A method to reduce delay and save battery life by aligning connected-mode discontinuous reception to application traffic

Abstract

A method for reducing packet delay between a base station of a wireless network and a user equipment (UE), includes: determining, by the base station, during a first long discontinuous reception (DRX) cycle, a DRX cycle start time offset parameter drx-StartOffset value for packet transmission, wherein one of i) for uplink (UE) transmission, drx-StartOffset is determined based on a time when a packet from the UE is received at the base station in the first long DRX cycle, or ii) for downlink (DE) transmission, drx-StartOffset is determined based on a time when a packet from the base station is ready to be transmitted in the first long DRX cycle; and applying, by the base station, the determined drx-StartOffset value for at least a second long DRX cycle following the first long DRX cycle.

Description

A METHOD TO REDUCE DELAY AND SAVE BATTERY LIFE BY ALIGNING CONNECTED-MODE DISCONTINUOUS RECEPTION TO APPLICATION TRAFFICBACKGROUND1. Field of the Disclosure

[0001] The present disclosure is directed to the field of Radio Access Network (RAN) systems (e g., 3GPP 4G and 5G RAN), and relates more particularly to a method to reduce packet delay in the RAN.2. Description of Related Art

[0002] In 4G and 5G RANs, a UL Grant Request Procedure is initiated by an active user equipment (UE) (e.g., UE 101 shown in FIG. 1, in Radio Resource Control (RRC)-connected state) sends Scheduling Request (SR) (shown by the reference 1001 in FIG. 1, which illustrates an example 4G and / or 5G procedure for a UE to request an uplink (UL) grant) to the eNodeB (eNB) or gNodeB (gNB) (commonly referenced in the present disclosure as a base station (BS) 102 in FIG. 1 for the sake of simplicity, i.e., a BS could be either eNB or gNB) to indicate that it needs uplink (UL) allocation. The opportunity to send SR is periodic (i.e., SR periodicity), which periodicity is fixed by the BS. Once the BS 102 receives the SR, it sends a UL allocation (referenced by 1002 in FIG. 1) to the UE, which in turn attaches a Buffer Status Report (BSR) (referenced by 1003 in FIG. 1) and transmits it back to the BS 102. The BS 102 then sends another UL allocation (referenced by 1004 in FIG. 1) to the UE 101, which in turn uses the allocation to transmit to the BS 102 (as shown by “UL Traffic 1005a”) all or part of the bits in its buffer, which transmission is relayed by the base station 102 (as shown by “UL Traffic 1005b”) to the core and beyond (which is generally referenced as 103). This SR is needed if there is no on-going traffic in the UL. Otherwise, the UE can attach a buffer status report (BSR) at the end of the data bits. The full process takes between 30-50 ms, depending on the SR periodicity, BS scheduling load (how many other UEs need to be scheduled by the BS), and the time between the BS UL schedule and the time the UE can transmit the UL data (parameter K2 in 5G, or fixed 4 ms in 4G).

[0003] The 3GPP 4G and 5G standards define QoS profiles for voice traffic, e.g., in 4G Technical Specification (TS) 23.203 Table 6.1.7 QCI table and 5G TS 23.501 2 Table 5.7.4-1 5QI table where the delay budget for QCI / 5QI 1 for voice application is 100 ms, measuring from the UE to the ingress of the Core network. The delay due to UL Grant Request takes 30-50% of the total delay budget, which leaves 50-70% of the total delay budget for the voice packet to traverse through the RAN.

[0004] Connected-Mode Discontinuous Reception (cDRX) in 4G and 5G RANs is used to improve UE battery power consumption by allowing the UE to periodically enter “sleep” state (Off duration) during which PDCCH need not be monitored. In order to monitor PDCCH for possible downlink / uplink data, the UE is allowed to wake up periodically and stay “awake” or “active” (On duration) for a certain amount of time before going to “sleep” again. Additionally, the UE may be required to wake up occasionally to monitor PDCCH, e.g., to receive a possible re-transmission.

[0005] There are two types of cDRX: Long DRX and Short DRX. For voice applications, the vocoder or codec usually generates a voice packet every 20 milliseconds (ms). Long DRX with 20 or 40 ms cycle is typically used so that the UE can be awake or active more frequently to match the voice packet arrival time to the MAC layer at the UE or the BS. In such case, Short DRX can be disabled. In the present disclosure, the focus is on only Long DRX (with disabled Short DRX).

[0006] The gNB configures UE with a set of cDRX parameters using RRC parameters from 3GPP Technical Specification (TS) 36.331 for 4G and TS 38.331 for 5G. FIG. 2, which is a timing diagram showing a basic connected-mode DRX (cDRX) operation, shows, e.g., two cycles of drx-LongCycle 201. Shown within each drx-LongCycle 201 are: drx-StartOffset 202 and drx-onDurationTimer 203. The drx-LongCycleStartOffset parameter (which is not shown) defines drx-LongCycle 201 in ms and drx-StartOffset 202 in multiples of 1 ms. The drx- LongCycle 201 is the DRX cycle length, and the drx-StartOffset 202 is the offset value in milliseconds from a subframe (4G) or slot (5G) boundary to the drx-onDurationTimer 203. If there is no PDCCH received by the end of drx-onDurationTimer 203, the UE would have the opportunity to enter DRX sleep state 204 until the start of next “on duration” (i.e., the start ofdrx-onDurationTimer 203). However, if the UE has a traffic to transmit, then it exits the DRX sleep state and starts the procedure to request for the UL grant.

[0007] Error! Reference source not found, is a timing diagram showing a basic cDRX operation when the UE receives a PDCCH 301 from the BS during the DRX On Cycle (i.e., when the drx-onDurationTimer has not expired). In this case, the UE starts drx-InactivityTimer 302, and this timer is restarted every time the UE receives additional PDCCH. The UE stays in DRX active state and keeps monitoring for PDCCH until the expiry of drx-InactivityTimer 302. After the expiry of drx-InactivityTimer 302, the UE has the opportunity to enter DRX sleep 303 until the start of next “on duration” (i.e., drx-onDurationTimer 203). If the UE has a traffic to transmit, then it exits the DRX sleep and starts the procedure to request for the UE grant.

[0008] FIG. 4 is an example timing diagram showing both a basic cDRX and UL Grant Request Procedure. The UE can generate voice packets at any time, and when the voice packet 401 is ready to be transmitted, the UE starts the UL Grant Request procedure by sending the SR 402 to the BS. If this happens during DRX sleep state, the UE exits the DRX sleep state. When the BS receives the SR 402 and if the UE was previously indicated as being in the DRX sleep state, the BS recognizes that the UE has exited the DRX sleep state. The BS schedules a UL grant for the UE to transmit the BSR, as indicated by the reference numeral 403. Because the UE is in DRX active state, the UE monitors the PDCCH for this UL grant. The UE transmits BSR 404 after 4 ms (for 4G LTE) or K2 ms (for 5G NR) later. The BS schedules another UL grant for the UE to transmit the voice packet 405. And after 4 ms (for 4G LTE) or K2 ms (for 5G NR) later, the UE transmits the voice packet. This example shows that the DRX does not facilitate or hinder the UL Grant Request procedure, and the UL voice packet still suffers high UL delay.

[0009] FIG. 5 is a timing diagram showing a typical technique of Proactive Grant to minimize UL voice packet delay. In this example, high UL delay due to UL Grant Request procedure is sought to be reduced by continually sending the UL grant in every subframe / slot (as referenced by Proactive Grant (PG) 501) starting from the beginning of the drx-onDurationTimer until the voice packet is sent from the UE to the BS (as referenced by 502). This typical technique is very wasteful because the BS does not know in advanced when the UE will send the voice packet, and the UE might not transmit anything for several subframes / slots. The UE also cannot enter theDRX sleep state because each PG (through PDCCH reception) will restart the drx- InactivityTimer and hence extend the DRX active time, which means the opportunity for DRX sleep 503 is much smaller. When the opportunity for DRX sleep 503 is much smaller, it significantly drains the UE battery life.

[0010] Alternative techniques that seek to optimize the proactive grant exist, e.g., sending PG for a limited subframe / slots, but the PGs might be too short and may not be able to align with the UL voice packets, thereby rendering the technique useless and wasteful.

[0011] Accordingly, there is a need for a method to reduce uplink packet delay and save batten life of a UE by aligning the periodic active time of the UE and the uplink application packet transmission from the UE.SUMMARY

[0012] Accordingly, it is desired to provide a system and method to improve reduce uplink packet delay and save battery life of a UE by aligning the periodic active time of the UE and the uplink application packet transmission from the UE.

[0013] According to an example embodiment, a method for reducing packet delay between a base station of a wireless network and a user equipment (UE), comprises: determining, by the base station, during a first long discontinuous reception (DRX) cycle, a DRX cycle start time offset parameter drx-StartOffset value for packet transmission, wherein one of i) for uplink (UL) transmission, drx-StartOffset is determined based on a time when a packet from the UE is received at the base station in the first long DRX cycle, or ii) for downlink (DL) transmission, drx-StartOffset is determined based on a time when a packet from the base station is ready to be transmitted in the first long DRX cycle; and applying, by the base station, the determined drx-StartOffset value for at least a second long DRX cycle following the first long DRX cycle.

[0014] According to an example embodiment, a method to reduce uplink packet delay and save battery life of a mobile station by aligning the periodic active time of the mobile station and the uplink application packet transmission from the mobile station comprises the following:i) scheduling, by the base station, UL proactive grant for a subset of subframes (for 4G) or slots (for 5G) in the first subset of cycles of the DRX cycle; ii) upon receiving the first voice packet from the UE in one of the UL slots by the base station, then the base station stops scheduling the UL proactive grant and marks the UL voice packet transmission being at time T; iii) sending, by the base station, RRC connection reconfiguration message to change the DRX start offset of the UE to time T-K2, wherein K2 is the round-trip time from scheduling to receiving the UL packet; and iv) scheduling, by the base station, UL proactive grant at time T-K2 and repeating UL proactive grant every DRX cycle, wherein the size of the UL proactive grant is calculated from the voice packet size multiplied by the number of voice packets accumulated in the preceding DRX cycles.

[0015] According to an example embodiment, a method to reduce downlink packet delay and save battery life of a mobile station by aligning the periodic wakeup time of the mobile station and the downlink application packet transmission from the mobile station comprises the following: i) measuring, by the base station, a time offset from the beginning of the DRX cycle T DL; ii) setting, by the base station, a new DRX start offset to the measured time offset value; iii) sending, by the base station, an RRC reconfiguration message to the UE to change the DRX start offset at the UE to the measured time offset value; iv) scheduling, by the base station at the start of a subsequent DRX on period, radio resources to transmit twice the amount of voice packets so both voice packets are transmitted together; iv) scheduling, by the base station in a next DRX, one voice packet at the start of the DRX on period; and v) continuing this process by the base station until the voice packet arrival time has changed or when the UE departs from the cell.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a signal flow diagram illustrating an example 4G / 5G procedure for a UE to request an uplink (UL) grant.

[0017] FIG. 2 is a timing diagram showing a basic connected-mode DRX (cDRX) operation.

[0018] FIG. 3 is a timing diagram showing a basic cDRX operation when the UE receives PDCCH.

[0019] FIG. 4 is an example timing diagram showing both a basic cDRX and UL Grant Request Procedure.

[0020] FIG. 5 is a timing diagram showing a typical Proactive Grant to minimize UL voice packet delay.

[0021] FIG. 6 is a timing diagram showing an example method of the invention where the drx- StartOffset is set to the T-K2 to align with UL voice packets.

[0022] FIG. 7 is a timing diagram showing both a basic DRX operation and DL voice packet transmission.

[0023] FIG. 8 is a timing diagram showing an example method of the present disclosure to set the drx-StartOffset to sync with the time point at which DL voice packet is ready to be transmitted.DETAILED DESCRIPTION

[0024] According to an example embodiment of the method, the DRX cycle is aligned with the UL voice packets, as illustrated in FIG. 6. First, as referenced by the reference numeral 601, the BS configures the drx-StartOffset to 0. After UL voice session starts, the BS Scheduler sends a series of Proactive Grants (as referenced by 602) during a period starting from the beginning of the DRX cycle (denoted in FIG. 6 as “drx-LongCycle 6011”) until the BS Scheduler receives the first voice packet sent by the UE (as referenced by 603), which period is denoted by “T” (and as referenced by 604). Subsequently, the BS Scheduler adjusts the drx-StartOffset to be offsetperiod T - K2 (referenced by 605) for the next DRX cycle (where K2 value is 4 ms (for 4G) or a parameter for time domain resource allocation as per TS 38.214 (for 5G), and the BS Scheduler sends RRC Connection Reconfiguration message to the UE to set this value (drx-StartOffset = T - K2) at the UE. For the purposes of this disclosure, K2 value can be considered to be the time period length from scheduling of the UL proactive grant (that is used by the UE) to the time the UL packet from the UE is received by the BS.

[0025] After the UE is reconfigured (which can be as soon as the next DRX cycle (denoted in FIG. 6 as “drx-LongCycle 6012”), the BS assigns one Proactive Grant (as referenced by 606) starting from the new drx-StartOffset = T - K2 (as referenced by 607). Subsequently, 4 ms (for 4G) or K2 ms (for 5G) after the Proactive Grant (PG), the UE transmits UL voice packet (as referenced by 608). To account for UE processing variation to generate the new UL voice packet, the BS scheduler can also assign more Proactive Grants, e.g., up to specified N grants. With this new drx-StartOffset = T - K2 (as referenced by 607), the UE has a new opportunity to enter a longer DRX sleep state (as referenced by 609). After the drx-InactivityTimer (as referenced by 611) has expired in drx-LongCycle 6012, the UE has a new opportunity to enter a longer DRX sleep state (as referenced by 610) in the next DRX cycle (denoted in FIG. 6 as “drx- LongCycle 6013”), which saves UE battery life. By having the PG align with the UL voice packet, the UL delay is reduced to merely 4 ms for 4G LTE or K2 ms for 5G NR, from 30-50 ms delay for conventional techniques. The BS transmits a series of PGs only once, so the alignment cost is low, and there is no waste of PGs in subsequent DRX cycles.

[0026] A conventional audio codec generator used in 4G and 5G, e.g., Adaptive Multi-Rate audio codec (AMR), alternates between talk and silence periods (durations). It generates voice packets every 20 ms during a talk duration and every 160 ms during a silence duration. If the BS assigns a PG every 40ms (Long DRX cycle), then the UE will only send one packet out of 4 PGs during a silence period. The BS can also detect this and only allocates one PG every 160 ms, which allows the UE to spend more time in DRX sleep period and save more battery life. To detect a transition from a silence duration to a talk duration, the PG size shall be large enough for the UE to send a BSR. If the BSR indicates a large buffer size (e.g., because the UE has switched to talk duration), the BS i) immediately assigns another PG with extra allocation to drain the buffer at the UE and ii) switches the PG interval to the talk duration pattern.

[0027] As illustrated in FIG. 7, which shows the timeline of both a basic DRX operation and DL voice packet transmission, DL voice packets can experience high delay due to misalignment with DRX On Duration (i.e., as represented by drx-onDurationTimer). FIG. 7 illustrates three consecutive Long DRX cycles (drx-LongCycle 7011a, drx-LongCycle 7011b, and drx-LongCycle 7011c). In a given Long DRX cycle, e.g., drx-LongCycle 7011a, if the DL voice packet readiness (as referenced by 701) does not align with the DRX active state (i.e., does not fall within drx- onDurationTimer 704a, or drx-inactivityTimer (611 in FIG. 6) has expired), then the transmission of the BS voice packet (as referenced by 702) has to wait until the next DRX active state, which is represented by drx-onDurationTimer 704b within the next Long DRX cycle (e.g., drx-LongCycle 7011b). This results in a high DL packet delay (as referenced by 703). Because of the periodic nature of voice codec, this delay persists for subsequent DL voice packets, as well (e.g., misalignment of voice packet readiness 701 and drx-onDurationTimer 704b in drx- LongCycle 7011b results in the transmission of the voice packet 702 during the subsequent drx- onDurationTimer 704c within the next drx-LongCycle 7011c).

[0028] FIG. 8 is a timing diagram showing an example method of the present disclosure to set the drx-StartOffset to sync with the time point at which DL voice packet is ready to be transmitted. In the first DRX cycle 'drx-LongCycle") 8001, the BS sets the drx-StartOffset to 0 (as referenced by 801) during the initial DRX setup with the UE. When the BS has received a voice packet and it is ready to be transmitted (as referenced by 802), i) the BS measures the time offset (T DL 803) from the beginning of drx-LongCycle 8001 to the time point (as referenced by 802) when the voice packet is ready to be transmitted (which is after the expiration of drx- onDurationTimer 81 within the drx-LongCycle 8001), and ii) the BS sets the new drx-StartOffset value to the measured T DL value and sends RRC reconfiguration message to the UE to change the value at the UE (whereby new drx-StartOffset = T DL, as referenced by 804, for the next drx-LongCycle 8002).

[0029] At the start of the next drx-onDurationTimer 82 (i.e., ON period) within the drx- LongCycle 8002, the BS schedules radio resources to transmit both i) the voice packet that was ready to be transmitted (as referenced by 802) from the previous drx-LongCycle 8001, and ii) the voice packet that is ready to be transmitted (as referenced by 805) in drx-LongCycle 8002, so that both of these voice packets are transmitted together (as referenced by 806). Thistransmission of both voice packets results in only the first voice packet (as referenced by 802) experiencing a high delay, while the subsequent voice packet (as referenced by 805) experiences zero delay.

[0030] In the next drx-LongCycle 8003, the BS only schedules one voice packet (as referenced by 807) at the start of drx-onDurationTimer 83 (i.e., ON period), and this voice packet similarly experiences zero delay (as referenced by 808). The BS continues this (with all subsequent DL packets having zero delay) until the voice packet arrival time at the BS (i.e., when the BS receives the voice packet) has changed (and hence changing when the voice packet is ready to be transmitted) or when the UE departs from the serving cell.

[0031] The codec’s alternating between talk and silent periods does not affect the drx-StartOffset setting. If the BS does not have a packet to transmit because the codec switches to a silent period and generates a sparser packet, then the BS simply does not schedule PDCCH. If the UE does not receive any PDCCH, then its drx-Inactivity Timer (e.g., 611 of FIG. 6) expires and the UE enters DRX sleep state.

[0032] Because it is not always feasible to set the same value of drx-StartOffset for both DL and UL voice packets, in conversational and / or interactive voice service where both DL and UL voice packets are present, one can choose to set the drx-StartOffset to align with UL voice packets, as the UL delay is more severe. In a DL voice-only service, e.g., a news broadcast or a podcast, where only or mostly DL voice packets are present, then the BS can set the drx- StartOffset to align with the DL voice packets.

[0033] While the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. For example, although the example methods have been described in the context of 4G and 5G cellular networks, the example methods are equally applicable for other similar wireless networks. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated, but that the disclosure will include all embodimentsfalling within the scope of the appended claims.

[0034] For the sake of completeness of disclosure, the following lists of acronyms and definitions are provided:ACRONYMS:3GPP: Third generation partnership project4G: Forth Generation Cellular Wireless System5G: Fifth Generation Cellular Wireless System5QI: 5G QoS IdentifierBS: base stationBSR: Buffer Status ReportDL: Downlink eNB: Enhance Node B (4G base station) gNB: Next Generation Node B (5G base station)HARQ: Hybrid Automatic Repeat RequestK2: The time from the BS sends the grant for the UL data until the time the UE can transmit the UL data.NR: New RadioPDCCH: Physical Downlink Control ChannelPG: Proactive GrantQCI: QoS Class IdentifierQoS: Quality of ServiceRAN: Radio Access NetworkRRC: Radio Resource ControlSR: Scheduling RequestUE: User EquipmentUL: Uplink

Claims

What is claimed is:

1. A method for reducing packet delay between a base station of a wireless network and a user equipment (UE), comprising: determining, by the base station, during a first long discontinuous reception (DRX) cycle, a DRX cycle start time offset parameter drx-StartOffset value for packet transmission, wherein one of i) for uplink (UL) transmission, drx-StartOffset is determined based on a time when a packet from the UE is received at the base station in the first long DRX cycle, or ii) for downlink (DL) transmission, drx-StartOffset is determined based on a time when a packet from the base station is ready to be transmitted in the first long DRX cycle; and applying, by the base station, the determined drx-StartOffset value for at least a second long DRX cycle following the first long DRX cycle.

2. The method according to claim 1, further comprising: for UL transmission, the base station: i) schedules UL proactive grants for a subset of one of subframes or slots in the first long DRX cycle; ii) determines time T at which the base station receives a first packet from the UE in one of the subframes or slots in the first long DRX cycle; and iii) determines drx-StartOffset value as T - K2, wherein K2 is the time period length from scheduling of UL proactive grant for the one of the subframes or slots rant used by the UE for the first packet to the time the first packet from the UE is received by the BS.

3. The method according to claim 2, further comprising: for UL transmission, the base station: sends a radio resource control (RRC) connection reconfiguration message to the UE to change drx-StartOffset value as T - K2 at the UE.

4. The method according to claim 3, further comprising: for UL transmission, the base station stops scheduling UL proactive grants in the firstlong DRX cycle when the base station receives a first packet from the UE in one of the subframes or slots in the first long DRX cycle.

5. The method according to claim 3, further comprising: for UL transmission, the base station schedules a UL proactive grant in at least the second long DRX cycle at time T - K.

6. The method according to claim 4, further comprising: for UL transmission, the base station calculates a size of the UL proactive grant in the second long DRX cycle based on a number of voice packets accumulated in the first and second long DRX cycles multiplied by size of the voice packets.

7. The method according to claim 4, wherein for UL transmission, the subset of one of subframes or slots in the first long DRX cycle scheduled by the base station comprises every N subframes or slots, wherein N > 2.

8. The method according to claim 2, further comprising: for UL transmission, in the case the base station does not receive the first packet from the UE in the first long DRX cycle, restarting the method in the second long DRX cycle by scheduling UL proactive grants for a subset of one of subframes or slots in the second long DRX cycle.

9. The method according to claim 8, further comprising: for UL transmission, in the case the base station does not receive the first packet from the UE for Nsp long DRX cycles, wherein Nsp is the number of long DRX cycles in a codec silence period of a codec in the UE, the base station i) determines that the codec has entered a silent period, and ii) schedules UL proactive grants every Nsp long DRX cycle.

10. The method according to claim 9, further comprising: for UL transmission, the UL proactive grants are configured to be sufficiently large for the UE to send a buffer status report (BSR) regarding UE buffer to the base station; andin the case the BSR from the UE indicates an increased buffer occupancy reflecting the codec in the UE having switched from the codec silence period to a codec talk period, performing the following by the base station: i) assigning another proactive grant with extra resource allocation to drain the UE buffer, and ii) switching the scheduling of UL proactive grants to every long DRX cycle.

11. The method according to claim 1, further comprising: for DL transmission, the base station: i) measures a time offset T DL from the beginning of the first long DRX cycle to a time point when the packet is ready to be transmitted from the base station in the first long DRX cycle; and ii) determines drx-StartOffset value as T DL.

12. The method according to claim 11, further comprising: for DL transmission, the base station: sends a radio resource control (RRC) connection reconfiguration message to the UE to change drx-StartOffset value as T DL at the UE.

13. The method according to claim 12, further comprising: for DL transmission, scheduling by the base station at the start of ON period within the second long DRX cycle, radio resources to transmit both i) the packet that was ready to be transmitted in the first long DRX cycle, and ii) a second packet that is ready to be transmitted in the second long DRX cycle; and transmitting, by the base station in the second long DRX cycle, both the packet that was ready to be transmitted in the first long DRX cycle and the second packet that is ready to be transmitted in the second long DRX cycle.

14. The method according to claim 13, further comprising: for DL transmission, scheduling by the base station at the start of ON period within a third long DRX cycle following the second long DRX cycle, radio resources to transmit one packet.

15. The method according to claim 14, further comprising: for DL transmission, scheduling by the base station at the start of ON period within each successive long DRX cycles following the third long DRX cycle, radio resources to transmit one packet, until one of i) the time point when the packet is ready to be transmitted from the base station changes for one of the successive long DRX cycles following the third long DRX cycle, or ii) when the UE departs from a serving cell.

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