Base station-centric determination of best beamforming parameters for over-the-air communications with a user device

Abstract

A method for determining a best set of beamforming parameters for each of a plurality of UEs (User Equipment) that comprises cycling through a plurality of beamforming parameters for broadcasting a CSI-RS (Channel State Information – Reference Signal) as a scan beam to the plurality of UEs, and receiving CSI-RSRP (Channel State Information – Reference Signal Received Power) from each of the UEs. After transmitting a full set of scan beams, identifying the best CSI-RSRP from each UE and correlating that with the beamforming parameters, and using those beamforming parameters for the PDSCH channels for the corresponding UEs.

Description

Base Station-Centric Determination of Best Beamforming Parameters for Over-The-Air Communications with a User DeviceBACKGROU ND OF THE INVENTION

[0001] Modern cellular communications standards, such as 5G NR (New Radio), implement MIMO (Multiple Input Multiple Output) techniques to improve the gain of the RF (Radio Frequency) link between a base station and a UE (User Equipment). By improving the gain, higher data rates may be achieved over the air interface. Beamforming is an effective approach to achieving this, whereby the base station may apply differential amplitude and phase weights (hereinafter "beamforming parameters") to each copy of the RF signal being transmitted by a plurality of base station antennas. However, the base station needs information about the nature of the channel between it and the UE.

[0002] The ability to dynamically determine and improve beamforming parameters is particularly important in higher frequency regimes, such as FR2 (Frequency Range 2) bands employed by 5G, which include millimeter wave radio bands.

[0003] A deficiency exists in that conventional approaches to determine best beamforming parameters are not consistently supported in FR2 chipsets used by UEs.

[0004] Accordingly, what is needed is a method for a base station to dynamically determine the best beamforming parameters that is universally supported across UE types and manufacturers.SUMMARY OF THE INVENTION

[0005] An aspect of the disclosure involves a method for selecting a best set of beamforming parameters for communicating with a UE (User Equipment). The method comprises setting a first set of scan beam beamforming parameters for transmitting a first CSI-RS (Channel State Information - Reference Signal); transmitting the first CSI-RS; receiving a first CSI-RSRP (Channel State Information - Reference Signal Received Power) report data from a UE, the first CSI-RSRP report data corresponding to the first CSI-RS; storing the first set of scan beam beamforming parameters and the first CSI-RSRP report data; setting a second set of scan beam beamforming parameters for transmitting a second CSI-RS; transmitting the second CSI-RS; receiving a secondCSI-RSRP report data from the UE, the second CSI-RSRP report data corresponding to the second CSI-RS; storing the second set of scan beam beamforming parameters and the second CSI-RSRP report data; setting a third set of scan beam beamforming parameters for transmitting a third CSI-RS; transmitting the third CSI-RS; receiving a third CSI-RSRP report data from the UE, the third CSI-RSRP report data corresponding the third CSI-RS; storing the third set of scan beam beamforming parameters and the third CSI-RSRP report data; selecting a best set of scan beam beamforming parameters corresponding to a best CSI-RSRP report data; and setting a main beam beamforming parameters based on the best set of scan beam beamforming parameters

[0006] Another aspect of the disclosure involves a method for selecting a best set of beamforming parameters for communicating with each of a plurality of UEs (User Equipment). The method comprises setting a first set of scan beam beamforming parameters for transmitting a first CSI-RS (Channel State Information - Reference Signal); transmitting the first CSI-RS; receiving a first plurality of CSI-RSRP report data, each of the first plurality of CSI-RSRP report data received from a corresponding one of the plurality of UEs; storing the first set of scan beam beamforming parameters and the first plurality of CSI-RSRP report data; setting a second set of scan beam beamforming parameters for transmitting a second CSI-RS; transmitting the second CSI-RS; receiving a second plurality of CSI-RSRP report data, each of the second plurality of CSI- RSRP report data received from a corresponding one of the plurality of UEs; storing the second set of scan beam beamforming parameters and the second plurality of CSI-RSRP report data; setting a third set of scan beam beamforming parameters for transmitting a third CSI-RS; transmitting the third CSI-RS; receiving a third plurality of CSI-RSRP report data, each of the third plurality of CSI-RSRP report data received from a corresponding one of from the plurality of UEs; storing the third set of scan beam beamforming parameters and the third CSI-RSRP report data; selecting a plurality of best scan beam beamforming parameters corresponding to each of the plurality of UEs; and setting a main beam beamforming parameters for each of the plurality of UEs based on the plurality of best set of scan beam beamforming parameters.

[0007] Another aspect of the disclosure involves a method for selecting a best set of beamforming parameters for communicating with a UE (User Equipment). The method comprises setting a first set of scan beam beamforming parameters for transmitting a first CSI- RS (Channel State Information - Reference Signal); transmitting the first CSI-RS; receiving a first CSI-CQI (Channel State Information - Channel Quality Information) data and a first CSI-RSRP (Channel State Information - Reference Signal Received Power) report data from the UE, thefirst CSI-CQJ data and the first CSI-RSRP report data corresponding to the first CSI-RS; storing the first set of scan beam beamforming parameters and the first CSI-CQJ data and the first CSI-RSRP report data; setting a second set of scan beam beamforming parameters for transmitting a second CSI-RS; transmitting the second CSI-RS; receiving a second CSI-CQI data and a second CSI- RSRP report data from the UE, the second CSI-CQI data and the second CSI-RSRP report data corresponding to the second CSI-RS; storing the second set of scan beam beamforming parameters and the second CSI-CQI data and the second CSI-RSRP report data; setting a third set of scan beam beamforming parameters for transmitting a third CSI-RS; transmitting the third CSI-RS; receiving a third CSI-CQI data and a third CSI-RSRP report data from the UE, the third CSI- CQI data and the third CSI-RSRP report data corresponding to the third CSI-RS; storing the third set of scan beam beamforming parameters and the third CSI-CQI and the third CSI-RSRP report data; selecting a best set of beamforming parameters; and setting a main beam beamforming parameters based on the best set of beamforming parametersBRI EF DESCRI PTION OF DRAWINGS

[0008] FIG. 1 illustrates an 5G scenario in which an exemplary gNodeB according to the disclosure is connected to a UE over a radio link.

[0009] FIG. 2 illustrates the operation of the exemplary gNodeB as it identifies best beamforming parameters according to the disclosure.

[0010] FIG. 3 illustrates an exemplary process for base station-centric determination of best beamforming parameters according to the disclosure.

[0011] FIG. 4 illustrates an exemplary process for selecting a main beam from among transmitted scan beams according to the disclosure.

[0012] FIG. 5 is an exemplary timing diagram of the process for selecting best beamforming parameters according to the disclosure.DETAI LED DESCRIPTION OF TH E I NVENTION

[0013] FIG. 1 illustrates a 5G scenario 100 in which a gNodeB 105 performs gNodeB-based determination of best beamforming parameters according to the disclosure. As illustrated, gNodeB 105 is connected to a UE 110 over a radio link 170. gNodeB includes a 5G protocol stack implementation 115, which has a downlink component 115a and an uplink component 115b. Protocol stack implementation 115 is coupled to a plurality of antennas 165 over one or more RF (Radio Frequency) cables 160, one per antenna 165. Although RF cables 160 are illustrated ashaving two paths, one for uplink and one for downlink, it will be understood that this is for the convenience of illustration, and that the uplink and downlink signals may be carried on a single RF cable.

[0014] Coupled to protocol stack implementation 115 is an exemplary beam selector 140 of the disclosure. Beam selector 140 may have a processor 145 and a memory 155. The functionality of beam selector 140 may be implemented by a software module that runs on processor 145.

[0015] Protocol stack downlink component 115a may implement downlink functionality called for in the 3GPP (Third Generation Partnership Project) 5G specification, including a downlink PDCP (Packet Data Convergence Protocol) 120a; downlink RLC (Radio Link Control) 125a; downlink MAC (Medium Access Control) 130a; and a downlink PHY (Physical) layer 135a. Downlink PDCP 120a, RLC 125a, MAC 130a, and PHY layer 135a may be conventional implementations of the 5G protocol stack specification defined by 3GPP, with certain enhancements that are described below.

[0016] Similarly, protocol stack uplink component 115b may implement uplink functionality called for in the 3GPP (Third Generation Partnership Project) 5G specification, including a PHY layer 135b; uplink MAC 130b; uplink RLC 125b; and uplink PDCP 120b. Uplink PDCP 120b, RLC 125b, MAC 130b, and PHY layer 135b may be conventional implementations of the 5G protocol stack specification defined by 3GPP, with certain enhancements that are described below.

[0017] Reference to a protocol stack element within protocol stack implementation 115 that does not specify uplink or downlink (e.g., "MAC 130") may refer to the module in both its upload downlink functions.

[0018] In an example, antennas 160 may be integral to gNodeB 105. In this case, RF cables 160 may be interconnects, such as coaxial interconnects, between antennas 160 and the amplifiers (not shown) within the housing of gNodeB 105. This example is particularly likely if gNodeB 105 operates in the FR2 frequency range, in which case antennas 165 may be relatively small and easily integrated into the housing of gNodeB 105. It will be understood that such variations are possible and within the scope of the disclosure.

[0019] As used herein, the term "software module" or "module" may refer to a set of machine- readable instructions that are encoded within one or more non-transitory memory devices and executed on one or more processors that host the illustrated components, including the protocol stack implementation 115 as well as the beam selector module 140. As used herein, the term "non-transitory memory" may refer to any tangible storage medium (as opposed to anelectromagnetic or optical signal) and refer to the medium itself, and not to a limitation on data storage (e.g., RAM vs. ROM). For example, non-transitory medium may refer to an embedded memory that is encoded with instructions whereby the memory may have to be re-loaded with the appropriate machine-readable instructions after being power cycled. Further, if an action is described herein as being done by a referenced module (e.g., "e.g., beam selector module 145 stores the data..."), it will be understood that this may describe one or more processors executing the module's machine-readable instructions to perform that particular action. Further, the processors that execute instructions for protocol stack implementation 115 and beam selector module 140 may be servers or embedded processors. As used herein, the term "processor" may refer to an FPGA (Field Programmable Gate Array).

[0020] Radio link 170 may be the result of beamforming performed by the aggregate signals of antennas 165 constructive and destructively interfering with each other, according to differential amplitude and phase weights applied to the RF signals sent to each antenna 165, wherein the differential amplitude and phase weights are the beamforming parameters generated in the disclosed process.

[0021] Although gNodeB 105 is illustrated as a single unit, it will be understood that gNodeB 105 may be partitioned into a 5G Centralized Unit and a 5G Distributed Unit that communicate with each other over an Fl interface (not shown). Further, a 5G Distributed Unit within gNodeB 105 may be further partitioned such that PHY layer 135a / b may be partitioned into an O-RAN Distributed Unit and an O-RAN Remote Unit that communicate with each other over an eCPRI (enhanced Common Public Radio Interface) (not shown) using 7.2x packetized data defined by the O-RAN consortium. It will be understood that such variations are possible and within the scope of the disclosure.

[0022] FIG. 2 illustrates an operation 200 of the exemplary gNodeB 105 as it identifies best beamforming parameters according to the disclosure. Illustrated is gNodeB 105, which is coupled to an antenna array 205 having the plurality of antennas 165 as illustrated in FIG. 1 (not shown in FIG. 2). Each antenna 165 of antenna array 205 is coupled to gNodeB 105 over a dedicated RF cable within the RF cables 160.

[0023] gNodeB 105 with antenna array 205 generates a plurality of scan beams 215a-h. Each scan beam 215a-h has a distinct set of beamforming parameters (amplitude and phase weights), resulting in a distinct gain pattern. Also illustrated are three UEs 210a, 210b, and 210c. UE 210a is connected to gNodeB 105 over beam 215b; UE 210b is connected to gNodeB 105 over beam215e; and UE 210c is connected to gNodeB 105 over beam 215g. These respective beams 215b, 215e, and 215g have the best beamforming parameters for maintaining an RF (Radio Frequency) link with their respective UEs 210a / b / c. However, as a given UE 210a / b / c moves, its current beam 215b / e / g may no longer be the best for connection and may be within the gain pattern of a different beam within beams 215a-h.

[0024] As illustrated in FIG. 2, beams 215b, 215e, and 215g may each be two beams having the same beamforming parameters. For example, a scan beam may impinge on UE 210a for one TTI as scan beam sweeps through 215a-h according to process 300; and there may be a main beam that maintains a persistent link between gNodeB 105 and UE 210a. Both of these beams (scan beam and main beam) may be illustrated as beam 215b in FIG. 2 because they both have the same beamforming parameters, although scan beam and the main beam may have different frequencies.

[0025] gNodeB 105 employs digital beamforming, whereby the Resource Blocks (not shown) corresponding to a given UE 210 may have individual beamforming parameters. This enables simultaneous formation of multiple beams. For example, beams 215b / e / g may be formed simultaneously so that their corresponding UEs 210a / b / c may share RF resources (sub-carriers, etc.).

[0026] FIG. 3 illustrates an exemplary process 300 for gNodeB-based selection of best beamforming parameters according to the disclosure. Process 300 may be executed by processors within gNodeb 105, including processor 145 hosting beam selector 140. As used herein, "main beam" refers to a beam (e.g., beams 215b, 215e, and 215g) that is maintained such that it is in continuous link with its intended UE 210 (in this example, UE 210a, 210b, and 210c, respectively). The beamforming parameters of a main beam may remain constant across multiple TTIs (Transmit Time Intervals). In contrast, as used herein, "CSI-RS scan beam" refers to a Channel State Information Reference Signal that is defined in the 3GPP specification. Under the 3GPP specification, a gNodeB broadcasts a CSI-RS signal periodically that is received by each UE 210. However, under the disclosed system and method, each time a CSI-RS is broadcast, exemplary gNodeB 105 does so with a distinct set of beamforming parameters, causing the CSI- RS beam to scan through beams 215a-h. Each UE 210, in turn, measures the strength of its reception of each CSI-RS signal carried in the scan beams 215a-h and reports that signal measurement to gNodeB 105 over a CSI-RSRP (Channel State Information - Reference Signal Received Power) report, which is in turned received by gNodeB 105.

[0027] Process 300 may have two nested loops, 340 and 345. gNodeB 105 performs loop 340 for each CSI-RS scan beam 215a-h; and performs loop 345 for each UE 210 connected to gNodeB 105 (in this example, one per UE 210a / b / c).

[0028] In step 305, MAC module 130 sets the beamforming parameters for the main beam that will be in continuous contact with a first UE 210a. These initial beamforming parameters may be from a previous iteration of process 300, may be a default setting, or may be an initial guess.

[0029] In step 310, beam selector 140 sets the CSI-RS beamforming parameters for a first scan beam 215a. The set CSI-RS beamforming parameters are such that the scan beam 215a will be broadcast for reception by all UEs. The CSI-RS beamforming parameters may be preset values for each scan beam, creating a set number of beams 215a-h having minimal overlap, or a mutually distinct gain pattern. In the example described herein, there are eight scan beams 215a-h, although it will be understood that more or fewer scan beams are possible and within the scope of the disclosure.

[0030] In step 315, downlink component 115a of protocol stack implementation 115 transmits a resource grid (not shown) having the CSI-RS signal with the beamforming parameters set in step 310. Further to step 315, processor 145 of beam selector 140 stores the transmit time and the CSI-RS beamforming parameters in memory 155. Beam selector 140 may also store an index indicating the first scan beam 215a.

[0031] In step 320, gNodeB 105 receives the CSI-CQI and CSI-RSRP report signals from first UE 210a. via uplink PHY layer 135b. The CSI-RSRP report data represents the RSRP (Reference Signal Received Power) of the CSI-RS signal measured by UE 210a.

[0032] In step 325, beam selector 140 retrieves the CSI-CQI and CSI-RSRP report data from the received signals from first UE 210a and stores the CSI-CQI and CSI-RSRP report data in memory 155, along with the current beamforming parameters of the scan beam.

[0033] gNodeB 105 repeats steps 310-325 in a loop 340. For subsequent iterations of loop 340, beam selector 140 selects and sets CSI-RS beamforming parameters for second scan beam 215b through eighth scan beam 215h. Accordingly gNodeB 105 transmits scan beams 215a-h in sequence over eight iterations of loop 340. At the end of eight iterations of loop 340, processor 145 has stored within memory 155 the CSI-CQI and CSI-RSRP report data from first UE 210a for each scan beam 215a-h.

[0034] Beam selector 140 performs loop 340 (steps 310-325) loop continuously. For every instance in which a beam selector 140 selects a new best beam in step 325, it provides the newbest beam beamforming parameters to serve as the main beam for communications between gNodeB 105 and first UE 210a.

[0035] In step 335, beam selector 140 selects the best beam among the scan beams 215a-h (each from an iteration of loop 340) to serve as the main beam for communication with UE 210a.

[0036] FIG. 4 illustrates an exemplary process 400 for implementing step 335, in which beam selector 140 selects the best beam among the scan beams 215a-h for use as the main beam for communications with UE 210a.

[0037] In step 405, beam selector 140 queries memory 155 and identifies which scan beam has the highest RSRP value.

[0038] In step 410, beam selector 140 compares the highest RSRP value retrieved in step 405 with the RSRP corresponding to the current main beam used to communicate with UE 210a. If the highest RSRP value retrieved in step 405 is NOT more than 2dB higher than the RSRP corresponding to the current main beam, then process 400 follows the "NO" logic path to step 425, in which beam selector 140 selects the current main beam as the best beam for communication with UE 210a. The purpose for this is that if the highest RSRP value extracted in step 405 is within 2dB of the current main beam's RSRP, then there is not a sufficient improvement in RSRP to warrant changing the main beam. If the highest RSRP value is more than 2dB above the RSRP corresponding to the current main beam, then process 400 follows the "YES" logic path to step 415.

[0039] In step 415, beam selector 140 retrieves the CQI data corresponding to the scan beam with the highest RSRP. If this CQI value is lower than the CQI value corresponding to the current main beam, then process 400 follows the "YES" logic path to step 425, in which beam selector 140 selects the current main beam as the best beam for communication with UE 210a. If the CQI value for the scan beam with the highest RSRP is NOT lower than the CQI value for the current main beam, then process 400 follows the "NO" logic path to step 420.

[0040] In step 420, beam selector 140 selects the scan beam with the highest RSRP to be the new main beam. In doing so, beam selector 140 retrieves the beamforming parameters for the scan beam with the highest RSRP and assigns them for the main beam parameters that beam selector 140 will use in the next iteration of step 305 (the next iteration of loop 345).

[0041] The logic tests in steps 410 and 415 may serve to dampen the reactivity of process 300 to minor changes in RSRP, thereby preventing beam selector 140 from overreacting to minor changes in channel conditions.

[0042] Although a 2dB threshold is used in step 410, it is exemplary. It will be understood that other threshold values may be used and that such variations are within the scope of the disclosure.

[0043] As indicated by loop 345, process 300 returns to step 305. However, in this iteration of step 305, beam selector 140 provides the beamforming parameters of the best beam selected in step 325 to MAC module 130. The next iteration of loop 345 is for second UE 210b. Process 300 may iterate loop 345 for each UE 210 connected to gNodeB 105.

[0044] In a variation of process 300, gNodeB 105 may perform steps 305-335 for all connected UEs 210 in a single iteration. In this case, beam selector 140 may process the received CSI-CQ.I and CSI-RSRP reports from all of the connected UEs 210 in one iteration of steps 320-330. In this case, in each iteration of loop 340, in step 320, processor 145 may retrieve the CSI-CQI and CSI- RSRP report data from all of the connected UEs 210a / b / c, and in step 325 store the data in memory 155 with an index linking each CSI-CQI and CSI-RSRP report data to its corresponding UE 210a / b / c. Accordingly, in this variation, loop 345 may be omitted.

[0045] In another variation of process 300, beam selector 140 may rely only on CSI-RSRP information and not CSI-CQI. In this variation, step 325 is similar to that done above except that the CSI-CQI data is not stored. Step 335 is different, however, in that process 400 is not performed. Instead, in step 335, processor 145 simply selects the scan beam with the highest RSRP. This variation does not have the advantages of the process described above, but it offers simplified processing.

[0046] FIG. 5 is a timing diagram for the transmission of CSI-RS signals (step 315) and reception of a CSI-RSRP report (step 320) for each iteration of loop 340 in process 300. Illustrated are eight transmit / receive timeline (steps 315 / 320). Each transmit / receive timeline may have an index 505 and may correspond to a distinct set of beamforming parameters. For example, transmit / receive timeline 1 may correspond to the transmission of scan beam 215a, transmit / receive timeline 2 may correspond to the transmission of scan beam 215b, and so on. There may be a period P between a given scan beam transmission and reception. Period P may be obtained from the 3GPP specification as representing the expected accumulated time oftransmit signal propagation, UE signal measurement, receive signal propagation, resulting in a reporting time requirement as defined by 3GPP.

[0047] Although the period P is illustrated as being longer than the time between CSI-RS transmissions, it will be understood that this is an example and that the relative timing of period P to the interval between transitions may vary and that such variations are within the scope of the disclosure.

Claims

Claims1. A method for selecting a best set of beamforming parameters for communicating with a UE(User Equipment), comprising: setting a first set of scan beam beamforming parameters for transmitting a first CSI-RS (ChannelState Information - Reference Signal); transmitting the first CSI-RS; receiving a first CSI-RSRP (Channel State Information - Reference Signal Received Power) report data from a UE, the first CSI-RSRP report data corresponding to the first CSI-RS; storing the first set of scan beam beamforming parameters and the first CSI-RSRP report data; setting a second set of scan beam beamforming parameters for transmitting a second CSI-RS; transmitting the second CSI-RS; receiving a second CSI-RSRP report data from the UE, the second CSI-RSRP report data corresponding to the second CSI-RS; storing the second set of scan beam beamforming parameters and the second CSI-RSRP report data; setting a third set of scan beam beamforming parameters for transmitting a third CSI-RS; transmitting the third CSI-RS; receiving a third CSI-RSRP report data from the UE, the third CSI-RSRP report data corresponding the third CSI-RS; storing the third set of scan beam beamforming parameters and the third CSI-RSRP report data; selecting a best set of scan beam beamforming parameters corresponding to a best CSI-RSRP report data; and setting a main beam beamforming parameters based on the best set of scan beam beamforming parameters.

2. The method of claim 1, wherein the setting a main beam beamforming parameters comprises providing the main beam beamforming parameters to a MAC (Medium Access Control) module.

3. The method of claim 1, further comprising: setting an eighth set of scan beam beamforming parameters for transmitting an eighth CSI-RS); transmitting the eighth CSI-RS;receiving an eighth CSI-RSRP report data from the UE, the eighth CSI-RSRP report data corresponding to the eighth CSI-RS; and storing the eighth set of scan beam beamforming parameters and the eighth CSI-RSRP report data.

4. A method for selecting a best set of beamforming parameters for communicating with each of a plurality of UEs (User Equipment), comprising: setting a first set of scan beam beamforming parameters for transmitting a first CSI-RS (Channel State Information - Reference Signal); transmitting the first CSI-RS; receiving a first plurality of CSI-RSRP report data, each of the first plurality of CSI-RSRP report data received from a corresponding one of the plurality of UEs; storing the first set of scan beam beamforming parameters and the first plurality of CSI-RSRP report data; setting a second set of scan beam beamforming parameters for transmitting a second CSI-RS; transmitting the second CSI-RS; receiving a second plurality of CSI-RSRP report data, each of the second plurality of CSI-RSRP report data received from a corresponding one of the plurality of UEs; storing the second set of scan beam beamforming parameters and the second plurality of CSI- RSRP report data; setting a third set of scan beam beamforming parameters for transmitting a third CSI-RS; transmitting the third CSI-RS; receiving a third plurality of CSI-RSRP report data, each of the third plurality of CSI-RSRP report data received from a corresponding one of from the plurality of UEs; storing the third set of scan beam beamforming parameters and the third CSI-RSRP report data; selecting a plurality of best scan beam beamforming parameters corresponding to each of the plurality of UEs; and setting a main beam beamforming parameters for each of the plurality of UEs based on the plurality of best set of scan beam beamforming parameters.

5. The method of claim 4, wherein the setting a main beam beamforming parameters comprises providing the main beam beamforming parameters for each of the plurality of UEs to a MAC (Medium Access Control) module.

6. The method of claim 4, further comprising: setting an eighth set of scan beam beamforming parameters for transmission in a eighth CSI-RS); transmitting the eighth CSI-RS; receiving an eighth plurality of CSI-RSRP report data, each of the eighth plurality of CSI-RSRP report data received from a corresponding one of from the plurality of UEs; and logging the eighth set of scan beam beamforming parameters and the eighth plurality of CSI- RSRP report data.

7. A method for selecting a best set of beamforming parameters for communicating with a UE (User Equipment), comprising: setting a first set of scan beam beamforming parameters for transmitting a first CSI-RS (Channel State Information - Reference Signal); transmitting the first CSI-RS; receiving a first CSI-CQ.I (Channel State Information - Channel Quality Information) data and a first CSI-RSRP (Channel State Information - Reference Signal Received Power) report data from the UE, the first CSI-CQI data and the first CSI-RSRP report data corresponding to the first CSI-RS; storing the first set of scan beam beamforming parameters and the first CSI-CQI data and the first CSI-RSRP report data; setting a second set of scan beam beamforming parameters for transmitting a second CSI-RS; transmitting the second CSI-RS; receiving a second CSI-CQI data and a second CSI-RSRP report data from the UE, the second CSI- CQI data and the second CSI-RSRP report data corresponding to the second CSI-RS; storing the second set of scan beam beamforming parameters and the second CSI-CQI data and the second CSI-RSRP report data; setting a third set of scan beam beamforming parameters for transmitting a third CSI-RS; transmitting the third CSI-RS; receiving a third CSI-CQI data and a third CSI-RSRP report data from the UE, the third CSI-CQI data and the third CSI-RSRP report data corresponding to the third CSI-RS;storing the third set of scan beam beamforming parameters and the third CSI-CQJ and the third CSI-RSRP report data; selecting a best set of beamforming parameters; and setting a main beam beamforming parameters based on the best set of beamforming parameters.

8. The method of claim 7, wherein the selecting the best set of beamforming parameters comprises:Identifying a highest CSI-RSRP report data value among the stored CSI-RSRP report data values; determining that highest CSI-RSRP report data value is greater than a main beam CSI-RSRP report data value by a threshold; determining that a CSI-CQJ data value corresponding to highest CSI-RSRP report data value is not lower than a main beam CSI-CQI data value; and selecting a set of scan beam parameters corresponding to the highest CSI-RSRP report data value as the best set of beamforming parameters.

9. The method of claim 7, wherein the selecting the best set of beamforming parameters comprises:Identifying a highest CSI-RSRP report data value among the stored CSI-RSRP report data values; determining that highest CSI-RSRP report data value is not greater than a main beam CSI-RSRP report data value by a threshold; and selecting a set of scan beam parameters corresponding to a current main beam as the best set of beamforming parameters.

10. The method of claim 7 , wherein the selecting the best set of beamforming parameters comprises:Identifying a highest CSI-RSRP report data value among the stored CSI-RSRP report data values; determining that highest CSI-RSRP report data value is greater than a main beam CSI-RSRP report data value by a threshold; determining that a CSI-CQI data value corresponding to highest CSI-RSRP report data value is lower than a main beam CSI-CQI data value; andselecting a set of scan beam parameters corresponding to a current main beam as the best set of beamforming parameters.

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