WO2017086922A1

WO2017086922A1 - Devices for and methods of beam tracking for 5g high frequency bands

Info

Publication number: WO2017086922A1
Application number: PCT/US2015/060974
Authority: WO
Inventors: Qian Li; Huaning Niu; Gang Xiong; Geng Wu; Apostolos Papathanassiou; Pingping Zong
Original assignee: Intel IP Corp
Current assignee: Intel IP Corp
Priority date: 2015-11-17
Filing date: 2015-11-17
Publication date: 2017-05-26
Anticipated expiration: 2018-05-17

Abstract

User equipment (UE), an enhanced NodeB (eNB) and method of beamforming are generally described. The UE may perform beam scanning for coarse beam tracking to an eNB tracking reference signal in a downlink (DL) subframe during an eNB tracking interval and train a beamforming matrix of the UE, perform channel sounding based on the eNB tracking reference signal to obtain an optimal direction to communicate with the eNB and transmit, during a UE tracking interval in an uplink (UL) subframe, a UE tracking reference signal using the optimal direction. A backup beam on a different channel may be used when the eNB or UE tracking reference signal is missed. The UE may re-sync with the eNB based on determining that the eNB tracking reference signal is missed or upon receiving an instruction from an anchor eNB. If re-synchronization fails, the UE may transmit to the anchor eNB a blockage report.

Description

DEVICES FOR AND METHODS OF BEAM TRACKING FOR 5G HIGH

FREQUENCY BANDS

TECHNICAL FIELD

[0001] Embodiments pertain to radio access networks. Some embodiments relate to tracking in cellular networks, including Third Generation Partnership Project Long Term Evolution (3GPP LTE) networks and LTE advanced (LTE-A) networks as well as 4^th generation (4G) networks and 5^th generation (5G) networks.

BACKGROUND

[0002] The use of personal communication devices has increased astronomically over the last two decades. The penetration of mobile devices (user equipment or UEs) in modern society has continued to drive demand for a wide variety of networked devices in a number of disparate environments. The use of networked UEs using 3 GPP systems has increased in all areas of home and work life. Among the various issues of import in communication systems is the link budget due to concerns about, for example, interference by enhanced Node-Bs (eNBs) and power usage of the UEs. Various applications have been introduced for UEs specifically and functionality of the 3 GPP system, such as idle mode and discontinuous transmission/reception have been introduced in an attempt to extend battery life of UEs. With the seeming never-ending increase in applications continuously communicating data, for example those providing data to companies for use in Big Data Analytics, network bandwidth, UE power control and link budget are undergoing even more scrutiny.

[0003] The upcoming generation of 3GPP systems, 5G, are expected to exploit frequency bands at above 6 GHz. To boost link budget for signals in the high frequency band, large antenna array and beamforming (analog and/or digital) may be used. High antenna array gain, however, comes at the expense of highly directional transmission and reception. This limitation on geographical coverage may be a significant bottleneck in air- interface design at high frequency band as, unlike omnidirectional antennas of a single eNB used at lower frequencies, the network may not be able to assume that all UEs are able to be addressed by a particular broadcast. It thus may be desirable to provide UE-based tracking in 5G systems.

BRIEF DESCRIPTION OF THE FIGURES

[0004] In the figures, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The figures illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0005] FIG. 1 is a functional diagram of a 3 GPP network in accordance with some embodiments.

[0006] FIG. 2 is a block diagram of a 3 GPP device in accordance with some embodiments.

[0007] FIG. 3 illustrates a Time Division Duplex (TDD) frame structure in accordance with some embodiments.

[0008] FIG. 4 illustrates another TDD frame structure in accordance with some embodiments.

[0009] FIGS. 5 A and 5B illustrate Downlink (DL) tracking within one tracking field duration in accordance with some embodiments.

[0010] FIG. 6A and 6B illustrate eNB and UE lost-tracking detection and recovery procedure, respectively, in accordance with some embodiments.

[0011] FIG. 7 illustrates a flowchart of beam tracking in accordance with some embodiments.

[0012] FIG. 8 illustrates example components of a UE in accordance with some embodiments.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims.

[0014] FIG. 1 shows an example of a portion of an end-to-end network architecture of a Long Term Evolution (LTE) network with various components of the network in accordance with some embodiments. As used herein, LTE and LTE-A networks and devices, including 3G, 4G and 5G networks and devices, are referred to merely as LTE networks and devices. The network 100 may comprise a radio access network (RAN) (e.g., as depicted, the E-UTRAN or evolved universal terrestrial radio access network) 101 and the core network 120 (e.g., shown as an evolved packet core (EPC)) coupled together through an SI interface 1 15. For convenience and brevity, only a portion of the core network 120, as well as the RAN 101, is shown in the example.

[0015] The core network 120 may include mobility management entity

(MME) 122, serving gateway (serving GW) 124, and packet data network gateway (PDN GW) 126. The RAN includes enhanced node Bs (eNBs) 104 (which may operate as base stations) for communicating with user equipment (UE) 102. The eNBs 104 may include macro eNBs and low power (LP) eNBs. The eNBs 104 and UEs 102 may perform the tracking methods described herein.

[0016] The MME 122 may be similar in function to the control plane of legacy Serving GPRS Support Nodes (SGSN). The MME may manage mobility aspects in access such as gateway selection and tracking area list management. The serving GW 124 may terminate the interface toward the RAN 101, and route data packets between the RAN 101 and the core network 120. In addition, it may be a local mobility anchor point for inter-eNB handovers and also may provide an anchor for inter-3GPP mobility. Other responsibilities may include lawful intercept, charging, and some policy enforcement. The serving GW 124 and the MME 122 may be implemented in one physical node or separate physical nodes. The PDN GW 126 may terminate an SGi interface toward the packet data network (PDN). The PDN GW 126 may route data packets between the EPC 120 and the external PDN, and may be a key node for policy enforcement and charging data collection. The PDN GW 126 may also provide an anchor point for mobility with non-LTE accesses. The external PDN can be any kind of IP network, as well as an IP Multimedia Subsystem (IMS) domain. The PDN GW 126 and the serving GW 124 may be implemented in one physical node or separated physical nodes.

[0017] The eNBs 104 (macro and micro) may terminate the air interface protocol and may be the first point of contact for a UE 102. In some embodiments, an eNB 104 may fulfill various logical functions for the RAN 101 including but not limited to RNC (radio network controller functions) such as radio bearer management, uplink and downlink dynamic radio resource management and data packet scheduling, and mobility management. In accordance with embodiments, UEs 102 may be configured to communicate Orthogonal Frequency-Division Multiplexing (OFDM) communication signals with an eNB 104 over a multicarrier communication channel in accordance with an OFDMA communication technique. The OFDM signals may comprise a plurality of orthogonal subcarriers. Each of the eNBs 104 may be able to transmit a reconfiguration message to each UE 102 that is connected to that eNB 104. The reconfiguration message may contain reconfiguration information including one or more parameters that indicate specifics about reconfiguration of the UE 102 upon a mobility scenario (e.g., handover) to reduce the latency involved in the handover. The parameters may include physical layer and layer 2 reconfiguration indicators, and a security key update indicator. The parameters may be used to instruct the UE 102 to avoid or skip one or more of the processes indicated to decrease messaging between the UE 102 and the network. The network may be able to automatically route packet data between the UE 102 and the new eNB 104 and may be able to provide the desired information between the eNBs 104 involved in the mobility. The application, however, is not limited to this, however, and additional embodiments are described in more detail below.

[0018] The S 1 interface 1 15 is the interface that separates the RAN 101 and the EPC 120. The SI interface 1 15 may be split into two parts: the Sl-U, which carries traffic data between the eNBs 104 and the serving GW 124, and the S 1 -MME, which is a signaling interface between the eNBs 104 and the MME 122. The X2 interface is the interface between eNBs 104. The X2 interface may comprise two parts, the X2-C and X2-U. The X2-C may be the control plane interface between the eNBs 104, while the X2-U may be the user plane interface between the eNBs 104.

[0019] With cellular networks, LP cells may be used to extend coverage to indoor areas where outdoor signals do not reach well, or to add network capacity in areas with very dense phone usage, such as train stations. As used herein, the term low power (LP) eNB may refer to any suitable relatively low power eNB for implementing a narrower cell (narrower than a macro cell) such as a femtocell, a picocell, or a microcell. Femtocell eNBs may be typically provided by a mobile network operator to its residential or enterprise customers. A femtocell may be typically the size of a residential gateway or smaller and generally connect to the user's broadband line. Once plugged in, the femtocell may connect to the mobile operator's mobile network and provide extra coverage in a range of typically 30 to 50 meters for residential femtocells. Thus, an LP eNB might be a femtocell eNB since it is coupled through the PDN GW 126. Similarly, a picocell may be a wireless communication system typically covering a small area, such as in-building (offices, shopping malls, train stations, etc.), or more recently in-aircraft. A picocell eNB can generally connect through the X2 link to another eNB such as a macro eNB through its base station controller (BSC) functionality. Thus, LP eNB may be implemented with a picocell eNB since it is coupled to a macro eNB via an X2 interface. Picocell eNBs or other LP eNBs may incorporate some or all functionality of a macro eNB. In some cases, this may be referred to as an access point base station or enterprise femtocell.

[0020] Other wireless communication devices may be present in the same geographical region as the RAN 101. As shown in FIG. 1 , WLAN devices including one or more access points (APs) 103 and one or more stations (STAs) 105 in communication with the AP 103. The WLAN devices may communicate using one or more IEEE 802.1 1 protocols, such as IEEE 802.1 la/b/n/ac protocols. As the power of the WLAN devices 103, 105 may be fairly limited, compared with the eNBs 104, the WLAN devices 103, 105 may be

geographically localized.

[0021] Communication over an LTE network may be split up into 10ms frames, each of which contains ten 1ms subframes. Each subframe, in turn, may contain two slots of 0.5ms. Each slot may contain 6-7 symbols, depending on the system used. A resource block (RB) (also called physical resource block (PRB)) may be the smallest unit of resources that can be allocated to a UE 102. A resource block may be 180 kHz wide in frequency and 1 slot long in time. In frequency, resource blocks may be either 12 x 15 kHz subcarriers or 24 x 7.5 kHz subcarriers wide. For most channels and signals, 12 subcarriers may be used per resource block. In Frequency Division Duplexed (FDD) mode, both the uplink and downlink frames may be 10ms and may be frequency (full-duplex) or time (half-duplex) separated. In a Time Division Duplex (TDD) structure, the uplink and downlink subframes may be transmitted on the same frequency and may be multiplexed in the time domain. A downlink resource grid may be used for downlink transmissions from an eNB to a UE. The grid may be a time- frequency grid, which is the physical resource in the downlink in each slot. Each column and each row of the resource grid may correspond to one OFDM symbol and one OFDM subcarrier, respectively. The duration of the resource grid in the time domain may correspond to one slot. The smallest time-frequency unit in a resource grid may be denoted as a resource element. Each resource grid may comprise a number of the above resource blocks, which describe the mapping of certain physical channels to resource elements. Each resource block may comprise 12 (subcarriers) * 14 (symbols) =168 resource elements.

[0022] There may be several different physical downlink channels that are conveyed using such resource blocks. Two of these physical downlink channels may be the physical down link control channel (PDCCH) and the physical downlink shared channel (PDSCH). Each subframe may be partitioned into the PDCCH and the PDSCH. The PDCCH may normally occupy the first two symbols of each subframe and carry, among other things, information about the transport format and resource allocations related to the PDSCH channel, as well as H-ARQ information related to the uplink shared channel. The PDSCH may carry user data and higher- layer signaling to a UE 102 and occupy the remainder of the subframe. Typically, downlink scheduling (assigning control and shared channel resource blocks to UEs 102 within a cell) may be performed at the eNB 104 based on channel quality information provided from the UEs 102 to the eNB, and then the downlink resource assignment information may be sent to each UE 102 on the PDCCH used for (assigned to) the UE 102. A TTI Transmission Time Interval (TTI) may be the smallest unit of time in which an eNB 104 is capable of scheduling a UE 102 for uplink or downlink transmission. The PDCCH may contain downlink control information (DCI) in one of a number of formats that tell the UE 102 how to find and decode data, transmitted on PDSCH in the same subframe, from the resource grid. The DCI format may provide details such as number of resource blocks, resource allocation type, modulation scheme, transport block, redundancy version, coding rate etc. Each DCI format may have a cyclic redundancy code (CRC) and may be scrambled with a Radio Network Temporary Identifier (RNTI) that identifies the target UE 102 for which the PDSCH is intended. Use of the UE 102-specific RNTI may limit decoding of the DCI format (and hence the corresponding PDSCH) to only the intended UE 102.

[0023] FIG. 2 is a functional diagram of a 3 GPP device in accordance with some embodiments. The device may be a UE or eNB, for example, such as the UE 102 or eNB 104 shown in FIG. 1 that may be configured to track the UE as described herein. In some embodiments, the eNB may be a stationary non- mobile device. The 3GPP device 200 may include physical layer circuitry 202 for transmitting and receiving signals using one or more antennas 201. The antennas 201 on the eNB 104 may permit the eNB 104 to use beamforming. The beamforming may be provided via one or more of a directional antenna, phased array antennas, or antennas with multiple apertures for directional transmissions. Tracking, as described below, may be used to train an analog beamforming matrix to obtain an optimal direction to communicate with the eNB 104 and perform wideband channel sounding, which can be used in physical control channel decoding and digital beamforming refinement, using the antennas 201 on the eNB 104 and UE 102.

[0024] The 3GPP device 200 may also include medium access control layer (MAC) circuitry 204 for controlling access to the wireless medium. The 3 GPP device 200 may also include processing circuitry 206, such as one or more single-core or multi-core processors, and memory 208 arranged to perform the operations described herein. The physical layer circuitry 202, MAC circuitry 204 and processing circuitry 206 may handle various radio control functions that enable communication with one or more radio networks compatible with one or more radio technologies. The radio control functions may include signal modulation, encoding, decoding, radio frequency shifting, etc. For example, in some embodiments, communication may be enabled with one or more wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), and a wireless personal area network (WPAN). In some embodiments, the device can be configured to operate in accordance with 3 GPP standards or other protocols or standards, including Institute of Electrical and Electronic Engineers (IEEE) 802.16 wireless technology (WiMax), IEEE 802.1 1 wireless technology (WiFi) including IEEE 802 ad, which operates in the 60 GHz millimeter wave spectrum, various other wireless technologies such as global system for mobile communications (GSM), enhanced data rates for GSM evolution (EDGE), GSM EDGE radio access network (GERAN), universal mobile telecommunications system (UMTS), UMTS terrestrial radio access network (UTRAN), or other 2G, 3G, 4G, 5G, etc. technologies either already developed or to be developed.

[0025] In some embodiments, mobile devices or other devices described herein may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a smartphone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other device that may receive and/or transmit information wirelessly. In some embodiments, the device 200 may include one or more user interfaces designed to enable user interaction with the system and/or peripheral component interfaces designed to enable peripheral component interaction with the system. For example, the device 200 may include one or more of a keyboard, a keypad, a touchpad, a display, a sensor, a non-volatile memory port, a universal serial bus (USB) port, an audio jack, a power supply interface, one or more antennas, a graphics processor, an application processor, a speaker, a microphone, and other I/O components. The display may be an LCD or LED screen including a touch screen. The sensor may include a gyro sensor, an accelerometer, a proximity sensor, an ambient light sensor, and a positioning unit. The positioning unit may communicate with components of a positioning network, e.g., a global positioning system (GPS) satellite.

[0026] The antennas 201 may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some multiple-input multiple-output (MIMO) embodiments, the antennas 201 may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result.

[0027] Although the 3 GPP device 200 is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements may refer to one or more processes operating on one or more processing elements.

[0028] Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable storage device, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable storage device may include any non-transitory mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a computer-readable storage device may include readonly memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. Some embodiments may include one or more processors and may be configured with instructions stored on a computer-readable storage device.

[0029] The term "machine readable medium" may include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) configured to store one or more instructions. The term "machine readable medium" may include any medium that is capable of storing, encoding, or carrying instructions for execution by the 3GPP device 200 and that cause it to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. The term "transmission medium" shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution, and includes digital or analog

communications signals or other intangible medium to facilitate communication of such software. In some embodiments, some of the elements described in FIG. 2 may be omitted or additional elements may be provided. The device shown and described herein is thus not limited to the embodiment shown in FIG. 2.

[0030] As above, for 5G systems, link maintenance may be UE or UE group-specified, leading to the desire for the network to not only constantly track active UEs 102 or UE groups by the eNBs 104, but in addition employ functionality dependent on the tracking. Tracking may occur after the UE 102 has been associated with and synchronized to a serving eNB 104 (as determined by control signal measurement, for example), and beam alignment between the eNBs 104 and the UE 102 has occurred so that a connection is established. In particular, for each active UE or UE group it may be desirable for the network to obtain the link status of the UE or UE group and adjust beamforming to maintain link budget, so that when traffic arrives for the UE a communication link between the eNB 104 and the UE 102 is able to be established. The beamforming may be performed by multiple eNBs 104 acting in concert with the appropriate phase differences to provide the desired beam index (or direction) for communication with the UE 102 or UEs 102 in the tracking group. Tracking by the UEs 102 or the eNBs 104 may be performed using a tracking reference signal first within one or more TTIs, following which a downlink control channel (PDCCH) may be conveyed to the scheduled UEs 102 or an uplink control channel (PUCCH) may be transmitted to the serving eNB 104. The tracking reference signal transmitted by the UE 102 or eNB 104 may also serve as a reference signal for wideband channel sounding. If precoding is used to minimize the error at the receiver, the tracking reference signal, whether transmitted by the UE 102 or the eNB 104, may be added prior to or after precoding.

[0031] FIG. 3 illustrates a Time Division Duplex (TDD) frame structure in accordance with some embodiments. The TDD frame structure may be used by the UEs 102 and eNBs 104 shown in FIG. 1. As shown in FIG. 3, the frame 302 contains 10 subframes 304, each of which may be a sync subframe 312, an uplink (UL) subframe 314, or a downlink (DL) subframe 316. The sync subframe 312 may permit UEs 102 to synchronize with the eNB 104, while the UL subframes 314 and DL subframes 316 may provide time for data to be respectively sent from the UE 102 to the eNB 104 and from the eNB 104 to the UE 102. A complete DL and UL tracking may include multiple subframes. A tracking subframe group may be defined as the group of subframes for a complete tracking. One UE tracking group may be defined as the UEs 102 that are tracked simultaneously by the eNB 104. The UE tracking group may be dynamically configurable, that is, UEs 102 in the group may change from time to time. The UE tracking group may be, for example, the group of UEs 102 scheduled in MU-MIMO transmission.

[0032] In FIG. 3, the TDD frame shown has symmetric DL and UL subframes 314, 316; every DL subframe 314 alternates with a UL subframe 316. In this case, the tracking subframe group may accordingly consist of one DL subframe 314 and one UL subframe 316. Although not shown in FIG. 3 for convenience, in some embodiments a portion of the active UEs 102 may be tracked in each DL and UL subframe.

[0033] The DL subframe 314 may contain three sections: a tracking interval 322 in which the tracking reference signals are transmitted from the eNB 104 to the UEs 102 and may be used for sounding, a dedicated DL control interval 324 containing control signals for the UE 102, and a DL data/per port demodulation reference signals interval 326 carrying data for the UE 102 from the eNB 104. The UL subframe 316 may similarly contain three sections: a tracking and sounding interval 342 in which tracking reference signals are transmitted from the UE 102 to the eNB 104, a dedicated UL control interval 344 containing control signals for the eNB 104, and a UL data/per port demodulation reference signals interval 346 carrying data for the eNB 104 from the UE 102. Either or both the various UL and DL intervals may be in any order within the particular subframe. The proportions of the intervals shown in the DL subframe 314 and UL subframe 316 may differ from that show in FIG. 3 (as shown in FIG. 4, in which the tracking intervals are shown as being a small portion of the respective subframe). The DL control signal interval 324 and UL control signal interval 344 may be the PDCCH and PUCCH, respectively. Similarly, the DL data/per port demodulation reference signals interval 326 and UL data/per port demodulation reference signals interval 346 may be the PDSCH and PUSCH, respectively. The symbol(s) used in the tracking/sounding interval 322 may, as shown, be separate from the symbols in either the PDCCH or PUCCH. In some embodiments, one symbol per UE group may be used in the tracking/sounding interval 322. The number of symbols may be configured by control signaling from the eNB 104, such as RRC signaling. Multiple tracking symbols in the tracking/sounding interval 322 may be packed into single OFDM symbol via multiplexing.

[0034] Each tracking interval 322 in the DL subframe 314 may also contain three fields. These fields may include a DL tracking field 334 for the UEs scheduled for DL transmission in the current DL subframe, a UL tracking field 336 for UEs scheduled for UL transmission in the subsequent UL subframe(s) in the frame, and an active tracking field 332 for the active UEs that are to be tracked but are not yet scheduled for data transmission in the tracking subframe group, for each of which different tracking reference signals may be transmitted by the eNB 104. The last group may include UEs that have not been tracked for a predetermined amount of time and thus a tracking update may be desirable. The periodicity of transmission of the tracking reference signals for this last group of UEs may be configured based on the number of UE groups to track, the average rate of speed of UEs in the group, the increase in missed tracking attempts with increasing time, etc.... The tracking fields 332, 334, 336 may be in any order within the tracking and sounding interval 322.

[0035] Likewise, each tracking interval 342 in the UL may have three fields. These fields may similarly include a DL tracking field 354 for scheduled UEs in the next DL subframe(s), a UL tracking field 356 for scheduled UEs in the current UL subframe and an active tracking field 352 for UEs that were tracked in the next DL subframe(s), each of which may transmit different tracking reference signals. The use of a field to track the UEs that are not scheduled for data transmission may maintain the connection between the UEs and the eNB, as the tracking interval for each UE should be less than the channel coherence time. A UE may be tracked if not scheduled within the channel coherence time to maintain the link with the eNB.

[0036] FIG. 4 illustrates another TDD frame structure in accordance with some embodiments. The TDD frame 402 in FIG. 4 is similar to FIG. 3, having sync sub frames 412, DL sub frames 414 and UL sub frames 416, except that the DL and UL sub frames 414, 416 are asymmetric. For a TDD frame with asymmetric DL and UL subframes, each DL subframe may implement DL tracking for UEs in multiple UL subframes or each UL subframe may implement UL tracking for UEs in multiple DL subframes, depending on the structure of the particular TDD frame.

[0037] As shown in FIG. 4, the DL subframes 414 occupy a larger portion of the total resource, as shown there are three times as many DL subframes 414 as UL subframes 416. This is more typical than the subframe 302 of FIG. 3 as there is usually more DL traffic for a UE than UL traffic from the UE. The number of the different types of subframes and location of the subframes within the frame, however, may vary from the examples shown in FIGS. 3 and 4. As in FIG. 4 there are a greater number of DL subframes 414 than UL subframes 416 in the TDD frame 402, and each UL subframe 416 may perform UL tracking for multiple subsequent DL subframes 414. Resources allocated for the tracking field may be configured semi- statically based on the frame structure and the channel dynamics. In particular, the resources allocated for the tracking field may be dependent on the channel coherence time, which is statistical in nature. For example, as the channel coherence time decreases (e.g., as the eNB operates at higher frequencies) and the eNB thus changes channels at a faster rate, a greater number of tracking groups may be in the same interval, thereby increasing the number of resources used by the eNB during the tracking interval. The UEs may be informed about the tracking interval configuration via system broadcasting such as via a system information broadcast (SIB). [0038] As shown in FIG. 4, the first DL subframe 414 in a set of DL subframes may include a tracking interval 420 having two fields: a tracking field 424 for transmitting tracking reference signals to the scheduled UEs in the current DL subframe and a tracking field 422 for transmitting tracking reference signals to the active UEs that are to be tracked but are not yet scheduled for data transmission in the tracking subframe group, which may be in any order. The DL subframe 414 immediately prior to the first UL subframe 416 may include a tracking interval 430 having three fields: a tracking field 434 for transmitting tracking reference signals to the scheduled UEs in the current DL subframe, a tracking field 436 for transmitting tracking reference signals to scheduled UEs in the subsequent UL subframe, and a tracking field 432 for transmitting tracking reference signals to the active UEs that are to be tracked but are not yet scheduled for data transmission in the tracking subframe group, which again may be in any order. As the UL subframe 416 may have several DL subframes 414 to provide tracking for, the tracking interval 440 of the UL subframe 416 may have more fields than either of the DL subframes 414. In particular, as shown, the tracking interval 440 of the UL subframe 416 may contain a separate tracking field 452, 454, 456 for transmitting tracking reference signals to scheduled UEs in each DL subframe before the next UL subframe 416, tracking for transmitting tracking reference signals to scheduled UEs in the current UL subframe 456 and a separate tracking field 442, 444, 446 for transmitting tracking reference signals to UEs that are to be tracked in each DL subframe before the next UL subframe 416, and a tracking field 458 for scheduled UEs in the current UL subframe, which may as above be in any order.

[0039] As illustrated in FIGS. 3 and 4, in each DL and UL subframe, a portion of the active UEs 102 may be tracked. Tracking scheduling (for transmitting the tracking reference signals) may be performed at the eNB 104. With the knowledge of the UEs to be scheduled in the current DL subframe and the subsequent UL subframe(s), the eNB 104 may schedule tracking accordingly. The eNB 104 may inform the UEs of the tracking scheduling in DL control information, such as in the PUCCH (or PUSCH). In each DL subframe, each active UE may monitor the tracking interval, adjust the UE analog beamforming matrix, and perform blind detection (for the particular RNTI in the common and UE-specific search space during PDCCH detection and decoding). When a UE detects a tracking reference signal addressed to an ID of the UE (in the case of a UE-specific tracking signal) or detects channel gain above a predefined threshold (in the case of cell-specific tracking signal), the UE may proceed to detect the downlink control information. The threshold may be configurable, depending on the channel conditions associated with the UE obtained from the previous transmissions. In some embodiments, if the UE detects good channel conditions, the UE may set a higher threshold, while if the UE detects channel conditions have deteriorated, the UE may set a lower threshold. The DL control information may contain information addressed to the UEs that are being tracked in the tracking field. The DL control information may indicate the DL data transmission scheduling for the UEs scheduled in the current DL subframe, indicate the UL tracking and data transmission scheduling to the UEs scheduled in the subsequent UL subframes and indicate the UL tracking scheduling for the UEs that were tracked in the DL subframe. Having obtained the tracking scheduling information, the UE may be able to implement tracking in the subsequent UL subframes in the tracking subframe group.

[0040] FIGS. 5 A and 5B illustrate DL tracking within one tracking field duration in accordance with some embodiments. FIG. 5A shows an embodiment in which channel reciprocality in the TDD frames is assumed. In the DL communication, within each of the tracking fields in one tracking interval, the eNB 504 (abbreviated as Base Station or BS in the figure) may transmit tracking reference signals in N tracking fields 512 to the UEs 502. The number (N) of tracking fields transmitted by the eNB 504 corresponds to the number of tracking groups tracked by the eNB 504 during the particular subframe. The UE groups may include, as indicated in FIGS. 3 and 4, one or more of UEs scheduled for DL transmission in the current DL subframe, UEs scheduled for UL transmission in the subsequent UL subframe(s) in the frame, and active UEs that are to be tracked but are not yet scheduled for data transmission in the tracking subframe group. The tracking reference signals in each tracking field 512 may be transmitted to the UEs in an associated tracking group using a direction obtained over the previous tracking and channel training efforts for the UEs in the tracking group. Thus, the transmission direction for each tracking group may be independent of any other tracking group, i.e., the transmission direction for a particular tracking group may differ or may be the same as that of another tracking group.

[0041] The UEs in each tracking group may perform analog beam scanning for coarse beam tracking to detect the tracking reference signal in the tracking field 512 associated with that tracking group. The UEs may monitor for the tracking reference signal starting with an analog beam direction obtained over an immediate previous tracking interval. Within each analog beam direction, each UE 502 may subsequently perform a refined wideband channel estimation in the digital domain. In some embodiments, multiple UEs may receive the same transmission from the eNB 504 in a particular direction, which may correspond to multi-user MIMO (MU-MIMO) communications in which multiple UEs may be tracked simultaneously. In such embodiments, FDM can also be used for multiplexing multiple UEs in the same tracking duration. After the tracking reference signals in the tracking fields are transmitted by the eNB 504, the eNB 504 may transmit to the UEs 502 the DL and/or UL scheduling 514 described above in relation to FIGS. 3 and 4 in the DL control information. The control information 514 may comprise scheduling for subsequent transmission of an eNB tracking reference signal from the eNB to the UE and/or a UE tracking reference signal from the UE to the eNB, as well as for UL and DL transmissions involving the UE 502. In some embodiments, the tracking signal reference signals in the tracking fields 512 and the control information 514 can be time-multiplexed such that DL tracking is followed by DL control.

[0042] Subsequent to transmission of the DL and/or UL scheduling 514, the UEs 502 in the UE tracking fields 516 may transmit tracking reference signals simultaneously from their respective directions obtained from the previous tracking effort during UL tracking transmission times. Similar to the DL tracking transmission, the eNB 504 may receive the tracking reference signal transmissions from the UEs in the tracking group of a particular direction and perform analog beam scanning for coarse analog beam tracking and digital domain wideband channel sounding for refined tracking. Unlike the DL transmissions from the eNB 504, in which there were N tracking fields associated with the UEs 502, there may be M tracking fields associated with the different UEs 502 for UL transmissions, dependent, as shown in FIGS. 3 and 4 on the relationship between UL and DL subframes within the frame. Thus, as shown in FIG. 3 for example, N=M for a symmetric TDD case. Subsequently, the UEs 502 may transmit to the eNB 504 a UL control report 518. The tracking signal reference signals in the tracking fields 516 and the control report 518, similar to the above, can be time-multiplexed such that UE tracking is followed by UL control.

[0043] As above, FIG. 5A assumes channel reciprocality in the TDD frames. For TDD (and FDD) frames without channel reciprocality (for example, using different antenna sets), shown in FIG. 5B, transmission analog beam scanning may also be used in each DL tracking field 522. The receiver may detect the best transmission analog beam directions and provide feedback of this information via the UE report 518 on a control channel.

[0044] As in FIG. 5A, within each of the tracking fields in one tracking interval of the DL communication 522 in FIG. 5B, the eNB 504 may transmit tracking reference signals to the UEs 502 in each of N tracking fields 512 corresponding to the number of tracking groups that the eNB 504 is tracking during the subframe. However, unlike FIG. 5A, the eNB 504 may perform a transmission scan within each tracking field. The UEs in each tracking group may perform analog beam scanning for coarse beam tracking to detect the tracking field 522 associated with that tracking group. Within each analog beam direction, each UE 502 may subsequently perform a refined wideband channel estimation in the digital domain. The eNB 504 may then report to the UEs 502 the best transmission direction in the DL control signal 524 following the tracking field transmissions. The eNB 504 may again transmit to the UEs 502 the DL and/or UL scheduling 524 above.

[0045] Subsequent to transmission of the DL and/or UL scheduling 526, the UEs 502 may transmit simultaneously from their respective directions during a UL tracking field 528. Similar to the DL tracking transmission, the UEs 502 may perform a transmission scan within each tracking field. The eNB 504 may receive the transmissions from the UEs in the tracking group of a particular direction and perform analog beam scanning for coarse analog beam tracking and digital domain wideband channel sounding for refined tracking. The UEs 502 may then report to the eNB 504 the best transmission direction in the UL control signal 532 following the UL tracking field transmissions 528.

[0046] In designing the tracking reference signal, several aspects may be considered. The tracking signal may be used by the UE (or eNB) to perform the wideband channel sounding indicated above. Assuming the eNB or UE has Mt physical antennas, Nt RF+ADC/DAC chains and Nt analogy beams, the number of tracking reference signals that may be simultaneously transmitted is Nt. To reduce tracking overhead, it may be desirable for a tracking signal to be able to support beam scanning within one OFDM symbol. The tracking reference signal may be used for channel estimation for the subsequent control channel.

Therefore, it may be desirable for the length of the tracking reference signal to be longer than NBW/MC, where NBW is the number of resource elements for a given system bandwidth, and Mc is the number of resource elements in the coherence bandwidth. The tracking signal may be either cell-specified or UE- specified.

[0047] Based on the above considerations, a possible choice for the tracking reference signal is to use a Zadoff-Chu sequence similar to a PUSCH demodulation reference signal (DMRS). The tracking reference signal applied in each antenna port of the UE or eNB may be a cyclic shift of the base sequence. To support analog beam scanning in Q direction combinations, the subcarrier spacing for transmitting the tracking reference signal can be Q times that used for data transmission. In the time domain, the tracking reference signal may be repeated Q times in one symbol.

[0048] When choosing the Q value, other aspects may be considered. These include robustness of the tracking and the length of the tracking reference signal. For robust tracking, a greater number of directions may be scanned in each tracking effort, which means a larger Q value. The tracking robustness can be evaluated by determining the miss tracking probability (the probability of having missed a UE during tracking). The tracking reference signal length, as indicated above, should be longer than NBW/MC. AS a result, it may be desirable for the Q values to be less than Mc. If it is desired to scan more than Q beam directions, then an increased number of OFDM symbols may be used. The Q value can be configurable, depending on channel dynamics, desired tracking robustness, and overhead budget. A larger Q value may be expected when multiple analog beams are used.

[0049] Regarding tracking scheduling, as mentioned above, selected groups of UEs may be tracked in each subframe. For UEs having a pending data transmission, the tracking scheduling can be done together with DL and UL data transmission scheduling. In this case, while scheduling the data transmission, the tracking interval may be taken into consideration, i.e., the tracking interval should be less than the channel coherence time. For the UEs that are active but do not have a pending UL or DL data transmission, the tracking scheduler may schedule tracking within the channel coherence time of the second order statistics so that the active UEs are able to maintain their link connection and report back channel state information to the eNB.

[0050] In support of the tracking operation, various pieces of information may be provided in the DL control signal 514, 526. The DL control signal may contain, for example, the tracking scheduling in the current DL subframe. This information may be combined with the DL control information for data transmission scheduling in the current subframe. In addition, the DL control signal may contain the tracking scheduling for subsequent UL subframes for the tracking subframe group. The tracking scheduling for the UEs that are tracked in the current tracking subframe group but not scheduled for data transmission may also be provided in the DL control signal.

[0051] The DL control signal may contain several intervals and thresholds, for example, the tracking time interval as well as the missed tracking time threshold. The latter of these is the time threshold for the UE to detect that it has missed a tracking signal. Further, for non-reciprocal transmission and reception opportunities, the DL control may indicate the best transmission direction for the UE.

[0052] The UL control report 518, 532 may contain similar information.

For example, the UL control report 518, 532 may carry channel state information feedback of the tracked-but-not-scheduled UEs. The UL control signal may also carry a scheduling request of a tracked-but-not-scheduled UE if the UE has pending UL traffic. For non-reciprocal transmission and reception opportunities, the UL control signal may also indicate the best transmission direction to the eNB. Tracking scheduling for both DL and UL may thus be performed by the eNB 504.

[0053] As mentioned above, a SIB may be used to inform the UEs about the tracking interval configuration. In some embodiments, the SIB may be broadcast from different types of eNBs, including an LTE macro eNB (also called an anchor eNB), a low power eNB (such as an access point) or from a mmWave (5G) eNB. To assist tracking, the maximum tracking time interval, the UE re-sync time interval and the time threshold for deciding the occurrence of blockage of the eNB signal may be used. The UE is scheduled to be tracked over the maximum tracking time interval. The actual tracking interval can be reset (semi-dynamically) to a smaller value by the physical control. The semi- dynamic tracking interval setting may, for example, depend on the channel coherence time. The UE re-sync time interval is the time interval that the UE uses to monitor and detect system synchronization signals.

[0054] Missed tracking, blockage and channel reacquisition may be determined by either or both the eNB or the UE. FIGS. 6A and 6B illustrate eNB and UE lost-tracking detection and recovery procedure, respectively, in accordance with some embodiments. The UEs and eNBs shown in FIGS. 6A and 6B may be the UEs and eNBs shown in FIG. 1. In FIG. 6A, the UE 602 is served by a mmWave eNB 604 which is connected with the anchor (LTE macro) eNB 606. The anchor eNB 606 may have a wider coverage than the mmWave eNB 604, operating at a lower frequency band and thus able to broadcast to UEs without having to worry about directionality as the mmWave eNB 604.

[0055] The mmWave eNB 604 may initiate multiple tracking attempts 612. The mmWave eNB 604 may, if no UE UL tracking or feedback is detected after a predetermined number of attempts, schedule follow up tracking attempts after a predetermined time. Whether or not the follow-up attempts are performed, the mmWave eNB 604 may determine that it has lost track of the UEs and may report the loss to the anchor eNB in a UE loss signal 614.

[0056] The anchor eNB 606 may then inform the UE 602 about the missed tracking attempts via an anchor air interface between the anchor eNB 606 and the UE 602 using a re-sync message 616. The UE 602, upon receiving the re-sync message 616 may initiate a UE resync procedure 618 with the mmWave eNB 604. If, after a predetermined number of attempts or time to resync with the mm Wave eNB 604 the UE 602 is unable to establish a connection with the mm Wave eNB 604, the UE 602 may report that a blockage has occurred between it and the mm Wave eNB 604 to the anchor eNB 606.

[0057] Similarly, FIG. 6B a UE-initiated missed tracking detection procedure. Specifically, the mmWave eNB 604 may again initiate multiple tracking attempts 612. However, in this embodiment, rather than the mm Wave eNB 604 determining whether or not UE UL tracking or feedback has been detected, the UE 602 may determine whether or not it has detected a tracking reference signal within a preset amount of time. The preset amount of time may differ from the time used for the number of tracking attempts in FIG. 6A and may be, for example, transmitted to the UE 602 via a control channel signal or SIB. The preset time may thus be configurable, or in some embodiments may be preset and unchangeable. After the preset time has elapsed, the UE 602 may initiate the UE resync procedure 618. As in FIG. 6A, in FIG. 6B if, after a predetermined number of attempts or time to resync with the mm Wave eNB 604 the UE 602 is unable to establish a connection with the mmWave eNB 604, the UE 602 may report that a blockage has occurred between it and the mmWave eNB 604 to the anchor eNB 606.

[0058] In some embodiments, the processes of FIGS. 6A and 6B may be combined such that both the mmWave eNB 604 and the UE 602 may determine whether tracking attempts by the mmWave eNB 604 are likely to have been missed by the UE 602. In this case, for example, if the UE 602 has not received any tracking attempts, nor a re-sync message 616 from the anchor eNB 606, the UE 602 may automatically engage the re-sync process 618. In both the eNB- based and UE-based missed tracking detection procedure shown in FIGS. 6A and 6B, if the mmWave eNB 604 does not hear from the UE UL tracking or reporting as scheduled, the mmWave eNB 604 may reduce the tracking interval for the UE 602. That is the mmWave eNB 604 may schedule more frequent tracking to the UE 602.

[0059] In some embodiments, a backup beam can be maintained by the

UE to provide diversity for quick missed tracking recovery. The backup beam may operate using a different channel. The backup beam channel may have lower channel quality than channel used for the main beam. The use of beam diversity (the backup beam kept in reserve) may increase the tracking overhead significantly. The decision of whether or not to enable beam diversity, however, may be decided based on the recovery time for missed tracking opportunities in addition to the tracking overhead alone. If link robustness and speedy recovery of missed tracking is paramount, then beam diversity may be enabled. If, however, keeping tracking overhead low is more desirable, then beam diversity may be disabled. The decision of whether or not to use tracking diversity, if available, may be made depending on the expected QoS of the UE, the type of application providing data, the type of UE, etc...

[0060] Moreover, either or both the size of the tracking field and the control channel may be configurable. The configuration information may be provided by higher layer signaling via master information block (MIB), SIB or dedicated RRC signaling from a macro cell or small cell. Resources allocated for tracking may depend on the number of antennas used for tracking by the eNB, the number of simultaneously supported streams/users, the degree of beam diversity, and the channel variations (i.e., coherence time). With analog beamforming, the control channel may be transmitted directionally and is thus dedicated control may be used. The size of the control channel in the DL and UL may also be configurable, depending on the number of UEs to be supported and the resources used for scheduling information and channel state information reporting. Bi-directional and configurable tracking and control resource may enable symmetric DL and UL tracking. The directional transmission may also help in reducing interference and improve control channel robustness.

[0061] Besides being used in an LTE-based network, similar features may be used for device-to-device (D2D) communications and networks. The symmetric and asymmetric frame structures shown in FIGS. 3 and 4 may be applied to D2D communications, although the symmetric frame structure in FIG. 3 may facilitate tracking in such communications. In particular, when applied in D2D communications, the wireless device acting as transmitter may be responsible for tracking and data transmission scheduling. The physical control channel of the transmitting wireless device may be configured to support the tracking and transmission functionalities. [0062] FIGS. 3 and 4 show general frame structures including a tracking field, a physical control field and a data field. In some embodiments, the tracking field and control field shown may be time multiplexed. As wideband channel estimation is conducted during tracking, the use of a time-multiplexing approach may give more accurate channel information for decoding the control channel. The time slot assigned for tracking may also be able to carry physical control information by multiplexing the tracking reference signal and physical control information. Generally, if the coherence bandwidth of the tracking signal is large and the number of analog beams to be scanned is less than the number of REs within the coherence bandwidth, the tracking reference signal may be multiplexed with the physical control information in one OFDM symbol. This is to say that, assuming the number of REs within the coherence bandwidth is N and the number of analog beam directions to be scanned is M, then within one OFDM symbol, M/N portion of the resource may be used for tracking and (N-M)/N portion of the resource may be used for downlink control. In the UL, the tracking signal may be able to carry a scheduling request.

[0063] FIG. 7 illustrates a flowchart of beam tracking in accordance with some embodiments. The method shown by the flowchart may be performed by one of the eNBs in FIGS. 1-6B. At operation 702, a UE may connect to and synchronize with an eNB. The eNB may be a 5G eNB operating in the mm wave bandwidth of around 6GHz. In this case, the UE and eNB may determine an initial beam alignment to enable communication between the two. The UE may be informed about the tracking interval configuration when tracking reference signals, if present, are to be expected within each subframe via RRC signaling or a SIB. The tracking interval for the UE may be less than the channel coherence time.

[0064] At operation 704, the eNB may determine whether there is data to be transmitted between the eNB and the UE (or a UE tracking group using the same beam index). The data may be DL data scheduled for transmission in the current subframe of the frame. The data may instead be UL data scheduled for transmission in subsequent UL subframe(s) of the frame.

[0065] If no DL or UL data is scheduled for the UE, the eNB may determine whether a tracking period has expired at operation 706. As the alignment between the UE and eNB may change over time, even if no data has been transmitted to or from the UE over the tracking period, tracking may be desirable to maintain a connection between the UE and eNB. If no DL or UL data is scheduled for the UE and the tracking period has not expired at operation 706, the eNB may return to operation 704 where the eNB may wait for the next DL subframe to determine whether or not to transmit a tracking reference signal to the UE.

[0066] At operation 708, the eNB determines whether reciprocality (the

UE and eNB use the same beam index) is present in the TDD frame structure. If reciprocality is present, the eNB may skip to operation 716.

[0067] If at operation 708, the eNB determines that reciprocality is not present, the eNB may perform transmission analog beam scanning at operation 710. The transmission analog beam scanning may be used to determine the best transmission direction for the eNB to communicate with the UE.

[0068] The eNB may at operation 712 transmit the best transmission direction for the eNB to communicate with the UE to the UE for the UE to use in setting the UE beam directionality. The eNB may report to the UE the best transmission direction in the DL control signal following the tracking reference signal transmission.

[0069] If DL or UL data is scheduled for the UE at operation 704 or the tracking period has expired at operation 706, the eNB may transmit the tracking reference signal to the UE at operation 714. The tracking reference signal may also serve as a reference signal for wideband channel sounding. The tracking reference signal applied to each antenna port of the eNB may be a cyclically- shifted Zadoff-Chu base sequence, which may be a predetermined times in one OFDM symbol. The UE may perform analog beam scanning for coarse beam tracking to detect the tracking reference signal and subsequently perform a refined wideband channel estimation in the digital domain. This may occur prior to the transmission at operation 712.

[0070] After the tracking reference signal has been transmitted to the UE

(and all other tracking reference signals have been transmitted), at operation 716, the eNB may transmit control information in a PDCCH. The eNB may inform the UE of the DL data transmission and tracking scheduling in the control information. In each DL subframe, each active UE may monitor the tracking interval, adjust the beamforming matrix, and perform blind detection to detect the tracking reference signal. When the UE detects the tracking reference signal addressed to an ID of the UE or detects channel gain above a configurable threshold (dependent, for example, on channel conditions), the UE may proceed to detect the control information and implement tracking in subsequent UL subframes.

[0071] Although not shown, a similar set of operations may occur on the

UE side subsequent to transmission of the tracking reference signal. In addition, the eNB and/or UE may determine whether the tracking reference signal has been received by the UE (e.g., whether blocking has occurred) and, if not, attempt a re-synchronization with the eNB. In some embodiments in which the eNB makes the determination, if the eNB determines that no UE UL tracking or control feedback has been received, the eNB may report this to the anchor eNB. The anchor eNB may, in response, transmit control signaling to the UE instructing the UE to re-sync with the eNB. After attempting and failing to re- sync with the eNB, the UE may report a blockage to the eNB. In some embodiments in which the UE makes the determination, the UE may attempt to re-sync with the eNB without being instructed by the anchor eNB and subsequently report a blockage to the eNB if re-syncing ends in failure. In some embodiments, the eNB or UE may use a backup beam to provide diversity for quick missed tracking recovery after determining that the tracking reference signal has not been received by the UE.

[0072] In addition, although eNBs communicating with UEs using mm wavelength signals has been described, the embodiments are not limited solely to eNBs operating on such wavelengths. Similar procedures may be used for eNBs using antenna arrays and/or directional antennas that operate at lower frequencies, such as LTE eNBs.

[0073] As used herein, the term "circuitry" may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. In some embodiments, the circuitry may be implemented in, or functions associated with the circuitry may be implemented by, one or more software or firmware modules. In some embodiments, circuitry may include logic, at least partially operable in hardware.

[0074] Embodiments described herein may be implemented into a system using any suitably configured hardware and/or software. FIG. 8 illustrates example components of a UE in accordance with some embodiments. In some embodiments, the UE 800 may include application circuitry 802, baseband circuitry 804, Radio Frequency (RF) circuitry 806, front-end module (FEM) circuitry 808 and one or more antennas 810, coupled together at least as shown.

[0075] The application circuitry 802 may include one or more application processors. For example, the application circuitry 802 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include any combination of general-purpose processors and dedicated processors (e.g., graphics processors,

application processors, etc.). The processors may be coupled with and/or may include memory/storage and may be configured to execute instructions stored in the memory/storage to enable various applications and/or operating systems to run on the system.

[0076] The baseband circuitry 804 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The baseband circuitry 804 may include one or more baseband processors and/or control logic to process baseband signals received from a receive signal path of the RF circuitry 806 and to generate baseband signals for a transmit signal path of the RF circuitry 806. Baseband processing circuity 804 may interface with the application circuitry 802 for generation and processing of the baseband signals and for controlling operations of the RF circuitry 806. For example, in some embodiments, the baseband circuitry 804 may include a second generation (2G) baseband processor 804a, third generation (3G) baseband processor 804b, fourth generation (4G) baseband processor 804c, and/or other baseband processor(s) 804d for other existing generations, generations in development or to be developed in the future (e.g., fifth generation (5G), 6G, etc.). The baseband circuitry 804 (e.g., one or more of baseband processors 804a-d) may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry 806. The radio control functions may include, but are not limited to, signal modulation/demodulation,

encoding/decoding, radio frequency shifting, etc. In some embodiments, modulation/demodulation circuitry of the baseband circuitry 804 may include Fast-Fourier Transform (FFT), precoding, and/or constellation

mapping/demapping functionality. In some embodiments, encoding/decoding circuitry of the baseband circuitry 804 may include convolution, tail-biting convolution, turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoder functionality. Embodiments of modulation/demodulation and encoder/decoder functionality are not limited to these examples and may include other suitable functionality in other embodiments.

[0077] In some embodiments, the baseband circuitry 804 may include elements of a protocol stack such as, for example, elements of an evolved universal terrestrial radio access network (EUTRAN) protocol including, for example, physical (PHY), media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), and/or radio resource control (RRC) elements. A central processing unit (CPU) 804e of the baseband circuitry 804 may be configured to run elements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP and/or RRC layers. In some embodiments, the baseband circuitry may include one or more audio digital signal processor(s) (DSP) 804f. The audio DSP(s) 804f may be include elements for

compression/decompression and echo cancellation and may include other suitable processing elements in other embodiments. Components of the baseband circuitry may be suitably combined in a single chip, a single chipset, or disposed on a same circuit board in some embodiments. In some embodiments, some or all of the constituent components of the baseband circuitry 804 and the application circuitry 802 may be implemented together such as, for example, on a system on a chip (SOC).

[0078] In some embodiments, the baseband circuitry 804 may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry 804 may support communication with an evolved universal terrestrial radio access network (EUTRAN) and/or other wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), a wireless personal area network (WPAN). Embodiments in which the baseband circuitry 804 is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry.

[0079] RF circuitry 806 may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry 806 may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. RF circuitry 806 may include a receive signal path which may include circuitry to down-convert RF signals received from the FEM circuitry 808 and provide baseband signals to the baseband circuitry 804. RF circuitry 806 may also include a transmit signal path which may include circuitry to up-convert baseband signals provided by the baseband circuitry 804 and provide RF output signals to the FEM circuitry 808 for transmission.

[0080] In some embodiments, the RF circuitry 806 may include a receive signal path and a transmit signal path. The receive signal path of the RF circuitry 806 may include mixer circuitry 806a, amplifier circuitry 806b and filter circuitry 806c. The transmit signal path of the RF circuitry 806 may include filter circuitry 806c and mixer circuitry 806a. RF circuitry 806 may also include synthesizer circuitry 806d for synthesizing a frequency for use by the mixer circuitry 806a of the receive signal path and the transmit signal path. In some embodiments, the mixer circuitry 806a of the receive signal path may be configured to down-convert RF signals received from the FEM circuitry 808 based on the synthesized frequency provided by synthesizer circuitry 806d. The amplifier circuitry 806b may be configured to amplify the down-converted signals and the filter circuitry 806c may be a low-pass filter (LPF) or band-pass filter (BPF) configured to remove unwanted signals from the down-converted signals to generate output baseband signals. Output baseband signals may be provided to the baseband circuitry 804 for further processing. In some embodiments, the output baseband signals may be zero-frequency baseband signals, although this is not a requirement. In some embodiments, mixer circuitry 806a of the receive signal path may comprise passive mixers, although the scope of the embodiments is not limited in this respect.

[0081] In some embodiments, the mixer circuitry 806a of the transmit signal path may be configured to up-convert input baseband signals based on the synthesized frequency provided by the synthesizer circuitry 806d to generate RF output signals for the FEM circuitry 808. The baseband signals may be provided by the baseband circuitry 804 and may be filtered by filter circuitry 806c. The filter circuitry 806c may include a low-pass filter (LPF), although the scope of the embodiments is not limited in this respect.

[0082] In some embodiments, the mixer circuitry 806a of the receive signal path and the mixer circuitry 806a of the transmit signal path may include two or more mixers and may be arranged for quadrature downconversion and/or upconversion respectively. In some embodiments, the mixer circuitry 806a of the receive signal path and the mixer circuitry 806a of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g.,

Hartley image rejection). In some embodiments, the mixer circuitry 806a of the receive signal path and the mixer circuitry 806a may be arranged for direct downconversion and/or direct upconversion, respectively. In some embodiments, the mixer circuitry 806a of the receive signal path and the mixer circuitry 806a of the transmit signal path may be configured for super-heterodyne operation.

[0083] In some embodiments, the output baseband signals and the input baseband signals may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, the output baseband signals and the input baseband signals may be digital baseband signals. In these alternate embodiments, the RF circuitry 806 may include analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry and the baseband circuitry 804 may include a digital baseband interface to communicate with the RF circuitry 806.

[0084] In some dual-mode embodiments, a separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the embodiments is not limited in this respect.

[0085] In some embodiments, the synthesizer circuitry 806d may be a fractional-N synthesizer or a fractional N/N+l synthesizer, although the scope of the embodiments is not limited in this respect as other types of frequency synthesizers may be suitable. For example, synthesizer circuitry 806d may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer comprising a phase-locked loop with a frequency divider.

[0086] The synthesizer circuitry 806d may be configured to synthesize an output frequency for use by the mixer circuitry 806a of the RF circuitry 806 based on a frequency input and a divider control input. In some embodiments, the synthesizer circuitry 806d may be a fractional N/N+l synthesizer.

[0087] In some embodiments, frequency input may be provided by a voltage controlled oscillator (VCO), although that is not a requirement. Divider control input may be provided by either the baseband circuitry 804 or the applications processor 802 depending on the desired output frequency. In some embodiments, a divider control input (e.g., N) may be determined from a lookup table based on a channel indicated by the applications processor 802.

[0088] Synthesizer circuitry 806d of the RF circuitry 806 may include a divider, a delay-locked loop (DLL), a multiplexer and a phase accumulator. In some embodiments, the divider may be a dual modulus divider (DMD) and the phase accumulator may be a digital phase accumulator (DPA). In some embodiments, the DMD may be configured to divide the input signal by either N or N+1 (e.g., based on a carry out) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded, tunable, delay elements, a phase detector, a charge pump and a D-type flip-flop. In these embodiments, the delay elements may be configured to break a VCO period up into Nd equal packets of phase, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle.

[0089] In some embodiments, synthesizer circuitry 806d may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with quadrature generator and divider circuitry to generate multiple signals at the carrier frequency with multiple different phases with respect to each other. In some embodiments, the output frequency may be a LO frequency (fLo). In some embodiments, the RF circuitry 806 may include an IQ/polar converter.

[0090] FEM circuitry 808 may include a receive signal path which may include circuitry configured to operate on RF signals received from one or more antennas 810, amplify the received signals and provide the amplified versions of the received signals to the RF circuitry 806 for further processing. FEM circuitry 808 may also include a transmit signal path which may include circuitry configured to amplify signals for transmission provided by the RF circuitry 806 for transmission by one or more of the one or more antennas 810.

[0091] In some embodiments, the FEM circuitry 808 may include a

TX/RX switch to switch between transmit mode and receive mode operation. The FEM circuitry may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry may include a low-noise amplifier (LNA) to amplify received RF signals and provide the amplified received RF signals as an output (e.g., to the RF circuitry 806). The transmit signal path of the FEM circuitry 808 may include a power amplifier (PA) to amplify input RF signals (e.g., provided by RF circuitry 806), and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas 810.

[0092] In some embodiments, the UE device 100 may include additional elements such as, for example, memory/storage, display, camera, sensor, and/or input/output (I/O) interface.

[0093] Example 1 is an apparatus of user equipment (UE) comprising: a transceiver arranged to communicate with an enhanced NodeB (eNB) using beamformed signals; and processing circuitry arranged to: configure the transceiver to monitor for an eNB tracking reference signal associated with the UE from the eNB in a downlink (DL) subframe in an eNB tracking interval, the transceiver configured to, during the eNB tracking interval, perform beam scanning for coarse beam refinement for fine beam tracking based on the eNB tracking reference signal; and in response to detection of the eNB tracking reference signal, train a beamforming matrix of the UE and perform wideband channel sounding based on the detected eNB tracking reference signal to determine a desired direction for communication with the eNB. [0094] In Example 2, the subject matter of Example 1 optionally includes that the processing circuitry is further arranged to: configure the transceiver to monitor for the eNB tracking reference signal starting using a beam direction obtained during a previous tracking interval, and the eNB tracking interval is separate from a control interval comprising control signals for the UE and a DL data interval carrying data for the UE and is less than a channel coherence time.

[0095] In Example 3, the subject matter of any one or more of Examples

1-2 optionally include that: the eNB tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in the DL subframe, an uplink (UL) tracking field for UEs scheduled for UL data transmission in an immediately subsequent UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission, and the UE is at least one of: scheduled for DL data transmission in the DL subframe, scheduled for UL data transmission in the immediately subsequent UL subframe, and not scheduled for DL data transmission in the DL subframe, not scheduled for UL data transmission in the immediately subsequent UL subframe and has not been tracked for a predetermined period.

[0096] In Example 4, the subject matter of Example 3 optionally includes that: a size of the one or more of the DL tracking field, the UL tracking field, and the active tracking field and a size of a control channel used to transmit the eNB tracking reference signal are configurable by the eNB.

[0097] In Example 5, the subject matter of any one or more of Examples

1-4 optionally include that the processing circuitry is further arranged to:

configure the transceiver to receive from the eNB control information in the control interval using the direction, the eNB control information comprising tracking scheduling information indicating scheduling for at least one of transmission of an eNB tracking reference signal from the eNB to the UE in the DL subframe and a UE tracking reference signal from the UE to the eNB in an uplink (UL) subframe, the tracking scheduling information combinable with DL control information for data transmission scheduling in the DL subframe.

[0098] In Example 6, the subject matter of Example 5 optionally includes that: the eNB control information further comprises a tracking time interval that the UE is scheduled to be tracked by the eNB and a missed-tracking time threshold that the UE is to use to detect that the UE has missed the eNB tracking reference signal.

[0099] In Example 7, the subject matter of any one or more of Examples

1-6 optionally include that the processing circuitry is further arranged to:

configure the transceiver to receive from the eNB an indication of the direction.

[00100] In Example 8, the subject matter of any one or more of Examples

1-7 optionally include that the processing circuitry is further arranged to:

configure the transceiver to transmit to the eNB, during a UE tracking interval in an uplink (UL) subframe, a UE tracking reference signal using the direction determined by beam training and beam refinement.

[00101] In Example 9, the subject matter of Example 8 optionally includes that: the UE tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in an immediately subsequent DL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the subsequent DL subframe, and the UE is at least one of: scheduled for DL data transmission in the immediately subsequent DL subframe, scheduled for UL data transmission in the UL subframe, and not scheduled for DL data transmission in the immediately subsequent DL subframe, not scheduled for UL data transmission in the UL subframe and has not been tracked for a predetermined period.

[00102] In Example 10, the subject matter of any one or more of

Examples 8-9 optionally include that: the DL and UL subframes are in an asymmetric time division duplexed (TDD) frame comprising a greater number of DL subframes than UL subframes, and the UE tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in each subsequent DL subframe prior to an immediately subsequent UL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the DL subframes prior to the immediately subsequent UL subframe, and the UE is at least one of: scheduled for DL data transmission in one or more of the subsequent DL subframes, scheduled for UL data transmission in the UL subframe, and not scheduled for DL data transmission in the subsequent DL subframes, not scheduled for UL data transmission in the UL subframe and has not been tracked for a predetermined period.

[00103] In Example 1 1, the subject matter of any one or more of

Examples 8-10 optionally include that the processing circuitry is further arranged to: configure the transceiver to transmit to the eNB, after the UE tracking interval, at least one of: a UE control report comprising channel state information feedback from the UE when the UE is not scheduled for data transmission and an indication of the direction, and a UL scheduling request to schedule data transmission during a subsequent UL subframe.

[00104] In Example 12, the subject matter of any one or more of

Examples 1-1 1 optionally include that: the transceiver is arranged to communicate with the eNB using beamformed signals having a frequency about 6 - 60 GHz.

[00105] In Example 13, the subject matter of any one or more of

Examples 1-12 optionally include that the processing circuitry is further arranged to: configure the transceiver to receive, from an anchor eNB in communication with the UE at a frequency lower than the eNB, an instruction to re-synchronize with the eNB, the instruction received after the UE has failed to receive or respond to a plurality of tracking reference signals transmitted by the eNB, configure the transceiver to transmit to the eNB a re-synchronization signal to the eNB, and in response to being unable to re- synchronize with the eNB, configure the transceiver to transmit to the anchor eNB a blockage report indicating a blockage between the UE and the eNB.

[00106] In Example 14, the subject matter of any one or more of

Examples 1-13 optionally include that the processing circuitry is further arranged to: determine that the UE has failed to receive the tracking reference signal during the tracking interval, configure the transceiver to transmit to the eNB a re-synchronization signal, and in response to being unable to re- synchronize with the eNB, configure the transceiver to transmit to the anchor eNB a blockage report indicating a blockage between the UE and the eNB.

[00107] In Example 15, the subject matter of any one or more of

Examples 1-14 optionally include that the processing circuitry is further arranged to: configure the transceiver to at least one of receive the eNB tracking reference signal from the eNB and transmit a UE tracking reference signal to the eNB using a backup beam on a different channel to recover from a missed eNB tracking reference signal and the eNB from a missed UE tracking reference signal, respectively.

[00108] In Example 16, the subject matter of any one or more of

Examples 1-15 optionally include that the processing circuitry is further arranged to: configure the transceiver to receive control information in a system broadcast, the control information comprising at least one of a maximum tracking time interval that the UE is scheduled to be tracked, a UE re-sync time interval that UE is to monitor and detect system synchronization signals, and a blockage time threshold that is a time for the UE to decide that signals from the eNB are blocked.

[00109] In Example 17, the subject matter of any one or more of

Examples 1-16 optionally include, further comprising a plurality of antennas configured to transmit and receive communications between the transceiver and the eNB, the plurality of antennas including one or more of a directional antenna, phased array antennas, and multiple aperture antennas.

[00110] Example 18 is an apparatus of an enhanced NodeB (eNB) comprising: a transceiver arranged to communicate with a plurality of user equipment (UEs) using beamformed signals; and processing circuitry arranged to: group the UEs into UE tracking groups, each UE tracking group associated with a different beamforming direction; configure the transceiver to transmit to each UE in each UE tracking group an eNB tracking reference signal associated with the UE tracking group in a downlink (DL) subframe in an eNB tracking interval; configure the transceiver to receive, from each UE in each UE tracking group, a UE tracking reference signal associated with the UE tracking group in an uplink (UL) subframe in a UE tracking interval; and train a beamforming matrix of the eNB to establish, for each UE tracking group, a direction for transmission to the UE tracking group using at least one of: a UE report from the UE tracking group indicating the direction based on the eNB tracking reference signal the transceiver configured to, during the eNB tracking interval, and beam tuning for beam refinement of the UE tracking reference signals from the UEs of the UE tracking group.

[00111] In Example 19, the subject matter of Example 18 optionally includes that: the eNB tracking reference signal is repeated for each UE tracking group, and the eNB tracking reference signals are transmitted to the UEs in a single Orthogonal Frequency-Division Multiplexing (OFDM) symbol.

[00112] In Example 20, the subject matter of any one or more of

Examples 18-19 optionally include that the processing circuitry is further arranged to: schedule tracking for the UEs for both the DL and UL subframes.

[00113] In Example 21, the subject matter of any one or more of

Examples 18-20 optionally include that the processing circuitry is further arranged to: time multiplex transmission of each eNB tracking reference signal and eNB control information, the eNB control information comprising tracking scheduling information indicating scheduling for at least one of transmission of the eNB tracking reference signal in the DL subframe from the eNB to the UE tracking group and the UE tracking reference signal from the UE tracking group to the eNB in the UL subframe, the tracking scheduling information combinable with DL control information for data transmission scheduling of the UE tracking group in the DL subframe.

[00114] In Example 22, the subject matter of any one or more of

Examples 18-21 optionally include that at least one of: at least one of the eNB tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in the DL subframe, an uplink (UL) tracking field for UEs scheduled for UL data transmission in an immediately subsequent UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission, at least one of the UE tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in an immediately subsequent DL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the subsequent DL subframe, and the DL and UL subframes are in an asymmetric time division duplexed (TDD) frame comprising a greater number of DL subframes than UL subframes, and at least one of the UE tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in each subsequent DL subframe prior to an immediately subsequent UL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the DL subframes prior to the immediately subsequent UL subframe.

[00115] In Example 23, the subject matter of any one or more of

Examples 18-22 optionally include that the processing circuitry is further arranged to: determine that determine that the transceiver has failed to receive at least one of the UE tracking reference signal and UE feedback from at least one UE during the UL tracking interval, configure the transceiver to transmit, to an anchor eNB in communication with the UEs at a frequency lower than the eNB, a report that the transceiver has failed to receive the at least one of the UE tracking reference signal and UE feedback from the at least one UE during the UL tracking interval, and configure the transceiver to receive from the at least one UE, based on the report to the anchor eNB, a re-synchronization signal to resynchronize with the eNB.

[00116] In Example 24, the subject matter of any one or more of

Examples 18-23 optionally include that the processing circuitry is further arranged to: configure the transceiver to at least one of receive the UE tracking reference signal from at least one of the UEs and transmit the eNB tracking reference signal to the at least one of the UEs using a backup beam on a different channel to recover from a missed UE tracking reference signal and the UE from a missed eNB tracking reference signal, respectively.

[00117] Example 25 is a non-transitory computer-readable storage medium that stores instructions for execution by one or more processors of a user equipment (UE) to configure the UE to communicate with an enhanced NodeB (eNB) using beamformed signals, the one or more processors to configure the UE to: perform beam tuning for beam tracking and refinement to an eNB tracking reference signal associated with the UE in a downlink (DL) subframe during an eNB tracking interval; train a beamforming matrix of the UE and perform wideband channel sounding based on the detected eNB tracking reference signal to obtain a direction to communicate with the eNB; transmit to the eNB, during a UE tracking interval in an uplink (UL) subframe, a UE tracking reference signal using the direction determined by the training and wideband channel sounding; transmit to the eNB a re-synchronization signal in response to the UE one of: a determination that the UE has failed to receive the tracking reference signal during the tracking interval, or reception of an instruction, from an anchor eNB in communication with the UE at a frequency lower than the eNB, to re-synchronize with the eNB, the instruction received after the UE has failed to receive or respond to a plurality of tracking reference signals transmitted by the eNB; and transmit to the anchor eNB a blockage report indicating a blockage between the UE and the eNB in response to being unable to re- synchronize with the eNB.

[00118] In Example 26, the subject matter of Example 25 optionally includes that: the eNB tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in the DL subframe, a UL tracking field for UEs scheduled for UL data transmission in an immediately subsequent UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission, the UE tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in an immediately subsequent DL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the subsequent DL subframe, and the DL and UL subframes are in an asymmetric time division duplexed (TDD) frame comprising a greater number of DL subframes than UL subframes, and at least one of the UE tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in each subsequent DL subframe prior to an immediately subsequent UL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the DL subframes prior to the immediately subsequent UL subframe.

[00119] Although an embodiment has been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the present disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part hereof show, by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled.

[00120] Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term "invention" merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

[00121] In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In this document, the terms "including" and "in which" are used as the plain- English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, that is, a system, UE, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

[00122] The Abstract of the Disclosure is provided to comply with 37 C.F.R. § 1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claims

CLAIMS What is claimed is:

1. An apparatus of user equipment (UE) comprising:

a transceiver arranged to communicate with an enhanced NodeB (eNB) using beamformed signals; and

processing circuitry arranged to:

configure the transceiver to monitor for an eNB tracking reference signal associated with the UE from the eNB in a downlink (DL) subframe in an eNB tracking interval, the transceiver configured to, during the eNB tracking interval, perform beam scanning for coarse beam refinement for fine beam tracking based on the eNB tracking reference signal; and

in response to detection of the eNB tracking reference signal, train a beamforming matrix of the UE and perform wideband channel sounding based on the detected eNB tracking reference signal to determine a desired direction for communication with the eNB.

2. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

configure the transceiver to monitor for the eNB tracking reference signal starting using a beam direction obtained during a previous tracking interval, and the eNB tracking interval is separate from a control interval comprising control signals for the UE and a DL data interval carrying data for the UE and is less than a channel coherence time.

3. The apparatus of claim 1, wherein:

the eNB tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in the DL subframe, an uplink (UL) tracking field for UEs scheduled for UL data transmission in an immediately subsequent UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission, and

the UE is at least one of: scheduled for DL data transmission in the DL subframe, scheduled for UL data transmission in the immediately subsequent UL subframe, and

not scheduled for DL data transmission in the DL subframe, not scheduled for UL data transmission in the immediately subsequent UL subframe and has not been tracked for a predetermined period.

4. The apparatus of claim 3, wherein:

a size of the one or more of the DL tracking field, the UL tracking field, and the active tracking field and a size of a control channel used to transmit the eNB tracking reference signal are configurable by the eNB.

5. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

6. The apparatus of claim 5, wherein:

the eNB control information further comprises a tracking time interval that the UE is scheduled to be tracked by the eNB and a missed-tracking time threshold that the UE is to use to detect that the UE has missed the eNB tracking reference signal.

7. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

8. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

9. The apparatus of claim 8, wherein:

the UE tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in an immediately subsequent DL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the subsequent DL subframe, and the UE is at least one of:

scheduled for DL data transmission in the immediately subsequent DL subframe,

scheduled for UL data transmission in the UL subframe, and not scheduled for DL data transmission in the immediately subsequent DL subframe, not scheduled for UL data transmission in the UL subframe and has not been tracked for a predetermined period.

10. The apparatus of claim 8, wherein:

the DL and UL subframes are in an asymmetric time division duplexed (TDD) frame comprising a greater number of DL subframes than UL subframes, and

the UE tracking interval comprises at least one of: a DL tracking field for

UEs scheduled for DL data transmission in each subsequent DL subframe prior to an immediately subsequent UL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the DL subframes prior to the immediately subsequent UL subframe, and

the UE is at least one of: scheduled for DL data transmission in one or more of the subsequent DL subframes,

scheduled for UL data transmission in the UL subframe, and not scheduled for DL data transmission in the subsequent DL subframes, not scheduled for UL data transmission in the UL subframe and has not been tracked for a predetermined period.

1 1. The apparatus of claim 8, wherein the processing circuitry is further arranged to:

configure the transceiver to transmit to the eNB, after the UE tracking interval, at least one of:

a UE control report comprising channel state information feedback from the UE when the UE is not scheduled for data transmission and an indication of the direction, and

a UL scheduling request to schedule data transmission during a subsequent UL subframe.

12. The apparatus of claim 1, wherein:

the transceiver is arranged to communicate with the eNB

beamformed signals having a frequency about 6 - 60 GHz.

13. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

configure the transceiver to receive, from an anchor eNB in

communication with the UE at a frequency lower than the eNB, an instruction to re-synchronize with the eNB, the instruction received after the UE has failed to receive or respond to a plurality of tracking reference signals transmitted by the eNB,

configure the transceiver to transmit to the eNB a re-synchronization signal to the eNB, and

in response to being unable to re-synchronize with the eNB, configure the transceiver to transmit to the anchor eNB a blockage report indicating a blockage between the UE and the eNB.

14. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

determine that the UE has failed to receive the tracking reference signal during the tracking interval,

configure the transceiver to transmit to the eNB a re-synchronization signal, and

15. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

configure the transceiver to at least one of receive the eNB tracking reference signal from the eNB and transmit a UE tracking reference signal to the eNB using a backup beam on a different channel to recover from a missed eNB tracking reference signal and the eNB from a missed UE tracking reference signal, respectively.

16. The apparatus of claim 1, wherein the processing circuitry is further arranged to:

configure the transceiver to receive control information in a system broadcast, the control information comprising at least one of a maximum tracking time interval that the UE is scheduled to be tracked, a UE re- sync time interval that UE is to monitor and detect system synchronization signals, and a blockage time threshold that is a time for the UE to decide that signals from the eNB are blocked.

17. The apparatus of claim 1, further comprising a plurality of antennas configured to transmit and receive communications between the transceiver and the eNB, the plurality of antennas including one or more of a directional antenna, phased array antennas, and multiple aperture antennas.

18. An apparatus of an enhanced NodeB (eNB) comprising:

a transceiver arranged to communicate with a plurality of user equipment (UEs) using beamformed signals; and

processing circuitry arranged to:

group the UEs into UE tracking groups, each UE tracking group associated with a different beamforming direction;

configure the transceiver to transmit to each UE in each UE tracking group an eNB tracking reference signal associated with the UE tracking group in a downlink (DL) subframe in an eNB tracking interval; configure the transceiver to receive, from each UE in each UE tracking group, a UE tracking reference signal associated with the UE tracking group in an uplink (UL) subframe in a UE tracking interval; and train a beamforming matrix of the eNB to establish, for each UE tracking group, a direction for transmission to the UE tracking group using at least one of:

a UE report from the UE tracking group indicating the direction based on the eNB tracking reference signal the transceiver configured to, during the eNB tracking interval, and beam tuning for beam refinement of the UE tracking reference signals from the UEs of the UE tracking group.

19. The apparatus of claim 18, wherein:

the eNB tracking reference signal is repeated for each UE tracking group, and

the eNB tracking reference signals are transmitted to the UEs in a single

Orthogonal Frequency-Division Multiplexing (OFDM) symbol.

20. The apparatus of claim 18, wherein the processing circuitry is further arranged to:

schedule tracking for the UEs for both the DL and UL subframes.

21. The apparatus of claim 18, wherein the processing circuitry is further arranged to:

time multiplex transmission of each eNB tracking reference signal and eNB control information, the eNB control information comprising tracking scheduling information indicating scheduling for at least one of transmission of the eNB tracking reference signal in the DL subframe from the eNB to the UE tracking group and the UE tracking reference signal from the UE tracking group to the eNB in the UL subframe, the tracking scheduling information combinable with DL control information for data transmission scheduling of the UE tracking group in the DL subframe.

22. The apparatus of claim 18, wherein at least one of:

at least one of the eNB tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in the DL subframe, an uplink (UL) tracking field for UEs scheduled for UL data transmission in an immediately subsequent UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission,

at least one of the UE tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in an immediately subsequent DL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the subsequent DL subframe, and

the DL and UL subframes are in an asymmetric time division duplexed (TDD) frame comprising a greater number of DL subframes than UL subframes, and at least one of the UE tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in each subsequent DL subframe prior to an immediately subsequent UL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the DL subframes prior to the immediately subsequent UL subframe.

23. The apparatus of claim 18, wherein the processing circuitry is further arranged to:

determine that determine that the transceiver has failed to receive at least one of the UE tracking reference signal and UE feedback from at least one UE during the UL tracking interval,

configure the transceiver to transmit, to an anchor eNB in communication with the UEs at a frequency lower than the eNB, a report that the transceiver has failed to receive the at least one of the UE tracking reference signal and UE feedback from the at least one UE during the UL tracking interval, and

configure the transceiver to receive from the at least one UE, based on the report to the anchor eNB, a re- synchronization signal to resynchronize with the eNB.

24. The apparatus of claim 18, wherein the processing circuitry is further arranged to:

configure the transceiver to at least one of receive the UE tracking reference signal from at least one of the UEs and transmit the eNB tracking reference signal to the at least one of the UEs using a backup beam on a different channel to recover from a missed UE tracking reference signal and the UE from a missed eNB tracking reference signal, respectively.

25. A non-transitory computer-readable storage medium that stores instructions for execution by one or more processors of a user equipment (UE) to configure the UE to communicate with an enhanced NodeB (eNB) using beamformed signals, the one or more processors to configure the UE to:

perform beam tuning for beam tracking and refinement to an eNB tracking reference signal associated with the UE in a downlink (DL) subframe during an eNB tracking interval;

train a beamforming matrix of the UE and perform wideband channel sounding based on the detected eNB tracking reference signal to obtain a direction to communicate with the eNB; transmit to the eNB, during a UE tracking interval in an uplink (UL) subframe, a UE tracking reference signal using the direction determined by the training and wideband channel sounding;

transmit to the eNB a re-synchronization signal in response to the UE one of:

a determination that the UE has failed to receive the tracking reference signal during the tracking interval, or

reception of an instruction, from an anchor eNB in communication with the UE at a frequency lower than the eNB, to re- synchronize with the eNB, the instruction received after the UE has failed to receive or respond to a plurality of tracking reference signals transmitted by the eNB; and

transmit to the anchor eNB a blockage report indicating a blockage between the UE and the eNB in response to being unable to re-synchronize with the eNB.

26. The medium of claim 24, wherein:

the eNB tracking interval comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in the DL subframe, a UL tracking field for UEs scheduled for UL data transmission in an immediately subsequent

UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission,

the UE tracking interval comprises at least one of: a DL tracking field for

UEs scheduled for DL data transmission in an immediately subsequent DL subframe, a UL tracking field for UEs scheduled for UL data transmission in the

UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the subsequent DL subframe, and the DL and UL subframes are in an asymmetric time division duplexed

(TDD) frame comprising a greater number of DL subframes than UL subframes, and at least one of the UE tracking intervals comprises at least one of: a DL tracking field for UEs scheduled for DL data transmission in each subsequent

DL subframe prior to an immediately subsequent UL subframe, a UL tracking field for UEs scheduled for UL data transmission in the UL subframe, and an active tracking field for UEs that are to be tracked but are not yet scheduled for data transmission in the DL subframes prior to the immediately subsequent UL subframe.