Method and apparatus for beam control in a beamformed system

Abstract

Antennas implementing beamforming techniques may need to provide high gain and thus be highly directional, which may require the use of large antenna arrays that are electronically steerable at both the transmitter and receiver.SOLUTION: Methods and apparatus are described. A method implemented in a wireless transmit / receive unit (WTRU) includes monitoring a first control channel search space (CSS) associated with a first normal beam set including a first beam set. The WTRU initiates enhanced monitoring and monitors a control channel SS associated with an enhanced beam set comprising a first beam set and one or more additional beam sets following a trigger based on measurements by the WTRU. The WTRU determines a second beam set from the enhanced beam set.SELECTED DRAWING: FIG. 13B

Description

[Technical Field]

[0001] The present application relates to a method and apparatus for beam control in a beamformed system. [Background technology]

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 302,962, filed March 3, 2016, the contents of which are incorporated herein by reference.

[0003] Frequencies above 6 GHz, such as mmW and cmW, have not traditionally been used in cellular systems due to propagation characteristics that have been assumed to be undesirable for wireless communications in outdoor environments. Higher frequency transmissions generally tend to experience higher free-space path loss. Compared to frequencies below 6 GHz, precipitation, atmospheric gases (e.g., oxygen), and foliage can add additional attenuation. In addition, transmission and diffraction attenuation can be more severe at frequencies above 6 GHz as opposed to frequencies below 6 GHz. Such propagation characteristics of frequencies above 6 GHz can result in significant non-line-of-sight (NLOS) propagation path loss. For example, at mmW frequencies, NLOS path loss can be more than 20 dB higher than line-of-sight (LOS) path loss, severely limiting the coverage of mmW transmissions.

[0004] Recent channel measurements have demonstrated the feasibility of outdoor mmW cellular coverage with the aid of beamforming technologies. Measurement data shows that beamforming gain can not only provide the coverage required for cellular control signaling in NLOS conditions, but can also boost link capacity to achieve higher data throughput in LOS conditions. Summary of the Invention [Problem to be solved by the invention]

[0005] Antennas implementing such beamforming techniques may need to provide high gain and therefore be highly directional, which may require the use of large antenna arrays that are electronically steerable at both the transmitter and receiver. [Means for solving the problem]

[0006] A method and apparatus are described. The method, implemented in a wireless transmit / receive unit (WTRU), includes monitoring a first control channel search space (SS) associated with a first normal beam set that includes a first beam set. The WTRU initiates extended monitoring and, following a trigger based on measurements by the WTRU, monitors a control channel SS associated with an extended beam set that includes the first beam set and one or more additional beam sets. The WTRU determines a second beam set from the extended beam set. The determination is based on a received control channel beam switch command or a control channel SS in which the beam switch command was received. The WTRU monitors a second control channel SS associated with a second normal beam set that includes the determined second beam set. [Brief explanation of the drawings]

[0007] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which: [Figure 1A] FIG. 1 illustrates an example communication system in which one or more disclosed embodiments may be implemented. [Figure 1B] 1B is a diagram of an exemplary wireless transmit / receive unit (WTRU) that may be used within the communication system of FIG. 1A. [Figure 1C] 1B is a diagram of an example radio access network and core network used within the communication system of FIG. 1A. [Figure 2]1 is an exemplary orthogonal frequency division multiplexing (OFDM) frame structure diagram for an exemplary 1 GHz system bandwidth. [Figure 3] FIG. 1 is an exemplary single carrier frame structure diagram for an exemplary 2 GHz system bandwidth. [Figure 4] FIG. 1 is a diagram of an exemplary phased antenna array (PAA) with fully digital beamforming. [Figure 5] FIG. 1 is a diagram of an example of analog beamforming with one PAA including one radio frequency (RF) chain for several antenna elements. [Figure 6] FIG. 1 is a diagram of an example of analog beamforming with one PAA and two RF chains. [Figure 7] FIG. 1 is a diagram of an example of analog beamforming with two PAAs and two RF chains. [Figure 8] FIG. 1 is a diagram of an example of analog beamforming with two PAAs and one RF chain. [Figure 9] FIG. 1 illustrates an example of adaptability properties in ultra-high density deployments. [Figure 10] FIG. 1 is a flow diagram of an exemplary method for beamforming and scheduling. [Figure 11] 10 is a flow diagram of an example method for enhanced monitoring implemented in a WTRU. [Figure 12] 1 is a flow diagram of an exemplary method of enhanced monitoring implemented in a base station, such as a millimeter-wave base station (mB). [Figure 13A] 13A is a diagram 1300A of a more specific example of enhanced monitoring. [Figure 13B] FIG. 1300B is a diagram of a more specific example of enhanced monitoring. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1A is a diagram of an example communication system 100 in which one or more disclosed embodiments can be implemented. The communication system 100 may be a multiple-access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communication system 100 may enable the multiple wireless users to access such content through sharing of system resources, including wireless bandwidth. For example, the communication system 100 may use one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), etc.

[0009] 1A, communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d may be configured to transmit and / or receive wireless signals and may include user equipment (UE), mobile stations, fixed or mobile subscriber units, pagers, cellular phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless sensors, consumer electronics devices, etc.

[0010] The communications system 100 may also include a base station 114a and a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communications networks, such as the core network 106, the Internet 110, and / or other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node B, an eNodeB, a Home Node B, a Home eNodeB, a site controller, an access point (AP), a wireless router, etc. Although the base stations 114a, 114b are each illustrated as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0011] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or base station 114b may be configured to transmit and / or receive wireless signals within a particular geographic area, sometimes referred to as a cell (not shown). A cell may be further divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In another embodiment, the base station 114a may employ multiple-input multiple-output (MIMO) technology and thus utilize multiple transceivers for each sector of the cell.

[0012] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communications link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0013] More specifically, as noted above, the communications system 100 may be a multiple-access system and may employ one or more channel access schemes such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using Wideband CDMA (WCDMA). WCDMA may include communications protocols such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink Packet Access (HSDPA) and / or High Speed ​​Uplink Packet Access (HSUPA).

[0014] In another embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE Advanced (LTE-A).

[0015] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE), GSM EDGE (GERAN), or others.

[0016] The base station 114b in FIG. 1A may be a wireless router, a Home NodeB, a Home eNodeB, or an access point and may utilize any suitable RAT to facilitate wireless connectivity in a localized area, such as a business, a home, a vehicle, a campus, or other location. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114 b may not be required to access the Internet 110 via the core network 106 .

[0017] The RAN 104 may be in communication with the core network 106, which may be any type of network configured to provide voice, data, application, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions such as user authentication. Although not shown in FIG. 1A , it will be appreciated that the RAN 104 and / or core network 106 may be in direct or indirect communication with other RANs that use the same RAT as the RAN 104 or a different RAT. For example, the core network 106 may also be in communication with another RAN (not shown) that uses GSM radio technology, in addition to being connected to the RAN 104, which may utilize E-UTRA radio technology.

[0018] The core network 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network providing plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Internet Protocol (IP) in the TCP / IP Internet protocol suite. The network 112 may include wired or wireless communication networks owned and / or operated by other service providers. For example, the network 112 may include another core network connected to one or more RANs that may use the same RAT as the RAN 104 or a different RAT.

[0019] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities, i.e., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a that can use cellular-based wireless technology and with a base station 114b that can use IEEE 802 wireless technology.

[0020] 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B, the WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals 138. It will be appreciated that the WTRU 102 may include any subcombination of the above-described elements while remaining consistent with an embodiment.

[0021] The processor 118 may be a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. While FIG. 1B illustrates the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be incorporated together in an electronic package or chip.

[0022] The transmit / receive element 122 may be configured to transmit signals to or receive signals from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In another embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive, for example, IR signals, UV signals, or visible light signals. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and receive both RF signals and light signals. It will be appreciated that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0023] 1B as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO techniques. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0024] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and demodulate signals received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as, for example, UTRA and IEEE 802.11.

[0025] The processor 118 of the WTRU 102 may be coupled to and may receive user input data from a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. Additionally, the processor 118 may access information from and store data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 may include random access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, etc. In other embodiments, the processor 118 may access information from and store data in memory that is not physically located on the WTRU 102, such as on a server or home computer (not shown).

[0026] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control the power to other components of the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0027] The processor 118 may also be coupled to a GPS chipset 136 that may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or instead of, information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and / or determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information via any suitable location determination method while remaining consistent with an embodiment.

[0028] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos or videos), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, a Bluetooth module, a frequency modulation (FM) radio unit, a digital music player, a media player, a video game player module, an internet browser, and the like.

[0029] 1C is a system diagram of the RAN 104 and the core network 106 according to an embodiment. As noted above, the RAN 104 may use E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106.

[0030] The RAN 104 may include eNodeBs 140a, 140b, and 140c, although it will be appreciated that the RAN 104 may include any number of eNodeBs while remaining consistent with an embodiment. The eNodeBs 140a, 140b, and 140c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the eNodeBs 140a, 140b, and 140c may implement MIMO technology. Thus, for example, the eNodeB 140a may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0031] Each of the eNodeBs 140a, 140b, 140c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users on the uplink and / or downlink, etc. As shown in FIG. 1C, the eNodeBs 140a, 140b, 140c may communicate with one another over an X2 interface.

[0032] 1C may include a mobility management entity gateway (MME) 142, a serving gateway 144, and a packet data network (PDN) gateway 146. Although each of the above elements is illustrated as part of the core network 106, it will be appreciated that any one of these elements may be owned and / or operated by an entity other than the core network operator.

[0033] The MME 142 may be connected to each of the eNodeBs 140a, 140b, 140c of the RAN 104 via an S1 interface and may act as a control node. For example, the MME 142 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during initial attach of the WTRUs 102a, 102b, 102c, etc. The MME 142 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0034] The serving gateway 144 may be connected to each of the eNodeBs 140a, 140b, 140c of the RAN 104 via an S1 interface. The serving gateway 144 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The serving gateway 144 may also perform other functions, such as anchoring the user plane during handover between eNodeBs, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, etc.

[0035] The serving gateway 144 may also be connected to a PDN gateway 146, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0036] The core network 106 may facilitate communications with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional landline communications devices. For example, the core network 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that interfaces between the core network 106 and the PSTN 108. Additionally, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to the network 112, which may include other wired or wireless networks owned and / or operated by other service providers.

[0037] The other network 112 may be further connected to an IEEE 802.11-based wireless local area network (WLAN) 160. The WLAN 160 may include an access router 165. The access router may house gateway functionality. The access router 165 may be in communication with multiple access points (APs) 170a, 170b. Communication between the access router 165 and the APs 170a, 170b may be via wired Ethernet (IEEE 802.3 standard) or any type of wireless communication protocol. The AP 170a is in wireless communication with the WTRU 102d over the air interface.

[0038] For example, a number of frequency bands above 6 GHz are being evaluated, including the 10 GHz and 15 GHz bands (cmW frequency bands), and the 28 GHz, 39 GHz, 60 GHz, and 73 GHz bands (mmW frequency bands). These higher frequency bands may be allocated, for example, as licensed, semi-licensed, and unlicensed spectrum.

[0039] Depending on the spectrum allocation and its propagation characteristics, high frequency bands such as those described above can be deployed in various cellular network configurations. For example, mmW frequencies can be used for a homogeneous network with mmW standalone macro base stations, micro base stations, and small cell base stations (SCmBs). A heterogeneous network can include an mmW standalone small cell network overlaid with a Long Term Evolution (LTE) macro network and / or micro network at frequencies below 6 GHz. In such a network, a network node can be connected to both frequencies above 6 GHz (e.g., an mmW system) and frequencies below 6 GHz (e.g., a 2 GHz LTE system). This type of connectivity may be referred to as dual connectivity. In embodiments, carrier aggregation may be applied to combine above-6 GHz carriers (e.g., mmW carriers) and below-6 GHz carriers (e.g., 2 GHz LTE carriers). The embodiments described herein may be applied to any above-6 GHz cellular deployment.

[0040] Waveforms such as OFDM, broadband single-carrier (SC), SC-OFDM, generalized OFDM, filter-bank multicarrier (FBMC), or multicarrier CDMA (MC-CDMA) can be used for systems above 6 GHz. Waveforms can have different peak-to-average power ratio (PAPR) performance, sensitivity to transmitter nonlinearities, bit error rate (BER) performance, resource channelization, and implementation complexity. The frame structure may depend on the applied waveform, but it may also be sized to meet the system requirements above 6 GHz. For example, to achieve very low latency, a higher frequency cellular system may have a subframe length of 100 us.

[0041] 2 is a diagram 200 of an exemplary OFDM frame structure for an exemplary 1 GHz system bandwidth. In the example shown in FIG. 2, the OFDM-based frame structure has a subcarrier spacing of 300 kHz with a corresponding symbol length of 3.33 μs. Considering that the cyclic prefix (CP) length may span the entire length of the channel time dispersion to eliminate inter-symbol interference, a T symbol An example of CP is T at 0.833 μs. symbol This example numerology can be used for a range of system bandwidths above 6 GHz (e.g., 50 MHz to 2 GHz) with corresponding Fast Fourier Transform (FFT) lengths.

[0042] Figure 3 is a diagram 300 of an exemplary single-carrier frame structure for an exemplary 2 GHz system bandwidth. The frame structure shown in Figure 3 is based on the use of a single carrier across the entire system bandwidth, which is 2 GHz in the example shown, but which may range, for example, from 50 MHz to 2 GHz. The sampling frequency may be 1.536 GHz with a 1024 FFT. A subframe may be 100 μs and may have 150 SC blocks. Each block may be 1024 symbols that may be used for synchronization, reference, control, data, cyclic prefix, or other system purposes.

[0043] Systems above 6 GHz, such as cmW or mmW systems, may apply any waveform and frame structure, or any combination of waveforms and frame structures, as described above, and the embodiments described herein may apply to any or all of these waveforms and frame structures.

[0044] Systems above 6 GHz may use frequency division duplex (FDD), time division duplex (TDD), spatial division duplex (SDD), or any combination thereof along with either half-duplex or full-duplex mechanisms. Full-duplex FDD systems may use duplex filters to enable simultaneous downlink and uplink operations on different frequencies separated by a duplex distance. Half-duplex FDD systems may not use duplex filters because downlink and uplink operations may occur at different time instances on their dedicated frequencies. TDD systems may have downlink and uplink operations on the same frequency at different time instances. For example, in a beamformed system, an SDD system may enable network nodes to transmit and receive at the same frequency and time instance, but in different originating and terminating spatial directions.

[0045] Networks above 6 GHz may use, for example, FDMA, TDMA, spatial division multiple access (SDMA), code division multiple access (CDMA), non-orthogonal multiple access (NOMA), or any combination thereof. FDMA, TDMA, SDMA, and CDMA may be applied in an orthogonal manner to avoid interference.

[0046] Multiple network nodes may be assigned to use different frequency resources simultaneously in an FDMA system or to access system frequency resources at different time instances in a TDMA system. Moreover, network nodes may access the same frequency resources at the same time but using different codes in a CDMA system. An SDMA system may assign spatial resources to network nodes to operate with the same frequency, time, and code resources. For example, in a beamformed network, WTRUs may use different beams.

[0047] In a NOMA system, multiple network nodes may be assigned overlapping or identical resources in the frequency, time, code, or spatial domains, but additional mechanisms may be applied to remove interference caused by non-orthogonal use of resources between users. For example, two WTRUs may be located relatively far from each other, and the difference in their path losses to the base station may be large. They may be assigned the same frequency resources in the same subframe with very different transport formats. Superposition coding and successive interference cancellation (SIC) receivers may be used for the WTRUs to remove received signals intended for the other.

[0048] Systems above 6 GHz, e.g., cmW or mmW systems, may employ any duplexing scheme, multiple access, or combination thereof, as described above, and the embodiments described herein may apply to all of these duplexing and multiple access schemes.

[0049] Systems above 6 GHz may have several physical channels and signals for various system purposes. Certain signals may be used for numerous system procedures. For example, synchronization signals may be predefined and used for cell timing / frequency synchronization. The synchronization signals may be transmitted according to a predefined periodicity. In beamformed systems, such as cmW or mmW networks, signals may provide assistance for beam timing and frequency acquisition. A physical broadcast channel (PBCH) may carry broadcast information, such as cell-specific system information (SI). Downlink reference signals may be predefined sequences transmitted to enable various system procedures, such as channel estimation for control channels, channel condition measurements, timing and frequency fine adjustments, and system measurements. There may be different types of reference signals. For example, in beamformed systems, such as cmW or mmW networks, downlink reference signals may be used for beam acquisition, beam pairing, beam tracking, beam switching, and beam measurements.

[0050] The physical downlink control channel (PDCCH) can carry all data-related control information, for example, to properly identify, demodulate, and decode the associated data channel. The physical downlink data channel can carry payload information from the media access control (MAC) layer in the form of MAC protocol data units (PDUs). Resource allocation for this channel can be carried in the scheduling information of the PDCCH. A data demodulation reference signal can have symbols that can be transmitted for channel estimation of the downlink control channel or data channel. The symbols can be co-located with the associated control or data symbols in the time and frequency domain according to a predefined pattern to ensure correct interpolation and reconstruction of the channel.

[0051] The uplink reference signal can be used, for example, for uplink channel sounding and uplink system measurements. In a beamformed system, such as a cmW or mmW network, the uplink reference signal can be used, for example, for uplink beam acquisition, beam pairing, beam tracking, beam switch, and beam measurement. The physical random access channel (PRACH) can carry a predefined sequence for the random access procedure. The physical uplink control channel (PUCCH) can carry uplink control information, such as channel state information, data acknowledgments, and scheduling requests. The physical uplink data channel can carry payload information from the WTRU MAC layer in the form of MAC PDUs. Resource allocation for this channel can be conveyed on the PDCCH. The data demodulation reference signal can have symbols that can be transmitted for channel estimation of the uplink control channel or data channel. The symbols can be co-located with associated data symbols in the time and frequency domains according to a predefined pattern to ensure correct interpolation and reconstruction of the channel.

[0052] Systems above 6 GHz, such as cmW or mmW systems, may deploy the signals and channels described above, and the embodiments described herein may apply to all of these physical signals and channels.

[0053] Beamforming can be important in systems above 6 GHz, such as cmW and mmW systems. For example, outage studies conducted in the 28 GHz and 38 GHz bands in urban areas using a steerable 10° beamwidth and a 24.5 dBi horn showed that consistent coverage could be achieved with cell radii of up to 200 meters.

[0054] LTE WTRUs are currently assumed to have omnidirectional beam patterns and can sense superimposed channel impulse responses across the entire angular domain. Therefore, aligned beam pairs, such as at mmW frequencies, can provide additional degrees of freedom in the angular domain compared to current LTE systems.

[0055] A phased antenna array (PAA), with element spacing at, for example, 0.5λ, may be used for beamforming, and the phased antenna can apply different beamforming algorithms, such as fully digital beamforming, analog beamforming (e.g., for one or more radio frequency (RF) chains), and hybrid beamforming.

[0056] FIG. 4 is a diagram 400 of an example PAA for fully digital beamforming. A fully digital beamforming approach, such as that shown in the example of FIG. 4, can have a dedicated RF chain, including RF processing and analog-to-digital conversion (ADC), for each antenna element. The signals processed by each antenna element can be independently controlled in phase and amplitude to optimize channel capacity. Thus, for fully digital beamforming, a configuration can have the same number of RF chains and ADCs as there are antenna elements. While fully digital beamforming offers very high performance, it can impose high cost and complexity in implementation and can cause high energy consumption in operation.

[0057] Figure 5 is a diagram 500 of an example of analog beamforming with one PAA containing one RF chain for several antenna elements. In the example shown in Figure 5, each antenna element is connected to a phase shifter that can be used to set weights for beamforming and steering. The number of RF chains implemented can be significantly reduced, as can energy consumption.

[0058] The phase shifting and combining may be implemented in different stages, such as an RF stage, a baseband beamforming (BB) analog stage, or a local oscillator (LO) stage. One example is a single-beam analog configuration that can steer one beam at a time, where the single beam may be positioned in the strongest angular direction, such as the line-of-sight (LOS) path obtained from beam measurements. A wide beam pattern can cover a range of angular directions at the expense of reduced beamforming gain.

[0059] Hybrid beamforming can combine digital precoding with analog beamforming, which may be performed across phased array antenna elements, each associated with a phase shifter and all connected to one RF chain, and digital precoding may be applied to the baseband signal of each RF chain.

[0060] Example system parameters for hybrid beamforming may include the number of data streams (NDATA), the number of RF chains (NTRX), the number of antenna ports (NAP), the number of antenna elements (NAE), and the number of phased antenna arrays (NPAA). The configuration of these parameters can affect system functionality and performance, as described in more detail below.

[0061] FIG. 6 is a diagram 600 of an example of analog beamforming with one PAA and two RF chains. In such an embodiment, one antenna port can carry a beamformed reference signal uniquely associated with the antenna port, which can be used to identify the antenna port. In the example shown in FIG. 6, one PAA of size 4×4 is connected to two RF chains, each with a set of 16 phase shifters. The PAA can form two narrow beam patterns within the coverage of +45° and −45° in the azimuth plane. In this configuration, N PAA <N AP=N TRX <N AE is.

[0062] 7 is a diagram 700 of an example of analog beamforming with two PAAs and two RF chains. In the example shown in FIG. 7, each PAA has a dedicated RF chain (i.e., N PAA =N AP =N TRX ≦N AE ). This configuration can enable spatial independence between two simultaneous beams by placing the PAAs at different orientations (e.g., in the azimuth plane). Aligned PAA arrays can provide larger aggregate coverage. The examples shown in Figures 6 and 7 with two RF chains can apply multiple-input multiple-output (MIMO) with two data streams.

[0063] 8 is a diagram 800 of an example of analog beamforming with two PAAs and one RF chain. In an embodiment such as that shown in FIG. 8, multiple PAAs can be connected to a single RF chain using switches (i.e., N AE >N PAA >N AP =N TRX Each PAA can form a narrow beam pattern covering +45° to -45° in the azimuth plane. They can be aimed separately, allowing a single-beam network node to have good coverage using beams in different directions at different time instances.

[0064] Above 6 GHz systems, such as cmW and mmW systems, can apply different beamforming techniques, such as analog, hybrid, and digital beamforming as described above, and the embodiments described herein can be applied to all of these beamforming techniques.

[0065] To overcome the high path loss at frequencies above 6 GHz, transmit and / or receive beamforming may be applied to the transmission / reception of the control channel. The resulting beamformed link may be thought of as spatial filtering and may limit the WTRU's reception of incoming angular paths. Legacy cellular systems rely on omnidirectional or cell-wide beams for control channel transmission, and in these systems, the placement of the control channel is well defined from the WTRU's perspective (e.g., in a control region). However, at higher frequencies, each base station may have multiple control channel beams to cover the cell, and the WTRU may only be able to receive a subset of them. Embodiments described in this invention may provide methods and apparatus for identifying candidate control channel beams and their locations in the subframe structure.

[0066] Millimeter-wave base stations (mBs) and WTRUs in a beamformed system can have diverse sets of capabilities, such as different numbers of radio frequency (RF) chains, different beamwidths, or different numbers of phased antenna arrays (PAAs). An mB with multiple RF chains can transmit multiple control channel beams in the same symbol, and a WTRU with multiple RF chains can receive the same control symbol using multiple receive beam patterns. An mB with one RF chain may need to multiplex control channel beams in the time domain (e.g., different symbols and / or different subframes). An mB with multiple RF chains can multiplex control channel beams in both the time and spatial domains. The embodiments described herein can provide a framework for beamformed control channel design that can support various capabilities of mBs and WTRUs and support both time- and spatial-domain multiplexing of control channel beams.

[0067] The Long Term Evolution (LTE) common reference signal design assumes cell-wide transmission. For multi-beam systems, modifications to the reference signal design may be required to discover, identify, measure, and decode each control channel beam. In multi-beam systems, interference between beams may reduce overall cell capacity. The embodiments described herein may provide additional mechanisms to mitigate inter-beam interference for both intra-cell and inter-cell scenarios.

[0068] As mentioned above, to achieve the high throughput requirements of 5G systems, beamforming may be required at both the transmitter and receiver. The embodiments described herein may provide the ability to support WTRUs with diverse beamforming capabilities. Furthermore, the embodiments described herein may provide a WTRU-assisted, network-controlled procedure for narrow beam pairing on the uplink (UL) and downlink (DL).

[0069] The directional nature of mmW links can mean that the number of radio link failure (RLF) events can be increased when compared to LTE links for the same small cell inter-site distance (ISD) and WTRU speed. In addition to mobility, changes to the orientation of the WTRU can also cause RLF events when using mmW links. Furthermore, mmW links can be susceptible to disturbances due to changes in the environment, such as from moving people or buses. Embodiments described herein can provide methods and apparatus for a WTRU to detect and recover from beam failures. Furthermore, connectivity concepts can be provided that help overcome issues related to beamforming and can make mmW carriers viable for cellular access.

[0070] The basic components for beam control for a beamformed system include a subframe structure, a beamformed control channel, a beamformed data channel, a data region with one or more beamformed data channels, a control region with one or more beamformed control channels, and a gap, each of which is described in detail below.

[0071] In terms of subframe structure, each subframe may include a number of symbols, one or more of which may be used to transmit or receive one or more control signals, control channels, control information, and / or data channels. As referred to herein, a subframe may be used interchangeably with a scheduling interval, a slot, or a predefined unit of time.

[0072] With respect to beamformed control and data channels, the control or data channel can be transmitted using a unique radiation pattern or beam. Each control or data channel beam may be associated with one or more of a unique reference signal, steering vector, scrambling code, antenna port, time, code, space, frequency resource, or control channel identification information. Each mB or cell can transmit multiple beamformed control and / or data channels. In some embodiments, the beamformed control and / or data channels can be multiplexed in time.

[0073] With respect to a data region having one or more beamformed data channels, one or more symbols in a subframe in which the data channels are transmitted may be referred to as a data region. Within a subframe, a data region may include multiple data channel beams multiplexed in time. For example, a data channel in a particular beam may occupy one or more symbols, and the remaining symbols in the same subframe may be used to transmit data channels in other beams. Each data channel beam in a data region may have a variable beamwidth. In some embodiments, the maximum data channel beamwidth for a WTRU may be as wide as its control channel beamwidth. A single WTRU may receive one or more data channels transmitted using one or more beams or beamwidths within a subframe or across different subframes. Multiple WTRUs may be time-multiplexed within the same data channel beam or across different data channel beams within a subframe. The minimum schedulable time resource within a subframe may be a symbol or a group of symbols. The scheduling granularity may be smaller than a subframe (eg, new downlink control information (DCI) formats can carry allocation information at the symbol level or symbol groups).

[0074] With respect to a control region having one or more beamformed control channels, one or more symbols in a subframe in which the control channels are transmitted may be referred to as a cell-specific control region. Within a subframe, a cell-specific control region may include multiple control channel beams multiplexed in time. One or more symbols in a subframe in which the control channels for a specific beam are transmitted may be referred to as a beam-specific control region. In some embodiments, a control region may refer to a cell-specific control region and / or a beam-specific control region. The control region size may be fixed or flexible. In some embodiments, the control region and data region may overlap, and one or more symbols may carry both control and data channels, multiplexed in the frequency, code, or spatial domain.

[0075] With regard to gaps, they may be placed between two consecutive symbols carrying transmissions with different beam directions, radiation patterns, or steering vectors. As referred to herein, gap may be used interchangeably with switching period, guard period, silence period, no transmission, or discontinuous transmission (DTX) period. Depending on the placement, different gap types may be identified, including, for example, a gap between two control symbols or groups of control symbols, a gap between two data symbols or groups of data symbols, and a gap between a control symbol and a data symbol (e.g., between the last control symbol and the first data symbol, or vice versa).

[0076] Different gap types may be preconfigured with different time lengths. The same gap type may be preconfigured with different time lengths in different subframes. Gaps may be selectively placed between two consecutive symbols transmitted with different radiation patterns, beam patterns, directions, or channel types. Gaps may be selectively placed between control symbols and data symbols. Gaps within the same subframe may have different time lengths. Gaps may or may not be present in all subframes. Gaps may be placed between control symbols and not data symbols, or vice versa. Within the control or data region, gaps may be selectively placed between a subset of symbols.

[0077] A gap may be defined from the perspective of a WTRU. The WTRU may not be required to receive on the downlink (DL) during a gap period (e.g., a gap between control symbols and data symbols for a particular WTRU). The WTRU may use the gap period to decode a control channel that may be received before the beginning of the gap period. The WTRU may use the gap period to switch its receive beam or apply a new steering vector, which may be different from the receive beam or steering vector used to receive the downlink control channel, to receive a downlink data channel. The WTRU may use the gap period (e.g., a gap between data symbols or groups of data symbols for a particular WTRU) to switch its receive beam or apply a new steering vector, which may be different from the receive beam or steering vector used to receive a previous downlink data channel in the same or a different subframe, to receive a downlink data channel.

[0078] A cell, such as an mmW cell or a 5G cell, may be defined by one or more transmissions that share at least one discovery signal characteristic. In embodiments, the one or more transmissions that share at least one discovery signal characteristic may be confined in the spatial domain. A physical transmission may originate from multiple transmission points. Discovery signals between different physical transmissions may be multiplexed in the time, frequency, code, and / or spatial domains. In embodiments, a cell may be defined as a collection of beams from one or more transmission points. Each transmission point may be associated with one or more cells, where only a subset of beams from a transmission point may be associated with each cell. A 5G cell may be characterized by a virtual-ness property and / or an elasticity property.

[0079] The virtual-ness property can indicate that a cell is logical and not tied to a physical transmission point. Multiple transmission points associated with a cell can be considered to form a cluster.

[0080] In traditional cellular architectures, hard edges / borders are created between adjacent cells. WTRUs located at these edges may experience low throughput, high interference, call drops, or data interruptions due to frequent handovers. While cell densification can be a step toward improving airborne capacity, cell densification can also lead to more edges per unit area.

[0081] The virtuality property can be extended to create edgeless cells from the WTRU's perspective. Dynamically adjusted transmissions can enable WTRU-centric cells, where the WTRU can always receive the best possible signal-to-interference-plus-noise ratio (SINR). Cell densification can also lead to increased mobility events (e.g., handovers) that can result in data interruptions. The virtuality property can be used to create WTRU-specific moving cells, where the cell follows the WTRU and mobility can be handled by node-to-node coordination with minimal feedback (e.g., measurement reports) from the WTRU.

[0082] Each mB or DL ​​beam from an mB may be logically associated with multiple virtual cells, where each cell may be WTRU-specific or service-specific. This may be enabled by transmitting multiple discovery signals on the same beam separated in frequency or time.

[0083] The elasticity property of a cell may refer to its flexibility to adapt coverage to satisfy predefined criteria, which may include one or more of: reducing inter-cell interference, adapting coverage according to WTRU distribution (e.g., increased capacity in locations with higher WTRU density), and time-dependent coverage adaptation (e.g., based on time of day, day of the week, etc.). In ultra-high-density deployments with coverage diversity, the elasticity property can be used to provide self-healing capabilities. For example, if one cell (cell 2) loses power, another cell (cell 1) can temporarily increase its coverage area to serve WTRUs in cell 2. In the case of directional transmissions at higher frequencies, etc., spatial coverage adaptation may be used to overcome interference. Additionally, flexible coverage adaptation may be viewed as inter-cell interference coordination in the spatial domain. Turning small cells on and off may be considered a promising approach to energy savings in ultra-high-density deployments. With beamformed cells, selectively turning off directional transmissions instead of turning them off for the entire cell can provide finer grained control over energy efficiency.

[0084] FIG. 9 is a diagram 900 illustrating examples of adaptability properties in an ultra-high density deployment. Four examples are shown in FIG. 9. In example 908a, three mBs 902, 904, and 906 operate with omnidirectional coverage. The mBs can dynamically learn interference patterns, such as from WTRU feedback, and self-organize themselves to optimally serve a given topology, WTRU distribution, and service requirements, as in examples 908b and 908c. In the event of extreme interference or a sudden failure, the mBs can perform self-healing to adapt their coverage area and serve the WTRUs previously served by mB 904, as shown in example 908c for mB 904. Thus, using self-healing, a sudden coverage hole can be corrected with graceful degradation in overall areal capacity.

[0085] In an embodiment, a WTRU may be associated with two or more mBs. In such an embodiment, in the downlink, the WTRU may obtain DL time synchronization for each of the mBs. Furthermore, the WTRU may determine the best beam pair for receiving downlink transmissions from multiple cells. Such beam pairs may be mB-specific (i.e., different mBs may have different preferred receiving beams at the WTRU). Multiple mBs to which a WTRU is connected may form a logical cluster. Coordination between clusters may be centralized or distributed.

[0086] In the uplink, the WTRU may transmit random access or other reference signals on the UL so that the WTRU is uplink time synchronized with multiple mBs. Additionally, such UL transmissions may be beamformed so that preferred UL beam pairs can be established between the WTRU and the mB. Such beam pairs may be mB-specific (i.e., different mBs may have different preferred WTRU transmission beams).

[0087] Portions of the WTRU context may be stored in multiple mBs. The WTRU context may include both semi-static and dynamic parameters. The semi-static parameters may include, for example, a WTRU ID, active radio bearer information, and / or WTRU capability information. The dynamic parameters may include Layer 2 (L2) context (e.g., an Automatic Repeat Request (ARQ) context and / or a Packet Data Convergence Protocol (PDCP) context, a Radio Resource Control (RRC) context, a security configuration, an mB-specific DL beam ID, and / or channel state information (CSI)). The dynamic parameters may be periodically synchronized among all mBs in a WTRU-specific cluster.

[0088] DL data may be made available to one or more mBs forming a WTRU cluster. For example, data from a serving gateway (SGW) may be multicast to the mBs in the cluster. Additionally or alternatively, an anchor mB may receive the data flow from the SGW and then broadcast the data to the mBs in the cluster. Additionally or alternatively, a macro eNB in ​​a dual connectivity context may broadcast data to one or more mBs in the cluster.

[0089] In ultra-high density deployments, the WTRU may be configured to search for a backup mB. The trigger for the backup mB search may depend on the signal quality of the serving mB. The backup mB search may be a function of, for example, one or more of a periodic timer expiration, the number of discovered backup mBs, and the WTRU capabilities (e.g., the number of RF chains or the number of PAAs). The value for the periodic timer may be broadcast in the system information (SI).

[0090] The radio link between the WTRU and the network may be characterized by a beam pair formed from a transmit beam and a receive beam. In some embodiments, the beam pair on the DL may be different from the beam pair used in the UL, or vice versa. Each beam may be identified by a reference signal, a sequence number, a logical antenna port, and / or any other unique identifying information. The two beams in a beam pair may have the same beamwidth. In some embodiments, a WTRU may be connected to multiple base stations, and a separate beam pair may be defined for each of the radio links.

[0091] For example, different levels of beam pairing may be defined, including wide beam pairs, narrow beam pairs, and wide-narrow beam pairs. In an embodiment, a WTRU may determine one or more preferred DL beams during a cell search and / or synchronization procedure, such as during reception of a synchronization signal, a PBCH signal, and / or a system information broadcast. The network may determine one or more preferred UL beams during a random access or sounding procedure. The WTRU and the network may establish the beam pairs upon completion of the random access procedure. A WTRU in connected mode may receive commands from the network to update beam pairing, optionally agree on backup beam pairs, perform beamformed transmissions on the UL for UL beam training, and transmit and / or receive data channels on specific narrow beams that may be specified, for example, via a scheduling grant or higher layer message.

[0092] In addition to beamforming at the mB, beamforming at the WTRU may be required to compensate for the additional path loss at higher frequencies. Detailed methods and apparatus for UL beamforming and scheduling are described below.

[0093] FIG. 10 is a flow diagram 1000 of an example method of beamforming and scheduling. In the example shown in FIG. 10, the WTRU 1002 performs a RACH procedure with the mB 1004 (1006). As described in more detail below, the WTRU 1002 may perform random access using multiple transmit beams or steering vectors to obtain an initial coarse estimate for a preferred UL wide beam and timing advance. The WTRU 1002 may then enter an RRC connected mode (1008). The WTRU 1002 and the mB 1004 may further perform a UL narrow beam pairing procedure to determine the best beam pair to use for high-throughput data transfer and to reduce interference due to coexisting links.

[0094] Once in the RRC Connected mode, the WTRU 1002 may send beamforming capability information to the mB 1004 (e.g., in a WTRU Capability Report) (1010). As described in more detail below, the WTRU 1002 may, for example, send a beamforming capability message autonomously after entering the RRC Connected state, or the mB 1004 may request beamforming capability information via a request message. The WTRU 1002 and mB 1004 may then engage in a beam pairing procedure 1012, which may involve an exchange of beam pairing commands (1014) and beam pairing responses (1016) between the WTRU 1002 and the mB 1004.

[0095] In the example shown in FIG. 10 , the mB 1004 triggers 1018 a beamformed reference signal from the WTRU 1002. Further, in the example shown in FIG. 10 , the WTRU 1002, in response to the trigger 1018, can map 1020 a reference signal configuration or sequence to multiple transmit beams and transmit a reference signal on each of the beams 1022, 1024, 1026. Different procedures for transmitting beamformed reference signals are described in detail in the following embodiments. The mB 1004 can grant 1028 resources for the triggered UL reference signal transmission in the DCI and simultaneously provide an explicit reference signal sequence to be used for transmission on that resource. As described in more detail below, the mB 1004 can also include a one-bit command indicating the linkage of the reference signal sequence.

[0096] The WTRU may perform random access using multiple transmit beams or steering vectors to obtain an initial coarse estimate for a preferred UL wide beam and timing advance. The WTRU and mB may further perform a UL narrow beam pairing procedure to determine the best beam pair to use for high-throughput data transfer and to reduce interference from coexisting links. The embodiments described herein can be used for narrow beam pairing and / or wide beam pairing, or re-pairing. In the embodiments described below, the UL reference signal transmission may be replaced by a random access preamble transmission.

[0097] The WTRU may be configured with dedicated UL resources for the UL beam pairing procedure. In one embodiment, the resource configuration may depend on the WTRU capabilities. The WTRU capabilities may include one or more of the following: the total number of TX beams supported by the WTRU (which may include TX beams from multiple PAAs in the WTRU), the number of narrow TX beams associated with each Random Access Channel (RACH) beam (e.g., within spatial coverage), the number of narrow TX beams associated with the current UL control channel beam (e.g., within spatial coverage), the quantized beamwidths supported by the WTRU, the number of PAAs in the WTRU, the number of RF chains in the WTRU, and the type of beamforming technique (e.g., analog, digital, or hybrid) used by the WTRU.

[0098] In an embodiment, the WTRU capabilities may be expressed by different classes of devices, such as class low, medium, or high, etc. The WTRU class may determine the UL beamforming resource allocation.

[0099] The WTRU may transmit its beamforming capability via higher layer messaging (e.g., using an RRC message). The WTRU may send the message autonomously after entering the RRC connected state, or the mB may request the capability via a request message. In an embodiment, different groups of random access resources may be associated with a WTRU class (e.g., low, medium, or high). The WTRU may implicitly indicate its device class by choosing a random access resource group. In other embodiments, the mB may always configure a predefined set of resources for UL beam pairing, regardless of the WTRU capabilities. In some cases, the WTRU may only need to indicate that it is capable of transmitting a beam narrower than the UL beam used for random access. This one bit of information may be implicitly indicated via choosing a random access preamble. The mB can then further trigger a capability request message to obtain the number of UL narrow beams supported by the WTRU.

[0100] The WTRU may use the dynamic indication to signal changes in its TX beam capabilities (e.g., self-blocking by hand, head, or body). The WTRU may be configured to transmit a beamformed reference signal on UL resources configured for beam pairing. Such a configuration may include, for example, two parts: a semi-static and a dynamic part.

[0101] The semi-static UL beam pairing resource configuration may be cell-specific, mB-RX beam-specific, and / or WTRU-specific. The WTRU may receive the semi-static configuration via a system information block (SIB) and / or a WTRU-specific RRC configuration. The semi-static UL beam pairing resource configuration may include a beamformed reference signal sequence and a cyclic shift, which may be a function of, for example, the RX beam in the mB, a WTRU ID, a cell ID, a subframe number, or a symbol number. The semi-static UL beam pairing resource configuration may also or alternatively include a frequency-domain resource configuration, which may include, for example, a bandwidth, a starting RB position, a hopping configuration, or a transmit comb coefficient. The frequency-domain resource configuration may be a function of, for example, the system bandwidth or the WTRU density. The semi-static UL beam pairing resource configuration may also or alternatively include a time-domain resource configuration, which may include, for example, a subframe, a symbol within a subframe, to be used for the UL beam pairing reference signal, a periodicity, or a repetition factor. In one example, a base time domain resource may be configured, and the WTRU may then determine subsequent resources according to a pre-configured offset / periodicity.

[0102] One or more symbols in a subframe may be allocated for UL beam pairing reference signal transmission. For example, a WTRU may use the same transmit beam to transmit multiple UL beam pairing reference signals in one subframe.

[0103] The WTRU may transmit a UL beam pairing reference signal, for example, based on an mB command or pre-configured criteria. The WTRU may receive a trigger to transmit a UL beam pairing reference signal in several different manners. For example, the mB may dynamically schedule a UL beam pairing reference signal transmission with or without data in the same UL subframe. Resources for UL beam pairing reference signal transmission may be allocated similarly to UL data transmission. This may provide additional granularity in terms of frequency and time domain resources within a subframe. Multiple symbols within a subframe may be allocated for UL beam pairing reference signal transmission. Alternatively, the mB may use only a one-bit field in the DCI to turn on / off beam pairing reference signal transmission. Detailed resource allocation information may be signaled as a semi-static configuration prior to the trigger DCI. The DCI embodiment may be used, for example, for one-time beam reference signal transmission.

[0104] Another example of how the WTRU can receive a trigger to transmit an UL beam pairing reference signal is the use of a MAC control message to activate and deactivate UL beam pairing reference signal transmission. Similar to the DCI embodiment, the resource allocation information may be configured semi-statically. Once activated, the WTRU can transmit the UL beam pairing reference signal according to a predefined periodicity until deactivated by the mB. In another example, the WTRU can receive a trigger to transmit an UL beam pairing reference signal based on a multi-beam PDCCH indication that triggers the WTRU to perform multiple UL transmissions of the reference signal using multiple time-multiplexed TX beams, or based on a random access response (RAR) following that PDCCH indication.

[0105] Another example of how a WTRU can receive a trigger to transmit a UL beam pairing reference signal is that the WTRU may be configured to transmit a UL beam pairing reference signal while in RRC connected mode. Such configuration may be provided using higher layer signaling (e.g., using an RRC message, or an RAR), where the RAR message may include a configuration for a subsequent UL reference signal transmission. The WTRU may stop transmitting a UL beam pairing reference signal when it leaves connected mode.

[0106] Yet another example of how a WTRU can receive a trigger to transmit an UL beam pairing reference signal is that the WTRU can trigger the UL beam pairing reference signal based on a preconfigured event. Such events can include one or more of the following: a number of negative acknowledgments (NACKs) to an UL data transmission above a predefined threshold, a WTRU-based rotation or motion detection (e.g., via an accelerometer or gyroscope) above a predefined threshold, and a change in the serving DL beam (e.g., a control beam or a narrow data beam). In an embodiment, the WTRU can transmit an UL beam pairing request on an UL control channel based on one or more of these preconfigured events.

[0107] The WTRU may transmit UL reference signals periodically while sweeping all TX beams or a subset of TX beams, or may perform a one-time complete sweep or one-time transmission of a subset of TX beams. Provided that a subset of TX beams is used, the WTRU may choose the subset of beams autonomously, or the subset of beams to use may be specified via DCI, MAC, and / or RRC signaling. The TX beams may be identified by a UL reference signal ID or beam ID. The subset may be determined based on one or more of: selecting a beam that is within the spatial coverage of the current UL control channel; selecting a TX beam associated with an RX beam used for DL ​​data channel reception, whose association may be defined by a steering vector or spatial proximity value; based on angle of arrival (AOA) estimation at the WTRU; and based on previous aperiodic measurements from the mB.

[0108] In an embodiment, the WTRU may transmit only narrow beams within the coverage of the current UL wide control beam used by the WTRU. In an embodiment, the UL beamformed reference signal may be configured as a sounding reference signal.

[0109] An exemplary UL resource configuration may include information regarding the start of UL resource allocation (e.g., as a predefined offset in terms of the number of subframes or TTIs), information regarding the periodicity T (e.g., in terms of the number of subframes or TTIs), the number of symbols and / or symbol numbers in each subframe allocated for UL reference signal transmission, a bandwidth and hopping configuration, a sequence number set S0 to SN, and a repetition factor. For the sequence numbers, the starting sequence number may be S0, and the number of sequences N may be derived from the starting sequence number (e.g., the number of times a UL TX beam can be transmitted before switching to the next TX beam in the sequence). For example, the starting sequence number may be a base sequence, and other sequences may be derived by cyclic shifts of the base sequence. The mBs may receive repetitions of the same TX beam using different RX beams.

[0110] Given an UL resource configuration, the WTRU can associate each TX beam n with a unique sequence number Sn within the sequence number set. For example, let M be the number of TX beams supported by the WTRU. If M<=N, the WTRU can use the first M sequence numbers from the set. If M>N, the WTRU can select the N beams based on a prioritization criterion. For example, the prioritization criterion can be based on the spatial proximity between the current UL control beam and the selected TX beam, or can be based on a WTRU-based TX beam subset selection criterion.

[0111] Starting with the first configured UL resource and first selected beam, the WTRU may sequentially sweep each of its selected TX beams with each subsequent UL resource, where each TX beam transmission is repeated by the configured repetition factor. When the WTRU has exhausted all of its selected TX beams, the WTRU may start again with the first TX beam, maintaining the same order of sweeps each time. From the mB's perspective, there are only two possibilities for an upcoming UL reference signal transmission: either the next sequence number in the sequence or wrap around to the starting sequence number. The WTRU may maintain a mapping between sequence numbers and TX beams for every sweep operation. This mapping may be used by the mB to indicate the selected beam for a subsequent data or control transmission.

[0112] In an embodiment, the WTRU may decouple or reset the mapping between the UL reference signal sequence and the TX beam in one or more of the following scenarios: when there is a change in the uplink control beam; an explicit indication is provided during an uplink control beam switch procedure; there is a change in the uplink data channel beam; an explicit indication is provided during an uplink data channel grant or switch procedure; when the WTRU receives a deactivation command for UL reference signal transmission; when an explicit reset command to erase the mapping is received; and / or when a beam failure procedure or a cell-level monitoring procedure is triggered.

[0113] In the mapping from a WTRU-based implicit reference signal sequence number to a TX beam, when N < M, when the UL control beam is updated, or when one or more TX beams cannot be received at mB, the network and the WTRU may end up with a sequence number mismatch. To address this, the WTRU can receive a reset command from mB to invalidate the current mapping between the reference signal sequence number and the TX beam. The WTRU can then resume the procedure and re-assign a new mapping as described above.

[0114] In an embodiment, in addition to UL reference signal transmission, the WTRU can transmit an explicit sequence number to identify the UL TX beam. The sequence number can be added to the UL reference signal transmission, for example, by adding a preamble for identifying the UL beam ID to the UL transmission and / or by assigning the beam ID to the TX beam, according to a WTRU implementation with the constraint that the mapping is one-to-one.

[0115] In another embodiment, the mB may assign a unique reference signal sequence to an upcoming WTRU UL reference signal transmission. The reference signal sequence may be signaled along with the UL resource allocation (e.g., each UL resource may be associated with a predefined reference signal sequence). For example, the DCI may grant a resource for triggering a UL reference signal transmission while simultaneously providing an explicit reference signal sequence to be used for transmission on that resource. The mB may additionally include a 1-bit command indicating the linkage of the reference signal sequence. The linkage bit may be defined such that, when the linkage bit is 0, the WTRU can clear or reset any previous association between the specified reference signal sequence and the TX beam from the WTRU. The WTRU may consider the reference signal sequence available or free to associate with any TX beam that does not have a valid reference signal sequence linked to it. The WTRU may also store the linkage between the TX beam and the specified reference signal sequence. The WTRU may transmit an UL reference signal on the UL resource using the TX beam linked to the reference signal sequence. If the linkage bit is 1, the WTRU may use the UL resources to transmit a UL reference signal using a TX beam previously linked to a reference signal sequence.

[0116] In other embodiments, the reference signal sequence may be defined as a function of the radio frame number, subframe number, symbol, and / or frequency resource on which the UL reference signal is transmitted. In this approach, a WTRU-specific UL reference signal sequence may be allocated, and the WTRU may use the same UL reference signal for multiple TX beams.

[0117] Alternatively, an mB-based allocation scheme may be used for beam IDs rather than reference signal sequence numbers. In one example, the reference signal sequence numbers may be replaced with beam IDs, and together with the linkage bits, the mB can control and adjust the mapping between beam IDs and WTRU TX beams.

[0118] The embodiments described with respect to UL data channel beams and pairing can also be used for UL control channel beams. In one example, the UL control channel beam may be characterized by wider spatial coverage compared to the data channel beam. In some embodiments, UL reference signal transmission for the data channel beam and the control channel beam can coexist or be performed in parallel. For example, separate sets of UL resources in time and / or frequency may be reserved for transmitting UL reference signals using candidate control channel TX beams. In another example, separate sets of reference signals may be reserved for transmitting UL reference signals using candidate control channel TX beams. In yet another example, non-overlapping beam ID spaces may be reserved for the control channel beam and the data channel beam.

[0119] The mB may use the UL reference signal transmitted by the WTRU to evaluate the quality of the UL TX beam. The WTRU may perform UL transmission using the TX beam associated with the beam ID or reference signal sequence number in the UL grant. The association / mapping between the beam ID or reference signal sequence number and the TX beam ID may be determined based on an implicit or explicit WTRU or mB method, as described above. If the beam ID or reference signal sequence number carries a predefined or reserved value, or if the beam information is not present in the scheduling grant, the WTRU may perform UL data transmission using the UL control beam.

[0120] The mB may determine a timing advance for each WTRU TX beam during the UL reference signal transmission procedure. At least two TX beams from the WTRU may be associated with different timing advance values. The WTRU may apply a timing advance to one or more TX beams based on the timing advance configuration in the MAC message or in a higher layer signaling (e.g., RRC) message. The timing advance value may be indexed by the TX beam ID or UL reference signal sequence number. Alternatively, the WTRU may receive an RAR message with individual TX beam responses, or a block response in which each TX beam may be referenced by its RA-RNTI and include the associated timing advance and / or transmit power setting. The WTRU may apply the same timing advance value to two or more TX beams and consider them as belonging to a timing advance group. The WTRU may configure the initial transmission for the multi-beam UL reference signal based on the current wide-beam PUSCH power. Alternatively, the WTRU may set a maximum power for the UL reference signal beam and may receive closed-loop feedback via transmit power control (TPC) bits to reduce the UL transmit power from the maximum power.

[0121] A receiver in a beam-paired link can use beam tracking to update its receive beam, which increases the SNR during directional data transmission. The transmitter can assist the beam tracking procedure by transmitting a reference signal at a predefined position with reference to the actual data transmission. Beam tracking may be considered open-loop beam pairing because no feedback from the receiver is required. Beam tracking can enable the receiver to choose the optimal RX beam for a given TX beam. Beam tracking can be used to compensate for rapid changes in WTRU orientation / blocking when the amount of spatial shift is small. The reference signal used for beam tracking may be referred to as a beam tracking symbol. One or more beam tracking symbols may be appended to the beginning of a data channel (e.g., PDSCH or PUSCH), appended to the end of a data channel (e.g., PDSCH or PUSCH), and / or transmitted on the data channel (e.g., PDSCH or PUSCH) with an offset, where the offset can be negative or positive.

[0122] Guard periods may be introduced between beam tracking symbols and / or between beam tracking symbols and data to allow the receiver to evaluate different RX beams. During downlink transmission, the mB may allocate one or more beam tracking symbols to assist RX beam tracking at the WTRU side. Similarly, in uplink transmission, the WTRU may transmit one or more beam tracking symbols to enable RX beam tracking at the mB side. The resources occupied by the beam tracking symbols may be signaled using one or more of the following: for example, semi-static resource allocation via RRC signaling that provides beam tracking symbol resource allocation and / or periodicity; multiple PDSCH / PUSCH formats defined to indicate the presence or absence of beam tracking symbols in a given resource allocation; and an explicit schedule for beam tracking symbols (e.g., the start and number of beam tracking symbols) similar to the scheduling grant for data allocation. The scheduling grant in the DCI may indicate the PDSCH / PUSCH format. The predefined number of beam tracking symbols may be implicitly determined based on the PDSCH / PUSCH format.

[0123] A WTRU can monitor one or more control channel beams to receive control information in the connected mode. The control channel beam may be a WTRU-specific control channel beam or a cell-specific common control channel beam. The set of control channel beams that a WTRU can monitor may be referred to as serving control channel beams. The WTRU may be assigned one or more serving control channel beams, or the WTRU may consider all control channel beams from the mB as the serving control channel. Alternatively, the WTRU may consider the control channel beam selected during idle mode operation as the WTRU-specific control channel beam for connected mode operation. The WTRU can distinguish common control channel beams from WTRU-specific control channel beams by the presence of a predefined beam reference signal. The WTRU can utilize RX beamforming for additional antenna gain to improve the reliability of the DL control channel. Therefore, a beam pair concept can be established between the WTRU and the mB. The WTRU-specific search space may be a function of, for example, the number of control channel beams transmitted by the mB, the number of control channels selected by and / or assigned to the WTRU, the beam-specific control region size / duration, the total control region duration, the cell bandwidth, the aggregation level, the WTRU ID, the subframe number, or the subframe. The WTRU-specific search space may be defined as the union of the beam-specific search spaces of all serving control channel beams selected by or assigned to the WTRU.

[0124] While in connected mode, the WTRU may evaluate the suitability of non-serving control channel beams from the serving cell. The quality of the serving control channel beam may be determined not only by the transmit beam at the mB, but also by the receive beam at the WTRU. The WTRU may provide feedback to the mB based on the evaluation.

[0125] Based on the WTRU feedback, the mB can determine a serving control channel beam to serve the WTRU based on one or more of the quality of the control channel beam conditioned on receive beamforming at the WTRU, the number of WTRUs in the control channel beam and the capacity of the control channel, interference of the control channel beam from other coexisting beams from the serving mB, interference of the serving control channel beam on neighboring cells, and interference of neighboring cell control channels on the WTRU receive beam.

[0126] The mB may indicate a new serving control channel beam using RRC signaling or DCI-based signaling. In another embodiment, the WTRU may autonomously select a preferred control channel beam using one or more of the criteria described above. The WTRU may obtain assistance information from the serving mB to evaluate and select a serving control channel beam. Such assistance information may include, for example, bias or offset values ​​that implicitly indicate the capacity of the control channel, inter-mB interference, and / or BRS thresholds for considering a control channel beam for selection.

[0127] The beam switch command from the mB may include one or more of the following: identification information (explicit or implicit as a function of the BRS sequence number or cell ID) for the new control channel beam, a beamformed data channel associated with the new control channel beam, a search space configuration associated with the new control channel beam, resources for UL beamforming (e.g., a dedicated RACH preamble and / or time / frequency resources), a fallback TTI associated with the target control channel beam, a beam-specific PCFICH associated with the target control channel beam, resources for transmitting a beam switch ACK (e.g., a dedicated PRACH resource with optional repetition or a beamformed UL PUCCH channel), and / or a UL control channel beam associated with the target control channel beam. The UL control beam from the WTRU may be identified by a reference signal sequence ID. In an embodiment, the search space and control channel may be semi-static and configured by a SIB. Upon receiving the beam switch command, the WTRU may read the SIB associated with the control channel beam to determine the new search space. The search space configuration may also include control channel beam-to-symbol mapping information.

[0128] Upon receiving a beam switch command to transition from a source control channel beam to a target control channel beam, the WTRU may switch its receiving beam associated with the target control channel beam that results in a better signal quality metric for the target control channel beam, update the control channel search space according to the received configuration, add, modify, or remove a serving control channel beam, apply a TTI or symbol mapping for the serving control channel beam (such updates may be effective at a pre-configured offset from the current TTI), monitor the cell-specific control channel beam at the pre-configured location and the WTRU-specific control channel at all other times / locations, stop monitoring the source control channel beam and ignore any pending scheduling grants received on the source control channel beam, update the UL control channel to the PUCCH configuration, and / or apply the target DL control channel configuration and begin monitoring the target control beam, e.g., using a new BRS to determine the presence of the target control channel beam.

[0129] Provided that a dedicated random access resource is configured, the WTRU may transmit a dedicated random access preamble on the pre-configured RACH resource (possibly multiple times according to a configured repetition factor), perform RACH using one or more UL beams corresponding to the configured target DL control channel beam, and / or receive an RAR including a preferred UL beam, which may be identified by a preamble IE or RA-RNTI. The WTRU may use the selected UL beam for ACK / NACK / CSI feedback. The WTRU may additionally receive an updated timing advance corresponding to the new UL transmission beam.

[0130] If random access resources are not configured, the WTRU may assume that UL beam information is available at the mB, and the WTRU may transmit a beam switch ACK on a PUCCH resource. In an embodiment, the WTRU may transmit the ACK on a preconfigured UL control beam. The timing relationship between the beam switch command and the UL ACK may be predefined or explicitly configured by the beam switch command. In an embodiment, the WTRU may be configured with exactly one UL control beam even if multiple DL control channels are allocated, and the WTRU may transmit the ACK on the configured UL control beam regardless of the DL beam that carries the data.

[0131] If the target DL beam configuration is associated with the same serving mB, the WTRU may not reset the MAC / RLC context. Additionally, different levels of Layer 2 (L2) reset may be configured in the WTRU for a beam switch between different mBs. For example, the WTRU may be transparent to whether the beam switch occurs in the same mB, between different mBs in the same cell, or between different mBs in different cells or clusters. However, from the network's perspective, different beam switches may lead to different levels of L2 reset. The WTRU may be configured to reset only the hybrid automatic repeat request (HARQ) context but retain all ARQ contexts (e.g., sequence numbers), or to reset both the HARQ and ARQ contexts.

[0132] Occasionally, for example, a WTRU may not receive a beam switch command from the mB or a measurement report to the mB may be lost due to unexpected degradation in the serving control channel beam quality. Such rapid degradation may be attributed, for example, to dynamic obstructions or a change in the WTRU's orientation. In an embodiment, the WTRU may enter an extended monitoring mode and monitor one or more control channel beams in addition to the current serving control channel beam. The extended monitoring mode may provide an additional opportunity for the mB to reach the WTRU and adjust the beam switch procedure in order to restore the radio link.

[0133] The WTRU can use a proactive enhanced monitoring procedure to temporarily increase its beam search space when there is a sudden degradation in the serving control beam quality. The terms beam re-establishment and beam recovery may be used interchangeably herein. The beam pairs before and after beam re-establishment may be the same or different.

[0134] FIG. 11 is a flow diagram 1100 of an example method for extended monitoring implemented in a WTRU. In the example shown in FIG. 11, the WTRU may monitor a first control channel search space (SS) associated with a first normal beam set (1102). The first normal beam set may include the first beam set. The WTRU may monitor a control search space associated with an extended beam set (1104). The WTRU may perform monitoring of the control search space associated with the extended beam set upon initiating and / or entering the extended monitoring mode, for example, following a trigger based on measurements by the WTRU. The trigger may be received, for example, from the mB. The extended beam set may include the first beam set and one or more additional beam sets.

[0135] The WTRU may determine a second beam set from the extended beam set (1106). The determination may be based on, for example, the received control channel beam switch command or the SS in which the beam switch command was received. The WTRU may monitor a second control channel SS associated with the second normal beam set (1108). The second normal beam set may include the determined second beam set.

[0136] In an embodiment, a WTRU can enter extended monitoring based on one or more criteria, which may be preconfigured. Such criteria may include, for example, the beamformed reference signal received power (BRSRP) of one or more serving control beams falling below a threshold, the BRSRP of one or more non-serving control beams rising above a threshold, and / or reaching a predefined offset from a measurement report transmission triggered based on the BRSRP being above or below a threshold. The BRSRP may be measured, for example, on a beamformed reference signal associated with a control beam, a linked PBCH, and / or a SYNC beam of a non-serving control beam. In both cases, the threshold may be absolute or relative to one or more other beams in the cell. Additionally or alternatively, the criteria for a WTRU to enter extended monitoring may include a running counter for NACK or CRC failures being greater than a predefined value.

[0137] In the extended monitoring mode, the WTRU may consider several different candidate beams for monitoring in the extended beam set in addition to the first beam set. Such candidate beams may include, for example, one or more of: all control and / or common control channel beams in the serving cell, one or more control or common control channel beams spatially adjacent to the current serving control channel beam (e.g., the beams immediately to the left and right of the serving control channel beam), a subset of control or common control channel beams explicitly linked to or pre-configured to be associated with the serving control channel beam, one or more control or common control channel beams having a quality above a threshold (e.g., the BRSRP threshold described above), one or more control or common control channel beams included in the latest measurement report, and one or more WTRU-specific control channel beams configured as backup or candidate beams for extended monitoring.

[0138] The WTRU may monitor one or more of the additional beams in the extended monitoring mode in one or more TTIs and / or subframes, such as all subsequent downlink TTIs and / or subframes while the WTRU is in the extended monitoring mode, pre-configured TTIs and / or subframes specifically configured for extended mode monitoring, all subsequent TTIs and / or subframes in which candidate control channel beams are transmitted, and / or TTIs and / or subframes carrying broadcast signaling such as PBCH and / or SYNC signals. The WTRU may be configured with a unique control channel beam mapping within one or more of these TTIs and / or subframes. Additionally, the WTRU may be configured with a unique search space and / or DCI reserved for beam switch control messages.

[0139] In an embodiment, a paging message may be used as a mechanism for beam re-establishment and / or beam switch. The WTRU may monitor paging messages in all of the candidate beams during the extended monitoring mode. The paging type may indicate the reason as a beam re-establishment and / or beam switch. The CRNTI may be used as a WTRU identity, and additional dedicated resources may be allocated to trigger a UL response transmission from the WTRU.

[0140] In an embodiment, the WTRU may explicitly indicate entry into the enhanced monitoring mode by transmitting a NACK on predefined reserved resources, which may be preconfigured for the serving control beam or the backup control beam. Alternatively, the WTRU may transmit a RACH on preconfigured resources to indicate entry into the enhanced monitoring mode.

[0141] In an embodiment, the WTRU may indicate a preferred beam and an explicit WTRU ID to reinstate the radio link. For example, one or more RACH preambles or preamble groups and / or time / frequency resources may be pre-configured to implicitly indicate one or more of the cause of a RACH transmission (e.g., re-establishment, a serving control beam below a threshold, and / or a resource request for measurement reporting), entry into an extended monitoring mode, and / or a set of preferred beams.

[0142] The WTRU may exit the extended monitoring mode when one or more conditions are met. Such conditions may include, for example, receiving a beam switch command on the serving control beam, backup control beam, or other common control beam, and / or not receiving a DL DCI and beam switch command within a predefined time from the beginning of the extended monitoring mode. Upon exiting the extended monitoring mode, the WTRU may perform cell-level monitoring or declare a radio link failure (RLF).

[0143] FIG. 12 is a flowchart 1200 of an example method for extended monitoring implemented in a base station, such as an mB. In the example shown in FIG. 12, the base station may determine 1202 that a WTRU has initiated extended monitoring and may send 1204 a beam switch command upon the condition that the base station has determined that the WTRU has initiated extended monitoring. In an embodiment, the WTRU initiating extended monitoring may include, for example, switching from monitoring a first control channel SS associated with a first normal beam set that includes the first beam set to monitoring a control channel SS associated with an extended beam set that includes the first beam set and one or more additional beam sets following a measurement-based trigger. The beam switch command may be a command for the WTRU to switch to monitoring a second control channel SS associated with a second normal beam set that includes the second beam set.

[0144] In an embodiment, the mB may implicitly or explicitly determine that the WTRU has entered the extended monitoring mode. The mB may implicitly determine that the WTRU has entered the extended monitoring mode based on the lack of an acknowledgment for a scheduled downlink transmission or the lack of an UL data transmission in response to an UL grant. The mB may explicitly determine that the WTRU has entered the extended monitoring mode based on the lack of a response to a status inquiry message, a poll request message, a PDCCH indication, or other message. Such an explicit request / response may be faster and more resource efficient than implicit methods.

[0145] To perform beam level monitoring, the WTRU may perform BRS measurements on a PBCH beam linked to a serving control channel beam. The transmission schedule of the PBCH beam, such as its periodicity and location in the frame structure, may be predefined. Additionally or alternatively, the WTRU may perform BRS measurements on a common control channel beam linked to the serving control channel beam. The transmission schedule of the common control channel beam, such as its periodicity and location in the frame structure, may be preconfigured. Additionally or alternatively, the WTRU may perform opportunistic BRS measurements on the serving control channel beam.

[0146] The outcome of beam level monitoring may be an average of BRSRP measurements over a predefined time period. The average BRSRP value may indicate the quality of the serving control channel beam. For purposes of beam level monitoring, in-sync and out-of-sync states may be defined based on the measured BRSRP values. The WTRU may determine a beam level failure based on one or more criteria, such as the BRSRP measurement falling below a predefined threshold and N consecutive out-of-sync indications being received.

[0147] Provided that the WTRU determines a beam-level failure, it may enter an enhanced monitoring mode and perform actions specified as part of the enhanced monitoring procedure. Additionally or alternatively, the WTRU may begin monitoring normal DCI and / or fallback DCI in all (or a subset of) the control channel beams in a subset of TTIs that includes the fallback TTI. Additionally or alternatively, the WTRU may determine a loss of the DL beam and, as a result, suspend all UL transmissions, including ACK / NACK feedback and pending UL transmissions, which may include measurement reports, upper layer feedback (e.g., RLC ARQ), buffer status reports, and / or any other upper layer data. Additionally or alternatively, the beam-level failure may trigger the WTRU to perform cell-level monitoring.

[0148] In an embodiment, the WTRU may perform cell-level monitoring by performing BRS measurements on all PBCH beams in the current serving cell, where the transmission schedule of the PBCH beams, such as their periodicity and location in the frame structure, may be predefined. Additionally or alternatively, the WTRU may perform cell-level monitoring by performing BRS measurements on all common control channel beams in the current serving cell, where the transmission schedule of the common control channel beams, such as their periodicity and location in the frame structure, may be preconfigured. Additionally or alternatively, the WTRU may perform cell-level monitoring by performing BRS measurements on all control channel beams in the current serving cell, where the periodicity and location in the frame structure, e.g., in fallback TTIs and / or subframes, may be preconfigured.

[0149] In an embodiment, the WTRU may perform cell-level monitoring upon a beam-level failure, or alternatively, whenever the WTRU enters connected mode. In another embodiment, the WTRU may perform cell-level monitoring at all times, including during idle mode.

[0150] During cell-level monitoring, if the WTRU finds a suitable beam, it can trigger a beam re-establishment or beam switch procedure. The beam re-establishment or beam switch procedure can include, for example, performing a RACH procedure to notify the mB of the need to switch beams, for example, using predefined RACH resources for the beam re-establishment or beam switch. Additionally or alternatively, the beam re-establishment or beam switch procedure can include using the grant received in the RAR to send a higher layer message indicating the beam re-establishment or beam switch, for example, by including an old RNTI or measurement report for one or more control channels. If, during cell-level monitoring, a suitable beam is not found, such as when higher layers receive Qout on all of the control channel beams in the cell, the WTRU can trigger an RLF procedure, such as performing cell selection and RRC re-establishment.

[0151] 13A and 13B are diagrams 1300A and 1300B of more specific examples of extended monitoring. In the example shown in FIG. 13A, mB 1302 sequentially sweeps control channel beams 1304, 1306, 1308, 1310, and 1312. In the example shown in FIG. 13B, WTRU 1320a monitors 1322 the control channel search space associated with control channel beam 1308b. The WTRU 1320 may then determine 1324 whether the extended mode has been triggered. Provided that the extended mode has not been triggered, the WTRU may continue to monitor 1322 the original control channel search space for the beam or beam set. In the example shown in FIG. 13B, WTRU 1320b is moving, so that it may no longer be able to receive control channel beam 1308c and therefore determine that the extended mode has been triggered.

[0152] On the condition that the WTRU 1320 has entered the extended mode, the WTRU 1320 determines 1326 an extended set of control channel beams to monitor and monitors 1328 the extended set for a beam switch command. In the example shown in FIG. 13B, the WTRU 1320c monitors an extended set that includes the original serving control channel beam 1308d and immediately adjacent beams 1306b and 1308d. The WTRU 1320 may also transmit an indication of a preferred beam on pre-configured resources. On the condition that a beam switch command has not been received, the WTRU continues to monitor 1328 the extended set. On the condition that a beam switch command has been received, the WTRU 1320 monitors 1334 a new control channel search space that includes one or more control channel beams. In the example shown in FIG. 13B, the new control channel search space includes the new serving control channel beam 1310c. In an embodiment, the WTRU 1320 may optionally wait 1332 a delay time before monitoring 1334 the new control channel search space. In an embodiment, the WTRU 1320 may optionally send 1336 a beam switch ACK, provided that the WTRU 1320 receives the beam switch command.

[0153] In at least some embodiments described herein, mB, SCmB, mmW eNB, eNB, cell, small cell, PCell, and SCell may be used interchangeably. Further, in at least some embodiments, "operate" may be used interchangeably with "transmit" and / or "receive." Further, in at least some embodiments, component carrier and mmW carrier may be used interchangeably with serving cell.

[0154] In embodiments, an mB may transmit and / or receive one or more mmW channels and / or signals in licensed and / or unlicensed bands. In at least some embodiments, a WTRU may substitute for an eNB, and / or vice versa. Furthermore, in at least some embodiments, an UL may substitute for a DL, and vice versa.

[0155] In at least some embodiments, a channel may refer to a frequency band, which may have a center or carrier frequency and a bandwidth. Licensed and / or unlicensed spectrum may include one or more channels, which may or may not overlap. Channel, frequency channel, wireless channel, and mmW channel may be used interchangeably. Accessing a channel may be the same as using the channel (e.g., transmitting on the channel, receiving on the channel, and / or using the channel).

[0156] In at least some embodiments, a channel may refer to an mmW channel or signal, such as an uplink or downlink physical channel or signal. Downlink channels and signals may include one or more of a mmW synchronization signal, a mmW broadcast channel, a mmW cell reference signal, a mmW beam reference signal, a mmW beam control channel, a mmW beam data channel, a mmW hybrid ARQ indicator channel, a mmW demodulation reference signal, a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a demodulation reference signal (DMRS), a cell-specific reference signal (CRS), a CSI-RS, a PBCH, a PDCCH, a PHICH, an EPDCCH, and / or a PDSCH. Uplink channels and signals may include one or more of a mmW PRACH, a mmW control channel, a mmW data channel, a mmW beam reference signal, a mmW demodulation reference signal, a PRACH, a PUCCH, an SRS, a DMRS, and a PUSCH. Channel and mmW channel may be used interchangeably. Channel and signal may be used interchangeably.

[0157] In at least some embodiments, data / control may refer to data and / or control signals and / or data and / or control channels. Control may include synchronization. Data / control may be mmW data / control. Data / control and data / control channels and / or data / control signals may be used interchangeably. Channel and signal may be used interchangeably. Control channel, control channel beam, PDCCH, mPDCCH, mmW PDCCH, mmW control channel, directional PDCCH, beamformed control channel, spatial control channel, and control channel slice, high-frequency control channel may be used interchangeably. Data channel, data channel beam, PDSCH, mPDSCH, mmW PDSCH, mmW data channel, directional PDSCH, beamformed data channel, spatial data channel, data channel slice, high-frequency data channel may be used interchangeably.

[0158] In at least some embodiments, a channel resource may be, for example, a resource such as a time, frequency, code, and / or space resource (e.g., a 3GPP LTE or LTE-A resource) that can carry one or more channels and / or signals at least some of the time. In at least some embodiments, a channel resource may be used interchangeably with a channel and / or a signal.

[0159] The terms mmW beam reference signal, mmW reference resource for beam measurements, mmW measurement reference signal, mmW channel condition measurement reference signal, mmW demodulation reference signal, mmW sounding reference signal, reference signal, CSI-RS, CRS, DM-RS, DRS, measurement reference signal, reference resource for measurements, CSI-IM, and measurement RS may be used interchangeably. The terms mmW cell, mmW small cell, S cell, secondary cell, licensed-assisted cell, unlicensed cell, and LAA cell may be used interchangeably. The terms mmW cell, mmW small cell, P cell, primary cell, LTE cell, and licensed cell may be used interchangeably. Interference and interference-plus-noise may be used interchangeably.

[0160] The WTRU may determine the UL and / or DL ​​direction of one or more subframes according to one or more received and / or configured TDD UL / DL configurations. UL / DL and UL-DL may be used interchangeably.

[0161] The embodiments described herein may be applicable to any system, regardless of frequency band, usage (e.g., licensed, unlicensed, shared), antenna configuration (e.g., phased array, patch, or horn), RF configuration (e.g., single or multiple RF chains), beamforming method used (e.g., digital, analog, hybrid, codebook-based, or other), deployment (e.g., macro, small cell, heterogeneous network, dual connectivity, remote radio head, or carrier aggregation). In some embodiments, mmW may be used instead of cmW, or LTE / LTE-A / LTE Evolution, LTE Advanced, or LTE Advanced Pro.

[0162] In at least some embodiments, a scheduling interval may refer to a subframe, a slot, a frame, a schedulable slice, a control channel periodicity, or any other predefined unit of time. Gap, guard period, silence period, switching period, no transmission, or DTX period may be used interchangeably.

[0163] Antenna pattern, phase weight, steering vector, codebook, precoding, radiation pattern, beam pattern, beam, beamwidth, beamformed transmission, antenna port, virtual antenna port, or transmission associated with a unique reference signal, directional transmission, or spatial channel may be used interchangeably.

[0164] In the embodiments described herein, a radiation pattern may refer to the angular distribution of a radiated electromagnetic field or the power level in the far-field region. Furthermore, in embodiments, a beam may refer to one of the lobes, such as the main, side, and / or grating lobes, of the transmit radiation pattern and receive gain pattern of an antenna array ([ ]). A beam may also represent a spatial direction that may be expressed by a beamforming weight vector. A beam may be identified by or associated with a reference signal, an antenna port, a beam identification (ID), and / or a scrambling sequence number, and may be transmitted and / or received on specific time, frequency, code, and / or space resources. A beam may be formed digitally, analogically, or both (e.g., hybrid beamforming). Analog beamforming may be based on a fixed codebook or continuous phase shifting. A beam may also include omnidirectional or quasi-omnidirectional transmission. Two beams may be differentiated by the direction of highest radiated power and / or by beamwidth.

[0165] In an embodiment, a data channel beam may be used to transmit a data channel, data channel beam, PDSCH, mPDSCH, mmW PDSCH, mmW data channel, directional PDSCH, beamformed data channel, spatial data channel, data channel slice, or high frequency data channel. A data channel beam may be identified by or associated with a reference signal, antenna port, beam identification (ID), scrambling sequence number, or data channel number, and may be transmitted and / or received on specific time, frequency, code, and / or space resources.

[0166] In an embodiment, a control channel beam may be used to transmit a control channel, a PDCCH, an mPDCCH, an mmW PDCCH, an mmW control channel, a directional PDCCH, a beamformed control channel, a spatial control channel, a control channel slice, or a high-frequency control channel. The control channel may carry DCI for one or more users. The control channel may also carry the PHICH and PCFICH in the downlink and the PUCCH in the uplink. The control channel beam may be identified by or associated with a reference signal, an antenna port, a beam identification (ID), a scrambling sequence number, or a control channel number, and may be transmitted and / or received on specific time, frequency, code, and / or space resources. The control channel beam may be cell-specific or WTRU-specific.

[0167] In an embodiment, a common control channel beam may refer to a control channel beam that can be used to carry control information related to broadcast or multicast information, such as SI, paging, and / or beam switch commands.

[0168] In an embodiment, half-power beamwidth (HPBW) may refer to the angle between two directions where the radiation intensity is half of the maximum value in the radiation pattern cut that accommodates the direction of the maximum lobe. The exact beamwidth of the beamformed control / data channel may not be specified and may depend on the implementation of the mB or the WTRU. An mB may support WTRUs with different capabilities, and vice versa.

[0169] In an embodiment, the control channel beam time length may refer to the number of OFDM symbols in a scheduling interval occupied by one control channel beam, and the control region may be the number of OFDM symbols in a scheduling interval occupied by all control channel beams transmitted in the scheduling interval.

[0170] In embodiments, fixed-codebook-based analog beamforming may refer to a grid of beams that may include or consist of a set of fixed beams, each beam being assigned to a predefined codebook v∈{v1, v2, v3, ... v N}, where N represents the number of fixed beams. The number of beams can depend on the HPBW of the beamforming and the desired coverage.

[0171] In an embodiment, continuous phase-shifting analog beamforming may refer to desired weights for each phase shifter calculated based on estimated channel information (e.g., angle information converted using a high-resolution digital-to-analog converter (DAC) for application to the phase shifters), which can provide continuous, adaptive beamforming to track channel conditions.

[0172] In an embodiment, antenna ports may be defined such that the channel over which a symbol on an antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed. There may be one resource grid per antenna port.

[0173] In embodiments, linkage may refer to a predefined offset between two channels and / or beams. Linkage can be used to determine the transmission schedule, time, and frequency location of one channel and / or beam when the time and / or frequency location of another channel / beam is known.

[0174] In an embodiment, the BRSRP may be defined as the average power received by a WTRU from a beam-specific reference signal resource element associated with a control channel beam. In an embodiment, cell, 5G cell, mmW cell, transmission point, and cluster may be used interchangeably.

[0175] While features and elements have been described above in particular combinations, those skilled in the art will recognize that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein can be implemented in a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random-access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs). A processor in association with software can be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

1. a processor; Transceiver and 1. A wireless transmit receive unit (WTRU) for communicating with a base station, comprising: The processor and the transceiver monitoring a first physical downlink control channel (PDCCH) search space using the first beam to detect first control information; Detecting a beam failure of the first beam based on a quality of the first beam being below a first threshold; determining, in response to the detection of the beam failure of the first beam, that a quality of a second beam exceeds a second threshold configured by the base station; determining a second PDCCH search space based on configuration information from the base station, the second PDCCH search space being associated with beam recovery in response to the beam failure of the first beam; and further configured to monitor the second PDCCH search space using the second beam to detect second control information. WTRU.

2. The processor and the transceiver a channel state information reference signal (CSI-RS) associated with the first beam; or Detecting the beam failure of the first beam based on beam reference signal (BRS) measurements using a physical broadcast channel (PBCH) beam associated with the first beam; or a CSI-RS associated with the second beam, or determining, based on a BRS measurement using a PBCH beam associated with the second beam, that the quality of the second beam exceeds the second threshold; The WTRU of claim 1 , further configured to perform at least one of the following:

3. The BRS measurement includes measuring a reference signal received power (BRSRP), and the processor and the transceiver: Detecting a beam failure of the first beam by comparing the BRSRP of the first beam with the first threshold; Comparing the BRSRP of the second beam with the second threshold to determine that the quality of the second beam exceeds the second threshold. The WTRU of claim 2 further configured to:

4. The processor and the transceiver receiving, from the base station, information configuring one or more dedicated random access resources; Initiating a random access transmission based on the detection of the beam failure of the first beam. The WTRU of claim 1 further configured to:

5. The processor and the transceiver receiving signaling from the base station, the signaling including a media access control (MAC) command; Sending an acknowledgement (ACK) to the base station; receiving the second control information in the second PDCCH search space using the second beam; The WTRU of claim 1 further configured to:

6. The second control information is an indication of physical uplink control channel (PUCCH) resources; and Timing information for transmitting the ACK using the indicated PUCCH resource The WTRU of claim 5 , comprising:

7. The processor and the transceiver The WTRU of claim 6 , further configured to transmit the ACK to the base station on the indicated PUCCH resource using the timing information provided in the second control information.

8. The processor and the transceiver The WTRU of claim 6 , further configured to continue monitoring the second PDCCH search space using the second beam until a control command is received from the base station.

9. the first beam comprises a plurality of first beams; or The second beam includes a plurality of second beams. The WTRU of claim 1, wherein the WTRU is at least one of:

10. 2. The WTRU of claim 1, wherein the processor and the transceiver are further configured to perform monitoring of the second PDCCH search space using both the first beam and the second beam based on the detection of the beam failure of the first beam.

11. 1. A method implemented in a wireless transmit receive unit (WTRU), comprising: performing monitoring of a first physical downlink control channel (PDCCH) search space using a first beam to detect first control information; detecting a beam failure of the first beam based on a quality of the first beam being below a first threshold; determining, in response to the detection of the beam failure of the first beam, that a quality of a second beam exceeds a second threshold configured by the base station; determining a second PDCCH search space based on configuration information from the base station, the second PDCCH search space being associated with beam recovery in response to the beam failure of the first beam; monitoring the second PDCCH search space using the second beam to detect second control information; A method for providing the above.

12. a channel state information reference signal (CSI-RS) associated with the first beam; or Detecting the beam failure of the first beam based on beam reference signal (BRS) measurements using a physical broadcast channel (PBCH) beam associated with the first beam; or a CSI-RS associated with the second beam, or determining, based on BRS measurements using a PBCH beam associated with the second beam, that the quality of the second beam exceeds the second threshold; The method of claim 11 , further comprising at least one of:

13. The BRS measurements include measurements of reference signal received power (BRSRP); detecting a beam failure of the first beam by comparing the BRSRP of the first beam with the first threshold; determining that the quality of the second beam exceeds the second threshold by comparing the BRSRP of the second beam with the second threshold; The method of claim 12 further comprising:

14. receiving, from the base station, information configuring one or more dedicated random access resources; initiating a random access transmission based on the detection of the beam failure of the first beam; The method of claim 11 further comprising:

15. receiving signaling from the base station, the signaling including a media access control (MAC) command; sending an acknowledgement (ACK) to the base station; receiving the second control information in the second PDCCH search space using the second beam; The method of claim 14 further comprising:

16. The second control information is an indication of physical uplink control channel (PUCCH) resources; and Timing information for transmitting the ACK using the indicated PUCCH resource 16. The method of claim 15, comprising:

17. transmitting the ACK to the base station on the indicated PUCCH resource using the timing information provided in the second control information. The method of claim 16 further comprising:

18. continuing to monitor the second PDCCH search space using the second beam until a control command is received from the base station. The method of claim 11 further comprising:

19. the first beam comprises a plurality of first beams; or The second beam includes a plurality of second beams.

12. The method of claim 11, wherein at least one of

20. performing monitoring of the second PDCCH search space using both the first beam and the second beam based on the detection of the beam failure of the first beam. The method of claim 11 further comprising:

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