US 20140071868A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2014/0071868 A1 Bergquist et al. (43) Pub. Date: Mar. 13, 2014
(54) APPARATUSES AND METHODS FOR Publication Classi?cation MANAGING PENDING HARQ RETRANSMISSIONS (51) Int. Cl. H04W 76/04 (2006.01) (71) Applicants:Gunnar Bergquist, Kista (SE); Riikka H04L 1/18 (2006.01) Susitaival, Helsinki (Fl); Anders Ohlsson, Jarfalla (SE); Mikael (52) US. Cl. Wittberg, Uppsala (SE) CPC ...... H04W 76/048 (2013.01); H04L 1/1803 (2013.01) (72) Inventors: Gunnar Bergquist, Kista (SE); Riikka USPC ...... 370/311; 370/328 Susitaival, Helsinki (Fl); Anders Ohlsson, Jarfalla (SE); Mikael Wittberg, Uppsala (SE) (57) ABSTRACT (73) Assignee: Telefonaktiebolaget L M Ericsson (publ), Stockholm (SE) Methods and systems present solutions to, for example, the (21) Appl. No .: 13/825,462 problem of unnecessary preparedness for suspended retrans missions in the user equipment (UE) Which contributes to (22) PCT Filed: Nov. 9, 2012 poWer drain in the device battery. One method for monitoring a Physical DoWnlink Control Channel (PDCCH) for adaptive PCT No.: PCT/SE2012/051225 (86) retransmission grants in a radio communication system § 371 (0X1), includes: monitoring, by a user equipment (U E), the PDCCH (2), (4) Date: Mar. 21, 2013 for adaptive retransmission grants; receiving, by the UE, a Related US. Application Data hybrid automatic repeat request (HARQ) acknowledge (ACK) message, and ceasing, by the UE, to monitor the (60) Provisional application No. 61/646,757, ?led on May PDCCH for adaptive retransmission grants after receipt of the 14, 2012. HARQ ACK message.
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Patent Application Publication Mar. 13, 2014 Sheet 6 0f 15 US 2014/0071868 A1 @m/ XE kzéo //A 8/ 21 § //A 92: v2 @.QI XE EEQ 35% wmw EEO .2300£553 E300mz/Elmzw E38mzémmzw m2:mag/32a 20:2 Patent Application Publication Mar. 13, 2014 Sheet 7 0f 15 US 2014/0071868 A1 c2szmwNEQEDOEEEa EE amma588E253 EE mas2zEaEDSMEEa EE OZ$2fOP@0213? ///7//MEEEEQ Fo_Qwwmoomémé /////,7//AEEEEQ 0wcFOmwwQEOE 222E0EE9E0 //AMEEEEQ/ PEQ20:2EEOE2% PE2%76:2V22% E32% E:2% E:E@ E E E Patent Application Publication Mar. 13, 2014 Sheet 8 0f 15 US 2014/0071868 A1 S S 2% i /// 0%: /// w.QI K 3 5:00mzémmpw .2300mzémmaw E300mzélmzm 22% Patent Application Publication Mar. 13, 2014 Sheet 9 0f 15 US 2014/0071868 A1 zmNwoEDGE/Emma %a2% a@Nahzno?zémma %Va2% az2sahzzoomgémma %a2% 0%:5% 22% 0%:S% 222 a;5% 5Q %/£52556 Patent Application Publication Mar. 13, 2014 Sheet 10 0f 15 US 2014/0071868 A1 55555555555555?i--...... -. 555555 25saNm55855555550, 555N55mamm555558555555 555aN55mmms5555585555555 555 .55 .-5.5555<.5.%55.m.5--1...... - 555 .55 5/5515.55,55 ///A555555555 2.@I 5555555555055 2555555255555555555555 57-55555 55550555555 5%/555557- 5555 //555555555 555555555555...... - //555552555 Patent Application Publication Mar. 13, 2014 Sheet 11 0f 15 US 2014/0071868 A1 RECEIVING, BY THE USER EQUIPMENT, AN ADAPTIVE RETRANSMISSION GRANT CONTROL MESSAGE WHICH / I00 INSTRUCTS THE USER EQUIPMENT HOW TO MONITOR THE PDCCH FOR ADAPTIVE RETRANSMISSION GRANTS II RECEIVING, BYAUSER EQU|PMENT,AHYBR|D 102 AUTOMATIC REPEAT REQUEST (HARQ) ACKNOWLEDGE / (ACK) MESSAGE, AND V SELECTIVELY (a) MONITORING THE PDCCH, (b) POSTPONING MONITORING OF THE PDCCH OR (0) HALTING MONITORING OF THEPDCCH, BY THE 104 USER EQUIPMENT, AFTER RECEIPT OF THE HARQ / . ACK MESSAGE, IN AMANNER WHICH IS BASED ON THE ADAPTIVE RETRANSSQII/IESION GRANT CONTROL ME E. FIG. 11 Patent Application Publication Mar. 13, 2014 Sheet 12 0f 15 US 2014/0071868 A1 MONITORING, BYA USER EOUIPMENT(UE), THE PDCCH /-200 FOR ADAPTIVE RETRANSMISSION GRANTS II RECEIVING, BY THE DE, A HYBRID AUTOMATIC REPEAT REQUEST (HARQ) /202 ACKNOWLEDGE (ACK) MESSAGE V CEASING, BY THE UE, TO MONITOR THE PDCCH FOR ADAPTIVE /204 RETRANSMISSION GRANTS AFTER RECEIPT OF THE HARQ ACK MESSAGE FIG. 12 Patent Application Publication Mar. 13, 2014 Sheet 13 0f 15 US 2014/0071868 A1 TRANSMITTING, BY AN NETWORK NODE, A MESSAGE WHICH INSTRUCTS A 300 USER EQUIPMENT TO CEASE MONITORING THE PDCCH AFTER RECEIPT OF / A HYBRID AUTOMATIC REPEAT REQUEST (HARQ) ACKNOWLEDGE (ACK) MESSAGE FIG. 13 Patent Application Publication Mar. 13, 2014 Sheet 14 0f 15 US 2014/0071868 A1 /400 404\\ PROCESSING CIRCUITRY NETWORK /4oa /J:—— INTERFACE RADIO . MEMORY FIG. 14 Patent Application Publication Mar. 13, 2014 Sheet 15 0f 15 US 2014/0071868 A1 '98 RADIO CiRCUiTRY PROCESSING <1 504"\ CIRCUITRY - FIG. 15 US 2014/0071868 A1 Mar. 13, 2014 APPARATUSES AND METHODS FOR either sends a positive acknoWledgment (“ACK”) (data block MANAGING PENDING HARQ is received or decoded successfully) or a negative acknoWl RETRANSMISSIONS edgement (“NACK”) (data block is undecodable). The trans mitter responds to a NACK by re-transmitting the informa TECHNICAL FIELD tion. [0001] The present disclosure generally relates to appara [0007] HARQ is a stop-and-Wait protocol. Being a stop and-Wait protocol, (re)transmissions are restricted to occur at tuses and methods for radio communications and, more spe ci?cally, to Hybrid Automatic Repeat reQuest (HARQ) and knoWn time instants, in betWeen Which the sender stops and Discontinuous Reception (DRX) algorithms. Waits for ACK/NACK feedback from the receiver. As used herein, “feedback”, and particularly HARQ feedback, includes both feedback of a positive acknoWledgement BACKGROUND (“ACK”) and feedback of negative acknoWledgement [0002] In the last years, mobile devices have become ubiq (“NACK”). Thus, subsequent transmission of neW data can uitous, applications for these mobile devices have ?ooded the take place only after Waiting to receive ACK/NACK from the market, and clients’ expectations for omnipresent high qual receiving entity. In case an ACK is received a neW transmis ity service have challenged the netWork service providers. sion occurs, otherWise a retransmission occurs. This scheme Among other things, users expect services to be delivered can be improved by using multiple channels for supporting With high quality, and some services require high quality in HARQ service. The HARQ receiver must transmit either the radio communications in order to be perceived by users as ACK or NACK, still of course there is the possibility that the being delivered satisfactorily. Unfortunately, in a radio envi sender detects neither. This is referred to as detection of a ronment, there Will be situations Where some, e.g., data pack Discontinuous Transmission (DTX). There are tWo possible ets, are not received properly by a user’s equipment and, in reasons for a DTX detection to occur, either the data Was lost such cases, it may be necessary to retransmit those data pack or the forWard transmission Was lost and not detected by the ets in order to provide an appropriate level of service. receiver. [0003] The telecommunications industry has used the [0008] When the HARQ transmitter has reached the maxi Automatic Repeat reQuest (ARQ) layer 2 protocol for many mum number of retransmissions for a transport block Without years as a retransmission mechanism to ensure that data is getting an ACK, the HARQ transmitter Will stop transmitting sent reliably from one node to another. More recently, certain and let a higher layer ARQ take over, if any such higher layer standards, such as the Third Generation Partnership Project ARQ exists. Examples of such higher layers that engageARQ (3GPP) Long Term Evolution (LTE) standard, have taken are the Radio Link Control (RLC), 3GPP TS 36.322 V11.0.0 advantage of a Hybrid ARQ (HARQ) process to counteract (2012-09), and the Transmission Control Protocol (TCP), errors. See FIG. 1 and FIG. 2 for the illustrations of the Layer RFC 2581 (1999-04). 2 architecture used in LTE. [0009] The standards document 3GPP TS 36.300, Evolved [0004] FIG. 1 shoWs the Layer 2 architecture for doWnlink Universal Terrestrial Radio Access (E-UTRA) and Evolved (DL) 2 used in LTE and includes the Packet Data Conver Universal Terrestrial Radio Access NetWork (E-UTRAN); gence Protocol (PDCP) sublayer 4, the Radio Link Control Overall description; Stage 2, version 11.3.0, sub-clause 9.1 (RLC) sublayer 6 and the Medium Access Control (MAC) explains some of the principles of LTE HARQ used by 3GPP. sublayer 8. The PDCP layer 4 includes a plurality of Robust For LTE HARQ, there are several channels of interest, includ Header Compression (ROHC) functions 10 each of Which has ing the Physical Uplink Control Channel (PUCCH); the its oWn security function 12 Which can perform, for example, Physical Uplink Shared Channel (PUSCH); the Physical ciphering. The RLC sublayer 6 can perform error correction DoWnlink Control Channel (PDCCH); and, the Physical through ARQ and re-segmentation as shoWn in function Hybrid ARQ Indicator Channel (PHICH). blocks 14. The MAC sublayer 8 can include a scheduling and [0010] For the UL, i.e., for transmissions in the UL from a priority handling function 16, perform multiplexing/demul user equipment (UE) to the base station, the LTE HARQ is a tiplexing of data as shoWn in blocks 18 and 20. Additionally, Synchronous HARQ. There is a maximum number of retrans error correction through HARQ 22 can also be performed. missions con?gured per UE (as opposed to per radio bearer) The Layer 2 architecture for DL 2 also includes control chan With RRC parametermaxHARQ-Tx. DoWnlink ACK/ nels such as a Broadcast Control Channel (BCCH) 24, a NACKs in response to uplink (re)transmissions are sent on Common Control Channel (CCCH) 26 and a Paging Control the PHICH. The radio channel may act in an obstructive Way Channel (PCCH) 28. such that ACK can be received as NACK and vice versa. The [0005] FIG. 2 shoWs the Layer 2 architecture for uplink PHICH can also be totally obscured in such a Way that the (UL) 30 used in LTE Which is similar to the architecture peer receiver detects DTX. described above With respect to FIG. 1, i.e., FIG. 2 includes [0011] In general, HARQ operation on the UL is governed some of the same type of functions designed foruse in the UL. by the folloWing basic principles. A ?rst UL HARQ operation For more information regarding these Layer 2 architectures principle is that, regardless of the content of the received the interested reader is directed to 3GPP TS 36.300 V11.3.0 HARQ feedback (ACK, NACK or DTX), When a PDCCH for (2012-09). the UE is correctly received, the UE folloWs What the PDCCH [0006] HARQ involves an encoded forWard link for error asks the UE to do, e. g., the UE performs a transmission or a correction and detection, and a feedback link for possible retransmission (referred to as adaptive retransmission). A retransmission. At the transmitter, parity bits are added to a second UL HARQ operation principle is that, When no data block Which is to be transmitted, the parity bits serving to PDCCH addressed to the Cell Radio NetWork Temporary facilitate detection and correction of errors. In case the Identi?er (C-RNTI) of the UE is detected, the HARQ feed receiver is not able to correct these errors, the data block is back on PHICH dictates hoW the UE performs retransmis transmitted again. For each received data block the receiver sions. If the HARQ feedback to the UE is either NACK or US 2014/0071868 A1 Mar. 13, 2014 DTX, the UE performs a non-adaptive retransmission, i.e., a (CE) or a Common Control Channel (CCH) Service Data retransmission on the same uplink resource as previously Unit (SDU), submitted from an upper layer and associated used by the same process. If the HARQ feedback to the UE is With the UE contention resolution identity, as part of a ran an ACK, the UE does not perform any UL (re)transmission dom access procedure. but still keeps the data in a buffer knoWn as the HARQ buffer. [0020] There are other scenarios Which bene?t from the The PDCCH can then be used to perform a retransmission, postponement of HARQ retransmissions in the UL, e. g., but a non-adaptive retransmission cannot folloW. When an eNodeB experiences congestion on PDCCH, [0012] 3GPP TS 36.321, Evolved Universal Terrestrial PDSCH or PUSCH. In a high netWork load scenario, the Radio Access (E-UTRA); Medium Access Control (MAC) processing capability decreases as tra?ic groWs closer to sys protocol speci?cation, Medium Access Control (MAC) pro tem capacity limits. In this case, the netWork elements Will tocol speci?cation, version 11.0.0, sub-clause 5.4.2, speci?es bene?t from the possibility to ease the load by postponing the HARQ transmitter operation of the E-UTRAN UE as a set some retransmissions. of sub layer procedures of layer 2.According to this standards [0021] NACK-to-ACK errors are another reason Why it is speci?cation and sub-clause, an identi?ed HARQ process of useful to be able to perform HARQ retransmissions instead of the UE (HARQ transmitter over the Uplink Shared Channel stopping them after HARQ ACK. The radio quality gets [UL-SCH]) is instructed to generate an adaptive retransmis Worse as UE moves close to the cell border. Not only does the sion if an uplink grant is detected, and otherWise to generate occurrence of NACK increase but also the probability of a non-adaptive retransmission. NACK-to-ACK error. In the case of NACK-to-ACK error, the [0013] 3GPP TS 36.321 speci?es in different sub-clauses UE does not perform non-adaptive retransmission even three different conditions that each by itself Will clear any though it is instructed to do so. The netWork can detect miss pending HARQ retransmission in a UE. Each is associated to ing UL retransmission and trigger adaptive retransmission an explicit ?ush of the HARQ buffer, Which effectively clears one HARQ RTT later. Thus, there are good reasons Why ACK any pending retransmissions. More speci?cally: alone shall not alWays unconditionally ?ush the HARQ [0014] Sub-clause 5.2. The UE is not alloWed to transmit buffer. When it is not synchronized to the reception timing used by [0022] Turning noW to the topic of discontinuous reception the base station; the UE Will ?ush the HARQ buffer at expiry (DRX), the “alWays-on” type of behavior that is arriving With of the timer supervising time alignment (timeAlignment smartphones adds much strain on the battery economy in the Timer); UE. There are different methods in LTE to limit the poWer [0015] Sub-clause 5.4.2.2. The HARQ persistency are consumption in the UE, one such method being DRX. brought to an end When the maximum number of transmis [0023] DRX can be applied both in RRC_IDLE and in sions is reached; the UE Will ?ush the HARQ buffer When the RRC_CONNECTED states. The principles are the same. The variable CURRENT_TX_NB:maximum number of trans description hereafter applies to DRX during RRC_CON missions-1; and NECTED Which is the relevant state for the abovementioned [0016] Sub-clause 5.9. The MAC layer in UE Will reset if “alWays-on” type of behavior. requested by higher layers; all timers are stopped, all vari [0024] DRX is a method to reduce battery consumption in ables reset and all buffers are ?ushed. the UE by alloWing the UE to stop monitoring the PDCCH, [0017] In addition, 3GPP TS 36.321 speci?es in sub-clause i.e., it can turn off the receiver during short and even lengthy 5.4.2.2 one condition that Will postpone any pending HARQ times and just discontinuously listen during shorter so called retransmission. It is summariZed in the folloWing note. on-duration phases, the occurrence of Which are knoWn to NOTE: When receiving a HARQ ACK alone, the UE keeps both sides of the protocol. The time periods Where the UE is the data in the HARQ buffer. Such a postponed HARQ alloWed to turn off the receiver are con?gured by the netWork retransmission is alWays an adaptive retransmission, i.e., its and acknoWledged by the UE. The reoccurring periods of the occurrence is explicitly controlled by an eNodeB and the UE on-duration phase is illustrated in FIG. 3. must conclude indication of an uplink grant for the associated [0025] For example, as shoWn in FIG. 3, there is a DRX HARQ process. Cycle 32 Which includes an On Duration Time 34, Which is [0018] There are certain conventional scenarios Which ben When the UE monitors the PDCCH, and an opportunity for e?t from the postponing of HARQ retransmissions, e.g., DRX 36, i.e., a time When the UE can turn off its receiver. When some parallel procedures occur. For example, Change [0026] FIG. 4 illustrates the LTE state model and the deno Request (CR) 5 on 36.321 in 3GPP R2-084875 made it clear tations used in this description. For example, FIG. 4 shoWs the that measurement gaps have high priority. The UE Will not transition paths betWeen RRC_IDLE state 38 and RRC_CO perform UL transmissions based on an UL grant in such a gap. NNECTED state 40 and furthermore the DRX transitions This is one scenario Where an eNodeB may not yet have betWeen sub-states (Continuous/Active sub-state 42, Short successfully received some UL transmission but decides to DRX sub-state 44 and Long DRX sub-state 46) While in the postpone all associated HARQ retransmissions in the UE. RRC_CONNECTED state 40. FIG. 4 also shoWs the conven This can be done sending HARQ ACK before the measure tional vieW of energy and latency associated to the states and ment gap. sub-states of LTE Which is that the more poWer that is used by [0019] The same CR also made it clear that random access the device modem, the faster it Will respond to data commu has higher priority, even higher priority than measurement nication. Staying in the Continuous/Active sub-state 42 is gaps. This is another scenario Where an eNodeB may not yet better for having a more immediate connection than staying in have successfully received some UL transmission but decides the loWer DRX sub-states 44 and 46. Staying in the Short to postpone all associated HARQ retransmission in the UE, DRX sub-state 44 in turn provides better responsiveness than e.g., the netWork may Want to give priority to a Msg3 over staying in the Long DRX sub-state 46. Staying in the RRC_ HARQ retransmission. A Msg3 is a message transmitted on CONNECTED state 40 in turn results in faster reaction (bet the UL-SCH containing a C-RNTI MAC Control Element ter latency) than staying in the RRC_IDLE state 38. FIG. 4 US 2014/0071868 A1 Mar. 13, 2014 also illustrates hoW the energy consumed by the device Will Acronyms/Abbreviations change and suggests that the battery lifetime is shortest When [0038] ACK Acknowledge (HARQ AcknoWledge) staying all the time in Continuous/Active sub-state 42 of the [0039] ARQ Automatic Repeat request RRC_CONNECTED state 40. [0040] CCCH Common Control Channel [0027] DRX involves the use of timers to supervise active [0041] CE Control Element (as in MAC control element) reception time. The 3GPP TS 36.321 , chapter 3 and chapter 5, [0042] C-RNTI Common Radio NetWork Temporary Iden sub-clause 5.7 speci?es the drx-InactivityTimer (denoted T1 tity in FIG. 4) to be the number of consecutive doWnlink subframe [0043] CQI Channel Quality Identi?er (s) during Which the UE shall monitor the PDCCH after [0044] DCI DoWnlink Control Information successfully decoding a PDCCH indicating an initial UL or [0045] DL DoWnLink DL user data transmission for this UE. [0046] DRX DiscontinuousReception [0028] 3GPP TS 36.321 also speci?es drxShortCycleTimer [0047] DTX Discontinuous Transmission (denoted T2 in FIG. 4) to be the number of consecutive [0048] eNodeB enhancedNodeB subframe(s) the UE shall folloW the short DRX cycle after the [0049] HARQ Hybrid ARQ drx-InactivityTimer has expired. FIG. 5 is an illustration of [0050] HARQ RTT HARQ Round Trip Time the sub-state transitions folloWing upon inactivity. [0051] IE Information Element (RRC “control element”) [0029] As shoWn in FIG. 5, the UE Will start the drx-Inac [0052] LCID Logical Channel Identity tivityTimer 48 each time it terminates and decodes a PDCCH [0053] MAC Medium Access Control indicating neW transmission. It Will then continue to monitor [0054] NACK Negative AcknoWledge (HARQ Negative PDCCH as long as the timer is running, i.e., the drx-Inactivi AcknoWledge) tyTimer 48 Will keep the UE from falling asleep. After the [0055] NDI NeW Data Indicator drx-InactivityTimer 48 has expired the drxShortCycleTimer [0056] PDCCH Physical DL Control Channel 50 is started to supervise a sWitch to the next loWer DRX [0057] PDCP Packet Data Convergence Protocol sub-state using Long DRX cycles 52. The Short DRX cycles [0058] PDU Protocol Data Unit 54 are typically much shorter than the Long DRX cycles 52. [0059] PHICH Physical HARQ Indicator channel [0030] The concept of “Active Time” is also used in DRX. [0060] PUCCH Physical UL Channel 3GPP TS 36.321, version 11.0.0, chapter 5, subclause 5.7, [0061] PUSCH Physical UL Shared Channel de?nes the Active Time as the aggregated phases While either: [0062] RLC Radio Link Control [0031] on DurationTimer or drx-InactivityTimer or drx [0063] ROHC Robust Header Compression RetransmissionTimer (used to supervise any DL [0064] RRC Radio Resource Control retransmission that UE expects) or mac-Contention [0065] RV Redundancy Version ResolutionTimer (used to supervise the completion of [0066] SDU Service Data Unit random access) is running; or [0067] SPS Semi-Persistent Scheduling [0032] a Scheduling Request for UL transmission is sent [0068] UE User Equipment on PUCCH and is pending (no grant for UL transmission [0069] UL UpLink has yet been received); or SUMMARY [0033] an uplink grant for a pending HARQ retransmis sion can occur and there is data in the corresponding [0070] The embodiments present solutions to, for example, HARQ buffer; or the problem of unnecessary preparedness for suspended [0034] a PDCCH indicating a neW transmission retransmissions in the user equipment (U E) Which contrib addressed to the C-RNTI of the UE has not been utes to poWer drain in the device battery. The embodiments received after successful reception of a Random Access provide, for example, a more effective duty-cycle for the UE Response for the preamble not selected by the UE. and thereby a potential for an improved conservation of its battery resources. An advantage of these embodiments is that [0035] In particular, 3GPP TS 36.321, subclause 5.7, man they can avoid UE autonomous solutions and retain eNodeB dates the UE to start or restart drx-InactivityTimer if the control of uplink (UL) data transfer. It Will be appreciated by PDCCH indicates a neW transmission (DL or UL). The on those skilled in the art, hoWever, that the invention is not DurationTimer mentioned above is another standardized limited to those embodiments Which produce any or all of timer that supervises the duration of the on-duration phase. these advantages or bene?ts and that other advantages and [0036] It should be noted that the third requirement above bene?ts may be realiZed depending upon the particular imple intends to make sure that the UE is monitoring PDCCH for mentation. adaptive retransmission grants When the HARQ retransmis [0071] According to an embodiment, there is method for sion has been suspended by HARQ ACK or there has been monitoring a Physical DoWnlink Control Channel (PDCCH) NACK-to -ACK error. for adaptive retransmission grants in a radio communication [0037] From the foregoing discussion, it Will be apparent system, the method includes: monitoring, by a user equip that in current systems the eNodeB does not have any imme ment (UE), the PDCCH for adaptive retransmission grants; diate means to completely stop retransmissions, but can only receiving, by the UE, a hybrid automatic repeat request halt non-adaptive retransmissions, e.g., ACK on PHICH (HARQ) acknoWledge (ACK) message, and ceasing, by the alWays results in suspension. One problem With systems and UE, to monitor the PDCCH for adaptive retransmission methods Which employ such an unconditional ACK suspen grants after receipt of the HARQ ACK message. sion is a Waste of battery poWer. Accordingly, it Would be [0072] According to another embodiment, there is a user desirable to provide devices, systems, nodes and methods that equipment (U E) for monitoring a Physical DoWnlink Control Would alleviate the impact of these problems. Channel (PDCCH) for adaptive retransmission grants in a US 2014/0071868 A1 Mar. 13, 2014 radio communication system, the UE includes: a processing [0087] FIG. 13 is another ?owchart illustrating a method circuitry con?gured to monitor the PDCCH for adaptive according to an embodiment; retransmission grants; a radio circuitry con?gured to receive [0088] FIG. 14 depicts an exemplary base station in which a hybrid automatic repeat request (HARQ) acknowledge embodiments can be implemented; and (ACK) message; and the processing circuitry con?gured to [0089] FIG. 15 shows an exemplary user equipment (U E) in cease monitoring the PDCCH for adaptive retransmission which embodiments can be implemented. grants after receipt of the HARQ ACK message. [0073] According to another embodiment, there is a DETAILED DESCRIPTION method for monitoring a Physical Downlink Control Channel [0090] The following description of the exemplary (PDCCH) for adaptive retransmission grants in a radio com embodiments refers to the accompanying drawings. The munication system, the method comprising: transmitting, by same reference numbers in different drawings identify the a network node, a message which instructs a user equipment same or similar elements. The following detailed description to cease monitoring the PDCCH after receipt of a hybrid does not limit the embodiments. Instead, the scope of the automatic repeat request (HARQ) acknowledge (ACK) mes invention is de?ned by the appended claims. The following sage. embodiments are discussed, for simplicity, with regard to the [0074] According to another embodiment, there is a net terminology and structure of a network communication sys work node for monitoring a Physical Downlink Control tem. However, the embodiments to be discussed next are not Channel (PDCCH) for adaptive retransmission grants in a limited to these systems, but may be applied to other existing radio communication system, the network node comprising: systems that provide services based on exchanging packets of a radio circuitry con?gured to transmit a message which data among devices. instructs a user equipment to cease monitoring the PDCCH [0091] Reference throughout the speci?cation to “one after receipt of a hybrid automatic repeat request (HARQ) embodiment” or “an embodiment” means that a particular acknowledge (ACK) message. feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of BRIEF DESCRIPTION OF THE DRAWINGS the present disclosure. Thus, the appearance of the phrases “in [0075] The accompanying drawings, which are incorpo one embodiment” or “in an embodiment” in various places rated in and constitute a part of the speci?cation, illustrate one throughout the speci?cation is not necessarily all referring to or more embodiments and, together with the description, the same embodiment. Further, the particular features, struc explain these embodiments. In the drawings: tures or characteristics may be combined in any suitable [0076] FIGS. 1 and 2 illustrate the Layer 2 architecture for manner in one or more embodiments. the downlink and uplink, respectively, in Long Term Evolu [0092] As mentioned above, and from the foregoing Back tion (LTE); ground discussion, it will be apparent that in current systems [0077] FIG. 3 shows Discontinuous Reception (DRX) the base station, e.g., an eNodeB, does not have any immedi opportunities between periods of on-duration; ate means to completely stop retransmissions, but can only [0078] FIG. 4 illustrates an LTE state model including sub halt non-adaptive retransmissions, e.g., a positive acknowl states and transitions; edgement (ACK) on a Physical HARQ Indicator Channel (PHICH) always results in suspension. To more fully under [0079] FIG. 5 illustrates transitions following inactivity stand this problem, consider the following. from Continuous/Active to DRX using Short DRX cycles and then to DRX using Long DRX cycles; [0093] In current Discontinuous Reception (DRX) opera tion, the user equipment (UE) must stay active for receiving [0080] FIG. 6 illustrates Rel-8/9/ 10/11 DRX behaviour possible adaptive retransmission grants until the Hybrid with a Semi-Persistent Scheduling (SPS) interval of 40 ms, Automatic Repeat reQuest (HARQ) buffer is ?ushed. The UE and DRX parameters of: OnDurationTimer:l ms, drx-Inac is active unconditionally, even after receiving a positive tivityTimeFl ms, DRX Cycle:40 ms, and DRX offset:8; HARQ acknowledgement, HARQ ACK, as a response to an [0081] FIG. 7 illustrates Rel-8/ 10/11 DRX behaviour with uplink (UL) transmission. The UE must always stay prepared an SPS interval of 20 ms, and with DRX parameters of: to receive a grant for an adaptive retransmission and many OnDurationTimeFl ms, drx-InactivityTimer:l ms, DRX times that preparedness comes with little or no gain. If the UE Cycle:40 ms, and DRX offset:8; does not need to monitor Physical Downlink Control Channel [0082] FIG. 8 illustrates an optimiZed DRX behavior with (PDCCH) for adaptive retransmission grants when it has an SPS interval of 40 ms, and DRX parameters: OnDuration received a HARQ ACK, the UEs power consumption can be TimeFl ms, drx-InactivityTimer:l ms, DRX Cycle:40 ms, greatly reduced. DRX offset:8 according to an embodiment; [0094] However, there are some reasons why it can be [0083] FIG. 9 shows optimiZed DRX behavior with an SPS bene?cial to monitor PDCCH even when a HARQ ACK is interval of 20 ms, and DRX parameters: OnDurationTimeFl received: ms, drx-InactivityTimer:l ms, DRX Cycle:40 ms, DRX [0095] (1) there might be NACK-to-ACK errors in the offset:8 according to an embodiment; HARQ feedback. The network can ?nd this error from detect [0084] FIG. 10 shows optimiZed DRX behavior with an ing missing UL retransmission and let that trigger a new SPS interval of 20 ms, and DRX parameters: OnDuration transmission one HARQ RTT later; and/ or TimeFl ms, drx-InactivityTimer:l ms, DRX Cycle:40 ms, [0096] (2) the network may suspend the UL retransmission and DRX offset:8 according to an embodiment; with a HARQ ACK. This could be done, for example, when [0085] FIG. 11 is a ?owchart illustrating a method accord radio resources need to be allocated for another UE having ing to an embodiment; higher priority traf?c, e.g., the transmission of a Msg3. How [0086] FIG. 12 is another ?owchart illustrating a method ever, it is also important to consider power ef?ciency, as is according to an embodiment; described in more detail later in the speci?cation.