Patent ID: 12199724

DETAILED DESCRIPTION

FIGS.1through40, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

Aspects, features, and advantages of the disclosure are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the disclosure. The disclosure is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. The disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

The present disclosure covers several components which can be used in conjunction or in combination with one another, or can operate as standalone schemes. Certain embodiments of the disclosure may be derived by utilizing a combination of several of the embodiments listed below. Also, it should be noted that further embodiments may be derived by utilizing a particular subset of operational steps as disclosed in each of these embodiments. This disclosure should be understood to cover all such embodiments.

To meet the demand for wireless data traffic having increased since deployment of 4G communication systems and to enable various vertical applications, efforts have been made to develop and deploy an improved 5G/NR or pre-5G/NR communication system. Therefore, the 5G/NR or pre-5G/NR communication system is also called a “beyond 4G network” or a “post LTE system.” The 5G/NR communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 28 GHz or 60 GHz bands, so as to accomplish higher data rates or in lower frequency bands, such as 6 GHz, to enable robust coverage and mobility support. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beam forming, large scale antenna techniques are discussed in 5G/NR communication systems.

In addition, in 5G/NR communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancelation and the like.

The discussion of 5G systems and frequency bands associated therewith is for reference as certain embodiments of the present disclosure may be implemented in 5G systems. However, the present disclosure is not limited to 5G systems or the frequency bands associated therewith, and embodiments of the present disclosure may be utilized in connection with any frequency band. For example, aspects of the present disclosure may also be applied to deployment of 5G communication systems, 6G or even later releases which may use terahertz (THz) bands.

FIGS.1-4Bbelow describe various embodiments implemented in wireless communications systems and with the use of orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) communication techniques. The descriptions ofFIGS.1-4Bare not meant to imply physical or architectural limitations to the manner in which different embodiments may be implemented. Different embodiments of the present disclosure may be implemented in any suitably-arranged communications system.

FIG.1illustrates an example wireless network according to embodiments of the present disclosure. The embodiment of the wireless network shown inFIG.1is for illustration only. Other embodiments of the wireless network100could be used without departing from the scope of this disclosure.

As shown inFIG.1, the wireless network includes a gNB101(e.g., base station, BS), a gNB102, and a gNB103. The gNB101communicates with the gNB102and the gNB103. The gNB101also communicates with at least one network130, such as the Internet, a proprietary Internet Protocol (IP) network, or other data network.

The gNB102provides wireless broadband access to the network130for a first plurality of UEs within a coverage (or broadcast) area120of the gNB102. The first plurality of UEs includes a UE111, which may be located in a small business; a UE112, which may be located in an enterprise (E); a UE113, which may be located in a WiFi hotspot (HS); a UE114, which may be located in a first residence (R); a UE115, which may be located in a second residence (R); and a UE116, which may be a mobile device (M), such as a cell phone, a wireless laptop, a wireless PDA, or the like. The gNB103provides wireless broadband access to the network130for a second plurality of UEs within a coverage area125of the gNB103. The second plurality of UEs includes the UE115and the UE116. In some embodiments, one or more of the gNBs101-103may communicate with each other and with the UEs111-116using 5G/NR, LTE, LTE-A, WiMAX, WiFi, or other wireless communication techniques.

Depending on the network type, the term “base station” or “BS” can refer to any component (or collection of components) configured to provide wireless access to a network, such as transmit point (TP), transmit-receive point (TRP), an enhanced base station (eNodeB or eNB), a 5G/NR base station (gNB), a macrocell, a femtocell, a WiFi access point (AP), or other wirelessly enabled devices. Base stations may provide wireless access in accordance with one or more wireless communication protocols, e.g., 5G/NR 3GPP new radio interface/access (NR), LTE, LTE advanced (LTE-A), high speed packet access (HSPA), Wi-Fi 802.11a/b/g/n/ac, etc. For the sake of convenience, the terms “BS” and “TRP” are used interchangeably in this patent document to refer to network infrastructure components that provide wireless access to remote terminals. Also, depending on the network type, the term “user equipment” or “UE” can refer to any component such as “mobile station,” “subscriber station,” “remote terminal,” “wireless terminal,” “receive point,” or “user device.” For the sake of convenience, the terms “user equipment” and “UE” are used in this patent document to refer to remote wireless equipment that wirelessly accesses a BS, whether the UE is a mobile device (such as a mobile telephone or smartphone) or is normally considered a stationary device (such as a desktop computer or vending machine).

Dotted lines show the approximate extents of the coverage areas120and125, which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with gNBs, such as the coverage areas120and125, may have other shapes, including irregular shapes, depending upon the configuration of the gNBs and variations in the radio environment associated with natural and man-made obstructions.

As described in more detail below, one or more of the UEs111-116include circuitry, programming, or a combination thereof for time-delay based hybrid beamforming. In certain embodiments, and one or more of the gNBs101-103includes circuitry, programming, or a combination thereof for time-delay based hybrid beamforming.

AlthoughFIG.1illustrates one example of a wireless network, various changes may be made toFIG.1. For example, the wireless network could include any number of gNBs and any number of UEs in any suitable arrangement. Also, the gNB101could communicate directly with any number of UEs and provide those UEs with wireless broadband access to the network130. Similarly, each gNB102-103could communicate directly with the network130and provide UEs with direct wireless broadband access to the network130. Further, the gNBs101,102, and/or103could provide access to other or additional external networks, such as external telephone networks or other types of data networks.

FIG.2illustrates an example gNB102according to embodiments of the present disclosure. The embodiment of the gNB102illustrated inFIG.2is for illustration only, and the gNBs101and103ofFIG.1could have the same or similar configuration. However, gNBs come in a wide variety of configurations, andFIG.2does not limit the scope of this disclosure to any particular implementation of a gNB.

As shown inFIG.2, the gNB102includes multiple antennas205a-205n, multiple RF transceivers210a-210n, transmit (TX) processing circuitry215, and receive (RX) processing circuitry220. The gNB102also includes a controller/processor225, a memory230, and a backhaul or network interface235.

The RF transceivers210a-210nreceive, from the antennas205a-205n, incoming RF signals, such as signals transmitted by UEs in the network100. The RF transceivers210a-210ndown-convert the incoming RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuitry220, which generates processed baseband signals by filtering, decoding, and/or digitizing the baseband or IF signals. The RX processing circuitry220transmits the processed baseband signals to the controller/processor225for further processing.

The TX processing circuitry215receives analog or digital data (such as voice data, web data, e-mail, or interactive video game data) from the controller/processor225. The TX processing circuitry215encodes, multiplexes, and/or digitizes the outgoing baseband data to generate processed baseband or IF signals. The RF transceivers210a-210nreceive the outgoing processed baseband or IF signals from the TX processing circuitry215and up-converts the baseband or IF signals to RF signals that are transmitted via the antennas205a-205n.

The controller/processor225can include one or more processors or other processing devices that control the overall operation of the gNB102. For example, the controller/processor225could control the reception of forward channel signals and the transmission of reverse channel signals by the RF transceivers210a-210n, the RX processing circuitry220, and the TX processing circuitry215in accordance with well-known principles. The controller/processor225could support additional functions as well, such as more advanced wireless communication functions. For instance, the controller/processor225could support methods for time-delay based hybrid beamforming. Any of a wide variety of other functions could be supported in the gNB102by the controller/processor225.

The controller/processor225is also capable of executing programs and other processes resident in the memory230, such as an OS. The controller/processor225can move data into or out of the memory230as required by an executing process.

The controller/processor225is also coupled to the backhaul or network interface235. The backhaul or network interface235allows the gNB102to communicate with other devices or systems over a backhaul connection or over a network. The interface235could support communications over any suitable wired or wireless connection(s). For example, when the gNB102is implemented as part of a cellular communication system (such as one supporting 5G/NR, LTE, or LTE-A), the interface235could allow the gNB102to communicate with other gNBs over a wired or wireless backhaul connection. When the gNB102is implemented as an access point, the interface235could allow the gNB102to communicate over a wired or wireless local area network or over a wired or wireless connection to a larger network (such as the Internet). The interface235includes any suitable structure supporting communications over a wired or wireless connection, such as an Ethernet or RF transceiver.

The memory230is coupled to the controller/processor225. Part of the memory230could include a RAM, and another part of the memory230could include a Flash memory or other ROM.

AlthoughFIG.2illustrates one example of gNB102, various changes may be made toFIG.2. For example, the gNB102could include any number of each component shown inFIG.2. As a particular example, an access point could include a number of interfaces235, and the controller/processor225could support routing functions to route data between different network addresses. As another particular example, while shown as including a single instance of TX processing circuitry215and a single instance of RX processing circuitry220, the gNB102could include multiple instances of each (such as one per RF transceiver). Also, various components inFIG.2could be combined, further subdivided, or omitted and additional components could be added according to particular needs.

FIG.3illustrates an example UE116according to embodiments of the present disclosure. The embodiment of the UE116illustrated inFIG.3is for illustration only, and the UEs111-115ofFIG.1could have the same or similar configuration. However, UEs come in a wide variety of configurations, andFIG.3does not limit the scope of this disclosure to any particular implementation of a UE.

As shown inFIG.3, the UE116includes an antenna305, a radio frequency (RF) transceiver310, TX processing circuitry315, a microphone320, and RX processing circuitry325. The UE116also includes a speaker330, a processor340, an input/output (I/O) interface (IF)345, a touchscreen350, a display355, and a memory360. The memory360includes an operating system (OS)361and one or more applications362.

The RF transceiver310receives, from the antenna305, an incoming RF signal transmitted by a gNB of the network100. The RF transceiver310down-converts the incoming RF signal to generate an intermediate frequency (IF) or baseband signal. The IF or baseband signal is sent to the RX processing circuitry325, which generates a processed baseband signal by filtering, decoding, and/or digitizing the baseband or IF signal. The RX processing circuitry325transmits the processed baseband signal to the speaker330(such as for voice data) or to the processor340for further processing (such as for web browsing data).

The TX processing circuitry315receives analog or digital voice data from the microphone320or other outgoing baseband data (such as web data, e-mail, or interactive video game data) from the processor340. The TX processing circuitry315encodes, multiplexes, and/or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceiver310receives the outgoing processed baseband or IF signal from the TX processing circuitry315and up-converts the baseband or IF signal to an RF signal that is transmitted via the antenna305.

The processor340can include one or more processors or other processing devices and execute the OS361stored in the memory360in order to control the overall operation of the UE116. For example, the processor340could control the reception of forward channel signals and the transmission of reverse channel signals by the RF transceiver310, the RX processing circuitry325, and the TX processing circuitry315in accordance with well-known principles. In some embodiments, the processor340includes at least one microprocessor or microcontroller.

The processor340is also capable of executing other processes and programs resident in the memory360, such as processes for time-delay based hybrid beamforming. The processor340can move data into or out of the memory360as required by an executing process. In some embodiments, the processor340is configured to execute the applications362based on the OS361or in response to signals received from gNBs or an operator. The processor340is also coupled to the I/O interface345, which provides the UE116with the ability to connect to other devices, such as laptop computers and handheld computers. The I/O interface345is the communication path between these accessories and the processor340.

The processor340is also coupled to the touchscreen350and the display355. The operator of the UE116can use the touchscreen350to enter data into the UE116. The display355may be a liquid crystal display, light emitting diode display, or other display capable of rendering text and/or at least limited graphics, such as from web sites.

The memory360is coupled to the processor340. Part of the memory360could include a random access memory (RAM), and another part of the memory360could include a Flash memory or other read-only memory (ROM).

AlthoughFIG.3illustrates one example of UE116, various changes may be made toFIG.3. For example, various components inFIG.3could be combined, further subdivided, or omitted and additional components could be added according to particular needs. As a particular example, the processor340could be divided into multiple processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Also, whileFIG.3illustrates the UE116configured as a mobile telephone or smartphone, UEs could be configured to operate as other types of mobile or stationary devices.

FIG.4Aillustrates a high-level diagram of an orthogonal frequency division multiple access (OFDMA) transmit path400according to embodiments of the present disclosure.FIG.4Billustrates a high-level diagram of an OFDMA receive path450according to embodiments of the present disclosure. InFIGS.4A and4B, for downlink communication, the transmit path400may be implemented in a base station (gNB)102or a relay station, and the receive path450may be implemented in a user equipment (e.g., user equipment116of FIG.1). In other examples, for uplink communication, the receive path450may be implemented in a base station (e.g., gNB102ofFIG.1) or a relay station, and the transmit path400may be implemented in a user equipment (e.g., user equipment116ofFIG.1).

The transmit path400comprises channel coding and modulation block405, serial-to-parallel (S-to-P) block410, Size N Inverse Fast Fourier Transform (IFFT) block415, parallel-to-serial (P-to-S) block420, add cyclic prefix block425, and up-converter (UC)430. The receive path450comprises down-converter (DC)455, remove cyclic prefix block460, serial-to-parallel (S-to-P) block465, Size N Fast Fourier Transform (FFT) block470, parallel-to-serial (P-to-S) block475, and channel decoding and demodulation block480.

At least some of the components inFIGS.4A and4Bmay be implemented in software, while other components may be implemented by configurable hardware or a mixture of software and configurable hardware. In particular, it is noted that the FFT blocks and the IFFT blocks described in this disclosure document may be implemented as configurable software algorithms, where the value of Size N may be modified according to the implementation.

Furthermore, although this disclosure is directed to an embodiment that implements the Fast Fourier Transform and the Inverse Fast Fourier Transform, this is by way of illustration only and may not be construed to limit the scope of the disclosure. It may be appreciated that in an alternate embodiment of the present disclosure, the Fast Fourier Transform functions and the Inverse Fast Fourier Transform functions may easily be replaced by discrete Fourier transform (DFT) functions and inverse discrete Fourier transform (IDFT) functions, respectively. It may be appreciated that for DFT and IDFT functions, the value of the N variable may be any integer number (i.e., 1, 4, 3, 4, etc.), while for FFT and IFFT functions, the value of the N variable may be any integer number that is a power of two (i.e., 1, 2, 4, 8, 16, etc.).

In the transmit path400, the channel coding and modulation block405receives a set of information bits, applies coding (e.g., LDPC coding) and modulates (e.g., quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM)) the input bits to produce a sequence of frequency-domain modulation symbols. The serial-to-parallel block410converts (i.e., de-multiplexes) the serial modulated symbols to parallel data to produce N parallel symbol streams where N is the IFFT/FFT size used in the gNB102and the UE116. The Size N IFFT block415then performs an IFFT operation on the N parallel symbol streams to produce time-domain output signals. The parallel-to-serial block420converts (i.e., multiplexes) the parallel time-domain output symbols from the Size N IFFT block415to produce a serial time-domain signal. The add cyclic prefix block425then inserts a cyclic prefix to the time-domain signal. Finally, the up-converter430modulates (i.e., up-converts) the output of the add cyclic prefix block425to RF frequency for transmission via a wireless channel. The signal may also be filtered at baseband before conversion to RF frequency.

The transmitted RF signal arrives at the UE116after passing through the wireless channel, and reverse operations to those at the gNB102are performed. The down-converter455down-converts the received signal to baseband frequency, and the remove cyclic prefix block460removes the cyclic prefix to produce the serial time-domain baseband signal. The serial-to-parallel block465converts the time-domain baseband signal to parallel time-domain signals. The Size N FFT block470then performs an FFT algorithm to produce N parallel frequency-domain signals. The parallel-to-serial block475converts the parallel frequency-domain signals to a sequence of modulated data symbols. The channel decoding and demodulation block480demodulates and then decodes the modulated symbols to recover the original input data stream.

Each of gNB s101-103may implement a transmit path that is analogous to transmitting in the downlink to the UEs111-116and may implement a receive path that is analogous to receiving in the uplink from the UEs111-116. Similarly, each one of the UEs111-116may implement a transmit path corresponding to the architecture for transmitting in the uplink to the gNBs101-103and may implement a receive path corresponding to the architecture for receiving in the downlink from the gNBs101-103.

FIG.5illustrates an example beamforming architecture500according to embodiments of the present disclosure. The embodiment of the beamforming architecture500illustrated inFIG.5is for illustration only.FIG.5does not limit the scope of this disclosure to any particular implementation of the beamforming architecture500. In certain embodiments, one or more of gNB102or UE116can include the beamforming architecture500. For example, one or more of antenna205and its associated systems or antenna305and its associated systems can be configured the same as or similar to the beamforming architecture500.

Rel.14 LTE and Rel.15 NR support up to 32 CSI-RS antenna ports which enable an eNB to be equipped with a large number of antenna elements (such as 64 or 128). In this case, a plurality of antenna elements is mapped onto one CSI-RS port. For mmWave bands, although the number of antenna elements can be larger for a given form factor, the number of CSI-RS ports—which can correspond to the number of digitally precoded ports—tends to be limited due to hardware constraints (such as the feasibility to install a large number of analog-to-digital converts/digital-to-analog converts (ADCs/DACs at mmWave frequencies)).

In the example shown inFIG.5, the beamforming architecture500includes analog phase shifters505, an analog beamformer (BF)510, a hybrid BF515, a digital BF520, and one or more antenna arrays525. In this case, one CSI-RS port is mapped onto a large number of antenna elements in antenna arrays525, which can be controlled by the bank of analog phase shifters505. One CSI-RS port can then correspond to one sub-array which produces a narrow analog beam through analog beamforming by analogy BF510. The analog beam can be configured to sweep530across a wider range of angles by varying the phase shifter bank505across symbols or subframes. The number of sub-arrays (equal to the number of RF chains) is the same as the number of CSI-RS ports NCSI-PORT. A digital BF515performs a linear combination across NCSI-PORT analog beams to further increase precoding gain. While analog beams are wideband (hence not frequency-selective), digital precoding can be varied across frequency sub-bands or resource blocks.

Since the above system utilizes multiple analog beams for transmission and reception (wherein one or a small number of analog beams are selected out of a large number, for instance, after a training duration—to be performed from time to time), the term “multi-beam operation” is used to refer to the overall system aspect. This includes, for the purpose of illustration, indicating the assigned DL or UL transmit (TX) beam (also termed “beam indication”), measuring at least one reference signal for calculating and performing beam reporting (also termed “beam measurement” and “beam reporting”, respectively), and receiving a DL or UL transmission via a selection of a corresponding receive (RX) beam.

Additionally, the beamforming architecture500is also applicable to higher frequency bands such as >52.6 GHz (also termed the FR4). In this case, the beamforming architecture500can employ only analog beams. Due to the O2 absorption loss around 60 GHz frequency (˜10 decibels (dB) additional loss @ 100 m distance), larger numbers of and sharper analog beams (hence larger number of radiators in the array) will be needed to compensate for the additional path loss.

As previously discussed, fully digital transceiver implementations, where each antenna element is fed by a dedicated radio-frequency (RF) chain, are impractical. To keep the hardware cost and power consumption of such large antenna arrays manageable, typically an analog beamforming or hybrid beamforming architecture is adopted where the large antenna array is fed with a much smaller number of RF chains via the use of analog hardware such as phase shifters. This reduces the number of mixed-signal components, which significantly reduces the cost, size and power consumption of the transceivers. When transmitting a signal at the transmitter, a combination of digital beamforming before DAC and analog beamforming using the phase shifters is used to create the overall beam shape in the desired direction. Similarly, when receiving a signal at the receiver, a combination of analog beamforming using phase shifters and digital beamforming after ADC is used to create the overall beam shape in the desired direction.

Conventional forms of analog beamforming or hybrid beamforming rely on the analog hardware components (e.g., phase shifters and switches) to create the beam shapes. However, these analog hardware components create a frequency-flat response, i.e., all components of the input signal frequency undergo a similar transformation after passing through them. This reduces the flexibility of the beamforming that is possible in such analog or hybrid beamforming systems, as compared to fully digital architectures where each antenna array is fed with a dedicated RF chain. This limitation of frequency-flat beamforming is further exacerbated at the mm-wave and THz frequencies, where beam-alignment, beam-tracking, link blockage and initial access are difficult problems to solve and usually involve significant overhead. There also exist several scenarios where the frequency flat-beamforming can limit the number of users that can be served simultaneously with the full beamforming gain.

FIG.6illustrates a system600that performs phase shifter based hybrid beamforming with a single RF chain, i.e., R=1. Note that with M antennas, the maximum possible beamforming gain in any direction is M. In that case, with frequency-flat beamforming, two spatially separated users cannot be simultaneously (at the same time) served on half the bandwidth with the maximum beamforming gain of M. Similarly, in a scenario that includes many internet-of-things (IoT) users (each requiring a low bandwidth) that are spread uniformly in the angular space, they cannot all be served simultaneously (at the same time) with the full beamforming gain of M. Note that here, angular space refers to the angle subtended by the receiver's line-of-sight path at the transmitter. Furthermore, the beams that can achieve the full beamforming gain of M are often pencil thin and are highly prone to blockage, or misalignment caused by user mobility/rotation. The overhead for tracking these beam directions (in case of misalignment) and also to perform the initial alignment can be very high in large antenna systems with very few RF chains. This limits the performance gains achievable using frequency-flat hybrid beamforming.

To address these and other issues, this disclosure provides a system and method for time-delay based hybrid beamforming. As described in more detail below, the disclosed embodiments utilize a type of analog hardware called true-time delay (TTD). Unlike switches and phase shifters, TTDs have a frequency-dependent behavior, i.e., different components of the input signal frequency undergo different transformations after passing through the TTD. Thus, the disclosed embodiments feature hybrid transceiver architectures where a small number of RF chains are connected to a large antenna array using TTDs. Using such architectures, the disclosed embodiments can achieve frequency-dependent beamforming that is more versatile than conventional, frequency-flat beamforming methods. Note that, here, frequency-dependent beamforming refers to a technique where different components of the input signal may encounter a differently shaped analog beam based on their frequency. The disclosed embodiments feature any of several transceiver architectures that use a combination of phase shifters, switches, and TTDs as analog components that connect the large antenna array to a small number of RF chains. The disclosed embodiments also feature several key frequency-dependent beamforming behaviors that can be realized, and also feature multiple algorithms for realizing the frequency-dependent beamforming behaviors.

Note that while some of the embodiments discussed below are described in the context of hybrid beamforming systems, these are merely examples. It will be understood that the principles of this disclosure may be implemented in any number of other suitable contexts or systems.

FIGS.7through10illustrate several desirable frequency-dependent beam behaviors that can be useful in different scenarios.

Beam Behavior 1: As shown inFIG.7, in frequency-dependent beam forming scenarios that exhibit this behavior, the maximum gain region of the beam sweeps over an angle range as the signal frequency varies. This behavior can be useful at a BS in scenarios where many users are uniformly distributed in an angular region and require simultaneous service in downlink and uplink (PDSCH and PUSCH). For such uniformly spread users, the physical uplink control channel (PUCCH) overhead can also be reduced with this beam behavior, since it enables all users to send small uplink control packets (e.g. HARQ-ACK packets) simultaneously. This behavior is also desirable in scenarios where the users are moving at a high velocity, and good link reliability and fast beam re-alignment are needed. In addition, such a beam behavior is also beneficial in scenarios where the BS wishes to obtain initial beam alignment with one or more users at a very low overhead. Finally, this behavior is also useful for increasing the uplink cell coverage range, by allowing each user device on cell edge to accumulate more power by transmitting longer.

Beam Behavior 2: As shown inFIG.8, in frequency-dependent beam forming scenarios that exhibit this behavior, the maximum gain region points in one angular direction over the lower half of the signal bandwidth and it points in another angular direction over the upper half bandwidth. This behavior is useful in scenarios where the users are sparsely distributed in the angular domain, and the BS wishes to provide service to multiple users simultaneously on different portions of the large available system bandwidth. Such service on portions of the bandwidth is helpful, for example, if each user is incapable of utilizing the full system bandwidth or if each user only has very low traffic to send. Extensions of such behavior that cover more than two angular directions can also be considered, such as shown in the bottom ofFIG.8.

Beam Behavior 3: As shown in the examples ofFIG.9, the maximum gain region spans region1of the angular space at one subset of frequencies (subset1) and region2of the angular space at a disjoint set of frequencies (subset2). Within each of subset1and subset2frequencies, the maximum gain region sweeps across angular space region1and angular space region2, respectively. This behavior is useful when the users are clustered in several different localized regions and require simultaneous service or require fast beam realignment.

Beam Behavior 4: As shown inFIG.10, in this behavior, a wide beam is constructed that provides coverage for a certain angular region for most of the bandwidth. However, for a sub-band of the bandwidth, the width of the wide beam may be adapted to reduce co-channel interference to some incumbent users using that sub-band.

Similar behaviors of the frequency-dependent beam can also be useful at a user device in several scenarios, e.g. for initial beam alignment and tracking. Note that this kind of frequency-dependent beamforming is not possible using conventional hybrid beamforming techniques that use only phase shifters or switches. In the present disclosure, several different embodiments of transceiver architectures are described that utilize a combination of phase shifters, TTDs, and switches that can realize the aforementioned beam behaviors. In addition, multiple design algorithms are provided for choosing the values of the phase-shifts and the TTDs that can achieve these beam-behaviors.

FIG.11illustrates an example transceiver1100for performing TTD-based hybrid beamforming according to embodiments of the present disclosure. As shown inFIG.11, the transceiver1100is a BS transceiver that is equipped with M antennas1105and one RF chain1110. Each antenna1105(represented as m) is connected to L different phase shifters1115via one or more power amplifiers1120. In the figure, the corresponding frequency-independent phase-shifts are identified as {φm,1, φm,1, . . . , φm,L}. For each l∈{1, . . . , L} the phase shifts {φ1,l, φ2,l, . . . , φM,l} are connected to N dedicated TTDs1125having delay values {τ1,l, τ2,l, . . . , τN,l}, where N≤M, via a mapping matrix1130(represented as Pl). The mapping matrix1130Plessentially determines how the N TTDs1125connect to the corresponding M phase shifters1115. In some embodiments, each mapping matrix1130may be simply a set of fixed connections. In some embodiments, the mapping can be performed using one or more RF switches, which create re-configurable mappings.

The inputs to the TTDs1125are all directly fed by the output of the RF chain1110of the transceiver1100. Thus in total, the transceiver1100has ML phase shifters1115, L mapping matrices1130and NL TTD elements1125(where N≤L). Here the TTD elements1125can be implemented using electronic components or using photonic components. Moreover, the TTD elements1125can have either fixed or reconfigurable delay values. Additionally, some of the TTD elements1125can also be implemented in the digital domain by including more RF chains.

It is noted that the architecture of the transceiver1100shown inFIG.11is only one example and should not be interpreted as a limitation of the present disclosure. For example, the same architecture can also be extended to a multiple-RF chain scenario by incorporating several such arrays in parallel, each having their own separate RF chain. It is noted that for this architecture at the transmitter, assuming orthogonal frequency division multiplexing (OFDM), the transmit signal on subcarrier k∈can be expressed as:

xk=∑l=1L1M[ej⁢φ1,lej⁢φ2,l⋮ej⁢φM,l]⊙Pl[e-j⁢2⁢π⁢fk⁢τ1,le-j⁢2⁢π⁢fk⁢τ2,l⋮e-j⁢2⁢π⁢fk⁢τN,l]⁢sk=∑l=1L(Tl⊙(Pl⁢Dk,l))⁢sk(1)
where ⊙ is the Hadamard product (i.e., the element-wise matrix product), Tlis the l-th phase-shifter vector, and Dk,lis the TTD vector at subcarrier k∈, respectively.

The desired frequency-dependent beam-behaviors described above (i.e., Behavior 1, Behavior 2, Behavior 3, and Behavior 4) can all be interpreted as wanting the maximum beamforming (of M) in some desired angular regions Θ=Ui=1l[θi−Δθi, θi+Δθi] as the transceiver1100sweeps across the frequencies within the system bandwidth. For example, in Behavior 1, I=1, θ1is the center angle of the angular region over which the BS intends to sweep the beam, and 2Δθ1is the overall angle of sweep. Similarly in Behavior 2, I=2, θ1and θ2are the angles corresponding to user1and user2, respectively, and Δθ1=Δθ2=0 (i.e., no beam sweeping). Since in many scenarios, it does not matter which frequency region is assigned to each of the angular regions of interest, in some embodiments, the phase shifter and TTD design problem can be formulated as:

argmaxT,{τ1,…,τN}⁢{∑θ∈Θ∑k∈𝒦❘"\[LeftBracketingBar]"∑latx(θ)†⁢(T1⊙(Pl⁢Dk,l))❘"\[RightBracketingBar]"2⁢β∑l(Tl⊙(Pl⁢Dk,l))2⁢β}(2)
where β can be a system design parameter, † represents the transpose operation, and αtx(θ) is the array response vector of the antenna array in direction θ. For example, for a uniform linear antenna array with half-wave inter-element spacing, the array response vector αtx(θ) can be expressed as:

atx(θ)=[1e-j⁢π⁢sin(θ)⋮e-j⁢π⁢Msin(θ](3)

It is noted the problem formulation in Equation (2) is not limited to uniform linear arrays, and one can use the proper αtx(θ) that matches the array structure. Other array structures may include planner uniform arrays and non-uniform arrays.

Next, some embodiments for realizing the desired beam behaviors will be described.

Beam Behavior 1:

Beam Behavior 1 can be useful in scenarios where simultaneous service is required for several users in a localized region with the full beamforming gain, or in scenarios where link reliability and easy beam-tracking are desired, or where fast initial beam-alignment is desired. In this scenario, it is assumed without loss of generality that the desired coverage region is Θ=[θ1−Δθ1θ1+Δθ1].

FIG.12illustrates an example transceiver1200for performing TTD-based hybrid beamforming for Beam Behavior 1 according to embodiments of the present disclosure. As shown inFIG.12, the transceiver1200includes multiple antennas1205, a RF chain1210, multiple phase shifters1215, multiple amplifiers1220, and multiple TTDs1225. The transceiver1200is a special case of the transceiver1100shown inFIG.11, with L=1, N=M, Pl=M. Thus in the transceiver1200, the number of phase shifters1215and the number of TTDs1225are both set to M, and each mapping matrix is just a straight wire connection. In some embodiments, the TTDs1225are reconfigurable, and the TTD1225corresponding to antenna m is configured to have a delay variation between τm,1∈[0, (m−1) sin (Δθmax)/W], where W is the system bandwidth and Δθmaxis the maximum desired beam-sway in one direction of the center angle. In some embodiments, to achieve the desired behavior over Θ, the TTD delays and phase shifts can be set based on the example algorithm1300shown inFIG.13.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=N=64, θ1=0 and Δθ1=π/8 is illustrated inFIG.14. As can be seen fromFIG.14, this design can achieve the desired Beam Behavior 1.

In the architecture represented by the transceiver1200, for each angle in the vicinity of θ1, there is a unique frequency region where the peak beamforming gain is obtained. Thus in fast user mobility scenarios, by observing the frequency or sub-carrier where the highest signal power is obtained, the receiver can estimate the best beam direction or the required beam correction to be used at the transmitter. Thus fast beam-alignment can be achieved using this architecture. Furthermore, as the user moves away by more than a 3 dB beam-width on one frequency, the SNR doesn't completely fall to zero on the whole band. Rather the maximum beamforming gain shifts to a different frequency. This can beneficial since it can provide a graceful degradation of service with user mobility and does not cause sudden outage as in the case of frequency-flat beamforming.

In some scenarios, it might be costly to implement finely tunable TTDs. And so, in a related embodiment, the transceiver1200may support only discrete beam-sway values 2Δθ1. In this case, selectable fixed delay TTDs can be used. For example, to support three beam-sway options

Δ⁢θ1=0,π16,or⁢π8,
the algorithm1300can be used to compute three sets of TTDs1225, then switches can be implemented to select one on the three fixed TTD options per antenna1205. The transceiver1200may be designed such that the maximum beam-sway value 2Δθmaxis less than or equal to the beam-width of the individual antenna elements in the array.

In the aforementioned embodiment, the required delay values for larger antenna indices m≈M can be quite large: [0, (m−1) sin (Δθmax)/πW]. Correspondingly, in another embodiment (referred to as Embodiment 2 for clarity), the antenna array can be divided into [M/M] sub-arrays, each containingMadjacent antenna elements. For example,FIG.15illustrates another example transceiver1500for performing TTD-based hybrid beamforming for Behavior 1 (Embodiment 2) according to embodiments of the present disclosure. As shown inFIG.15, the transceiver1500includes multiple antennas1505, a RF chain1510, multiple phase shifters1515, multiple amplifiers1520, and multiple TTDs1525-1526. Each sub-array has a dedicated TTD1525for providing a large delay value, while each antenna within the sub-array may also have a TTD1526providing small intra-sub-array delays that require a much smaller max delay range.

The transceiver1500is a special case of the transceiver1100shown inFIG.11, with L=1, N=M, Pl=M, and τn,1=τ[n/M]+{circumflex over (τ)}n. In the transceiver1500, the number of phase shifters1515is M and number of TTDs1525-1526is M+[M/M], whereMis a design parameter and each mapping matrix is just a straight wire connection. However for the TTDs1525-1526, the required tunable delay range is: {circumflex over (τ)}m∈[0, (mod(m−1,M)) sin (Δθmax)/W] andτu∈[0, (u−1)Msin (Δθmax)/W]. Thus in other words, out of the total TTDs, M TTDs1526only require a small max-delay while the [M/M] TTDs1525require a larger delay value. Since the number of TTDs1525with large delay is reduced, the hardware cost can be lower than Embodiment 1 described with respect toFIG.12. In some embodiments, to achieve the desired behavior over Θ, the TTD delays and phase-shifts can be set based on the example algorithm1600shown inFIG.16.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=N=64, θ1=0 and Δθ1=π/8 is illustrated inFIG.17. As can be seen fromFIG.17, this design can achieve the desired Beam Behavior 1. By comparingFIG.14andFIG.17, it can be seen that this architecture can achieve identical performance as Embodiment 1 described with respect toFIG.12.

In some embodiments, in the transceiver1500, instead of one RF chain1510, U RF chains can be used to allow for a digital implementation of the TTDsτuwhile keeping the analog implementation of {circumflex over (τ)}m.

In both the aforementioned two embodiments, the number of TTDs1525-1526is equal to or larger than the number of antenna elements1505, M, which could be difficult to fabricate in some scenarios. Therefore, in another embodiment (referred to as Embodiment 3 for clarity), the antenna array can be divided into [M/M] sub-arrays, each containingMadjacent antenna elements. For example,FIG.18illustrates another example transceiver1800for performing TTD-based hybrid beamforming for Behavior 1 (Embodiment 3) according to embodiments of the present disclosure. As shown inFIG.18, the transceiver1800includes multiple antennas1805, a RF chain1810, multiple phase shifters1815, multiple amplifiers1820, and multiple TTDs1825. Unlike Embodiment 2 (FIG.15), the transceiver1800does not include any intra-sub-array TTD elements.

The transceiver1800is a special case of the transceiver1100shown inFIG.11, with L=1, N=[M/M], P1=N⊗M×1. In the transceiver1800, the number of phase shifters1815is M and number of TTDs1825is only [M/M], whereMis a design parameter and each mapping matrix is just a splitter that connects each delay output to all theMphase shifters in the corresponding sub-array. The desired tunable delay range is: τn,1∈[0, nMsin (Δθmax)/W]. In some embodiments, to achieve the desired behavior over Θ, the TTD delays and phase shifts can be set based on the example algorithm1900shown inFIG.19.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=N=64,M=8, θ1=0 and Δθ1=π/8 is illustrated inFIG.20. As can be seen fromFIG.20, this design can approximately achieve the desired Beam Behavior 1. Due to the limited number of TTDs1825, the beamforming gain is less then M as the beam sweeps away from the center angle. Thus the transceiver1800can be a good choice when the desired sweep angle Δθ1is small, which can limit the loss due to reduction in the beamforming gain. For larger values of Δθ1, the loss in beamforming gain can be significant with this low-complexity architecture. To avoid such loss,Mcan be chosen such thatM≤π/2Δθ1. In some embodiments, in the transceiver1800, instead of one RF chain, N RF chains can be used to allow for a digital implementation of the TTDs τu.

Beam Behavior 2:

Beam Behavior 2 can be useful in scenarios where simultaneous service is required for users that are spatially far apart with the full beamforming gain. In this scenario, it is assumed without loss of generality that the desired coverage region is Θ={θ1,θ2}. In Beam Behavior 2, it is possible to create good beamforming gain in two discontinuous angular regions, albeit on different portions of the bandwidth.

FIG.21illustrates an example transceiver2100for performing TTD-based hybrid beamforming for Beam Behavior 2 according to embodiments of the present disclosure. As shown inFIG.21, the transceiver2100includes multiple antennas2105, a RF chain2110, multiple phase shifters2115, multiple amplifiers2120, and multiple TTDs2125.

The transceiver2100is a special case of the transceiver1100shown inFIG.11, with N=1, Pl=M×1. For clarity and ease of discussion, this embodiment is referred to as Embodiment 4. Each antenna2105is connected to L different phase shifters2115with the frequency-independent phase-shifts being {φm,1, φm,1, . . . , φm,L}. The l-th phase shifters2115from all the antennas2105are connected together and fed by a common TTD2125with delay τ1,l. Thus in the transceiver2100, the number of phase shifters2115is ML and number of TTDs2125is L, and each mapping matrix is a splitter that connects the l-th TTD2125to each of the l-th phase shifters2115corresponding to the M antennas2105. In some embodiments, the TTDs2125are reconfigurable, and the TTD l is designed to have a delay variation between τ1,l∈[0, (l−1)/W], where W is the system bandwidth. In one embodiment where L=2, to achieve the desired behavior over Θ, the TTD delays and phase shifts can be set based on the example algorithm2200shown inFIG.22.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=64, L=2, θ1=π/4 and θ2=−π/4 is illustrated inFIG.23. As can be seen fromFIG.23, the transceiver2100can achieve the desired Beam Behavior 2, where a nearly-full beamforming gain (of52) is achievable in the two directions on two halves of the system bandwidth. In a related embodiment, in the transceiver2100, instead of one RF chain2110, L RF chains2110can be used to allow for a digital implementation of the TTDs τ1,l.

In the transceiver2100(Embodiment 4), although the number of required TTDs2125is very few, the architecture may require many phase shifters2115(ML) and the corresponding routing of the phase shifters2115to the TTDs2125can be complex. Therefore, the TTD-based architecture of the transceiver1200(Embodiment 1) can be used in conjunction with another algorithm to achieve the desired Beam Behavior 2. Note that this is a special case of the transceiver1100shown inFIG.11, with L=1, N=M, Pl=M. The number of phase shifters1215and number of TTDs1225are both set to M, and each mapping matrix is just a straight wire connection. In one embodiment, the TTDs1225are reconfigurable and the TTD1225corresponding to antenna m is designed to have a delay variation between τm,1∈[0, 3/(4W)], where W is the system bandwidth. This delay range can be much smaller than what is required to achieve Beam Behavior 1 using Embodiment 1. In some embodiments, to achieve the desired behavior over Θ, the TTD delays and phase-shifts can be set based on the example algorithm2400shown inFIG.24.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=N=64, L=1, θ1=π/4 and θ2=−π/4 is illustrated inFIG.25. As can be seen fromFIG.25, this design can achieve the desired Beam Behavior 2, where a nearly-full beamforming gain (of 64) is achievable in the two directions on two halves of the system bandwidth. In comparison to Embodiment 4, the main difference is there can be a small side-lobe of the beam in the vicinity of θ=0.

As shown above, both the transceiver1200(Embodiment 1) and the transceiver2100(Embodiment 4) can generate the desired Beam Behavior 2. However, the transceiver1200may need many TTDs (albeit with small maximum required delay), and the transceiver2100may require many phase shifters and complex signal routing. Therefore, in another embodiment (referred to as Embodiment 5 for clarity), the number of phase shifters and TTDs is kept to a low number.

For example,FIG.26illustrates another example transceiver2600for performing TTD-based hybrid beamforming for Behavior 2 (Embodiment 5) according to embodiments of the present disclosure. As shown inFIG.26, the transceiver2600includes multiple antennas2605, a RF chain2610, multiple phase shifters2615, multiple amplifiers2620, multiple TTDs2625, and multiple switches2630.

The transceiver2600is a special case of the transceiver1100shown inFIG.11, with L=1, and P1being realized using the bank of switches2630. In the transceiver2600, the RF chain2610can be connected to N TTDs2625each having a distinct and fixed delay value: τn,1=3 (n−1)/[4(N−1)W]. Each antenna2605also has one dedicated phase shifter2615and the phase shifter2615can be connected to any of the N fixed TTDs2625using the bank of switches2630. Thus for any desired beam behavior, each antenna2605can be connected to one of the N fixed TTDs2625. In some embodiments, to achieve the desired behavior over Θ, the TTD delays and phase shifts can be set based on the example algorithm2700shown inFIG.27.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=64, N=4, θ1=π/4 and θ2=−π/4 is illustrated inFIG.28. As can be seen fromFIG.28, the transceiver2600can achieve the desired Beam Behavior 2, where a nearly-full beamforming gain (of 64) is achievable in the two directions on two halves of the system bandwidth, with just four TTDs2625. However, as with Embodiment 4, it can be seen that there can be a small side-lobe outside of the angles of interest in Θ. In some embodiments, in the transceiver2600, instead of one RF chain, N RF chains can be used to allow for a digital implementation of the TTDs τn,1.

Beam Behavior 3:

Beam Behavior 3 can be useful in scenarios where simultaneous service is required for several users that are distributed in two disjoint localized regions with the full beamforming gain, or in scenarios where link reliability and easy beam-tracking are desired. In this scenario, it is assumed without loss of generality that the desired coverage region is Θ=[θ1−Δθ1, θ1+Δθ1]U[θ2−Δθ2, θ2+Δθ2]. In some respects, Beam Behavior 3 can be considered as a modified combination of Beam Behavior 1 and Beam Behavior 2.

FIG.29illustrates an example transceiver2900for performing TTD-based hybrid beamforming for Beam Behavior 3 (Embodiment 6) according to embodiments of the present disclosure. As shown inFIG.29, the transceiver2900includes multiple antennas2905, a RF chain2910, multiple phase shifters2915-2916, multiple amplifiers2920, and multiple TTDs2925-2926.

The architecture of the transceiver2900is different from the generic transceiver1100shown inFIG.11, since the transceiver2900includes two different phase shifter arrays2915-2916separated by intermediary TTDs2925. Here the signal from the RF chain2910is split and fed to L TTDs2926that can implement large delays {τ1, . . . ,τL}. The outputs of the TTDs2926are fed to an L×L array of phase shifters2916, with phase shifts {φ1,2, . . . ,φL,L}, to generate L transformed signals. Similarly, each antenna2905(m={1, . . . M}) is connected to L different phase shifters2915, with the frequency-independent phase-shifts being {φm,1, φm,1, . . . , φm,L}. Each of these phase shifters2915also has a dedicated TTD2925with delay {circumflex over (τ)}m,lthat can achieve a small delay range. In turn, the l-th TTDs from all the antennas2905are connected together and fed by the l-th transformed signal. Thus in the transceiver2900, the number of phase shifters2915-2916is ML+L2, and the number of TTDs2925-2926is ML+L, and each mapping matrix Plis a straight wire connection for each phase shifter.

In some embodiments, the TTDs2925-2926are reconfigurable and are designed to have a delay variation betweenτl∈[0, 25(1−1)/W] and {circumflex over (τ)}m,L∈[0, (m−1) sin (Δθmax)/W] for l∈{1, . . . , L}, m∈{1, . . . , M}, where W is the system bandwidth and Δθmaxis the maximum desired beam-sway in one direction of the center angle. In one embodiment where L=2, to achieve the desired behavior over Θ, the TTD delays and phase shifts can be set based on the example algorithm3000shown inFIG.30.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=64, L=2, θ1=π/4, Δθ1=π/16, θ2=−π/4 and Δθ2=0 is illustrated inFIG.31. As can be seen fromFIG.31, the transceiver2900can generate the desired Beam Behavior 3, while also providing a nearly-full beamforming gain (of 64). In a related embodiment, in the transceiver2900, instead of one RF chain2910, L RF chains can be used to allow for a digital implementation of the TTDsτl.

Although the transceiver2900can generate the Beam Behavior 3, it may involve a large hardware cost of implementation. Therefore, in another embodiment (referred to as Embodiment 7 for clarity), to reduce the complexity, a slight relaxation of Beam Behavior 3 can be considered, where the desired coverage region is Θ=[θ1−Δθ, θ1+Δθ]U[θ2−Δθ, θ2+Δθ]. In other words, the same squint of the beams is desired in the two angular directions: Δθ1=Δθ2=Δθ.

For example,FIG.32illustrates another example transceiver3200for performing TTD-based hybrid beamforming for Behavior 3 (Embodiment 7) according to embodiments of the present disclosure. As shown inFIG.32, the transceiver3200includes multiple antennas3205, a RF chain3210, multiple phase shifters3215, multiple amplifiers3220, and multiple TTDs3225-3226.

The transceiver3200is a special case of the transceiver1100shown inFIG.11, with N=M, Pl=M. Each antenna3205is connected to L different phase shifters3215with the frequency-independent phase-shifts being {φm,1, φm,1, . . . , φm,L}. Each phase shifter3215also has a dedicated TTD3225with delay {circumflex over (τ)}m,lthat can achieve a small delay variation. In addition, the l-th TTDs3225from all the antennas3205are connected together and fed by a common TTD3226with larger delay rateτl. Thus in the transceiver3200, the number of phase shifters3215is ML and number of TTDs3225-3226is ML+L, and each mapping matrix Plis a straight wire connection for each phase shifter3215.

In a variant of this embodiment, the L large common TTDs3226can be merged with the smaller per-antenna TTDs3225(τm,l=τl+{circumflex over (τ)}m,l) to create an architecture having only M TTDs. In some embodiments, the TTDs3225-3226are reconfigurable and are designed to have a delay variation betweenτl∈[0, 25(l−1)/W] and {circumflex over (τ)}m,L∈[0, (m−1)sin(Δθmax)/W] for l∈{1, . . . , L}, m∈{1, . . . , M}, where W is the system bandwidth and Δθmaxis the maximum desired beam-sway in one direction of the center angle. In one embodiment where L=2, to achieve the desired behavior over Θ, the TTD delays and phase shifts can be set based on the example algorithm3300shown inFIG.33.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=64, L=2, θ1=π/4, Δθ=π/16 and θ2=−π/4 is illustrated inFIG.34. As can be seen fromFIG.34, the transceiver3200generate the desired relaxed Beam Behavior 3, while also providing a nearly-full beamforming gain (of 64). In a related embodiment, in the transceiver3200, instead of one RF chain3210, L RF chains can be used to allow for a digital implementation of the TTDsτl

Although the transceiver3200(Embodiment 7) is able to generate the relaxed Beam Behavior 3, the transceiver3200may still require many phase shifters3215(ML) and TTDs3225-3226(ML+L), and the corresponding routing of the phase shifters3215to the TTDs3225-3226can be complex. Therefore, the TTD-based architecture of the transceiver1200(Embodiment 1) can be used in conjunction with another algorithm to achieve the desired Beam Behavior 3. Note that this is a special case of the transceiver1100shown inFIG.11, with L=1, N=M, Pl=M. The number of phase shifters3215and the number of TTDs3225-3226are both set to M, and each mapping matrix is just a straight wire connection. In one embodiment, the TTDs3225-3226are reconfigurable and the TTD3225-3226corresponding to antenna m is designed to have a delay variation between τm,1∈[0, (m−1)sin(Δθmax)/W], where W is the system bandwidth. In some embodiments, to achieve the desired behavior over Θ, the TTD delays and phase-shifts can be set based on the example algorithm3500shown inFIG.35.

As an example, the achievable antenna gain for a TX with a half-wavelength spaced uniform linear array with M=N=64, L=1, θ1=π/4, Δθ=π/16 and θ2=−π/4 is illustrated inFIG.36. As can be seen fromFIG.36, this design can achieve the desired relaxed Beam Behavior 3, however the achievable beamforming gain can be half the maximum (≤32).

In some scenarios, there are benefits to using fully digital chains with low resolution data converters. In such fully-digital architecture, the previously mentioned behaviors can be synthesized by applying the algorithms described herein and using digital TTDs and digital phase shifters. Also, in this fully-digital architecture, these behaviors can be implemented using only phase shifters, e.g., by applying different phase-shifts to different sub-carriers. Moreover, the previously mentioned architectures can be implemented in a hybrid digital and analog beamforming architectures. For example, in the transceiver3200inFIG.32, L digital and RF chains can be used instead, then theτlcan be implemented as digital TTDs.

FIG.37illustrates a flow diagram of an example process3700for configuring hardware to achieve the desired beam behaviors according to embodiments of the present disclosure. Here the determination of desired beam behavior can be based on an external trigger such as a scheduler, etc.

In some embodiments, the algorithm to generate the hardware parameters can be pre-computed offline and the values stored in a dictionary. The dictionary can be based on a discretization of the acceptable parameters for the BS and the desired beam behaviors. Based on the desired behavior and the BS parameters, the corresponding hardware parameters can then be fetched from the dictionary. For example,FIG.38illustrates a flow diagram of an example process3800for configuring hardware to achieve desired beam behaviors using offline computation according to embodiments of the present disclosure.

Generic beamformer design to achieve desired beam behavior:

In some embodiments, an algorithm can be performed to design the beamformer to achieve any arbitrary desired beam behavior. For an OFDM system with subcarriers in set, the desired beam behavior can be defined as the set of desired beamforming vectors {bk|k∈}. Here bkis the desired beamforming vector on OFDM subcarrier k. For example, for Beam Behavior 1, bk=αtx(θ1+kΔθ1/|) where it is assumed that the sub-carrier index is centered. For the TTD architecture, a special case of the transceiver1100shown inFIG.11is considered, with L=1. In other words, each antenna m is connected to only one phase shifter, a power amplifier, and the corresponding frequency-independent phase-shift is {φm}. These phase shifters are connected to N TTDs with delay values {τ1, τ2, . . . , τN} where N≤M via a mapping matrix P. The mapping matrix P essentially determines how the N TTDs connect to the corresponding M phase shifters. Thus in total, the transceiver has M phase shifters, one mapping matrix and N TTD elements. Note that for this architecture at the transmitter, assuming orthogonal frequency division multiplexing (OFDM), the transmit signal on subcarrier k∈can be expressed as:

xk=1M[ej⁢φ1ej⁢φ2⋮ej⁢φM]⊙P[e-j⁢2⁢π⁢fk⁢τ1e-j⁢2⁢π⁢fk⁢τ2⋮e-j⁢2⁢π⁢fk⁢τN]⁢sk=T⊙(PDk)⁢sk(4)
where ⊙ is the Hadamard product (i.e., the element-wise matrix product), T is the phase-shifter vector, and Dkis the TTD vector at subcarrier k∈, respectively. Here fkrepresents the frequency of the k-th subcarrier (including the carrier frequency). In some embodiments, the beamformer design to achieve the desired behavior {bk|k∈} is obtained as the solution to the problem:

ϕ°,τ°=argmax{φ1,…,φM},{τ1,…,τN}⁢∑k∈𝒦❘"\[LeftBracketingBar]"b_k†⁢T⊙(PDk)❘"\[RightBracketingBar]"=argmax{φ1,…,φM},{τ1,…,τN}⁢{minψ∑k∈𝒦Re[e-j⁢ψk⁢b_k†⁢T⊙(PDk)]},(5)
wherebk=bk/∥bk∥, and auxiliary variable set ψ={ψk|k∈}. In some embodiments, the solution to Equation (5) can be obtained using an iterative optimization algorithm, such as the example algorithm3900shown inFIG.39.

In a variant of the algorithm3900, the computation of τninside the for loop of i can be obtained as a solution of the weighted least squares problem:

argminτn,{φm|m∈ℳn}⁢{∑m∈ℳn∑k∈𝒦❘"\[LeftBracketingBar]"[b_k]m❘"\[RightBracketingBar]"[2⁢π⁢fk⁢τn+ϕm-𝒰⁡(ψk+∠[b_k]m)]2}(6)
where(·) is the phase unwrapping function that for each k adds phase-shifts of integer multiples of 2π to the argument to make the argument to ensure that the phase-difference between adjacent sub-carriers satisfies:
|(ψk+∠[bk]m)−(ψk−1+∠[bk−1]m)|≤π  (7)

FIG.40illustrates an example process4000for determining delay values and phase shift values according to embodiments of the present disclosure. As shown inFIG.40, the process4000includes obtaining various inputs4005. At operation4010, one or more delay values and one or more phase shift values for fixed digital precoding are updated. At operation4015, clipping and/or rounding are performed to ensure a maximum delay or ensure one or more phase constraints are satisfied. At operation4020, digital precoding is updated for fixed delay values and fixed phase shift values. The operations4010-4020can be repeated in an iterative fashion until convergence or a maximum number of iterations is performed.

AlthoughFIGS.7through40illustrates examples of beamforming behaviors, multiple example transceivers for performing TTD-based hybrid beamforming, and related details, various changes may be made toFIGS.7through40. For example, various components inFIGS.7through40could be combined, further subdivided, or omitted and additional components could be added according to particular needs. In addition, various operations inFIGS.7through40could overlap, occur in parallel, occur in a different order, or occur any number of times. The embodiments shown inFIGS.7through40are for illustration only. Other embodiments could be used without departing from the scope of this disclosure.

The frequency-dependent hybrid beamforming architectures described herein can significantly improve the capabilities of beamforming in high frequency systems like mm-wave and THz systems. The additional capabilities can be quite useful at a base station in a wide variety use cases, and can also help make the beam alignment and tracking easier. For example, the architectures can be used to serve multiple users in disconnected regions with full beamforming gain with just one ADC at the base station.

Although the present disclosure has been described with exemplary embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims. None of the description in this application should be read as implying that any particular element, step, or function is an essential element that must be included in the claims scope. The scope of patented subject matter is defined by the claims.