Patent Description:
An example telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). LTE is designed to support mobile broadband access through improved spectral efficiency, lowered costs, and improved services using OFDMA on the downlink, SC-FDMA on the uplink, and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology.

<CIT> relates to a method for performing random access by a User Equipment (UE) in a wireless network, comprises configuring at least one UE transmit beam for a transmission of a random access signal, generating the at least one UE transmit beam using an antenna array according to the configuration, and transmitting the random access signal to a base station (BS) on the at least one UE transmit beam.

<CIT> relates to a method in a wireless device for performing random access to a network node. The method comprises receiving a set of downlink beam-specific reference signals, BRS, from the network node, and determining a preferred BRS based on the received signal power for each BRS.

<CIT> relates to methods and apparatus for sending and receiving mobile station (MS) specific channel state indication reference symbols (CSI-RS).

<CIT> relates to a method for transmitting a user equipment (UE)-triggered channel status information (CSI).

Path loss may be relatively high in millimeter wave (mmW) systems. Transmission may be directional to mitigate path loss. A base station may transmit one or more beam reference signals by sweeping in all directions so that a user equipment (UE) may identify a best "coarse" beam. Further, the base station may transmit a beam refinement request signal so that the UE may track "fine" beams. If a "coarse" beam identified by the UE changes, the UE may need to inform the base station so that the base station may train one or more new "fine" beams for the UE.

In various aspects, the UE may send an index of a best beam and corresponding beam refinement reference signal session request to the base station in a subframe reserved for a random access channel (RACH). The UE may occupy one or more tones reserved for RACH. Further, the UE may occupy tones that are reserved for scheduling request but not for RACH transmission.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be configured to detect a set of beams from a base station. The apparatus may be further configured to select a beam of the set of beams. The apparatus may be further configured to determine at least one resource based on the selected beam. In an aspect, the at least one resource may be at least one of a radio frame index, a subframe index, a symbol index, or a subcarrier region. The apparatus may be further configured to transmit, on the at least one determined resource, a beam adjustment request, e.g., a request for beam tracking to the base station. In an aspect, the at least one determined resource may indicate an index associated with the selected beam.

In another aspect of the disclosure, another method, another computer-readable medium, and another apparatus are provided. The other apparatus may be configured to transmit a first set of beams. The other apparatus may be further configured to receive a beam adjustment request, e.g., a request for beam tracking on at least one resource. In an aspect, the at least one resource may be at least one of a radio frame index, a subframe index, a symbol index, or a subcarrier region. The other apparatus may be further configured to determine a beam index of a beam in the first set of beams based on the at least one resource.

The macro cells include eNBs.

A network that includes both small cell and macro cells may be known as a heterogeneous network. The communication links <NUM> may use MIMO antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The base stations <NUM> / UEs <NUM> may use spectrum up to Y MHz (e.g., <NUM>, <NUM>, <NUM>, <NUM>) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL).

When operating in an unlicensed frequency spectrum, the small cell <NUM>' may employ LTE and use the same <NUM> unlicensed frequency spectrum as used by the Wi-Fi AP <NUM>. The small cell <NUM>', employing LTE in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network. LTE in an unlicensed spectrum may be referred to as LTE-unlicensed (LTE-U), licensed assisted access (LAA), or MuLTEfire.

The millimeter wave (mmW) base station <NUM> may operate in mmW frequencies and/or near mmW frequencies in communication with the UE <NUM>. In one aspect, the UE <NUM> may be an aspect of the UE <NUM>.

The IP Services <NUM> may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service (PSS), and/or other IP services.

The base station may also be referred to as a Node B, evolved Node B (eNB), an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The base station <NUM> provides an access point to the EPC <NUM> for a UE <NUM>. Examples of UEs <NUM> include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, or any other similar functioning device.

Referring again to <FIG>, in certain aspects, the mmW base station <NUM> and the base station <NUM> may be integrated into a single base station (although not necessarily). In an aspect, the mmW base station <NUM> may be configured to transmit a first set of beams to the UE <NUM>. The first set of beams may be considered "coarse" beams.

The UE <NUM> may receive, from the mmW base station <NUM>, the first set of beams. The UE <NUM> may be configured to select a beam of the set of beams. For example, the UE <NUM> may be configured to select a beam having a strongest received power. The selected beam may be associated with an index at the mmW base station <NUM>, and the UE <NUM> may be configured to index this index to the mmW base station <NUM>.

In an aspect, the UE <NUM> may indicate an index of a selected beam to the mmW base station <NUM> using at least one resource. Accordingly, the UE <NUM> may be configured to determine at least one resource based on the selected beam. For example, the at least one resource may include a radio frame index, a subframe index, a symbol index, or a subcarrier index. The UE <NUM> may transmit, on the at least one determined resource, a beam adjustment request <NUM> (e.g., a request for beam tracking, a request for the mmW base station <NUM> to start transmitting at an indicated beam ID without any further beam tracking, and the like). The at least one resource may indicate the index associated with the selected beam.

The mmW base station <NUM> may receive the request <NUM> on the at least one determined resource. The mmW base station <NUM> may be configured to determine a beam index of a beam in the first set of beams based on the at least one resource. For example, the request <NUM> may include a request to transmit a "fine" beam set based on the selected beam, for example, so that the UE <NUM> may perform beam refinement.

<FIG> is a diagram <NUM> illustrating an example of a DL frame structure in LTE. <FIG> is a diagram <NUM> illustrating an example of channels within the DL frame structure in LTE. <FIG> is a diagram <NUM> illustrating an example of an UL frame structure in LTE. <FIG> is a diagram <NUM> illustrating an example of channels within the UL frame structure in LTE. In LTE, a frame (<NUM>) may be divided into <NUM> equally sized subframes. Each subframe may include two consecutive time slots. A resource grid may be used to represent the two time slots, each time slot including one or more time concurrent resource blocks (RBs) (also referred to as physical RBs (PRBs)). In LTE, for a normal cyclic prefix, an RB contains <NUM> consecutive subcarriers in the frequency domain and <NUM> consecutive symbols (for DL, OFDM symbols; for UL, SC-FDMA symbols) in the time domain, for a total of <NUM> REs. For an extended cyclic prefix, an RB contains <NUM> consecutive subcarriers in the frequency domain and <NUM> consecutive symbols in the time domain, for a total of <NUM> REs.

As illustrated in <FIG>, some of the REs carry DL reference (pilot) signals (DL-RS) for channel estimation at the UE. The DL-RS may include cell-specific reference signals (CRS) (also sometimes called common RS), UE-specific reference signals (UE-RS), and channel state information reference signals (CSI-RS). <FIG> illustrates CRS for antenna ports <NUM>, <NUM>, <NUM>, and <NUM> (indicated as R<NUM>, R<NUM>, R<NUM>, and R<NUM>, respectively), UE-RS for antenna port <NUM> (indicated as R<NUM>), and CSI-RS for antenna port <NUM> (indicated as R). <FIG> illustrates an example of various channels within a DL subframe of a frame. The physical control format indicator channel (PCFICH) is within symbol <NUM> of slot <NUM>, and carries a control format indicator (CFI) that indicates whether the physical downlink control channel (PDCCH) occupies <NUM>, <NUM>, or <NUM> symbols (<FIG> illustrates a PDCCH that occupies <NUM> symbols). The PDCCH carries downlink control information (DCI) within one or more control channel elements (CCEs), each CCE including nine RE groups (REGs), each REG including four consecutive REs in an OFDM symbol. A UE may be configured with a UE-specific enhanced PDCCH (ePDCCH) that also carries DCI. The ePDCCH may have <NUM>, <NUM>, or <NUM> RB pairs (<FIG> shows two RB pairs, each subset including one RB pair). The physical hybrid automatic repeat request (ARQ) (HARQ) indicator channel (PHICH) is also within symbol <NUM> of slot <NUM> and carries the HARQ indicator (HI) that indicates HARQ acknowledgement (ACK) / negative ACK (NACK) feedback based on the physical uplink shared channel (PUSCH). The primary synchronization channel (PSCH) is within symbol <NUM> of slot <NUM> within subframes <NUM> and <NUM> of a frame, and carries a primary synchronization signal (PSS) that is used by a UE to determine subframe timing and a physical layer identity. The secondary synchronization channel (SSCH) is within symbol <NUM> of slot <NUM> within subframes <NUM> and <NUM> of a frame, and carries a secondary synchronization signal (SSS) that is used by a UE to determine a physical layer cell identity group number. Based on the PCI, the UE can determine the locations of the aforementioned DL-RS. The physical broadcast channel (PBCH) is within symbols <NUM>, <NUM>, <NUM>, <NUM> of slot <NUM> of subframe <NUM> of a frame, and carries a master information block (MIB). The MIB provides a number of RBs in the DL system bandwidth, a PHICH configuration, and a system frame number (SFN).

As illustrated in <FIG>, some of the REs carry demodulation reference signals (DM-RS) for channel estimation at the eNB. The UE may additionally transmit sounding reference signals (SRS) in the last symbol of a subframe. The SRS may be used by an eNB for channel quality estimation to enable frequency-dependent scheduling on the UL. <FIG> illustrates an example of various channels within an UL subframe of a frame. A physical random access channel (PRACH) may be within one or more subframes within a frame based on the PRACH configuration. The PRACH may include six consecutive RB pairs within a subframe. The PRACH allows the UE to perform initial system access and achieve UL synchronization. A physical uplink control channel (PUCCH) may be located on edges of the UL system bandwidth.

<FIG> is a block diagram of an base station <NUM> in communication with a UE <NUM> in an access network. In an aspect, the base station <NUM> may be an aspect of the mmW base station <NUM> and/or the base station <NUM>.

<FIG> are diagrams illustrating an example of the transmission of beamformed signals between a base station (BS) and a UE. The BS may be embodied as a BS in a mmW system (mmW BS). Referring to <FIG>, diagram <NUM> illustrates a BS <NUM> of a mmW system transmitting beamformed signals <NUM> (e.g., beam reference signals) in different transmit directions (e.g., directions A, B, C, and D). In an example, the BS <NUM> may sweep through the transmit directions according to a sequence A-B-C-D. In another example, the BS <NUM> may sweep through the transmit directions according to the sequence B-D-A-C. Although only four transmit directions and two transmit sequences are described with respect to <FIG>, any number of different transmit directions and transmit sequences are contemplated.

After transmitting the signals, the BS <NUM> may switch to a receive mode. In the receive mode, the BS <NUM> may sweep through different receive directions in a sequence or pattern corresponding (mapping) to a sequence or pattern in which the BS <NUM> previously transmitted the synchronization/discovery signals in the different transmit directions. For example, if the BS <NUM> previously transmitted the synchronization/discovery signals in transmit directions according to the sequence A-B-C-D, then the BS <NUM> may sweep through receive directions according to the sequence A-B-C-D in an attempt to receive an association signal from a UE <NUM>. In another example, if the BS <NUM> previously transmitted the synchronization/discovery signals in transmit directions according to the sequence B-D-A-C, then the BS <NUM> may sweep through receive directions according to the sequence B-D-A-C in an attempt to receive the association signal from the UE <NUM>.

A propagation delay on each beamformed signal allows a UE <NUM> to perform a receive (RX) sweep. The UE <NUM> in a receive mode may sweep through different receive directions in an attempt to detect a synchronization/discovery signal <NUM> (see <FIG>). One or more of the synchronization/discovery signals <NUM> may be detected by the UE <NUM>. When a strong synchronization/discovery signal <NUM> is detected, the UE <NUM> may determine an optimal transmit direction of the BS <NUM> and an optimal receive direction of the UE <NUM> corresponding to the strong synchronization/discovery signal. For example, the UE <NUM> may determine preliminary antenna weights/directions of the strong synchronization/discovery signal <NUM>, and may further determine a time and/or resource where the BS <NUM> is expected to optimally receive a beamformed signal. Thereafter, the UE <NUM> may attempt to associate with the BS <NUM> via a beamformed signal.

The BS <NUM> may sweep through a plurality of directions using a plurality of ports in a cell-specific manner in a first symbol of a synchronization subframe. For example, the BS <NUM> may sweep through different transmit directions (e.g., directions A, B, C, and D) using four ports in a cell-specific manner in a first symbol of a synchronization subframe. In an aspect, these different transmit directions (e.g., directions A, B, C, and D) may be considered "coarse" beam directions. In an aspect, a beam reference signal (BRS) may be transmitted in different transmit directions (e.g., directions A, B, C, and D).

In an aspect, the BS <NUM> may sweep the four different transmit directions (e.g., directions A, B, C, and D) in a cell-specific manner using four ports in a second symbol of a synchronization subframe. A synchronization beam may occur in a second symbol of the synchronization subframe.

Referring to diagram <NUM> of <FIG>, the UE <NUM> may listen for beamformed discovery signals in different receive directions (e.g., directions E, F, G, and H). In an example, the UE <NUM> may sweep through the receive directions according to a sequence E-F-G-H. In another example, the UE <NUM> may sweep through the receive directions according to the sequence F-H-E-J. Although only four receive directions and two receive sequences are described with respect to <FIG>, any number of different receive directions and receive sequences are contemplated.

The UE <NUM> may attempt the association by transmitting beamformed signals <NUM> (e.g., association signals or another indication of a best "coarse" beam or a best "fine" beam) in the different transmit directions (e.g., directions E, F, G, and H). In an aspect, the UE <NUM> may transmit an association signal <NUM> by transmitting along the optimal receive direction of the UE <NUM> at the time/resource where the BS <NUM> is expected to optimally receive the association signal. The BS <NUM> in the receive mode may sweep through different receive directions and detect the association signal <NUM> from the UE <NUM> during one or more timeslots corresponding to a receive direction. When a strong association signal <NUM> is detected, the BS <NUM> may determine an optimal transmit direction of the UE <NUM> and an optimal receive direction of the BS <NUM> corresponding to the strong association signal. For example, the BS <NUM> may determine preliminary antenna weights/directions of the strong association signal <NUM>, and may further determine a time and/or resource where the UE <NUM> is expected to optimally receive a beamformed signal. Any of the processes discussed above with respect to <FIG> may be refined or repeated over time such that the UE <NUM> and BS <NUM> eventually learn the most optimal transmit and receive directions for establishing a link with each other. Such refinement and repetition may be referred to as beam training.

In an aspect, the BS <NUM> may choose a sequence or pattern for transmitting the synchronization/discovery signals according to a number of beamforming directions. The BS <NUM> may then transmit the signals for an amount of time long enough for the UE <NUM> to sweep through a number of beamforming directions in an attempt to detect a synchronization/discovery signal. For example, a BS beamforming direction may be denoted by n, where n is an integer from <NUM> to N, N being a maximum number of transmit directions. Moreover, a UE beamforming direction may be denoted by k, where k is an integer from <NUM> to K, K being a maximum number of receive directions. When the UE <NUM> detects a synchronization/discovery signal from the BS <NUM>, the UE <NUM> may discover that the strongest synchronization/discovery signal is received when the UE <NUM> beamforming direction is k = <NUM> and the BS <NUM> beamforming direction is n = <NUM>. Accordingly, the UE <NUM> may use the same antenna weights/directions for responding (transmitting a beamformed signal) to the BS <NUM> in a corresponding response timeslot. That is, the UE <NUM> may send a signal to the BS <NUM> using UE <NUM> beamforming direction k = <NUM> during a timeslot when the BS <NUM> is expected to perform a receive sweep at BS <NUM> beamforming direction n = <NUM>.

Path loss may be relatively high in millimeter wave (mmW) systems. Transmission may be directional to mitigate path loss. A BS may transmit one or more beam reference signals by sweeping in all directions so that a user equipment (UE) may identify a best "coarse" beam. Further, the BS may transmit a beam refinement request signal so that the UE may track "fine" beams. If a "coarse" beam identified by the UE changes, the UE may need to inform the BS so that the BS may train one or more new "fine" beams for the UE.

In various aspects, the UE may send an index of a best beam and corresponding beam refinement reference signal session request to the BS in a subframe reserved for RACH. The UE may occupy one or more tones reserved for RACH. Further, the UE may occupy tones that are reserved for scheduling request but not for RACH transmission.

<FIG> are diagrams illustrating an example of the transmission of beamformed signals between a BS and a UE. The BS <NUM> may be embodied as a BS in a mmW system (mmW BS). It should be noted that while some beams are illustrates as adjacent to one another, such an arrangement may be different in different aspects (e.g., beams transmitted during a same symbol may not be adjacent to one another).

In an aspect, a beam set may contain eight different beams. For example, <FIG> illustrates eight beams <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> for eight directions. In aspects, the BS <NUM> may be configured to beamform for transmission of at least one of the beams <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> toward the UE <NUM>. In one aspect, the BS <NUM> can sweep/transmit <NUM> directions using eight ports during the synchronization sub-frame.

In an aspect, a BS may transmit a beam reference signal (BRS) in a plurality of directions during a synchronization subframe. In one aspect, this transmission may be cell-specific. Referring to <FIG>, the BS <NUM> may transmit a first set of beams <NUM>, <NUM>, <NUM>, <NUM> in four directions. For example, the BS <NUM> may transmit a BRS in a synchronization subframe of each of the transmit beams <NUM>, <NUM>, <NUM>, <NUM>. In an aspect, these beams <NUM>, <NUM>, <NUM>, <NUM> transmitted in the four directions may be odd-indexed beams <NUM>, <NUM>, <NUM>, <NUM> for the four directions out of a possible eight for the beam set. For example, the BS <NUM> may be capable of transmitting beams <NUM>, <NUM>, <NUM>, <NUM> in directions adjacent to other beams <NUM>, <NUM>, <NUM>, <NUM> that the BS <NUM> is configured to transmit. In an aspect, this configuration in which the BS <NUM> transmits beams <NUM>, <NUM>, <NUM>, <NUM> for the four directions may be considered a "coarse" beam set.

In <FIG>, the UE <NUM> may determine or select a beam index that is strongest or preferable. For example, the UE <NUM> may determine that the beam <NUM> carrying a BRS is strongest or preferable. The UE <NUM> may select a beam based by measuring values for a received power or received quality associated with each of the first set of beams <NUM>, <NUM>, <NUM>, <NUM>, comparing respective values to one another, and selecting the beam that corresponds to the greatest value. The selected beam may correspond to a beam index at the BS <NUM>. The UE <NUM> may transmit an indication <NUM> of this beam index to the BS <NUM>. In an aspect, the indication <NUM> may include a request to transmit a beam refinement reference signal (BRRS). The BRRS may be UE-specific. One of ordinary skill would appreciate that the BRRS may be referred to by different terminology without departing from the present disclosure, such as a beam refinement signal, a beam tracking signal, or another term.

In various aspects, the UE <NUM> may determine a resource that corresponds to the selected beam index. A resource may include one of a radio frame, a subframe, a symbol, or a subcarrier region. Each resource may correspond to a value, for example, a radio frame index, a subframe index, a symbol index, or a subcarrier region. In one aspect, the UE <NUM> may have stored therein or may have access to a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the UE <NUM> may determine the beam index and then access a lookup table to determine a resource index or region that corresponds to the determined beam index.

In one aspect, the resource may be included in the PUCCH. In one aspect, the at least one resource may be included in subframe associated with a random access channel (RACH). For example, the resource may be included in a bandwidth reserved for RACH transmission. In another example, the at least one resource is included in a bandwidth that is unreserved for RACH transmission. According to another example, the bandwidth is reserved for scheduling request transmission.

The BS <NUM> may receive the indication <NUM>, which may include a beam adjustment request (e.g., a request for beam tracking, a request for a BRRS, a request for the BS to start transmitting on an indicated beam ID without any further beam tracking, and the like). Based on the indication <NUM>, the BS <NUM> may determine the index corresponding to the selected beam <NUM>. That is, the indication <NUM> may be carried on a resource determined to correspond to the index of the selected beam <NUM>. In one aspect, the BS <NUM> may have stored therein or may have access to a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the BS <NUM> may determine the resource on which the indication <NUM> is received and then access a lookup table to determine a beam index (e.g., the index corresponding to the selected beam <NUM>) or region that corresponds to the determined beam index.

In <FIG>, the BS <NUM> may transmit a second set of beams based on the index included in the indication <NUM>. For example, the UE <NUM> may indicate that a first beam <NUM> is strongest or preferable and, in response, the BS <NUM> may transmit a second set of beams <NUM>, <NUM>, <NUM> to the UE <NUM> based on the indicated beam index. In an aspect, the beams <NUM>, <NUM>, <NUM> transmitted based on the indicated beam index may be closer (e.g., spatially and/or directionally) to the selected beam <NUM> than those other beams <NUM>, <NUM>, <NUM> of the first set of beams. In an aspect, the beams <NUM>, <NUM>, <NUM> transmitted based on the indicated beam index may be considered a "fine" beam set. In an aspect, a BRRS may be transmitted in each of the beams <NUM>, <NUM>, <NUM> of the fine beam set. In an aspect, the beams <NUM>, <NUM>, <NUM> of the fine beam set may be adj acent.

Based on one or more BRRSs received in the beams <NUM>, <NUM>, <NUM> of the fine beam set, the UE <NUM> may transmit a second indication <NUM> to the BS <NUM> to indicate a best "fine" beam. In an aspect, the second indication <NUM> may use two (<NUM>) bits to indicate the selected beam. For example, the UE <NUM> may transmit an indication <NUM> that indicates an index corresponding to the selected beam <NUM>. The BS <NUM> may then transmit to the UE <NUM> using the selected beam <NUM>.

Referring to <FIG>, the BS <NUM> may transmit a BRS in a plurality of directions during a synchronization subframe. In an aspect, the BS <NUM> may transmit the BRS continuously, e.g., even after the UE <NUM> has communicated the indication <NUM> of a selected beam <NUM>. For example, the BS <NUM> may transmit beams <NUM>, <NUM>, <NUM>, <NUM> that each include a BRS (e.g., a "coarse" beam set).

Referring to <FIG> and according to the claimed invention, the quality of the selected beam <NUM> deteriorates so that the UE <NUM> no longer prefers to communicate using the selected beam <NUM>. Based on the BRS that is transmitted in synchronization subframes (e.g., continuously transmitted), the UE <NUM> may determine a new beam <NUM> on which to communicate. For example, the UE <NUM> may determine that the beam <NUM> carrying a BRS is strongest or preferable. The UE <NUM> may select a beam based by measuring values for a received power or received quality associated with each of the set of beams <NUM>, <NUM>, <NUM>, <NUM>, comparing respective values to one another, and selecting the beam that corresponds to the greatest value. According to the claimed invention, the selected beam corresponds to a beam index at the BS <NUM>. The UE <NUM> transmits an request <NUM> indicating this beam index to the BS <NUM>. In an aspect, the indication <NUM> may include a request to transmit a beam refinement reference signal (BRRS). The BRRS may be UE-specific.

According to the claimed invention, the UE <NUM> determines a resource that corresponds to the selected beam index. A resource includes one of a radio frame, a subframe, a symbol, or a subcarrier region. Each resource may correspond to a value, for example, a radio frame index, a subframe index, a symbol index, or a subcarrier region. According to the claimed invention, a beam adjustment request (BAR) is used to request the BS <NUM> to transmit a BRRS.

According to the claimed invention, the UE <NUM> has stored therein a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the UE <NUM> may determine the beam index and then access a lookup table to determine a resource index or region that corresponds to the determined beam index.

In an aspect, the at least one resource may be included in a physical uplink control channel (PUCCH). However, the BS <NUM> may only be able to detect signals from the UE <NUM> in the first indicated beam <NUM> (<FIG>). Thus, the UE <NUM> may require a link budget on the PUCCH in order to indicate the request <NUM> using the PUCCH.

In another aspect, the at least one resource is included in a subframe associated with a RACH. In an aspect, the at least one resource is included in a bandwidth reserved for RACH transmission. In an aspect, the at least one resource may be included in a bandwidth that is unreserved for RACH transmission. In an aspect, the at least one resource may be included in a bandwidth that is reserved for scheduling request (SR) transmission, which may be in a RACH subframe but may be unreserved for RACH transmission.

With respect to <FIG>, the BS <NUM> may receive the request <NUM> from the UE <NUM>. The BS <NUM> may be configured to determine a beam index of the set of beams (e.g., the set of beams illustrated in <FIG>) based on at least one of the request and/or the at least one resource. For example, the request <NUM> may be carried on a resource determined to correspond to the index of the selected beam <NUM>. In one aspect, the BS <NUM> may have stored therein or may have access to a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the BS <NUM> may determine the resource on which the request <NUM> is received and then access a lookup table to determine a beam index (e.g., the index corresponding to the selected beam <NUM>) or region that corresponds to the determined beam index. In an aspect, an uplink receive beam during reception of the request <NUM> may be based on the first set of beams <NUM>, <NUM>, <NUM>, <NUM>.

In an aspect, the BS <NUM> may be configured to transmit a second set of beams <NUM>, <NUM>, <NUM> based on at least one of the request <NUM> and/or the at least one resource on which the request <NUM> is carried. In an aspect, the BS <NUM> may be configured to determine, from the request <NUM> and/or the at least one resource carrying the request <NUM>, a range of indexes. In an aspect, the BS <NUM> determines the beam index based on at least one subcarrier of the at least one resource on which the request <NUM> is carried.

In an aspect, the BS <NUM> determines, from within the range, the beam index based on a strength of a signal in different receive chains of the BS <NUM> through which the request <NUM> is received. For example, the BS <NUM> may receive the request <NUM> through a plurality of receive chains of the BS <NUM>. The BS <NUM> may determine a signal strength of the request <NUM> for each receive chain through which the request <NUM> is received. The BS <NUM> may determine that each receive chain is associated with at least one beam index (e.g., the beam index for beam <NUM>), and so the BS <NUM> may determine the beam index that corresponds to the receive chain in which the highest signal strength of the request <NUM> is detected.

In an aspect, the BS <NUM> may transmit, to the UE <NUM>, an instruction to perform beam refinement based on the request <NUM>. In an aspect, the instruction to perform beam refinement may be based on the selected beam <NUM> indicated to the BS <NUM> by the UE <NUM>. In an aspect, the BS <NUM> may transmit one or more BRRSs in one or more synchronization subframes of the second set of beams <NUM>, <NUM>, <NUM>. The UE <NUM> may measure the BRRS in the scheduled subframe(s) to determine the best beam of the BS <NUM>, such as by measuring a respective value for a received power and/or received quality of each beam of the second set of beams <NUM>, <NUM>, <NUM>, and comparing the measured values to one another to determine the highest values corresponding to a beam of the second set of beams <NUM>, <NUM>, <NUM>.

Referring to <FIG>, a block diagram for indicating a selected beam is illustrated. In aspects, the BS <NUM> may transmit a set of beams A-H <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In aspects, the UE <NUM> may need to indicate a newly selected beam of the beams A-H <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to the BS <NUM>, e.g., when a first selected beam deteriorates. However, because the BS <NUM> may only be able to detect transmission from the UE <NUM> in the direction of the first selected beam, the UE <NUM> may use a RACH subframe <NUM> in order to identify a new beam (e.g., because beamforming may not be required for RACH in a cell).

In one aspect, at least one of the BS <NUM> and/or the UE <NUM> maintains a mapping between beams (e.g., beams A-H <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) associated with a synchronization (or BRS) session and RACH session. That is, the UE <NUM> may be configured to indicate a beam index using one or more resources of a RACH subframe <NUM>, such as by transmitting a request (e.g., the request <NUM>) on at least one resource corresponding to the beam index selected by the UE <NUM>.

For example, the UE <NUM> may be configured to transmit the request <NUM> as a RACH sequence in a symbol <NUM> and <NUM> of the RACH subframe <NUM> if the selected beam index (e.g., the beam <NUM>) corresponds to one of beams A-D <NUM>, <NUM>, <NUM>, <NUM>. Similarly, the UE <NUM> may be configured to transmit the request <NUM> as a RACH sequence in a symbol <NUM> and <NUM> of the RACH subframe <NUM> if the selected beam index corresponds to one of beams E-H <NUM>, <NUM>, <NUM>, <NUM>.

In one aspect, UE <NUM> may indicate a specific beam within the range using at least one subcarrier. For example, the UE <NUM> may indicate a beam within the range of beams A-D <NUM>, <NUM>, <NUM>, <NUM> by using at least one of a pair of subcarriers <NUM>, <NUM>, <NUM>, <NUM>. Similarly, the UE <NUM> may indicate a beam within the range of beams EH <NUM>, <NUM>, <NUM>, <NUM> by using at least one of a pair of subcarriers <NUM>, <NUM>, <NUM>, <NUM>. For example, subcarriers <NUM> may indicate a first beam of a range and, therefore, when the UE <NUM> transmits a RACH sequence on symbols <NUM> and <NUM> and subcarriers <NUM>, the UE <NUM> is indicating a selected beam A <NUM>. By way of another example, the UE <NUM> may indicate a selected beam G <NUM> by transmitting a RACH sequence on subcarriers <NUM> (corresponding to a third beam within a range) on symbols <NUM> and <NUM>. The BS <NUM> may therefore determine a selected beam index based on the at least one resource on which the RACH sequence is transmitted.

In another aspect, the BS <NUM> determines, from within the range, the beam index based on a strength of a signal in different receive chains of the BS <NUM> through which the request <NUM> is received. For example, the BS <NUM> may receive the request <NUM> through a plurality of receive chains of the BS <NUM>. The BS <NUM> may determine a signal strength of the request <NUM> for each receive chain through which the request <NUM> is received. The BS <NUM> may determine that each receive chain is associated with at least one beam index (e.g., the beam index for beam <NUM>), and so the BS <NUM> may determine the beam index that corresponds to the receive chain in which the highest signal strength of the request <NUM> is detected. For example, the UE <NUM> may select beam E <NUM> as the newly selected beam. To indicate the selected beam E <NUM>, the UE <NUM> may transmit a RACH sequence on symbols <NUM> and <NUM> of the RACH subframe. The BS <NUM> may receive the RACH sequence through one or more receive chains of the BS <NUM>. The BS <NUM> may determine signal strengths of the RACH sequence for each receive chain of the BS <NUM>. The BS <NUM> may determine the selected beam E <NUM> because the highest signal strength of the RACH sequence may occur at the receive chain corresponding to a third beam of a range (and the range may be indicated by the symbols <NUM> and <NUM>).

Indication of the selected beam index using a RACH subframe may experience various limitations. For example, the UE <NUM> may not be timing aligned with the BS <NUM> when transmitting a RACH sequence. A cyclic prefix in a RACH sequence may be greater than the summation of round trip time (RTT) and delay spread (e.g., in regular transmission, a cyclic prefix may need to be greater than a delay spread). Thus, the available number of cyclic shifts for UEs may be low. For example, the available number of cyclic shifts may be less than or equal to a sequence duration and/or cyclic prefix duration. Accordingly, the number of degrees of freedom in the RACH-reserved region of a RACH subframe <NUM> may be low. Further, there may be collision if many UEs transmit a beam adjustment request in the RACH subframe <NUM>. Further, the RACH framework may include additional overhead (e.g., BS <NUM> sends a RACH response and allocates a separate grant to a UE to transmit additional information).

Accordingly, the UE <NUM> may transmit a beam adjustment request (e.g., a request for BRRS) in an unoccupied bandwidth of a RACH subframe. This region may be unreserved for RACH transmission. In an aspect, this region may be reserved for scheduling request (SR) transmission.

Referring to <FIG>, a block diagram for indicating a selected beam is illustrated. In aspects, the BS <NUM> may transmit a set of beams A-H <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In aspects, the UE <NUM> may need to indicate a newly selected beam of the beams A-H <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to the BS <NUM>, e.g., when a first selected beam deteriorates. However, because the BS <NUM> may only be able to detect transmission from the UE <NUM> in the direction of the first selected beam, the UE <NUM> may use a RACH subframe <NUM> in order to identify a new beam.

In aspects, the UE <NUM> may use a region <NUM> that may be unreserved for RACH transmission. In an aspect, this region <NUM> may be reserved for SR transmission (e.g., the region <NUM> may be used to collect buffer status report). In an aspect, a BAR procedure may be configured in the UE <NUM>. For example, if a dedicated SR for BRRS request is configured to the UE <NUM>, a PHY layer of the UE <NUM> may signal a dedicated SR for BRRS request in the SR region <NUM> of the RACH subframe <NUM>.

In an aspect, the UE <NUM> may only transmit in the region <NUM> when the UE <NUM> is timing aligned with the BS <NUM>. The number of available cyclic shifts associated with the region <NUM> may be higher than those available in the region <NUM> reserved for RACH transmission. Accordingly, there may be a higher degree of freedom associated with the region <NUM> compared to the region <NUM>. For example, a plurality of UEs may be able to transmit requests (e.g., requests for beam tracking and/or BRRS) through the region <NUM> (e.g., more UEs than able to transmit requests through the RACH transmission region <NUM>).

In an aspect, the UE <NUM> may select a transmission time for SR based on symbol index of the strongest beam (e.g., a beam in which a strongest BRS is received during a synchronization subframe). In an aspect, the UE <NUM> may transmit an SR during a RACH subframe <NUM> if instructed by a higher layer. For example, a PHY layer of the UE <NUM> may be provided with a plurality of parameters, including a band number NSR, cyclic shift v, a root u, a parameter f', a system frame number (SFN), a BRS transmission period NBRS, a number of symbols NRACH during the RACH subframe <NUM> for which the BS <NUM> may apply a different beams (e.g., different receive beams), a number of RACH subframes M in each radio frame, an index the current RACH subframe m, a symbol with the strongest synchronization beam <MAT>. The root u may be cell specific. The UE <NUM> may calculate a symbol index l based on the SFN, NBRS, NRACH, M, m, and <MAT>. For example, <MAT>.

Where Nrep may denote the number of symbols dedicated to a single RACH transmission (e.g., Nrep = <NUM>).

In one aspect, at least one of the BS <NUM> and/or the UE <NUM> maintains a mapping between beams (e.g., beams A-H <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) associated with a synchronization (or BRS) session and region <NUM>. That is, the UE <NUM> may be configured to indicate a beam index using one or more resources of a RACH subframe <NUM>, such as by transmitting a request (e.g., the request <NUM>) on at least one resource corresponding to the beam index selected by the UE <NUM>.

For example, the UE <NUM> may be configured to transmit the request <NUM> in a symbol <NUM> and <NUM> of the RACH subframe <NUM> if the selected beam index (e.g., the beam <NUM>) corresponds to one of beams A-D <NUM>, <NUM>, <NUM>, <NUM>. Similarly, the UE <NUM> may be configured to transmit the request <NUM> in a symbol <NUM> and <NUM> of the RACH subframe <NUM> if the selected beam index corresponds to one of beams E-H <NUM>, <NUM>, <NUM>, <NUM>.

In one aspect, UE <NUM> may indicate a specific beam within the range using at least one subcarrier. For example, the UE <NUM> may indicate a beam within the range of beams A-D <NUM>, <NUM>, <NUM>, <NUM> by using at least one of a pair of subcarriers <NUM>, <NUM>, <NUM>, <NUM>. Similarly, the UE <NUM> may indicate a beam within the range of beams EH <NUM>, <NUM>, <NUM>, <NUM> by using at least one of a pair of subcarriers <NUM>, <NUM>, <NUM>, <NUM>. For example, subcarriers <NUM> may indicate a first beam of a range and, therefore, when the UE <NUM> transmits a request on symbols <NUM> and <NUM> and subcarriers <NUM>, the UE <NUM> is indicating a selected beam A <NUM>. By way of another example, the UE <NUM> may indicate a selected beam G <NUM> by transmitting a request on subcarriers <NUM> (corresponding to a third beam within a range) on symbols <NUM> and <NUM>. The BS <NUM> may therefore determine a selected beam index based on the at least one resource on which the request is transmitted.

In another aspect, the BS <NUM> determines, from within the range, the beam index based on a strength of a signal in different receive chains of the BS <NUM> through which the request <NUM> is received. For example, the BS <NUM> may receive the request <NUM> through a plurality of receive chains of the BS <NUM>. The BS <NUM> may determine a signal strength of the request <NUM> for each receive chain through which the request <NUM> is received. The BS <NUM> may determine that each receive chain is associated with at least one beam index (e.g., the beam index for beam <NUM>), and so the BS <NUM> may determine the beam index that corresponds to the receive chain in which the highest signal strength of the request <NUM> is detected. For example, the UE <NUM> may select beam E <NUM> as the newly selected beam. To indicate the selected beam E <NUM>, the UE <NUM> may transmit a request on symbols <NUM> and <NUM> of the RACH subframe. The BS <NUM> may receive the request through one or more receive chains of the BS <NUM>. The BS <NUM> may determine signal strengths of the request for each receive chain of the BS <NUM>. The BS <NUM> may determine the selected beam E <NUM> because the highest signal strength of the request may occur at the receive chain corresponding to a third beam of a range (and the range may be indicated by the symbols <NUM> and <NUM>).

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by a UE (e.g., the UE <NUM>). One of ordinary skill would understand that one or more operations may be omitted, transposed, and or performed contemporaneously.

At operation <NUM>, the UE may detect a set of beams from a BS, such as by detecting a BRS transmitted in a synchronization subframe of each beam of the first set of beams. In the context of <FIG>, the UE <NUM> may detect the first set of beams <NUM>, <NUM>, <NUM>, <NUM>, such as by detecting a BRS transmitted in a synchronization subframe of each beam <NUM>, <NUM>, <NUM>, <NUM>. The first set of beams may be odd-indexed beams.

At operation <NUM>, the UE may select a beam of the set of beams. For example, the UE may determine that the beam carrying a BRS that is strongest or preferable. The UE may select a beam based by measuring values for a received power or received quality associated with each of the first set of beams, comparing respective values to one another, and selecting the beam that corresponds to the greatest value. The selected beam may correspond to a beam index at the BS. In the context of <FIG>, the UE <NUM> may select the beam <NUM>.

At operation <NUM>, the UE may determine at least one resource based on the selected beam. In the context of <FIG>, the UE <NUM> may determine at least one resource based on the selected beam <NUM>. In the context of <FIG>, the UE <NUM> may determine symbols <NUM> and <NUM> and/or subcarriers <NUM>. In the context of <FIG>, the UE <NUM> may determine symbols <NUM> and <NUM> and/or subcarriers <NUM> of the region <NUM>.

In an aspect, the at least one resource indicates at least one of a radio frame index, a subframe index, a symbol index, or a subcarrier region. In an aspect, the at least one resource is included in a PUCCH. In an aspect, the at least one resource is included in a subframe associated with RACH. In one aspect, the at least one resource is included in a bandwidth associated with RACH. In an aspect, the at least one resource is included in a bandwidth that is unreserved for RACH transmission, such as a bandwidth reserved for SR transmission. In one aspect, the UE may have stored therein or may have access to a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the UE may determine the beam index and then access a lookup table to determine a resource index or region that corresponds to the determined beam index.

At operation <NUM>, the UE may transmit, on the at least one determined resource, a beam adjustment request (e.g., a request for BRRS) to the BS. The request may indicate the index associated with the selected beam. In the context of <FIG>, the UE <NUM> may transmit the request <NUM>.

At operation <NUM>, the UE may receive an instruction to perform beam refinement (e.g., a BRRS) based on the request. In the context of <FIG>, the UE <NUM> may receive, from the BS <NUM>, an instruction to perform beam refinement based on the request <NUM>.

At operation <NUM>, the UE may perform beam refinement based on the instruction. The UE may perform beam refinement based on the selected beam. In the context of <FIG>, the UE <NUM> may perform beam refinement based on an instruction from the BS <NUM>.

In an aspect, operation <NUM> may include operations <NUM> and <NUM>. At operation <NUM>, the UE may receive, from the BS, the selected beam. In an aspect, the selected beam is included in a first set of beams from the BS. In the context of <FIG>, the UE <NUM> may receive the set of beams <NUM>, <NUM>, <NUM>.

At operation <NUM>, the UE may determine a best receiver beam of the UE that corresponds to the selected beam received from the BS. In the context of <FIG>, the UE <NUM> may receive a best receiver beam of the UE <NUM> for a beam within the set of beams <NUM>, <NUM>, <NUM> - e.g., the UE <NUM> may determine a best receiver beam for beam <NUM>.

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by a BS (e.g., the BS <NUM>). One of ordinary skill would understand that one or more operations may be omitted, transposed, and or performed contemporaneously.

At operation <NUM>, the BS may transmit a first set of beams, such as by transmitting a BRS a synchronization subframe of each beam of the first set of beams. The first set of beams may be odd-indexed beams. In the context of <FIG>, the BS <NUM> may transmit the first set of beams <NUM>, <NUM>, <NUM>, <NUM>.

At operation <NUM>, the BS may receive a beam adjustment request on at least one resource. In the context of <FIG>, the BS <NUM> may receive the request <NUM> from the UE <NUM>.

At operation <NUM>, the BS may determine a beam index of a beam in the first set of beams based on the request and/or the at least one resource carrying the request. In one aspect, the BS may have stored therein or may have access to a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the BS may determine the resource on which the request is received and then access a lookup table to determine a beam index (e.g., the index corresponding to the selected beam) or region that corresponds to the determined beam index.

In the context of <FIG>, the BS <NUM> may determine at least one resource based on the request <NUM> and at least one resource carrying the request <NUM>, for example, when the UE <NUM> indicates selected beam <NUM>. In the context of <FIG>, the BS <NUM> may detect the request <NUM> on symbols <NUM> and <NUM> and/or subcarriers <NUM>, which may indicate the selected beam <NUM>. In the context of <FIG>, the BS <NUM> may detect the request <NUM> symbols <NUM> and <NUM> and/or subcarriers <NUM> of the region <NUM>, which may indicate the selected beam <NUM>.

In an aspect, the at least one resource is included in a PUCCH. In an aspect, the at least one resource is included in a subframe associated with RACH. In one aspect, the at least one resource is included in a bandwidth associated with RACH. In an aspect, the at least one resource is included in a bandwidth that is unreserved for RACH transmission, such as a bandwidth reserved for SR transmission.

In an aspect, operation <NUM> may include operations <NUM> and <NUM>. At operation <NUM>, the BS may determine a range of indexes based on the at least one resource. In the context of <FIG>, the BS <NUM> may determine a range of indexes based on the at least one resource carrying the request <NUM>. In the context of <FIG>, the BS <NUM> may determine symbols <NUM> and <NUM> to indicate a range of beam indexes. In the context of <FIG>, the BS <NUM> may determine symbols <NUM> and <NUM> to indicate a range of beam indexes.

At operation <NUM>, the BS may determine the beam index based on at least one subcarrier carrying the request or a receive chain of the BS through which the request is received. In the context of <FIG>, the BS <NUM> may determine subcarriers <NUM> to indicate a beam index within the range of beam indexes. In the context of <FIG>, the BS <NUM> may determine subcarriers <NUM> to indicate a beam index within the range of beam indexes. Alternatively, the BS <NUM> may determine a beam index based on a receive chain of the BS <NUM> through which the request is received.

At operation <NUM>, the BS may transmit a second set of beams based on the beam index. The second set of beams may be "fine" beams. In the context of <FIG>, the BS <NUM> may transmit the second set of beams <NUM>, <NUM>, <NUM>. In an aspect, the BS <NUM> may receive another beam index based on the second set of beams, such as two (<NUM>) bits from the UE <NUM>.

<FIG> is a conceptual data flow diagram <NUM> illustrating the data flow between different means/components in an exemplary apparatus <NUM>. The apparatus may be a UE. The apparatus <NUM> includes a reception component <NUM> that may be configured to receive signals from a mmW BS (e.g., the BS <NUM>). The apparatus <NUM> may include a transmission component <NUM> configured to transmit signals to a mmW BS (e.g., the BS <NUM>).

The apparatus <NUM> may include a beam detection component <NUM> configured to detect one or more beams transmitted by a mmW BS <NUM>. In an aspect, the beam detection component <NUM> may be configured to detect one or more BRSs transmitted on a "coarse" set of beams by the mmW BS <NUM>. The beam detection component <NUM> may monitor one or more synchronization subframes and detect one or more BRSs transmitted by the mmW BS <NUM>.

The beam selection component <NUM> may be configured to select a beam based on the BRSs detected by the beam detection component <NUM>. For example, the beam selection component <NUM> may be configured to measured received power or received quality of one or more BRSs and selected the beam corresponding to the highest received power or received quality. The beam selection component <NUM> may provide an indication of this selected beam to a resource determination component <NUM>.

The selected beam may correspond to an index. The resource determination component <NUM> may be configured to determine the resource that is to carry a beam adjustment request (e.g., a request for BRRS) in order to indicate the selected beam. For example, a resource may include one of a radio frame, a subframe, a symbol, or a subcarrier region. Each resource may correspond to a value, for example, a radio frame index, a subframe index, a symbol index, or a subcarrier region. In one aspect, the resource determination component <NUM> may have stored therein or may have access to a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the resource determination component <NUM> may determine the beam index and then access a lookup table to determine a resource index or region that corresponds to the determined beam index.

In one aspect, the resource is included in subframe associated with a RACH. In one aspect, the resource is included in a bandwidth reserved for RACH transmission. In one aspect, the resource is included in a bandwidth that is unreserved for RACH transmission. In one aspect, the bandwidth is reserved for scheduling request transmission. In one aspect, the resource is included in a PUCCH.

The resource determination component <NUM> may provide an indication of the determined resource to a transmission component <NUM>. The transmission component <NUM> may be configured to transmit a beam adjustment request to the mmW BS <NUM> on the determined resource in order to indicate an index associated with the selected beam. The beam adjustment request may include a request for a BRRS.

In one aspect, the beam detection component <NUM> may receive, from the mmW BS <NUM>, an instruction to perform beam refinement at a receiver (e.g., the reception component <NUM>) of the apparatus <NUM>. The beam detection component <NUM> may perform beam refinement based on the request.

<FIG> is a diagram <NUM> illustrating an example of a hardware implementation for an apparatus <NUM>' employing a processing system <NUM>. The processing system <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing system <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware components, represented by the processor <NUM>, the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and the computer-readable medium / memory <NUM>. The bus <NUM> may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system <NUM> may be coupled to a transceiver <NUM>. The transceiver <NUM> is coupled to one or more antennas <NUM>. The transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. The transceiver <NUM> receives a signal from the one or more antennas <NUM>, extracts information from the received signal, and provides the extracted information to the processing system <NUM>, specifically the reception component <NUM>. In addition, the transceiver <NUM> receives information from the processing system <NUM>, specifically the transmission component <NUM>, and based on the received information, generates a signal to be applied to the one or more antennas <NUM>. The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium / memory <NUM>. The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory <NUM>. The software, when executed by the processor <NUM>, causes the processing system <NUM> to perform the various functions described supra for any particular apparatus. The computer-readable medium / memory <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software. The processing system <NUM> further includes at least one of the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The components may be software components running in the processor <NUM>, resident/stored in the computer readable medium / memory <NUM>, one or more hardware components coupled to the processor <NUM>, or some combination thereof. The processing system <NUM> may be a component of the UE <NUM> and may include the memory <NUM> and/or at least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM>.

In one configuration, the apparatus <NUM>/<NUM>' for wireless communication includes means for detecting a set of beams from a base station. The apparatus <NUM>/<NUM>' may further include means for selecting a beam of the set of beams. The apparatus <NUM>/<NUM>' may further include determining at least one resource based on the selected beam. In an aspect, the at least one resource may include at least one of a radio frame index, a subframe index, a symbol index, or a subcarrier region. The apparatus <NUM>/<NUM>' may further include means for transmitting, on the at least one determined resource, a beam adjustment request to the base station, wherein the at least one determined resource indicates an index associated with the selected beam.

In an aspect, the beam adjustment request to the base station comprises a request for a BRRS. In an aspect, the at least one resource is included in subframe associated with a RACH. In an aspect, the at least one resource is included in a bandwidth reserved for RACH transmission. In an aspect, the at least one resource is included in a bandwidth that is unreserved for RACH transmission. In an aspect, the bandwidth is reserved for scheduling request transmission. In an aspect, the at least one resource is included in a PUCCH.

In an aspect, the apparatus <NUM>/<NUM>' may further include means for receiving, from the base station, an instruction to perform beam refinement at a receiver of the UE based on the request. The apparatus <NUM>/<NUM>' may further include apparatus <NUM>/<NUM>' performing beam refinement based on the request. In an aspect, the performance of beam refinement at the UE receiver is further based on the selected beam.

<FIG> is a conceptual data flow diagram <NUM> illustrating the data flow between different means/components in an exemplary apparatus <NUM>. The apparatus may be a base station (e.g., a mmW base station). The apparatus <NUM> includes a reception component <NUM> that may receive signals from a UE (e.g., the UE <NUM>). The apparatus <NUM> may include a transmission component <NUM> that may transmit signals to a UE (e.g., the UE <NUM>).

In an aspect, the beam transmission component <NUM> may be configured to transmit a first of beams to the UE <NUM>. For example, the beam transmission component <NUM> may be configured to transmit a respective BRS in a respective synchronization subframe of a respective beam. The first set of beams may be a "coarse" set of beams.

The UE <NUM> may receive the first set of beams and select a best or preferred beam. The UE <NUM> may then transmit a beam adjustment request (e.g., a BRRS request. The reception component <NUM> may receive this request, which is carried on at least one resource, and provide the same to an index determination component <NUM>.

The index determination component <NUM> may be configured to determine a beam index of a beam in the first set of beams based on the at least one resource that carries the request. The index determination component <NUM> may be configured to determine the resource carries the beam adjustment request in order to determine a beam selected by the UE <NUM>. For example, a resource may include one of a radio frame, a subframe, a symbol, or a subcarrier region. Each resource may correspond to a value, for example, a radio frame index, a subframe index, a symbol index, or a subcarrier region. In one aspect, the index determination component <NUM> may have stored therein or may have access to a mapping or table (e.g., a lookup table) that indicates a respective resource (e.g., a value or index) to which the beam index corresponds. For example, the index determination component <NUM> may determine the beam index and then access a lookup table to determine a resource index or region that corresponds to the beam index.

In an aspect, the index determination component <NUM> determines, from within a range, the beam index based on a strength of a signal in different receive chains of the apparatus <NUM> (e.g., the receive chains included in the receive chains of the reception component <NUM>) through which the request is received. For example, the reception component <NUM> may receive the request through a plurality of receive chains. The index determination component <NUM> may determine a signal strength of the request for each receive chain through which the request is received. The index determination component <NUM> may determine that each receive chain is associated with at least one beam index, and so the index determination component <NUM> may determine the beam index that corresponds to the receive chain in which the highest signal strength of the request is detected.

The index determination component <NUM> may provide an indication of the beam index selected by the UE <NUM> to a beam refinement component <NUM>. The beam refinement component <NUM> may determine a second set of beams to transmit to the UE <NUM>. The second set of beams may be a "fine" beam set, which may be directionally and/or spatially closer to the beam selected by the UE <NUM>, the index of which may be determined by the index determination component <NUM>. The beam refinement component <NUM> may provide an indication of the indexes of the second set of beams to the beam transmission component <NUM>.

The beam transmission component <NUM> may be configured to transmit the second of beams to the UE <NUM>. For example, the beam transmission component <NUM> may be configured to transmit a respective BRRS in a respective synchronization subframe of a respective beam. The second set of beams may be a "fine" set of beams.

In an aspect, the beam transmission component <NUM> may transmit, to the UE <NUM>, an instruction to perform beam refinement based on the request. In an aspect, the instruction to perform beam refinement may be based on the selected beam determined by the index determination component <NUM>. The beam transmission component <NUM> may perform beam tracking with the UE <NUM>.

The processing system <NUM> may be coupled to a transceiver <NUM>. The transceiver <NUM> is coupled to one or more antennas <NUM>. The transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. The transceiver <NUM> receives a signal from the one or more antennas <NUM>, extracts information from the received signal, and provides the extracted information to the processing system <NUM>, specifically the reception component <NUM>. In addition, the transceiver <NUM> receives information from the processing system <NUM>, specifically the transmission component <NUM>, and based on the received information, generates a signal to be applied to the one or more antennas <NUM>. The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium / memory <NUM>. The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory <NUM>. The software, when executed by the processor <NUM>, causes the processing system <NUM> to perform the various functions described supra for any particular apparatus. The computer-readable medium / memory <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software. The processing system <NUM> further includes at least one of the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The components may be software components running in the processor <NUM>, resident/stored in the computer readable medium / memory <NUM>, one or more hardware components coupled to the processor <NUM>, or some combination thereof. The processing system <NUM> may be a component of the base station <NUM> and may include the memory <NUM> and/or at least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM>.

In one configuration, the apparatus <NUM>/<NUM>' for wireless communication includes means for transmitting a first set of beams. The apparatus <NUM>/<NUM>' may further include means for receiving a beam adjustment request on at least one resource. In an aspect, the at least one resource may include at least one of a radio frame index, a subframe index, a symbol index, or a subcarrier region. The apparatus <NUM>/<NUM>' may further include means for determining a beam index of a beam in the first set of beams based on the at least one resource.

In an aspect, the beam adjustment request comprises a request to transmit a BRRS. In an aspect, the apparatus <NUM>/<NUM>' may further include means for transmitting an instruction to perform beam tracking based on the request and determined beam index. In an aspect, the apparatus <NUM>/<NUM>' may further include means for performing beam tracking with the UE. In an aspect, the apparatus <NUM>/<NUM>' may further include means for transmitting a second set of beams based on the determined beam index to perform the beam tracking.

In an aspect, the at least one resource is included on a PUCCH. In an aspect, the at least one resource is included on subframe associated with a RACH. In an aspect, the at least one resource is included in a bandwidth associated with RACH transmission. In an aspect, the at least one resource is included in a bandwidth that is unreserved for RACH transmission. In an aspect, the bandwidth is reserved for scheduling request transmission. In an aspect, the at least one resource indicates a range of indexes and a subcarrier of the at least one resource indicates the beam index within the range.

In an aspect, a subframe of the at least one resource indicates a range of indexes, and the apparatus <NUM>/<NUM>' further includes means for determining, from within the range, the beam index based on a strength of a signal in different receive chains of the base station through which the request is received.

Claim 1:
A method (<NUM>) of wireless communication for a user equipment, UE, the method comprising:
based on determining that quality of a selected beam (<NUM>) deteriorates, so that the UE no longer prefers to communicate with a base station using the selected beam (<NUM>), the selected beam (<NUM>) being a beam from the base station, detecting (<NUM>) a set of beams from the base station;
selecting (<NUM>) a new beam (<NUM>) from the set of beams;
determining (<NUM>) at least one resource based on the new beam (<NUM>), the at least one resource including at least one of a radio frame index, a subframe index, a symbol index, or a subcarrier region, wherein the UE has stored therein a mapping that indicates the at least one resource to which the beam index of the new beam (<NUM>) corresponds; and
transmitting (<NUM>), to the base station on the at least one determined resource, a beam adjustment request, wherein the at least one determined resource indicates the beam index of the new beam (<NUM>).