Patent Description:
In other examples (e.g., in a next generation, a new radio (NR), or <NUM> network), a wireless multiple access communication system may include a number of distributed units (DUs) (e.g., edge units (EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs), transmission reception points (TRPs), etc.) in communication with a number of central units (CUs) (e.g., central nodes (CNs), access node controllers (ANCs), etc.), where a set of one or more DUs, in communication with a CU, may define an access node (e.g., which may be referred to as a BS, next generation NodeB (gNB or gNodeB), TRP, etc.). A BS or DU may communicate with a set of UEs on downlink channels (e.g., for transmissions from a BS or DU to a UE) and uplink channels (e.g., for transmissions from a UE to a BS or DU).

3GPP draft R1-<NUM> relates to wake-up signal for efeMTC.

The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later.

Certain aspects of the present disclosure provide a method for wireless communication by a User Equipment (UE). A sample method generally includes determining one or more System Frame Number (SFN) hypotheses, each of the one or more SFN hypotheses representing a possible SFN at which the UE can wake up from a sleep state of a Discontinuous Reception (DRX) cycle. For at least one of the one or more SFN hypotheses a detection metric is generated based at least partially on a Physical Broadcast Control Channel (PBCH) sequence received from a base station; and the UE determines, based on a value of the detection metric, whether the at least one SFN hypothesis represents a current SFN in accordance with a clock source used by the base station for communicating with the UE. The UE determines, based on the at least one SFN hypothesis, a timing to be used for communicating with the base station, when the at least one SFN hypothesis is determined as representing the current SFN; and communicates with the base station based on the determined timing.

In an aspect, the method further includes determining a timing error related to a sleep state clock used by the UE in the sleep state of the DRX cycle, wherein the one or more SFN hypotheses is determined based at least one the timing error. In an aspect the timing error includes a a maximum timing error related to the seep state clock source used in the sleep state.

In an aspect, wherein determining the timing error includes determining the timing error as a function of a timing offset error related to the sleep state clock source and a sleep duration of the sleep state, wherein a value of the timing error comprises a number of frames, and wherein the one or more SFN hypotheses comprises one or more SFN hypothesis from a range of SFN hypotheses, wherein the range is a function of the value of the timing error.

In an aspect, determining whether the at least one SFN hypothesis represents a current SFN includes determining that the at least one SFN hypothesis represents a current SFN in accordance with the clock source, when a value of the detection metric exceeds a threshold value.

In an aspect, the method further includes for the at least one SFN hypothesis, generating a Physical Broadcast Channel (PBCH) sequence.

In an aspect, generating the detection metric includes comparing each coded bit in the generated PBCH sequence with a Log Likelihood Ratio (LLR) value representing a corresponding coded bit in the PBCH sequence received from the base station; flipping a sign of the LLR value when the corresponding coded bit in the generated PBCH sequence is minus one; and after the comparing and flipping has been performed for all coded bits in the generated PBCH sequence, generating a value of the detection metric by adding the remaining LLR values.

In an aspect, a PBCH payload corresponding to the generated PBCH sequence for the at least one SFN hypothesis comprises a first portion indicating an SFN corresponding to the SFN hypothesis and a second portion indicating other system information, wherein the SFN changes for only certain SFN hypotheses while the other system information remains the same.

In an aspect, generating the PBCH sequence for the at least one SFN hypothesis includes obtaining system information from a previous transmission of the PBCH; constructing a PBCH payload based on the obtained system information and the SFN corresponding to the at least one SFN hypothesis; generating PBCH data by adding cyclic redundancy check (CRC) bits to the constructed PBCH payload; coding the generated PBCH data to generate coded PBCH data; and scrambling the coded PBCH data to generate the PBCH sequence.

In an aspect, the generating the PBCH data and the coding is performed every fourth SFN hypothesis, wherein mod (SFN,<NUM>) = <NUM>, and wherein the scrambling is performed for every SFN hypothesis.

In an aspect, the detection metric indicates a level of correlation between the generated PBCH sequence and the actual PBCH sequence, wherein a higher value of the metric indicates a higher level of correlation.

In an aspect, the one or more SFN hypotheses is further based on an SFN calculated by the UE at start of SFN acquisition assuming zero timing error.

Certain aspects of the present disclosure provide an apparatus for wireless communication by a UE. The apparatus generally includes at least one processor and a memory coupled to the at least one processor. The processor is generally configured to determine one or more System Frame Number (SFN) hypotheses, each of the one or more SFN hypotheses representing a possible SFN at which the UE can wake up from a sleep state of a Discontinuous Reception (DRX) cycle. For at least one of the one or more SFN hypotheses the at least one apparatus generates a detection metric based at least partially on a Physical Broadcast Control Channel (PBCH) sequence received from a base station; and determines, based on a value of the detection metric, whether the at least one SFN hypothesis represents a current SFN in accordance with a clock source used by the base station for communicating with the UE. The at least one apparatus determines, based on the at least one SFN hypothesis, a timing to be used for communicating with the base station, when the at least one SFN hypothesis is determined as representing the current SFN; and communicates with the base station based on the determined timing.

In an aspect, the at least one processor is further configured to determine a timing error related to a sleep state clock used by the UE in the sleep state of the DRX cycle, wherein the one or more SFN hypotheses is determined based at least one the timing error.

In an aspect, the timing error comprises a maximum timing error related to the seep state clock source used in the sleep state.

In an aspect, the at least one processor is configured to determine that the at least one SFN hypothesis represents a current SFN in accordance with the clock source, when a value of the detection metric exceeds a threshold value.

In an aspect, the at least one processor is further configured to for the at least one SFN hypothesis, generate a Physical Broadcast Channel (PBCH) sequence.

In an aspect, the at least one processor is further configured to compare each coded bit in the generated PBCH sequence with a Log Likelihood Ratio (LLR) value representing a corresponding coded bit in the PBCH sequence received from the base station; flip a sign of the LLR value when the corresponding coded bit in the generated PBCH sequence is minus one; and after the comparing and flipping has been performed for all coded bits in the generated PBCH sequence, generate a value of the detection metric by adding the remaining LLR values.

Certain aspects of the present disclosure provide a computer-readable medium for wireless communication by a UE. The computer-readable medium generally stores instructions which when processed by at least one processor performs a method. The method generally includes determining one or more System Frame Number (SFN) hypotheses, each of the one or more SFN hypotheses representing a possible SFN at which the UE can wake up from a sleep state of a Discontinuous Reception (DRX) cycle. For at least one of the one or more SFN hypotheses a detection metric is generated based at least partially on a Physical Broadcast Control Channel (PBCH) sequence received from a base station; and the UE determines, based on a value of the detection metric, whether the at least one SFN hypothesis represents a current SFN in accordance with a clock source used by the base station for communicating with the UE. The UE determines, based on the at least one SFN hypothesis, a timing to be used for communicating with the base station, when the at least one SFN hypothesis is determined as representing the current SFN; and communicates with the base station based on the determined timing.

In an aspect, the computer-readable medium further includes instructions for determining a timing error related to a sleep state clock used by the UE in the sleep state of the DRX cycle, wherein the one or more SFN hypotheses is determined based at least one the timing error.

In an aspect, determining whether the at least one SFN hypothesis represents a current SFN comprises determining that the at least one SFN hypothesis represents a current SFN in accordance with the clock source, when a value of the detection metric exceeds a threshold value.

In an aspect, the computer-readable medium further includes instructions for the at least one SFN hypothesis, generating a Physical Broadcast Channel (PBCH) sequence.

Certain aspects of the present disclosure provide a method for wireless communication by a User Equipment (UE). A sample method generally includes determining, for a System Frame Number (SFN) hypothesis, a detection metric based at least partially on a Physical Broadcast Control Channel (PBCH) sequence received from a base station, the SFN hypothesis representing a possible SFN at which the UE can wake up from the sleep state; determining, based on a value of the detection metric, whether the SFN hypothesis represents a current SFN in accordance with a clock source used by the base station for communicating with the UE; determining, based on the SFN hypothesis, a timing to be used for communicating with the base station, when the SFN hypothesis is determined as representing the current SFN; and communicating with the base station based on the determined timing.

In an aspect, the method further includes determining a timing error related to a sleep state clock source used by the UE in a sleep state of a Discontinuous Reception (DRX) cycle; and determining a plurality of System Frame Number (SFN) hypotheses based at least on the timing error, each of the plurality of SFN hypotheses representing a possible SFN at which the UE can wake up from the sleep state, wherein the SFN hypothesis is one of the plurality of SFN hypotheses
In an aspect, the timing error comprises a maximum timing error related to the sleep state clock source used in the sleep state.

In an aspect, determining the timing error includes determining the timing error as a function of a timing offset error related to the sleep state clock source and a sleep duration of the sleep state, wherein a value of the timing error comprises a number of frames, and wherein the SFN hypothesis is a SFN hypothesis from a range of SFN hypotheses, wherein the range is a function of the value of the timing error.

In an aspect, determining whether the SFN hypothesis represents a current SFN includes determining that the SFN hypothesis represents a current SFN in accordance with the clock source, when a value of the detection metric exceeds a threshold value.

In an aspect, the method further includes generating, for the SFN hypothesis, a Physical Broadcast Channel (PBCH) sequence.

In an aspect, a PBCH payload corresponding to the generated PBCH sequence for the SFN hypothesis includes a first portion indicating an SFN corresponding to the SFN hypothesis and a second portion indicating other system information, wherein the SFN changes for only certain SFN hypotheses while the other system information remains the same.

In an aspect, generating the PBCH sequence for the SFN hypothesis includes
In an aspect, obtaining system information from a previous transmission of the PBCH; constructing a PBCH payload based on the obtained system information and the SFN corresponding to the SFN hypothesis; generating PBCH data by adding cyclic redundancy check (CRC) bits to the constructed PBCH payload; coding the generated PBCH data to generate coded PBCH data; and scrambling the coded PBCH data to generate the PBCH sequence.

Certain aspects provide a method for wireless communication by a User Equipment (UE). A sample method generally includes determining a potential timing error related to a clock source used in the sleep state of a Discontinuous Reception (DRX) cycle; determining a number of System Frame Number (SFN) hypotheses based on the potential timing error, each SFN hypothesis representing a possible SFN at which the UE can wake up from the sleep state; and for each of the SFN hypothesis, generating a Physical Broadcast Channel (PBCH) sequence; generating a detection metric by comparing the generated PBCH sequence with an actual PBCH sequence received from a base station; and determining, based on a value of the detection metric, whether the SFN hypothesis represents a current SFN in accordance with a correct clock source.

Certain aspects provide an apparatus for wireless communication by a User Equipment (UE). A sample apparatus generally includes at least one processor and a memory coupled to the at least one processor. The at least one processor is generally configure to determine a potential timing error related to a clock source used in the sleep state of a Discontinuous Reception (DRX) cycle; determine a number of System Frame Number (SFN) hypotheses based at least on the potential timing error, each SFN hypothesis representing a possible SFN at which the UE can wake up from the sleep state; and for each of the SFN hypothesis: generate a Physical Broadcast Channel (PBCH) sequence; generate a detection metric by comparing the generated PBCH sequence with an actual PBCH sequence received from a base station; and determine, based on a value of the detection metric, whether the SFN hypothesis represents a current SFN in accordance with a correct clock source.

Certain aspects provide an apparatus for wireless communication by a User Equipment (UE). An example apparatus generally includes means for determining a potential timing error related to a clock source used in the sleep state of a Discontinuous Reception (DRX) cycle; means for determining a number of System Frame Number (SFN) hypotheses based at least on the potential timing error, each SFN hypothesis representing a possible SFN at which the UE can wake up from the sleep state; and means for performing for each of the SFN hypothesis: generating a Physical Broadcast Channel (PBCH) sequence; generating a detection metric by comparing the generated PBCH sequence with an actual PBCH sequence received from a base station; and determining, based on a value of the detection metric, whether the SFN hypothesis represents a current SFN in accordance with a correct clock source.

Certain aspects provide a computer-readable medium for wireless communication by a User Equipment (UE). A sample computer-readable medium generally stores instructions which when processed by at least one processor performs a method. The method generally includes determining a potential timing error related to a clock source used in the sleep state of a Discontinuous Reception (DRX) cycle; determining a number of System Frame Number (SFN) hypotheses based on the potential timing error, each SFN hypothesis representing a possible SFN at which the UE can wake up from the sleep state; and for each of the SFN hypothesis, generating a Physical Broadcast Channel (PBCH) sequence; generating a detection metric by comparing the generated PBCH sequence with an actual PBCH sequence received from a base station; and determining, based on a value of the detection metric, whether the SFN hypothesis represents a current SFN in accordance with a correct clock source.

Aspects of the present disclosure provide means for, apparatus, processors, and computer-readable mediums for performing techniques and methods that may be complementary to UE operations described herein, for example, by a BS.

Other aspects, features, and embodiments of the technology will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments in conjunction with the accompanying figures. While features of the technology discussed below may be described relative to certain embodiments and figures below, all embodiments can include one or more of the advantageous features discussed. While one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments discussed. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments such exemplary embodiments can be implemented in varying shapes, sizes, layouts, arrangements, circuits, devices, systems, and methods.

It is contemplated that elements disclosed in one aspect, figures, or embodiments may be beneficially utilized on others without specific recitation.

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums fast timing acquisition in a variety of scenarios (e.g., Enhanced DRX (eDRX)).

Certain aspects of the present disclosure discuss a technique for faster correction of timing offset errors upon DRX wakeup. Such techniques may aid in timing corrections by hypothesizing PBCH payloads over a number of SFN hypotheses determined based on a potential timing error as a result of a sleep state clock source.

In an aspect, faster correction of timing offset errors allows for a shorter modem warmup time allowing the UE to wakeup closer in time to an expected paging occasion, thus saving modem power. In an aspect, the discussed techniques are beneficial for longer DRX cycles and low SNR applications.

While aspects and embodiments are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases may come about in many different arrangements and scenarios. Innovations described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, packaging arrangements. For example, embodiments and/or uses may come about via integrated chip embodiments and other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, AI-enabled devices, etc.). While some examples may or may not be specifically directed to use cases or applications, a wide assortment of applicability of described innovations may occur. Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or OEM devices or systems incorporating one or more aspects of the described innovations. In some practical settings, devices incorporating described aspects and features may also necessarily include additional components and features for implementation and practice of claimed and described embodiments. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including antenna, RF-chains, power amplifiers, modulators, buffer, processor(s), interleaver, adders/summers, etc.). It is intended that innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, end-user devices, etc. of varying sizes, shapes, and constitution.

The techniques described herein may be used for various wireless communication technologies, such as 3GPP Long Term Evolution (LTE), LTE-Advanced (LTE-A), code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), single-carrier frequency division multiple access (SC-FDMA), time division synchronous code division multiple access (TD-SCDMA), and other networks.

NR access (e.g., <NUM> NR) may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., <NUM> or beyond), millimeter wave (mmW) targeting high carrier frequency (e.g., <NUM> or beyond), massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC).

In certain aspects, a UE 120a includes a timing acquisition module configured to perform certain aspects of the techniques discussed herein with respect to a UE.

As illustrated in <FIG>, the wireless communication network <NUM> may include a number of base stations (BSs) <NUM> and other network entities. A BS may be a station that communicates with user equipments (UEs). Each BS <NUM> may provide communication coverage for a particular geographic area. In some examples, the BSs may be interconnected to one another and/or to one or more other BSs or network nodes (not shown) in wireless communication network <NUM> through various types of backhaul interfaces, such as a direct physical connection, a wireless connection, a virtual network, or the like using any suitable transport network.

A finely dashed line with double arrows indicates potentially interfering transmissions between a UE and a BS.

<FIG> illustrates example components of BS <NUM> and UE <NUM> (e.g., in the wireless communication network <NUM> of <FIG>), which may be used to implement aspects of the present disclosure. For example, antennas <NUM>, processors <NUM>, <NUM>, <NUM>, and/or controller/processor <NUM> of the UE <NUM> and/or antennas <NUM>, processors <NUM>, <NUM>, <NUM>, and/or controller/processor <NUM> of the BS <NUM> may be used to perform the various techniques and methods described herein. For example, in certain aspects, controller/processor <NUM> includes a timing acquisition module configured to perform certain aspects of the techniques discussed herein with respect to a UE.

The transmit processor <NUM> may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and cell-specific reference signal (CRS). A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a-232t. Downlink signals from modulators 232a-232t may be transmitted via the antennas 234a-234t, respectively.

At the UE <NUM>, the antennas 252a-252r may receive the downlink signals from the BS <NUM> and may provide received signals to the demodulators (DEMODs) in transceivers 254a-254r, respectively. A MIMO detector <NUM> may obtain received symbols from all the demodulators 254a-254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols.

The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the demodulators in transceivers 254a-254r (e.g., for SC-FDM, etc.), and transmitted to the base station <NUM>.

The controllers/processors <NUM> and <NUM> may direct the operation at the BS <NUM> and the UE <NUM>, respectively. The controller/processor <NUM> and/or other processors and modules at the BS <NUM> may perform or direct the execution of processes for the techniques described herein.

Each radio frame, represented by a system frame number (SFN), may have a predetermined duration (e.g., <NUM>) and may be partitioned into <NUM> subframes, each of <NUM>, with indices of <NUM> through <NUM>.

Extended Discontinuous Reception (eDRX) with longer sleep cycles was introduced in <NUM>rd Generation Partnership Project (3GPP) Rel. eDRX cycles generally include up to <NUM>. 24secs in connected mode and up to <NUM> minutes in idle mode (also referred to as sleep state). A UE modem generally goes to sleep between DRX wakeups in order to save power.

UE modems generally use a low accuracy clock during eDRX sleep states. Thus, UE modems generally drift in time and frequency accuracy during the sleep state, which results in a frequency offset (FO) error and/or a timing offset (TO) error when the UE wakes up from a sleep state.

For example, if the frequency offset error of a sleep state clock is 1ppm, for a carrier frequency fc = <NUM>, the frequency offset at wakeup is about <NUM> on either side of the actual carrier frequency (fc).

Further, if the timing offset error of the sleep state clock is 10ppm, for sleep duration of <NUM>*128secs, the timing offset at wakeup is about <NUM> on either side of the expected wakeup time.

In order to correct the frequency offset and timing offset, the UE modem generally wakes up delta time (DT) ahead of an expected paging occasion (PO). In an aspect, DT represents a modem warmup duration which includes time required by the modem to resolve the error and acquire the correct timing to receive a page from the network. For example, the UE wakes up a certain number of frames before the frame in which it expects to receive a page from the network, in order to allow the UE modem sufficient time to acquire the correct timing.

<FIG> illustrates an exemplary timing acquisition <NUM> upon wakeup from a eDRX sleep state, in accordance with certain aspects of the present disclosure.

As shown in <FIG>, the UE modem is in a DRX sleep state between time instants <NUM> and <NUM>. PO represents a paging opportunity expected by the UE at time instant <NUM>. As shown, the modem wakes up at time instant <NUM>, which is DT duration ahead of the PO to allow the UE time to correct any timing error as a result of the low accuracy clock reference used during the sleep state.

In certain aspects, power consumption of the UE modem heavily depends on the warmup duration, DT of the modem. Thus, it is desirable that the modem warmup time is as short as possible to save power consumption so that the UE wakes up from a sleep state as close as possible to the paging occasion.

Certain aspects of the present disclosure discuss a technique for faster correction of timing offset errors upon DRX wakeup, by hypothesizing PBCH payloads over a number of SFN hypotheses determined based on a potential timing error as a result of a sleep state clock source.

It may be noted that while techniques for fast timing offset correction and acquisition are discussed in the present disclosure with reference to eDRX, these techniques are equally applicable to DRX.

The PBCH is broadcasted by a base station and includes the Master Information Block (MIB). The PBCH generally includes a 24bit PBCH payload (e.g., MIB payload) and <NUM> bits for cyclic redundancy check (CRC) for a total of <NUM> PBCH bits. The <NUM> bit PBCH payload generally includes <NUM> bits for SFN indication and 16bits for other system information. The PBCH is transmitted once every frame (10msec).

When generating PBCH at a base station, a <NUM> bit CRC is generated and the generated CRC is attached to the PBCH/MIB payload after which the size of the payload is <NUM> bits (<NUM> bit of MIB + <NUM> bit of CRC). Tail-Bit Convolution Encoding (TBCC) is performed over the <NUM> bits and the output is <NUM> streams of <NUM> bits each (a total of <NUM> bits). Rate matching is performed which includes repetition coding, where the <NUM> streams of size <NUM> bits (40x3bits) is repeated <NUM> times to get <NUM> bits. The repetition rate is very high since the MIB is vital information and the UE cannot afford to lose it. These <NUM> bits are scrambled with a scrambling sequence. Finally, QPSK modulation is performed over these <NUM> bits to obtain <NUM> complex QPSK symbols.

In an aspect, the scrambling sequence used for generating the PBCH sequence changes every SFN. However, the <NUM> bit PBCH payload remains constant for four consecutive frames or SFNs (a duration of <NUM>). That is the PBCH payload changes every four frames or <NUM>. In an aspect, only the eight MSB bits of the <NUM> bit PBCH payload changes every four frames or <NUM> as the SFN increments every four frames. The remaining <NUM> bit system information of the PBCH payload is not expected to change at all.

At a receiving UE, the PBCH is conventionally decoded using combining and TBCC decoding using Viterbi's algorithm or other algorithm. At lower SNRs PBCH payloads are combined over multiple TTIs (e.g., TTI=<NUM>) to achieve successful decoding.

In certain aspects, as discussed in the following paragraphs, the fact that the <NUM> SFN bits of the PBCH payload changes every four SFNs and that the <NUM> system information bits are not expected to change may be leveraged to hypothesize PBCH payloads for different SFN hypotheses. This may allow a UE to quickly resolve any timing error when the UE wakes up after a DRX sleep cycle.

<FIG> illustrates example operations 500A performed by a UE (e.g., UE modem) for fast timing acquisition upon wake up after a sleep state in DRX, in accordance with certain aspects of the present disclosure.

Operations 500A begin, at <NUM>, by determining one or more SFN hypotheses. In some cases, each of the one or more SFN hypotheses represents a possible SFN at which the UE can wake up from a sleep state of a DRX cycle (e. g, eDRX cycle). A number of individual SFN hypotheses can be grouped into a set of SFN hypotheses. In an aspect, the UE determines a timing error related to a sleep state clock source used by the UE in the sleep state of the DRX cycle. The UE determines the one or more SFN hypotheses based at least on the timing error. In an aspect, the timing error is a maximum timing error associated with the sleep state clock source. As mentioned above, a UE's clock may drift while in a sleep state. This drift can cause communication challenges and concerns. Determination of potential timing errors helps to resolve issues associated with clock drift. In an aspect, the timing error is a maximum timing error associated with the sleep state clock source.

At <NUM>, for at least one of the one or more SFN hypotheses, the UE generates a detection metric based least partially on a PBCH sequence received from a base station. The UE further determines, based on a value of the detection metric, whether the at least one SFN hypothesis represents a current SFN in accordance with a clock source used by the base station for communicating with the UE. In an aspect, for the at least one SFN hypothesis, the UE generates a Physical Broadcast Channel (PBCH) sequence. The UE generates the detection metric for the at least one SFN hypothesis by comparing the generated PBCH sequence with the PBCH sequence received from the base station. In an aspect, the UE determines that the at least one SFN hypothesis represents a current SFN in accordance with the second clock source, when the value of the detection metric exceeds a threshold value.

At <NUM>, the UE determines, based on the at least one SFN hypothesis, a timing to be used for communicating with the base station, when the at least one SFN hypothesis is determined as representing the current SFN.

At <NUM>, the UE communicates with the base station based on the determined timing.

<FIG> illustrates another set of example operations 500B performed by a UE (e.g., UE modem) for fast timing acquisition upon wake up after a sleep state in DRX, in accordance with certain aspects of the present disclosure.

Operations 500B begin, at <NUM>, by determining a timing error related to a first clock source used by the UE in a sleep state of a DRX cycle (e.g., eDRX). As mentioned above, a UE's clock may drift while in a sleep state. This drift can cause communication challenges and concerns. Determination of potential timing errors helps to resolve issues associated with clock drift. In an aspect, the timing error is a maximum timing error associated with the sleep state clock source.

At <NUM>, the UE determines one or more SFN hypotheses based at least one on the timing error. In some cases, each of the one or more SFN hypotheses can represent a possible SFN at which the UE can wake up from the sleep state. A number of individual SFN hypotheses can be grouped into a set of SFN hypotheses.

At <NUM>, for at least one SFN hypothesis, the UE generates a PBCH sequence, and generates a detection metric by comparing the generated PBCH sequence with an actual PBCH sequence received from a base station. The UE determines, based on a value of the detection metric, whether the at least one SFN hypothesis represents a current SFN in accordance with a second clock source used by the base station for communicating with the UE. In an aspect, as discussed in the following paragraphs, the UE acquires the correct timing (e.g., timing in accordance with the second clock source) based on evaluating the detecting metric generated for one or more SFN hypotheses. For instance, when the UE determines that the detection metric generated for a particular SFN hypothesis exceeds a threshold value, the UE determines that the SFN of the particular SFN hypothesis is according to the correct timing (e.g., based on the second clock source). The UE then adjusts its own clock reference based on the timing of the particular SFN hypothesis.

<FIG> illustrates another set of example operations 500C performed by a UE (e.g., UE modem) for fast timing acquisition upon wake up after a sleep state in DRX, in accordance with certain aspects of the present disclosure.

Operations 500C begin, at <NUM>, by determining, for a SFN hypothesis, a detection metric based at least partially on a PBCH sequence received from a base station, the SFN hypothesis representing a possible SFN at which the UE can wake up from the sleep state. In an aspect, the UE determines a timing error related to a sleep state clock source used by the UE in the sleep state of the DRX cycle. The UE determines the SFN hypothesis based at least on the timing error. In an aspect, the timing error is a maximum timing error associated with the sleep state clock source. As mentioned above, a UE's clock may drift while in a sleep state. This drift can cause communication challenges and concerns. Determination of potential timing errors helps to resolve issues associated with clock drift. In an aspect, the timing error is a maximum timing error associated with the sleep state clock source.

At <NUM>, the UE determines, based on a value of the detection metric, whether the SFN hypothesis represents a current SFN in accordance with a clock source used by the base station for communicating with the UE.

At <NUM>, the UE determines based on the SFN hypothesis, a timing to be used for communicating with the base station, when the SFN hypothesis is determined as representing the current SFN.

In certain aspects, if PO denotes the system frame number at which the UE is expecting to receive a transmission from the base station, the modem generally needs to wake up at a system frame number SF_wu ahead of the PO, where SF_wu is given as, <MAT>.

where Nmax is the maximum expected timing error in terms of number of radio frames. In an aspect, the UE determines the Nmax as a function of ppm clock error of the sleep state clock source and a sleep duration of the eDRX cycle. In an aspect, the ppm error dictates how much earlier from the PO the UE needs to wake up. For example, the higher is the ppm error, the earlier the UE needs to wake up.

D_init is the time required for modem initial wakeup procedures including time required for PSS/SSS detection.

D_sfn represents the delay in acquiring the correct timing (e.g., using PBCH detection). In an aspect, the UE determines the D_sfn as a function of the sleep duration of the eDRX cycle, SNR and expected time to correct the timing error and acquire the correct timing. In an aspect, the faster the UE expects to acquire the correct timing, the shorter is D_sfn and the later the UE can wake up ahead of the PO, which as described earlier translates to power savings.

<FIG> illustrates actual UE wake up times after sleep state for different clock references, in accordance with aspects of the present disclosure. The illustrated wake up times may correspond to either DRX or eDRX scenarios. As shown, there are various example timelines showing a variety of clock scenarios for a UE: <NUM> represents a timeline corresponding to a correct clock, <NUM> represents a timeline corresponding to a fast clock, and <NUM> represents a timeline corresponding to a slow clock. As shown, the UE sleeps at time instant <NUM>. The UE expects to receive a page from the network at PO <NUM>.

As shown with reference to timeline <NUM>, in accordance with a correct clock reference (TO=<NUM>), the UE wakes up at SF_wu (SF_wu = PO - D_init - D_sfn - Nmax), and is expected to be at "SF_wu + Dinit" after performing the modem initial wakeup procedures. In an aspect, if the clock is correct with no timing offset error (e.g., according to timeline <NUM>), the UE at "SFP_wu" and at "SF_wu + Dinit" is at the correct corresponding SFNs it expects to be at.

Yet if there is a timing offset error, the UE may awake at an improper timing. For example, a UE may wake up at an SFN which is not the SFN the UE is expecting to wake up at. For example, if the sleep state clock reference has a positive time offset, the sleep state clock runs faster than the correct clock and the UE will actually wake up earlier than it expects to wake up. As shown with reference to timeline <NUM>, in accordance with a fast clock with a positive actual timing error of "+n_e", the UE actually wakes up at "SF_wu - n_e" which is n_e earlier than the SFN "SF_wu" the UE expects to wake up at, and the UE is actually at "SF_wu + Dinit - n_e" after initial wakeup procedures which is also n_e earlier than "SF_wu + Dinit" the UE is expected to be at. Similarly, if the sleep state clock reference has a negative time offset, the sleep state clock runs slower than the correct clock and the UE will actually wake up later than it expects to wake up. As shown with reference to timeline <NUM>, in accordance with a slow clock with a negative actual timing error of "-n_e", the UE actually wakes up at "SF_wu + n_e" which is n_e later than the SFN "SF_wu" the UE expects to wake up at, and the UE is actually at "SF_wu + Dinit + n_e" after initial wakeup procedures which is also n_e later than "SF_wu + Dinit" the UE is expected to be at.

In an aspect, when the UE wakes up at an improper SFN, the UE may take appropriate action. For example, when a UE awakes at an SFN that is not the SFN the UE is expecting to wake up at (e.g., as a result of a clock error), the UE needs to determine the SFN of the frame it actually woke up at in order to acquire the correct timing with respect to the correct clock reference. Determination of a correct awakening SFN by the UE may help a UE take action to align or re-align to proper timing for quality communication purposes.

As may be inferred from the above discussion with reference to <FIG>, given that n_e is the actual TO error, the UE, when attempting to wakeup at SF_wu may actually wakeup at any time instant between "SF_wu - n_e" and "SF_wu + n_e". The actual timing error n_e may take a maximum value of Nmax (e.g., +Nmax or -Nmax depending on whether the UE clock is faster or slower respectively). Thus, after frame boundary acquisition using PSS/SSS, the UE may wakeup at any SFN between "SF_wu+D_init-Nmax" and "SF_wu+D_init+Nmax". That is the SFN, after initial wakeup procedures are completed, is bounded by ["SF_wu+D_init-Nmax", "SF_wu+D_init+Nmax"].

So, the uncertainty in SFN upon wakeup is (<NUM>*Nmax+<NUM>) SFN values. In an aspect, for eDRX, since the only factor of the <NUM> bit PBCH payload that changes is the <NUM> bit SFN, the uncertainty in the PBCH payload upon wake up is also (<NUM>*Nmax+<NUM>) values. That is, if the UE starts acquiring SFN information at any SFN between "SF_wu+D_init-Nmax" and "SF_wu+D_init+Nmax", the PBCH payload at that SFN can take (<NUM>*Nmax+<NUM>) values.

In certain aspects, the UE, upon waking up from an eDRX sleep state (e.g., after initial wakeup procedures, for e.g., D_init), may hypothesize the PBCH payload over (<NUM>*Nmax+<NUM>) SFN hypotheses, in order to determine the actual SFN the UE woke up at and thus acquire the correct timing. For example, the UE, upon wakeup from an eDRX sleep state (e.g., after initial wakeup procedures), may hypothesize the PBCH payload over (<NUM>*Nmax+<NUM>) SFN hypotheses from "SF_wu+D_init-Nmax" to "SF_wu+D_init+Nmax". Once the UE determines the PBCH payload corresponding to the SFN the UE is actually positioned at on the timeline (e.g., based on the hypothesizing the PBCH payloads), the UE can determine the SFN number of the frame the UE is positioned at based on the <NUM> MSB bits of the PBCH payload. The UE then knows its position on the timeline according to the correct clock reference.

In some scenarios, if the UE attempts to decode the PBCH payload upon waking up from a sleep state using the conventionally used method (e.g., TBCC decoding using Viterbi's algorithm), the UE may have to decode the entire convolutional code which has <NUM><NUM> codewords. Hypothesizing the PBCH payload over only (<NUM>*Nmax+<NUM>) possibilities as discussed herein is significantly less than attempting to decode <NUM><NUM> codewords. Detecting the PBCH payload by hypothesizing over a significantly lower number of possibilities in accordance with aspects of the present disclosure results in a reliable and quick PBCH detection.

<FIG> illustrates an example block diagram <NUM> for fast PBCH detection, in accordance with certain aspects of the present disclosure. In an aspect, the operations described herein with reference to block diagram <NUM> may be implemented by the timing acquisition module of the controller/processor <NUM> of the UE <NUM> as shown in <FIG>.

As shown in <FIG>, block diagram <NUM> generates a PBCH sequence for each of the (<NUM>*Nmax+<NUM>) consecutive SFN hypotheses. In an aspect, the generation of the PBCH sequence for each SFN hypothesis is similar to how the PBCH sequence is generated by a base station for broadcasting in a cell.

In an aspect, when the UE wakes up from an eDRX sleep state at a particular SFN, the UE obtains the values of SF_wu, D_init and Nmax. The UE may calculate these values as discussed in the above paragraphs. In an aspect, these calculations may be performed by the controller/processor <NUM> of UE <NUM> as shown in <FIG>. The UE then generates a PBCH sequence for each SFN hypothesis from "SF_wu+D_init-Nmax" to "SF _wu+D_init+Nmax".

As shown in <FIG>, the PBCH sequence generation for each SFN hypothesis includes PBCH data generation (702a-702n), TBCC coding (704a-704n) and scrambling (706a-706n). PBCH data generation <NUM> includes constructing the <NUM> bit PBCH/MIB payload based on PBCH prior information. In an aspect, the PBCH prior information includes the known <NUM> bit system information of the <NUM> bit payload and the fact that the <NUM> bit system information remains unchanged. In an aspect, generating PBCH data for a particular SFN hypothesis includes appending the known <NUM> bit system information to the <NUM> bit SFN of the SFN hypothesis, and then attaching a <NUM> bit CRC to the <NUM> bit payload to generate 40bits of PBCH data.

As shown in <FIG>, for each SFN hypothesis, the <NUM> bit PBCH data is then TBCC encoded at <NUM> to generate a <NUM> bit PBCH sequence. The <NUM> bit PBCH sequence is then scrambled at <NUM> to generate a scrambled PBCH sequence.

As noted in the above paragraph, the PBCH payload changes only every four SFNs. Thus, the PBCH data generation <NUM> and the TBCC encoding needs to be performed only every four consecutive SFN hypotheses. This further reduces processing at the UE resulting in additional power savings. However, the scrambling sequence changes every SFN and thus the scrambling needs to be performed for every SFN hypothesis.

<FIG> illustrates an example table <NUM> showing a number of SFN hypotheses and corresponding number of maximum turbo coding instances for different timing errors and maximum timing error values, in accordance with aspects of the present disclosure.

Column <NUM> shows example clock timing errors in milli seconds, column <NUM> shows Nmax corresponding to each of the timing errors, column <NUM> shows a number of SFN hypotheses for each Nmax (calculated as (<NUM>*Nmax+<NUM>)) and column <NUM> shows the maximum number of TBCC coding instances for a corresponding number of hypotheses. As shown in table <NUM>, for each value of Nmax, the number of TBCC coding instances is less than the number of SFN hypotheses, indicating that TBCC coding need not be performed for every SFN hypothesis.

In an aspect, for each SFN hypothesis i, the metric computation and comparison block calculates a detection metric (di) for the generated scrambled PBCH sequence, wherein the detection metric (di) detects the PBCH payload by evaluating a correlation of the bit stream of the scrambled PBCH sequence with input LLRs <NUM> received in the frame identified by the SFN of the SFN hypothesis, the LLRs corresponding to a coded PBCH bit stream received by the UE in the frame identified by the SFN of the SFN hypothesis.

In an aspect, the detection metric di for an SFN hypothesis i is calculated as,
<MAT>
where,.

In an aspect, the flip(LLR, ci) function compares the input LLR vector with the generated PBCH coded bit stream, and flips the sign of an LLR value (e.g., '+<NUM>' to '-<NUM>' or '-<NUM>' to '+<NUM>') if the corresponding ci coded bit is '-<NUM>'. On the other hand, the function keeps the sign of an LLR value unchanged if the corresponding ci coded bit is '+<NUM>'. As an example, if an LLR value is '+<NUM>' and the corresponding ci coded bit is '-<NUM>', the flip(. ) function flips the sign of the LLR value to '-<NUM>'. However, if the ci coded bit is '+<NUM>', the LLR value is left unchanged. Once the flip(. ) function has been executed, the remaining LLR values are added by the sum (. ) function.

Thus, the sum(flip(LLR, ci)) function determines how closely correlated the generated ci coded bits are to the actual PBCH coded bits for the SFN i by comparing the input LLR vector corresponding to the actual PBCH coded bits with the generated ci coded bits. A higher value of the detection metric di indicates a higher correlation between the ci coded bits with the actual PBCH coded bits for the SFN i. On the other hand a lower value of the detection metric di indicates that a lower correlation between the ci coded bits with the actual PBCH coded bits for the SFN i.

For example, assuming that the LLR vector is (+<NUM>, +<NUM>, -<NUM>, -<NUM>, +<NUM>, +<NUM>) and the ci is (+<NUM>, +<NUM>, -<NUM>, -<NUM>, +<NUM>, +<NUM>). Since the third and fourth values of the ci bits is '-<NUM>', the signs of the corresponding third and fourth LLR values will be flipped. Thus, the values of the LLR vector after the flip(. ) function has been executed is (+<NUM>, +<NUM>, +<NUM>, +<NUM>, +<NUM>, +<NUM>). Adding these values results in di = <NUM>. The high value of di shows that the generated ci bits and the actual PBCH coded bits received at SFN i are highly correlated. In another example, assuming that the LLR vector is (+<NUM>, +<NUM>, -<NUM>, -<NUM>, +<NUM>, +<NUM>) and the ci is (+<NUM>, +<NUM>, -<NUM>, -<NUM>, -<NUM>, - <NUM>). Since the third, fourth, fifth and sixth values of the ci bits is '-<NUM>', the signs of the corresponding third, fourth, fifth and sixth LLR values will be flipped. Thus, the values of the LLR vector after the flip(. ) function has been executed is (+<NUM>, +<NUM>, +<NUM>, +<NUM>, -<NUM>, -<NUM>). Adding these values results in di = <NUM> The lower value of di shows that the generated ci bits and the actual PBCH coded bits received at SFN i are not as highly correlated. It may be noted that the lengths of the input LLR vector and the ci bit stream in the above examples has been selected for ease of explanation, and do not represent the actual lengths of either vectors.

In an aspect, the UE starts PBCH detection at SFN hypothesis "SF_wu+D_init-Nmax" and calculates the detection metric di for each SFN hypothesis i. The UE stops the detection once detection metric di for a particular SFN hypothesis exceeds a threshold value, and the SFN i corresponding to the winning SFN hypothesis is determined as the actual SFN according to the correct timing. Once the UE has determined the actual SFN according to the correct timing, the UE knows its position on the timeline according to the correct clock source (e.g., clock source maintained at the network) and the UE has acquired the correct timing, and is ready to receive pages from the network. In an aspect, the threshold value of the detection metric di is designed to meet less than x% (e.g., <NUM>%) probability of missed detection, meaning the threshold value of the detection metric di is high enough such that the detection is stopped only when the generated ci bit stream and the input LLR vector are highly correlated. This ensures that the UE determines the correct timing with high accuracy.

In certain aspects, the UE may combine subsequent PBCH transmissions to improve PBCH detection. For example, if the value of the detection metric di does not exceed the threshold value for the (<NUM>*Nmax+<NUM>) SFN hypotheses at a particular frame, the UE may perform PBCH detection for multiple frames and combine the results of the detection over the multiple frames.

<FIG> illustrates an example table <NUM> showing an example comparison between a baseline (e.g., currently existing) scheme for PBCH detection and the proposed scheme of SFN hypotheses based PBCH detection as discussed (e.g., with reference to <FIG>) in accordance with aspects of the present disclosure.

The example of <FIG> assumes a sleep duration <=<NUM>*<NUM> and max. clock error = +/-<NUM> PPM. This results in a timing error <= +/- <NUM>. As shown in the first row or table <NUM> of <FIG>, for a timing error of <NUM> or less, SFN can be acquired using the proposed scheme by hypothesizing PBCH over only <NUM> SFN possibilities.

Table <NUM> shows example data relating to PBCH detection performed for different SNR values using the proposed scheme as discussed in aspects of this disclosure and a baseline scheme (e.g., a currently used scheme). For example, the baseline scheme may use a tail biting Viterbi decoder to decode the PBCH.

In table <NUM>, column <NUM> shows different values of SNR in db, column <NUM> shows time taken in milli seconds for PBCH detection in accordance with the proposed scheme, column <NUM> shows time taken in milli seconds for PBCH detection using the baseline scheme and column <NUM> shows the percentage power savings of the proposed scheme over the baseline scheme for each SNR value.

As shown in table <NUM>, the proposed scheme provides significant power savings as compared to the baseline scheme by acquiring the correct timing considerably faster than the baseline scheme.

For example, instructions for performing the operations described herein and illustrated in <FIG>, <FIG> and <FIG>.

Claim 1:
A method for wireless communication by a User Equipment, UE (<NUM>), comprising:
determining (<NUM>) one or more System Frame Number, SFN, hypotheses, each of the one or more SFN hypotheses representing a possible SFN at which the UE (<NUM>) can wake up from a sleep state of a Discontinuous Reception, DRX, cycle;
for at least one of the one or more SFN hypotheses:
generating (<NUM>) a detection metric based at least partially on a Physical Broadcast Control Channel, PBCH, sequence received from a base station (<NUM>); and
determining (<NUM>), based on a value of the detection metric, whether the at least one SFN hypothesis represents a current SFN in accordance with a clock source used by the base station (<NUM>) for communicating with the UE (<NUM>);
determining (<NUM>), based on the at least one SFN hypothesis, a timing to be used for communicating with the base station (<NUM>), when the at least one SFN hypothesis is determined as representing the current SFN; and
communicating (<NUM>) with the base station (<NUM>) based on the determined timing.