BR112017000407B1 - METHODS AND EQUIPMENT FOR BEAM SEARCH AND TRACKING IN MM WAVE ACCESS SYSTEMS - Google Patents

Abstract

A method, an apparatus and a computer program product for operating a user equipment (UE) are presented. The equipment determines a first coarse set of beamforming paths between the UE and a first millimeter wave base station (mmW-BS), receives on a first set of narrow beamforming paths close to a first beams within the first coarse set of beamforming paths, requests the first mmW-BS to transmit on a second set of narrow beamforming paths close to a second set of narrow beamforming paths within the first coarse set of beamforming paths when the signal quality of the first beamforming path and the first set of narrow beamforming paths is less than a first threshold, and communicates via one of the second beamforming paths or a path within of the second set of narrow beamforming paths.

Description

CROSS REFERENCE TO RELATED ORDER

[0001] This application claims the benefit of US patent application No. 14/332 353 entitled “METHODS AND EQUIPMENT FOR SEARCHING AND TRACKING BEAM IN MM WAVE ACCESS SYSTEMS”, and filed on July 15, 2014, which is expressly incorporated herein in its entirety by way of reference.

BACKGROUND Field

[0002] The present disclosure relates generally to communication systems, and more specifically to methods and equipment for searching and tracking beams in millimeter wave (mmW) access systems.

Background

[0003] Wireless communication systems are widely deployed to provide various telecommunication services, such as telephony, types of communication content, video, data, messaging, broadcast. Typical wireless communication systems may use multiple access technologies capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmission power, for example). Examples of such multiple access technologies include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, and Synchronous Time Division Code Division Multiple Access (TD-SCDMA) systems

[0004] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that allows different wireless devices to communicate at a municipal, national, regional and even global level. An example of an emerging telecommunications standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard enacted by the Third Generation Partnership Project (3GPP). LTE is 3GPP designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other standards that use OFDMA downlink (DL ), SC-FDMA on the uplink (UL), and multi-input, multi-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there is a need for further enhancements to LTE technology. Preferably these improvements should be applicable to other multiple access technologies to telecommunication standards using these technologies.

SUMMARY

[0005] Under one aspect of the disclosure, a method, a computer program product and an apparatus are presented. The equipment determines a first coarse set of beamforming paths between the UE and a first millimeter wave base station (mmW-BS) receives on a first set of narrow beamforming paths close to a first beamforming path within the first coarse set of beamforming paths, requests the first mmW-BS to transmit on a second set of beamforming paths near a second coarse set of beamforming paths within the first coarse set of beamforming paths when the signal quality of the first beamforming path and the first set of narrow beamforming paths are less than a first threshold and communicate via one of the second beamforming path or a path within the second set of beamforming paths narrow beamforming paths.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a diagram showing an example of network architecture.

[0007] Figure 2 is a diagram showing an example of an access network.

[0008] Figure 3 is a diagram showing an example of DL frame structure in LTE.

[0009] Figure 4 is a diagram showing an example of UL frame structure in LTE.

[0010] Figure 5 is a diagram showing an example radio-protocol architecture for the user and control planes.

[0011] Figure 6 is a diagram showing an example of evolved Node B and user equipment in an access network.

[0012] Figure 7 is a diagram of a device-to-device communication system.

[0013] Figure 8 is a diagram showing an mmW system.

[0014] Figure 9 is a diagram showing a procedure for a UE to select between different mmW-BS and track the paths between multiple mmW-BSs over the duration of mmW activity in a UE.

[0015] Figure 10 is a flowchart of a wireless communication method.

[0016] Figure 11 is a data flow diagram showing the data flow between different modules/devices/components in exemplary equipment.

[0017] Figure 12 is a diagram that shows an example of hardware implementation for equipment that uses a processing system.

DETAILED DESCRIPTION

[0018] The detailed description presented below in connection with the accompanying drawings is intended to be a description of various configurations and is not intended to represent the only configurations in which the concepts described herein can be put into practice. The detailed description includes specific details intended to provide a complete understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts can be put into practice without these specific details. In some cases, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

[0019] Various aspects of telecommunication systems will now be presented with reference to various equipment and methods. These equipment and methods will be described in the following detailed description and shown in the attached drawings by different blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements”). These elements can be implemented using electronic hardware, computer software or combinations thereof. Whether such elements are implemented as hardware or software depends on the specific application and the design constraints imposed on the system as a whole.

[0020] By way of example, an element or any part of an element or any combination of elements may be implemented with a "processing system" that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionalities described throughout this disclosure. One or more processors in the processing system can run software. Software will be interpreted broadly to mean instructions, sets of instructions, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, execution flows, procedures, functions, etc., whether referred to as software/firmware, middleware, microcode, hardware description language or otherwise.

[0021] Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or combinations thereof. If implemented in software, functions may be stored or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media include storage media. Storage media can be any available media that can be accessed by a computer. By way of example and not limitation, such computer readable media may comprise random access memory (RAM), read only memory (ROM), electrically erasable programmable ROM (EEPROM), compact disk ROM ( CD-ROM) other optical disk storage or magnetic disk storage or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Combinations of the above elements are also included within the range of computer readable media.

[0022] Figure 1 is a diagram showing an LTE network architecture 100. The LTE network architecture 100 may be referred to as an Evolved Packet System (EPS) 100. The EPS 100 may include one or more user equipment ( UEs) 102, an Evolved Terrestrial Radio Access (UMTS) network (E-UTRAM) 104, an Evolved Packet Core (EPC) 110, and Carrier IP Service 122. The EPS can interconnect with other access networks, but for simplicity, these entities/interfaces are not shown. As shown, EPS provides packet-switched services, but as will be readily understood by those skilled in the art, the various concepts presented throughout this disclosure can be extended to networks that provide circuit-switched services.

[0023] The E-UTRAM includes the Evolved Node B (eNB) 106 and other eNBs 108 and may include a Multicast Coordination Entity (MCE) 128. The eNB provides protocol terminations in the user and control plane towards the UE 102. The eNB 106 may be connected to the other eNBs 108 via a backhaul channel (an X2 interface, for example). ECM 128 allocates radio time/frequency resources for Evolved Multicast/Multimedia Broadcast Service (MBMS) (eMBMS) and determines the radio configuration (a modulation and coding scheme (MCS), for example) for the eMBMS. The MCE 128 may be a separate entity or part of the eNB 106. The eNB 106 may also be referred to as a base station, NodeB, base transceiver station, radio base station, radio transceiver, transceiver function, Basic Service Set (BSS) ), extended service set (ESS), access point, or some other suitable terminology. The eNB 106 may provide an access point to the EPC 110 for a UE 102. Examples of UEs 102 include a cell 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 (an MP3 player, for example), a camera, a game console, a tablet, or whatever similar operating device. UE 102 may also be referred to by those skilled in the art as a mobile station, subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, remote apparatus, wireless apparatus, wireless communication apparatus, remote apparatus, station mobile subscriber, access terminal, mobile terminal, wireless terminal, remote terminal, handset, user agent, mobile client, client or some other suitable terminology.

[0024] The eNB 106 is connected to the EPC 110. The EPC 110 includes a Mobility Management Entity (MME) 112, a Native Subscriber Server (HSS) 120, other MMEs 114, a Server Gateway 116 and a Services Gateway broadcast/multicast service center (MBMS) 124, a broadcast/multicast service center (BM-SC) 126, and a Packet Data Network (PDN) Gateway 118. The MME 112 is the control node that processes the signaling between the UE 102 and the EPC 110. Generally the MME 112 provides bearer and connection management. All IP packets are transferred through Server Gateway 116, which is itself connected to PDN Gateway 118. PDN Gateway 118 provides UE IP address allocation as well as other functions. PDN Gateway 118 and BM-SC 126 are connected to IP Services 122. IP Services 122 may include the Internet, the Intranet, and a Stream Service (PS) (PSS) and/or other IP services. The BM-SC 126 can perform functions for providing and delivering MBMS user service. The BM-SC 126 can function as an entry point for content provider MBMS transmission, can be used to authorize and initiate MBMS bearer services within a PLMN, and can be used to schedule and deliver MBMS transmissions. The MBMS Gateway 124 can be used to distribute MBMS traffic to the eNBs (106, 108, for example) belonging to a Multicast/Broadcast Single Frequency Network (MBSFM) area that broadcasts a specific service and can be responsible managing sessions (start/stop) and collecting eMBMS-related billing information.

[0025] In one aspect, the UE 102 is capable of transmitting signals via the LTE network and an mmW system. Therefore, the UE 102 can communicate with the eNB 106 and/or the other eNB 108 over an LTE link. Furthermore, the UE 102 can communicate with a connection point (CP) or base station (BS) 130 (capable of mmW system communication) over an mmW link.

[0026] In another aspect, at least one of the other eNBs 108 may be able to communicate signals via the LTE network and the mmW system. Therefore, an eNB 108 can be referred to as an LTE + mmW eNB. In another aspect, CP-BS 130 can be able to communicate signals through LTE network and mmW system. Therefore, CP/BS 130 can be referred to as CP/BS LTE + mmW. The UE 102 can communicate with the other eNB 108 over an LTE link as well as over an mmW link.

[0027] In yet another aspect, the other eNB 108 may be capable of color signals via the LTE network and the mmW system, while the CP/BS 130 is capable of communicating signals via the mmW system only. Therefore, the CP/BS 130 unable to signal the other eNB 108 over the LTE network, can communicate with the other eNB 108 over an mmW backhaul link.

[0028] Figure 2 is a diagram showing an example access network 200 in an LTE network architecture. In this example, the access network 200 is divided into multiple cellular regions (cells) 202. One or more lower power class eNBs 208 may have cellular regions 210 that overlap one or more of the cells 202. of lower power 208 can be a femto cell (native eNB (HeNB)), pico cell or micro cell, or remote radio head (RRH). The macro-eNBs 204 are each assigned to a respective cell 202 and are configured to provide an access point to the EPC 110 for all UEs 206 in the cells 202. There is no centralized controller in this example access network 200, but a centralized controller can be used in alternative configurations. The eNBs 204 are responsible for all radio-related functions, which include radio-carrier control, admission control, mobility control, scheduling, security, and connectivity to the Server Gateway 116. An eNB can support one or several (three, for example) cells (also referred to as sectors). The term "cell" can refer to the smallest coverage area of an eNB or to an eNB subsystem serving a specific coverage network. Furthermore, the terms "eNB", "base station" and "cell" may be used interchangeably herein.

[0029] In one aspect, the UE 206 can communicate signals via the LTE network and an mmW system. Therefore, the UE 206 can communicate with the eNB 204 over an LTE link and communicate with a CP or BS 212 (capable of mmW system communication) over an mmW link. In another aspect, eNB 204 and CP/BS 212 can communicate signals via LTE network and mmW system. Therefore, the UE 206 can communicate with the eNB 204 via an LTE link and an mmW link (when the eNB 204 is capable of mmW system communication) or communicate with the CP/BS 212 via a mmW link and an LTE link (when the CP/BS is capable of LTE network communication). In yet another aspect, the eNB 204 communicates signals via the LTE network and the mmW system, while the CP/BS 202 communicates signals via the mmW system only. Therefore, the CP/BS 212 communicates signals with the mmW system only. Therefore, the CP/BS 212, unable to signal the eNB 204 over the LTE network, can communicate with the eNB 204 over an mmW backhaul link.

[0030] The modulation and multiple access scheme used by the access network 200 may vary depending on the specific telecommunications standard that is deployed. In LTE applications, OFDM is used in DL and SC-FDMA is used in UL to support both frequency division duplex (FDD) and time division duplex (TDD). As will be readily understood by those skilled in the art from the following detailed description, the various concepts presented here are well suited for LTE applications. However, these concepts can be readily extended to other telecommunication standards that use other modulation and multiple access techniques. As an example, these concepts can be extended to Evolution-Data Optimized (EV-DO) or Ultra-Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and use CDMA to provide broadband Internet access to mobile stations. These concepts can also be extended to Universal Radio-Terrestrial Access (UTRA), which uses Broadband CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA; and the Global System for Mobile Communications (GSM) using TDMA; and Evolved UTRA (E-UTRA), (IEEE) 802.11 (WiFi), IEEE 802.16 (WiMAX) IEEE 802.20 and Flash-OFDM which uses OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described as 3GPP organization documents. CDMA2000 and UMB are described in 3GPP2 organization documents. The actual wireless communication standard and multiple access technology used will depend on the specific application and design constraints placed on the system.

[0031] The eNBs 204 may have multiple antennas that support MIMO technology. The use of MIMO technology allows the eNBs 204 to exploit the spatial domain to support spatial multiplexing, beamforming and transmission diversity. Spatial multiplexing can be used to transmit different streams of data simultaneously on the same frequency. Data streams can be transmitted to a single UE 206 in order to increase the data rate or to multiple UEs 206 in order to increase the capacity of the total system. This is achieved by spatially precoding each data stream (applying amplitude and phase scaling, for example) and then transmitting each spatially precoded stream through multiple transmit antennas in the DL. The spatially precoded data streams arrive at the UEs 206 with different spatial signatures, which allows each of the UEs 206 to retrieve the data stream or streams destined for that UE 206. In the UL, each UE 206 transmits a data stream spatially precoded, which allows the eNB 204 to identify the source of each spatially precoded data stream.

[0032] Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming can be used to focus transmission energy in one or more directions. This can be achieved by spatially precoding the data for transmission over multiple antennas. In order to obtain good coverage at the cell edges, a single stream beamforming transmission can be used in combination with transmission diversity.

[0033] In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system that supports OFDM in DL. OFDM is a spectrum multiplexing technique that modulates data across multiple subcarriers within an OFDM symbol. The sub-carriers are spaced apart at precise frequencies. The offset provides “orthogonality” that allows a receiver to retrieve data from subcarriers. In the time domain, a guard interval (a cyclic prefix, for example) can be added to each OFDM symbol to combat OFDM inter-symbol interference. The UL can use SC-FDMA in the form of an OFDM signal with DFT spreading to compensate for the peak-to-average power ratio (PAPR).

[0034] Fig. 3 is a diagram 300 showing an example of DL frame structure in LTE. A frame (10 msg) can be divided into 10 sub-frames of equal size. Each subframe can include two consecutive time slices. A resource grid can be used to represent two time slices, each time slice including a block of resources. The resource grid is divided into several resource elements. In LTE, for a normal cyclic prefix, a resource block contains 12 consecutive subcarriers in the frequency domain and 7 consecutive OFDM symbols in the time domain, for an 84 resource elements. For an extended cyclic prefix, a feature block contains 12 consecutive subcarriers in the frequency domain and 6 consecutive OFDM symbols in the time domain, for a total of 72 feature elements. Some of the resource elements indicated as R 302, R 304, include DL reference signals (DL-RS). DL-RS include Cell Specific RS (CRS)(also sometimes called common RS) 302 and UE Specific RS (UE-RS) 304. UE-RS 304 are transmitted only in resource blocks where the channel is shared corresponding physical DL (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks a UE receives and the higher the modulation scheme, the higher the data rate for the UE.

[0035] Fig. 4 is a diagram 400 showing an example of a UL frame structure in LTE. The resource blocks available to the UL can be partitioned into a data section and a control section. The control section can be formed on both edges of the system bandwidth and can have a configured size. Resource blocks in the control section can be assigned to UEs for transmitting control information. The data section can include all resource blocks not included in the control section. The UL frame structure results in the inclusion of contiguous subcarriers in the data section, which may allow a single UE to be assigned all contiguous subcarriers of the data section.

[0036] A UE can be assigned resource blocks 410a, 410b in the control section for transmitting control information to an eNB. The UE may also be assigned resource blocks 420a, 420b in the data section for transmitting data to the eNB. The UE may transmit control information on a physical UL control channel (PUCCH) in resource blocks assigned in the control section. The UE can transmit only data or both data and control information on a physical UE shared channel (PUSCH) in the resource blocks allocated in the data section. A UL transmission can span both partitions of a subframe and can hop across the frequency.

[0037] A set of resource blocks can be used to perform initial access to the system and obtain UL synchronization on a physical random access channel (PRACH) 430. The PRACH 430 carries a random sequence and cannot carry any UL data/sync . Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried over a single subframe (1 msec) or a sequence of a few contiguous subframes, and a UE can make only a single PRACH attempt per frame (10 msec).

[0038] Figure 5 is a diagram 500 showing an example radio protocol architecture for user and control planes in LTE. The radio protocol architecture for UE and eNB is shown with three layers: Layer 1, Layer 2 and Layer 3. Layer 1 (Layer L1) is the lowest layer and implements various signal processing functions physical layer. The L1 layer will be referred to here as the physical layer 506. The Layer 2 (L2 layer) 508 lies above the physical layer 506 and is responsible for the link between the UE and the eNB through the physical layer 506.

[0039] In the user plane, the L2 layer 508 includes a Media Access Control (MAC) sub-layer 510, a Radio Link Control (RLC) sub-layer 512, and a Link Protocol sub-layer. packet data convergence (PDCP) 514 that are terminated in the eNB on the network side. Although not shown, the UE can have several upper layers above the L2 layer that include a network layer (IP layer) that terminates at PDN Gateway 118 on the network side and an application layer that terminates at the other end of the connection ( Far-end UE, server, etc., eg).

[0040] The PDCP sub-layer 514 provides multiplexing between radio-carriers and different logical channels. PDCP sublayer 514 also provides header compression for upper layer data packets to reduce radio transmission overhead. Security by encryption of data packets and handover support for UEs to UEs between eNBs. RLC sublayer 512 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to HARQ hybrid autorepeat request. MAC sublayer 510 provides multiplexing between logical and transport channels. The MAC sublayer 510 is also responsible for allocating the various radio resources (resource blocks, for example) in a cell among the UEs. MAC sublayer 510 is also responsible for HARQ operations.

[0041] In the control plane, the radio protocol architecture for the UE and the eNB is substantially the same for the physical layer 506 and the L2 layer 508, with the exception that there is no header compression function for the plane of control. The control plane also includes a radio resource control (RRC) sub-layer 516 at Layer 3 (L3). The RRC sublayer 516 is responsible for obtaining radio resources (i.e., radio carriers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

[0042] Figure 6 is a block diagram of a base station 610 in communication with a UE 650 in an access network. The base station 610 can be, for example, an eNB of an LTE system, a point of connection (CP)/access point/base station of an mmW system, an eNB capable of communicating signals via the LTE system and the system mmW, with a point of connection (CP)/access point/base station capable of communicating signals via the LTE system and the mmW system. UE 650 may be capable of communicating signals via the LTE system and/or the mmW system. In the DL core network upper layer packets are sent to a controller/processor 675. The controller/processor 675 implements the functionality of the L2 layer. In the DL, controller/processor 675 provides header compression, encryption, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to UE 650 based on various priority metrics. Controller/processor 675 is also responsible for HARQ operations, retransmission of lost packets, and signaling to UE 650.

[0043] Transmission (TX) processor 616 implements various signal processing functions for L1 layer (i.e. physical layer). Signal processing functions include encoding and interleaving to facilitate forward error correction (FEC) in the UE 650 and mapping into signal constellations based on various modulation schemes (Binary Phase Key Shift (BPSK) keying, by quadrature key shift (QPSK), M phase shift keying (M-PSK), M quadrature amplitude modulation (M-QAM)). The encoded and modulated symbols are then divided into parallel streams. Each stream is then mapped onto an OFDM subcarrier, multiplexed with a reference signal (pilot, for example) in the time and/or frequency domain, and then combined with each other using an inverse Fast Fourier transform. (IFFT) to produce a physical layer that carries a stream of OFDM symbols in the time domain. The OFDM stream is spatially pre-coded in order to produce multiple spatial streams. Channel estimates from a channel estimator 674 can be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a channel condition feedback or reference signal transmitted by UE 650. Each spatial stream is then sent to a different antenna 620 via a separate transmitter 618TX. Each 618TX transmitter modulates an RF carrier with its own special stream for transmission.

[0044] At the UE 650, each receiver 654RX receives a signal through its respective antenna 652. Each receiver 654RX receives modulated information on an RF carrier and provides the information to the receive processor (RX) 656. The processor RX656 implements various functions of L1 layer signal processing. The RX656 processor can perform spatial processing on the information in order to retrieve any spatial streams destined for the UE 650. If multiple spatial streams are destined for the UE 650, they can be combined by the RX656 processor into a single OFDM symbol stream. The RX656 processor then converts the OFDM symbol stream from the time domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each sub-carrier of the OFDM signal. The symbols on each subcarrier and the reference signal are recovered and demodulated by determining the most likely signal constellation points transmitted by base station 610. These timing decisions may be based on channel estimates computed by channel estimator 658. The temporary decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by base station 610 on the physical channel. The data and control signals are then sent to the 659 controller/processor.

[0045] The 659 controller/processor implements the L2 layer. The controller/processor may be associated with a memory 660 which stores program codes and data. Memory 660 may be referred to as a computer-readable medium. In DL, controller/processor 659 provides demultiplexing between transport and logical channels, packet reassembly, decryption, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then sent to a data bucket 662, which represents all protocol layers above the L2 layer. Various control signals can also be sent to data warehouse 663 for L3 processing. Controller/processor 659 is also responsible for error detection using an acknowledgment (ACK) and/or negative acknowledgment (NACK) protocol to support HARQ operations.

[004] In the UL, a data source 667 is used to send upper layer packets to controller/processor 659. Data source 667 represents all protocol layers above the L2 layer. Similar to the functionality described in connection with DL transmission by base station 610, controller/processor 659 implements the L2 layer for the user plane and control plane providing header compression, scrambling, packet segmentation and reordering, and multiplexing. between logical and transport channels based on allocations of radio resources by base station 610. Controller/processor 659 is also responsible for HARQ operations, retransmission of lost packets, and signaling to base station 610.

[0047] The channel estimates derived by a channel estimator 658 from a reference or feedback signal transmitted by the base station 610 can be used by the TX processor 668 to select the appropriate coding and modulation schemes and to facilitate spatial processing . The spatial streams generated by the TX processor 668 are sent to different antennas 652 via separate transmitters 654TX. Each 654TX transmitter can modulate an RF carrier with a respective spatial stream for transmission.

[0048] The UL transmission is processed at base station 610 in a similar manner as described in connection with the receiver function at UE 650. Each receiver 618RX receives a signal through its respective antenna 620. Each receiver 618RX receives information modulated on a carrier RF and sends the information to an RX670 processor. The RX670 processor can implement the L1 layer.

[0049] The 675 controller/processor implements the L2 layer. Controller/processor 675 may be associated with a memory 676 that stores program code and data. Memory 676 may be referred to as a computer-readable medium. At the UL the controller/processor 675 provides demultiplexing between transport and logical channels, packet reassembly, decryption, header decompression, control signal processing to recover upper layer packets from UE 650. Controller/processor upper layer packets can be sent to the core network. Controller/processor 675 is also responsible for error detection which uses an ACK and/or NACK protocol to support the HARQ partitions.

[0050] Figure 7 is a diagram of a device-to-device communication system 700. The device-to-device communication system includes a series of wireless devices 704, 706, 708, 710. The device-to-device communication system apparatus 700 can be superimposed on a cellular communication system, such as, for example, a wireless wide area network (WWAN). Some of the wireless handsets 704, 706, 708, 710 can communicate together in handset-to-device communication using the WWAN DL/UL spectrum, some can talk to the base station 702, and some can do both. As shown in Figure 7, for example, wireless devices 708, 710 are in device-to-device communication and wireless devices 704, 706 are in device-to-device communication. Wireless handsets 704, 706 are also communicating with base station 702.

[0051] The exemplary methods and equipment discussed below are applicable to any of a number of wireless device-to-device communication systems, such as, for example, a wireless device-to-device communication system based on FlashLinQ, WiMedia, Bluetooth , ZigBee or Wi-Fi based on the IEEE 802.11 standard. To simplify the discussion, exemplary methods and equipment are discussed within the context of LTE. However, those skilled in the art would understand that the exemplary methods and equipment are more generally applicable to various other device-to-device wireless communication systems.

[0052] An mmW system is a wireless communication system designed to operate at very high frequency bands (an mmW system that uses carriers in the frequency range from 10.0 GHz to 300.o GHz), for example). Such high carrier frequencies allow the use of large bandwidths. While typical use cases in such bands have a backhaul, the spectrum can be implemented for use by UEs to access the network.

[0053] Under one aspect, devices (a UE or a mmW/BS for example) at both ends of a link in an mmW system may utilize multiple antennas (also referred to as phased arrays) to perform beamforming in order to get a better link gain. Channel characteristics at high carrier frequencies necessitate beamforming approaches to overcome propagation losses. Such beamforming can allow a network to avoid being heavily jammed by interference and can allow the network to support parallel scheduling of many links due to their spatial and angular separation.

[0054] Figure 8 is a diagram showing an mmW system 800. As shown in Figure 8, the mmW system 800 includes mmW-BSs 802, 804 and UEs 806, 808. In an aspect of Figure 8, the mmW-BSs 802, 804, in a region that allows the UEs 806, 808 to connect to the mmW-BSs 802, 804 through high bandwidth, through high bandwidth, highly beamformed channels. Beamforming is the operation in which different antennas of a UE are combined with different weights in order to obtain a higher gain in one or more antenna directions and reject the received signal from other directions. For example, UE 806 may communicate with mmW-BS 802 via mmW link 810 and may communicate with mmW-BS 804 via mmW 812. In such an example, UE 808 may communicate mmW-BS 802 via mmW link 814 and can communicate with mmW-BS 804 via mmW link 816. In one respect, mmW-BSs 802, 804 can play a role similar to that of eNBs or access points.

[0055] Under one aspect, an array of antennas of a device (a UE, for example) in an mmW system can be directed by directing beams in the direction of arrival angles and/or departure angles that correspond to the path between devices in the mmW system. For example, an angle of departure in azimuth can be denoted as “Φr” and an angle of arrival in azimuth can be denoted as “ΦR”, and an angle of departure in elevation can be denoted as “θT” and the angle of arrival in in elevation can be denoted as “θR”. A beamforming scheme may correspond to directing an array of antennas to a subset of the dominant scatterpaths between an apparatus (the UE 806, for example) and/or another apparatus (the mmW-BS 802, for example). Therefore, an mmW-BS and/or a UE can transmit training symbols via training beamforming vectors with array property and can scan through angular space. In one aspect, the mmW-BS and/or UE can scan through a subset of angular space.

[0056] The angles and gains (magnitude and phase) of the paths between the devices in the mmW system (the mmW 800 system, for example) can change over time due to the relative mobility between the mmW-BS (the mmW -BS 810, for example), the scatterers and/or the UE (the UE 806, for example). In one scenario, such relative mobility might include angular movement (spatial rotation, for example) of the UE by the user. In another scenario, paths between fixtures in the mmW system may be momentarily blocked by obstacles. Determining the different directions and paths between devices in the mmW system without any prior information can be difficult and may require more signaling and resources than the paths over time of the initial search point.

[0057] Under one aspect, the behavior of several specular components can be traced, with respect to a specific mmW-BS. In one aspect, the UE (the UE 806, for example) or mmW-BS (the mmW-BS 802, for example) can track the currently used dominant paths. In another aspect, the UE or the mmW-BS can switch to a better path. given the presence of multiple mmW-BS within an area, switching between one mmW-BS and another mmW-BS may be preferable to switching to a different path or subpaths to the same mmW-BS.

[0058] Figure 9 is a diagram 900 showing a procedure for a UE (the UE 806, for example) to select between different mmW-BSs (the mmW-BSs 802, 804, for example) and track the paths between different mmW-BSs over the duration of mmW activity in a UE. In one aspect, a UE may perform an initial search (also referred to as a primary search) to determine beam angles and to associate with an mmW-BS ("the mmW-BS1 802", for example) with dominant L paths, where each one of the L dominant paths is defined by a set of arrival and departure angles. For example, the set of arrival and departure angles i between UE 806 and mmW-BS 802 can be denoted as For each path, the corresponding index i in the set of arrival and departure angles can be an integer from 1 to L in descending order of dominance and typically L = 2 paths would be a compromise between path/angular diversity and complexity drawing of the beamformer. For example, the set of arrival and departure angles for the most dominant path (i = 1, for example) can be denoted as

[0059] As shown in Figure 9, a UE (UE 806, for example) may initiate an initial search 902 and perform a coarse angular scan 904 of a set of training beamforming vectors received from mmW-BSs. In one aspect, and as shown in Figure 9, the coarse angle sweep 904 can allow the UE to determine 906 the number of paths and angles between a first mmW-BS (the mmW-BS1 802, for example) and the UE. In another aspect, the coarse angular sweep 904 may also allow the UE to determine 908 the number of paths and angles between a second mmW-BS (the mmW-BS2 804, for example) and the UE. In one respect, a third mmW-BS (the mmW-BS3, for example) may not be discovered, but could potentially be used for beam switching at a later point in time. In one aspect, the UE 904 may continue to perform coarse angular scanning 904 as long as a connection to an mmW-BS is required, as indicated by arrow 905.

[0060] In one respect, if the first mmW-BS generates a higher signal quality than or a higher beamforming quality than the second mmW-BS, the UE can associate with the mmW-BS (setting a communication link with the first mmW-BS, for example) and may not associate with the second mmW-BS. For example, the UE can identify dominant paths to different mmW-BSs (the mmW-BS1 802, the mmW-BS2 804, for example) and can choose to associate with mmW-BS that have a dominant path with a quality of higher signal or with a signal frame that exceeds a threshold. In one aspect, the UE may determine a channel quality (a SINR value, for example) between different beams. In this regard, the UE can choose the mmW-BS with the highest SINR value and can establish a communication link for data transmission.

[0061] Over the duration of the communication link, the path of the communication link may change and/or the UE and the first mmW-BS may need to track the path of the communication link. For example, the path of the communication link may change due to the relative mobility discussed earlier between the first mmW-BS, the scatterers and/or the UE. In one aspect, the UE may request a fine-grained search 910 of a subset of paths close to the path of the communication link. For example, the UE can make the request by transmitting a signal to the first mmW-BS. The UE and the first mmW-BS may exchange specific communication link path tracking signals 912. In one aspect, the UE and the first mmW-BS can send and receive training signals formed by beams and update their beams/steering angles to track the path of the communication link. If the beamformed training signals are not received by either the UE or the first mmW-BS within a timeout period, stereo 914 may revert to signaling 912 by requesting retransmission of the beamformed training links. In one aspect, the UE and the first mmW-BS can perform a fine tuning 910 by performing a fine-tuning of a subset of paths or performing either a path switch or a switch of mmW-BSs depending on the measured channel quality.

[0062] In one scenario, the UE (the UE 906, for example) can perform the coarse angular sweep 904 and can identify the presence of several mmW-BSs (the mmW-BS1 802 and the mmW-BS2 804, for example) . The UE may choose to associate with or select a subset of the mmW-BSs to establish a communication link or for additional tracking. In one aspect, selection can be performed based on the coarse angular scan 904. The mmW-BS (the mmW-BS1 802 and/or mmW-BS2 804, for example) and/or the UE can identify the dominant paths between a given pair of mmW-BS and a UE.

[0063] In another scenario, the dominant set of angles ( , for example) that connects the UE (the UE 806 for example) and the first mmW-BS (the mmW-BS1 802 for example) can be separated by a small margin. In such a scenario, connected angles can be corrected and refined with a beam realignment phase (which consists of a bundle of beams located around the connected angles discovered in the primary search, for example). For example, a fine-tuning algorithm can use a set of k angles in the vicinity of the known angle for probing/training and estimating the received SNR. A mmW-BS and UE pair may choose to refine only a subset of the beams identified in the coarse angular scan 904. For example, the fine-tuning algorithm may consist of three closely spaced beams around a dominant direction in the first mmW - BS and by sweeping through the UE of some directions around each dominant angle for each of the first dominant mmW-BS directions.

[0064] In another scenario, the SINR received from the dominant path may drop significantly due to the physical rotations caused in the UE (the UE 806, for example) by the user. In such a scenario, the first mmW-BS (mmW-BS1 802 for example) may discover SINR loss in the dominant path and request a fine tuning algorithm as described above and correct the beamforming for the dominant path.

[0065] In an alternative scenario, the SINR associated with the dominant path may drop significantly due to mobility or changes in propagation dynamics. Such a scenario can occur, for example, when a route is physically blocked by an obstacle. In this scenario, the communication link between the first mmW-BS (mmW-BS1 802, for example) and the UE (UE 806, for example) can either switch to the known angles of the next dominant best path ( for example) or start a fine tuning phase for the selected hostage beam realignment phase as described in the first scenario.

[0066] In another scenario, the SINR received from all known dominant paths associated with the first mmW-BS (mmW-BS1 802, for example) may be too low to satisfy the data rate needs of the UE (or UE 806, for example). In such a scenario, the UE may determine that the second mmW-BS (mmW-BS2 804, for example) may be preferred over the first mmW-BS with respect to a specific purpose (data rate purposes or security purpose, for example). In such a scenario, the UE may request the second mmW-BS either for an initial angle discovery or for an incremental angle learning phase. For example, the UE may make the request despite any knowledge the UE may already have of the angles connecting the UE to the second mmW-BS. The association of paths between the UE and the second mmW-BS can be performed as discussed above.

[0067] In another scenario, the SINR received from all known dominant paths that associate both a first mmW-BS (mmW-BS1 802, for example) and a second mmW-BS (mmW-BS2 804, for example) may fail to meet the data rate requirements of the UE (the UE 806, for example). In such a scenario, the UE may initiate the initial search 902 (or a reset process) and search for a coarse angular scan 904 that can discover the first mmW-BS, the second mmW-BS or the third mmW-BS. The UE may then associate with the first discovered mmW-BS, second mmW-BS, or third discovered mmW-BS that satisfy the data rate requirements of the UE.

[0068] Fig. 10 is a flowchart 1000 of a wireless communication method. The method can be performed by a UE (the UE 806, the equipment 1102/1102', for example). It should be understood that the steps indicated by dotted lines in Figure 10 represent optional steps.

[0069] In step 1002, the UE determines a first coarse set of beamforming paths between the UE and a first mmW-BS. For example, the user can receive a first signal from a first mmW-BS and can use the first signal to determine at least two pairs of beamforming directions (ik and jk, k^2), with ik corresponding to first mmW-BS and jk corresponding to UE.

[0070] In step 1004, the UE selects at least one first or second beamforming path within the first coarse set of beamforming paths. In one aspect, the UE can select the beamforming path with the highest signal quality (highest signal strength, for example). For example, if the first beamforming path has the highest signal quality within the first coarse set of beamforming paths, the UE can select the first beamforming path.

[0071] In step 1006, the UE receives in a first set of narrow beamforming paths close to a first beamforming path within the first set of coarse beamforming paths.

[0072] In step 1008, the UE requests the first mmW-BS to transmit on a second set of narrow beamforming paths close to a second beamforming path within the first coarse set of beamforming paths when the signal quality of the first beamforming path and the first set of narrow beamforming paths is less than a first threshold. In one aspect, the UE may make the request by transmitting a second signal to the first mmW-BS that requests adjustment of the transmission beamforming direction to be used by the first mmW-BS. In one aspect, the UE may receive a third signal from the first mmW-BS to track the selected first beamforming path as a function of the received signal strength of the third signal.

[0073] In step 1010, the UE transmits a message that indicates at least a direction index or signal strength for one of the second beamforming paths or a path within the second set of narrow beamforming paths. In one aspect, the message may be transmitted to the mmW-BS with which a communication link is established.

[0074] In step 1012, the UE communicates over one of the second beamforming paths or a path within the second set of narrow beamforming paths.

[0075] In step 1014, the UE determines a second coarse set of beamforming path between a UE and a second mmW. For example, the UE may receive a fourth signal from a second mmW-BS and may use the fourth signal to determine at least two other pairs of beamforming directions between the second mmW-BS and/or the UE.

[0076] In step 1016, the UE selects at least one first or second beamforming path within the second coarse set of beamforming paths. In one aspect, the UE selects at least the first or second beamforming path by measuring the signal strength of the first and second beamforming paths and selecting the beamforming path (one beamforming pair corresponds to one beamforming path, for example) with the highest signal strength.

[0077] In step 1018, the UE requests the second mmW-BS to transmit on a first set of narrow beamforming paths close to a first set of beamforming paths within the second coarse set of beamforming paths when the Signal quality of all selected beamforming paths that correspond to the first mmW-BS is less than a second threshold.

[0078] In step 1020, the UE requests that the first mmW-BS refrain from signaling on any selected beamforming paths.

[0079] In step 1022, the UE requests the second mmW-BS to communicate over one of the first set of narrow beamforming paths.

[0080] Figure 11 is a conceptual data flow diagram 1100 showing data flow between modules/devices, different components in exemplary equipment 1202. The equipment can be a UE. The apparatus includes a module 1104 that receives in a first set of narrow beamforming paths next to a first set of narrow beamforming paths within the first coarse set of beamforming paths, a module 1106 that determines a first coarse set of beamforming paths between the UE and a first mmW-BS (the mmW-BS 1150, for example), a module 1108 that selects at least a first or second beamforming path within the first coarse set of forming paths of beamforming paths, a module 1110 that requests the first mmW-BS to transmit on a second set of narrow beamforming paths close to a second beamforming path within the first coarse set of beamforming paths when the beam quality signal of the first beamforming path and the first set of narrow beamforming paths is less than a first threshold, a modulo 1112 which determines a coarse second set of beamforming paths between the UE and a second mmW-BS (the mmW-BS 1160, for example), a module 1114 that selects a first or second beamforming path within the second coarse set of beamforming paths, a module 1116 that requests the second mmW-BS to transmit first set of narrow beamforming paths close to a first narrow beamforming path within the second coarse set of beamforming paths when the signal quality of all selected beamforming paths that match the first mmW-BS is less than a second threshold, a module 1118 that requests the first mmW-BS to refrain from signaling on any selected beamforming paths and/or requests that the second mmW-BS through one of the first set of beamforming paths of narrow beams, a module 1120 that communicates via one of the second beamforming paths or a path within the second set of narrow beamforming paths, a module 1122 that transmits a message that indicates at least one receive diversity or signal strength for one of the second beamforming paths or a path within the second set of narrow beamforming paths...

[0081] The equipment may include additional modules that execute each of the steps of the algorithm in the aforementioned flowchart of Figure 10. Therefore, each step in the aforementioned flowchart of Figure 10 can be performed by a module and the equipment may include one or more more of these modules. Modules may be one or more hardware components specifically configured to execute the declared processes/algorithm, implemented by a processor configured to execute the declared processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination of them.

[0082] Figure 12 is a diagram 1200 showing an example of hardware implementation for equipment 1102' that uses a processing system 1214. The processing system 1214 can be implemented with a bus architecture, generally represented by bus 1224 Bus 1224 may include any number of buses and interconnecting bridges depending on the specific application of processing system 1214 and overall design constraints. The bus 1224 connects together several circuits, which include one or more processors and/or hardware modules, represented by the processor 1204, the modules 1104, 1106, 1108, 1110, 1112, 1114, 1116, 1118, 1120 2 1122 and the computer/memory readable medium 1206. Bus 1224 may also connect 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 discussed. described in more detail.

[0083] The processing system 1214 may be coupled to a transceiver 1210. The transceiver 1210 is coupled to one or more antennas 1220. The transceiver 1210 provides a means for communicating with various other equipment over a transmission medium. The transceiver 1210 receives a signal from the antenna or antennas 1220, extracts information from the received signal and sends the extracted information to the processing system 1214, specifically the receiver module 1104. Furthermore, the transceiver 1210 receives information from the processing system 1214, specifically the transmitter module 1122 and, based on the received information, generate a signal to be applied to the antenna or antennas 1220. The processing system 1214 includes a processor 1204 coupled to a computer readable medium/memory 1206. The processor 1204 is responsible for by general processing, including executing software stored on computer/memory readable medium 1206. The software, when executed by processor 1204, causes processing system 1214 to perform the various functions described above for any specific device. Computer readable/memory medium 1206 may also be used to store data that is manipulated by processor 1204 when it would run software. The processing system also includes one of the modules 1104, 1106, 1108, 1110, 1112, 1114, 1116, 1118, 1120 and 1122. The modules may be software modules that run on the processor 1204 resident/stored on the readable medium by computer/memory 1206, one or more hardware modules coupled to processor 1204, or some combination thereof. Processing system 1214 may be a component of UE 650 and may include memory 260 and/or at least one of TX processor 668, RX processor 656, and controller/processor 659.

[0084] In one embodiment, the equipment 1102/1102' for wireless communication includes a device for determining a first coarse set of beamforming path between the UE and a first mmW-BS, a device for receiving in a first set of narrow beamforming paths next to a first coarse beamforming path within the first coarse set of beamforming paths, a device for requesting the first mmW-BS to transmit on a second set of narrow beamforming paths close to a second beamforming path within the first set of coarse beamforming path when the signal quality of the first beamforming path and the first set of narrow beamforming path is less than a first threshold, a device for communicating via one of the second beamforming paths or a path within the second set of narrow beamforming paths, a device for determining a coarse second set of beamforming paths between the UE and a second mmW-BS, a device for requesting the second mmW-BS to transmit on a first set of narrow beamforming paths close to a first beamforming path within the second coarse set of beamforming paths when the quality of all selected beamforming paths that match the first mmW-BS is less than a second threshold, a device for requesting that the first mmW refrain from signaling on any selected beamforming paths, a device for requesting that the second mmW-BS communicates over one of the first set of narrow beamforming paths, a device for selecting at least a first or second beamforming path within the first coarse set of beamforming paths, a device for selecting at least one first or second beamforming path within the second coarse set of beamforming paths, means for transmitting a message indicating at least a direction index or signal strength for one of the second beamforming paths beamforming or one within the second set of narrow beamforming paths.

[0085] The aforementioned devices may be one or more of the aforementioned modules of the equipment 1102 and/or the processing system 1214 of the equipment 1102' configured to perform the functions enumerated by the aforementioned devices. As described above, processing system 1214 may include TX processor 668, RX processor 656, and controller/processor 659. Thus, in one embodiment, the aforementioned devices may be TX processor 668, RX processor 656, and the controller/processor 659 configured to perform the functions enumerated by the aforementioned devices.

[0086] It should be understood that the specific order or hierarchy of steps in the disclosed processes/flowcharts is an illustration of exemplary approaches. Based on design preferences, it should be understood that the specific order or hierarchy of steps in processes/flowcharts can be rearranged. In addition, some steps can be combined or omitted. The appended method claims present elements of the various steps in a sample order, and are not intended to be limited to the particular order or hierarchy presented.

[0087] Furthermore, the term “or” is intended to mean an inclusive “or” and not an exclusive “or”. That is, unless otherwise specified or clear from the context, the phrase, for example, "X uses A or B" is intended to mean any of the natural inclusive permutations. That is, for example the allocation “X use it A or B” is satisfied by any of the following occurrences: X uses A; X uses B; or X uses both A and B. In addition, the articles "an(a)" used in this application and the appended claims shall generally be interpreted to mean "one or more", unless otherwise specified or clear from the context as being directed to a singular form. A phrase referring to “at least one of”, a list of items refers to any combination of those items, including single elements. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0121] The foregoing description is presented to enable anyone skilled in the art to put into practice the various aspects described herein. Various modifications in these aspects will be readily apparent to those skilled in the art and the general principles defined herein can be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown here, but must be given the full scope compatible with the language of the claims, in which reference to an element in the singular is not intended to mean “one and only one”, unless specifically so asserted, but rather "one or more." The word "exemplary" is used here to mean "which serves as an example, occurrence, or illustration." Any feature described herein as "exemplary" should not necessarily be construed as preferred or advantageous compared to other features. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as "at least one of A, B or C", and "A, B, C or any combination thereof" include any combination of A, B and/or C and may include multiples of A, multiples of B or multiples of B of C. Specifically, combinations such as "at least one of A, B or C", "at least one of A, B and C", and "A, B, C or any combination thereof" can be A only, B only , C only and A and B, A and C, B and C or A and B and C, where any such combinations may contain one or more elements or elements of A, B, or C. All structural and functional equivalents of the Elements of the various aspects described throughout this disclosure that are known or will become known to those skilled in the art are expressly incorporated herein by reference and are intended to be covered by the claims. Furthermore, nothing disclosed herein is intended to be dedicated to the public regardless of whether or not such disclosure is explicitly enumerated in the claims. No claim element shall be construed as a device plus function unless the element is expressly enumerated using the phrase “device for”.

Claims (9)

1. Method for wireless communication to a user equipment, UE, characterized in that it comprises: determining (1002) a first coarse set of beamforming paths between the UE and a first millimeter wave base station, mmW- BS; selecting (1004) a first beamforming path and a second beamforming path within the first coarse set of beamforming paths; receiving (1006) into a first set of narrow beamforming paths proximate the first coarse beamforming path within the first coarse set of beamforming paths; request (1008) the first mmW-BS to transmit on a second set of narrow beamforming paths near the second beamforming path within the first coarse set of beamforming paths when a first path signal quality of beamforming and the first set of narrow beamforming paths is less than a first threshold; and communicating (1012) via one of the second beamforming paths or a path within the second set of narrow beamforming paths; determining (1014) a second coarse set of beamforming paths between the UE and a second mmW-BS; ask the second mmW-BS to transmit on a third set of narrow beamforming paths next to a third set of narrow beamforming paths within the second coarse set of beamforming paths when a signal quality of all the forming paths of selected beams corresponding to the first mmW-BS is less than a second threshold; request (1020) the first mmW-BS to refrain from signaling on any selected beamforming paths; and requesting the second mmW-BS to communicate via one of the third set of narrow beamforming paths. Method according to claim 1, characterized in that the first beamforming path has a higher signal quality than beamforming paths in the first coarse set of beamforming paths. 3. Method according to claim 1, characterized in that it further comprises selecting at least a third or fourth beamforming path within the second coarse set of beamforming paths. 4. Method according to claim 1, characterized in that it further comprises transmitting (1010) a message indicating at least a direction index or a signal strength for one of the second beamforming paths or a path within the second narrow beam forming set. 5. User equipment, UE, for wireless communication, comprising: means for determining (1002) a first coarse set of beamforming paths between the UE and a first millimeter wave base station, mmW- BS; means for selecting (1004) a first beamforming path and a second beamforming path within the first coarse set of beamforming paths; means for receiving (1006) into a first set of narrow beamforming paths proximate the first beamforming path within the first coarse set of beamforming paths; means for requesting (1008) the first mmW-BS to transmit on a second set of narrow beamforming paths proximate the second beamforming path within the first coarse set of beamforming paths when a signal quality of the first beamforming path and the first set of narrow beamforming paths is less than a first threshold; and means for communicating (1012) via one of the second beamforming paths or a path within the second set of narrow beamforming paths; means for determining (1014) a second coarse set of beamforming paths between the UE and a second mmW-BS; means for requesting the second mmW-BS to transmit on a third set of narrow beamforming paths next to a third set of beamforming paths within the second coarse set of beamforming paths when a signal quality of all paths of selected beamforming corresponding to the first mmW-BS is less than a second threshold; means for requesting (1020) the first mmW-BS to refrain from signaling on any selected beamforming paths; and means for requesting the second mmW-BS to communicate via one of the third set of narrow beamforming paths. 6. UE according to claim 5, characterized in that the first beamforming path has a higher signal quality than beamforming paths in the first coarse set of beamforming paths. 7. UE according to claim 5, characterized in that it additionally comprises means for selecting at least a third or fourth beamforming path within the second coarse set of beamforming paths. 8. UE according to claim 5, characterized in that it additionally comprises means for transmitting (1010) a message indicating at least a direction index or a signal strength for one of the second beamforming paths or a path within the second narrow beamforming set. 9. Memory characterized by the fact that it comprises instructions stored therein, the instructions being executed by a computer to carry out the method as defined in any one of claims 1 to 4.