Measurement Signals for Channel Estimation

Abstract

A method of a transmitter is disclosed, which is configured to transmit a physical layer packet in accordance with a listen-before-talk process. The method includes: obtaining an indication of a specific time for channel estimation, providing at least one measurement signal for channel estimation based on the specific time for the physical layer packet, and transmitting the physical layer packet. In some embodiments, the physical layer packet is provided with a plurality of intermediate codes, wherein each intermediate code includes one or more measurement signals for channel estimation. In some embodiments, the physical layer packet is provided with a floating intermediate code including one or more measurement signals for channel estimation. A method of a receiver is also disclosed, the receiver being configured to receive a physical layer packet transmitted in accordance with a listen-before-talk process. The method includes: obtaining an indication of a specific time for channel estimation, receiving the physical layer packet, the physical layer packet being provided with at least one measurement signal for channel estimation based on the specific time, and performing channel estimation for the specific time based on the at least one measurement signal. Corresponding apparatuses, devices, and computer program products are also disclosed.

Description

Technical Field

[0001] The present disclosure generally relates to the field of wireless communication, and more particularly, to measurement signals for channel estimation. Background Art

[0002] As is well known, channel estimation can be achieved by performing measurements on a received signal that is transmitted with known content. Such a signal is referred to herein as a measurement signal.

[0003] Problems related to channel estimation based on measurement signals occur when a receiving / measuring device performs channel estimation for one or more specific time points. Thus, the receiving / measuring device needs to receive measurement signals from a transmitting device in association with each specific time point, which can be cumbersome in some communication scenarios.

[0004] For example, for a transmitter configured to transmit according to a listen-before-talk (LBT) procedure, due to the unpredictability of the transmission time when applying the LBT procedure, the transmission of measurement signals at a pre-specified time point can be cumbersome.

[0005] Therefore, there is a need for a method capable of achieving channel estimation based on measurement signals from a transmitter operating according to a listen-before-talk procedure. Summary of the Invention

[0006] It should be emphasized that when used herein, the word "comprising" (which may be replaced by "including") indicates the presence of the stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. As used herein, the singular forms "a", "an", and "the" are intended to also include the plural forms unless the context clearly dictates otherwise.

[0007] Generally, when arrangements are mentioned herein, they should be understood as physical products; for example, devices. A physical product may include one or more parts, such as control circuits in the form of one or more controllers, one or more processors, etc.

[0008] Similarly generally, when time distance values are mentioned herein, they can be interpreted as any suitable time distance value (e.g., a specific time distance value or a time distance threshold). For example, time distance can be interpreted as a duration. The time distance (duration) between a first time point and a second time point is generally interpreted as having a positive value (i.e., the time distance can be defined as the absolute value of the first time point minus the second time point, or as the absolute value of the second time point minus the first time point).

[0009] The purpose of some embodiments is to solve or mitigate, alleviate or eliminate at least some of the above-mentioned drawbacks or other drawbacks.

[0010] A first aspect is a method for a transmitter configured to send a physical layer packet in accordance with a listen-before-talk procedure, the method comprising: obtaining an indication of a specific time for channel estimation; providing at least one measurement signal for the physical layer packet for channel estimation based on the specific time; and sending the physical layer packet.

[0011] In some embodiments, the midamble may be interpreted as having properties similar to those of the preamble, and / or being used for similar purposes as the preamble. However, unlike the preamble, the midamble typically does not precede the packet for transmission, but occurs during / within the packet.

[0012] In some embodiments, providing at least one measurement signal for the physical layer packet for channel estimation based on the specific time comprises: providing a plurality of midambles for the physical layer packet, wherein each midamble comprises one or more measurement signals for channel estimation.

[0013] In some embodiments, the plurality of midambles have a time distance (or duration) between adjacent midambles that is less than twice a first time distance value (or less than twice a first duration value).

[0014] In some embodiments, sending the physical layer packet comprises: timing an initial midamble of the plurality of midambles to occur before or at the specific time, and / or timing a last midamble of the plurality of midambles to occur after or at the specific time.

[0015] In some embodiments, sending the physical layer packet comprises: timing a midamble to be at the specific time.

[0016] In some embodiments, providing at least one measurement signal for the physical layer packet for channel estimation based on the specific time comprises: providing a floating midamble for the physical layer packet, the floating midamble comprising one or more measurement signals for channel estimation.

[0017] In some embodiments, providing the floating midamble for the physical layer packet and sending the physical layer packet comprises: timing the floating midamble to be at the specific time, or to occur at a time less than a second time distance value (or less than a second duration value) from the specific time.

[0018] Note that the term "second duration" is a term used to distinguish from the "first duration". Therefore, the second duration can have any suitable length (i.e., the length of the second duration is not limited to one second).

[0019] In some embodiments, the method further includes: including an indication of the position of the floating intermediate code within the physical layer packet in a preamble of the physical layer packet.

[0020] In some embodiments, transmitting the physical layer packet is performed within a transmission opportunity, and wherein the timing includes: extending a previous physical layer packet of the transmission opportunity to adjust a transmission time of the physical layer packet.

[0021] In some embodiments, providing at least one measurement signal for channel estimation of the physical layer packet based on the specific time includes: providing at least two fields for the physical layer packet, wherein each field includes one or more measurement signals for channel estimation, and wherein each field is an intermediate code of the physical layer packet or a part of a preamble of the physical layer packet.

[0022] In some embodiments, the at least two fields have a time distance (or duration) less than twice a third time distance value (or less than twice a third duration value) between adjacent fields.

[0023] In some embodiments, providing a field for the physical layer packet and transmitting the physical layer packet includes: timing an initial field to occur before or at the specific time, and timing an end field to occur after or at the specific time.

[0024] In some embodiments, providing a field for the physical layer packet and transmitting the physical layer packet includes: timing one of the fields to be at or to occur at a time less than a fourth time distance value (or less than a fourth duration value) from the specific time.

[0025] In some embodiments, the method further includes: determining a number of fields based on a maximum time distance (or maximum duration) between the specific time and a field closest to the specific time.

[0026] In some embodiments, the method further includes: obtaining an indication of a maximum acceptable absolute deviation. In some of these embodiments, the step of providing at least one measurement signal for the physical layer packet is performed only when the possible timing of the at least one measurement signal for channel estimation is within the maximum acceptable absolute deviation from the specific time. When the measurement signal for channel estimation does not have a possible timing within the maximum acceptable absolute deviation from the specific time, the method may include: avoiding providing the at least one measurement signal for the physical layer packet based on the specific time.

[0027] In some embodiments, the at least one measurement signal for channel estimation includes: at least two measurement signals for channel estimation.

[0028] In some embodiments, the method further includes: preparing two or more versions of the physical layer packet, where each version inserts the at least one measurement signal at a different position. Thus, providing the at least one measurement signal for channel estimation based on the specific time for the physical layer packet includes: selecting one of the versions of the physical layer packet for transmission.

[0029] In some embodiments, selecting one of the versions of the physical layer packet for transmission includes: selecting the version having the measurement signal closest to the specific time.

[0030] In some embodiments, the intermediate code includes: an additional preamble inserted in the data field of the physical layer packet.

[0031] In some embodiments, the physical layer packet includes: an indication of the presence of the intermediate code and / or an indication of the position of the intermediate code within the physical layer packet.

[0032] In some embodiments, the indication of the presence of the intermediate code and / or the indication of the position of the intermediate code are included in the preamble of the physical layer packet and / or in one or more symbols before the intermediate code.

[0033] A second aspect is a method for a receiver, the receiver being configured to receive a physical layer packet transmitted in accordance with a listen-before-talk procedure, the method including: obtaining an indication of a specific time for channel estimation; receiving a physical layer packet that is provided with at least one measurement signal for channel estimation based on the specific time; and performing channel estimation for the specific time based on the at least one measurement signal.

[0034] In some embodiments, the physical layer packet is received from a transmitter configured to perform the method of the first aspect.

[0035] In some embodiments, the method further includes: providing the transmitter with one or more of the following: an indication of a specific time for channel estimation, and an indication of a maximum acceptable absolute deviation.

[0036] In some embodiments, the physical layer packet is provided with at least one measurement signal for channel estimation based on the specific time by being provided with a floating intermediate code including one or more measurement signals for channel estimation.

[0037] In some embodiments, the method further includes: extracting, from a preamble of the physical layer packet, an indication of a position of the floating intermediate code within the physical layer packet.

[0038] In some embodiments, the physical layer packet is provided with at least two fields, where each field includes one or more measurement signals for channel estimation, and where each field is an intermediate code of the physical layer packet or a part of a preamble of the physical layer packet.

[0039] In some embodiments, a first field appears at a first time and a second field appears at a second time, and performing channel estimation for the specific time includes: (when the first time is before the specific time and the second time is after the specific time) performing channel estimation by interpolation between the first time and the second time, and / or (when the first time and the second time are on the same side of the specific time) performing channel estimation by extrapolation between the first time and the second time.

[0040] In some embodiments, the at least one measurement signal for channel estimation includes: at least two measurement signals for channel estimation.

[0041] In some embodiments, the method further includes: operating the receiver in a sleep mode at a time other than the specific time for channel estimation.

[0042] A third aspect is a computer program product including a non-transitory computer-readable medium having a computer program including program instructions. The computer program is loadable into a data processing unit and is configured to cause a method according to any one of the first aspect and the second aspect to be performed when the computer program is run by the data processing unit.

[0043] A fourth aspect is a device for a transmitter, the transmitter being configured to send a physical layer packet in accordance with a listen-before-talk procedure. The device includes a control circuit configured to cause: obtaining an indication of a specific time for channel estimation; providing at least one measurement signal for channel estimation based on the specific time in the physical layer packet; and transmitting the physical layer packet.

[0044] A fifth aspect is a device for a receiver, the receiver being configured to receive a physical layer packet transmitted according to a listen-before-talk process. The device includes control circuitry configured to cause: obtaining an indication of a specific time for channel estimation; receiving a physical layer packet provided with at least one measurement signal for channel estimation based on the specific time; and performing channel estimation for the specific time based on the at least one measurement signal.

[0045] A sixth aspect is a transmitter device including the device of the fourth aspect.

[0046] A seventh aspect is a receiver device including the device of the fifth aspect.

[0047] An eighth aspect is a wireless communication device including one or more of the following: the device of the fourth aspect, the device of the fifth aspect, the transmitter device of the sixth aspect, and the receiver device of the seventh aspect.

[0048] In some embodiments, any of the above aspects may additionally have the same or corresponding features as any one of the various features set forth above for any other aspect.

[0049] An advantage of some embodiments is that it enables channel estimation to be achieved based on measurement signals from a transmitter operating according to a listen-before-talk process.

[0050] An advantage of some embodiments is that it alleviates jitter in the timing (near a specific time) of the measurement signals transmitted for channel estimation. For example, alleviating may include reducing jitter caused by the transmitter and / or improving the receiver's handling of jitter.

[0051] For example, in some embodiments, a method is provided for the transmitter to reduce jitter in the actual transmission time of the measurement signal relative to a deterministic target transmission schedule (the schedule for a specific time).

[0052] An advantage of some embodiments is that it avoids jitter greater than the maximum acceptable absolute deviation.

[0053] An advantage of some embodiments is that jitter mitigation affects (e.g., improves) the robustness and / or accuracy of channel estimation. Description of the Drawings

[0054] Further objectives, features, and advantages will become apparent from the following detailed description of embodiments with reference to the drawings. The drawings are not necessarily to scale, but rather focus on illustrating example embodiments.

[0055] Figure 1 is a flowchart illustrating example method steps according to some embodiments;

[0056] Figure 2 is a flowchart illustrating example method steps according to some embodiments;

[0057] Figure 3 is a signaling diagram illustrating example signaling according to some embodiments;

[0058] Figure 4 is a schematic diagram illustrating an example physical layer packet according to some embodiments;

[0059] Figure 5 is a schematic block diagram illustrating an example apparatus according to some embodiments;

[0060] Figure 6 is a schematic block diagram illustrating an example apparatus according to some embodiments; and

[0061] Figure 7 is a schematic diagram illustrating an example computer-readable medium according to some embodiments. DETAILED DESCRIPTION

[0062] As already mentioned above, it should be emphasized that when used in this specification, the word "comprising" (which may be replaced by "including") is used to indicate the presence of the stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise.

[0063] Embodiments of the present disclosure will be described and illustrated more fully hereinafter with reference to the accompanying drawings. However, the solutions disclosed herein may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein.

[0064] Even though some examples herein focus on applications of wireless local area network (WLAN) sensing under the standardization of IEEE 802.11, it should be noted that the embodiments are equally applicable to other scenarios. For example, applicability under other standardizations (e.g., the standardization of the 3rd Generation Partnership Project (3GPP)) and / or other functions besides sensing (e.g., for radio calibration purposes) can be envisioned.

[0065] Generally, the embodiments are applicable to any situation including channel estimation based on measurement signals from a transmitter operating according to a listen-before-talk process, where channel estimation is desired for a specific time point.

[0066] Similarly, generally, references to a listen-before-talk (LBT) process are intended to include any process in which a transmitter is required to perform measurements to determine that a channel is available (e.g., idle) before beginning transmission. Examples include carrier sense multiple access with collision avoidance (CSMA / CA).

[0067] In some embodiments, references herein to transmissions in accordance with an LBT process may be interpreted as the following definition: The transmissions are not according to fixed timing, i.e., the measurement signals for channel estimation are not sent according to a deterministic (e.g., centralized) scheduling manner.

[0068] Embodiments will be described below in which methods are provided for performing channel estimation based on measurement signals from a transmitter operating in accordance with a listen-before-talk process when a desired channel estimation is for a particular time.

[0069] Figure 1 An example method 100 according to some embodiments is illustrated. The method is for a transmitter configured to transmit a physical layer packet in accordance with a listen-before-talk process. As will be illustrated below, the method includes: providing at least one measurement signal (e.g., at least two measurement signals) for channel estimation for the physical layer packet.

[0070] When the transmitter is a WLAN transmitter, the physical layer packet may be a physical layer (PHY) protocol data unit (PPDU), and each measurement signal may correspond to a long training field (LTF).

[0071] In step 110, an indication of a particular time for channel estimation is obtained. The particular time may be defined by a time point and / or a time interval. For example, the indication of the particular time may indicate one or more of the following: a time point, a start of a time interval, an end of a time interval, a middle of a time interval, and a duration of a time interval.

[0072] In some embodiments, the obtaining of the particular time includes obtaining multiple particular times. For example, the multiple particular times may occur within a specified time period. Alternatively or additionally, the multiple particular times may be particular times that occur periodically, non-periodically, or otherwise repetitively. For example, particular times that occur periodically may facilitate the application of a Fourier transform when processing the resulting channel estimation (e.g., for WLAN sensing).

[0073] In some embodiments, an indication of a maximum acceptable absolute deviation (MAAD) may also be obtained, as illustrated in optional step 120.

[0074] It should be noted that even though Figure 1is illustrated as two separate steps, and according to some embodiments, the indication of a specific time and the indication of the MAAD may also be obtained in a single step.

[0075] When the specific time is defined by a time point, it may be expected that the time point is included within the time range for performing channel estimation, or that the time point deviates from the time range for performing channel estimation (e.g., its end point) by no more than a time distance value (no more than a duration value; e.g., no more than the MAAD).

[0076] When the specific time is defined by a time interval, it may be expected that the duration is included within the time range for performing channel estimation, or that the duration has (at least partial) overlap with the time range for performing channel estimation, or that the duration (e.g., its end point) deviates from the time range for performing channel estimation (e.g., its end point) by no more than a time distance value (no more than a duration value; e.g., no more than the MAAD).

[0077] The obtaining of step 110 may include one or more of the following: determining a specific time (possibly in combination with sending an indication of the determined specific time; e.g., as described later herein, sending to a receiver device), receiving an indication of a specific time from another device (e.g., a receiver device as described later herein, or a central configuration node), and obtaining an indication of a predetermined (e.g., standardized) specific time from a memory associated with the transmitter.

[0078] Alternatively or additionally, the obtaining of step 120 may include one or more of the following: determining the MAAD (possibly in combination with sending an indication of the determined MAAD; e.g., as described later herein, sending to a receiver device), receiving an indication of the MAAD from another device (e.g., a receiver device as described later herein, or a central configuration node), and obtaining an indication of a predetermined (e.g., standardized) MAAD from a memory associated with the transmitter.

[0079] As illustrated in optional step 130, it may be determined (according to some embodiments) whether it is possible to send a measurement signal for channel estimation as needed in association with a specific time. For example, it may be determined whether it is possible to send a measurement signal for channel estimation that overlaps with the specific time. Alternatively or additionally, it may be determined whether it is possible to send a measurement signal for channel estimation within the MAAD from the specific time (i.e., whether the possible timing of the measurement signal for channel estimation is within the MAAD from the specific time).

[0080] When it is determined that it is possible to send a measurement signal for channel estimation as needed in association with a specific time (Y path of step 130), the method proceeds to step 140.

[0081] When it is determined that it is not possible to send a measurement signal for channel estimation as needed and associated with a specific time (the N path of step 130), the method may proceed to step 150 as Figure 1 illustrated.

[0082] Then, in step 150, a default physical layer packet may be sent; that is, a physical layer packet transmission in which an attempt is not made to send a measurement signal for channel estimation associated with a specific time. It should be noted that even if no such attempt is made, a default physical layer packet may be sent (accidentally) such that even if no measurement signal for channel estimation is explicitly and intentionally provided for the physical layer packet for channel estimation based on that specific time, the measurement signal for channel estimation (e.g., the LTF in the preamble of the PPDU) ends associated with a specific time. Thus, the N path of step 130 represents avoiding providing a measurement signal for channel estimation for the physical layer packet based on that specific time.

[0083] Alternatively, when it is determined that it is not possible to send a measurement signal for channel estimation as needed and associated with a specific time, the method may end without transmitting a physical layer packet.

[0084] When it is determined that it is possible to send a measurement signal for channel estimation as needed and associated with a specific time (the Y path of step 130), at least one measurement signal for channel estimation based on that specific time is provided for the physical layer packet, as illustrated in step 140. Then the physical layer packet is sent in step 150. It should be noted that step 150 may include the transmission of one or more physical layer packets.

[0085] The transmission time range of the measurement signal for channel estimation corresponds to the possible time range for which channel estimation is to be performed. Thus, as needed, it is desirable for the transmission time range of the measurement signal for channel estimation to be associated with a specific time (e.g., consistent with a specific time, overlapping with a specific time, occurring within the MAAD from a specific time, etc.). This can be accomplished in various ways, and some of these ways will be described by some examples below. In combination Figure 4 further examples are provided. It should be noted that even if not explicitly mentioned herein, appropriate combinations of different examples may apply.

[0086] In one example, providing at least one measurement signal for channel estimation based on a specific time for the physical layer packet includes: timing the transmission of the physical layer packet (step 150) such that a standardized measurement signal (e.g., the LTF of the PPDU preamble) is sent as needed and associated with a specified time.

[0087] One way to achieve such timing can be accomplished by adjusting the transmission time of physical layer packets within a transmission opportunity (e.g., according to the TXOP of IEEE 802.11). For example, the adjustment can be achieved by delaying or advancing the default transmission time of the physical layer packet. Padding the data to extend the previous physical layer packet is one possibility for delaying the default transmission time of the physical layer packet. Performing data reduction (e.g., data puncturing) to shorten the previous physical layer packet is one possibility for advancing the default transmission time of the physical layer packet.

[0088] In one example, providing at least one measurement signal for channel estimation for a physical layer packet includes: providing a plurality of intermediate codes for the physical layer packet, where each intermediate code includes one or more measurement signals for channel estimation.

[0089] Generally, an intermediate code can be defined as a block of symbols that do not carry data and are inserted into the data-carrying portion of the physical layer packet.

[0090] For example, the plurality of intermediate codes can be equally spaced within the data field of the physical layer packet.

[0091] Alternatively or additionally, the plurality of intermediate codes can have a time distance (duration) between adjacent intermediate codes that is less than twice a first time distance value (less than twice a first duration value; e.g., less than twice the MAAD).

[0092] By using a plurality of intermediate codes that include measurement signals for channel estimation, the probability that the measurement signals are transmitted in association with a specified time as needed is increased.

[0093] To further increase this probability, the transmission step 150 of some embodiments includes: timing the initial intermediate code among the plurality of intermediate codes to occur before or coincide with a specific time, and / or timing the last intermediate code among the plurality of intermediate codes to occur after or coincide with a specific time, and / or timing one intermediate code among the plurality of intermediate codes to coincide with a specific time.

[0094] One way to achieve such timing can be accomplished by adjusting the transmission time of physical layer packets within a transmission opportunity (e.g., according to the TXOP of IEEE 802.11). For example, the adjustment can be achieved by delaying or advancing the default transmission time of the physical layer packet. Padding the data to extend the previous physical layer packet is one possibility for delaying the default transmission time of the physical layer packet. Performing data reduction (e.g., data puncturing) to shorten the previous physical layer packet is one possibility for advancing the default transmission time of the physical layer packet.

[0095] In one example, providing at least one measurement signal for channel estimation based on a specific time for a physical layer packet includes: providing a floating midamble for the physical layer packet, the floating midamble including one or more measurement signals for channel estimation.

[0096] Optionally, the floating midamble can be inserted so that it is transmitted in association with a specified time. Thus, the floating midamble can be timed (in step 140 and step 150) to coincide with a specific time, or occur at a time less than a second time distance value (less than a second duration value; e.g., less than MAAD) from a specific time.

[0097] As an alternative or supplement to adjusting in the physical layer packet provided with a floating midamble, one way to achieve such timing can be done by adjusting the transmission time of the physical layer packet within a transmission opportunity (e.g., TXOP according to IEEE802.11). For example, the adjustment can be achieved by delaying or advancing the default transmission time of the physical layer packet. Padding data to extend the previous physical layer packet is one possibility for delaying the default transmission time of the physical layer packet. Truncating data (e.g., data puncturing) to shorten the previous physical layer packet is one possibility for advancing the default transmission time of the physical layer packet.

[0098] Generally, the floating midamble can be implemented in any suitable form. For example, the floating midamble can be implemented as an additional preamble that can be inserted at any position in the data field of the physical layer packet.

[0099] In some embodiments, an indication of the presence and / or an indication of the position of the floating midamble within the physical layer packet are provided to the receiver of the physical layer packet (e.g., by including such an indication in the preamble of the physical layer packet and / or in one or more symbols (e.g., orthogonal frequency division multiplexing (OFDM) symbols) before the midamble). These methods may facilitate the receiver to identify and / or locate the midamble (e.g., prevent the receiver from attempting to process the midamble as input data, e.g., decoding).

[0100] Some different possibilities for indicating the presence and / or position of the midamble are given below.

[0101] The OFDM symbol immediately preceding the midamble can signal that one or more subsequent (e.g., the next) symbols are not OFDM symbols but midamble. This method can provide an agile and flexible solution. For example, a specific constellation or content of the OFDM symbol can be used to indicate to the receiver to "skip" one or more subsequent symbol durations when it processes the input data.

[0102] The transmitter can use the "minimum MPDU start interval field" (e.g., as specified in IEEE802.11, 2016, 10.13.3) to include the intermediate code. For example, the receiver can be configured to interpret all interval fields as intermediate codes. Alternatively or additionally, a combination of reserved bits in an aggregated MAC (Media Access Control) protocol data unit (A-MPDU) can indicate that the interval field of the A-MPDU includes an intermediate code. The end-of-file (EOF) padding subframe / octet can be used in this context.

[0103] An indication that the A-MPDU does not carry data but carries an intermediate code can be used to insert the A-MPDU. For example, the MPDU delimiter field includes reserved bits that can be used to convey this information. Alternatively or additionally, a special MAC address in the locally administered space can be used to indicate the presence of an intermediate code in the A-MPDU.

[0104] The LTF can imply its own presence. For example, the receiver can be configured to perform matched filtering (in the time domain and / or frequency domain) and detect the intermediate code when the filter output exceeds a threshold. For example, the matched filtering can be performed based on the overall LTF content or based on a subset of the LTF frequency symbols. The latter may reduce the computational complexity and / or may be particularly applicable to the frequency domain and / or with a relatively high signal-to-noise ratio (SNR).

[0105] A cell can be included in the MAC header of the first MPDU to indicate the OFDM symbol containing the intermediate code.

[0106] In one example (particularly applicable when the channel estimation device is configured to apply interpolation and / or extrapolation to two or more measurement signals), providing at least one measurement signal for channel estimation for a physical layer packet includes: providing at least two fields for the physical layer packet, where each field includes one or more measurement signals for channel estimation, and where each field is an intermediate code of the physical layer packet or a part of the preamble of the physical layer packet.

[0107] For example, there can be a time distance (duration) less than twice a third time distance value (less than twice a third duration value; e.g., less than twice the MAAD, or a longer duration acceptable for interpolation and / or extrapolation) between adjacent fields of the at least two fields.

[0108] In some embodiments, the number of fields to be provided is determined based on the maximum possible time distance (maximum possible duration) between a specific time and the field closest to the specific time. Typically, the longer such maximum possible distance, the larger the number of fields to be provided.

[0109] In some embodiments (particularly applicable when the channel estimation device is configured to apply interpolation between two or more measurement signals), providing fields to a physical layer packet and transmitting the physical layer packet includes: timing an initial field to occur before or at a specific time, and timing an end field to occur after or at a specific time.

[0110] Alternatively or additionally, in some embodiments (particularly applicable when the channel estimation device is configured to apply interpolation and / or extrapolation for two or more measurement signals), providing fields to a physical layer packet and transmitting the physical layer packet includes: timing one of the fields to be at or occur at a time less than a fourth time distance value (less than a fourth duration value; e.g., less than MAAD, or a longer duration acceptable for interpolation and / or extrapolation) from the specific time.

[0111] One way to achieve such timing can be done by adjusting the transmission time of the physical layer packet within a transmission opportunity (e.g., TXOP according to IEEE 802.11). For example, the adjustment can be achieved by delaying or advancing the default transmission time of the physical layer packet. Padding the data to extend the previous physical layer packet is one possibility for delaying the default transmission time of the physical layer packet. Truncating the data (e.g., data puncturing) to shorten the previous physical layer packet is one possibility for advancing the default transmission time of the physical layer packet.

[0112] Generally, it should be noted that the various time distance values (various duration values) referred to here (e.g., any one of the first time distance value, the second time distance value, the third time distance value, the fourth time distance value, the fifth time distance value, and the sixth time distance value) can be the same or different values, depending on the situation.

[0113] In some embodiments, the transmitter may prepare several (e.g., two or more) versions of the physical layer packet, where each version inserts the measurement signal at a different position, and step 140 may include: selecting one of the versions of the physical layer packet for transmission (typically, the version with the measurement signal acceptably close to a specific time; e.g., the version with the measurement signal closest to the specific time). The preparation of the several versions of the physical layer packet may be performed at any suitable time (e.g., at the default time of packet preparation). Alternatively or additionally, the selection may be performed at any suitable time (e.g., when the transmission time has been obtained; e.g., when the backoff has expired and / or when the transmitter has acquired access to the transmission medium).

[0114] Embodiments in which the transmitter prepares several versions of the physical layer packet may be particularly beneficial when the transmitter has hardware limitations that prevent dynamically inserting the measurement signal at a time very close to the transmission time.

[0115] Figure 2 An example method 200 according to some embodiments is illustrated. The method is for a receiver configured to receive a physical layer packet in accordance with a listen-before-talk process. The physical layer packet is provided with at least one measurement signal (e.g., at least two measurement signals) for channel estimation.

[0116] When the receiver is a WLAN receiver, the physical layer packet may be a physical layer (PHY) protocol data unit (PPDU), and each measurement signal may correspond to a long training field (LTF).

[0117] In step 210, an indication of a specific time for channel estimation is obtained (compared to Figure 1 step 110). The specific time may be defined by a time point and / or a time interval. For example, the indication of the specific time may indicate one or more of the following: a time point, the start of a time interval, the end of a time interval, the middle of a time interval, and the duration of a time interval.

[0118] In some embodiments, the obtaining of the specific time includes obtaining multiple specific times. For example, the multiple specific times may occur within a specified time period. Alternatively or additionally, the multiple specific times may be specific times that occur periodically, non-periodically, or otherwise repetitively.

[0119] The obtaining of step 210 may include one or more of the following: determining the specific time (possibly combined with sending an indication of the determined specific time; e.g., sending to a transmitter device such as the transmitter described in conjunction with Figure 1 ), receiving from another device (e.g., such as described in conjunction with Figure 1The transmitter device of the described transmitter, or a central configuration node) receives an indication of a specific time and obtains an indication of a predetermined (e.g., standardized) specific time from a memory associated with the receiver.

[0120] In some embodiments, an indication of the maximum acceptable absolute deviation (MAAD) can also be obtained (compared with Figure 1 step 120).

[0121] In step 250, a physical layer packet is received (compared with Figure 1 step 150), where the physical layer packet is provided with at least one measurement signal for channel estimation based on the specific time.

[0122] For example, the physical layer packet can be received from a transmitter configured to perform the method described in connection with Figure 1 and, in accordance with any of the embodiments described in connection with Figure 1 the physical layer packet is provided with at least one measurement signal for channel estimation based on the specific time.

[0123] In step 260, channel estimation is performed for the specific time based on the at least one measurement signal. If there are more physical layer packets to be received, the method can return to step 250 after performing step 260.

[0124] In some embodiments, the receiver can be in a sleep mode (e.g., a light sleep mode or a doze mode) before the reception of the physical layer packet and / or during a partial reception of the physical layer packet (e.g., before and / or after and / or between the specific times for channel estimation). This can have the advantage of improving the energy efficiency of the receiver. Typically, the receiver is not in a sleep mode during the reception of the initial part of the physical layer data (e.g., the preamble).

[0125] When the physical layer packet is provided with a floating intermediate code including one or more measurement signals for channel estimation, method 200 can further include: determining the presence of the floating intermediate code (e.g., based on the preamble of the physical layer packet and / or based on one or more symbols before the intermediate code (e.g., OFDM symbols)) and / or extracting an indication of the position of the floating intermediate code within the physical layer packet (e.g., from the preamble of the physical layer packet and / or from one or more symbols before the intermediate code (e.g., OFDM symbols)).

[0126] Channel estimation methods based on measurement signals transmitted in association with a specific time (e.g., continuously with the specific time, overlapping with the specific time, deviating from the specific time by less than the MAAD, etc.) can be performed according to any suitable channel estimation method.

[0127] In some embodiments, the receiver may be able to apply interpolation and / or extrapolation to two or more measurement signals to achieve channel estimation. For example, interpolation or extrapolation may be related to at least two fields provided in a physical layer packet, where each field includes one or more measurement signals for channel estimation, and where each field is an intermediate code of the physical layer packet or a part of the preamble of the physical layer packet.

[0128] Assuming that the first field appears at a first time and the second field appears at a second time, when the first time is before a specific time and the second time is after the specific time, channel estimation for the specific time may be performed by interpolation between the first time and the second time, and when the first time and the second time are on the same side of the specific time (i.e., both before the specific time or both after the specific time), channel estimation for the specific time may be performed by extrapolation between the first time and the second time.

[0129] For example, when the time distance (duration) between the specific time and the closest field is less than a fifth time distance value (less than a fifth duration value; e.g., which defines when interpolation and / or extrapolation is appropriate or even possible) and / or when the time distance (duration) between the specific time and the closest field is greater than a sixth time distance value (greater than a sixth duration value; e.g., which defines when channel estimation based on one measurement signal is inappropriate or even impossible; e.g., exceeding the MAAD), interpolation or extrapolation may be used.

[0130] In some embodiments, the more fields used for interpolation and / or extrapolation, the greater the time distance (duration) between the specific time and the closest field.

[0131] In some embodiments, method 200 may include the step of determining whether the measurement signal for channel estimation is sent as needed in association with a specific time. For example, it may be determined whether a measurement signal for channel estimation that overlaps with the specific time is sent. Alternatively or additionally, it may be determined whether the measurement signal for channel estimation is sent within the MAAD from the specific time.

[0132] As shown in example alternative sub-step 261, the step of determining whether the measurement signal for channel estimation is sent as needed in association with a specific time may be regarded as a sub-step of step 260 or as a separate step before step 260.

[0133] When it is determined that the measurement signal for channel estimation is sent as needed in association with a specific time, the method continues to perform channel estimation based on the measurement signal in step 260.

[0134] When it is determined that the measurement signal for channel estimation is not sent as required in association with a specific time, if possible, the method may continue to perform channel estimation based on other measurement signals.

[0135] Alternatively or additionally, when it is determined that the measurement signal for channel estimation is not sent as required in association with a specific time, the method may end without channel estimation.

[0136] In addition, alternatively or additionally, as illustrated in optional sub-step 262, when it is determined that the measurement signal for channel estimation is not sent as required in association with a specific time (N-path of step 261); for example, when the time distance (duration) between the specific time and the closest field is greater than the sixth time distance value), channel estimation may be performed by interpolation and / or extrapolation. For example, as long as the time distance (duration) between the specific time and the closest field is less than the fifth time distance value, interpolation and / or extrapolation may be used, and the method may end without channel estimation.

[0137] Generally, the result of channel estimation can be used for any suitable purpose. For example, the channel estimation result can be used for positioning and / or radio environment derivation (e.g., in the context of WLAN sensing). Alternatively or additionally, the channel estimation result can be used for radio calibration.

[0138] In some embodiments, a sensing method (e.g., a WLAN sensing method) includes: causing method 200 to be executed in a plurality of receiver devices, collecting corresponding channel estimation results, and using machine learning based on the statistics of the collected channel estimation results to provide sensing results (e.g., positioning information and / or radio environment information). Such a sensing method may be executed in a receiver device (e.g., one of the receivers executing method 200) or in a central node associated with the plurality of receiver devices.

[0139] Figure 3 Illustrated is an example signaling between a transmitter (TX; e.g., a transmitter suitable for executing Figure 1 method 100) 310 and a receiver (RX; e.g., a receiver suitable for executing Figure 2 method 200) 320 according to some embodiments.

[0140] The process is initiated by the receiver 320 by sending a request signal 331. For example, when a measurement signal for channel estimation is needed, the request signal may indicate one or more specific times (compared with Figure 2 step 210 of

[0141] It may be in any suitable manner (e.g., in combination with Figure 1 and / orFigure 2 in any of the ways described) to define the one or more specific times. For example, the request signal 331 may indicate the start time of a period including measurement signals for channel estimation, the duration of a period including measurement signals for channel estimation, and the period of the measurement signals for channel estimation.

[0142] In various embodiments, the request signal 331 may also indicate a maximum acceptable absolute deviation and / or indicate that the receiver is capable of interpolation and / or extrapolation.

[0143] When the request signal has been received by the transmitter 310 (compared with Figure 1 step 110), the transmitter responds by transmitting a response signal 332. For example, the response signal may indicate an affirmative response to the following: that measurement signals for channel estimation will be provided in association with the one or more specific times.

[0144] Before starting to transmit measurement signals for channel estimation as described in connection with Figure 1 , the transmitter 310 may alert the receiver 320 by starting to transmit a start signal 333. For example, the start signal may indicate the start time of a period including measurement signals for channel estimation. In some embodiments, the start signal 333 may be included in the response signal 332.

[0145] In Figure 3 , the measurement signals for channel estimation (compared with Figure 1 step 150 and Figure 2 step 250) are illustrated by four example signals 334, 335, 336, and 337. For example, the signals 334, 335, 336, and 337 may represent the transmission of a PPDU including one or more LTFs.

[0146] It should be noted that in various embodiments, the process may be initiated by the receiver (as illustrated in Figure 3 ), or by the transmitter, or by a central node.

[0147] Figure 4 Schematically illustrates some example physical layer packets according to various embodiments. Figure 4 The example physical layer packets of Figure 1 and Figure 2 are applicable in the context of the methods described above.

[0148] (a) depicts a physical layer packet 400a for transmission by a transmitter (TX). The physical layer packet 400a is provided with a plurality of intermediate codes 404, 405, 406, 407, 408, where each intermediate code includes one or more measurement signals for channel estimation. The intermediate code 407 coincides with a specific time 409, as detailed above.

[0149] When the physical layer packet 400a is an IEEE 802.11 PPDU, the measurement signal for channel estimation can be an LTF. The PPDU can include a preamble 401 having a preamble LTF 402 and a data field 403 including intermediate codes, which in turn include one or more LTFs.

[0150] As previously mentioned, using a plurality of intermediate codes including measurement signals for channel estimation increases the probability that the measurement signal (of the preamble or any intermediate code) is transmitted in association with the specified time 409 as needed.

[0151] The plurality of intermediate codes can have a time distance (duration) less than twice the first time distance value (less than twice the first duration value; e.g., less than twice the MAAD) between adjacent intermediate codes (and possibly, between the LTF of a possible preamble and the first intermediate code), further increasing the above probability.

[0152] If the transmission time of the physical layer packet 400a can be adjusted, it may be beneficial to transmit the physical layer packet such that the initial intermediate code 404 (or the LTF 402 of a possible preamble) occurs before the specific time 409 or coincides with the specific time 409. Alternatively or additionally, it may be beneficial to transmit the physical layer packet such that the last intermediate code 408 occurs after the specific time 409 or coincides with the specific time 409. Additionally alternatively or additionally, it may be beneficial to transmit the physical layer packet such that an intermediate code coincides with the specific time 409.

[0153] (b) depicts a physical layer packet 400b for transmission by a transmitter (TX). The physical layer packet 400b is provided with a plurality of intermediate codes 414, 415, 416, 417, 418, where each intermediate includes one or more measurement signals for channel estimation. The intermediate code 415 coincides with a specific time 419, as detailed above.

[0154] When the physical layer packet 400b is an IEEE 802.11 PPDU, the measurement signal for channel estimation can be an LTF.

[0155] As described above, using a plurality of intermediate codes including measurement signals for channel estimation increases the probability that the measurement signals (of the preamble or any intermediate code) are transmitted as needed in association with a specified time 419.

[0156] The plurality of intermediate codes may have a time distance (duration) less than twice a first time distance value (less than twice a first duration value; e.g., less than twice the MAAD) between adjacent intermediate codes (and possibly, between the LTF of a possible preamble and the first intermediate code), further increasing the above probability.

[0157] If the transmission time of the physical layer packet 400b can be adjusted, it may be beneficial to transmit the physical layer packet such that the initial intermediate code 414 occurs before or coincides with a specific time 419. Alternatively or additionally, it may be beneficial to transmit the physical layer packet such that the trailing intermediate code 418 occurs after or coincides with the specific time 419. Additionally alternatively or additionally, it may be beneficial to transmit the physical layer packet such that an intermediate code coincides with the specific time 419.

[0158] (b) part illustrates a situation where it is possible to adjust the transmission time of the physical layer packet 400b due to the transmission within the transmission opportunity 413 (compared to the TXOP of IEEE 802.11).

[0159] The transmission opportunity 413 starts with the transmitter (TX) sending a request to send (RTS) signal 410 and the receiver (RX) sending a corresponding clear to send (CTS) signal 411.

[0160] Within the transmission opportunity 413, the transmitter has the possibility to adjust the transmission time of the physical layer packet 400b; for example, delaying or advancing the default transmission time of the physical layer packet. Padding the data to extend the previous physical layer packet 412 is one possibility for delaying the default transmission time of the physical layer packet. Shrinking the data (e.g., data puncturing) to shorten the previous physical layer packet 412 is one possibility for advancing the default transmission time of the physical layer packet.

[0161] (c) part illustrates the physical layer packet 400c transmitted by the transmitter (TX). The physical layer packet 400c is provided with a floating intermediate code 427, and the floating intermediate code 427 includes one or more measurement signals for channel estimation. The floating intermediate code 427 coincides with a specific time 429, as detailed above.

[0162] When the physical layer packet 400c is an IEEE 802.11 PPDU, the measurement signal for channel estimation can be the LTF. The PPDU can include a preamble 421 having a preamble LTF 422 and a data field 423 including a floating middle code, and the floating middle code in turn includes one or more LTFs. The preamble can include an indication of the position of the floating middle code within the physical layer packet.

[0163] Preferably, the floating middle code 427 is inserted at a position that will coincide with a specific time 429, or occurs at a time that is less than a second time distance value (less than a second duration value; e.g., less than MAAD) from the specific time.

[0164] If the transmission time of the physical layer packet 400c can be adjusted, it may be beneficial to transmit the physical layer packet so that the floating middle code 427 (or possibly the LTF 422 of the preamble) coincides with the specific time 429.

[0165] (d) Part illustrates a physical layer packet 400d transmitted by a transmitter (TX). The physical layer packet 400d is provided with a floating middle code 437, which includes one or more measurement signals for channel estimation. The floating middle code 437 coincides with a specific time 439, as detailed above.

[0166] When the physical layer packet 400d is an IEEE 802.11 PPDU, the measurement signal for channel estimation can be the LTF.

[0167] If the transmission time of the physical layer packet 400d can be adjusted, it may be beneficial to transmit the physical layer packet so that the floating middle code 437 coincides with the specific time 439.

[0168] (d) Part illustrates a situation where it is possible to adjust the transmission time of the physical layer packet 400d because the transmission is within a transmission opportunity 433 (compared to a TXOP of IEEE 802.11).

[0169] The transmission opportunity 433 is started by the transmitter (TX) sending a request to send (RTS) signal 430 and the receiver (RX) sending a corresponding clear to send (CTS) signal 431.

[0170] Within the transmission opportunity 433, the transmitter has the possibility to adjust the transmission time of the physical layer packet 400d; for example, delay or advance the default transmission time of the physical layer packet. Padding the data to extend the previous physical layer packet 432 is one possibility for delaying the default transmission time of the physical layer packet. Truncating the data (e.g., data puncturing) to shorten the previous physical layer packet 432 is one possibility for advancing the default transmission time of the physical layer packet.

[0171] (e) shows a situation where it is possible to adjust the transmission time of the physical layer packet 400e due to transmission within the transmission opportunity 443 (compared to the TXOP of IEEE 802.11).

[0172] The transmission opportunity 443 starts when the transmitter (TX) sends a Request to Send (RTS) signal 440 and the receiver (RX) sends a corresponding Clear to Send (CTS) signal 441.

[0173] Within the transmission opportunity 443, the transmitter may adjust the transmission time of the physical layer packet 400e; for example, delay or advance the default transmission time of the physical layer packet. Performing data padding 444 to extend the previous physical layer packet 442 is one possibility for delaying the default transmission time of the physical layer packet. Performing data reduction (e.g., data puncturing) to shorten the previous physical layer packet is one possibility for advancing the default transmission time of the physical layer packet.

[0174] Generally, the possibility of adjusting the transmission time of the physical layer packet can be used to transmit the physical layer data 400e so that any suitable measurement signal 447 (e.g., the LTF of a possible preamble or midamble) included in the physical layer packet for channel estimation is consistent with a specific time 449, as detailed above.

[0175] Figure 5 Schematically illustrates an example device 510 according to some embodiments. The device is for a transmitter (TX; e.g., a transmission circuit or a transmission module), configured to send a physical layer packet in accordance with a listen - before - talk process, and the transmitter is illustrated here as part of a transceiver (TX / RX) 530.

[0176] The device 510 and / or the transceiver 530 may be included in a transmitter device, such as a wireless communication device. An example wireless communication device is a station (STA) configured to operate in accordance with IEEE 802.11.

[0177] For example, the device 510 may be configured to perform one or more of the method steps described in conjunction with Figure 1 or cause one or more of the method steps described in conjunction with Figure 1 to be performed.

[0178] The device 510 includes a controller (CNTR; e.g., a control circuit or a control module) 500.

[0179] The controller 500 is configured to cause an indication of a specific time for channel estimation to be obtained (compared to Figure 1compared to step 110 of ). For this purpose, the controller may include an acquirer (ACQ; e.g., an acquisition circuit or an acquisition module) 501, or be otherwise associated with (e.g., connectable or connected to) the acquirer 501. The acquirer may be configured to acquire an indication of a specific time for channel estimation (e.g., by determining the specific time, by receiving an indication of the specific time from another device, or by obtaining an indication of the specific time from a memory associated with the transmitter).

[0180] The controller 500 is further configured to cause at least one measurement signal for channel estimation based on the specific time to be provided in the physical layer packet (compared to Figure 1 step 140 of ). For this purpose, the controller may include a provider (PROV; e.g., a providing circuit or a providing module) 502, or be otherwise associated with (e.g., connectable or connected to) the provider 502. The provider may be configured to provide at least one measurement signal for channel estimation in the physical layer packet based on the specific time (e.g., according to any example mentioned herein).

[0181] The controller 500 is further configured to cause the physical layer packet to be transmitted (compared to Figure 1 step 150 of ). For this purpose, the controller may be included in a transmitter (TX), or be otherwise associated with (e.g., connectable or connected to) the transmitter (TX). The transmitter may be configured to transmit the physical layer packet (e.g., according to any example mentioned herein).

[0182] Figure 6 Schematically illustrates an example apparatus 610 according to some embodiments. The apparatus is for a receiver (RX; e.g., a receiving circuit or a receiving module), configured to receive a physical layer packet in accordance with a listen-before-talk process, and the receiver is illustrated herein as part of a transceiver (TX / RX) 630.

[0183] The apparatus 610 and / or the transceiver 630 may be included in a receiver device, such as a wireless communication device. An example wireless communication device is a station (STA) configured to operate in accordance with IEEE 802.11.

[0184] For example, the apparatus 610 may be configured to perform one or more method steps described in connection with Figure 2 or cause one or more method steps described in connection with Figure 2 to be performed.

[0185] The apparatus 610 includes a controller (CNTR; e.g., a control circuit or a control module) 600.

[0186] The controller 600 is configured to cause an indication of a specific time for channel estimation to be acquired (compared toFigure 2 compared to step 210 of []. For this purpose, the controller may include an acquirer (ACQ; e.g., an acquisition circuit or an acquisition module) 601, or be otherwise associated with (e.g., connectable or connected to) the acquirer 601. The acquirer may be configured to acquire an indication of a specific time for channel estimation (e.g., by determining the specific time, by receiving an indication of the specific time from another device, or by obtaining an indication of the specific time from a memory associated with the receiver).

[0187] The controller 600 is further configured to cause a physical layer packet to be received, the physical layer packet being provided with at least one measurement signal for channel estimation based on the specific time (compared to Figure 2 step 250 of []. For this purpose, the controller may be included in a receiver (RX), or be otherwise associated with (e.g., connectable or connected to) the receiver (RX). The receiver may be configured to receive a physical layer packet (e.g., according to any of the examples mentioned herein).

[0188] The controller 600 is further configured to cause channel estimation to be performed for the specific time based on the at least one measurement signal (compared to Figure 2 step 260 of []. For this purpose, the controller may include a channel estimator (CE; e.g., a channel estimation circuit or a channel estimation module) 602, or be otherwise associated with (e.g., connectable or connected to) the channel estimator 602. The channel estimator may be configured to perform channel estimation for the specific time based on the at least one measurement signal.

[0189] Specific applications of some embodiments will now be described in the context of WLAN sensing.

[0190] The IEEE 802.11 Standards Organization has approved a Project Authorization Request (PAR) for Wireless Local Area Network (WLAN) sensing, one of the purposes of which is to develop the following modifications to the IEEE 802.11 standard.

[0191] "The modification defines modifications to the IEEE 802.11 Media Access Control (MAC) layer, the Physical layer (PHY) of Directional Multi-Gigabit (DMG), and the PHY of the upcoming Next Generation 60 GHz (NG60), which enhance the operation of Wireless Local Area Network (WLAN) sensing (SENS) in unlicensed bands between 1 GHz and 7.125 GHz and above 45 GHz. The amendment defines:

[0192] -At least one mode that enables a station (STA) to perform one or more of the following: exchange WLAN sensing capabilities, request and set transmissions that allow WLAN sensing measurements to be performed, indicate that a transmission is available for WLAN sensing, and exchange WLAN sensing feedback and information;

[0193] -WLAN sensing operations that rely on requested, unrequested, or both transmissions

[0194] Some sensing methods use statistics based on channel estimation. Typically, several channel estimations are performed over time, and machine learning techniques are applied to the channel estimations for inference and / or decision-making (e.g., regarding device location, radio environment, etc.).

[0195] In WLAN sensing, it may be necessary to enable the sensing STA (the receiver in the above terms) to perform channel estimation at regular time intervals. For example, it has been proposed to define a period for channel measurement (e.g., 50 ms or 200 ms) and a time mask that the transmitter needs to satisfy so that any jitter around the ideal period (the specified time in the above terms) can be handled.

[0196] Channel estimation in IEEE 802.11 is typically based on the LTF. The LTF is an orthogonal frequency division multiplexing (OFDM) symbol known to the receiver. Typically, one or more LTFs are located in the physical layer (PHY) preamble of each PPDU, and the sensing STA can utilize the LTF for channel estimation. Usually, the PPDU used for sensing can also carry data, and the receiver of the data can be the sensing STA or another STA.

[0197] Ideally, the sensing STA will receive the LTF at each specified time (e.g., at a fixed period). However, this is typically difficult to achieve because channel access in WLAN is based on the LBT process (CSMA / CA) with random backoff. For this reason, there is usually some jitter in the transmission time of the LTF that involves the specified time.

[0198] It can be understood from the description herein that some embodiments provide methods for reducing such jitter for channel estimation and / or methods for handling the remaining jitter.

[0199] In the following example, the specified time will be referred to as the Target LTF Transmission Time (TLTT). The TLTT can be used to roughly define the LTF transmission time, and PPDU padding and / or PPDU midamble can be used to finely control the LTF transmission time.

[0200] For example, a fixed schedule can be defined that includes TLTTs that occur periodically within a bounded time interval. The TLLT period and the start and duration of the bounded time interval can be negotiated / handshaked between the transmitting STA and the receiving STA (compared with step 110 of Figure 1 and step 210 of Figure 2 and 331, 332 of Figure 3 ).

[0201] In some embodiments, the transmitting STA and the sensing STA can negotiate / handshake the maximum acceptable absolute deviation (MAAD) of the TLTT. If the transmitting STA determines for some reason (e.g., because the transmission medium is busy) that it cannot transmit the LTF within the MAAD from the TLTT, it can avoid transmitting the PPDU altogether or can avoid inserting the LTF for sensing in the PPDU.

[0202] In some embodiments, the transmitting STA and the sensing STA can negotiate / handshake the number of spatio-temporal streams.

[0203] Thus, the use of TLTT allows for a rough timing of LTF transmissions. The LTF transmission time can be further refined by the midamble. IEEE 802.11ax and IEEE 802.11bd utilize the midamble, which is LTFs (e.g., in a periodic manner) scattered in the data. The original purpose of the midamble was to allow the receiving STA to update the channel estimate when the channel changes rapidly over time. The sensing STA can utilize the LTF in the PHY preamble and / or the LTF in the midamble for channel estimation.

[0204] For example, if the medium is idle and the random backoff is small, the transmitting STA may gain access to the channel earlier than the time suitable for the PHY preamble LTF to match the TLTT. Then, the jitter in the LTF transmission (i.e., the deviation of the closest LTF from the TLTT) can be reduced by inserting the midamble; e.g., as illustrated in part (a) of Figure 4 .

[0205] However, using multiple midambles may result in unnecessary overhead (especially when the channel changes slowly). This can be addressed by the transmitting STA inserting one (or a few) floating midambles; e.g., as shown in part (c) of Figure 4 . Different from the IEEE802.11ax / bd midambles, the floating midamble is typically not periodic but typically occurs only once in the PPDU. Its position in the PPDU is arbitrary and is adjusted by the transmitting STA. The presence and position of the floating midamble can be indicated in the signaling field of the PHY preamble.

[0206] Typically, if the actual LTF transmission time occurs within a transmission opportunity (TXOP), it may be easier for the STA to control it. In some embodiments, the transmitting STA contends for the channel and (conditional on obtaining the TXOP) calculates the transmission time of the PPDUs within the TXOP, and inserts an intermediate code or a floating intermediate code in the PPDU whose transmission time is closest to the TLTT; for example, as illustrated in parts (b) and (d) of Figure 4 shown.

[0207] Alternatively or additionally, the transmission times of the PPDUs in the PPDU sequence may be adjusted to reduce the jitter of the LTF transmission time. For example, the adjustment may be achieved by delaying or advancing the default transmission time of the physical layer packet. Padding the data to extend the previous physical layer packet is one possibility for delaying the default transmission time of the physical layer packet; for example, as illustrated in part (e) of Figure 4 shown. Reducing the data (e.g., data puncturing) to shorten the previous physical layer packet is one possibility for advancing the default transmission time of the physical layer packet.

[0208] Thus, an objective of various embodiments may be to ensure that the LTF is transmitted at a specified time (or within the MAAD). However, there may be cases where it is difficult for the transmitter to meet such requirements (e.g., because it is not possible to obtain channel access and / or because the intermediate code overhead is more desirable). For this purpose, methods are also provided for the receiving / sensing STA to handle the situation where no LTF is transmitted at the specified time (or within the MAAD). This is achieved by interpolation or extrapolation (as applicable) at the sensing STA. However, even in these embodiments, the transmitting STA needs to position the LTF in a manner that enables interpolation or extrapolation.

[0209] For channel estimation by interpolation, the transmitter transmits at least two LTFs (fields in the above terms), where at least one LTF is transmitted earlier than the TLTT and at least one LTF is transmitted later than the TLTT. The receiver uses the at least two LTFs to calculate the channel estimate at the TLTT.

[0210] For example, the receiver may perform channel estimation at the two LTFs closest to the TLTT and combine the channel estimates by linear interpolation.

[0211] Alternatively, the channel estimation may be performed based on the interpolation of the two LTFs, which corresponds to the LTF content estimated at the TLTT.

[0212] In either case, more than two LTFs can be used to further improve interpolation; for example, by non-linear fitting. This may be more desirable, for example, when the time distance (duration) between LTFs is relatively large and / or when the channel changes rapidly.

[0213] It can be expected that interpolation produces high precision at the cost of a limited increase in complexity at the receiver side. However, the requirement to send LTFs on both sides of the TLTT may lead to problems similar to those of sending LTFs at the TLTT (or within the MAAD from the TLTT). For example, a relatively large number of LTFs may need to be sent; meaning relatively large overhead and / or relatively long channel occupancy. To achieve a more spectrum-efficient method of providing the receiver with information for estimating the channel at the TLTT, the receiver can be configured to perform extrapolation, and the transmitter does not have to send LTFs on both sides of the TLTT.

[0214] For channel estimation by means of extrapolation, the transmitter sends at least two LTFs (fields in the above terms), where both LTFs are sent earlier than the TLTT, or both LTFs are sent later than the TLTT. The receiver uses the at least two LTFs to calculate the channel estimate at the TLTT.

[0215] For example, the receiver can perform channel estimation at the two LTFs closest to the TLTT and combine the channel estimates by means of linear extrapolation.

[0216] Alternatively, the channel estimation can be performed based on the extrapolation of the two LTFs, which corresponds to the LTF content estimated at the TLTT.

[0217] In either case, more than two LTFs can be used to further improve extrapolation; for example, by non-linear fitting. This may be more desirable, for example, when the time distance (duration) between the closest LTF and the TLTT is relatively large.

[0218] For example, when it is possible for a transmitter to obtain channel access within 2 μs after starting to attempt to obtain channel access, the transmitter can initiate the LBT process 1 μs before the TLTT, so that it may obtain access to the channel at TLTT ± 1 μs. Whenever the transmitter obtains access to the channel, it transmits two LTFs. If the transmitter obtains access to the channel earlier (such that both of the two LTFs are transmitted before the TLTT), the channel estimate at the TLTT can be obtained by prediction of the future (i.e., by extrapolation). If the transmitter obtains access to the channel slightly later (such that the first LTF is transmitted before the TLTT and the second LTF is transmitted after the TLTT), the channel estimate at the TLTT can be obtained by interpolation. If the transmitter obtains access to the channel later (such that both of the two LTFs are transmitted after the TLTT), the channel estimate at the TLTT can be obtained by backward prediction to the past (i.e., by extrapolation).

[0219] The described embodiments and their equivalents can be implemented in software or hardware or a combination thereof. These embodiments can be executed by a general-purpose circuit. Examples of general-purpose circuits include digital signal processors (DSPs), central processing units (CPUs), coprocessor units, field programmable gate arrays (FPGAs), and other programmable hardware. Alternatively or additionally, the embodiments can be executed by a special-purpose circuit such as an application specific integrated circuit (ASIC). The general-purpose circuit and / or the special-purpose circuit can be associated with, for example, a device such as a wireless communication device, or be included in a device such as a wireless communication device.

[0220] Embodiments can be present within an electronic device (such as a wireless communication device) including an arrangement, circuit, and / or logic according to any of the embodiments described herein. Alternatively or additionally, an electronic device (such as a wireless communication device) can be configured to perform a method according to any of the embodiments described herein.

[0221] According to some embodiments, a computer program product includes a tangible or intangible computer-readable medium such as, for example, a universal serial bus (USB) memory, a plug-in card, an embedded drive, or a read-only memory (ROM). Figure 7Illustrated is an example computer-readable medium in the form of a compact disc (CD) ROM 700. A computer program including program instructions is stored on the computer-readable medium. The computer program can be loaded into a data processor (PROC; e.g., a data processing circuit or a data processing unit) 720, which may be included, for example, in a wireless communication device 710. When loaded into the data processor, the computer program can be stored in a memory (MEM) 730 associated with or included in the data processor. According to some embodiments, when the computer program is loaded into and run by the data processor, it causes the execution of method steps according to any of the methods illustrated in, for example Figure 1 and Figure 2 or other methods described herein.

[0222] In general, all terms used herein should be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is explicitly given and / or implied from the context in which it is used.

[0223] Reference is made herein to various embodiments. However, those skilled in the art will recognize many variations of the described embodiments that will still fall within the scope of the claims.

[0224] For example, the method embodiments described herein disclose example methods by steps performed in a particular order. However, it should be recognized that the sequence of these events can occur in another order without departing from the scope of the claims. Furthermore, some method steps, even though described as being performed in sequence, can be executed in parallel. Thus, the steps of any method disclosed herein need not be performed in the exact order disclosed, unless a step is explicitly described as being after or before another step and / or it is implied that one step must be after or before another step.

[0225] Similarly, it should be noted that in the description of embodiments, the division of functional blocks into specific units is in no way restrictive. On the contrary, these divisions are merely examples. A functional block described herein as one unit can be divided into two or more units. Furthermore, functional blocks described herein as being implemented as two or more units can be combined into fewer (e.g., a single) unit.

[0226] Whenever appropriate, any feature of any embodiment disclosed herein can be applied to any other embodiment. Similarly, any advantage of any embodiment can be applied to any other embodiment, and vice versa.

[0227] Therefore, it should be understood that the details of the described embodiments are merely examples presented for illustrative purposes, and all variations falling within the scope of the claims are intended to be included within the scope of the claims.

Claims

1. A method performed by a transmitter configured to send a physical layer packet in accordance with a listen - before - talk procedure, the method comprising: Obtaining (110) an indication of a specific time for channel estimation; Providing (140) for the physical layer packet at least one measurement signal for channel estimation based on the specific time, wherein providing (140) for the physical layer packet at least one measurement signal for channel estimation based on the specific time includes: providing a floating midamble for the physical layer packet, the floating midamble including one or more measurement signals for channel estimation; and Sending (150) the physical layer packet, wherein the method includes preparing two or more versions of the physical layer packet, wherein each version inserts the at least one measurement signal at a different position, and wherein providing for the physical layer packet at least one measurement signal for channel estimation based on the specific time includes selecting one of the versions of the physical layer packet for transmission, wherein selecting one of the versions of the physical layer packet for transmission includes selecting the version having the measurement signal closest to the specific time.

2. The method according to claim 1, wherein, Providing (140) the floating midamble for the physical layer packet and sending (150) the physical layer packet includes: timing the floating midamble to coincide with the specific time, or timing it to occur at a time less than a second time - distance value or less than a second duration value from the specific time.

3. The method according to claim 1 further comprises: Including an indication of the position of the floating midamble within the physical layer packet in a preamble of the physical layer packet.

4. The method according to claim 2, wherein Sending (150) the physical layer packet is performed within a transmission opportunity, and wherein timing includes: extending a previous physical layer packet of the transmission opportunity to adjust the transmission time of the physical layer packet.

5. The method according to any one of claims 1 to 4, wherein, Providing (140) for the physical layer packet at least one measurement signal for channel estimation based on the specific time includes: providing at least two fields for the physical layer packet, wherein each field includes one or more measurement signals for channel estimation, and wherein each field is a midamble of the physical layer packet or a part of a preamble of the physical layer packet.

6. The method according to any one of claims 1 to 4 further comprises: Obtaining (120) an indication of a maximum acceptable absolute deviation.

7. The method according to any one of claims 1 to 4, wherein The at least one measurement signal for channel estimation includes: at least two measurement signals for channel estimation.

8. A computer program product comprising a non - transitory computer - readable medium (700) having thereon a computer program including program instructions, the computer program being loadable into a data processing unit and configured to cause the method according to any one of claims 1 to 7 to be performed when the computer program is run by the data processing unit.

9. An apparatus for a transmitter configured to send a physical layer packet in accordance with a listen - before - talk procedure, the apparatus including a control circuit (500) configured to cause: Obtaining an indication of a specific time for channel estimation; Provide at least one measurement signal for channel estimation based on the specific time in the physical layer packet, where, The control circuit is configured to: provide at least one measurement signal for channel estimation based on the specific time for the physical layer packet by providing a floating intermediate code for the physical layer packet, wherein the floating intermediate code includes one or more measurement signals for channel estimation; and transmit the physical layer packet, wherein the control circuit is further configured to prepare two or more versions of the physical layer packet, each version inserting the at least one measurement signal at a different position, and wherein providing at least one measurement signal for channel estimation based on the specific time for the physical layer packet includes selecting one of the versions of the physical layer packet for transmission, and wherein selecting one of the versions of the physical layer packet for transmission includes selecting the version having the measurement signal closest to the specific time.

10. The device according to claim 9, wherein, The control circuit is configured to: provide the floating intermediate code for the physical layer packet and transmit the physical layer packet by timing the floating intermediate code to coincide with the specific time, or to occur at a time less than a second time distance value or less than a second duration value from the specific time.

11. The apparatus according to claim 9, wherein, The control circuit is further configured to: cause an indication of the position of the floating intermediate code within the physical layer packet to be included in the preamble of the physical layer packet.

12. The device according to claim 10, wherein, The control circuit is configured to: cause the transmission of the physical layer packet to be performed within a transmission opportunity, and to perform timing by causing the previous physical layer packet in the transmission opportunity to be extended to adjust the transmission time of the physical layer packet.

13. The device according to any one of claims 9 to 12, wherein, The control circuit is configured to: provide at least one measurement signal for channel estimation based on the specific time for the physical layer packet by providing at least two fields for the physical layer packet, each field including one or more measurement signals for channel estimation, and wherein each field is an intermediate code of the physical layer packet or a part of the preamble of the physical layer packet.

14. The device according to any one of claims 9 to 12, wherein The control circuit is further configured to: cause an indication of the maximum acceptable absolute deviation to be obtained.

15. The device according to any one of claims 9 to 12, wherein The at least one measurement signal for channel estimation includes: at least two measurement signals for channel estimation.

16. A transmitter device comprising the apparatus according to any one of claims 9 to 15.

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