WO2017111961A1

WO2017111961A1 - Fast directional cell acquisition and differential beam tracking in millimeter-wave cellular system with hybrid beamforming architecture

Info

Publication number: WO2017111961A1
Application number: PCT/US2015/067493
Authority: WO
Inventors: Roya Doostnejad; Jing Zhu; Ehsan ARYAFAR; Nageen Himayat; Shilpa Talwar
Original assignee: Intel Corporation
Priority date: 2015-12-22
Filing date: 2015-12-22
Publication date: 2017-06-29

Abstract

For cell acquisition a UE receives concurrently from a base station (BS), during a single time symbol, a cell ID via a plurality of electromagnetic beams that include data signals and spatial-frequency multiplexed orthogonal synchronization signals, the beams having different angles of arrival. The UE processes the beams to determine the identity of the beam that was received with maximum signal strength and the angle of arrival of the beam, and transmits the identity and the angle of arrival to the BS. For beam tracking the UE similarly receives a plurality of the same beams but including reference signals, each beam transmitted at the same power and received at different angles of arrival. The plurality of beams comprise a central beam and pairs of beams on either side of the central beam, the pairs respectively arranged at differing equal angles of arrival from the central beam. The UE processes the beams in parallel to track movement of the UE by determining the identity of the beam received with maximum signal strength and the angle of arrival of the beam, by using the central beam and the pairs of beams. The UE transmits the identity and the angle of arrival to the BS.

Description

FAST DIRECTIONAL CELL ACQUISITION AND DIFFERENTIAL BEAM TRACKING IN MILLIMETER- WAVE CELLULAR SYSTEM WITH HYBRID BEAMFORMING ARCHITECTURE

TECHNICAL FIELD

Some embodiments relate to millimeter-wave communication. Some devices relate to wireless devices. Some embodiments relate to Institute of

Electrical and Electronics Engineers (IEEE) 802.11. Some embodiments relate to 5G. Some embodiments relate to fast acquisition cell acquisition using hybrid beamforming architecture. Some embodiments relate to differential beam tracking through hybrid processing of reference signals in downlink millimeter wave channels.

BACKGROUND

In millimeter wave (mm-Wave) wireless communications, highly directional transmissions are essential for cellular communication. This is to compensate for high isotropic path loss. This requirement on directional beamforming complicates initial cell search and acquisition, and beam selection. In addition to detecting the corresponding base stations and their timing as required in conventional cell search, mm-Wave mobiles must also detect the spatial angles of transmissions on which the synchronization signals are being received. Further, short wavelengths lead to much higher path loss and increased susceptibility to blockage by obstacles. Even after a link is established, a minor change in user configuration and/or the channel may cause a blockage. As a result, beam maintenance and tracking is a key component for

communications in mm-Wave channels.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates various network elements of a wireless network in accordance with some embodiments. FIG. 2 illustrates a mobile station (MS) device in accordance with some embodiments;

FIG. 3 illustrates modular antenna array hybrid beamforming architecture in accordance with some embodiments;

FIG. 4 illustrates full antenna array hybrid beamforming architecture in accordance with some embodiments;

FIG. 5 illustrates subcarrier allocation and symbol structure for hybrid beam formed synchronization signals in accordance with some embodiments;

FIG. 6 illustrates a small cell cluster in accordance with some embodiments.

FIG. 7 illustrates array factor for analog beamforming (ABF) and hybrid beamforming (HBF) with a center beam at a first angle, in accordance with some embodiments;

FIG. 8 illustrates array factor for ABF and HBF with a center beam at a second angle, in accordance with some embodiments;

FIG. 9 illustrates symbol structure integrating data and hybrid beam formed reference signals for beam tracking in accordance with some embodiments; and

FIG. 10 illustrates a block diagram of an example machine in accordance with some embodiments.

DETAILED DESCRIPTION

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

FIG. 1 illustrates various network elements of a wireless network in accordance with some embodiments. Wireless network 100 includes a plurality of communication stations (STAs) and one or more access points (APs) which may communicate in accordance with IEEE 802.11 communication techniques. One or more communication station 104, illustrated as STA-B or User

Equipment (UE) may be a mobile station (MS) device that is non-stationary and does not have fixed locations. One or more access point (AP) 102 may be stationary and have fixed locations. The AP 102 may be a communication station such as a base station (BS) that communicates with UE STA-B 104 using Full- Duplex Microchip Media Access Controller (FD-MiMAC) protocol. The Access Point Station A (AP STA-A) may AP announce its available remaining antenna capability as well as the channel information of a winning client in a contention for a transmission opportunity (TXOP). Both AP 102 and UE 104 may be configured for operation in millimeter-wave (mm Wave) communication, particularly 5G. In some 5G embodiments, a UE may communicate data (e.g., using a PDSCH and/or a PUSCH) with a small cell or secondary cell while configured by a larger serving cell or primary cell and receiving control signals from the primary cell (with a PDCCH). In these embodiments, communications with the smaller cell may take place using mmW frequencies while

communications with the larger cell may take place using microwave frequencies. In practice there may be several BSs and several UEs to allow for tracking and for such processes as hand-off, as needed.

FIG. 2 illustrates a Mobile Station (MS) device 200 in some embodiments. MS device 200 is a more detailed description of STA-B 104 of FIG. 1. MS device 200 may be a millimeter-wave (mmWave) compliant MS device that may be arranged to communicate with one or more other MS devices or one or more Base Station (BS). MS device 200 may be suitable for operating as User Equipment (UE). In some embodiments, MS device 200 may include, among other things, a transmit/receive element 201 (for example an antenna), a transceiver 203, physical (PHY) circuitry 205, and media access control (MAC) circuitry 207. PHY circuitry 205 and MAC circuitry 207 may be mm Wave compliant layers and may also be compliant with one or more other IEEE 802.11 ax or IEEE 802.13 standards. MAC circuitry 207 may be arranged to configure packets such as a physical layer convergence procedure (PLCP) protocol data unit (PPDUs) and arranged to transmit and receive PPDUs, among other things. MS device 200 may also include circuitry 209 configured to perform the various operations described herein. The circuitry 209 may be coupled to the transceiver 203, which may be coupled to the transmit/receive element 201. While FIG. 2 depicts the circuitry 209 and the transceiver 203 as separate components, the circuitry 209 and the transceiver 203 may be integrated together in an electronic package or chip.

In some embodiments, the MAC circuitry 207 may be arranged to contend for a wireless medium during a contention period to receive control of the medium for an appropriate control period and configure a High Efficiency WLAN Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (HEW PPDU). In some embodiments the PHY circuitry 205 may be arranged to transmit 5G mmWave packets. In some embodiments, the MAC circuitry 207 may be arranged to contend for the wireless medium based on channel contention settings, a transmitting power level, and a Clear Channel Assessment (CCA) level.

In some embodiments the PHY circuitry 205 may be arranged to transmit the HEW PPDU. The PHY circuitry 205 may include circuitry for

modulation/demodulation, upconversion/downconversion, filtering, amplification, and the like. In some embodiments, the circuitry 209 may include one or more processors which may be configured for parallel processing. The circuitry 209 may be configured to perform functions based on instructions being stored in a RAM or ROM, or based on special purpose circuitry. The circuitry 209 may include processing circuitry and/or transceiver circuitry in some embodiments. The circuitry 209 may include a processor such as a general purpose processor or special purpose processor. The circuitry 209 may implement one or more functions associated with transmit/receive elements 201, the transceiver 203, the PHY circuitry 205, the MAC circuitry 207, and/or the memory 211.

In some embodiments, the circuitry 209 may be configured to perform one or more of the functions and/or methods described herein and/or in conjunction with FIGS. 3-10.

In some embodiments, the transmit/receive elements 201 may be two or more antennas that may be coupled to the PHY circuitry 204 and arranged for sending and receiving signals including transmission of the HEW packets. The transceiver 202 may transmit and receive data such as HEW PPDU and packets that include an indication that the MS device 200 should adapt the channel contention settings according to settings included in the packet. The memory 211 may store information for configuring the other circuitry to perform operations for configuring and transmitting HEW packets and performing the various operations to perform one or more of the functions and/or methods described herein and/or in conjunction with FIGS. 3 -10

In some embodiments, the MS device 200 may be configured to communicate using OFDM communication signals over a multicarrier communication channel. In some embodiments, MS device 200 may be configured to communicate in some one or more specific communication standards, such as the Institute of Electrical and Electronics Engineers (IEEE) standards including IEEE 802.11-2012, 802.11n-2009, 802.11 ac-2013, 802.11 ax, DensiFi, standards and/or proposed specifications for WLANs, or other standards as described in conjunction with FIG. 2, although the scope of the embodiments is not limited in this respect as they may also be suitable to transmit and/or receive communications in some other techniques and standards. In some embodiments, the MS device 200 may use 4x symbol duration of 802.l ln or 802.l lac.

In some embodiments, an MS device 200 may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a smartphone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, and the like.), an access point, a base station, a transmit/receive device for a wireless standard such as 802.11 or 802.16, or other device that may receive and/or transmit information wirelessly. In some embodiments, the MS device may include one or more of a keyboard, a display, a non- volatile memory port, multiple antennas, a graphics processor, an application processor, speakers, and other mobile device elements. The display may be an LCD screen including a touch screen.

The transmit/receive element 201 may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some MIMO embodiments, the antennas may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result. Although the MS device 200 is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements may refer to one or more processes operating on one or more processing elements.

Some embodiments may be implemented fully or partially in software and/or firmware. This software and/or firmware may take the form of instructions contained in or on a no n- transitory computer-readable storage medium, or a machine-readable hardware storage device. Those instructions may then be read and executed by one or more processors to enable performance of the operations described herein. Those instructions may then be read and executed by one or more processors to cause the MS device 200 to perform the methods and/or operations described herein. The instructions may be in any suitable form, such as but not limited to source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. Such a computer-readable medium may include any tangible non-transitory medium for storing information in a form readable by one or more computers, such as but not limited to read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; a flash memory, and the like.

In millimeter wave (mm-Wave) wireless communications, highly directional transmissions are essential for cellular communication. This is to compensate for high isotropic path loss. This requirement of directional beamforming complicates initial cell search, and beam selection. Here "beam selection" refers to a process in which the user equipment (UE) switches to a beam that is received with higher signal strength than the currently received beam, while remaining connected to a cell with multiple mm-Wave beams.

In addition to detecting the corresponding base stations and their timing in conventional cell search, mm-Wave a mobile stations (MS) detect the spatial angles of transmissions on which the synchronization signals are being received. A general approach suggests scanning the angular space sequentially at the base station (BS) and at the UE. The terms MS and UE may be used interchangeably herein. The terms BS and evolved Node B (eNB) may also be used interchangeably herein. Two downlink synchronization signals are used by the UE to obtain the cell identity and frame timing, namely the primary synchronization (PSS) and the secondary synchronization signal (SSS). These are beam formed in different directions and transmitted over different time symbols. The UE measures the beam-formed signal in different receiver directions as well. This process will take several time symbols and as a result the acquisition time is very long. Transmission of synchronization signals is a periodic event and therefore the above process has a large overhead. In view of the above problems it is desirable to find a way to implement faster acquisition with lower overhead.

Hybrid beamforming architecture may be used to reduce the acquisition time and overhead through space-frequency multiplexing of synchronization signal beams formed at different angles and transmitted at the BS, and space- frequency processing of the received signal at the UE. This can be applied to both initial cell search/acquisition and to beam selection. For initial cell search, the UE may be pre-configured with the information about where the synchronization signals (SS) is allocated in the frequency domain, and the SS must be unique in order to identify the cell. In some embodiments the cell ID is included in the SS.

Further, for the purpose of beam selection, which may take place after the UE is attached, the SS allocation may be dynamically configured, and provisioned by the serving eNB using, for example, system broadcast information. The same SS can be sent over multiple beams simultaneously, and the serving eNB will provide the UE the information about how to identify a beam based on where its corresponding SS is located in the time and frequency domain.

For the purpose of fast directional cell acquisition and beam selection in the mm-Wave frequency range, advantage may be taken of digital processing in hybrid digital- analog BF for parallel transmission of synchronization reference signals from base stations as well as parallel processing at the UE receiver to detect the best cell ID and beam directions at both ends, BS and UE. The process would include, at least in part due to the combination of digital and analog beamforming, that:

A set of distributed subcarriers can be assigned to every RF chain for transmission of the PSS/SSS signal. The subcarriers in every set are separated by the channel coherence band width to provide frequency diversity. Different sets in different RF chains are orthogonal in frequency.

The synchronization signal is transmitted from every RF chain in specified subcarriers and in a different direction.

At the UE, the channel measurement is done over one or a few symbols but in different frequency sets to define the strongest cell and direction.

Different cells in the same cluster are made orthogonal in time and/or frequency.

The UE may also take advantage of multiple RF chains for parallel processing of the received signal at different directions.

For the purpose of beam selection, the serving eNB may configure the SS allocation dynamically, and provide the UE the information via a control channel, e.g., system broadcast information, about where SS is located in the time/frequency domain, and how to identify a beam accordingly.

In mm- Wave wireless communications, a basic design for cell and beam acquisition relies on sequential training. At the BS, the synchronization reference signal is transmitted in different directions (with predefined analog beams) over a sequence of time symbols. At the UE, the channel strength is measured over several time symbols to define the best cell ID and beam ID. Then the UE has to scan the angular space to determine the best beam direction at the receiver as well. In those schemes, there is no mechanism to take advantage of digital processing component of hybrid beamforming architecture to improve the efficiency of beam acquisition. Since analog beamforming weights are constant over the entire frequency band, this procedure requires several symbols for the training. In the current disclosure, the acquisition time is significantly reduced through transmission of the beam formed synchronization signals in parallel from RF transmitters that are orthogonal in the frequency domain. In addition at the UE, parallel processing of the initial acquisition signal is facilitated which reduces the acquisition time further. In a mm- Wave cellular network such as that disclosed, hybrid beamforming architecture is assumed at both BS and UE. FIG. 3 illustrates modular antenna array (MAA) hybrid beamforming architecture in accordance with some embodiments. The hybrid beamforming architecture at the BS may include a transceiver comprising digital precoder 302, for modulating information into a plurality of N analog RF chains 304I-304N. Stated another way, hybrid beamforming comprises digital operation and analog operation in the beamforming process, unlike beamforming in other technologies such as, for example, Long Term Evolution (LTE) which includes only digital processes in beamforming. The RF chains are connected to N phase shifters, one of which is illustrated at 3081, which provide appropriate phase shift for each RF chain. Each phase shifter is respectively coupled to an antenna, one of which is represented at 310i, in a multiple input and multiple output (MIMO) configuration. The RF chains are transmitted via the respective antennas by way of MIMO channel H at 301 for reception at mobile stations in the system. A typical MS comprises antennas, one of which is represented at 312i each coupled respectively to a phase shifter, one of which is represented at 314i. The analog RF chains are received at 316I-316N and the information is demodulated by digital baseband processing module 318. As can be seen from FIG. 3, hybrid beamforming comprises a hybrid of digital precoding at digital precoder 302 and analog processes at the phase shifters.

FIG. 4 illustrates full antenna array (FAA) hybrid beamforming architecture in accordance with some embodiments. The FAA hybrid beamforming architecture 400 of FIG. 4 is essentially the same as the MAA hybrid beamforming architecture of FIG. 3 with the exception of OR gates 404i, 4042, 404N. The architecture of either FIG. 3 or FIG. 4 may be used for the embodiments described herein. The beamforming gain is necessary even for the cell search phase. The key challenge, then, is fast acquisition of both cell ID and beam direction. In previous work, this is done through one of the following scenarios:

i. Base station (BS) 102 of FIG. 1 transmits the synchronization signal (SS) beam formed in different predefined angles over different time symbols. The user equipment (UE) 104 of FIG. 1 applies omnidirectional or semi omnidirectional beams and scans over several time symbols to detect the best cell ID and beam ID and sends the feedback to the network including a selected BS such as 102 of FIG. 1. In the next step, the selected BS transmits with omnidirectional beams for the UE 104 to scan through different beams and define the best direction. This takes several time symbols for the UE to define the best BS and beam direction.

ii. UE 104 then transmits with omnidirectional beams for the base stations to browse over different angles of arrival (AO A) and define the best beam ID, then the appropriate BS 103 will transmit beam formed SS for the UE to search over the predefined angles and define the best beam direction for the UE side.

In above schemes only RF beamforming is employed for transmission of the SS. As RF beamforming weights are the same for entire frequency band, this beam training requires several symbols which cause long acquisition time. Considering the low coherence time in mm- Wave channels, delays in cell and beam direction acquisition should be minimized.

In the current embodiments, the extra degrees of freedom provided by digital baseband processing of the hybrid beam forming are an advantage that leads to a reduction of the acquisition time through spatial-frequency multiplexing of SS in different angles.

CELL ACQUISITION AND BEAM SELECTION

A. Transmission of beam formed synchronization signals at the BS

As seen in the hybrid beamforming architecture of FIG. 3 and of FIG. 4, there are N RF chains at the BS which are used to transmit SS in N different angles in the same time symbol.

a. Subcarrier allocation for frequency multiplexing

FIG. 5 illustrates subcarrier allocation and symbol structure for hybrid beamformed synchronization signals in accordance with some embodiments. The RF transmitters 5011, 5012,■■· , 501N-I, 501N transmit RF chains 502i, 5022, ... , 502N-I, 502N at respective angles 0i, 02, ... , 0N-I, 0N that are provided by the analog component of the hybrid RF beamforming architecture. A set of subcarriers 503i, 5032,■■· , 503N-I, 503N are respectively assigned to each RF chain 502i, 5022, ... , 502N-I, 502N to transmit the SS at each respective specific angle, 0i, 02, ... , 0N I, 0N. These subcarriers are separated by the channel coherence bandwidth to extract the frequency diversity. The N sets of subcarriers allocated to N RF chains are orthogonal in frequency as shown in FIG. 5. This way, the SS transmitted in N different angles, although multiplexed in space (antennas), are orthogonal in frequency. This has the following benefits:

1. The transmitted power on every SS subcarrier is the same as if all

RF chains were used for SS transmission and there is no loss in range because of this spatial multiplexing. In fact the power is boosted in the SS subcarriers because of orthogalization.

2. The UE is able to process N different sets of carriers in parallel to measure the channel strength in every direction and feedback the best beam direction.

3. If there are more beams (angles) than the available orthogonal SS subcarrier sets, a different symbol may be used to send the SS, i.e., time multiplexing.

4. The serving eNB may configure the SS time/frequency allocation dynamically, and provide the information to the UE via a common control channel, e.g., system broadcast information. b. The browsing time is reduced by number ofRF chains.

If the size of RF beamforming codebook is larger than the number of antennas, N, this procedure is repeated over time to cover all candidate spatial angles.

B. Received beamforming process at the UE

As seen in FIG. 3, there are N_m RF chains at the UE. The UE measures the SNR at the dedicated SS subcarriers and defines the best cell ID, as well as cell direction. The UE may also use N_m RF chains for parallel processing of the received signal at different angle of arrivals (AOA). Angular space for the UE is divided by N_m fat beams and the received signal in every RF chain is processed, for example by the one or more processor of the circuitry 209 of FIG. 2 at that specific beam angle. At the end of this process the UE is able to define the best angular space out of N_m angles as well as the best cell/beam ID for the BS. Further beam refinement processing is also performed at the UE to select the best beam at the defined angular beam. The browsing time at the UE side is reduced by the number of RF chains in the UE. C. Multi cell Transmission

The above design can be extended for enabling multi-cell transmission to the UE. FIG. 6 illustrates a small cell cluster in accordance with some embodiments. Consider a cluster of n adjacent small cells (e.g., n =3) as shown in FIG. 6. Parallel transmission of the beam formed SS can be performed on every small cell as explained above. The SS subcarrier allocation in FIG. 5 is extended to facilitate the frequency multiplexing of SS in all the small cells in the same cluster. In fact orthogonal subcarrier sets are assigned to the small cells in the same cluster. The UE will be able to synchronize with two or more cells with selected directions. However, unlike in the beam selection process, the SS time/frequency allocation for initial cell search must be static, and known to the UE in advance (through pre-configuration), because the UE is not attached yet.

D. Two dimensional antennas

The above discussion can be easily extended to two-dimensional (2D) antenna architecture to include both azimuth and vertical directions. The beamforming codebook will be extended over both azimuth and vertical directions.

In net, for acquiring cell ID and beam direction the disclosure to transmit/process in parallel using available RF transceivers in the BS and the UE reduces the cell acquisition time in every side by the number of RF chains.

BEAM TRACKING

Because of the sensitivity of mm Wave to changes in the environment, the above cell acquisition process is repeated, perhaps periodically, to make sure cell acquisition is maintained. In millimeter wave (mm- Wave) wireless communications, the short wavelengths lead to much higher path loss and increased susceptibility to blockage by obstacles. Therefore, even after a link is established by cell acquisition, a minor change in user configuration and/or the channel may cause a blockage. As a result, beam maintenance and tracking is a key component for communications in mm-Wave channels between the repetitions of the cell acquisition process. To obtain channel state information (CSI) for user tracking, beamforming (BF) will be required for reference signals (RS). In previous work, sequential beam training is employed using predefined codebooks. Considering the fact that analog beamforming weights cannot be changed for different subcarriers, the beam training requires several time symbols and cannot be integrated with data symbols transmission.

Further, it is common for the UE tracking process to be done separately from data transmission. In the instant disclosure we propose differential tracking at the same time as data transmission using hybrid beamforming for CSI RS at both base station (BS) and user device (UE) to facilitate fast and accurate beam tracking for users. The advantages of the proposed scheme are as follows:

Higher beamforming granularity through digital beamforming in different subcarriers

Major reduction in acquisition and tracking time

OVERHEAD REDUCTION

In a mm- Wave wireless communications system, consider hybrid beamforming architecture at both the BS and the UE. For the purpose of fast beam tracking, we take advantage of the digital beamforming component of hybrid beamforming for RS as follows:

A number of subcarriers are assigned for transmission of beam formed CSI RS.

The analog reference beams are weighted and combined in different subcarriers to generate different effective beam directions at different subcarriers.

At the UE rather than only browsing over analog beams, the hybrid processing is applied on the associated subcarriers to calculate the received signal strength for all different combinations of transmit/receive beam directions and adjust the beam direction accordingly. The BS may also adjust the beam direction.

This hybrid processing can be applied at transmitter and/or receiver.

This scheme facilitates transmission of CSI RS and adjusting the beam direction at UE simultaneously with receiving data symbols. In this case the same analog beams which are used for data transmission will be the center beams for hybrid beam formed reference signals.

In mm- Wave communications, a basic design for beam acquisition and tracking relies on iterative beamforming training. The reference signals are predefined analog beams which are transmitted iteratively from the BS and the UE. Since analog beamforming weights are constant over the entire frequency band, this procedure requires several symbols for the training which is not desired especially for beam tracking. Also the accuracy of beam tracking will depend on the number of antenna elements (phase shifters) at each analog chain. In those schemes, there is no mechanism to take advantage of the digital beamforming component of hybrid beamforming architecture to improve the efficiency of reference signals for beam acquisition and beam tracking (time, accuracy, array gain) compared to analog beamforming architecture. Besides, in our proposed scheme here, digital beamforming facilitates the transmission of reference beam vectors at the same time a data symbol is transmitted. This significantly reduces the network load and tracking time.

Beamforming plays a fundamental role in enabling mm- Wave communications between a UE and a BS. For the cases that the UE is expected to have some mobility, beamforming training has to be a recurrent procedure to re-establish the mm- Wave link. This is different than other types of mm- Wave backhaul usages which are static. Therefore an efficient beamforming tracking is required for a fast re-establishment of the beam-formed link following changes in the environment and/or UE location.

Implementation of digital beamforming for massive MIMO is not feasible as it requires a massive number of RF chains. In a practical massive MIMO deployment, hybrid beamforming (HBF) is a better option where the number of RF chains are much less than the number of antenna elements. FIG. 9 illustrates symbol structure integrating data and hybrid beam formed reference signals for beam tracking in accordance with some embodiments. In FIG. 3, the architecture of HBF with modular antenna array (MAA) is shown. As seen in FIG. 5, each RF transmitter 5011, 5012, ... , 501NI I, 50lNb respectively transmits beams 502i, 5022, ... , 502NI I, 502m at different directions denoted by the angle 0 associated with each beam. The symbol structure for each beam is illustrated at 503i, 5032, ... , 503NI I, 503NI Hybrid beamforming has a digital component and an analog component, discussed in greater detail below. Analog beamforming (ABF) is applied to each transceiver where the weights will be the same over one OFDM symbol. Digital beamforming (DBF) is performed on input/output of RF chains at transmitter/receiver (as seen at 302 of FIG. 3) to maximize the array gain and facilitate multiuser beamforming. In MAA HBF architecture of FIG. 3, we have:

where W_BS , i— 1, ...,N_b, is the analog beam vector (phase shifters, illustrated as 308I-308N of FIG. 3) at the i^th BS transmitter

and W_MS , i = l,— ,N_m, is the analog beam vector (phase shifters, illustrated as 314I-314N of FIG. 3) at the i'^h MS receiver. Nb may be used to designate the number of RF chains at the BS and N_m may be used to designate the number RF chains at the MS for the purposes of the equations herein and for the purposes of FIG. 9. The transmitted signal at the carrier k is:

where Pesk is Nb x Nb digital BF matrix and x_k is a Nb x 1 transmitted signal at carrier k, which may be used to transmit the data or reference signal.

The received signal at carrier k is:

r_k = P_MSkW_MS.H_k J_k + n (3)

where PMSI_C is Nm x Nm digital BF matrix at UE, and Hk is the channel at the kth carrier.

The analog BF vector is adjusted for every user at both ends according to the angular position of the UE related to the strongest BS direction, and DBF weights are calculated for further processing at baseband to add array gain and/or provide multiuser beamforming. The challenge of HBF is obtaining CSI at either the BS or the UE to adjust beamforming weights accordingly. Per antenna element CSI acquisition is not feasible because:

a) There are too many antenna elements and there will be a large overhead to transmit/measure reference signals from/at all elements.

b) Analog beamforming is required for channel measurements as a result of high path loss in mm-Wave channels and reference signals should be beam formed as well.

Therefore typical CSI RS and/or uplink sounding methodology (similar to LTE) will not work for updating the ABF weights. The initial beam acquisition (ABF weights) is assumed to be performed based on the iterative training concept in 802.1 lad. For beamforming tracking the same training concept can be repeated frequently. This will have a high overhead on the network and also the accuracy of angle of arrival and/or angle of departure (AOA/AOD) estimation will depend on the number of phase array elements in each RF chain.

In the instant disclosure, advantage may be taken of the baseband digital processing component of HBF illustrated at 302 of FIG. 3 to generate different beam directions, around the main ABF direction, in different subcarriers and use these beams for CSI RS beamforming at both transmitter and receiver. This facilitates the UE and the BS to adjust the direction in small steps in short time periods. This is called differential beam tracking. For the maximum efficiency in this scheme beam tracking may be done in conjunction with data transmission. I. Hybrid beam formed reference signals

The array factor for analog beam formed RS is:

where M is the number of phase array elements such as those illustrated in FIG. 3, the antenna spacing is AJ2 (λ is the wave length) and 0o is the beam direction for analog BF (which is going to be the same for an OFDM symbol). If the subcarrier k is weighted over different RF transceivers of FIG. 5 (/ = 0, ... , N - 1) with the factor έ^~'^β' , where N is the number of RF chains, the equivalent array factor is:

as a result if we set

θ, = ΙπΜ cos0_M , where 0_Ak = 0_o ± A_k , 1 = 0,..., N - l (6)

The array factor for HBF is maximized at 0 = Ak which is the desired direction for RS transmission at carrier k. At defines the change in the beam direction in subcarrier k compared to the main analog beam. FIG. 7 illustrates the array factor for analog beamforming (ABF) and hybrid beamforming (HBF) with a center beam at a seventy (70) degrees, in accordance with some embodiments. FIG. 8 illustrates the array factor for ABF and HBF with a center beam at a one hundred fifty (150) degrees, in accordance with some embodiments. Assuming the number of array elements at each RF chain is MBS at the BS and MUE at the UE:

At the BS, from equation (2) it means that RS is transmitted at the kth carrier with iL, =

At the UE, from equation (3) it means that at kth subcarrier UE is receiving at angle 0 and P_MSk = Diag{ ,e^~ie[ ,...,e ^je"^m"> ) II. Subcarrier allocation for differential beam tracking in conjunction with data transmission:

Subcarrier allocation in one OFDM symbol is shown in FIG. 9. For maximum efficiency, the reference signals for beam tracking are piggybacked to data symbols so that the system can track the UE while sending data. In every symbol, L subcarriers are specified for transmission of beam formed RS signals. In multiuser MEVIO (MU-MIMO), the data symbols are transmitted to K < Nb scheduled users (K different directions) at the same time.

There are K analog BF directions that can be used as the main beam directions (0o in equations 5, 6) for RS signals transmitted from BS in a specific time duration of one OFDM symbol.

Hybrid beams are generated at directions (equation 6, FIGS. 7 and 8) in k different subcarriers. HA (e.g., n = 5 in FIG. 7 and ra=4 in FIG. 8) subcarriers are assigned to carry beam formed RS signals at the directions 0M- This is for tracking small changes and we select Δ < + 4 (deg) in FIGS. 7 and 8.

To capture frequency diversity of the channel, RS can be re-transmitted at the carriers which are separated by the coherence bandwidth (BW) of the channel. As shown in FIG. 9, the beam formed RS are transmitted in Ι.ΠΑ subcarriers where 1 is the number of re-transmissions of RS in every direction at the same time data is transmitted resulting in tracking the UE while data is being sent.

The reference signals transmitted at the directions with different main ABF are orthognalized in frequency so that UE can measure the received signals with different angle of departure (AOD) at different subcarriers. For example, taking the subcarriers illustrated at subcarrier block 902 of FIG. 9, the subcarriers illustrated at 901, 903 are used to send data and control signals to different users. This can be seen at the left of FIG. 9 as User 1 , User 2, ... , User k, each at an angle of 0o. On the other hand, subcarriers 905, 907, 909, 911 can be reserved for beam formed reference signals RS. Each of the subcarriers being orthogonal to each other, and in a different direction as illustrated if FIGS. 7 and 8, allows the UE to determine both the strength and direction of each beam for differential beam tracking, and at the same time receive the data associated with the beam.

The transmitted power on every RS subcarrier is the same as if all RF chains were used for RS transmission and there is no loss in range as a result of this spatial multiplexing. The reason is RS transmitted in different directions are orthogonalized in frequency with each other as well as with data.

Consider the case at FIG. 7 where the center beam is at 70 degrees and the BS is tracking small changes using beams at a selected Δ < + 4 (deg). The UE will determine the strongest beam, for example by measuring the SNR of each beam. If the UE has moved, or the channel environment has changed, a beam other than the center beam at 70 degrees will be detected by the UE as strongest. For example it may be the strongest beam that is at 72 degrees, or two degrees off the center beam of 70 degrees of FIG. 7. That information will be fed back to the BS as the direction of the UE for beam tracking. The new direction, at 72 degrees, will be used by the BS for adjustment to transmit the next center beam in the process at 72 degrees with Δ < + 4 (deg) again, and the process then continues. Detecting the SNR at each data symbol allows for differential beam tracking, including tracking the direction in which the UE might be moving by using the plurality of beams being sent at different angles of departure.

III. Multi-Cell Design: The above reference signal design can be extended for multi-cell transmission to the UE. Consider a cluster 600 of n adjacent small cells (e.g., n =3) as shown in FIG. 6. CSI-RS hybrid beamforming is performed on every small cell as explained earlier. The analog BF directions for current data transmission in every cell are used as the main beam directions for CSI-RS. The RS subcarrier allocation in FIG. 9 is extended to facilitate the frequency multiplexing of CSI-RS in all the small cells in the same cluster. For this purpose, orthogonal sets of subcarriers are assigned for RS transmission in different cells in the same cluster. In this way, the UE is able to measure SNR for all CSI-RS transmitted from the small cells , and defines the strongest direction(s) and cell(s).

IV. UE differential beam tracking: Active UEs measure signal-to-noise ratio (SNR) at the assigned subcarriers for RS and feedback to the BS on the best direction. More importantly, the UE is also able to measure SNR at different angles of arrival (AOA):0 ^(l¾). The main beam direction at the UE is the ABF weights of the UE at the previous stage. The UE can adjust its ABF direction by Δ as well.

The idle UEs can also measure SNR at RS subcarriers to select the candidate cell and beam.

V. Two dimensional antennas: The above discussion can be easily extended to two-dimensional (2D) antenna architecture to include both azimuth and vertical directions.

In general, tracking small changes in the channel and/or the UE position, beams at both the BS and the UE can be differentially adjusted. In every time symbol the directions may be adjusted by Δ + 4 (deg), at both ends, compared to the last OFDM symbol. The training is facilitated by hybrid BF on CSI RS and performed in conjunction with data transmission. Orthogonal subcarriers are assigned for RS transmission in different directions and for different cells in the same cluster.

FIG. 10 illustrates a block diagram of an example machine 1000 in accordance with some embodiments upon which any one or more of the techniques (e.g., methodologies) discussed herein may perform. In alternative embodiments, the machine 1000 may operate as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine 1000 may operate in the capacity of a server machine, a client machine, or both in server-client network environments. In an example, the machine 1000 may act as a peer machine in peer-to-peer (P2P) (or other distributed) network environment. The machine 1000 may be a UE, eNodeB, AP, STA, personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile telephone, a smart phone, a web appliance, a network router, switch or bridge, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term "machine" shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.

Examples, as described herein, may include, or may operate on, logic or a number of components, modules, or mechanisms. Modules are tangible entities (e.g., hardware) capable of performing specified operations and may be configured or arranged in a certain manner. In an example, circuits may be arranged (e.g. , internally or with respect to external entities such as other circuits) in a specified manner as a module. In an example, the whole or part of one or more computer systems (e.g., a standalone, client or server computer system) or one or more hardware processors may be configured by firmware or software (e.g., instructions, an application portion, or an application) as a module that operates to perform specified operations. In an example, the software may reside on a machine readable medium. In an example, the software, when executed by the underlying hardware of the module, causes the hardware to perform the specified operations.

Accordingly, the term "module" is understood to encompass a tangible entity, be that an entity that is physically constructed, specifically configured (e.g., hardwired), or temporarily (e.g., transitorily) configured (e.g., programmed) to operate in a specified manner or to perform part or all of any operation described herein. Considering examples in which modules are temporarily configured, each of the modules need not be instantiated at any one moment in time. For example, where the modules comprise a general-purpose hardware processor configured using software, the general-purpose hardware processor may be configured as respective different modules at different times. Software may accordingly configure a hardware processor, for example, to constitute a particular module at one instance of time and to constitute a different module at a different instance of time. Machine (e.g., computer system) may include a hardware processor 1002 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 1004 and a static memory 1006, some or all of which may communicate with each other via an interlink (e.g., bus) 1008. The machine 1000 may further include a display unit 1010, an alphanumeric input device 1012 (e.g. , a keyboard), and a user interface (UI) navigation device 1014 (e.g., a mouse). In an example, the display unit 1010, input device 1012 and UI navigation device 1414 may be a touch screen display. The machine 1000 may additionally include a storage device (e.g., drive unit) 1016, a signal generation device 1018 (e.g., a speaker), a network interface device 1020, and one or more sensors, such as a global positioning system (GPS) sensor, compass, accelerometer, or other sensor. The machine 1000 may include an output controller 1028, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), and the like.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, and the like).

The storage device 1016 may include a machine readable medium 1022 on which is stored one or more sets of data structures or instructions 1024 (e.g. , software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions 1024 may also reside, completely or at least partially, within the main memory 1004, within static memory 1006, or within the hardware processor 1002 during execution thereof by the machine. In an example, one or any combination of the hardware processor 1002, the main memory 1004, the static memory 1006, or the storage device 1016 may constitute machine readable media.

While the machine readable medium 1022 is illustrated as a single medium, the term "machine readable medium" may include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) configured to store the one or more instructions 1024.

The term "machine readable medium" may include any medium that is capable of storing, encoding, or carrying instructions for execution by the machine and that cause the machine to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non- limiting machine readable medium examples may include solid-state memories, and optical and magnetic media. Specific examples of machine readable media may include: no n- volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; Random Access Memory (RAM); and CD-ROM and DVD-ROM disks. In some examples, machine readable media may include non-transitory machine readable media. In some examples, machine readable media may include machine readable media that is not a transitory propagating signal.

The instructions 1024 may further be transmitted or received over a communications network 1026 using a transmission medium via the network interface device 1020 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), and the like). Example communication networks may include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g. , cellular networks), Plain Old Telephone (POTS) networks, and wireless data networks (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as Wi-Fi®, IEEE 802.16 family of standards known as WiMax®), IEEE 802.15.4 family of standards, a Long Term Evolution (LTE) family of standards, a Universal Mobile

Telecommunications System (UMTS) family of standards, peer-to-peer (P2P) networks, among others. In an example, the network interface device 1020 may include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to the communications network 1026. In an example, the network interface device 1020 may include a plurality of antennas to wirelessly communicate using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. In some examples, the network interface device 1020 may wirelessly communicate using Multiple User MIMO techniques. The term "transmission medium" shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the machine, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.

EXAMPLES

Example 1 is an apparatus of User equipment (UE) configured for cell acquisition, the apparatus comprising: at least one transceiver configured to receive, with a plurality of antennas, concurrently from an enhanced Node B (eNB), during a same time symbol, a cell ID via a plurality of electromagnetic beams each comprising a set of carriers that include data signals and spatial- frequency multiplexed orthogonal synchronization signals (SS), the beams arriving at different angles of arrival; and processing circuitry configured to process the sets of carriers to determine the identity of a beam that was received with greatest signal strength, and the angle of arrival of the determined beam, the transceiver further configured to transmit to the eNB the identity and the angle of arrival of the determined beam.

In Example 2, the subject matter of Example 1 optionally includes wherein the apparatus is further configured to receive signals arriving via the determined beam and at the angle of arrival of the determined beam

subsequently to the transmission of the identity and the angle of arrival of the determined beam to the eNB.

In Example 3, the subject matter of any one or more of Examples 1-2 optionally include wherein the apparatus is preconfigured with information about where the (SS) are allocated in the frequency domain.

In Example 4, the subject matter of any one or more of Examples 1-3 optionally include wherein the SS are received as part of a set of subcarriers each transmitted at a specific angle and separated by a channel coherence bandwidth.

In Example 5, the subject matter of any one or more of Examples optionally include wherein the concurrently received signals are each associated with an RF chain and the apparatus is further configured to use the RF chains for parallel processing of the received signals.

In Example 6, the subject matter of Example 5 optionally includes wherein the angular space for the apparatus is divided by a number of fat beams equal to the number of RF chains, and the processing circuitry processes each RF chain at a specific angle at which each of the set of subcarriers is transmitted. In Example 7, the subject matter of any one or more of Examples 1-6 optionally include wherein multiple ones of the plurality of beams received simultaneously comprise the cell ID, the SS are dynamically configured, and the apparatus is further configured to use the SS to identify a subsequently received second beam that is received with greater strength than the determined beam, based on where the SS of the second beam is located in the time/ frequency domain.

In Example 8, the subject matter of any one or more of Examples 1-7 optionally include wherein the cell ID comprises a plurality of cell IDs, the SS time/frequency allocation is static, the apparatus is preconfigured with the SS time/frequency allocation, and orthogonal subcarrier sets each include one of the plurality of cell IDs and are respectively assigned to individual small cells in a cluster of small cells.

In Example 9, the subject matter of any one or more of Examples 1-8 optionally include wherein each of the plurality of antennas transmits a respective electromagnetic beam comprising a respective RF chain that comprises a digital component and an analog component, wherein the analog component is generated by phase shifters of the plurality of antennas.

Example 10 is therein a set of instructions which, when executed by a processor of an apparatus of User Equipment (UE) causes the apparatus to: receive concurrently from an enhanced Node B (eNB), during a same time symbol, a cell ID via a plurality of electromagnetic beams each comprising a set of carriers that include data signals and spatial-frequency multiplexed orthogonal synchronization signals (SS), the beams arriving at different angles of arrival; process the sets of carriers to determine the identity of a beam that was received with greatest signal strength, and the angle of arrival of the determined beam; and transmit to the eNB the identity and the angle of arrival of the determined beam.

In Example 11 , the subject matter of Example 10 optionally includes wherein execution of the set of instructions further causes the apparatus to receive signals that arrive via the determined beam and at the angle of arrival of the determined beam, subsequently to the transmission of the identity and the angle of arrival of the determined beam to the eNB. In Example 12, the subject matter of any one or more of Examples 10-11 optionally include wherein the processing of the sets of carriers is carried out by parallel processing, and execution of the set of instructions further causes the UE to use information about where the SS is allocated in the frequency domain in the parallel processing of the sets of carriers.

In Example 13, the subject matter of any one or more of Examples 10-12 optionally include wherein execution of the set of instructions further causes the apparatus to receive the SS as part of a set of subcarriers each transmitted at a specific angle and separated by a channel coherence bandwidth.

In Example 14, the subject matter of any one or more of Examples 10-13 optionally include wherein multiple ones of the plurality of beams comprise the cell ID and are received simultaneously, the SS is dynamically configured, and the execution of the set of instructions further causes the apparatus to use the SS to identify a subsequently received beam received with greater signal strength than the determined beam, based on where the SS of the beam is located in the time/frequency domain.

Example 15 is an apparatus of a User Equipment (UE) configured for differential beam tracking when the apparatus is attached to an identified cell, the apparatus comprising: at least one transceiver configured to receive, with a plurality of antennas, concurrently from an enhanced Node B (eNB), a plurality of electromagnetic beams having a digital component and an analog component and comprising different subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam, the pairs respectively arranged at different equal angles of arrival from the central beam; and processing circuitry configured to process the sets of carriers to differentially track the plurality of beams by determining an identity of a beam received with greatest signal strength and the angle of arrival of the determined beam by use of the central beam and of the pairs of beams, the transceiver further configured to transmit to the eNB the identity and angle of arrival of the determined beam.

In Example 16, the subject matter of Example 15 optionally includes wherein subsequently to transmitting of the identity and the angle of arrival of the determined beam to the eNB, the plurality of antennas is configured to receive a second plurality of electromagnetic beams having a digital component and an analog component, the second plurality of beams comprising subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam, the pairs respectively arranged at different equal angles of arrival from the central beam, wherein the angle of arrival of the central beam is the angle of arrival transmitted to the eNB.

In Example 17, the subject matter of any one or more of Examples 15-16 optionally include wherein the reference signals are orthogonalized with respect to each other and with respect to the data signals.

In Example 18, the subject matter of any one or more of Examples 15-17 optionally include wherein the different angles of arrival are constant during an orthogonal frequency division multiplex (OFDM) symbol and the apparatus is further configured to receive the reference signals and the data signals concurrently.

In Example 19, the subject matter of any one or more of Examples 15-18 optionally include wherein the apparatus is further configured to use the different subcarriers for hybrid beamforming to transmit the identity and the angle of arrival of the determined beam to the eNB.

In Example 20, the subject matter of any one or more of Examples 15-19 optionally include wherein each beam comprises an RF chain, the antennas comprise antenna elements, and the number of RF chains is less than the number of antenna elements.

In Example 21, the subject matter of any one or more of Examples 15-20 optionally include wherein the plurality of beams each comprise an analog beamforming vector at the apparatus of the form wherein WMSi is the analog beam vector at an ith apparatus receiver, wherein the apparatus comprises a plurality of transceivers each coupled to a plurality of antennas for receiving the determined beam, and the apparatus transceiver that receives the determined beam, is configured to adjust the analog beamforming vector according to the angle of arrival of the determined beam.

In Example 22, the subject matter of any one or more of Examples 15-21 optionally include wherein the apparatus is further configured to use the digital components of the plurality of beams to generate different beam directions in different subcarriers for channel state information reference signals (CSI RS) beamforming, to transmit the identity and the angle of arrival of the determined beam to the eNB.

Example 23 is therein a set of instructions which, when executed by a processor of apparatus of User Equipment (UE) causes the apparatus to: receive concurrently from an evolved Node B (eNB), a plurality of electromagnetic beams having a digital component and an analog component and comprising different subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam, the pairs respectively arranged at different equal angles of arrival from the central beam; process the sets of carriers to differentially track the plurality of beams by determining the identity and the angle of arrival of the beam received with maximum signal strength, by using the central beam and the pairs of beams; and transmit to the eNB the identity and the angle of arrival of the determined beam.

In Example 24, the subject matter of Example 23 optionally includes wherein the set of instructions when executed further causes the apparatus, subsequently to the transmission of the identity and the angle of arrival of the determined beam to the eNB, to receive a second plurality of electromagnetic beams having a digital component and an analog component, the second plurality of beams comprising subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam the pairs respectively arranged at different equal angles of arrival from the central beam, wherein the angle of arrival of the central beam is the angle of arrival that was transmitted to the eNB.

In Example 25, the subject matter of any one or more of Examples 23-24 optionally include wherein the reference signals are orthogonalized with respect to each other and with respect to the data signals.

In Example 26, the subject matter of any one or more of Examples 23-25 optionally include wherein the different angles of arrival are constant during an orthogonal frequency division multiplex (OFDM) symbol. In Example 27, the subject matter of any one or more of Examples 23-26 optionally include wherein the set of instructions when executed further causes the UE to receive the reference signals and the data signals concurrently.

In Example 28, the subject matter of any one or more of Examples 23-27 optionally include wherein the set of instructions when executed further causes the UE to use the digital components of the plurality of beams to generate different beam directions in different subcarriers for channel state information reference signals (CSI RS) beamforming, to transmit the identity and the angle of arrival of the determined beam to the eNB.

In Example 29, the subject matter can include, or can optionally be combined with any portion or combination of, any portions of any one or more of Examples 1 through 28 to include, subject matter that can include means for performing any one or more of the functions of Examples 1 through 28, or a machine-readable medium including instructions that, when performed by a machine, cause the machine to perform any one or more of the functions of Examples 1 through 28.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as "examples." All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

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

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. An apparatus of User equipment (UE) configured for cell acquisition, the apparatus comprising:

at least one transceiver configured to receive, with a plurality of antennas, concurrently from an enhanced Node B (eNB), during a same time symbol, a cell ID via a plurality of electromagnetic beams each comprising a set of carriers that include data signals and spatial-frequency multiplexed orthogonal synchronization signals (SS), the beams arriving at different angles of arrival; and

processing circuitry configured to process the sets of carriers to determine the identity of a beam that was received with greatest signal strength, and the angle of arrival of the determined beam,

the transceiver further configured to transmit to the eNB the identity and the angle of arrival of the determined beam.

2. The apparatus of claim 1 wherein the apparatus is further configured to receive signals arriving via the determined beam and at the angle of arrival of the determined beam subsequently to the transmission of the identity and the angle of arrival of the determined beam to the eNB.

3. The apparatus of claim 1 wherein the apparatus is preconfigured with information about where the (SS) are allocated in the frequency domain.

4. The apparatus of claim 1 wherein the SS are received as part of a set of subcarriers each transmitted at a specific angle and separated by a channel coherence bandwidth.

5. The apparatus of claim 1 wherein the concurrently received signals are each associated with an RF chain and the apparatus is further configured to use the RF chains for parallel processing of the received signals.

6. The apparatus of claim 5 wherein the angular space for the apparatus is divided by a number of fat beams equal to the number of RF chains, and the processing circuitry processes each RF chain at a specific angle at which each of the set of subcarriers is transmitted.

7. The apparatus of claim 1 wherein multiple ones of the plurality of beams received simultaneously comprise the cell ID, the SS are dynamically configured, and the apparatus is further configured to use the SS to identify a subsequently received second beam that is received with greater strength than - the determined beam, based on where the SS of the second beam is located in the time/frequency domain.

8. The apparatus of claim 1 wherein the cell ID comprises a plurality of cell IDs, the SS time/frequency allocation is static, the apparatus is preconfigured with the SS time/frequency allocation, and orthogonal subcarrier sets each include one of the plurality of cell IDs and are respectively assigned to individual small cells in a cluster of small cells.

9. The apparatus of claim 1 wherein each of the plurality of antennas transmits a respective electromagnetic beam comprising a respective RF chain that comprises a digital component and an analog component, wherein the analog component is generated by phase shifters of the plurality of antennas.

10. One or more computer-readable hardware storage device having embedded therein a set of instructions which, when executed by a processor of an apparatus of User Equipment (UE) causes the apparatus to:

receive concurrently from an enhanced Node B (eNB), during a same time symbol, a cell ID via a plurality of electromagnetic beams each comprising a set of carriers that include data signals and spatial-frequency multiplexed orthogonal synchronization signals (SS), the beams arriving at different angles of arrival;

process the sets of carriers to determine the identity of a beam that was received with greatest signal strength, and the angle of arrival of the determined beam; and

transmit to the eNB the identity and the angle of arrival of the determined beam.

11. The one or more computer -readable hardware storage device of claim 10 wherein execution of the set of instructions further causes the apparatus to receive signals that arrive via the determined beam and at the angle of arrival of the determined beam, subsequently to the transmission of the identity and the angle of arrival of the determined beam to the eNB.

12. The one or more computer -readable hardware storage device of claim 10 wherein the processing of the sets of carriers is carried out by parallel processing, and execution of the set of instructions further causes the UE to use information about where the SS is allocated in the frequency domain in the parallel processing of the sets of carriers.

13. The one or more computer -readable hardware storage device of claim 10 wherein execution of the set of instructions further causes the apparatus to receive the SS as part of a set of subcarriers each transmitted at a specific angle and separated by a channel coherence bandwidth.

14. The one or more computer -readable hardware storage device of claim 10 wherein multiple ones of the plurality of beams comprise the cell ID and are received simultaneously, the SS is dynamically configured, and the execution of the set of instructions further causes the apparatus to use the SS to identify a subsequently received beam received with greater signal strength than the determined beam, based on where the SS of the beam is located in the time/frequency domain.

15. An apparatus of a User Equipment (UE) configured for differential beam tracking when the apparatus is attached to an identified cell, the apparatus comprising:

at least one transceiver configured to receive, with a plurality of antennas, concurrently from an enhanced Node B (eNB), a plurality of electromagnetic beams having a digital component and an analog component and comprising different subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam, the pairs respectively arranged at different equal angles of arrival from the central beam; and

processing circuitry configured to process the sets of carriers to differentially track the plurality of beams by determining an identity of a beam received with greatest signal strength and the angle of arrival of the determined beam by use of the central beam and of the pairs of beams,

the transceiver further configured to transmit to the eNB the identity and angle of arrival of the determined beam.

16. The apparatus of claim 15 wherein subsequently to transmitting of the identity and the angle of arrival of the determined beam to the eNB, the plurality of antennas is configured to receive a second plurality of electromagnetic beams having a digital component and an analog component, the second plurality of beams comprising subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam, the pairs respectively arranged at different equal angles of arrival from the central beam,

wherein the angle of arrival of the central beam is the angle of arrival transmitted to the eNB.

17. The apparatus of claim 15 wherein the reference signals are orthogonalized with respect to each other and with respect to the data signals.

18. The apparatus of claim 15 wherein the different angles of arrival are constant during an orthogonal frequency division multiplex (OFDM) symbol and the apparatus is further configured to receive the reference signals and the data signals concurrently.

19. The apparatus of claim 15 wherein the apparatus is further configured to use the different subcarriers for hybrid beamforming to transmit the identity and the angle of arrival of the determined beam to the eNB.

20. The apparatus of claim 15 wherein each beam comprises an RF chain, the antennas comprise antenna elements, and the number of RF chains is less than the number of antenna elements.

21. The apparatus of claim 15 wherein the plurality of beams each comprise an analog beamforming vector at the apparatus of the form

wherein WMsi is the analog beam vector at an ith apparatus receiver, wherein the apparatus comprises a plurality of transceivers each coupled to a plurality of antennas for receiving the determined beam, and the apparatus transceiver that receives the determined beam, is configured to adjust the analog beamforming vector according to the angle of arrival of the determined beam.

22. The apparatus of claim 15 wherein the apparatus is further configured to use the digital components of the plurality of beams to generate different beam directions in different subcarriers for channel state information reference signals (CSI RS) beamforming, to transmit the identity and the angle of arrival of the determined beam to the eNB.

23. One or more computer-readable hardware storage device having embedded therein a set of instructions which, when executed by a processor of apparatus of User Equipment (UE) causes the apparatus to:

receive concurrently from an evolved Node B (eNB), a plurality of electromagnetic beams having a digital component and an analog component and comprising different subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam, the pairs respectively arranged at different equal angles of arrival from the central beam;

process the sets of carriers to differentially track the plurality of beams by determining the identity and the angle of arrival of the beam received with maximum signal strength, by using the central beam and the pairs of beams; and transmit to the eNB the identity and the angle of arrival of the determined beam.

24. The one or more computer -readable hardware storage device of claim 23 wherein the set of instructions when executed further causes the apparatus, subsequently to the transmission of the identity and the angle of arrival of the determined beam to the eNB, to receive a second plurality of electromagnetic beams having a digital component and an analog component, the second plurality of beams comprising subcarriers that include data signals and reference signals, each beam transmitted at the same power and received at different angles of arrival, the plurality of beams comprising a central beam and pairs of beams on either side of the central beam the pairs respectively arranged at different equal angles of arrival from the central beam, wherein the angle of arrival of the central beam is the angle of arrival that was transmitted to the eNB.

25. The one or more computer -readable hardware storage device of claim 23 wherein the reference signals are orthogonalized with respect to each other and with respect to the data signals.

26. The one or more computer -readable hardware storage device of claim 23 wherein the different angles of arrival are constant during an orthogonal frequency division multiplex (OFDM) symbol.

27. The one or more computer -readable hardware storage device of claim 23 wherein the set of instructions when executed further causes the UE to receive the reference signals and the data signals concurrently.

28. The one or more computer -readable hardware storage device of claim 23 wherein the set of instructions when executed further causes the UE to use the digital components of the plurality of beams to generate different beam directions in different subcarriers for channel state information reference signals (CSI RS) beamforming, to transmit the identity and the angle of arrival of the determined beam to the eNB.