BACKGROUND

A wireless communication system typically includes a number of access nodes that are configured to provide wireless coverage areas in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices (whether or not user operated), can operate. Further, each access node could be coupled with a core network that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the system could engage in air interface communication with an access node and could thereby communicate via the access node with various remote network entities or with other UEs served by the access node.

Such a system could operate in accordance with a particular radio access technology, with air-interface communications from the access nodes to UEs defining a downlink or forward link and air-interface communications from the UEs to the access nodes defining an uplink or reverse link.

Over the years, the industry has developed various generations of radio access technologies, in a continuous effort to increase available data rate and quality of service for end users. These generations have ranged from “1G,” which used simple analog frequency modulation to facilitate basic voice-call service, to “4G”—such as Long Term Evolution (LTE), which facilitates mobile broadband service using technologies such as orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO). And most recently, the industry is now exploring developments in “5G” and particularly “5G NR” (5G New Radio), which may use a scalable OFDM air interface, advanced channel coding, massive-MIMO, beamforming, and/or other features, to support higher data rates and countless applications, such as mission-critical services, enhanced mobile broadband, and massive Internet of Things (IoT).

In accordance with the radio access technology, each access node could be configured to provide service on one or more carrier frequencies or “carriers.” Each carrier could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), defining a single frequency channel multiplexed over time between downlink and uplink use. Further, each frequency channel of a carrier could occupy a particular frequency bandwidth defining a range of frequency at a particular position (e.g., defined by a center frequency or low-end and high-end frequencies) in radio-frequency spectrum.

On the downlink and uplink, each carrier could be structured to define various physical resources and channels for carrying information between the access nodes and UEs.

In an example configuration for instance, the air interface could be divided over time into frames, subframes, and symbol time segments, and the carrier bandwidth could be divided over frequency into subcarriers, so that the air interface would define an array of resource elements each occupying one subcarrier and one symbol time segment. With this example configuration, the resource elements could be grouped within each subframe to define physical resource blocks (PRBs) in which the subcarriers can be modulated to carry data.

Further, certain resource elements or PRBs could be reserved for use to carry particular types of data, such as control signaling and/or user-plane communications.

For instance, in each downlink subframe, the resource elements in the first symbol time segments could be generally reserved to define a control region for carrying control signaling such as PRB-scheduling directives from the access node to UEs, and the resource elements in the remaining symbol time segments could be generally reserved to define a downlink shared traffic channel in which PRBs could be used to carry data from the access node to UEs. Further, other resource elements could be reserved for other purposes. For instance, resource elements distributed throughout each downlink subframe could be reserved to carry a reference signal from the access node that UEs could measure as a basis to gauge coverage strength.

And in each uplink subframe, certain PRBs at the low-frequency end of the carrier bandwidth and at the high-frequency end of the carrier bandwidth could be generally reserved to define a control region for carrying control signaling such as uplink scheduling requests from UEs to the access node, and other PRBs could be generally reserved to define an uplink shared channel in which PRBs could be used to carry data from UEs to the access node.

OVERVIEW

When a UE enters into coverage of an access node under in an example system, the UE could discover threshold strong coverage on one of the access node's carriers, and the UE could then responsively engage in signaling to connect with the access node on that carrier, such as to establish a Radio Resource Control (RRC) connection. Further, a core-network controller could then coordinate setup or transfer of one or more user-plane bearers defining virtual packet tunnels for carrying user-plane data communications between the UE and a core-network gateway system that provides connectivity with a transport network such as the Internet. Each such bearer could include a data-radio bearer (DRB) tunnel that extends over the air between the UE and then access node and an access-bearer that extends within the core network between the access node and the gateway system.

Once the UE is so connected and has one or more established bearers, the access node could then serve the UE on the carrier, scheduling use of the carrier's PRBs as needed to carry communications to or from the UE.

For instance, when packet-data arrives at the access node for transmission to the UE, the access node could schedule use of certain downlink PRBs in subframe to carry a transport-block of that data to the UE, the access node could transmit to the UE in the control region of that subframe a scheduling directive (e.g., a Downlink Control Information (DCI) message) that specifies the PRBs that will carry the data, and the access node could transmit the data to the UE in those PRBs. And when the UE has packet-data to transmit to the access node, the UE could transmit to the access node a scheduling request including a buffer status report (BSR) indicating the quantity of data to be transmitted, the access node could schedule use of certain uplink PRBs in an upcoming subframe to carry a transport-block of that data from the UE and could transmit to the UE an advanced scheduling directive that specifies those PRBs, and the UE could then transmit the data to the access node in those PRBs.

For such scheduled downlink or uplink communication on PRBs, the access node and UE could use a modulation and coding scheme (MCS) that is selected based on the UE's wireless channel quality, which the access node could specify in its scheduling directive to the UE. In a representative implementation, the MCS could define a coding rate based on the extent of error-correction coding data or the like that would be transmitted together with the user-plane data being communicated, and a modulation scheme that establishes how many bits of data could be carried by each resource element. When channel quality is better, the access node may direct use of a higher-order MCS that has a higher coding rate (e.g., with more error-correction coding) and/or hat supports more bits per resource element, and when channel quality is worse, the access node may direct use of a lower-order MCS that may have a lower coding rate and/or supports fewer bits per resource element.

In practice, the access node could determine the MCS to be used use in a given instance based on wireless channel quality reported by the UE.

For instance, as the access node serves the UE, the UE could transmit channel quality reports to the access node periodically and/or as part of the UE's scheduling requests or other communications to the access node, with each report including a channel-quality indicator (CQI) value representing the UE's determined channel quality and perhaps one or more other channel metrics such as downlink reference signal receive power (RSRP), signal-to-noise-plus interference ratio (SINR), or the like. When the access node schedules communications to or from the UE, the access node could then map the UE's latest reported CQI value to a corresponding MCS value using a standard CQI-MCS mapping table, and the access node could direct use of that MCS in the scheduling directive that the access node sends to the UE. Communication could thus occur using that directed MCS.

In addition, for uplink communication, the access node might also base the determination of MCS on an evaluation of the UE's uplink transmission power, namely, the extent to which the UE is transmitting with sufficient power.

As the access node serves the UE, for instance, the access node and UE may engage in an uplink power-control process through which the access node directs the UE incrementally increase or decrease its transmission power in an effort to keep the uplink receive power at a desired level. But the UE may be limited to a maximum transmission power level. Therefore, the UE may have a level of power-headroom that defines the difference between (i) the transmission power that the UE should be using based on the power control process and (ii) the UE's maximum transmission power. A positive power-headroom value would mean that the UE has transmission power to spare and can increase its transmission power more if directed to do so, whereas a zero or negative power-headroom value would mean that the UE has already reached its maximum transmission power level and may be unable to transmit with sufficient power.

When the UE sends a scheduling request to the access node, the UE could include in the scheduling request a power-headroom report (PHR) indicating the UE's current power headroom. And the access node could use that reported power headroom as a basis to set or adjust the MCS that the access node will direct the UE to use for uplink transmission. If the power headroom is negative, for instance, the access node might artificially reduce the MCS-order from the MCS indicated by the UE's channel quality report. Use of a lower-order MCS might be more robust and better able to facilitate successful uplink communication with constrained uplink transmission power.

In practice, the uplink bandwidth of the carrier on which an access node serves a UE could pose an effective limit on the peak rate of data transmission from the UE to the access node, as the uplink bandwidth would contain only a limited number of PRBs per subframe or other transmission time interval (TTI), with the data rate per PRB being further limited based on the MCS set as discussed above for instance, and with the number of allocated PRBs being limited based on how many other UEs the access node is concurrently serving on that uplink channel.

One way to help overcome this uplink data rate limitation is to have the access node serve the UE with uplink carrier aggregation, by serving the UE on uplink channels of multiple carriers concurrently. To provide uplink carrier-aggregation service for the UE, the access node could add one or more additional carriers to the UE's connection with the access node, and the access node could then schedule uplink communication from the UE to occur concurrently on the uplink channels of the multiple carriers, with the UE transmitting some data on one or more PRBs of one carrier's uplink channel concurrently with transmitting other data on one or more PRBs of another carrier's uplink channel.

In a representative uplink carrier-aggregation scenario, the UE would be served on two carriers at once (as a “2CA” arrangement), with one carrier being deemed a primary carrier or primary cell (PCell) and the other being deemed a secondary carrier or secondary cell (SCell). The PCell could function as the anchor for certain control signaling related to the carrier-aggregation service, such as for scheduling requests and scheduling directives, and the SCell could function generally to supplement the UE's uplink bandwidth so as to help provide the UE with increased peak uplink data rate.

One technical problem that can occur with uplink carrier aggregation, however, is that the UE's limited uplink transmission power may strain the UE's ability to transmit concurrently on the uplink channels of the multiple component carriers. When the UE transmits concurrently on PRBs of multiple uplink channels, the UE may need to distribute its transmission power across those uplink channels, and so the UE's per-PRB transmission power may be relatively low. This could be especially problematic in a scenario where the UE has reached its maximum transmission power and is strained to transmit with sufficient power in the first place.

To help address this problem, the access node could apply an uplink-SCell-deconfiguration process by which, when the UE's reported channel quality becomes threshold low, the access node would automatically release the UE's SCell—possibly transitioning the UE from uplink-carrier-aggregation service to service on a single uplink channel. In particular, the access node could regularly evaluate the UE's reported channel quality (e.g., RSRP or CQI) as to the SCell specifically or cooperatively as to the multiple carriers on which the UE is served, and when the channel quality becomes at least as low as a threshold level, UL-SCell-Deconfig, the access node could drop the UE's uplink SCell from the UE's connection, so as to help alleviate the UE's uplink power distribution problem.

Unfortunately, however, a further technical problem with this process is that the access node may be preconfigured to apply a fixed UL-SCell-deconfig threshold that may not be optimal.

In practice, certain operational circumstances may benefit from the access node applying of a higher or lower UL-SCell-deconfig threshold.

By way of example, the type of communication in which the UE is engaged may justify application of a higher or lower UL-SCell-deconfig threshold. For instance, if the UE is engaged in relatively heavy uplink communication such as uplink video streaming, it may be useful to apply a lower UL-SCell-deconfig threshold in order to help maintain the UE's SCell longer (requiring worse reported channel quality before releasing the UE's uplink SCell) so that the UE could benefit more from the increased uplink peak data rate provided by the SCell. Whereas, if the UE is engaged in relatively light uplink communication such as web browsing traffic, it may be useful to apply a higher UL-SCell-deconfig threshold, to more readily release the UE's SCell so as to more readily address the uplink-power-distribution problem noted above.

As another example, the UE's maximum transmission power level may justify application of a higher or lower UL-SCell-deconfig threshold. A UE's maximum transmission power may be indicated by the UE's power class. For instance, a standard-power UE may have a maximum transmission power of 23 dBm, whereas a high-power UE may have a maximum transmission power of 26 dBm. If a UE has a lower maximum transmission power level, then it may be useful to apply a higher UL-SCell-deconfig threshold, since the UE may be more susceptible to the uplink-power-distribution problem noted above. Whereas, if a UE has a higher maximum transmission power level, then it may be useful to apply a lower UL-SCell-deconfig threshold, since the UE may be less susceptible to the uplink-power-distribution problem.

Further, a preconfigured UL-SCell-deconfig threshold may not be optimal in terms of the access node's uplink spectral efficiency. Uplink spectral efficiency of the access node is a measure of the quantity of data that the access node's uplink could carry per unit of frequency spectrum per unit time, possibly measured as a quantity of bits per Hertz per second across the multiple uplink carrier channels on which the access node is configured to operate. If the access node is configured to apply an UL-SCell-deconfig threshold that is too low, then the access node's served UEs may more often end up using a reduced-order MCS, and the access node may therefore generally have undesirably low spectral efficiency. If the access node's spectral efficiency is too low, then a provider of the access node may be compelled to add additional uplink spectrum to the access node, which may be expensive and therefore undesirable.

Disclosed herein is a technical solution to help address these problems. In accordance with the disclosure, an access node will dynamically vary the UL-SCell-deconfig threshold that the access node applies, with the dynamic varying being based upon operational circumstances and/or an evaluation of the access node's spectral efficiency.

In one respect, the access node could dynamically vary the UL-SCell-deconfig threshold that the access node applies, with the dynamic varying being based on operational circumstances such as the type of communication in which the UE is engaged and/or based on the UE's power class.

For example, the access node could determine if the UE is engaged in relatively heavy uplink communication or rather relatively light uplink communication, and the access node could select an UL-SCell-deconfig threshold based on that determination and could apply the selected UL-SCell-deconfig threshold to control whether and when to release an SCell from the UE's connection. If the UE is engaged in relatively heavy uplink communication rather than relatively light uplink communication, then the access node could select and apply a first UL-SCell-deconfig threshold rather than a second UL-SCell-deconfig threshold based on the first UL-SCell deconfig threshold being lower than the second UL-SCell-deconfig threshold. Whereas, if the UE is engaged in relatively light uplink communication rather than relatively heavy uplink communication, then the access node could select and apply the second UL-SCell-deconfig threshold rather than the first UL-SCell-deconfig threshold based on the second UL-SCell deconfig threshold being higher than the second UL-SCell-deconfig threshold.

Alternatively, the access node might generally be set to apply a default UL-SCell-deconfig threshold and may dynamically switch to apply an UL-SCell-deconfig threshold that is lower or higher than the default UL-SCell-deconfig threshold based on a determination of the type of communication in which the UE is engaged. For instance, if the UE is engaged in relatively heavy uplink communication, then the access node may responsively switch to apply an UL-SCell-deconfig threshold that is lower than the default UL-SCell-deconfig threshold. Whereas, if the UE is engaged in relatively light uplink communication, then the access node may responsively switch to apply an UL-SCell-deconfig threshold that is higher than the default UL-SCell-deconfig threshold.

As another example, the access node could determine the UE's power class, and the access node could select an UL-SCell-deconfig threshold based on the determined UE power class and could apply the selected UL-SCell-deconfig threshold to control whether and when to release an SCell from the UE's connection. If the UE is a high-power UE rather than a standard-power UE, then the access node could select and apply a first UL-SCell-deconfig threshold rather than a second UL-SCell-deconfig threshold based on the first UL-SCell deconfig threshold being lower than the second UL-SCell-deconfig threshold. Whereas, if the UE is a standard-power UE rather than a high-power UE, then the access node could select and apply the second UL-SCell-deconfig threshold rather than the first UL-SCell-deconfig threshold based on the second UL-SCell deconfig threshold being higher than the second UL-SCell-deconfig threshold.

Alternatively or additionally, the access node might generally be set to apply a default UL-SCell-deconfig threshold and may dynamically switch to apply an UL-SCell-deconfig threshold that is lower or higher than the default UL-SCell-deconfig threshold based on a determination of the UE's power class. For instance, if the UE is a high-power UE, then the access node may responsively switch to apply an UL-SCell-deconfig threshold that is lower than the default UL-SCell-deconfig threshold. Whereas, if the UE is a standard-power UE, then the access node may responsively switch to apply an UL-SCell-deconfig threshold that is higher than the default UL-SCell-deconfig threshold.

Further, in another respect, the access node could dynamically vary the UL-SCell-deconfig threshold that the access node applies, with the dynamic varying being based on an evaluation of the access node's uplink spectral efficiency. Here, for instance, the access node could be configured with an uplink-spectral-efficiency set point that defines an optimal desired level of uplink spectral efficiency. Further, the access node could be set with an initial UL-SCell-deconfig threshold to apply generally (e.g., as a default UL-SCell-deconfig threshold for use when serving UEs). And the access node could then regularly evaluate its actual uplink spectral efficiency and could dynamically adjust the UL-SCell-deconfig threshold, or select an UL-SCell-deconfig threshold to apply, based on the current level of its uplink spectral efficiency.

With this implementation, the access node could measure its uplink spectral efficiency over a sliding window of time, generally across the multiple carriers on which the access node is configured to operate. And the access node could regularly compare its latest measure of uplink spectral efficiency with its uplink-spectral-efficiency set point.

If and when the access node thereby determines that its uplink spectral efficiency is less than its uplink-spectral-efficiency set point, the access node could responsively increase its UL-SCell-deconfig threshold or select a higher UL-SCell-deconfig threshold to apply. The access node could then apply the increased UL-SCell-deconfig threshold, which may result in the access node more readily releasing UEs' SCells and may thereby help reduce the extent to which UEs will face the MC S-reduction noted above. Reducing the extent of MCS reduction may in turn help increase the access node's uplink spectral efficiency, approaching the uplink-spectral-efficiency set point.

Whereas, if and when the access node thereby determines that its uplink spectral efficiency is greater than its uplink-spectral-efficiency set point, the access node could responsively decrease its UL-SCell-deconfig threshold or select a lower UL-SCell-deconfig threshold to apply. The access node could then apply the decreased UL-SCell-deconfig threshold, which may result in the access node less readily releasing UEs' SCells and may thereby increase the extent to which UEs will face the MCS-reduction noted above. Increasing the extent of MCS reduction may in turn help decrease the access node's uplink spectral efficiency, likewise approaching the uplink-spectral-efficiency set point.

These as well as other aspects, advantages, and alternatives will become additionally apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. Further, it should be understood that the descriptions provided in this overview and below are intended to illustrate the invention by way of example only and not by way of limitation.

