Patent Publication Number: US-2023163828-A1

Title: Method and Apparatus for Beam Selection in a Wireless Communication Network

Description:
BACKGROUND 
     “Link adaptation or “LA” refers to the practice of changing one or more transmission parameters used for transmitting a communication signal, to account for changing radio conditions. Manipulating the modulation and coding scheme (MCS) responsive to measured changes in the radio link represents one example of link adaptation. Lower modulation orders are more robust but convey fewer bits per modulation symbols, and higher coding rates are more robust but decrease the throughput of new information. Additionally, or alternatively, link adaptation involves dynamic adjustment of transport block sizes or transmission power. 
     Taking an example case of a wireless communication network in which a base station transmits data to a User Equipment (UE), the base station adapts the downlink toward the UE in response to Channel Quality Indicator (CQI) feedback, or, more broadly, Channel State Information (CSI) feedback from the UE, such as feedback indicating Reference Signal Received Power (RSRP) at the UE, for a reference signal transmitted by the base station. Consistent with the above examples, a non-limiting approach involves the base station adapting the MCS used for transmitting data to the UE, responsive to changes in the CQI or CSI feedback from the UE. 
     As a specific example of a LA algorithm, a so-called “jump” algorithm backs off from a control target more quickly than it returns. When performing LA on a radio link between a TRP and a UE, the jump algorithm decreases a target level by a downward step in response to a negative acknowledgment (NACK) of a Hybrid Automatic Repeat reQuest (HARQ) transmission over the involved radio link and increases the target level by an upward step in response to a positive acknowledgement (ACK). However, the upward step size is a fraction of the downward step size, meaning that the target level operated on by the jump algorithm climbs back towards its pre-NACK level more slowly than it fell. The climbing rate may be, for example, 1/10th or 1/100th of the fall-back rate. Consequently, while jump algorithms respond well to sudden decreases in channel quality, the long “time constant” associated with climbing back to a more aggressive target level in response to improved channel conditions makes it difficult for the jump algorithm to handle certain scenarios. 
     SUMMARY 
     A network node identifies radio beams that are affected by periodic fading at a User Equipment (UE) and penalizes the identified beams with respect to a serving-beam selection procedure that is used to select a serving radio beam for the UE. For example, among a set of radio beams that are candidates for serving the UE, the serving-beam selection procedure selects one or more of the candidate beams according to rankings determined from radio-signal measurements reported by the UE or from measurements on Sounding Reference Signals (SRS) transmitted by the UE. In this context, penalizing a beam means discounting its ranking for purposes of considering it within the beam-selection procedure. 
     In an example embodiment, a method of operation by a network node of a wireless communication network includes identifying radio beams that are affected by periodic fading at a UE, from among a set of radio beams that are candidates for serving the UE. The method further includes associating a penalty with each identified one of the radio beams and applying the penalties in a serving-beam selection procedure that is used to select one of the radio beams for serving the UE. 
     A related embodiment involves a network node configured for operation in a wireless communication network. The network node includes communication interface circuitry and processing circuitry operative to send and receive signals via the communication interface circuitry. The processing circuitry is configured to identify radio beams affected by periodic fading at a UE, from among a set of radio beams that are candidates for serving the UE. The processing circuitry is further configured to associate a penalty with each identified one of the radio beams and apply the penalties in a serving-beam selection procedure that is used to select one of the radio beams for serving the UE. 
     In another embodiment, the network node includes an identifying module configured to identify radio beams affected by periodic fading at a UE, from among a set of radio beams that are candidates for serving the UE. Additional modules of the network node include an associating module configured to associate a penalty with each identified one of the radio beams, and an applying module configured to apply the penalties in a serving-beam selection procedure that is used to select one of the radio beams for serving the UE. 
     In yet another embodiment, a non-transitory computer-readable medium storing a computer program comprising instructions that, when executed by a processor of a network node in a wireless communication network, causes the network node to: identify radio beams affected by periodic fading at a User Equipment UE, from among a set of radio beams that are candidates for serving the UE, associate a penalty with each identified one of the radio beams, and apply the penalties in a serving-beam selection procedure that is used to select one of the radio beams for serving the UE. 
     In a further embodiment, a network node configured for operation in a wireless communication network includes communication interface circuitry and processing circuitry that is operative to send and receive signals via the communication interface circuitry. Further, the processing circuitry is configured to conditionally penalize one or more candidate beams in a set of candidate beams that, with respect to a Transmission Reception Point (TRP) of the wireless communication network, are candidates for serving a UE. Each penalized candidate beam is excluded from or disfavored in a serving-beam selection procedure used to select a serving beam for the UE, from among the set of candidate beams. The processing circuitry conditions the penalization of individual ones or related groups of the candidate beams in the set of candidate beams, in dependence on determining whether the UE experiences periodic fading with respect to the individual ones or related groups of the candidate beams in the set of candidate beams. 
     Of course, the present invention is not limited to the above features and advantages. Indeed, those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of a radio environment involving a Transmission Reception Point (TRP) of a wireless communication network and a User Equipment (UE), where the UE is vulnerable to periodic fading. 
         FIG.  2    is a diagram of example Time Division Duplexing (TDD) configurations individually usable by a TRP, and with each TDD configuration being associated with a different Link Adaptation (LA) time constant, as a consequence of the particular ratio and distribution of uplink and downlink allocations defined as the TDD configuration. 
         FIGS.  3 A,  3 B, and  3 C  are block diagrams of example embodiments of a wireless communication network that includes a network node that is operative to apply penalties in serving-beam selection procedure performed for a User Equipment (UE). 
         FIG.  4    is a block diagram of one embodiment of an antenna system, suitable for use by a TRP in performing transmission or reception beamforming. 
         FIG.  5    is a diagram of an example set of beams used by a TRP. 
         FIG.  6    is a block diagram of one embodiment of a network node that is operative to apply penalties in serving-beam selection procedure performed for a UE. 
         FIGS.  7 A,  7 B, and  7 C  are diagrams illustrating radio beams that are candidates for serving a UE from a TRP. 
         FIG.  8    is a diagram of an example data structure, illustrating rankings of radio beams that are candidates for serving a UE, and associated penalties for identified ones of those beams that are affected by periodic fading at a UE. 
         FIG.  9    is a block diagram of another embodiment of a network node that is operative to apply penalties in serving-beam selection procedure performed for a UE. 
         FIGS.  10  and  11    are logic flow diagrams of respective embodiments of a method implemented by a network node, for applying penalties in serving-beam selection procedure performed for a UE. 
     
    
    
     DETAILED DESCRIPTION 
     In general, Link Adaptation (LA) algorithms, such as jump algorithms, prevent long sequences of errors when the radio link (channel) suddenly becomes bad. However, such algorithms perform less well when the radio conditions change more rapidly than the time constant of the LA algorithm. A point recognized herein is that the overall network or system performance suffers when the involved radio channels have relatively good radio quality between impairment occurrences, where the impairments occur on a time scale on par with, or slightly shorter than, the time constant of the LA algorithm. 
     In an example case, the jump algorithm reacts to an occurrence of link impairment by jumping back, e.g., in terms of Modulation and Coding Scheme (MCS). Depending on the specific configuration, it may take about 10 times to 100 times as long to step back up. Depending on the interval between impairment events on the radio link, the jump algorithm may not have returned to an appropriate MCS before being knocked down again, because of a negative acknowledgement of a preceding transmission. Consequently, there are scenarios, where the jump algorithm may result in the involved transmission parameters being maintained well below their optimal values, despite the link quality being good during the intervals between the impairment events. Such applies to instances where the impairments are rather short, as compared to the intervals during which the channel has good quality. 
     While incorporating “freeze” or “no-action” mechanisms prevent the jump algorithm from stepping back too far in the presence of burst errors, a key point recognized herein is that such mechanisms leave unaddressed scenarios where the link quality is good except for periodic impairment events occurring on a periodicity at or near the LA time constant of the jump algorithm. Of course, LA algorithms besides the jump algorithm may suffer the same or similar deleterious behavior in the presence of periodic fading. 
       FIG.  1    illustrates a scenario associated with periodic fading; namely, in propagation scenarios where there is a Line-of-Sight (LOS) ray and a ground-reflected ray between a Transmission Reception Point (TRP) and a User Equipment (UE), the LOS ray and the ground-reflected ray may combine at the UE constructively (add) or destructively (subtract). In particular, when the UE moves towards or away from the TRP, the two rays may exhibit a periodic alternation between adding and subtracting, meaning that the UE experiences a characteristic periodic fading. The phenomenon depends on the real-world propagation environment, carrier frequency, relevant geometries, such as antenna height(s) above the ground, and further on the velocity of the UE relative to the TRP. 
     Consider an example scenario where a downlink transmission beam of a beamforming TRP aligns with a highway. Vehicle-mounted or vehicle-carried UEs traveling along that stretch of highway may experience periodic fading due to two-ray ground reflection in their uplink and/or downlink connections as they approach the TRP or recede from it, with the periodicity of the fading depending on vehicle speed. For simplicity, the phrase “periodic fading” refers to the foregoing fading phenomenon, unless otherwise qualified in context. Similar effects apply to UEs integrated with or conveyed on trains moving along stretches of track that are aligned with downlink/uplink transmission beams of a TRP. If the TRP uses a LA algorithm with a LA adaptation time constant that is about the same or greater than the periodicity of periodic fading experienced by one or more UEs being served by the TRP, link adjustments will never “catch up” to or account for the periodic fading impairments. 
     More particularly, the periodic fading impairments will drive link adaptations towards transmission-parameter settings that are too conservative with respect to the radio-link conditions experienced between the periodic fading events. Hence, the UE(s) experiencing those conditions will operate with radio links having transmission-parameter adaptations that are too conservative, meaning that system efficiency suffers. With wireless communication networks evolving towards higher carrier frequencies, extensive use of beamforming, and higher bitrates, the underperformance of established LA algorithms in the presence of periodic fading will become an increasingly significant problem. 
     Adaptations of the Time Division Duplexing (TDD) configuration of a TRP represents an advantageous mechanism for adapting the time constant of the LA algorithm used by the TRP for performing link adaptations on the radio link(s) between it and the UEs served by it. Broadly, the term “TDD configuration” describes the duplexing arrangement applied to downlink and uplink directions, and a key aspect is that the TDD configuration used by a TRP defines the rate or number of opportunities provided for the exchange of feedback information between the TRP and its served UEs. For example, consider an example where the TRP performs link adaptations for a radio link between the TRP and a UE in dependence on the feedback of downlink measurements from the UE. The response time or time constant of the LA algorithm used to perform the link adaptations depends on how frequently the TRP receives new feedback from the UE, and the TDD configuration influences the possible feedback rates. 
       FIG.  2    provides a non-limiting example of possible TDD configurations that may be used by a TRP, where the letter “D” denotes a downlink allocation and “U” represents an uplink allocation. For example, the TRP uses a radio signal structure based on recurring “frames” with each frame subdivided into a number of subframes. In that context, each “D” in  FIG.  2    may represent a subframe allocated for downlink transmissions and “U” may represent a subframe allocated for uplink transmissions. The TDD configuration denoted as “#0” has many more uplink subframes than downlink subframes and may be an advantageous configuration to use when there is more uplink traffic than downlink traffic. Conversely, the TDD configuration denote as “#N” has many more downlink subframes than uplink subframes and may be an advantageous configuration to use when there is more downlink traffic than uplink traffic. 
     Of course, there may be many defined TDD configurations that can be used at the TRP and the pattern or distribution of uplink and downlink subframes is also an important consideration. Compare the “#1” configuration in  FIG.  2    with the “#2” configuration. While both configurations may have an overall 1:1 ratio of downlink-to-uplink subframes, the #1 configuration offers a uniform distribution of alternating downlink and uplink subframes, whereas the #2 configuration includes a run of downlink subframes followed by a run of uplink subframes. As such, recognizing that the TDD configuration influences the time constant of the LA algorithm employed by a TRP encompasses at least two aspects. First, the “TDD ratio” of uplink and downlink allocations represents one factor that determines how frequently LA feedback can be exchanged between the served UEs and the TRP. Second, the “TDD pattern” of uplink and downlink allocations—the distribution or arrangement of uplink and downlink allocations over a defined interval, such as a frame—represents another factor that determines how frequently LA feedback can be exchanged between the served UEs and the TRP. 
     However, even in cases involving the dynamic adaptation of the TDD configuration used by a TRP to ameliorate impairments arising from UEs experience periodic fading in the radio beam or beams used by the TRP to serve the UEs, a key recognition herein is that the procedure used to select a serving beam for a particular UE should account for the effects of periodic fading at the UE. 
     Consider an example serving-beam selection procedure used to find the “best” one among the radio beams that are candidates for serving a UE. Here, a “serving” radio beam provides radio connectivity between the UE and the network. In an example case, the radio beams are downlink radio beams—directionally-focused emissions of electromagnetic energy conveying information—and particular radio beams from one or more TRPs are candidates for serving the UE if they meet some minimum threshold for received-signal quality or strength at the UE, as measured by the UE on reference signals or other signals conveyed in the radio beams, which may be more simply referred to as “beams.” 
     Although more than one serving beam may be selected and used, a simple example involves selecting a single serving radio beam from among the candidate beams, based on ranking the candidate beams according to their corresponding “scores,” which may be the received-signal strengths or qualities indicated by the UE. In more detail, to find the best beam to use for serving the UE, the network performs a beam sweep, i.e., it transmits a selected set of candidate beams, and selects the active beam based on radio-signal measurements reported by the UE for the candidate beams. The process typically includes a TRP selecting a set of candidate beams, which may include the currently active transmit beam of the UE, and the TRP transmits a Channel-State-Information Reference Signal (CSI-RS) in each of the candidate beams. 
     The UE measures CSI-RS on assigned resources for the respective candidate beams and reports up to N best CSI-RS resources and corresponding quality values, such as Reference Signal Received Power, as measured at the UE for the received CS-RSs. The TRP receives the measurement report from the UE and selects which one of the candidate beams to use as the serving beam for the UE. The process may be repeated in recurring intervals, where each round of selection involves time for the beam sweep, the reporting by the UE, and the corresponding evaluation and selection by the TRP, and may involve milliseconds, for example. 
     As recognized herein, however, one of the issues with periodic fading at the UE with respect to any particular beam is that the UE may experience good reception conditions during the intervals between periodic fading events. Consequently, the UE may report good signal conditions for the beam, although actual communication performance on the beam will be less good than the reported signal conditions indicate, because of the deleterious effects of periodic fading on LA performed by the TRP with respect to the UE. Various embodiments of a solution contemplated in this disclosure incorporate consideration of periodic fading into the beam selection process, to penalize beams for purposes of the selection process, in dependence on whether the UE experiences periodic fading with respect to them. 
     In at least one embodiment, saying that the UE “experiences periodic fading” with respect to any particular beam means that the UE experiences periodic fading that satisfies one or more conditional criteria, such as periodic fading having a periodicity in or above the range of the LA “time constant”, which can be understood as reflecting the responsiveness of the LA used by the TRP for adapting the radio link between the UE and the TRP. Additionally, or alternatively, the UE is not considered to be experiencing periodic fading with respect to a particular beam unless the severity of the fading satisfies some minimum or threshold condition. 
     In any case,  FIGS.  3 A,  3 B, and  3 C  illustrate example embodiments of a wireless communication network  10  that includes one or more entities operative to trigger TDD configuration adaptations at one or more TRPs in the network, to ameliorate the problem(s) in beam selection that arise when the periodicity of fading at the UE for one or more of the beams under consideration approaches the time constant of the LA algorithm(s) in use at the TRP(s). The wireless communication network  10 —“network  10 ”—comprises, for example, a Third Generation Partnership Project (3GPP) network, such as a Fifth Generation (5G) New Radio (NR) network. 
     The depicted network  10  provides communication services to one or more User Equipments (UEs)  12 , with UEs  12 - 1 ,  12 - 2 ,  12 - 3 ,  12 - 4 , and  12 - 5  depicted by way of example. For the reference number “12,” suffixing may be used for clarity, but the number “12” without suffixing may also be used, either to refer to UEs in a singular or a plural sense. The same approach holds for other references numbers that may have suffixing in the drawings. 
     Providing communication services to the UEs  12  comprises, for example, providing access to one or more external networks (“NW(s)”)  14 , which may include or provide access to one or more external servers  16 . For example, the network  14  is the Internet or another Packet Data Network (PDN). Broadly, the communication services provided by or through the network  10  include, for example, voice services, data services, messing services, machine-communication services, etc. The particular services used by a given UE  12  depends on its capabilities and intended use, and the UEs  12  may be of the same or different types, e.g., a mix of smartphones, mobile computing devices, Machine Type Communication (MTC) devices, etc. As such, the term “User Equipment” has broad meaning, with the “User” component of the term denoting equipment that uses the network  10  rather than entities that belong to the network infrastructure. In an example case, one or more of the UEs may be embedded, such as integrated into automobiles for Vehicle-to-Everything (V2X) operations. 
     A Radio Access Network (RAN)  20  portion of the network  10  includes one or more TRPs  22 , with TRPs  22 - 1 ,  22 - 2 , and  22 - 3  shown by way of example. The TRPs  22  may or may not be of like types and capabilities, e.g., they may have different transmit-power capabilities, different antenna arrangements, etc. Thus, although each TRP  22  is depicted with a corresponding antenna system  24  and a corresponding coverage area  26 , there may be differences in the antenna systems  24  and/or the coverage areas  26 . At least one of the TRPs  22  is configured for beamforming operations, e.g., transmit beamforming and/or uplink beamforming, with the antenna system  24  comprising, for example, an array of antenna elements supporting beamforming. Correspondingly, although the coverage areas  26  appear uniform, one or more of the TRPs  22  may use a plurality of directional transmission and/or reception beams to “cover” the depicted coverage area. 
     A Core Network (CN) portion  28  of the network  10  provides, among other functions, routing, authentication, mobility control, and policy control for UEs  12  served via the RAN  20 . One or more routing nodes  30 , authentication nodes  34 , mobility management nodes  32 , and policy control nodes  36  cooperate to provide the various core-network functionality. At least some of the CN nodes may be implemented in a cloud-computing or data-center computing environment, e.g., via virtualized instantiation on data-center servers, which are broadly denoted as “cloud resources”  38  in the diagram. Of course, the cloud resources  38  may additionally or alternatively support RAN functionality, and, correspondingly, they are showing as extending into or otherwise supporting the RAN  20 . 
     Various details regarding the network  10  may be varied as a function of intended use and network type, e.g., different “generations” of standards-based networks may split, rearrange, or add functions and the nodal/functional nomenclature may change accordingly. Such details are, in general, not germane to the techniques of interest herein, which are represented by way of example via a network node  18  (“NN” in  FIGS.  3 A,  3 B, and  3 C ) and its associated functionality. 
       FIG.  3 A  depicts a copy or instantiation of the network node  18  at each of the three example TRPs  22 , e.g., a network node  18 - 1  at the TRP  22 - 1 , a network node  18 - 2  at the TRP  22 - 2 , and a network node  18 - 3  at the TRP  22 - 3 . Each network node  18  in this scenario may be co-located with its respective TRP  22 . Here, the term “co-located” encompasses integration, such that a network node  18  can be considered as a functional portion of a corresponding TRP  22 . 
     In one example where the network nodes  18  are integrated with respective TRPs  22 , communications between network nodes  18  may be carried out using inter-TRP communication links, possibly with appropriate protocol provisions or extensions. Alternatively, the network nodes  18  may include dedicated interfaces and protocols for exchanging communications. As a further alternative, at least some of the functionality of the network node(s)  18  resides in the cloud resources  38 , with corresponding connectivity into the RAN  20 . 
       FIG.  3 B  differs from  FIG.  3 A  by depicting an alternative implementation that involves a centralized implementation of the network node  18 . A single network node  18  serves all three TRPs  22 - 1 ,  22 - 2 , and  22 - 3  in the depicted example. More generally, the network  10  may include multiple network nodes  18 , with each one serving a given number of TRPs  22 , or with individual network nodes  18  allocated to defined “areas” of the network  10 , such as defined mobility or tracking areas. With centralization, a given network node  18  may be co-located with a given TRP  22  and provide processing and control for multiple TRPs  22 , or it may reside physically and geographically separate from any of the TRPs  22  that it supports. A centralized network node  18  may be at least partly implemented via the cloud resources  38 . 
       FIG.  3 C  illustrates another implementation example, where one or more network nodes  18  reside in the CN  28 , meaning that the network node(s)  18  communicate with one or more corresponding TRPs  22  in the RAN  20 . A CN-based implementation of the network node  18 , or any number of copies or instantiations thereof, means that the network node  18  may be co-located with or integrated within another node in the CN  28 , or may be implemented as a stand-alone node within the CN  28 . And, as with the other embodiments, the network node(s)  18  may be at least partly implemented in the cloud resources  38 . 
       FIG.  4    illustrates an example antenna system  24  for a TRP  22  that is configured for beamforming operation. Included in the antenna system  24  is an antenna array  40  comprising a plurality of antenna elements  42 . With 5G NR and future evolutions of wireless networks, the antenna array  40  may comprise a relatively large number of antenna elements  42 , allowing for narrow, high-gain transmission and/or reception beams. One or more beam directions may align with coverage areas where served UEs  12  are particularly vulnerable to periodic fading, such as beams that align with a stretch of highway, a stretch of train tracks, etc. Here, a UE  12  is a “served UE” with respect to a TRP  22  if it has a radio link with the TRP  22 . 
       FIG.  5    illustrates an example beamforming scenario for a TRP  22  and its associated antenna system  24 . The TRP  22  provides radio coverage for a given overall coverage area  26  using a plurality of directional beams  50 , e.g.,  50 - 1  through  50 - 14 . The beams  50  may represent direction transmission, directional reception, or both. In a transmit-beam example, the TRP  22  may transmit each beam  50  individually, in a sequence or pattern referred to as a “beam sweep”. 
       FIG.  6    illustrates an example implementation of a network node  18 , with the understanding that the depicted embodiment is non-limiting. Other arrangements of processing and communication circuitry may be used to realize the functionality described herein for the network node  18 . 
     Elements of the example network node  18  include communication interface circuitry  70 , including transmitter circuitry  72  and receiver circuitry  74 . Further elements include processing circuitry  76  and integrated or associated storage  78 , such as may be used for holding one or more computer programs  80  (“CPs”) or configuration data  82  (“CFG. DATA”). 
     The implementation details of the communication interface circuitry  70  depend on whether the network node  18  is standalone or integrated with another node in the network  10  or implemented at least partly within the cloud resources  38 . In general, however, the communication interface circuitry  70  includes wireline or wireless physical-layer circuitry configured for transmitting and receiving over the involved propagation medium. Non-limiting examples include inter-processor or inter-server parallel or serial bus interface circuitry or computer-network interface circuitry, such an Ethernet-based interface circuitry. 
     The processing circuitry  76  is operatively associated with the communication interface circuitry  70 , e.g., it is configured to send and receive messages or other signaling via the communication interface circuitry  70 . The processing circuitry  76  comprises programmed circuitry or fixed circuitry, or a combination of programmed and fixed circuitry. In an example embodiment, the processing circuitry  76  comprises one or more microprocessors, Digital Signal Processors (DSPs), Field Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuits (ASICs), or other digital processing circuits. 
     In at least one embodiment, the processing circuitry  76  is configured at least in part based on its execution of computer instructions included in one or more computer programs  80  stored in the storage  78 . As noted, the storage  78  may also store one or more items of configuration data  82  associated with operation of the network node  18 . The storage  78  comprises, for example, one or more types of computer-readable media, such as a Solid State Disk (SSD), FLASH, DRAM, SRAM, etc. In one embodiment, the storage  78  provides for long-term storage of the computer program(s)  80 , and further provides working memory for operation of the processing circuitry  76 . 
     With the example details of  FIG.  6    in mind,  FIG.  7 A  illustrates a TRP  22  transmitting, via its beamforming antenna  24 , Channel State Information Reference Signals (CSI-RS) in each beam  50  in a set  52  of beams  50 , e.g., beams  50 - 1 ,  50 - 2 , and  50 - 3 . A UE  12  may use a beam  54  for receiving the CSI-RS transmissions in each of the beams  50 . 
     In the context of  FIG.  7 B , the UE  12  uses beam  56  for transmitting measurement reports to the TRP  22 , indicating the results of its CSI-RS measurements. The TRP  22  may use a beam  58  for receiving the measurement-report transmission from the UE. In an example case, the UE  12  sends the measurement-report information via a Physical Uplink Control Channel (PUCCH) transmission or a Physical Uplink Shared Channel (PUSCH) transmission, beamformed according to the beam  56 . 
     In the context of  FIG.  7 C , the TRP  22  evaluates the measurement-report information to select a “best” one of the beams  50  in the set  52 , to use as a serving beam  60  for the UE  12 , at least for a current or next evaluation interval. In the depicted example, the TRP  22  selects the beam  50 - 3  as the serving beam  60  to use for the UE  12 , and the UE  12  uses the beam  54  for receiving the serving beam  60 —i.e., for receiving the directional downlink transmission by the TRP  22  transmitted via the serving beam  60 . The TRP  22  may repeatedly perform measurement-report evaluations to update its serving-beam selection for the UE  12 , to account for changing reception conditions, e.g., arising from movement of the UE  12 . 
     Unlike any conventional beam-selection procedure, however, selection of the “best” beam  50  for serving the UE  12  penalizes individual ones or related groups of the beams  50  that are candidates for serving the UE  12 , in dependence on whether the individual ones or related groups of the beams  50  are affected by period fading at the UE. In one example case, a network node  18  associated with the TRP  22  determines penalties for any beams  50  in the set  52  that are detected as being affected by periodic fading at the UE  12 , so that the rankings or scores of the penalized beams  50  are reduced for purposes of the serving-beam selection procedure, so that the penalized beams are discounted—disfavored or eliminated from consideration. 
     In an example implementation, a network node  18  is configured for operation in a wireless communication network, e.g., the network  10  depicted in any of  FIGS.  3 A,  3 B, and  3 C . With reference back to  FIG.  6   , the network node  18  includes communication interface circuitry  70  and processing circuitry  76  that is operative to send and receive signals via the communication interface circuitry  70 . The processing circuitry  76  is configured to: (a) identify radio beams  50  affected by periodic fading at a UE  12 , from among a set  52  of radio beams  50  that are candidates for serving a UE  12 , (b) associate a penalty with each identified one of the radio beams  50 , and (c) apply the penalties in a serving-beam selection procedure that is used to select one of the radio beams  50  for serving the UE  12 . 
     For example, each radio beam  50  in the set  52  has a corresponding ranking determined in dependence on radio-signal measurement reports from the UE  12 , and, correspondingly, the processing circuitry  76  is configured to apply the penalties in the serving-beam selection procedure. In particular, the processing circuitry  76  penalizes the corresponding ranking of each identified one of the radio beams  50  according to the associated penalty. 
     In at least one embodiment of the network node  18 , unless doing so would exclude all of the radio beams  50  in the set  52  from selection consideration in the serving-beam selection procedure, the penalties associated with the identified ones of the radio beams  50  exclude the identified ones of the radio beams  50  from selection consideration in the serving-beam selection procedure. When considering each penalty as being a “discount” or “derating factor” or “scalar” to be applied to the corresponding rank or score of the beam  50  (or related beams  50 ) with which the penalty is associated, the penalty may zero or otherwise null the rank or score, so that the associated beam(s)  50  are excluded from consideration in the serving-beam selection procedure. 
     In one or more other embodiments, the penalty associated with each identified one of the radio beams  50  has a value dependent on a determined severity of the period fading at the UE  12  for the identified one of the radio beams  50 . For example, the processing circuitry  76  calculates a fractional weight value as the penalty, in dependence on the severity of the periodic fading experienced by the UE  12  with respect to the associated beam(s)  50 . Here, “severity” denotes, for example, the extent to which the detected fading meets or exceeds one or more conditions that are known or expected to reduce communication throughput. Severity can be assessed, for example, in terms of the fading periodicity, where a shorter periodicity is more problematic, at least when the periodicity is in the range of the LA time constant or even shorter. Additionally, or alternatively, severity may be evaluated based on the measurement report(s) from the UE  12 , such as the magnitude of the loss in received-signal quality or strength during the periodic fading events. Additionally, or alternatively, the presence or severity of periodic facing may be detected or determined from Sounding Reference Signals (SRS) transmitted by the UE  12  and received by one or more TRPs  22 . 
     Another embodiment of the network node  18  also determines the penalty to be associated with a radio beam  50  in dependence on the severity of the periodic fading experienced at the UE  12  with respect to the beam  50 . Here, however, the penalty levels or values are quantized, meaning that there is a predefined set of penalty values. Different ones of the penalty values correspond to different levels or extents of “severity” regarding the periodic fading. 
     In the same or another embodiment, the penalty associated with each identified one of the radio beams  50  has a corresponding duration dependent on a determined severity of the periodic fading at the UE  12  for the identified one of the radio beams  50 . Additionally, or alternatively, the processing circuitry  76  is configured to make new penalty decisions for the UE  12  in recurring evaluation intervals. Additionally, or alternatively, for at least one of the identified ones of the radio beams  50 , the processing circuitry  76  is further configured to associate the penalty with each of one or more directionally-adjacent ones of the radio beams  50  in the set  52 . Such operations are an example of penalizing a related group of beams  50 , responsive to the UE  12  being affected by periodic fading on any one or more of the beams  50  in the related group. 
     In at least one embodiment, the processing circuitry  76  is configured to identify radio beams  50  affected by periodic fading at the UE  12  by determining whether radio-signal measurements reported by the UE  12  for respective ones of the radio beams  50  in the set  52  exhibit periodic fading with a fading periodicity above or in a range that corresponds to a LA time constant used by the one or more TRPs  22  in the network  10  that are associated with the radio beams  50  in the set  52 . As one example, the processing circuitry  76  evaluates RSRP measurements or other types of radio-signal measurements made by the UE  12  with respect to individual beams  50 , in one or multiple measurement reports by the UE  12 , to detect whether the UE  12  experiences periodic fading with respect to the individual beams  50 . To the extent that the network node  18  is remote from the TRP(s)  22  receiving the measurement report(s) from the UE  12 , the TRP(s)  22  may forward the measurement report(s) to the network node  18 , or forward information derived therefrom. 
     Where the network node  18  is remote from a TRP  22 , the TRP  22  performs the serving-beam selection procedure, and the processing circuitry  76  is configured to apply the penalties in the serving-beam selection procedure by sending signaling to the TRP  22 , to indicate the penalties and thereby cause the TRP  22  to perform the serving-beam selection procedure in dependence on the penalties. Where the network node  18  is co-located with the TRP  22 , the processing circuitry  76  is configured to apply the penalties in the serving-beam selection procedure by performing the serving-beam selection procedure in dependence on the penalties. In this latter case, the described functionality of the network node  18  can be considered as a subset of or a supplement to the overall set of functions performed by the TRP  22 , for operation as a TRP in the network  10 . 
       FIG.  8    illustrates a data structure  84 , depicted as a table for ease of understanding. The data structure  84  may include at least some information read from the configuration data  82  depicted in  FIG.  6    and the network node  18  may maintain separate instances of all or at least UE-specific parts of the data structure  84  for each UE  12  for which it is responsible for determining penalties to apply in corresponding beam-selection procedures for the UEs  12 . In an example scenario, a TRP  22  transmits a number of beams  50  to cover a corresponding overall coverage area, with each beam  50  having a designated direction and providing coverage for a corresponding portion of the overall coverage area. Here, there are N beams  50 ,  50 - 1  through  50 -N. 
     As seen, the data structure  84  may include a column (“EVAL?”) that indicates whether each particular one of the beams  50  should be evaluated for fading periodicity. For the involved UE  12 , the data structure  84  includes a column (“CANDIDATE”) that indicates whether each particular one of the beams  50  is a candidate for serving the UE  12 . Which beams  50  are candidates may change over time, so the data structure  84  can be understood as a “snapshot” of information used with respect to one or more particular evaluation cycles. 
     The data structure  84  also includes or links to a ranking column (“RAW RANKING”) that indicates the baseline ranking of the beams  50  that are candidates for serving the UE  12 . Here, “baseline” denotes the rankings without application of any determined penalties. Correspondingly, the data structure  84  includes a column (“PENALIZE?”) that indicates whether individual ones of the beams  50  that are candidates for serving the UE  12  should be penalized. The network node  18  determines whether any given beam  50  that is a candidate for serving a UE  12  should be penalized in the serving-beam selection procedure performed to select a serving beam  60  for the UE  12 . As explained above, the network node  18  makes the determination for each candidate beam  50  in dependence on whether the UE  12  experiences periodic fading with respect to each candidate beam  50 , or, in at least some embodiments, with respect to any candidate beam  50  that is related to the candidate beam  50 . 
     The data structure  84  further includes a column (“P. VALUE”) that indicates the determined penalties. In at least some embodiments, the network node  18  determines the life or duration of each penalty, e.g., so that the associated beam  50  is penalized only temporarily. In such embodiments, the data structure  84  includes a timer column (“P. TMR”) that indicates the duration of each determined penalty, e.g., by indicating one among a defined number of timers having different expiry periods. 
     A network node  18  that is remote from a TRP  22  “applies” the penalties determined for beams  50  that are going to be evaluated by the TRP  22  for selecting a serving beam  60  for a UE  12  by sending signaling that indicates at least those portions of the data structure  84  not already known to the TRP  22  for the current evaluation interval, e.g., the newly-determined penalty values, penalty durations, etc. 
       FIG.  9    illustrates yet another embodiment of the network node  18 , where the network node  18  may be regarded as a virtual machine implemented, for example, as computer processing units or functional modules that are configured to carry out the operations described herein. Nonetheless, the depicted units or modules involve physical processing and communication circuits. 
     In the example, the network node  18  includes (a) an identifying module  90  configured to identify radio beams  50  affected by periodic fading at a UE  12 , from among a set  52  of radio beams  50  that are candidates for serving the UE  12 , (b) an associating module  92  configured to associate a penalty with each identified one of the radio beams  50 , and (c) an applying module  94  configured to apply the penalties in a serving-beam selection procedure that is used to select one of the radio beams  50  for serving the UE  12 . The modules  90 ,  92 , and  94  may use configuration data  82  stored in the network node  18 , e.g., threshold values, etc. 
     Further, the modules  90 ,  92 , and  94  are operative to determine penalties, as needed, for each UE  12  that is served by a TRP  22  for which the network node  18  is responsible. And, as noted, the penalty determinations by the network node  18  for each UE  12  may be performed on an ongoing basis, e.g., newly determined in each recurring interval. The interval duration may be, e.g., on the order of a few milliseconds. 
     With respect to programmatic implementation of the functionality described for a network node  18  herein, in at least one embodiment, a non-transitory computer-readable medium stores computer program instructions that, when executed by a microprocessor or other processing circuit of a network node  18  in a wireless communication network  10 , configures the network node  18  to (a) identify radio beams  50  affected by periodic fading at a UE  12 , from among a set  52  of radio beams  50  that are candidates for serving the UE  12 , (b) associate a penalty with each identified one of the radio beams  50 , and (c) apply the penalties in a serving-beam selection procedure that is used to select one of the radio beams  50  for serving the UE  12 . 
     In related example details, the computer program instructions are stored as one or more computer programs (CPs)  80 , as seen in  FIG.  6   , with the storage  78  constituting one or more types of computer-readable media that provides storage of at least some persistence for the computer program instructions, e.g., in one or both of a long-term or non-volatile storage medium and a short-term or volatile medium, such as working computer memory used for program execution. In either case, the storage constitutes non-transitory storage of at least some minimum persistence, wherein the computer program instructions are held for execution or recall. 
       FIG.  10    illustrates an example method  1000  of operation by a network node  18 . The method  1000  may be carried out on a continuing or repeating basis, e.g., with respect to the described monitoring operations. In at least one embodiment, the processing circuitry  76  of the network node  18  comprises one or more microprocessors or other computer circuitry that is configured to carry out the method  1000  based on executing computer program instructions from one or more computer programs  80  held in the storage  78 . 
     Regardless of the implementation details, the method  1000  includes the network node  18  ( a ) identifying (Block  1002 ) radio beams  50  that are affected by periodic fading at a UE  12 , from among a set  52  of radio beams  50  that are candidates for serving the UE  12 , (b) associating (Block  1004 ) a penalty with each identified one of the radio beams  50 , and applying (Block  1006 ) the penalties in a serving-beam selection procedure that is used to select one of the radio beams  50  for serving the UE  12 . 
     Each radio beam  50  in the set  52  has a corresponding ranking determined in dependence on radio-signal measurement reports from the UE  12 , and applying  1006  the penalties in the serving-beam selection procedure comprises penalizing the corresponding ranking of each identified one of the radio beams  50  according to the associated penalty. The ranking of each beam  50  comprises a relative or absolute value that reflects how well a corresponding signal-strength or quality measure compares to like measures for the other beams  50  to be considered in the serving-beam selection procedure. 
     Unless doing so would exclude all of the radio beams  50  in the set  52  from selection consideration in the serving-beam selection procedure, in one or more embodiments of the method  1000 , the penalties associated with the identified ones of the radio beams  50  exclude the identified ones of the radio beams  50  from consideration in the serving-beam selection procedure. In such embodiments, the penalties serve as “do not consider” flags for the serving-beam selection procedure, meaning that penalized ones of the candidate beams  50  are not considered for selection. 
     In one or more other embodiments, associating (Block  1004 ) the penalty with each identified one of the radio beams  50  comprises determining a penalty value for each identified one of the radio beams  50  in dependence on a determined severity of the periodic fading at the UE  12  for each identified one of the radio beams  50 . In yet other embodiments, there is only one value of penalty—i.e., a beam  50  either is or is not penalized, but the penalized beams are still considered in the serving-beam selection procedure, although the penalization may change how they rank. 
     One or more embodiments of the method  1000  include determining a duration of the associated penalty in dependence on a determined severity of the periodic fading at the UE  12  for each identified one of the radio beams  50 . Further, as noted, the method  1000  in one or more embodiments is repeated in recurring evaluation intervals, such that new penalty decisions are made with respect to the UE  12  in each evaluation interval. 
     In at least one embodiment, associating (Block  1004 ) the penalty with each identified one of the radio beams  50  further comprises, for at least one of the identified ones of the radio beams  50 , associating the penalty with each of one or more directionally-adjacent ones of the radio beams  50  in the set  52 . As explained, two or more of the candidate beams  50  may be deemed to be related, e.g., each beam  50  may be considered as forming a related group of beams  50  with the directionally-adjacent beams  50 , or with only one of the adjacent beams  50 . 
     In at least one embodiment, identifying (Block  1002 ) radio beams  50  that are affected by periodic fading at the UE  12  comprises determining whether radio-signal measurements reported by the UE  12  for respective ones of the radio beams  50  in the set  52  exhibit periodic fading with a fading periodicity above or in a range that corresponds to a LA time constant used by the involved TRP(s)  22 . 
     In an embodiment where the network node  18  is remote from a TRP  22 , the TRP  22  performs a serving-beam selection procedure for a UE  12  served by the TRP  22 , and the network node  18  sends signaling to the TRP  22 , to indicate the penalties and thereby cause the TRP  22  to perform the serving-beam selection procedure in dependence on the penalties. Alternatively, in an embodiment where the network node  18  is co-located with the TRP  22 , applying (Block  1006 ) the penalties to the serving-beam selection procedure comprises the network node  18  performing the serving-beam selection procedure in dependence on the penalties. 
       FIG.  11    illustrates a method  1100  of operation by a network node  18  which can be understood as a variation of the method  1000 . The method  1100  includes (Block  1102 ) determining whether individual beams  50  in a set  52  of beams  50  are candidates for serving a UE  12  to satisfy a condition for penalization, and conditionally penalizing (Block  1104 ) individual ones or related groups of the beams  50 , in dependence on the determination. 
     Thus, in the context of the method  1100 , the network node  18  conditionally penalizes one or more candidate beams  50  in a set  52  of candidate beams  50  that, with respect to a TRP  22 , are candidates for serving a UE  12 . Each penalized candidate beam  50  is excluded from or disfavored in a serving-beam selection procedure used to select a serving beam  60  for the UE  12 , from among the set  52  of candidate beams  50 . The penalization of individual ones or related groups of the candidate beams  50  in the set  52  of candidate beams  50  is conditioned on determining whether the UE  12  experiences periodic fading with respect to the individual ones or related groups of the candidate beams  50  in the set  52  of candidate beams  50 . 
     Broadly, the technique(s) disclosed herein involve determining beam penalties for beams  50  for which a UE  12  experiences periodic fading, so that those beams  50  are deprecated in the context of a serving-beam selection procedure used to select a “best” one among a set  52  of beams  50  that are candidates for serving the UE  12 . For example, consider three beams  50 - 1 ,  50 - 2 , and  50 - 3 . Based only on signal-strength or quality measurements in an example scenario, the beam  50 - 2  has the highest strength or quality measurement and therefore is ranked “best” among the three beams  50 . The beam  50 - 1  has the next-highest strength or quality measurement and therefore is ranked “second best” among the three beams  50 , and the beam  50 - 3  is ranked last or least preferable. 
     However, upon determination that the UE  12  experiences periodic fading with respect to the beam  50 - 2 , e.g., fading that is detected as being periodic with at least a defined minimum amount of signal strength or quality loss during the fading events and with a fading periodicity that is relevant to the LA time constant(s) used by the involved TRP(s)  22 , a penalty is associated with the beam  50 - 2 . The penalty discounts the ranking of the beam  50 - 2 , e.g., it is a negative offset that is applied to the signal strength or quality measurement reported by the UE  12  for the beam  50 - 2 . By comparing the offset strength or quality of the beam  50 - 2  to the unadjusted signal strength or quality measurement reported by the UE  12  for the beams  50 - 1  and  50 - 3 , the overall ranking of the beams  50  may change, in dependence on how much better the beam  50 - 3  was in the original rankings and the degree or size of penalty applied. 
     An applicable scenario is where periodic fading significantly impacts the performance of LA being performed by a TRP  22  with respect to one or more UEs  12 . For example, problematic periodic fading may occur for UEs  12  moving towards or away from the TRP  22  at speeds of 50 km/h or greater. Of course, the critical speeds or speed ranges depend on a variety of factors and the TDD configuration in use at the TRP  22 . 
     For example, a TDD configuration that is downlink-heavy may cause poor LA performance for UEs  12  moving above a certain speed, while a TDD configuration that includes a better balance or distribution of uplink subframes may allow for good LA performance for the same speed or higher. A key recognition here is that a given LA time constant may result in LA that is too slow for the periodicity of channel variations being experienced by one or more of the involved UEs  12 . Here, the LA time constant may be understood as the convergence time of the LA, and when the LA time constant is on par with or longer than the time available until next fading dip between periodic fading events, the transmission parameters controlled by LA are driven to lower-performance values despite the existence of good channel conditions between the fading dips. 
     Consider an example case where a UE  12  performs RSRP measurements for CSI-RS transmitted in each of a plurality of beams  50  transmitted by a TRP  22 , and reports measurements for the N best ones of the beams  50 . Here, “N” is an integer, e.g., three, four, five, etc., and “best” means the highest values of measured RSRP. On a comparative scoring or ranking basis, the N beams  50  have an ordering corresponding to their respective RSRP measurements at the UE  12 . Of course, this ranking pertains to the particular UE  12 , in the sense that the measurements are made by the UE  12  and provide a basis for deciding which beam  50  from the TRP  22  is best for serving the UE  12 . 
     While the “raw” rankings reflect the underlying unadjusted evaluation measure for each of the beams  50 , e.g., the underlying RSRP measures or some value derived therefrom, serving-beam selection according to the network node  18  provides a more nuanced or intelligent approach by considering whether individual ones in a set  52  beams  50  that are candidates for serving a particular UE  12  are affected by periodic fading at the UE  12 . 
     In such approaches, the set  52  of beams  50  may be referred to as a “Grid of Beams” or “GoB” for short. In one or more embodiments, the network node  18  initializes its beam-penalty operations with respect to a particular UE  12  by associating a void penalty with each of the beams  50  in the GoB under consideration. Here, a “void” penalty is no penalty. As an example, the penalty type is an offset or adjustment factor expressed in dBs, applied as a reduction factor to the RSRP measurement reported by the UE  12  for each beam  50 . Referring to the reduction factor as a “BeamSpecificOffset”, the network node  18  initializes the BeamSpecificOffset associated with each beam  50  in the GoB to 0 dB, meaning no initial penalty. 
     Over one or more time periods, the network node  18  evaluates reported values of RSRP from the UE  12 , for each of the beams  50  in the GoB, and assesses the reported values to determine whether they are characteristic of periodic fading at the UE  12 . As an example, the network node  18  determines whether the reported values for each beam  50  indicate that the beam  50  is affected by periodic fading at the UE  12 . 
     Determining whether the beam  50  is affected by periodic fading at the UE  12  comprises, for example, one or more qualifying or conditioning operations. First, the network node  18  determines whether the RSRP or other radio-signal measurements made by the UE  12  for the beam  50  exhibits a periodic fading pattern, or whether SRS from the UE  12  exhibit a periodic fading patter, denoted as FadingPeriodicityPattern or simply FPP. Further, in one or more embodiments, the network node  18  further determines whether the periodicity of fading exhibited in the FPP is deemed to be problematic. 
     In an example implementation, the network node  18  deems the detected periodic fading to be problematic if the periodicity of the fading is in the range of or faster than the LA time constant used by the TRP  22  for performing LA for the radio connections supported via the beam  50 . As a non-limiting example, “in the range” of the LA time constant means that the period of the detected periodic fading is in the same order as the LA time constant. Periodic fading having that periodicity, or a faster periodicity, may be deemed to be problematic. Additionally, or alternatively, in the context of determining whether detected periodic fading is deemed to be problematic—i.e., warranting beam penalization—the network node  18  further evaluates one or more of: whether the severity of fading satisfies a threshold level of fading, such as measured in dB loss; and whether the periodic fading persists for longer than some defined interval Ti. 
     For each beam  50  that the network node  18  deems to be affected by periodic fading at the UE  12 , the network node associates a penalty with the beam  50  by changing the value of the corresponding BeamSpecificOffset from its initialized void value to a non-void value that imposes a penalty on the beam  50 , in terms of how the beam  50  ranks within the context of a serving-beam selection procedure to be performed for the UE  12  with respect to the GoB. For example, the network node  18  sets the BeamSpecificOffset to X dB, in a case where the beams  50  in the GoB are ranked for purposes of serving-beam selection according to corresponding per-beam RSRP measurements expressed in dB. In this context, X may be a fractional or integer value, e.g., −0.5 dB, or −1 dB. 
     Of course, the BeamSpecificOffset maintained for each beam  50  in the GoB need not be stored as a negative value—the point is that its value, as a penalty, is subtracted from, or applied as an offset to, the corresponding “raw” RSRP value reported for the beam  50 , to “penalize” the beam  50  with respect to consideration in the serving-beam selection procedure performed for the UE  12 . Notable points include that the “units” of measure used to express the BeamSpecificOffsets for each beam  50  in a GoB depend on the units of measure used to express the raw beam rankings or scores. For example, the beams  50  may be ranked in terms of Channel Quality Index (CQI) values comprising integer values reflecting quantized measures of channel quality. Corresponding BeamSpecificOffsets comprise, for example, integer values that deduct from the reported CQI values. 
     Other points of implementation flexibility involve determining the BeamSpecificOffsets or, more generally, the beam penalties, as weighted or proportionate values that reflect an assessment of the severity of periodic fading experienced at the UE  12  with respect to the individual beams  50  in the GoB. Weighted penalties can be but need not be continuous values. For example, the network node  18  may define a set of penalty values going from smallest penalty to largest penalty and decide which penalty value from the set to apply to a particular beam  50  in dependence on the severity of periodic fading experienced by the UE  12  for the beam  50 . Alternatively, the beam penalties may be defined or used as all-or-nothing penalties, meaning that a beam  50  in the GoB is, at least within the current evaluation period, either considered to be unpenalized or penalized, with penalized beams  50  being excluded from consideration in the serving-beam selection procedure. 
     Penalizing beams  50  in this manner can be understood as effectively zeroing or nulling the corresponding beam rankings. However, the network node  18  in one or more embodiments does not apply exclusionary penalties in scenarios where the exclusions would leave no beams  50  remaining for selection consideration. Further, even in embodiments that express penalties in 0 dB or other signal-related units of measure, the serving-beam selection procedure can be configured to exclude any beam  50  that has a non-void (non-zero) penalty associated with it. In a simplifying extension of that approach, the network node  18  may determine penalties as simple logical flags, where setting the flag for a beam  50  means that the beam  50  shall be treated as a penalized beam. Thus, in scenarios where the network node  18  is remote from a TRP  22  that performs the serving-beam selection procedure for a particular UE  12 , for a set  52  of beams  50  that are controlled by the TRP  22  and are candidates for serving the UE  12 , the network node  18  may send the penalties as computed values, e.g., penalties expressed in dBs, or may send the penalties as logical flags, e.g., a bitmap corresponding to the set  52  of beams  50 . Each position in the bitmap corresponds to a respective one of the beams  50  and the state of the bit in that position indicates whether the respective beam  50  is or is not penalized. 
     A further point of flexibility involves penalty persistence. Because reception conditions at the UE  12  are dynamic, the penalties associated with particular beams  50  in one evaluation cycle may or may not be appropriate at future times. Making new penalty decisions in recurring evaluation cycles, e.g., as often as the serving-beam selection procedure runs for the UE  12 , prevents the beam penalties from becoming stale or aged and accounts for the fact that the beams  50  that are candidates for serving the UE  12  at any particular time may change with respect to any particular previous or future time, e.g., as a function of mobility of the UE  12 . 
     Controlling penalty persistence in at least one embodiment involves using penalty timers. Upon associating a penalty with a beam  50 , with respect to a particular UE  12  that has the beam  50  as one of its candidates for serving-beam selection, the network node  18  starts a corresponding penalty timer, which may be a software-based timer running in the processing circuitry  76  of the network node  18 . 
     Penalty timers offer several points of advantage and flexibility. As one example, the penalty expires upon expiration of its associated penalty timer. By setting the expiry period of the penalty timers in relation to the period of the evaluation intervals used to make penalty decisions, penalties may be made to expire within the current evaluation interval and before the next evaluation interval. That arrangement provides the advantage of allowing longer intervals between making new penalty decisions while simultaneously preventing the penalty associated with any particular beam  50  from becoming stale. For example, upon expiry of its associated penalty timer, the corresponding penalty reverts back to its void value or state—i.e., no penalization of the involved beam  50  with respect to the involved UE  12 . 
     Further, rather than simply using penalty timers to control how long an associated penalty remains active or valid, the weight of the penalty may change with the running of the associated penalty timer, decreasing from an initial maximum penalty value down to a minimum penalty value or no penalty value. The weighting may be a continuous or stepped function of the remaining time in the expiry period. A further point of flexibility used in one or more embodiments is setting the expiry period of a penalty timer of a beam  50  in dependence on the periodic fading experienced at the involved UE  12  for the beam  50 . 
     With the above-detailed points of flexibility in mind, an example approach to determining per-beam penalties as BeamSpecificOffsets is as follows. For a beam  50  where rapid variations in time and large amplitude characterizes the FPP for the involved UE  12 , the network node  18  sets the BeamSpecificOffset for the beam  50  to X dB. Where rapid variations in time and small amplitude characterizes the FPP for the involved UE  12 , the network node  18  sets the BeamSpecificOffset for the beam  50  to Y dB, where Y&lt;X. Where slow variations in time and small amplitude characterizes the FPP for the involved UE  12 , the network node  18  sets the BeamSpecificOffset for the beam  50  to Z dB, where Z&lt;Y. 
     Similarly, an example approach to determining penalty timer is as follows. For a beam  50  where rapid variations in time and large amplitude characterizes the FPP for the involved UE  12 , the network node  18  sets the timer for the corresponding beam penalty, e.g., the BeamSpecificOffset for the beam  50 , to P milliseconds (ms). Where rapid variations in time and small amplitude characterizes the FPP for the involved UE  12 , the network node  18  sets the penalty timer to Q ms, where Q&lt;P. Where slow variations in time and small amplitude characterizes the FPP for the involved UE  12 , the network node  18  sets the penalty timer to R ms, where R&lt;Q. 
     In another example of controlling or defining penalty timers, the penalty timer used to time expiry of a beam penalty may be set in dependence on a detected or reported velocity of the involved UE  12 . Because beam penalties for a UE  12  moving at a high velocity are likely to become outdated more rapidly than beam penalties for a UE  12  that is stationary or moving at a low velocity, the penalty timers used for timing the expiry of beam penalties used for the serving-beam selection procedure for a particular UE  12  are, in one or more embodiments, determined in dependence on the speed and direction (velocity) of the UE  12 . Here, the term “low” and “high” are relative and may be defined by one or more thresholds. For example, UEs  12  that are detected or reported as having rates-of-travel below, say, 30 km/h, are considered to be low-velocity UEs, while UEs  12  that are detected or reported as having rates-of-travel above 30 km/h are considered to be high-velocity UEs. Of course, higher or lower rates-of-travel may be used to establish the thresholds, e.g., in dependence on the geography of the involved coverage areas, the type(s) of vehicular traffic in the involved coverage areas, etc. Further, more granularity may be used to define a set of timer expiry periods, with one in the set selected in dependence on the speed of the involved UE  12 . 
     Also as noted, the serving-beam selection procedure for a particular UE  12  may be performed periodically, e.g., every 10 ms. The network node  18  may determine penalties on the same time basis, in synchronization with the performance of the serving-beam selection procedure, so that the procedure has new or fresh penalty decisions each time it runs. The expiry period of the penalty timers may be set in view of how frequently new penalty decisions are made, meaning that penalties may expire before or in conjunction with the beginning of a new penalty-decision cycle. If the penalty-decision cycle is slower than the serving-beam selection cycle, the expiry period of the penalty timers to control whether the penalties determined in penalty-decision cycle remain active for longer than one serving-beam selection cycle. 
     Further refinements and extensions used in one or more embodiments of a network node  18  or its associated method of operation include considering beam groups where the beams  50  in the beam group exhibit similar FPP characteristics with respect to a UE  12 . Such a scenario might arise with respect to “adjacent” beams  50  in a millimeter wave (mmW) installation with a large number of beams  50 . That is, when a TRP  22  uses a large number of high-frequency beams  50  to cover a defined angular range, a beam  50  transmitted in the n-th direction may be considered to have as its adjacent beams, at least the beam  50  transmitted at the (n+1)-th direction and the beam  50  transmitted at the (n−1)-th direction. Put simply, a UE  12  may experience similar periodic fading with respect to each beam  50  in a group of beams  50  pointing in similar directions. Here, the beams  50  may be downlink radio beams used by a TRP  22  to transmit reference signals, such as CSI-RS, for use by the UE  12  in assessing beam qualities or preferences. 
     In such cases, the network node  18  in one or more embodiments may apply the same penalty to all beams  50  in the affiliated group of beams  50 . In a further alternative, the BeamSpecificOffsets or other type of beam penalty for a set of sufficiently “similar” beams  50  (e.g., adjacent beams) could be applied using a Gaussian filter or similar spatial smoothing, such that a defined penalty value is applied in smoothed manner over the group of beams  50 . 
     Notably, modifications and other embodiments of the disclosed invention(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention(s) is/are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.