Random access channel (RACH) transmission based on multiple synchronization signal blocks

Abstract

The present application relates to a wireless device for transmitting a random access channel (RACH) transmission based on a plurality of synchronization signal (SS) blocks. The wireless device divides a burst set of SS blocks into a plurality of SS block groups, each SS block group comprising a plurality of SS blocks. The wireless device measures and selects the strongest SS block as a group serving SS block for each SS block group. The wireless device may: maintain timing and frequency tracking for a plurality of group service (SS) blocks; in response to a trigger for the RACH procedure, selecting one or more RACH occasions, each RACH occasion associated with a different SS block group; and transmitting a physical RACH (PRACH) preamble during the one or more RACH occasions. The wireless device may also monitor during the period a random access response (RAR) message for each of the PRACH preambles, and cease the monitoring after receiving an RAR message corresponding to one of the PRACH preambles.

Description

Technical Field

[0001] The described embodiments relate to wireless communications, including methods and apparatus for transmitting random access channel (RACH) transmissions by a wireless device based on multiple synchronization signal (SS) blocks. Background Art

[0002] Newer generations of cellular wireless networks (e.g., fifth-generation (5G) New Radio (NR)) implementing one or more Third Generation Partnership Project (3GPP) 5G standards are rapidly evolving and being deployed by network operators worldwide. Newer cellular wireless networks offer a range of packet-based services, with 5G technology providing increased data throughput and lower latency connections that promise enhanced mobile broadband services for wireless devices. The higher data throughput and lower latency promised by 5G are expected to spur a range of new applications and services and improve existing ones. Users expect higher quality of service from newer 5G technology. Latency incurred during certain procedures, such as during the Random Access Channel (RACH) procedure used to synchronize a wireless device with the cellular wireless network, can impact the user experience. For example, during a voice handover affected by RACH latency, voice quality can degrade and the time required to adjust service can be affected. A need exists for a mechanism for wireless devices to use multiple synchronization signal (SS) blocks transmitted by the cellular wireless network to reduce latency associated with the RACH procedure. Summary of the Invention

[0003] The present application relates to wireless communications, including methods and apparatus for transmitting random access channel (RACH) transmissions by a wireless device based on multiple synchronization signal (SS) blocks. 5G NR technology allows multiple SS blocks to be transmitted by a cellular wireless network entity (e.g., a gNodeB). The cellular wireless network entity may transmit a set of SS blocks sequentially using a set of different directional transmit beams (e.g., using transmit beam scanning to provide spatial directional transmit diversity) to cover a wide area. The cellular wireless network entity may indicate a random access configuration in a system information block type 1 (SIB-1) message broadcast to the wireless device. The random access configuration includes a first parameter specifying the number of SS blocks mapped to each RACH opportunity and a second parameter specifying the number of contention-based (CB) preambles per SS block per valid RACH opportunity. Each SS block is mapped to a specific RACH opportunity, and in some cases, multiple SS blocks may be mapped to the same RACH opportunity on which a preamble is transmitted to initiate a RACH procedure. The set of SS blocks may be divided into different non-overlapping SS block groups, each SS block group being associated with a different set of RACH opportunities. For example, the set of SS blocks may include eight SS blocks divided into two groups of four SS blocks each, wherein each SS block group is mapped to a different RACH opportunity. The wireless device may measure a performance metric for each SS block received from the cellular wireless network and may determine the SS block with the strongest measured performance metric in each SS block group. The determined SS block with the strongest performance may be designated as the group serving SS block for the SS block group. The wireless device may maintain downlink (DL) timing and frequency tracking for each group serving SS block. In some cases, only those group serving SS blocks for which the measured performance metric meets a performance threshold are tracked. The wireless device may use the RACH opportunity associated with any group serving SS block for which the measured performance metric meets the performance threshold to send a preamble to the cellular wireless network to initiate a RACH procedure (assuming there is sufficient time to prepare for the preamble transmission and to send the preamble during the RACH opportunity). In some embodiments, the wireless device selects a RACH opportunity that is closest in time to a RACH triggering event, for which the group serving SS block meets a performance threshold, and for which sufficient time is available to prepare a physical RACH (PRACH) preamble and transmit the PRACH preamble to the cellular wireless network to initiate a RACH procedure with the cellular wireless network. In some cases, the RACH opportunity that is closest in time to the RACH triggering event is used for PRACH preamble transmission. In some cases, the RACH opportunity that is second closest in time to the RACH triggering event is used for PRACH preamble transmission. In some embodiments, SS block indices are assigned to SS blocks to provide wide spatial directional transmit diversity for each SS block group.In some cases, SS blocks associated with adjacent transmit beams are assigned SS block indices to distribute the SS blocks into different SS block groups. In some embodiments, the wireless device transmits multiple preambles to initiate a RACH procedure, each preamble being associated with a different SS block group and a different associated RACH opportunity. The wireless device may monitor for a random access response (RAR) message for each of the transmitted preambles until a RAR message is received from the cellular wireless network in response to one of the transmitted preambles. The wireless device may respond to the RAR message (as part of the 4-step RACH procedure) and may stop monitoring for RAR messages for other transmitted preambles.

[0004] Other aspects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrate by way of example the principles of the described embodiments.

[0005] This summary is provided for the purpose of summarizing some example embodiments only, in order to provide a basic understanding of some aspects of the subject matter described herein. Therefore, it should be understood that the above-mentioned features are merely examples and should not be construed as narrowing the scope or essence of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following detailed description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present disclosure will be more readily understood through the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals designate like structural elements.

[0007] Figure 1 A block diagram illustrating communications between a wireless device and a cellular wireless network for a random access channel (RACH) procedure according to some embodiments is illustrated.

[0008] Figure 2 A diagram illustrating the format of a synchronization signal (SS) block sent by a cellular wireless network in accordance with some embodiments.

[0009] Figure 3 An exemplary grouping of synchronization signal (SS) blocks into SS block burst sets and the association of SS blocks with different transmit beams according to some embodiments is illustrated.

[0010] Figure 4 A frame format including multiple RACH opportunities grouped into specific subframes according to some embodiments is illustrated.

[0011] Figure 5A A diagram illustrating an example of a delay incurred by a wireless device initiating a RACH procedure according to some embodiments.

[0012] Figure 5B A diagram illustrating an example of channel fading affecting a wireless device's RACH procedure in accordance with some embodiments.

[0013] Figure 5C A diagram illustrating an example of latency reduction resulting from a wireless device initiating a RACH procedure according to some embodiments.

[0014] Figure 5D A diagram illustrating exemplary synchronization signal (SS) block grouping based on SS block index mapping according to some embodiments is illustrated.

[0015] Figure 5E A diagram illustrating an example of a wireless device sending multiple preambles to initiate a RACH procedure in accordance with some embodiments.

[0016] Figure 6 A flow chart illustrating an example method for improving RACH performance using multiple SS blocks by a wireless device in accordance with some embodiments.

[0017] Figure 7 A block diagram illustrating exemplary elements of a wireless device according to some embodiments is illustrated. DETAILED DESCRIPTION

[0018] This section describes representative applications of the methods and apparatus according to the present application. These examples are provided solely to add context and aid in understanding the described embodiments. Therefore, it will be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other cases, well-known processing steps have not been described in detail to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be considered limiting.

[0019] The present application relates to wireless communications, including methods and apparatus for transmitting random access channel (RACH) transmissions by a wireless device based on multiple synchronization signal (SS) blocks. 5G NR technology allows a cellular wireless network entity (e.g., a gNodeB) of a cellular wireless network to transmit multiple SS blocks. The gNodeB may sequentially transmit a set of SS blocks using a set of different directional transmit beams (e.g., using transmit beam scanning to provide spatial directional transmit diversity) to cover a wide spatial area. Each SS block is assigned an SS block index and may be associated with a different transmit beam. The gNodeB may broadcast a random access configuration in a System Information Block Type 1 (SIB-1) message, which indicates parameters for random access communications between the gNodeB and a wireless device of the cellular wireless network. The random access configuration may include a first parameter specifying the number of SS blocks mapped to a single RACH opportunity, where the first parameter may vary from a fraction less than 1 (e.g., 1 / 8, where each SS block is associated with multiple RACH opportunities) to an integer power of 2 (e.g., 4, where four different SS blocks are associated with a single RACH opportunity). The random access configuration may also include a second parameter specifying the number of contention-based (CB) preambles per SS block per valid RACH opportunity.Multiple CB preambles may be used for each unique SS block.

[0020] The set of all available SS blocks is mapped to different RACH opportunities, and in some cases, multiple SS blocks may be mapped to the same RACH opportunity for use as part of a multi-step (e.g., 2-step or 4-step) RACH procedure. The set of SS blocks may be partitioned into SS block groups, each SS block group being associated with a different set of RACH opportunities that periodically repeat in different uplink (UL) transmission frames. For example, the set of SS blocks may include eight SS blocks, which may be partitioned into two groups of four SS blocks each, wherein each SS block group is mapped to a different set of RACH opportunities. The wireless device measures a performance metric for each SS block received from the cellular wireless network and determines, from each SS block group, the SS block with the strongest measured performance metric, wherein the determined SS block is designated as the group serving SS block for the associated SS block group. Partitioning the set of SS blocks and selecting an SS block from each SS block group differs from a previous RACH procedure in which only a single SS block is selected from the set of SS blocks. Multiple SS blocks belonging to different SS block groups are mapped to different RACH opportunities, which allows the wireless device to flexibly select a RACH opportunity to initiate a RACH procedure by sending a physical RACH (PRACH) preamble during the selected RACH opportunity.

[0021] The wireless device may maintain downlink (DL) timing and frequency tracking for each group service SS block. In some cases, only those group service SS blocks for which a measured performance metric meets a performance threshold are tracked, for example, those group service SS blocks for which signal strength and / or signal quality meet a performance threshold, where meeting the performance threshold indicates a high probability of successfully receiving a transmission on the RACH opportunity associated with those group service SS blocks. The wireless device may use the RACH opportunity associated with any group service SS block for which the measured performance metric meets the performance threshold. In some embodiments, the wireless device selects a RACH opportunity that is closest in time to a RACH triggering event, for which the group service SS block meets the performance threshold, and for which sufficient time is available to prepare a PRACH preamble and send the PRACH preamble to the cellular wireless network to initiate a RACH procedure with the cellular wireless network. In some cases, the RACH opportunity selected by the wireless device for the PRACH preamble transmission is closest in time to the RACH triggering event. In some cases, the RACH opportunity selected by the wireless device for PRACH preamble transmission is the second closest in time to the RACH triggering event, i.e., not the first RACH opportunity available after the RACH triggering event, but the second RACH opportunity available after the RACH triggering event.

[0022] In some embodiments, SS block indices are assigned to SS blocks to provide broad spatial directional transmit diversity for each SS block group. In some embodiments, SS block indices are sequentially assigned to different SS block groups in a round-robin manner to distribute the SS block indices across the different SS block groups, wherein the cellular wireless network further sequentially assigns the SS block indices to different transmit beams in a round-robin manner. In some cases, SS blocks associated with adjacent transmit beams are assigned SS block indices to distribute the SS blocks to different SS block groups.

[0023] In some embodiments, the wireless device transmits multiple preambles during different RACH opportunities to initiate a RACH procedure, where each RACH opportunity is associated with a different SS block group. Each preamble may be associated with an SS block from a different SS block group mapped to different RACH opportunities. Rather than transmitting a single preamble during a single RACH opportunity to initiate a RACH procedure, the wireless device transmits multiple preambles during multiple RACH opportunities, thereby increasing transmit diversity (in time), with each preamble associated with a different SS block (and therefore, a different transmit beam from the cellular wireless network). The wireless device monitors the cellular wireless network for a random access response (RAR) message for each of the transmitted preambles until a RAR message is received from the cellular wireless network in response to one of the transmitted preambles. The wireless device may respond to the RAR message (to continue the steps of the 4-step RACH procedure) and stop monitoring for RAR messages for the other transmitted preambles.

[0024] These and other embodiments are referenced below. Figures 1 to 7 however, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for illustrative purposes only and should not be construed as limiting.

[0025] Figure 1A block diagram 100 illustrates communication between a wireless device 102 and a gNodeB 112 for a 5G NR random access channel (RACH) procedure. The wireless device 102 may determine future RACH opportunities on which to send preambles to the gNodeB 112 based on measurements of synchronization signal (SS) blocks received from the gNodeB 112. Each SS block may be associated with a corresponding RACH opportunity, and the wireless device 102 may select a RACH opportunity for received SS blocks that meet a performance threshold. At 104, the wireless device 102 transmits a physical RACH (PRACH) preamble to the gNodeB 112 during the selected RACH opportunity. The wireless device 102 may repeatedly transmit the PRACH preamble to the gNodeB 112 at gradually increasing transmit power levels until a response is received from the gNodeB 112. At 106, the wireless device 102 receives a random access response (RAR) message from the gNodeB 112 indicating that the cellular wireless network has received the PRACH preamble. The RAR message may include a timing advance (TA) command to instruct the wireless device 102 to adjust the alignment of the uplink (UL) transmission. At 108, the wireless device sends an uplink message (designated "Message 3") to the gNodeB 112, and at 110, the gNodeB 112 responds with a downlink message (designated "Message 4"). Figure 1 The four-step RACH procedure illustrated in FIG. 1 is used by the wireless device 102 to acquire timing and transmit in synchronization with the gNodeB 112 to achieve contention-free communication with the cellular wireless network.

[0026] Figure 2 A diagram illustrates a representative format of a synchronization signal (SS) block 200 sent by a gNodeB 112 to a wireless device 102. The SS block 200 spans four consecutive orthogonal frequency division multiplexing (OFDM) symbols and includes a primary synchronization signal (PSS) 202 in the first OFDM symbol of the SS block and a secondary synchronization signal (SSS) 206 in the third OFDM symbol of the SS block. The wireless device 102 can use the PSS 202 and SSS 206 to identify the cellular wireless network and synchronize with the gNodeB 112 of the cellular wireless network. The SS block 200 also includes a physical broadcast channel (PBCH) 204 in the second and fourth OFDM symbols, as well as in selected frequency subcarriers of the third OFDM symbol. The PBCH 204 includes system information in a master information block (MIB) and indicates where the wireless device 102 can obtain additional broadcast system information (SI) (e.g., SI block type 1 (SIB-1)). The SS blocks 200 are periodically transmitted by the gNodeB 112, with a typical spacing of 20 ms between consecutive SS blocks 200 associated with a particular transmit beam.

[0027] Figure 3A diagram 300 illustrates an exemplary SS block burst set 302 transmitted by a gNodeB 112. The gNodeB 112 may transmit consecutive SS blocks 200 by using transmit beam sweeping on the SS block burst set 302 to provide wider spatial coverage, wherein each SS block 200 is transmitted on a different transmit beam in a different direction. The SS blocks are arranged into SS block burst sets 302, each including N SS blocks, where each SS block is labeled with an SS block index (e.g., SS block 0, then SS block 1, etc.). Successive SS blocks may be sequentially transmitted by the gNodeB 112 on different transmit beams in a round-robin manner, with each SS block burst set 302 returning to the initial transmit beam to transmit the first SS block 200 in the SS block burst set 302. The SS block burst set 302 repeats according to the SS block burst set periodicity, and consecutively transmitted SS blocks 200 with the same SS block index are separated by a time interval equal to the SS block burst set period. For example, SS block 0 in the first SS block burst set 302 is transmitted in time with SS block 0 in the second SS block burst set 302 by the SS block burst set period. Similarly, SS block 1 in the first SS block burst set 302 is separated from SS block 1 in the second SS block burst set 302 by the same time interval. A shorter SS block burst set periodicity allows the wireless device 102 to perform cell searches faster, but requires the gNodeB 112 to transmit more frequently, which consumes power, while a longer SS block burst set periodicity allows for greater energy efficiency but may cause the wireless device 102 to acquire cells for a longer period of time. The number of SS blocks 200 within an SS block burst set 302 may depend on the frequency range used by the gNodeB 112, where lower frequency ranges may use fewer SS blocks 200 per SS block burst set 302 and higher frequency ranges may use more SS blocks 200 per SS block burst set 302. The PBCH 204 for each SS block 200 includes an SS block index value to indicate the location of the SS block 200 within the SS block burst set 302. Different SS blocks 200 with different SS block indices are transmitted on different transmit beams and may be associated with different RACH opportunities. The PBCH 204 includes a MIB that may indicate to the wireless device 102 an additional broadcast system information (SI) message (e.g., an SI block type 1 (SIB-1) message) that includes information specifying a random access configuration used by a gNodeB 112 of the cellular wireless network. Exemplary random access configuration parameters include a physical RACH (PRACH) preamble pattern and time / frequency resources for the RACH opportunity, an allowable PRACH preamble transmit power level, and a mapping from SS block index values to RACH opportunities.The wireless device 102 may receive the set of SS block bursts 302, calculate and select the strongest SS block 200 that meets a performance threshold, determine the RACH opportunity to which the selected SS block 200 is mapped, select a PRACH preamble appropriate for the SS block 200 and the RACH opportunity, and send the PRACH preamble on the selected RACH opportunity.

[0028] Figure 4 A diagram 400 illustrates RACH opportunities 402 in an uplink (UL) transmission frame that may be used by a wireless device 102 for an UL transmission to a gNodeB 112 of a cellular wireless network. A RACH configuration, which maps SS block 200 indices to RACH opportunities 402, is broadcast by the gNodeB 112 to the wireless device in a SIB-1 message. The RACH configuration specifies the time / frequency resources for the RACH slots in a frame where RACH opportunities 402 may occur, as well as the RACH frame periodicity, which may vary from one frame (i.e., a RACH slot occurs in every frame) to 16 frames (i.e., a RACH slot occurs in every 16 frames). The RACH configuration also specifies the number of RACH slots available in a given frame, and each RACH slot may include multiple RACH opportunities 402. The RACH configuration also indicates the number N of SS block 200 indices that map to a single RACH opportunity 402, as well as the number R of contention-based (CB) preambles per SS block 200 index value per valid RACH opportunity 402. Different wireless devices 102 may select the same RACH opportunity 402 on which to initiate a RACH procedure, and may each randomly select a CB preamble code applicable to the selected RACH opportunity 402 to use when transmitting on the selected RACH opportunity 402. Figure 4 In the typical RACH configuration shown, RACH opportunities 402 are available in RACH time slots of subframes 0 and 9 of a frame and recur periodically according to the RACH frame period as directed by the gNodeB 112 of the cellular wireless network. The number of SS blocks 200 mapped to a RACH opportunity 402 specified in the RACH configuration broadcast by the gNodeB 112 can range from 1 / 8 (where each SS block 200 maps to 8 different RACH opportunities 402) to 16 (where 16 different SS blocks 200 map to the same RACH opportunity 402). The embodiments described herein are applicable to scenarios where multiple SS blocks 200 map to the same RACH opportunity 402.

[0029] Figure 5AGraph 500 illustrates an example of a delay incurred by a wireless device 102 when initiating a RACH procedure. In an exemplary implementation, each SS block burst set 302 includes eight SS blocks 200, and four different SS blocks 200 are mapped to the same RACH opportunity 402. Thus, the SS block burst set 302 may be divided into two SS block groups, each group including four SS blocks 200, each SS block group being associated with a different RACH opportunity 402. The RACH opportunities 402 occur in subframes 4 and 9. The wireless device 102 may measure the SS blocks 200 received from a gNodeB 112 of a cellular wireless network and, in response to a trigger to initiate a RACH procedure, select the SS block 200 that is measured to be the strongest and that meets a performance threshold. Figure 5A In the example of , the selected SS block 200 is associated with a RACH opportunity 402 occurring in subframe 9. The wireless device 102 requires a minimum amount of time after triggering the RACH procedure to select a PRACH preamble and prepare to send the PRACH preamble to the gNodeB 112 during the RACH opportunity in subframe 9. Figure 5A In the illustrated example, the RACH procedure is triggered close in time to the next subframe 9, so the wireless device 102 does not have sufficient time to prepare for the PRACH preamble transmission. The RACH opportunity 402 in the next subframe 9 could instead be used to transmit the PRACH preamble to the gNodeB 112; however, depending on the spacing between frames including RACH opportunities 402 (e.g., consecutive frames with RACH opportunities 402 may occur every 10 ms or up to 160 ms apart), a significant delay may be incurred before the RACH procedure begins. Furthermore, because the selected SS block 200 maps to a RACH opportunity 402 that only occurs in subframe 9, the RACH opportunity 402 in subframe 4 (which occurs earlier than the used RACH opportunity 402 of subframe 9) is not used. Limiting the wireless device 102 to selecting only a single SS block 200 may result in increased latency in initiating the RACH procedure.

[0030] Figure 5BDiagram 510 illustrates time-frequency domain fading that causes a PRACH preamble transmitted by a wireless device 102 to fail to reach a gNodeB 112 of a cellular wireless network. The gNodeB 112 transmits different SS blocks 200 of an SS block burst set 302 using different directional transmit beams. For a heavily diffuse communication channel between the gNodeB 112 and the wireless device 102, multiple SS blocks 200 may arrive at the wireless device 102 in overlapping diffuse clusters. SS blocks 200 transmitted on different beams at different times over the diffuse channel may overlap in time when arriving at the wireless device 102. The wireless device 102 selects a group serving SS block with a measurement that meets a performance threshold. To avoid ping-pong switching between different SS blocks 200 when rapid fading in the communication channel between the wireless device 102 and the gNodeB 112 may cause the measured performance of the SS blocks 200 to vary rapidly, the wireless device 102 may switch to another, stronger SS block 200 only after a certain amount of time (e.g., based on a hysteresis timer). In the case of a deep fade, the previously selected group serving SS block may not be the strongest SS block 200 beam during the associated RACH opportunity 402 in which the PRACH preamble is transmitted, and the PRACH preamble may not be received by the gNodeB 112 due to the deep fade. As shown in diagram 520, the wireless device 102 may select an SS block 200 with SS block index 4 or 5 at a first time, and transmit the PRACH preamble during the RACH opportunity 402 associated with SS block index 4 or 5 at a future time when SS blocks 200 with SS block indexes 2 and 3 have higher performance than SS blocks 4 and 5. The delay caused by the hysteresis (and waiting for the appropriate RACH opportunity 402) may cause the wireless device 102 to transmit the PRACH preamble to the gNodeB 112 using the RACH opportunity 402 of the suboptimal performing SS block 200. Furthermore, as shown in diagram 530, the time-frequency resource blocks available for PRACH preamble transmission may span a frequency range that is much narrower than the frequency range of the SS blocks 200 measured by the wireless device 102 to select the SS blocks 200 and the associated RACH opportunities 402 on which to transmit the PRACH preamble. Frequency selective fading may affect the PRACH preamble more severely than the SS blocks 200, and thus the measured SS blocks 200 from which the wireless device 102 estimates the communication channel performance may not reflect the conditions of the PRACH preamble transmission, and the gNodeB 112 may not be able to receive the preamble when deep fading occurs.

[0031] Figure 5CDiagram 540 illustrates an example of a wireless device 102 using multiple SS blocks 200 associated with different RACH opportunities 402 to reduce latency in initiating a RACH procedure. A gNodeB 112 of a cellular wireless network transmits a set of SS block bursts 302 comprising eight SS blocks 200 sequentially transmitted at different times on different transmit beams in different directions. The eight SS blocks 200 are mapped to two different sets of RACH opportunities 402. The first set of RACH opportunities 402 is associated with a first SS block group 0, which includes SS blocks 200 with indices 0, 1, 2, and 3, and occurs in subframe 4 of a frame, which includes RACH opportunity 402. The second set of RACH opportunities 402 is associated with a second SS block group 1, which includes SS blocks 200 with indices 4, 5, 6, and 7, and occurs in subframe 9 of the frame, which includes RACH opportunity 402. The wireless device 102 may select a plurality of SS blocks 200 that are measured to have sufficient signal strength / quality to meet a performance threshold, and use a RACH opportunity 402 associated with one of the plurality of SS blocks 200 that is closest in time to the occurrence of a trigger for the RACH procedure and has sufficient time to prepare for a PRACH preamble transmission and transmit the PRACH preamble on the RACH opportunity 402 for the selected SS block 200. Figure 5C In the illustrated example, the wireless device 102 may select SS block 200 from SS block group 0 associated with the RACH opportunity 402 occurring in subframe 4 and use SS block 200 from SS block group 1 associated with the RACH opportunity 402 occurring in subframe 9 (which results in more latency to initiate the RACH procedure, as shown in FIG. Figure 5A Compared with the above example, the delay of initiating RACH process is shorter. Figure 5CThe example of FIG1 divides the SS blocks 200 into two SS block groups of four SS blocks 200, but different RACH configurations may specify two SS blocks 200 per RACH opportunity 402, and the wireless device 102 may divide the SS blocks 200 into four SS block groups of two SS blocks 200, select an SS block 200 that meets the performance threshold from any of the four SS block groups, and transmit the PRACH preamble on the RACH opportunity 402 associated with the selected SS block 200. If no SS block 200 within the SS block group meets the performance threshold, the wireless device 102 does not select an SS block 200 from that SS block group. In some embodiments, the wireless device 102 selects the strongest SS block 200 from each SS block group as the group serving SS block and may use the RACH opportunity 402 associated with the group serving SS block if the group serving SS block meets the performance threshold. When multiple group serving SS blocks are available and meet the performance threshold, the wireless device 102 may maintain downlink timing and frequency tracking based on each group serving SS block. When the RACH procedure is triggered, the wireless device 102 may select the group serving SS block associated with the RACH opportunity 402 that is closest to the trigger (and has enough time to prepare for and send a PRACH preamble transmission to the gNodeB 112).

[0032] Figure 5D Diagrams 550 and 560 illustrate examples of mapping SS block 200 indices to SS block groups. Each SS block 200 of an SS block burst set 302 is transmitted by the gNodeB 112 using different transmit beams focused in different directions so that the entire SS block burst set 302 provides wide spatial coverage. The RACH configuration broadcast by the gNodeB 112 indicates the number of SS blocks 200 mapped to a single RACH opportunity 402. Figure 5DIn the example of FIG5 , four SS blocks 200 are mapped to each RACH opportunity 402, and the SS block burst set 302 is divided into two SS block groups. In diagram 550, the SS block burst set 302 is divided into SS block group 0 associated with SS block indices 0, 1, 2, and 3, and SS block group 1 associated with SS block indices 4, 5, 6, and 7. This arrangement of sequentially dividing SS blocks into SS block groups with consecutive SS block indices results in SS block groups with spatially concentrated transmit beam patterns, which may cause the SS blocks 200 in SS block group 0 to perform significantly differently from the SS blocks 200 in SS block group 1, where SS block group 0 may encounter different communication channel conditions than SS block group 1. In diagram 560, the SS block burst set 302 is divided into SS block group 0 associated with SS block indices 0, 2, 4, and 6, and SS block group 1 associated with SS block indices 1, 3, 5, and 7. This arrangement of partitioning the SS blocks 200 using alternating groupings results in SS block groups having similar spatially dispersed transmit beam patterns, which may result in the SS blocks 200 in SS block group 0 having similar performance as the SS blocks 200 in SS block group 1. It is preferred to have comparable spatial transmit beam diversity in each SS block group to increase the chance that at least one SS block 200 in each SS block group meets the performance threshold and to avoid the situation where no SS blocks 200 in any given SS block group meet the performance threshold.

[0033] Figure 5EA diagram 570 is illustrated in which the wireless device 102 transmits PRACH preambles during multiple RACH opportunities 402 associated with SS blocks 200 in different SS block groups. The wireless device 102 can measure and select multiple SS blocks 200 that each meet a performance threshold, where each SS block 200 is in a different SS block group and associated with a different RACH opportunity 402. The wireless device 102 can transmit PRACH preambles during different RACH opportunities 402 to initiate a RACH procedure and provide time diversity for reception of the PRACH preambles by the gNodeB 112. The wireless device 102 divides the SS blocks 200 into multiple SS block groups based on the RACH opportunities 402 associated with the SS blocks, e.g., SS block group 0 with SS block indices 0, 1, 2, and 3, and SS block group 1 with SS block indices 4, 5, 6, and 7. The wireless device 102 selects the strongest measured SS block 200 from each SS block group as the group serving SS block. When a group serving SS block meets a performance threshold, the RACH opportunity 402 associated with the group serving SS block is available for PRACH preamble transmission. The wireless device 102 maintains downlink timing and frequency tracking for each of the group serving SS blocks. When a RACH procedure is triggered, the wireless device 102 selects a plurality of RACH opportunities 402 based on the group serving SS blocks that meet the performance threshold. The wireless device 102 selects two (or more) RACH opportunities 402 and transmits PRACH preambles on the two (or more) RACH opportunities, where at least one SS block from each SS block group with a set of serving SS blocks meets the performance threshold. The RACH opportunity 402 closest in time to the RACH procedure trigger is used only if there is sufficient time to prepare for and transmit the PRACH preamble during the RACH opportunity 402. After transmitting multiple PRACH preambles, the wireless device 102 calculates a random access radio network temporary identifier (RA-RNTI) for each PRACH preamble transmission and initiates a corresponding random access (RA) response window to monitor for random access response (RAR) messages corresponding to the PRACH preamble transmission. In the case of multiple PRACH preamble transmissions, the wireless device 102 determines multiple RA-RNTI values and multiple RA response windows for concurrently monitoring for RAR messages. When the wireless device 102 receives a RAR message from the gNodeB 112 for one of the multiple RA-RNTI values, the wireless device 102 may stop monitoring for RAR messages associated with the other RA-RNTI values.By transmitting multiple PRACH preamble transmissions in different RACH opportunities 402 (which are associated with different SS blocks 200 and, therefore, different transmit beams), the wireless device 102 improves both latency (sending the PRACH preamble earlier than when using only one RACH opportunity 402) and transmit diversity (using different transmit beams and RACH opportunities 402), thereby improving the successful execution of the RACH procedure with the gNodeB 112 of the cellular wireless network.

[0034] Figure 6 A flowchart 600 illustrates an exemplary method for initiating a RACH procedure using multiple SS blocks 200 by a wireless device 102. At 602, the wireless device 102 measures signal performance metrics for multiple SS blocks 200, each SS block 200 having a different SS block index value and belonging to a unique SS block group. At 604, the wireless device 102 selects the SS block 200 with the strongest signal performance metric from each SS block group as the group serving SS block for the corresponding SS block group. At 606, the wireless device 102 detects a trigger for a RACH procedure. At 608, the wireless device 102 selects a first physical RACH (PRACH) preamble 402 that is closest in time to the trigger and has sufficient time after the trigger to transmit a first RACH opportunity, for which the signal performance metric of the group serving SS block associated with the first RACH opportunity 402 meets a performance threshold. At 610, the wireless device 102 transmits the first PRACH preamble to the cellular wireless network during the first RACH opportunity 402.

[0035] In some embodiments, the plurality of SS blocks 200 are divided into different SS block groups, each SS block group being associated with a different set of non-overlapping periodic RACH opportunities 402. In some embodiments, each SS block index is associated with a different transmit beam on which the cellular wireless network transmits the SS block 200 having the associated SS block index. In some embodiments, the SS block indices of the plurality of SS blocks 200 of each SS block group are assigned to different transmit beams to provide spatial directional diversity for transmitting the SS blocks 200. In some embodiments, the SS block indices of the plurality of SS blocks 200 are assigned in a manner that sequentially assigns one SS block index to each SS block group at a time in a round-robin manner to distribute the SS blocks 200 over the widest possible span of transmit directions for each SS block group. In some embodiments, the wireless device 102 maintains downlink (DL) timing and frequency tracking for each SS block group based on the group service SS block selected for the corresponding SS block group. In some embodiments, the wireless device 102: selects a second RACH opportunity 402 that is closest in time to the first RACH opportunity 402, for which a signal performance metric for an SS block index value associated with the second RACH opportunity 402 satisfies a performance threshold; and transmits a second PRACH preamble to the cellular wireless network during the selected second RACH opportunity 402. In some embodiments, the wireless device 102: i) calculates a first random access radio network temporary identifier (RA-RNTI) for the first PRACH preamble and a second RA-RNTI for the second PRACH preamble, ii) monitors for reception of a random access response (RAR) message from the cellular wireless network during a corresponding RAR window, and iii) stops monitoring for RAR messages after receiving a RAR message from the cellular wireless network in response to the first PRACH preamble or the second PRACH preamble. In some embodiments, the first RACH opportunity 402 is the RACH opportunity 402 that is closest in time to a RACH trigger detected by the wireless device 102. In some implementations, the first RACH opportunity 402 is the RACH opportunity 402 that is second closest in time to the detection of the RACH trigger by the wireless device 102 .

[0036] Representative exemplary devices

[0037] Figure 7 An exemplary computing device 700 that can be used to implement the various components and techniques described herein according to some embodiments is illustrated in a block diagram format. Specifically, the detailed view of the exemplary computing device 700 illustrates various components that can be included in the wireless device 102. Figure 7As shown, computing device 700 may include one or more processors 702, representing microprocessors or controllers for controlling the overall operation of computing device 700. In some embodiments, computing device 700 may also include a user input device 708 that allows a user of computing device 700 to interact with computing device 700. For example, in some embodiments, user input device 708 may take a variety of forms, such as buttons, a keypad, a dial, a touch screen, an audio input interface, a visual / image capture input interface, input in the form of sensor data, etc. In some embodiments, computing device 700 may include a display 710 (screen display) that can be controlled by processor 702 to display information to the user (e.g., information related to incoming, outgoing, or active communication sessions). A data bus 716 may facilitate data transfer between at least storage device 740, processor 702, and controller 713. Controller 713 may be used to interact with and control various devices via an equipment control bus 714. Computing device 700 may also include a network / bus interface 711 coupled to data link 712. In the case of a wireless connection, the network / bus interface 711 may include wireless circuitry, such as a wireless transceiver and / or a baseband processor. The computing device 700 may also include a secure element 724. The secure element 724 may include an eUICC.

[0038] The computing device 700 also includes a storage device 740, which may include a single storage device or multiple storage devices (e.g., a hard drive), and a storage management module that manages one or more partitions within the storage device 740. In some embodiments, the storage device 740 may include flash memory, semiconductor (solid-state) memory, or the like. The computing device 700 may also include random access memory (RAM) 720 and read-only memory (ROM) 722. ROM 722 may store programs, utilities, or processes to be executed in a non-volatile manner. RAM 720 may provide volatile data storage and store instructions related to the operation of the computing device 700.

[0039] Wireless Terminology

[0040] According to various embodiments described herein, the terms "wireless communication device," "wireless device," "mobile device," "mobile station," and "user equipment (UE)" may be used interchangeably herein to describe one or more common consumer electronic devices that may be capable of performing the processes associated with various embodiments of the present disclosure. According to various specific implementations, any of these consumer electronic devices may relate to: a cellular telephone or smartphone, a tablet computer, a laptop computer, a notebook computer, a personal computer, a netbook computer, a media player device, an e-reader device, Devices, wearable computing devices, and any other type of electronic computing device with wireless communication capabilities, which may include communication via one or more wireless communication protocols, such as protocols used to communicate over the following networks: wireless wide area networks (WWANs), wireless metropolitan area networks (WMANs), wireless local area networks (WLANs), wireless personal area networks (WPANs), near field communication (NFC), cellular wireless networks, fourth generation (4G) LTE, advanced LTE (LTE-A) 5G and / or 5G advanced or other currently or future developed advanced cellular wireless networks.

[0041] In some embodiments, the wireless communication device may also operate as part of a wireless communication system, which may include a group of client devices, which may also be referred to as stations, client wireless devices, or client wireless communication devices, interconnected to an access point (AP) (e.g., as part of a WLAN) and / or interconnected with each other (e.g., as part of a WPAN and / or "ad hoc" wireless network). In some embodiments, the client device may be any wireless communication device capable of communicating via WLAN technology (e.g., according to a wireless local area network communication protocol). In some embodiments, the WLAN technology may include a Wi-Fi (or more generally, WLAN) wireless communication subsystem or radio component, which may implement the Institute of Electrical and Electronics Engineers (IEEE) 802.11 technology, such as one or more of the following: IEEE 802.11a; IEEE 802.11b; IEEE 802.11g; IEEE 802.11-2007; IEEE 802.11n; IEEE 802.11-2012; IEEE 802.11ac; or other currently or future developed IEEE 802.11 technologies.

[0042] In addition, it should be understood that the UE described herein can be configured as a multimode wireless communication device that is also capable of communicating via different third generation (3G) and / or second generation (2G) RATs. In these cases, the multimode user equipment (UE) can be configured to prefer attaching to an LTE network that provides a faster data rate throughput over other 3G legacy networks that provide a lower data rate throughput. For example, in some specific implementations, the multimode UE can be configured to fall back to a 3G legacy network, such as an evolved high speed packet access (HSPA+) network, or a code division multiple access (CDMA) 2000 evolution-data only (EV-DO) network, when 5G, LTE, and LTE-A networks are otherwise unavailable.

[0043] It is understood that the use of personally identifiable information should be subject to privacy policies and practices that are generally recognized to meet or exceed industry or government requirements for maintaining user privacy. Specifically, personally identifiable information data should be managed and processed to minimize the risk of unintentional or unauthorized access or use, and the nature of authorized use should be clearly stated to users.

[0044] The various aspects, embodiments, implementations, or features of the described embodiments may be used individually or in any combination. Various aspects of the described embodiments may be implemented by software, hardware, or a combination of hardware and software. The described embodiments may also be implemented as computer-readable code on a non-transitory computer-readable medium. A non-transitory computer-readable medium is any data storage device that can store data that can then be read by a computer system. Examples of non-transitory computer-readable media include read-only memory, random access memory, CD-ROM, HDD, DVD, magnetic tape, and optical data storage devices. Non-transitory computer-readable media may also be distributed on network-coupled computer systems so that the computer-readable code is stored and executed in a distributed manner.

[0045] For illustrative purposes, the foregoing description uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to those skilled in the art that specific details are not required in order to practice the described embodiments. Therefore, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. The foregoing descriptions are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to those skilled in the art that, in light of the above teachings, many modifications and variations are possible.

Claims

1. A method for uplink (UL) random access channel (RACH) transmission by a wireless device, the method comprising: By the wireless device: measuring a signal performance metric for a plurality of synchronization signal (SS) blocks, each SS block having a different SS block index value and belonging to a unique SS block group; Selecting the SS block with the strongest signal performance metric from each SS block group as the group service SS block for the corresponding SS block group; Detecting triggering for the RACH process; selecting a first physical RACH (PRACH) opportunity that is closest in time to the trigger and has sufficient time after the trigger to be used to send a first RACH preamble, for which the signal performance metric of the set of serving SS blocks associated with the first RACH opportunity satisfies a performance threshold; as well as The first PRACH preamble is transmitted to a cellular wireless network during the first RACH opportunity.

2. The method of claim 1, wherein the plurality of SS blocks are divided into different SS block groups, each SS block group being associated with a different set of non-overlapping periodic RACH opportunities.

3. The method of claim 2, wherein each SS block index is associated with a different transmit beam, and the cellular wireless network transmits the SS blocks with the associated SS block index on the different transmit beams. 4 . The method of claim 3 , wherein SS block indices of the plurality of SS blocks of each SS block group are assigned to different transmit beams to provide spatial directional diversity for transmitting the SS blocks.

5. The method of claim 3 , wherein the SS block indices of the plurality of SS blocks are assigned in a manner that one SS block index is assigned to each SS block group sequentially in a round-robin manner to distribute the SS blocks over the widest possible transmission direction span for each SS block group.

6. The method according to claim 1, further comprising: By the wireless device: Downlink (DL) timing and frequency tracking is maintained for each SS block group based on the set of serving SS blocks selected for the corresponding SS block group.

7. The method according to claim 1, further comprising: By the wireless device: selecting a second RACH opportunity that is closest in time to the first RACH opportunity, for which the signal performance metric of the SS block index value associated with the second RACH opportunity satisfies the performance threshold; as well as A second PRACH preamble is sent to the cellular wireless network during the second RACH opportunity.

8. The method according to claim 7, further comprising: By the wireless device: calculating a first random access radio network temporary identifier (RA-RNTI) for the first PRACH preamble and calculating a second RA-RNTI for the second PRACH preamble; monitoring reception of a random access response (RAR) message from the cellular wireless network during a corresponding RAR window; as well as After receiving a RAR message in response to the first PRACH preamble or the second PRACH preamble from the cellular wireless network, monitoring the RAR message is stopped.

9. The method of claim 1, wherein the first RACH opportunity is a RACH opportunity that is closest in time to detection of the trigger for the RACH procedure by the wireless device.

10. The method of claim 1, wherein the first RACH opportunity is a RACH opportunity that is second closest in time to detection of the trigger for the RACH procedure by the wireless device.

11. A wireless device, comprising: wireless circuitry, the wireless circuitry including a plurality of antennas; at least one processor communicatively coupled to the wireless circuitry and to a memory storing instructions that, when executed by the at least one processor, configure the wireless device to: measuring a signal performance metric for a plurality of synchronization signal (SS) blocks, each SS block having a different SS block index value and belonging to a unique SS block group; Selecting the SS block with the strongest signal performance metric from each SS block group as the group service SS block for the corresponding SS block group; Detecting triggering for the RACH process; selecting a first physical RACH (PRACH) opportunity that is closest in time to the trigger and has sufficient time after the trigger to be used to send a first RACH preamble, for which the signal performance metric of the set of serving SS blocks associated with the first RACH opportunity satisfies a performance threshold; as well as The first PRACH preamble is transmitted to a cellular wireless network during the first RACH opportunity.

12. The wireless device of claim 11, wherein the plurality of SS blocks are divided into different SS block groups, each SS block group being associated with a different set of non-overlapping periodic RACH opportunities.

13. The wireless device of claim 12, wherein each SS block index is associated with a different transmit beam, and the cellular wireless network transmits the SS blocks with the associated SS block index on the different transmit beams.

14. The wireless device of claim 13, wherein SS block indices of the plurality of SS blocks of each SS block group are assigned to different transmit beams to provide spatial directional diversity for transmitting the SS blocks.

15. The wireless device of claim 13, wherein the SS block indices of the plurality of SS blocks are assigned in a manner that one SS block index is sequentially assigned to each SS block group at a time in a round-robin manner to distribute the SS blocks over the widest possible transmission direction span for each SS block group.

16. The wireless device of claim 11, wherein the wireless device is further configured to maintain downlink (DL) timing and frequency tracking for each SS block group based on the group serving SS block selected for the corresponding SS block group.

17. The wireless device of claim 11, wherein the wireless device is further configured to: selecting a second RACH opportunity that is closest in time to the first RACH opportunity, for which the signal performance metric of the SS block index value associated with the second RACH opportunity satisfies the performance threshold; and A second PRACH preamble is sent to the cellular wireless network during the selected second RACH opportunity.

18. The wireless device of claim 17, wherein the wireless device is further configured to: calculating a first random access radio network temporary identifier (RA-RNTI) for the first PRACH preamble and calculating a second RA-RNTI for the second PRACH preamble; monitoring reception of a random access response (RAR) message from the cellular wireless network during a corresponding RAR window; and After receiving a RAR message in response to the first PRACH preamble or the second PRACH preamble from the cellular wireless network, monitoring the RAR message is stopped.

19. The wireless device of claim 11, wherein the first RACH opportunity is a RACH opportunity closest in time to detection of the trigger for the RACH procedure by the wireless device.

20. The wireless device of claim 11, wherein the first RACH opportunity is a RACH opportunity that is second closest in time to detection of the trigger for the RACH procedure by the wireless device.

21. A non-transitory computer-readable medium storing instructions that, when executed by at least one processor of a wireless device, configure the wireless device to perform the method according to any one of claims 1 to 10.

22. An apparatus configurable for operation in a wireless device, the apparatus comprising one or more processors coupled to a memory storing instructions that, when executed by the one or more processors, configure the wireless device to perform the method according to any one of claims 1 to 10.

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