Patent Publication Number: US-2022239330-A1

Title: Discrete time cancellation for providing coexistence in radio frequency applications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/949,388, filed Oct. 28, 2020, and titled “DISCRETE TIME CANCELLATION FOR PROVIDING COEXSITENCE IN RADIO FREQUENCY COMMUNICATION SYSTEMS,” which claims priority to U.S. application Ser. No. 16/541,530, filed Aug. 15, 2019, and titled “DISCRETE TIME CANCELLATION FOR PROVIDING COEXSITENCE IN RADIO FREQUENCY COMMUNICATION SYSTEMS,” which claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Patent Application No. 62/720,514, filed Aug. 21, 2018, and titled “DISCRETE TIME CANCELLATION FOR PROVIDING COEXSITENCE IN RADIO FREQUENCY COMMUNICATION SYSTEMS,” each of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     Embodiments of the invention relate to electronic systems, and in particular, to radio frequency electronics. 
     Description of Related Technology 
     Radio frequency (RF) communication systems can be used for transmitting and/or receiving signals of a wide range of frequencies. For example, an RF communication system can be used to wirelessly communicate RF signals in a frequency range of about 30 kHz to 300 GHz, such as in the range of about 410 MHz to about 7.125 GHz for fifth generation (5G) frequency range  1  (FR1) communications. 
     Examples of RF communication systems include, but are not limited to, mobile phones, tablets, base stations, network access points, customer-premises equipment (CPE), laptops, and wearable electronics. 
     SUMMARY 
     In certain embodiments, the present disclosure relates to a mobile device. The mobile device includes a first front end system configured to output a radio frequency receive signal and a first radio frequency observation signal, and a first transceiver including a receive channel configured to process the radio frequency receive signal to generate a first digital baseband receive signal, a first observation channel configured to process the first radio frequency observation signal to generate a first digital observation signal, a first spectral regrowth baseband sampling circuit configured to process the first digital observation signal to generate spectral regrowth observation data, and a discrete time cancellation circuit configured to compensate the first digital baseband receive signal for radio frequency signal leakage based on the spectral regrowth observation data and on direct transmit leakage observation data. 
     In some embodiments, the mobile device further includes a second transceiver configured to provide the direct transmit leakage observation data to the first transceiver. 
     According to various embodiments, the second transceiver includes a second observation channel configured to process a second radio frequency observation signal to generate a second digital observation signal, and a direct transmit leakage baseband sampling circuit configured to process the second digital observation signal to generate the direct transmit leakage observation data. In accordance with a number of the embodiments, the mobile device further includes a second front end system configured to output the second radio frequency observation signal and a radio frequency transmit signal. According to several embodiments, the first front end system includes a first directional coupler configured to generate the first radio frequency observation signal, and the second front end system includes a second directional coupler configured to generate the second radio frequency observation signal. In accordance with various embodiments, the mobile device further includes a first antenna coupled to the first front end system and a second antenna coupled to the second front end system, the first directional coupler configured to generate the first radio frequency observation signal based on a reverse coupled path to the first antenna, and the second directional coupler configured to generate the second radio frequency observation signal based on a forward coupled path to the second antenna. According to a number of embodiments, the direct transmit leakage observation data indicates an amount of direct transmit leakage present in the radio frequency transmit signal. In accordance with several embodiments, the first transceiver is a cellular transceiver and the second transceiver is a WiFi transceiver. According to a number of embodiments, the first transceiver is a WiFi transceiver and the second transceiver is a cellular transceiver. In accordance with various embodiments, the second transceiver includes a discrete time cancellation circuit configured to compensate a second digital baseband receive signal for radio frequency signal leakage. 
     In some embodiments, the spectral regrowth observation data indicates an amount of aggressor spectral regrowth present in the radio frequency receive signal. 
     In a number of embodiments, the first front end system includes a first directional coupler configured to generate the first radio frequency observation signal. 
     In several embodiments, the mobile device further includes a first antenna coupled to the first front end system, and the first directional coupler is configured to generate the first radio frequency observation signal based on a reverse coupled path to the first antenna. According to various embodiments, the first front end system includes a duplexer, and the first directional coupler is positioned between an output of the duplexer and the first antenna. In accordance with a number of embodiments, the first front end system includes a duplexer and a power amplifier, and the first directional coupler is positioned between an output of the power amplifier and an input to the duplexer. 
     In certain embodiments, the present disclosure relates to a transceiver. The transceiver includes a receive channel configured to process a radio frequency receive signal to generate a digital baseband receive signal, a first observation channel configured to process a first radio frequency observation signal to generate a first digital observation signal, a spectral regrowth baseband sampling circuit configured to process the first digital observation signal to generate spectral regrowth observation data, and a discrete time cancellation circuit configured to compensate the digital baseband receive signal for radio frequency signal leakage based on the spectral regrowth observation data and on direct transmit leakage observation data. 
     In a number of embodiments, the spectral regrowth observation data indicates an amount of aggressor spectral regrowth present in the radio frequency receive signal. 
     In various embodiments, the direct transmit leakage observation data indicates an amount of direct transmit leakage present in an aggressor radio frequency transmit signal. 
     In several embodiments, the transceiver is configured to receive the direct transmit leakage observation data from another transceiver. 
     In some embodiments, the transceiver is implemented as cellular transceiver. 
     In a number of embodiments, the transceiver is implemented as WiFi transceiver. 
     In various embodiments, the transceiver further includes a second observation channel configured to process a second radio frequency observation signal to generate a second digital observation signal, and a first direct transmit leakage baseband sampling circuit configured to process the second digital observation signal to generate first transmit leakage observation data. 
     According to a number of embodiments, the transceiver is configured to output the first transmit leakage observation data to another transceiver. 
     In accordance with several embodiments, the transceiver further includes a second direct transmit leakage baseband sampling circuit configured to process a third digital observation signal to generate second transmit leakage observation data, and an observation switch configured to selectively provide the first transmit leakage observation data or the second transmit leakage observation data as an output of the transceiver. According to various embodiments, the transceiver further includes a third observation channel configured to process a third radio frequency observation signal to generate the third digital observation signal. In accordance with a number of embodiments, the transceiver further includes a transmit power control circuit configured to receive second digital observation signal. 
     In certain embodiments, the present disclosure relates to a method of coexistence management in a mobile device. The method includes processing a radio frequency receive signal to generate a digital baseband receive signal using a receive channel of a first transceiver, processing a first radio frequency observation signal to generate a first digital observation signal using a first observation channel of the first transceiver, generating spectral regrowth observation data based on processing process the first digital observation signal using a first spectral regrowth baseband sampling circuit of the first transceiver, and compensating the digital baseband receive signal for radio frequency signal leakage based on the spectral regrowth observation data and on direct transmit leakage observation data using a discrete time cancellation circuit of the first transceiver. 
     In some embodiments, the spectral regrowth observation data indicates an amount of aggressor spectral regrowth present in the radio frequency receive signal. 
     In various embodiments, the direct transmit leakage observation data indicates an amount of direct transmit leakage present in an aggressor radio frequency transmit signal. 
     In several embodiments, the method further includes receiving the direct transmit leakage observation data from a second transceiver. According to a number of embodiments, the first transceiver is a cellular transceiver and the second transceiver is a WiFi transceiver. In accordance with various embodiments, the first transceiver is a WiFi transceiver and the second transceiver is a cellular transceiver. 
     In some embodiments, the method further includes processing a second radio frequency observation signal to generate a second digital observation signal using a second observation channel of the first transceiver, and processing the second digital observation signal to generate leakage observation data using a direct transmit leakage baseband sampling circuit of the first transceiver. According to several embodiments, the method further includes providing the leakage observation data from the first transceiver to a second transceiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of one example of a mobile device communicating via cellular and WiFi networks. 
         FIG. 2  is a schematic diagram of one example of signal leakage for an RF communication system. 
         FIG. 3A  is a schematic diagram of one example of direct transmit leakage for an RF communication system. 
         FIG. 3B  is a schematic diagram of one example of regrowth leakage for an RF communication system. 
         FIG. 4A  is a schematic diagram of an RF communication system with coexistence management according to one embodiment. 
         FIG. 4B  is a schematic diagram of an RF communication system with coexistence management according to another embodiment. 
         FIG. 5  is a schematic diagram of an RF communication system with coexistence management according to another embodiment. 
         FIG. 6  is a schematic diagram of an RF communication system with coexistence management according to another embodiment. 
         FIG. 7  is a schematic diagram of an RF communication system with coexistence management according to another embodiment. 
         FIG. 8  is a schematic diagram of one embodiment of a mobile device with coexistence management. 
         FIG. 9A  is a schematic diagram of one embodiment of a packaged module with coexistence management. 
         FIG. 9B  is a schematic diagram of a cross-section of the packaged module of  FIG. 9A  taken along the lines  9 B- 9 B. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The following detailed description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings. 
       FIG. 1  is a schematic diagram of one example of a mobile device  2   a  communicating via cellular and WiFi networks. For example, as shown in  FIG. 1 , the mobile device  2   a  communicates with a base station  1  of a cellular network and with a WiFi access point  3  of a WiFi network.  FIG. 1  also depicts examples of other user equipment (UE) communicating with the base station  1 , for instance, a wireless-connected car  2   b  and another mobile device  2   c . Furthermore,  FIG. 1  also depicts examples of other WiFi-enabled devices communicating with the WiFi access point  3 , for instance, a laptop  4 . 
     Although specific examples of cellular UE and WiFi-enabled devices is shown, a wide variety of types of devices can communicate using cellular and/or WiFi networks. Examples of such devices, include, but are not limited to, mobile phones, tablets, laptops, Internet of Things (IoT) devices, wearable electronics, customer premises equipment (CPE), wireless-connected vehicles, wireless relays, and/or a wide variety of other communication devices. 
     In certain implementations, UE, such as the mobile device  2   a  of  FIG. 1 , is implemented to support communications using a number of technologies, including, but not limited to, 2G, 3G, 4G (including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (for instance, WiFi), WPAN (for instance, Bluetooth and ZigBee), WMAN (for instance, WiMax), and/or GPS. In certain implementations, enhanced license assisted access (eLAA) is used to aggregate one or more licensed frequency carriers (for instance, licensed 4G LTE and/or 5G NR frequencies), with one or more unlicensed carriers (for instance, unlicensed WiFi frequencies). 
     Furthermore, certain UE can communicate not only with base stations and access points, but also with other UE. For example, the wireless-connected car  2   b  can communicate with a wireless-connected pedestrian  2   d , a wireless-connected stop light  2   e , and/or another wireless-connected car  2   f  using vehicle-to-vehicle (V2V) and/or vehicle-to-everything (V2X) communications. 
     Although various examples of communication technologies have been described, mobile devices can be implemented to support a wide range of communications. 
     Various communication links have been depicted in  FIG. 1 . The communication links can be duplexed in a wide variety of ways, including, for example, using frequency-division duplexing (FDD) and/or time-division duplexing (TDD). FDD is a type of radio frequency communications that uses different frequencies for transmitting and receiving signals. FDD can provide a number of advantages, such as high data rates and low latency. In contrast, TDD is a type of radio frequency communications that uses about the same frequency for transmitting and receiving signals, and in which transmit and receive communications are switched in time. TDD can provide a number of advantages, such as efficient use of spectrum and variable allocation of throughput between transmit and receive directions. 
     Different users of the illustrated communication networks can share available network resources, such as available frequency spectrum, in a wide variety of ways. In one example, frequency division multiple access (FDMA) is used to divide a frequency band into multiple frequency carriers. Additionally, one or more carriers are allocated to a particular user. Examples of FDMA include, but are not limited to, single carrier FDMA (SC-FDMA) and orthogonal FDMA (OFDMA). OFDM is a multicarrier technology that subdivides the available bandwidth into multiple mutually orthogonal narrowband subcarriers, which can be separately assigned to different users. 
     Other examples of shared access include, but are not limited to, time division multiple access (TDMA) in which a user is allocated particular time slots for using a frequency resource, code division multiple access (CDMA) in which a frequency resource is shared amongst different users by assigning each user a unique code, space-divisional multiple access (SDMA) in which beamforming is used to provide shared access by spatial division, and non-orthogonal multiple access (NOMA) in which the power domain is used for multiple access. For example, NOMA can be used to serve multiple users at the same frequency, time, and/or code, but with different power levels. 
     Examples of Radio Frequency Systems with Coexistence Management 
     Radio frequency (RF) communication systems can include multiple transceivers for communicating using different wireless networks, over multiple frequency bands, and/or using different communication standards. Although implementing an RF communication system in this manner can expand functionality, increase bandwidth, and/or enhance flexibility, a number of coexistence issues can arise between the transceivers operating within the RF communication system. 
     For example, an RF communication system can include a cellular transceiver for processing RF signals communicated over a cellular network and a wireless local area network (WLAN) transceiver for processing RF signals communicated over a WLAN network, such as a WiFi network. For instance, the mobile device  2   a  of  FIG. 1  is operable to communicate using cellular and WiFi networks. 
     Although implementing the RF communication system in this manner can provide a number of benefits, a mutual desensitization effect can arise from cellular transmissions interfering with reception of WiFi signals and/or from WiFi transmissions interfering with reception of cellular signals. 
     In one example, cellular Band 7 can give rise to mutual desensitization with respect to 2.4 Gigahertz (GHz) WiFi. For instance, Band 7 has an FDD duplex and operates over a frequency range of about 2.62 GHz to 2.69 GHz for downlink and over a frequency range of about 2.50 GHz to about 2.57 GHz for uplink, while 2.4 GHz WiFi has TDD duplex and operates over a frequency range of about 2.40 GHz to about 2.50 GHz. Thus, cellular Band 7 and 2.4 GHz WiFi are adjacent in frequency, and RF signal leakage due to the high power transmitter of one transceiver/front end affects receiver performance of the other transceiver/front end, particularly at border frequency channels. 
     In another example, cellular Band 40 and 2.4 GHz WiFi can give rise to mutual desensitization. For example, Band 40 has a TDD duplex and operates over a frequency range of about 2.30 GHz to about 2.40 GHz, while 2.4 GHz WiFi has TDD duplex and operates over a frequency range of about 2.40 GHz to about 2.50 GHz. Accordingly, cellular Band 40 and 2.4 GHz WiFi are adjacent in frequency and give rise to a number of coexistence issues, particularly at border frequency channels. 
     Desensitization can arise not only from direct leakage of an aggressor transmit signal to a victim receiver, but also from spectral regrowth components generated in the transmitter. Such interference can lie relatively closely in frequency with the victim receive signal and/or directly overlap it. Although a receive filter can provide some filtering of signal leakage, the receive filter may provide insufficient attenuation of the aggressor signal, and thus the sensitivity of the victim receiver is degraded. 
     Conventional techniques alone are insufficient for providing mutual coexistence. In one example, a very high quality-factor (high Q) bandpass filter (for instance, an acoustic bandpass filter) can be included at the output of a power amplifier of an aggressor transmitter to attenuate spectral regrowth. When the attenuation provided by the filter is sufficiently high, the victim receiver may not be significantly desensitized due to non-linearity of the aggressor transmitter. However, such high-Q bandpass filters can be prohibitively expensive and/or introduce insertion loss that degrades transmit performance. 
     In another example, a very high Q bandpass filter can be included on the victim receiver to attenuate high power leakage coupled in from the aggressor transmitter. When the attenuation is sufficiently high, the victim receiver is not significantly desensitized from coupling of the high power leakage into non-linear receive circuitry of the victim receiver. However, such high-Q bandpass filters can be prohibitively expensive and/or introduce insertion loss that degrades receiver sensitivity. 
     RF communication systems with coexistence management are provided herein. In certain embodiments, a mobile device includes a first antenna, a first front end system that receives an RF receive signal from the first antenna, a first transceiver coupled to the first front end system, a second antenna, a second front end system that provides an RF transmit signal to the second antenna, and a second transceiver coupled to the second front end system. The first front end system generates a first observation signal by observing the RF receive signal, and the second front end system generates a second observation signal by observing the RF transmit signal. The first transceiver also downconverts the RF receive signal to baseband, and uses the first observation signal and the second observation signal to compensate the baseband receive signal for RF signal leakage. 
     By implementing the mobile device in this manner, compensation for signal leakage arising from signal coupling from the second antenna to the first antenna is provided. Thus, the mobile device operates with enhanced receiver sensitivity when the first transceiver is receiving and the second transceiver is transmitting. 
     In certain implementations, the first transceiver/first front end system can process RF signals of a different type than the second transceiver/second front end system. In one example, the first transceiver/first front end system processes cellular signals while the second transceiver/second front end system processes WLAN signals, such as WiFi signals. Accordingly, in certain implementations herein, coexistence management is provided between cellular and WiFi radios. 
     In certain implementations, the first observation signal indicates spectral regrowth leakage and the second observation signal indicates direct transmit leakage. For example, the first observation signal can include extracted samples of aggressor regrowth, while the second observation signal can include extracted samples of aggressor direct transmit leakage. Accordingly, multiple components of RF signal leakage can be compensated. 
     In certain implementations, the baseband receive signal is compensated using discrete time cancellation. For example, compensation can be provided using a discrete time cancellation loop having multiple inputs. The cancellation loop can be adapted to reduce unwanted signal components using any suitable cancellation algorithm, including, but not limited to, a least mean squares (LMS) algorithm. In one embodiment, a transceiver includes a discrete time cancellation circuit including a finite impulse response (FIR) filter having coefficients adapted over time to reduce or eliminate RF signal leakage. 
     The first observation signal and the second observation signal can be generated in a wide variety of ways. In one example, the first front end system includes a first directional coupler along a first RF signal path to the first antenna and the second front end system includes a second directional coupler along a second RF signal path to the second antenna. Additionally, the first directional coupler generates the first observation signal based on sensing an incoming RF signal from the first antenna, while the second directional coupler generates the second observation signal based on sensing an outgoing RF signal to the second antenna. Thus, the first observation signal can be generated based on a reverse coupled path of the first directional coupler, and the second observation signal can be generated based on a forward coupled path of the second directional coupler. 
     The second transceiver can also be implemented with circuitry for compensating for RF signal leakage. For example, the first front end system can observe an outgoing transmit signal to the first antenna to generate a third observation signal, and the second front end system can observe an incoming receive signal to generate a fourth observation signal. Additionally, the second transceiver downconverts the incoming receive signal to generate a second baseband receive signal, which the second transceiver compensates for RF signal leakage based on the third observation signal and the fourth observation signal. Accordingly, in certain implementations, both the first transceiver and the second transceiver operate with coexistence management. 
     In certain implementations, observation paths used for power control (for instance, transmit power control or TPC) and/or predistortion control (for instance, digital predistortion or DPD) are also used for observations of regrowth and/or direct transmit leakage. By implementing the RF communication system in this manner, circuitry is reused. Not only does this reduce cost and/or component count, but also avoids inserting additional circuitry into the RF signal path that may otherwise degrade receiver sensitivity and/or transmitter efficiency. 
     The coexistence management schemes herein can provide a number of advantages. For example, the coexistence management schemes can reduce an amount of receive filtering and/or transmitter filtering, thereby relaxing filter constraints and permitting the use of lower cost filters. Furthermore, compensation for RF signal leakage enhances receiver sensitivity and/or transmitter efficiency with little to no increase in power consumption and/or componentry to RF signal paths. Moreover, multiple types of aggressor leakage components can be compensated using common cancellation circuitry, thereby providing a centralized and effective mechanism for coexistence management. 
       FIG. 2  is a schematic diagram of one example of signal leakage for an RF communication system  70 . As shown in  FIG. 2 , the RF communication system  70  includes a first transceiver  51 , a second transceiver  52 , a first front end system  53 , a second front end system  54 , a first antenna  55 , and a second antenna  56 . 
     Including multiple transceivers, front end systems, and antennas can enhance the flexibility of the RF communication system  70 . For instance, implementing the RF communication system  70  in this manner can allow the RF communication system  70  to communicate using different types of networks, for instance, cellular and WiFi networks. 
     In the illustrated embodiment, the first front end system  53  includes a transmit front end circuit  61 , a receive front end circuit  63 , and an antenna access circuit  65 , which can include one or more switches, duplexers, diplexers, and/or other circuitry for controlling access of the transmit front end circuit  61  and the receive front end circuit  63  to the first antenna  55 . The second front end system  54  includes a transmit front end circuit  62 , a receive front end circuit  64 , and an antenna access circuit  66 . 
     Although one example implementation of front end systems is shown in  FIG. 2 , the teachings herein are applicable to front end systems implemented in a wide variety of ways. Accordingly, other implementations of front end systems are possible. 
     RF signal leakage  69  between the first antenna  55  and the second antenna  56  can give rise to a number of coexistence issues. The coexistence management schemes herein provide compensation to reduce or eliminate the impacts of such RF signal leakage. 
       FIG. 3A  is a schematic diagram of one example of direct transmit leakage for an RF communication system  80 . The RF communication system  80  includes a power amplifier  81 , a victim receiver  82 , a first antenna  83 , and a second antenna  84 . 
     In this example, the RF signal outputted from the power amplifier  81  serves an aggressor transmit signal that is close in frequency to RF signals processed by the victim receiver  82 . Thus, direct transmit leakage from the aggressor transmit signal gives rise to a degradation in receiver sensitivity. 
       FIG. 3B  is a schematic diagram of one example of regrowth leakage for an RF communication system  90 . The RF communication system  90  includes a power amplifier  81 , a victim receiver  82 , a first antenna  83 , and a second antenna  84 . 
     In this example, the power amplifier  81  receives an RF input signal, which is amplified by the power amplifier  81  to generate an RF output signal that is wirelessly transmitted using by the first antenna  83 . Additionally, non-linearity of the power amplifier  81  gives rise to spectral regrowth in the RF output signal that is close in frequency to RF signals processed by the victim receiver  82 . Thus, regrowth leakage from the RF output signal gives rise to a degradation in receiver sensitivity. 
       FIG. 4A  is a schematic diagram of an RF communication system  150  with coexistence management according to one embodiment. The RF communication system  150  includes a first baseband modem  101 , a first transceiver  103 , a first front end system  105 , a first antenna  107 , a second baseband modem  102 , a second transceiver  104 , a second front end system  106 , and a second antenna  108 . 
     In the illustrated embodiment, the first transceiver  103  includes a leakage correction circuit  110 , a transmit channel  111 , an observation channel  112 , and a receive channel  114 . Additionally, the first front end system  105  includes a transmit front end circuit  115 , an observation front end circuit  116 , a receive front end circuit  118 , a directional coupler  121 , and an antenna access circuit  122 . Furthermore, the second transceiver  104  includes a transmit channel  131 , an observation channel  132 , and a receive channel  134 . Additionally, the second front end system  106  includes a transmit front end circuit  135 , an observation front end circuit  136 , a receive front end circuit  138 , a directional coupler  141 , and an antenna access circuit  142 . 
     Although one embodiment of circuitry for front end systems and transceivers is shown, the teachings herein are applicable to front end system and transceivers implemented in a wide variety of ways. Accordingly, other implementations are possible. 
     In the illustrated embodiment, the first front end system  105  receives an RF receive signal from first antenna  107 . The RF receive signal travels through the antenna access component  122  to reach the directional coupler  121 , which senses the RF receive signal. The sensed signal by the directional coupler  121  is processed by the observation front end circuit  116  and the observation channel  112  to generate a first observation signal, which serves as a first input to the leakage correction circuit  110 . 
     With continuing reference to  FIG. 4A , baseband transmit data from the second baseband modem  102  is provided to the transmit channel  131  of the second transceiver  104 , which processes the baseband transmit data to generate an RF input signal to the transmit front end circuit  135 . The RF input signal is processed by the transmit front end circuit  135  to generate an RF transmit signal that is provided to the second antenna  108 . 
     As shown in  FIG. 4A , the directional coupler  141  senses the RF transmit signal outputted by the transmit front end circuit  135 . Additionally, the sensed signal by the directional coupler  141  is processed by the observation front end circuit  136  and the observation channel  132  to generate a second observation signal, which serves as a second input to the leakage correction circuit  110 . 
     With continuing reference to  FIG. 4A , the RF receive signal from the first antenna  107  is also processed by the receive front end circuit  118  and downconverted and further processed by the receive channel  114  to generate a baseband receive signal that serves as a third input to the leakage correction circuit  110 . 
     The leakage correction circuit  110  compensates the baseband receive signal for RF signal leakage based on the first observation signal and the second observation signal. Additionally, the leakage correction circuit  110  provides a compensated baseband receive signal to the first baseband modem  101  for further processing. 
     In certain implementations, the first observation signal indicates an amount of aggressor spectral regrowth present in the RF receive signal received on the first antenna  107 , and the second observation signal indicates an amount of direct transmit leakage present in the RF transmit signal transmitted by the second antenna  108 . Thus, the leakage correction circuit  110  can serve to provide compensation for multiple components of RF signal leakage, thereby providing a centralized and effective mechanism for coexistence management. 
     As shown in  FIG. 4A , the first observation signal is generated based on a reverse coupled path to the first antenna  107 , and the second observation signal is generated based on a forward coupled path to the second antenna  108 . For example, the first observation signal is generated based on the directional coupler  121  sensing an incoming RF signal from the first antenna  107 , while the second observation signal is generated based on the directional coupler  141  sensing an outgoing RF signal to the second antenna  108 . 
     In certain implementations, the baseband modem  101 , the first transceiver  103 , the first front end system  105 , and the first antenna  107  handle a first type of RF signals, while the second baseband modem  102 , the second transceiver  104 , the second front end system  106 , and the second antenna  108  handle a second type of RF signals. In one example, the first type of RF signals are cellular signals and the second type of RF signals are WLAN signals, such as WiFi signals. In a second example, the first type of RF signals are WLAN signals and the second type of RF signals are cellular signals. Although two examples of RF signal types have been provided, the RF communication system  150  can operate using other RF signal types. Accordingly, other implementations are possible. 
       FIG. 4B  is a schematic diagram of an RF communication system  160  with coexistence management according to another embodiment. The RF communication system  160  of  FIG. 4B  is similar to the RF communication system  150  of  FIG. 4A , except that the RF communication system  160  illustrates a specific implementation of a leakage correction circuit. 
     For example, the RF communication system  160  includes a first transceiver  153  that includes a discrete time cancellation circuit  151 . In the illustrated embodiment, the discrete time cancellation circuit  151  receives a first observation signal indicating an amount of aggressor spectral regrowth present in the RF receive signal received on the first antenna  107  and a second observation signal indicating an amount of direct transmit leakage present in the RF transmit signal transmitted by the second antenna  108 . The discrete time cancellation circuit  151  compensates a baseband receive signal received from the receive channel  114  to generate a compensated baseband receive signal in which spectral regrowth and/or direct transmit leakage is reduced and/or eliminated. 
     The RF communication system  160  of  FIG. 4B  illustrates one embodiment of coexistence management provided by a discrete time cancellation loop having multiple inputs. The cancellation loop can be adapted to reduce unwanted signal components using any suitable cancellation algorithm. Although one example of a discrete time cancellation loop is shown, the teachings herein are applicable to other implementations of coexistence management. In one embodiment, the discrete time cancellation circuit  151  includes a FIR filter having coefficients adapted over time to reduce or eliminate RF signal leakage. 
       FIG. 5  is a schematic diagram of an RF communication system  170  with coexistence management according to another embodiment. The RF communication system  170  includes a first baseband modem  101 , a first transceiver  163 , a first front end system  165 , a first antenna  107 , a second baseband modem  102 , a second transceiver  164 , a second front end system  166 , and a second antenna  108 . 
     In the illustrated embodiment, the first transceiver  163  includes a discrete time cancellation circuit  151 , a transmit channel  111 , a first observation channel  112 , a second observation channel  113 , and a receive channel  114 . Additionally, the first front end system  165  includes a transmit front end circuit  115 , a first observation front end circuit  116 , a second observation front end circuit  117 , a receive front end circuit  118 , a directional coupler  121 , and an antenna access circuit  122 . Furthermore, the second transceiver  164  includes a discrete time cancellation circuit  152 , a transmit channel  131 , a first observation channel  132 , a second observation channel  133 , and a receive channel  134 . Additionally, the second front end system  166  includes a transmit front end circuit  135 , a first observation front end circuit  136 , a second observation front end circuit  137 , a receive front end circuit  138 , a directional coupler  141 , and an antenna access circuit  142 . 
     The RF communication system  170  of  FIG. 5  is similar to the RF communication system  160  of  FIG. 4B , except that the RF communication system  170  is implemented not only to provide discrete time cancellation in the first transceiver  163 , but also to provide discrete time cancellation in the second transceiver  164 . 
     For example, with respect to discrete time cancellation in the first transceiver  163 , the directional coupler  121  senses an incoming RF signal from the first antenna  107  to generate a sensed signal that is processed by the first observation front end circuit  116  and the first observation channel  112  to generate a first observation signal for the discrete time cancellation circuit  151 . Furthermore, the directional coupler  141  senses an outgoing RF signal to the second antenna  108  to generate a sensed signal that is processed by the first observation front end circuit  136  and the first observation channel  132  to generate a second observation signal for the discrete time cancellation circuit  151 . The incoming RF signal from the first antenna  107  is also processed by the receive front end circuit  118  and the receive channel  114  to generate a first baseband receive signal, which the discrete time cancellation circuit  151  compensates for RF signal leakage using the first observation signal and the second observation signal. 
     With respect to discrete time cancellation in the second transceiver  164 , the directional coupler  141  senses the incoming RF signal from the second antenna  108  to generate a sensed signal that is processed by the second observation front end circuit  137  and the second observation channel  133  to generate a third observation signal for the discrete time cancellation circuit  152 . Furthermore, the directional coupler  121  senses an outgoing RF signal to the first antenna  107  to generate a sensed signal that is processed by the second observation front end circuit  117  and the second observation channel  113  to generate a fourth observation signal for the discrete time cancellation circuit  152 . The incoming RF signal from the second antenna  108  is also processed by the receive front end circuit  138  and the receive channel  134  to generate a second baseband receive signal, which the discrete time cancellation circuit  152  compensates for RF signal leakage using the third observation signal and the fourth observation signal. 
       FIG. 6  is a schematic diagram of an RF communication system  450  with coexistence management according to another embodiment. The RF communication system  450  includes a cellular antenna  301 , a WiFi antenna  302 , a cellular transceiver  303 , a WiFi transceiver  304 , a cellular front end system  305 , and a WiFi front end system  306 . 
     Although one embodiment of an RF communication system is shown, the teachings herein are applicable to RF communication systems implemented in a wide variety of ways. For example, an RF communication system can include different implementations of antennas, transceivers, and/or front end systems. 
     In the illustrated embodiment, the cellular transceiver  303  includes a digital baseband circuit  360  including a cellular transmit baseband sampling circuit  361 , a WiFi spectral regrowth baseband sampling circuit  362 , a cellular transmit power control circuit  363 , a discrete time cancellation circuit  381 , and a digital receiver  382  that is coupled to a cellular modem (not shown in  FIG. 6 ). The cellular transceiver  303  operates using Band 7 (B7), in this example. 
     The cellular transceiver  303  further includes a first observation channel including a first input amplifier  351   a , a first controllable attenuator  352   a , a first downconverting mixer  353   a , a first low pass filter  354   a , a first post-filtering amplifier  355   a , and a first analog-to-digital converter (ADC)  356   a . The cellular transceiver  303  further includes a second observation channel including a second input amplifier  351   b , a second controllable attenuator  352   b , a second downconverting mixer  353   b , a second low pass filter  354   b , a second post-filtering amplifier  355   b , and a second ADC  356   b . The cellular transceiver  303  further includes a receive channel including an input amplifier  371 , a downconverting mixer  373 , a low pass filter  374 , a post-filter amplifier  375 , and an ADC  376 . As shown in  FIG. 6 , an observation local oscillator (LO)  359  generates an observation LO signal for providing downconversion in the observation channels, while a receive LO  379  generates a receive LO signal for providing downconversion in the receive channel. 
     The cellular front end system  305  includes a diplexer  311 , a directional coupler  313 , and a cellular front end module  315 . The cellular front end module  315  includes an antenna switch module (ASM)  321 , a low noise amplifier and switches (LNA/SW)  322 , a duplexer  323 , a power amplifier module  324 , a control circuit  325 , and a transmit input switch  326 . 
     With continuing reference to  FIG. 6 , the WiFi transceiver  304  includes a digital baseband circuit  410  including a WiFi transmit baseband sampling circuit  411 , a cellular spectral regrowth baseband sampling circuit  412 , a discrete time cancellation circuit  431 , and a digital receiver  432  that is coupled to a WiFi modem (not shown in  FIG. 6 ). The WiFi transceiver  303  operates using 2.4 GHz WiFi, in this example. 
     The WiFi transceiver  304  further includes a first observation channel including a first input amplifier  401   a , a first controllable attenuator  402   a , a first downconverting mixer  403   a , a first low pass filter  404   a , a first post-filtering amplifier  405   a , and a first ADC  406   a . The WiFi transceiver  304  further includes a second observation channel including a second input amplifier  401   b , a second controllable attenuator  402   b , a second downconverting mixer  403   b , a second low pass filter  404   b , a second post-filtering amplifier  405   b , and a second ADC  406   b . The WiFi transceiver  304  further includes a receive channel including an input amplifier  421 , a downconverting mixer  423 , a low pass filter  424 , a post-filter amplifier  425 , and an ADC  426 . As shown in  FIG. 6 , an observation LO  409  generates an observation LO signal for providing downconversion in the observation channels, while a receive LO  429  generates a receive LO signal for providing downconversion in the receive channel. 
     As shown in  FIG. 6 , a first transceiver-to-transceiver connection  307  and a second transceiver-to-transceiver connection  308  provide connectivity between the cellular transceiver  303  and the WiFi transceiver  304 . In certain implementations, the cellular transceiver  303  and the WiFi transceiver  304  are a relative far distance from one another, and the connections  307 - 308  include printed circuit board (PCB) trace and/or cables (for instance, cross-UE cables). 
     The WiFi front end system  306  includes a diplexer  312 , a directional coupler  314 , and a WiFi front end module  316 . The WiFi front end module  316  includes a transmit/receive switch  341 , a power amplifier  342 , and an LNA  343 . 
     With continuing reference to  FIG. 6 , the directional coupler  313  of the cellular front end system  305  provides sensing of incoming and outgoing RF signals to the cellular antenna  301  travelling along the cellular signal path  317 . Additionally, the directional coupler  314  of the WiFi front end system  306  provides sensing of incoming and outgoing RF signals to the WiFi antenna  302  travelling along the WiFi signal path  318 . 
     The discrete time cancellation circuit  381  of the cellular transceiver  303  and the discrete time cancellation circuit  431  of the WiFi transceiver  304  operate in a manner similar to that described above with respect to  FIG. 5 . 
       FIG. 7  is a schematic diagram of an RF communication system  500  with coexistence management according to another embodiment. The RF communication system  500  of  FIG. 7  is similar to the RF communication system  450  of  FIG. 6 , except that the RF communication system  500  includes a different implementation of a cellular transceiver  451  and of a cellular front end  455 . 
     Relative to the cellular transceiver  303  of  FIG. 6 , the cellular transceiver  451  of  FIG. 7  includes an additional observation path including a third controllable attenuator  352   c , a third downconverting mixer  353   c , a third low pass filter  354   c , a third post-filtering amplifier  355   c , and a third ADC  356   c . Additionally, the cellular transceiver  451  further includes an observation selection switch  464 , and has a digital baseband circuit  460  that further includes a baseband sampling circuit  461 . 
     The cellular front end system  455  of  FIG. 7  is similar to the cellular front end system  301  of  FIG. 6 , except that the cellular front end system  455  includes a cellular front end module  465  including a directional coupler  327  between an output of the power amplifier  324  and an input to the duplexer  323 . As shown in  FIG. 7 , the directional coupler  327  provides a sensed signal to the third observation channel of the cellular transceiver  451 . The sensed signal is processed by the third observation channel and the baseband sampling circuit  461  to generate an observation signal with relatively less group delay effects relative to the observation signal generated by the baseband sampling circuit  361 . 
     In this embodiment, the observation selection switch  464  selectively provides the observation signal from the baseband sampling circuit  461  or the observation signal from the baseband sampling circuit  361  to the discrete time cancellation circuit  381 . 
     By implementing coexistence management in this manner, enhanced reduction of RF signal leakage can be achieved. 
       FIG. 8  is a schematic diagram of one embodiment of a mobile device  800  with coexistence management. The mobile device  800  includes a digital processing system  801 , a first transceiver  802 , a second transceiver  812 , a first front end system  803 , a second front end system  813 , a first antenna  804 , a second antenna  814 , a power management system  805 , a memory  806 , and a user interface  807 . 
     The mobile device  800  can be used communicate using a wide variety of communications technologies, including, but not limited to, 2G, 3G, 4G (including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (for instance, WiFi), WPAN (for instance, Bluetooth and ZigBee), WMAN (for instance, WiMax), and/or GPS technologies. 
     In the illustrated embodiment, the digital processing circuit  801  includes a first baseband modem  821  and a second baseband modem  822 . In certain implementations, the first baseband modem  821  and the second baseband modem  822  control communications associated with different types of wireless communications, for instance, cellular and WiFi. As shown in  FIG. 8 , the first baseband modem  821 , the first transceiver  802 , and the first front end system  803  operate to transmit and receive RF signals using the first antenna  804 . Additionally, the second baseband modem  822 , the second transceiver  812 , and the second front end system  813  operate to transmit and receive RF signals using the second antenna  814 . Although an example with two antennas is shown, the mobile device  800  can include additional antennas including, but not limited to, multiple antennas for cellular communications and/or multiple antenna for WiFi communications. 
     The first front end system  803  operates to condition RF signals transmitted by and/or received from the first antenna  804 . Additionally, the second front end system  804  operates to condition RF signals transmitted by and/or received from the second antenna  814 . The front end systems can provide a number of functionalities, including, but not limited to, amplifying signals for transmission, amplifying received signals, filtering signals, switching between different bands, switching between different power modes, switching between transmission and receiving modes, duplexing of signals, multiplexing of signals (for instance, diplexing or triplexing), or some combination thereof. 
     In certain implementations, the mobile device  800  supports carrier aggregation, thereby providing flexibility to increase peak data rates. Carrier aggregation can be used for both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD), and may be used to aggregate a plurality of carriers or channels. Carrier aggregation includes contiguous aggregation, in which contiguous carriers within the same operating frequency band are aggregated. Carrier aggregation can also be non-contiguous, and can include carriers separated in frequency within a common band or in different bands. 
     The first antenna  804  and the second antenna  814  can include antenna elements implemented in a wide variety of ways. In certain configurations, the antenna elements are arranged to form one or more antenna arrays. Examples of antenna elements include, but are not limited to, patch antennas, dipole antenna elements, ceramic resonators, stamped metal antennas, and/or laser direct structuring antennas. 
     In certain implementations, the mobile device  800  supports MIMO communications and/or switched diversity communications. For example, MIMO communications use multiple antennas for communicating multiple data streams over a single radio frequency channel. MIMO communications benefit from higher signal to noise ratio, improved coding, and/or reduced signal interference due to spatial multiplexing differences of the radio environment. Switched diversity refers to communications in which a particular antenna is selected for operation at a particular time. For example, a switch can be used to select a particular antenna from a group of antennas based on a variety of factors, such as an observed bit error rate and/or a signal strength indicator. 
     In certain implementations, the mobile device  800  operates with beamforming. For example, the first front end system  803  and/or the second front end system  813  can include phase shifters having variable phase to provide beam formation and directivity for transmission and/or reception of signals. For example, in the context of signal transmission, the phases of the transmit signals provided to an antenna array used for transmission are controlled such that radiated signals combine using constructive and destructive interference to generate an aggregate transmit signal exhibiting beam-like qualities with more signal strength propagating in a given direction. In the context of signal reception, the phases are controlled such that more signal energy is received when the signal is arriving to the antenna array from a particular direction. 
     The first transceiver  802  includes one or more transmit channels  831 , one or more receive channels  832 , one or more observation channels  833 , and a discrete time cancellation circuit  834 . Additionally, the second transceiver  812  includes one or more transmit channels  841 , one or more receive channels  842 , one or more observation channels  843 , and a discrete time cancellation circuit  844 . 
     The mobile device  800  of  FIG. 8  illustrates one embodiment of a mobile device implemented with coexistence management using discrete time cancellation. Although one example of a mobile device is shown, the teachings herein are applicable a wide range of coexistence management schemes. 
     The digital processing system  801  is coupled to the user interface  807  to facilitate processing of various user input and output (I/O), such as voice and data. The digital processing system  801  provides the transceivers with digital representations of transmit signals, which are processed by the transceivers to generate RF signals for transmission. The digital processing system  801  also processes digital representations of received signals provided by the transceivers. As shown in  FIG. 8 , the digital processing system  801  is coupled to the memory  806  of facilitate operation of the mobile device  800 . 
     The memory  806  can be used for a wide variety of purposes, such as storing data and/or instructions to facilitate the operation of the mobile device  800  and/or to provide storage of user information. 
     The power management system  805  provides a number of power management functions of the mobile device  800 . In certain implementations, the power management system  805  includes a PA supply control circuit that controls the supply voltages of the power amplifiers of the front end systems. For example, the power management system  805  can be configured to change the supply voltage(s) provided to one or more of the power amplifiers to improve efficiency, such as power added efficiency (PAE). 
     In certain implementations, the power management system  805  receives a battery voltage from a battery. The battery can be any suitable battery for use in the mobile device  800 , including, for example, a lithium-ion battery. 
       FIG. 9A  is a schematic diagram of one embodiment of a packaged module  900  with coexistence management.  FIG. 9B  is a schematic diagram of a cross-section of the packaged module  900  of  FIG. 9A  taken along the lines  9 B- 9 B. 
     The packaged module  900  includes radio frequency components  901 , a semiconductor die  902 , surface mount devices  903 , wirebonds  908 , a package substrate  920 , and encapsulation structure  940 . The package substrate  920  includes pads  906  formed from conductors disposed therein. Additionally, the semiconductor die  902  includes pins or pads  904 , and the wirebonds  908  have been used to connect the pads  904  of the die  902  to the pads  906  of the package substrate  920 . 
     The semiconductor die  902  includes an RF communication system implemented with discrete time cancellation  941  in accordance with the teachings herein. Although the packaged module  900  illustrates one example of a module implemented in accordance with the teachings herein, other implementations are possible. 
     As shown in  FIG. 9B , the packaged module  900  is shown to include a plurality of contact pads  932  disposed on the side of the packaged module  900  opposite the side used to mount the semiconductor die  902 . Configuring the packaged module  900  in this manner can aid in connecting the packaged module  900  to a circuit board, such as a phone board of a wireless device. The example contact pads  932  can be configured to provide radio frequency signals, bias signals, and/or power (for example, a power supply voltage and ground) to the semiconductor die  902 . As shown in  FIG. 9B , the electrical connections between the contact pads  932  and the semiconductor die  902  can be facilitated by connections  933  through the package substrate  920 . The connections  933  can represent electrical paths formed through the package substrate  920 , such as connections associated with vias and conductors of a multilayer laminated package substrate. 
     In some embodiments, the packaged module  900  can also include one or more packaging structures to, for example, provide protection and/or facilitate handling. Such a packaging structure can include overmold or encapsulation structure  940  formed over the packaging substrate  920  and the components and die(s) disposed thereon. 
     It will be understood that although the packaged module  900  is described in the context of electrical connections based on wirebonds, one or more features of the present disclosure can also be implemented in other packaging configurations, including, for example, flip-chip configurations. 
     Applications 
     Some of the embodiments described above have provided examples in connection with mobile devices. However, the principles and advantages of the embodiments can be used for any other systems or apparatus that have needs for coexistence management. Examples of such RF communication systems include, but are not limited to, mobile phones, tablets, base stations, network access points, customer-premises equipment (CPE), laptops, and wearable electronics. 
     CONCLUSION 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
     Moreover, conditional language used herein, such as, among others, “may,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     The above detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are presented in a given order, alternative embodiments may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times. 
     The teachings of the invention provided herein can be applied to other systems, not necessarily the system described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.