Systems and methods for beam-based physical random access

Abstract

A method in a wireless device for performing random access to a network node. The method includes: receiving a set of downlink beam-specific reference signals (BRS) from the network node; and determining a preferred BRS based on the received signal power of each BRS. The method further includes: selecting a random access resource to be used for sending a random access attempt to the network node based on the preferred BRS; and using the selected random access resource when sending the random access attempt to the network node, whereby the selection of the random access resource indicates to the network node which downlink beam the wireless device prefers to use for downlink transmission.

Description

[0001] This application is a divisional application, with parent application number 201480079313.9, application date August 27, 2014, and invention title "System and method for beam-based physical random access". Technical Field

[0002] Specific embodiments relate generally to wireless communication, and more specifically to systems and methods for beam-based physical random access. Background Technology

[0003] The current fourth-generation (4G) radio access within the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is based on Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT) Spread Spectrum OFDM in the uplink, also known as Single Carrier Frequency Division Multiple Access (SC-FDMA).

[0004] A candidate for the fifth-generation (5G) air interface is to scale the current LTE air interface (which is limited to 20MHz bandwidth) by a factor of N using a transmission duration shortened to 1 / N. A typical value could be N=5, resulting in a carrier with a 100MHz bandwidth and a slot length of 0.1 milliseconds. This approach allows many functions in LTE to remain the same, simplifying standardization efforts and enabling the reuse of technical components.

[0005] The carrier frequency of 5G systems is expected to be higher than that of current 4G systems. Values ​​in the 10-80 GHz range have been discussed. At such high frequencies, array antennas are suitable for achieving beamforming gain. Due to the small wavelength (e.g., less than 3 cm), array antennas with a large number of antenna elements can be fitted into antenna housings of comparable size to today's 3G and 4G base station antennas.

[0006] Figure 1 This is a block diagram illustrating a radio network 100, which includes one or more wireless devices 110A-C and network nodes 115A-C. Figure 1 The diagram shows a base station, a radio network controller 120, and a packet core network 130.

[0007] Wireless device 110 can communicate with network node 115 via a wireless interface. For example, wireless device 110 can send wireless signals to network node 115 and / or receive wireless signals from network node 115. The wireless signals may contain voice services, data services, control signals, and / or other suitable information.

[0008] Figure 2This is a block diagram illustrating network 200, which includes three transmission points (TPs) 202 for communicating with wireless devices or other user equipment (UEs) via an array antenna that generates multiple beams 203. Transmission points can include any network node, such as... Figure 1 Network node 115 is shown in the figure.

[0009] Because a large number of antenna elements are involved in beamforming, the beams generated by array antennas can typically be highly directional and provide beamforming gain of 20 dB or more. This means that the angle of each beam is relatively narrow, and a half-power beamwidth (HPBW) of 5 degrees is unlikely. Therefore, sectors of network nodes such as base stations must be covered by a large number of beams.

[0010] Among them, such as Figure 2 The system 200 includes multiple transmission nodes, each of which may have an array antenna capable of generating numerous beams 203 with small HPBWs. These nodes may, for example, use one or more carriers, thereby enabling a total transmission bandwidth of hundreds of MHz, resulting in downlink (DL) peak user throughput of up to 10 Gbit / s or more.

[0011] During LTE access, the radio device or UE first uses a cell search procedure to search for cells, where, in the context of LTE, each network node or eNodeB transmits a unique primary synchronization signal and secondary synchronization signal (PSS and SSS, respectively). Once a cell is discovered, the radio device can proceed to become associated with that cell, which is then called the radio device's serving cell. After cell discovery, the radio device can read system information called the Master Information Block (MIB) (transmitted on the physical broadcast channel), which is located in a known time-frequency position relative to the PSS and SSS. After the MIB is detected, the system frame number (SFN) and downlink system bandwidth are known.

[0012] In LTE, as in any communication system, a mobile terminal may need to contact the network when dedicated uplink resources are unavailable from the wireless device to the network node or base station. To address this, a random access procedure is available, in which a wireless device lacking dedicated uplink resources can send signals to the base station.

[0013] Figure 3 This is a block diagram illustrating the random access preamble transmission 300. The first message of this process is typically transmitted on the Physical Random Access Channel (PRACH), a special communication resource reserved for random access. This channel may be time- and / or frequency-restricted, as in LTE.

[0014] Provide communication resources available for PRACH transmission to the wireless device as part of the broadcast system information in System Information Block 2 (SIB-2) or as part of the dedicated radio resource control (RRC) signaling, for example, during handover.

[0015] These resources include preamble sequences and time / frequency resources. There are 64 available preamble sequences in each cell. Two subsets of these 64 sequences are defined, with the set of sequences from each subset being signaled as part of the system information.

[0016] Figure 4 This is a signaling diagram illustrating the contention-based random access procedure used in LTE. Radio device 110 initiates the random access procedure by randomly selecting one of the preambles available for contention-based random access. In step 402, radio device 110 sends a random access preamble (MSG1) to network node 115 on the Physical Random Access Channel (PRACH).

[0017] In step 404, the Radio Access Network (RAN) acknowledges any preamble it has detected by sending a Random Access Response (MSG2) from network node 115. The Random Access Response (MSG2) includes an initial grant used on the uplink shared channel, a Radio Network Temporary Identifier (TC-RNTI), and a Time Alignment (TA) update. Upon receiving the response, in step 406, the Radio Device 110 uses the grant to send a scheduled transport message (MSG3) to network node 115.

[0018] The process ends when the RAN resolves any preamble contention that may occur if multiple radio devices transmit the same preamble at the same time. This is possible because each radio device 110 randomly chooses when to transmit and which preamble to use. If multiple radio devices choose the same preamble for transmission on PRACH, there will be contention that needs to be resolved via a contention resolution message (MSG4) that can be transmitted in step 408.

[0019] Figure 4 The transmission of the Hybrid Automatic Repeat Request Acknowledgment (HARQ ACK) message is also shown.

[0020] Figure 5 This is a block diagram illustrating contention-based random access, where contention exists between two wireless devices. Specifically, two wireless devices, 110A and 110B, transmit the same preamble at the same time. The third wireless device, 110C, also transmitted at the same time, but because it transmitted a different preamble... There is no competition between this wireless device and the other two wireless devices.

[0021] Wireless device 110 is also capable of performing contention-free random access. Figure 6 This is a flowchart illustrating the process by which wireless device 110 performs contention-free random access based on a random access (RA) sequence message received from network node 115. Contention-free random access is typically used for handover between two network nodes, such as... Figure 1 Any two of the network nodes 115A, 115B, and 115C shown. In this case, a non-contention-based random access sequence is sent from the source network node, while the random access preamble (MSG 1) is received at another target network node, which also sends a random access response (MSG 2). Similar to contention-based random access, after successful detection of the random access preamble (MSG 1), the random access response (MSG 2) is sent to the wireless device 110 in the downlink (DL). Summary of the Invention

[0022] In a beam-based radio access system, it is a question of which beam the network side (i.e., network node 115) selects to send the random access response (MSG2) to the wireless device 110.

[0023] Furthermore, detecting the random access preamble (MSG1) on the network side in a beam-based radio access system is a complex problem because network nodes do not know which receive beam is optimal for receiving the preamble, and therefore network node 115 needs to repeatedly search in each beam. Using the optimal beam received on the uplink to transmit the downlink signal to the same wireless device also requires well-calibrated uplink and downlink radio frequency (RF) chains in the network to ensure that favorable reception conditions on the optimal beam received on the uplink are also reflected on the downlink, which is costly to implement.

[0024] One object of this disclosure is to provide at least one wireless device, network node, and method for random access that seeks to mitigate, alleviate, or eliminate one or more, or individually or in any combination, the defects of the prior art as indicated above.

[0025] This objective is achieved by performing a method for random access to a network node in a wireless device. The method includes receiving a set of downlink beam-specific reference signals (BRS) from the network node and determining a preferred BRS based on the received signal power of each BRS. The method also includes selecting a random access resource to be used for transmitting a random access attempt to the network node based on the preferred BRS, and using the selected random access resource when transmitting the random access attempt to the network node, thereby instructing the network node which downlink beam the wireless device prefers for downlink transmission.

[0026] Therefore, since the network (i.e., network nodes) knows the beam that the random access response will use, the coverage of the random access response is improved. Furthermore, the random access process can be completed earlier, which improves latency and reduces interference in the network.

[0027] Another technical advantage is that no calibration and alignment of the RF used for uplink and downlink is required, which reduces implementation costs and power consumption.

[0028] This objective can also be achieved through methods used in network nodes to support random access from wireless devices. The method includes transmitting a set of beam-specific reference signals (BRS) and detecting a preamble in the signals received from the wireless device. The preamble detection indicates the preferred BRS for the wireless device. The method also includes transmitting a random access response with the same beam, and / or beam direction, and / or the same beamforming weights as the preferred BRS indicated by the preamble detection.

[0029] Furthermore, since the network (i.e., network nodes) knows the beam that the random access response will use, the coverage of the random access response is improved. In addition, the random access process can be completed earlier, which improves latency and reduces interference in the network.

[0030] Another technical advantage is that no calibration and alignment of the RF used for uplink and downlink is required, which reduces implementation costs and power consumption.

[0031] A further technical advantage is the reduction in computational complexity in network nodes (such as eNodeBs) through this teaching. The random access preamble detector in the network node only needs to search a subset of the preamble sequence in each uplink receiver direction. This subset is equivalent to those random access sequences mapped to the same downlink transmission beam (or spatial direction) as the receiver's uplink beam (or spatial direction).

[0032] Some embodiments may benefit from some or all of the advantages mentioned above, or may not benefit from the advantages mentioned above. Other technical advantages can be readily identified by those skilled in the art. Attached Figure Description

[0033] For a fuller understanding of the invention and its features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0034] Figure 1 This is a block diagram illustrating a radio network;

[0035] Figure 2 This is a block diagram illustrating a 5G radio network;

[0036] Figure 3This is a block diagram illustrating the transmission of the random access preamble;

[0037] Figure 4 This is a flowchart illustrating a competition-based random access procedure;

[0038] Figure 5 This is a block diagram illustrating a system for performing a contention-based random access procedure;

[0039] Figure 6 This is a flowchart illustrating the execution of contention-free random access via a wireless device;

[0040] Figure 7 This is a block diagram illustrating some embodiments of a system for beam selection based on the received signal strength in the downlink;

[0041] Figure 8 This is a flowchart illustrating certain embodiments for performing preferred downlink beam selection;

[0042] Figure 9 This is a block diagram illustrating certain embodiments of a wireless device;

[0043] Figure 10 This is a block diagram illustrating some embodiments of a network node;

[0044] Figure 11 This is a block diagram illustrating certain embodiments of a packet core network node; and

[0045] Figure 12 This is a flowchart illustrating certain embodiments of performing preferred downlink beam selection. Detailed Implementation

[0046] Please refer to the attached diagram below. Figure 7-12 Specific embodiments are described, with the same reference numerals used for the same and corresponding parts of the various figures.

[0047] Figure 7 A system 700 according to certain embodiments is shown. The system 700 includes a wireless device 110 (in... Figure 7 (Seen as "Terminal"), wireless device 110 is operable to select beam 704 based on the received signal strength in the downlink (DL). As shown, system 700 includes multiple network nodes 115A, 115B, each transmitting a unique reference signal for each beam. In a specific embodiment, two network nodes 115A, 115B may be two transmission points (TPs) capable of performing multi-beam transmission in the same cell (same physical cell ID), or they may be nodes belonging to different cells.

[0048] In a specific embodiment, wireless device 110 is capable of detecting the preferred downlink beam (and ultimately the network node). In the described example, wireless device 110 has detected beam-specific reference signals (BRS-1-3) from network node 1. Wireless device 110 can then select the PRACH signal to be transmitted on the uplink so that the network obtains information about which BRS is "optimal" for wireless device 110, and thus the network knows which downlink beam is used for subsequent messages such as the Random Access Channel (RACH) response. Note that if the two network nodes are coordinated, the preamble associated with network node 115A can also be detected by network node 115B.

[0049] Therefore, the PRACH signal transmitted on the uplink is selected by the UE or the wireless device 110 based on the transmission conditions on the downlink from the network node 115 to the wireless device 110.

[0050] As mentioned in the background section, PRACH resources include preamble sequences and time / frequency resources. PRACH resources can be obtained from a subset of all available preamble sets and / or the wireless device can transmit the preamble in a certain frequency band within the system bandwidth. Once the network has detected the preamble transmitted from the wireless device, it knows which downlink beam is preferred for downlink transmission (e.g., the subsequent RACH response).

[0051] Therefore, the preamble and / or time / frequency resources used for transmitting the preamble are selected by the UE or the wireless device 110 based on the transmission conditions of the downlink from the network node 115 to the wireless device 110.

[0052] Figure 8 A flowchart illustrating exemplary method steps performed according to certain embodiments for selecting a preferred downlink beam is shown. Specifically, according to certain embodiments, the right-hand side of the flowchart describes steps that can be performed by wireless device 110, and the left-hand side describes steps that can be performed by network node 115.

[0053] More specifically, the right-hand side illustrates a method in wireless device 110 for performing random access to network node 115. The method includes receiving a set of downlink beam-specific reference signals (BRS) 804 from network node 115. The method also includes determining a preferred BRS 806 based on the received signal power of each BRS, and selecting a random access resource 808 for transmitting a random access attempt to network node 115 based on the preferred BRS. The method further includes using the random access resource selected 810 when transmitting a random access attempt to network node 115, whereby the selection of the random access resource indicates to the network node which downlink beam the wireless device prefers to use for downlink transmission.

[0054] exist Figure 8 The left-hand side of the flowchart shown illustrates a method for supporting random access from wireless device 110 in network node 115. The method includes transmitting a set of beam-specific reference signals (BRS) 802. The method also includes detecting a preamble in a signal received from wireless device 110 820, the preamble detection indicating a preferred BRS for the wireless device. The method further includes transmitting a random access response 814 with the same beam, and / or beam direction, and / or with the same beamforming weight as the preferred BRS indicated by the preamble detection.

[0055] Of course, network node 115 will attempt to detect more than one single preamble during a given duration, and will therefore attempt to detect all relevant preambles in the communication system sequentially or in parallel.

[0056] Figure 8 The method shown can begin at step 802, where network node 115 (eNB, base station) can transmit a set of beam-specific reference signals in the downlink. At step 804, the wireless device can receive this signal. The wireless device 110 can then perform measurements on these different (preferably orthogonal) reference signals and then determine the preferred BRS at step 806. This can be accomplished by measuring the reference signal received power (RSRP). The reference signal can be a beamforming synchronization signal (primary synchronization signal PSS / secondary synchronization signal SSS), a beamforming channel state information reference signal (CSI-RS), a beamforming discovery signal, or it can be a newly designed sequence of beam-specific reference signals (BRS). For simplicity, we refer to and classify beam-specific reference signals as BRS in this document.

[0057] Before a wireless device can begin measuring and identifying the preferred downlink beam, it is assumed that the beam-specific reference signal is known, for example, through specifications or from (broadcast) system information. However, in one embodiment, configuration signaling occurs before identification, but in a non-beam-based legacy system such as LTE. In practice, the wireless device detects the preferred beam-specific reference signal from a set of beam-specific reference signals, and therefore the wireless device is unaware of the actual beam direction of the beam radiation pattern, or the exact beamforming weights used on the transmitter side.

[0058] In step 808, wireless device 110 selects a random access resource to send a random access attempt to network node 115.

[0059] According to some embodiments, selecting 808 includes selecting an 808a preamble from a set of preambles for sending a random access attempt.

[0060] According to some embodiments, selection 808 includes selecting 808b the time and / or frequency resources to be used for transmitting the random access attempt. According to this embodiment, PRACH resources (potentially one of multiple resources distributed across time or frequency) are used when transmitting a preamble depending on the detected preferred BRS. Therefore, the network learns from the frequency band and / or time domain location of the preamble that the network has detected in the uplink which the radio device or UE prefers. And thus, the network knows the direction for transmitting the random access response (MSG 2) since it is the same as the preferred BRS. This embodiment can be combined with previous embodiments, including selecting a preamble so that a subset of the preamble and a certain frequency band and / or subframe can be used to transmit the preamble.

[0061] According to further aspects, the selection of 808 includes selecting 808c random access resources based on predefined association rules known in the wireless device.

[0062] In one embodiment, after determining the preferred downlink BRS, the wireless device uses a function or lookup table specified in a manual or standard, given by previously broadcast signaling, or configured by dedicated signaling (such as RRC signaling) in a secondary legacy network, to select an 808d random access preamble from the preamble set. The wireless device then uses the selected preamble in its random access attempt in step 810.

[0063] The network can then determine from the detected PRACH preamble (in step 820) which downlink beam the wireless device has discovered is the strongest, and therefore will preferentially use this beam when the network sends a random access response message (or multiple random access response messages) in step 814. The network has several options when selecting beamforming weights for the random access response message. It can simply select the same beamforming weights used when forming the beam to send the wireless device's preferred BRS.

[0064] According to some embodiments, the network node sends an 814a random access response based on one or more predefined association rules known at network node 115.

[0065] Optionally, a wider or narrower beam, or a beam with lower sidelobes, can be generated for subsequent random access responses using beamforming weights different from those used for BRS transmission. This allows BRS to be transmitted with a larger HPBW, and Physical Downlink Shared Channel (PDSCH) beams (such as random access responses) to be transmitted in beams with smaller HPBWs. In any case, the beam direction of the preferred BRS beam provides network information about the direction of the subsequent random access response beam (even if the beamforming weights are not exactly the same).

[0066] According to some aspects, Figure 8 The method shown further includes selecting an 813 uplink beam for detecting the 820 preamble based on an association rule between one or more preambles and uplink beams known in network node 115.

[0067] According to some further aspects, the method further includes selecting 813a time and / or frequency resources for preamble detection based on association rules between one or more preambles and time / frequency resources known in network node 115.

[0068] In some embodiments, the set of preambles and resources is grouped, with each group associated with a beam-specific reference signal (BRS). The association between the BRS and the preamble can be specified by a standard specification. The wireless device randomly or otherwise selects an 808e preamble from the associated group for use in its random access attempts. This group can, for example, be all available preamble sequences using a PRACH resource.

[0069] If the available preamble set is divided into too many smaller groups, resulting in a small number of preambles in each group, this can lead to a high RACH collision probability. In a relevant embodiment, the set of BRSs (more than one BRS) is all associated with a group of PRACH preambles. The network is then able to use the set of BRSs associated with the same PRACH preamble group in a neighboring downlink beam (proximity in the downlink transmit beam direction). If there are many BRSs, the set of available PRACH preambles associated with the best detected BRS is quite large, keeping the preamble collision probability (in the case of contention-based random access) low.

[0070] In another variation of this embodiment, some BRS and preambles can be associated with multiple groups. Beam directions can partially overlap between two groups. If a preamble belongs to two groups, the network node should use the overlapping beam direction between the two groups to send a DL RACH response.

[0071] In a further network embodiment, the network searches for a subset of the 820a preamble only in each uplink beam, where associated BRS are transmitted in the downlink. Each BRS indicates a subset of the preamble used in the PRACH preamble receiver. Therefore, the complexity of preamble detection in the network is reduced. However, this solution requires that the relationship between the uplink receive beam and the downlink transmit beam be known, for example, through RF calibration on the network side.

[0072] In another embodiment, the preamble sequence and PRACH resources are reused with BRS associated with a beam having sufficient angular spacing, so that they can be distinguished by using different uplink beams.

[0073] According to some aspects, in step 811, the wireless device receives a random access response from the network node.

[0074] For example in Figure 1 The wireless device 110 and network node 115 shown can use any suitable radio access technology, such as LTE, LTE Advanced, UMTS, HSPA, GSM, CDMA 2000, WiMAX, WiFi, another suitable radio access technology, or any suitable combination of one or more radio access technologies. For illustrative purposes, various embodiments may be described in the context of certain radio access technologies. However, the scope of this disclosure is not limited to this example, and other embodiments are capable of using different radio access technologies. Each of the wireless device 110, network node 115, radio network controller 120, and packet core network 30 may include any suitable combination of hardware and / or software. Reference is made below. Figure 9 , 10 Examples of specific embodiments of wireless device 110, network node 115, and network node (such as radio network controller 120 or packet core network 130) are described, respectively.

[0075] Figure 9 This is a block diagram illustrating certain embodiments of a UE or wireless device 110. Examples of wireless devices 110 include mobile phones, smartphones, personal digital assistants (PDAs), portable computers such as laptops, tablet devices, sensors, modems, machine-type (MTC) devices / machine-to-machine (M2M) devices, laptop embedded devices (LEEs), laptop mounted devices (LMEs), Universal Serial Bus (USB) dongles, devices with device-to-device capabilities, or other devices capable of providing wireless communication. Wireless device 110 can also be a radio communication device, a target device, a device-to-device UE, a machine-type UE, or a wireless device capable of machine-to-machine communication, a sensor equipped with a wireless device, an iPad, a tablet computer, a mobile terminal, a smartphone, a laptop embedded device (LEE), a laptop mounted device (LME), a USB dongle, a consumer premises equipment (CPE), and so on.

[0076] Although the terms UE and wireless device 110 are used primarily herein, in some embodiments the device may also be referred to as a station (STA), device, or terminal. As shown, wireless device 110 includes a transceiver 910, a processor 920, and a memory 930.

[0077] In some embodiments, transceiver 910 facilitates sending and receiving wireless signals to and from network node 115, for example, via an antenna; processor 920 executes instructions to provide some or all of the above-described functionalities as provided by wireless device 110; and memory 930 stores the instructions executed by processor 920.

[0078] Processor 920 may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and operational data to perform some or all of the functions described in wireless device 110. In some embodiments, processor 920 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and / or other logic.

[0079] Memory 930 is generally operable to store instructions, such as computer programs, software, applications (including one or more of logic, rules, algorithms, code, tables, etc.) and / or other instructions executable by a processor. Examples of memory 930 include computer memory (e.g., random access memory (RAM) or read-only memory (ROM)), mass storage media (e.g., hard disk), removable storage media (e.g., optical disc (CD) or data video disc (DVD)), and / or any other volatile or non-volatile, non-transitory computer-readable and / or computer-executable memory device for storing information.

[0080] Other embodiments of the wireless device 110 may include Figure 9 Additional components other than those shown may be responsible for providing certain aspects of the functionality of the wireless device, including any of the functionalities described above and / or any additional functionalities (including any functionality required to support the solutions described above).

[0081] Figure 10This is a block diagram illustrating certain embodiments of network node 115. Examples of network node 115 include eNodeB, Node B, base station, wireless access point (e.g., Wi-Fi access point), low-power node, base transceiver station (BTS), transmission point, transmission node, remote radio unit (RRU), remote radio head (RRH), and so on. Network node 115 can be deployed throughout network 100 as a homogeneous, heterogeneous, or hybrid deployment. Homogeneous deployment typically describes a deployment consisting of network nodes 115 of the same (or similar) type and / or similar coverage, cell size, and inter-site distance. Heterogeneous deployment typically describes a deployment using different types of network nodes 115 with different cell sizes, transmit power, capacity, and inter-site distances. For example, heterogeneous deployment may include multiple low-power nodes placed throughout a macrocell layout. Hybrid deployment may include a combination of homogeneous and heterogeneous components.

[0082] Network node 115 may include one or more transceivers 1010, processor 1020, memory 1030, and network interface 1040. In some embodiments, transceiver 1010 facilitates the transmission of wireless signals to and from network node 110 (e.g., via an antenna), processor 1020 executes instructions to provide some or all of the functionalities described above to be provided by network node 115, memory 1030 stores the instructions executed by processor 1020, and network interface 1040 transmits signals to back-end network components such as gateways, switches, routers, the Internet, public switched telephone network (PSTN), packet core network 130, radio network controller 120, etc.

[0083] Processor 1020 may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and operational data to perform some or all of the functions described in network node 115. In some embodiments, processor 1020 may include, for example, one or more calculators, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and / or other logic.

[0084] Memory 1030 is generally operable to store instructions, such as computer programs, software, applications (including one or more of logic, rules, algorithms, code, tables, etc.), and / or other instructions executable by a processor. Examples of memory 1030 include computer memory (e.g., random access memory (RAM) or read-only memory (ROM)), mass storage media (e.g., hard disk), removable storage media (e.g., optical disc (CD) or data video disc (DVD)), and / or any other volatile or non-volatile, non-transitory computer-readable and / or computer-executable memory device for storing information.

[0085] In some embodiments, network interface 1040 may be communicatively coupled to processor 1020 and may refer to any suitable device operable to receive input from network node 115, send output from network node 115, perform appropriate processing on the input or output or both, communicate with other devices, or any combination thereof. Network interface 1040 may include suitable hardware (e.g., port, modem, network interface card, etc.) for communicating over a network and software including protocol conversion and data processing capabilities.

[0086] Other embodiments of network node 115 may include Figure 10 Additional components beyond those shown may be responsible for providing certain aspects of the functionality of a network node, including any of the functionalities described above and / or any additional functionalities (including any functionality required to support the solutions described above). Various types of network nodes may include components with the same physical hardware but configured (e.g., through programming) to support different radio access technologies, or may represent partially or completely different physical components.

[0087] In some embodiments, this is also a general term, and "network node" or simply "network node (NW node)" may be used. The term can refer to any kind of network node, which may include base stations, radio base stations, base transceivers, base station controllers, network controllers, evolved Node B (eNB), Node B, RNC, relay nodes, location nodes, E-SMLC, location servers, repeaters, access points, radio access points, remote radio units (RRU), remote radio heads (RRH), multi-standard radio (MSR) radio nodes in distributed antenna systems (DAS) (such as MSR BS nodes), SON nodes, O&M, OSS, MDT nodes, core network nodes, MME, etc.

[0088] Figure 11This is a block diagram illustrating certain embodiments of nodes in a radio network controller 120 or a packet core network 130. Examples of network nodes may include a mobile switching center (MSC), a serving GPRS support node (SGSN), a mobility management entity (MME), a radio network controller (RNC), a base station controller (BSC), etc. The network node includes a processor 1120, a memory 1130, and a network interface 1140. In some embodiments, the processor 1120 executes instructions to provide some or all of the functions described above to be provided by the network node, the memory 1130 stores the instructions executed by the processor 1120, and the network interface 1140 transmits signals to appropriate nodes, such as gateways, switches, routers, the Internet, the Public Switched Telephone Network (PSTN), network node 115, the radio network controller 120, nodes in the packet core network 130, etc.

[0089] Processor 1120 may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and operational data to perform some or all of the described functions of the network node. In some embodiments, processor 1120 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and / or other logic.

[0090] Memory 1130 is generally operable to store instructions, such as computer programs, software, applications (including one or more of logic, rules, algorithms, code, tables, etc.), and / or other instructions executable by a processor. Examples of memory 1130 include computer memory (e.g., random access memory (RAM) or read-only memory (ROM)), mass storage media (e.g., hard disk), removable storage media (e.g., optical disc (CD) or data video disc (DVD)) and / or any other volatile or non-volatile, non-transitory computer-readable and / or computer-executable memory device for storing information.

[0091] In some embodiments, network interface 1140 may be communicatively coupled to processor 1120 and may refer to any suitable device operable to receive input from network nodes, send output from network nodes, perform appropriate processing on the input or output or both, communicate with other devices, or any combination thereof. Network interface 1140 may include suitable hardware (e.g., port, modem, network interface card, etc.) for communicating over a network and software including protocol conversion and data processing capabilities.

[0092] Other embodiments of the network node may include Figure 11Additional components, other than those shown, may be responsible for providing certain aspects of the functionality of the network node, including any of the functionalities described above and / or any additional functionalities (including any functionality required to support the solutions described above).

[0093] Figure 12 A flowchart illustrating exemplary method steps performed for selecting a preferred downlink beam, according to certain embodiments, is shown. Specifically, according to certain embodiments, the right side of the flowchart depicts steps that can be performed by UE 110, and the left side depicts steps that can be performed by network node 115.

[0094] The method can begin at step 1802, where network node 115 (eNB, base station) can transmit a set of beamforming reference signals in the downlink. The signals can be received by the UE in step 804. UE 110 can then perform measurements on these different (preferably orthogonal) reference signals and then determine the preferred downlink beam in step 1806. This can be done by measuring the received signal power (RSRP) of each beam. The reference signals can be beamforming synchronization signals (PSS / SSS), beamforming channel state information signals (CSI-RS), beamforming discovery signals (DSS), or newly designed beam reference signal sequences (BRS). For simplicity, beam-specific reference signals will be represented and classified as BRS below.

[0095] Before the UE can begin measuring and identifying the preferred downlink beam, it is assumed that the beam-specific reference signal is obtained through specifications or from broadcast system information so that no dedicated configuration signaling is required between network node 115 and UE 110. However, in one embodiment, configuration signaling occurs before identification, but this is in the case of non-beam-based legacy systems such as LTE. (In practice, the UE detects the preferred beam-specific RS from the set of beam-specific RSs, so the UE is unaware of the actual beam orientation of the beam pattern or the specific beamforming weights used on the transmitter side.)

[0096] In step 1808, terminal 110 selects a random access response resource. In one embodiment, after determining the preferred downlink beam RS, the UE uses a function or lookup table specified by a manual or standard, given by previously broadcast signaling, or configured by dedicated signaling (such as RRC signaling) in a secondary legacy network, to select a random access preamble from the preamble set. The UE then uses the selected preamble in its random access attempt in step 1810.

[0097] In a further embodiment, when the preferred BRS is transmitted as a preamble, a PRACH resource (which is one of multiple resources distributed across time or frequency) is used. Therefore, the network learns from the frequency bands in which the network detects the preamble in the uplink which BRS is preferred from the UE side. And thus, the network learns the direction to send the random access response (MSG 2), since it is the same as the preferred BRS. This embodiment can be combined with previous embodiments to enable both a subset of preambles and certain frequency bands (and / or subframes) to be used for transmitting the preamble.

[0098] The network can then determine from the detected PRACH preamble (in step 1812) which downlink beam the UE has discovered is the strongest, and therefore will preferentially use this beam when sending the random access response message in step 1814. The network has several options when selecting beamforming weights for the random access response message. It can simply select the same beamforming weights used when forming the beam to send the UE's preferred BRS. Alternatively, a wider or narrower beam, or a beam with lower sidelobes, can be generated by using different beamforming weights for the subsequent random access response compared to the beam used for BRS transmission. It is possible to send the BRS with a larger HPBW and the PDSCH beam (such as the random access response) in a beam with a smaller HPBW. In any case, the beam direction of the preferred BRS beam provides network information about the direction of the subsequent random access response beam (even if the beamforming weights are not exactly the same).

[0099] In one embodiment, preambles and resource sets are grouped, with each group associated with a beam-specific reference signal (BRS). The association between the BRS and preambles can be specified by a standard specification. The UE randomly selects a preamble from the associated groups for use in its random access attempts. A group could be, for example, all available preamble sequences using a PRACH resource.

[0100] If the available preamble set is divided into too many smaller groups, resulting in a small number of preambles in each group, it can become a problem because it can lead to a high RACH collision probability. In a relevant embodiment, the BRS set (more than one BRS) is associated with a set of PRACH preambles. In step 1813, the network is then able to use the BRS set associated with the same PRACH preamble group in the adjacent downlink beams (adjacent in the downlink transmit beam direction). If there are many BRSs, the available PRACH preamble set associated with the best detected BRS is quite large, keeping the preamble collision probability (in the case of contention-based random access) low.

[0101] In another variation of this embodiment, some BRS and preambles can be associated with multiple groups. The beam direction can partially overlap between two groups. If preambles belonging to two groups are selected, the network node should send a DL RACH response using the overlapping BRS between the two groups.

[0102] In a further network embodiment, the network searches for a subset of the preamble only in each uplink beam, where the associated BRS is transmitted in the downlink. Each BRS indicates a subset of the preamble used in the PRACH preamble receiver. Therefore, the complexity of network preamble detection is reduced. However, this solution requires that the relationship between the uplink receive beam and the downlink transmit beam be known, for example, through RF calibration on the network side.

[0103] In yet another embodiment, the preamble sequence and PRACH resources are reused with BRS associated with a beam having sufficient angular spacing, so that they can be distinguished by using different uplink beams.

[0104] This document further discloses various additional exemplary embodiments. Some of these embodiments propose solutions for selecting a physical random access channel based on the strongest beam received in the downlink. In one exemplary embodiment, a user equipment may perform the steps:

[0105] • Receive and detect the transmitted beam-specific reference signal (BRS);

[0106] • Determine the preferred BRS based on the received BRS power;

[0107] • Select random access response resources based on the preferred BRS;

[0108] • Send the Physical Random Access Channel (PRACH) to the network node using the selected resources;

[0109] • Optionally, random access response resources may be selected based on predefined association rules known to the user equipment;

[0110] • Optionally, the random access response resource is the preamble and / or time / frequency resource;

[0111] In another exemplary embodiment, a network node may perform the following steps:

[0112] • Transmit a unique BRS in each downlink beam;

[0113] • Randomly select a new prefix for detection;

[0114] • Select the uplink beam based on predefined association rules known at the network nodes;

[0115] • Detect the preamble;

[0116] • Send random access response with the same beam / beam direction / beamforming weight as the preferred BRS indicated by preamble detection;

[0117] • Optionally, possible time / frequency resources can be selected based on predefined association rules known to the network nodes;

[0118] • Optionally, a random access response may be sent based on predefined association rules known to the network nodes.

[0119] Other implementations may include wireless communication devices and / or access nodes configured to implement the described methods, or wireless communication systems in which the wireless communication devices and / or access nodes implement the described methods.

[0120] Some embodiments of this disclosure can provide one or more technical advantages. For example, in some embodiments, coverage of the random access channel response is improved because the network learns the beam used for the random access channel response. Another technical advantage is that the random access channel procedure can be completed earlier, which improves latency and reduces interference in the network. Yet another technical advantage is that no calibrated and aligned RFs are required for the uplink and downlink, which reduces implementation costs and power consumption.

[0121] A further technical advantage could be reduced computational complexity in the eNode. In eNode B, the physical random access channel preamble detector only needs to search for a subset of sequences in each uplink receiver direction. This subset is equivalent to those physical random access channel sequences mapped to the same downlink transmission beam (or spatial direction) as the receiver uplink beam (or spatial direction).

[0122] Some embodiments may benefit from some or all of these advantages, or may not benefit from them. Other technical advantages can be readily identified by those skilled in the art.

[0123] In a specific exemplary implementation, the proposed solution can provide a method for random access selection to optimize downlink beamforming. In one exemplary embodiment, the user equipment may perform the following steps:

[0124] • Receive and detect transmitted beam-specific reference signals (BRS);

[0125] • Determine the preferred BRS based on the received BRS power;

[0126] • Select random access response resources based on the preferred BRS;

[0127] • Send the Physical Random Access Channel (PRACH) to the network node using the selected resources;

[0128] • Optionally, random access response resources may be selected based on predefined association rules known to the user equipment;

[0129] • Optionally, the random access response resource is the preamble and / or time / frequency resource;

[0130] In another exemplary embodiment, a network node may perform the following steps:

[0131] • Transmit a unique BRS in each downlink beam;

[0132] • Randomly select a new prefix for detection;

[0133] • Select the uplink beam based on predefined association rules known at the network nodes;

[0134] • Detect the preamble;

[0135] • Send random access response with the same beam / beam direction / beamforming weight as the preferred BRS indicated by preamble detection;

[0136] • Optionally, possible time / frequency resources can be selected based on predefined association rules known to the network nodes;

[0137] • Optionally, a random access response may be sent based on predefined association rules known to the network nodes.

[0138] Other implementations may include wireless communication devices and / or access nodes configured to implement the described methods, or wireless communication systems in which the wireless communication devices and / or access nodes implement the described methods.

[0139] Some embodiments of this disclosure can provide one or more technical advantages. For example, in some embodiments, coverage of the random access channel response is improved because the network learns the beam used for the random access channel response. Another technical advantage is that the random access channel procedure can be completed earlier, which improves latency and reduces interference in the network. Another technical advantage is that no calibration and alignment RFs are required for the uplink and downlink, which reduces implementation costs and power consumption.

[0140] A further technical advantage could be reduced computational complexity in the eNode. In eNode B, the physical random access channel preamble detector only needs to search for a subset of sequences in each uplink receiver direction. This subset is equivalent to those physical random access channel sequences mapped to the same downlink transmission beam (or spatial direction) as the receiver uplink beam (or spatial direction).

[0141] Some embodiments may benefit from some or all of these advantages, or may not benefit from them. Other technical advantages can be readily identified by those skilled in the art.

[0142] Modifications, additions, or omissions may be made to the systems and apparatus disclosed herein without departing from the scope of the invention. Components of the systems and apparatus may be integrated or separated. Furthermore, the operation of the systems and apparatus may be performed by more, fewer, or other components. Additionally, any suitable logic, including software, hardware, and / or other logic, may be used to perform the operation of the systems and apparatus. As used herein, "each" means each member of a set or each member of a subset of a set.

[0143] Modifications, additions, or omissions may be made to the methods disclosed herein without departing from the scope of the invention. The methods may include more, fewer, or other steps. Furthermore, the steps may be performed in any suitable order.

[0144] Although this disclosure has been described with reference to certain embodiments, changes and substitutions to the embodiments will be apparent to those skilled in the art. Therefore, the above description of the embodiments does not limit this disclosure. Other changes, substitutions, and modifications are possible without departing from the spirit and scope of this disclosure as defined by the appended claims.

Claims

1. A method in a wireless device (110) for performing random access to a network node (115), the method comprising: - Receive (804) a set of downlink beam-specific reference signals (BRS) from the network node (115); - The preferred BRS is determined based on the received signal power of each BRS in the set; - Based on the preferred BRS, a random access preamble for sending a random access attempt to the network node (115) is selected (808) according to one or more predefined association rules that define the association between the random access resource and the BRS. The selection is performed using a function that takes the preferred BRS as input and provides the selected random access preamble as output. The function is specified in the standard. as well as - The selected random access preamble is sent to the network node (115), thereby indicating to the network node (115) which downlink beam the wireless device (110) prefers to use for downlink transmission.

2. The method of claim 1, wherein the selection (808) comprises selecting (808a) the random access preamble to be used for sending the random access attempt from a set of preambles.

3. The method according to any one of claims 1-2, wherein the selection (808) includes selecting (808b) the time and / or frequency resources to be used for sending the random access attempt.

4. The method according to any one of claims 1-2, wherein the selection (808) comprises selecting (808c) the random access resource based on one or more predefined association rules known to the wireless device (110).

5. The method according to any one of claims 1-2, wherein the preamble is divided into groups, wherein each group is associated with a beam-specific reference signal, and the association between the BRS and the random access preamble is given by a standard specification.

6. A method in a network node (115) for supporting random access from a wireless device (110), the method comprising: - Transmit (802) the set of downlink beam-specific reference signals (BRS); - Detect (820) a random access preamble in a signal received from the wireless device (110), the preamble detection indicating a preferred BRS in the set of downlink BRSs, the preferred BRS being selected by the wireless device according to one or more predefined association rules defining the association between random access resources and BRSs, wherein the random access preamble is based on a function that takes the preferred BRS as input and provides the selected random access preamble as output, the function being specified in the standard; and - Send (814) random access response with the same beam and / or beam direction and / or with the same beamforming weight as the preferred BRS indicated by the random access preamble detection.

7. The method of claim 6, further comprising: - Select (813) the uplink beam for the detection (820) of the random access preamble based on one or more predefined association rules between the random access preamble and the uplink beam known at the network node (115).

8. The method according to any one of claims 6 or 7, further comprising: - Select (813a) time and / or frequency resources for random access preamble detection based on one or more predefined association rules between the random access preamble and time / frequency resources known at the network node (115).

9. The method according to any one of claims 6-7, wherein the sending (814) further comprises: - Send (814a) the random access response according to one or more predefined association rules known at the network node (115).

10. The method according to any one of claims 6-7, wherein the detection (820) further comprises searching (820a) a subset of random access preambles in each uplink beam, for which an associated BRS is transmitted in the downlink, each BRS indicating a subset of random access preambles to be searched.

11. The method according to any one of claims 6-7, wherein the random access preamble sequence and resources are reused for the BRS associated with a downlink beam having a predetermined angular spacing.

12. The method according to any one of claims 6-7, wherein the random access preamble is divided into groups, wherein each group is associated with a beam-specific reference signal, and the association between the BRS and the random access preamble is given by a standard specification.

13. A wireless device (110) configured to perform random access to a network node (115), the wireless device including a processing unit configured to: - A set of downlink beam-specific reference signals (BRS) received from the network node (115); - Determine the preferred BRS based on the received signal power of each BRS in the set; - Based on the preferred BRS, a random access resource for sending a random access attempt to the network node (115) is selected according to one or more predefined association rules that define the association between the random access resource and the BRS. The selection is performed using a function that takes the preferred BRS as input and provides the selected random access preamble as output. This function is specified in the standard. - The selected random access preamble is sent to the network node (115), thereby indicating to the network node which downlink beam the wireless device prefers to use for downlink transmission.

14. The wireless device (110) according to claim 13, wherein the processing unit is further configured to: - Select the random access preamble from the set of preambles to be used for sending the random access attempt.

15. The wireless device (110) according to any one of claim 13 or 14, wherein the processing unit is further configured to: - Select the time and / or frequency resources to be used to send the random access attempt.

16. The wireless device (110) according to any one of claims 13-14, wherein the processing unit is further configured to: - Select the random access resource based on one or more predefined association rules known to the wireless device (110).

17. The wireless device (110) according to any one of claims 13-14, wherein the random access preamble is divided into groups, wherein each group is associated with a beam-specific reference signal, and the association between the BRS and the preamble is given by a standard specification.

18. The wireless device (110) according to any one of claims 13-14, wherein the processing unit includes a processor (920) and a memory (930), wherein the memory contains instructions executable by the processor.

19. The wireless device (110) according to any one of claims 13-14, further comprising a transceiver (910) arranged to transmit wireless signals to and receive wireless signals from the network node (115).

20. A network node (115) configured to support random access from a wireless device (110), the network node including a processing unit configured to: - A set of downlink beam-specific reference signals (BRS) that are transmitted; - Detecting a random access preamble in a signal received from the wireless device (110), the preamble detection indicating a preferred BRS in the set of downlink BRSs, the preferred BRS being selected by the wireless device according to one or more predefined association rules defining the association between random access resources and BRSs, wherein the random access preamble is based on a function that takes the preferred BRS as input and provides the selected random access preamble as output, the function being specified in the standard; and - Send a random access response with the same beam and / or beam direction as the preferred BRS indicated by the random access preamble detection, and / or with the same beamforming weight.

21. The network node (115) according to claim 20, wherein the processing unit is further configured to: - The uplink beam is selected for detecting the random access preamble based on one or more predefined association rules between the preamble and the uplink beam known at the network node (115).

22. The network node (115) according to any one of claim 20 or 21, wherein the processing unit is further configured to: - Select time and / or frequency resources for preamble detection based on one or more predefined association rules between the random access preamble and time / frequency resources known at the network node (115).

23. The network node (115) according to any one of claims 20-21, wherein the processing unit is further configured to: - Send the random access response according to one or more predefined association rules known at the network node (115).

24. The network node (115) according to any one of claims 20-21, wherein the processing unit is further configured to: - Search for a subset of random access preambles in each uplink beam, and send an associated BRS for that subset in the downlink, with each BRS indicating the subset of random access preambles to be searched.

25. The network node (115) according to any one of claims 20-21, wherein the random access preamble sequence and resources are reused for the BRS associated with a downlink beam having a predetermined angular interval.

26. The network node (115) according to any one of claims 20-21, wherein the random access preamble is divided into groups, wherein each group is associated with a beam-specific reference signal, and the association between the BRS and the random access preamble is given by a standard specification.

27. The network node (115) according to any one of claims 20-21, wherein the processing unit includes a processor (1020) and a memory (1030), wherein the memory contains instructions executable by the processor.

28. The network node (115) according to any one of claims 20-21, further comprising: - A transceiver (1010) is arranged to transmit wireless signals to the wireless device (110) and receive wireless signals from the wireless device (110); as well as - Network interface (1040) is configured to transmit signals to backend network components.

29. A wireless communication system comprising a wireless device according to any one of claims 13-19 and a network node according to any one of claims 20-28.

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