Hybrid massive multiple-input multiple-output (MIMO) system and a method thereof

Abstract

Embodiments of the present disclosure relate to a method for generating highly directional beams in a massive multiple-input multiple-output (MIMO) system. The method comprising segmenting, by the massive MIMO system, a plurality of physical antenna elements into a plurality of analog ports and a plurality of digital logical ports. Each analog port comprises a group of physical antenna elements and each digital logical port is associated with one or more analog ports. Also, the method comprises performing a digital beamforming on a predetermined set of users using a predetermined digital beamforming weights to generate a plurality of digitally beamformed data streams. Further, the method comprises performing an analog beamforming on the digitally beamformed data streams using one or more predetermined analog beamforming weights. Thereafter, transmitting the analog beamformed streams via the corresponding analog ports using the associated physical antenna elements, thereby producing highly directional pencil beams.

Description

15809-27HYBRID MASSIVE MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) SYSTEM AND A METHOD THEREOFTECHNICAL FIELD

[0001] Embodiments of the present disclosure are related, in general to communication, but exclusively related to Hybrid massive multiple input multiple output (MIMO) systems and methods thereof.BACKGROUND

[0002] Existing 5G networks use two-dimensional (2D) antenna arrays that consist of antenna elements distributed in azimuth (horizontal) and elevation (vertical) dimensions. Typically, one patch antenna or a sub-array comprising multiple patch antennas connected together is called a port, and each such port has a sectoral coverage of 120 degrees in azimuth and approximately 60 degrees in elevation. Most of the operators have deployed mMIMO using 32 or 64-antenna ports, where 8 ports are available in elevation and 8 ports are available in azimuth. Further, the existing deployments comprise 3 sectors, with each sector having 32 or 64 port 2D rectangular array operating at a typical 3.5 GHz carrier frequency. With such an antenna array, the base station relies on precoding or beamforming in the downlink (DL) and serves multiple users on the same timefrequency slots to achieve a multi-fold increment in the network capacity.

[0003] To realize this, the scheduler selects or picks a group of users that are spatially well separated from the available active users for the multi-user MIMO (MU-MIMO) transmission. The selection or pairing of the users is done based on the channel state information (CSI) of the active users. The base station can obtain this CSI of the users in many ways, such as CSI feedback from the users, estimations on the sounding reference signals (SRS) transmitted by the users in the uplink (UL), and TDD reciprocity calibration of the SRS-based CSI, etc. Using this DL CSI, the base station pairs a group of users for the DL transmission and formulates the precoder weights for the paired users. In the uplink direction, the channel estimations on the reference signals associated with the 32 or 64-antenna ports are used to combine the data received on the 64-antenna ports in the uplink equalizer.15809-27

[0004] The base station uses techniques such as MMSE (Minimum Mean-Square Estimation) for this uplink data detection. Note that the signal power associated with the uplink signal received at each port is low because of low directivity due to a limited number of antenna elements associated with a port. Although the post-processing signal-to-noise-plus-interference (SINK) power at the output of the equalizer is high, the pre-processing SINK associated with the DMRS signals of each antenna port is low, and therefore, the channel estimation quality tends to be poor, especially for users who are located at the cell boundaries (or cell edge users). Likewise, SRS channel estimation quality is low; consequently, the DL precoder weights will be prone to errors, especially for celledge users. This is a key bottleneck in maximizing the network throughputs with MU-MIMO.

[0005] In each sector, using 64 antenna ports and DL MU-MIMO, the base station is capable of serving 16 layers (each layer corresponds to an antenna of a user in a paired MU MEMO group). While one can expect a 16-fold notional increase in the capacity of the network compared to a single antenna system, in practice, the limited antenna directivity associated with each port, the interference arising from the neighboring sectors, and the division of available power among the scheduled layers, limit the achievable number of users that can be paired and subsequently limit the achievable network capacity.

[0006] To achieve coverage in FR3 bands comparable to the mid-band, it is necessary to substantially increase the number of antenna elements. Simply increasing the number of digital antenna ports would lead to high costs and greater power consumption. However, using 32 digital antenna ports and combining them with analog phase shifters can create a 256-antenna system that offers significantly better beamforming gain and higher capacity. The following sections describe how to utilize the available 5 G NR 3 GPP specifications to construct a system that leverages hybrid beamforming capabilities.SUMMARY

[0007] The shortcomings of the prior art are overcome and additional advantages are provided through the provision of method of the present disclosure.15809-27

[0008] Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

[0009] In an aspect of the present disclosure, a method for generating highly directional beams in a massive multiple- input multiple-output (MIMO) system is disclosed. The massive MIMO system comprises a plurality of antennas, at least one radio unit (RU), at least one distributed unit (DU), an interface configured for a communication between the at least one RU and the at least one DU, the method comprising segmenting, by the massive MIMO system, a plurality of physical antenna elements into a plurality of analog ports and a plurality of digital logical ports. Each analog port comprises a group of physical antenna elements and each digital logical port is associated with one or more analog ports. The method also comprises performing, by the massive MIMO system, a digital beamforming on a predetermined set of users (or spatial layers) using a predetermined digital beamforming weights to generate a plurality of digitally beamformed data streams. Further, the method comprises performing, by the massive MIMO system, an analog beamforming on the digitally beamformed data streams using one or more predetermined analog beamforming weights; and transmitting, by the massive MIMO system, the analog beamformed streams via the corresponding analog ports using the associated physical antenna elements, thereby producing highly directional pencil beams.

[0010] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of device or system and / or15809-27 methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:

[0012] Figure 1 shows an illustration of a structural hybrid massive MIMO (hm-MIMO) system model, in accordance with some embodiments of the present disclosure;

[0013] Figure 2A shows an illustration of resources for beam-specific transmissions and commonbeam transmissions in hm-MIMO;

[0014] Figure 2B shows an illustration of multiple scenarios with different beam configurations in hm-MIMO;

[0015] Figure 3 shows an illustration of SSB Beam Sweeping, in accordance with some embodiments of the present disclosure;

[0016] Figure 4 shows an illustration of a method of downlink (DL) transmission in a multi user (MU) MIMO, in accordance with an embodiment of the present disclosure;

[0017] Figure 5 shows an illustration of a method of downlink (DL) transmission in a MU MIMO, in accordance with another embodiment of the present disclosure;

[0018] Figure 6 shows an illustration of a method of downlink (DL) transmission in MU MIMO, in accordance with yet another embodiment of the present disclosure;

[0019] Figure 7 shows an example illustration of DMRS ports reuse within a sector with multiple beams, in accordance with an embodiment of the present disclosure;

[0020] Figure 8 shows an illustration of uplink signals reception;

[0021] Figure 9 shows an illustration flowchart for the HM-MIMO;

[0022] Figure 10 shows an illustration of the method- 1 performed by a receiver, in accordance with an embodiment of the present disclosure; and

[0023] Figure 11 shows an illustration of the method-2 performed by a receiver, in accordance with another embodiment of the present disclosure.

[0024] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.15809-27DETAILED DESCRIPTION

[0025] In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0026] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

[0027] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a device or system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the device or system or apparatus.

[0028] The terms "an embodiment", "embodiment", "embodiments", "the embodiment", "the embodiments", "one or more embodiments", "some embodiments", and "one embodiment" mean "one or more (but not all) embodiments of the invention(s)" unless expressly specified otherwise.

[0029] The terms "including", "comprising", “having” and variations thereof mean "including but not limited to", unless expressly specified otherwise. The enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms "a", "an" and "the" mean "one or more", unless expressly specified otherwise.

[0030] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention.15809-27

[0031] Embodiments of the present disclosure address the limitations of conventional massive multiple input multiple output (mMIMO) systems, specifically the restricted directivity of each antenna port, by implementing the at least one of employing highly directional and narrow beams for each antenna port through analog or hybrid beamforming; and multi user MIMO (MU-MIMO) precoding and beamforming in the downlink (DL), and joint equalization and processing of uplink (UL) signals from multiple antenna ports.

[0032] In an aspect of the present disclosure, a method for generating highly directional beams in a massive multiple- input multiple-output (MIMO) system is disclosed. The massive MIMO system comprises a plurality of antennas, at least one radio unit (RU), at least one distributed unit (DU), an interface configured for a communication between the at least one RU and the at least one DU, the method comprising segmenting, by the massive MIMO system, a plurality of physical antenna elements into a plurality of analog ports and a plurality of digital logical ports. Each analog port comprises a group of physical antenna elements and each digital logical port is associated with one or more analog ports. The method also comprises performing, by the massive MIMO system, a digital beamforming on a predetermined set of users (or spatial layers) using a predetermined digital beamforming weights to generate a plurality of digitally beamformed data streams. Further, the method comprises performing, by the massive MIMO system, an analog beamforming on the digitally beamformed data streams using one or more predetermined analog beamforming weights; and transmitting, by the massive MIMO system, the analog beamformed streams via the corresponding analog ports using the associated physical antenna elements, thereby producing highly directional pencil beams.

[0033] In an embodiment, the method comprising configuring the MIMO system with a predefined number of digital logical ports, each digital logical port is associated with a predefined number of analog ports, each analog port comprises a uniform rectangular subarray of antenna elements. As an example, the MIMO system uses thirty-two (32) digital logical ports, each mapped to eight (8) analog ports, with each analog port including four (4) antenna elements, forming a 1024-element array. Each of the digital logical ports is mapped to a specific group of analog ports via a predefined codebook.15809-27

[0034] The digital beamforming weights are selected from a predefined codebook based on user equipment (UE) location or feedback. In an embodiment, the digital beamforming is performed using one of a Zero-Forcing (ZF) precoding and a Minimum Mean Squared Error (MMSE) precoding. In an embodiment, the digital beamforming weights are adapted based on a channel state information (CSI) obtained using sounding reference signals (SRS). The digital beamforming enables multiplexing of multiple spatial layers for different users. The digital beamforming weights are applied on each OFDM subcarrier to achieve frequency-selective beamforming. Also, the digital beamforming supports spatial multiplexing of multiple users using multi-user MIMO (MU-MIMO).

[0035] In an embodiment, the digitally beamformed data streams comprises physical downlink shared channel (PDSCH) transmissions, said PDSCH transmissions are simultaneously scheduled for multiple UEs in the MU-MIMO. In an embodiment, the digital beamforming weights are determined at the DU, said DU transmits the determined digital beamforming weights to the RU via a user-plane fronthaul signaling.

[0036] In an embodiment of the present disclosure, the method comprising sweeping a plurality of synchronization signal blocks (SSBs) across analog beams formed via analog beamforming weights to facilitate UE beam identification. Each of the plurality of SSB beam carries a unique identifier transmitted via the Physical Broadcast Channel (PBCH). Also, the method comprising receiving a physical random-access channel (PRACH) preamble on an uplink resource corresponding to the strongest detected SSB beam.

[0037] In an embodiment, each of the plurality of digital logical ports is mapped to a distinct group of analog logical ports via a predefined codebook. The codebook is selected based on the direction of the detected SSB beam during initial access. In an embodiment, the codebook is selected from a vendor-specific analog codebook set.

[0038] In an embodiment, the digital logical ports are partitioned into one or more mutually exclusive segments, each serving an associated UE scheduled for a multi-user MIMO (MU- MIMO). The UE scheduled in a segment supports one or more spatial layers using single-user MIMO (SU-MIMO). Each segment is mapped to a distinct group of analog logical ports using a15809-27 predefined codebook. The analog beamforming weights for each segment are configured to suppress inter-segment interference below a predefined threshold. In an embodiment, the method comprising assigning demodulation reference signal (DMRS) ports to each beam and reusing DMRS ports among spatially separated beams with a configurable reuse factor. An additional DMRS symbols are allocated when the angular separation between beams sharing the same DMRS ports falls below a predefined threshold.

[0039] In an embodiment, the method comprising dynamically reconfiguring a number of segments based on the number of MU-MIMO users or CSI feedback reported by UEs.

[0040] In an embodiment, the analog beamforming is implemented using phase shifters that steer beams in both azimuth and elevation planes. The combined digital and analog beamforming weights result in pencil beams having a 3 dB beamwidth narrower than five degrees.

[0041] In an embodiment, the method comprising receiving physical uplink shared channel (PUSCH) signals through the segmented logical-port structure and filtering the received signals using matched filtering, ZF, MMSE, or MMSE with Interference Rejection Combining (IRC). The method comprising reconfiguring the mapping between digital and analog logical ports to alternate between beam-specific and common-beam transmission modes. The common-beam transmission mode involves transmitting identical data across a group of contiguous analog beams to enhance coverage at the cell edge.

[0042] In an embodiment, the method comprising time-division multiplexing of beam-specific and common-beam transmissions to avoid overlap on time-frequency resources.

[0043] In an embodiment, at least one digitally beamformed data stream carries System Information Block type 1 (SIB-1) directed toward the identified UE beam. In an embodiment, the method comprising adjusting the segmentation and beamforming weights when the signal-to- interference-plus-noise ratio (SINR) measured at the UE falls below a predefined threshold.

[0044] One embodiment of the present disclosure is a massive multiple-input multiple-output (MEMO) system for generating highly directional beams. The massive MIMO system comprises a15809-27 plurality of antennas, at least one radio unit (RU), at least one distributed unit (DU), an interface configured for a communication between the at least one RU and the at least one DU.

[0045] All available antenna elements for a base station (BS) in the radio unit (RU) are used to sweep the SSB beams over a defined coverage area of the base station. A user equipment (UE) responds with a physical random-access channel (PRACH) on a resource corresponding to the strongest detected synchronization signal block (SSB) beam, allowing the base station to identify the beam in which the UE is present. Cell specific channels such as SSB, cell specific physical downlink control channel (PDCCH), PRACH are transmitted / received using the SSB beam.

[0046] For a user specific transmission or reception, the PDSCH, the PUSCH and the control channels such as a physical uplink control channel (PUCCH), the UE specific beamforming methods are used. For this purpose, antenna elements, corresponding to all or a subset of antenna ports, are beamformed towards the UE's location, enhancing directivity and SNR for the user. The beamforming method may be either analog or hybrid. The beam weights, either analog or digital are communicated to the RU by a distributed unit. The resulted beams will be narrow and highly directional, thereby reducing the inter beam interference to a great extent. In the uplink, the signals received from all antenna ports are used for equalization using one of Open Radio Access Network (ORAN) class B or uplink performance improvement (ULPI) -A or ULPI-B methods.

[0047] One embodiment of the present disclosure is a hybrid beamforming-MIMO (HM-MIMO). Figure 1 shows an illustration of a structural hybrid massive MIMO (hm-MIMO) system model, in accordance with some embodiments of the present disclosure. Considering a RU equipped with N1 digital antenna ports, wherein each digital port is associated with N2 analog ports, and each analog port has a N3 element patch array. For example, consider a 2*2 array. For instance, N1 may be 32 or 16, N2 may be 8 or 16, and N3 may be 4. Each RF chain comprises an analog to digital converter (ADC) or a digital to analog converter (DAC), radio frequency (RF) combiner, RF filters, mixers, etc. This configuration enables the physical steering of the signal in both azimuth and elevation directions using analog or hybrid beamforming. A group of these antenna ports or all available ports are exploited to define a sector or a base station that uses a cell ID. This configuration or setup is termed as a structural hybrid massive MIMO (hm-MIMO) as shown in Figure 1.15809-27

[0048] Figure 2A shows an illustration of resources for beam-specific transmissions and commonbeam transmissions in HM-MIMO. Considering two types of transmission / reception of the signals, i.e. (a) beam-specific transmission and (b) common-beam transmission. In the beamspecific transmission, each beam is identified with a unique id also referred as beam-specific-id, and allowing distinct transmissions across those individual beams. Considering minimal interference between the beam-specific transmissions, considered as highly directional beams. Further, to ensure better channel estimation and equalization, orthogonal transmissions of reference signals corresponding to each beam are considered and scramble the transmissions of each beam with a beam-specific-id. This way, the base station (BS) may schedule multiple such beam-specific transmissions simultaneously for the users that are spatially well separated and attain multi-fold improvements in the network capacity. The BS has to obtain spatially well- separated users and schedule them appropriately in order to attain such multi-fold improvements.

[0049] Further, there may be users who are at the beam edge or cell edge. For those users, the signal transmission / reception can happen in multiple beams or a group of beams, this is termed as the common beam. This common beam may be realized by transmitting the same information across a group of individual beams or by transmitting in a wide beam covering a region similar to that of a group of beams. The number of individual beams covered by the common beam can be generic and there can be multiple such common beams. All this information regarding the common beams is conveyed to the user accordingly during the initial access procedure. Additionally, whenever the user fails to transmit or decode the information from the beam-specific signals, it can fall back to the common beam for better transmission or reception. However, the beam-specific transmissions and common-beam transmissions cannot overlap, and they have to be orthogonal across time / frequency / code (TDM / FDM / CDM).

[0050] Further, at any given instant, the base station can perform beam-specific transmissions, common-beam transmissions, or both. Figure 2B shows an illustration of multiple scenarios with different beam configurations in HM-MIMO. As shown in Figure 2B, some of the possible scenarios are presented, where the simultaneous transmission of different information across various beams is shown, the transmission of the same information across all the beams, and a combination of beam-specific and common beam transmissions.15809-27

[0051] One embodiment of the present disclosure is cell search and synchronization. As per the current 5G-NR specifications, the base station (BS) employs a synchronization signal block (SS- Block) consisting of primary and secondary synchronization signals, which are pre-defined and known to both the transmitter and receiver. Additionally, the SS-Block includes physical broadcast channel (PBCH) that carries a master information block (MIB) and conveys basic system information like operating bandwidth, etc. The BS may transmit these synchronization signals using directional beams, with each beam being active at a specific time instant. The MIB payload transmitted with the SS-Block carries the beam-id, enabling the base station to determine the best beam detected by the UE at a later stage.

[0052] Figure 3 shows an illustration of SSB Beam Sweeping, in accordance with some embodiments of the present disclosure. The BS transmits the SSB beams in a time division multiplexing manner with each beam transmitted at a different time instant. As per the 5G specifications, which allow a maximum of 8-beam transmissions or 64 beam transmissions depending on the operating frequency. All antenna elements at the BS are used to sweep the SSB beams over a defined coverage area of the sector or cell. Considering that there are N1 (Ex: 32) digital antenna ports and each port associated with N2 (Ex: 8) analog port, with each analog port having N3 (Ex:4) antenna elements, then all the N1*N2*N3 =1024 antenna elements are used for SSB beam sweeping. Each beam has a unique ID and defines a portion of the coverage area of a cell or sector.

[0053] The analog weights is applied on antenna elements associated with each of the ports are selected from a code book. The design of the code book is vendor specific. For each SSB beam, the DU provides the RU with the necessary information about the weights that need to be applied to the antenna elements associated with each digital port. This information is included as part of the U-plane message.

[0054] Embodiments of the present disclosure relates to system information block (SIB)-l transmissions. In fifth generation (5G) new radio (NR), remaining minimum system information (RMSI) is the minimum amount of system information (SI) that a user Equipment (UE) needs to know to connect to a 5G cell (or base station BS) and communicate. The remaining minimum15809-27 system information (RMSI) consists of the system information required to access the system and is conveyed using SIB1. The SIB-1 message carries the required information for the UE to carry out the initial random-access procedure and enables further processing till the RRC attach. The SIB-1 is transmitted on the physical downlink shared channel (PDSCH) with the corresponding downlink control information (DCI) contained in CORESET-0. For FR-1, since SSBs are time spaced, and so are the CORESET-O corresponding to each SSB.

[0055] Similar to SSB, all antenna elements at the base station (BS) are used to transmit SIB-1 over a defined coverage area of the sector or cell. Considering that there are N1 (32) digital antenna ports and each port associated with N2(8) analog port, with each analog port having N3 (4) antenna elements, then all N1 *N2*N3 =1024 antenna elements are used for transmitting SIB-1, each beam has a unique ID and defines a portion of coverage area of a cell or sector.

[0056] For each SIB-1 transmission, the DU provides the RU with the necessary information about the weights that need to be applied to the antenna elements associated with each digital port. This information is included as part of the U-plane message.

[0057] Once a UE or user successfully decodes the SIB-1, it gets to know the time / frequency locations, known as PRACH occasions, where it can perform the initial random-access procedure. All the SSB beam IDs have corresponding PRACH occasions. These occasions include orthogonal PRACH resources in terms of preamble IDs, as well as specific frequency and time locations.

[0058] For example, consider two users with beam #7 and beam #4. Each user decodes their respective beam IDs and identifies the corresponding PRACH occasions from SIB-1. This ensures that their uplink transmissions do not interfere with each other, allowing the base station to handle both simultaneously. Based on the location where the PRACH signal is received, the base station determines the best beam detected by each user (beam #7 and beam #4).

[0059] Similar to SSB and SIB-1, all antenna elements in the panel are configured to receive the PRACH signal. This means the PRACH signal is received on all Nl*N2*N3=1024 antenna elements but observable as N=32 digital ports and subsequently processed in the RU to detect the PRACH transmissions.15809-27

[0060] Embodiments of the present disclosure relates to downlink shared channel (PDSCH) and DMRS. Depending on the requirements, the BS invokes MU-MIMO and may schedule the shared channel transmissions of multiple UEs on the same time and frequency resources. A scheduler configured in the BS picks spatially well separated users and performs MU-MIMO with as many as 12 simultaneous UE / layer transmissions in DL.

[0061] An exemplary embodiment of the present disclosure is a method that enables spatial multiplexing in DL transmissions. The following is the first method.

[0062] Figure 4 shows an illustration of a method of downlink transmission in DL MU-MIMO, in accordance with an embodiment of the present disclosure. This method is also referred to as a first method or method-1. In the first method, successful SSB-PRACH decoding allows a base station (BS) to identify the beam of each connected user equipment (UE).Considering that M UEs are scheduled for MU-MIMO operation at a given instance 't'.

[0063] An antenna panel of the BS is divided into M segments, with each segment comprising Nl / M ports, where N1 is the total number of digital ports. Each port in these segments has N2*N3 antenna elements that are analog beamformed where the analog weights are selected using a code book to form in the direction of a S SB beam. The code book designed is vendor specific.

[0064] The antenna ports (^) in each segment are beamformed using digital weights to point towards respective UE, where these digital weights associated with each segment is selected from a code book. The code book designed is vendor specific.

[0065] The DL streams of a particular UE are fed to the respective segment. As part of the C-plane message, the DU informs the RU about the number of MU-MIMO UEs scheduled, the number of segments, the digital ports in each segment, and the number of antenna elements per digital port.

[0066] In the U-plane message, the DU informs the RU about the analog weights to be applied to the N2 antenna elements for each segment. As an illustration, Segment- 1 uses weights Wl, Segment-2 uses weights W2, and so forth. Similarly, the DU also communicates the digital weights for the (Nl / M) ports for each segment, with Segment-1 having weights VI, Segment-2 having15809-27 weights V2, and so on. The result of this hybrid beamforming is that, the beam is precisely directed towards the known UE SSB beam, significantly minimizing inter-beam interference.

[0067] Also, in this method, CSI of multiplexed users is not required at the base station. Further, it is possible to transmit more than one layers for each of the MU-MIMO UEs in the respective beams for example using the existing CQI, PMI feedback mechanisms available in the 3GPP 5G NR specifications. This first method is applicable to the single user (SU) MIMO as well.

[0068] Figure 5 shows an illustration of a method of downlink (DL) transmission in a MU MIMO, in accordance with another embodiment of the present disclosure. This method is also referred to as a second method or method-2. As shown in the Figure 5, the method comprises the following steps.

[0069] The first three steps of the second method are same as first method. However, the digital precoding is based on channel state information (CSI) feedback from the UE or based on sounding reference signal (SRS) based CSI estimation. Also, the CSI is obtained using SRS, which is used to construct the digital precoder using a zero-forcing methodology. Further, these analog beamforming steps reduces inter-beam interference, while digital beamforming attempts to eliminate remaining intra-beam interference to increase overall SNR of the user.

[0070] Figure 6 shows an illustration of a method of downlink (DL) transmission in a MU MIMO, in accordance with yet another embodiment of the present disclosure. This method is also referred to as a third method or method-3.

[0071] In the third method, considering the antenna panel has N 1 *N2*N3 elements with N 1 digital ports. Each digital port has N2*N3 antenna elements, and these antenna elements are analog beamformed where the analog weights are selected using a code book to form a beam in the direction of a SSB beam. The design of such a codebook is vendor specific. The CSI feedback is obtained in uplink using SRS on all the available N1 digital ports. Subsequently, DU constructs a digital precoder using methods such as zero-forcing or MMSE. Thereafter, the analog beamforming steps reduce inter-beam interference, while digital beamforming attempts to eliminate remaining intra-beam interference to increase overall SNR of the user.15809-27

[0072] In an embodiment of the present disclosure to maximize the channel estimation quality, orthogonal transmission of DMRS signals is needed across all the layers of a given UE, to facilitate that a unique DMRS port is allocated to each layer of a UE. Considering HM-MIMO comprising a large number of beams within the sector, while a given beam serves one of a MU-MIMO UE. To enable such large number of DMRS ports within the sector, the available DMRS ports are reused among the spatially separate beams. The DMRS port reuse factor may be generic. For example, the reuse may happen with one of every 30-degree or 60-degree or 90-degree separation between the beams.

[0073] Figure 7 shows an example illustration of DMRS ports reuse within a sector with multiple beams, in accordance with an embodiment of the present disclosure. As shown in the example illustration in Figure 7, where 3 sectors are considered, each with multiple beams, and each beam supports multiple DMRS ports i.e. 8 ports in an embodiment. Considering the increase in number of available ports from 12 to 24, it is assumed that 24 orthogonal DMRS ports are available. We then reuse these 24 ports after every 3 beams in the sector as shown in Figure 7. Since the resultant beams form analog beamforming are very narrow and directional, it is considered that beam 1 and 4 are spatially separated and cause less interference to each other.

[0074] Further, in 5G-NR, the base station can allocate additional DMRS symbols for the allocated ports. So, in scenarios where the beams are not well separated while reusing the ports, the base station can increase the DMRS overhead and allocate additional DMRS symbols. This can further enhance the channel estimation quality at the receiver. With increase in this DMRS overhead, the per user throughput will decrease. However, with increase in the spatial multiplexing factor, the achievable cell-throughputs will be significantly enhanced.

[0075] One embodiment of the present disclosure is related to physical uplink shared channel (PUSCH). Depending upon the requirements, the base station exploits MU-MIMO or SU-MIMO in uplink and may schedule the shared channel transmissions of multiple UEs on the same time and frequency resources.15809-27

[0076] Figure 8 shows an illustration of uplink signals reception. The scheduler of the BS selects spatially well separated users, i.e. based on SSB beam locations or CSI measured from SRS, and performs MU-MIMO with a total 8 simultaneous UE / layer transmission in UL.• Successful SSB-PRACH decoding allows the base station to identify the SSB beam of each connected UE.• Considering that M UEs are scheduled for Uplink MU-MIMO operation at a given instance 'f.• The antenna elements (^) in each segment beamformed, using analog weights, towards each one of the ‘M’ MU-MIMO users. This step is same for downlink (DL) and uplink (UL).• The PUSCH signal is received on all N1*N2*N3 antenna elements but observable as N1 digital ports• The RU has received signal streams that will be filtered using ORAN Class -B or ULPI-A or ULPI-B receivers.

[0077] Figure 9 shows an illustration flowchart for the HM-MIMO.

[0078] In an embodiment of the present disclosure, CSI-RS sounding may happen in many ways namely periodic, semi-persistent, and aperiodic. With the current specifications, a configured CSI- RS can correspond up to 32 different ports. An example case of realizing 32 ports is sounding (8CDM x 4FDM) using 32 resource elements in a resource block. In periodic sounding, the current specifications allow the system to configure the periodicity of CSI-RS i.e., the UE can expect CSI- RS transmission with a periodicity of every Nth slot, where N varies from as low as 4 to as high as 640, and also an offset with which it occurs, offset in time or slots. In aperiodic scenario, the base station will trigger CSI-RS transmission instant by using DCI signaling. Similar to CSI-RS in DL, the SRS is transmitted in UL. The SRS in current 5G NR may span over one, two, or four consecutive OFDM symbols and in frequency it has comb-structure where the SRS is transmitted every Nth sub carrier with N taking values of either 2 or 4, (i.e., either comb-2 or comb-4). Similar to the DL, the SRS in UL may also be configured with periodicity and time / slot offsets and aperiodic sounding is triggered by DCI signaling.15809-27

[0079] For PDSCH third method, which does not segment the antenna panel, all available digital ports are used to indicate the CSI ports. Conversely, in PDSCH-Method-2, the CSI ports are used orthogonally among the segmented panels; the CSI ports indicated in one panel are different from those in another panel. The users will then provide feedback only for the CSI ports on a specific segmented panel. Consequently, the downlink precoder is applied exclusively to transmissions corresponding to that segmented panel.

[0080] In another embodiment, uplink control information (UCI) in 5G-NR is transmitted using one of many PUCCH formats (PF-0 / 1 / 2 / 3 / 4). The uplink control information includes ACK / NACK, scheduling request (SR), and CSI. In PF-0, ACK / NACK / SR are sequence-based transmissions, and the rest of the formats comprise DMRS along with UCI payload transmissions.

[0081] Successful SSB-PRACH decoding allows the base station to identify the SSB beam of each connected UE. Considering that M UEs are spatially multiplexed for UCI transmission at a given instance 't'. M can be 1.

[0082] The PUCCH signal is received on all N1*N2*N3 antenna elements but observable as N1 digital ports

[0083] The RU has received N1 signal streams that will be filtered using ORAN Class-B or UEPI- A or ULPI-B receivers that are described in Annexure-x, except format-0.

[0084] Format-0 PUCCH processing, follows the PRACH processing procedure at RU.

[0085] Further, note that in 5G-NR the transmission of UCI can also happen on PUSCH. Since PUSCH can support large number of simultaneous uplink transmissions, the base station logically trigger UCI over PUSCH for the users and increase the control channel capacity. In such cases, the UCI reception and processing will follow PUSCH processing procedure. Nevertheless, UCI is demultiplexed from user data in DU.

[0086] In an embodiment of the present disclosure, the region for control channel in the 5G NR is indicated using two configurations, namely (1) PDCCHConfig and (2) PDCCHCommonConfig. The PDCCHCommonConfig is a cell-specific configuration and is unique to all the users in the cell-site, whereas PDCCHConfig is a UE-specific configuration assigned to users during the RRC connection establishment. Both these configurations convey all the required information to decode15809-27 the control payload such as CORESET regions, search spaces, reference signal transmissions, etc. In 5G-NR, the time frequency regions over which the control information is transmitted is conveyed in form of two parameters, CORESET and search space. The base station can configure multiple CORESETs and each CORESET can have multiple search spaces. The UE has to blindly decode over the configured CORESETS and the search space regions to decode the DCI payload. Further, in 5G-NR, the spatial multiplexing of the DCI payloads is not supported as there is no notion of multiple ports for DMRS in PDCCH.

[0087] Similar to SSB and SIB-1, all the antenna elements at the base station can be used to transmit the control channel over a defined coverage area of the sector or cell. Considering that there are N1 (32) digital antenna ports and each port associated with N2(8) analog port, with each analog port having N3 (4) antenna elements, then all N1*N2*N3 =1024 antenna elements are used for transmitting PDCCH, where each beam has got a unique ID and defines a portion of coverage area of a cell or sector. For each such transmission, the DU provides the RU with the necessary information about the weights that need to be applied to the antenna elements associated with each digital port. This information is included as part of the U-plane message.

[0088] Embodiments of the present disclosure relate to uplink performance improvement (ULPI). When 32 RF chains are available, a radio unit (RU) must send baseband EQ (in-phase and quadrature) samples corresponding to all the received signals from a distributed unit (DU). The fibre bandwidth required to transmit such a large number of baseband EQ samples is so high that it makes the cost of the DU-RU interface a limiting factor. Therefore, it is necessary for the RU to condense the data from for e.g. 32 antennas into a smaller number before sending the EQ samples back to the DU.

[0089] To condense a large number of incoming signal streams into a smaller number, there are two methods, i.e. ULPI- A option and ULPI-B option. The ULPI-B option is also referred to as Method- 1 and the ULPI-B option is referred to as Method-2.

[0090] Embodiments of the present disclosure relates to Method- 1 i.e. ULPI-B option. In this method, a receiver processing is performed in two stages. First stage of filtering is performed in the RU and second stage of filtering is performed in the DU. The first stage of filtering at RU helps15809-27 in condensing or reducing the received signals on all antennas to a comparatively lesser number of streams. The second stage filtering is done at the DU on the filtered data passed from the RU, where it produces equalized outputs corresponding to number of layers.

[0091] Figure 10 shows an illustration of the method- 1 performed by a receiver, in accordance with an embodiment of the present disclosure. The first stage filtering at RU comprises the following method steps:

[0092] 1. Grouping: The received signal streams are grouped such that each subgroup contains signals from a distinct set of antennas. For instance, the signals from antennas in any vertical column of a given polarization could be grouped together. With 32 antennas, we could create 8 groups, each containing 4 antenna streams from a single column.

[0093] 2. Filtering: Group-specific filtering is applied to the signals in each group. Each group is designated to filter signal streams of one layer from the total configured layers within a PRG. For example, Group- 1 may be assigned to filter streams of layer- 1, Group-2 can be dedicated to filter streams of layer-2, and so on.

[0094] For example, if the total number of layers configured per PRG is 1, all groups are utilized to beamform that single layer. In another example, if the total number of layers configured per PRG is 2, the groups are split evenly between two layers. Half of the groups are used to beamform layer- 1 , and the other half are used to beamform layer-2. In yet another example, if the total number of layers configured per PRG is 4, the groups are divided into quarters. Each quarter of the groups is used to beamform one of the four layers.

[0095] If the total number of layers configured per PRG equals the number of groups, each group is dedicated to beamform a distinct layer. For example, group- 1 can be assigned to beamform layer- 1, group-2 to beamform layer-2, and so on. In another embodiment, if the total number of layers configured per PRG is greater than the number of groups, each group may be configured to beamform multiple layers. For instance, group-1 can be assigned to beamform layers 1 and 2, group-2 to beamform layers 3 and 4, and so forth.

[0096] 3. Filter Construction: The group specific filter in Stage- 1 can be a Matched filter (MF) or an Interference Rejection Filter (IRC). The filter coefficients of a given group is obtained using the channel estimates of the corresponding layer in the group and / or estimated noise-plus-15809-27 interference covariance matrix (NICM) associated with the received signals of the group. One Filter will be constructed for each group. Each group undergoes at least one of the operations DMRS generation, modulation removal, Time Offset Estimation and Correction (ToE & ToC), Tone (sub-carrier) averaging of channel estimates, Noise Plus Interference Covariance Estimation (NICM), Filter Construction and Filtering.

[0097] The second stage (Stage-2) filtering at the DU, processes data that has already been filtered at the RU. This stage can use either a Matched Filter (MF) or an Interference Rejection Filter (IRC). At the DU, channel estimates, time offset estimates, and NICM are re-estimated using the Stage- 1 filtered DMRS signals from the RU. The second stage filter equalizes these filtered data signals, producing a number of streams equal to the configured number of layers.

[0098] Figure 11 shows an illustration of the method-2 performed by a receiver, in accordance with another embodiment of the present disclosure. In the method-2, also referred as ULPI-A or DU Bye-pass, both beamforming and equalization are done in RU itself. This makes it easier for different vendors to work together because the roles of the RU and DU are clearly separated. This setup reduces the amount of data sent between the RU and DU, which helps minimize fronthaul load. The method steps performed for the beamforming comprises:

[0099] 1. Grouping: The received signal streams are grouped such that each subgroup contains signals from a distinct set of antennas. For instance, the signals from antennas in any vertical column of a given polarization could be grouped together. With 32 antennas, we could create 8 groups, each containing 4 antenna streams from a single column.2. Filtering: Group-specific filtering is applied to the signals in each group. Each group is designated to filter signal streams of all configured layers within a PRG. The filtered streams corresponding to a particular layer from all groups are then combined to create a single filtered stream respective to that layer.

[0100] For example, in the case of SU-MIMO, if four layers are configured for a user within a PRG, each group of the antenna array filters the signal streams of all the 4 layers. The filtered streams corresponding to a particular layer from each group are then combined to create a single filtered stream. This process is repeated for each of the four layers.15809-27

[0101] 3. Filter Construction: The group specific filter in Stage- 1 is a Matched filter(MF). This step is similar to Method- 1, with the difference being that instead of constructing a single filter per group, the number of filters created per group is equal to the number of configured layers. The filter coefficients are obtained using the channel estimates of the corresponding layer in the group.

[0102] Equalization: This step processes the outputs from the Layer Combiner. In the case of 8 layers, there will be 8 streams. An IRC filter is used to derive equalized outputs for each configured layer. The steps involved are at least one of re-estimating channel states for each layer on each stream, performing ToE and ToC (this step may be avoided by performing equivalent in beamforming), collecting interference samples, computing NICM, constructing the IRC filter by incorporating the channel estimates (CEs) of all layers on all streams, and performing equalization.

[0103] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention.

[0104] When a single device or article is described herein, it will be clear that more than one device / article (whether they cooperate) may be used in place of a single device / article. Similarly, where more than one device or article is described herein (whether they cooperate), it will be clear that a single device / article may be used in place of the more than one device or article or a different number of devices / articles may be used instead of the shown number of devices or programs. The functionality and / or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality / features. Thus, other embodiments of the invention need not include the device itself.

[0105] Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention.15809-27

[0106] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting.

Claims

15809-27WE CLAIM:

1. A method for generating highly directional beams in a massive multiple-input multiple-output (MIMO) system, said massive MIMO system comprises a plurality of antennas, at least one radio unit (RU), at least one distributed unit (DU), an interface configured for a communication between the at least one RU and the at least one DU, the method comprising: segmenting, by the massive MIMO system, a plurality of physical antenna elements into a plurality of analog ports and a plurality of digital logical ports, wherein each analog port comprises a group of physical antenna elements and each digital logical port is associated with one or more analog ports; performing, by the massive MEMO system, a digital beamforming on a predetermined set of users (or spatial layers) using a predetermined digital beamforming weights to generate a plurality of digitally beamformed data streams; performing, by the massive MIMO system, an analog beamforming on the digitally beamformed data streams using one or more predetermined analog beamforming weights; and transmitting, by the massive MEMO system, the analog beamformed streams via the corresponding analog ports using the associated physical antenna elements, thereby producing highly directional pencil beams.

2. The method as claimed in claim 1, wherein the method comprising configuring the MIMO system with a predefined number of digital logical ports, each digital logical port is associated with a predefined number of analog ports, each analog port comprises a uniform rectangular subarray of antenna elements.

3. The method as claimed in claim 2, wherein each of the digital logical ports is mapped to a specific group of analog ports via a predefined codebook.

4. The method as claimed in claim 1, wherein the digital beamforming weights are selected from a predefined codebook based on user equipment (UE) location or feedback.

5. The method as claimed in claim 1, wherein the digital beamforming is performed using one of a Zero-Forcing (ZF) precoding and a Minimum Mean Squared Error (MMSE) precoding.15809-276. The method as claimed in claim 1, wherein the digital beamforming weights are adapted based on a channel state information (CSI) obtained using sounding reference signals (SRS).

7. The method as claimed in claim 1 , wherein the digital beamforming enables multiplexing of multiple spatial layers for different users.

8. The method as claimed in claim 1, wherein the digital beamforming weights are applied on each OFDM subcarrier to achieve frequency-selective beamforming.

9. The method as claimed in claim 1, wherein the digital beamforming supports spatial multiplexing of multiple users using multi-user MIMO (MU-MIMO).

10. The method as claimed in claim 1, wherein the digitally beamformed data streams comprises physical downlink shared channel (PDSCH) transmissions, said PDSCH transmissions are simultaneously scheduled for multiple UEs in the MU-MIMO.

11. The method as claimed in claim 1, wherein the digital beamforming weights are determined at the DU, said DU transmits the determined digital beamforming weights to the RU via a userplane fronthaul signaling.

12. The method as claimed in claim 1, wherein the method comprising sweeping a plurality of synchronization signal blocks (SSBs) across analog beams formed via analog beamforming weights to facilitate UE beam identification.

13. The method as claimed in claim 12, wherein each of the plurality of SSB beam carries a unique identifier transmitted via the Physical Broadcast Channel (PBCH).

14. The method as claimed in claim 12, wherein the method comprising receiving a physical random-access channel (PRACH) preamble on an uplink resource corresponding to the strongest detected SSB beam.

15. The method as claimed in claim 1, wherein each of the plurality of digital logical ports is mapped to a distinct group of analog logical ports via a predefined codebook.15809-2716. The method as claimed in claim 15, wherein the codebook is selected based on the direction of the detected SSB beam during initial access.

17. The method as claimed in claim 16, wherein the codebook is selected from a vendor-specific analog codebook set.

18. The method as claimed in claim 2, wherein the digital logical ports are partitioned into one or more mutually exclusive segments, each serving an associated UE scheduled for a multi-user MIMO (MU-MIMO).

19. The method as claimed in claim 18, wherein the UE scheduled in a segment supports one or more spatial layers using single-user MIMO (SU-MIMO).

20. The method as claimed in claim 18, wherein each segment is mapped to a distinct group of analog logical ports using a predefined codebook.

21. The method as claimed in claim 20, wherein analog beamforming weights for each segment are configured to suppress inter-segment interference below a predefined threshold.

22. The method as claimed in claim 21, wherein the method comprising assigning demodulation reference signal (DMRS) ports to each beam and reusing DMRS ports among spatially separated beams with a configurable reuse factor.

23. The method as claimed in claim 22, wherein additional DMRS symbols are allocated when the angular separation between beams sharing the same DMRS ports falls below a predefined threshold.

24. The method as claimed in claim 18, wherein the method comprising dynamically reconfiguring a number of segments based on the number of MU-MIMO users or CSI feedback reported by UEs.

25. The method as claimed in claim 1, wherein the analog beamforming is implemented using phase shifters that steer beams in both azimuth and elevation planes.15809-2726. The method as claimed in claim 1, wherein the combined digital and analog beamforming weights result in pencil beams having a 3 dB beamwidth narrower than five degrees.

27. The method as claimed in claim 1, the method comprising receiving physical uplink shared channel (PUSCH) signals through the segmented logical-port structure and filtering the received signals using matched filtering, ZF, MMSE, or MMSE with Interference Rejection Combining (IRC).

28. The method as claimed in claim 1, wherein the method comprising reconfiguring the mapping between digital and analog logical ports to alternate between beam-specific and common-beam transmission modes.

29. The method as claimed in claim 28, wherein the common-beam transmission mode involves transmitting identical data across a group of contiguous analog beams to enhance coverage at the cell edge.

30. The method as claimed in claim 28, wherein the method comprising time-division multiplexing of beam-specific and common-beam transmissions to avoid overlap on time-frequency resources.

31. The method as claimed in claim 1, wherein at least one digitally beamformed data stream carries System Information Block type 1 (SIB-1) directed toward the identified UE beam.

32. The method as claimed in claim 1, the method comprising adjusting the segmentation and beamforming weights when the signal-to-interference-plus-noise ratio (SINR) measured at the UE falls below a predefined threshold.

33. A massive multiple-input multiple-output (MIMO) system for generating highly directional beams by implementing steps as claimed in claims 1-32, said massive MIMO system comprises a plurality of antennas, at least one radio unit (RU), at least one distributed unit (DU), an interface configured for a communication between the at least one RU and the at least one DU.

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