Patent Description:
<CIT> provides an electronic device that includes a plurality of antennas, a radio frequency (RF) circuit configured to electrically connect with the plurality of antennas, and a processor. The plurality of antennas include a first main antenna, a first sub-antenna, a second main antenna, and a second sub-antenna. The processor controls the RF circuit to operate in a first mode of receiving a signal using the first main antenna and the first sub-antenna. The processor controls the RF circuit to operate in a second mode different from the first mode to receive the signal based on a signal state. <CIT> discloses a wireless device that operates in accordance with the IEEE <NUM> standard that receives the preamble of a packet with the highest number of receive chains enabled, thereby obtaining the highest gain, detection sensitivity and range. The wireless device determines a signal-to-noise ratio (SNR) in response to two different short training fields (STFs) in the preamble. The wireless device also determines a modulation and coding scheme (MCS) and a number of spatial streams (Nss) used to transmit the received packet in response to a signal field of the preamble. The wireless device uses these determined parameters to identify a minimum number of the receive chains required to reliably receive the packet. The wireless device uses only the identified minimum number of receive chains to perform channel estimation and receive the data portion of the packet.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The apparatus measures a downlink packet error rate (PER); and determines a number of antennas for receiving a downlink transmission based on the measured, downlink PER.

In adaptive receive diversity (ARD), a UE may manage a number of reception antennas in order to balance power consumption and performance. The UE may adapt its reception (Rx) antennas depending on one or more metrics, for example, radio frequency conditions, a downlink traffic pattern (i.e. a number of downlink grants received over a threshold number of subframes), a downlink scheduling rate (i.e. an average number of downlink grants received per subframe), a reference signal received power (RSRP), a signal-to-noise ratio (SNR), spectral efficiency, or antenna correlation. For instance, based on one or more of these metrics, a UE with four Rx antennas may transition between different Rx states including one active Rx antenna (1Rx), two active baseline Rx antennas (baseline2Rx, or a default pair of antennas), two active best Rx antennas (best2Rx, or any pair of antennas), and four active Rx antennas (4Rx). When the UE moves between the different Rx states, the UE may report its current, maximum receive capability to the base station through channel state feedback (CSF). For example, the UE may report a rank indicator (RI) indicating a rank of the UE in multiple-input-multiple-output (MIMO) communication. For instance, if the UE is in the 4Rx state, the UE may report a RI of <NUM> or <NUM> informing the base station of a current reception capability up to four layers, while if the UE is in the best2Rx state, the UE may report a RI of <NUM> informing the base station of a current reception capability only up to two layers. The base station may then transmit scheduling grants to the UE over four or less layers accordingly based on the report. Thus, ARD may allow the UE to balance power savings (e.g. by switching to an Rx state with a lower number of active reception antennas such as 1Rx) with performance (e.g. by switching to an Rx state with a higher number of active reception antennas such as 4Rx) while maintaining communication with the base station.

In addition to transitioning between the aforementioned Rx states, the UE may also transition between different macro states. These macro states may be part of an ARD state machine of the UE, and may include an advanced receiver (ARx) standby state, an ARx disallowed state, and a force rank <NUM> (R1) state. The Rx states may also be dependent upon the current macro state of the UE. For example, when a UE with <NUM> reception antennas is in the ARx standby state, the UE may select between the 4Rx state or the best2Rx state. When the UE is in the ARx disallowed state, the UE may be restricted to the baseline2Rx state. If the UE is in the force R1 state, the UE may be forced to the 1Rx state to save power and to report CSF of MIMO rank <NUM> during this time.

The UE may switch between different macro states depending on the downlink scheduling rate of the base station, which refers to the average number of downlink grants the UE receives per subframe. For example, the UE may enter the ARx standby state when the UE expects significant downlink traffic over time (e.g. where the downlink scheduling rate is at or above <NUM>%), the ARx disallowed state when the downlink scheduling rate is low (e.g. where the downlink scheduling rate is below <NUM>% but at or above <NUM>%), and the force R1 state when the downlink utilization is trivial (e.g. where the downlink scheduling rate is below <NUM>%). An example illustrating downlink scheduling rates is described below with respect to <FIG>.

Each macro state (e.g. ARx standby and ARx disallowed) may have different sub-states or modes, including a steady state and a fallback state. The steady state is a default sub-state which the UE enters when it expects downlink traffic (e.g. when the UE receives a downlink grant). While in the steady state, the UE may select one of the default Rx states of the corresponding macro state. For example, the UE may select between 4Rx and best2Rx while in the steady state of the ARx standby state, or baseline 2Rx while in the steady state of the ARx disallowed state.

In contrast, the fallback state is a sub-state which the UE enters when downlink traffic is idle. For example, the UE may enter the fallback state if the UE has not received a downlink grant within a threshold number of subframes. While in the fallback state, the UE may be restricted to selecting 1Rx (e.g. in a conditional 1Rx mode). Thus, the UE may save more power in the fallback state (e.g. with 1Rx) than when the UE is in the steady state (e.g. with 4Rx or best2Rx). In some cases, while in the fallback state, the UE may also select baseline2Rx as an alternative to 1Rx to maintain PDCCH reception performance.

The UE may switch between the steady state and fallback state for a given macro state based on a downlink traffic pattern for that macro state. The downlink traffic pattern refers to the number of downlink grants the UE receives over a threshold number of subframes. The threshold number of subframes may be configured by the base station and depend on the given macro state. For instance, the threshold may be <NUM> subframes for the ARx standby state and <NUM> subframes for the ARx disallowed state. The time period represented by this threshold number of subframes (e.g. <NUM> or <NUM> subframes) may be referred to as a fallback window. If a UE in the steady state for a given macro state does not receive a downlink grant within the fallback window for that macro state, the UE enters the fallback state. If the UE in the fallback state later receives a downlink grant, the UE re-enters the steady state.

Generally, in ARD, the UE only reports CSF to the base station while in a steady state. For example, while the UE is in the steady state of the ARx standby state, the UE may report a MIMO rank of four to the base station in CSF indicating that the UE is operating under 4Rx. Therefore, if the UE later transitions from steady state to a fallback state based on downlink traffic patterns or scheduling rates as described above, the UE may not report the downgrade from 4Rx to 1Rx/baseline2Rx in CSF while in the fallback state. Moreover, the UE may take a significant amount of time (e.g. <NUM>-<NUM>) to transition from the fallback state back to the steady state to again report CSF. As a result, misalignment or mismatch between the number of layers for transmission and the number of antennas for reception may occur during the transition time between steady states and fallback states. Such mismatch may be especially prominent when the UE has dropped from 4Rx to 1Rx.

Due to this mismatch or lack of synchronization with the base station, the UE may prune or discard numerous downlink grants on PDCCH. For instance, while the UE is in a fallback state, the UE may discard <NUM> to <NUM> downlink grants during the <NUM> to <NUM> transition time back to the steady state. Moreover, the UE may fail to successfully receive downlink data on PDSCH during this transition time, for instance, due to numerous decoding failures of cyclic redundancy checks (CRCs) on PDSCH. As a result, the UE may frequently discard the PDSCH data and transmit non-acknowledgments (NACKs) to the base station during automatic repeat request (ARQ) or hybrid automatic repeat request (HARQ) reporting. When the base station receives the NACKs from the UE, the base station may determine to adapt its downlink transmissions, such as in outer loop link adaptation (OLLA), by reducing the modulation coding scheme (MCS) of subsequent data transmissions, the number of allocated resource blocks for subsequent transmissions, the frequency of grants scheduling subsequent transmissions, or other parameters. Such adaptation may result in a degradation of downlink data throughput when the UE is back in the steady state.

Moreover, the lack of synchronization and degradation of downlink data throughput may be especially prominent in secondary component carriers (SCCs) where high and low downlink traffic may be more intermittent (e.g. in bursts), than in primary component carriers (PCCs) where high downlink traffic may be more constant. For example, the UE may receive data from the base station over a PCC and multiple SCCs. For each PCC and SCC, the UE may initially be in the steady state of a given macro state, during which the UE may report a MIMO rank of <NUM> or <NUM> for each component carrier. If the UE later detects a low amount of downlink traffic on any of the SCCs (e.g. zero downlink grants within a threshold number of subframes), the UE may transition to the corresponding fallback state on those SCCs with a reduced number of active antennas (e.g. <NUM> or <NUM>). As a result, the UE may experience a high packet error rate or ratio (PER) (also referred to as block error rate or ratio (BLER)) due to frequent pruning or discarding of downlink grants on PDCCH and CRC decoding failures on PDSCH in these SCCs. While the UE may in some cases recover lost data on PDSCH in response to multiple HARQ-level retransmissions or other ARQ mechanism, the overall round trip time (RTT) for the UE to receive and successfully acknowledge the data may be increased. Additionally, transmission control protocol (TCP) window sizes of the SCCs may be throttled at the transport layer due to the downgrade of number of antennas, resulting in an overall reduction of downlink throughput which may impact the UE experience. Persistent PER may also trigger OLLA (including reduction in MCS and scheduling as described above), which may further degrade downlink performance.

One approach that may improve downlink performance is to double the fallback window. For example, if the fallback window for the ARx standby state is increased from <NUM> (e.g., spanning <NUM> subframes) to <NUM> (e.g., spanning <NUM> subframes), the UE may remain in the steady state for twice the original amount of time before transitioning to the fallback state. As a result, the UE may remain in 4Rx for a longer amount of time, potentially reducing the PER and improving performance.

However, while fixedly increasing the size of the fallback window may reduce PER, such static increase may also inefficiently increase UE power consumption. For example, if the fallback window in the ARx standby state is doubled such that the UE spends twice the original amount of time in 4Rx before switching to the fallback state, the UE may effectively double its power consumption (or halve its power savings). Such loss in power savings may be especially inefficient in SCCs where there may be downlink inactivity for frequent periods of time, during which the UE may burn additional power, reduce battery life, or possibly experience other thermal triggers.

To resolve the power inefficiencies associated with statically increasing the size of the fallback window in ARD as described above, the UE may employ a more dynamic approach to enhance ARD performance. For example, the UE may dynamically increase the size of the fallback window, and thus the amount of time the UE remains in a steady state before switching to a fallback state, based on a measurement of PER. PER refers to the number of erroneous packets or transport blocks which the UE receives with at least one bit error over the total number of received packets or transport blocks. For example, the UE may measure PER over a given period of time by counting the number of transport blocks which the UE fails to decode during that time (e.g. in response to a mismatch between the CRC attached to the transport block and an expected CRC calculated by the UE) and dividing that number by the total number of transport blocks received at the UE during that time. Thus, if the UE receives <NUM> transport blocks during a predetermined period of time and fails to decode <NUM> of these blocks (e.g. due to CRC mismatch), the UE may measure a PER of <NUM>%. Depending on the measured PER, the UE may determine a scaling factor for the fallback window (e.g. 1x, <NUM>. 5x, or 2x of the size of the original fallback window). Accordingly, the UE may dynamically change the length of time that the UE remains in the steady state based on measured PER, rather than merely increasing the time by a fixed amount regardless of PER. In this way, balance between power savings and performance may be optimized.

The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations <NUM>, user equipment(s) (UE) <NUM>, an Evolved Packet Core (EPC) <NUM>, and another core network <NUM> (e.g., a <NUM> Core (5GC)).

The base stations <NUM> configured for <NUM> Long Term Evolution (LTE) (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC <NUM> through first backhaul links <NUM> (e.g., S1 interface). The base stations <NUM> configured for <NUM> New Radio (NR) (collectively referred to as Next Generation RAN (NG-RAN)) may interface with core network <NUM> through second backhaul links <NUM>. In addition to other functions, the base stations <NUM> may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, Multimedia Broadcast Multicast Service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages.

The base stations <NUM> / UEs <NUM> may use spectrum up to Y megahertz (MHz) (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc. MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction.

The wireless communications system may further include a Wi-Fi access point (AP) <NUM> in communication with Wi-Fi stations (STAs) <NUM> via communication links <NUM>, e.g., in a <NUM> gigahertz (GHz) unlicensed frequency spectrum or the like.

The EPC <NUM> may include a Mobility Management Entity (MME) <NUM>, other MMEs <NUM>, a Serving Gateway <NUM>, an MBMS Gateway <NUM>, a Broadcast Multicast Service Center (BM-SC) <NUM>, and a Packet Data Network (PDN) Gateway <NUM>.

Generally, the AMF <NUM> provides Quality of Service (QoS) flow and session management. All user IP packets are transferred through the UPF <NUM>. The IP Services <NUM> may include the Internet, an intranet, an IMS, a Packet Switch (PS) Streaming Service, and/or other IP services.

Referring again to <FIG>, in certain aspects, the UE <NUM> may include a PER component <NUM> that is configured to measure a downlink PER and determine a number of antennas for receiving a downlink transmission based on the measured, downlink PER.

Although the present disclosure may focus on <NUM> NR, the concepts and various aspects described herein may be applicable to other similar areas, such as LTE, LTE-Advanced (LTE-A), Code Division Multiple Access (CDMA), Global System for Mobile communications (GSM), or other wireless/radio access technologies.

In the examples provided by <FIG>, the <NUM> NR frame structure is assumed to be TDD, with subframe <NUM> being configured with slot format <NUM> (with mostly DL), where D is DL, U is UL, and F is flexible for use between DL/UL, and subframe <NUM> being configured with slot format <NUM> (with mostly UL).

A frame, e.g., of <NUM> milliseconds (ms), may be divided into <NUM> equally sized subframes (<NUM>). The symbols on DL may be cyclic prefix (CP) orthogonal frequency-division multiplexing (OFDM) (CP-OFDM) symbols. For slot configuration <NUM>, different numerologies µ <NUM> to <NUM> allow for <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> slots, respectively, per subframe. The subcarrier spacing may be equal to <NUM>µ * <NUM> kilohertz (kHz), where µ is the numerology <NUM> to <NUM>. <FIG> provide an example of slot configuration <NUM> with <NUM> symbols per slot and numerology µ=<NUM> with <NUM> slots per subframe. The slot duration is <NUM>, the subcarrier spacing is <NUM>, and the symbol duration is approximately <NUM>. Within a set of frames, there may be one or more different bandwidth parts (BWPs) (see <FIG>) that are frequency division multiplexed. Each BWP may have a particular numerology.

A PDCCH within one BWP may be referred to as a control resource set (CORESET). Additional BWPs may be located at greater and/or lower frequencies across the channel bandwidth. The physical broadcast channel (PBCH), which carries a master information block (MIB), may be logically grouped with the PSS and SSS to form a synchronization signal (SS)/PBCH block (also referred to as SS block (SSB)).

The PUCCH carries uplink control information (UCI), such as scheduling requests, a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and hybrid automatic repeat request (HARQ) acknowledgement (ACK) / non-acknowledgement (NACK) feedback.

At least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM> may be configured to perform aspects in connection with PER component <NUM> of <FIG>.

In ARD, a UE may manage a number of reception antennas in order to balance power consumption and performance. The UE may adapt its Rx antennas depending on one or more metrics, for example, radio frequency conditions, a downlink traffic pattern (i.e. a number of downlink grants received over a threshold number of subframes), a downlink scheduling rate (i.e. an average number of downlink grants received per subframe), a RSRP, a SNR, spectral efficiency, or antenna correlation. For instance, based on one or more of these metrics, a UE with four Rx antennas may transition between different Rx states including one active Rx antenna (1Rx), two active baseline Rx antennas (baseline2Rx, or a default pair of antennas), two active best Rx antennas (best2Rx, or any pair of antennas), and four active Rx antennas (4Rx). When the UE moves between the different Rx states, the UE may report its current, maximum receive capability to the base station through CSF. For example, the UE may report a RI indicating a rank of the UE in MIMO communication. For instance, if the UE is in the 4Rx state, the UE may report a RI of <NUM> or <NUM> informing the base station of a current reception capability up to four layers, while if the UE is in the best2Rx state, the UE may report a RI of <NUM> informing the base station of a current reception capability only up to two layers. The base station may then transmit scheduling grants to the UE over four or less layers accordingly based on the report. Thus, ARD may allow the UE to balance power savings (e.g. by switching to an Rx state with a lower number of active reception antennas such as 1Rx) with performance (e.g. by switching to an Rx state with a higher number of active reception antennas such as 4Rx) while maintaining communication with the base station.

In addition to transitioning between the aforementioned Rx states, the UE may also transition between different macro states. These macro states may be part of an ARD state machine of the UE, and may include an ARx standby state, an ARx disallowed state, and a force R1 state. The Rx states may also be dependent upon the current macro state of the UE. For example, when a UE with <NUM> reception antennas is in the ARx standby state, the UE may select between the 4Rx state or the best2Rx state. When the UE is in the ARx disallowed state, the UE may be restricted to the baseline2Rx state. If the UE is in the force R1 state, the UE may be forced to the 1Rx state to save power and to report CSF of MIMO rank <NUM> during this time.

The UE may switch between different macro states depending on the downlink scheduling rate of the base station, which refers to the average number of downlink grants the UE receives per subframe. For example, the UE may enter the ARx standby state when the UE expects significant downlink traffic over time (e.g. where the downlink scheduling rate is at or above <NUM>%), the ARx disallowed state when the downlink scheduling rate is low (e.g. where the downlink scheduling rate is below <NUM>% and at or above <NUM>%), and the force R1 state when the downlink utilization is trivial (e.g. where the downlink scheduling rate is below <NUM>%). An example illustrating downlink scheduling rates is described below with respect to <FIG>.

<FIG> illustrate examples <NUM>, <NUM> of graphs depicting a comparison of downlink scheduling rates with a number of received grants over time. Each sample is taken at <NUM> intervals in this example, although in other examples other intervals may be used for sampling. In this example, the UE receives a total of <NUM> downlink grants from the base station after <NUM>, a total of <NUM> downlink grants from the base station after <NUM>, a total of <NUM> downlink grants from the base station after <NUM>, and so forth as illustrated in <FIG>. Accordingly, assuming each subframe spans <NUM>, the downlink scheduling rate after <NUM> may be <NUM> or <NUM>% (i.e. <NUM> grants/<NUM>, or <NUM> grants per ms/subframe), the downlink scheduling rate after <NUM> may be <NUM> or <NUM>% (i.e. <NUM> grants/<NUM>, or <NUM> grants per ms/subframe), the downlink scheduling rate after <NUM> may be <NUM> or <NUM>% (i.e. <NUM> grants/<NUM>, or <NUM> grants per ms/subframe), and so forth. Thus, the UE may enter the ARx standby state a short time before the <NUM> sample time, at which point the downlink scheduling rate exceeds <NUM>%. The downlink scheduling rate corresponding to each sampled time may also be a filtered quantity (e.g. a weighted average of current and prior sampled rates). For instance, the downlink scheduling rate may be calculated such that the number of grants more recently received are given less weight than the number of grants less recently received.

When downlink traffic arrives in bursts, the relative number of grants received between sampled times may frequently increase and decrease, such as illustrated in <FIG>. Thus, the downlink scheduling rate over time may increase during traffic bursts and decrease at other times, for instance, ranging generally between rates of <NUM> and <NUM> as illustrated in the example of <FIG>. Although not shown, in some cases the scheduling rate may also drop below this range (e.g. below <NUM>) or in some cases significantly below this range (e.g. below <NUM>) at times when bursts of downlink traffic are infrequent. This drop in downlink burst frequency and thus the scheduling rate may cause the UE to transition from the ARx standby state to the ARx disallowed state (or even the force R1 state). If the downlink burst frequency later increases, the UE may transition back from the force R1 state or ARx disallowed state to the ARx standby state.

<FIG> illustrates an example <NUM> of an ARD state machine including macro states (e.g. an ARx standby state <NUM>, an ARx disallowed state <NUM>, and a forced R1 state <NUM>), steady states <NUM>, <NUM> and fallback states <NUM>, <NUM>, <NUM> within macro states, and Rx states <NUM> (e.g. 1Rx, baseline2Rx, best2Rx, 4Rx) within steady states and fallback states. The UE may transition between steady states <NUM>, <NUM> and fallback states <NUM>, <NUM>, <NUM> within a given macro state depending on the downlink traffic pattern or fallback window as described above, while the UE may transition between different macro states depending on the downlink scheduling rate as described above.

In one example of operation, a UE with <NUM> reception antennas may initially be in the steady state <NUM> of the ARx standby state <NUM>. While in the steady state <NUM>, the UE may operate under 4Rx or best2Rx, and the UE may receive a burst of downlink data from the base station using the active antennas accordingly. After receiving the data, the UE may monitor for downlink grants during the fallback window for the ARx standby state <NUM> (e.g. <NUM> subframes or another configured threshold number of subframes). If the UE determines that it has not received any downlink grants during the fallback window, the UE may transition at <NUM> to the fallback state <NUM> of the ARx standby state <NUM>. While in the fallback state <NUM>, the UE may operate under 1Rx or baseline2Rx to save power until the UE later receives another downlink grant. Once the UE receives the grant (e.g. indicating a new data burst), the UE may transition at <NUM> back to the steady state <NUM> and receive the new data using 4Rx or best2Rx. The UE may also reset the fallback window at <NUM> and restart the monitoring for downlink grants.

Moreover, while the UE is operating in the ARx standby state <NUM>, the UE may determine that the downlink scheduling rate has reduced to or below a first threshold (e.g. <NUM>%). For instance, the UE may determine that the average number of grants received per subframe has dropped to less than <NUM>, indicating a low scheduling rate. In such case, the UE may transition at <NUM> to the steady state <NUM> of the ARx disallowed state <NUM> to save power compared to the ARx standby state <NUM>. While in the steady state <NUM>, the UE may operate under baseline 2Rx and receive downlink data from the base station accordingly. The UE may also monitor for downlink grants during the fallback window for the ARx disallowed state (e.g. <NUM> subframes or another configured threshold number of subframes). If the UE determines that it has not received any downlink grants during the fallback window, the UE may transition at <NUM> to the fallback state <NUM> of the ARx disallowed state <NUM>. While in the fallback state <NUM>, the UE may operate under 1Rx or baseline2Rx to save additional power until the UE later receives another downlink grant and transitions at <NUM> back to the steady state <NUM>.

Additionally, while the UE is operating in the ARx disallowed state <NUM>, the UE may determine that the downlink scheduling rate has reduced to or below a second threshold (e.g. <NUM>%). For instance, the UE may determine that the average number of grants received per subframe has dropped to less than <NUM>, indicating trivial downlink utilization. In such case, the UE may transition at <NUM> to the forced R1 state <NUM> to save additional power compared to the ARx disallowed state <NUM>. While in the forced R1 state <NUM>, the UE may operate in fallback state <NUM> under 1Rx or baseline 2Rx and receive downlink data from the base station accordingly. If the UE later receives a downlink grant for MIMO rank <NUM> or above, or if the UE determines that the downlink scheduling rate has increased back above the second threshold (e.g. <NUM>%), the UE may transition at <NUM> back to the steady state <NUM> of the ARx disallowed state <NUM>. Similarly, while in the ARx disallowed state <NUM>, if the UE subsequently determines that the downlink scheduling rate has increased back above the first threshold (e.g. <NUM>%) in response to detecting a burst of data, the UE may transition at <NUM> back to the steady state <NUM> of the ARx standby state <NUM>.

Generally, in ARD, the UE only reports CSF to the base station while in a steady state. For example, while the UE is in the steady state <NUM>, the UE may report a MIMO rank of four to the base station in CSF indicating that the UE is operating under 4Rx. Therefore, if the UE later transitions from steady state <NUM> to fallback state <NUM>, <NUM>, <NUM> based on downlink traffic patterns or scheduling rates as described above, the UE may not report the downgrade from 4Rx to 1Rx/baseline2Rx in CSF while in the fallback state. Moreover, the UE may take a significant amount of time (e.g. <NUM>-<NUM>) to transition from the fallback state <NUM>, <NUM>, <NUM> back to the steady state <NUM> to again report CSF. As a result, misalignment or mismatch between the number of layers for transmission and the number of antennas for reception may occur during the transition time between steady states and fallback states. Such mismatch may be especially prominent when the UE has dropped from 4Rx to 1Rx.

Due to this mismatch or lack of synchronization with the base station, the UE may prune or discard numerous downlink grants on PDCCH. For instance, while the UE is in fallback state <NUM>, <NUM>, <NUM>, the UE may discard <NUM> to <NUM> downlink grants during the <NUM> to <NUM> transition time back to steady state <NUM>. Moreover, the UE may fail to successfully receive downlink data on PDSCH during this transition time, for instance, due to numerous decoding failures of CRCs on PDSCH. As a result, the UE may frequently discard the PDSCH data and transmit NACKs to the base station during ARQ or HARQ reporting. When the base station receives the NACKs from the UE, the base station may determine to adapt its downlink transmissions, such as in OLLA, by reducing the MCS of subsequent data transmissions, the number of allocated resource blocks for subsequent transmissions, the frequency of grants scheduling subsequent transmissions, or other parameters. Such adaptation may result in a degradation of downlink data throughput when the UE is back in the steady state.

Moreover, the lack of synchronization and degradation of downlink data throughput may be especially prominent in SCCs where high and low downlink traffic may be more intermittent (e.g. in bursts), than in PCCs where high downlink traffic may be more constant. For example, the UE may receive data from the base station over a PCC and multiple SCCs. For each PCC and SCC, the UE may initially be in the steady state of a given macro state, during which the UE may report a MIMO rank of <NUM> or <NUM> for each component carrier. If the UE later detects a low amount of downlink traffic on any of the SCCs (e.g. zero downlink grants within a threshold number of subframes), the UE may transition to the corresponding fallback state on those SCCs with a reduced number of active antennas (e.g. <NUM> or <NUM>). As a result, the UE may experience a high PER (also referred to as BLER) due to frequent pruning or discarding of downlink grants on PDCCH and CRC decoding failures on PDSCH in these SCCs. While the UE may in some cases recover lost data on PDSCH in response to multiple HARQ-level retransmissions or other ARQ mechanism, the overall RTT for the UE to receive and successfully acknowledge the data may be increased. Additionally, TCP window sizes of the SCCs may be throttled at the transport layer due to the downgrade of number of antennas, resulting in an overall reduction of downlink throughput which may impact the UE experience. Persistent PER may also trigger OLLA (including reduction in MCS and scheduling as described above), which may further degrade downlink performance.

One approach that may improve downlink performance is to double the fallback window. For example, if the fallback window for the ARx standby state is increased from <NUM> (e.g., spanning <NUM> subframes) to <NUM> (e.g., spanning <NUM> subframes), the UE may remain in the steady state for twice the original amount of time before transitioning to the fallback state. As a result, the UE may remain in 4Rx for a longer amount of time, potentially reducing the PER and improving performance. Examples of possible PER reductions measured over a specified period of time for different SCCs are illustrated below in Tables <NUM> and <NUM>. For instance, Table <NUM> illustrates an example where doubling the fallback window for one SCC has reduced PER by more than <NUM>% during one period of time, while Table <NUM> illustrates a similar example where doubling the fallback window for another SCC has reduced PER by more than <NUM>% during another period of time.

To resolve the power inefficiencies associated with statically increasing the size of the fallback window in ARD as described above, the UE may employ a more dynamic approach to enhance ARD performance. For example, the UE may dynamically increase the size of the fallback window, and thus the amount of time the UE remains in a steady state <NUM>, <NUM> before switching to a fallback state <NUM>, <NUM>, <NUM>, based on a measurement of PER. PER refers to the number of erroneous packets or transport blocks which the UE receives with at least one bit error over the total number of received packets or transport blocks. For example, the UE may measure PER over a given period of time by counting the number of transport blocks which the UE fails to decode during that time (e.g. in response to a mismatch between the CRC attached to the transport block and an expected CRC calculated by the UE) and dividing that number by the total number of transport blocks received at the UE during that time. Thus, if the UE receives <NUM> transport blocks during a predetermined period of time and fails to decode <NUM> of these blocks (e.g. due to CRC mismatch), the UE may measure a PER of <NUM>%. Depending on the measured PER, the UE may determine a scaling factor for the fallback window (e.g. 1x, <NUM>. 5x, or 2x of the size of the original fallback window). Accordingly, the UE may dynamically change the length of time that the UE remains in the steady state based on measured PER, rather than merely increasing the time by a fixed amount regardless of PER. In this way, balance between power savings and performance may be optimized.

For example, the UE may determine the PER to be in a low region if the UE measures the PER to be within a first range (e.g. below <NUM>%), a middle region if the UE measures the PER to be within a second range higher than the first range (e.g. between <NUM>% and <NUM>%), and a high region if the UE measures the PER to be within a third range higher than the second range (e.g. above <NUM>%). If the UE measures the PER to be in the low region, the UE may determine that PER is insignificant, and therefore the UE may maintain the current fallback window size (e.g. 1x scaling factor, such as <NUM> for ARx standby state or <NUM> for ARx disallowed state). If the UE measures the PER to be in the middle region, the UE may determine that PER is substantial but not significant, and therefore the UE may slightly increase the current fallback window size (e.g. <NUM>. 5x scaling factor, such as <NUM> for ARx standby state or <NUM> for ARx disallowed state). If the UE measures the PER to be in the high region, the UE may determine that PER is significant, and therefore the UE may further increase the current fallback window size (e.g. 2x scaling factor, such as <NUM> for ARx standby state or <NUM> for ARx disallowed state). In other examples, the UE may change the fallback window size by other factors (e.g. other than <NUM>. 5x or <NUM>. 0x) or for other PER regions (e.g. within other ranges than described above).

When employing the dynamic approach described above, the UE may detect and monitor PER periodically during the transition period from the fallback state to the steady state. The UE may change the fallback window size depending on the measured PER during this transition period. For example, if the UE takes a certain period of time (e.g. <NUM>-<NUM>) to transition from the fallback state <NUM>, <NUM>, <NUM> to the steady state <NUM> in the ARx standby state <NUM> as described above, the UE may measure PER during this period of time and change the fallback window size for future transitions based on the measured PER. Moreover, the UE may also measure a filtered PER (e.g. based on an infinite impulse response (IIR) filter or some other filter), and change the fallback window size depending on the measured, filtered PER. For instance, the UE may measure filtered PER as a weighted average of multiple sampled PERs, using different weights for current and prior samples, or in other ways. Based on the measured PER, the UE may increase or decrease the fallback window size accordingly to maintain a desired PER. Additionally, the UE may change the fallback window size depending on a variation in MCS for downlink transmissions. For example, if the UE determines that the base station has decreased MCS from 16QAM to QPSK in subsequent downlink transmissions (e.g. in OLLA), the UE may increase the fallback window size to reduce PER or otherwise remain for a longer time in the steady state to reduce the possibility of NACKs, thus causing the base station to increase MCS back to 16QAM. As a result, downlink data throughput may be improved.

The UE may also measure PER and change the fallback window size independently for different component carriers. For example, the UE may determine low region, middle region, or high region PER separately for PCC and for each SCC, and the UE may change the fallback window respectively within each PCC and SCC. Furthermore, the UE may periodically monitor various metrics and move between different ARD macro states based on one or more of the metrics. The metrics may include, for example, downlink traffic pattern, downlink scheduling rate, downlink utilization rate, rank (in MIMO), and SNR. As described above, downlink traffic pattern refers to the number of grants received over a threshold number of subframes, while downlink scheduling rate refers to the average number of grants received per subframe. Utilization rate refers to the number of received data bytes (by the UE) over the total number of transmitted data bytes (by the base station), which may be based on the number of active reception antennas and channel conditions (e.g. SNR). The UE may monitor these metrics and move between different macro states independently for different component carriers. For example, the UE may determine downlink traffic pattern, scheduling rate, utilization rate, MIMO rank, and SNR separately for PCC and for each SCC, and the UE may switch to a different macro state respectively within each PCC and SCC.

Furthermore, the UE may disable switching to a fallback state of a given macro state based on the measured PER, as well as based on one or more of the other aforementioned metrics such as downlink scheduling rate, rank, and SNR. For example, the UE may determine whether to disable switching to a fallback state depending on the aforementioned region (e.g. low, middle, or high) the UE determines for the PER. For example, if the UE measures the PER to be in the low region, the UE may determine that PER is insignificant, and therefore the UE may allow transitions to the fallback state. Thus, the UE may transition from the steady state to the fallback state if the UE does not receive a downlink grant within the dynamic fallback window. If the UE measures the PER to be in the high region, the UE may determine that PER is significant, and therefore the UE may disable switching to the fallback state. Thus, the UE may remain in the steady state even if the UE does not receive a downlink grant within the dynamic fallback window. On the other hand, if the UE measures the PER to be in the middle region, the UE may determine that PER is substantial, and therefore the UE may determine to disable switching depending on the other metrics described above. For example, the UE may determine whether the downlink scheduling rate is low (e.g. less than <NUM>% or some other threshold), the SNR is high (e.g. greater than <NUM> decibels (dB) or some other threshold), and the MIMO rank is low (e.g. RI <= <NUM> or some other threshold). If all of these conditions are met, the UE may allow switching to the fallback state. Otherwise, the UE may disable transitioning to the fallback state. When the UE disables transitioning to the fallback state (in either the middle or high region of PER), the UE may again allow transitioning to the fallback state if the aforementioned conditions later become met or the PER drops to a lower value.

<FIG> illustrates an example <NUM> of a process for dynamically increasing fallback window size and disabling fallback state transitions based on PER. At <NUM>, the UE determines whether the UE is in a standby macro state (e.g. ARx standby state <NUM>) or disallowed macro state (e.g. ARx disallowed state <NUM>). If so, at <NUM>, the UE monitors PER. For example, the UE may measure and filter a number of packets lost over a period of time during which the UE transitions from a fallback state to a steady state. After the UE measures the PER, the UE first determines at <NUM> whether the measured PER is less than <NUM>% (e.g. within a low region). If so, at <NUM>, the UE changes the fallback window for the current macro state to its default value (e.g. 1x scaling). Moreover, at <NUM>, the UE refrains from disabling (or allows) switching to the fallback state of the given macro state. Alternatively, if at <NUM> the UE determines that the measured PER is not within the low region, then at <NUM>, the UE determines whether the measured PER is at least <NUM>% and less than <NUM>% (e.g. within a middle region). If so, then at <NUM>, the UE slightly increases the fallback window for the current macro state with respect to the default value (e.g. <NUM>. 5x scaling). Moreover, at <NUM>, the UE determines whether to refrain from disabling switching to the fallback state based on other metrics such as MIMO rank, SNR, and downlink scheduling rate. For instance, the UE may check whether the rank is at most <NUM>, whether the SNR is at least <NUM> dB, and whether the scheduling rate is at most <NUM>%. If all these conditions are met, then the UE allows switching to the fallback state at <NUM>. On the other hand, if any of these conditions are not met, then at <NUM>, the UE disables switching to the fallback state. Moreover, if at <NUM> the UE determines that the measured PER is not within the middle region, then at <NUM>, the UE determines whether the measured PER is at least <NUM>% (e.g. within a high region). If so, then at <NUM>, the UE further increases the fallback window for the current macro state with respect to the default value (e.g. 2x scaling), and disables switching to the fallback state at <NUM>. Alternatively, the UE may simply conclude that the measured PER is within a high region upon determining the measured PER to not be within the low or middle regions (e.g., block <NUM> may be omitted).

<FIG> is an example <NUM> of a call flow between a UE <NUM> and a base station <NUM>. Initially, the UE <NUM> may be in the steady state of a given macro state and include an active number of reception antennas. For example, referring to <FIG>, the UE may be in the steady state <NUM> of the ARx standby state <NUM>, during which the UE may be in a 4Rx state or a best2Rx state. While in the steady state, the UE may receive one or more downlink grants <NUM> each scheduling a downlink transmission <NUM> from the base station <NUM>. The base station <NUM> may transmit the downlink grants and downlink transmission according to a configured MCS <NUM> (e.g. 16QAM). The UE may also send CSF <NUM> to the base station indicating the current rank of the UE for MIMO (e.g. <NUM> or <NUM>) as well as other channel state information.

After the UE <NUM> receives each downlink grant(s) <NUM>, the UE may count an amount of time (or number of subframes) that has elapsed within a fallback window <NUM>. If the UE receives a subsequent downlink grant during this time, the UE may reset the fallback window <NUM> and restart counting. Otherwise, the UE transitions to the fallback state. In the example of <FIG>, the UE has not received another downlink grant within the fallback window <NUM>, and therefore at <NUM>, the UE switches from the steady state to the fallback state. For example, referring to <FIG>, the UE may transition from the steady state <NUM> to the fallback state <NUM> at <NUM>, during which the UE may be restricted to 1Rx or baseline2Rx. The UE may not report CSF to the base station of the change in MIMO rank at this time, leading to possible misalignment between the number of reception antennas at the UE and the number of layers for transmission at the base station. Thus, pruned or discarded PDCCH transmissions (e.g. downlink grants <NUM>) and unsuccessfully decoded PDSCH transmissions (e.g. downlink transmissions <NUM>) may result.

At <NUM>, the UE measures a downlink PER. For example, while in the fallback state, the UE may receive multiple downlink grants scheduling downlink transmissions, some of which include at least one bit error (e.g. downlink grants <NUM> and downlink transmissions <NUM>) and others which do not include a bit error (e.g. downlink grants <NUM> and downlink transmissions <NUM>). In such case, the UE may measure PER by counting the number of downlink grants <NUM> and downlink transmissions <NUM> and dividing that value by the total number of downlink grants <NUM>, <NUM> and downlink transmissions <NUM>, <NUM>. The UE may alternatively measure PER in other ways (e.g. by only counting downlink grants).

While the UE is receiving downlink grants <NUM>, <NUM> and downlink transmissions <NUM>, <NUM> and measuring PER at <NUM>, the UE also determines whether to switch from the fallback state back to the steady state. In the example of <FIG>, the UE successfully receives downlink grant <NUM>, and therefore at <NUM>, the UE switches from the fallback state to the steady state. For example, referring to <FIG>, while in the ARx standby state <NUM> and at <NUM>, the UE transitions from fallback state <NUM> back to steady state <NUM> in response to receiving the downlink grant from the base station.

At <NUM>, the UE determines a number of antennas for receiving downlink transmissions based on the measured, downlink PER. For example, referring to <FIG>, the UE may determine an Rx state <NUM> (e.g. 4Rx, best2Rx, baseline2Rx, or 1Rx) for a given macro state depending on whether the UE is in the steady state <NUM>, <NUM> or fallback state <NUM>, <NUM>, <NUM>. For instance, while in the steady state <NUM>, the UE may select 4Rx or best2Rx, and while in the fallback state <NUM>, <NUM>, <NUM>, the UE may select 1Rx or baseline2Rx. The Rx state <NUM> may depend on the amount of time the UE remains in the steady state <NUM>, <NUM>, which in turn may dynamically change based on the PER measured at <NUM>. For example, the UE may scale the fallback window <NUM> differently (e.g. 1x, <NUM>. 5x, or 2x the size of the original fallback window) depending on the measured PER, which may lengthen the amount of time the UE is in a steady state when a downlink grant has not been received. Thus, when the fallback window is scaled to be twice as long in response to the measured PER, the UE may remain for a longer amount of time in the steady state <NUM> and thus determine to select four antennas (e.g. 4Rx), rather than transition earlier to the fallback state <NUM>, <NUM>, <NUM> with restriction to only one or two antennas (e.g. 1Rx or baseline2Rx). Accordingly, the UE may determine the number of antennas corresponding to Rx state <NUM> based on the measured PER at <NUM>.

For instance, at <NUM>, the UE may change the size of fallback window <NUM> based on the PER measured at <NUM>. For example, referring to <FIG>, after the UE measures the PER, the UE may first determine at <NUM> whether the measured PER is less than <NUM>% (e.g. within a low region). If so, at <NUM>, the UE changes the fallback window for the current macro state to its default value (e.g. 1x scaling). Alternatively, if at <NUM> the UE determines that the measured PER is not within the low region, then at <NUM>, the UE may determine whether the measured PER is at least <NUM>% and less than <NUM>% (e.g. within a middle region). If so, then at <NUM>, the UE slightly increases the fallback window for the current macro state with respect to the default value (e.g. <NUM>. 5x scaling). Alternatively, if at <NUM> the UE determines that the measured PER is not within the middle region, then at <NUM>, the UE may determine whether the measured PER is at least <NUM>% (e.g. within a high region). If so, then at <NUM>, the UE further increases the fallback window for the current macro state with respect to the default value (e.g. 2x scaling). In other examples, the UE may change the fallback window size by other factors (e.g. other than <NUM>. 5x or <NUM>. 0x) or for other PER regions (e.g. within other ranges corresponding to other percentages of PER than described above).

Moreover, at <NUM>, the UE may determine a variation in MCS for downlink transmissions. For instance, when the UE prunes or discards PDCCH transmissions such as downlink grants <NUM> and unsuccessfully decodes PDSCH transmissions such as downlink transmissions <NUM>, the UE may send a NACK to the base station requesting re-transmission. Accordingly, to improve the likelihood of a successful subsequent reception at the UE, the base station may re-transmit the downlink grants or transmissions according to a different MCS <NUM>. The base station may also transmit subsequent downlink grants and transmissions according to the different MCS. For instance, when transmitting downlink grant <NUM> and downlink transmission <NUM>, the base station may reconfigure the MCS from 16QAM to QPSK to increase the likelihood of successful reception. Thus, at <NUM>, the UE may determine the variation between a previous MCS (e.g. configured MCS <NUM>) and a current MCS (e.g. different MCS <NUM>) for downlink transmissions. For example, the UE may determine that the MCS has varied from 16QAM to QPSK.

The UE may determine the number of antennas for receiving downlink transmissions at <NUM> based on the variation in MCS determined at <NUM>. For example, if the UE determines that the MCS has decreased (e.g. from 16QAM to QPSK or some other MCS) between MCS <NUM> and MCS <NUM>, the UE may determine to increase the scaling factor of the fallback window <NUM> (e.g. as described above at <NUM>) and thus the length of time the UE remains in the steady state. As a result, the UE may remain for a longer amount of time in the steady state and thus determine to select four antennas (e.g. 4Rx), rather than transitioning sooner to the fallback state and thus being restricted to selecting only one or two antennas (e.g. 1Rx or baseline2Rx). Contrarily, if the UE determines that the MCS has increased between MCS <NUM> and MCS <NUM>, the UE may determine to decrease the scaling factor of the fallback window <NUM> and thus similarly the length of time that the UE remains in the steady state. Accordingly, the UE may determine the number of antennas corresponding to Rx state <NUM> based on variation in MCS as well as the measured PER.

At <NUM>, the UE may disable switching from the steady state to the fallback state. For example, referring to <FIG>, if the UE determines at <NUM> that the measured PER is at least <NUM>% and less than <NUM>% (e.g. within a middle region), then at <NUM>, the UE may determine whether to refrain from disabling switching to the fallback state based on MIMO rank, SNR, and downlink scheduling rate. For instance, the UE may check whether the rank is at most <NUM>, whether the SNR is at least <NUM> dB, and whether the scheduling rate is at most <NUM>%. The UE may alternatively check one or two of these conditions, other conditions (e.g. downlink traffic pattern and utilization rate), or any combination of the these conditions. If any of these conditions are not met, then at <NUM>, the UE disables switching to the fallback state. Alternatively, if the UE determines at <NUM> that the measured PER is at least <NUM>% (e.g. within a high region), then at <NUM>, the UE may simply disable switching to the fallback state at <NUM> without checking any of the aforementioned conditions. In other examples, the UE may determine whether to disable switching to the fallback state based on conditions for other PER regions (e.g. within other ranges corresponding to other percentages of PER than described above).

Accordingly, after the UE <NUM> determines the number of antennas at <NUM>, the UE may receive one or more downlink grants <NUM> each scheduling a downlink transmission <NUM> based on the determined number of antennas. For example, if the UE determines to operate under 4Rx while in the steady state of the ARx standby state (which determination is based on the measured PER or MCS variation as described above), the UE may receive downlink grant(s) <NUM> and downlink transmission(s) <NUM> using four antennas. The UE may also transmit CSF <NUM> while in the steady state informing the base station of the current rank of the UE as well as other channel state information.

Thus, the UE may periodically receive bursts of downlink data from the base station with a balance of power consumption and performance. However, as described above with respect to <FIG>, if the UE determines that the downlink scheduling rate of downlink grants <NUM> received in various bursts decreases below a threshold, then at <NUM>, the UE may switch to a different reception state (macro state) to save power. For instance, referring to <FIG>, if the downlink scheduling rate drops below <NUM>%, the UE may transition at <NUM> from the ARx standby state <NUM> to the ARx disallowed state <NUM>, and if the downlink scheduling rate further drops below <NUM>%, the UE may transition at <NUM> from the ARx disallowed state <NUM> to the force R1 state <NUM>. The UE may also transition between macro states based on other metrics than the downlink scheduling rate (e.g. downlink traffic pattern, utilization rate, MIMO rank, or SNR).

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by a UE (e.g., the UE <NUM>, <NUM>, <NUM>; the apparatus <NUM>). Optional aspects are illustrated in dashed lines. The method allows a UE to employ a dynamic approach to ARD based on measured PER in order to optimize balancing between power savings and performance.

At <NUM>, the UE may switch from a steady state to a fallback state prior to receiving a downlink transmission (e.g., downlink transmission <NUM>) when a downlink grant is not received within a threshold number of subframes. For example, <NUM> may be performed by steady state component <NUM>. For instance, referring to <FIG>, after the UE <NUM> receives each downlink grant(s) <NUM>, the UE may count an amount of time (or number of subframes) that has elapsed within a fallback window <NUM> (a threshold number of subframes). If the UE receives a subsequent downlink grant during this time, the UE may reset the fallback window <NUM> and restart counting. Otherwise, the UE transitions to the fallback state. In the example of <FIG>, the UE has not received another downlink grant within the fallback window <NUM>, and therefore at <NUM>, the UE switches from the steady state to the fallback state. For example, referring to <FIG>, the UE may transition from the steady state <NUM> to the fallback state <NUM> at <NUM>, during which the UE may be restricted to 1Rx or baseline2Rx.

At <NUM>, the UE measures a downlink PER. For example, <NUM> may be performed by measurement component <NUM>. For instance, referring to <FIG>, at <NUM>, the UE may measure a downlink PER. For example, while in the fallback state, the UE may receive multiple downlink grants scheduling downlink transmissions, some of which include at least one bit error (e.g. downlink grants <NUM> and downlink transmissions <NUM>) and others which do not (e.g. downlink grants <NUM> and downlink transmissions <NUM>). In such case, the UE may measure PER by counting the number of downlink grants <NUM> and downlink transmissions <NUM> and dividing that value by the total number of downlink grants <NUM>, <NUM> and downlink transmissions <NUM>, <NUM>. The UE may alternatively measure PER in other ways (e.g. by only counting downlink grants).

At <NUM>, the UE may switch from a fallback state to a steady state in response to receiving a downlink grant and prior to receiving the downlink transmission (e.g., downlink transmission <NUM>), where the downlink PER is measured at <NUM> during the switching. For example, <NUM> may be performed by fallback state component <NUM>. For instance, referring to <FIG>, while the UE is receiving downlink grants <NUM>, <NUM> and downlink transmissions <NUM>, <NUM> and measuring PER at <NUM>, the UE also determines whether to switch from the fallback state back to the steady state. In the example of <FIG>, the UE successfully receives downlink grant <NUM>, and therefore at <NUM>, the UE switches from the fallback state to the steady state. For example, referring to <FIG>, while in the ARx standby state <NUM> and at <NUM>, the UE transitions from fallback state <NUM> back to steady state <NUM> in response to receiving the downlink grant from the base station.

At <NUM>, the UE may determine a variation in MCS for downlink transmissions. For example, <NUM> may be performed by MCS component <NUM>. For instance, referring to <FIG>, at <NUM>, the UE may determine a variation in MCS for downlink transmissions. For instance, when the UE prunes or discards PDCCH transmissions such as downlink grants <NUM> and unsuccessfully decodes PDSCH transmissions such as downlink transmissions <NUM>, the UE may send a NACK to the base station requesting re-transmission. Accordingly, to improve the likelihood of a successful subsequent reception at the UE, the base station may re-transmit the downlink grants or transmissions according to a different MCS <NUM>. The base station may also transmit subsequent downlink grants and transmissions according to the different MCS. For instance, when transmitting downlink grant <NUM> and downlink transmission <NUM>, the base station may reconfigure the MCS from 16QAM to QPSK to increase the likelihood of successful reception. Thus, at <NUM>, the UE may determine the variation between a previous MCS (e.g. configured MCS <NUM>) and a current MCS (e.g. different MCS <NUM>) for downlink transmissions <NUM>, <NUM>. For example, the UE may determine that the MCS has varied from 16QAM to QPSK.

At <NUM>, the UE determines a number of antennas for receiving a downlink transmission (e.g., downlink transmission <NUM>) based on the measured, downlink PER. For example, <NUM> may be performed by determination component <NUM>. For instance, referring to <FIG>, at <NUM>, the UE determines a number of antennas for receiving downlink transmissions <NUM> based on the measured, downlink PER. For example, referring to <FIG>, the UE may determine an Rx state <NUM> (e.g. 4Rx, best2Rx, baseline2Rx, or 1Rx) for a given macro state depending on whether the UE is in the steady state <NUM>, <NUM> or fallback state <NUM>, <NUM>, <NUM>. For instance, while in the steady state <NUM>, the UE may select 4Rx or best2Rx, and while in the fallback state <NUM>, <NUM>, <NUM>, the UE may select 1Rx or baseline2Rx. The Rx state <NUM> may depend on the amount of time the UE remains in the steady state <NUM>, <NUM>, which in turn may dynamically change based on the PER measured at <NUM>. For example, the UE may scale the fallback window <NUM> differently (e.g. 1x, <NUM>. 5x, or 2x the size of the original fallback window) depending on the measured PER, which may lengthen the amount of time the UE is in a steady state when a downlink grant has not been received. Thus, when the fallback window is scaled to be twice as long in response to the measured PER, the UE may remain for a longer amount of time in the steady state <NUM> and thus determine to select four antennas (e.g. 4Rx), rather than transition earlier to the fallback state <NUM>, <NUM>, <NUM> with restriction to only one or two antennas (e.g. 1Rx or baseline2Rx). Accordingly, the UE may determine the number of antennas corresponding to Rx state <NUM> based on the measured PER at <NUM>.

The number of antennas may be determined further based on the variation in MCS (determined at <NUM>). For instance, referring to <FIG>, the UE may determine the number of antennas for receiving downlink transmissions at <NUM> based on the variation in MCS determined at <NUM>. For example, if the UE determines that the MCS has decreased (e.g. from 16QAM to QPSK or some other MCS) between MCS <NUM> and MCS <NUM>, the UE may determine to increase the scaling factor of the fallback window <NUM> (e.g. as described above at <NUM>) and thus the length of time the UE remains in the steady state. As a result, the UE may remain for a longer amount of time in the steady state and thus determine to select four antennas (e.g. 4Rx), rather than transitioning sooner to the fallback state and thus being restricted to selecting only one or two antennas (e.g. 1Rx or baseline2Rx). Contrarily, if the UE determines that the MCS has increased between MCS <NUM> and MCS <NUM>, the UE may determine to decrease the scaling factor of the fallback window <NUM> and thus similarly the length of time that the UE remains in the steady state. Accordingly, the UE may determine the number of antennas corresponding to Rx state <NUM> based on variation in MCS as well as the measured PER.

At <NUM>, the UE may change a size of a fallback window based on the measured, downlink PER. For example, <NUM> may be performed by fallback window component <NUM>. The changing may be performed independently for different component carriers. For instance, referring to <FIG>, at <NUM>, the UE may change the size of fallback window <NUM> based on the PER measured at <NUM> separately for each PCC and individual SCC. For example, referring to <FIG>, after the UE measures the PER for a given SCC, the UE may first determine at <NUM> whether the measured PER is less than <NUM>% (e.g. within a low region). If so, at <NUM>, the UE changes the fallback window for the current macro state to its default value (e.g. 1x scaling) in the given SCC. Alternatively, if at <NUM> the UE determines that the measured PER is not within the low region, then at <NUM>, the UE may determine whether the measured PER is at least <NUM>% and less than <NUM>% (e.g. within a middle region). If so, then at <NUM>, the UE slightly increases the fallback window for the current macro state with respect to the default value (e.g. <NUM>. 5x scaling) in the given SCC. Alternatively, if at <NUM> the UE determines that the measured PER is not within the middle region, then at <NUM>, the UE may determine whether the measured PER is at least <NUM>% (e.g. within a high region). If so, then at <NUM>, the UE further increases the fallback window for the current macro state with respect to the default value (e.g. 2x scaling) in the given SCC. In other examples, the UE may change the fallback window size by other factors (e.g. other than <NUM>. 5x or <NUM>. 0x) or for other PER regions (e.g. within other ranges corresponding to other percentages of PER than described above).

At <NUM>, the UE may disable switching from a steady state to a fallback state prior to receiving the downlink transmission (e.g., downlink transmission <NUM>) based on at least one of a downlink scheduling rate, a rank (for MIMO), or a signal to noise ratio. For example, <NUM> may be performed by fallback state disabler component <NUM>. The disabling switching may further be based on the measured, downlink PER. For instance, referring to <FIG>, at <NUM>, the UE may disable switching from the steady state to the fallback state. For example, referring to <FIG>, if the UE determines at <NUM> that the measured PER is at least <NUM>% and less than <NUM>% (e.g. within a middle region), then at <NUM>, the UE may determine whether to refrain from disabling switching to the fallback state based on MIMO rank, SNR, and downlink scheduling rate. For instance, the UE may check whether the rank is at most <NUM>, whether the SNR is at least <NUM> dB, and whether the scheduling rate is at most <NUM>%. The UE may alternatively check one or two of these conditions, other conditions (e.g. downlink traffic pattern and utilization rate), or any combination of the these conditions. If any of these conditions are not met, then at <NUM>, the UE disables switching to the fallback state. Alternatively, if the UE determines at <NUM> that the measured PER is at least <NUM>% (e.g. within a high region), then at <NUM>, the UE may simply disable switching to the fallback state at <NUM> without checking any of the aforementioned conditions. In other examples, the UE may determine whether to disable switching to the fallback state based or not on conditions for other PER regions (e.g. within other ranges corresponding to other percentages of PER than described above).

Finally, at <NUM>, the UE may switch from a first reception state to a second reception state after receiving the downlink transmission (e.g., downlink transmission <NUM>) based on at least one of a downlink scheduling rate, a downlink traffic pattern, a utilization rate, a rank (for MIMO), or a signal to noise ratio. For example, <NUM> may be performed by reception state component <NUM>. The first reception state may comprise an ARx standby state, and the second reception state may comprise an ARx disallowed state. The switching may be performed independently for different component carriers. For instance, referring to <FIG>, the UE may periodically receive bursts of downlink data from the base station in individual SCCs. However, as described above with respect to <FIG>, if the UE determines for a given SCC that the downlink scheduling rate of downlink grants <NUM> received in various bursts decreases below a threshold, then at <NUM>, the UE may switch to a different reception state (macro state) to save power in that SCC. For instance, referring to <FIG>, if the downlink scheduling rate drops below <NUM>% for a given SCC, the UE may transition at <NUM> from the ARx standby state <NUM> to the ARx disallowed state <NUM> for that SCC, and if the downlink scheduling rate further drops below <NUM>%, the UE may transition at <NUM> from the ARx disallowed state <NUM> to the force R1 state <NUM> for that SCC. The UE may also transition between macro states based on other metrics than the downlink scheduling rate (e.g. downlink traffic pattern, utilization rate, rank, or SNR) for each SCC.

The communication manager <NUM> includes a steady state component <NUM> that is configured to switch from a steady state to a fallback state prior to receiving a downlink transmission when a downlink grant is not received within a threshold number of subframes, e.g., as described in connection with <NUM>. The communication manager <NUM> further includes a measurement component <NUM> that is configured to measure a downlink PER, e.g., as described in connection with <NUM>. The communication manager <NUM> further includes a fallback state component <NUM> that receives input in the form of the downlink PER from the measurement component <NUM> and is configured to switch from a fallback state to a steady state in response to receiving a downlink grant and prior to receiving the downlink transmission, e.g., as described in connection with <NUM>. The measurement component <NUM> is further configured to measure the downlink PER during the switching performed by the fallback state component <NUM>, e.g., as described in connection with <NUM> and <NUM>. The communication manager <NUM> further includes a MCS component <NUM> that is configured to determine a variation in MCS for downlink transmissions, e.g., as described in connection with <NUM>.

The communication manager <NUM> further includes a determination component <NUM> that receives input in the form of the downlink PER from the measurement component <NUM> and is configured to determine a number of antennas for receiving a downlink transmission based on the measured, downlink PER, e.g., as described in connection with <NUM>. The determination component <NUM> also is configured to determine the number of antennas further based on the variation in MCS determined by MCS component <NUM>, e.g., as described in connection with <NUM> and <NUM>. The communication manager <NUM> further includes a fallback window component <NUM> that receives input in the form of the downlink PER from the measurement component <NUM> and is configured to change a size of a fallback window based on the measured, downlink PER, e.g., as described in connection with <NUM>. The fallback window component <NUM> is further configured to perform the changing independently for different component carriers, e.g., as described in connection with <NUM>. The communication manager <NUM> further includes a fallback state disabler component <NUM> that is configured to disable switching from a steady state to a fallback state prior to receiving the downlink transmission based on at least one of a downlink scheduling rate, a rank, or a signal to noise ratio, e.g., as described in connection with <NUM>. The fallback state disabler component <NUM> also receives input in the form of the downlink PER from the measurement component <NUM> and is further configured to disable the switching from the steady state to the fallback state based on the measured, downlink PER, e.g., as described in connection with <NUM> and <NUM>. The communication manager <NUM> further includes a reception state component <NUM> that is configured to switch from a first reception state to a second reception state after receiving the downlink transmission based on at least one of a downlink scheduling rate, a downlink traffic pattern, a utilization rate, a rank, or a signal to noise ratio, e.g., as described in connection with <NUM>. The reception state component <NUM> is further configured to perform the switching independently for different component carriers, e.g., as described in connection with <NUM>.

In one configuration, the apparatus <NUM>, and in particular the cellular baseband processor <NUM>, includes means for measuring a downlink packet error rate (PER); and means for determining a number of antennas for receiving a downlink transmission based on the measured, downlink PER. In one configuration, the means for determining may be configured to determine a variation in modulation coding schemes (MCS) for downlink transmissions, wherein the number of antennas may be determined further based on the variation in MCS.

In one configuration, the apparatus <NUM>, and in particular the cellular baseband processor <NUM>, may include means for switching from a steady state to a fallback state prior to receiving the downlink transmission when a downlink grant is not received within a threshold number of subframes.

In one configuration, the apparatus <NUM>, and in particular the cellular baseband processor <NUM>, may include means for switching from a fallback state to a steady state in response to receiving a downlink grant and prior to receiving the downlink transmission, wherein the downlink PER is measured during the switching.

In one configuration, the apparatus <NUM>, and in particular the cellular baseband processor <NUM>, may include means for switching from a first reception state to a second reception state after receiving the downlink transmission based on at least one of a downlink scheduling rate, a downlink traffic pattern, a utilization rate, a rank, or a signal to noise ratio. In one configuration, the first reception state may comprise an advanced receiver (ARx) standby state, and the second reception state may comprise an ARx disallowed state. In one configuration, the switching may be performed independently for different component carriers.

In one configuration, the apparatus <NUM>, and in particular the cellular baseband processor <NUM>, may include means for changing a size of a fallback window based on the measured, downlink PER. In one configuration, the changing may be performed independently for different component carriers.

In one configuration, the apparatus <NUM>, and in particular the cellular baseband processor <NUM>, may include means for disabling switching from a steady state to a fallback state prior to receiving the downlink transmission based on at least one of a downlink scheduling rate, a rank, or a signal to noise ratio. In one configuration, the disabling switching may further be based on the measured, downlink PER.

The aforementioned means may be one or more of the aforementioned components of the apparatus <NUM> configured to perform the functions recited by the aforementioned means. As described supra, the apparatus <NUM> may include the TX Processor <NUM>, the RX Processor <NUM>, and the controller/processor <NUM>.

Misalignment between the number of layers for transmission and the number of antennas for reception may occur during the transition time between steady states and fallback states in ARD. As a result, the UE may experience a high PER due to frequent pruning or discarding of downlink grants on PDCCH and CRC decoding failures on PDSCH. While fixedly disabling transitions to fallback states or fixedly increasing the size of fallback windows may reduce PER, such static increases may also inefficiently increase UE power consumption. To resolve these power inefficiencies, the UE may employ a more dynamic approach for employing ARD to provide an optimized balance between power savings and performance. Rx chains or numbers of antennas may be managed based on PER and other metrics (e.g. downlink scheduling rate, downlink traffic pattern, etc.), thereby maximizing UE reception performance with reduced PDCCH pruning and reduced PDSCH decoding failures while also maximizing power savings during low data scheduling. Additionally, improved downlink data throughput may be achieved due to the reduced PDCCH pruning and PDSCH decoding failures when the base station adapts subsequent downlink transmissions (e.g. based on OLLA).

Claim 1:
A method (<NUM>) of wireless communication at a user equipment, UE (<NUM>), comprising:
switching (<NUM>) from a steady state to a fallback state prior to receiving a downlink transmission when a downlink grant is not received within a threshold number of subframes, wherein in the fallback state the UE is restricted to selecting only one or two antennas, wherein the UE enters the steady state when it expects downlink traffic;
measuring (<NUM>) a downlink packet error rate, PER; and
determining (<NUM>) a number of antennas for receiving the downlink transmission based on the measured, downlink PER.