audio signals from the user  302  via a microphone, and may provide audio data corresponding to those signals as an input audio stream to the set top box  306  via BT communication as described herein. Upon receiving the input audio stream, the set top box  306  may transmit the audio data to one or more other endpoints (not depicted in  FIG. 3 ) and/or intermediate servers (not depicted in  FIG. 3 ) involved in the videoconference via the Internet. 
     As another variation on the wireless communication system of  FIG. 3 , instead of a set top box  306  as shown in  FIG. 3 , the wireless communication system may include a BT-capable television system that, in addition to performing functionality performed by a television system (e.g. rendering video data onto a display, and so on), includes components that perform the functionality described above as performed by the set top box  306 . 
     Similar to the wireless devices of the systems of  FIGS. 1-2 , the wireless devices  304 ,  306  of  FIG. 3  may be configured to communicate using at least one wireless communication technique that utilizes differential modulation, and may implement high frequency domain noise prediction in conjunction with non-coherent demodulation of a differentially modulated signal and/or any other features described herein with respect to  FIGS. 6-11 . 
     While the exemplary wireless communication systems illustrated in  FIGS. 1-3  represent possible scenarios in which aspects of the present disclosure may be implemented, it should be recognized that the techniques described herein may also or alternatively be implemented in a variety of alternate scenarios, in conjunction with a variety of other device combinations, as will be apparent to those skilled in the art. 
       FIGS. 4-5 —Exemplary Device Block Diagrams 
       FIG. 4  illustrates an exemplary wireless device  400  that may be configured for use in conjunction with various aspects of the present disclosure. The device  400  may be any of a variety of types of device and may be configured to perform any of a variety of types of functionality. The device  400  may be a substantially portable device (a mobile device), such as a mobile phone, a personal productivity device, a computer or a tablet, a handheld gaming console, a portable media player, etc. Alternatively, the device  400  may be a substantially stationary device, such as a desktop computer, set top box, television, or other type of substantially stationary device. The device  400  may be configured to operate as a master or central device in a Bluetooth wireless communication scheme, and/or may be configured to operate as a slave or peripheral device in a Bluetooth wireless communication scheme. 
     As shown, the device  400  may include a processing element  402 . The processing element may include or be coupled to one or more memory elements. For example, the device  400  may include one or more memory media (e.g., memory  406 ), which may include any of a variety of types of memory and may serve any of a variety of functions. For example, memory  406  could be RAM serving as a system memory for processing element  402 . Other types and functions are also possible. 
     Additionally, the device  400  may include wireless communication circuitry  430 . The wireless communication circuitry may include any of a variety of communication elements (e.g., antenna for wireless communication, analog and/or digital communication circuitry/controllers, etc.) and may enable the device to wirelessly communicate using one or more wireless communication protocols. 
     Note that in some cases, the wireless communication circuitry  430  may include its own processing element (e.g., a baseband processor), e.g., in addition to the processing element  402 . For example, the processing element  402  might be an ‘application processor’ whose primary function may be to support application layer operations in the device  400 , while the wireless communication circuitry  430  might be a ‘baseband processor’ whose primary function may be to support baseband layer operations (e.g., to facilitate wireless communication between the device  400  and other devices) in the device  400 . In other words, in some cases the device  400  may include multiple processing elements (e.g., may be a multi-processor device). Other configurations (e.g., instead of or in addition to an application processor/baseband processor configuration) utilizing a multi-processor architecture are also possible. 
     The device  400  may additionally include any of a variety of other components (not shown) for implementing device functionality, depending on the intended functionality of the device  106 , which may include further processing and/or memory elements (e.g., audio processing circuitry), one or more power supply elements (which may rely on battery power and/or an external power source) user interface elements (e.g., display, speaker, microphone, camera, keyboard, mouse, touchscreen, etc.), and/or any of various other components. 
     The components of the device  400 , such as processing element  402 , memory  406 , and wireless communication circuitry  430 , may be operatively coupled via one or more interconnection interfaces, which may include any of a variety of types of interface, possibly including a combination of multiple types of interface. As one example, a USB high-speed inter-chip (HSIC) interface may be provided for inter-chip communications between processing elements. Alternatively (or in addition), a universal asynchronous receiver transmitter (UART) interface, a serial peripheral interface (SPI), inter-integrated circuit (I2C), system management bus (SMBus), and/or any of a variety of other communication interfaces may be used for communications between various device components. Other types of interfaces (e.g., intra-chip interfaces for communication within processing element  402 , peripheral interfaces for communication with peripheral components within or external to device  400 , etc.) may also be provided as part of device  400 . 
     The device  400  (e.g., wireless communication circuitry  430  in conjunction with processing element  402 , memory  406 , and/or other components of device  400 ) may be configured to implement features for performing differential demodulation in a drift robust manner. For example, the wireless device  400  may represent an example of a possible wireless device such as illustrated in any of  FIGS. 1-3 , and may be capable of performing non-coherent demodulation of differentially modulated signals using a high-frequency domain noise prediction scheme and/or other features described herein with respect to  FIGS. 6-11 . 
       FIG. 5  is an exemplary block diagram illustrating details of a UE  500 , which may be one possible exemplary implementation of the device  400  illustrated in  FIG. 4 . As shown, the UE  500  may include a system on chip (SOC)  508 , which may include portions for various purposes. For example, as shown, the SOC  508  may include processor(s)  502  which may execute program instructions for the UE  500  and display circuitry  504  which may perform graphics processing and provide display signals to the display  560 . The processor(s)  502  may also be coupled to memory management unit (MMU)  540 , which may be configured to receive addresses from the processor(s)  502  and translate those addresses to locations in memory (e.g., memory  506 , read only memory (ROM)  550 , NAND flash memory  510 ) and/or to other circuits or devices, such as the display circuitry  504 , wireless communication circuitry  530 , connector I/F  520 , and/or display  560 . The MMU  540  may be configured to perform memory protection and page table translation or set up. In some embodiments, the MMU  540  may be included as a portion of the processor(s)  502 . 
     As shown, the SOC  508  may be coupled to various other circuits of the UE  500 . For example, the UE  500  may include various types of memory (e.g., including NAND flash  510 ), a connector interface  520  (e.g., for coupling to a computer system, dock, charging station, etc.), the display  560 , and wireless communication circuitry  530  (e.g., for LTE, LTE-A, CDMA2000, Bluetooth, Wi-Fi, GPS, etc.). 
     The UE  500  may be configured to communicate wirelessly using multiple wireless communication standards. In such instances, the wireless communication circuitry  530  may include radio components which are shared between multiple wireless communication standards and/or radio components which are configured exclusively for use according to a single wireless communication standard. As shown, the UE device  500  may include at least one antenna (and possibly multiple antennas, e.g., for MIMO and/or for implementing different wireless communication technologies, among various possibilities), for performing wireless communication with base stations, access points, and/or other devices. For example, the UE device  500  may use antenna(s)  535  to perform the wireless communication. 
     The UE  500  may also include and/or be configured for use with one or more user interface elements. The user interface elements may include any of various elements, such as display  560  (which may be a touchscreen display), a keyboard (which may be a discrete keyboard or may be implemented as part of a touchscreen display), a mouse, a microphone and/or speakers, one or more cameras, one or more buttons, and/or any of various other elements capable of providing information to a user and/or receiving/interpreting user input. 
     As described herein, the UE  500  may include hardware and software components for implementing features for performing differential demodulation in a drift robust manner. For example, the UE  500  may represent an example of a possible wireless device such as illustrated in any of  FIGS. 1-3 , and may be capable of performing non-coherent demodulation of differentially modulated signals using a high-frequency domain noise prediction scheme and/or other features described herein with respect to  FIGS. 6-11 . The wireless communication circuitry  530  of the UE device  500  may be configured to implement part or all of the features described herein, e.g., using various circuitry components of the wireless communication circuitry. Alternatively (or in addition), the wireless communication circuitry  530  of the UE device  500 , in conjunction with one or more of the other components  502 ,  504 ,  506 ,  508 ,  510 ,  520 ,  535 ,  540 ,  550 ,  560 , may be configured to implement part or all of the features described herein, such as the features described herein with reference to any or all of  FIGS. 6-11 . 
       FIG. 6 —Flowchart 
     Differential modulation techniques may make use of the difference between successive symbols transmitted in a signal to convey information, e.g., in contrast to coherent modulation techniques that may rely on a comparison of the transmitted signal with a reference signal known by both transmitter and receiver to convey information. Differential modulation techniques are employed in a number of wireless communication technologies, among possible applications. For example, as one possibility, the differentially modulated signal may be a Bluetooth signal, such as an enhanced data rate 2 (EDR2) signal modulated using 4-differential quadrature phase shift keying (4DQPSK), or an enhanced data rate 3 (EDR3) signal modulated using 8-differential phase shift keying (8DPSK). Other types of differentially modulated signals are also possible. 
     It may be possible for a coherent or non-coherent approach to be used for demodulation of a differentially modulated signal. Coherent demodulation may include performing phase acquisition, which may be more complex than the phase discrimination on which non-coherent demodulation may be based. In addition to avoiding the need for phase acquisition (and thus potentially allowing for a more simple implementation), non-coherent demodulation may also be relatively robust to frequency offset compared to coherent demodulation. However, absent any mitigating factors, non-coherent demodulation may suffer from a gain loss (e.g., approximately 2.5 dB, in some instances) relative to coherent decoding. 
     One possibility for regaining the loss when employing non-coherent demodulation may include utilizing a noise prediction scheme. However, such noise prediction mechanisms can have the potential to be sensitive to constant frequency offset and frequency offset drift (e.g., translated to additive DC or carrying sine wave in the differentiated phase domain). As a result, existing differential demodulation techniques may be forced to accept a trade off between decreased gain and susceptibility to frequency offset effects. Accordingly, it would be desirable, at least in some instances, to provide techniques that are capable of benefiting from noise prediction gain while preserving robustness to constant frequency offset and/or frequency offset drift. 
       FIG. 6  is a flowchart diagram illustrating an example method for performing differential demodulation in a drift robust manner while also obtaining noise prediction gain. The method of  FIG. 6  may be implemented by a wireless user equipment (UE) device or other device capable of performing communication involving differential demodulation, such as a device capable of performing enhanced data rate (EDR) BT communication. The method shown in  FIG. 6  may be used in conjunction with any of the computer systems or devices shown in the above Figures, among other devices. Some of the method elements shown may be performed concurrently, in a different order than shown, substituted for by other elements, or may be omitted. Additional method elements may also be performed as desired. As shown, the methods may operate as follows. 
     A differentially modulated signal may be received ( 602 ). The differentially modulated signal may be modulated according to any of a variety of modulation techniques. For example, the differentially modulated signal may be a Bluetooth (or Bluetooth based) signal, such as a 4QDPSK EDR2 signal or a 8DPSK EDR3 signal, among various possibilities. 
     The differentially modulated signal may include multiple symbols, e.g., received successively over time. For example, EDR2 and EDR3 schemes may specify communication of 1M symbols per second. Each symbol may represent one or more (e.g., depending on the modulation scheme) bit values, for example using the angular phase of the symbol relative to the previous symbol received. 
     The differentially modulated signal may be demodulated ( 604 ), e.g., using non-coherent demodulation. Demodulating the differentially modulated signal may include (e.g., for each symbol of the differentially modulated signal subsequent to the first symbol) subtracting a previous symbol of the differentially modulated signal from the current symbol of the differentially modulated signal. The angle of difference between the two symbols (i.e., the angular domain result of the subtraction) may be compared with a constellation diagram indicating possible ideal sample values corresponding to possible decoded symbol bits according to the modulation scheme in use. A ‘slicer’ may make a decision matching the angular domain result with the closest available constellation symbol based on this comparison. This ideal symbol/angular domain result, and/or the symbol value/bits associated with this ideal symbol/angular domain result, may be output from the slicer. 
     In order to obtain noise prediction benefits while preserving robustness to frequency offset effects, one or more feedback loops may be used in conjunction with the demodulation of the differentially modulated signal. As one such feedback loop, a noise prediction loop for performing noise prediction in the high frequency domain may be used ( 606 ). 
     The noise prediction loop may receive an estimated error signal associated with the current symbol of the differentially modulated signal, perform noise prediction for the subsequent symbol of the differentially modulated signal based on the estimated error signal associated with the current symbol, and generate a signal configured to modify the subsequent symbol to mitigate (or reduce) noise effects in that symbol. For example, the noise prediction scheme may act to ‘whiten’ the noise in that symbol, i.e., to flatten the noise levels across the spectrum of that symbol. The signal configured to modify the subsequent symbol may be combined with the subsequent symbol (e.g., in the differentiated phase domain) of the differentially modulated signal before the subsequent symbol is sliced. 
     The estimated error signal used by the noise prediction loop may be calculated as (or more generally may be based upon) a difference between the angular domain result of the subtraction of the previous symbol from the current symbol and the ideal angular domain result selected by the slicer for the current symbol. The estimated error signal may further be high-pass filtered (e.g., using a high-pass filter) before noise prediction is performed. This may result in the noise prediction being performed in the high frequency domain (e.g., rather than the low frequency domain or across the entire frequency range of the signal), which may (at least in some instances) help avoid increasing the susceptibility of the demodulation process to constant frequency offset and/or frequency offset drift. 
     For example, consider the differentially modulated signal in the differentiated phase domain. It may be the case that the constant frequency offset and frequency offset drift typically occur in the low frequency domain, while noise predominantly occurs in the high frequency domain. As a result, it may be possible to gain the benefit of noise prediction without exacerbating frequency offset susceptibility by utilizing a high pass filter to perform noise prediction in the high frequency domain. 
     As another possible feedback loop, a frequency offset estimation loop for estimating frequency offset effects for the differentially modulated signal may be used ( 608 ), if desired. For example, while performing the noise prediction in the high frequency domain may reduce the impact of frequency offset effects from the noise prediction process, an additional frequency offset estimation loop may further reduce or nullify the effect of constant frequency offset and/or frequency offset drift when performing non-coherent demodulation of the differentially modulated signal. 
     The frequency offset estimation loop may also receive the error signal associated with the current symbol of the differentially modulated signal. The frequency offset estimation loop may perform estimation of constant frequency offset and/or frequency offset drift, and may generate a signal configured to modify the subsequent symbol to mitigate frequency offset effects in that symbol. The signal configured to modify the subsequent symbol may be combined with the subsequent symbol (e.g., in the differentiated phase domain) of the differentially modulated signal before the subsequent symbol is sliced. 
     Note that one or more convergence conditions may be used in conjunction with either or both of the noise prediction loop and the frequency offset estimation loop, as desired. For example, a timer (or multiple timers) may be used to cause the noise prediction loop and/or the frequency offset estimation loop to wait a certain amount of time after receiving the error signal for the current symbol prior to modifying the subsequent symbol, e.g., in order to allow sufficient time for the noise prediction and/or frequency offset estimation to converge to stable results. 
     Note further that the techniques described herein may be used in succession to decode each successive symbol of the differentially modulated signal in turn and thus to produce a bit stream at the device receiving the differentially modulated signal. At least according to some embodiments, the bit stream may be subject to fewer errors and/or may be produced with less power consumption than might otherwise occur, as a result of utilizing noise prediction performed in the high frequency domain (and potentially as a result of utilizing frequency offset estimation) to obtain the noise prediction gain while preserving robustness to frequency offset effects. 
     
       FIGS. 7-11 
     
       FIGS. 7-11  and the description thereof are provided by way of example, and are not intended to be limiting to the disclosure as a whole. Numerous alternatives to and variations of the details provided herein below are possible and should be considered within the scope of the present disclosure. 
       FIGS. 7-8  are constellation diagrams illustrating possible differential modulation constellations.  FIG. 7  illustrates an example constellation diagram that may be used in conjunction with 4QDPSK, while  FIG. 8  illustrates an example constellation diagram that may be used in conjunction with 8DPSK. As shown, in each case the value of a symbol may be determined based on the relative (differential) phase of the symbol in comparison to the previous symbol. As further shown, in the case of 4QDPSK, there may be four possible symbol values (e.g., 00, 01, 10, 11) associated with a symbol, while in the case of 8DPSK, there may be eight possible symbol values (e.g., 000, 001, 010, 011, 100, 101, 110, 111) associated with a symbol. 
       FIG. 9  illustrates an example circuit for performing non-coherent demodulation of a differentially modulated signal that utilizes noise prediction but is non-robust with respect to frequency offset effects. As shown, the circuit may receive the signal in the differentiated phase domain r[t]. This signal may be combined with the output z[n] of the noise prediction loop at combiner  902 , and the resulting signal x[t]+z[t] may be provided to the slicer  904 . The slicer  904  may determine the symbol value {circumflex over (x)}[t], which may be output from the circuit as the decoded signal. 
     In addition, the signal x[t]+z[t] and the ideal signal for that signal as determined by the slicer  904  may be combined at combiner  906 , such that the ideal signal is subtracted from the actual signal, to generate (calculate) an error signal e[t]. The error signal e[t] may be provided to a noise prediction circuit  908 , which may estimate the noise conditions based on the error signal e[t] and generate a signal z[n] to be combined with the differentiated phase domain signal r[t] as previously noted. Note that, as shown, the noise preduction output signal z[n] may be (optionally) scaled according to a scaling factor ‘c’ using amplifier  910 , e.g., to allow the amount of noise prediction feedback applied to the input signal to be scaled as desired. 
     Since the circuit of  FIG. 9  performs noise prediction using an unfiltered error signal, the circuit of  FIG. 9  may be vulnerable to frequency offset effects, which could result in decoding errors.  FIG. 10  illustrates an alternate circuit for performing non-coherent demodulation of a differentially modulated signal that utilizes noise prediction and is robust with respect to frequency offset effects. 
     As shown, the circuit may receive the signal in the differentiated phase domain r[t]. This signal may be combined with the output of a frequency offset estimation loop at combiner  1002  and further combined with the output d[n] of a noise prediction loop at combiner  1004 , and the resulting signal x[t]+z[t] may be provided to the slicer  1006 . The slicer  1006  may determine the symbol value {circumflex over (x)}[t], which may be output from the circuit as the decoded signal. 
     In addition, the signal x[t]+z[t] and the ideal signal for that signal as determined by the slicer  1006  may be combined at combiner  1008 , such that the ideal signal is subtracted from the actual signal, to generate (calculate) an error signal e[t]. The error signal e[t] may be provided to a noise prediction circuit  1012  by way of a high pass filter  1010 . The noise prediction circuit  1012  may perform noise prediction in the high frequency domain based on the high-pass filtered error signal and generate a signal z[n] to be combined with the differentiated phase domain signal r[t] as previously noted. As shown, the noise prediction output signal z[n] may (optionally) be scaled according to a scaling factor ‘c’ using amplifier  1014 , e.g., to allow the amount of noise prediction feedback applied to the input signal to be scaled as desired. 
     Further, the error signal may be provided to a frequency offset estimation circuit portion  1016 , which may include multiple loops, for estimating the frequency offset of the differentially modulated signal (e.g., including constant frequency offset and frequency offset drift), with proportional (Kp) and integral (Ki) constants being used as desired to weight the amount of signal modification to be implemented to mitigate constant and time-varying frequency offset effects respectively. The frequency offset estimation circuit portion  1016  may generate a frequency offset estimation signal d[n], which may be combined with (e.g., subtracted from) the differentiated phase domain signal r[t] as previously noted. 
       FIG. 11  illustrates a circuit for performing non-coherent demodulation of a differentially modulated signal that utilizes noise prediction and is robust with respect to frequency offset effects, similar to the circuit of  FIG. 10 , but additionally including circuit portions implementing a convergence condition with respect to the frequency offset estimation. 
     As shown, the circuit may include a slicer  1106 , and a noise prediction circuit portion  1108  whose output z[n] may be combined with the differentiated phase domain signal r[t] at combiner  1104 . The circuit further can include a frequency offset estimation circuit portion  1110  whose output d[n] may be combined with the differentiated phase domain signal r[t] at combiner  1102 . 
     In addition, the circuit may utilize a timer to control when the frequency offset estimation d[n] is applied to the differentiated phase domain signal r[t]. The timer may be initiated, for example, when the error signal for the current symbol is provided to the noise prediction circuit portion  1108  and the frequency offset estimation circuit portion  1110 . A time value (e.g., ‘t0’) may be selected, and it may be determined whether the timer exceeds the selected time value ( 1112 ). The result of the determination may be provided to a pair of muxes  1114 ,  1116 . These muxes may be configured such that if the timer exceeds the selected time value, the frequency offset estimation d[n] is output to be combined with the differentiated phase domain signal r[t] at combiner  1102 , but if the timer does not exceed the selected time value, the frequency offset estimation is fed back into the error signal, either prior to being provided to both the noise prediction circuit portion  1108  and the frequency offset estimation circuit portion  1110 , or after being provided to the noise prediction circuit portion  1108  but prior to being provided to the frequency offset estimation circuit portion  1110 . 
     Whether the frequency offset estimation is fed back into the error signal before or after the noise prediction circuit portion  1108  may similarly be controlled by a pair of muxes  1118 ,  1120 , which may be configured to feed back the frequency offset estimation at a desired location based on any of various desired conditions. For example, as one possibility (as shown), a condition on whether only DC feedback is present may be used, such that a positive result of the condition results in the frequency offset estimation being fed back into the error signal just prior to being provided to the frequency offset estimation circuit portion  1110 , while a negative result of the condition results in the frequency offset estimation being fed back into the error signal prior to being provided to both the noise prediction circuit portion  1108  and the frequency offset estimation circuit portion  1110 . Note that other conditions may additionally or alternatively be used in conjunction with such a circuit, as desired. Use of such convergence conditions as illustrated in the circuit of  FIG. 11  and/or other conditions may allow the frequency offset estimation to converge to a stable result prior to being fed back to the differentiated phase domain signal r[t], at least according to some embodiments. Note further that, while not shown in  FIG. 11 , similar or different convergence conditions may also or alternatively be implemented with respect to the noise prediction circuit portion  1108 , if desired. 
     Embodiments of the present disclosure may be realized in any of various forms. For example some embodiments may be realized as a computer-implemented method, a computer-readable memory medium, or a computer system. Other embodiments may be realized using one or more custom-designed hardware devices such as ASICs. Still other embodiments may be realized using one or more programmable hardware elements such as FPGAs. 
     In some embodiments, a non-transitory computer-readable memory medium may be configured so that it stores program instructions and/or data, where the program instructions, if executed by a computer system, cause the computer system to perform a method, e.g., any of a method embodiments described herein, or, any combination of the method embodiments described herein, or, any subset of any of the method embodiments described herein, or, any combination of such subsets. 
     In some embodiments, a device (e.g., a wireless device) may be configured to include a processor (or a set of processors) and a memory medium, where the memory medium stores program instructions, where the processor is configured to read and execute the program instructions from the memory medium, where the program instructions are executable to implement any of the various method embodiments described herein (or, any combination of the method embodiments described herein, or, any subset of any of the method embodiments described herein, or, any combination of such subsets). The device may be realized in any of various forms. 
     While examples have been provided above that relate to Bluetooth, it should be understood that the techniques described herein may also be used, mutatis mutandis, in the context of any other appropriate wired or wireless communications technology, including but not limited to cellular, IEEE 802.11, Bluetooth Low Energy, or other technologies. Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Metadata:
Filing Date: 20160629
Publication Date: 20180102
Grant Date: 20180102
Priority Date: 20160629
Inventors: AVNER YUVAL
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W4/008", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/148", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L27/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2334", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/205", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2334", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/205", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W4/80", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 60788975