Patent Description:
Wireless communication systems are rapidly growing in usage. In recent years, wireless devices such as smart phones and tablet computers have become increasingly sophisticated. In addition to supporting telephone calls, many mobile devices now provide access to the internet, email, text messaging, and navigation using the global positioning system (GPS), and are capable of operating sophisticated applications that utilize these functionalities. Additionally, there exist numerous different wireless communication technologies and standards. Some examples of wireless communication standards include GSM, UMTS (associated with, for example, WCDMA or TD-SCDMA air interfaces), LTE, LTE Advanced (LTE-A), HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), IEEE <NUM> (WLAN or Wi-Fi), BLUETOOTH™, etc..

The ever increasing number of features and functionality introduced in wireless communication devices also creates a continuous need for improvement in both wireless communications and in wireless communication devices. To increase coverage and better serve the increasing demand and range of envisioned uses of wireless communication, in addition to the communication standards mentioned above, there are further wireless communication technologies under development, including fifth generation (<NUM>) new radio (NR) communication. Accordingly, improvements in the field in support of such development and design are desired.

<NPL> describes UE RF chain assumptions for dual active protocol stacks (DAPS) handover (HO) and how to enable UE to have simultaneous connectivity to both source and target eNB during DAPS based enhanced MBB HO execution by using UL TDM mechanism.

<NPL> describes LTE UE capability sharing aspects for DAPS based enhanced MBB HO.

While the features described herein may be 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.

The following is a glossary of terms used in this disclosure:
Memory Medium - Any of various types of non-transitory 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 non-transitory 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.

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), 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 or devices that are mobile or portable and that perform 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™, PlayStation 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.

Processing Element (or Processor) - refers to various elements or combinations of elements that are capable of performing a function in a device, such as a user equipment or a cellular network device. Processing elements may include, for example: processors and associated memory, portions or circuits of individual processor cores, entire processor cores, individual processors, processor arrays, circuits such as an ASIC (Application Specific Integrated Circuit), programmable hardware elements such as a field programmable gate array (FPGA), as well any of various combinations of the above.

The base station (BS) 102A may be a base transceiver station (BTS) or cell site (a "cellular base station"), and may include hardware that enables wireless communication with the UEs 106A through 106N.

The communication area (or coverage area) of the base station may be referred to as a "cell. " The base station 102A and the UEs <NUM> may be configured to communicate over the transmission medium using any of various radio access technologies (RATs), also referred to as wireless communication technologies, or telecommunication standards, such as GSM, UMTS (associated with, for example, WCDMA or TD-SCDMA air interfaces), LTE, LTE-Advanced (LTE-A), <NUM> new radio (<NUM> NR), HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), etc. Note that if the base station 102A is implemented in the context of LTE, it may alternately be referred to as an 'eNodeB' or 'eNB'. Note that if the base station 102A is implemented in the context of <NUM> NR, it may alternately be referred to as a 'gNodeB' or 'gNB'.

In some embodiments, base station 102A may be a next generation base station, e.g., a <NUM> New Radio (<NUM> NR) base station, or "gNB". In some embodiments, a gNB may be connected to a legacy evolved packet core (EPC) network and/or to a NR core (NRC) network. In addition, a gNB cell may include one or more transition and reception points (TRPs). For example, it may be possible that that the base station 102A and one or more other base stations <NUM> support joint transmission, such that UE <NUM> may be able to receive transmissions from multiple base stations (and/or multiple TRPs provided by the same base station).

Note that a UE <NUM> may be capable of communicating using multiple wireless communication standards. For example, the UE <NUM> may be configured to communicate using a wireless networking (e.g., Wi-Fi) and/or peer-to-peer wireless communication protocol (e.g., Bluetooth, Wi-Fi peer-to-peer, etc.) in addition to at least one cellular communication protocol (e.g., GSM, UMTS (associated with, for example, WCDMA or TD-SCDMA air interfaces), LTE, LTE-A, <NUM> NR, HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), etc.). The UE <NUM> may also or alternatively be configured to communicate using one or more global navigational satellite systems (GNSS, e.g., GPS or GLONASS), one or more mobile television broadcasting standards (e.g., ATSC-M/H), and/or any other wireless communication protocol, if desired. Other combinations of wireless communication standards (including more than two wireless communication standards) are also possible.

<FIG> illustrates user equipment <NUM> (e.g., one of the devices 106A through 106N) in communication with a base station <NUM>, according to some embodiments. The UE <NUM> may be a device with cellular communication capability such as a mobile phone, a hand-held device, a computer, a laptop, a tablet, a smart watch or other wearable device, or virtually any type of wireless device.

The UE <NUM> may include a processor (processing element) that is configured to execute program instructions stored in memory. Alternatively, or in addition, the UE <NUM> may include a programmable hardware element such as an FPGA (field-programmable gate array), an integrated circuit, and/or any of various other possible hardware components that are configured to perform (e.g., individually or in combination) any of the method embodiments described herein, or any portion of any of the method embodiments described herein.

The UE <NUM> may include one or more antennas for communicating using one or more wireless communication protocols or technologies. In some embodiments, the UE <NUM> may be configured to communicate using, for example, NR or LTE using at least some shared radio components. As additional possibilities, the UE <NUM> could be configured to communicate using CDMA2000 (1xRTT / 1xEV-DO / HRPD / eHRPD) or LTE using a single shared radio and/or GSM or LTE using the single shared radio. The shared radio may couple to a single antenna, or may couple to multiple antennas (e.g., for MIMO) for performing wireless communications. In general, a radio may include any combination of a baseband processor, analog RF signal processing circuitry (e.g., including filters, mixers, oscillators, amplifiers, etc.), or digital processing circuitry (e.g., for digital modulation as well as other digital processing). Similarly, the radio may implement one or more receive and transmit chains using the aforementioned hardware. For example, the UE <NUM> may share one or more parts of a receive and/or transmit chain between multiple wireless communication technologies, such as those discussed above.

For example, the UE <NUM> might include a shared radio for communicating using either of LTE or <NUM> NR (or either of LTE or 1xRTT, or either of LTE or GSM, among various possibilities), and separate radios for communicating using each of Wi-Fi and Bluetooth.

<FIG> illustrates an example simplified block diagram of a communication device <NUM>, according to some embodiments. It is noted that the block diagram of the communication device of <FIG> is only one example of a possible communication device. According to embodiments, communication device <NUM> may be a user equipment (UE) device, a mobile device or mobile station, a wireless device or wireless station, a desktop computer or computing device, a mobile computing device (e.g., a laptop, notebook, or portable computing device), a tablet, and/or a combination of devices, among other devices. As shown, the communication device <NUM> may include a set of components <NUM> configured to perform core functions. For example, this set of components may be implemented as a system on chip (SOC), which may include portions for various purposes. Alternatively, this set of components <NUM> may be implemented as separate components or groups of components for the various purposes. The set of components <NUM> may be coupled (e.g., communicatively; directly or indirectly) to various other circuits of the communication device <NUM>.

For example, the communication device <NUM> may include various types of memory (e.g., including NAND flash <NUM>), an input/output interface such as connector I/F <NUM> (e.g., for connecting to a computer system; dock; charging station; input devices, such as a microphone, camera, keyboard; output devices, such as speakers; etc.), the display <NUM>, which may be integrated with or external to the communication device <NUM>, and wireless communication circuitry <NUM> (e.g., for LTE, LTE-A, NR, UMTS, GSM, CDMA2000, Bluetooth, Wi-Fi, NFC, GPS, etc.).

The wireless communication circuitry <NUM> may couple (e.g., communicatively; directly or indirectly) to one or more antennas, such as antenna(s) <NUM> as shown. The wireless communication circuitry <NUM> may include cellular communication circuitry and/or short to medium range wireless communication circuitry, and may include multiple receive chains and/or multiple transmit chains for receiving and/or transmitting multiple spatial streams, such as in a multiple-input multiple output (MIMO) configuration.

In some embodiments, as further described below, cellular communication circuitry <NUM> may include one or more receive chains (including and/or coupled to (e.g., communicatively; directly or indirectly) dedicated processors and/or radios) for multiple RATs (e.g., a first receive chain for LTE and a second receive chain for <NUM> NR). For example, a first radio may be dedicated to a first RAT, e.g., LTE, and may be in communication with a dedicated receive chain and a transmit chain shared with a second radio. The second radio may be dedicated to a second RAT, e.g., <NUM> NR, and may be in communication with a dedicated receive chain and the shared transmit chain.

As shown, the SOC <NUM> may include processor(s) <NUM>, which may execute program instructions for the communication device <NUM> and display circuitry <NUM>, which may perform graphics processing and provide display signals to the display <NUM>. The processor(s) <NUM> may also be coupled to memory management unit (MMU) <NUM>, which may be configured to receive addresses from the processor(s) <NUM> and translate those addresses to locations in memory (e.g., memory <NUM>, read only memory (ROM) <NUM>, NAND flash memory <NUM>) and/or to other circuits or devices, such as the display circuitry <NUM>, wireless communication circuitry <NUM>, connector I/F <NUM>, and/or display <NUM>. The MMU <NUM> may be configured to perform memory protection and page table translation or set up. In some embodiments, the MMU <NUM> may be included as a portion of the processor(s) <NUM>.

As noted above, the communication device <NUM> may be configured to communicate using wireless and/or wired communication circuitry. As described herein, the communication device <NUM> may include hardware and software components for implementing any of the various features and techniques described herein. The processor <NUM> of the communication device <NUM> may be configured to implement part or all of the features described herein, e.g., by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium). Alternatively (or in addition), processor <NUM> may be configured as a programmable hardware element, such as an FPGA (Field Programmable Gate Array), or as an ASIC (Application Specific Integrated Circuit). Alternatively (or in addition) the processor <NUM> of the communication device <NUM>, in conjunction with one or more of the other components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be configured to implement part or all of the features described herein.

Further, as described herein, wireless communication circuitry <NUM> may include one or more processing elements. In other words, one or more processing elements may be included in wireless communication circuitry <NUM>. Thus, wireless communication circuitry <NUM> may include one or more integrated circuits (ICs) that are configured to perform the functions of wireless communication circuitry <NUM>. In addition, each integrated circuit may include circuitry (e.g., first circuitry, second circuitry, etc.) configured to perform the functions of wireless communication circuitry <NUM>.

The base station <NUM> includes at least one antenna <NUM>, and possibly multiple antennas.

As another possibility, the base station <NUM> may include a multi-mode radio which is capable of performing communications according to any of multiple wireless communication technologies (e.g., <NUM> NR and LTE, <NUM> NR and Wi-Fi, LTE and Wi-Fi, LTE and UMTS, LTE and CDMA2000, UMTS and GSM, etc.).

In addition, as described herein, processor(s) <NUM> may include one or more processing elements.

Further, as described herein, radio <NUM> may include one or more processing elements.

<FIG> illustrates an example simplified block diagram of cellular communication circuitry, according to some embodiments. It is noted that the block diagram of the cellular communication circuitry of <FIG> is only one example of a possible cellular communication circuit; other circuits, such as circuits including or coupled to sufficient antennas for different RATs to perform uplink activities using separate antennas, or circuits including or coupled to fewer antennas, e.g., that may be shared among multiple RATs, are also possible. According to some embodiments, cellular communication circuitry <NUM> may be included in a communication device, such as communication device <NUM> described above. As noted above, communication device <NUM> may be a user equipment (UE) device, a mobile device or mobile station, a wireless device or wireless station, a desktop computer or computing device, a mobile computing device (e.g., a laptop, notebook, or portable computing device), a tablet and/or a combination of devices, among other devices.

The cellular communication circuitry <NUM> may couple (e.g., communicatively; directly or indirectly) to one or more antennas, such as antennas 335a-b and <NUM> as shown. In some embodiments, cellular communication circuitry <NUM> may include dedicated receive chains (including and/or coupled to (e.g., communicatively; directly or indirectly) dedicated processors and/or radios) for multiple RATs (e.g., a first receive chain for LTE and a second receive chain for <NUM> NR). For example, as shown in <FIG>, cellular communication circuitry <NUM> may include a first modem <NUM> and a second modem <NUM>. The first modem <NUM> may be configured for communications according to a first RAT, e.g., such as LTE or LTE-A, and the second modem <NUM> may be configured for communications according to a second RAT, e.g., such as <NUM> NR.

As shown, the first modem <NUM> may include one or more processors <NUM> and a memory <NUM> in communication with processors <NUM>.

Similarly, the second modem <NUM> may include one or more processors <NUM> and a memory <NUM> in communication with processors <NUM>.

Thus, when cellular communication circuitry <NUM> receives instructions to transmit according to the first RAT (e.g., as supported via the first modem <NUM>), switch <NUM> may be switched to a first state that allows the first modem <NUM> to transmit signals according to the first RAT (e.g., via a transmit chain that includes transmit circuitry <NUM> and UL front end <NUM>). Similarly, when cellular communication circuitry <NUM> receives instructions to transmit according to the second RAT (e.g., as supported via the second modem <NUM>), switch <NUM> may be switched to a second state that allows the second modem <NUM> to transmit signals according to the second RAT (e.g., via a transmit chain that includes transmit circuitry <NUM> and UL front end <NUM>).

As described herein, the first modem <NUM> and/or the second modem <NUM> may include hardware and software components for implementing any of the various features and techniques described herein. The processors <NUM>, <NUM> may be configured to implement part or all of the features described herein, e.g., by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium). Alternatively (or in addition), processors <NUM>, <NUM> may be configured as a programmable hardware element, such as an FPGA (Field Programmable Gate Array), or as an ASIC (Application Specific Integrated Circuit). Alternatively (or in addition) the processors <NUM>, <NUM>, in conjunction with one or more of the other components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> may be configured to implement part or all of the features described herein.

In addition, as described herein, processors <NUM>, <NUM> may include one or more processing elements. Thus, processors <NUM>, <NUM> may include one or more integrated circuits (ICs) that are configured to perform the functions of processors <NUM>, <NUM>. In addition, each integrated circuit may include circuitry (e.g., first circuitry, second circuitry, etc.) configured to perform the functions of processors <NUM>, <NUM>.

In some embodiments, the cellular communication circuitry <NUM> may include only one transmit/receive chain. For example, the cellular communication circuitry <NUM> may not include the modem <NUM>, the RF front end <NUM>, the DL front end <NUM>, and/or the antenna 335b. As another example, the cellular communication circuitry <NUM> may not include the modem <NUM>, the RF front end <NUM>, the DL front end <NUM>, and/or the antenna 335a. In some embodiments, the cellular communication circuitry <NUM> may also not include the switch <NUM>, and the RF front end <NUM> or the RF front end <NUM> may be in communication, e.g., directly, with the UL front end <NUM>.

New cellular communication techniques are continually under development, to increase coverage, to better serve the range of demands and use cases, and for a variety of other reasons. One technique that is currently under development may include dual active protocol stack (DAPS) handover. This handover technique may include a wireless device maintaining both uplink and downlink links with both the source cell and the target cell of the handover, e.g., to potentially reduce any potential interruption to service when performing handover. <FIG> illustrates aspects of such a possible dual active protocol stack handover. In the illustrated example, a wireless device <NUM> may keep both uplink and downlink connections with both a source cell <NUM> and a target cell <NUM> during the handover operation.

In some instances, it may be possible that there is a difference in the propagation delay between the wireless device and the source cell and between the wireless device and the target cell when performing such a DAPS handover. Such differences could result in collisions between scheduled uplink transmissions of a wireless device, such that the wireless device could end up dropping one of the uplink transmissions, e.g., if the wireless device does not have sufficient hardware resources to perform both uplink transmissions simultaneously. Thus, it may be beneficial, at least in some instances, to provide techniques for scheduling uplink transmissions during dual active protocol stack handovers such that overlapping uplink transmissions can be avoided.

Accordingly, <FIG> is a communication flow diagram illustrating example aspects of such a method, at least according to some embodiments. Aspects of the method of <FIG> may be implemented by a wireless device <NUM> (such as a UE <NUM> illustrated in various of the Figures herein), source cell <NUM> and/or a target cell <NUM> (e.g., which may be provided by one or more base stations such as a BS <NUM> illustrated in various of the Figures herein), and/or more generally in conjunction with any of the computer circuitry, systems, devices, elements, or components shown in the above Figures, among others, as desired. For example, a processor (and/or other hardware) of such a device may be configured to cause the device to perform any combination of the illustrated method elements and/or other method elements.

It should be noted that while the techniques of <FIG> are described primarily in conjunction with DAPS handovers, various of the techniques described herein may also or alternatively be applicable in any of various other scenarios, such as in other scenarios in which a wireless device maintains simultaneous active uplink connections with multiple cells of a cellular network.

In various embodiments, some of the elements of the methods shown may be performed concurrently, in a different order than shown, may be substituted for by other method elements, or may be omitted. Additional elements may also be performed as desired. As shown, the method of <FIG> may operate as follows.

In <NUM>, a wireless device may measure the propagation delay between the wireless device and a source cell of the DAPS handover, as well as between the wireless device and a target cell of the DAPS handover. The propagation delays may be determined as part of radio resource management (RRM) measurements, in some embodiments.

In <NUM>, the wireless device may report the measured propagation delays, the subcarrier spacing for each of the source cell and the target cell, and possibly wireless device capability information, e.g., relating to DAPS handover capabilities of the wireless device, such as whether the wireless device is capable of supporting DAPS handover, a propagation delay difference handling capability of the wireless device, and/or any of various other capability information. Note that if the wireless device indicates that it is not capable of supporting DAPS handover (or possibly if the wireless device does not report the capability to support DAPS handover), it may be the case that fallback to non-DAPS handover occurs, e.g., in which case the wireless device may keep only an uplink connection with the target cell.

At least according to some embodiments, the propagation delay difference handling capability may provide an indication of the difference between propagation delays that can be handled by the wireless device. For example, the propagation delay difference handling capability may include a value (or an index configured to indicate a value) indicative of the maximum difference in propagation delays between cells that the wireless device can handle without dropping an uplink transmission when switching uplink transmissions from one cell to another during a DAPS handover. Additionally or alternatively, the propagation delay difference handling capability may include include any of various other types of indication related to the difference in propagation delays between cells that the wireless device can handle under certain circumstances. In some instances, the time difference between propagation delays that can be handled by the wireless device may be determined by the wireless device based at least in part on wireless device hardware capabilities. For example, the wireless device may determine whether it can handle a certain amount of delay difference (e.g., in a specified unit/quantity, such as one or multiple cyclic prefixes (CPs)) based at least in part on how many power amplifiers (PAs) are available for the uplink transmissions, and/or based at least in part on any of various other device characteristics.

In <NUM>, the source cell may calculate the propagation time difference between the target cell and the source cell, may determine whether the source cell and the target cell are in the same timing advance group (TAG) for the wireless device, and may provide an indication of whether the source cell and the target cell are in the same TAG to the wireless device (e.g., a TAG indication). At least according to some embodiments, the source cell and the target cell may be considered in the same TAG if the difference in propagation delay to the wireless device of the source cell and the target cell is below a certain threshold. This may occur, for example, if the source cell and the target cell are collocated, or if the source cell and the target cell have approximately equal cell sizes and the wireless device is approximately equidistant between the source cell and the target cell, or possibly in any of various other scenarios.

In <NUM>, the source cell may coordinate uplink transmission for the wireless device during the DAPS handover. This may include determining a time division multiplexing (TDM) communication pattern that allows the wireless device to perform uplink transmissions with both the source cell and the target cell in a time division multiplexed manner. In some instances, one or more guard periods may be included in the TDM communication pattern, e.g., based at least in part on the propagation time difference between the target cell and the source cell and the time difference between propagation delays that can be handled by the wireless device. If the propagation time difference between the target cell and the source cell is greater than the time difference between propagation delays that can be handled by the wireless device, the source cell includes one or more guard periods when determining the TDM communication pattern.

The guard period(s) may be included to avoid the possibility that an overlap in transmission timing for two temporally adjacent communication slots could occur due to the propagation timing difference, which would be beyond the capability of the wireless device to handle. For example, it may be the case that a guard period is included in the TDM pattern after a communication slot for uplink transmission to the source cell and before a communication slot for uplink transmission to the target cell if the propagation delay between the wireless device and the target cell is greater than the propagation delay between the wireless device and the source cell by more than the propagation delay difference handling capability of the wireless device. Similarly, it may be the case that a guard period is included in the TDM pattern after a communication slot for uplink transmission to the target cell and before a communication slot for uplink transmission to the source cell if the propagation delay between the wireless device and the source cell is greater than the propagation delay between the wireless device and the target cell by more than the propagation delay difference handling capability of the wireless device. It may be the case that no guard period is included in the TDM pattern if the propagation delay difference is not greater than the propagation delay difference handling capability of the wireless device, for example if the source cell and the target cell are in the same TAG for the wireless device, or if the source cell and the target cell are not in the same TAG for the wireless device, but the difference in propagation delays of the source cell and the target cell is within the capability of the wireless device to handle without dropping an uplink transmission.

At least in some instances, the cellular base station that provides the source cell may determine the length of the guard period(s) based at least in part on the subcarrier spacing of the target cell (e.g., as reported to the source cell by the wireless device), as well as on the subcarrier spacing of the source cell. For example, the cellular base station that provides the source cell may select a guard period length corresponding to the length of a communication slot for whichever of the source cell or the target cell has a larger subcarrier spacing. The cellular base station that provides the source cell may select this guard period length to minimize any throughput losses due to the guard period inclusion while operating within the cellular communication system timing framework, at least according to some embodiments.

In <NUM>, the source cell may inform the target cell of the TDM pattern determined by the source cell for the wireless device for the DAPS handover. The source cell and the target cell may schedule uplink transmissions for the wireless device during the DAPS handover in accordance with the determined TDM pattern. Thus, the source cell may schedule uplink transmissions between the wireless device and the source cell during communication slots of the TDM pattern that are specified as available for uplink transmissions to the source cell, and the target cell may schedule uplink transmissions between the wireless device and the target cell during communication slots of the TDM pattern that are specified as available for uplink transmissions to the target cell. It may be the case that neither cell schedules an uplink communication for the wireless device during guard periods of the TDM pattern, e.g., to attempt to avoid the possibility of an uplink transmission being dropped by the wireless device.

In <NUM>, the wireless device may determine the TA to use for uplink transmissions to each of the source cell and the target cell. This may include determining separate TAs (e.g., using separate TA commands) for each of the source cell and the target cell if the source cell and the target cell are in different TAGs, or determining one TA (e.g., using one TA command) to use for both the source cell and the target cell if the source cell and the target cell are in the same TAG.

For example, if the wireless device receives an indication from the source cell that the source cell and the target cell are in the same TAG, the wireless device may receive a TA command from one of the source cell or the target cell, and may determine the timing advance for uplink transmissions to both of the source cell and the target cell based on the same TA command. If the wireless device receives an indication from the source cell that the source cell and the target cell are not in the same TAG, the wireless device may receive a first TA command from the source cell, determine the timing advance for uplink transmissions to the source cell based on the first TA command, separately receive a second TA command from the target cell, and determine the timing advance for uplink transmissions to the target cell based on the second TA command.

Thus, the method of <FIG> may be used by a wireless device to perform uplink transmissions with a cellular network during a DAPS handover, in such a manner that there may be no need to drop a colliding uplink transmission, e.g., by avoiding any such uplink transmission collisions and/or by determining that any uplink transmission collisions that may occur are within the capability of the wireless device to handle, at least according to some embodiments.

<FIG> illustrate further aspects that might be used in conjunction with the method of <FIG> if desired. It should be noted, however, that the exemplary details illustrated in and described with respect to <FIG> are not intended to be limiting to the disclosure as a whole: numerous variations and alternatives to the details provided herein below are possible and should be considered within the scope of the disclosure.

One objective that may be targeted in cellular communication technology developments, potentially including in 3GPP cellular technologies such as LTE and NR, may include reducing any potential interruption time during cell handovers. One approach to meeting this objective may include developing and utilizing DAPS handover techniques. To support DAPS handover, a UE may need to keep UL and DL links with both the source cell and the target cell.

There may be numerous possible handover scenarios in which DAPS handover may be used, potentially including any or all of intra-frequency intra-band handover, inter-frequency handover, synchronous handover, and asynchronous handover. For intra-frequency asynchronous handover, it may be the case that the UE can only transmit on one UL link at a time. If the source cell and the target cell are non-collocated, and the cell radius difference is relatively large, the timing advance difference or gap between the source cell and the target cell could be substantial.

As an example, <FIG> illustrates aspects of a possible approach to determining propagation delay between a wireless device and each of multiple cells, according to some embodiments. In the scenario illustrated in <FIG>, in <NUM>, a source cell may provide a downlink symbol to a UE with a certain timing. In <NUM>, the UE may receive the source cell downlink symbol after a propagation delay of T_ps. The UE may determine the timing advance for uplink transmissions to the source cell as <NUM>*T_ps. In <NUM>, the UE may perform an uplink transmission to the source cell using the timing advance for uplink transmissions to the source cell. In <NUM>, a target cell may provide a downlink symbol to a UE with a certain timing. In <NUM>, the UE may receive the target cell downlink symbol after a propagation delay of T_pt. The UE may determine the timing advance for uplink transmissions to the target cell as <NUM>*T_pt. In <NUM>, the UE may perform an uplink transmission to the target cell using the timing advance for uplink transmissions to the target cell. As illustrated in <FIG>, it may be the case that the propagation delays for the source cell and the target cell (T_ps and T_pt), as well as the timing advances for the source cell and the target cell, may differ significantly.

In view of the potential for such a scenario, it may be beneficial to specify how a UE should determine which TA to use (or if multiple TAs should be used) for adjusting uplink transmission timing, and/or how to avoid the possibility of uplink transmissions overlapping temporally when performing uplink transmission switching from one cell to another.

According to some embodiments, as a first step to handling such a potential scenario, a UE may perform radio resource management (RRM) measurements, which may include measuring the propagation delay with the source cell and with the target cell. The UE may report the propagation delays, and may also report the propagation delay difference handling capability of the wireless device, to the source cell.

At least according to some embodiments, the propagation delay difference handling capability of the wireless device may include the amount of propagation delay difference for which the wireless device can still perform uplink transmissions in adjacent communication slots. Note that the propagation delay difference handling capability of the wireless device may be determined based at least in part on the hardware resources/capabilities of the wireless device. For example, as one possibility, it may be the case that a wireless device with a single power amplifier (PA) uplink transmission configuration may be able to handle a time difference of <NUM>. As another possibility, it may be the case that a wireless device with a multiple PA uplink transmission configuration may be able to handle a time difference that is greater than <NUM>. In some instances, the propagation delay difference handling capability may be reported in increments of a predefined value, such as the length of one cyclic prefix (CP).

The cellular base station (e.g., gNB) providing the source cell may calculate the propagation delay difference between the target cell and the source cell, and may determine whether the two cells are in the same TAG for the UE. If the two cells are in the same TAG, the UE may be able to maintain a single timeAlignmentTimer. The source cell may be able to determine a TDM uplink transmission pattern to coordinate the uplink transmissions of the wireless device without inserting any guard period(s) when switching between uplink transmissions from either cell to the other cell. The UE may be able to adjust its uplink transmission timing according to one TA command received during the uplink synchronization update process, and may ignore the TA command from the other cell (e.g., since they may be identical).

Otherwise (e.g., if the two cells are not in the same TAG), the UE may maintain separate timeAlignmentTimers for the source cell and the target cell. The source cell may be able to determine a TDM uplink transmission pattern to coordinate the uplink transmissions of the wireless device, which may include inserting a guard period when switching from uplink transmissions to the cell with the smaller propagation delay to the cell with the larger propagation delay, if the difference in propagation delay is greater than the propagation delay difference handling capability of the UE. Alternatively, if the difference in propagation delay is not greater than the propagation delay difference handling capability of the UE, it may be the case that the source cell does not insert any guard period when switching uplink transmissions between cells. The UE may be able to adjust its uplink transmission timing for the source cell and the target cell separately, e.g., according to the respective TA commands received during the uplink synchronization update process.

The possibility of adding a guard period in the TDM uplink transmission pattern may be used to avoid the possibility of a colliding (e.g., overlapping, due to the propagation time difference) uplink transmission being dropped by the UE. For example, due to the different TAs for the source cell and the target cell, when uplink transmission is switched from one cell to the other, it could cause an overlap in the transmission times, which could result in one of the transmissions being dropped, e.g., if the UE does not have the hardware capability to handle such an overlap in transmission times, such as might be the case for a UE with a single PA uplink transmission configuration for an intra-frequency asynchronous handover.

<FIG> illustrate various possible TDM patterns that might be selected by a source cell in various scenarios, e.g., depending on the measured transmission delay to the UE. As shown in <FIG>, if the target cell and the source cell are in the same TAG, there may be no need to insert a guard period when switching uplink transmissions between cells. As shown in <FIG>, if the target cell and the source cell are in different TAGs, and T_ps<T_pt, a guard period may be included in the TDM pattern when uplink transmission by the UE switches from the source cell to the target cell. As shown in <FIG>, if the target cell and the source cell are in different TAGs, and T_ps>T_pt, a guard period may be included in the TDM pattern when uplink transmission by the UE switches from the target cell to the source cell. At least according to some embodiments, the guard period may have a length of at least one communication slot, e.g., according to the cell with the shorter slot length / larger subcarrier spacing (e.g., max {source SCS, target SCS}).

Note that it may be possible, in some instances, that a UE does not report having the capability to support DAPS handover. In such a scenario, fallback to non-DAPS handover may occur, e.g., such that the UE may keep the uplink with the target cell, at least according to some embodiments.

Claim 1:
A cellular base station (<NUM>) configured to provide a first cell (<NUM>), comprising:
at least one antenna (<NUM>);
at least one radio (<NUM>) coupled to the at least one antenna (<NUM>); and
a processor (<NUM>) coupled to the at least one radio (<NUM>);
wherein the cellular base station (<NUM>) is configured to:
receive an indication from a wireless device (<NUM>) of a propagation delay between the wireless device (<NUM>) and the first cell (<NUM>), a propagation delay between the wireless device (<NUM>) and a second cell (<NUM>), and a propagation delay difference handling capability of the wireless device (<NUM>),
wherein the first cell (<NUM>) is a source cell of a dual active protocol stack, DAPS, handover by the wireless device (<NUM>), wherein the second cell (<NUM>) is a target cell of the DAPS handover; and
determine a time division multiplexing, TDM, pattern for uplink communication for the wireless device (<NUM>) during the DAPS handover, wherein the TDM pattern is determined based at least in part on the propagation delay between the wireless device (<NUM>) and the first cell (<NUM>), the propagation delay between the wireless device (<NUM>) and the second cell (<NUM>), and the propagation delay difference handling capability of the wireless device(<NUM>), wherein to determine the TDM pattern for uplink communication for the wireless device during the DAPS handover, the cellular base station (<NUM>) is further configured to:
determine a propagation delay difference for the wireless device (<NUM>), wherein the propagation delay difference comprises a difference between the propagation delay between the wireless device (<NUM>) and the first cell (<NUM>) and the propagation delay between the wireless device (<NUM>) and the second cell (<NUM>); and
insert at least one guard period in the TDM pattern if the propagation delay difference is greater than the propagation delay difference handling capability of the wireless device (<NUM>),
wherein no guard period is inserted in the TDM pattern if the propagation delay difference is not greater than the propagation delay difference handling capability of the wireless device (<NUM>).