TECHNICAL FIELD

The invention relates generally to power control in wireless communication networks and, more particularly, to methods and apparatus for uplink power control in wireless communication networks.

BACKGROUND

Long Term Evolution (LTE) employs power control in the uplink (UL) to ensure that the UL signals from the wireless device are received with sufficient power at the base station to enable the base station to demodulate the receive signals with a desired low error rate. At the same time, the power of the UL signal should not be unnecessarily high as to cause unnecessary interference with other signals and to consume battery power at the wireless device.

LTE uses a combination of open loop and closed loop power control to control the transmit power of wireless devices. The open loop control mechanism is implemented by the wireless device. The wireless device measures the downlink (DL) path loss and adjusts its transmit power responsive to variations in the DL path loss. The closed loop power control mechanism is controlled by the base station. The base station detects changes in the received signal power of UL signals transmitted by the wireless device and directly adjusts the UL transmit power of the wireless device by sending explicit transmit power control commands to the wireless device.

The UL power control mechanism specified by the LTE standard does not provide the wireless device information about the UL channel quality, and the interaction between the base station and the wireless device is limited. Because the wireless device lacks information about the UL channel quality, it uses the DL path loss in its transmit power calculations. However, the DL path loss may not be the same as the UL path loss. Thus, the UL path loss is not effectively compensated in actual Physical Uplink Shared Channel (PUSCH) transmissions. Also, the open loop and closed loop control mechanisms used in conventional LTE systems may independently adjust the wireless device transmit power to compensate for the same cause, resulting in an over-adjustment of the UL transmit power. Also, when deep fading is detected, the base station has to rely on the slow closed loop mechanism to adjust the UL transmit power of the wireless device instead of direct setting, which can result in long delays in transmit power adjustment. Such delays can make it impossible for the base station to react to fast fading conditions.

Another problem with the current UL power control mechanism is that the base station's estimates of the UL path loss, which are used for resource allocation and link adaptation, are based on power headroom reports from the wireless device. Under the current standards, the wireless device sends the power headroom reports responsive to two conditions: (1) when the change in the DL path loss exceeds a threshold; and (2) responsive to the expiration of a predetermined timer. Due to the mismatch between the UL and DL path loss, the UL path loss may change beyond the threshold for triggering the power headroom report, while the DL path loss is still below the threshold. In this case, the wireless device will not report the power headroom in the next UL transmission even if the wireless device has changed its transmit power.

Consequently, the base station will continue to use the "old" power headroom to estimate the UL path loss resulting in larger estimation errors of the UL path loss.

Accordingly, there is a need for a more efficient UL power control mechanism that provides the wireless device with a better overall view of the UL channel conditions.

Additionally, it would be desirable to provide the base station with greater control over the wireless device UL transmit power.

SUMMARY

The present disclosure provides a new mechanism for UL power control that resolves some of the problems in the prior art methods. According to one aspect of the present disclosure, the base station measures the UL path loss and reports the UL path loss to the wireless device. The wireless device can then use the reported UL path loss rather than the DL path loss in its transmit power calculations, thus avoiding problems caused by the mismatch between UL and DL path loss.

According to a second aspect of the disclosure, a mechanism is provided to allow the base station to trigger a power headroom report from the wireless device so that the estimates of UL path loss more accurately reflect the actual UL channel conditions. The wireless device is configured to send a power headroom report responsive to receipt of the UL path loss from the base station. Thus, the base station may trigger a power headroom report from the wireless device by sending its current estimate of the UL path loss.

A third aspect of the disclosure provides a mechanism for fast adjustment of the UL transmit power. When the base station needs to adjust the baseline power level of a wireless device, the base station can add an adjustment factor to the reported UL path loss. Because the UL path loss is used by the wireless device to calculate its transmit power, adding an adjustment factor to the reported UL path loss allows large step changes in the UL transmit power responsive to deep fading.

According to a fourth aspect of the disclosure, a closed loop power control mechanism is modified to avoid the over-adjustment problem caused by the independent closed loop and open loop control mechanisms. In embodiments of the disclosure, the wireless device is configured to reset the accumulated power adjustment based on Transmit Power Control (TPC) commands, which is used to calculate the UL transmit power, to a pre-determined value (e.g., 0) responsive to receiving the UL path loss from the base station. Consequently, any previous over-adjustment caused by the TPC commands is immediately corrected when the wireless device receives the UL path loss.

Exemplary embodiments of the disclosure comprise methods of uplink power control implemented by a wireless device in a wireless communication network. One method comprises: receiving, from a base station, signaling on a downlink channel indicating an uplink path loss reported by the base station; and adjusting an uplink transmit power of the wireless device based on the reported uplink path loss.

Other embodiments of the disclosure comprise a wireless device in a wireless communication network configured to perform the above-described wireless device method. One embodiment of the wireless device comprises an interface circuit for transmitting signals to and receiving signals from a base station in the wireless communication network, and a processing circuit. The processing circuit is configured to: receive, from a base station, signaling on a downlink channel indicating an uplink path loss reported by the base station; and adjust an uplink transmit power of the wireless device based on the reported uplink path loss.

Other embodiments of the disclosure comprise a wireless device in a wireless communication network, wherein the wireless device is configured to: receive, from a base station, signaling on a downlink channel indicating an uplink path loss reported by the base station; and adjust an uplink transmit power of the wireless device based on the reported uplink path loss.

Other embodiments of the disclosure comprise a computer program comprising executable instructions that, when executed by a processing circuit in a wireless device of a wireless communication network, causes the wireless device to perform any one of the wireless device methods described above.

Other embodiments of the disclosure comprise a carrier containing a computer program as described above, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Other embodiments of the disclosure comprise a non-transitory wireless device computer-readable storage medium containing a computer program comprising executable instructions that, when executed by a processing circuit in a wireless device in a wireless communication network causes the wireless device to perform any one of the methods as described above.

Still other embodiments of the disclosure comprise a method of uplink power control implemented by a base station in a wireless communication network. One embodiment of base station the method comprises: estimating an uplink path loss associated with an uplink channel between a wireless device and the base station; and controlling an uplink transmit power of the wireless device by signaling a reported uplink path loss to the wireless device, the reported uplink path loss computed based on the estimated uplink path loss. Still other embodiments of the disclosure comprise a base station in a wireless communication network configured to perform the above-described base station method. One embodiment of the base station comprises: an interface circuit for communicating with a wireless device; and a processing circuit configured to: estimate an uplink path loss associated with an uplink channel between a wireless device and the base station; and control an uplink transmit power of the wireless device by signaling a reported uplink path loss to the wireless device, the reported uplink path loss computed based on the estimated uplink path loss.

Some embodiments of the disclosure comprise a base station in a wireless

communication network, wherein the base station is configured to: estimate an uplink path loss associated with an uplink channel between a wireless device and the base station; and control an uplink transmit power of the wireless device by signaling a reported uplink path loss to the wireless device, the reported uplink path loss computed based on the estimated uplink path loss.

Other embodiments of the disclosure comprise a computer program comprising executable instructions that, when executed by a processing circuit in a base station of a wireless communication network, causes the base station to perform any one of the base station methods described above.

Other embodiments of the disclosure comprise a carrier containing a computer program as described above, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Other embodiments of the disclosure comprise a non-transitory computer-readable storage medium containing a computer program comprising executable instructions that, when executed by a processing circuit in a base station in a wireless communication network causes the base station to perform any one of the base station methods described above.

Another embodiment of the disclosure comprises a wireless device in a wireless communication network, said wireless device comprising: an interface circuit for transmitting signals to and receiving signals from a base station in the wireless communication network; a processing circuit, and a power supply circuitry configured to supply power to said wireless device, wherein the processing circuit is configured to: receive, from a base station, signaling on a downlink channel indicating an uplink path loss reported by the base station; and adjust an uplink transmit power of the wireless device based on the reported uplink path loss; and

Another embodiment of the disclosure comprises a wireless device in a wireless communication network, said wireless device comprising: processing circuitry and memory connected to the processing circuitry, the memory containing instructions that, when executed, cause the wireless device to: receive, from a base station, signaling on a downlink channel indicating an uplink path loss reported by the base station; and adjust an uplink transmit power of the wireless device based on the reported uplink path loss. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates communications between a base station and a wireless device in a wireless communication network.

Figure 2 illustrates frequency division duplex mode in Band4.

Figure 3 illustrates path loss difference between UL and DL in time division duplex mode.

Figure 4 illustrates change in the device specific baseline power setting using closed loop power control.

Figure 5 illustrates an exemplary UL power control mechanism according to one embodiment.

Figure 6 illustrates using Power Headroom report from the wireless device as an explicit acknowledgement of the UL path loss.

Figure 7 illustrates change in the device specific baseline power setting by adding an adjustment factor to the UL path loss.

Figure 8 illustrates the splitting of the UL power control procedure into multiple power control segments.

Figure 9 illustrates an exemplary message format for signaling UL path loss to a wireless device.

Figure 10 illustrates an exemplary UL power control method implemented by a base station.

Figure 1 1 illustrates an exemplary UL power control method implemented by a wireless device.

Figure 12 illustrates an exemplary wireless device.

Figure 13 illustrates an exemplary base station.

DETAILED DESCRIPTION

Referring now to the drawings, an exemplary embodiment of the present disclosure will be described in the context of a LTE network. Those skilled in the art will appreciate that the power control techniques described herein are more generally applicable to any wireless communication network that uses UL power control. The UL power control techniques herein described can be easily modified by those skilled in the art for use in Fifth Generation (5G) networks, Next Radio (NR) networks, or other wireless communication networks using UL power control.

Figure 1 illustrates communications between a base station 300 and a wireless device 200 in a wireless communication network 10. The base station 300 transmits control information to the wireless device 200 on the Physical Downlink Control Channel (PDCCH), and user data to the wireless device 200 on the Physical Downlink Shared Channel (PDSCH). The wireless device 200 transmits control information to the base station 300 on the Physical Uplink Control Channel (PUCCH), and user data to the base station 300 on the PUSCH. The base station 300 is responsible for scheduling UL transmissions from the wireless device 200 and for allocating resources for the UL transmissions. After scheduling an UL transmission and allocating resources, the base station 300 sends a scheduling grant (SG) to the wireless device 200 indicating the resources on which the wireless device 200 has been scheduled and the transmission format for the scheduled transmission. The SG is sent to the wireless device 200 on the PDCCH. After receiving the SG, the wireless device 200 determines the UL transmit power for the transmission and transmits data to the base station 300 on the PUSCH resources indicated in the SG.

LTE uses a combination of open loop and closed loop power control to determine the UL transmit power of the wireless device 200. The open loop control mechanism is implemented by the wireless device 200. The wireless device 200 measures the DL path loss and adjusts its transmit power responsive to variations in the DL path loss. The open loop control mechanism is based on the assumption that the DL path loss mirrors the UL path loss, which is not true in many circumstances.

The closed loop power control mechanism is controlled by the base station 300. The base station 300 detects changes in the received signal power of signals transmitted by the wireless device 200 in the UL and directly adjusts the UL transmit power of the wireless device 200 by means of explicit transmit power control (TPC) commands.

The power control for the PUSCH in LTE is described in the following equation:

where

P _{PUSCH c} (z) is the UL transmit power calculated by the wireless device 200;

CMAX, ( ' ^s the configured maximum transmit power of the wireless device 200 in subframe i for serving cell c;

P _{USCH c} (z) is the bandwidth of the PUSCH resource assignment expressed in number of resource blocks (RBs) valid for subframe / ^' and serving cell c;

P ₀ pusc _H ,c(i) is the cell-specific baseline power level indicating the expected received power spectral density (PSD) of the UL transmissions at the base station 300;

PL _C is the DL path loss in dBs estimated by the wireless device 200 for serving cell c ; A _TFtC (/) = 10 log ₁₀ ( ( 2 ^BPRE - ^K> - 1) · ?™ ) for K _S = 1.25 and 0 for K _s = 0 where K _s is given by the parameter deltaMCS-Enabled as part of system information (SI) for each serving cell c ;

a _c (j) is a weighting coefficient between 0 and 1 to be applied to the DL path loss; and PC _C (z) is the accumulated power adjustment based on TPC commands from the base station 300.

From Equation 1 , it can be seen that the UL transmit power for the wireless device 200 on each Physical Resource Block (PRB) is determined primarily by three factors: the baseline power level P ₀ PUSCHP O) . the DL loss PL _C , and the accumulated power adjustment TPC _c (i) . The baseline power level P ₀ PUSCHP ) is ^a cell-specific parameter that is broadcast as part of the SI. All wireless devices 200 in the same cell share the same P ₀ PUSCHP O) value. In contrast, the DL path loss PL _C and accumulated power adjustment TPC _c (i) are device-specific and vary in each transmission time interval (TTI). The DL path loss is the wireless device's 200 own independent estimate of DL channel fading based on measurement of cell reference signals, which the base station 300 has no knowledge of. The accumulated power adjustment TPC _c (i) is based on the received TPC commands from the base station 300.

Ideally, the baseline power level p _{0 PU} scH _p ) would take the noise and interference levels into account and thus vary in time with the noise and interference levels. However, different wireless devices 200 will experience different levels of interference. Also, it is not feasible in practice to vary the baseline power level p ₀ PUSCHP ) . which is transmitted as part of system information.

To compensate for device specific variations in noise and interference levels, the base station 300 transmits explicit TPC commands to the wireless device 200 to adjust the baseline power level of the wireless device 200 as the instantaneous interference changes. The TPC commands are used to adjust the accumulated power adjustment term, TPC _c (i) , in Equation 1 . The TPC commands are accumulative, meaning that each TPC command increases or decreases TPC _c (i) by a certain amount.

The wireless device 200 calculates the transmit power for the PUSCH transmissions using Equation 1 above. The base station 300, however, has no knowledge of the UL transmit power used by the wireless device 200, which is used for link adaptation and resource allocation. The existing LTE standard defines a MAC (Medium Access Control) Control Element (MCE), called the Power Headroom MCE, which can be used by the base station 300 to determine the UL transmit power. Power headroom is the difference between the maximum transmit power of the wireless device 200 and its current UL transmit power calculated based on Equation 1 . Because the maximum transmit power of the wireless device 200 is known to the base station 300, the base station 300 can use the reported power headroom to determine the UL transmit power of the wireless device 200. However, the Power Headroom MCE is not included in every UL transmission. Rather, the Power Headroom MCE is transmitted only when the fluctuation in the DL path loss exceeds a pre-determined threshold (event driven), or when a pre-defined timer expires (time driven). When the Power Headroom MCE is triggered by a predetermined event, or by expiration of a timer, the wireless device 200 will piggy-back the Power Headroom MCE in the next PUSCH transmission.

The final UL transmit power of the wireless device 200 on the PUSCH is a result of independent decisions made by both the wireless device 200 and the base station 300.

However neither the wireless device 200 nor the base station 300 has knowledge of the other's behavior, so that both the wireless device 200 and the base station 300 have to make decisions independently based on their respective estimations of the UL channel conditions. The independent decision-making by the wireless device 200 and base station 300 may result in several problems.

One problem is that the closed loop power control mechanism performed by the wireless device 200 is based on DL path loss rather than the UL path loss. Because channel fading in the UL will deteriorate signal strength, the wireless device 200 must increase its UL transmit power to compensate for the UL loss. However, the UL path loss can only be measured by the base station 300, which is on the receiving end of the transmission. In the current solution, the wireless device 200 uses the DL path loss in place of the UL path loss when it computes its UL transmit power. This approach is based on the assumption that the DL path loss is equal to the UL path loss. However, this assumption is typically not true under many operating conditions, especially when Frequency Division Duplexing (FDD) is used.

The wireless device 200 estimates the DL path loss according to the following formula:

Where r is the distance between the base station 300 and wireless device 200, c is the speed of light, and f _c is the carrier frequency. From Equation 2, it can be seen that the path loss varies depending on frequency. When FDD mode is used, the difference in path loss between an UL frequency f _UL and a DL frequency f _DL car be calculated according to the following equation:

PL 'D, L DL 1 + L D-U

(3)

PL ',UL UL UL where f _D is the frequency spacing between DL and UL, f _DL is the frequency in the DL, f _UL is frequency in UL.

Figure 2 illustrates the FDD mode in the widely used Band4. In this example, the UL frequency f _UL is in the range of 1710-1755 MHz and the DL frequency f _DL is between 21 10 and 2155 MHz with 400 MHz duplex spacing. In this case, the path loss difference between DL and UL is in the range of 1 .78dB- 1 .82 dB, almost a 50% difference.

Even in Time Division Duplexing (TDD) mode, where the same frequency is used for both UL and DL transmissions, the mismatch between UL and DL path loss may still exist. Referring to Figure 3, the base station 300 may perform beamforming on the DL based on the measurement of the main beam angle of arrival (AoA) of the corresponding UL signal.

However, the wireless device 200 typically does not perform beamforming for UL transmissions due to fewer antennas and implementation complexity. Consequently, it is likely that the UL signal traverses a different path than the DL signal, resulting in different path losses.

A second problem with the existing UL power control mechanism is that the baseline power level P ₀ PUSCH _P O) ^use d i ⁿ the transmit power calculation is a cell-specific parameter used by all wireless devices 200. However, different wireless devices 200 may experience different levels of interference, different transmission modes, as well as different delay and Block Error Rate (BLER) requirements. Therefore, it is preferred that the base station 300 set device specific baseline power values based on the above characteristics of the wireless devices 200.

To adjust the baseline power level for a wireless device 200, the base station 300 can send a series of TPC commands to either increase or decrease the baseline power level for individual wireless devices 200. To avoid large fluctuations in transmit power, each TPC command adjusts the UL transmit power by a small amount (e.g., 0.1 dB). Therefore, in scenarios where a large adjustment in the UL transmit power is needed, such as deep fading, the base station 300 may need to send many TPC commands, resulting in a relatively long delay before the wireless device 200 reaches the desired baseline power level. Further, if the required baseline power level is varying due to factors such as the instantaneous interference level, transmission mode, wireless device 200 speed, and remaining battery power, a long delay caused by slow TPC adjustment may block adjustments to the baseline power needed to compensate for rapidly changing channel conditions.

Figure 4 illustrates the problem caused by slow TPC adjustment with a graph showing Power Density Spectrum (PDS) over time. At time t ₀ , the base station 300 decides to increase the baseline power level of the wireless device 200 from P ₀ to P and begins sending positive TPC commands to raise the baseline power level of the wireless device 200. At time t _{1 ;} the wireless device 200 encounters deep fading on the UL, which causes the received power at the base station 300 to decrease despite the positive TPC commands. The unexpected UL fading prolongs the transmit power adjustment window from t ₀ to t ₂ . Finally, at time t ₂ after multiple incremental increases in the UL transmit power, the wireless device 200 reaches the desired power level

Another problem with existing power control methods is that the open loop adjustment by the wireless device 200 based on the DL path loss and the closed loop adjustment by the base station 300 based on the received signal strength are performed independently. As a result, the combined effect of the open loop adjustment and the closed loop adjustment may cause the wireless device 200 to overshoot a target transmit power level. For example, consider the case where the wireless device 200 encounters deep fading that increases both DL and UL path loss. Before the DL path loss is detected by the wireless device 200, the base station 300 detects that the received signal strength of signals transmitted by the wireless device 200 has fallen below the baseline power level for the wireless device 200. In this case, the base station 300 will begin to send positive TPC commands to the wireless device 200 to increase its UL transmit power. After the base station 300 begins sending the TPC commands, wireless device 200 may also detect the deep fading by measuring the DL path loss and automatically increase its transmit power. The combined effect of the closed loop adjustment by the base station 300 and the open loop adjustment by the wireless device 200 may result in an over correction.

Another related issue is the estimation of the UL path loss by the base station 300. In order to estimate the UL path loss, the base station 300 needs to know the transmit power level of the wireless device 200. The UL path loss can be calculated by subtracting the received signal power from the UL transmit power. In LTE, the wireless device 200 reports its power headroom to the base station 300. Based on the power headroom, the base station 300 can derive the UL transmit power of the wireless device 200, which is equal to the maximum transmit power minus the power headroom. However, the power headroom is not reported in every UL transmission. Rather, the power headroom is reported only when the fluctuation in the DL path loss exceeds a predetermined threshold (event driven) or when a predefined timer expires (time driven). In response to either of these events, the wireless device 200 will transmit the Power Headroom MCE in an UL transmission on the PUSCH.

In the current LTE standard, the minimum threshold to trigger a Power Headroom MCE is 1 dB, which represents about a 25% change. Due to the mismatch between DL and UL path loss, the UL path loss may have changed beyond the threshold but the DL path loss change is still within the threshold. In this case, the wireless device 200 will not report power headroom, even if the wireless device 200 has changed its transmit power. Therefore, the base station 300 has no way to know about the change in transmit power and will continue to use the previous UL transmit power to calculate the UL path loss, resulting in an error of up to 25% in the estimated UL path loss.

In summary, the UL power control mechanism specified by the LTE standard, does not provide the wireless device 200 information about the UL channel quality, and the interaction between the base station 300 and wireless device 200 is limited. Without information about the UL channel quality, the wireless device 200 has to use the mismatched DL path loss in its transmit power calculations so that the UL path loss is not effectively compensated in actual PUSCH transmissions. Also, without information about the UL path loss, the open loop and closed loop control mechanisms may independently adjust the wireless device 200 transmit power to compensate for the same cause, resulting in an over-adjustment of the UL transmit power. Because interaction between the wireless device 200 and base station 300 is limited, the base station 300 has no way to proactively instruct the wireless device 200 to report its power headroom. Thus, the base station 300 is not able to derive the actual UL transmit power of the wireless device 200 for PRB allocation and link adaptation. Also, the base station 300 has to rely on the slow closed loop mechanism to adjust the UL transmit power of the wireless device 200 instead of direct setting which can result in long delays in transmit power adjustment.

The present disclosure provides a new mechanism for UL power control that resolves some of the problems with the prior art methods. Figure 5 illustrates one embodiment of the UL power control mechanism according to the present disclosure. The wireless device 200 transmits data to the base station 300 on the PUSCH with transmit power TXP (step 1 ). The base station 300 receives the UL transmission from the wireless device 200 with the received signal power RXP. The UL path loss is the difference between TXP and RXP. The base station 300 estimates the UL path loss based on the most recent power headroom report from the wireless device 200 (step 2). For example, the power headroom report allows the base station 300 to determine TXP, which is used to determine the UL path loss based on RXP and TXP. The base station 300 transmits a reported UL path loss to the wireless device 200 on the PDSCH (step 3). The reported UL path loss may comprise the UL path loss estimated in step 2. In other embodiments described more fully below, the reported UL path loss may additionally include a wireless device-specific adjustment to further adjust the baseline transmit power of the wireless device 200. . The UL path loss may, for example, be sent using a newly defined MAC control element. Responsive to receipt of the UL path loss from the base station 300, the wireless device 200 adjusts its UL transmit power according to the new UL path loss estimate, and determines its new power headroom (step 4). At the next scheduled UL transmission, the wireless device 200 transmits the new power headroom to the base station 300 on the PUSCH (step 5). According to one aspect of the present disclosure, the base station 300 measures the UL path loss and reports the UL path loss to the wireless device 200. The wireless device 200 can then use the UL path loss rather than the DL path loss in its transmit power calculations, thus avoiding problems caused by the mismatch between UL and DL path loss.

The base station 300 may notify the wireless device 200 of the measured UL path loss using a MCE similar to the time alignment (TA) procedure in LTE. A new MCE, referred to as the UL Path Loss MCE, is defined for reporting the UL path loss to the wireless device 200. The UL Path Loss MCE may be sent to the wireless device 200 at any time.

In some embodiments, the base station 300 may adopt an event driven approach where the UL Path Loss MCE is transmitted responsive to pre-determined events. In one

embodiment, the base station 300 may compare a change in the UL path loss to a threshold. If the change in the UL path loss meets or exceeds the threshold, the base station 300 may send the UL Path Loss MCE.

In other embodiments, the base station 300 may use a time-based approach for reporting the UL Path Loss. For example, the base station 300 may be configured to transmit the UL Path Loss MCE responsive to the expiration of a pre-determined time period.

With either the event-driven or time-based approach, the base station 300 may configure the wireless device 200 with a maximum waiting period. Each time the wireless device 200 receives the UL Path Loss MCE, it restarts a path loss timer whose duration is equal to the maximum waiting period. If the path loss timer expires before a new UL Path Loss MCE is received, the wireless device 200 enters an Out-of-Sync state similar to the TA timer expiration in LTE. If the wireless device 200 needs to send UL data, or send Hybrid Automatic Repeat Request (HARQ) feedback, the wireless device 200 may start a resynchronization procedure to resync its UL with the base station 300.

Figure 9 illustrates an exemplary UL Path Loss MCE according to one embodiment. The exemplary UL Path Loss MCE comprises one byte. The two highest bits indicate the UL carrier on which the path loss was measured. The lower six bits are the reported UL path loss for the carrier indicated by the two higher bits.

Upon receiving the UL Path Loss MCE from the base station 300, the wireless device 200 uses the reported UL path loss extracted from the UL Path Loss MCE to calculate its UL transmit power. In one embodiment of the present disclosure, the UL transmit power is calculated according to the following equation:

CMAX (0;

puscH ( = min (4)

10 log ₁₀ (M _{PUSCH C} ( )) + ₀ _ _PUSCH,C O ^' ) + (J) ^{■ PL} _r + ^A _TF,C (0 + TPC _C (i) Equation 4 is the same as Equation 1 except that the path loss parameter PLc in

Equation 1 is replaced by a new path loss parameter PLc , that more accurately reflects the conditions of the channel traversed by the UL signal, and will result in more efficient power control.

In practice, it may not be practical to include the UL Path Loss MCE in every dynamic transmission . Therefore, the wireless device 200 may still need to adjust its UL transmit power based on changes to the path loss in the time period between two adjacent UL Path Loss

MCEs. Thus, the UL path loss parameter PLc used in Equation 4 is calculated according to:

PLc— PL^ + APL ⁿ _c ^L (5) where PL? ¹ is the most recent UL path loss reported by the base station 300, and APL^ ^L is the wireless device's 200 estimate of the change in DL path loss since the last reported UL path loss.

Unlike the conventional approach, which directly uses the estimate of the DL path loss in the transmit power calculation, the new method uses the change in DL path loss to make minor adjustments in UL transmit power based on the latest UL path loss reported by the base station 300. According to Equation 4, the change on DL path loss should theoretically equal the change in UL path loss. Even in the presence of channel fading, the difference in DL and UL path loss change should be small, which significantly reduces error in the transmit power calculation.

According to a second aspect of the disclosure, a mechanism is provided to allow the base station 300 to trigger a Power Headroom MCE from the wireless device 200 so that the estimates of UL path loss made by the base station 300 more accurately reflect the current UL channel conditions. As described above, the wireless device 200 is typically configured to send a Power Headroom MCE to the base station 300 responsive to predetermined events and/or responsive to expiration of a timer. In one embodiment, the wireless device 200 is also configured to send a Power Headroom MCE in the next UL transmission on the PUSCH responsive to receipt of the UL Path Loss MCE from the base station 300. That is, the UL Path Loss MCE functions as a third triggering event for the Power Headroom MCE. Whenever the base station 300 needs to know the UL path loss, it can send its current estimate of the UL Path Loss MCE from to the wireless device 200 to trigger a Power Headroom MCE from the wireless device 200 in response to the UL Path Loss MCE from. Upon receiving the Power Headroom MCE, the base station 300 may recalculate the UL path loss. Therefore, the base station 300 is given greater ability to control the timing of the Power Headroom MCE.

As one example, the base station 300 can set a relatively low threshold (e.g. , 0.2 dB) to trigger a new UL Path Loss MCE. Once the UL path loss change exceeds 5%, the base station 300 can send the UL Path Loss MCE to the wireless device 200 which responds with a Power Headroom MCE in the next UL transmission. Thus, the base station 300 is provided with a polling mechanism to query the wireless device 200 for its current power headroom. Having the current power headroom of the wireless device 200 enables the base station 300 to generate more accurate estimates of the UL path loss.

The Power Headroom MCE triggered by the UL Path Loss MCE also functions as an implicit acknowledgment (ACK) of the UL Path Loss MCE. Due to the potential Block Error Rate (BLER) of HARQ feedback, the HARQ negative acknowledgement (NACK) may be

misinterpreted as an ACK by the base station 300. In this event, base station 300 will no longer retransmit the lost data and the wireless device 200 may fail to receive an UL Path Loss MCE transmitted by the base station 300. Unlike HARQ feedback, the Power Headroom MCE is embedded in PUSCH data, which can provide the same reliability as a Cyclic Redundancy Check (CRC)-protected RRC complete message.

Figure 6 illustrates how the power headroom is used as a form of an acknowledgement. In this example, the base station 300 transmits the UL Path Loss MCE to the wireless device 200 on the PDSCH (step 1 ). It is assumed that the wireless device 200 does not receive the first DL transmission of the UL Path Loss MCE. At the next scheduled UL transmission, the wireless device 200 transmits data to the base station 300 on the PUSCH (step 2). The UL transmission does not include the Power Headroom MCE. Because the UL transmission does not include the Power Headroom MCE, the base station 300 knows that the UL path loss sent to the wireless device 200 was not received. Therefore, the base station 300 may retransmit the UL Path Loss MCE on the PDSCH (step 3). Upon receipt of the UL Path Loss MCE at the next scheduled UL transmission, the wireless device 200 includes the Power Headroom MCE at the next scheduled UL transmission (step 4).

A third aspect of the disclosure provides a mechanism for fast adjustment of the UL transmit power to respond to changes in the instantaneous interference level or fading conditions for the UL channel used by the wireless device 200. In one embodiment, the UL path loss reported by the base station 300 to the wireless device 200 may be modified by an adjustment factor that accounts for changes in the device-specific noise and interference levels. Whenever the base station 300 needs to change the baseline power level for a wireless device 200, it may add an adjustment factor A _BL to the measured UL path loss PZ to compute the reported path loss, i.e., PZ™ = PZ + A _BL . Because the reported UL path loss is used by the wireless device 200 to calculate its UL transmit power, adding the adjustment factor A _BL to the

UL path loss allows the wireless device 200 to immediately impose a large step change in the UL transmit power responsive to deep fading. If no adjustment is required, the base station 300 reports the measured UL path loss PZ , i.e., PL" _c ^L = PL ^M _c . Figure 7 illustrates the adjustment of the baseline power level from P ₀ to P-i using this technique. As seen in Figure 7, the wireless device 200 can reach a desired baseline power level in one step without having to rely on multiple TPC commands, which greatly shortens the delay in shifting the base power level of the wireless device 200. At time t ₀ , the base station 300 decides to raise the baseline power level for the wireless device 200 from P ₀ to P-i and sends an UL Path Loss MCE to the wireless device 200. The base station 300 generates a "pseudo path loss" by adding a baseline adjustment factor equal to the difference between and P ₂ (A _BL = P ₁ - P ₀ ) to the measured UL path loss level, and sends an UL Path Loss

MCE to the wireless device 200. In response to the UL Path Loss MCE, the wireless device 200 recalculates its transmit power level, and sends a Power Headroom MCE in an UL transmission at time ti , which in this example is 4 TTIs later (i.e. = t ₀ +4). Consequently, it is possible to adjust the UL transmit power more quickly to respond to rapidly changing channel conditions. The conventional slow power adjustment may still be used to fine tune the UL transmit power responsive to small fluctuations in noise and interference levels.

According to a fourth aspect of the disclosure, a mechanism is provided to reset the accumulated transmit power adjustment TPC _c (i) used in calculating the UL transmit power to avoid the over-adjustment problem caused by the independent closed loop and open loop control. The closed loop power control mechanism is based on accumulated TPC commands, which affect the calculation of the UL transmit power for a relatively long period of time. The wireless device 200 is configured to reset all the accumulated power adjustments TPC _c (i) indicated by TPC commands responsive to receiving the UL Path Loss MCE. Consequently, any previous over-adjustment is immediately corrected when the wireless device 200 receives the UL Path Loss MCE.

The resetting of the accumulated power adjustment TPC _c (i) in Equation 4 effectively divides the power control process into multiple segments as shown in Figure 8. Each power control segment begins and ends with the receipt of the UL Path Loss MCE. At the beginning of each power control segment, the previous TPC commands are cleared so that the previous over-adjustment effect can be completely corrected in the new UL transmission power calculation and the TPC commands received in the current power control segment will not carry over to the next power control segment. Similarly, the UL transmit power is affected by changes in the DL path loss only within one power control segment.

The power control mechanism as herein described provides the wireless device 200 with more accurate information about the UL channel conditions, which can be used by the wireless device 200 to calculate its UL transmit power. The base station 300 can also directly set the device specific baseline power levels for the wireless devices 200 and proactively trigger the Power Headroom MCE from the wireless device 200. Another advantage is that over- adjustment caused by independent closed loop and open loop control is immediately corrected each time the UL Path Loss MCE is transmitted, thereby minimizing the effect of over- adjustments.

Embodiments of the present invention also provide the base station 300 with greater control over the UL transmit power of the wireless device 200. In the existing 3GPP standard, the base station 300 typically controls most procedures. However, in the case of UL power control, responsibilities for calculating the UL transmit power and reporting power headroom rest primarily in the wireless device 200, while the base station 300 only provides feedback in the form of TPC commands to the wireless device 200 to compensate for fluctuations in the channel conditions. The techniques herein described provide the base station 300 with greater control over the UL transmit power of the wireless device 200. The base station 300 can determine when to report the UL path loss, when to adjust the baseline transmit power for a wireless device 200, and when to trigger a Power Headroom MCE. These aspects provide the base station 300 with greater ability to coordinate the UL transmit power of multiple wireless devices 200 with an overall cell view.

Figure 10 illustrates an exemplary method 100 of UL power control implemented by a base station 300 in a wireless communication network 10. The method begins with the base station 300 estimating an UL path loss associated with an UL channel between a wireless device 200 and the base station 300 (block 1 10). After the UL path loss is estimated, the base station 300 controls the UL transmit power of the wireless device 200 by signaling a reported UL path loss to the wireless device 200 on a downlink channel (block 120). The reported UL path loss is computed based on the estimated UL path loss. In some embodiments, the reported UL path loss is equal to the estimated UL path loss. In other embodiments, the reported UL path loss is calculated based on the estimated UL path loss and a desired transmit power adjustment.

In some embodiments, the reported UL path loss is transmitted to the wireless device 200 on a DL shared channel. For example, the reported UL path loss may be transmitted in a MAC control element on the DL shared channel. In another embodiment, the reported UL path loss is transmitted on a DL control channel.

In some embodiments, the wireless device 200 may have multiple UL transmission paths to different base stations 300. The reported UL path loss may include one or more carrier selector bits to indicate the carrier associated with the reported UL path loss.

In some embodiments, the base station 300 transmits the reported UL path loss to the wireless device 200 to trigger a power headroom report by the wireless device 200. In this embodiment, the base station 300 receives, responsive to the transmission of the UL path loss, a power headroom report in the next uplink transmission from the wireless device 200 indicating a power headroom of the wireless device 200. The base station 300 may use the power headroom to recalculate the UL path loss. If the base station 300 does not receive the power headroom report in the next uplink transmission, the base station 300 retransmits the reported uplink path loss to the wireless device 200.

Figure 1 1 illustrates a method 150 of UL power control implemented by a wireless device 200. The method 150 begins with the wireless device 200 receiving, from a base station 300, signaling on a DL channel indicating an UL path loss reported by the base station 300 (block 160). The wireless device 200 then adjusts its UL transmit power based on the reported UL path loss (block 170). The wireless device 200 may at the next UL transmission, transmit uplink signals to base station 300 at adjusted transmit power level (block 180).

In some embodiments, the reported UL path loss comprises an estimate of the actual UL path loss measured by the base station 300. In other embodiments, the reported UL path loss comprises a value computed based on an estimate of the actual UL path loss measured by the base station 300 and a desired change in the UL transmit power.

In some embodiments, the wireless device 200 adjusts the UL transmit power by computing an UL path loss parameter based on the reported UL path loss received from the base station 300, and adjusting the UL transmit power based on the computed UL path loss parameter. For example, the wireless device 200 may set a value of the UL path loss parameter, at a first time instant, equal to a value of the reported UL path loss. The wireless device 200 may thereafter determine a change in the DL path loss, and compute the value of the UL path loss parameter, at a second time instant, based on the reported UL path loss and the change in the DL path loss.

In some embodiments, the wireless device 200 may additionally adjust the UL transmit power based on explicit power control commands received from the base station 300. In one embodiment, the wireless device 200 may discard previously accumulated power control commands responsive to receipt of the reported UL path loss.

In some embodiments, the wireless device 200 receives the reported UL path loss on a DL shared channel. For example, the reported UL path loss may be received in a MAC control element on the DL shared channel. In other embodiments, the wireless device 200 receives the reported UL path loss on a DL control channel.

In some embodiments, the wireless device 200 transmits, responsive to receiving the reported UL path loss, a power headroom report to the base station 300. The power headroom report indicates a reported power headroom of the wireless device 200.

In some embodiments, the wireless device 200 may have multiple UL transmission paths to different base stations 300. The wireless device 200 may receive an indication of the carrier associated with the reported UL path loss.

In some embodiments, the signaling of the UL path loss may be event driven, time driven, or both. For example, the base station 300 may be configured to signal the reported UL path loss when the estimated UL path loss exceeds the threshold, or when the base station 300 needs to impose a desired change in the UL transmit power. In some embodiments, the base station 300 may periodically report the UL path loss to the wireless device 200 to keep the wireless device 200 synchronized with the base station 300. Some embodiments may include a combination of event driven and time driven reporting.

Figure 12 illustrates the main functional components of wireless device 200 configured to implement UL power control as herein described. The wireless device 200 comprises a processing circuit 210, a memory 240, and an interface circuit 250. The wireless device 200 may also comprise other components, such as a power supply circuitry (not shown in Figure 12) configured to supply power to the wireless device 200, and user interface components to enable a user to interact with the wireless device 200 (not shown in Figure 12). The user interface components may, for example, comprise a display to display information to the user, user input devices such as a keypad, a microphone to input speech or audible sounds, and one or more speakers to output audible sounds to the user. In some embodiments, the wireless device 200 may include a touchscreen that functions as both a display and a user input device.

The interface circuit 250 includes a radio frequency (RF) circuit 255 coupled to one or more antennas 260. The RF circuit 255 comprises the radio frequency (RF) components needed for communicating with base stations 300 over a wireless communication channel. Typically, the RF components include a transmitter and receiver adapted for communications according to the 5G or NR standards, or other Radio Access Technology (RAT).

The processing circuit 210 processes the signals transmitted to or received by the wireless device 200. Such processing includes coding and modulation of transmitted signals, and the demodulation and decoding of received signals. The processing circuit 210 may comprise one or more microprocessors, hardware, firmware, or a combination thereof. In one embodiment, the processing circuit 210 may include a Path Loss (PL) receiving unit 215 to receive a reported UL path loss from the base station 300, a TPC unit 220 to adjust the UL transmit power as herein described, and a power headroom reporting unit 225 to report power headroom of the wireless device 200. The processing circuit 210 is configured to perform the methods and procedures as herein described, including without limitation method 150.

Memory 240 comprises both volatile and non-volatile memory for storing computer program code and data needed by the processing circuit 210 for operation. Memory 240 may comprise any tangible, non-transitory computer-readable storage medium for storing data including electronic, magnetic, optical, electromagnetic, or semiconductor data storage.

Memory 240 stores a computer program 245 comprising executable instructions that configure the processing circuit 210 to implement the methods and procedures described herein including the method shown in Figure 1 1 . In general, computer program instructions and configuration information are stored in a non-volatile memory, such as a read only memory (ROM), erasable programmable read only memory (EPROM) or flash memory. Temporary data generated during operation may be stored in a volatile memory, such as a random access memory (RAM). In some embodiments, the computer program 245 for configuring the processing circuit 210 may be stored in a removable memory, such as a portable compact disc, portable digital video disc, or other removable media. The computer program 245 may also be embodied in a carrier such as an electronic signal, optical signal, radio signal, or computer readable storage medium.

Figure 13 illustrates the main functional components of base station 300 configured to implement UL power control as herein described. The base station 300 comprises a processing circuit 310, a memory 340, and an interface circuit 350.

The interface circuit 350 includes a RF circuit 355 coupled to one or more antennas 360.

The RF circuit 355 comprises the RF components needed for communicating with wireless devices 200 over a wireless communication channel. Typically, the RF components include a transmitter and receiver adapted for communications according to the 5G or NR standards, or other RAT.

The processing circuit 310 processes the signals transmitted to or received by the wireless device 200. Such processing includes coding and modulation of transmitted signals, and the demodulation and decoding of received signals. The processing circuit 310 may comprise one or more microprocessors, hardware, firmware, or a combination thereof. In one embodiment, the processing circuit 310 may include a path loss measuring unit 315 to estimate the UL path loss, a path loss signaling unit 320 to signal the path loss to the wireless device 200 as herein described, and a TPC unit 325 to perform closed loop power control. The processing circuit 310 is configured to perform the methods and procedures as herein described, including without limitation method 100.

Memory 340 comprises both volatile and non-volatile memory for storing computer program code and data needed by the processing circuit 310 for operation. Memory 340 may comprise any tangible, non-transitory computer-readable storage medium for storing data including electronic, magnetic, optical, electromagnetic, or semiconductor data storage.

Memory 340 stores a computer program 345 comprising executable instructions that configure the processing circuit 310 to implement the methods and procedures described herein, including the method shown in Figure 10. In general, computer program instructions and configuration information are stored in a non-volatile memory, such as a ROM, EPROM or flash memory. Temporary data generated during operation may be stored in a volatile memory, such as a RAM. In some embodiments, the computer program 345 for configuring the processing circuit 310 may be stored in a removable memory, such as a portable compact disc, portable digital video disc, or other removable media. The computer program 345 may also be embodied in a carrier such as an electronic signal, optical signal, radio signal, or computer readable storage medium.